Lecs 15-21 Flashcards
(135 cards)
1
Q
LEC 15
CASTING: Name five holey defects
A
Misrun, cold shut, cold shot, shrinkage tear, microporosity.
All these involve air trapped inside the form.
2
Q
CASTING: Name five surface defects
A
Blister, blow, scab, scar, hot tear.
Four of these involve gas bubbles trapped near the surface. The last involves tearing due to shrinkage forces.
Organized from max to min protrusion.
3
Q
CASTING: Name seven sand defects.
Three categories
A
Cases we’ve covered (2)
Cases with Loose Sand (3)
Issues with Sand Mold technique. (2)
Sand blow, pinholes
Sand wash, mold crack, penetration
Mold shift, core shift
4
Q
CASTING: Why should we add ribs to large flat areas in our parts?
A
Ribs prevent them from warping.
5
Q
What are two consideration when designing the parting line of a mold?
A
1) It should be located along a flat plane, rather than a contour.
2) It should be located mid-height for dense materials, and low for lighter materials.
(To reduce needed clamping pressure)
6
Q
What are four things to keep in mind when designing casting gates?
A
1) Have many
2) Feed into thick parts
3) Avoid curved gates
4) Reduce turbulence (fillets)
7
Q
What are three things to avoid when designing a cast?
A
1) Corners
2) Uneven wall thicknesses
3) Large flat areas (add ribs)
8
Q
What should the draft be for
a) sand casting
b) Permament mold casting
?
And what are machining allowances for sand casting?
A
Sand casting: 1deg
Perm mold: 2-3deg
Sand casting machining allowance is between 1.5 to 3mm.
9
Q
Name the casting process which is:
a) Lowest cost
b) Highest cost
c) Lowest production rate
d) Highest production rate
A
a) Sand casting
b) Centrifugal casting
c) Plaster
d) Investment mold
10
Q
LEC 16
What’s the difference between direct and indirect extrusion?
A
Direct extrusion: Metal and ram flow in same direction. Imagine pasta noodles.
Indirect: opposite directions. Think pots and pans.
11
Q
What is the butt, and what is the extrudate?
A
The extrudate comes out the die opening, and the butt is a bit that can’t be forced through the die.
12
Q
What is the difference between hot and cold extrusion?
A
Hot extrusion’s great for greater deformation
Cold extrusion’s great for surface finish and strength.
13
Q
What is low and high die angle, and the characteristics of each?
A
A low die angle means a narrow opening.
A high die angle means a wide opening.
A low angle means lots of friction, but a high die angle means lots of turbulence. Both increase ram pressure, so work is needed to find a balance.
14
Q
Name three extrusion defects
A
1) Surface cracking
2) Pipe
3) Chevron cracking.
Surface cracking is caused by high temperatures.
Pipe is a metal flow pattern that tends to draw impurities and oxides to the center of the extrudate.
Chevron cracking caused by fluctuations.
15
Q
What’s two differences between wire drawing and bar drawing?
A
Wire drawing has small stock. Bar drawing has large stock.
Bar drawing is accomplished as one batch operation, while wire drawing can have multiple extrusions, with capstans in between.
16
Q
What are the four regions in a die, and their functions?
A
Entry Region - allows entrance of lubricant
Approach - where drawing occurs
Bearing Surface - determines final stock
Back relief - an angle of 30deg.
17
Q
Name two defects in drawing (not extrusion)
A
1) Center cracking
2) Seams. Longitudinal scratches.
18
Q
LEC 17 METAL ROLLING Metal rolling: What is a) flat rolling b) shape rolling c) hot rolling d) cold rolling?
A
a) Rolling to reduce thickness
b) Rolling to create a cross-section
c) Rolling for great deformation
d) Rolling for strength and surface finish
19
Q
What are four ways to reduce rolling forces in metal rolling?
A
1) Reduce friction
2) Reduce surface area
3) Work at elevated temperatures
4) Add a tension on the sheet.
