Unit IV Abrasive Process and Broaching
- 1. RAMCO INSTITUTE OF TECHNOLOGY Mr.M.LAKSHMANAN Assistant Professor (Senior Grade) Department of Mechanical Engineering
- 2. UNIT IV ABRASIVE PROCESS AND BROACHING
- 3. UNIT -IV ABRASIVE PROCESS AND BROACHING - Syllabus Abrasive processes: grinding wheel – specifications and selection, types of grinding process– cylindrical grinding, surface grinding, centre less grinding and internal grinding- Typical applications – concepts of surface integrity, broaching machines: broach construction – push, pull surface and continuous broaching machines.
- 4. Grinding Grinding is one of the abrasive processes. It’s a metal cutting process in which the metal is removed with the help of rotating grinding wheel. This process removes comparatively little material usually from 0.25mm to 0.5mm. It is a metal cutting operation performed by means of a rotating abrasive tool, called Grinding wheel. Such wheels are made of fine grains of abrasive materials held together by a bonding materials called a bond.
- 5. Grinding Wheel Grinding wheels are made up of small abrasive particles held together by bonding materials. Thus it forms a multi edge cutter. Grinding Wheel Abrasives: Abrasive is a hard material. Its used to cut or wear away other materials. Small sizes of abrasives particles are used in grinding wheels. They are called Abrasive Grains.
- 6. Types of Abrasive Materials 1.Natural abrasives 2.Artificial abrasives 1. Natural abrasives: These are produced by uncontrolled forces of nature. These are obtained from mines. • Solid quartz(sio2) • Emery (mixture of 50-60% Alumina + iron oxide)coated paper • Corundum (75-90% Crystalline Al2o3 + iron oxide) • Diamond Natural abrasives lack of uniformity of properties and the reliability has largely been replaced by Artificial abrasive.
- 7. 2. Artificial abrasives: Its manufactured under controlled conditions in closed electric furnace in order to avoid the introduction of impurities and to achieve the necessary temperature for the chemical reaction to take place. These abrasives have better cutting properties and higher efficiency than natural abrasives. The various manufactured abrasives are: • Silicon carbide • Aluminum oxide • Boron carbide • Cubic boron nitride
- 8. Silicon carbide (SiC): • Silica sand+ petroleum coke + salt mixed • 2000°c to 4000°c for 34 hours • Brittle • Used for low tensile strength such as cast iron, brass, copper, aluminum. SiO2 + 3C = SiC + 2CO
- 9. Aluminum oxide (Al2O3): • Very hard and tough grains having sharp cutting edges. • Bauxide + Coke + Iron scrap • Electric furnace • Tough, less brittle and high tensile strength • Used for high speed steel, malleable cast iron, wrought iron etc.
- 10. Boron Carbide (B4C): • It is harder than silicon carbide but not as hard as diamond • Coke + boric acid • Electric furnace • Used for grinding and lapping very hard metals, hard alloys, glass and jewels. Cubic Boron Nitride (CBN): • It is harder than Aluminum oxide • Boron + Nitrogen • Nitrogen atoms • Thermal resistance • Grinding HSS cutters, tool steels, punch press dies, hardenable stainless steels
- 11. BOND Bond is an adhesive substance which holds the abrasive grains together to form the grinding wheel. The bonds must sufficiently be strong to withstand the stresses of high speed rotating grinding wheel. Types of Bonds: 1. Organic Bonds Resinoid Rubber Shellac Oxychloride 2. Non Organic Bonds Vitrified Silicate
- 12. Non Organic Bonds Vitrified bond (V): • Clay+ Abrasive grains mixed with water • 715°c • Very strong • Acids and alkalis not affected • Brittleness • Long time
- 13. Silicate bond (S): • Abrasive grains + silicate of soda • 270°c for 20 to 80 hours. • Water proof • Wear quickly • Blades, grinding cutter • Large wheels upto 1500mm diameter can easily be produced.
