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Materials > Bob Temple - Manufacturing > Flashcards

Bob Temple - Manufacturing Flashcards

1
Q

What are the things to think about when choosing manufacturing processes

A

Cost
Shape (can you make it?)
Materials (can u process them?)
Quality (can u achieve required tolerance, surface finish, integrity
Production quantity (can you produce required quantity? Automation? )

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2
Q

What is casting and what materials is it used with?

A

1) pour molten material into mould
2) allow it to solidify
3) remove part from the mould

Used with metal, polymers, ceramics

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3
Q

What are the disadvantages of casting?

A

Dangerous – heat
Skill intensive – must be trained
Prone to errors – if cooled wrong get wrong properties
May not provide suitable material properties

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4
Q

What are the Advantages of casting

A

Capable of complex shapes with internal cavities
Capable of making large parts in one piece
Capable of processing material is not possible by other means or too expensive
Competitive with other manufacturing processes
Near net shape manufacturing process
Can make repeatable parts easily

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5
Q

What are the two types of casting and what is the difference between them

A

Expendable mould and permanent mould

A pattern is used to create the cavity in an expendable mould - They can handle larger and more complex parts

In permanent moulds cavity is machined into the mould they are used for high-volume production

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6
Q

What are the factors affecting casting

A 
The mould
Filling of the mould
Material shrinkage
Material cast structure
Defects
Removal and finishing of the part
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7
Q

What are the different parts of the mould and what do they do

A

The pattern creates a mould cavity in the shape of the desired casting
The flask is the outer container (Upper half is the cope and lower half is the drag)
Cores are used to create hollow features

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8
Q

What is the parts that is removed from the mould

A

A rough casting

It requires finishing operations to obtain the final product

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9
Q

What are the main features of the mould

A

The mould is designed to allow escape of gases and take account of material shrinkage

  • The molten metal is poured in through a spray which leads to a narrow gap called the gate that ensures uniform metal flow into the mould through the runners
  • A riser is used to allow air to escape indicate a full mould and supply molten metal as solidification shrinkage because event may also be used to allow small amounts of Excess gas to escape
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10
Q

Which features of the mould are removed from the casting during finishing

A

Risers and the gates

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11
Q

What are the factors in complete filling the mould

A

Fluidity of the metal
Metal fills mould before it solidifies
Air in the mould can escape as the liquid metal pushes it out
Evolve gases from the liquid metal can escape mould - don’t want slag in the mould

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12
Q

What is the fluidity index of a metal

A

The length it will flow and a standard spiral passage before solidifying
This depends on the thermal properties of the mould and metal

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13
Q

How can dissolved gases be removed

What’s the difference between gases in solids and in liquids?

A

Flushing with An inert gas
Melting and pouring under vacuum

More soluble in liquid metals than solid

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14
Q

How does the mould deal with material shrinkage?

A

Cavity is usually slightly oversized
Risers supply extra metal as it shrinks in the mould avoiding porosity
Casting strength is low when hot- vulnerable to heat tears - mould should not restrain the casting too much as it shrinks

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15
Q

What affects the mechanical properties of the casting?

A

Metal structure

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16
Q

What influences the metal structure obtained?

A

Metallurgy of alloy

Thermal properties of alloy and mould (sand takes a while to cool)

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17
Q

What is the structure of a pure metal casting?

A

Grains nucleate at mould walls (cool)
Chill zone there contains fine, multi-axed grains
Slower cooling rate= coarser grain structure
Bulk grain structure is columnar
Solidification front moves away from the walls with time

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18
Q

Where is the solidification front thinner?

A

Thinner at concave (corners pointing in) features, thicker at convex features (corners points outside)

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19
Q

What is the mushy zone?

A

Where the solid component of the alloy forms as dendrites (tree-like) surrounded by liquid

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20
Q

What is the advantage and disadvantage if grey cast iron?

A

Poor mech properties but easy to cast (high fluidity)

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21
Q

What effect does cooling rate have on the structure of castings?

What else affects the grain structure formed

A

Slow- coarse grain structure
Fast- finer grain structure

Alloy composition also affects grain structure

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22
Q

What affects the cooling rate of castings?

