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MEC109 > Welding > Flashcards

Welding Flashcards

1
Q

What is welding?

A

The Process of joining 2 or more parts using heat and/or pressure.
Sometimes a filler is used to facilitate coalescence.

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2
Q

Why is welding important?

A
  • Provides permanent joint
  • most economical way of joining
  • Can be done onsite, not only in a factory
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3
Q

What are the limitations of welding?

A
  • Expensive labour costs.
  • high energy & Dangerous.
  • doesn’t allow for easy disassembly.
  • can have quality defects that are hard to detect.
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4
Q

What are the 5 types of weld joints?

A
  • Butt
  • Corner
  • Tee
  • Lap
  • Edge
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5
Q

What is fusion welding?

A

Joining process that melts base metal.

normally uses filler.

when no filler is used its called an autogenous weld

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6
Q

What is a fillet weld?

A

The process of joining two pieces of metal together when they are perpendicular or at an angle, usually on Corner,Tee and Lap Joints.

Filler used

Commonly used in arc and oxyfuel welding

Requires minimum edge preparation.

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7
Q

What is a groove weld?

A

requires part edges to be shaped into a groove.

Similar to a butt joint.

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8
Q

What is a Plug weld?

A

process that fuses two metals together by making a weld inside small circular holes.

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9
Q

What is a Slot weld?

A

joins the surface of a piece of material to another piece through an elongated hole.

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10
Q

What is a flange weld?

A

It was originally developed for use on small diameter (½″ through 4″) high-pressure piping systems.

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11
Q

What is a surfacing weld?

A

used not to join parts but to deposit filler metal onto surface of a base part.

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12
Q

What are the features of fusion welded joints?

A

Fusion Zone
Weld interface
Heat affected zone
unaffected base metal zone

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13
Q

What is a heat affected zone (HAZ)?

A

Non-melted area of metal, properties changed as a result of being heated

-Solidification occurs to create the weld bead

-liquid to solid transformation

-it is within the HAZ that welding failures often occur.

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14
Q

what two categories can welding processes be divided into?

A

Fusion welding and solid state welding

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15
Q

What is Arc Welding?

A

a fusion welding process where a pool of molten metal is formed near electrode tip and as the electrode is moved along the joint, the weld pool solidifies.

produces temperatures of 5500 C.

Most AW processes add filler to increase volume and also the strength of the weld joint.

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16
Q

What is an electric Arc?

A

Arc Welding process using ac or dc power

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17
Q

What are the two types of AW Electrodes?

A

Consumable - consumed during welding process

Non-consumable - not consumed during welding process
Filler must be added separately

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18
Q

what are the two forms of consumable electrodes?

A

-Welding rods - must be changed frequently

-Weld wire - fed from spools with long lengths of wire

-both are used as the filler metal when welding.

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19
Q

What are non-consumable electrodes?

A

-made of tungsten (resists metal)

-gradually depleted during welding

-filler metal must be fed by a separate wire into weld pool.

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20
Q

What is arc shielding?

A

-This is the process of protecting the metal from oxygen, nitrogen and hydrogen in the air.

-Shielding gases and flux are used to do this.

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21
Q

What is Flux?

A

-Substance that prevents the formation of oxides when welding

-Creates a protective atmosphere and reduces splattering.

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22
Q

How is flux applied to a metal when welding?

A

Pouring granular flux

Stick electrode coated with flux material that melts during welding to cover operation.

Tubular electrodes where flux is contained ion the core and released as the electrode is consumed

23
Q

What is the power source in arc welding?

A

Direct current (DC) - can be used on all metals - for better arc control.

Alternating current (AC) - less expensive to purchase and operate - restricted to ferrous metals.

24
Q

What are the 5 consumable electrode AW processes?

A

Shielded metal arc welding
Gas metal arc welding
Flux-coated arc welding
Electrogas welding
Submerged arc welding

25
Q

What is shielded metal arc welding (SMAW)?

A

uses consumable electrode consisting of a filler metal rod coated with chemicals that provide flux and shielding.

Sometimes called stick welding

26
Q

What are the disadvantages of stick welding?

A

Sticks must be changes often

High current levels may melt coating prematurely

27
Q

What are the applications of stick welding?

A
  • Used for steels, stainless steels, cast irons and certain nonferrous alloys.
  • Not used for aluminium or its alloys, titanium or copper alloys.
28
Q

What is Gas metal arc welding (GMAW)?