- 14. Organic Bonds Resinoid / Bakelite bond (B): • Abrasive grains+ mixed with natural resin • 210°c to250° • Grinding Cams • High finish on the work piece • Speed upto 300m/min • Used in grinding of steel, cast iron, Malleable iron castings.
- 15. Rubber bond (R): • Abrasive grains+ Pure rubber and Sulphur • Sulphur vulcanizing agent • High class surface finish (Centreless Grinding) • Wheel thick upto125mm • Very strong and tough and close grained Shellac bond (E): • Abrasive grains+ coated with shellac • Elastic bonded wheel • 160°c to 200°c • Very thin wheels can be produced (for Cutting off operation) • Cam shaft and Mill Rolls
- 16. Oxychloride bond (O): • Abrasive grains+ mixed with Oxide and Chloride of magnesium • Disc shaped wheels. • Less brittle • Less sensitive to side loads as compared to vitrified bond wheel • Grinding in dry condition (Cool cutting action)
- 17. Specification of Grinding Wheel • Grit Number and Grain Size • Grade • Structure of Wheels
- 18. Specification of Grinding Wheel
- 19. Grit Number and Grain Size • It refers to the actual size of the abrasive particles. The grain size is denoted by the grit number. Grid Number is equal to the number of meshes in 254 mm of a sieve through which the grains can pass through. • Larger is the grit number, smaller will be the grain size (fine Grit) and vice versa. • For rough machining, coarse grained wheels (Smaller grit number) are used. • For finishing, fine grained wheels (large grit number) are used.
- 20. Grain size used for Grinding Operation Grit The size of the abrasive grains are indicated by grit number or grain number. Grinding Operation Grit number Coarse 10 12 14 16 20 24 - Medium 30 36 46 54 60 - - Fine 80 100 120 150 180 - - Very fine 220 240 280 320 400 500 600
- 21. GRADE • The term grade refers to the bond strength. • This is the strength with the bond holds the abrasive grains in place. • Grade or Hardness indicates the strength with which the bonding material holds the abrasive grains in the grinding wheel. • It does not refer the hardness of abrasive grains.
- 22. The degrees of hardness are specified by the use of letters of the Alphabet. “A” indicates the softest Grade whereas “Z” indicates the hardest Grade. Soft A B C D E F G H Medium I J K L M N O P Hard Q R S T U V W X Y Z
- 23. Structure of Wheels • This term denotes the spacing between abrasive grains or in other words the density of the wheel. • The abrasive grains in the grinding wheel are distributed through the bond. • The relative spacing of abrasive is referred as structure. • When the spacing is small, the structure is called Dense structure. • When the spacing is wide, the structure is called open structure. Structure Symbol Dense 1 2 3 4 5 6 7 8 Open 9 10 11 12 13 14 15 or higher
- 24. Designation of Grinding Wheel An Indian Standard Institution (IS:551 – 1954) has specified a standard system of marking the grinding wheels. Elements: • Type of abrasives • Grain size or grit number • Grade of the wheel • Structure • Type of bond • Manufacturer’s code
- 26. Selection of grinding wheels The following factor are to be considered. 1.Constant factor: • Physical properties of Material to be ground • Amount and rate of stock to be removed • Contact area • Type of grinding machine
- 27. 2. Variable factors • Work speed • Wheel speed • Condition of the grinding machine(Dry/Wet) • Personal factors
- 28. 1. Constant factor: • The material to be ground Abrasive Grain size Grade structure -Aluminum oxide wheel -Coarse grain wheel -hard grade wheel -open structure wheel For soft, ductile and high tensile material Abrasive Grain size Grade structure -silicon carbide wheel -fine grain wheel -soft grade wheel -dense structure wheel For hard and brittle the material
- 29. • The grit and grade range for various class of work Class of work Grit size Grade Rough work 14-30 Q-S Cylindrical work 35-150 J-N Centre less and crankshaft 46-80 J-N Surface grinding 20-36 G-M Tool grinding 30-80 M-Q Internal grinding 46-60 H-N
- 30. • Amount and rate of stock to be removed -Coarse grain and wide spacing are used for fast cutting. -Fine grain and close spacing are used for fine finish. • Contact area -When the contact area is small, fine grain and close spacing -When the contact area is large coarse grain and wide spacing
- 31. • Type of grinding machine -Heavy rigid machine -Light rigid machine 2. Variable factor: a) Work speed -Hard wheel -Soft wheel
- 32. b) Wheel speed -Soft wheel -Hard wheel c) Condition of the grinding machine -Dry conditions -Wet conditions d) Personal factor -Skilled worker -Unskilled worker
- 33. Reconditioning of Grinding Wheel During grinding operation, the grinding of the wheel are subjected to wear and the wheel loses its cutting capacity. Grinding wheels are dressed to restore their cutting capacity which is lost by the phenomenon of loading and Glazing. During the operation the chips formed get entrapped in the inner granular space of abrasive particles. Its called Loading. When the bond of the abrasive is very hard, it does not dislodge an abrasive particle. Therefore the surface of the wheel becomes smooth and gets a glassy like appearance. Its known as Glazing of the wheel.
