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How do water jets work? Waterjet is a generic term used to describe equipment that uses a high pressure stream of water for cutting or cleaning purposes.

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Presentation on theme: "How do water jets work? Waterjet is a generic term used to describe equipment that uses a high pressure stream of water for cutting or cleaning purposes."— Presentation transcript:



3 How do water jets work? Waterjet is a generic term used to describe equipment that uses a high pressure stream of water for cutting or cleaning purposes. Abrasivejet is a subcategory of waterjet in which abrasive is introduced to accelerate the process. Pure waterjet and water-only cutting are phrases for specifically distinguishing waterjets that do not use abrasive. In other words: abrasivejet and pure waterjet are kinds of waterjet, and waterjet is a kind of machinery. It is normal, and common, to use the term waterjet to refer to abrasivejets, though in some cases it can be confusing. On this web site, we'll use waterjet when referring to topics that cover both pure waterjets and abrasivejets, and use the terms pure waterjet and abrasivejet when discussing topics that are specific to one or the other

4 Take ordinary tap water and pressurize it to 60,000 psi (4,000 bar) and force it through a very small hole. Mix the water with garnet abrasive and you have a very thin stream of water traveling very fast that will rapidly erode most materials. Some water jets are "pure water jets" and don't add the garnet abrasive. These are used to cut softer materials, such as food, rubber, and foam. What can water jets cut? What can't they cut? Waterjets can cut just about any material that can be made into a sheet and placed in front of them. The most popular materials are metals (especially aluminum, because it's relatively soft and cuts quickly), because waterjets can cut intricate shapes to a high precision quickly and economically. Since metals are the most common material cut by machining shops, waterjets tend to cut a lot of metal. Waterjets also commonly cut stone and glass, because the waterjet can get intricate shapes not possible using traditional machining methods. These materials are popular with artists who like to work with these materials and waterjets because it lets them create almost anything they can envision.

5 Among the very few materials that water jets cannot cut are diamonds and tempered glass. Diamonds are too hard to cut (and there may be a few other very hard materials that can't be cut). Tempered glass will shatter when it is cut with a water jet (tempered glass is designed to shatter when it's disturbed and is frequently used in windshields for this very reason). A few advanced ceramics are so hard that it's not economical to cut them. Some composite materials (layers of different materials sandwiched together) can't be cut because the water can seep between the layers and "delaminate" the material. Many composite materials cut just fine, though, and there are some techniques to cutting laminated materials.techniques to cutting laminated materials What do they cost? Water jets typically come as complete systems, including the high-pressure water pump, a system to precisely position the water jet nozzle, a tank to catch the waste water, and an abrasive feed system. Prices run from $50,000 to 300,000, with $150,000 being about average for a mid-range water jet system. Prices can run considerably higher than this for custom systems or very large water jet cutting systems. Water jet systems are not currently something for the home workshop. You'll find them in use in machining shops and industrial workshops. Among other factors, you need industrial levels of electricity to power the pumps (which can pull as much as 50 amps; some pumps require 250 amps to get started). For the hobbyist interest in water jets, the more economical approach is to work with a job shop to make the parts. Most job shops can accept computer drawings you create to make exactly the part you want.

6 Basic water jet principles Water jets are fast, flexible, reasonably precise, and in the last few years have become friendly and easy to use. They use the technology of high-pressure water being forced through a small hole (typically called the "orifice" or "jewel") to concentrate an extreme amount of energy in a small area. The restriction of the tiny orifice creates high pressure and a high-velocity beam, much like putting your finger over the end of a garden hose. Pure water jets use the beam of water exiting the orifice to cut soft material like diapers, candy bars, and thin soft wood, but are not effective for cutting harder materials. Typical design of a pure waterjet nozzle

7 The inlet water for a pure water jet is pressurized between 20,000 and 60,000 Pounds Per Square Inch (PSI) (1300 to 6200 bar). This is forced through a tiny hole in the jewel, which is typically 0.007" to 0.020" in diameter (0.18 to 0.4 mm). This creates a very high-velocity, very thin beam of water (which is why some people refer to water jets as "water lasers") traveling as close to the speed of sound (about 600 mph or 960 km/hr). An abrasive jet starts out the same as a pure waterjet. As the thin stream of water leaves the jewel, however, abrasive is added to the the stream and mixed. The high-velocity water exiting the jewel creates a vacuum which pulls abrasive from the abrasive line, which then mixes with the water in the mixing tube. The beam of water accelerates abrasive particles to speeds fast enough to cut through much harder materials.

8 The cutting action of an abrasivejet is two-fold. The force of the water and abrasive erodes the material, even if the jet is stationary (which is how the material is initially pierced). The cutting action is greatly enhanced if the abrasivejet stream is moved across the material and the ideal speed of movement depends on a variety of factors, including the material, the shape of the part, the water pressure and the type of abrasive. Controlling the speed of the abrasivejet nozzle is crucial to efficient and economical machining Water jet nozzle fired into the air In this video below, a water jet nozzle is raised a few inches above the work surface, and fired for a few seconds into the air. Keep in mind that there is about 30 horsepower going through that little stream of water

9 Advantages of water jet machining There is a reason that water jet machining has rapidly grown in popularity since the mid-1990's. Actually there are a number of reasons, listed below, but they mostly come down to "versatility." A water jet is a versatile and flexible machining tool. You can cut a wide variety of material efficiently and cost- effectively and can create a wide variety of parts

10 Cut virtually any material Because water jets cut using water and abrasive, they can work with a wide variety of materials. These materials include: Copper, brass, aluminum: Pre-hardened steel Mild steel Exotic materialss such as titanium, Inconel and Hastalloy 304 stainless steel Brittle materials such as glass, ceramic, quartz, stone.Brittle materials Laminated material Flammable materials One of the few materials that cannot be cut with a water jet is tempered glass. Because tempered glass is under stress, as soon as you begin to cut it, it will shatter into small fragments—as it is designed to do.

11 Fast setup and programming With water jet machining, a flat piece of material is placed on a table and a cutting head moves across the material (although in some custom systems, the material moves past a fixed head). This simplicity means that it's fast and easy to change materials and that no tool changes are required. All materials use the same cutting head, so there is no need to program tool changes or physically qualify multiple tools. The movement of the machining head is controlled by a computer, which greatly simplifies control of the water jet. In most cases, "programming" a part means using a CAD program to draw the part. When you "push print," the part is made by the water jet machine. This approach also means that customers can create their own drawings and bring them to a water jet machine for creationCAD program Little fixturing for most parts There are very low sideway forces with water jet machining--cutting the material doesn't push it. The downward forces are also small, in the range of a few pounds. Typically, the largest force is from the water in the tank pushing back up against the material. FixturingFixturing is generally a matter of weighing down the material by placing weights on it. Small parts might require tabs to prevent them from falling into the tank. The low side forces, means you can machine a part with walls as thin as 0.01" (0.25 mm). This is one of the factors that make fixturing is so easy. Also, low side forces allow for close nesting of parts, and maximum material usage.

12 Almost no heat generated on your part What little heat is generated by the water jet is absorbed by the water and carried into the catch tank. The material itself experiences almost no change in temperature during machining. During piercing 2" (5 cm) thick steel, temperatures may get as high as 120° F (50° C), but otherwise machining is done at room temperature. The result is that there is no heat affected zone (HAZ) on the material. The absence of a HAZ means you can machine without hardening the material, generating poisonous fumes, recasting, or warping. You can also machine parts that have already been heat treated. No mechanical stresses Waterjet machining does not introduce any stresses into the material Machine thick material While most money will probably be made in thicknesses under 1" (2.5 cm) for steel, it is common to machine up to 4" (10 cm). The thicker the material, the longer it will take to cut. A part made from material twice as thick will take more than twice as long. Some companies make low tolerance parts out of metal that is up to 5" to 10" thick (12.5 cm-25 cm), but it takes a long time and tends to be an occasional operation. Typically, most waterjet parts are made from metal that is 2" (5 cm) or thinner.

13 Pictured here is a part made from 2" (5 cm) thick 304 stainless steel Are very safe Obviously, you don't put any body parts in front of a water jet machining head while it is on. Anything that can cut through 2" steel will make short work of flesh and bone. Aside from this, however, water jets are very safe. A leak in a high-pressure water system tends to result in a rapid drop in pressure to safe levels. Water itself is safe and non-explosive and the garnet abrasive is also inert and non-toxic. One of the largest hazards is cuts from the sharp edges of material created by the water jet.

14 Modern systems are now very easy to learn Control of the water jet head is complicated and requires careful calculation to get the proper speed that will give the best result. This means that the system needs to be controlled by a computer, which means that the user-interface for the system can be simplified and made friendlier. Modern systems are designed the same way as many other computerized CAD systems and are quickly learned. Environmentally friendly As long as you are not machining a material that is hazardous, the spent abrasive and waste material become suitable for land fill. The garnet abrasive is inert and can be disposed of with your other trash. If you are machining lots of lead or other hazardous materials, you will still need to dispose of your waste appropriately, and recycle your water. Keep in mind, however, that very little metal is actually removed in the cutting process. This keeps the environmental impact relatively low, even if you do machine the occasional hazardous material. In most areas, excess water is simply drained to the sewer. In some areas, water treatment may be necessary prior to draining to sewer. In a few areas, a "closed loop" system that recycles the water may be required. The pumps do use a considerable amount of electricity, though, so there is some additional environmental (and cost) impact due to this. No start hole required Start holes are only required for materials that are difficult or impossible to pierce. A few poorly bonded laminates can fall into this category, in which case pre-drilling or other special methods may be used.

