M.P- II-UNIT IV - ABRASIVE PROCESSES AND GEAR CUTTING.pptx
Download as PPTX, PDF0 likes240 views
The document discusses various abrasive processes and gear cutting. It describes different types of grinding processes like cylindrical grinding and surface grinding. It covers the selection and specifications of grinding wheels including abrasive materials, grain size, bonding materials, and wheel structures. Different grinding machines are also outlined, such as floor stand grinders, bench grinders, cylindrical grinders, and surface grinders. Key factors in selecting a grinding wheel like the material being machined and removal rate are also summarized.
M.P- II-UNIT IV - ABRASIVE PROCESSES AND GEAR CUTTING.pptx
- 1. UNIT – 4 ABRASIVE PROCESSES AND GEAR CUTTING
- 2. SYLLABI Abrasive processes: grinding wheel - specifications and selection, types of grinding process - cylindrical grinding, surface grinding, centreless grinding - Gear Finishing Process-honing, lapping, super finishing, polishing and buffing, abrasive jet machining, Gear cutting, forming, generation, shaping, hobbing
- 3. Abrasive Process • Abrasive machining Process is one of the oldest forms of metal removal. It is also one of the most important. Abrasive machining can produce surface finishes ranging from rough to extremely fine. • Abrasive machining is a process where chips are formed by small cutting edges on abrasive
- 4. CLASSIFICATION OF MACHINING BY ABRASION
- 5. INTRODUCTION • Grinding is a material removal process in which abrasive particles arc contained in a bonded grinding • The metal is removed with the help of rotating grinding wheel. • The grinding wheel is usually disk shaped and is precisely balanced for high rotational speeds.
- 8. Grinding Wheel Parameters • Abrasive material • Grain size • Bonding material • Wheel grade • Wheel structure
- 9. Abrasive Material Properties • High hardness • Wear resistance • Toughness • Friability - capacity to fracture when cutting edge dulls, so a new sharp edge is exposed
- 10. Abrasives • Grinding wheel is made up of small abrasive particles held together by bonding material. Thus it forms a multi edge cutter. CLASSIFICATION 1. Natural Abrasives 2. Artificial Abrasives
- 11. 1. Natural Abrasives These are obtained from mines a) Sandstone or solid quartz b) Emery (50 – 60 % crystalline Al2O3 + iron oxide) c) Corundum (75-90 % crystalline Al2O3 + iron oxide) d) Diamond
- 12. 2. Artificial Abrasives • To achieve the require property we go for artificial abrasives than natural. • These are manufactured under some pressure and temperature in a furnace • Aluminium oxide • Silicon carbide • Artificial Diamond • Boron Carbide • Cubic boron nitride
- 13. Traditional Abrasive Materials • Aluminum oxide (Al2O3) - most common abrasive – Used to grind steel and other ferrous high strength alloys • Silicon carbide (SiC) - harder than Al2O3 but not as tough – Used on aluminum, brass, stainless steel, some cast irons and certain ceramics
- 14. Newer Abrasive Materials • Cubic boron nitride (CBN) – very hard, very expensive – Suitable for steels – Used for hard materials such as hardened tool steels and aerospace alloys • Diamond – Even harder, very expensive – Occur naturally and also made synthetically – Not suitable for grinding steels – Used on hard, abrasive materials such as ceramics, cemented carbides, and glass
- 15. Grain Size • Coarse grained (small grit number)wheels are produce rough grinding. • Fine grained (larger grit number) wheels are produce finish grinding. • Soft grade wheels are used for grinding hard materials. • Hard grade wheels are used for grinding soft materials.
