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MATERIALS M3 > EXTRA EXTRA > Flashcards

EXTRA EXTRA Flashcards

1
Q

reasons for joining?

A

Economy
Ease of Transport
Ease of assembly

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2
Q

Difference between riveting and bolting?

A

Riveting involves shearing and thus shear stresses are present in the joint. Bolting can be thought of as clamping and so there are no shear stresses present. Thus bolting is stronger than riveting.

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3
Q

Selection criteria of joining processes?

A

Joint design and geometry, appearance, strength, materials, cost and availability, mobility of equipment, disassembly and accessibility to make the joint.

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4
Q

Advantages of welding?

A
  1. Lighter joints -> material savings
  2. Short production times
  3. More accurate joints (could be but not always)
  4. Tight, leak proof joints (compared to bolted)
  5. Cheaper production (compared to casting)
  6. Versatility
  7. Wide applicability
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5
Q

Definition of fusion welding?

A

A metal joining process where fusion is obtained by heat and pressure to create a metallurgical bond at atomic level. Thus vapours and oxides on contacting surfaces must be overcome.

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6
Q

Welding difficulties?

A
  1. Localised heat input and rapid cooling rates
  2. Non-equilibrium solidification of molten metal
  3. Thermo-mechanical influence on HAZ material
  4. Loss of strength in HAZ of work hardened metals (Al alloys)
  5. Contamination of molten metal (defects)
  6. Oxidisation of molten metal (defects)
  7. Restrained thermal expansion and contraction (residual stresses)
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7
Q

Can you draw the effect of heat input on cooling rate graph?

A

YES OR NO

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8
Q

Can you draw the effect of heat input on strength?

A

YES OR NO

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9
Q

What is required for design for welding?

A
  1. Good knowledge of welding processes
  2. Knowledge of metallurgy and welding technology
  3. Knowledge of functional requirements
  4. Material selection, loading and service history, in-house welding capabilites
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10
Q

Objectives of weld design?

A
  1. Fulfill functional requirement
  2. Cost
  3. Efficiency
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11
Q

Describe extrusion?

A

Extrusion is a bulk forming process, normally carried out in hot working conditions. A billet metal stock is heated to 0.6-0.7 Tm so that it is malleable. It is then compressed by a ram to force the material through a suitably shape die to form the product.

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12
Q

Widely used extrusion materials?

A

Aluminium, copper and lead.

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13
Q

Can steel be extruded?

A

Steel may also be extruded but at high cost due to its high melting temp and strength.

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14
Q

What determines grain size and defects for extrusion?

A
  1. Recrystallisation properties of the alloy and extrusion ratio
  2. Extrusion speed
  3. Extrusion temp
  4. final heat treatment
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15
Q

What is the transverse strength compared to the longitudinal strength?

A

Transverse is 80% of longitudinal strength

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16
Q

Advantages of extrusion?

A

Ability to produce a variety of shapes at good strength
Good accuracy and surface finish
High production speed
Relatively low die cost

17
Q

What good properties does the 6000 series Al alloy have?

A
  1. Extrudability
  2. Min wall thickness combined with good strength
  3. Weldability
  4. Machinability
  5. Corrosion resistance
18
Q

Design considerations for aluminium extrusion?

A
  1. Max section length (15m - machinability is important)
  2. Max section dimensions
  3. Min section dimensions
  4. Directionality of strength properties (longitudinal 100%, tansverse 80%, fusion weld 55%)
  5. Joining and welding difficulties (galvanic corrosion in dissimilar metals, reduction in strength for welded joint and need for anodising or adhesive bonding)
  6. Bending following extrusion sections (depends on heat treatment of extruded product - quenched or tempered)
  7. Limitations on local stiffness due to low modulus of elasticity compared to steel.
  8. limited wear resistance(hard anodizing needed).
  9. Low melting temp and high thermal conductivity make Al products vulnerable in fire conditions.
  10. Prototyping is inexpensive

MATERIALS M3 (5 decks)

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