2850 DIPLOMA IN ENGINEERING FABRICATION … Joint Butt joints are generally produced where the edges...

2850

DIPLOMA IN ENGINEERING

FABRICATION AND WELDING TECHNOLOGY

PRE-ATTENDANCE REVISION WORKBOOK FOR

UNITS 212, 214 AND 215

V1

Welcome

This booklet is designed to outline the areas that you will study when you complete units 212, 214 and 215 at the centre.

Throughout your time in centre you will have a qualified assessor there to help and advise you.

We want you to achieve the best possible benefits from your time in centre, therefore before attending we would like you to revise by carrying out the work detailed in this booklet.

Please remember that you should not carry out any welding practical work unless you are in class with one of our qualified assessors.

Please bring your completed workbook with you when you attend in class.

We very much look forward to welcoming you at the centre.

When you have studied this material please contact us to make arrangements for your practical training.

Date:

Title First name Last name College number

Please complete this page before attending the centre as there will be many other students who have this same workbook.

You do not need to leave this workbook at the centre. You can take it home with you and retain it for your future reference.

SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 1

Unit 212/255: Principles of Fabrication and Welding Handout 1: Electricity in welding

• Electricity is used extensively in welding and fabrication• Electrical polarity has a huge influence on heat distribution in a welded joint.

There are two types of current available:

• Alternating current (AC) (mains electricity)

• Direct current (DC) (battery or from a transformer)

Alternating current

• Electricity supplied to homes andfactories has an AC (alternating current) waveform.

• The frequency of the UK supply is 50hertz

• Hertz is a measure of cycles persecond.

• The polarity of the supply is switching 50times per second.

Direct current

• The DC (direct current) supply has nowaveform.

• Polarity is fixed

• High voltage DC for welding is achieved byconverting an AC current.

• The current supplied by a battery is DC.

© 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk


Terminology:

• Open Circuit Voltage (OCV)– The voltage needed to strike the arc

• Arc Voltage– The voltage needed to maintain the arc (lower than OCV)

Welding arc blow

• Arc Blow– Happens when using DC current– Arc is deflected either backwards or forwards.– Caused by magnetic build up in the weld metal.– More pronounced in corners of fillet welds

• Preventing Arc Blow– Move the current return lead– Weld in a different direction– Wrap the current return cable around the component being welded



Unit 212/255: Principles of Fabrication and Welding Handout 2: Electrode coatings

Electrode coverings or flux coatings are essential when manual metal arc (MMA) welding.

Purpose – Helps strike the arc– Forms a slag covering to prevent rapid cooling (thermal blanket)– De-oxidises (cleans) the metal surface– Forms a shielding gas– Adds alloying elements to improve the weld– Stabilises and directs the arc– Supplies additional metal to the weld pool– Controls size and frequency of metal droplets being transferred– Provides appropriate weld contour

Types of flux/electrodes

Arc stability, depth of penetration, metal deposition rate and positional capability are greatly influenced by the chemical composition of the flux coating on the electrode. Electrodes can be categorised into four main groups:

• Rutile• Basic• Cellulosic• Iron Powder

• Basic electrodes contain a high proportion of calcium carbonate (limestone) andcalcium fluoride (fluorspar) in the coating. This makes their slag coating more fluid than rutile coatings - this is also fast-freezing which assists welding in the vertical and overhead position. These electrodes are used for welding medium and heavy section fabrications where higher weld quality, good mechanical properties and resistance to cracking (due to high restraint) are required.

Features:

• low hydrogen weld metal• requires high welding currents/speeds• poor bead profile (convex and coarse surface profile)• slag removal difficult

• Rutile electrodes contain a high proportion of titanium oxide (rutile) in thecoating.

• Titanium oxide promotes easy arc ignition, smooth arc operation and low spatter.These electrodes are general purpose electrodes with good welding properties.

• They can be used with AC and DC power sources and in all positions. Theelectrodes are especially suitable for welding fillet joints in the horizontal/vertical (H/V) position.



Features:

• moderate weld metal mechanical properties• good bead profile produced through the viscous slag• positional welding possible with a fluid slag (containing fluoride)• easily removable slag

• Cellulosic electrodes contain organic materials that turn into gases in the arc.About 30% of the coating weight is cellulose. Paper pulp and wood powder are added to the coating to reduce the amount of cellulose.

• The materials in the coating melts in the arc to form carbon monoxide, carbondioxide and hydrogen. This increases the arc tension and produces a stronger and harder welding arc .

• At the same current level cellulosic electrodes can produce 70% deeper weldpenetration.

• The electrode produces a thin layer of slag with a large amount of spatter.• Cellulosic electrodes can be used in the vertical down position with good gap

filling and deep penetration welding possible.

Features:

- Deep penetrating welding in every position,- Vertical down welding capability,- Weld metal with good mechanical properties.

• Metal powder electrodes contain an addition of metal powder to the flux coatingto increase the maximum permissible welding current level.

• The slag is normally easily removed. Iron powder electrodes are mainly used inthe flat and H/V positions to take advantage of the higher deposition rates.

• Efficiencies as high as 130 to 140% can be achieved for rutile and basicelectrodes without marked deterioration of the arcing characteristics but the arc tends to be less forceful which reduces bead penetration.



Unit 212/255: Principles of Fabrication and Welding Handout 3: Shielding gases

During any welding process the arc and molten weld pool needs to be protected from the atmosphere.

Failure to protect the weld pool sufficiently will result in weld defects.

The main function of the shielding gas is to protect the arc and molten pool.

The choice of shielding gas can also influence welding speed, penetration, mechanical properties, arc stability, weld appearance and shape.

Welding arc

For the welding arc to be established the shielding gas must be ionized.

Ionization allows the shielding gas to conduct electricity.

Some gases ionize easier than others.

Argon ionizes easier than helium, allowing easier arc initiation.

TIG/TAG welding

TIG – Tungsten Inert Gas welding

TAG – Tungsten Active Gas welding

Inert gasses will not react with elements in the molten pool

Active gasses will react with elements in the molten pool

Inert gases

Argon

– Argon is the most commonly used gas when TIG welding.

– It can be used to weld most materials.

Helium

– Helium is used when a hotter arc is required

– As helium is lighter, higher flow rates will be required

Mixtures of argon and helium can be used

TIG gases

The higher heat input associated with helium provides deeper penetration and faster welding speeds.

Helium is used pure or mixed with argon when welding aluminium or copper alloys.

Argon/hydrogen mixtures (active) can be used when welding austenitic stainless steels.

Argon/hydrogen mixtures should not be used when welding carbon steels.


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 3 MIG/MAG welding

MIG – Metal Inert Gas welding

MAG – Metal Active Gas welding

Inert gasses will not react with elements in the molten pool

Active gasses will react with elements in the molten pool

Although referred to extensively as MIG welding, the majority of the time MAG welding is being undertaken.

MIG welding uses argon or helium as a shielding gas.

MIG welding is used on non-ferrous metals

MAG welding gases

• Carbon dioxide (CO2).

– Deep penetration welds possible

– Difficult to weld thinner materials

– Cheap shielding gas

– High spatter levels

– Heater required prior to the regulator

Due to the limitations listed CO2 is mixed with argon for most shielding applications.

MIG welding gases

Argon/CO2 mixtures

• As the percentage of CO2 increases the arc temperature will rise.

• Can be used to weld most materials

• Can affect the corrosion resistance of stainless steels so other mixtures need to be considered if this is important.

• Small additions of oxygen (O) can also be added.



