24ME303 MANUFACTURING PROCESS UNIT-V.pptx

METAL CUTTING PROCESS

1. UNIT V METAL CUTTING PROCESS Mechanics of chip formation, forces in machining, types of chip, cutting tools - single point cutting tool nomenclature. orthogonal and oblique metal cutting. Centre lathe, constructional features, specification, operations - Taper turning methods. Thread cutting methods, special attachments. Capstan and turret lathes

2. INTRODUCTION Components are made into various shapes and sizes by using metals. Depending the types of tools and operations. During the metal removal process, various forces act on the cutting tool and work piece.

3. Metal Removing P rocess Non-cutting process (or) Chipless process Forging, Drawing, Spinning, Rolling, Extruding Cutting process (or) Chip process Turning, Drilling, Milling, Planer, Shaping

4. Mechanism of metal cutting

5. Mechanism of Chip Formation The type of chip formed during metal cutting depends upon the machining condition and material to be cut. The following variables are influencing in producing the type of chip such as Mechanical properties of material to be cut in particular ductility and brittleness. Depth of cut Various angles of tool especially rake angle Cutting speed Feed rate Type of cutting fluid Surface finish required on work piece

6. SINGLE POINT CUTTING TOOL

7. Nomenclature of Single Point Cutting Tool Parts of a single point cutting tool Angles of single point cutting tool Effects of Back rake angle Effects of Side rake angle

8. Parts of a single point cutting tool Shank Face Flank Base Nose Cutting Edge

9. Shank: Main body of tool, it is part of tool which is gripped in tool holder Face: Top surface of tool b/w shank and point of tool. Chips flow along this surface. Flank: Portion tool which faces the work. It is surface adjacent to & below the cutting edge when tool lies in a horizontal position. Base : Bearing surface of tool on which it is held in a tool holder. Nose radius: Cutting tip, which carries a sharp cutting point. Nose provided with radius to enable greater strength, increase tool life & surface life. Cutting edge: It is the junction of face and flank.

10. Angles of single point cutting tool Rake angle Back rake angle Side rake angle Relief angle (or) clearance angle End relief angle Side relief angle Cutting edge angle End cutting edge Side cutting edge Nose radius

11. Effects of Back rake angle

12. When will be the positive rake angle used? To machine the work hardened materials To machine low strength ferrous and non-ferrous metals To turn the long shaft of smaller diameters To machine the metal having lesser recommended cutting speeds When will be the negative rake angle used? To machine high strength alloys The feed rates are high To give heavy and interrupted cuts

13. Effects of side rake angle During the cutting process, the amount of chip bend depends on side rake angle.

14. Tool Signature Tool angles given in a definite pattern is called tool signature. The tool angle have been standardized by the American Standards Association (ASA). Back rake angle Side rake angle End relief angle Side relief angle End cutting edge angle Side cutting edge angle Nose radius

15. Types of chip formation Continuous chip Discontinuous chip Continuous chip with built-up edge

16. Continuous chip During cutting of ductile material, a continuous ribbon such as chip is produced due to pressure of the tool cutting edge in compression and shear. It gives the advantage of, Good surface finish Improving tool life Less power consumption However, the chip disposal is not easy and the surface finish of the finished work get affected.

17. The following condition favors the formation of continuous chips Ductile material such as low carbon steel, aluminum, copper etc. Smaller depth of cut High cutting speed Large rake angle Sharp cutting edge Proper cutting fluid Low friction between tool face and chip interface.

18. Discontinuous chip Discontinuous chip produced while machining brittle materials such as grey cast iron, bronze, high carbon steel at low cutting speeds without fluids. During machining the brittle material lacks its ductility which results for plastic chip formation.

19. The following condition favors the formation of discontinuous chips Machining of brittle material Small rake angle Higher depth of cut Low cutting speeds Excess cutting fluid Cutting ductile material at very low feeds with small rake angle of the tool.

20. Continuous chip with built-up edge During the cutting process, the interface temperature and pressure are quite high and also high fiction between tool-chip interface. It causes the chip material to weld itself to the tool face near the nose is called “built-up edge”. This process gives the poor surface finish on the machined surface and accelerated wears on the tool face.