A
  • Uses consumable bare metal as electrode and uses shielding using gas.
  • Wire is fed from a spool to the welding gun (He,Al,CO2)
  • Eliminate slag on weld bead - sent need to sand after.
29
Q

What is submerged arc welding (SAW)?

A
  • Uses Consumable bare wire electrode, with arc shielding of granular flux.
  • Electrode fed automatically from a coil
  • Prevents sparks splatter and radiation.

Not good for nonferrous metals

30
Q

What is a non-consumable electrode process?

A
  • Gas tungsten arc welding
31
Q

What is Gas tungsten arc welding (GTAW)?

A
  • uses nonconsumable tungsten electrode and gas for arc shielding.
  • melting point of tungsten = 3410 C

used on aluminium and stainless steel mostly.

32
Q

what are the advantages and disadvantages of GTAW?

A

advantages
- high quality
- no splatter
- no cleaning afterwards

disadvantages
-slower = costs more compared to consumable electrode AW processes.

33
Q

What is Resistance welding (RW)?

A

Fusion welding processes that use both heat and pressure

34
Q

What are the advantages and disadvantages of resistance welding?

A

Advantages
- no filler needed
- high production rates
- can be automated
- lower operator skill required
- reliable

disadvantages
-expensive
- limited to lap joints mostly.

35
Q

What is resistance spot welding (RSW)?

A

fusion of faying surfaces of a lap joint is achieved at one location by opposing electrodes.

used to join sheet metal

used for building cars

36
Q

What is solid state welding?

A
  • joining process from pressure or combination of heat and pressure.
    if heat is used, temperature is below melting point of metals being welded.

There is no filler metal added in solid state welding.

37
Q

What are the success factors in SSW

A

The two saying surfaces must be:
- Very clean
- very close to each other to bond.

38
Q

What is Friction welding?

A

a SSW process using friction and pressure combined.

  • no melting occurs
  • no filler needed
  • can be used to join dissimilar metals
  • used in commercial process & mass production.
39
Q

What are the applications of friction welding?

A

Shafts and tubular shafts

  • Industries - automotive & aircraft.
40
Q

What are the limitations of friction welding?

A
  • One part must be rotating
  • Flash must be removed
41
Q

What is friction stir welding?

A

A SSW process where rotating tool is fed along joint line between the two pieces.

applications - butt joints in aircrafts or automobile.

42
Q

What are the advantages and disadvantages of friction stir welding?

A

Advantages
- good properties of weld joint
- avoids toxic fumes
- little shrinkage
- good weld appearance

Disadvantages
- exit hole is formed when tool is withdrawn
- heavy duty clamp is needed

43
Q

What are the two most common metals in use?

A

Aluminium alloys and steel

44
Q

Does steel have good or bad weldability

A

Good weldability if the carbon content is low.

The greater the carbon content the more difficult it is to weld.

45
Q

What is carbon equivalent?

A

A formula used to compare elements to carbon.

Example: 0.46 Carbon equivalent (percentage)

46
Q

What is Martensite?

A

a hard and very brittle solid solution of carbon in iron that is the main constituent of hardened steel.

Problem - quite brittle.

47
Q

How are Wrought aluminium alloys classified?

A

Using 4 digit codes.

1st letter gives the main alloy elements that’s added to aluminium.

48
Q

Why is aluminium difficult to weld by fusion welding?

A

-Melting point = low
-little warning to when its going to melt
-forms oxide skin when meets the air
-liquid aluminium = easily dissolves hydrogen but solid aluminium doesn’t dissolve H. causes bubbles

49
Q

What are the best methods for welding aluminium alloys?

A

MIG & TIG

50
Q

(PPQ) Name the principal groups of processes included in fusion welding.

A

-arc welding
-resistance welding
-oxyfuel welding other (EBW, LBW, thermit welding)

51
Q

(PPQ) What is the fundamental feature that distinguishes fusion welding from solid-state welding?

A

In fusion welding, melting occurs at the faying surfaces; in solid state welding, no melting occurs.

52
Q

(PPQ) Describe with labelled sketches the difference between MIG and TIG Welding.

A
53
Q

(PPQ) What do the terms arc on time and arc time mean?

A

The two terms mean the same thing: the proportion of the total time in a shift that the arc is actually on, indicating that welding is occurring.

54
Q
A

MEC109 (9 decks)

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