1. Machining Processes

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Machining process
Chip Formation 2
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Machining Advantages 3
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4. Advantages 1 2 3 High Surface Quality More dimensional accuracy
Parts may have external and internal profiles Or special surfaces

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Disadvantages 5
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6. Machining Disadvantages
Waste material
Time consuming
Require more energy

7. Typical Parts Made with These Processes
Machine Components
Engine Blocks and Heads
Parts with Complex Shapes
Parts with Close Tolerances
Externally and Internally Threaded Parts

8. Products and Parts Made By These Processes

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Machining Processes
Traditional cutting includes Three major types of operations:
Turning rotates a cylindrical workpiece, while a single-point tool cuts along its length
Drilling rotates a multi-point tool and guides it into the workpiece to create a hole.
Shaping moves a single cutting tools along flat surface 9
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10. Cutting variables
Lab6: Roundness Test
12/7/2018

11. Lab6: Roundness Test
12/7/2018

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Cutting Angles 12
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Rake angle 13
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Rake angle 14
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15. Orthogonal cutting Chip Formation by Shearing
The tool has a rake angle of α , and a relief (clearance) angle.
The shearing process in chip formation (Fig. 21.4a ) is similar to the motion of cards in a deck sliding against each other.
Figure (a) Schematic illustration of the basic mechanism of chip formation by shearing. (b) Velocity diagram showing angular relationships among the three speeds in the cutting zone.

16. Lab6: Roundness Test
12/7/2018

17. Effect of rake angle on cutting force
Lab6: Roundness Test
12/7/2018

18. Cutting Forces
Figure (a) Forces acting on a cutting tool during two-dimensional cutting. Note that the resultant force, R, must be collinear to balance the forces. (b) Force circle to determine various forces acting in the cutting zone.

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Chips
Metal cutting is essentially a chip formation process.
Metal chips are the unwanted bits of material that are removed from the workpiece during the cutting process. 19
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Chip Formation 20
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Chip Formation 21
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Chip Types
There are Two types of metal chips created by cutting tools:
discontinuous chips
continuous chips 22
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Chip types 23
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Continuous chips
This type is generally formed when machining ductile metals.
Ductile metals include mild steel, copper, and aluminum.
The resulting surface finish is generally good, 24
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Discontinuous chips
Discontinuous chips consist of distinct chip segments that come off the workpiece in small chunks or particles.
Discontinuous chips often form with hard or brittle workpiece material that cannot withstand the high shear stresse involved. 25
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Built-up Edge
Continuous chip with a built-up edge (BUE). The built-up edge often forms when cutting soft, ductile metals
Small workpiece particles adhere to the tool due to high pressure and heat.
By increasing speeds and cutting angle, you can reduce the occurrence of the built-up edge. 26
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Built Up Edge 27
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28. Lab6: Roundness Test
12/7/2018

29. Chips Produced in Turning
Figure Chips produced in turning: (a) tightly curled chip; (b) chip hits workpiece and breaks; (c) continuous chip moving radially away from workpiece; and (d) chip hits tool shank and breaks off. Source: After G. Boothroyd.

30. Cutting Tool Materials
Strength
Hardness
Toughness
Wear resistance for a long tool life. 30
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31. Cutting Tool Material Types
Carbon Steel
High Speed Steel (HSS)
Tungsten Carbide
Ceramics
Diamond 31
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Carbon Steels
It has a limited tool life.
Used for small production runs.
It has Low cost.
It is suited to hand tools, and wood working.
Carbon content is about 0.9 to 1.35% with.
Maximum cutting speed is about 7 m/min.
The hot hardness value is low 32
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High Speed Steel (HSS)
It consists of alloyed steel with tungsten.
It can cut materials with tensile strengths up to Kg /Sq.mm
It has hot hardness value much greater than Carbon Steels.
It is used in all type of cutters, single/multiple point tools, and rotary tools. 33
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Tungsten Carbide
It is produced by sintering grains of tungsten carbide in a cobalt matrix (it provides toughness).
Other materials are often included to increase hardness, such as titanium, chrome, molybdenum, etc.
Compressive strength is high compared to tensile strength
Speed up to 300 rpm is commonly used on mild steels.
Hot hardness properties are very good. 34
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Carbide tools 35
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Ceramics
Sintered or cemented ceramic oxides, such as aluminum oxides.
Mild steels can be cut at speeds up to 1500 rpm.
These tools are the best to be used in continuous cutting operations.
There is no occurrence of welding, or built up edges.
Coolants are not needed to cool the work piece.
Very high hot hardness properties.
Often used as inserts in special holders. 36
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Diamond
It is very hard material with high resistance to abrasion.
Operations must minimize vibration to prolong diamond life. Also used as diamond dust in a metal matrix for grinding and lapping.
For example, this is used in the finishing of tungsten carbide tools. 37
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Cutting Fluids 38
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39. TEMPERATURE IN CUTTING
The main sources of heat generation are the primary shear zone and the tool-chip interface.
If the tool is dull or worn, heat is also generated when the tool tip rubs against the machined surface.
Cutting temperatures increase with:
strength of the workpiece material
cutting speed
depth of cut
Cutting temperatures decrease with increasing specific heat and thermal conductivity of workpiece material.