20
Q
What’s one way of dealing with “crown” in metal rolling?
A
Adding a camber for your specific needs.
21
Q
In metal rolling, what is “spreading”?
A
The tendency of a metal billet to expand along its width when flattened.
Think of rolling cookie dough.
22
Q
In metal rolling, what is chatter, and how can you minimize it?
A
Chatter is self-excited vibration occuring from dynamics between the rolls and the workpiece.
You can minimize it by getting bigger rolls, or including dampeners in the roll supports.
23
Q
Why is hot-rolling a cast structure (above its recrystallization temp) a good idea?
A
A cast structure has brittle dendritic things. Hot rolling it breaks these dendritic structures out, flattens the thing, and makes it stronger.
24
Q
What’s the difference between a bloom, a slab, and a billet?
A
Purely dimensions. A bloom is the largest, a slab is what it sounds like, and a billet is a small bit that can be made into squares and rods.
25
Name four defects present in the rolling process.
a) Surface defects (from inclusions and impurities)
b) Cracks (from poor material ductility)
c) Wavy edges (from a bending roll)
d) Alligatoring (splitting of material into an alligator mouth)
26
What is tandem rolling?
Running a workpiece through multiple rolls.
27
What is roll forging?
Forging a part using rolls with a design on them. Think rollable cookie cutter.
28
What is skew rolling, ring rolling, and thread rolling?
Skew rolling is a way to make ball bearings using skewed rolls.
Ring rolling is a technique for shaping rings.
Thread rolling is a way to form threads.
29
What is the Mannesmann process?
A cool technique where you squeeze a rod to create an opening, and then force a mandrel into the opening to create a tube.
30
What is the difference between open-die forging and cogging?
Open-die is a compression force to reduce the height of a workpiece.
Cogging is a repeated motion to gradually reduce the thickness of a part.
31
What's the difference between open die, impression die, and closed die forging?
Open die reduces a part height.
Impression die is closed-die with flash.
Closed die has no flash.
32
What is coining?
Making coins. Adding text and features and such.
33
What is "heading"?
A way to create nuts, bolts, etc. Increase the cross section at the end of a round rod or wire.
34
What is piercing, hubbing, and orbital forging?
Piercing is a way of indenting the surface of a block of metal.
Hubbing is a way to add a cavity.
Orbital forging is a way to incrementally forge a part.
35
What is forgeability, and the two tests for it?
The capability of a material to undergo forging without cracking.
The first test is upsetting: How much can we deform the thing before it starts cracking.
The second is hot twist: at what temperature does the material last the longest before failing?
36
Name two forging defects.
1) Laps. When there's not enough material in the die.
| 2) Cracks. When there's too much.
37
What are three characteristics to pay attention to when designing a forging die?
1) Locating the parting line at the area of greatest cross section
2) Having a draft angle of 7-10deg internally, and half that externally.
3) Selecting proper radii and chamfers that metal can properly flow into.
38
What are some ways to create a die?
Casting, forging, machining, electrochemical methods.
39
What's the difference between hydraulic presses and mechanical presses?
Hydraulic is slower, has high installation costs, but low maintenance costs.
Mechanical is faster, can machine to high accuracy, and impart great forces.
40
What are five advantages of sheet metal parts?
1) High strength
2) Good dimensional accuracy
3) Good surface finish
4) Economical
5) Can be mass produced.
41
Name four basic types of sheet metal processes.
1) Cutting
2) Bending
3) Drawing
4) Spinning
42
What are the three main processes of pressworking, or cutting?
1) Shearing (cutting)
2) Blanking (create workpiece from roll)
3) Punching (create holes)
43
What are the four stages of shearing?
1) Contact
2) Plastic deformation
3) Penetration
4) Fracture
44
What's the name of the scrap cut piece in punching?
A "slug".
45
In sheet metal cutting, what is the typical clearance between the die cutting edge and punch cutting edge?