A

Mould material (metal is faster)

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23
Q

What properties occur when grain size decreases?

A

Strength and ductility increase
Microporosity decreases
Tendency to crack during cooling decreases
Lack of uniformity in grain structure causes anisotropic mechanical properties

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24
Q

How can the equiaxed zone of a casting be extended? How does this work?

A

Using an inoculant

Works by proving nucleation sites throughout the liquid metal

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25
Q

What does higher cooling rates cause for casting?

A

Reduce grain size
Microsegregation (cored dendrites - more alloy at surface than core)
Macrosegregation (dendritic structures result in lower conc of alloying elements at the centre of the casting)

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26
Q

What are chills and how do they avoid porosity?

A

Increase cooling rate at critical points

Internal ones become part of the casting, external ones can be removed

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27
Q

Where does porosity occur and what property does this cause?

A

Regions of larger section thickness- surrounding thinner regions solidify first
Reduces ductility impairs surface finish and makes casting permeable

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28
Q

What can be done to speed up post casting shrinkage?

A

Annealing

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29
Q

How is the metal heated and prepared for casting?

A

Gas/electric furnace
Crucibles made from ceramic (withstand high temps)
Induction heating makes eddy currents in iron and iron alloys-molten metal reactive with O2/dissolve atmospheric gases
Metal is de gassed before pouring otherwise the metal will be porous

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30
Q

What affects the time taken for the casting to solidify?

A

Volume
Surface area

T= C(V/A)^n

T=time
C= constant for process and alloy
N= constant between 1.5 and 2.5
V=volume 
A=SA
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31
Q

What is the equation to determine solidification time? Why is it useful?

A

Chvorinovs rule

Useful in designing castings to avoid shrinkage porosity and for feeding systems eg riser size and location

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32
Q

What are the examples of expendable mould casting?

A

Sand
Investment (lost wax)
Evaporative pattern (lost foam )

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33
Q

What are the types of permanent mould casting?

A

Gravity die
Pressure die
Centrifugal

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34
Q

Describe sand casting

A

Most used
Use pattern to make desired cavity in sand
Mould broken when casting removed
Cores also made from sand- broken for casting removal- must be supported by core prints and chaplets in mould

Sand bonded to form mould (still permeable for gases to escape)

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35
Q

What is the most common sand casting mixture?

A

Green moulding sand- sand with clay and water

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36
Q

What are the 4 important characteristics of sand for moulding?

A

Refractoriness (withstand high temps)
Cohesiveness (retain given shape)
Permeability (allow gas escape)
Collapsibility (allow metal to shrink, and free the casting)

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37
Q

What is the sequence of operations for sand casting?

A

1) mech drawing of part used to generate design for pattern
2) is patterns mounted on plates with pins for alignment
3) core boxes produce core halves which are pasted together
4) cope half of mould assembled by securing cope pattern plate to flask with aligning pins and attaching inserts to form the sprue and risers
5) flask rammed with sand and plate inserts removed
6) drag half produced - bottom board placed below drag and aligned with pins
7) all inverted, pattern withdrawn, leaving imprint
8) core set in place within drag cavity
9) mould closed, held closed
10) metal poured, metal solidifies and casting is removed
11) sprue and risers cut off, casting cleaned, inspected and heat treated

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38
Q

What are draft angles?

A

Sloping walls used to ease removal of the pattern from the mould (1-3 degrees)

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39
Q

What is a metal match plate?

A

Used for high volume manufacture of smaller castings

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40
Q

What should be taken into account when choosing the pattern material?

A

Used repeatedly so must be durable for expected no of castings
Low cost can be made from wood but aren’t v durable
More robust materials are hard to machine
Weight
Susceptibility to water attack

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41
Q

What do core prints do?

A

Hold and align core in the cavity?

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42
Q

What are chaplets?

A

Metal supports that can be used to provide additional stability to the core

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43
Q

What are the 2 advantages of sand casting?

A

Wide variety of metals and shapes- no limit to part size

Relatively cheap moulds- flexible, allow changes to mould if necessary

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44
Q

What are the disadvantages of sand casting?

A

Difficulties in meeting exact requirements eg tolerances, surface quality, internal soundness

More suited to lower production volumes except where mechanised mould making is employed

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45
Q

What is investment casting?