21. The following condition favors the formation of discontinuous chips with built-up edge. Low cutting speed Small rake angle Coarse feed Strong adhesion between chips and tool interface Insufficient cutting fluid Large uncut thickness

22. Types of metal cutting process Orthogonal cutting process (Two – dimensional cutting) Cutting edge of the tool is perpendicular to the cutting velocity vector. Oblique cutting process (Three dimensional cutting) Cutting edge is inclined at an acute angle with the normal to the cutting velocity vector.

23. Sl No Orthogonal cutting process Oblique cutting process 1 The chip flows over the tool face and the direction of chip flow velocity is normal to the cutting edge. The chip flows on the tool face making an angle with the normal on the cutting edge. 2 The maximum chip thickness occurs at its middle. The maximum chip thickness may not occur at the middle. 3 Tool is perfectly sharp and it contacts the chip on rake face only. Frequently, more than one cutting edges are in action. 4 Tool life is less Tool life is more

24. Thermal aspects The heat is generated in three region such as shear zone, chip tool interface region and tool work interface region. Shear zone The zone which is affected by the energy required to shear the chip or to separate the chip and work is called shear zone . The heat generation range is 80-85% Chip - tool interface region The energy used to overcome the friction completely is the source of the heat. The heat generation range is 15-20% Tool - work interface region The energy is supplied to overcome the rubbing friction between flank face of the tool and work piece is the source of the heat. The heat generation range is 1-3%

25. The tool temperature increases due to the following factors such as Cutting speed Feed Properties of tool materials etc.

26. TOOL WEAR Attrition

27. Diffusion

28. Classification of tool wear Flank wear Feed < 0.15 mm/revolution Crater wear Nose wear

29. TOOL LIFE Tool life is defined as the cutting time required for reaching a tool life criterion or time elapsed between two consecutive tool resharpening . The following are some of ways of expressing tool life. Volume of metal removed per grind Number of work pieces machined per grind Time unit

30. Factors affecting tool life Cutting speed Feed and depth of cut Tool geometry Tool material Cutting fluid Work material Rigidity of work, tool and machine

31. Cutting speed

32. Feed and depth of cut

33. Tool geometry

34. SURFACE FINISH Generally, the surface finish of any product depends on the following factors. Cutting speed Feed Depth of cut

35. CUTTING FLUIDS Cutting fluids are used to carry away the heat produced during the machining. At the same time, it reduces the friction between tool and chip.

36. Functions of cutting fluids It prevents the work piece from excessive thermal distortion It improves the surface finish It causes the chips to break up into small parts. It protects the finished surface from corrosion. It washes away the chip from the tool. It prevents the corrosion of work and machine.

37. Properties of cutting fluids It should have the high heat absorbing capacity It should be odourless It should be non-corrosive to work and tool It should have high flash point It should have low viscosity It should be economical to use

38. Types of cutting fluids Basically two main type of cutting fluids Water based cutting fluids Straight (or) heat oil based cutting fluids

39. Water based cutting fluids To improve the cooling and lubricating properties of water, the soft soap or mineral oils are added to it. These oils are known as soluble oils .

40. Straight (or) heat oil based cutting fluids Straight oil based cutting fluids means pure oil based fluids. Most of the oils are not directly used but it is mixed with other oils. It is classified into the following subgroups Mineral oils Straight fatty oils Mixed oils Sulphurised oils Chlorinated oils

41. Methods of applying cutting fluids Cutting fluids are used in many ways such as Drop by drop under gravity Flood under gravity Form of liquid jet Atomised form with compressed air Through centrifugal action

42. MACHINABILITY Machinability is defined as the ease with which a material can be satisfactorily machined. It can also be defined as follows The life of tool before tool failure The quantity of the machined surface The power consumption per unit volume of material removed.