15 Narrow kerf removes only a small amount of material The amount of material removed by the water jet stream is typically about 0.02" (0.5 mm) wide, meaning that very little material is removed. When you are working with expensive material (such as titanium) or hazardous material (such as lead), this can be a significant benefit. It also means that you can get more parts from a given sheet of material. When machining or roughing out expensive materials such as titanium, your scrap still has value. This is because you get chunks, not chips. Advantages of water jets compared with lasers Laser cutting involves using a laser focused on material to melt, burn, or vaporize the material. The laser can be a gas laser (such as CO 2 ) or a solid-state laser. The laser beam can be static, and the material moves in front of the laser, or the laser can itself be moved across the material. When the laser moves across the material, additional optics are required as the distance from the emitting end of the laser changes. Lasers have the advantage over traditional machining methods that the laser never touches the material (avoiding contamination) and the HAZ is relatively small. Advantages of waterjets Water jets have a number of advantages over lasers. In many respects, however, the two tools are complementary and many machine shops own both of them.

16 Can work with more materials Water jets can machine reflective materials that lasers cannot, such as copper and aluminum. Water jets cut a wide range of material with no changes in setup required. Also, materials which are heat-sensitive can be cut using water jets. No heat-affected zone (HAZ) with water jets Water jet cutting does not heat your part. There is no heat-affected zone (HAZ) or thermal distortion, which can occur with lasers. Water jets do not change the properties of the material. Water jets are more environmentally friendly Abrasivejets typically use garnet as the abrasive material. Garnet is a non-reactive mineral that is biologically inert. The only issue with water jets is when you are cutting a material that is potentially hazardous (such as lead), since small pieces of the material will be abraded and mix in with the spent garnet. Water jets are safer There are no noxious fumes, such as vaporized metal, and no risk of fires. The distance between the end of the water jet nozzle and the material is typically very small, although caution is needed when the water jet nozzle is raised. Uniformity of material not important With lasers, the material needs to be relatively uniform. In particular, when cutting over uneven surfaces, the laser can lose its focus and cutting power. A water jet will retain much of its cutting power over uneven material. Although the material may deflect the cutting stream, it typically has a negligible effect. Lower capital equipment costs The cost of a machine is generally much lower than that of a laser. For the price of a laser, you can purchase several water jet machining centers.

17 Better tolerances on thicker parts Waterjets offer better tolerances on parts thicker than 0.5" (12 mm). For thinner parts, both waterjets and lasers offer comparable tolerances. Waterjets can machine thicker materials How thick you can cut is a function of how long you are willing to wait. Waterjets easily handle 2" (5 cm) steel and 3" (7.6 cm). Although some people have used waterjets at thicknesses of up to 10" (25 cm) in steel, it is difficult to maintain precision in materials thicker than 2" (5 cm). Lasers seem to have a maximum practical cutting thickness of 0.5" (12 mm) to 0.75" (19 mm). Simpler maintenance Maintenance on a waterjet is simpler than that of a laser. Simpler operation Waterjets are computer controlled, so that the operator does not have to be highly skilled and trained. Better edge finish Material cut by waterjets have a fine, sand-blasted surface because of the way the material was abraded, which makes it easier to make a high-quality weld. Material cut by laser tends to have a rougher, scaly edge, which may require additional machining operations to clean up.

18 Advantages of water jets compared with EDM EDM stands for Electrical Discharge Machining and is used to machine electrically conductive materials, such as steel and titanium. An electrical arc rapidly discharges between an electrode and the workpiece material. The series of arcs removes metal by melting it and vaporizing it, essentially eroding the metal using electricity. The particles are flushed away by a continuously circulating non-conducting fluid, such as deionized water or kerosene. EDM can create intricate shapes in hard materials that are difficult to machine using traditional methods. Advantages of water jets Although the above part could be made using EDM, it's much faster to make it using a waterjet Many EDM shops are also buying water jets. Water jets can be considered to be like super-fast EDM machines with less precision. This means that many parts of the same catagory that an EDM would do can be done faster and cheaper on an abrasivejet, if the tolerances are not extreme. New technology allows Abrasive jets to obtain tolerances of up to +/-.003" (0.075mm) or better Abrasive Jet machining is useful for creating start holes for wire insertion later on. (a mill could do the job, but only after spotting the hole, changing tools to drill a pilot, then changing tools again to drill out the hole ).

19 Faster Abrasive jets are much faster than EDM, which slowly removes the metal. Can work with more materials Waterjets can machine non-conductive materials that EDM cannot, such as glass, wood, plastic, and ceramic. There is almost no limit to the type of materials that can be machined with waterjets. Uniformity of material not important A waterjet will retain much of its cutting power over uneven material. Although the material may deflect the cutting stream, it typically has a negligible effect. Such material aberrations would cause wire EDM to lose flushing. Waterjets make their own pierce holes Some types of EDM, such as wire-cut EDM, a hole needs to be first made in the material, which has to be done in a separate process. Waterjets can pierce the material, requiring no additional fixturing or machining. No heat-affected zone (HAZ) with waterjets Waterjet cutting does not heat your part. There is no heat-affected zone (HAZ) or thermal distortion, which can occur with EDM. Waterjets do not change the properties of the material. Waterjets require less setup Most of the fixturing with waterjets is weighing down the material so that it does not shift in the water tank. The fixturing needs to withstand forces of pounds and does not need to be elaborate or precise. Make bigger parts The size of the part created with a waterjet is limited by the size of the material. In setups where the material passes underneath the waterjet, the finished part size can be huge. Even with an X- Y table setup, part sizes can be quite large.

20 - cut EDM fixturing in a water jet machining center. This makes precision fixturing possible. It also allows for pre-machining on the waterj et to release stresses in the material, and then use the exact same fixturing on the EDM to do secondary operations and final cutting to extreme tolerance. The cheese slicer was made on a waterjet—note the very thin blade

21 Advantages of water jets compared with plasma In plasma cutting, a stream of gas is blown at high speed while an electrical arc is passed through it. This causes some of the gas to become very hot plasma. The gas, at about 27,000° F (15,000° C), then melts the metal or other substance it comes into contact with. The gas is moving fast enough that the molten metal is blown away from the cutting area. Advantages of water jets The clearest advantage that water jets have compared with plasma cutting is that water jets operate at much lower temperatures. During piercing, the temperature of the material may rise as high as 120° F (50° C), but cutting typically happens at room temperature. The presence of the catch tank (a large tank full of waste water) helps to moderate the temperature as well. This lower temperature means there is no Heat Affected Zone when material is cut with a water jet. Water jets also can cut materials that don't easily melt (such as granite) or that are destroyed by melting (many laminates). Water jets are also more precise than plasma cutting. Plasma cutting is typically faster than water jet, particularly with very thick metal. Plasma torches can pierce and cut steel up to 12" (30 cm) thick. Advantages of water jets compared with flame cutting Flame cutting, or oxy-fuel cutting, is used to cut metals by heating them to a high temperature and then introducing oxygen to melt the metal and perform the cut. Flame cutting only be used with iron and steel.

22 In flame cutting, the cutting torch combines oxygen with a fuel, such as acetylene, that heats up the metal. Once the metal is cherry red, a trigger on the torch is pressed that blasts oxygen at the metal. The hot metal reacts with the oxygen to form iron oxide (rust), which has a lower metal point than iron or steel. The iron oxide then flows away from the cutting zone. Some iron oxide may remain on the cut as slag, but it is easily removed by tapping or with a grinder. Advantages of water jets While flame cutting can work only with iron or steel, water jets can machine many different types of materials, both metal and non-metallic. Water jets also do not appreciably heat up the material they cut--during piercing, temperatures may rise to 120° F (50° C), but during cutting the material is heated only a degree or two. The edge finish created with a water jet is smooth, similar to a sandblasted finish, rather than the rough edges left by flame cutting. Water jets are more precise than flame cutting and have a much smaller kerf as less material is removed (particularly important when cutting expensive material). Flame cutting can be faster than water jets, especially when done using a multi-torch cutting machine, and as a result is cheaper than water jet cutting. The part on the top was roughed out with a water jet, with secondary machining creating the part shown on the bottom

23 Advantages of water jets compared with milling Milling is typically done with a milling machine that can perform a series of operations on material, typically cutting, drilling, lathing, and planing. Most modern milling machines are six-axis machines that can perform complex sequences of milling operations rapidly and precisely. typical modern milling machine Advantages of water jets Although mills cut faster, in most cases, than water jets, the setup and fixturing with water jets is much simpler. Setup with water jets is typically a matter of just loading the part drawing into the controller software, setting the material and thickness and beginning machining. Similarly, fixturing is mostly a matter of weighing down the material so that it doesn't move on the table during machining. Clean-up on a water jet is also faster and simpler. As a result, overall, a water jet can have a greater throughput than a mill on similar parts. Waterjets can also machine almost any material, including brittle materials, pre-hardened materials, and otherwise difficult materials such as Titanium, Hastalloy, Inconel, SS 304, and hardened tool steel.