A

Pattern is surrounded or ‘invested’ with a ceramic coating that becomes the mould

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46
Q

Describe the steps of investment casting

A

Produce master pattern if desired casting
Produce master die
Produce wax patterns.
Assemble wax patterns on a common sprue (tree)
Coat ‘tree’ with initial investment material
Finish coat- layers applied increasingly coarser particles to increase permeability of walls
Allow investment to harden
Melt out wax pattern
Fire investment to finish hardening process and burn off residual wax
Pour molten metal into mould cavity
Allow metal to solidify
Remove castings
Post processing

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47
Q

What’s the diff between an investment cast rotor and conventionally cast ones?

A

Investment cast has finer and more uniform grain

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48
Q

What are the advantages of investment casting?

A

Only method producing precision shapes castings and high mp materials
Parts require minimal finishing
High production rates and one off products possible
Flexible, range of alloys processable, fine surface detail, good dimensional tolerances

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49
Q

What are the disadvantages of investment casting?

A

V expensive as extra steps better for small products not big

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50
Q

What is evaporative pattern casting?

A

Similar to investment casting- pattern made from expanded polystyrene tho

Flask vibrated to pack sand before pouring in molten metal

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51
Q

What are permanent moulds?

A

2 part moulds made from durable and thermally resistant materials eg cast iron, steel, bronze, graphite, refractory alloys

Moulds not porous so air vents must be included

Moulds not broken up so parts must be designed to be removable from mould

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52
Q

What are the advantages of permanent moulds?

A

Reusable
Good surface finish
Good dimensional accuracy
Temp of mould controlled

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53
Q

What are the disadvantages of permanent moulds?

A

Better for low mp alloys eg Al and Zn
Mould costs can be high
Wear of mould

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54
Q

What affects the mould life of a permanent mould?

A 
Temp of alloy being poured 
Mould material
Mould temp
Thermal shock 
Mould configuration
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55
Q

What is gravity did casting?

A

Head of liquid and atm pressure applied to liquid
Feeder has higher level of metal in it than the casting
Feeder removed after casting has solidified and cooled

56
Q

What are the advantages of gravity die casting?

A

Long die life 25000+ cycles
No expensive machines or equipment required
Dies May be cheap- rough cast and minimal machining

57
Q

What are the disadvantages of gravity die casting?

A

Limited capabilities in part shape, complexity and fine detail
Production rates slow

58
Q

What alloys can be used for gravity die casting?

A

Al, Zn, Mg, Cu, brass

59
Q

What is pressure die casting?

A

Metal injected under action of external pressure
Greater capital expenditure incurred- high production rates, machines can inject and close dies, process semi/fully automated, need min 10000 production runs
Low labour costs

60
Q

What are the properties of pressure die casting dies

A

Heat resisting alloys used
Higher surface finish applied
Die wear increases with temp of metal
Multiple cycles can cause surface cracking of the dies
Water based lubes with graphite or other suspensions help reduce die temp
Life cycle of properly constructed and maintained can be 1/2 million cycles
Very rapid production

61
Q

What are the steps of pressure die casting?

A 
Lube dies
Close and lock dies
Molten metal forced into die cavity
Held under pressure till it solidifies
Die opens 
Casting is ejected
62
Q

What’s the hot chamber process? (Pressure die casting)

A

Metal in molten pot
Piston traps done and forced it into die cavity
Lower mp alloys cast (Zn)
Die cooled by circulating fluid

63
Q

What’s the cold chamber process? Pressure die casting?

A

Metal poured into injection cylinder
Cylinder not heated
Higher mp alloys cast (Al, Mg)
Large as high clamping force needed

64
Q

What are the advantages of pressure die casting?

A 
Dimensions accurate
Fine surface feature reproduction 
Thin walls
Little finishing required
Capital costs outweighed if production runs are high enough
65
Q

What are the disadvantages to pressure die casting?

A

Limited to metals with lower mp so mould isn’t destroyed
Part size limited
High tooling costs

66
Q

What’s a misrun and how can it be prevented?