43. Variables affecting machinability Work variables Tool variables Machine variables Cutting conditions

44. Evaluation of machinability Tool life per grind Rate of metal removal per tool grind Surface finish Dimensional stability of the finished work Chip hardness Shape and size of chips

45. Advantages of high machinability Good surface finish can be produced Higher cutting speed can be used Less power consumption Metal removal rate is high Less tool wear

46. Machinability index Machinability index I = I = The machinability index for some common materials is given by Low carbon steel - 55 - 60% Stainless steel - 25% Aluminium alloy - 390 - 1500%  

47. SHEAR STRAIN

48. TURNING MACHINES Centre lathe, constructional features, specification, operations – taper turning methods, thread cutting methods, special attachments, machining time and power estimation. Capstan and turret lathes- tool layout – automatic lathes: semi-automatic – single spindle: Swiss type, automatic screw type – multi spindle:

49. CENTRE LATHE

50. The following are the principle parts of the lathe Bed Head stock Tail stock Carriage Feed mechanism

51. BED Bed is the base of machines. It carries a headstock on its left end and tailstock on its right end. The carriage is mounted at the middle of bed.

52. Head stock The headstock assembly is permanently fastened to the left end of the bed. It carries a hollow spindle so that bars can be passed through it when it is required. There are two types of headstock driving mechanisms as follows Back geared headstock All geared head stock

53. Back gear arrangement is used for reducing the spindle speed which is necessary for thread cutting and knurling. Back geared headstock

54. All geared head stock All geared headstock is commonly used in modern lathes because of the following advantages It gives wider range of spindle speeds. It is more efficient and compact. The vibration of spindle is reduced. Belt shifting is eliminated. More power can be transmitted.

55. Tail stock Tailstock is situated at the right end of the bed. It is used for supporting the right end of the work piece.

56. Carriage The carriage is a moving part that slides over the guide ways between headstock and tailstock. It carries the following parts. Saddle Cross slide Compound rest Tool post Single screw tool post Open side tool post F our bolt tool post Four way tool post

57. Feed mechanism Feed is defined as the movement of the tool relative to the work. There are three types of feed longitudinal, cross and angular feed.

58. The following feed mechanisms are used Tumbler gear reversing mechanism Quick change gearbox Tumbler gear quick change gearbox Apron mechanism

59. Tumbler gear reversing mechanism

60. Quick change gearbox

61. Tumbler gear quick change gearbox

62. Apron mechanism

63. Specification of a lathe

64. Types of lathe Lathes are classified in many ways with respect to size, design, method of drive and purposes. Speed lathe Wood working lathe Metal spinning lathe Metal turning lathe Polishing lathe Engine lathe Step cone pulley drive lathe Geared lathe Variable speed lathe Bench lathe Tool room lathe Semi automatic lathe Capstan lathe Turret lathe Automatic lathe Special purpose lathe Copying lathe

65. Operations in lathe

66. TAPER TURNING METHODS Form tool method Tailstock set over method Compound rest method Taper turning attachment method

67. Form tool method It is one of the simplest methods to produce short taper. Taper length should be less than the tool cutting edge length.

68. Tailstock set over method

69. Compound rest method

70. Taper turning attachment method

71. THREAD CUTTING METHODS Thread cutting is done in different methods Reversing the machine Marketing the lathe parts Using a chasing dial or thread indicator Using thread chaser

72. Using a chasing dial or thread indicator

73. SPECIAL ATTACHMENTS Generally milling and grinding are performed on lathes by using special attachments Milling attachments Milling is the process of removing metal by moving the work against a rotating cutter. this operation is carried out in two methods depending upon the form of profiles. For cutting grooves or keyways For cutting multiple grooves and gear wheel

74. Grinding attachment Grinding is the operation of removing metal in fine form of chips. It is done by moving the work against a rotating abrasive wheel. This abrasive wheel is known as grinding wheel.

75. WORK HOLDING DEVICES Some of the standard work holding devices used to hold the work in a lathe are given below. Chucks Centres Face plate Angle plate Mandrels Steady and follower rest

76. Chucks Three jaw chuck or self centering chuck Four jaw chuck or independent chuck Magnetic chuck

77. Three jaw chuck or self centering chuck

78. Four jaw chuck or independent chuck

79. Magnetic chuck

80. Centres

81. Face plate

82. Angle plate

83. Steady and follower rest

84. AUTOMATIC LATHES AND SEMI AUTOMATIC LATHES In an ordinary centre lathe, changing and setting of tools consume more time. It reduces the rate of production and increases the cost of production. The changes of centre lathe into some special lathes is called semi automatic lathes and automatic lathes. The turret lathes are used in heavy jobs whereas the capstan lathe is used for light and small jobs.

