Types of Bonds Vitrified (ceramic bond) – most common type of bond. Resistant to water, oil, and acids. Sometimes made with steel backing plates to improve physical strength. Resinold (thermosetting resins) – Also known as organic wheels. Resistant to extremely high temperatures Reinforced Wheels – Made with layers of fiberglass. If it did break it would not disintegrate, it would just crack.
Types of Bonds Thermoplastic – sol-gel abrasives bonded with thermo plastics Rubber – the most flexible bond. Metal – lowest cost. Used mainly in small quantity production
Grinding Formula L = (Dd) Undeformed length = (Diameter)(depth)
Chip Formation When a chip forms ridges are formed where the chip left the material. This is known as plowing.
Considerations while grinding Temperature If it gets too high it can: Affect surface properties, including metallurgical change Cause residual stress on the work piece Cause distortions in the work piece, therefore accuracy goes down
Wheel wear Once a wheel starts wearing it becomes less accurate Grain wear – grains become flat and dull Bond fracture – the bond breaks and the grains come off the wheel
Grinding Ratio G = Volume of material removed These vary widely, ranging from 2 to 200+ Using grinding fluids can increase the life of a grinding wheel 10 fold. Volume of wheel wear
Shaping grinding wheels The edges of grinding wheels are shaped with diamond dressing tools controlled by computers. Shaping the wheel sharpens it and restores its accuracy.
Grinding Almost any material can be ground - aluminum, steel, ceramics, even diamond or glass.
Grinding is used whenever something needs to be smoothed or shaped. Grinding is used to form countless types of products such as automobile engines, sharp edges on knives, ball bearings and drills. The smooth, accurate surface of the Hubble Telescope lens was formed by a process of grinding and polishing. How Grinding Is Used
Types of grinding Machines Surface grinder Cylindrical grinder Universal Tool and Cutter Grinder Lapping and Polishing
Cylindrical grinding center cylindrical grinding centerless.
The bench grinder
chemical milling/blanking is a chemical process that dissolves material from unmasked (unprotected) areas of metallic parts immersed in a tank of heated and agitated chemical reagents. The term "blanking" denotes small, thin workpieces, and "milling" indicates relatively large workpieces. (a) Schematic illustration of the chemical machining process. Note that no forces or machine tools are involved in this process. (b) Stages in producing a profiled cavity by chemical machining; note the undercut.
considerable advantages compared to punching, laser- cutting and wire- erosion (left) Missile skin-panel section contoured by chemical milling to improve the stiffness to- weight ratio of the part. (top) Weight reduction of space launch vehicles by chemical milling aluminum-alloy plates. These panels are chemically milled after the plates have first been formed into shape by processes such as roll forming or stretch forming.
Chemical milling is used to reduce the overall weight and other non desirable factors of a workpiece
Process of Chem. Milling 1. Artwork and Negative Preparation An image is printed by a program with a laser plotter directly to the film at any size needed 2. Photoresist Application / Exposure / Develop Apply Photoresist coating to make the metal sensitive to light. Expose coated metal to UV light source which applies the image from the art work to the metal part. Treat exposed metal part with a developing solution which removes the soft portion of the Photoresist. 3. Etching / Resist Removal Process the metal through chemical etcher which dissolves all metal not protected by the hardened photoresist coating.
Electrochemical Machining (ECM) uses an electrolyte at a high rate from the tool piece to wash away the metal ions from the workpiece the tool is usually solid or tubular form Material removal rate is 1.5 – 4mm³
ECM was developed in 1929 Not as widely used as other processes Generally used to make complex cavities and shapes Finishes parts burr-free and bright surfaces Never has any thermal damage to part or wear on the tools
Parts From Electrochemical Mill
Design Considerations for ECM ECM is not suitable for producing sharp edges or flat sufaces Flow of electrolyte can become difficult Designs should make provision for a small taper for holes to be machined
Electrochemical Grinding (ECG) Process that combines electrochemical machining with conventional grinding Grinder wheel is embeded with abrasive particles of dimond or aluminum oxide
Abrassives on the spindle have two functions To act as insulators between the wheel and workpiece To remove electrolytic products from the work area Majority of material is removed by the electrolytic action, less than 5% is removed by the wheel
The ECG process is similar to that of milling, and grinding Much better than traditional grinding where wheel wear is high
Electrical discharge machining Erosion of metals by spark discharge Capacitor discharge is between 50 and 380 V EDM can be used on any material that is an electrical conductor
Uses an electrode that sends out the sparks which erodes the metal Uses dielectric fluids for cooling and flushing of the material
EDM wire Wire is brass, copper or tungsten With wire edm you can basically cut out any design
Laser-Beam Machining Focuses optical energy on the work piece The high focus high density energy melts the material Rough surface and has heat affected areas Oxygen maybe added to the laser for increase of energy, doing this leave a oxide free edge which improves welding Lasers are also used for etching
Design consideration with LBM Sharp corners should be avoided Deep holes will have tapered walls Don’t use highly reflective material
Electron-Beam Machining The energy source in EBM is high- velocity electrons that move from 50% to 80% the speed of light! It is a lot like Laser beam Machining but needs a vacuum because it puts of harmful x-rays, so is only used by trained personnel
Electron Beam Machine
Plasma arc cutting is a type of EBM its temp. gets from 9400 C to 17,000 C Which makes the process much faster the LBM and EDM with better products EBM have limited machining because of the vacuum capacity
Water Jet Machining Cut a variety of metal and nonmetal material up to 6-ft. x 12-ft. x 12-in. thick Reduce machining time by as much as 70% Provide a burr-free finished edge Leave no heat-affected zone (HAZ) Reduce waste material Eliminate costly set-up time
Water jet cutters have no start holes The jets have an extremely high velocity No heat during cutting Very intricate designs
The water jet is the most versatile machine on the market today The water leaving the nozzle is from 400 MPa to 1400 MPa The diameter of the spray is.05mm - 1mm It is used in lots of industries from wood, to food processing, metal working The material is wet very little It is environmentally safe process
Abrasive water jet machining The same thing is water jet but with added abrasive particle, such as silicon carbide or aluminum oxide This increases the material rate removal of the product The machine is a little more complicated cause it needs to mix the contents