1. Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 24: Machining Processes: Milling, Broaching, Sawing, Filing and Gear Manufacturing
Presentation slide for courses, classes, lectures et al.
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2. Chapter Outline Introduction Milling and Milling Machines
Planing and Shaping
Broaching and Broaching Machines
Sawing
Filing
Gear Manufacturing by Machining
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3. Introduction
Machining operations can produce many other parts with more complex shapes
Complex shapes need to be produced to very close tolerances and a fine surface finish
Die casting and precision forging can achieve such goals to some degree
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4. Milling and Milling Machines
Milling is machining operation for a variety of configurations with the use of a milling cutter
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5. Milling and Milling Machines: Peripheral Milling
The axis of cutter rotation is parallel to the workpiece surface
The cutter body has a number of teeth along its circumference
When the cutter is longer than the width of the cut, the process is called slab milling
Conventional Milling and Climb Milling
The cutter rotation can be clockwise or counter-clockwise
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6. Milling and Milling Machines: Peripheral Milling
Conventional Milling and Climb Milling
In conventional milling (also called up milling), the maximum chip thickness is at the end of the cut
Advantages are:
Tooth engagement is not a function of workpiece’s surface characteristics
Contamination or scale (oxide layer) on the surface does not adversely affect tool life
In climb milling (also called down milling), cutting starts at the surface of the workpiece where the chip is thickest
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7. Milling and Milling Machines: Peripheral Milling
Milling Parameters
The cutting speed in peripheral milling is the surface speed of the cutter is
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8. Milling and Milling Machines: Peripheral Milling
Milling Parameters
The approximate undeformed chip thickness (chip depth of cut) is
Feed per tooth is determined from
The cutting time, t, is given by
The material-removal rate (MRR) is
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9. Milling and Milling Machines: Peripheral Milling
Milling Parameters
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10. Milling and Milling Machines: Peripheral Milling
EXAMPLE 24.1
Material-removal Rate, Power, Torque, and Cutting Time in Slab Milling
A slab-milling operation is being carried out on a 300-mm- long, 100-mm-wide annealed mild-steel block at a feed f mm/tooth and a depth of cut d 3.0 mm. The cutter is D=50 mm in diameter, has 20 straight teeth, rotates at 100rpm and, by definition, is wider than the block to be machined. Calculate the material-removal rate, estimate the power and torque required for this operation, and calculate the cutting time.
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11. Milling and Milling Machines: Peripheral Milling
Solution
Material-removal Rate, Power, Torque, and Cutting Time in Slab Milling
The linear speed of the workpiece is
The material-removal rate is
The power required is
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12. Milling and Milling Machines: Peripheral Milling
Solution
Material-removal Rate, Power, Torque, and Cutting Time in Slab Milling
The torque acting on the cutter spindle is
The cutting time is
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13. Milling and Milling Machines: Face Milling
In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface
As the relative motion between the cutter teeth and the workpiece, face milling leaves feed marks on the machined surface
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14. Milling and Milling Machines: Face Milling
Lead angle of the insert in face milling has a direct influence on the undeformed chip thickness
As lead angle increases, the undeformed chip thickness decreases and the length of contact increases
Cutter diameter and their position relative to the milled surface will determine the angle at which an insert enters and exits the workpiece
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15. Milling and Milling Machines: Face Milling
The same insert may engage the workpiece at different angles, depending on the relative positions of the cutter and the workpiece width
The first contacts are at an angle and away from the tip of the insert
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16. Milling and Milling Machines: Face Milling
EXAMPLE 24.2
Material-removal Rate, Power Required, and Cutting Time in Face Milling
Assume that D = 150 mm, w = 60 mm, l = 500 mm, d = 3 mm, v = 0.6 m /min and N = 100 rpm.The cutter has 10 inserts, and the workpiece material is a high-strength aluminum alloy. Calculate the material-removal rate, cutting time, and feed per tooth, and estimate the power required.
