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Mec130 > EVERYTHING > Flashcards

EVERYTHING Flashcards

1
Q

What is the basic equation for calculating the MRR of a machining process?

A

MRR = (Removed Volume)/(Cutting Time)

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2
Q

What is adhesive wear?

A

Adhesive wear is incurred when a tangible force is applied and causes a shearing force between two contacted surfaces. Growth forms on the tool as a result.

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3
Q

Name three advantages of additive manufacturing.

A
  • Waste is reduced/removed
  • Multi-material objects are possible
  • Energy is used more efficiently
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4
Q

Name two disadvantages of additive manufacturing.

A
  • Production rate is very slow and expensive.

- Strength in z axis can be limited.

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5
Q

What is dot spacing in AM?

A

The distance between dot centers in inkjet printing.

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6
Q

What is the “Two Solvent System”.

A

It is a solution to coffee staining. You mix two solvents of different boiling points together.

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7
Q

What is Brazing?

A

A joining process in which a filler metal is placed at or in between two surfaces to be joined.

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8
Q

In brazing. What is the relationship between lap distance and metal thickness.

A

Lap Distance = 1.25 * Metal Thickness

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9
Q

Name three advantages of Brazing.

A
  • It can join different types of metals (ferrous to non-ferrous for example)
  • Less heating is required as compared to welding. So it is quicker/more economical with a lower HAZ.
  • Virtually all materials can be joined by some sort of brazing metal
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10
Q

Name two disadvantages of Brazing.

A
  • Subsequent heating of the assembly can cause the filler metal to melt - destroying the joint.
  • Brazed joints fail when heat is applied to repair damaged assemblies.
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11
Q

What is Resistance Welding?

A

The heat required for welding is produced by electrical resistance across the two components to be joined.

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12
Q

What is the sequence of resistance welding?

A

1-Apply pressure
2-Turn on current
3-Turn off current, keep pressure on
4-Release pressure, leaving weld nugget

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13
Q

Name the advantages, disadvantages and applications of resistance welding.

A

Advantages: No consumable electrodes, shielding gases or flux needed. It is easy and fast.

  • Disadvantages: The equipment is complex and expensive
  • Applications: Sheet metal fabrication and automotive body assembly
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14
Q

What is Cold Welding?

A

Metals are joined by the application of pressure to the work-piece via dies or roles. You have a cladding metal and a base metal.

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15
Q

In cold welding, what properties do the two metals need for the best bond.

A

The best bond is obtained with two similar metals.

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16
Q

Name an application of cold welding.

A

Welding wire stock (splicing wires together).

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17
Q

In Ultrasonic Welding, what forces are the two components subject to?

A
  • A static normal force.

- An oscillating shearing (tangential) force

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18
Q

What does the shearing stress in ultrasonic welding cause?

A

Plastic deformation at the interface of the two components.

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19
Q

True or false. Melting/fusion occurs in ultrasonic welding.

A

FALSE. Neither occur.

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20
Q

What temperatures (think fraction) occur in the weld zone in ultrasonic welding?

A

The temperatures generated in the weld zone are usually 1/3 to 1/2 of the melting point of the joined metals.

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21
Q

What are three advantages of ultrasonic welding?

A
  • It is versatile and reliable
  • It can be used with non-metallic materials (like plastics)
  • It can be used with dissimilar metallic work-pieces
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22
Q

What other process is friction welding technically known as? Why?

A

A forging process. Because plastic deformation occurs.

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23
Q

What are the advantages of friction welding?

A
  • No consumable electrodes, shielding gases or flux are needed.
  • It can join a variety of materials
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24
Q

What is the kerf?

A

The width of a cut made by a saw

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25
Q

How does Explosive Welding work?

A

Pressure is applied by detonating an explosive layer placed over one of the two components. It is detonated in a progressive fashion.

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26
Q

What causes the wavy interface in explosive welding?

A

The kinetic energy of the plate striking the mating component.

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27
Q

Name the advantages of explosive welding.

A
  • The bond strength is high.

- The ability to join many combinations of different metals

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28
Q

Name an application of explosive welding.

A

Corrosion-resistant claddings on mild steel structures.

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29
Q

What is mechanical alloying and why is it used?

A

Powders of multiple metals are combined in a ball mill. The powders fracture and mix to form allow powders. It can give your final product specific mechanical properties.

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30
Q

What is communition?

A

You crush, mill or grind your metal to get a powder. It uses a hollow cylinder with large metal balls.

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31
Q

Describe ATOMISATION.

