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Manufacturing Technology > Manufacturing Technology - Part A Content (Disposable mold casting, Powder metallurgy, Milling, Abrasive machining, Resistance & solid state welding) > Flashcards

Manufacturing Technology - Part A Content (Disposable mold casting, Powder metallurgy, Milling, Abrasive machining, Resistance & solid state welding) Flashcards

1
Q

Sand Casting - The main objectives of the gating system are to?

A
  • Ensure a continuous and uniform flow of metal into the mould cavity without turbulence
  • To protect the metal from oxidation

-To form a reservoir of molten metal which feeds the
casting as shrinking takes place

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2
Q

Sand Casting - When producing a mold the following criteria must be considered:

A

The weight of the component – the mould must be
strong enough to hold the final casting

The effect of pouring – the mould must be able to resist the erosive action of pouring

The temperature of the molten metal – the mould must
be able to withstand the high temperatures required.

Clean removal of the casting from the mould –
Trapped gasses must be able to escape

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3
Q

What are the Applications of Sand Casting?

  • general
  • specific
A

Sand casting is extensively used, for cast iron and steel parts of medium and large size where surface smoothness and dimensional precision are the main concerns

  • Pipelines
  • valves
  • heavy
  • machinery
  • industrial tooling
  • pressure-containing components
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4
Q

Sand Casting – Advantages

A
  • Low cost
  • Almost all engineering metals can be cast
  • No limit on maximum weight and thickness
  • Able to produce complex shapes
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5
Q

Sand Casting – Disadvantages

A

High porosity
Rough surface finish
Low dimensional accuracy

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6
Q

Investment Casting - Explain the process

A

Uses a pattern that is a modified replica of the product

Pattern is used to make a steel die

Die produces a sacrificial replica of the product using wax

Replica dipped into ceramic investment material or placed into a flask and material is poured around it
Left to harden creating a mould

Wax replica is melted and poured out of the mould

Mould is pre-heated and filled with molten metal

Mould is broken away from finished product

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7
Q

Investment Casting – How are wax patterns made?

a) wax patterns
b) alternate materials
c) what about cores?

A

a) By pouring molten wax into a master die or injecting
it under pressure and allowing it to harden

b)Plastic and frozen mercury can also be used as
pattern material

c) When cores are required, they can be made from
soluble wax and ceramic

-Soluble Wax Cores are dissolved from the patterns
prior to investment coating

-Ceramic Cores remain as part of the wax pattern
and are removed from the casting during
cleaning

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8
Q

Investment Casting – Explain the initial coating stage

A

The cluster is dipped or ‘invested’ into a watery slurry of finely ground ceramic refractory material

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9
Q

Investment Casting – Explain the final coating stage

  • what coating?
  • how long, how many times?
A

The cluster is re-dipped into watery slurry with a
layer of sand and allowed to dry

Then repeated until coating is in the desired
thickness (ranging between 5 -15mm)

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10
Q

Investment Casting – Explain the Hardening & Material removal stage

A

The investment is then left to harden, can take 16 to 48 hours

The moulds are placed upside down in an oven to melt
the wax and allow other residue to vaporise

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11
Q

Investment Casting – explain the pouring stage

A) how hot?
B) why?

A

A) The moulds are heated up to 550 - 1100°C

B)
-ensure complete removal of wax material

-cure moulds to give added strength

-allow molten metal to retain its heat and
flow readily into all thin sections

-Ensure the mold and metal shrink together, hence ensure dimensional accuracy

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12
Q

Investment Casting - Explain the Removal of Castings stage

a) removal techniques used
b) post removal procedure

A

a) Techniques used include mechanical vibration and
high-pressure water

b) Castings are then removed from the sprue and gate
stubs are ground off

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13
Q

Investment Casting – Applications

a) General
b) specific examples

A

A)

Products where high dimensional accuracy and surface finish is required

B)
-Mechanical components such as gears, valves,
precision housings

  • Titanium aircraft-engine and structural airframe
  • Bio-engineering components
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14
Q

Investment Casting – Advantages

A
  • Excellent surface finish
  • High dimensional accuracy
  • Almost unlimited intricacy
  • Most metals can be cast
  • No flash or parting line concerns
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15
Q

Investment Casting – Disadvantages

A
  • Costly pattern and moulds
  • High labour cost
  • Time consuming
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16
Q

Powder Metallurgy - What are the stages in powder metallurgy?