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17. Milling and Milling Machines: Face Milling
Solution
Material-removal Rate, Power Required, and Cutting Time in Face Milling
The material-removal rate is
The cutting time is
The feed per tooth is
The power is
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18. Milling and Milling Machines: End Milling
End milling is versatile and capability to produce various profiles and curved surfaces
An end mill has a straight shank or tapered shank which is mounted into the spindle of the milling machine
End milling can produce a variety of surfaces at any depth, such as curved, stepped, and pocketed
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19. Milling and Milling Machines: End Milling
High-speed End Milling
High-speed end milling has applications as the milling of large aluminum-alloy aerospace components and honeycomb structures with high spindle speeds
Machines must have high stiffness and accuracy
The production of cavities in metalworking dies (die sinking) can be done
The machines have four-axis or five-axis movements
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20. Milling and Milling Machines: Other Milling Operations and Milling Cutters
In straddle milling, two or more cutters are mounted on an arbor and are used to machine two parallel surfaces on the workpiece
Form milling produces curved profiles using cutters that have specially shaped teeth
Slotting and slitting operations are performed with circular cutters
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21. Milling and Milling Machines: Other Milling Operations and Milling Cutters
Slitting saws are thin and T-slot cutters are used to mill T-slots
A slot is first milled with an end mill and the cutter machines will then complete profile of the T-slot in one pass
Shell mills are hollow inside and are mounted on a shank which allows the same shank to be used for different-sized cutters
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22. Milling and Milling Machines: Toolholders
Arbor cutters are mounted on an arbor for peripheral, face, straddle and form milling
In shank-type cutters, the cutter and the shank are made in one piece
Hydraulic toolholders and arbors are available
Stiffness of cutters and toolholders is important for surface quality and in reducing vibration and chatter during milling operations
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23. Milling and Milling Machines: Milling Process Capabilities
Milling process capabilities include surface finish, dimensional tolerances, production rate, and cost considerations
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24. Milling and Milling Machines: Milling Process Capabilities
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25. Milling and Milling Machines: Design and Operating Guidelines for Milling
Additional factors relevant to milling operations include:
Standard milling cutters should be used as much as possible
Chamfers should be specified
Internal cavities and pockets with sharp corners should be avoided
Proper clearance should be provided in the design for milling cutters
Workpieces should be rigid to minimize deflections
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26. Milling and Milling Machines: Design and Operating Guidelines for Milling
Guidelines for avoiding vibration and chatter in milling:
Cutters should be mounted as close to the spindle base
Toolholders and fixturing devices should be rigid
Tool shape and process conditions should be modified and cutters with fewer cutting teeth
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27. Milling and Milling Machines: Milling Machines
Milling machines are among the most versatile and useful machine tools
Standard milling machines are now being replaced with computer controls and machining centers
Column-and-knee-type Machines
Column-and-knee-type machines are common milling machines
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28. Milling and Milling Machines: Milling Machines
Bed-type Milling Machines
The worktable replaces the knee and can move only longitudinally
Other Types of Milling Machines
Planer-type milling machines are equipped with several heads and cutters to mill different surfaces
Computer numerical-control (CNC) machines are for low production quantities
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29. Planing and Shaping Planing
A simple machining operation where flat surfaces are produced along the length of the workpiece
Usually done on large workpieces
Due to reciprocating motion of the workpiece, the non-cutting time elapsed is significant
Chips produced can be long which interfere the planing operation and becoming a safety hazard
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30. Planing and Shaping Shaping Same as planing except that
it is the tool, and not the workpiece
workpieces are smaller
In a horizontal shaper, the cutting tool travels back and forth along a straight path
Vertical shapers (slotters) are used to machine notches, keyways, and dies
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31. Broaching and Broaching Machines
Similar to shaping with a long multiple-tooth cutter and is used to machine internal and external surfaces
In a broach the total depth of material removed in one stroke is the sum of the depths of cut of each tooth of the broach
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32. Broaching and Broaching Machines
Broaches
The rake (hook) angle depends on the material cut
Too small a clearance angle causes rubbing of the teeth against the broached surface
The pitch of the teeth depends on factors such as the length of the workpiece (length of cut), tooth strength, and size and shape of chips
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33. Broaching and Broaching Machines
Broaches
The pitch for a broach to cut a surface of length is
Broaches are available with various tooth profiles, including some with chip breakers
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34. Broaching and Broaching Machines
Turn Broaching
Used for broaching the bearing surfaces of crankshafts and similar parts
Turn broaching is a combination of shaving and skiving
Broaching Machines
Simple in construction, have only linear motions, and actuated hydraulically, crank, screw or rack
The force required to pull or push the broach depends on strength of the workpiece material, total depth and width of cut, cutting speed, tooth profile, and cutting fluids
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35. Broaching and Broaching Machines
Process Parameters
Majority of broaches are coated with titanium nitride for improved tool life and surface finish
