welding lecture 4 fusion (liquid) state welding processes ( resistance welding)

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Fusion welding1-Arc welding• Shielded Metal Arc welding (SMAW)(Stick welding)

• Gas-Metal Arc welding (MIG)(GMAW)• Flux-Core Arc welding (FCAW)• Submerged Arc welding (SAW)• Electro Slag welding (ESW )• Gas-Tungsten Arc welding (TIG) (GTAW)• Plasma Arc welding (PAW)

Consumable electrode

Non consumable electrode

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Fusion Welding Processes(Liquid State welding)

1. Arc Welding

2. Oxyfuel Gas Welding

3. Resistance Welding (RW)

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Welding - How It Works عملى.flv

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Resistance Welding (RW)

A group of fusion welding processes that use a combination of heat and pressure to accomplish coalescence

• Heat generated by electrical resistance to current flow at junction to be welded

• Principal RW process is resistance spot welding (RSW)

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Resistance Welding (RW)

• RW components are:workpart to be welded, two opposing electrodes ,a means of applying to squeeze the parts between the electrodes, and AC power supply.

• How is the spot welds - animation.

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Power source in Resistance Welding

• . The amount of heat from the contact resistance at the contact between two materials can be expressed by:

H = R. I 2 . t• Where:

H = Heat generated (Joule) R = electric resistance (Ohm) I = electric current A (5000-2000) although voltage operations is very low (10 V) t = time (S)

• Duration time is short (0.1 to 0.4 )S

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Resistance Spot Welding (RSW)

Resistance welding process in which fusion of faying surfaces of a lap joint is achieved at one

location by opposing electrodes • Used to join sheet metal parts using a series of

spot welds • Widely used in mass production of

automobiles, appliances, metal furniture, and other products made of sheet metal

– Typical car body has ~ 10,000 spot welds – Annual production of automobiles in the

world is measured in tens of millions of units

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• The reason why such current in RW is because:

1. Square term in Equation ..amplifies the effect of current

2. The resistance is very low 0.0001 ohm• Resistance in the welding circuit is the

sum of1. Resistance of the electrodes2. Resistances of the workparts3. Contact resistances between electrodes and

workparts.4. Contact resistance of fly surfaces

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Examples31.2

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• Advantages: 1) The machine requires only a short time

which effect of welding temperature (rapid cooling of the weld) leads to a fine grain structure of weld metal which gives minimum stress and strain

2) No filler metal is required .3) High production rates are possible4) Operator skill level is lower than the required for arc

welding5) Good repeatability and reliability.• Drawbacks: 1) Equipment cost is high2) Requires large machinery and stronger construction

inputs 3) Types of joints that can be welded are limited to lap joint

for most RW processes

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Advantages / Drawbacks of RW

Advantages:• No filler metal required• High production rates possible• Lends itself to mechanization and automation• Lower operator skill level than for arc welding• Good repeatability and reliability

Disadvantages:• High initial equipment cost• Limited to lap joints for most RW processes

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Resistance welding

Spot welding Seam welding Projection welding

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1-Resistance Spot Welding (RSW)

Resistance spot welding process in which fusion of faying surfaces of a lap joint is achieved at one location by opposing electrodes

• Used to join sheet metal parts using a series of spot welds

• Widely used in mass production of automobiles, appliances, metal furniture, and other products made of sheet metal – Typical car body has ~ 10,000 spot welds – Annual production of automobiles in the

world is measured in tens of millions of units

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Electrode materials

• Materials used for RSW electrodes consist of two groups:

1. Copper based alloys.

2. Refractory metal compositions such as copper and tungsten combinations.

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(a) Spot welding cycle, (b) plot of squeezing force & current in cycle (1) parts inserted between electrodes, (2) electrodes close, force applied, (3) current on, (4) current off, (5) electrodes opened.

Spot Welding Cycle

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Components in Resistance of spot welding

• Parts to be welded (usually sheet metal)

• Two opposing electrodes

• Means of applying pressure to squeeze parts between electrodes

• Power supply from which a controlled current can be applied for a specified time duration

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Spot Welding Examples

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with Car-O-Liner Welder.flv

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2- Resistance Seam welding (RSEW)

Uses rotating wheel electrodes to produce a series of overlapping spot welds along lap joint

• Can produce air‑tight joints

• Applications: – Gasoline tanks

– Automobile mufflers

– Various other sheet metal containers

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Resistance seam welding (RSEW).

Resistance Seam Welding

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Different types of seam resistance welding and applications b-Continuous weld seam C-Continuous weld seam d- Gasoline seam welding

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3-Resistance Projection Welding (RPW)

A resistance welding process in which coalescence occurs at one or more small contact points on parts

• Contact points determined by design of parts to be joined– May consist of projections, embossments, or

localized intersections of parts

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Resistance projection welding (RPW): (1) start of operation, contact between parts is at projections; (2) when current is applied, weld nuggets similar to spot welding are formed at the projections.

Resistance Projection Welding

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Sketch of projection welding

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a-Sketch of projection weldingb-welded bracketc,d- projection welding of nuts and threaded bosses and stude- projection welding of grills

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Welding Video.flv..\ فيدو الباحة -Resistance Welding\9\لحامWeld Procedures Utube Welding Videos

- ARO Technologies - Projection Welding.flv

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Welding.mp4