W2 Subtractive Processes

Question 1

Define Machining and give 4 examples

Answer 1

A general term for manufacturing processes by which material is removed from a raw workpiece to achieve the desired geometry. Machining should be considered as a system consisting
of a workpiece; a cutting tool; a machine tool; and, production personnel and thus it can only
been done efficiently, economically and meet part specification if the interaction of all elements is
considered thoroughly.Eg Straight turning, cutting off, slab milling, end milling

Question 2

How is the classification of milling operations done?

Answer 2

Mainly by the relative orientations of the movements of the tool and workpiece.

Question 3

Mechanics of Metal cutting

Answer 3

Important for
* Motor selection
* Design of structure
* Life of tool vs Rate of cutting

Question 4

Turning

Answer 4

Turning where the workpiece is rotated and a cutting tool is moved in a controlled motion to
remove a layer of material

Question 5

Cutting off

Answer 5

Cutting off where the workpiece is rotated and a cutting tool is moved radially inwards to
separate the two parts of the workpiece.

Question 6

Slab milling

Answer 6

Slab milling where the rotating cutting tool is orientated in parallel to the surface of the part
and also moves in parallel to the surface of the part and a layer is removed from the top
surface.

Question 7

End milling

Answer 7

End milling where the rotating cutting tool is orientated perpendicular to the part and is
moved in parallel to the top surface of the workpiece at a certain depth to produce a cavity.

Question 8

Specific Cutting force

Answer 8

The ratio of the cutting force to the cross-sectional
area being cut (i.e. product of the width of cut and depth of cut) is the specific cutting force

Question 9

Milling

Answer 9

Milling is machining operation
for a variety of configurations
with the use of a milling cutter

Question 10

Peripheral Milling

Answer 10

• The cutter body has multiple teeth along its circumference.
• The axis of cutter rotation is parallel to the workpiece surface.
• Slab milling is a subset of milling processes in which the cutter is
  longer than the width of the cut.

Question 11

Conventional milling and climb milling

Answer 11

The cutter rotation can be clockwise
or counter-clockwise

Question 12

Tool Wear factors

Answer 12

Stresses
Friction
High Temperatures

Question 13

Why do we need Advanced machining technologies

Answer 13

• The strength and hardness of the material are very high.
• The workpiece is too brittle to be machined without damage. This is the case with heat
  treated alloys, glass, ceramics and powder metallurgy parts.
• The workpiece is too flexible to withstand mechanical machining forces.
• The shape of the part is complex. (for example, holes with high length to diameter relationships).
• Special surface finish and dimensional tolerance requirements that cannot be obtained
  are uneconomical using other processes.
• The temperature rise or the residual stress developed during the machining process are
  not desirable or acceptable.

Question 14

Economics of Advanced
Machining Processes

Answer 14

• Costs of tooling and equipment
• Operating costs
• Material-removal rate required
• Level of operator skills

Question 15

Flank wear

Answer 15

The failure of a tool
is an important consideration in manufacturing, not only because of the direct cost to replace the
tool, but also because of the disruption to the production line. Flank wear happens on the relief
surface of the tool mainly because of rubbing along the machined surface

Question 16

Design for Machining

Answer 16

Provide access for tools
Deep pockets also cause vibration of the tool
Design parts that are easy to fixture
Avoid long, thin sections that cause vibration
Holes cant change direction
Avoid outside rounds, which are difficult unless CNC machined.

Question 17

Advanced machining technologies examples

Answer 17

⋄ Chemical Machining
⋄ Electrochemical Machining
⋄ Electrical Discharge Machining(EDM)
⋄ Laser Beam Machining
⋄ Water-jet Machining
⋄ Abrasive Jet Machining

Question 18

Hybrid machining systems

Answer 18

Two
or more machining processes are combined into one system to take advantage of the capabilities
of each process to increase production speed or negate disadvantages of using one of the processes
individually.