40. TEMPERATURE IN CUTTING
The mean temperature in turning on a lathe is proportional to the cutting speed and feed:
Mean temperature α Va fb (21.19)
a and b are constants that depend on tool and workpiece materials, V is the cutting speed, and f is the feed of the tool.
Max temperature is about halfway up the face of the tool.
As speed increases, the time for heat dissipation decreases and temperature rises
Tool Material a B
Carbide
0.2
0.125
HSS
0.5
0.375

41. Cutting Fluids Purposes
Cooling Purpose
Lubricant Purpose 41
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42. Purposes of cutting fluids
Cool and lubrication of the tool bit and work piece that are being machined,
increase the life of the cutting tool,
make a smoother surface finish, deter rust, and wash away chips.
Cutting fluids can be sprayed, dripped, wiped, or flooded onto the point where the cutting action is taking place. 42
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Tool Wear 43
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Lubrication Process 44
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45. TOOL LIFE: WEAR AND FAILURE
Conditions that would cause tool wear:
High localized stresses
High temp
Sliding of chip along the rack face
Sliding of the tool along the machined surface
The rate of wear depends on:
Tool and workpiece materials
Tool shape
Cutting fluids
Process parameters
Machine tool characteristics

46. TOOL LIFE: WEAR AND FAILURE
The Cutting tool should be replaced when:
Surface finish of the workpiece is poor
Cutting force increases significantly
Temperature increases significantly
Poor dimensional accuracies

47. TOOL LIFE: WEAR AND FAILURE

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Tool Sharpening 48
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49. Tool-life Curves
Figure Tool-life curves for a variety of cutting-tool materials. The negative inverse of the slope of these curves is the exponent n in the Taylor tool-life equation and C is the cutting speed at T = 1 min, ranging from about 200 to 10,000 ft./min in this figure.

50. TOOL LIFE: WEAR AND FAILURE Allowable Wear Land

51. Feed Marks on a Turned Surface
Surface roughness:
the higher the feed, and the smaller the tool-nose radius, R, the more prominent these marks will be.
Vibration and chatter adversely affect surface finish because a vibrating tool periodically changes
the dimensions of the cut.
Figure Schematic illustration of feed marks on a surface being turned (exaggerated).

52. Lab6: Roundness Test
12/7/2018

53. Lab6: Roundness Test
12/7/2018

54. Lab6: Roundness Test
12/7/2018

55. Lab6: Roundness Test
12/7/2018

56. Lab6: Roundness Test
12/7/2018

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Cutting Conditions
Main cutting motion (R)
This is represented in either Linear cutting speed in m/min or in rotational cutting speed in rpm
Feed motion (S)
This is represented in either mm/min or in mm/rev.
Depth of Cut (a)
This is represented in mm 57
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Cutting Action 58
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Cutting Speed 59
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Depth of Cut 60
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61. Cutting variables in Turning
point 61
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Cutting Action 62
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Feed Motion 63
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Feed motion 64
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Feed Motion 65
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Surface Roughness 66
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67. Cutting variables in Turning
point 67
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Cutting Tool
Single point Cutting tool 68
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69. The factors that influence the feeds and speeds are:-
The maximum and minimum speeds available on the machine
The type of coolant used
Type of cutting tool used
The condition of the machine
The type of material being machined
The clamping method used to secure the component
Diameter of the cutting tool
The type of material the cutting tool is made of
The condition of the tool
Lab6: Roundness Test
12/7/2018

70. Cutting variables in Turning
point 70
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Milling 71
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72. Cutting Variables in Milling72
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73. Shaper and Planner variables
Lab6: Roundness Test
12/7/2018

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Drilling Process 74
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75. Cutting Variables in Drilling75
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Grinding 76
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77. Lab6: Roundness Test
12/7/2018

78. Cutting Variable in Grinding78
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