welding

Group Assignmentwelding Prepared by:

ABDUL JABBAR KHAN PANDIARAJ A/L RETENAM

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WELDINGDefinition: Material joining process. Two parts connected at their contacting surfaces by suitable heat and pressure.

Many welding processes are accomplished by heat alone, some others by heat and pressure, and some with pressure only.

In some welding operations a filler material is used.

Welding operation usually applied to metals but also used for plastics.

Parts produced by any of the manufacturing processes can be made into larger, more complex bodies via Joining processes

• Creating a metallurgical bond by adhesion and diffusion• Joining by fusion with the use of various heat sources• Brazing or soldering with a lower-melting metal• Mechanical fastening

Joining ProcessesJoining Processes

Fusion Welding Processes

Sources of Energy for Fusion Welding

• Chemical reactions– Burning gases

– GAS WELDING

• Heat from electricity– Arc– ARC WELDING SYSTEMS– Resistance welding

• LightLightLASERLASER

Three Specific Types of Welding Modules

• In this Welding, Cutting, and Brazing module, three specific types of welding are covered. These are listed below:– Oxygen-fuel gas welding and cutting– Arc welding and cutting– Resistance welding

• Definition:– This is a group of fusion welding processes

that use heat and pressure to make the coalescence.• The heat comes from electrical resistance

to current flow at the site of the weld.

– The processes include:

• Spot Welding• Projection Welding• Seam Welding

Resistance Welding

• Spot Welding–A process typically used in high-

volume, rapid welding applications.• The pieces to be joined are clamped between two electrodes under force, and an electrical current is sent through them.

Resistance Welding

Welding/Cutting Hazards• Potential Hazards

– Fires may start by hot materials igniting nearby combustibles.

– Burns to the operator may occur if unprotected skin comes into contact with the extremely hot work.

– Magnetic fields could easily destroy/disrupt electronic components, stored data if not careful.

Weldability and Weld Quality- Welding Defects-

1. Fusion welding defects due wrong heat input, insufficient rate of weld metal deposition, and cooling.

2. Lack of bonding or gas porosity due to surface contaminants, including oxides, oils, etc.

3. Undesirable reactions with surface contaminants

4. Solidification cracks in the weld.

5. Solidification shrinkage coupled with solid shrinkage imposes internal tensile stresses on the structure, may lead to distortion.

6. Gases released or formed during welding (eg CO) can lead to porosity which weakens the joint and acts as a stress raiser.

Welding Defects

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Weld jointThere are 5 basic joint types in welding

• Butt joint: Two materials are in the same plane, joined from the edges.

• Corner joint:The corners of two materials form a right angle and joined.

• Lap joint: Two parts overlaps.

• Tee joint: One part is perpendicular to the other, making a T shape.

• Edge joint: Edges of the two materials joined.

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Weld Joints

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Types of weld1. Fillet weld: Used in T joints,corner joints, lap

joints.

2. Groove weld:Used in butt joints.

3. Plug weld: Used in lap joints.

4. Slot weld: Used in lap joints.

5. Spot weld: Used in lap joints.

6. Seam weld: Used in lap joints.

7. Flange weld:Used in edge joints.

8. Surfacing weld:Not a joining process, it is used to increase the thickness of the plate, or provide a protective coating on the surface.

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Fillet Weld

Groove weld

Slot and Plug Weld

Oxyacetylene Gas Welding

Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing, flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene. (d) The principle of the oxyfuel-gas welding operation.

Oxygen-fuel gas welding & Cutting

• The elements of Oxygen-fuel gas welding and cutting:– General Requirements– Cylinders– Service Pipe Systems– Pipe System Protection

Oxygen-fuel gas welding and cutting

• General Requirements– Focuses on using Acetylene Safely

• Flammable• Unstable• Cannot be adjusted above 15 psi

– Safe Work Practices• Blow out cylinder valve • Turn on cylinder valve first and

then adjust the regulator pressure screw.• Never stand in front or behind

a regulator when opening the cylinder valve

• Open cylinder valve slowly

• The pressure adjusting screw:– Turning clockwise allows the gas

allows to flow.– Turning counterclockwise reduces

or stop the gas flow.

• General Requirements Cont.:– Safe Work Practices

• Purge oxygen and acetylene passages • Light the acetylene • Never use oil or grease• Do not use oxygen as a substitute for

air • Keep your work area clean

Oxygen-fuel gas welding and cutting

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Arc Welding

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Arc Welding and Cutting• Definition:

– A fusion process wherein the coalescence of the metals is achieved from the heat of an electric arc formed between an electrode and the work.