24 With a water jet, there is also no tool changing. The water jet nozzle is the only tool used, and it is used for all the different types of materials that a water jet cuts. There is also less wear on tools, especiall in harder and gummier materials, because the cutting action of the waterjet is the stream of water and abrasive. While there is wear on the mixing tube and high-pressure water componenets, this wear tends to be constant with time, and doesn't change with different materials. Wate rjets are frequently used for complimenting or replacing milling operations. They are used for roughing out parts prior to milling, for replacing milling entirely, or for providing secondary machining on parts that just came off the mill. For this reason, many traditional machine shops are adding water jet capability to provide a competitive edge This is a part you might otherwise do on a mill. It took less than 20 minutes to make with an abrasive jet, including setup and cleanup time! Actual machining time is about 6 minutes. Material is 0.5" (13mm) thick hastalloy with a tolerance about ±0.002" (0.05 mm).

25 Advantages of water jets compared with punch presses A punch press uses a set of punches and dies to form parts out of metal. The metal is formed and cut by the punch press into a part, which may have secondary machining done to it or not. Coins are a common part that are formed using punch presses. The typical commercial punch press exerts about 20 tons of pressure. Advantages of water jets Water jets have a lower cost-per-piece for short runs than a die press, because of the expense (and time) involved in creating the dies and punches. Creating the drawing for a part on a water jet machine is all that's needed to begin machining the part, where with a punch press, the drawing is usually only the first step to creating the die. Lateral forces wtih a water jet are negligible, which means that holes can be placed very close to the material edge, which is not the case with a punch press. Water jets can also work with very thick materials, while punch presses are limited in thickness to the amount of pressure they can apply. And, of course, water jets can work with many different types of materials, including brittle materials and laminates. brittle materialslaminates Some stamping houses are using water jets for fast turn-around and rapid prototyping work. Water jets make a complimentary tool for punch presses because they offer a wider range of capability for similar parts. For high production of thin sheet-metal, the stamp will be more profitable in many cases, but for short runs, difficult material, and thick material, water jets have their place.

26 Five minutes is all it took to make this custom file Water jets also play a big part as just one part in a larger manufacturing process. For example, water jets are often used to machine features into an existing part, or to do pre-machining to remove material before precision finishing on other machinery. Where water jets are used Water jet machines are not specialty machines for niche applications. They are general purpose tools that are useful in any machine shop. Following is is a small sampling of specialized applications. General purpose machine shops Water jets are good all-around machine tools, as it is fast and easy to go from idea to finished part. Water jets can also work with many different types of materials with minimal fixturing and setup.

27 Architectural Similar to the art market, there are many machines out there making custom flooring from stone, as well as making architectural details from metal Aerospace Companies that makes parts for the aerospace industry maching lots of aluminum, which is easily machined on a water jet. Exotic metals such as Inconel ®, titanium, and Hastalloy can also be machined by water jets. Manufacturing Water jets are used for making parts of products that are sold, as well as many of the parts used to make the machines on the assembly lines. Automotive & transportation Prototyping and production parts for automobiles, and the tooling for making automobiles. Also there are a lot of custom race car parts made on water jets. Laser shops Lasers and water jets are highly complementary tools. They both pick up where the other leaves off. EDM shops Some of the small size and higher precision water jet machining centers are great complementary tools to EDM because they allow for higher speed machining of similar shapes, and can provide other services for the EDM such as pre-drilling start holes or stress relieving the part prior to skim cutting on the EDM. Model shops / rapid prototyping Fast turn-around of single piece production in nearly any material makes water jets great for these kinds of applications. Schools Many of the larger size universities that offer engineering classes also have water jets. They are great tools for the classroom environment because they are easy to learn, program, and operate, and because they can make one-off kind of parts quickly. They also provide a great service to other departments within the university that may need job-shop services. Looking for somebody to make your part? Check our listings of waterjet job shopswaterjet job shops

28 What it costs to make water jet parts There are a variety of ways to calculate the cost of making parts with a water jet. This is true of most businesses, and the calculation of "Cost of Goods" is the subject of many books and business classes. This page looks at some approaches to calculating the cost of goods for parts made with a water jet, which will then help you determine how much to charge for a part. A lot of people price the work on their machines on dollars per hour basis. This may make sense for some kinds of machines, but not for a water jet. A job shop with a multi-head machine running two pumps or a high power pump might have a much higher cost of operation than a shop with a small machine with a low power pump. If these two shops compete against each other purely on dollars per hour, then the shop with the smaller cheaper machine will make a lot more money. This is because the parts will take longer to make, and they will be cheaper to make, so the customer pays more yet the part costs less to make. The shop with the faster machine must therefore charge more per hour to take advantage of their faster machine waterjet machine with four heads (Photo courtesy Pegasus Northwest, Inc.) Another strategy is to price the work based on a dollars per square inch basis. This has the drawback that a part with a lot of geometry to it (curves and corners and pierces) will take a much longer time than a straight line cut, because the water jet must slow down to avoid blow-out at the corners and turns. Likewise, material thickness and many other factors come into play, and cutting speed is not a linear function relating to thickness. So, while $/square inch may make sense for some machines, it does not for water jets blow-out

29 The best approach is to figure out how much it will cost you to make the part. Then estimate how much it would cost to make the part by competitive methods (either other kinds of machines, or your competitor with an waterjet). See if there are other savings such as being able to squeeze more parts from expensive material. Then, price from there. Your customer does not need to know if you are charging them $100per hour. They are not paying you for your time, they are paying your for the part. Another option that can work, if you prefer a simpler, more objective formula, is to simply cost your work based on your true cost to make the part. Many machines have software built in to make this easy. Simply take the cost to make the part, and multiply by a factor, and there you have it. The cost to make your part should include the following factors: How much time will it take to program the path into a tool path? (And if the customer provides the toolpath in a compatible file format, any price break you might choose to give them.) How much risk is there that you might break something (such as when cutting glass) and need to scrap it and start over? Does the customer provide the material, or do you need to purchase the material? How many times must you pierce the material? Each pierce is extra wear and tear on machine, and the associated risk of a nozzle plug or material cracking during piercing. How much do your consumables cost you?  Electricity  Water  Abrasive  Spares and wear parts Is there any special setup or risk to consider? How much time will it take to actually do the cutting? How much time will it take you to load and unload the parts and material, and clean up the machine afterwards? Is the customer ordering a large quantity? Is this taking your machine away from doing another possibly more profitable job? Typical price ranges Prices range up to $ per hour for some parts, but $100 to $135 per hour is more typical, and it can be as low as $80/hour. You should look at the part to machine, and think of what it would cost on a mill, or other competing equipment. Then price the part slightly under that, and make a good profit. However

30 The answer to the question "What kind of parts can a waterjet make?" isn't short or simple. Lots and lots of different types of parts made from lots and lots of different types of materials. In this section, we've collected photographs of different parts that have been made on waterjets. Most of them practical and some of them a little bit silly (while it's fun to cut up an Xbox case, it's not something there's much of a market for). cut up an Xbox case Pictures of parts made on waterjets ( 4 items ) This section contains lots of pictures of parts made on water jets, along with pictures of various water jets. The parts shown are mostly ones created for specific projects range from very small parts to larger ones.Pictures of parts made on waterjets Fun and interesting parts ( 7 items ) A collection of neat projects done with water jets, including wooden electric guitars, waffle irons, and aluminum palm trees. While these may not be typical water jet projects, they also help provide a sense of how many different types of projects water jets can do.Fun and interesting partswooden electric guitarswaffle ironsaluminum palm trees Material types that can be machinedMaterial types that can be machined ( 5 items ) What materials can a water jet cut? Oh, just about everything, from granite to glass to metal to composites to laminates. And with a wide range of thicknesses. This section talks about some of the materials that can be challenging to cut with a water jet, such as brittle materials, and ways to work with them. brittle materials

31 Pictures of various items cut with an abrasive water jet from various materials The key word to describe a water jet is "versatile." In the above picture, notice the wide variety of shapes created by the water jet, as well as the different thicknesses. notice also the range of materials shown-- various metals, Plexiglas ®, even granite. Pictures of various large parts machined on an abrasive water jet

32 spring machined from 1/8" (3 mm) brass Company name cut from a file The file shown in the above picture is made of hardened steel. With most machining tools, hardened steel takes considerably longer to cut than regular steel. With a waterjet, hardened steel takes only slightly longer to machine. This lets manufacturers harden their materials before cutting, which can be more efficient and cost-effective.