- 16. Bonding Material Properties • Must withstand centrifugal forces and high temperatures • Must resist shattering during shock loading of wheel • Must hold abrasive grains rigidly in place for cutting yet allow worn grains to be dislodged to expose new sharp grains
- 17. Wheel Structure Refers to the relative spacing of abrasive grains in wheel • In addition to abrasive grains and bond material, grinding wheels contain air gaps or pores • Volumetric proportions of grains, bond material, and pores can be expressed as: 0 1. p b g P P P
- 18. Typical structure of a grinding wheel. Wheel Structure
- 19. Wheel Structure • Measured on a scale that ranges between "open" and "dense." – Open structure means Pp is relatively large and Pg is relatively small - recommended when clearance for chips must be provided – Dense structure means Pp is relatively small and Pg is larger - recommended to obtain better surface finish and dimensional control
- 21. Grinding wheel marking Wheel grade (Hardness) Very soft: A,B,C,D, E, F, and G Soft: H, I, J, K Medium: L, M, N, O Hard: P, Q, R, S Very hard: T, U, V, X, Y, Z Soft grades are, generally, used for machining hard materials Hard wheels are used for soft materials Wheel bond Vitrified (V) Resinoid (B) Silicate (S) Rubber (R) Shellac (E) Oxychloride (O) Metal
- 22. GRINDING WHEEL Markings Wheel structure Open structure wheels are used for high material removal rates and consequently produce a rough surface finish. Dense structures are used for precision form grinding operations. Very compact: 1, 2 Compact: 3, 4 Semi-compact: 5, 6 Porous: 7, 8 Very porous: 9, 10 Extra porous: 11 to 15
- 23. TYPES OF BOND • Various types of bonds used in their choice depends on operating conditions of abrasive tool such as grinding speed pressure on the tool heat formation in the grinding zone S.NO BOND TYPE BOND 1 Organic Resinoid , rubber , oxy-Chloride 2 Non - Organic Metallic, Vitrified and silicate bond
- 24. 1. Vitrified Bond • This is made of the mixture of clay and water. • This mix is placed in mould to get require shape in wheel • Then the dried wheel is fed in to furnace few days at a temperature of 1260 deg.celcius. • This fusing gives the uniformity in the bond. • Then the wheel is trimmed to required shape & size.
- 25. 2.Silicate Bond • The abrasive particles are mixed with silicate of soda. • Then the mixture is moulded to get a required shape and dried for few hours • Then its kept in a furnace at about 260’c for 20 – 80 hours • This wheel having moderate tensile strength • Its used more rapidly than vitrified bond
- 26. 3. Resinoid Bond • The abrasive particles are mixed with synthetic resins. • This mixture is rolled to get a required shape & size • Then its kept in a furnace at about 210 – 250 ‘c for few hours • At this temp. the resins hold the abrasive particles firmly. • This wheel is strong and elastic • Operating speeds at 300m/min. • Used to machine cast iron , malleable cast iron.
- 27. 4. Rubber Bond • The abrasive particles are mixed with liquid rubber and sulphur. • This mixture is rolled in to sheet for require thickness and then vulcanized. • These are strong bonds having closed grains in thin sections also. • Its mainly used for very close surface finish. And also used in centreless grinding
- 28. 5. Shellac Bond • The abrasive particles are mixed with shellac. • Then the mixture is rolled and pressed to require shape and size. • Then its kept in furnace at about 160’c for few hours • These are strong and posses some elasticity like rubber bond • Used in the finishing of cam shaft and mill rolls
- 29. 6.Oxy-Chloride Bond • The abrasives are mixed with oxide and chloride of magnesium. • Then its is moulded to required shape and size • Then its kept in a furnace for few hours • These wheels are less brittle and less sensitive to side loads as compared to vitrified bond. • No coolant required in operation
- 30. FACTORS IN SELECTION OF GRINDING WHEEL COSTANT FACTORS 1. Material to be machined 2. Material removal rate 3. Area of contact 4. Type of grinding machine VARIABLE FACTORS 1. Work speed 2. Wheel speed 3. Condition of grinding machine 4. Personal factors ---- (labour ability)
- 31. Truing & Dressing of grinding wheel • Dressing is the term used to describe the process of cleaning the periphery of grinding wheels. This cleaning breaks away dull abrasive grains and smoothes the surface so that there are no grooves. • Truing is the term used to describe the removal of material from the cutting face of the wheel (Trimming) • so that the resultant surface runs absolutely true to some other surface such as the grinding wheel shaft.