A
  • Powder production
  • Blending
  • Compaction
  • Sintering
  • Finishing operations
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17
Q

Powder Metallurgy - What are the 4 types of powder production?

A
  • Comminution
  • Electroplating
  • Atomisation
  • Chemical reduction of powdered metal oxides
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18
Q

Powder Metallurgy - Explain Comminution

A

It is a mechanical process involves crushing, milling or
grinding

Often Small particles are produced using a ball mill

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19
Q

Powder Metallurgy - Explain Atomisation

a) process
b) what variable can be controlled and how?

A

a)
1) A liquid-metal stream is ejected through a small
orifice

2) The stream is broken up by jets of inert gas, air, or
water to create small particles

b)

The size of particles depends on the temperature of
the metal, rate of flow, nozzle size, and jet
characteristics

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20
Q

Powder Metallurgy - Explain Chemical reduction of powdered metal oxides (powder production)

a) Process, what gases are used?
b) What characteristics associated with this process?

A

A) Gases such as hydrogen and carbon monoxide
are used as reducing agents for metal oxides

B) Powders produced are spongy and porous, with
uniformly sized spherical or angular shapes

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21
Q

Powder Metallurgy - What factors should be considered when blending powders?

a) factors to consider
b) what characteristics are only found in metal parts produced through powder metallurgy?
c) why and how are powders mixed?

A

a)

  • selecting good particle size distribution
  • using suitable lubricant

b) lubricants are applied to the powders to create ‘self lubricating parts’ such as bearings.

c)
- to achieve specific characteristics, create hybrids.
- mixed in a ball mill to achieve uniformity

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22
Q

Powder Metallurgy - Compaction

a) what are the 5 common types of compaction?
b) what is the pressed powder called?
c) what factors can be controlled by compaction
d) how are internal geometries formed

A

a)

  • Cold Isostatic Pressing (CIP)
  • Hot Isostatic Pressing (HIP)
  • Powder Rolling
  • Extrusion
  • Injection molding

b) Green compact
c) Density, dependant on pressure applied
d) through use of a core rod

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23
Q

Powder Metallurgy - Explain Cold Isostatic Pressing (CIP)

A

Metal powders are placed in a flexible rubber mould and then pressurised hydro-statically in a chamber

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24
Q

Powder Metallurgy - Explain Hold Isostatic Pressing (HIP)

a) Process
b) Advantages

A

A)

1) A die is made of a high melting point metal
2) Inert gas is used as the pressurisation medium

B)
- produce compacts with 100% density
-produce good metallurgical bonding among
particles

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25
Q

Powder Metallurgy - Explain Powder rolling, Injection molding & extrusion

a) Powder rolling process
b) Injection molding process & advantages
c) extrusion process

A

a) Powders are fed through the gap between rollers
in a two-high rolling mill and compacted into a
continuous strip

b)
1) Very fine metal powders are blended with
polymer or wax-based binder and then
pressed
2) Moulded greens are placed in a low
temperature oven to remove the binder
and then sintered in a furnace
- Can be used to produce complicated shapes

c)Powders are encased in a metal die and extruded

26
Q

Powder Metallurgy - Sintering

A) Explain the basic principle
B) What preventative measures are taken?
C) What is achieved through sintering?
D) What negative effects occur?

A

A)

  • compressed metal powders are heated in controlled atmosphere to a temperature BELOW THERE MELTING POINT
  • Bonding occurs through diffusion

B) Protective atmosphere is employed to prevent oxidisation

C)

  • Porosity is decreased
  • Density, Strength & conductivity are increased

D) shrinkage occurs hence allowances should be made for this.

