ABRASIVE PROCESSES.pptx

Abrasive processes: grinding wheel - specifications and selection, types of grinding process - cylindrical grinding, surface grinding, centreless grinding

1. ABRASIVE PROCESSES

2. Content to be covered Abrasive processes: grinding wheel – specifications and selection, types of grinding process– cylindrical grinding, surface grinding, centreless grinding and internal grinding- Typical applications –concepts of surface integrity, broaching machines: broach construction – push, pull, surface and continuous broaching machines

3. Abrasive machining Process Abrasive machining 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.

6. Grinding Machine

7. Grinding wheel

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 Sandstone or solid quartz Emery (50 – 60 % crystalline Al 2 O 3 + iron oxide) Corundum (75-90 % crystalline Al 2 O 3 + iron oxide) 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 (Al 2 O 3 ) ‑ most common abrasive Used to grind steel and other ferrous high strength alloys Silicon carbide ( SiC ) ‑ harder than Al 2 O 3 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:

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 P p is relatively large and P g is relatively small - recommended when clearance for chips must be provided Dense structure means P p is relatively small and P g is larger - recommended to obtain better surface finish and dimensional control

20. Grinding wheel marking

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 Material to be machined Material removal rate Area of contact Type of grinding machine VARIABLE FACTORS Work speed Wheel speed Condition of grinding machine Personal factors ---- (labour ability)

31. THANK YOU

32. 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.

33. Types of dressing tools Star wheel dressing tool Round abrasive stick Diamond dressing tool

34. Shapes of grinding wheel

35. Mounting wheels and points These are small grinding wheels of different shapes. This is attached to the shank of the portable grinding machine

36. Types of grinding machine

37. 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 – reciprocating table (v) Tool and cutter grinders (vi) Special grinders

38. Floor stand grinder

39. Bench grinder

40. Portable Grinder

41. Abrasive belt Grinder

42. Swing Frame Grinder

43. Precision Grinder - Cylinderical Grinder

44. TYPES OF OPERATIONS IN CYLINDRICAL GRINDING ( i ). Traverse grinding. (ii). Plunge grinding.

45. Traverse Grinder

46. Plunge cut Grinder

47. CYLINDERICAL GRINDING

48. PLAIN CENTRE TYPE CYLINDERICAL GRINDING MACHINE

49. USES Used for machining cylindrical parts and also for tapers , fillets, contoured cylinders etc. It has base head stock tail stock wheel head

50. UNIVERSAL GRINDING MACHINE

51. 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.

52. 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

53. Horizontal spindle reciprocating table surface grinder

54. Horizontal spindle Rotary table surface grinder

55. Vertical Spindle reciprocating table surface grinder

56. Vertical Spindle Rotary table surface grinder

57. CENTRELESS GRINDING MACHINE

58. 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

59. 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

60. 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

61. INTERNAL GRINDERS They are used to finish straight , tapered or formed holes to the correct size, shape and finish. Chucking type Planetary Type Center less Type

62. 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

63. 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

64. 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.

65. SPECIAL PURPOSE GRINDING MACHINE

66. USES Its designed to do specific works like forming , gear teeth grinding, thread grinding, cam grinding , tool and cutter grinding etc.

67. FORM GRINDING To produce complex shapes. EXAMPLE. DOVE TAIL WAY

68. Gear Teeth Grinding Two methods Gear generating Process – using 2 saucer type wheel Gear Forming Process – Using Form tool with fixtures

69. Thread Grinding Its same like forming process. The grinding wheel itself having the contours of the thread to be machined on the work piece

70. 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

71. Tool post grinder This grinder is mounted on the tool post of the lathe for doing small operations.

72. Disc Grinder This is for removing material rapidly. Used for small polishing work Operated by hand wheel.

73. Tool and Cutter Grinder

74. 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.

75. ABRASIVE JET MACHINING 10 % MATERIAL REMOVAL BY ABRASIVE JET 90% MATERIAL REMOVAL BY WHEEL

76. Broaching

77. Introduction Broaching is the process of removing metal with a tool which has “teeth” arranged in a row. Each tooth is successively higher than the previous tooth and removes more material. In broaching, one stroke or cycle of the machine produces a finished part. Broaching is used to produce both internal and external features. Production rates are high and tolerances of +/- .0005” are possible.