Unit 212/255: Principles of Fabrication and Welding Handout 4: Flame conditions

There are three types of oxy-acetylene flame possible: • Neutral

– Equal mixtures of oxygen and acetylene • Carburising

– Excess of acetylene in the flame • Oxidising

– Excess of oxygen in the flame



212/255: Principles of Fabrication and Welding Technology Handout 5: Welding Joint Geometry and Weld Symbols Joint Geometry Welding is one of the most widely used method of joining metals. There is a wide variety of joints and configurations available to meet the requirements of a product design. When two or more pieces of metal are to be joined they are prepared and placed together to form a weld joint. Edge Preparation The edge of the metals to be joined needs to be prepared to allow the correct joint to be made. The edge preparation and joint types is selected to meet strength requirements and design needs. Metal edges can be prepared in a variety of ways including grinding, machining or thermal cutting. Basic Joints There are a number of basic joint designs available for the fabrication of a component. Butt Joint Butt joints are generally produced where the edges of two plates meet. A large number of variations are available depending on the thickness of the material and the design requirements of the joint. Preparing the joint edges as detailed below allows the weld to penetrate the full thickness of the metal producing the strongest joint possible.

Single V Butt Double V Butt

Single U Butt Double U Butt © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk


Other Joints. Other joints available include:

Butt welds can be applied to T joints where full weld penetration is required.

Corner Joint

Tee Joint

Lap Joint

Edge Joint


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 5 Butt Weld Features.

T Fillet Weld Feature


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 5 Application of weld symbols on drawings Weld symbols are used on fabrication drawings to inform the welder of type, size and process required to complete the welded joint. Symbols have been recognised within a number of standardised documents. In the UK BS 499 Part 2 has now been superseded by BS EN 2212/2553. The American Welding Society also have their own standards but often these are similar to the European standards. All the standards will have the same basic requirements which include an arrow line and head and a reference line.

The angle of the arrow line is unimportant and any intended edge preparation is not indicated on the drawing itself (see below)

The designer indicates the required joint geometry by using symbols on the reference line.

1. Single V butt joint 2. Single bevel joint 3. Double bevel joint 4. Double fillet joint 5. Single fillet joint

A dotted line indicates the “other side” of the joint

For resistance welding, a spot weld and seam weld are shown:

1 2 3 4 5

Spot weld Seam weld


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 5 Additional information for the welder can indicate the finished shape of the weld. Single V convex Profile Single fillet concave profile Double V face flushed flat Fillet Weld Size

Intermittent (stitch) welds Stitch weld information includes number of welds, length of weld and gap between welds.

a7 z10 The correct size of weld is important to ensure sufficient strength. BS EN 2212/2553 a = throat size z = leg length

7 x 100 x (150) x 100

Number of welds Gap between welds

Weld Weld


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 5 Stitch weld on both sides of the joint can be shown by adding a Z.

Supplementary symbols

Other information can be added to the weld symbol reference line.

7 x 100

7 x 100

(100) x 100

(100) x 100

Weld all round

Weld on site NDT

Non-destructive testing required


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 5 Welding process

Each welding process is identified within ISO 4063 by a reference number. In this example, 114 refers to MIG welding.

Number Welding Process 111 Metal arc welding with covered electrode (MMA) 114 Metal inert gas welding (MIG) 135 Metal active gas welding (MAG) 137 Flux-cored metal arc welding with inert gas 141 Tungsten inert gas welding (TIG)

114



Unit 212/255: Principles of Fabrication and Welding Handout 6: Heat generation Heat

Heat of sufficient temperature to melt a range of metals is required for welding.

Heat is generated by:

• electric arc

• electrical resistance

• flame combustion.

Electric arc

An arc is an electric current flowing between two electrodes through an ionized column of gas.

A negatively charged cathode and a positively charged anode create the intense heat of the welding arc.

A welding arc can achieve temperatures up to 33000C

Resistance heating

All conductors resists the flow of electricity.

As electricity flows through a conductor heat is generated.

The amount of heat generated depends on:

– Current

– Level of resistance

– Duration of current flow

Low voltage, high amperage currents are passed through the joint.

Heat is generated when an electrical current flows through a resistance.

Resistance is greatest at the plate interface.

Squeeze is applied by the electrodes to complete the weld



Flame heating

The heat generated by a gas flame is caused by a chemical reaction.

Various gas mixtures will produce different temperatures

Mixture Temperature 0C

Oxy-acetylene 3100

Oxy-propane 2815

Oxy-butane 2820

Measuring heat

For some welding procedures the temperature of the plate being welded needs to be monitored.

This may need to be done at 3 stages:

– Pre-welding

– Inter-pass

– Post welding


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 6 Temperature indicating crayons

Crayons are painted on the surface of the metal

When the temperature is reached the mark changes consistency.

Crayons are available in over 100 temperature ratings

Pyrometers

A pyrometer is an instrument for measuring temperatures

Infra-red thermometers

The most basic design consists of a lens to focus the infrared (IR) energy on to a detector, which converts the energy to an electrical signal that can be displayed in units of temperature



Heat transfer

Heat can be transferred from place to place by:

– Conduction

– Convection

– Radiation

Conduction

Heat causes the atoms in a material to vibrate. As they vibrate they cause the adjacent atoms to vibrate. These additional atoms vibrating cause the heat to move along the metal.

Convection



Heat energy is transferred from hot places to cooler places by convection.

The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas. The denser cold liquid or gas falls into the warm areas.

Radiators are often painted with white gloss paint. They would be better at radiating heat if they were painted with black matt paint, but in fact, despite their name, radiators transfer most of their heat to a room by convection

Radiation

• All objects emit and absorb thermal radiation, which is also called infrared radiation. The hotter an object is, the more infrared radiation it emits.

• Infrared radiation is a type of electromagnetic radiation that involves waves. No particles are involved, unlike in the processes of conduction and convection, so radiation can even work through the vacuum of space. This is why we can still feel the heat of the sun, although it is 150 million km away from the earth.

• Some surfaces are better than others at reflecting and absorbing infrared radiation.

• A dark, matt surface emits and absorbs thermal radiation better than light, shiny surfaces.



Unit 212/255: Principles of Fabrication and Welding Handout 7: Heat effect of welding

All metals are made up of grains

The grain structure of a metal is significant to its properties.

Small grains are exhibited by hard steels

Large grains by annealed steels

Medium grains by normalised steel

The grain sizes detailed are normally achieved by controlled heat treatment.

However, the welding process and its rate of cooling, can affect the grain structure and influence the welds properties.

The further from the centre of a weld, the cooler the metal will be.

Metal needs to be heated above its transformation temperature to change its properties

The heat affected zone (HAZ) is the area adjacent to weld where the crystal structure can change.



Unit 212/255: Principles of Fabrication and Welding Handout 8: Distortion Heat is used extensively in engineering and its effect, if not allowed for, can cause problems. When welding or thermal cutting stresses set up in the fabrication can cause distortion. Using distortion. By realising that distortion can happen, it can be used. Two different metals expand at different rates so the bi-metallic strip will bend and complete the circuit. Use in some fire alarm systems. The heat from a fire causes the strip to bend and sets off the alarm. What causes distortion? If a metal was heated then allowed to cool, unrestrained, it would return to its original size. If the metal was held (restrained) in some way, it would distort on heating due to expansion. A round bar is held in a vice and heated. Being unable to expand against the vice jaws (restrained) it would expand in diameter. On cooling there would be no restraint so it would be able to contract in all directions and would fall out of the vice.



Distortion and welding Any metal that has been heated wants to expand then contract on cooling. The weld metal in a butt weld needs to contract along length and across its width. The problem is that the two joined plates act as a restraint to stop the weld metal to contract as it wishes. This sets up stresses and causes distortion.



It is not only butt welds that are affected by welding.

Weld preparations and distortion. If we look at a 600 included angle preparation, it is obvious that the weld width at the top of the joint is greater than at the root. As the greater the amount of metal the greater the distortion the joint will move. This is known as angular distortion. To reduce this, the preparation could be re-designed to a double vee, and weld both sides. The equal amounts of weld metal will reduce the amount of distortion. Should welding from both sides not be possible, altering the weld preparation to have a more even distribution of weld metal through the joint thickness.



Pre-setting. Pre-setting joints can also allow for distortion.