A

It is a method of powder production. A liquid stream of metal is ejected through a small orifice. A stream of water or inert gas will break up this stream into particles.

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32
Q

Why use powder metallurgy?

A
  • No material is wasted
  • It requires semi-skilled labour
  • The final product needs little to no finishing
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33
Q

Define machining.

A

The process of removing material from a work-piece in the form of chips.

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34
Q

Name the three types of milling.

A

Up-milling, down-milling and slab-milling

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35
Q

What is backlash?

A

It’s an excessive amount of clearance (play) between the hand wheel screw and the nut attached to the machine table or slide.

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36
Q

Describe face-milling in terms of axis of rotation?

A

The cutter is mounted on a spindle with an axis of rotation perpendicular to the work surface.

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37
Q

For diffusion welding, what does a low pressure and elevated temperature promote?

A

Void shrinkage and grain-boundary migration to form a metallurgical bond.

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38
Q

Describe diffusion welding/bonding.

A

Occurs when surfaces are held in contact under sufficient pressure and time under an elevated temperature. The bonding mechanism is atomic diffusion.

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39
Q

Name three advantages of diffusion welding.

A
  • The ability to join dissimilar metals
  • Useful for titanium welding in the aerospace industry
  • Furnaces with protective atmospheres can be used to produce high-quality joints.
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40
Q

What is the name of the powder compact in powder metallurgy and what are the names of the two different types of compaction?

A
  • GREEN COMPACT
  • CIP (Cold Isostatic Pressing)
  • HIP (Hot Isostatic Pressing)
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41
Q

What is powder rolling in Powder Metallurgy?

A

Powders are fed between two rollers and compacted to form a continuous strip.

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42
Q

Describe injection moulding in Powder Metallurgy.

A

Very fine metal powders are blended with polymer or wax-based binders and pressed. Moulded greens are heated to a low temperature to remove the binder and then sintered in a furnace - giving you the ability to produce very complex shapes.

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43
Q

Describe infiltration in Powder Metallurgy.

A

A slug of lower melting point metal is placed against the sintered part and heated. The molten slug infiltrates the pores by capillary action.

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44
Q

What is an advantage of Powder Metallurgy.

A

You get a pore-free part with a good density/strength.

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45
Q

Name the four types of chip.

A
  • BUE (Built up edge)
  • Continuous Chip
  • Discontinuous Chip
  • Serrated Chip
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46
Q

What is abrasion?

A

Abrasion is a method of machining that is used to remove small amounts of material from a surface in the form of chips

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47
Q

Describe a discontinuous chip and the conditions needed for one.

A

They consist of segments that may be firmly or loosely attached to each other.
Requirements:
-Brittle work-piece
-High depth of cut
-Low stiffness of machine tool
-Lack of effective cutting fluid
-Workplace materials that contain impurities

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48
Q

What does the plastic deformation from the shear stress of ultrasonic welding allow?

A
  • Good contact
  • A good solid-state bond
  • Break up of oxide films and contaminants
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49
Q

What is the process called that makes single-crystal silicon?

A

The Czochralski Process.

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50
Q

Identify a use of single-crystal casting.

A

Gas turbines and aircraft engines.

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51
Q

Name 4 advantages of single crystal casting.

A
  • High quality casts
  • Materials maintain their shape during different stages of operation
  • It eliminates grain-boundaries
  • It makes high-strength materials that will survive high temperatures
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52
Q

Describe down-milling.

A
  • The cutter rotation is in the same direction as the feed rate.
  • Chips decrease in thickness as the tool rotates through the work-piece.
  • You get a larger tool life and a lower clamping force
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53
Q

What is important to remember with cutting fluids.

A
  • Reducing the temperature maintains the tool hardness and extends the tool life.
  • Apply lots of coolant to wash away hot chips.
  • You want to re-use and collect about 99% of your cutting fluid.
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54
Q

What is Fixed Cost.

A

Cost that is fixed per batch, regardless of size.

Fixed Cost = Tooling + (Setup Time * MHR)

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55
Q

Describe Broaching.

A

It is used to machine internal surfaces like holes or keyways. It has multiple teeth with each tooth slightly larger than the previous. It uses a single pass to machine the workpiece

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56
Q

Define feed rate

A

The distance a tool travels per unit revolution of a workpiece

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57
Q

What is Planing?

A

A machine operation used to produce flat surfaces and large machine components

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58
Q

What is reaming?

A

Reaming is used to enlarge a hole to improve tolerance and surface finish

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59
Q

What is facing?

