Presentation on theme: "Materials processing and forming Year 11 Resistant Materials PK/2011 Bitesize clip – Production techniques"— Presentation transcript:
Materials processing and forming Year 11 Resistant Materials PK/2011 Bitesize clip – Production techniques http://www.bbc.co.uk/schools/gcsebitesize/design/resistantmaterials /processtechniques_act.shtml Bitesize clip – Industrial practices http://www.bbc.co.uk/schools/gcsebitesize/design/resistantmaterials /processindpracrev_act.shtml
Materials processing and forming Deforming – allows the materials shape to changed without changing its state Reforming – involves a change of state within the material used; in other words, the material changes from a solid to a liquid or plasticised state
You need to know about Sand casting Drilling Turning in both wood and metal Blow moulding Injection moulding Vacuum forming Extrusion Wood laminating
Sand Casting The pouring, or forcing of molten metal into a cavity and then allowing it to cool and solidify. Used to produce complex shapes such as car engine parts and kitchen/bathroom taps Relatively cheap and simple to use in the school workshop Making the pattern can be difficult and time consuming
look in programmes: - design technology - Focus on metals - sand Casting - click on the green arrow Quick simulation http://www.youtube.com/watch?v=7BI4v0Gqc7k&feature=related
Advantages & disadvantages Waste can be reused Hollow parts can be made with the use of cores Consumes large amounts of energy to melt the metal A new sand cast has to be packed each time which is time consuming Secondary finishing required to produce a flat surface
Sand casting process Make a pattern of the required product Encase the pattern in moulding sand Split the sand box and remove pattern to leave an empty cavity Pour molten metal into the mould When the metal is solidified and cooled, remove the product
Sand casting cont. Split patterns allows two sides of a sand mould to be created and complex casting to be produced. The pattern must have sloping sides so it can be easily removed without damaging the walls of the sand. It must have not undercuts or sharp edges and finished off with a fillet radii. The pattern is usually finished off with a coating of gloss paint.
Sand casting cont. Most common sands are ‘green sand’ and ‘petrabond’. Green sand uses water to bond it together and can be reused. Petrabond is oil based and can only be used once. Sand has to be sieved and lumps removed. Green sand has to be kept slightly damp Before pouring molten metal into a mould with green sand, the sand must be dried out thoroughly or the mould will explode.
Have a go at an exam question Explain one reason why it is essential that a high-quality finish is achieved on the mould before casting. (2 marks) You have two minutes For top marks Make sure that you explain any defects appearing on the mould will also appear in the cast product, and that the product is likely to rejected, wasting time and effort.
Drilling The process of making holes by using rotating cutting tool that is secured in either a hand operated drill or a drilling machine. Most common type of drill is a twist drill, manufactured from high speed steel and can produce holes in most materials. Two types of twist drills: ◦ Parallel shank (held in by chuck) ◦ Taper shank (held in by friction)
Drilling continued NameAdvantagesDisadvantages Pillar drill Can be used continuously Chuck can be removed to accept larger bits Speed can be varied Fixed in one position can be dangerous Hand drill Portable You need to provide the power Will only hold bits up to 10mm Cordless drill Portable Usually has variable speed Can reverse the direction Can be used to put in & take out screws Power limited to battery type & size Batteries have to be charged Limited to max. 10mm bits
Types of drills found Flat bits – used to drill deep holes in wood Forstner bits – used to drill flat-bottomed holes in wood Auger bits – used to drill deep holes using a carpenter’s brace Countersink bits – conical drill bits that allow countersunk head screw to the inserted so it is flush with the surface of the material.
Types of drill bits continued Hole saws- saws that are circular shaped cutting rings that range from 20mm to 150mm diameter. Tank cutters – circular cutters that have an adjustable radius for cutting holes in sheet material.
Now think of 5 safety precautions 1. Use a chuck key to tighten and remove drill bits but never leave in the machine 2. Always wear protective equipment such as goggles and an apron 3. Tuck loose items of clothing such as ties out the way and fasten long hair back 4. Make sure that the object being drilled is held tightly and securely in the machine vice 5. Use the correct drill speed for the material being drilled and for the size of drill being used.
