Joining Processes WELDING. 2 WELDING Definition: Material joining process. Two parts connected at...

Joining ProcessesWELDING

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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

Note: FP&M only does spot 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.

Welding/Cutting Hazards• Potential Hazards Cont.:

– Metal fumes from vaporizing of the work with the extremely hot arcs may be inhaled into the worker’s lungs.

– Certain metals and metal oxide fumes, including zinc, cadmium and beryllium, produce serious illnesses when inhaled.

– Fluxes used with welding to create inert atmospheres at the point of the weld also present inhalation hazards.

– All welding and cutting must have adequate ventilation to protect the person doing the welding and those working around the welding area.

Weld Joint StructureCharacteristics of a typical fusion-weld zone in oxyfuel-gas and arc welding.

Microhardness (HV) profile across a weld bead.

A fusion joint is far from homogenous. Degree of inhomogeity increases from pure metals to multiphase alloys.

Typical weld zone in arc and gas welds• The base material adjacent to the melt boundary is exposed to high

temperatures, and the properties and structure are changed within the heat-affected zone.

• Cold worked base material will show recrystallization in HAZ, with coarse grain sizes.

• In either case, a coarse-grained structure of lower strength exits at the melt boundary.

Melt

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

http://www.mig-welding.co.uk/plug-weld.htm

1. Preheating the weld zone – reduces energy input, cooling rates in the weld and HAZ, reduces differential shrinkage, residual stresses, and distortion.

2. Postwelding heat treatment of the entire welded structure

a. Stress-relief anneal reduces residual stresses to acceptable level.

b. Normalizing a steel wipes out most undesirable effects of welding.

c. Full heat treatment (quenching and tempering of steels)

3. Peening (hammering or rolling) of weld bead improves the strength of welds.

Metal Treatment

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.

Oxyacetylene Torch

The acetylene valve is opened first; the gas is lit with a spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted.

Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, and acetylene regulators red.

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Oxyfuel gas welding

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


L10 : Joining processes L10 : Joining processes

• Cylinders– Cylinder approval and marking

• marked for the purpose of identifying the gas content, with either the chemical or trade name of the gas

– Storage of cylinders• Storage area must be well ventilated• Cylinders must be at least 20 feet from

combustibles• Valves must be closed• Valve protection must be in place• Inside storage must be limited to 2,000 cubic feet.• Cylinders must be stored in upright position• Oxygen must be at least 20 feet from fuel gas

or 5 feet with a 1/2 hour fire barrier• Separate oxygen from fuel gas


• Cylinders Cont.:– Operating Procedures

• Operation must emphasize the absence of oily or greasy substances. Follow these rules of operation:

– Cylinders, cylinder valves, couplings, regulators, hose, and apparatus shall be kept free from oily or greasy substances.

– Oxygen cylinders or apparatus shall not be handled with oily hands or gloves.

– A jet of oxygen must never be permitted to strike an oily surface, greasy clothes, or enter a fuel oil or other storage tank.


• Service Pipe Systems– There are special requirements for service

pipe systems when using oxygen or acetylene.

• Oxygen• Acetylene or Acetylene Compounds


• Pipe System Protection– The entire service pipe system must be

protected against build-up of excessive pressure and leaks. This protection is accomplished with:

• Protective equipment • Regulators • Proper hose and hose connections.


• Pipe System Protection Cont.:– Protective equipment is divided into the two

categories listed here:• Pressure Relief Devices

– The pressure relief device should discharge upwards to a safe location.

– Pressure relief valves are required in fuel-gas piping systems to prevent excessive pressure build up within the system.


• Pipe System Protection Cont.:

– Approved protective equipment shall be installed in fuel-gas piping to prevent: • Backflow of oxygen into the fuel-gas supply

system• Passage of a flash back into the fuel-gas

supply system• Excessive back pressure of oxygen in the

fuel-gas supply system.


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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.

• Operation and Maintenance Cont.:– During welding operations, cables with splices

within 10 feet (3m) of the holder shall not be used.

– Welders should not coil or loop welding electrode cable around parts of their body.

– Cables with damaged insulation or exposed bare conductors shall be replaced.

– Joining lengths of work and electrode cables shall be done by the use of connecting means specifically intended for that purpose.

– The connecting means shall have insulation adequate for the service conditions.

Arc Welding & Cutting

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

Electric Arc Welding- Classification -

• The Electrode– Consumable: melts and serves as a filling material– Non-consumable: does not melt, parent metal is used, or a

separate filler rod– Coated or Uncoated

• Coating– Provides a gaseous shield to prevent oxidation– Lowers the voltage needed to establish the arc– May provide slag-blanket to protect the joint– Add alloying elements to enhance the properties of the joint.