- 34. DRESSING It’s the process of loading and breaking away the glazed surface so that new sharp abrasive particles are again present to work for efficient cutting is called Dressing. The dressing is done using the tool called Dresser. Types of Dressing Tools: • Star Wheel Dressing Tool • Abrasive Stick • Diamond Dressing Tool
- 36. Abrasive Stick
- 39. TRUING Truing is the process of trimming the cutting surface of the wheel to run true with the axis. By truing the cutting surface of the worn out wheel can be shaped to the original form. Its also used to produce the required contour for form grinding. Truing is done with a Diamond Truing tool. Tis process is similar to dressing.
- 41. • The grinding face of the wheel may become irregular. • Hence it loses its original shape • Truing is done to bring back the original of the wheel.
- 42. Shapes of Grinding Wheel
- 43. Standard Shapes of Grinding Wheel Faces
- 44. Classification of Grinding Machine • According to type of operation Tool Grinders Cut off Grinders • According to the quality of surface finish Precision Grinders Rough Grinders • According to the type of surface generated Cylindrical Grinders Internal Grinders Surface Grinders Tool Grinders Special purpose Grinding Machines Surface finishing Grinders
- 45. 1. cylindrical grinders Plain cylindrical grinder Universal cylindrical grinder Centreless grinder 2. Internal grinders Plain internal grinder Centreless internal grinder Chucking internal grinder Universal internal grinder
- 46. 3.Surface grinder (i) Reciprocating table (a) Horizontal spindle (b) Vertical spindle (ii) Rotating table (a) Horizontal spindle (b) Vertical spindle 4. Tool and cutter grinder (a) Universal (b) Special
- 47. Rough Grinders Its used for removing large amount of metal from the workpiece. It is used for removing projections such as sprue pins from casting, projections in forging, finishing the weldments, sharpening of hand tools.
- 48. Bench Grinder
- 49. Portable Grinder
- 52. Precision Grinders Its used to manufacture parts of accurate dimensions and good surface finish. The workpiece and the grinding wheel are rigidly mounted but they are adjustable according to the requirement of the machining methods. It is used for cylinder bores, gauges, tools, cutters, machine guide ways, threads, gears, cams etc.
- 54. 1.1 Plain Centre Type Cylindrical Grinding Machine
- 55. 1.2 Centre Type Universal Grinder Machine
- 56. 2. Surface Grinders • Horizontal Spindle Reciprocating Table Surface Grinder • Horizontal Spindle Rotary Table Surface Grinder • Vertical Spindle Reciprocating Table Surface Grinder • Vertical Spindle Rotary Table Surface Grinder
- 57. 2.1 Horizontal Spindle Reciprocating Table Surface Grinder
- 60. 2.2 Horizontal Spindle Rotary Table Surface Grinder
- 61. 2.3 Vertical Spindle Reciprocating Table Surface Grinder
- 63. 2.4 Vertical Spindle Rotary Table Surface Grinder
- 66. 3. Centreless Grinding Centreless grinding differs from centered grinding operations in such a way that no spindle or fixture is used to locate and secure the workpiece. The workpiece is secured between two rotary wheels and speed of their rotation relative to each other determines the rate at which the material is removed from the workpiece. Its performed on cylindrical workpieces such as pistons, Valves, rings, tubes, balls, drills, shafts, etc. it can be done on both external and internal surfaces.