Heat distribution. Another method to reduce distortion is to control the heat input. If the heat source moves slowly along the joint the heat spreads further into the plates. The wider the heat band, the more hot metal to expand / contract. MIG welding, which has a fast travel speed, produces a narrow heat band compared to oxy-acetylene welding. It is possible to arrange these manual welding methods in order of least distortion produced: Least: MIG MMA TIG Most: Oxy-Acetylene. Welding procedures to reduce distortion.


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 8 By using weld procedures to help distribute heat evenly throughout a joint can reduce the amount of distortion. Step back welding. Rather than laying one continuous run the weld length is broken up into short lengths with each short run ending where the next began. This reduces the heat input into any one area. Another benefit of using this method is that where the end of weld 2 meets the beginning of weld 1 there are both expansion and contraction zones which help to neutralise each other’s effect.

Skip welding. Again the welding joint will be divided into shorter lengths. Welding section 1, then section 2 will distribute the heat more evenly throughout the component.

Stress relieving. However little distortion that may be apparent, there will always be a certain level of stress within a welded structure. Controlling heat input and employing correct weld geometry will help to reduce stress, but will never eliminate it completely. In many cases this residual stress will not cause a problem with the operation of the component. However, in some situations, such as pressure vessels and high pressure pipe work the relief of theses stresses are important. The most common method employed is a controlled heating and cooling cycle. In the case of a pressure vessel it is important that the whole fabrication reaches an even temperature so as not to create stresses elsewhere. Therefore vessels are normally stress relieved in a furnace, and “soaked” for up to 24 hours at the required temperature. The furnace also allows controlled cooling of the whole fabrication. © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk

SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 8 Stress reliving of pipe joints can cause problems as it is impractical to heat the complete pipe run. This is overcome by ensuring that the heat band created by the stress reliving heating elements spreads wide enough either side of the weld joints. Heating elements are normally covered by a insulating blanket to ensure controlled cooling times, especially for site welding, where draughts could chill the heated zone.



Unit 212/255: Principles of Fabrication and Welding Technology Handout 9: Weld defects

Assessment criteria

• Qualitive– Based on appearance or levels of defects– Quantitive– Based on numerical limits such as extent of defect, size of defect or

dimensional accuracy.

• Quantitive– Based on numerical limits such as extent of defect, size of defect or


• A weld defect can be caused by a number of factors.• 2 of the main causes of defects are:

• Operator error• Poor preparation

• Inspection and testing methods are used to detect any defects.• Some defects can be classed as a “lack of continuity”, (where the weld is not

continuous). • The most common method of inspection is visual examination.

Types of defect



Unit 212/255: Principles of Fabrication and Welding Technology. Handout 10: Inspection and testing Completed welds are often subjected to a system of inspection and testing to ensure its quality. • Testing has 2 main categories:

– Non-destructive – Destructive

Non-destructive – The completed weld does not need to be destroyed for testing to take place.

Methods: – Visual inspection – Dye penetrant – Magnetic particle

Visual inspection is the most commonly used non-destructive inspection method

• Every manually welded joint will be inspected by the operator on completion but no records are usually completed

• Limited to surface defects

• Aids can be used to assist assessment. Dye penetrant testing

• Dye penetrant testing uses “capillary attraction” • Capillary attraction is why a liquid will move into a tight gap. • Capillary attraction allows paper towels to soak up liquids • Capillary attraction enables soldered joints to be made in plumbing fittings.

Water is drawn further up the small diameter tube.



There are four stages to the dye penetrant test.

Advantages • Small cracks can be detected • A range of materials, both metallic and non-metallic can be inspected • Quick and low cost • Suitable for complex shapes • Portable • Direct indication of position of flaw

Limitations

• Only surface breaking defects can be detected • Material surface needs to be relatively non-porous • Pre-cleaning is essential • Poor surface finish can effect indications • Post cleaning of component • COSHH considerations for chemical storage and disposal


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 10 Magnetic particle testing

• A magnetic field will spread uniformly through a component unless disrupted by a defect.

• Should the defect break the surface, or slightly sub-surface, flux leakage will occur.

• Magnetic particles, usually iron filings in a liquid, applied to the surface of the component will be Material to be tested must be magnetic

• attracted to the flux leakage. • Iron filings attracted to the flux leakage will give a visual indication of the flaw.

• The electric flowing through the metal creates a magnetic field. • Permanent magnets can be used to create the magnetic field

• Defects show up best at 900 to the magnetic field

• The electric yoke or magnet should be rotated to ensure all defects are detected.



Macro etch testing •

• Test samples must be cut on a saw. • Cut samples are then polished. • An etchant is applied to the polished surface. • Macro examination uses low powered magnification to view defects (3x – 20x) • Cracks, slag inclusions, porosity and lack of fusion can be revealed

Types of etchant © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk


Metal Etchant

Steel • 10-20% Nitric acid in alcohol (Nital) • 8% cuprous ammonium chloride in water

Aluminium 10% hydrofluoric acid in water

Copper Ammonium hydrate

Brass 25% solution of nitric acid

Nick break test

• The nick break test is used to test the internal quality of a welded joint • The test reveals any lack of fusion, inclusions or porosity within the weld • The test piece must be cut from the weld • Thermal cutting must not be used • A saw cut (nick) is introduced into the weld • A force is applied to break the test piece

Bend testing



• Bend tests stretch the weld metal • Any lack of fusion or defects inside the weld will lead to the specimen cracking • Bend testing can be applied in 3 ways:

– Bend the face – Bend the root – Side bending

• Test specimen usually about 30mm wide • Any weld reinforcement to be ground flush • Edges of test piece should be radiused to prevent cracking • Bending should be through an angle between 900 and 1800 • Former should be 3 times the material thickness



Cupping test

• On thin metal a bend test is not effective. • A cupping test is preferred. • A domed mandrel is forced into the weld to be tested • Also known as an Erichson test



Unit 212/255: Principles of Fabrication and Welding Handout 11: Metals Ferrous metals

Ferrous metals contain iron (Fe)

Pure iron is a relatively weak material and not suitable for modern engineering products.

The addition of small amounts of carbon (C) produces steel.

Steel is the most widely used engineering material.

Steel

Steel is an alloy (mixture) of iron and carbon.

The percentage of carbon influences the properties of the steel.

Other metals can be added in small amounts to change steel properties further.

This group of metals are known as alloy steels

Low carbon steel (LCS)

contains up to 0.29% carbon

easily welded by a range of processes

easily formed into a range of shapes

sometimes known as mild steel

Medium carbon steel (MCS)

harder and stronger than LCS

contains from 0.3% to 0.54 carbon

Can be welded by a range of processes

Can be formed into a range of shapes

post production heat treatment may be required.

High carbon steel (HCS)

– hardest of the carbon steels

– hardness levels lead to a brittle material

– contains from 0.55% to 1.2% carbon

– difficult to weld



– can not be formed due to brittleness.

– may need to be annealed prior to machining

– post production hardening and tempering may be required.

Galvanised steel

Galvanising is a coating of zinc applied to steel.

Most commonly applied by a hot dip method where the steel is submerged in a tank of molten zinc

Galvanising prevents rusting of the steel component.

Stainless steels

Stainless steels are commonly used for their corrosion resistance properties.

Stainless steels contain a minimum of 10.5% chromium

Other metals can be added to improve properties including:

• Nickel

• Molybdenum

• Titanium

• Copper

Austenitic stainless

Austenitic stainless steels have good ductility and high strength compared to carbon steels.

Welding causes little or no effect on the material properties.

Austenitic stainless steels contain nickel

Non magnetic

Aluminium

Pure aluminium is a light metal, approx. ⅓ the density of steel.

Non magnetic

Corrosion resistant due to a naturally produced oxide layer.

Good conductor of heat and electricity

The addition of copper as an alloy can increase the strength of aluminium to that approaching steel.


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 11 Forms of supply

Metals are supplied in a wide range of forms.

