1. Metal Removal Processes
Lecture No 12
Metal Removal Processes
Dr. Ramon E. Goforth
Adjunct Professor of Mechanical Engineering
Southern Methodist University

2. Outline of Lecture Basic information on material removal
Lecture No 12
Outline of Lecture
Basic information on material removal
Factors involved in material removal
Independent variables
Dependent variables
Machining Processes
Machining Economics
Machines
Lecture 10
Lecture 11
Lecture 12

3. Basic Cutting Processes
Lecture No 12
Basic Cutting Processes
Rotating part - turning
Creates round shapes
Stationary part - milling, drilling, sawing, etc

4. Lecture No 12
Basic Turning
Part of cylindrical cross section clamped in a "chuck" so that it can rotate about its axis
Part is rotated at fixed speed
A cutting tool is brought to bear on the moving surface of the part cutting of material
The "chuck" is a kind of vice which has rotational symmetry

5. Turning Process Parameters
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Turning Process Parameters f d N

6. Turning Parameters Tool Geometry Rake angles
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Turning Parameters
Tool Geometry
Rake angles
Side rake angle - more important than
Back rake angle
Cutting edge angles

7. Turning Parameters Tool Geometry Tool Materials
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Turning Parameters
Tool Geometry
Tool Materials
Feeds and speeds, N,d,f
(see table 22.4 for recommendations)
Cutting fluids
Material Removal rates
= p Davg d f N
Where Davg is the average diameter, d is the depth of cut, f is the feed rate and N the rotational speed
Forces and power used
Surface finish (scallops)

8. Lecture No 12
Power used
Power used is the material removal rate, MRR, times the specific energy

9. Feed Marks in Turning Scallops created
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Feed Marks in Turning
Scallops created
The depth depends on the feed rate, surface velocity and tool shape
Scallops

10. Machining Processes for Round Shapes
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Machining Processes for Round Shapes
Turning
Facing
Boring
Produces circular internal profiles in hollow workpieces
Drilling
Produces round holes
Reaming
Produces more accurate holes than drilling
Parting
Threading
Knurling

11. Machining Processes for Round Shapes
Lecture No 12
Machining Processes for Round Shapes
Kalpakjian p 663

12. Turning Guidelines Avoid long skinny parts
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Turning Guidelines
Avoid long skinny parts
Request wide accuracy and surface finish parameters
Avoid sharp corners and tapers
Avoid major dimensional changes
Design blanks to be as close to final dimensions as possible

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Turning Guidelines
Allow for travel of tools across surfaces of workpiece
Design features so that standard tools can be used
Choose machinable materials
Minimize overhang of tool
Support workpiece
Use machines with high rigidity

14. Non Round Machining Processes
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Non Round Machining Processes
The operation
Clamp the workpiece onto a stationary bed or one that can move in multiple directions slowly
Bring a rotating tool to bear on the surface to be shaped
Move the rotating tool over the part or move the part past the rotating tool to shape it

15. Non Round Machining - Slab Milling
Lecture No 12
Non Round Machining - Slab Milling
Milling
Slab/Peripheral
Cutter rotation axis parallel to workpiece surface
Conventional/up
Maximum chip thickness at end of cut
Low impact of tool with workpiece
Climb/down
Maximum chip thickness at beginning of cut
High low impact of tool with workpiece

16. Non Round Machining - Face milling
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Non Round Machining - Face milling
Axis of rotation perpendicular to workpiece surface
Large multi-insert cutter

17. Non Round Machining - Face Milling
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Non Round Machining - Face Milling
Difference between climb and conventional face milling
Action of an insert in face milling
Climb Milling
Conventional milling
Parameters in face milling

18. Lecture No 12
Non Round Machining

19. Generic Milling formula
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Generic Milling formula
Cutting (peripheral) speed,
V = p D N
where D is the cutter diameter and N its rotational speed
Feed per tooth,
f = v/Nn
where v is the linear speed or feed rate of the workpiece, and n is the number of teeth
Undeformed chip thickness, (chip depth of cut),
tc = 2 f (d / D)
Where f is the feed per tooth, d is the depth of cut

20. Generic Milling formula
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Generic Milling formula
Cutting time, t = (l + 2lc)/ v
where v is the feed rate of the workpiece, l is the length of the workpiece and lc is the extent of the cutter’s first contact with the workpiece
Material removal rate, MRR
MRR = lwd/t = wdv
assuming the lc<<l and where w is the width of the cut
Power is equal to the MRR times the specific energy