- 67. Principle of Centreless Grinding
- 70. Methods of External Centreless Grinding Through Feed In Feed End Feed
- 71. 1. Through Feed: Its used for straight cylindrical workpiece such as long shafts or bars, roller pins etc. In this method regulating wheel is tilted at small angle. It makes the work to move axially through the space between grinding wheel and regulating wheel. The guides are provided at the ends of the wheel and guide the movement of the workpiece. The machine usually removes 0.2mm of stock in one pass on the diameter of the work.
- 72. Through Feed
- 73. 2. In Feed: Its similar to plunge grinding. The work is placed on the work rest against an end stop. It prevents the axial movement of the workpiece. The regulating wheel and work rest with the workpieces are moved towards the grinding wheel by hand feed. Its used to grind shoulders and formed surfaces.
- 74. 3. End Feed: In this method, both grinding and regulating wheels are tapered and thus, it produces tapered workpieces. The workpiece is fed lengthwise between wheels and its ground as it advances until it reaches the end stop.
- 75. Internal Grinding • Chucking Type • Planetary Type • Centreless Type
- 76. 1. Chucking Type Internal Grinders The workpiece is mounted in a chuck and rotated about its axis. The workpiece is mounted at the left side of the machine. The grinding wheel (wheel head) is mounted at the right end of the machine. The grinding wheel is rotated and at the same time, it reciprocates back and forth through the length of the hole.
- 78. 2. Planetary Type Internal Grinders In this grinders, the work remains stationary and the rotation of wheel spindle gives an eccentric motion according to the diameter of the hole to be ground. Therefore in this operation, the motion of the grinding wheel is in the form of the planet and hence, its called planetary grinding.
- 79. 3. Centreless Internal Grinding
- 80. In this centreless internal grinding, the work is supported by three rolls. One is the regulating wheel, The second one is a supporting roll and the last one is a pressure roll. The pressure roll is used to hold the workpiece against the support and regulating rolls.
- 82. Advantages of Centreless Grinding • Small diameter and long length work pieces can be ground without any deflection as the work piece. • Size of job can be controlled easily and accurately. • Suitable for mass production. • Work holding devices like,chucks,dogs are not possible. Disadvantages • It is not used for large diameter work piece • Jobs having flat surface on cylindrical can not be ground.
- 83. Size and specification of grinding machines • The largest work piece which can be held on a grinder • The normal capacity of the grinder • The width of the table • The maximum traverse of the table • Wheel diameter • Height of the grinding head
- 84. Grinding Ratio G= volume of material required volume of wheel wear
- 85. Applications of Grinding Wheel • Forming • Gear Teeth Grinding • Thread Grinding • Cam Grinding • Tool and Cutter Grinding
- 87. Surface Integrity Surface integrity is the surface condition of a workpiece after completing a particular manufacturing process. The concentrated energy consumption at the contact region of a machining process can be divided into Mechanical, Thermal and Chemical effects which lead to differing intensities of surface property alterations. Types of Surface integrity characteristics: Topography Characteristics – surface roughness, waviness, errors of forms and flaws. Surface layer Characteristics – Plastic deformation, residual stresses, cracks, hardness, phase change, recrystallization, etc.
- 88. Factors influence workpiece Surface Topographies in Grinding • Workpiece material – Harder materials allow finer finishes • Type of wheel – Fine Grains yield finer finishes • Dressing procedure – Improperly dressed wheels will damage the work surface. • Feed rate – Finer finishes are obtained with slower feed rates • Machine rigidity – Older, worn machines yield a poor quality finish • Wheel condition – Clogged wheels cannot produce a good finish • Lubricant cleanliness – Coolant filtration removes waste that could damage workpiece surface.