Forms usually describe the shape of the metal.

Plates or sheet

– Usually supplied in rectangular forms

– Common sizes are:

• 2m x 1m; 2.5m x 1.25m

• Sheets have thickness up to 3mm

• Plates have thicknesses above 3mm

Angle iron

– Available in equal or un-equal leg lengths


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 11 Hollow section

Available in a range of shapes.

Rectangular hollow section is available in a range of sizes.

Round hollow section is also known as pipe or tube.

Tubing is a structural member. Its outside diameter and wall thickness is important.

Pipe is used to convey fluids or gases so the internal diameter is important

Rectangular hollow section Square hollow section


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Handout 11 Other sections available



Unit 212/255: Principles of Fabrication and Welding Handout 12: Heat treatment The properties of carbon steels can be changed by heat treatment.

Four heat treatments available are:

– annealing

– normalising

– hardening

– tempering.

Three factors influence the heat treatment of carbon steels:

– Carbon content

– Temperature

– Cooling rate

The various combinations of iron and carbon, when subjected to suitable heat treatments result in an enormous range of properties.

At room temperature the micro structure of the normalised steel consists of grains of iron, and depending on the carbon present, the grains may display a striped appearance produced by alternate layers of iron and iron carbide.

This structure results because, at room temperature carbon is not soluble in iron.

As the temperature of the steel is raised the structure begins to break down and at a certain point the carbon begins to dissolve into the steel.

This is similar to sugar dissolving in hot tea but the difference being that the steel is still solid.

It is this transformation temperature that must be reached before we can change the properties of the steel by heat treatment.

The temperature at which the transformation takes place depends on the amount of carbon present and varies from around 9500 C for steel containing 0. 1% carbon to 7500 C for a 0. 83% carbon steel.



• The temperatures for hardening, normalising and annealing are the same.

• The only difference is the rate of cooling – quenching

Quenching mediums

Quenching mediums produce different cooling rates

• Air

– Metal left out in the workshop is being quenched by the surround air

• Oil

• Water

• Brine (salty water)

Annealing

• Annealing is a softening process

• Fully annealed steel produces a poor surface finish when machined.

• To anneal steel it is heated to its transformation temperature

• Cooled slowly

• Small items can be covered in a blanket of sand

• Larger items, following heating in a furnace, are allowed to cool within the furnace as it cools.



Normalising

Normalising is a softening process

Normalising does not produce as soft a structure as annealing.

Following heating to the transformation temperature the component is allowed to cool in air.

Normalising is returning the steel to its “normal” state i.e. as supplied.

Hardening

Steels with less than 0.3% carbon do not harden by heat treatment.

The higher the carbon content the harder the steel will become.

The faster the cooling, the harder the steel will become.

Quenching rates:

– Brine – cools quickest – produces the hardest state

– Water

– Oil – cools slowest – produces the least hard state

• Quenching can set up stresses within the component

The hardening process produces steels which are hard and have good wear resistance properties, unfortunately, the steel is too brittle to use.

This brittleness, combined with the possibility of quenching stresses, makes the use of steel in this state impractical unless the “dead hard” condition is desirable, as in the case of scrapers.

To reduce the brittleness of hardened carbon steel and induce some toughness, the steel is reheated or “tempered”.

Tempering

The tempering process relieves the quenching stresses.

A common workshop method of tempering is to make use of the oxide films that form on the surface of polished steel when it is heated.

Each change in oxide colour indicates a temperature range and is reasonably simple to quench the tool as the correct colour band appears at the cutting edge.

The table indicates the colours and their associated temperatures.



Unit 212/255: Principles of Fabrication and Welding Handout 13: Selection criteria Material selection

Selection of the correct material for a products manufacture is essential.

Incorrect material selection could effect:

– cost of product

– service life

– product failure

– production capabilities.

Choosing materials

Selecting the correct material for a product

• 10,000’s possible choices

• Physical properties of a material can reduce this choice:

– Can it be formed, welded?

– Is it strong enough?

• Computer modelling can reduce to a list of 5 – 10

• Working prototypes can be manufactured from 1 or 2 materials

Materials have at least one purpose

– Structural – supports a load

– Functional – it does something

• Conducts electricity

– Decorative – it looks good

Economic decisions

– Costs

– Can it be recycled

– Availability

Physical properties

• Mass (weight) © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk


Mechanical properties

– Hardness

– Toughness

– Stiffness

– Strength

Thermal

– Expansion rates

– Conductivity

Product life

– Oxidisation

– Corrosion resistance

– Wear resistance

Production restraints

– Malleable

– Ductile

– Heat treatment requirements (pre and post production)

– Weldability

– Finishing

Aesthetics

– Does it look good

– Colour

– Feel

– Texture

– Electrical and Heat

– Conductivity

– Resistance

Decisions on the material to be used for any product needs to be made before production can begin.

• Consider the three-pin plug.

• Identify the materials used for the parts.

• Discuss why each material was used for the component parts.



Unit 212/255: Principles of Fabrication and Welding Handout 15: Mean bending allowances

Using the mean line calculate the blank lengths required for the following fabricated shapes.


SmartScreen 2850 Level 2 in Engineering Unit 255 Handout 15

Unit 255: Principles of Fabrication and Welding Handout 15: Neutral bending allowances

Using the neutral line calculate the blank lengths required for the following fabricated shapes. Neutral line = 0.4t


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Worksheet 1

Unit 212/255: Principles of Fabrication and Welding Technology Worksheet 1: MIG Welding Gases Selection of the correct shielding gas to use when MIG welding is essential in ensuring weld quality is maintained. In most instances gas mixtures based on pure argon are used. You have been tasked with identifying the most appropriate shielding gas for the materials listed. Increasing deposition rates is important but ensuring weld quality is paramount. The gas selected for each metal should be explained. For each of the metals listed below identify a suitable shielding gas.

Material Shielding gas

Flow Rate

Explain your choice of shielding gas

Low Carbon Steel – 2mm thick

Low Carbon Steel – 20mm thick

Medium Carbon Steel – 10mm thick

Aluminium – 12mm thick

Stainless Steel – 5mm thick



Unit 212/255: Principles of Fabrication and Welding Technology Worksheet 2: TIG Welding Gases Selection of the correct shielding gas to use when MIG welding is essential in ensuring weld quality is maintained. In most instances gas mixtures based on pure argon are used. You have been tasked with identifying the most appropriate shielding gas for the materials listed. Increasing deposition rates is important but ensuring weld quality is paramount. The gas selected for each metal should be explained. For each of the metals listed below identify a suitable shielding gas.

Material Shielding gas

Flow rate

Explain your choice of shielding gas

Low carbon steel – 2mm thick

Aluminium – 5mm thick

Aluminium – 10mm Ttick

Austenitic stainless steel – 3mm thick

Copper – 5mm thick



Unit 212/255: Principles of Fabrication and Welding Worksheet 3: Weld symbols worksheet For each of the following descriptions on a welded joint:

1. Draw a diagram of the weld preparation 2. Using a reference line, draw the relevant weld symbol.

1. Single v butt 2. Double v butt 3. Tee fillet, concave profile 4. Stitched tee fillet, 6 welds, weld 100, gap of 100. 5. Double sided tee fillet, leg lengths of 10 and 12mm 6. Tee fillet, leg length 12mm, welded all round.

Questions:

1. What symbol represents a spot weld? 2. How would a joint that needed to be welded on site be indicated on a weld

symbol? 3. What does the dotted line below the reference line mean? 4. How could a weld symbol indicate that a joint needs to be welded by a

specific process? 5. How would a staggered stitch weld be indicated on a weld symbol.