Between 4% to 8% of the stock thickness.
46
What happens if you stray from the typical clearance between die and punch cutting edges in sheet metal cutting?
Not enough clearance = double burnishings and excessive force
Too much clearance = excessive burrs
47
In sheet metal cutting, what is the punch and what is the die?
The punch is the ram that comes down on the sheet metal, while the die is a hole in the table that allows the slug to fall through.
48
In sheet metal cutting, why does the punch determine the size of holes, but the die determines the size of blanks?
Holes: if the die was used, the hole will shrink on you as it nears the punch.
Blanks: if the punch was used, your blank will be a little larger.
49
What is the typical angular clearance on a die in sheet metal cutting?
0.25 to 1.5deg on each side, to allow the slug/blank to fall through.
50
What happens in sheet metal bending?
Material is compressed on one side of the NA, and stretched on the other side.
51
What's the difference between V-bending and edge bending?
V-bending is much cheaper than edge bending. V-bending is performed on a press brake, and edge bending requires a pressure pad.
52
What is deep drawing?
A method to make aluminum cans. A punch pushes some metal into a die
53
What is metal spinning?
Creating an axially symmetric part around a mandrel using a rounded tool or roller. Think salad bowl.
54
What is ironing, embossing, and the Guerin process?
Ironing's a process to reduce the wall thickness of a metal cup.
Embossing's a way to add indentations to a sheet.
The Guerin process is a way to shape sheet metal using a block of foam. It's a low-cost, low-production manufacturing method.
55
What is hydroforming?
A way to shape sheet metal or metal tubes into complex shapes using high pressure water.
56
What are two considerations when designing a sheet metal cutting/folding process?
1) Have parts that nest, to reduce scrap metal.
| 2) Cut notches to reduce possibility of buckling.
57
LEC 19 POWDER METALLURGY
| What is it, and what are the two typical steps?
A metalworking process where you sinter powder together.
1) Pressing into a "green compact"
2) Sintering at high temperature to bond powder together.
58
What are three benefits to powder metallurgy?
1) They can be produced to near-net shape, reducing the need for followup machining
2) Not wasteful - 97% of the starting powder is converted into the final product.
3) It can be used to create porous metal parts.
59
What are three things that make powder metallurgy important?
1) They can be used for hard-to-manufacture materials like tungsten.
2) They can be used to make certain alloys.
3) They can be used for high dimensional accuracy
60
What are three disadvantages to powder metallurgy?
1) They're expensive and dangerous
2) Part geometry can be limited by the flow of powder through a die
3) The density can vary through the part.
61
What are some common materials used in powder metallurgy?
Iron, steel, aluminum, copper.
| As well as refractory materials, like tungsten and molybdenum.
62
If you wanted to do PM from scratch (forming your own powder), what are the five steps?
1) Powder production
2) Blending powder
3) Pressing
4) Sintering
5) Finishing
63
What is the difference between true density and bulk density?
True density is the density of the metal - a "material property"
Bulk density is the density when you divide the volume of powder by the weight on the weighscale.
64
What are two ways to increase the packing factor?
1) introduce smaller powders to fit in between large ones
| 2) vibrate and compress the powder.
65
What are the four methods to powderize a metal?
1) Atomization
2) Chemical
3) Electrolytic
4) Mechanical methods.
66
What is atomization, and what are four factors that determine the powder size?
Atomization is when a stream of molten metal from a jet is dispersed by jets of air or water.
The size of particles are determined by the temperature, the speed of flow, the nozzle size, and jet characteristics.
67
What's the principal chemical method of creating metal powder?
Reduction. Allowing carbon monoxide and hydrogen to create with metals, and letting them decompose.
68
What's the principle electrolytic method of creating metal powder?
Aqueous solutions or fused salts. One of the best ways - lower an electrode into the solution, pass a current, and let the powder dissolve.