Turning Turning can be undertaken using either a metalworking lathe or a woodturning lathe. Two basic processes that the lathe can perform are: ◦ Facing off – the smoothing of the end of a piece of material ◦ Turning down – reducing the diameter of a piece of material Two types of chuck: ◦ Three jaw self centring for hold round or hexagonal bars ◦ Four jaw independent chuck for holding material of any cross section
Wood lathe The cutting tools are held in the hand and rested on the toolrest The work being machined is usually secured to a faceplate or turned between centres Three basic tools: ◦ Gouges ◦ Chisels ◦ scrapers
Wood lathe Before turning, timber has to be prepared – corners planed down or on small pieces cut off Avoid pieces of timber with knots On long pieces, the centre should be carefully established so that when it is secured and rotated it is not unbalanced. Once materials is secured on the machine, the tool should be checked for sharpness
Wood lathe Tool post positioned so that the top of the turning tool is at centre height of work Make sure the correct spindle speed is selected for the task in hand.
CNC lathe A computer automatically controls all the tools movement Identical items can be manufactured which is difficult to do by hand
Advantages of wood turning Waste can be reused for other purposes such as animal bedding One off shapes and products can be produced Small off cuts from the workshop can be turned into other products
Disadvantages of wood turning Long objects can flex if not correctly supported Once product removed, difficult to reset it to centre Tools need to be sharpened regularly Workpiece and tools get hot Difficult to make exact copies by hand Tools can catch on edges which can be dangerous
H&S points The user should wear a protective face mask The tool rest should be as closed as possible to the work without it touching to stop the tool snagging or being pulled out of the operator’s hand The tool rest and tool must be fixed at the correct height The bigger the diameter of the workpiece, the slower the speed Hold the tool firmly Use the correct shaped tool for the piece being turned
Metalworking Centre Lathe The Centre Lathe is used to manufacture cylindrical shapes from a range of materials including; steels and plastics. Many of the components that go together to make an engine work have been manufactured using lathes. These may be lathes operated directly by people (manual lathes) or computer controlled lathes (CNC machines) that have been programmed to carry out a particular task. A basic manual centre lathe is shown on the next slide. This type of lathe is controlled by a person turning the various handles on the top slide and cross slide in order to make a product / part.
‘Facing off’ A very basic operation is called ‘facing off’. A piece of steel has been placed in the chuck and the lathe cutting tool is used to level the end. This is done by turning the cross-slide handle so that the cross-slide moves and the cutting tool cuts the surface of the steel.
Drilling with the centre lathe The tailstock of a lathe can be used for drilling, with the aid of a drill chuck attachment. The drill chuck has a morse taper shaft which can be push into the shaft of the tailstock, locking it in position.
Centre drilling The usual starting point for drilling with a centre lathe is to use a countersink bit. This is used to drill slightly into the material and creates a starting point for other drills that are going to be used. Attempting to drill with a traditional drill bit without countersinking first will lead to the drill bit slipping straight away. It is not possible to drill a hole successfully or safely with out using a centre drill first.
Producing a screw-thread A cutting tool ground to the correct thread form angle is set up in the tool post and is used to cut along the bar to produce the correct thread profile of the bar Two important factors: ◦ The cutting tool profile must match the thread profile required ◦ The rate of rotation of the work must be in relation to the longitudinal cut in order to create correct thread pitch.
Knurling Used to put a pattern onto the surface of the material Often a shape of a diamond pattern Knurling tool consists of two hardened steel rollers that have the pattern to be cut engraved on them The pattern comes in two forms, straight or diamond shapes As the work rotates, the rollers on the knurling tool are pushed into the work As the steel rollers are harder than the bar being knurled a pattern is imprinted on the bar. Usually undertaken at slow speed
Parting off Usually the final stage of work A special tool is put into the tool post and used to cut right through the piece of work, thus severing it Must be kept sharp with correct angles ground into it Must be set exactly at centre height and fed into the work at a uniform rate
Metalworking centre lathe tools ToolApplication Right-hand knife toolUsed to face the left-hand edge or cut a shoulder to the left Left-hand knife toolUsed to face the right-hand edge or cut a shoulder to the right Round nose toolCut in any direction and produce radii Parting off toolMoves at right angles into the work to sever material Form toolSpecial profiles to cut specific shapes Knurling toolProduce pattern or textured surface Boring toolTool to enlarge existing hole when large drill unavailable or to produce a flat- bottomed hole.
