Ch. 26 – Abrasive Machining and Finishing OperationsAbrasive Machining and Finishing OperationsAbrasives and Bonded AbrasivesSlide 4FriabilityAbrasive TypesSlide 7Abrasive Grain SizeSlide 9Grinding WheelsBonding AbrasivesBond TypesSlide 13The Grinding ProcessSlide 15Grinding ForcesSlide 17Problems with GrindingSlide 19Slide 20Grain FractureBond FractureGrinding RatioDressing, Truing, ShapingGrinding Operations and MachinesSlide 26Slide 27Slide 28Slide 29Design Consideration for GrindingDesign Considerations for GrindingFinishing OperationsSlide 33Slide 34Slide 35Slide 36Deburring OperationsSlide 38Slide 39Economics of Abrasive Machining and Finishing OperationsChapter 27 – Advanced Machining ProcessesChapter 27 – Advanced Mechanical ProcessesAdvanced Mechanical ProcessesChemical MachiningSlide 45Slide 46Slide 47Slide 48Slide 49Electrochemical MachiningSlide 51Slide 52Slide 53Electrochemical GrindingSlide 55Electrical Discharge Machining (EDM)Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Wire EDMSlide 66Slide 67Electrical Discharge GrindingLaser Beam MachiningSlide 70Slide 71Slide 72Electron Beam MachiningSlide 74Water Jet MachiningSlide 76Slide 77Abrasive Jet MachiningEconomics of Advanced Machining ProcessesReferencesCh. 26 – Abrasive Machining and Finishing OperationsBrenton Elisberg, Jacob Hunner, Michael Snider, Michael AndersonAbrasive Machining and Finishing Operations•There are many situations where the processes of manufacturing we’ve learned about cannot produce the required dimensional accuracy and/or surface finish. –Fine finishes on ball/roller bearings, pistons, valves, gears, cams, etc. –The best methods for producing such accuracy and finishes involve abrasive machining.Abrasives and Bonded Abrasives•An abrasive is a small, hard particle having sharp edges and an irregular shape. •Abrasives are capable of removing small amounts of material through a cutting process that produces tiny chips.Abrasives and Bonded Abrasives•Commonly used abrasives in abrasive machining are:–Conventional Abrasives•Aluminum Oxide•Silicon Carbide–Superabrasives •Cubic boron nitride •DiamondFriability •Characteristic of abrasives.•Defined as the ability of abrasive grains to fracture into smaller pieces, essential to maintaining sharpness of abrasive during use. •High friable abrasive grains fragment more under grinding forces, low friable abrasive grains fragment less.Abrasive Types•Abrasives commonly found in nature include:–Emery –Corundum–Quartz–Garnet–DiamondAbrasive Types•Synthetically created abrasives include:–Aluminum oxide (1893)–Seeded gel (1987)–Silicon carbide (1891)–Cubic-boron nitride (1970’s)–Synthetic diamond (1955)Abrasive Grain Size•Abrasives are usually much smaller than the cutting tools in manufacturing processes.•Size of abrasive grain measured by grit number.–Smaller grain size, the larger the grit number.–Ex: with sandpaper 10 is very coarse, 100 is fine, and 500 is very fine grain.Grinding Wheels•Large amounts can be removed when many grains act together. This is done by using bonded abrasives. –This is typically in the form of a grinding wheel.–The abrasive grains in a grinding wheel are held together by a bonding material.Bonding Abrasives•Bonding materials act as supporting posts or braces between grains. •Bonding abrasives are marked with letters and numbers indicating:–Type of abrasive–Grain size–Grade–Structure–Bond typeBond Types•Vitrified: a glass bond, most commonly used bonding material.–However, it is a brittle bond.•Resinoid: bond consiting of thermosetting resins, bond is an organic compound.–More flexible bond than vitrified, also more resistant to higher temps.Bond Types•Reinforced Wheels: bond consisting of one or more layers of fiberglass.–Prevents breakage rather than improving strength. •Rubber: flexible bond type, inexpensive.•Metal: different metals can be used for strength, ductility, etc.–Most inexpensive bond type.The Grinding Process•Grinding is a chip removal process that uses an individual abrasive grain as the cutting tool.•The differences between grinding and a single point cutting tool is:–The abrasive grains have irregular shapes and are spaced randomly along the periphery of the wheel.–The average rake angle of the grain is typically -60 degrees. Consequently, grinding chips undergo much larger plastic deformation than they do in other machining processes.–Not all grains are active on the wheel.–Surface speeds involving grinding are very fast.(a) (b)Grinding Forces•A knowledge of grinding forces is essential for: –Estimating power requirements.–Designing grinding machines and work-holding fixtures and devices.–Determining the deflections that the work-piece as well as the grinding machine may undergo. Deflections adversely affect dimensioning.Grinding Forces•Forces in grinding are usually smaller than those in machining operations because of the smaller dimensions involved. •Low grinding forces are recommended for dimensional accuracy.Problems with Grinding•Wear Flat–After some use, grains along the periphery of the wheel develop a wear flat.•Wear flats rub along the ground surface, creating friction, and making grinding very inefficient.Problems with Grinding•Sparks–Sparks produced from grinding are actually glowing hot chips.•Tempering–Excessive heat, often times from friction, can soften the work-piece. •Burning–Excessive heat may burn the surface being ground. Characterized as a bluish color on ground steel surfaces.Problems with Grinding•Heat Checking–High temps in grinding may cause cracks in the work-piece, usually perpendicular to the grinding surface.Grain Fracture•Abrasive grains are brittle, and their fracture characteristics are important. •Wear flat creates unwanted high temps.•Ideally, the grain should fracture at a moderate rate so as to create new sharp cutting edges continuously.Bond Fracture•The strength of the abrasive bond is very important!•If the bond is too strong, dull grains cannot dislodge to make way for new sharp grains. –Hard grade bonds are meant for soft materials.•If too weak, grains dislodge too easily and the wear of the wheel increases greatly. –Soft grade bonds are meant for hard materials.Grinding Ratio•G = (Volume of material removed)/ Volume of wheel wear)•The higher the ratio, the