Non-Consumable Electrode Arc Welding

• Gas Tungsten Arc Welding ( TIG)

• Plasma arc welding

• Atomic hydrogen welding

Non-Consumable-Electrode Welding: Gas Tungsten-Arc Welding (GTAW)

• Nonconsumable gas tungsten Inert gas welding (TIG)

• Weld zone is protected by inert gas

• DC with straight polarity is used with steel, cast iron, and stainless

• AC with Al, Mg alloys where ac helps in stripping the oxide

• Both hand and automatic operations are possible

• The process demands considerable skill but produces very high-quality welds on almost any material

• No weld spatter or slag formation

Consumable Electrode Arc Welding Processes

• Shielded metal arc welding

• Submerged arc welding

• Gas metal arc welding

Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.

Consumable Electrode Arc Welding Shielded-Metal Arc Welding

Consumable-Electrode Welding: Gas Metal-Arc Welding (GMAW) - MIG

• Consumable gas metal-arc welding (MIG)

• Consumable electrode is metal which melts to become part of the weld seam.

• Weld zone is protected by a gas or a flux

• No slag is formed• Several layers could be build with little

or no intermediate cleaning• It is suitable for most metals• Wire electrode can be supplied in long,

coiled lengths which allow uninterrupted welds in any welding position.

(a) Schematic illustration of the gas metal-arc welding process, formerly known as MIG (for metal inert gas) welding. (b) Basic equipment used in gas metal-arc welding operations.

Consumable Electrode Arc Welding Gas - Gas Metal-arc Welding Process-

• 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

High Energy Beam Welding

• LASER Beam welding (LBW)– Uses a focused high power monochromatic

light beam as a source of heat to the metal– Beam can be directed to the welding spot

with a lens– Depth of welding similar to electron beam

welding– Vacuum is not necessary (advantage)– Workpiece usually needs protection by a

gas– Process is suitable for automation– Welding speeds can be upto 7 m/min

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Laser beam welding

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Thermit Welding

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Explosion Welding

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Resistance welding

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Forge welding

SolderingSoldering

Circuit BoardCircuit Board

ResistorResistor

Solder PadsSolder Pads

Side ViewSide View

Top ViewTop View

PCBPCB – printed circuit boards – printed circuit boards

SolderingSolderingIronIron

Move soldering iron until tip isMove soldering iron until tip istouching wire & solder padtouching wire & solder pad

Move solder to touch edge of tip. Move solder to touch edge of tip.

SolderSolder

Hold until solder melts Hold until solder melts on tip by wireon tip by wire

SolderSolder

Move solder back to touch wire onlyMove solder back to touch wire only

SolderSolder

Move solder in to form a Move solder in to form a small pocketsmall pocket

SolderSolder

Move soldering iron tip up. ThisMove soldering iron tip up. Thiswill drag solder up with it.will drag solder up with it.

SolderSolder

Look for Look for shinny filletsshinny fillets

Brazing• Definition:

– A process which a filler metal is placed at or between the faying surfaces, the temperature is raised high enough to melt the filler metal but not the base metal.

• The molten metal fills the spaces by capillary attraction.

• Torch Brazing– Oxy-fuel torch with a carburizing flame– First heat the joint then add the filler metal

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.

UW-Eau ClaireFacilities Planning & Management

Fire Protection & Prevention Cont.:• Welding areas should meet the following

requirements:– Floors swept & cleared of combustibles 35 ft.

radius of work area.– Flammable and combustible liquids kept 35 ft.

radius of work area.– At least one fire extinguisher – on site– Protective dividers to contain sparks and

slag• Welding curtains• Non-combustible walls• Fire resistant tarps & blankets

Proper Ventilation for Welding

• Ventilation– Proper ventilation can be obtained either naturally or

mechanically.• Natural Ventilation is considered sufficient for welding and

brazing operations if the present work area meets these requirements:

– Space of more than 10,000 square feet is provided per welder

– A ceiling height of more than 16 feet.

• Mechanical ventilation options generally fall into two basic categories.

– Low vacuum system which takes large volumes of air at low velocities.

– High vacuum system that are captured and extracted fumes as near to the work as possible.

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

Welding, Cutting and Brazing• Summary

– Major hazards include:• Fire• Burns• Shock• Toxic Exposure

– Follow proper procedures to prevent fires– Use appropriate engineering controls– Wear appropriate PPE

Joining Processes WELDING. 2 WELDING Definition: Material joining process. Two parts connected at...

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