A

When molten metal solidifies before it has filled the mould

Ensure high enough temp for fluid to melt
Add fluidising additives
Control conditions- no dendrites formed
Ensure thick walls to allow material flow
Remove sharp corners to promote flow
Run metal in at a few places at the same time
Use chvorinovs rule to balance solidification times

67
Q

How is porosity avoided?

A

Use rises to supply extra metal during shrinkage
Vents to allow has escape
Permeable mould materials
Degas casting metal
Use chills at thicker sections
Avoid thickness variation in the casting
Avoid hot spots- big thickness changes in wall

68
Q

What are the reasons for choosing a casting process?

A 
Size of parts
Configuration (complexity, finish etc) 
Production quantity
Tolerances
Metals castable
69
Q

What is the ranking order in terms of part size of castings?

A

Biggest

Sand
Centrifugal
Gravity die, investment, evaporative
Pressure die

Smallest

70
Q

What’s the configuration ranking order?

A

Best

Investment 
Evap pattern, sand
Gravity die
Pressure die,
Centrifugal

Worst

71
Q

Which has the best finish?

A

Pressure die casting?

72
Q

What’s the production costs ranking?

A

Perm mould- high mould costs, low labour- low cost in high volume

Sand- cheap moulds, moderate labour costs, low cost for low to medium volume

Investment casting- high labour costs

73
Q

What’s the tolerance ranking?

A

Good

Squeeze casting
Pressure die
Investment
Gravity die
Centrifugal
Sand

Poor

74
Q

General disadvantages of casting?

A

High forces required- large and expensive equipment, heavy duty equip, tooling expensive and needs replacing when wears out

Generally only justified for large scale production

75
Q

How much force is required for casting?

A

Flow force
Friction- can be needed eg in rolling
Shape/tooling forces (redundant work)

76
Q

What’s working?

A

Plastically deforming a metal to change us shape or properties

77
Q

What are the advantages of hot working?

A 
Lower flow stress
Improved ductility
Lots of deformation possible 
Improved mech properties- crystal structure refined
Directional flow lines- more strength
Better machining properties than cold working 
Promotes internal difFusion 
Pores and vacancies removed
78
Q

What’re the disadvantages of hot working?

A 
Heating costs 
Poor surface condition
Handling problems
Poor dimensional tolerances
Distortion on cooling and residual stress possible
79
Q

What’re the advantages of cold working?

A 
No heating required
Good surface finish
Good dimensional accuracy
Strength, fatigue, wear properties improved 
Contamination problems reduced
Good reproducibility
80
Q

What’re the disadvantages of cold working?

A

Higher force to initiate and complete deformation
Heavier and stronger equip needed- more expensive
Strain hardening occurs- may need annealing
Residual stresses may be present
Surface must be clean and scale free
Elastic memory may be present

81
Q

Warm working vs cold working? Discuss

A

Reduced loads on equip and tools
Increased metal ductility
Reduced straining allows more processing without annealing
Less residual stress induced

82
Q

Discuss warm working vs hot working

A 
Less scaling, oxidation, de-carbonisation
Better dimensional control
Smoother finish possible
Less need for finishing processes
Lower energy consumption in heating
Longer tool life (reduced thermal shock)
83
Q

What’s rolling?

What does it do to ingots?

A

Squeezing metal between 2 rolls to reduce thickness and increase length

Breaks down coarse brittle and porous structure of ingots Ito wrought structure then cold rolling improves strength hardness and finish

84
Q

Describe flat rolling

A

Rolls pull material between them through frictional force

Fr on exit must be higher than entry on the no slip point

85
Q

What’s draft and how is the max calculated?

A

Diff between initial and final thickness

ho - hf = mue^2 R
R is radius
ho- hf is draft

86
Q

List the defects in flat rolling

A

Wavy edges
Zipper cracks
Edge cracks
Alligatoring

87
Q

What’s doll bending?

A

Bending of straight cylindrical rolls, caused by rolling force

Produces strip with uniform thickness

88
Q

What’s forging?

A

Forming of discrete metal parts by application of compressive forces using tooling and dies

Good strength and toughness
Not usually high precision
Can be hot or cold
Force supplied by presses or hammers

89
Q

What’s the forging force equation?