33 A rack and a gear machined with a water jet from ½" (13 mm) steel (Left) Friction plate made from ¼" (6 mm) stainless steel While etching is not the strong suit of water jets, it can be done. The above photographs show two samples of etching. For the friction plate, the speed of the water jet head was rapid enough that the material didn't cut all the way through. The etching in the glass on the right was done using low pressure, again so that it wouldn't cut

34 through the material. Etching works best with hard materials, although even then, it is difficult to get a consistent, even depth with a water jet. saw blade made from 3/8" (10 mm) mild steel Cheese cutter demonstrating how thin you can machine using a water jet

35 Water jets generate very small side forces as they maching. Most of the energy is directed straight down on the material. As a result, it is possible to make parts with very thin features, such as the cheese cutter shown above where the blade is less that 0.020" (0.5 mm) thick Another example of thin wall cutting in ½" (13 mm) aluminum The walls in the above honeycomb piece are about 0.025" (0.6 mm) thick. Note the uniformity of the walls as well as their thinness. Rack and gear in 1/8" (3 mm) aluminum

36 Part assembled from 1/8" aluminum pieces machined on a water jet Introduction to materials Because water jets cut by rapidly eroding material with a mixture of high-pressure water and abrasive, they can cut most materials in flat sheets. They can also cut non- flat materials, such as pipes, although with varying degrees of precision, depending on the shape of the material. Heat-treated material is easily machined, as water jets generate little or no additional heat and will not affect heat treatments. The additional time to cut heat-treated material with a water jet is negligible, which means that you can heat treat the material before you machine it. Water jets are great for exotic materials like Inconel, Hastalloy and titanium, as they have a narrow kerf (cutting width) and tend to leave usable pieces of these expensive materials. But don't forget that water jets are also a great choice for less exotic materials such as mild steel or aluminum.

37 Water jets do have trouble with piercing some materials, and may cause delamination of other materials. Often, in these cases, it is still possible to cut by reducing pressure, or by pre-drilling start holes, or coming in from the edge of the material without piercing. Tempered glass can not be cut with an abrasivejet.Tempered glass is formed by rapidly cooling the glass, so that there is stress applied across the surface of the glass. As soon as this stress is relieved—whether by a blow or by a water jet—the glass shatters into many small square pieces. This is what it's supposed to do, and tempered glass is frequently used in safety applications such as automobile windshields, where you don't want glass to fragment into sharp shards. So if you try to cut tempered glass with a water jet, it will shatter into many small pieces as soon as you cut through the surface, just as it's designed to. You can, however, easily cut un-tempered glass and then temper it.

38 Life of cutting nozzles The main wear part in a nozzle is the mixing tube. This is where the high-pressure water and the abrasive are mixed together before striking the material. The mixing tube is typically made of a very hard, but brittle material. A "worn" mixing tube is like a worn tool bit: it is difficult to say when a mixing tube is fully worn, but as it wears, it becomes a less effective cutting tool. For precision work, a new mixing tube performs better than a used one. How long a mixing tube lasts depends on a number of factors. Numbers from 20 to 80 hours are fairly typical, although it is possible that they may wear faster, or last longer, depending on circumstances. Recycling mixing tubes It is possible to recycle mixing tubes by drilling it out using Wire EDM to increase the bore size. Typically, a mixing tube has a diameter of 0.030" (0.76 mm). Once the mixing tube is about 75% worn, you can have it bored out to 0.040" (1.0 mm). The new tube will not cut quite as fast, or as precisely, but you have significantly extended its life. You will have to use an EDM to make the bore, but it can be done, although the nozzle cannot be completely worn out for this to wor Wire EDM Water jet vs. abrasive jet nozzles There is a difference between a pure water jet nozzle and an abrasive jet nozzle. With the abrasive jet nozzle, an opening in the side of the nozzle allows for the introduction of the abrasive to the high-pressure water stream. The two are mixed in a mixing tube and then exit the nozzle. With a pure water jet nozzle, there is no opening and no mixing tube and the high-pressure water is directed to the material after it exits the jewel pure water jet abrasive jet

39 If you will always be cutting the same type of material, you can choose the nozzle that works best for that material. In most cases, however, you will be cutting a variety of different materials (one of the strengths of a water jet) and you may want to change nozzles as needed. Many machines let you swap nozzles in a matter of minutes. Alternately, you can simply turn off the abrasive, and get a somewhat inefficient water jet from your abrasive jet nozzle. You can improve the performance somewhat by plugging the abrasive hole. Which nozzle is best for my material? Water Jet Nozzle Soft rubber Foam Extremely thin stuff like Foil Carpet Paper and cardboard Soft Gasket material Candy bars Diapers Soft, or thin wood AbrasiveJet Nozzle Hardened tool steel Titanium Aluminum Hard Rubber Stone Inconel® Hastalloy Copper Exotic materials Hard, or thick Wood Glass (even bullet proof!) Marble Plastic Nylon Graphite Many ceramics Carbon Fiber Composites mild steel Stainless Steel Kevlar Granite Mixed materials Brass

40 Cost comparison Complete water jet nozzle assemblies cost around $ to $ (US), while abrasive jet nozzles cost from $800 to $2000. The abrasive nozzle also requires support hardware for abrasive feed which can cost anywhere from $500 to $2,000. (These numbers are not precise—for exact pricing, contact a water jet supplier or water jet equipment manufacturer.) Cost of operation is much higher for the abrasive jet because of mixing tube wear, and abrasive consumption. water jet supplier water jet equipment manufacturer Limitations to pure water jet nozzles Typically, the only problems that arise with a pure water jet nozzle will be with the jewel (the orifice with the tiny hole that the water squirts through). Jewels can crack, plug, or form deposits on them. Cracking and plugging happens as a result of dirty inlet water, and is typically avoided with proper filtration. Deposits accumulate gradually as a result of minerals in the water. Depending on your water supply, slightly fancier filtering may be necessary. Jewels are easily replaced in about two to ten minutes, and are typically cheap ($5 to $50). There are also diamond orifices for sale for $200 and up, which can last longer in many applications.

41 Limitations of abrasive jet nozzles Despite their simple design, abrasive jet nozzles can be troublesome at times. There are many designs, but they share the same problems: Short life of the mixing tube The abrasive jet can cut through just about anything — including itself. This mixing tube is expensive and wears out in only a few hundred hours of use. Replacing mixing tubes will be a large part of your operating cost. Occasional plugging of mixing tube Plugging is usually caused by dirt or large particles in abrasive. This used to be a big problem with abrasive jet nozzles, but has been getting better as manufacturers fine- tune mixing tube designs. Wear, misalignment, and damage to the jewel The jewel needs to be precisely positioned in the nozzle while water and thousands of pounds of pressure impacts it What goes into a water jet Although every water jet model is different, there are certain standard features that will be present in all water jets in one form or another. Although the following discussion uses OMAX Corporation equipment as an example, every manufacturer's machines will have similar parts.


43 Controller The controller is the "brains" of the water jet: it turns the high-pressure water pump on and off, moves the nozzle head and controls the abrasive flow. Most modern water jets use a standard PC with custom software running on it. In the above picture, the computer is enclosed in a cabinet to protect it from water and abrasives Nozzle The nozzle is the business end of the water jet. High-pressure water flows into the nozzle, where it is mixed with abrasive and the combined stream then exits directly onto the material to be cut. The motion system moves the nozzle across the material. Pump The high-pressure water pump takes water and pressurizes it to between 40,000 and 60,000 PSI (2800 and 4,000 bar). For comparison, your garden hose can supply water at a pressure of about 60 PSI (4 bar). The pump is the major wear component of a waterjet and requires periodic maintenance to replace components. In the picture above, the pump is enclosed in a cabinet to reduce noise

44 Abrasive delivery system Abrasive, typically a hard reddish mineral called garnet (visible in the clear cylinder in the above picture) is fed through a tube into the nozzle. In the nozzle it is mixed with the high-pressure water to form the water/abrasive stream that cuts through the material. The abrasive flows at a rate of between one-half and one pound per minute (0.2 and 0.5 kg/minute) and is usually gravity fed. Motion System The motion system moves the nozzle head along an X-Y axis. In the above picture, each axis is covered with a black bellows that can expand and contract. The bellows protects the precision gears used to position the nozzle from water and abrasive. The precision and accuracy of a water jet begins with the precision of the motion system—for the 2652 system shown above, the nozzle can be positioned to an repeatable accuracy of " (0.03 mm). Catch tank All that water and abrasive (and bits of eroded material) needs to go somewhere and that somewhere is the catch tank. The catch tank also serves to dissipate the energy of the water jet stream so that it doesn't cut into the floor. The excess water flowing into the catch tank can be recirculated or sent to a storm drain. The spent abrasive typically accumulates in the catch tank and is periodically shoveled out.

45 As with automobiles, there are los of accessories and options, such as automatic tank clean-out systems, water recyclers, special tilting heads, fixturing, or motorized Z axis, and so forth but the above form the basic system, and is everything you need for making most water jet parts. Tips on making good drawings One of the big advantages to computer-controlled water jet systems is that you can draw a part on your computer, take it to a job shop, and have them quickly turn your drawing into reality. This also introduces a brand-new area where mistakes can be made and the nice little five inch part you drew comes back as a five foot giant because you labeled the dimensions incorrectly. The better your drawing, the better your part will be. Following are some tips on creating good drawings that will minimize the chance for mistakes. Draw your part to scale When drawing your part in your CAD program, use a scale of 1:1, or else when the part is made, it may be off by whatever odd scale you drew it in. It is easy for the jobshop to rescale the part, but they need to know ahead of time that this is needed. This might not be caught until after your part is made; therefore, just draw it to 1:1 scale to start with. Keep your drawings clean Remember, your CAD drawing will be turned into a tool path eventually. If you have lines on top of lines, or other stray entities in your drawing, it will make it difficult for the programmer to turn it into a tool path, especially if their CAD / CAM system does not have good automatic "cleaning" functionality. Make sure your drawing matches your dimensions If you draw a circle that is 5.3" (13.4 cm), but then put a dimension on it that says it is 5.0" (12.7 cm), it will probably still be cut at 5.3" (13.4 cm). Therefore, draw it the size you want it, so it gets cut that way.