- 32. Types of dressing tools 1. Star wheel dressing tool 2. Round abrasive stick 3. Diamond dressing tool
- 36. Shapes of grinding wheel
- 37. Mounting wheels and points • These are small grinding wheels of different shapes. • This is attached to the shank of the portable grinding machine
- 39. Types grinding machines 1. Rough grinders (a) Floor stand grinders (b) Bench grinders (c) Portable grinders (d) Abrasive belt grinders (e) Swing frame grinders 2. Precision grinders (a) Cylindrical grinders (i) Plain centre type grinders (ii) Universal centre type grinders (iii) Centreless grinders (b) Internal grinders (i) Chucking type grinders (ii) Planetary type grinders (iii) Centreless grinders (c) Surface grinders (i) Horizontal spindle – reciprocating table (ii) Horizontal spindle – rotary table (iii) Vertical spindle – reciprocating table (iv) Vertical spindle – rotary table (v) Tool and cutter grinders (vi) Special grinders
- 41. Bench grinder
- 42. Portable Grinder
- 45. Precision Grinder - Cylinderical Grinder
- 46. TYPES OF OPERATIONS IN CYLINDRICAL GRINDING (i). Traverse grinding. (ii). Plunge grinding.
- 47. Traverse Grinder
- 50. PLAIN CENTRE TYPE CYLINDERICAL GRINDING MACHINE
- 52. USES • Used for machining cylindrical parts and also for tapers , fillets, contoured cylinders etc. • It has base head stock tail stock wheel head
- 54. Universal grinding Machine • These grinders are used in tool room for grinding tools. • It has same operation as like of plain type grinding M/C • The wheel head can be swiveled into any shape • The head stock can be swiveled in to any angle in horizontal plane.
- 55. Surface grinder • To machine flat plane surface • The various machine parts such as machine guide ways, piston rings, dies, surface plates, valves are finished by surface grinding. • Small work pieces are held by magnetic chuck and heavy work pieces are clamped on the table by means of pads, strap clamps and other devices or fixtures. Types 1. Horizontal spindle reciprocating table surface grinder 2. Horizontal spindle Rotary table surface grinder 3. Vertical Spindle reciprocating table surface grinder 4. Vertical Spindle Rotary table surface grinder
- 56. Horizontal spindle reciprocating table surface grinder
- 57. Horizontal spindle Rotary table surface grinder
- 58. Vertical Spindle reciprocating table surface grinder
- 59. Vertical Spindle Rotary table surface grinder
- 61. CENTRELESS GRINDING • Its performed on the work pieces which do not having centers such as pistons, valves, rings, tubes, balls, wrist pins, drills , bushings, shafts etc • It can be done on both external and internal cylindrical surfaces. • It has two wheels – larger grinding wheel small regulating wheel
- 62. CENTRELESS GRINDING The regulating wheel make the work piece to rotate. So the work piece is pressed between the wheel Grinding wheel only remove the material
- 63. METHODS OF CENTRELESS GRINDING • Through feed - This is used for machining lengthy work piece. Regulating wheel tilted to some angle. • In Feed – Its similar to plunge grinding. The end stop limit the axial movement of the work piece • End Feed – Here both grinding and regulating wheels are tapered. So it can machine tapered surfaces
- 64. INTERNAL GRINDERS • They are used to finish straight , tapered or formed holes to the correct size, shape and finish. 1. Chucking type 2. Planetary Type 3. Center less Type
- 65. Chucking type Internal Grinder • The work is held in the chuck and rotated. • The rotating grinding wheel is moved from left to right for making hole
- 66. Planetary Type Internal Grinder • Here the work is stationary and the rotation of the wheel spindle gives an eccentric motion according to the diameter of the hole to be ground
- 67. Center less Type Internal Grinder • It has the same working like external centre less grinding. The work is supported by three rollers. • It has one regulating wheel and supporting wheel and one pressure roll to hold the work piece on the other two wheels The grinding wheel directly contact the inside diameter of the work piece and reciprocates about its axis for the given feed.
