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ME2162 > Chapter 3 Cutting Tool Technology > Flashcards

Chapter 3 Cutting Tool Technology Flashcards

1
Q

How does tool wear occur and how does it affect the workpiece?

A

Tool wear occurs as the machining operations undergo friction force, especially at the face of the tool & chip interface + tool & surface interface -> generating heat, wear and tear.

Affects the dimension accuracy & finishing

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2
Q

Where does tool wear usually occur?

A

Rake face & Flank Face

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3
Q

What are the regions of tool wear vs cutting time graph?

A

Rapid-initial wear (break-in)
Steady-state wear region
Failure region (accelerated wear)

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4
Q

What are the parameters affecting tool wear rate? (3)

A
  1. Cutting speed (most significant)
  2. Tool material/design
  3. Taylor Tool life eqn
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5
Q

What is the purpose of the Taylor’s Tool Life Equation?

A

It is used to predict the lifespan of cutting tools in machining operation. The equation gives us the relationship between cutting speed and tool life, allowing us to optimise machining operations. (however, only the cutting speed is considered)

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6
Q

What is the purpose of the Extended Taylor’s equation?

A

(Also known as General Tool Life equation)

Includes additional machining parameters that influence tool life & cutting speed, giving a more detailed/accurate prediction of tool life.

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7
Q

What are the 3 critical attributes of tool materials?

A

High temperature stability (hot hardness)
Brittle fracture resistance (toughness & strength)
Abrasive wear resistance (hardness)

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8
Q

What are the tool wear mechanisms?

A
  1. Abrasion
  2. Diffusion
  3. Oxidation
  4. Fatigue
  5. Adhesion
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9
Q

How does abrasion affect tool wear?

A

Abrasion causes flank & crater wear.

How does it happen?
Frictional force occurring at cutting tool & chip interface mainly, and as the chip forms, the tool continues to rub against it, causing abrasion.

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10
Q

How does Diffusion affect tool wear?

A

Diffusion causes crater wear.

How does it happen?
Due to high temp (around 500 deg) it gives the atoms enough energy to diffuse across the interface (chip and cutting tool)
e.g. cutting tool high in C & Co, workpiece high in Fe. Fe from chips to diffuse to tool, C & Co diffuse to chips, as diffusion occurs form high concentration to low concentration,

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11
Q

How does Oxidation affect tool wear?

A

Changes in-material properties.

How does it happen?
High temp due to machining, causes metal to naturally react more with air to produce oxides (mainly at workpiece and tool interface + tool and chip interface)

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12
Q

How does Fatigue affect tool wear?

A

Causes fatigue failure if too extreme, and also a mechanism of wear and tear.

How does it happen?
Occurs due to cyclic loading, which occurs at the chip and tool interface. As chip flows along the cutting, it gives a tensile force on the cutting tool, but as it flows away the tensile force becomes a compression force.

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13
Q

Whats the difference between M03 and H23 ISO Classified Tool Materials?

A

M03 is a Stainless/Heat-resisting steel while H23 is a Hardened steel

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14
Q

How does Adhesion affect tool wear?

A

Causes flank wear.

How does it happen?
Deposition of BUE onto cutting tool (including workpiece) occurs when high hardness of work material.

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15
Q

Whats the difference between K023 and K030 ISO Classified Cast Iron Tool Materials?

A

K023 has a higher hardness but lower toughness than K030.

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16
Q

What are the features of High Speed Steels (HSS) as a tool material?

A
  1. High toughness
  2. 10% Turning, 80% Drilling, 40% Milling
  3. Max cutting spd = 50m/min @ 600 oC
  4. Tin coating for high speeds
  5. Manufactured via hot working & powder metallurgy
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17
Q

What are cemented carbides made of?

A

Composite made of Tungsten Carbides (WC) + Cobalt (Co) as binder.
Additives such as Titanium Carbide (TiC) and Tantalum Carbide (TaC) to improve certain properties.

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18
Q

How does one change the material properties of cemented carbides?

A
  1. Tungsten Carbide (WC) grain size:
    + size, + shock resistance, - hardness
  2. Cobalt (Co) content %:
    + Co%, + toughness, - hardness, - wear resistance

(Note: Useful range is Co @ 5-12%, WC grain size @ 0.5 to 5 µm)

19
Q

What is the role of additives in Cemented Carbides?

A
  1. Motivation: Fe absorbs WC at high temp
  2. Constituents: Titanium (TiC), Tantalum carbides (TaC)
  3. Mechanism: Low solubility in Fe, +hot hardness
  4. Results: Prevent edge deformation, + resistance to crater wear, + thermal stability
20
Q

Comparing Steel and Cast Iron workpieces, why do we use HIGH binder content cement carbide cutting tools for STEEL and LOW binder content for CAST IRON?

A

For Cast Iron, high wear resistance is more important than toughness in the cutting tool, hence low Co% will allow a higher WC%, leading to a higher wear resistance.
Vice versa for Steel, higher toughness is required so increase Co%, and TiC + TaC % is increased to help with the reactivity of Fe with WC, and improve hardness (since sharpness is important here)

21
Q

How does heat affect Cemented Carbides? And how do you solve it?

A

High temperatures causes the WC in the carbides to react with any Fe workpieces, reducing the WC%, leading to lower hardness at high temps, in the tool.

Can be solved by introducing additives (other carbides) that do not react with iron. Coating can also be introduced to reduce solubility in Fe (increased hot hardness)

22
Q

What are the features of Coated Carbides?