46 Include only the part you want made in the file In the file you supply to your vendor, include only the stuff that you want cut to avoid confusion. Don't include related parts, or information about drawing revisions. Every line in the file should belong to the part. Ask your vendor what kind of file they prefer to get Your vendor may prefer files from a particular drawing program or in a particular format. There are a lot of different CAD programs available and chances are that your vendor is experienced with only a few. Work with them to figure out what their preferred format is. If you are using CorelDraw or Adobe Illustrator, then you may need to go through additional file conversions to deal with curves. These programs will typically convert all curves to many short line segments when creating DXF files. This can result in your final part having curves that are faceted (although typically each facet is very very tiny). There are a few ways to deal with this situation. The first is to just do nothing, and live with the faceted faces if this is low precision artwork. Another suggestion is to save as an Adobe Illustrator AI file, and then use a third party convertor such as Bezarc from Kandu Software to convert the file into a much better DXF than CorelDraw makes. Some vendors may also have the option of a "smooth" command to help automate the task of converting the lines back into curves (OMAX Layout software has such a command ).Bezarc Kandu Software

47 Compatible file types Computer-controlled water jets use files to transfer information about parts. When you draw a part using a computer program, you create a file with the instructions necessary to draw the part. Whether or not another program can correctly read that information depends on the file type. If it is a standard file type, then many other programs can read the file. The most common file types for drawing data (or CAD data) are DXF and DWG. The DXF (Drawing eXchange Format) file format is a public standard that is published and available to all developers. The DWG (DraWinG) file format is proprietary to the company that creates and sells AutoCAD. This has not prevented other developers from writing programs to read and translate DWG files, but it does make their job harder. Of course, each developer likes to "improve" the standard and many of them will add these improvements to their version of the file. This can cause problems when you try to read a DXF file written by Developer A (with all their improvements to the format) using a program from Developer B (and all their improvements). Fortunately, it's not total chaos, and for the most part isn't particulary confusing. But you can take some steps to make sure that the file you create can be read accurately by the person you're giving it to. AutoCAD Release 12 DXF files are widely compatible Newer versions of the AutoCAD DXF file are less likely to be supported. Generally speaking, the newer the format, the less compatible it is. If you have a choice when you save the file, choose the AutoCAD 12 DXF version. Avoid "binary" dxf files Virtually nobody supports binary DXF files Explode or ungroup all entities Before saving as a DXF, "Explode" all entities that define the geometry of the part. Most CAD programs let you group together entities to make it easier to copy and move them. Be sure to explode (or "ungroup" or "convert to curves") before saving the DXF file. Use simple lines and arcs whenever possible The DXF file format doesn't support Bezier curves or other fancy (and convenient) ways of creating complex curves. When you export the DXF file, they will be translated and might not turn out the way you want them to. The best thing is to start with simple lines and arcs which are exported exactly as they appear. You may find that your drawing program does not allow you to "Save" the file as a DXF. Most likely, there is another command such as "Export " or "dxfout" that will do the job.

48 If you have trouble reading a file after it was ed, then ZIP it up first, using a program such as WinZIP or PKZip. Some programs will alter DXF files as they appear to be text files that can be formatted WinZIP PKZip Document your file You can also make sure that you include documentation when you send your file to somebody who will be making your part. This will help make sure that you get the part you think you will get. Provide a print-out, with dimensions, so the programmer can check the file conversion against known geometry and dimensions. The units of a DXF or DWG file are sometimes ambiguous, so the part will likely import at the wrong scale. (In fact, the DXF file format doesn't include dimensions at all.) Draw two concentric squares on each drawing that you send. The outer square should have a dimension of 1" x 1", and the inside square should have a dimension of 1 cm by 1 cm, as in the picture below:

49 Whoever you give the drawing to can quickly see if the drawing is properly scaled by simply measuring the edge of one of the squares. This will prevent mistakes such as cutting a part that is 25.4 times too big due to some metric conversion problem. (The tiny text underneath the 1 cm square says, "Note: If the dimensions of this box are not what is specified, then this drawing is not to scale and should be re-sized accordingly.") Tip: If the file will eventually end up on an OMAX system, then you can use the "Layers" in your CAD system to specify cutting Quality (Layer 0 is for heads-down traverse, 1-5 are Qualities 1-5, 6 is "etch", 7 is "scribe", 8 is "water only", 9 is for leads, 10 is for "heads-up traverse", and 11 is for "Minimum Taper."Quality Water jet machine sizes Water jet machines come in a variety of sizes, from small ones that fit into one corner of a machine shop to large ones that completely fill a shop. Machine size is typically measured as the size of the "bed" or area where the material to be cut is placed. Note that the cutting area (the area that can be cut with the water jet head) is usually slightly smaller than the bed (you do not want the water jet head cutting into the sides of the machine). So when a machine is referred to as a "2 ft by 4 ft (0.6 x 1.2 m)" machine, that is not the total size of the machine, but the size of the bed. Typically, machines are made to accommodate standard material sizes to simplify loading. Water jets are machine shop tools and even a "small" machine requires industrial levels of power and water supply not found in a home workshop.

50 For "off-the-shelf" machines, there are basically three sizes : Small water jet machines Medium water jet machines Large water jet machines Some machine shops will have a single small machine to supplement the other machine tools they use. Other shops, with more water jet work, will have several medium machines, while a dedicated water jet shop might have several small machines, one medium sized one, and one large water jet running multiple nozzles Custom machines Custom machines are built and designed for specific purposes. In some cases, they are built into a production line, so that the material is constantly moving past them as they cut. Custom machines are used for diaper cutting, food cutting, cutting automotive carpet, mining applications, eye surgery, and cardboard box making (if the material moves quickly enough it doesn't have time to get wet).

51 Are big water jets faster than small water jets? It seems like a large water jet machine should be faster than a small water jet, since that's the case in many other areas. But just as a sports car can be faster than a dump truck, that's not always the case with water jets. With larger machines, you can run multiple nozzles at one time. Since the nozzles need to move together, this is typically used for larger production runs, but it will be much faster than a smaller machine with a single nozzle making the same part. You can also load larger pieces of material into big water jets. Time spent loading and unloading material is time not spent making parts. If you can reduce the amount of time (per part) spent loading and unloading material, you can make each part more quickly. On the other hand, with larger machines, the plumbing between the pump and the nozzle tends to be longer and more complex, resulting in pressure loss. While the pressure might be 60,000 PSI (4,100 bar) at the pump, it may only be 55,000 PSI (3,800 bar) at the nozzle. This pressure loss means that the pump must either work harder to produce more pressure at the nozzle (and use more energy and increase maintenance), or the cutting must be slowed down to compensate. Small machines have shorter plumbing runs and lose less pressure. Small water jet machines Small water jet machines are smaller than 2 x 4 feet (0.6 x 1.2 m) in size and are typically they are used in general machine shops. They are also popular in EDM shops, schools, and other places where a multipurpose machining tool is handy.

52 If you are looking at a first machine to purchase, these are great choices because they don't cost much and there is little risk in purchasing one. The water jet can pay for itself if you keep it busy as little as a half day per week. Advantages The initial payment on machine is low, so the machine doesn't have to spend as much time working to pay for itself. There is a low risk to purchase. For price of some of the big machines, you may be able to buy two small machines, and double your productivity. The small size makes them convenient for secondary machining. Ergonomically, they are simply more fun to use. Small footprint does not take up a lot of shop space. Easy to move around as your shop flooring arrangement changes. Easier than larger machines to setup and install. Generally offer higher precision than their larger cousins. In some cases, smaller machines can offer faster cutting, because shorter plumbing lengths reduce pressure loss between the nozzle and the pump.

53 Disadvantages Small cutting area, although on some machines you can feed larger stock into the machine. Investment Complete systems can be had for less than $80,000. A complete system is everything you need to get a new machine and have it running including the pump, XY table, nozzles, abrasive delivery system, controller, software, installation, and training. While at first this may seem like a lot of money for a machine tool, keep in mind that small machines can quickly pay for themselves. Water jets bring in more revenue per hour than traditional tools and can pay for themselves quickly Medium-sized water jet machines Medium-sized water jet systems range from 4 x 4 feet to 4 x 8 feet (1.2 x 1.2 m to 1.2 x 2.4 m) in size. Sometimes they are used with multiple cutting heads, although multiple heads usually work better with larger machines. These are typically purchased by machine shops who do larger work, or simply want a machine that is large enough that they can fit big sheets of material to reduce the time spent loading and unloading material.