69
In powder metallurgy, what's the difference between blending and mixing?
Blending is the combination of different particle sizes of the same element to reduce porosity.
Mixing is the combination of different elements to create alloys.
70
In powder metallurgy, what two characteristics does a higher density impart?
1) A higher strength
| 2) A higher elastic modulus
71
In powder metallurgy, what's the difference between a single action press and a dual action press, and why?
In PM, the pressed side of a part has a greater density. The loading is not symmetrical, because the force isn't reliably transmitted throughout the powder. I think.
A dual action press ensures that both sides of the part have a greater density.
72
What's the two advantages of HIP over pressing and sintering?
What's one drawback?
1) HIP gets both done at once.
2) HIP can achieve 100% density
But HIP is high cost and low production.
73
At what temperature is sintering usually carried out at, and what usually happens to the part during sintering?
Usually between 70%-90% of the metal's melting point.
| The part usually shrinks, because of the "reduction of surface energy" and the shrinkage of pores.
74
What are the three typical stages of a continual conveyor-belt style sintering oven?
1) Burn-off
2) Actual sintering
3) Cooldown
75
What are three secondary operations that can be performed after a part is sintered?
1) Repressing to increase density or dimensional accuracy.
2) Coining
3) Machining parts like threads and side holes.
76
What's the difference between impregnation and infiltration?
Impregnation is when the part absorbs a fluid, such as oil.
Infiltration is when a molten metal is placed on the part surface, and capillary action draws the metal into all the pores in the part.
77
What are the four classes as defined by the Metal Powder Industries Federation?
Class I: Simple thin
Class II: Simple thick
Class III: Two thicknesses
Class IV: Multiple thicknesses.
78
What are four design considerations when designing a PM pressing operation?
1) Simple uniform shapes
2) Easy to eject
3) No walls less than 1.5mm thick
4) No sharp radii.
79
LEC 18 PART 2: GLASS/CERAMIC
| What are four characteristics of glass and ceramic?
1) Strength and hardness at high temperature
2) Chemically inert
3) Low conductivity to electricity and heat
4) Resistant to wear and corrosion.
80
What's one way to make thin ceramic sheets?
The doctor blade process. Use a thin film and a blade and a chamber of ceramic slurry to create your thin ceramic sheets.
81
What is plastic forming?
Squishing a clay slug between two dies.
82
What is dry pressing good for?
Simple shapes, high production rates, and strong dimensional control.
83
What is the difference between dry and wet pressing?
Wet pressing is performed under high pressure. It's expensive.
84
There are three finishing options and four unconventional ones for glass manufacturing. Can you name them all?
Grinding
Lapping/honing
Drilling
EDM
LBM
Ultrasonic
Abrasive water-jet cutting
85
How is glass formed?
By melting, blowing, shaping, molds.
86
What are the four categories of glass products?
Discrete products
Glass sheets
Glass rods/tubes
Glass fibers
87
What are three ways of forming glass sheets?
1) Float method, with a bath of tin.
2) Drawing method, with rollers
3) Rolling method, with rollers.
All involve molten glass.
88
How are glass tubes formed?
Air is forced through a tube and mandrel to keep the molten glass supported.
89
What are two ways of forming discrete glass products?
1) Blowing
| 2) Pressing (similar to a closed-die)
90
How are glass fibers made? And wool?
They are pulled through multiple orifices and wound together like yarn.
Glass wool can be made by centrifuge spinning molten wool through a rotating head.
91
What are three methods for strengthening glass after production?
1) Thermal tempering - cooling the outside of the glass first so that the surface is under heavy tensile stress.
2) Chemical tempering - infiltrating the glass with KNO3 and other chemicals that lend strength.
3) Laminating the glass with plastic or wire.
92
Do automobile windshields use tempered glass?
No, they do not. Complete shattering would prove dangerous. They use laminated windshields instead.