27
Q

Powder Metallurgy - Explain the 5 common types of finishing process

a) Open die forging
b) Closed Die Forging
c) Coining
d) Infiltration
e) Plating

A

a) Open die forging - deforming a piece of metal between multiple dies that do not completely enclose the material
b) Closed Die Forging is a forging process in which dies that contain a precut profile of the desired part move towards each other and covers the workpiece in whole
c) Coining - the the slug is coined in a completely closed die cavity
d) Infiltration - used to increase density and eliminate porosity. A slug of a lower melting point metal is placed next to the product and heated. the metal is drawn within the shape and fills the pores.
e) Plating - This is a coating process that imparts resistance to wear and corrosion, high electrical conductivity, better appearance and reflectivity and other desirable properties

28
Q

Powder Metallurgy - what are the 5 common types of finishing process

A
  • Open die forging
  • Closed Die Forging
  • Coining
  • Infiltration
  • Plating
29
Q

Powder Metallurgy - Advantages vs Disadvantages

a) Advantages
b) Disadvantages
c) what is a justifiable production volume?

A

a)
- Products are produced at near net shape to
eliminate scraps

  • Properties can be easily controlled
  • eliminates many secondary machining costs

b)
-products have lower tensile strength then
those wrought of a similar composition

  • initial cost for punches, dies, and
    equipment is high

c) 10,000 + Units to break even

30
Q

What products are made through powder metallurgy?

A
  • gears
  • cams
  • bushes
  • cutting tools
  • porous products (e.g., filters, oilimpregnated
    bearings) and piston rings
31
Q

Machining - Geometry of chip formation

A) What are the 3 angles associated with chip formation and what do they represent
B) what effect does changing the subsequent angles have?

A

A)

  • Rake angle, (α) - the angle between the tool face and the vertical
  • Shear angle, (ϕ) - the angle between the shear plane (Perpendicular to the tool face) and the workpiece
  • Relief angle - the angle between the flank (underside of the tool) and the work piece

B)

  • High rake angle/small shear angle is associated with high shear stress, and thick chips
  • small relief angle results in tool damage
32
Q

Machining - what are the four types of chip? describe each and there characteristics.

A
  1. Continuous
  2. Build-up edge (BUE)
  3. Serrated
  4. Discontinuous
33
Q

Machining - Describe continuous chips and there formation

A
  • formed with ductile materials at high cutting speeds and/or large rake angles
  • result in good surface finish but not always desirable (may become entangled)
34
Q

Machining - Describe Build up Edge chips and there there formation

A
  • Formed at the tip of a tool during cutting Consists of layers of material from the work-piece that are gradually deposited on the tool, BUE grows with time and eventually breaks off
  • Generally undesirable, as the BUE is deposited on the work-piece surface
  • Can be desirable to have stable BUE as it protects the tool
  • occurs at small rake angles
35
Q

Machining - Describe Serrated chips and there there formation

A
  • chips are relatively continuoius
  • occurs in materials with a low thermal conductivity
  • occurs in weak materials
36
Q

Machining - Describe discontinuous chips, there formation and characteristics

A

-Consists of segments that may be firmly or
loosely attached to each other
-Generally bad as the discontinuous nature causes the tooling to vibrate hence damage the workpiece.
-Occurs under the following conditions: (generally negative attributes)
Brittle
Work-piece contains impurities
High depth of cut and small rake angle
Lack of cutting fluid

37
Q

Machining - Describe the two types of tool wear

A

1) Adhesive wear - part of the workpiece will adhere to the tool under conditions where the temperature is raised, e.g friction. the adhesions will break off taking part of the tool with them.
2) Abrasive wear, tool is worn down through contact with the workpiece

38
Q

Machining - Define material removal rate (MRR);

A

MRR = The volume of material removed per unit time

39
Q

Milling - what are the 3 types of milling and the 2 subgroups within each type

A

1) Slab Milling
2) Face Milling
3) End Milling

-within each category there is also Up & Down milling

40
Q

Milling - what Is Slab milling and how is the MRR calculated?

A
  • Slab milling involves the tool rotating parallel with the work-piece.
  • The MRR is found by calculating the volume of material removed W x D. and multiplying it by the table feed rate. ‘‘fm’’.

MRR = (W x D) x fm

Note: fm can be calculated in different ways

1) feed per tooth x Number of teeth x cutting speed.
2) (Length of table + approach) / time taken

-Approach distance must also be considered.