54 Advantages Fit larger sized sheets of material into the machine. Not only does this allow for larger pieces, it also lets the operator cut more pieces before having to change the material. Smaller footprint relative to a larger machine means less space used. Easier than the giants to setup and install. Disadvantages More expensive than smaller machines. Sometimes you may be better off with multiple smaller machines. More difficult to load and unload materials, because material sheets can be larger. Awkward to use for secondary operations due to their large size Investment Complete systems are available for around $100,000 to $200,000, depending on options. A complete system is everything you need to get a new machine and have it running including the pump, XY table, nozzles, abrasive delivery system, controller, software, installation, and training

55 Large water jet machines Large machines can fit material that is 8 x 16 feet (2 x 4 meters), or larger in their beds. They typically run multiple cutting heads, and are used in high production environments. Large water jet- only job shops and laser shops are typical buyers of such machines. A large water jet machine (shown on the manufacturing floor) Advantages Fit huge sheets of material into the machine Run multiple cutting heads at once Large material size means more parts per sheet, which translates into less time changing material per part

56 Disadvantages Large initial cost More difficult to load and unload materials because of their size Awkward to use "as a machine tool" for secondary operations Large enough to require specialized shipping and installation in most cases Need to have a lot of work to pay for the machine. The tolerances on such big machines can be lower than other water jet machines low (but this is not always the case) More expensive to own and operate Pressure loss in long length of plumbing between pump and nozzle can result in less efficient cutting (higher costs for lower cutting speeds.) Investment Complete systems are available for around $200,000 to $400,000, depending on options. A complete system is everything you need to get a new machine and have it running including the pump, XY table, nozzles, abrasive delivery system, controller, software, installation, and training.

57 Related articles Controller types Choosing a pump Tank and table size Basic water jet safety In general, are quite safe. The nozzle is typically 0.1" (2.5 mm) or so from the material, so it is difficult to get your fingers under it. High pressure tubing does not explode because water is not very compressible. When a leak occurs, the pressure quickly drops to a safe level. That said, like any machining tool, there are hazards to working with a water jet. You should refer to the manufacturer's material for complete safety information. The information provided here is basic and does not cover all the potential hazards and should not substitute for carefully reading the safety information provided by the manufacturer of the water jet.

58 Beware the water jet stream Remember that the water jet stream can cut through 2" steel, so it will make short work of any body parts you place in front of it. It is a very dangerous cutting edge. Always take care before turning on the machine to make sure that no body parts are in the way. Eye protection You can put splash guards on the nozzle and cover it with rags and you will still get the occasional splash of water mixed with abrasive. You do not want to get abrasive in your eye—although it's inert, it's still abrasive and will irritate your eyes and possibly scratch your cornea. Motion control system The motion control system precisely positions the nozzle at various locations on the table and can move at up to 100 inches per minute (2.5 meters per minute). Don't let body parts get between the nozzle and a solid object or they can be crushed. Ear protection When you are cutting above water always wear ear protection. The water exits the nozzle at about the speed of sound and makes a lot of noise—enough noise to damage your hearing. When cutting underwater, the noise level is much lower, but depending on your shop environment, you may still want to use ear protection

59 Water jet abrasives An abrasive jet uses a mixture of water and abrasive to more effectively cut through materials. A pure water jet (one without abrasives) is effectively only for very soft materials, such as rubber or food products. Adding abrasive, however, greatly enhances the cutting capability and the abrasive water jet can cut through steel. As you might expect, the type of abrasive is important. The overwhelming choice for most water jets is garnet abrasive. Garnet is a gemstone that has been known and used by humans for many thousands of years. The type used in water jet machining is red garnet. Garnet is fairly hard and when it fractures, it forms sharp edges. Both of these qualities are advantages in water jet machining. Garnet is also relatively chemically inert, and won't react with materials being cut, making its disposal simpler as well. A boulder with crystals of garnet embedded in it (boulder courtesy of Barton Mines)Barton Mines

60 Garnet used for water jet machining is either alluvial or mined (sometimes called "hard rock"). Alluvial garnet comes from river beds, where it has been smoothed by the constant running water. Because the grains of alluvial garnet are smooth, it's not as effective as mined garnet at cutting. Alluvial garnet doesn't require expensive mining, however, so it is sold at a lower price. Mined garnet is typically found mixed with other minerals and must be blasted out of the mine. Then it is crushed, and separated from the rest of the rock. The crushing causes the edges of the garnet to be sharp, and therefore cut better with less taper and minimal burr. Water jet garnet is sold commercially specifically for waterjetting—you can buy bags of water jet garnet from suppliers. Abrasive usage A water jet will use from about 0.25 pound (0.1 kg) per minute to 2.0 pounds (1 kg) per minute depending on the pump and nozzle you are using. The typical usage is about one pound (0.45 kg) per minute. The flow rate of abrasive will generally be constant for a given setup. The flow rate does not vary depending on what you are making (unless you turn abrasive flow off and use water-only cutting).

61 Abrasive cost Prices for abrasive varies from 15 cents per pound to 40 cents per pound, depending on the quality of the abrasive, and where you buy it. You should pay the extra money for good abrasive, especially if you are new to this technology, as quality abrasive will result in quality products. Abrasive is one of the biggest operating costs associated with running the machine. Consider purchasing abrasive in large quantities for a discount. You might even coordinate your purchase with a nearby competitor, as you will both save money. Garnet can be purchased in 100 lb (44 Kg) bags and in 50 Lb (22 Kg) bags and buckets

62 Alternative abrasives You can use other abrasive types, some of which can make your machining cheaper. For example, if you cut a lot of aluminum, you can use a softer abrasive, such as olivine, than you would use for steel. The advantage of using a softer abrasive is that you wear out your mixing tube (nozzle) slower. Garnet is a very good general purpose abrasive, which is why it is so popular. Warning Never use abrasives containing silica, such as beach sand. The dust generated by silica abrasives can cause silicosis, a deadly and painful lung disease. Qualities to look for in abrasives You should avoid purchasing abrasive on price alone., as it will often be the case that you get what you pay for. There are many factors that determine a good abrasive, and the advantage of using a high quality abrasive is that you will get faster cutting, higher precision, and less frequent nozzle plugging. Here are some qualities to look for in an abrasive: Double sifted This means that the abrasive has the fine particles removed, as well as the big particles. Therefore, you have a consistent mesh size. Fine particles and large particles both contribute to nozzle plugging, inefficient cutting, and other problems. While there will always be a range of particle sizes in an abrasive, the narrower the range, the better

63 Sharp Sharp abrasive particles cut better. Mined garnet is sharper than garnet from a beach, or alluvial garnet, that has been worn into round beads. Purity Look for an abrasive that is pure. An abrasive with impurities will affect your cutting performance. Softer impurities will lengthen your cutting time, while garnet with unusually hard bits in it, such as aluminum oxide, may cut marginally faster with a severe drop in nozzle life. Price Of course price should be a primary concern, but not the primary concern. Understand that a higher priced abrasive may actually reduce your hourly cost of operation. This is because a good abrasive, that does a good job cutting, will allow you to cut faster. Thus, you can get more inches of cutting out per dollar spent on abrasive. If you want maximum cutting speed, then you can choose a coarser abrasive, such as 60 mesh or 80 mesh. If you want smoother surface finish, then choose a finer abrasive such as 100, 120, or 150 mesh. Consult the manufacturer of your nozzle for recommendations. The 80 mesh abrasive is very popular, and in high demand. Therefore, it is also the most expensive. If you go with a coarser or finer abrasive, then you can save some money. The trade-off is that you may not cut as well.mesh

64 When you first get your machine, use the machine with whatever brand of abrasive your equipment manufacturer recommends. Most likely, they will recommend either their own brand, or one that causes the least trouble. Later, as you gain experience with the machine, you can shop around for better deals. Be careful of being locked into long term deals on abrasive unless you are 100% sure that the abrasive you are ordering is right for your long term needs. If you think you are getting a good deal by signing a contract for a years' worth of 80 mesh garnet to cut your thin aluminum, at $0.25 / lb, then discover that you could have used a softer or lower grade abrasive at $0.15/lb, then you are stuck for an entire year using the wrong garnet for the job. Recycling abrasives There are used (or "spent") abrasive recyclers available from Ward Jet. According to the manufacturer, the WARD (Water Abrasive Recycling Dispenser) recovers a large percentage of used abrasive for re-use. When the grains of the abrasive strike the metal, some of them are fractured into smaller pieces, which means that the spent abrasive is not all the same size as it used to be.Ward Jet This means that you'll need to screen the spent abrasive to remove particles that are too small, as well as remove the small pieces of material from what you were cutting. Reusing abrasive is more complicated than just shoveling your tank into your abrasive hopper. "The function of the WARD 24 is to remove the sludge from an abrasive water jet cutting tank, separate out the sludge and all abrasive that is smaller than 100 mesh, then wash the abrasive larger than 100 mesh, dry it and screen it once more, simultaneously allowing operators to add new abrasive to the recycled abrasive at the desired ratio." - Quote from Easi Jet web site

65 Cutting speeds Ideally, you want to make the most precise part possible in the least amount of time, and for the least amount of money. Cutting speeds are a function of the material to cut, the geometry of the part, the software and controller doing the motion, the power and efficiency of the pump making the pressure, and a few other factors such as the abrasive used. A typical part in ½" (1.3 cm) aluminum might take 2 to 10 minutes to make. In ½" (1.3 cm) steel, it takes twice that time. A 2" (5 cm) thick part might take hours, while a 1/16" (1.5 mm) part will cut in seconds. Time to make parts will also vary based on the equipment used in making the water jet machine. If you need a specific time, you should contact a water jet jobshop or a water jet manufacturer, but be sure to have a drawing of your part ready. As you will see in the discussion below, the shape of the part affects how long it takes to make.water jet manufacturer The chart below shows how long a few typical water jet parts take to machine.