• Application• Installation• Operation & Maintenance

• Application– Applies to a large and varied group of

processes that use an electric arc as the source of heat to melt and join metals.

• Installation– Arc welding requires proper installation of

equipment. – A critical part of installation is ensuring that

proper grounding is completed.

Arc Welding & Cutting

Arc Welding & Cutting• Operation & Maintenance

– All connections to the machine shall be checked to make certain that they are properly made.

– The work lead shall be firmly attached to the work.

– Magnetic work clamps shall be free from adherent metal particles of spatter on contact surfaces.

– Coiled welding cable shall be spread out before use to avoid serious overheating and damage to insulation.

Methods of Arc Welding

• Three Types of Welding Methods:– Tungsten Inert Gas Welding (TIG) – Gas Metal Arc Welding (MIG)– Shielded Metal Arc Welding (SMAW)/

Stick Welding

• Heat is produced from electric arc between workpiece and electrode material for melting the workpiece material.

• AC and DC are used• An Inert gas shields both

electrodes• Most heat energy is due to

electron flow to metal

Direct Current Electrode Negative (DCEN): Deeper weld.

Direct Current Electrode Positive (DCEP): Shallower and Wider

Heat input v

EIH H- heat input, E, Voltage, I, Current, and v the

velocity of the arc travels along the weld line

Electric Arc Welding

• Electron Beam welding (EBW)– Heat is produced by high velocity

electron gun in a narrow beam

– No filler material

– High rate of heating results in greater depth and heat-affected zone is very small

– Suitable for welding refractory materials like: molybdenum and zirconium

– Requires a vacuum (limitation)

– x-ray will be generated around the welding gun which may be cancerous

Other Welding Processes High Energy Beam Welding

Safe Work Practices

• Electric & Gas Welding– Safety Check:

•Ensure electrical cord, electrode holder and cables are free from defects

– No cable splices within 10 feet of electrode holder.

•Ensure welding unit is properly grounded. This helps to avoid over heating.

•All defective equipment shall be repaired or replaced before using.

Safe Work Practices• Electric & Gas Welding Cont.:

– Safety Check:• Remove all jewelry – rings, watches,

bracelets, etc…• Ensure PPE e.g.. welding hood, gloves,

rubber boots or safety shoes, apron are available and in good condition.

• Ensure fire extinguisher is charged and available.

• Ensure adequate ventilation and lighting is in place.

• Set Voltage Regulator to Manufacture’s specifications.

• Avoid electrical shock DON’T wrap cables around any body part.

• Ensure fittings are tight.

Safe Work Practices

• Electric & Gas Welding Cont.:– Safety Check:

•Inspect hoses for cuts and frayed areas.

•Set gauges to desired PSI.•Ensure that sufficient PPE is made

available.•Locate welding screens to protect

employee’s – DON’T block your exit.•Ensure that adequate ventilation and

lighting are in place.

Fire Protection & Prevention

• Fire hazards must be removed, or– Guards installed, or– Welding/cutting must NOT take place

• Hot work permit should be used outside designated areas to ensure that all fire hazards are controlled

• Use of fire watch– 1/2 hour after operation ceases

L10 : Joining processes L10 : Joining processes Proper Ventilation for Welding

• Ensure protection from fumes and gases by one or a combination of the following:– Good general ventilation.– Use of a booth.– Local exhaust ventilation

on the hand piece.– Air supply to the helmet.

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Welding Operators Protection

• Welding involves specialized personal protection that must be worn every time you perform welding operations. The following is a list of basic PPE: – Fire-resistant gloves – Aprons – Safety shoes – Helmet – Ultraviolet radiation filter plate (arc welding) – Goggles with filter lenses

Sequences of welding 1.Do not over weld2.Control fit up4.For groove welds, use joints that will minimize the volume of weld metal. Consider double-sided joints instead of single-sided joints5.Weld alternately on either side of the joint when possible with multiple-pass welds6.Use minimal number of weld passes7.Use low heat input procedures. This generally means high deposition rates and higher travel speeds9.Use welding positioners to achieve the maximum amount of flat-position welding. 10.Balance welds about the neutral axis 11.Distribute the welding heat as evenly as possible through a planned welding sequence 12.Weld toward the unrestrained part of the member13.Use clamps, fixtures, and strong backs to maintain fit up and alignment14. welds being made continually balance each other

Any Questions

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