41
Q

Milling - what Is face and end milling and how is the MRR calculated?

A
  • Face Milling & End Milling - The cutter is mounted on a spindle having an axis of rotation perpendicular to the work-piece surface
  • Face Milling is used similar to a planer, to create a flat surface
  • End Milling involves a smaller tool and can be used to cut shapes within a work-piece.
  • Overrun should be allowed for when calculating the MRR, Must be greater than half the width of the tool.
42
Q

Milling - what Is UP milling and what are the advantages and disadvantages?

A) Process
B) Advantages
C) Disadvantages

A

A)
- the cutter rotates against the feed direction of the
work-piece, hence the thickness increases with cut.
- known as conventional milling

B) Less load on the tooling as load increases gradually

C) Poor surface finish, Damage to tool, loosens the workpiece

  • Poor surface finish, as the Tooth initially slides along surface until the pressure on the material is enough to start cutting
    -Sliding action causes work hardening on the material and can dull the cutting edges
    -Chips can also be carried onto the newly machined
    surface contributing to a poorer (rougher) surface
    finish
    -The cutter pushes the workpiece away and lifts it
    from the table
43
Q

Milling - what Is DOWN milling and what are the advantages and disadvantages?

A) Process
B) Advantages
C) Disadvantages

A

A)
- the cutter rotates with the feed direction of the
work-piece, hence the thickness decreases with cut.
- known as climb milling

B)
-No slide-cut mechanism so tool life is longer
-Chips are carried away from the cutting surface so
cannot impair surface finish
-The cutter pulls a work-piece towards itself and
pushes the work-piece down onto the table

C) Higher load on the tooling as load is sudden

44
Q

Machining - Define Backlash

A

Backlash refers to the “play” or excessive amount of clearance between the machine hand wheel screw and the nut attached to the machine table or slide.

45
Q

What is a metal planer used for?

A
  • Achieves the same outcome as face and slab milling, but in a linear form.
  • used to cut grooves in a metal sheet. Successive metal grooves will ‘plane the surface’
  • A tool similar to a turning tool is used, the work-piece is moved beneath the tool and the tool cuts from the metal.
46
Q

how does metal shaping differ from metal planing? why would you use shaping/planing over milling?

A
  • In shaping, the tool moves whilst the work-piece remains stationary.
  • Metal shaping is used for smaller work-pieces.

-Shaping and planing are cheaper than milling, however milling is more prominent in industry

47
Q

Explain the broaching technique. what is RPT?

A

-Used to machine internal and external surfaces i.e. holes
-Uses a broach tool
-Has multiple teeth, with each tooth standing
slightly higher than the previous tooth
-Uses a single pass to machine the work-piece
-The feed per tooth is the change in height of two
successive teeth called rise per tooth (RPT)

48
Q

Abrasive machining - Bonded Abrasives

  • what is it made from?
  • describe its structure? why is it like this?
  • how strong are the bonds?
  • where are they used?
A
  • Made from clay and feldspar grains
  • Vitrification process is carried out to form a glass like, porous structure, the porosity allows for removal of heat
  • If the bonds are too strong, dull particles will not break off to be replaced by sharper grains
  • too weak and the structure will not hold.

Grind wheels, sand paper…

49
Q

Ultrasonic machining
what is it and how does it work?
where is it used?
what are the limitations?

A

A form of abrasive machining where the tool vibrates at a high frequency of 20KHz. a abrasive slurry containing abrasive grains is driven at the work-piece which causes micro-chipping and erosion through impact stresses.

Used with hard brittle materials e.g (glass, ceramic, precious stones…)

Limited as each job requires a specific tool

50
Q

What are the 5 main abrasive finishing techniques? explain them.

what specific materials are used in some of the process’?

A

1) Sanding - grains are electro-statically deposited on a backing material

2 )Honing - uses an abrasive stone to remove metal, often used in engine cylinders to remove the errors of boring

3) Lapping - two materials rubbed together with abrasive between them. can be a lapping pad or a production lapping technique, where a circular plate with grooves is used
4) Polishing - uses discs or belts with fine powders of aluminium oxide or diamond
5) Electro-polishing - opposite of electroplating, the workpiece is the anode, the material is dissolved by the the electrolyte.