66 Picture of partDescriptionApproximate Cutting time 2.5" x 2.5" Box cut from 0.5" thick mild steel (6 x 6 cm from 1.2 cm steel) 5 minutes Same part as above, only in 3" (7.6 cm) mild steel 2.25 hours 8" wide Electrical Panel cut from 0.06" mild steel (20 cm from 1.5 mm steel) 1 to 3 minutes 3" wide gear cut from 0.25" thick nylon (7.5 cm from 6 mm nylon) 1.25 minutes 10" wide part cut from 1" thick titanium (25 cm wide from 2.5 cm thick titanium) 22 minutes 7" tall horse cut from 0.25" thick aluminum (18 cm tall cut from 6 mm thick aluminum) 4.8 minutes

67 Material being cut and thickness Hardness Generally speaking, harder materials cut slower than soft materials. However, there are a lot of exceptions to this. For example, granite, which is quite hard, cuts significantly faster than copper, which is quite soft. This is because the brittle granite easily breaks up under the water jet stream. It is also interesting to note that hardened tool steel cuts almost as quickly as mild steel. Even with granite, there is some variation in cutting speeds. "Absolute black" granite, which is tough as nails, cuts a little slower than copper. Thickness The thicker the material, the slower the cut, with no exceptions For example, a part that might take one minute in 1/8" (3 mm) steel, might take half an hour in 2" (5 cm) thick steel, and as much as 20 hours in 10 inch (25 cm) thick steel.

68 Geometry of the part The water jet stream cuts most efficiently when it is moving in a straight line. The cutting head must slow down to navigate sharp corners and curves. A part with a lot of curves and angles will take longer to make than a part with long straight lines. It also takes additional time for a water jet to pierce the material. Therefore, parts with lots of holes requiring pierces will cut much slower than simpler shapes. Desired Result If you want a high tolerance part or one with a smooth surface finish, then the part will take longer to make. By changing the machining speed, you can make some areas of a part high tolerance and other areas fast, so you can mix and match to get the optimal balance between cutting speed and final part quality.

69 Software controlling the motion The software controlling the water jet head is probably one of the most overlooked aspects of abrasive jet machining. You would not think that software would have much to do with the speed of cutting. In fact, this is (mostly) true if all you are doing is cutting in a straight line. However, as soon as you introduce any complexity to the part, such as a corner, there is great opportunity for software to optimize the cutting speed. A part to be machined from ½" (1.2 cm) mild steel Notice the subtle difference between the two pictures show above. (The colors represent cutting speeds, with yellow being the fastest areas, and blue being the slowest.)

70 The part on the left took 3.3 minutes to machine, while the part on the right took 4.4 minutes to machine. That's a one minute difference, or about 25%. The difference, as it turns out, is the software that automatically optimizes the tool path to provide the desired precision in the least amount of time. The software looks at the geometry of the part, and then modifies the feed rates and adjusts the cutting to get the maximum speed. The optimizations include finding the best speeds and accelerations for all curves and corners, setting the best length and feed rate for all pierce points, adding special "corner pass" elements at corners to allow the cutting to go right past the corners where it can, and so forth. In the last 15 years, software has gone from simply optimizing corners to adjusting more and more factors as processing speed improves and cutting models improve. Predicting the behavior of a high-pressure stream of water mixed with abrasive as it strikes different materials is becoming more refined, which lets software better predict the ideal speed and acceleration for a part. Power at the nozzle The more horsepower at the nozzle, the faster it can cut. How much horsepower makes it to the nozzle is a function of the pressure and the orifice that the water passes through. Note that there is a difference between "horsepower of the motor" and "horsepower at the nozzle." It is the power that actually makes it to the nozzle that is most important. Having a big motor makes no difference, if the power all goes into wasted heat.

71 Simply put, the higher the pressure, the faster the cut. The more water you flow, the faster the cut. Unfortunately, as the pressure increases, so does the cost and maintenance, so this is not as simple as it seems. This is also why you rarely see production pumps that run more than 60,000 PSI (4,100 bar). A good way to learn more about how pressure and jewel size affect cutting rates, and to calculate "nozzle horsepower" is to download and run Water jet Web Reference Calculator.Water jet Web Reference Calculator Quality and amount of abrasive Quality of abrasive In the industry, most machines run 80 mesh garnet for abrasive. However, it is possible to cut slightly faster with harder abrasives, but the harder abrasives also cause the mixing tube on the nozzle to wear rapidly. Garnet turns out to be a good compromise. Not all garnet is the same, however, and the differences start with where the garnet was obtained (alluvial garnet is rounder and smoother than crushed garnet from a mine). There are also big variations in purity and uniformity between brands of garnet that can affect the cutting speed and accuracy of water jet machining.

72 Amount of abrasive Typically, water jets consume between 0.5 and 1 lb (0.25 and 0.5 kg) of abrasive per minute. More abrasive will, up to a point, improve cutting efficiency, although at a higher cost. There is a sweet spot for every nozzle size and pressure as to what abrasive flow rate will cut the fastest, and what flow rate will cut the cheapest. Water quality considerations The main reason you care about water quality when you use a is that it has a large effect on how long various components in your machine last. Components in high- pressure water pumps and nozzles will wear out much faster if you have poor water quality, especially if there are a lot of minerals in it. Paradoxically, you don't want your water to be too clean, as water is an excellent solvent and if you remove all the trace materials from it, it will begin to dissolve your pump and nozzle parts. Have your water quality tested while you are evaluating equipment to purchase. Some manufacturers will do this for you, and give you suggestions on any action you may need to take if your water requires it. In the worst case scenario, you will have to purchase some sort of water cleaning system such as a reverse osmosis filter, or water softener, or water chiller. Follow the manufacturer's recommendation. If they say you need extra equipment, then believe them. They don't want unnecessary technical support calls, and neither do you.

73 Also remember that just because you have your water quality tested once, does not mean your water quality will stay consistently good. When there is unusual weather, or for other reasons, your water department may switch reservoirs. If you suddenly find that you are wearing out nozzles faster than normal, suspect water quality to be the culprit. Make sure your water quality is tested for "total dissolved solids" (or TDS), and not just bacteria. You won't be drinking the water—you will be using it to make parts. It is the dissolved minerals in the water that will cause the most trouble. Other problem areas are solids in the water that may clog filters. Water temperature Water temperature has a big effect on seal life in high-pressure water pumps. Keep the water cold (below 70° F / 20° C). Otherwise, the seals may tend to soften, extrude much faster than normal, and result in dramatically more frequent maintenance of the pump. If you are recycling your water this is especially important, since heat will accumulate in the water as it cycles through the system. In some cases, a water chiller may be recommended. Talk to your manufacturer for recommendations.

74 An Ebco brand closed-loop filtration system A closed-loop filtration system will recycle your water and filter it, both reducing your water consumption and keeping your water clean. If you are cutting a lot of toxic substances such as lead, something like this may be necessary. If you do use a closed-loop filtration system, you may need to add a chiller to keep your water temperature low to avoid excessive wear on your water pump. Water jets use between ½ and two gallons (2 to 8 liters) of water per minute when cutting. Some of the water is used for cutting, and some for cooling. The water is typically treated as "gray water" which can be recycled, or sent directly to the sewer. Again, if you are cutting something toxic, you may need to filter water, and recycle or dispose of it in special circumstances. SUPER-WATER® SUPER-WATER® is a chemical you can add to the water of an water jet to focus the cutting stream, increase cutting speed, and reduce wear of high pressure components. Traditionally it has been used for high-pressure cleaning and water-only cutting applications. Although it is not widely used in the water jet cutting industry, it may offer some benefits

75 Tilting the machine head There are several reasons why you might want to tilt the machining head which contains the nozzle. These include Increasing precision by removing tapertaper Creating beveled edges for artistic purposes or for die relief Creating sharp edges to use for knives or cutters There are two main ways in which tilting is achieved: manual tilting, and tilting under program controlmanual tiltingtilting under program

76 Automatic tilting heads A more complex method for tilting is with an automatic tilting head, that tilts the nozzle during machining. In most cases, the main purpose of the multi-axis cutting head is for taper removal to make perfectly straight edges in the part for high-precision work. Multi- axis heads like this can also be used to purposely introduce small angles into the part as well (but things get a bit more complex when this is desired taper A programmable 5-axis tilting head

77 ( Right) Water jet part with virtually no taper. On the left is a picture of the same part set vertically next to a 123 block on a surface plate, demonstrating its lack of taper. Another pair of parts cut with a tilting head: 0.5" (1.2 cm) brass bicycle and 0.5" (1.2 cm) stainless steel test part

78 Computer controlled tilting cutting heads can offer a significant improvement in cutting precision over non-tilting cutting heads. The big advantage is that you can make a virtually taper-free part, without having to slow the cutting down. It's also possible to cut almost taper free parts without tilting. However, it takes a much more careful setup, and it also takes slowing the machine way down. The end results are not quite as good as when cut with tilting, and the part is way more expensive to make, but if you rarely care about taper, then maybe a no-tilt strategy is fine. A water jet cutting Teflon

