1. MSE 440/540: Processing of Metallic Materials
Instructors: Yuntian Zhu
Office: 308 RBII
Ph:
Lecture 13: Machining I
Text book,
Office hour, by appointment
Department of Materials Science and Engineering 1

2. Machining
Cutting action involves shear deformation of work material to form a chip, and as chip is removed, new surface is exposed: (a) positive and (b) negative rake tools

3. Machining Operations Most important machining operations:
Turning
Drilling
Milling
Other machining operations:
Shaping and planing
Broaching
Sawing

4. Turning and Drillng
Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape
Used to create a round hole, usually by means of a rotating tool (drill bit) with two cutting edges

5. Milling
Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface
Two forms: (c) peripheral milling and (d) face milling

6. Cutting Tool Classification
Single-Point Tools
One dominant cutting edge
Point is usually rounded to form a nose radius
Turning uses single point tools
Multiple Cutting Edge Tools
More than one cutting edge
Motion relative to work achieved by rotating
Drilling and milling use rotating multiple cutting edge tools

7. Cutting Conditions in Machining
Three dimensions of a machining process
Cutting speed v – primary motion
Feed f – secondary motion
Depth of cut d – penetration of tool below original work surface
For certain operations (e.g., turning), material removal rate RMR can be computed as
RMR = v f d

8. Orthogonal Cutting Model
Simplified 2-D model of machining that describes the mechanics of machining fairly accurately

9. Chip Thickness Ratio
where r = chip thickness ratio; to = thickness of the chip prior to chip formation; and tc = chip thickness after separation
Chip thickness after cut is always greater than before, so chip ratio is always less than 1.0

10. Determining Shear Plane Angle
Based on the geometric parameters of the orthogonal model, the shear plane angle Φ can be determined as:
where r = chip ratio, and α = rake angle
Derivation: ls=t0/sin(f) = tc/sin(90+a-f), cos(a-b)=cosa*cosb+sina*sinb

11. Shear Strain in Chip Formation
(a) Chip formation depicted as a series of parallel plates sliding relative to each other, (b) one of the plates isolated to show shear strain, and (c) shear strain triangle used to derive strain equation

12. Chip Formation
More realistic view of chip formation, showing shear zone rather than shear plane
Also shown is the secondary shear zone resulting from tool‑chip friction

13. Four Basic Types of Chip in Machining
(a) Brittle materials, (b) ductile material, high speed, low feed and depth, long chip may be a problem

14. Four Basic Types of Chip in Machining
c) Gummy, d) Best way,
Best condition: not too hard or too soft
Ductile materials
Low‑to‑medium cutting speeds
Tool-chip friction causes portions of chip to adhere to rake face
BUE forms, then breaks off, cyclically
Serrated Chip

15. Generating Shape
Generating shape: (a) straight turning, (b) taper turning, (c) contour turning, (d) plain milling, (e) profile milling

16. Forming to Create Shape
Forming to create shape: (a) form turning, (b) drilling, and (c) broaching

17. Forming and Generating
Combination of forming and generating to create shape: (a) thread cutting on a lathe, and (b) slot milling

18. Turning Operation

19. More Operations Related to Turning
(d) Form turning, (e) chamfering, (f) cutoff

20. Methods of Holding Workpiece in a Lathe
(a) Holding the work between centers, (b) chuck, (c) collet, and (d) face plate

21. More Operations Related to Turning
(g) Threading, (h) boring, (i) drilling

22. Operations Related to Drilling
(a) Reaming, (b) tapping, (c) counterboring

23. More Operations Related to Drilling
(d) Countersinking, (e) center drilling, (f) spot facing

24. Two Forms of Milling
(a) Peripheral milling and (b) face milling

25. Types of Peripheral Milling
(a) Slab milling, (b) slotting, (c) side milling, (e) straddle milling, and (e) form milling

26. Types of Face Milling
(a) Conventional face milling, (b) partial face milling, (c) end milling, and (d) profile milling using an end mill

27. Types of Face Milling (e) Pocket milling and (f) contour milling

28. Shaping and Planing
Similar operations, both use a single point cutting tool moved linearly relative to the workpart

29. Shaper

30. Broaching
A multiple tooth cutting tool is moved linearly relative to work in direction of tool axis

31. Broaching Advantages: Good surface finish Close tolerances
Variety of work shapes possible
Cutting tool called a broach
Owing to complicated and often custom‑shaped geometry, tooling is expensive

32. Power Hacksaw
Linear reciprocating motion of hacksaw blade against work
Rotating saw blade provides continuous motion of tool past workpart

33. Geometric Factors Affecting Surface Finish
Effect of (a) nose radius, (b) feed, and (c) ECEA

34. Ideal Surface Roughness
where Ri = theoretical arithmetic average surface roughness; f = feed; and NR = nose radius

35. Work Material Factors Built‑up edge effects
Damage to surface caused by chip
Tearing of surface when machining ductile materials
Cracks in surface when machining brittle materials
Friction between tool flank and new work surface

36. Effect of Work Material Factors
Multiply theoretical surface roughness by the ratio of actual to theoretical roughness for the given cutting speed to obtain estimate of actual surface roughness

37. HW assignment Reading assignment: Chapters 17
Review Questions: 15.4, 15.5, 15.11, 16.2, 16.5, 16.6, 16.13, 16.14
Problems: 15.1, 15.3, 15.4, 15.6, 15.10, 16.1, 16.2, 16.6, 16.8,
Department of Materials Science and Engineering 37