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Materials 2 > Machining > Flashcards

Machining Flashcards

1
Q

Define turning.

A

A single point cutting tool removing material from a rotating workpiece.

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2
Q

Define drilling.

A

A rotating two edged tool creating a hole in a workpiece.

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3
Q

Define milling.

A

A rotating multi-edged tool moved across a workpiece to create a plane or straight surface.

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4
Q

What is peripheral milling? Face milling?

A

Peripheral rotates parallel to the plane, face rotates perpendicular to the plane.

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5
Q

What are the parts of a single point tool?

A

Point (with a nose radius)
Rake face
Flank
Cutting edge

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6
Q

How is material removal rate calculated for turning?

A

R = v f d
Where R is material removal rate
v is cutting speed (rotation speed of workpiece)
f is feed (motion of tool)
d is depth of cut (penetration of tool below original surface)

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7
Q

What is the chip thickness ratio?

A

r = to/tc < 1

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8
Q

How is shear strain calculated for chips?

A

gamma = tan(theta - alpha) + cot(theta)
Where gamma is shear strain
theta is shear plane angle
alpha is rake angle

tan(theta) = rcos(alpha) / (1 - rsin(alpha))

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9
Q

What is the orthogonal model of chip formation? The realistic model?

A

The orthogonal model is where chips shear in separate planes at the shear plane.
Realistic is that there are shear zones along the shear plane and where the chip runs along the tool.

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10
Q

What causes discontinuous chips?

A

Brittle materials
Low cutting speeds
Large feed and depth
High tool-chip friction

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11
Q

What causes continuous chips?

A 
Ductile materials
High cutting speeds
Small feeds and depths
Sharp cutting edges
Low tool-chip friction
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12
Q

What is continuous with BUE? What causes it?

A

It is a continuous chip, but with small particles of built up edge left along the cut surface.
Caused by:
Ductile materials
Low/medium cutting speeds
Tool-chip friction causing portions of chip to stick to rake face, forming BUE, which breaks off cyclically

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13
Q

What causes serrated chips?

A

Alternating high and low shear strain, with new chips formed at the high strain boundaries, but longer chips building up in between due to the low shear strain.
Associated with hard to work with materials at high speeds.

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14
Q

How are the friction forces of the tool and the shear forces of the chip/work related?

A

The resultant of the friction and normal forces in the tool is equal and opposite to the resultant of the shear and normal forces of the work.

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15
Q

How are shear angle, rake angle, and friction angle related? How do we increase shear plane angle?

A

theta = 45 + alpha/2 - beta/2
where beta is the friction angle (the angle of the resultant of the tool friction and normal forces)

Shear plane angle is increased by increasing rake angle or reducing friction angle (or coefficient of friction)

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16
Q

Why do we want a high shear plane angle?

A

Lower shear force! (smaller area needs less force)

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17
Q

Define generating. What are some examples?

A 
When part geometry is determined by feed trajectory of tool (turning is about where the point is pointed, not what shape it is).
Straight turning
Taper turning
Contour turning
Plain milling
Profile milling
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18
Q

Define forming. What are some examples?

A

When part geometry is determined by the shape of the tool.
Form turning
Drilling
Broaching

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19
Q

What are examples of processes that use both forming and generating?

A

Thread cutting on a lathe

Slot milling

20
Q

What are the various methods of holding work in a lathe?

A

Holding between centers
Chuck
Collet
Face plate

21
Q

What are the types of peripheral milling?

A 
Slab milling
Slotting
Side milling
Straddle milling
Form milling
22
Q

What are the types of face milling?

A

Conventional face milling
Partial face milling
End milling (kinda like drilling)
Profile milling

23
Q

What are the three modes of tool failure?

A

Fracture
Temperature
Gradual wear

24
Q

Where does the energy go in machining?

A

98% of energy turns into heat. Very efficient, really. Other 2% is retained as elastic energy in the chip.

25
Q

Why are high cutting temperatures a problem?

A

Reduce tool life
Hot chips hurt people
Inaccuracies in parts dimensions due to thermal expansion

26
Q

What is the relationship between speed and temperature?

A

T = K v^m
T is temp
v is cutting speed
K&m are constants

27
Q

What are the two types of gradual wear?

A 
Crater wear (top rake face)
Flank wear
28
Q

What is the relationship between speed and tool wear?

A

v T^n = C
v is cutting speed
T is tool life
n&C are constants

29
Q

What are the signs of end of tool life?

A 
Complete failure of cutting edge
Visual wear
Fingernail test
Changes in sound during operation
Crappy chips
Bad surface finish
Increased power
Decreased production / increased cutting time
30
Q

What are the important properties of tool materials?

A

Toughness - to avoid fracture
Hot Hardness - to maintain hardness at high temps
Wear Resistance - to resist abrasive wear

31
Q

What materials have good hot hardness?

A

Ceramics, then cemented carbides, then HSS, then plain carbon steels suck.

32
Q

What are cemented carbides? What are it’s general properties?

A

Tungsten carbide (WC) with Cobalt (CO) binder.
High compressive but low tensile strength.
High hot hardness and wear resistance
High thermal conductivity
High E
Lower toughness

33
Q

Describe non-steel cutting carbides

A

Used for nonferrous metals and cast iron
Properties are determined by grain size and cobalt content:
As grain size or cobalt content increases, hardness decreases but toughness increases

34
Q

Describe steel cutting carbides

A

Used for low carbon, stainless and alloy steels

Increased crater wear resistance for steels but decreased flank wear resistance for non steels

35
Q

Describe cermets as a tool material

A

Used for finishing of steels and cast irons
Uses higher speeds and lower feeds than cemented carbides
Better finish

36
Q

Describe coated carbides

A

One or more layers of hard material added to create a thin coat.
Used in high speed, low force applications
Controls thermal expansion of tool.

37
Q

Describe ceramics as a tool material

A

Usually Al2O3, has low toughness and therefore used for high speed turning of steel and cast iron

38
Q

What are the three methods of holding a single point tool?

A 
Solid shank (tool is part of the shank)
Brazed insert (tool is brazed into shank)
Mechanically clamped (used for very hard tool materials)
39
Q

What tool shapes are stronger? Require more power? Are more versitile?

A

The round and square ones are stronger, require more power, and are less versitile than the triangle and rhombus shapes.

40
Q

What is the difference between drilling and boring?

A

Drilling creates a hole, boring enlarges one.

41
Q

What are twist drills usually made of? What is the flute? What is the helix angle?

A

Made of HSS
Flute is the groove of the two edges
Helix angle is the angle of the flute.

42
Q

What is the cutting velocity at the drill point? What is the consequence of that?

A

0

Large thrust force is required to drive the drill forward into the hole.

43
Q

How are chips removed in drilling? What are the consequences of this?

A

They go up the flute. This prevents lubrication from going down the flute.

44
Q

What is a straight-flute drill?

A

Uses carbide inserts at tip for higher cutting speeds.

45
Q

What is a gun drill?

A

Used for deep holes, has a carbide cutting edge, a straight flute, and a coolant hole down the center.

46
Q

What is a spade drill?

A

Used for large diameters, has a larger tip than shaft.

Materials 2 (12 decks)

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