79 The above picture shows a lot of things: In the foreground, there is a mechanical drill mounted to the same motion system as the nozzle. This is used primarily to pre-drill start holes for cutting. Pre-drilling is almost never required, but is useful when cutting materials that don't pierce well, such as some laminates that otherwise might blister. Although this picture shows Teflon ® being cut, the drill was not used in this case, as Teflon cuts nicely without it.) In the background is a tilting cutting head for taper removal. In this setup with both accessories attached, the drill drills, and the cutting head then moves over to do the cutting. Some Teflon plastic material, and some parts cut from it. Notice that all of the parts are linked together with short bridges so it's one single part that is cut, and then the small pieces are cut off with wire cutters or similar later. Water jet brick supporting the material. This is useful to use when the splash-back from the slats might mar the material (in this case, to prevent the Teflon from getting scratched up). It is also useful for supporting the material when cutting tiny parts that might otherwise fall through the slats. In this particular machine setup, the water jet brick is mounted on half of the machine, while traditional slats are mounted on the other side.Water jet brick Aluminum "square" that the Teflon is pushed against. By cutting a square like this from a sheet of aluminum bolted to the table, it is possible to precisely locate parts for secondary machining. Because the machine was used to cut the square, it is assured that the square is indeed "square" to the machine, and the corner of the square's position is known exactly, so that it can be used as a reference point. Notice the Quick-Grip clamp and weight used to fixture the materials. This is a pretty typical fixturing setup

80 Another picture of a tilting cutting head with a splash guard is in front Programmable tilting heads are excellent for making precision parts, because taper is almost completely eliminated. Because the head can tilt in all directions (including towards the operator and towards the side of the catcher tank), the tilting movement of the head may be restricted for safety reasons. If a part made with a given material has a lot of taper, it may not be possible to remove it all using the automatic tilting head. You do not have to use a tilting cutting head to make precision parts. You can make nearly taper-free parts without tilting by simply slowing the cutting down. However, it is usually necessary to slow the cutting down a lot to get rid of taper in many parts, so the tilting head allows you to make the same part in less time. Control of the tilting head is handled by software, as it can be quite complex to calculate the position and angle of the head for the entire tool path. As a result, it is easy to use a tilting head. With most software, there is simply a check box that turns on the tilting calculations.

81 The tilting head won't completely eliminate taper for all parts. In very thick parts, where barrel taper can occur, the tilting will only get rid of some of the taper, but not the barrel. When cutting over water jet brick, tilting the head will cause the brick to wear out faster than usual because the stream is hitting the brick in the sides.water jet brick Manual tilting of the nozzle One of the easiest ways to create angled cuts is by simply tilting the nozzle to the desired angle. The advantage of this is that it is cheap and easy to do. No special programming is required. A disadvantage is that significant more splash will occur, since the nozzle is now pointing diagonally across the catcher tank. You also cannot change the tilt for different features of the part without having to stop and readjust the nozzle angle. If you modify your machine to do this kind of work, be sure to consider the splash. You should aim the nozzle so that the splash shoots towards the back of the machine, and away from you. Also, cut a nozzle guard from a piece of pipe, that is at an angle, so that the bottom of the pipe is flush with the surface to cut. And, as always, wear eye protection

82 Also, remember that the jet is a lot more powerful than it looks. When you tilt it sideways, it shoots sideways, and ricochets sideways. Take extra precautions with this in mind— don't cut too close to the edge of the catcher tank. Don't cut yourself to pieces, and don't cut your machine to pieces either. Below are some pictures of some blades cut with a fixed tilt water jet. Blades with tapered cuts in stainless steel, and the one with the blue background is in M2 high speed steel. A typical part like this would take perhaps 2-5 minutes to cut depending on the complexity of the shape. With precision water jet machines, little or no additional grinding is needed

83 Close-up of the edge of the blade. Special mounting for the nozzle to allow it to tilt

84 You can get a special mounting for your nozzle which makes it easy to tilt the nozzle. All you do is loosen a nut, and the nozzle is manually tilted to the desired angle, then the nut is retightened. Depending on how the plumbing for the high pressure tubing is handled, it may need some adjusting as well. The big red plug in the side of this assembly shown above is a plastic plug to prevent dirt from falling into the nozzle assembly, since the plumbing is not hooked up in this picture Controller types The controller is the brains of the water jet. It turns the high-pressure water pump on and off, and sets the pressure if the water pump is capable of it. The controller also controls the abrasive feed, and it also positions and moves the nozzle on the table. A good controller moves the nozzle at exactly the right speed to cut through the material with a good finish. If the nozzle moves too quickly, then the material isn't cut all the way through; too slow and money is wasted (and sometimes, the part has lower tolerance). The controller's job is made harder because a water jet is a "floppy tool" that is picky about feed rates and accelerations. Unlike a saw with a rigid blade, a water jet is a stream that bounces off the material, lags behind when moved, and generally behaves in a chaotic and difficult to predict way. Predicting the behavior of the water jet stream requires complex algorithms in the controller. Traditionally, water jets have used CNC controllers, but CNC controllers are just not good at automatically setting feed rates and accelerations. Some can do it, but not very well. If the controller does not automatically handle this chore, you have to do it by hand. CNC's have the advantage of being able to do highly sophisticated multi-axis work, but are much more difficult to program, even for 2-D work, especially in the area of setting speeds and accelerations. Since the mid-1990's standard PC computers have become the platform of choice for controllers. They have the advantage of being relatively low-cost and since computer power is always increasing, the controller software benefits from this speed increase. When the controller software is moved to a new generation of computers, the software is faster with little or no adjustment to the code.

85 User interface The "user interface" (UI) is what you see when you work with the controller (or any piece of software). The UI can make sense and be easy to use, or it can be complicated and difficult to figure out, with many obscure icons. In general, the UI has to find the right balance between simplicity and power. If the UI is too simple, then there's not much you can do with it. Adding power and flexibility to the UI will complicate it and make it more difficult to learn and use. You are the best judge of whether or not the software is easy to use, so you should be sure to work with the software before purchasing the system. The other important thing about controller sofware is how compatible it is with other CAD / CAM software. Can you import files from AutoCAD, MasterCAM, Adobe Illustrator, and other popular CAD / CAM packages?CAD / CAM

86 Water jet operating costs A ball park figure for a generic machine would be roughly $25 to $30 per hour plus whatever you pay your employees. The operating costs include the following: Abrasive An abrasive jet uses abrasive at a rate of between one-half and one pound per minute (0.2 and 0.5 kg/min). Over the course of an hour, it can consume up to 60 pounds of abrasive, or about a bag of abrasive. Electricity The high-pressure pump consumes a lot of electricity, so even though electrical rates are cheap in most parts of the country, these costs can add up quickly. Water The price of water will depend on whether you recycle, but a waterjet consumes about a gallon per minute of water. Replacement of worn parts Nozzles wear out with time and need to be replaced between every 40 and 100 hours. They are expensive and cost hundreds of dollars. Similarly, replacing worn parts for the high-pressure pump adds to the per hour cost. Clearly, carefully tracking costs can make a big difference in making a profit with a water jet machine. Fortunately, most modern water jet control software keeps track of how many hours the machine is running, so this simplifies the task of calculating the per hour rate. Some software even lets you enter notes about when maintenance was done, making it even easier to accurate calculate your true costs.

87 Building your own water jet In general, this is something you should avoid unless: you think building it yourself would be fun, but you don't intend to run it as a business, there is no machine available on the market that can do the particular highly specialized job that you want to do, and none of the machine builders want to make a custom machine for you. Many of the early machines were home-built systems consisting of purchased components such as pumps and nozzles married to other components for control and positioning. But these were prone to a lot of problems that have been addressed in the factory-built systems. Here are some recommendations: Learn what the new machines can do Visit several manufacturers and trade shows. This will help you understand what you are getting yourself into, and so that you can get some ideas if you still want to continue. You may also find that a manufactured machine will suit your needs very well.

88 Join the water jets discussion group The Water jets discussion group is a community of over 2500 water jet users from around the world. There, you can ask questions and discuss ideas with other people who have done this.Join the water jets discussion group Use this web site as a resource for finding vendors of spare parts and accessories.spare parts and accessories X-Y positioning system Making the X-Y positioning system to position the cutting head is the easy part. Just be sure it is well-protected from dust, grit, and moisture, and that the operator of the machine is safely protected. Use enclosed bellows and non-rusting components wherever you can. Be wary of simply adapting an old plasma table, because it probably will not have the protection needed. Controller The controller is the part that controls the movement of the water jet head. Since water jets cut mostly by moving across material, controlling the speed of movement is critical to getting efficient cutting

89 Making your own controller is not easy. You should definitely read the controller section of this web site for a brief overview of the complexity involved, and options in this regard. Doing it right is a huge effort, but the differences in ease of use, cutting speed, and part quality are dramatic. One manufacturer was able to speed up cutting by well over 200% over traditional non-water jet specific controllers by optimizing the tool paths based on precision cutting models and such. Precision and edge quality of the cut were also improved dramatically. And all of this was achieved by optimizing the controller software.controller section That said, if precision and cutting speed and cutting quality are of no concern to you, then there are many controllers out there to choose from. Though if this is the case, you may also want to consider some other technology for your cutting, such as plasma or torch cutting.

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