Unit 212/255: Principles of Fabrication and Welding Worksheet 4: Flame conditions

Questions:

1. What colour is an acetylene cylinder?

2. What colour is an oxygen cylinder?

3. List the 3 types of flame available .

4. Which flame would be produced with equal amounts of oxygen andacetylene?

5. What type of flame would be produced if there was an excess of oxygen?



6. What type of flame would be produced if there was an excess of acetylene?

7. Draw a diagram of an oxy-acetylene flame and label the main parts including the hottest point.

8. What temperature will an oxy-acetylene flame produce?

9. Describe the correct method for lighting and extinguishing an oxy-

acetylene flame.



10. Describe why step back welding reduces distortion



Unit 212/255: Principles of Fabrication and Welding Technology Worksheet 5: Weld defects Identify the following defects and their likely cause by selecting one of the three options. Defect Description Cause

1. Excessive

spatter 2. Cracking 3. Porosity

1. Low amps 2. High amps 3. Short arc

length

1. Undercut 2. Cracking 3. Porosity

1. No shielding

gas 2. Low amps 3. Misalignment

1. Uneven

leg length 2. Underfill 3. Lack of

fusion

1. Low amps 2. High amps 3. No shielding

gas

1. Excessive

spatter 2. Poor root

penetration

3. Overfill

1. Poor technique 2. High amps 3. Dirty metal



1. Overlap 2. Cracking 3. Porosity

1. Dirty metal 2. Wrong weld

prep 3. Wrong

electrode material

1. Underfill 2. Inclusions 3. Lack of

fusion

1. Wrong

electrode material

2. Poor cleaning 3. Porosity

1. Overlap 2. Overfill 3. Excess

weld metal

1. Dirty metal 2. Incorrect weld

prep 3. Wrong

electrode

1. Excess

weld metal 2. Overlap 3. Cracking

1. Fast travel 2. Slow travel 3. High amps

1. Excessive

spatter 2. Cracking 3. Underfill

1. Fast travel 2. Slow travel 3. Low amps



Unit 212/255: Principles of Fabrication and Welding Worksheet 6: Materials Material properties For each of the materials listed below identify:

1. their properties 2. two forms of supply 3. two typical uses.

Material Properties Two forms of supply Two typical uses Low Carbon Steel

Stainless Steel

Cast Iron

Aluminium

Copper

Brass

Bronze


SmartScreen 2850 Level 2 in Engineering Unit 212/255 Worksheet 6 All steel can be supplied in different shapes and sizes to suit the needs of the fabrication being built. List six forms of supply of steel and draw a sketch of the shape: Form of supply Sketch of shape



Unit 212/255: Principles of Fabrication and Welding Worksheet 7: Criteria selection

The TIG torch shown below is manufactured from a range of materials.

1. Identify the parts and the material they are made from.2. Explain why that choice of material was made.



Description Material Reason for choice

A bench is to be manufactured for a seafront town. Consider the following criteria, identify suitable materials for its manufacture.

• Looks good• No maintenance• Long life• Comfortable• Seat feels warm• Cheap• Light



Unit 214: Welding By MIG Welding Process Handout 1: Health And Safety Statistics:

• 500 people are killed • 30,000 seriously Injured • 30 million working days lost

PER YEAR TO WORK RELATED INJURIES

• Engineering health and safety is very important • Every year people working in engineering need to have time off, lose a finger, a

leg and die due to not following health and safety guidelines. • The Health & Safety at Work act is law in the UK. • The employers’ and employees’ responsibilities regarding Health and Safety are

defined within the act. • Everyone has their responsibilities in health and safety.

Employer and employee responsibilities Under laws and regulations everyone have their responsibilities when it comes to health and safety. Your responsibilities (the employee)

– Don’t do anything that might endanger you. – Don’t do anything that might endanger someone else. – Always use any safety equipment given to you. – Co-operate with your employer or tutor. To protect others when welding you can:

• work behind fixed barriers or curtains • erect temporary barriers or curtains • display signs that warn people as they enter the welding area • Verbal – most welders shout “eyes” just before they start welding.

Employers’ responsibilities – Provide a safe place of work – Provide safe equipment – Provide welfare facilities – Provide personal protective equipment


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 1 Person protective equipment (PPE) PPE is there to protect you from hazards in the workplace. Your employer or tutor will provide the correct PPE for you to carry out the task safely. It is important that you know how to use any PPE provided. If you are not sure ask! If PPE is provided you must use it.

• The filter lens is available in different shades. • The selection of lens depends on the amperage being used:

Shade 9EW = up to 100 amps (lightest Shade) Shade 10EW = up to 150 amps Shade 11EW = up to 225 amps Shade 12EW = up to 300 amps Shade 13EW = up to 500 amps (darkest Shade)

EW = electric welding Arc eye (welder’s flash)

• Arc eye is painful and repeated exposure to UV radiation can cause permanent damage .

• Welding head shields should always be worn when welding or working close to another welder

• You do not need to look directly at the arc to get arc eye, it can be reflected off shiny surfaces into your eyes.

• Wearing safety glasses that have UV protection will help reduce the risk of arc eye.

• Good practice is to wear a pair of safety glasses under your welding helmet.

Designed to protect the welder from the bright lights and rays produced by the welding arc. Modern helmets auto-darken as the arc is struck:

• The lens of the head shield is made up of 3 parts. • 2 cover lenses to protect the central filter lens • The filter lens is dark to protect your eyes

The arc gives ff three types of radiation:

• Visible light – causes glare • Infra-red – causes an effect similar to sunburn • Ultra-violet – causes arc eye (welders flash)


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 1 Other protection

• Welders often work in areas where there is a risk of falling objects. Helmets should be worn at all times.

• Engineering can be noisy, protect your hearing at all times. • When welding make sure your throat is protected, button overalls all the way up.

Welding leathers

• When working with high amperages or in locations where welding sparks will fall on the welder, welding leathers are an additional layer of PPE.

PPE problems

• All PPE must be kept in good condition. • In certain circumstances PPE may become unsafe or not protect the user

completely. • Overalls

– The flame retardant chemical in the overalls washes out over a period of time

– Ripped overalls will catch fire easily – Oily or greasy overalls can catch fire.

Welding fumes

• Welding Fumes are Influenced By: – type of process – welding consumable – presence of any material coatings



– welding parameters – shielding gas composition

The fume given off by welding is a mixture of gases and very fine particles which can cause illness. Gases that can be present in welding are:

• nitrous oxide (NO), • carbon dioxide (CO2), • carbon monoxide (CO) • shielding gas (e.g. Argon, helium) and • ozone (O3).

The visible fume includes particles of metal, metal oxide and flux (if used) The level of risk from the fume will depend on:

• How toxic the fume is • How concentrated the fume is • How long you are breathing the fume

Welding illness

• Occupational asthma – Stainless steel fume contain chemicals that can cause asthma.

• Cancer – Welding fume is internationally recognised as carcinogenic.

• Metal fume fever – Metal fume fever has flu like symptoms linked to the welding of

galvanised metals. • Irritation of throat and lungs

– Welding fume can cause dryness to the throat, coughing or a tight chest. Ozone can cause of this.

Fume removal Depending on the amount of welding taking place various forms of fume attraction are available.

• For low levels a simple extractor fan in the wall will provide a level of background ventilation.

• Natural ventilation can be achieved by opening windows and doors or when working outdoors.

• Local exhaust ventilation (LEV) © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk

SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 1 Electrical hazards

• Electric shocks occur when the current flows through you. • It’s the current (amps) not voltage that causes injury.

To protect against shock it is important that electric circuits:

• are insulated • are earthed • contain fuses and circuit breakers

Besides shocks there are other hazards associated with electricity.

• Faulty connections can generate sparks which can cause fires. • Loos connections can heat up causing burns to the welder of melting of the

insulating cover. Risk assessment Prior to starting welding you should:

• Check all connections • are connected correctly • are tight

• Check all cables – no damage to insulation – return lead is correct size for the amperages being used – earth is connected (fixed sets)

Hot metal Hot metal is a common hazard in the welding workshop.