A

Facing produces a flat surface at the end of a part.

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60
Q

What is chip compression ratio?

A

A measure of how thick a chip has become compared to the depth of cut

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61
Q

What direction does the thrust force act for a tool on a workpiece.

A

Perpendicular to the workpiece.

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62
Q

What is the purpose of the cutting force (Fc) for chip formation?

A

It acts in the direction of the cutting speed and supplies the energy required for cutting.

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63
Q

When machining, what happens if the thrust force is too high or the machine tool isn’t sufficiently stiff?

A

The tool will be pushed away from the surface which will reduce the depth of cut.

64
Q

What two things can be used to measure cutting forces?

A
  • Dynamometers
  • Force transducers

These are both mounted to the workpiece

65
Q

Where does flank wear occur?

A

At the relief face of the tool.

66
Q

What is the F.W. Taylor equation for tool life?

A

VT^n = C

  • V = cutting speed
  • T = Time it takes to develop flank wear
  • n = an exponent that depends on tool and workpiece cutting conditions
  • C = a constant, the cutting speed at T=1
67
Q

Describe crater wear.

A

It occurs on the rake face of a tool. It is a diffusion process - a movement of atoms across the chip-tool interface.

68
Q

Describe the two main influences of crater wear.

A
  • Tool-chip interface temperature.

- Chemical affinity between the tool and workpiece material.

69
Q

What are the four desirable characteristics of a cutting tool?

A

> Hardness - for good cutting at an elevated temperature
Toughness - so that impact forces don’t fracture the tool
Wear resistance - to achieve an acceptable tool life
Chemical inertness - so that adverse chemical reactions to decrease tool life are avoided

70
Q

What are the top and bottom parts of the mould in sand -casting called?

A

TOP - COPE

BOTTOM - DRAG

71
Q

What is the flask in sand-casting?

A

The frame that holds the entire moulding assembly together.

72
Q

What is the pouring cup in sand-casting?

A

The entrance for molten material.

73
Q

What is the sprue in sand-casting?

A

A channel used to deliver molten material.

74
Q

What is the gating system in sand-casting?

A

A channel used to deliver molten material to the mould cavity.

75
Q

What is the riser in sand-casting?

A

An extra void (part of the gating system) created to be filled with molten material.

76
Q

What is the core in sand-casting?

A

A sand/metal shape used to produce an internal feature of a casting.

77
Q

What is the core print in sand-casting?

A

An area used to locate and support the core within a mould.

78
Q

What is the draft in sand-casting?

A

Taper on a casting that permits the casting to be withdrawn from the mould.

79
Q

What is the pattern in sand casting?

A

It’s a replica of the object to be cast. It is used to form the mould cavity.

80
Q

In sand casting, what are the main objectives of the gating system?

A
  • To ensure a continuous and uniform flow of metal into the mould cavity.
  • To form a reservoir of molten metal to feed into the casting and shrinking takes place
  • To protect the metal from oxidation
81
Q

Name three applications of sand casting.

A
  • Pipelines
  • Valves
  • Railway wheels
82
Q

Name four advantages of sand casting.

A
  • Low cost
  • Almost all metals and polymers can be cast
  • No weight/thickness limit
  • Complex shapes can be made
83
Q

Name three disadvantages of sand casting.

A
  • High porosity
  • Rough surface finish
  • Low dimensional accuracy
84
Q

Why do you need to consider the effect of pouring in sand casting?

A

The mould must be able to resist the EROSIVE ACTION of pouring.

85
Q

In investment casting, what is a pattern?

A

It is a modified replica of your final product?

86
Q

For investment casting, what is the sacrificial replica made from?

A

Wax

87
Q

For investment casting, what happens after the wax is melted and poured out of the investment mould?

A

The mould is pre-heated and molten metal is poured into it.

88
Q

What is the main difference between disposable and permanent mould casting?

A

With disposable mould casting, you always break the mould.

89
Q

Why pre-heat moulds in investment casting?

A
  • To cure moulds
  • To ensure complete wax removal
  • To provide dimensional control because the mould and metal shrink during cooling
90
Q

Name some applications of investment casting.

A
  • Making gears/valves.
  • Titanium aircraft engine/structural airframe
  • Bio-engineering components
91
Q

What are the advantages of investment casting?

A
  • Excellent surface finish
  • High dimensional accuracy
  • Almost unlimited intricacy
  • Most metals can be cast
  • No flash or parting-line concerns
92
Q

What are the disadvantages of investment casting?

