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Grinding Machine

Grinding Machine. Grinding is a metal removal process by the action of a rotating abrasive wheel. An abrasive is a material whose particles are extremely hard and can be used to machine materials such as hardened steel, glass, carbides, ceramics, etc.

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Grinding Machine

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  1. Grinding Machine • Grinding is a metal removal process by the action of a rotating abrasive wheel. • An abrasive is a material whose particles are extremely hard and can be used to machine materials such as hardened steel, glass, carbides, ceramics, etc. • Grinding operation may be used for removing a thick layer (about 0.5 mm) of material in general class of work. • Usually grinding is used for finishing & polishing of parts produced by other machining process. P R Venkatesh, Mech Dept, RVCE, B'lore

  2. Abrasives • Abrasive is the mineral material employed for sharpening, grinding & polishing operations. • Two types of abrasives are commonly used; 1. Natural abrasives Ex: Emery, Sand stone, Quartz, Corundum, Diamond. (Corundum & Emery mainly consist of Aluminium oxide) 2. Artificial or synthetic abrasives. Ex: Silicon carbide, Aluminium oxide, artificial diamond. P R Venkatesh, Mech Dept, RVCE, B'lore

  3. Grinding Wheels P R Venkatesh, Mech Dept, RVCE, B'lore

  4. Grinding Wheel (Bonded Abrasives) • In a grinding wheel, the abrasive grains are held together by a bonding material. • Grinding wheels are specified by the standardized system of letters & numbers Indicating the type of abrasive, grain size, grade, structure & bond type. • Abrasive type: The most commonly used abrasives are Aluminium oxide usedto grind steel and its alloys. Silicon carbide used to grind cast iron & non ferrous metals. Diamond used to grind carbides, marbles, gems, P R Venkatesh, Mech Dept, RVCE, B'lore

  5. Grain size: It is used to describe the fineness of the mesh used in grading the abrasive grits (particles). • Coarse grains are used to grind soft, ductile materials. • Fine grains are used for hard and brittle materials and also when close accuracy is required. • Grade:It indicates the relative strength of the bond that holds the abrasive particles in place. P R Venkatesh, Mech Dept, RVCE, B'lore

  6. Structure: It indicates the relative spacing of the abrasive grains. • A wheel with wide spacing between the grains is best suited for grinding soft materials. • A closely spaced structure is suitable for grinding hard materials. • Bond:It is the medium that holds the grains together in the form of a wheel. The various bond materials generally used are Vitrified : ( Feldspar & clay) Silicate : (Silicate of soda) Shellac : (resin secreted by a lac bug on a tree) rubber : (pure rubber with sulphur as vulcanizing agent) P R Venkatesh, Mech Dept, RVCE, B'lore

  7. Standard Marking System of a grinding wheel P R Venkatesh, Mech Dept, RVCE, B'lore

  8. Typical structure of a grinding wheel. Grinding wheel structure P R Venkatesh, Mech Dept, RVCE, B'lore

  9. Dressing of Grinding Wheel • As the grinding wheel is used, it gets loaded with metal chips in between the cavities of the grains. • Dressing is the process of removing all dull grains and chips from the wheel surface and exposing new sharp grains. • An abrasive stick is used for dressing. P R Venkatesh, Mech Dept, RVCE, B'lore

  10. Truing of Grinding Wheel • Grinding wheels lose their geometry during use. • Truing is a dressing operation by which a wheel is restored its original shape. • A single point diamond tool can be used to true the wheel. P R Venkatesh, Mech Dept, RVCE, B'lore

  11. Classification of Grinding Machines Grinding machines are classified according to the type of surface they produce. • Surface grinding machine (For finishing flat surfaces) • Cylindrical grinding machine (For finishing the outside/inside diameter of cylindrical workpiece) • Centerless grinder ( For grinding curved surfaces of long slender rods) P R Venkatesh, Mech Dept, RVCE, B'lore

  12. Surface Grinding Machine P R Venkatesh, Mech Dept, RVCE, B'lore

  13. Surface Grinding Machine • Grinding of flat surfaces is known as surface grinding. • Two general types of machines are available; those with reciprocating table & the other with rotating table. • Each type has possible variations of having grinding wheel spindle either in horizontal position or vertical position. P R Venkatesh, Mech Dept, RVCE, B'lore

  14. Cylindrical Grinding Machine P R Venkatesh, Mech Dept, RVCE, B'lore

  15. Cylindrical Grinding Machine • Grinding of straight or tapered cylindrical surfaces is known as cylindrical grinding. • The work piece is mounted between two centers or in a chuck and revolves in opposite direction to that of grinding wheel. • The table which carries the headstock & tailstock centers and the work can be reciprocated by a hydraulic drive. P R Venkatesh, Mech Dept, RVCE, B'lore

  16. Centerless Grinding P R Venkatesh, Mech Dept, RVCE, B'lore

  17. Centerless Grinding • Centerless grinding is used for producing parallel, tapered or contoured surfaces on long & slender rods. • The work piece is not supported between centers and hence the name centerless. • The work piece rests on a work rest blade and is backed by a second wheel called regulating wheel. P R Venkatesh, Mech Dept, RVCE, B'lore

  18. Centerless Grinding • The regulating wheel is of rubber bonded abrasive having the frictional characteristics to rotate the work piece at its own rotational speed. • The grinding wheel & the regulating wheel rotate in the same direction. • In through feed grinding, the axial movement of the work past the grinding wheel is obtained by tilting the regulating wheel at slight angle from the horizontal. P R Venkatesh, Mech Dept, RVCE, B'lore

  19. Lapping • Lapping is a precision grinding technique employed in finishing of valve seats, cutting edge of dies, optical lenses, etc. • It uses fluid suspension of very small abrasive particles (Lapping compound) between workpiece and lap (tool) P R Venkatesh, Mech Dept, RVCE, B'lore

  20. Honing • Honing is also a precision grinding technique employed in reshaping & polishing cylinder bores, gauges, connecting rod bushes, etc. • It uses abrasive bonded sticks known as hones which will be given combined rotary & reciprocating motions. P R Venkatesh, Mech Dept, RVCE, B'lore

  21. Honing • Abrasive process performed by a set of bonded abrasive sticks using a combination of rotational and oscillatory motions. • Common application is to finish the bores of internal combustion engines • Surface finishes of 0.12 m or better. • Creates a characteristic cross‑hatched surface that retains lubrication. P R Venkatesh, Mech Dept, RVCE, B'lore

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