78. SPECIFICATION Max. length of stroke in mm. Type of drive: Electro-Mechanical or Hydraulic drive. Power range. Speed and Feed. Weight of the machine. Floor space.

79. Broaching machine

80. Broach

81. TYPES OF BROACHES According to types of tool movement (a) Horizontal type (b) Vertical type (c) Continuous type 2.According to the types of operation (a) Push type (b) Pull type 3. According to the types of surface to be broached (a) Internal type (b) External type 4. According to the construction of broach (a) Solid type (b) Progressive cut type 5. According to the operation to be performed on the work piece (a) Surface broach (b) Round hole broach (c) Keyway broach (d) Spline broach (e)Burnishing broach

82. Broaching methods Pull Broaching Workpiece is clamped to the broaching machine in stationary position and the broach is pulled through the work. Broaches are usually long and are held in a special head. Pull broaching is mostly used for internal broaching. Push Broaching Workpiece is held in the broaching machine in stationary position and broach is pushed through the portion of workpiece to the machined. Normally push broaching is done by hand and arbor presses (hydraulic press). This method is also recommended for internal broaching like for sizing and finishing the holes, cavities, and key ways. Surface Broaching Any one of two, either workpiece or the broach (tool) is kept moving and other is kept stationary. The method is widely used as surface finishing operation. In case of surface broaching, the broaching tool is specifically designed for the shape to be finished. Continuous Broaching In continuous broaching the broach is held stationary in the broaching machine and workpiece is moved continuously. The teeth of movement of the workpiece may be either straight, horizontal or circular. This is generally used for broaching a large number of similar workpieces at a time.

83. Operation

84. Horizontal type internal broaching machine

85. Horizontal type surface broaching machine

86. Vertical broaching machine - push down type

87. Vertical broaching machine - pull down type

88. Continuous type Broaching Machine

89. Rotary table continuous Broaching Machine

90. Broach tool nomenclature

91. Nomenclature Pull End ---- Pull end is made to attach the broach to the broaching machine through the puller head. Front Pilot -- This centres the broach in the hole to be finished just before start of processing. Roughing Teeth -- These are the cutting edges which remove larger amount of stocks during cutting. Larger amount removal generates poor quality of surface finish but makes the operation faster. Finishing Teeth --- These are cutting edges removing smaller stocks of material. These are used for final finishing of the surfaces and their accurate sizing. Rear Pilot and Follower Rest -- This is a supporting device to the broach when it is likely to complete its operation of broaching. Land -- It is the width of flank face of the broach normally it is kept slightly inclined to give relief angle to the flank face of broach. Pitch -- It is the distance between two corresponding points on two successive teeth of a broach. Normally pitch of finishing teeth of a broach is kept comparatively smaller than the rough cutting teeth. Height of the Teeth --- Height of the roughing and finishing teeth gradually increases from the shank to the finishing teeth. This increment is called the cut per tooth, it depends on the material being machined. Normally the cut per tooth is taken from 0.01 or 0.2 mm for the finishing teeth and it may go up 0.2 mm for the cutting teeth.

92. Parts produced in broaching

93. Advantages ( a) Used in mass production. (b) Production run time is less (c) cheaper. (d) Both rough cutting as well as finished cutting can be completed in a single pairs of tool. (e) Semi skilled labors enough (f) Broaching provides accurate and excellent quality of surface finish. It is capable to maintain tolerance of the order of  0.007 mm and surface finish CLA value upto 0.8 . (g) It is also capable to process internal and external surface including intricate shaped cavities. (h) Broaching makes the effective use of cutting fluids as it facilitates the flow of cutting fluid into the cuts.

94. Disadvantages Its initial cost is quite high. (b) Very large sized work pieces can not be subjected to broaching operation. (c) Broaching is not possible for the surfaces having obstructions. (d) Removal of larger stocks is not possible in broaching operation. (e) Clamping devices require frequent maintenance and cost.