93
How long should the annealing process take, when compared to the glass thickness?
thickness ^ 2 (is proportional to) time
94
What are two ways to soften the edge of glass?
1) Grinding
| 2) Fire polishing
95
What are three considerations when designing glass?
1) It's stronger in compression than in tension.
2) It's brittle. Try to avoid using it in impact or high stress situations.
3) Try to design parts with large radii.
96
Can I include threads with my glass parts?
Yes, but they have to be course.
97
Can I use glass in high temperature applications?
Yes, but select the glasses with low thermal expansion coefficients.
98
LEC 20: PLASTICS FORMING AND SHAPING
| What are six uses of plastics?
```
Molding
Extrusion of cross-sections
Films
Sheets
Insulation for electrical wires
Fibers for clothing.
```
99
What are four advantages to plastics forming?
1) Almost unlimited part geometries
2) Cheaper; can be done at much lower temperatures
3) It's a net-shape process.
4) Painting/colouring is not required.
100
What's the difference between thermoplastics and thermosets?
Thermoplastics don't change chemical composition during heating. They comprise 70% of plastic tonnage.
Thermosets undergo a reaction when heated. They can't be recycled.
101
Plastics shaping processes can be classified as three continuous-product processes, two discrete product processes, and three other processes. What are they?
Continuous extruded cross-section
Sheets and film
Fibers
Solid mold
Hollow mold
Discrete product from sheet plastic
Casting
Foam products
102
What is a polymer melt?
It's a thermoplastic that's been melted to the consistency of liquid. It can be used in this form.
103
What's viscosity usually like in polymer melts, and what does it mean for our manufacturing process?
They're usually high, because of high molecular weights. We usually have small die openings and large flow rates, though, which means we need lots of pressure to overcome our viscous liquids.
104
What is viscoelasticity? What does this mean for our extruded shape?
The tendency for our polymer melt to expand the moment it's left the die. This means our die has to account for this - if you want a square shape, your die needs a starburst sort of shape.
105
What are the two main components of an extruder? Is the die a component?
Barrel, and screw.
| The die has to be specially manufactured for our part, so it's not considered part of the extruder.
106
What are the two methods used by an extruder to create the polymer melt?
1) Electrical heaters around the barrel.
| 2) Friction between the screw and the thermoplastic.
107
What are the three sections of a screw and their purposes?
1) Feed section - for accepting the thermoplastic and begin heating it
2) Compression section - material is compressed and heated further.
3) Metering section - for homogenizing the flow
108
What are three functions of the screen pack at the front of an extruder?
1) Filter out lumps or contaminants
2) Remove the melt's "memory" of the rotary movement.
3) build pressure before the die.
109
Plastics: What's the difference between extruding hollow shapes and wire/cable coating?
In a hollow shape, air is added to support the shape, while in wire/cable coating, air is removed to encourage the coating to stick to the wire.
110
Plastics: What's the difference between film and sheet?
Film is less than 0.5mm thick.
| Sheets are 0.5mm and thicker.
111
What are the three processes for producing film plastics?
1) Slit extrusion
2) Blown film
3) Calendaring
112
Compare and contrast the three processes for producing film plastics.
Slit extrusion makes sense, but there are difficulties with thickness control.
Blown film has good thickness control and isn't too expensive.
Calendaring is expensive, but posessess high production and great surface finishes
113
What is the definition of a fiber? And the definition of a film?
A fiber has a length at least 100 times as long as its cross-sectional length.
A film is 0.5mm or less.
114
Are fibers natural, or synthetic?
The market is currently sitting at 25% natural, 75% synthetic.
Cotton and wool mostly for natural.
As for synthetic, polyester, rayon, acrylics are common.
115
What is spinning?
The process of drawing polymer melt or solution through a spinneret, before winding them together onto a bobbin.
116
What are the three variations of spinning?
1) Melt spinning
2) Dry spinning
3) Wet spinning.
117
Compare and contrast the three types of spinning.