- 69. USES • Its designed to do specific works • like forming , gear teeth grinding, thread grinding, cam grinding , tool and cutter grinding etc.
- 70. FORM GRINDING • To produce complex shapes. • EXAMPLE. DOVE TAIL WAY
- 71. Gear Teeth Grinding • Two methods Gear generating Process – using 2 saucer type wheel Gear Forming Process – Using Form tool with fixtures
- 72. Thread Grinding • Its same like forming process. • The grinding wheel itself having the contours of the thread to be machined on the work piece
- 73. Cam Grinder • From the rotation of cam shaft , the grinding wheel having the up and down movement in radial direction. • A hardened steel roller in conjunction with the template actuates the movement of whole unit to produce the desired shape
- 74. Tool post grinder • This grinder is mounted on the tool post of the lathe for doing small operations.
- 75. Disc Grinder • This is for removing material rapidly. • Used for small polishing work • Operated by hand wheel.
- 76. Tool and Cutter Grinder
- 77. Tool and Cutter Grinder • To reconditioning various tools like milling, drilling, tapping, hobs and single point tools • By using special attachment this machine perform various operations • Single purpose and cutter grinder – to grind drills , tool bits • Universal tool and cutter grinder – to sharpening milling tool , reamer, special driller etc.
- 78. HONING • Honing is a low abrading process using bonded abrasive sticks for removing stock from metallic and non-metallic surfaces. However, it can also be used for external cylindrical surfaces as well as flat surfaces, for which it is rarely used. Commonly it is used for internal surfaces.
- 79. Honing Conditions All materials can be honed. However, the material removal rate is affected by the hardness of the work material. The typical rates are: • Soft material 1.15 mm/min on diameter • Hard materials 0.30 mm/min on diameter
- 80. LAPPING Lapping is generally the final finishing operation done with loose abrasive grains. The process is employed to get • Extreme accuracy of dimension • Correction of minor imperfection of shape • Refinement of surface finish • Close fit between mating surfaces
- 81. SUPER FINISHING
- 82. SUPER FINISHING
- 83. POLISHING AND BUFFING • Both these processes are used for making the surfaces smoother along with a glossy finish. Polishing and buffing wheels are made of cloth, felt or such material, which is soft and have a cushioning effect. Polishing is done with a very fine abrasive in loose form smeared on the polishing wheel with the work rubbing against the flexible wheel. A very small amount of material is removed in polishing. In buffing the abrasive grains in a suitable carrying medium such as grease are applied at suitable intervals to the buffing wheel.
- 84. ABRASIVE BELT GRINDING This method is most suitable for flat surfaces. However, cylindrical surfaces can also be belt ground by using a suitable contact wheel. Abrasive belt with a very fine grit may be used for polishing application.
- 85. ABRASIVE JET MACHINING • 10 % MATERIAL REMOVAL BY ABRASIVE JET • 90% MATERIAL REMOVAL BY WHEEL Abrasive jet machining is the process of impinging the high- speed stream of abrasive particles by high-pressure gas or air on the work surface through a nozzle and metal removal occurs due to erosion caused by high-speed abrasive particles. Because of repeated impacts small bits of material get loosened which is carried away by jet and exposing the fresh surface to the jet.
- 86. Applications • Cutting slots and thin sections. • Contouring and drilling operation. • Producing shallow crevices and deburring. • Producing intricate hole shapes in a hard and brittle material. • Cleaning and polishing the plastic, nylon and Teflon component. • Frosting of the interior surface of glass tubes. • Etching of marking of glass cylinders. • Machining super-alloys and refractory material.