- 89. BROACHING Broaching is a process of machining a surface with a special multipoint cutting tool called Broach which has successively higher cutting edges in a fixed path. It is faster and cheaper method of machining but depth of removed material is limited to 6mm or less. External and Internal surfaces can be machined by broaching. It is used to machine key ways,splines,square, rectangular and polygon holes, internal gear etc.
- 94. Specification of Broaching Machine Main Specifications: • Maximum length of the stroke in mm • Maximum force developed by the slide in Tonnes. Minor Specifications: • Power rating of electrical motor in H.P • Speed and feed Range • Weight of thee machine in Tonnes • Floor space required in square meter.
- 95. Types of Broaching Machine • According to the direction of the cutter 1.Horizontal 2. Vertical • According to the method of cutting 1.Pull type 2.Push type 3. Continuous type • According to the type of drive 1.Mechanical drive 2. Hydraulic drive • According to the number of pull heads 1.single head 2. multiple pull head • According to the type of operation 1.External type 2. Internal type
- 96. Horizontal Broaching Machines 1.Horizontal type Internal Broaching Machine
- 97. All Horizontal broaching machines are of pull type and provided with either hydraulic or an electric drive. Its operated at a low speed of 2 to 15m per minute. Its used for small and medium sized works like keyways and internal gears, etc.
- 99. 2. Horizontal Type Surface Broaching Machine The broach is pulled over the top surface of the workpiece. The cutting speed ranges from 3 to 12 mpm with a return speed up to 30mpm.
- 100. Vertical Broaching Machine 1. Push Down Type 2. Pull Down Type 3. Pull Up Type 1. Push Down Type Vertical Broaching Machine The push type vertical broaching machine is used in the surface broaching operation. It consists of a box shaped column, slide and drive mechanism. The slide is provided with a quick return mechanism.
- 103. 2. Pull Down Type Vertical Broaching Machine These machines are mostly used for internal broaching operations. Its pulled through the job. The tail end of the broach is automatically engaged by a pulling mechanism and it is pulled down through the job.
- 104. Pull Down Type Vertical Broaching Machine
- 105. 3. Pull Up Type Vertical Broaching Machine In this type, the ram slides on the vertical column of the machine. The ram carries the pulling head at its bottom. The broach is pulled upward.
- 106. Continuous Broaching Machines Its used for high production rate of small parts. Types: • Horizontal Type • Vertical Type • Rotary Type
- 107. 1. Horizontal Type Continuous Broaching Machine It is one type of surface broaching machine. It has a driving unit which consists of two sprockets. They are connected by an endless chain. Fixtures are mounted at intervals on the chain for loading and holding workpieces. The broach is horizontally fixed in the frame of the machine. The rigid guiding member is arranged under the chain in the zone where the workpiece passes under the broach. The work is automatically clamped before it reaches the Tool.
- 109. 2. Vertical Type Continuous Broaching Machine When the axes of two sprockets are vertical. Its called Vertical Broaching Machining. The broach is vertically placed on the frame of the machine.
- 110. 3. Rotary Type Continuous Broaching Machine The machine has a rotary table and vertical column. In vertical column the broach is horizontally fitted above the table. A series of fixtures are mounted on the rotary table for locating and holding workpieces.
- 111. Broach Nomenclature The broach is composed of a series of teeth. Each tooth is standing slightly higher than the previous one. This rise per tooth is the feed per tooth and it determines the material removed by the tool.
- 113. Types of Broaching Tools • Push Broach • Pull Broach • Progressive Broach • Push Broach:
- 114. • Pull Broach:
- 116. Broaching Tool Materials • High speed tool steel such as alloy steel and stainless steel • TiN Coated carbides • Aluminium • Brass • 12L14
- 117. Applications of Broaching Machines • Straight and helical slots • External surfaces of various shape • External and internal toothed gears • Holes of cross sectional shape
- 118. HONING Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive stone against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but may also improve the surface texture.