Injection Moulding Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process called injection moulding. These are thermoplastics - this means when they are heated and then pressured in a mould they can be formed into different shapes
Injection moulding: the process The injection moulder is made up of: A hopper unit A screw and injector unit A heating element A mould http://www.youtube.com/watch?v=XqoecH2AtaQ
Advantages Can operate 24 hours a day Can be used to make different coloured products Inserts can moulded directly in Several smaller items can be manufactured into a single mould
Advantages Suitable for high volume continuous production High level of accuracy Identical components formed each time Little or no secondary surface finishing required Unit costs low in comparisons with the initial set up costs
Disadvantages Initial machine and mould costs high Some flashing may have to be removed Sprue pins need to be cut off
Blow moulding Blow moulding follows the same stages of manufacture as injection moulding. Polymer granules / powder is placed into the hopper. It drops down on to a rotating thread and travels along its distance. During this process the granules / powder is heated and becomes fluid. However, when it reaches the mould compressed air is also blown into the mould. This pushes the polymer around the edges of the mould, forming a hollow shape
Advantages Very cheap unit costs Highly automated process Not very labour intensive Ideal for high volume, continuous production since it can run for 24 hours a day Very little secondary finishing required due to nature of plastic material and mould surface finish
Disadvantages Initial costs of machine and tooling very high Not suitable for small production methods Sometimes a seam is left around the product where the mould closes Products sometimes need to have flashing removed
Dome moulding Involves blowing compressed air through a small inlet valve onto the softened polymer. http://www.youtube.com/watch?v=WMICBr7L GqU
Vacuum forming Vacuum forming is a technique that is used to shape a variety of plastics. In school it is used to form/shape thin plastic, usually plastics such as; polythene and acrylic. Vacuum forming is used when an unusual shape like a ‘dish’ or a box-like shape is needed.
Vacuum forming Vertical surfaces have to slightly tapered (5 o ) – this is called draught angle. Round off sharp corners so they don’t puncture the plastic. Incorporate vent holes to avoid pockets of air to get trapped which would stop the plastic from not forming correctly. Round off internal edges to help plastic form over the moulded surfaces.
Designing vacuum forming moulds External edge radiused Draught angle 5o5o Internal radius softened Vent holes to allow air to escape
Advantages Lightweight, hollow products can be made Relatively cheap moulds can be made from MDF in the school workshop for one-off products Surface textures can be moulded into products
Disadvantages Thermoplastic material sometimes thins too much and may burst or pop Webs sometimes form between items Products need to be trimmed and cut out
Extrusion Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process called extrusion. These are thermoplastics - this means when they are heated and then pressured in a mould they can be formed into different shapes and sections These are cut and welded to form whole units such as uPVC window frames
Plastic extrusion Used to coat products such as copper wire, this is called extrusion coating.
Metal extrusion Aluminium and copper are cold extruded This leaves no surface oxidation which would occur if heated so better surface finish In hot extrusion - starts with a billet (a large lump of metal) that is heated up in an oven Placed into the extrusion machine A ram is used to push the material from behind through the die
Steel die The picture below shows a close up of the steel die. The hole in its centre is a hexagon. This means that the fluid metal forms a hexagonal section when it is forced through the hole. Dies can be manufactured to almost any section / shape, including tubes
advantages Continuous lengths Complex profiles Seamless tubes Small production runs achievable Excellent surface finish on plastics High tolerances achieved
disadvantages Initial set up costs of machinery and up- keep are high Die costs can be very high Hot extrusion of metals such as steel leaves oxidised surface finish
Wood laminating Involves building up thin layers of around a former Uses thin veneers or skin ply The grain has to run in the same direction and following the curve
Glued together using PVA or cascamite Then trapped in a former or a jig and held under pressure by clamps Left until the adhesive is set Can also use a vacuum bag – the air is sucked out using a pump. The atmospheric pressure forces the layers together and around the former while the adhesive sets
advantages Complex shapes Large sections can be built up Several small products can be laminated at the same time
disadvantages Requires a former to be made Special adhesives required if product to be used outside Must be left for 24 hours to let the glue set
Exam questions Salad servers are laminated from thin pieces of plywood. Choose one adhesive from the list below which is best suited to gluing the pieces of plywood together. 1 mark. Tensol cement PVA Contact adhesive Epoxy resin
Exam questions Draw a cross section of the mould which would have been used to form this package.
Exam questions Explain two advantages of producing the handle for a screw driver using the injection moulding process. (4 marks)