A
  • Costly patterns and moulds.
  • High labour costs
  • Time consuming
93
Q

True or false: OVER 70% OF ALL METAL CASTINGS ARE PRODUCED VIA A SAND CASTING PROCESS.

A

TRUE!

94
Q

What is an abrasive?

A

It’s a small, non-metallic hard particle with sharp edges. It’s irregular in shape.

95
Q

Why do you bond abrasives together?

A

For a higher material removal rate.

96
Q

What type of bond do you want for abrasives?

A

Strong, stiff, resistant to oil, acid and water.

97
Q

Why do you want porosity in your abrasives?

A

It provides clearance for minute chips being produced and allows for cooling.

98
Q

How does ultrasonic machining work?

A

The tip of the tool vibrates at a high frequency. This drives abrasive grains at a high velocity into the workpiece.

99
Q

What process is ultrasonic machining best suited for?

A

Hard and brittle materials.

100
Q

Name five examples of abrasive finishing operations.

A
  • Sanding
  • Honing
  • Lapping
  • Polishing
  • Electropolishing
101
Q

What is honing?

A

This is a stock-removal process using abrasive stones to remove very small amounts of metal.

102
Q

Name three uses of honing.

A
  • Size and finish bore holes
  • Remove errors left by boring
  • Remove tool marks left by grinding
103
Q

What is lapping?

A

It is a process wherein fine abrasive particles are embedded into a relatively soft material called a lap

104
Q

For polishing, what do you coat your leather/fabric with?

A

Aluminium oxide or diamond.

105
Q

In electropolishing, is the workpiece the anode or the cathode?

A

The anode

106
Q

How does electroploshing work?

A

The workpiece is submerged in an electrolyte and a DC circuit is constructed. The material on the workpiece is oxidised and dissolved by the workpiece.

107
Q

What is an advantage of electropolishing?

A

It is suitable for polishing irregular shaped workpieces.

108
Q

Why can’t powder-metallurgy be used to produce thin sections?

A

The thin parts may distort during sintering.

109
Q

Why is die casting used for large batch production.

A

Because one die can be used thousands of times over.

110
Q

Why do you want to cool your dies in die casting?

A

To improve die life and aid rapid cooling.

111
Q

What materials is hot-chamber die casting commonly used for?

A

Zinc, tin and lead-based alloys

112
Q

Can hot chamber die casting be used for high-melting point metals.

A

NO

113
Q

What are the advantages of die casting.

A
  • Fast cycle times
  • Excellent precision and surface finish
  • Good strength product
114
Q

Do finishing teeth on broaching tools count towards the MMR?

A

No

115
Q

What is the HAZ?

A

It is a region either side of the weld zone that has been subject to large temperatures and undergone metallurgical changes as a result.

116
Q

Name to property changes that happen in the HAZ.

A

> Embrittlement

>Re-crystallisation

117
Q

How do you reduce the severity of the property changes that occur in the HAZ?

A

Preheat your metal.

118
Q

True or false: Components made from single-crystal casting don’t suffer from thermal creep?

A

TRUE

119
Q

What is the masking process in chemical machining|?

A

An etch-resistant maskant is used to cover a certain region of the workpiece. The uncovered region is exposed for etching.

120
Q

What is stripping in chemical machining?

A

The maskant is removed from the workpiece and its surface is cleaned.

121
Q

What are the four steps in chemical machining?

A
  • CLEANING
  • MASKING
  • ETCHING
  • STRIPPING
122
Q

What does the photo-resist do in chemical machining and what types are there?

A

Serves as a mask.

  • Dry-film photoresists
  • Liquid photoresists
123
Q

What are the advantages of chemical machining?

A

> It is simple and no high-skilled labour is needed
It induces no stress in your workpiece
-Large areas can be machined
-You can machine any shape
-Thin sections can be machined
-Suitable for materials that can’t sustain a large cutting force

124
Q

Name two disadvantages of chemical machining

A
  • Dangerous chemicals are handled which can result in injury or harmful by-products
  • The MRR is slow
125
Q

True or false: In electro-chemical machining, the tool is the cathode and the workpiece is the anode.

A

TRUE

126
Q

What is the main concept of electro-chemical machining?

A

The tool advances into the workpiece at a constant penetration rate that matches the deplating rate of the workpiece

127
Q

Besides being conductive, what is the purpose of the electrolyte?

A

To wash away metal ions that have left the workpiece. The sludge will be captured and removed from the electrolyte through filtration.