A 
F= Yf pie r^2 (1+(2mue r /3h)) 
Yf- flow stress of material
R- radius of part
H- height of part
Mue - coefficient of friction
90
Q

What’re the steps of forging?

A 
Heat blank
Descale blank
Lubricate
Forging -preforming, finish 
Trimming etc
91
Q

Why’s lube required for forging?

A

Wear reduction
Help metal flow
Thermal barrier
Parting agent

Hot-graphite, molybdenum disulphides, glass
Cold- soap, oil, conversion coatings

92
Q

What’s forgeability?

And what’re the tests for it?

A

Ability of a material to deform without cracking

Upset test- max height reduction in upsetting before surface cracking occurs

Hot twist test- number of turns before failure

93
Q

What’re the factors affecting forging die design?

A

Parting line should be a flat plane through centre of forging
Adequate draft required
Generous fillets and radio reduce wear and help with filling
Keep ribs wide and low
Balance section changes to help flow
Take advantage of fibre flow lines
Keep tolerances as large as poss

94
Q

What’re the die material requirements?

A 
Strength and toughness resistance
Hardenability
Mech/thermal shock resistance
Wear resistance
Tool and die steels containing Cr, Ni, Mo, V
95
Q

What’s isothermal/ hot die forging?

A

Dies heated to same temp as forging
Maintains ductility and malleability of the workpiece during forging
Complex parts with high dimensional accuracy can be made
High cost, low production rate

96
Q

What’s upset forging? (Cold heading)

What are parts limited by?

A

Cold working operation
Used for wire and rod mostly <50mm
High speed production
Parts limited by
- limiting length of unsupported metal that can be upset is 3 times bar diameter
- lengths greater than 3X Diameter May be upset if die cavity is <1.5x bar diameter

97
Q

What is extrusion?

A

Forces a metal volley through a die
Part produced has uniform thickness
Metal is forced through the die using a ram to either push the metal through the die or the die through the metal

98
Q

What does drawing do?

A

Produces v small diameter parts eg wire and rod where the original billet would buckle if it were compressed

99
Q

What is the drawing ratio and what’s the normal value for it?

A

Final area/initial area

Generally about 0.4- giving reduction in area per mass of 60%

100
Q

What material properties are affected by elongation and how?

A

High elongation for formability
Large strain hardening component
High strain rate sensitivity

High uniform elongation desired as materials are being stretched

101
Q

What material properties are affected by grain size?

A

Coarser the grain, rougher the surface
Affects mech properties
Surface appearance- orange peel affect

102
Q

What is shearing?

A

Cutting metal between rotating blades or punch and die

Metal sheet fractured along a line between the die and punch

103
Q

What affects quality of cut edge in shearing?

A

Clearance

Low- excessive tool wear
High- poor edge quality but long tool life
Tool wear shows an increase in clearance

If too small- line of failure from punch to die is irregular
Too large - excessive plastic deformation occurs- deformed edge without parallel sides and plus tear and blurred top surface

104
Q

What’re the characteristics of a sheared edge?

A

Small region of parallel sided plastic deformation- called burnished zone
Fractured surface

105
Q

What’s the approx optimum separation value for a shearing operation?

A

K x sheet thickness

More ductile 0.04

106
Q

What’s the equation for shearing force and what affects it?

A

Shearing force = 0.85to0.65x UTS x thickness x cut length

Usually less tho (average only 70% hence the 0.65 to 0.85)

107
Q

What does a rake angle do in shearing?

A

Reduces contact area of blade/die/punch this reducing shearing force

108
Q

Whatre the major processing parameters in shearing?

A

Shape and materials of punch and die
Speed of punching
Lubrication
Clearance between punch and die

109
Q

What’re the process categories of shearing?

A

Spitting
Nibbling
Die cutting
Fine (fein) blanking

110
Q

What are the key factors in shearing? (8)

A 
Punch determines hole size
Die determines blank size
Punches should be kept short 
Weak parts in dies should be inserts 
Punches are slightly tapered 
Dies last 2-3 times longer than punches 
6% material thickness clearance between punch and die 
Material thickness < punch diameter
111
Q

What’s slitting?

A

Produces straight or curved cut in the workpiece

Pair of circular blades can be used

112
Q

What’s nibbling?

