Cutting Tools

Question 1

What are the key properties of cutting tools?

Answer 1

• Hardness
• Toughness
• Wear resistance
• Strength to resist bulk deformation
• Adequate thermal properties
• Correct geometry

Question 2

What is the basic principle of hardness in cutting?

Answer 2

You need a tool material with a higher hardness than your workpiece material

Question 3

What are the three modes of tool failure?

Answer 3

1. Fracture failure
2. Temperature failure
3. Gradual wear

Question 4

What is fracture failure?

Answer 4

When the forces on the tool exceed the tool’s strength, leating to brittle fracture.

Question 5

What is temperature failure in cutting?

Answer 5

high temperatures leading to plastic deformation or premature wear

Question 6

What is gradual wear in cutting?

Answer 6

Gradual wearing of the cutting tool

Question 7

What is the most preferred mode of wear?

Answer 7

Gradual - both of the thers are premature, gradual allows for longest lifespan

Question 8

Where are the two locations that gradual wear occurs on a tool?

Answer 8

Crater - top rake face
Flank - side of tool

Question 9

What is abrasion?

Answer 9

Mechanical wear due to hard particles (primary cause of flank wear)

Question 10

What does hot hardness value mean?

Answer 10

Can cutting tool material retain hardness at high temperatures

Question 11

What is adhesion?

Answer 11

Workplace material adheres/fuses to the cutting tool, causing rupturing

Question 12

What chemical reaction is a primary cause of wear?

Answer 12

Oxidation

Question 13

What is the break-in period on a wear curve?

Answer 13

Represents rapid wearing of the tool, usually within first minute or two of use

Question 14

What is the steady-state wear period in a wear curve?

Answer 14

A region of gradual linear wearing of the tool

Question 15

What is the failure region on a wear curve?

Answer 15

The tool is so worn out that it can no longer cut efficiently.

Question 16

What is the relationship between cutting speed and tool wear?

Answer 16

As cutting speed increases, tool wear will occur much faster, and tool life decreases

Question 17

How do we know when a machine is failing?

Answer 17

• Machine makes strange noise
• An increase in power
• Change in the quality of chips
• Conducting a “fingernail test” to see if the cutting tool is usable

Question 18

Generally, what happens to hardness as temperature increases?

Answer 18

Rapidly decreases

Question 19

What types of materials are significantly harder at elevated temperatures?

Answer 19

Cemented carbides + ceramics

Question 20

What material is used when high cutting speeds are NOT a priority?

Answer 20

plain carbon steel

Question 21

What are common uses of plain carbon steel in manufacturing?

Answer 21

• Taps, dies, chisels, and cheap drills
• Custom tools
• Not used much in modern manufacturing, as it loses hardness around 300-650F

Question 22

What are characteristics of tools such as taps, chisels, and dies?

Answer 22

• Go through large deformations when used
• Used at low speeds, heat generation not a concern
• Toughness of cutting tool material is main priority

Question 23

What are the two basic types of high speed steel (HSS) used in cutting?

Answer 23

Tungsten (T grades,) and Molybdenum (M grades)

Question 24

What are the benefits of using high speed steel?

Answer 24

• Capable of maintaining hardness at elevated temps. better than high carbon and low alloy steels
• Suited to applications involving complex tool shapes (drills, taps, milling, broaches.)

Question 25

What are some other alloying ingredients for high speed steel?

Answer 25

Chromium + Vanadium, carbon, and cobalt

Question 26

What are cemented carbides?

Answer 26

Class of hard tool material based on tungsten carbide (WC) using power metallurgy techniques w/ cobalt as the binder

Question 27

What are the two basic types of cemented carbides?

Answer 27

Non-steel cutting grades, and steel cutting grades

Question 28

What are some general properties of cemented carbides?

Answer 28

* High compressive strength + hardness + thermal conductivity + elastic modulus * Good hot hardness + wear resistance * Low to moderate tensile strength * Toughness lower than HSS

Question 29

What are cermets?

Answer 29

Combinations of TiC, TiN, and titanium carbonitride (TiCN) w/nickel or molybdenum as binders

Question 30

What are the benefits of using cermets?

Answer 30

Higher speeds and lower feeds than steel-cutting cemented carbide grades, and better finish achieved.

Question 31

What are some applications of cermets?

Answer 31

High speed finishing/semifinishing of steels, stainless steels, and cast irons

Question 32

What are coated carbides?

Answer 32

Cemented carbide insert coated w/ 1 or more layers of TiC, TiN, and/or Al2O3 (or other hard metals)

Question 33

How are the coating of coated carbides applied?

Answer 33

chemical vapor deposition or physical vapor deposition

Question 34

What are some key applications where coated carbides are used?

Answer 34

cast irons and steels in turning and milling operations, best applied at high speeds where dynamic force + thermal shock are minimal

Question 35

Why are coatings added to tool materials?

Answer 35

increase resistance to wear

Question 36

What does a cutting tool wear curve represent?

Answer 36

The tool flank wear (FW) vs. cutting time (min)

Question 37

What graph is used to monitor if a tool needs repair?

Answer 37

A cutting force vs. time graph

Question 38

What is the shape of a cutting speed vs. tool life plot?

Answer 38

Natural log - log.

Question 39

What is the Taylor Tool Life Equation?

Answer 39

Relates cutting speed, tool life, slope of graph, and C (intercept on the speed axis at 1minute tool life)

Question 40

What are key applications of ceramics in cutting?

Answer 40

high speed turning of cast iron and steel, grinding.

Question 41

Why is it not reccomeded to use ceramics for rough milling/heavy interrupted cuts?

Answer 41

low toughness

Question 42

when are diamonds used in cutting?

Answer 42

high speed machining of nonferrous metals and abrasive nonmetals (figerglass, polymer, graphite, and wood.) **NOT** for steel cutting