Ceramic inserts are used for finishing operations in some applications
Smaller, high-speed steel blanks for broaches can be made with powder-metallurgy techniques for better control of quality
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36. Broaching and Broaching Machines
Design Considerations
Broaching requires certain guidelines:
Parts should be designed so that they can be clamped securely
Use of standardized parts is important for broaches
Balanced cross sections are preferable
Chamfers are preferred
Inverted or dovetail splines should be avoided
Broaching blind holes should be avoided
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37. Broaching and Broaching Machines
EXAMPLE 24.3
Broaching Internal Splines
Example of a part with internal splines that were produced by broaching
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38. Sawing
Cutting tool is a blade (saw) having a series of small teeth, each tooth removing a small amount of material with each stroke or movement of the saw
Can be used for all metallic and nonmetallic materials and is capable of producing various shapes
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39. Sawing
A wide variety of sizes, tooth forms, tooth spacing, and blade thicknesses and widths are available
Saw blades are made from high-carbon and high- speed steels
Carbide or high-speed steel-tipped steel blades are used to saw harder materials
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40. Sawing
Types of Saws
Hacksaws have straight blades and reciprocating motions
Hand hacksaw blades are thinner and shorter than power hacksaw blades
Circular saws are used for high-production-rate sawing, a process called cutting off
Band saws have continuous, long, flexible blades and have a continuous cutting action
Vertical band saws are used for straight and contour cutting of flat sheets
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41. Sawing Friction Sawing
Friction sawing is a process in which a mild-steel blade or disk rubs against the workpiece
Frictional energy is converted into heat, which rapidly softens a narrow zone in the workpiece
Heat generated in the workpiece produces a heat- affected zone on the cut surfaces
Friction sawing process is suitable for hard, ferrous metals and reinforced plastics but not for nonferrous metals
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42. Filing
Filing involves the small-scale removal of material from a surface, corner, edge, hole or burrs
Files can have many tooth forms and grades of coarseness
Filing machines with automatic features are available for high production rates
Band files consist of file segments that are riveted to a flexible steel band
Rotary files and burs are used for deburring and removing scale from surfaces
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43. Gear Manufacturing by Machining
Casting, forging, extrusion, drawing, thread rolling, and powder metallurgy can be used to manufacture gears
The dimensional accuracy and surface finish required for gear teeth depend on the intended use
Poor gear-tooth quality contributes to inefficient energy transmission, vibration and noise
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44. Gear Manufacturing by Machining: Form Cutting
Cutting tool is similar to a form-milling cutter made in the shape of the space between the gear teeth
Each cutter is designed to cut a range of numbers of teeth
Precision of the form-cut tooth profile depends on the accuracy of the cutter and on the machine and its stiffness
It is a slow operation
Broaching can be used to machine gear teeth and is particularly suitable for producing internal teeth
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45. Gear Manufacturing by Machining: Gear Generating
Cutting tool used may be a:
Pinion-shaped cutter
Rack shaper
Hob
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46. Gear Manufacturing by Machining: Cutting Bevel Gears
Straight bevel gears are roughed out in one cut with a form cutter on machines that index automatically
The cutters will reciprocate across the face of the bevel gear as does the tool on a shaper
Spiral cutter is a face-milling cutter with a number of straight-sided cutting blades protruding from its periphery
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47. Gear Manufacturing by Machining: Cutting Bevel Gears
Burnishing
Surface finish of gear teeth is improved by burnishing
The resulting cold working of the tooth surfaces improves the surface finish, induces compressive residual stresses and fatigue life
Grinding, Honing, and Lapping
For the highest dimensional accuracy, tooth spacing and form, and surface finish, gear teeth subsequently may be ground, honed, and lapped
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48. Gear Manufacturing by Machining: Cutting Bevel Gears
Grinding, Honing, and Lapping
In form grinding, the shape of the grinding wheel is identical to that of the tooth spacing
In generating, the grinding wheel acts in a manner similar to the gear generating cutter
The honing tool is a plastic gear impregnated with fine abrasive particles
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49. Gear Manufacturing by Machining: Cutting Bevel Gears
Grinding, Honing, and Lapping
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50. Design considerations for gear-cutting:
Gear Manufacturing by Machining: Design Considerations and Economics of Gear Machining
Design considerations for gear-cutting:
Wide gears are more difficult to machine than narrow ones
Gears should be machined prior to their assembly on shafts
Sufficient clearance should be provided between gear teeth and flanges
Blank design is important for proper fixturing and to ease cutting operations
Spur gears are easier to machine than helical gears
Dimensional tolerances and standardized gear shapes are specified by industry standards
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51. The cost of gears increases with improved surface finish and quality
Gear Manufacturing by Machining: Design Considerations and Economics of Gear Machining
Economics
The cost of gears increases with improved surface finish and quality
The higher the number, the higher is the dimensional accuracy of the gear teeth
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52. CASE STUDY 24.1 Ping Golf Putters
Gear Manufacturing by Machining: Design Considerations and Economics of Gear Machining
CASE STUDY 24.1
Ping Golf Putters
Advanced machining practices is used in the design and production processes for a new style of putter, the Anser® series
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