Chapter 6 part 2 Final Exam

Question 1

CWhat are the three possible failures associated with tool life

Answer 1

fracture failure
temperature failure
gradual wear

Question 2

What is fracture failure

Answer 2

This mode of failure occurs when the cutting FORCE at the tool point becomes excessive, causing it to fail suddenly due to BRITTLE FRACTURE.

Question 3

What is temperature failure

Answer 3

This failure occurs when the cutting TEMPERATURE is too HIGH for the tool material, causing the material at the TOOL POINT to SOFTEN, which leads to plastic deformation and LOSS of the SHARP EDGE.

Question 4

What is gradual failure

Answer 4

Gradual wearing of the cutting edge causes LOSS of TOOL SHAPE, reduction in cutting efficiency, and acceleration of wearing as the tool becomes heavily worn, and finally tool failure in a manner similar to a temperature failure.

Question 5

Which form of tool failure is preferred

Answer 5

gradual failure because it leads to the longest possible lifespan of the tool

Question 6

What is a crater wear

Answer 6

cavity in the rake face of the tool that forms and grows from the chip sliding against the surface. High temperatures and stresses cause this

Question 7

What is flank wear

Answer 7

occurs on flank and results from rubbing between the work surface and the flank face adjacent to cutting edge. Characterized by plastic deformation

Question 8

What is tool life

Answer 8

length of time a cutting tool can be used

Question 9

Describe the visual graph and relation between tool flank wear (FW) and time of cutting

Answer 9

The initial stage of cutting is the break-in period, where rapid initial wear takes place.

Then, it is followed by a uniform wear rate in what is known as the steady-state wear region.

Until the Failure region, where an accelerating wear rate results in a final failure

Question 10

What are the effects of cutting speed on tool life

Answer 10

higher cutting speeds shorten tool life

Question 11

What are the three important properties that a tool requires? and which mode of tool failure does each correspond to

Answer 11

Toughness - Fracture Failure
Hot Hardness - Temperature failure
Wear resistance - gradual wear

Question 12

What is toughness

Answer 12

To avoid fracture failure, toughness is the capacity of a material to absorb energy without failing

Question 13

What is hot hardness

Answer 13

To avoid temperature failure, hot hardness is the ability of a material to retain hardness at high temperatures

Question 14

What is wear resistance

Answer 14

To avoid gradual wear, wear resistance is directly tied to hardness, surface finish of tool, and application of cutting fluids

Question 15

What are premature failures

Answer 15

Temperature and fracture failures because the tool was not used for its entire possible lifespan

Question 16

What is a cutting fluid

Answer 16

Any liquid or gas applied directly to the machining operation to improve cutting performance

Question 17

What main problems do cutting fluids address

Answer 17

Heat generation at shear and friction zones
and
Friction at tool-chip and tool-work interfaces

Question 18

What other benefits do cutting fluids bring

Answer 18

1. Wash away chips from grinding and milling
2. Reduce the temperature of work part for easier handling
3. Improve dimensional stability of work part

Question 19

What are the cutting fluid classifications and describe the specifications of each classification

Answer 19

1. Coolants - designed to reduce the effects of heat in machining
2. Lubricants - designed to reduce tool-chip and tool-work friction

Question 20

What is the base of coolants

Answer 20

Water

Question 21

Where are coolants most effective and generally best used

Answer 21

At high cutting speeds where heat generation and high temperatures are problems. most effective on TOOL MATERIALS susceptible to TEMPERATURE FAILURES

Question 22

What is the base of lubricants

Answer 22

Oil

Question 23

Where are lubricants most effective

Answer 23

At lower cutting speeds. also reduces temperature but not as greatly

Question 24

What is dry machining

Answer 24

no cutting fluid is used

Question 25

What are the benefits of dry machining

Answer 25

Avoids cutting fluid contamination, disposal, and filtration

Question 26

What are the problems of dry machining

Answer 26

1. overheating of tool
   2.operating at lower cutting speeds and production rates to prolong tool life
2. Absence of chip removal benefits of cutting fluids in grinding and millin