51
Q

What is resistance welding? what is the most common type of resistance welding?

A
  • The heat required for welding is produced by electrical resistance across two components to be joined
  • Resistance Spot Welding is the most common resistance welding method
52
Q

What are the advantages/disadvantages of RESISTANCE welding? where is it applied?
A) Advantages
B) Disadvantages
C) Applications

A

A)
-Does not require consumable electrodes, shielding gases or flux

-Easy and fast

B)
-Complex and expensive equipment

C)

  • Sheet metal fabrication
  • Automotive body assembly
53
Q

What is solid state welding? where does it work best? what are the five types?

A
  • Welding at temperatures below the melting point
  • Works best for ductile materials
  • Cold Welding
  • Ultrasonic Welding
  • Friction Welding
  • Explosion Welding
  • Diffusion Welding / Bonding
54
Q

What is COLD welding? what are the characteristics? where is it applied?
A) Describe the Process
B) What are the bond characteristics?
C) what are its applications (general & specific)?

A

A)

  • Pressure is applied to the work-piece either through dies or rolls
  • Plastic deformation takes place
  • It is necessary that at least one, but preferably both mating parts be ductile

B)
-weak joints, particularly weak & brittle when different metals are used

C)

  • Cold welding is used to join small work-pieces made of soft, ductile metals
  • Welding wire stock (splicing wire together) e.g. barbed wire
55
Q

What is ULTRASONIC welding? what are the Advantages? where is it applied?
A) Process
B) Advantages
C) Applications (general & specific)

A

A)

  • Normal force shear stress and are applied to the weld site by an oscillating tool
  • The product is a good solid state bond
  • the process breaks up contaminants so less cleaning is needed

B)

  • Versatile and reliable
  • Can be used with a wide variety of materials, Dissimilar metals. Non-metals
  • Cheap

C)

  • Lap welding of sheet, foil, and thin wire (automotive)
  • Foil packaging
  • Plastics
56
Q

What is FRICTION welding? what are the Advantages? where is it applied?
A) What are the two types?
B) Advantages
C) Applications (general & specific)

A

A)
1)
-One component remains stationary
Other is placed in a chuck/collet and is rotated at a constant high speed
-The two components to be joined are brought into contact under increasing force
-A weld is formed however ‘flashing’ needs to be removed by grinding, this is metal build up at the weld site
2)
-Workpiece remains stationary
-Rotating tool forced onto joint area and traverses its entire length
-Material plastically deforms and fuses together

B)

  • Does not require consumable electrodes, shielding gases or flux
  • Produces a strong joint

C)
- used for solid tubular parts primarily

57
Q

What is EXPLOSIVE welding? what are the Advantages? where is it applied?
A) process, what causes the welding?
B) Advantages
C) Applications (general & specific), what materials?

A

A)

  • An explosive film is placed over the top surface to be welded
  • The pressure of the explosion is what causes the welding
  • The weld produced has a ‘wavy’ appearance

B)

  • High bond strength
  • Ability to join numerous combinations of dissimilar metals

C)

  • High strength joints between aluminium, copper and stainless steel
  • used for cladding, e.g corrosion resistant cladding for stainless steel.
58
Q

What is DIFFUSION welding? what are the Advantages? where is it applied?
A) process, what causes the welding?
B) What are the joint characteristics, how can they be improved?
C) Applications (Specific)

A

A)
- Atomic diffusion occurs when surfaces are held in contact under sufficient pressure and time at elevated temperature

B)

  • Ability to join dissimilar metals
  • Furnaces with inert/protective atmospheres can be used to produce high quality joints

C)
-Titanium welding in aerospace industry

59
Q

What is crater wear? what factors affect crater wear?

A

crater wear in which contact with chips erodes the rake face. This is somewhat normal for tool wear

  1. The temperature at the tool-chip interface
  2. The chemical affinity between tool and work-piece material
60
Q

What causes the tool to be pushed away from the workpiece? how can it be resolved?

A
  • Thrust force too high
  • Machine tool is not sufficiently stiff

-Can be resolved by reducing the depth of cut

Manufacturing Technology (2 decks)

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