- 87. GEAR CUTTING
- 88. GEAR CUTTING METHODS • By single point form tool • By shear speed shaping process • Gear milling using a formed end mill • Gear broaching • Template method
- 89. Gear cutting - single point form tool • Using the single point cutting tool in planner and shaper we can produce spur and bevel gears. • Here form tool is used to make gear on the blank. • The work is held between the centers and the cutter reciprocates along the length of the work piece.
- 91. Gear cutting - speed shaping process • Here the form tools are arranged radially in the cutter head. • The number of form tools are equal to the number of teeth to be cut on the gear blank • All the tooth spaces are cut at the same time by feeding along with tools towards the centre of the blank during cutting stroke • The depth of cut can be adjusted by radial movement.
- 93. Gear milling using a formed end mill • The cutting edges are formed to the shape of the gear tooth space. • The formed end mill cutter is held on the spindle of a vertical milling machine • The blank is held in the dividing head and fed against the cutter. • The axis of cutter and blank is perpendicular to each other
- 96. Principle • This is based on the fact that any two involutes gears of same module will mesh together. • One of the meshing gear as cutter and the other will reciprocate and rotate along the width • For producing high accurate gears the following process are used Gear Shaping Process Gear Planning Process Gear Hobbing process
- 97. Gear Shaping Process • A pinion type of cutter is used. • Proper angles are given to the cutter initially • A hole is made on the cutter for mounting on a stub arbor or spindle of the machine. • The cutter axis and work axis are parallel to each other. • The cutter reciprocates vertically and parallel to the axis of the blank. • During this both cutter and work rotated slowly. • So the rotation of the cutter generates the gear profile.
- 99. Gear Hobbing • The gear blank is mounted on a rotating vertical arbor • The rotating hobber is in horizontal position • The intersection of these two makes a gear profile on the blank.
- 103. FINISHING OF GEAR
- 104. GEAR SHAVING
- 106. ROLL FINISHING OF GEAR TOOTH
- 107. GEAR BURNISHING
- 108. GEAR LAPPING (Polishing machine) • It’s a fine polishing process carried out by hand or machine. • The fine abrasive particles are mixed with oil like vegetable oil, mineral oil, kerosene, olive oil and machine oil. • This oil is fed between the two surfaces . • Then the surfaces are rubbed or rotated one over other for getting fine finishing.
- 109. Types of lapping • Hand lapping – for doing ordinary operations. example : moulding die , press die
- 110. Types of lapping – machine lapping • Machine lapping - for getting highly finished jobs. ex – crank shaft , piston, gauges, bearing etc.
- 111. Lapping media • Metal laps and abrasive powder • Bonded abrasive • Abrasive paper or cloth
- 112. OTHER PROCESS • POLISHING - This is Similar to grinding process .using abrasive belt or coated wheel we polish the work surface. The wheel is made up of abrasive paper, cloth etc BUFFING ----- Using the binding solution the fine abrasive particles are added to rotating wheel. Then this wheel is rotated on work for fine finishing
- 113. GEAR HONING PROCESS • It’s a process carried out for finishing previously machined surfaces. • Its mostly used for finishing internal cylindrical surfaces such as drilled or bored holes
- 114. Horizontal honing machine • There is no reciprocating motion to the work in the machining process. • But the honing tool rotated and reciprocated for machining lengthy work piece.
- 115. Vertical honing machine • The work is stationary • But the honing tool in the vertical spindle rotated and reciprocated to machine the work piece.
- 116. Advantages – Favourable surface texture reduces the noise emission in the transmission. – Induced residual stresses in tooth flanks increase the bearing capacity. – Low cutting speed prevents structure damages (burning). – It needs low cost and the process is economical process. – It reduces or corrects the geometrical errors induced by previous manufacturing or finishing processes.
- 117. Disadvantages of gear honing • It has limited life of honing gear tool. • Honing time is increased as error in tool shape increases.
- 118. Applications of gear honing • It can be used for finishing hardened external and internal gears. • Honing can do crowning of gears • Applied to improve the geometric accuracy and surface conditions and to remove nicks and burrs. • It is used for minor corrections in tooth shape which increases wear resistanceand reduces noise generation.