Melt spinning uses polymer melt. Dry spinning uses a solvent which can evaporate, while wet spinning uses an acid bath to coagulate the material.
Dry spinning is good for cellulose acetate and some acrylics.
Wet spinning is good for rayon and some acrylics.
118
Why is it important to further cold draw filaments after spinning?
The process aligns the crystal structures and gives the material more strength.
119
LEC 21 PLASTICS FORMING PART TWO
| Name three advantages and one disadvantage to injection molding.
1) Can create super intricate parts
2) Can create them super fast (10-30s sometimes)
3) Can create many at the same time
4) They're net shape
1) They're extremely expensive to tool
120
What are the three types of injection molding molds you saw in class, and how do they differ?
1) Two plate mold
2) Three plate mold
3) Hot runner mold
Two plate mold is the most basic, involving scrap runners and the actual part.
Three plate mold separates the runners from the parts.
Hot runner mold ensures no waste, through the use of a heated plate.
121
What are four ways to reduce shrinkage in plastic parts?
Really two ways, with three ways to accomplish the latter.
1) Add filler material to the plastic.
2) Pack more polymer melt into the mold, via
2a) Increasing the extrusion pressure
2b) Extruding more plastic into the mold
2c) Superheating polymer to be less viscous.
122
What are the two big differences between thermoset injection molding and thermoplastic injection molding?
The two differences aim to minimize premature setting.
1) Extruder barrels are shorter and aren't heated
2) The molds are heated.
123
What is Reaction Injection Molding?
A way to produce car bumpers. Two highly reactive materials are quickly mixed before rapidly being pumped into the mold.
124
What is compression molding?
It's the name for closed die forging with thermosetting plastics.
125
What are two benefits and two other characteristics of compression molding?
1) They're simpler than injection molding
2) They don't produce scrap runners
1) They're limited to simpler part geometries.
2) The mold must be heated.
126
What is transfer molding?
A process super similar to injection molding.
| A charge is placed in a heated area before a plunger drives it into the die.
127
What is blow molding, and two ways to accomplish it?
A way to form hollow objects like bottles. You start with a "parison" which is inflated to fit the mold.
1) Extrudate, where the tube is continually coming out
2) Injection molding, where the injection mold is swapped out for a blow mold after injection.
128
What are some things that are made from thermoforming?
Blister packs.
| Boat hulls, shower stalls, some toys.
129
What is plastic casting?
When you pour a liquid resin into a mold via gravity. Thermosets and thermoplastics both can be done this way.
130
What do you know about polymer foam?
1) There are open-cell and closed-cell types.
| 2) The most common are polystyrene and polyurethane.
131
What are two advantages and three disadvantages to using plastic over metal?
1) Plastics have good strength for their weight
2) They're good at absorbing impacts
1) They have a limited service temperature
2) They tend to "creep"
3) They're not as strong or stiff as metals.
132
What are some material properties of plastic in comparison to metal?
1) They don't rust
2) They degrade in sunlight sometimes
3) They degrade in oxygen-rich environments sometimes
4) Some solvent dissolve them
5) They have a high thermal expansion coefficient. :(
133
What are three ways to minimize distortion in plastic parts?
1) Keep a constant thickness when possible, to minimize shrinkage distortion. e.g. cut out a slot at a joint.
2) Add ribs
3) Add domes
134
```
In plastic extrusion design, what do you think about
a) Wall thickness
b) Hollow sections
c) Corners
?
```
a) Wall thickness should be kept constant when possible, and should be kept thin. Add ribs if needed. Thick sections, or uneven sections, tend to warp the final product.
b) Hollow sections should be avoided when possible. They're complicated to do.
c) Avoid them. They
i) interrupt smooth flow of melt, and
ii) create stress concentrations
135
In terms of production quantity, when should you go for injection molding and when should you go for compression molding?
Injection molding - at least 10 000 parts.
| Compression molding - at least 1000.