85. Capstan and Turret lathe

86. THE MAIN PARTS OF CAPSTAN AND TURRET LATHES Bed Cross slide Head stock Turret head and saddle

87. BED Bed is the base part of the lathe. It is box type which is made of cast iron. The bed should be strong and rigid to withstand heavy loads, force and vibrations during machining.

88. CROSS SLIDE The two types of cross slides are as follows Reach over type It is mounted on bed guide ways in between head stock and turret. The cross slide has two tool posts. The tool post can move both in perpendicular and parallel direction to the spindle axis. In the rear tool post, the parting off tool is clamped in an inverted position to make the direction of work piece anti clock wise with respect to tool movement. Side hung type This type of cross slide is entirely supported on the front way which has no rear tool post. It provides a greater swing capacity to accommodate large diameter work piece. It is mainly used in turret lathe.

89. HEAD STOCK Headstock of capstan and turret lathe is similar to a head in ordinary centre lathes but heavier in construction. The four main types of head stock are as follows Step cone pulley driven head stock Direct electric motor driven head stock All geared head stock Pre-selective stock

90. SADDLE

91. In a capstan lathe, the turret head is mounted on a ram which slides on the saddle. It can be positioned on lathe bed ways and clamped well. In a turret lathe, the turret head is mounted on the saddle itself which slides on the bed ways during machining. It is mainly used in turret lathes.

92. TURRET HEAD A turret head has a hexagonal block having six faces with a bore for mounting six or more than six tools at a time. Turret head is mounted on the ram fitted with turret slides longitudinally on a saddle. Each tool is indexed through 60° by the rotation of a circular plate. The circular plate is automatically indexed along with the turret head. Bringing the next tool into the cutting position is known as Geneva mechanism.

93. GENEVA MECHANISM (OR) INDEXING MECHANISM The turret is provided with automatic indexing mechanism. To index the turret by 1/6 of a revolution, the ram is returned to the starting position. Then, the next tool comes into position to perform the machining operation.

94. WORKING PRINCIPLE OF CAPSTAN AND TURRET LATHES Drilling, boring, reaming, counter boring, turning and threading tools are mounted on the hexagonal turret head. Forming, chamfering, knurling and necking tools are mounted at the front end of the square turret. Parting off tool is mounted on the rear end of the square turret in an inverted or in a reversed position.

95. SPECIFICATION OF CAPSTAN AND TURRET LATHES Number of spindle speeds Number of feeds for the carriage Number of feeds for the turret Net weight of the machine Floor space required Power of the motor required

96. ADVANTAGES OF CAPSTAN AND TURRET LATHES The production rate is high Heavier and larger work piece chucking can be done It has wider range of speeds Larger number of tools can be held More than one operation can be performed at the same time It is more rigid. Hence, its withstands heavy cuts Semi skilled operators are enough Labour cost is less

97. Sl No. CAPSTAN LATHE TURRET LATHE 1 Turret head is mounted on a ram which slides over the saddle Turret head is directly mounted on saddle. But it slides on the bed 2 The turret movement is limited The turret moves on the entire length of the bed without any restrictions 3 Hence, shorter workpiece can be machined Longer workpiece can be machined 4 It does not provide rigidity It provide rigidity and strong 5 It is very much useful for light duty application It is useful for heavy duty application 6 Turret head moved manually Turret head cannot moved manually 7 The maximum size of 60 mm diameter work can be accommodated It can accommodate only 125 mm to 220mm

98. WORK HOLDING DEVICES The work holding devices used on capstan and turret lathes are mostly automatic types. It reduces the setting time. Collets Draw back collet Push out collet Dead length collet Chucks F ixture

99. COLLETS

100. Draw back collet

101. Push out collet

102. Dead length collet

103. Chucks

104. Fixture A specially designed member to locate and grip a work piece is called as fixture. It is mounted on the spindle by replacing a chuck or collet.