• To protect yourself and others make sure: – All hot metal is marked as “HOT”, with date and time included. – Only carry metal using tongs. – Quench (dip in water) to cool down unless the weld is going to be tested. – Good practice is to treat every piece of metal as hot, don’t pick it up

unless you are sure it’s cool! Good housekeeping At the end of the shift or lesson it is important to leave the work area in a safe state.

• This includes: – isolating the welding set – turning the shielding gas off – returning all tools to storage area – dispose of any scrap material – generally tidy up the area.



Unit 214: Welding by MIG process Handout 2: MIG welding equipment Types of welding sets Transformer/rectifier: • A transformer reduces volts and increases amperages • Transformers only work on alternating current (ac) supplies • Rectifiers convert ac current into direct current (dc) supplies • Mig welders only work on dc • Transformers are heavy and generate a lot of heat.

Inverters: • Inverters are high speed electronic switches • transformers are still needed but are much smaller • Inverter technology has seen smaller, lighter sets available for the welding industry • Inverter machines are more energy efficient that traditional transformer/inverter sets Engine driven generators • do not require a mains supply to operate • generator driven by a diesel or petrol engine • ideal for site work MIG Torches

• MIG torches come in different sizes to suit the

welding machine output. • They need to be light and flexible. • They can be either air cooled or water cooled • Welding torches are fitted to the positive

connection of the set. • Connection is usually shown as DCEP

• Standard torches, both air and water cooled are classified as push torches. The wire feed mechanism situated within the welding set pushes the wire towards the weld pool. This system is ideal where the operator is working close to the welding set with a short welding lead..

• Push – pull torches have an additional set of rollers built into the MIG torch. The welding set pushes the wire, the torch pulls the wire. This system is beneficial where the welding is taking place away from the welding set.



• The spool on torch allows welders to operate a distance from the welding sets where small reels of welding wire is located on the rear of the gun itself. It is also ideal where there needs to be multiple changes for different materials where small reels of various materials can be made available.


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 2 Welding leads The welding harness must transport a number of functions from the welding set to the torch Other connections

• Electricity needs to be a circuit to operate. • To complete the circuit in welding a current return is connected to the workpiece. • Current return clamps are rated to match the amperage of the welding set.

Grinders and sanders

• Grinders and sanders remove metal by abrasion. • Grinding machines come in different sizes and are identified by the disc diameter

that can be fitted. • Gloves, overalls and eye protection must be used when using these machines. • Beware of the direction of the sparks to protect others nearby. • Sparks are hot, make sure no flammables are near.


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 2 Linishers Linishers are continuous sanding belt machines

Flame cutting

• The edge preparation for a vee butt weld can be produced by flame cutting. • This can be done by machine or manually.



Unit 214: Welding by MIG Process Handout 3: MIG process General set up

Process • There are a range of variables associated with MIG welding • If any one of these is wrong it could result in a poor weld. • The variables are:

– Voltages – Wire speed (amperage) – Gas flow – Inductance



Volts and amps • Volts are the main setting on a MIG set • Amps are altered by changing the wire speed. • Your tutor will tell you the recommended starting point for the welding sets in the

workshop. • There are apps available for smartphones to give you a guide for settings for

different materials and joints

• Welding sets have parameter bands • These are set by the manufacturer and are a recommended setting for volts/amps • When the correct setting is found, the welding will produce a sizzling sound. • If you increase the volts, you will need to increase the wire speed to return to the

correct balance but the heat input will be greater


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 3 Wire feed speed/amperage relationship As the wire speed increases an increase in amperage is required to ensure wire burn off rates are optimised.

Shielding gases In addition to providing a protective environment, the shielding gas and flow rate also have a pronounced effect on the following:

• arc characteristics • mode of metal transfer • penetration and weld bead profile • speed of welding • undercutting tendency • cleaning action • weld metal mechanical properties


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 3 Gas flow • Gas flow is measured in litres per minute (Lp/m) • Low gas flow will not protect the molten pool from the atmosphere. • Too high a gas flow will cause turbulence and drag the surrounding air into the weld,

again causing defects. • Gas flow rates can vary depending on the gas, material thickness and joint type. • Gas flow is regulated by a flow meter. • As a general guide flow rates should be:

• 1 - 3mm thick - 8 -12 lp/m • 4mm and above - 15 -20 lp/m



MIG SHIELDING GAS SELECTION GUIDE

Metal Thickness in. (mm) Recommended Shielding Gas Advantages

MIG SHORT ARC

Carbon Steel Up to 14 gauge (0.1) 92% Argon / 8% CO2 Good burn through and distortion control. Used also for spray arc welding

14 gauge - 1/8 (3.2) 75% Argon / 25% CO2

88% Argon / 12% CO2

High welding speeds without burn through. Minimum distortion and spatter. Best puddle control for out of position welding. Provides best mechanical properties for any given wire

Over 1/8 (3.2) 75% Argon / 25% CO2

88% Argon / 12% CO2

High welding speeds without burn through. Minimum distortion and spatter. Best puddle control for out of position welding. Provides best mechanical properties for any given wire

50% Argon / 50% CO2 Deep penetration; spatter

CO2 Deep penetration; faster welding speeds; high spatter

Stainless Steel Up to 14 gauge (0.1) 92% Argon / 8% CO2 Good burn through and distortion control. For use where corrosion resistance is not mandatory

Over 14 gauge (0.1) 92% Argon / 8% CO2 Good burn through and distortion control. For use where corrosion resistance is not mandatory

90% He 7.5% Ar 2.5% CO2 No effect of corrosion resistance. Small heat-affected zone. No undercutting, minimum distortion. Good bead shape and mechanical properties

High Yield Strength Steels Up to 14 gauge (0.1) 92% Argon / 8% CO2 Good burn through and distortion control. Used also

for spray arc welding

Over 14 gauge (0.1) Argon - Hydrogen Excellent arc stability, welding characteristics bead contour, little spatter, high impacts

MIG SPRAY ARC

Carbon Steel All thicknesses 95% Argon / 5% O2 Improves droplet rate and arc stability

92% Argon / 8% CO2 Produces a more fluid and controllable weld puddle; good coalescence and bead contour. Minimizes undercutting; permits high speeds

Aluminium Up to 3/8 (12.7) Argon Best metal transfer, arc stability and plate cleaning. Little or no spatter.

Over 3/8 (12.7) Argon - Helium Higher heat input. Produces more fluid puddle and flatter bead. Minimizes porosity.

Helium Highest heat input. Good for mechanized welding.

Low Alloy Steel Up to 3/32 (2.4) 98% Argon / 2% O2 Reduces undercutting. Improves coalescence and bead contour. Good mechanical properties.


Over 3/32 (2.4) 92% Argon / 8% CO2 Excellent arc and weld characteristics.

Stainless Steel All thicknesses 99% Argon / 1% O2 Good arc stability. Produces a fluid and controllable weld puddle; good coalescence and bead contour. Minimizes undercutting.

98% Argon / 2% O2 Can be used on more sluggish alloys to improve puddle fluidity, coalescence and bead contour.

Copper, Nickel & Copper-Nickel alloys

Up to 1/8 (3.2) Argon Good arc stability.

Over 1/8 (3.2) Argon - Helium Higher heat input of helium mixture offsets high heat conductivity of heavier gauges.

Helium Higher heat input and improved penetration.

Magnesium Titanium -- Argon Excellent cleaning action. Provides more stable arc

than helium-rich mixtures

MIG CORED WIRE

Carbon Steel All thicknesses CO2 Deep penetration.

75% Argon / 25% CO2 Low smoke and spatter. Good puddle control. Bridges gaps

Stainless Steel All thicknesses CO2 Deep penetration.

