2 definition: material joining process. two parts connected at their contacting surfaces by suitable...

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Definition: 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.

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

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Fusion Welding Processes

Chemical reactions Burning gases GAS WELDING

Heat from electricity Arc ARC WELDING SYSTEMS Resistance welding

• LightLightLASERLASER

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

Note: FP&M only does spot welding.

Spot WeldingA 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.

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.

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.

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

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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There 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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1. 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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Groove weld

Slot and Plug Weld

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

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

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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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

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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.

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.

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

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.

• 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

• 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 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

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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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

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

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.

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.

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.

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

UW-Eau ClaireFacilities Planning & Management

• 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 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

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.

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

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Summary Major hazards include:

Fire Burns Shock Toxic Exposure

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

Any Questions

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