105. BAR FEEDING MECHANISM

106. TOOL HOLDING DEVICES To hold these tools in the respective positions, the various types of tool holders are fitted in a hexagonal turret or front tool post of the square turret or in the rear tool post. The following are the various types of tool holders Straight cutter tool holder Adjustable angle cutter tool holder Multiple cutter holder Offset cutter holder Sliding tool holder Knee tool holder Flange tool holder Roller steady box tool holder Self opening type die holder Knurling tool holder Collapsible taps Combination tool holder

107. Straight cutter tool holder

108. Adjustable angle cutter tool holder

109. Multiple cutter holder

110. Offset cutter holder

111. Sliding tool holder

112. Knee tool holder

113. Flange tool holder

114. Roller steady box tool holder

115. Combination tool holder

116. Self opening type die holder

117. Knurling tool holder

118. Collapsible taps

119. TOOL LAYOUTS Turret and capstan lathe are mainly used for machining workpieces in rapid speed. Before starting the production, the following works are carried out. Selection of tools Designing of special tools Selection of speeds Selection of feeds Setting the required length of work piece.

120. Tool layouts mainly consist of three stages Planning and scheduling stage Detailed sketching of various stages Sketching the plan showing the various tools

121. AUTOMATIC LATHES In automatic lathes, all operations required to finish off the work piece are automatically done without the attention of an operator. These machines are meant for producing identical parts without participation of an operator. All operations including loading and unloading are automatically done. By using the control system, all working and idle operations are performed in a definite sequence.

122. ADVANTAGES OF AUTOMATIC LATHES Mass production of identical parts is highly achieved High accuracy is maintained Time of production is minimized Less floor space is required Unskilled labour is enough It minimizes the labour cost One operator can be utilized to operate more than one machine.

123. Classification of automatic lathes Classification according to the type of work material used Bar stock machine Chucking machine Classification according to the number of spindles Single spindle automats Multi spindle automats Classification according to the arrangements of spindles Horizontal spindle type Vertical spindle type Classification according to the feed control Single cam shaft rotating at constant speed Single cam shaft with two speeds Two cam shaft Classification according to the use Single purpose machine General purpose machine

124. SINGLE SPINDLE AUTOMATIC LATHES

125. The following types of single spindle automatic lathe are mostly used Automatic cutting off machine Automatic screw cutting machine Swiss type automatic screw machine

126. Automatic cutting off machine

127. Automatic screw cutting machine

128. Swiss type automatic screw machine

129. It consists of four major parts The sliding headstock through which the bar stock is passed and gripped by a carbide lined guide bush The camshaft which controls the bar stock and cutting tool movements The tool bracket which supports five tool slides and a bush for stock Auxiliary attachments for performing various operations such as knurling, drilling, tapping, screwing, slotting, recessing etc.

130. Working principle The bar stock is held in the rotating spindle by a collet check. head stock slides along the bed ways with the rotating bar stock. This headstock movement gives a longitudinal feed to the work. All tools in the tool slides remove materials from the work piece at the same time. The tool in the feed base attachment may also do operations such as drilling.

131. Advantages of Swiss type screw machine It is used to manufacture precision turning of small parts It has five tool slides Wide range of speeds is available It is rigid in construction Tolerance of 0.005 to 0.0125mm is obtained

132. Multi spindle automatic lathes Multiple spindle automatic lathes are machines which can produce larger work pieces than single spindle automats. The principle advantage of the multi spindle automat is that it has a tool slide working simultaneously on the jobs on all spindles and hence, the time for producing a piece is the time for the longest cut

133. Classification of multi spindle automatic lathes According to the type of work piece used Bar type machine Chucking type machine According to the arrangement of spindle Horizontal spindle type Vertical spindle type According to the principle of operation Parallel action type Progressive action type

134. Parallel action Multiple spindle automatic machine

135. Progressive action Multiple spindle automatic machine

136. Sl No. Parallel action machine Progressive action machine 1 Same operation is done on all jobs in all spindles Different operations are done on jobs at each station one after another 2 The rate of production is very high The rate of production is moderate 3 If anything goes wrong in one station, the production in that particular station only is affected If anything goes wrong in one station, the production is completely affected in all station. 4 Small parts of simple shapes are produced Parts of complicated shapes can be produced

137. Sl No. Single spindle Multi spindle 1 There is only one spindle There are 2,4,5,6 or 8 spindle 2 Only one work piece is machined at a time A number of work pieces are machined at a time 3 The rate of production is low The rate of production is high 4 Machining accuracy is higher Machining accuracy is lower 5 Tool setting time and tooling cost is less Tool setting time and tooling cost is more