Cutting tool

Question 1

what is the relationship between hardness and toughness

Answer 1

high hardness (hot hardness) will have poor toughness (print to facture failure)

Question 2

What are the 3 modes of tool failure

Answer 2

1. fracture failure
2. temperature failure
3. Gradual wear

Question 3

what is fracture failure

Answer 3

Cutting force becomes excessive and/or dynamic (forces on the tool exceed the tool’s strength), leading to brittle fracture Often occurs in interrupted cuts, or when inclusions in the workpiece are encountered

Question 4

what is temperature failure

Answer 4

high temperatures lead to plastic deformation or premature wear

Question 5

what is gradual wear

Answer 5

Gradual wearing of the cutting tool

Question 6

what is the perferred mode of failure

Answer 6

Gradual wear bc it leads to longest possible use of tool
(fracture and temperature failures are premature failures)

Question 7

what are the two locations where gradual wear happens on the tool

Answer 7

1. crater wear - on top rake face
2. flank wear - on the flank (side of tool) ~more important is flank wear

Question 8

what are the 4 cutting wear modes

Answer 8

1. abrasion
2. adhesion
3. chemical reaction
4. Plastic deformation

Question 9

abrasion

Answer 9

main cause of flank wear, mechanical wearing bc of hard particles

Question 10

adhesion

Answer 10

high pressure localized fusion and rupturing

Question 11

chemical reaction

Answer 11

oxidation (oxide layer softer than parent tool layer)

Question 12

Plastic deformation

Answer 12

contributes to flank wear

Question 13

cutting wear models

Answer 13

1. break-in period
2. steady state wear
3. failure region

Question 14

relationship between cutting speed and tool life

Answer 14

when u increase cutting speed tool life reduces

Question 15

use the right tool ___ of the time

Answer 15

50%

Question 16

use the right cutting speed ____ of the time

Answer 16

58%

Question 17

use the tools to full life only ___ of the time

Answer 17

38%
(wastes $10 billion)

Question 18

plain carbon steel in cutting

Answer 18

• Plain-carbon steel 0.9-1.3% carbon.
• Can be alloyed with Mo, Cr, W
• Not used much in modern manufacturing, loses hardness around 300-650 F
• Taps, dies, chisels and cheap drills
• custom tools

Question 19

high speed steel (HSS)

Answer 19

Highly alloyed tool steel capable of maintaining hardness at elevated temperatures better than high carbon and low alloy steels (cost not too high)
- good for complicated tool shapes

Question 20

what are the 2 basic types of HSS (AISI)

Answer 20

1. Tungsten-type, designated T- grades
2. Molybdenum-type, designated M-grades

Question 21

high speed steel composition

Answer 21

Alloying ingredients:
- tungsten and molybdenum
- chromium and vanadium
- carbon
- some grades have cobalt

Question 22

Cemented carbides

Answer 22

hard tool material based on tungsten carbide (WC) using powder metallurgy techniques with Cobalt (Co) as the binder

Question 23

cemented carbides properties

Answer 23

 High compressive strength but low-to moderate
tensile strength
 High hardness (90 to 95 HRA)
 Good hot hardness
 Good wear resistance
 High thermal conductivity

Question 24

Coated carbides

Answer 24

Cemented carbide insert coated with one or more layers of TiC, TiN, and/or Al2O3 or other hard materials
- small thickness 2.5 - 13 m (0.0001 to 0.0005 in)

Question 25

how is the coating applied in coated carbides

Answer 25

by chemical vapor deposition or physical vapor deposition

Question 26

applications of coated carbides

Answer 26

cast irons and steels in turning and milling operations: - Best applied at high speeds where dynamic force and thermal shock are minimal

Question 27

Ceramics

Answer 27

Primarily fine-grained Al2O3, pressed and sintered at high pressures and temperatures into insert form with no binder

Question 28

Synthetic Diamonds (hardest material, withstands high temp, best surface finish)

Answer 28

Sintered polycrystalline diamond (SPD) - fabricated by sintering very fine-grained diamond crystals under high temperatures and pressures into the desired shape with little or no binder NOT FOR STEEL CUTTING (ferrous materials)

Question 29

Cubic Boron Nitride

Answer 29

Next to diamond, cubic boron nitride (cBN) is the hardest material known - maintains its hardness and resistance to wear at elevated temperatures - low chemical reactivity to the chip/tool interface (can use ferrous material, steel)

Question 30

if the material is hard what type of rake angle should u have

Answer 30

negative rake angle

Question 31

purpose of cutting fluid

Answer 31

1. Heat generation at shear and friction zones 2. Friction at tool-chip and tool-work interfaces