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QE 107: Workshop Technology Section 4: Metal Cutting

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QE 107: Workshop Technology Section 4: Metal Cutting Asanga Ratnaweera Department of Mechanical Engineering University of Peradeniya Peradeniya – PowerPoint PPT presentation

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Title: QE 107: Workshop Technology Section 4: Metal Cutting


1
QE 107 Workshop Technology Section 4 Metal
Cutting
  • Asanga Ratnaweera
  • Department of Mechanical Engineering
  • University of Peradeniya
  • Peradeniya

2
Material Removal Processes
3
Basic Cutting Principle
  • The basic principle is the use of a cutting tool
    to form a chip removed from the part (by shear).
  • It requires the relative motion between the tool
    and part.
  • The primary motion is called speed, v, and the
    secondary motion is called feed, f.
  • The cutting tool needs to cut into the part,
    called the depth of cut, d.

4
Cutting Mechanism
  • During machining, the material is removed in form
    of chips, which are generated by shear
    deformation along a plane called the shear plane.

5
Chip Types
  • Continuous chips
  • Ductile material
  • Ex Mild steel, Al
  • High speed
  • Low feed
  • Small depth of cut

6
Chip Types
  • Discontinuous chips
  • Brittle material
  • Ex Cast iron
  • Low speed
  • High feed
  • Large depth of cut

7
Chip Types
8
Chip Types
  • Built Up Edge (BUE)
  • Some of the cut material will attach to the
    cutting point.
  • This tends to cause the cut to be deeper than the
    tip of the cutting tool and degrades surface
    finish.
  • Also, periodically the built up edge will break
    off and remove some of the cutting tool. Thus,
    tool life is reduced.

BUE
9
Chip Types
  • Built Up Edge (BUE)
  • built up edge can be reduced by
  • Increasing cutting speed
  • Decreasing feed rate
  • Increasing rake angle
  • Reducing friction (by applying cutting fluid)

BUE
10
Tool Geometry
  • The shape and orientation of the cutting tool
    greatly affects the chip formation mechanics

11
Rake Angle
  • Of particular importance is the rake angle that
    the tool makes with the workpiece normal
  • Effects on the chip formation

12
Clearance angle
  • Clearance angle is that the tool makes with the
    newly machined work surface
  • Avoids the work-surface being rubbed by the tool

13
Basic Cutting Geometry
  • Orthogonal cutting the cutting edge of the tool
    is straight and perpendicular to the direction of
    motion.
  • Oblique cutting the tool edge is set at angle.

14
Cutting Tools
  • There are basically two types of cutting tools
  • Single point (e.g. turning tools).
  • Multiple point (e.g. milling tools).

turning tools
drilling tools
milling tools
15
Cutting Tools
16
Geometry of turning tool
17
Turning operations
18
Milling
  • Work is fed into the rotating cutter
  • Typically uses a multi-tooth cutter.
  • Cutting tools for this process are called milling
    cutters.
  • Capable of high material removal rate
  • Two basic milling operations
  • Peripheral milling
  • Face milling

19
Peripheral Milling
  • Peripheral milling is also called plain milling
  • axis of the tool parallel to the surface,
  • cutting operation is performed by cutting edges
    on the outside periphery of the cutter.

20
Face milling
  • Axis of rotation perpendicular to workpiece
    surface
  • The milled surface is flat and has no
    relationship to the contour of the cutter
  • Combined cutting action of the side and face of
    the milling cutter

21
(No Transcript)
22
Feed Direction
  • Conventional milling (up milling)
  • Most common method of feed
  • Feed work against the rotation of the cutter
  • Maximum chip thickness at end of cut
  • Climb milling (down milling)
  • Maximum chip thickness at beginning of cut
  • Suited for machining of thin and hard to hold
    parts
  • 20 less Hp than conventional milling
  • Machine must be very rigid to safely

23
Geometry of milling tools
24
Chip Thickness
  • f - is the feed per tooth
  • d - is depth of cut
  • N cutter speed
  • D diameter of the cutter
  • tc - undeformed chip
  • thickness
  • v - linear speed of the workpiece
  • n number of teeth in the cutter

25
Chip Thickness
  • f v / Nn

26
Drilling Operation
  • Basic hole making processes
  • account for approximately 50-70
  • of all the metal removal processes
  • utilized today.
  • Hole making methods
  • Casting
  • Punching
  • Flame cutting
  • Machining including
  • Drilling, milling, EDM, etc.

27
Geometry of drilling tools
28
Rake angle
29
Rake angle
30
Chip thickness
31
The cutting force
  • Externally applied forces

Fc Cutting force, Ft Thrust force
32
The cutting force
  • Forces on the tool

F Friction force, Fn Normal force
33
The cutting force
  • Forces on the chip

Fs
Fco
Fs Shear force, Fco Compressive force
34
The cutting force
  • Merchants theory

a
? -a
Fc
?
a
? friction angle
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