21. Feed Marks from Milling
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Feed Marks from Milling

22. Design Guidelines for Milling
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Design Guidelines for Milling
Design for standard cutters
Use chamfers instead of radii
Avoid internal cavities and pockets with sharp corners
Design workpieces with sufficient rigidity

23. Other Non Round Machining Processes
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Other Non Round Machining Processes
Drilling
Straddle milling
Planing
Broaching
Sawing
Generally used for cutting off pieces to be worked on by other processes
Filing and finishing
Gear machining

24. Drilling Practices Type of drill bit, drill point geometry
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Drilling Practices
Type of drill bit, drill point geometry
Type of machine
Drill, press, radial drills, gang drills, NC controlled
Capabilities of drilling and boring operations (p 633)
HP used = Spec. Energy times MRR (pD2fN/4)

25. Drilling Operations and Drill bits
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Drilling Operations and Drill bits

26. Drilling Guidelines Design holes perpendicular to the surface
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Drilling Guidelines
Design holes perpendicular to the surface
Do not design interrupted/overlapping holes
Design bottoms to match standard drill-point angles
Through holes are preferred over blind holes
If need large diameter holes design in smaller hole for casting
Design to minimize fixturing
Avoid reaming blind or intersecting holes

27. Machining Economics Cost per piece decreases with cutting speed
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Machining Economics
Cost per piece decreases with cutting speed
Tool cost increases with cutting speed
Tool change time increases with cutting speed
Total cost goes through a minimum
Time spent removing material usually small fraction (<5%) of total time on machine
Kalpakjian p 775/698

28. Lecture No 12
Machining Economics

29. Metal Removal Machines
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Metal Removal Machines

30. Lecture No 12
Basic Lathe

31. Turning Machine Components
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Turning Machine Components
Bed
Supports all other major components
Top part has two ways
Carriage
Slides along the ways
Consists of the cross-slide, tool post and apron

32. Turning Machine Components
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Turning Machine Components
Headstock
Fixed
Contains the motors, pulley and belts to drive the spindle
Spindle has fixtures for attaching the workpiece
Tailstock
Can slide along the ways
Supports the other end of the workpiece
Feed rod and lead screw
Provides motion to the carriage and cross slide

33. Lecture No 12
A Manual Lathe

34. Turning Machines Lathes Tracer Automatic Automatic bar machines Turret
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Turning Machines
Lathes
Tracer
Automatic
Automatic bar machines
Turret
Vertical
For very large diameters
Boring
Horizontal (like a milling machine)
Computer controlled

35. Lecture No 12
Turret Lathe

36. MORI SEIKI SL-3 SLANT BED CNC LATHE
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MORI SEIKI SL-3 SLANT BED CNC LATHE

37. Lecture No 12
Vertical Boring Mill

38. Milling Machines Column and Knee type Bed type Other types
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Milling Machines
Column and Knee type
Horizontal spindle
Vertical spindle
Bed type
Skin mills
Other types
Planer type
Rotary tables
Duplicating machines
Profiling milling
More than three axes

39. #4 VERTICAL MILLING MACHINE W/SLIDING HEAD
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#4 VERTICAL MILLING MACHINE W/SLIDING HEAD

40. Machining and Turning Centers
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Machining and Turning Centers
Combines turning with milling
Computer control essential
Multiaxis capabilities
Replacing simple lathes or milling machines

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NC Turning Center

42. Lecture No 12
Giddings & Lewis dv15-l smart turn twin-spindle vertical production center

43. Drilling Machines Drill presses Radial machines
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Drilling Machines
Drill presses
Radial machines
CNC Three axis drilling machine

44. Trends High speed machining Dry machining
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Trends
High speed machining
Dry machining
Combining milling, drilling and turning operations
New, stiffer and highly damped machine tools
Graphite epoxy, ceramics (high modulus)
Modular machines
Multiple loading stations
More sensors
More and more automation
Automated program generation

45. Summary There are many different types of machining operations
Lecture No 12
Summary
There are many different types of machining operations
That is what makes it so versatile and attractive to industry
The basic cutting process is the same in all
Must consider the cutting operation as a system
Actual cutting time is a small fraction of the total time to create a part by machining