75% Argon / 25% CO2 Low smoke and spatter. Good puddle control. Bridges gaps

SmartScreen Level 2 in Engineering Unit 214 Handout 5

Unit 214: Welding by MIG Process Handout 5: Constant Voltage The volt-ampere characteristic curve, which should be flat or level in a true constant voltage supply is usually designed to have a slight slope as shown below. Its purpose is to maintain a constant arc voltage irrespective of the current flowing. The wire feed speed is pre-set for a particular welding operation. Once pre-set the motor feeds the wire to the arc at constant speed. For the arc to function correctly the rate of wire-feed must be exactly balanced by the burn-off rate to keep the arc length constant. The constant voltage characteristic keeps a constant arc length by self-adjusting. So if the arc shortens (manually or due to slight variation in motor speed), the voltage decreases resulting in increased current which in turn gives a greater burn-off rate of the wire and the arc is lengthened to re-establish the original arc length. Similarly if the arc lengthens, then the voltage increases, the current decreases and therefore the burn-off rate of the wire is decreased and the arc shortens to its original length. This arc length control system is known as the self-adjusting arc:


Unit 214: Welding by MIG process Handout 6: MIG welding MIG electrode wire

• Material of the wire matches the material being welded • Various diameters available

• Ø0.8, Ø1.0, Ø1.2 • Carbon steel wires are usually copper coated

• Good conductor of electricity • Protects the wire from corrosion • Lubricates as the wire passes through the machine

Flux cored MIG electrode wire

• Available with a flux core • Flux core can provide additives to improve the weld quality • Flux core produces a slag that needs to be removed after welding • Flux cored electrodes can be used with no additional gas shielding • Iron particles added to the core can increase deposition efficiency

Storage

• MIG wire should be stored by material type to prevent incorrect use. • Steel electrode wire must be stored in a dry environment to prevent corrosion.

Supply • Electrode wire can be supplied in 0.7kg, 5kg and 25Kg spools. • For high production and robotic applications 250Kg drums are available.

Distortion

• As a weld cools it can cause distortion. • Being aware of distortion and trying to reduce it can save a lot of work. • One way to reduce the effects of distortion is called pre-setting.



Pre-setting

The amount of pre-setting can’t be calculated, it comes with experience. Distortion control

• Distortion can also be controlled by restraint. • Restraint means holding the metal and not letting it move.

Jigs and fixtures not only hold the pieces to be welded in the correct position they also help restrain distortion


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 6 Welding positions


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 6 Torch angles


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 6 Torch movement


SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 6 Welding techniques

Post welding

• Visually check welds for any defects • Welds should be wire brushed on completion. • The weld itself shouldn’t be cleaned up using a grinder. • Spatter needs to be removed, usually with a hammer and chisel.

Hot metal

• Hot metal is a common hazard in the welding workshop. • To protect yourself and others make sure:

– All hot metal is marked as “HOT”, with date and time included. – Only carry metal using tongs. – Quench (dip in water) to cool down unless the weld is going to be tested. – Good practice is to treat every piece of metal as hot, don’t pick it up

unless you are sure its cool! Good housekeeping At the end of the shift or lesson it is important to leave the work area in a safe state.



Unit 214: Welding by MIG process Handout 7: Welding Defects Assessment criteria

• Qualitive – Based on appearance or levels of defects – Quantitive – Based on numerical limits such as extent of defect, size of defect or


• Quantitive – Based on numerical limits such as extent of defect, size of defect or


• A weld defect can be caused by a number of factors. • 2 of the main causes of defects are:

• Operator error • Poor preparation

• Inspection and testing methods are used to detect any defects. • Some defects can be classed as a “lack of continuity”, (where the weld is not

continuous). • The most common method of inspection is visual examination.

Types of defect



Unit 214: Welding by MIG process Handout 8: Inspection and Testing Completed welds are often subjected to a system of inspection and testing to ensure its quality. • Testing has 2 main categories:














Limitations



SmartScreen 2850 Level 2 in Engineering Unit 214 Handout 8 Magnetic particle testing












Types of etchant

Metal Etchant







Nick break test


Bend testing




Cupping test



SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 1

Unit 214: Welding By MIG Welding Process Worksheet 1: Health and Safety Statistics:



• Engineering health and safety is very important • Every year people working in engineering need to have time off, lose a finger, a

leg and die due to not following health and safety guidelines. • The Health & Safety at Work act is law in the UK. • The employers’ and employees’ responsibilities regarding Health and Safety are

defined within the act. • Everyone has their responsibilities in health and safety.


– Don’t do anything that might endanger you. – Don’t do anything that might endanger someone else. – Always use any safety equipment given to you. – Co-operate with your employer or tutor. To protect others when welding you can:

• work behind fixed barriers or curtains • erect temporary barriers or curtains • display signs that warn people as they enter the welding area • Verbal – most welders shout “eyes” just before they start welding.

Employers’ responsibilities – Provide a safe place of work – Provide safe equipment – Provide welfare facilities – Provide personal protective equipment


SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 1 Person protective equipment (PPE) PPE is there to protect you from hazards in the workplace. Your employer or tutor will provide the correct PPE for you to carry out the task safely. It is important that you know how to use any PPE provided. If you are not sure ask! If PPE is provided you must use it.

• The filter lens is available in different shades. • The selection of lens depends on the amperage being used:

Shade 9EW = up to 100 amps (lightest Shade) Shade 10EW = up to 150 amps Shade 11EW = up to 225 amps Shade 12EW = up to 300 amps Shade 13EW = up to 500 amps (darkest Shade)

EW = electric welding Arc eye (welder’s flash)





• Good practice is to wear a pair of safety glasses under your welding helmet.

Designed to protect the welder from the bright lights and rays produced by the welding arc. Modern helmets auto-darken as the arc is struck:


The arc gives ff three types of radiation:



SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 1 Other protection



Welding leathers


PPE problems





Welding fumes

• Welding Fumes are Influenced By: – type of process – welding consumable – presence of any material coatings



– welding parameters – shielding gas composition


• nitrous oxide (NO), • carbon dioxide (CO2), • carbon monoxide (CO) • shielding gas (e.g. Argon, helium) and • ozone (O3).



Welding illness









• Local exhaust ventilation (LEV) © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk

SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 1 Electrical hazards










• To protect yourself and others make sure: – All hot metal is marked as “HOT”, with date and time included. – Only carry metal using tongs. – Quench (dip in water) to cool down unless the weld is going to be tested. – Good practice is to treat every piece of metal as hot, don’t pick it up





Unit 214: Carrying out MIG welding processes Worksheet 2: Workshop risk assessment Task 1: On a separate sheet of paper draw a diagram of the workshop. Try and keep your drawing to scale. Your tutor will explain what is meant by this and help you understand why this is important. When you have completed your drawing you need to include the location of the following:

• Fire escapes • Emergency stops • Fire extinguishers • First aid box

Task 2: Walk around the workshop and make a note of anything you would consider a hazard and decide if there is any risk to you and your fellow students. Remember a HAZARD is anything that could cause harm, the RISK is the likelihood of that happening. Hazard description What is the risk of it causing

harm What can be done to reduce the risk

Does something need to be done now



Unit 214: Carrying out MIG welding processes Worksheet 3: Welding bay risk assessment Items Condition Recommendation Status Level General Housekeeping

Welding Set

Welding Cables

Electrode Holder

Return Clamp

Mains Leads & Plug

Electrical Test Date:

Tools

Welding Helmet

Gauntlets

Pressure Gauges

Extraction System

Machine Earth

Curtains

Gas Hoses

Level: 1: Very Dangerous; 2: Use with Caution; 3: Suitable for Use Status: 1: Do not use this bay; 2: Action required; 3: Suitable for Use.