A

Extremely low solubility in Fe
Good hot hardness
Enable high cutting speeds
Increase wear resistance

Constituents:
Titanium Carbide (TiC), Titanium Nitride (TiN), Titanium Carbonitride (TiCN), Alumina (Al2O3)

23
Q

What are the +ve and -ve of ceramic tool material?

A

+ve:
very high hardness
no affinity with work material
applicable to hardened steel
inert (does not react to oxygen/steel)

-ve:
very brittle

performance:
high speed machining - good efficiency and surface finishing
good wear resistance - stable dimension and longer tool life

24
Q

Ceramics can also be used to make composites to improve/introduce certain properties, what are examples of such?

A

Alumina based ceramics - Al2O3 -> improve thermal stability

with ZrO2 -> improves crack resistance by volume expansion

with TiC -> improves hardness

with SiC (w) -> whiskers, that reduce crack propogation

25
Q

What is cermet commonly made of?

A

Composite:
Ceramic + Metal = Cermet

Common Ceramics: TiC, TaC, NbC, TiN, TICN
Common Metals: Ni, Mo, Ti, etc.
Major components: Carbides/Nitrides of Ti, Ta, Nb. less tungsten carbide

26
Q

What is Cermet’s features?

A

+ve:
high hardness
high thermal stability
high deformation resistance
Low affinity with Fe (reduced BUE formation) -> better surface finish/finishing operations

-ve:
low shock resistance
not suitable for heavy machining

performance:
excellent for finishing through medium to light cutting

27
Q

Why use Cubic Boron Nitride (cBN) over Sintered Polycrystalline Diamond (SPD)?

A

cBN is used for:
- ferrous materials (inert)
- high temp application (higher thermal stability than SPD)
- used for machining of tool steel, case-hardened steel, cast iron (2nd hardest on earth, for cutting harder materials)

SPD is used for:
- non-ferrous materials (unstable with Fe, Co, Ni)
- lower tamp application (thermal stability up to 700oC)
- used for machining of soft abrasive materials (hardest on earth)

28
Q

How does an increase in Silicon (Si) % in an aluminium alloy affect its properties?

A

Al:
- soft and low density

Increase in Si %:
- Increase strength and wear resistance
- decrease thermal expansion
- however, decrease in machinability (from increased wear resistance)

29
Q

For a machining operation on a workpiece, Al-alloy (18% Si) to give the same effect but with different cutting tools (Carbide & PCD), what should one do if the depth, d = 2.0mm and feed, f = 0.2mm/rev?

refer to graph on week 3 slides, page 55 if not sure

A

Change of cutting speed will allow the same effect, and can be completed within a varying cutting time.

lower cutting speed for carbide, and shorter cutting time
high cutting speed for PCD, but higher cutting time

30
Q

How do we make the raw material into a cutting tool?

A

The raw material, usually in powder form, is made into a blank using high pressure sintering

31
Q

How does one test the hardness of a material?

A

Brinell indentation - measurement of diameter of impression for a specified force value
Vickers indentation - measurement of hardness value via a diamond square based pyramidal indenter

normally vicker’s indentation is more commonly used in the industry

32
Q

What are the categories for tool geometry?

A

Single point:
- used for turning, boring, shaping and planning

Multiple cutting edge:
- used for drilling, reaming, tapping, milling, broaching and sawing

33
Q

What are the 7 key variable in a solid tool shank?

A

Side rake angle, side relief angle, side cutting edge angle (SCEA), end cutting edge angle, nose radius, end relief angle, back rake angle.

34
Q

What is the purpose of a chip breaker?

A

Chip breaker is a form of chip control to prevent continuous flowing chips, by breaking the chips via forcing them to bend at an angle larger than the rake face.
Continuous flowing chips may not be desired because it will lead to curling of the chip (due to shear deformation & gravity) that obstructs the ‘chip & tool interface’ and ‘workpiece & tool interface’, that leads to other problems like damaging the cutting tool or reduced surface finishing, etc.

35
Q

What are the different types of chip breakers?

A
  1. Groove-type
  2. Obstruction-type
36
Q

What is the purpose of having inserts for single point tools?

A

For single-point tools, theres alot of material wastage in its older form (solid tool), as after usage, the whole tool would be thrown out. SO inserts are used instead.

37
Q

Whats the difference between Brazed insert and Mechanically clamped insert?

A

Brazed insert takes too much time, effort and costly, while mechanically clamped insert is slightly better.

38
Q

How does varying insert shapes affect the properties?

A

Different shapes have different versatility and accessibility. Where the smaller the approach/corner angle, the lower the strength, power requirements, and vibration tendencies, but higher versatility and accessibility

Versatility refers to the finishing of the material. So high versatility means better surface finishing.

39
Q

What are the different cutting edge preparation?

A

Radius, Chamfer, Land, Sharp (No prep)

Preparation is done to reduce the peak and stress concentration at the sharp edge.

40
Q

What is the purpose of cutting edge measurement?

A

(for single-point cutting tools mainly)
As designed, there is a value for the cutting edge (e.g. rake face to the flank face). Hence the value measured, can be used to check if its intended.

41
Q

What is the part of a twist drill that helps with chip removal?

A

Flutes

42
Q

What happens when the strength of the twist drill material is low?

A

If the cutting condition is set that there is a large force applied on the workpiece material (note: the workpiece material will also have force acting on the twist drill), this will cause BUCKLING of the twist drill.

43
Q

What are the alternative designs of drills?

A

Straight flute w/ insert
Gun Drill (Heavy duty use)
Spade Drill (Heavy duty use)
BTA Drill (similar to boring process - large holes)

ME2162 (6 decks)

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