Tutorial A1 q11-20

Question 1

What were the results of initial physical tests of ceramic/superhard inserts?

Answer 1

Slowing down speeds, feeds, and reducing depth of cut to prevent tool breakage

Question 2

How did process modelling help develop use of ceramic/superhard inserts?

Answer 2

Showed that if machining is run at very high surface speeds, inserts heat up and soften, overcoming brittleness but maintaining cutting performance
Productivity increases by 10x from carbide tools

Question 3

What 3 types of vibration occur during machining operations?

Answer 3

Free vibrations
Forced vibrations
Self-excited vibrations

Question 4

Give an overview of free vibrations

Answer 4

Rapid reversals of reciprocating masses, initial engagement of cutting tool

Question 5

Give an overview of forced vibrations

Answer 5

unbalanced rotating shafts in the machine, intermittent engagement of teeth on a milling cutter, transmitted through foundations from other nearby machines operating

Question 6

Give an overview of self-excited vibrations

Answer 6

Unwanted relative movement occurs between workpiece and tool during machining

Question 7

Which vibration type is known as chatter?

Answer 7

Self-excited vibrations

Question 8

What does chatter cause?

Answer 8

Poor surface finish (generates waves)
Unstable cutting (varying forces)
Tool breakage

Question 9

How can chatter be avoided?

Answer 9

Operator must change process parameters to avoid self-excitation

Question 10

What is the disadvantage to avoiding chatter?

Answer 10

Productivity is lowered as optimum parameters cannot be used

Question 11

What causes chatter?

Answer 11

Mode coupling

Regeneration of surface waviness

Question 12

What is mode coupling?

Answer 12

Relative motion between tool/workpiece exists in at least two directions, causing periodic elliptical movement of the tool tip

Question 13

What is regeneration of surface waviness?

Answer 13

When the tool tip moves over the surface already cut

Question 14

How does process modelling help avoid chatter?

Answer 14

Allows changing of process parameters (often in real time), allowing

• stable cutting
• opportunities to increase cutting speed/depth of cut by knowing what to change to move to the nearest stable region and maximise depth of cut

Question 15

How does process modelling affect productivity?

Answer 15

Increases it

Question 16

How can machine design minimise chatter?

Answer 16

Use machines/tooling which is self-damping
Deliberately avoid regenerative effects
Use self-tuning machines

Question 17

Why are machine parts inspected?

Answer 17

Process control
Acceptability & conformance
Post-assembly performance

Question 18

Why is process control needed?

Answer 18

To select process parameters and develop new ones

Question 19

Why is acceptability & conformance needed?

Answer 19

Helps maintain quality and commercial relationships

Question 20

Give an example of post-assembly performance

Answer 20

Balancing of turbine blades

Question 21

List inspection equipment (7 examples)

Answer 21

1. vernier calipers
2. dial gauges
3. micrometers
4. profilometers
5. ultrasonic sensors
6. endoscopes
7. coordinate measuring machines

Question 22

What are coordinate measuring machines?

Answer 22

Structures that support a sensitive probing system that is connected to a data acquisition system, allowing points in 3D space to be recorded as CAD data

Question 23

What are CMMs used for?

Answer 23

Comparing recorded 3D data against original data for inspection reasons
Creating new data as part of reverse engineering

Question 24

What is the main problem limiting the productivity of CMMs?

Answer 24

They can be very slow - time must be allowed:

• between touches for vibrations (due to machine motion) to dissipate
• to wait for the probe to reposition at pre-calibrated positions