128
Q

What are the advantages of Electro-Chemical Machining?

A
  • Well suited for machining complex shapes and conductive materials that can’t withstand high machining forces.
  • Good surface finish.
  • No residual stress left in the machined surface
  • No tool wear developed
129
Q

What are the disadvantages of Electro-Chemical Machining?

A
  • Preparation of tool electrode can be time consuming and costly
  • You have damaging by-products that are hard to dispose of
130
Q

In Water Jet Cutting (WJC), what pressure is the water fired at the workpiece?

A

Up to 400MPa - producing a jet velocity faster than the speed of sound!

131
Q

What are the two main advantages of WJC?

A
  • Inexpensive

- The ability to cut materials without burning or crushing

132
Q

What are the disadvantages of WJC?

A
  • It’s noisy, you need ear protection
  • It can’t be used on brittle materials as they’ll just crack
  • It’s not powerful so you’re limited to thin sheets
133
Q

Why would you use abrasive WJC instead of regular WJC?

A

It can cut through thicker materials (up to 8 inches)

134
Q

What happens in AFM (abrasive flow machining)?

A

Pistons drive a gel (laden with abrasives ) back and forth through a workpiece.

135
Q

Why would you use AFM?

A

For polishing and deburring features normally inaccessible in internal passageways.

136
Q

What is the green compact equation?

A

Vs=Vg(1-lchange/lo)^3

137
Q

Describe Injection Moulding.

A

Very fine powders are blended with polymer/wax based powders and compressed to make the moulded green. This is then heated to remove the binder and sintered in a furnace.

138
Q

In continuous casting, why is a mould flux added to the top of the steel?

A

To provide lubrication and control heat transfer. They also provide thermal insulation.

139
Q

What is the formula for MRR for a broaching tool?

A 
MRR=R*N*W*V
R=Rise per tooth
N=Number of roughing teeth in contact with a part
W=Width of broaching tool
V=Velocity of broaching tool
140
Q

What is extrusion in powder metallurgy?

A

It’s a compaction method. Powders are encased in a metal die and extruded.

141
Q

Name three applications of slush casting.

A
  • Hollow castings
  • Ornamental objects
  • Silicon props in the film industry
142
Q

What are the four main steps of slush casting?

A

1) Pour molten material into the mould
2) Allow desired skin thickness to develop with time, invert the mould to pour our remaining liquid
3) Open mould halves
4) Remove casting

143
Q

What does turning produce?

A

Straight, conical, curved or grooved work-pieces such as shafts, spindles pins and handles.

144
Q

What are the four different types of turning.

A

Straight, taper, contour and form.

145
Q

What is drilling usually followed by to improve accuracy?

A

BORING

146
Q

What is parting?

A

One section of a workpiece is severed from the remainder by means of a cut-off tool

147
Q

In lathing, what is knurling?

A

Producing a regularly shaped roughness on a cylindrical surface.

148
Q

For lathing, what is the equation of MRR?

A

MRR=Nsfrdpi(D1+D2)/2

149
Q

For slab-milling, what is the MRR equation?

A

MRR=wfmd
w=width of the workpiece
fm=feed of table
d=depth of cut

150
Q

What is the most common type of milling machine? Identify the six parts to it.

A
  • Column knee construction
  • COLUMN
  • KNEE
  • TABLE
  • SADDLE
  • SPINDLE
  • BASE
151
Q

Does up-milling give a good or a bad surface finish?

A

Bad

152
Q

What is cheaper, planing and shaping or milling and grinding?

A

Planing and shaping. However they have been mostly replaced by milling and grinding.

153
Q

What does a boring machine do?

A

Enlarge a hole that has already been cut.

154
Q

Is Aluminium suited for HIP or CIP die casting why?

A

Aluminium has a high melting and boiling point, hence it is only suitable for CIP casting. You use low boiling point metals for HIP casting.

155
Q

In terms of the economics of machining, what is the typical proportion of time the workpiece spends on the machine?

A

5%.

The other 95% is spent moving and waiting.

156
Q

What is a serrated chip and what conditions are needed for one?

A

Semi-continuous chips with high and low shear strain zones.

  • Workpiece with a low thermal conductivity
  • Strength that decreases sharply with temperature
157
Q

Discontinuous chips.

A

Segments that are loosely attached to each other.

  • High depth of cut
  • Brittle material
  • Lack of effective cutting fluid
  • Very low or very high cutting speeds
  • Low machine tool stiffness

Mec130 (1 decks)

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