A

Small traumatic punch and die is used to rapidly make many overlapping holes

113
Q

What’s a piercing?

A

The metal not under the punch

114
Q

What’s a blank?

A

The metal not under the punch

115
Q

What’s fein/ precision blanking?

A

V ring or gripper is used to keep deformation zone in compression, ensuring the whole region is plastically sheared
Produces v smooth square edges
Need fine Grain material
Clearances about 1%
Requires triple action press with control of punch, pressure pad, and die

116
Q

How are bending force and weight related?

A

Bending force is inversely proportional to weight

117
Q

How does tube bending work?

A

Need special tubing to avoid buckling and folding
Need internal support to prevent buckling eg mandrels (plug, balls etc, particulate matter (sand)
Depends on thickness of tube

118
Q

What’s stretch forming?

A

A die or punch stretches metal

119
Q

What’s stretch drawing?

A

Punch and die squeeze metal into shape between them

120
Q

What’s embossing?

A

Uses friction between die and sheet to clamp sheet

121
Q

What’re blank holder in drawing?

A

Pressure hold down ring

Stops wrinkling

122
Q

What’re the variables of deep drawing? (8)

A 
Properties of sheet metal
Ratio of blank to punch diameter 
Clearance between punch and die 
Punch radius
Die corner radius
Blankholder force
Friction
Lube
123
Q

What’s the draw limit ratio eqn?

A

Original blank diameter/ cup diameter
Varies 1.6-2.4
Large corner radii required on tools

124
Q

What’s the steps of multistage drawing?

A

Redrawing- reduces wall diameter
Ironing- wall thickness reduced
Reverse drawing- stress in opposite direction

125
Q

Whats peen forming? How does it work?

A

Peeling with cast iron or steel shot
Create smooth and complex surfaces

1) sheet surface subjected to compressive stresses which expand surface layer
2) material below peened surface remains rigid, surface expansion cause sheet to develop curvature
3) process induces compressive residual stresses, improved fatigue strength of material

126
Q

What’s spinning?

A

Forming axi-symmetric parts over a mandrel with tools or rollers

127
Q

Whats tube spinning?

A

Cylindrical part thickness reduced by spinning them on cylindrical mandrel using rollers

128
Q

What’s superplastic forming? What materials can be used for it?

A

Forming into complex shapes with lots of deformation

Fine grained alloys eg Al, Zn Titanium

129
Q

What’re the advantages of superplastic forming?

A

Low strength of tooling so low costs
Complex shapes in one price, fine detail, close tolerances and no secondary ops needed
Weight and material savings as high formability
Little/no residual stresses in formed parts

130
Q

What’re the limitations of superplastic alloys

A

Material must not be superplastic at room temp

Must be formed slowly

131
Q

What’s bulging?

A

Placing tubular, conical or curvilinear part in a split female die and expanding against walls of die
Expansion can be achieved

132
Q

What’re rubber forming?

A

One of the dies is made from flexible material eg rubber
Die does not damage or scratch surface of sheet
Process is used for bending and embossing surfaces
Typical pressures about 10Mpa

133
Q

What’s hydroforming/fluid forming?

A

Pressure over rubber membrane controlled up to 100 MPa
Allows close control of part, avoiding wrinkling or tearing
Deeper draws obtainable as- high pressure forces cup against punch, friction at punch/cup interface reduces longitudinal tensile stress
Low tooling costs, flexibility and ease of operation, no damage to surface of sheet metal

134
Q

What’s explosive forming?

A

Sheet metal clamped over die and assembly lowered into water tank
Air in die evacuated
Explosive charge denoted a distance from sheet, shock waves force material into die cavity
Material needs to be ductile at high rates of deformation
Versatile, no limit to size of workparts, suites to low volume production of large parts

135
Q

What’s magnetic pulse forming?

A

Energy in capacitor bank discharged through magnetic coil
Eddy currents induced in part create opposing magnetic field which collapses the part onto die or workpart
Higher electrical conductivity of material=greater forces (don’t need Ferro-magnetic material)
Process suited for shallow drawing on thin sheet, collapsing sheet onto tubes and in bulging and flaring operations

Materials (15 decks)

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