Download to read offline
More Related Content
Abrasive machining
- 2. Medisetty Harish ¾-A ;Roll-47 MechanicalEngineering Gitam Institute of Technology
- 3. Basics Types of AbrasiveMachining Processes • Grinding • Honing • Lapping • Superfinishing • Polishing • Buffing • Abrasive water jet machining • Ultrasonic machining content Grinding Wheel Parameters • Properties Abrasive material • Grain size • Wheel grade • Wheel structure • Bonding material • Grinding chip • Chip formation • Testing of grinding wheel
- 5. An abrasive isa material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflective surface, the process can also involve roughening as in satin, matte or beaded finishes. In short, the ceramics which are used to cut, grind and polish other softer materials are known as abrasives. Lets go the basics What is an abrasive? ???
- 6. • Grinding • Honing •Lapping • Superfinishing • Polishing • Buffing • Abrasive water jet machining • Ultrasonic machining Types of Abrasive Machining Processes
- 7. Grinding is anabrasive machining process that uses a grinding wheel as the cutting tool. A wide variety of machines are used for grinding: • Hand-cranked knife-sharpening stones (grindstones) • Handheld power tools such as angle grinders and die grinders • Various kinds of expensive industrial machine tools called grinding machines • Bench grinders Grinding
- 8. HONING • Honing isan abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive grinding stone or grinding wheel against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but can also improve the surface finish. • Typical applications are the finishing of cylinders for internal combustion engines, air bearing spindles and gears. There are many types of hones, but all consist of one or more abrasive stones that are held under pressure against the surface they are working on.
- 9. LAPPING • Lapping isa machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine.
- 10. SUPERFINISHIN G • Superfinishing, alsoknown as micromachining, microfinishing, and short-stroke honing, is a metalworking process that improves surface finish and workpiece geometry. This is achieved by removing just the thin amorphous surface layer left by the last process with an abrasive stone or tape; this layer is usually about 1 μm in magnitude. Superfinishing, unlike polishing which produces a mirror finish, creates a cross-hatch pattern on the workpiece.
- 11. • Polishing isthe process of creating a smooth and shiny surface by rubbing it or by applying a chemical treatment, leaving a clean surface with a significant specular reflection (still limited by the index of refraction of the material according to the Fresnel equations).In some materials (such as metals, glasses, black or transparent stones), polishing is also able to reduce diffuse reflection to minimal values. Polishing
- 12. A water jetcutter, also known as a water jet , is an industrial tool capable of cutting a wide variety of materials using an extremely high- pressure jet of water, or a mixture of water and an abrasive substance. The term abrasive jet refers specifically to the use of a mixture of water and abrasive to cut hard materials such as metal, stone or glass, while the terms pure waterjet and water-only cutting refer to waterjet cutting without the use of added abrasives, often used for softer materials such as wood or rubber Abrasive Water jet
- 13. • Ultrasonic machiningis a subtractive manufacturing process that removes material from the surface of a part through high frequency, low amplitude vibrations of a tool against the material surface in the presence of fine abrasive particles. The tool travels vertically or orthogonal to the surface of the part at amplitudes of 0.05 to 0.125 mm (0.002 to 0.005 in.).The fine abrasive grains are mixed with water to form a slurry that is distributed across the part and the tip of the tool. Typical grain sizes of the abrasive material range from 100 to 1000, where smaller grains (higher grain number) produce smoother surface finishes. Ultrasonic machining
- 14. • Properties ofAbrasive material • Grain size • Wheel grade • Wheel structure • Bonding material • Grinding chip • Chip formation • Testing of grinding wheel Grinding Wheel Parameters
- 15. General Properties Hardness, wearresistance, toughness, friability Properties of Abrasive material
- 16. Grain size isexpressed in terms of a SIEVE NUMBER, Sn which corresponds to the number of openings per linear inch. The diameter of an abrasive grain is given by Dg = 0.6 𝑆𝑛 The larger the size of grains, more will be material removal, but surface finish will be worse. Sieve No. Type of Grain • 10-24 Coarse • 30-60 Medium • 70-180 Fine • 220-600 Very Fine Grain size
- 17. “Open” and “dense” Inwhat conditions these structures be provided? Grinding Wheel Structure
- 18. Indicates the strengthof the binding material. When the work material is hard, the grains wear out easily and the sharpness of the cutting edges is quickly lost. This is known as WHEEL GLAZING. To avoid this problem, a soft wheel should be used. A-H – Soft Wheel J-P – Medium Wheel Q-Z – Hard Wheel Wheel grade
- 19. • Vitrified Bond(V) – Strong and Rigid, commonly used. • Resinoid (B) – Provides shock absorption and elasticity. They are strong enough. • Silicate (S) – Provides softness (grains dislodge quickly) • Shellac (E) – Used for making thin but strong wheels possessing some elasticity. • Rubber Bonds (R) – For making flexible wheels. • Metallic Bond (M) – For diamond wheels only. Bonding material
- 20. Grinding Chips Fig: (a)Grinding chip being produced by a single abrasive grain. (A) chip, (B) workpiece, (C) abrasive grain. Note the large negative rake angle of the grain. The inscribed circle is 0.065mm in diameter. (b) Chip formation by an abrasive grain with a wear flat. Note the negative rake angle of the grain and the small shear angle
- 21. • Chips inthis process are formed by the same mechanism of compression and shear as other machining processes. • As the grains or abrasives become dull, the cutting forces increase. The increase in the cutting force causes the grains to plow and rub rather than cut. As the plowing and rubbing increases, the grains fracture at the cutting edge to revile a new cutting edge. Chip Formation
- 22. • The importanceof the grit shape can be easily realized because it determines the grit geometry e.g. rake and clearance angle. • The grits do not have definite geometry and the grit rake angle may vary from +45 to -60 or more. • Grit with favorable geometry can produce chip in shear mode. However, grits having large negative rake angle or rounded cutting edge do not form chips but may rub or make a groove by plowing leading to lateral flow of the workpiece material.
- 23. • Strength ofa bond: pass a sintered metal carbide or diamond chisel over the wheel surface in such a way that it tears a layer of grains from the bond. • The forces required to separate a layer of grains from the bond are taken as a measure of the strength of the bond. Hardness • a) Drill the wheel with a hard spade-type drill with a constant force. The depth of penetration in a given time is a measure of wheel hardness. • b) Use an air/abrasive jet to break the bond. The depth of penetration of the jet erosion in a standard period of time is used to determine equivalent wheel hardness. • c) Measure the resonant frequency of an isolated wheel after a sharp blow with a rubber hammer and relate it to hardness Testing of Grinding Wheels
- 25.