Unit 214: Welding by MIG process Worksheet 4: Weld defects Identify the following defects and their likely cause by selecting one of the three options. Defect Description Cause

1. Excessive

spatter 2. Cracking 3. Porosity

1. Low amps 2. High amps 3. Short arc

length


1. No shielding


1. Uneven leg

length 2. Underfill 3. Lack of

fusion


gas

1. Excessive


penetration 3. Overfill

1. Poor

technique 2. High amps 3. Dirty metal





prep 3. Wrong

electrode material


fusion

1. Wrong

electrode material

2. Poor cleaning 3. Porosity

1. Overlap 2. Overfill 3. Excess

weld metal

1. Dirty metal 2. Incorrect weld

prep 3. Wrong

electrode

1. Excess

weld metal 2. Overlap 3. Cracking


1. Excessive




SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 5 Task title: Open corner joint PA Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean & tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up & de-burred. Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when

finished

Task completed List the tools you used List the machines you used List the PPE you used

SmartScreen 2850 Level 2 in Engineering Unit Task planning sheet

No. Description Tools required Machines required

PPE

Welding procedure sheet

Volts Wire speed

Wire diameter Weld joint type

Shielding gas Gas flow rate

Weld position Material

SmartScreen 2850 Level 2 in Engineering Unit

Quality control Visual inspection Description Weld acceptable

y/n If not acceptable explain

Weld width consistent

Stop/starts merge smoothly

Tack welds blend in (no humps)

Weld surface free from cracks & porosity

Weld finish crater filled

Weld & parent metal free from arcing

No grinding or chipping marks

Destructive testing Macro etch (if applicable) Weld acceptable


Good fusion

No inclusions or porosity

Nick break test (if applicable) Weld acceptable y/n

If not acceptable explain

Good sidewall fusion

No cracking


List three problems you had when completing this task and then explain how you overcame them.

Problem description What did you do to overcome this?

If you had to re-do this welded joint, what would you do differently?

What did you learn completing this assessment?

Assessor feedback


I confirm that the practical task and written planning is my own work.

Candidate: _________________________________ date: __________________ Assessor: _________________________________ date: ___________________

SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 6 Task title: Lap joint PB Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before

starting

Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred

Tools returned to storage

Weld tested Scrap material removed Paperwork complete Work area clean and tidy when

finished




PPE


Volts Wire speed
















Good fusion





No cracking






Assessor feedback



Candidate: _________________________________ Date: __________________ Assessor: _________________________________ date: ___________________

SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 7 Task title: Tee joint PB Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before

starting




finished




PPE


Volts Wire speed
















Good fusion





No cracking






Assessor feedback

SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 8 Task title: Lap joint PC Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when

checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


Volts Wire speed












Weld and parent metal free from arcing




Good fusion





No cracking






Assessor feedback

SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 9 Task title: Butt weld PA Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before

starting

Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when

finished




PPE


Volts Wire speed










Weld surface free from cracks and porosity






Good fusion





No cracking






Assessor feedback



Candidate: _________________________________ Date: __________________ Assessor: _________________________________ Date: ___________________

SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 10 Task title: Butt joint PC Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before

starting

Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when

finished


SmartScreen 2850 Level 2 in Engineering Unit 2 Task planning sheet


PPE


Volts Wire speed




SmartScreen 2850 Level 2 in Engineering Unit 2












Good fusion





No cracking






Assessor feedback


SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 11 Task title: Open corner PF (vertical up) Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before

starting




finished



Task planning sheet


PPE


Volts Wire speed





Quality control

Visual inspection

Description Weld acceptable y/n









Destructive testing

Macro etch (if applicable) Weld acceptable y/n


Good fusion





No cracking






Assessor feedback

SmartScreen 2850 Level 2 in Engineering Unit 214 Worksheet 12 Task title: Tee joint PF (vertical up) Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before

starting




finished




PPE


Volts Wire speed










Weld surface free from cracks and porosity






Good fusion






No cracking





Assessor feedback



Candidate: _________________________________ Date: __________________

Assessor: _________________________________ Date: ___________________


Unit 215: Welding by TIG welding process Handout 1: Health and safety Statistics



• Engineering health & safety is very important • Every year people working in engineering need to have time off, lose a finger, a

leg and die due to not following health and safety guidelines. • The Health & Safety at Work act is law in the UK • The employers and employees responsibilities regarding H&S are defined within

the act. • Everyone has their responsibilities in health and safety.


– Don’t do anything that might endanger you – Don’t do anything that might endanger someone else. – Always use any safety equipment given to you – Co-operate with your employer or tutor To protect others when welding you can:

• work behind fixed barriers or curtains • erect temporary barriers or curtains • display signs that warn people as they enter the welding area • Verbal – most welders shout “eyes” just before they start welding

Employers responsibilities – Provide a safe place of work – Provide safe equipment – Provide welfare facilities – Provide personal protective equipment


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 1 Person protective equipment (PPE) PPE is there to protect you from hazards in the workplace. Your employer or tutor will provide the correct PPE for you to carry out the task safely. It is important that you know how to use any PPE provided. If you are not sure ask! If PPE is provided you must use it.

• The filter lens is available in different shades. • The selection of lens depends on the amperage • • • •

• Shade 9EW = up to 100 amps (lightest Shade)

Shade 10EW = up to 150 amps Shade 11EW = up to 225 amps Shade 12EW = up to 300 amps Shade 13EW = up to 500 amps (darkest Shade)

EW = electric welding Arc Eye (welders flash)





• Good practice is to wear a pair of safety glasses under your welding helmet

Designed to protect the welder from the bright lights and rays produced by the welding arc. Modern helmets auto-darken as the arc is struck


The arc gives off 3 types of radiation:



SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 1 Other protection



Welding leathers


PPE problems





Welding fumes

• Welding Fumes are Influenced By: – type of process – welding consumable



– presence of any material coatings – welding parameters – shielding gas composition


• nitrous oxide (NO), • carbon dioxide (CO2), • carbon monoxide (CO) • shielding gas (eg Argon, helium) and • ozone (O3)



Welding illness









• Local exhaust ventilation (LEV)



•

Electrical hazards










• To protect yourself and others make sure: © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk




• This includes: – Isolating the welding set – Turning the shielding gas off – Returning all tools to storage area – Dispose of any scrap material – Generally tidy up the area



Unit 215: Welding by TIG process Handout 2: TIG welding equipment Types of welding sets • Transformer/rectifier • a transformer reduces volts and increases amperages • transformers only work on alternating current (AC) supplies. • rectifiers convert AC current into direct current (DC) supplies • transformers are heavy and generate a lot of heat.

• Inverters • Inverters are high speed electronic switches • transformers are still needed but are much smaller • Inverter technology has seen smaller, lighter sets available for the welding industry • Inverter machines are more energy efficient that traditional transformer/inverter sets Engine driven generators • do not require a mains supply to operate • generator driven by a diesel or petrol engine • ideal for site work TIG Torches

• TIG torches come in different sizes to suit the welding

machine output. • They need to be light and flexible. • They can be either air cooled or water cooled • TIG torches are generally fitted to the negative

connection of the set.


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 2 Torch parts

TIG Electrodes

• TIG electrodes are an alloy of tungsten and other elements. • Additional elements improve arc initiation and stability • They are available in a range of diameters: • 1.6mm, 2.4mm, 3.2mm being the most common • Tungsten electrodes are identified by the coloured tip.

Thorium is radioactive and care needs to be taken when sharpening. A risk assessment is required.



Welding leads

Other connections

• Electricity needs to be a circuit to operate. • To complete the circuit in welding a current return is connected to the workpiece. • Current return clamps are rated to match the amperage of the welding set.


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 2 TIG filler wire

• Filler wire is selected to suit the material being welded. • It is available in a range of diameters

• 1mm, 1.6mm, 2.4mm, 3.3mm. • Steel filler wire is normally copper coated to prevent rusting. • Filler wire should be segregated in storage to prevent incorrect selection. • They should be stored in a warm, dry room to prevent corrosion.

Grinders and sanders • Grinders and sanders remove metal by abrasion. • Grinding machines come in different sizes and are identified by the disc diameter

that can be fitted. • Gloves, overalls and eye protection must be used when using these machines. • Beware of the direction of the sparks to protect others nearby. • Sparks are hot, make sure no flammables are near.

Linishers Linishers are continuous sanding belt machines



Unit 215: Welding by TIG process Handout 3: TIG electrodes

Types of tungsten electrodes Tungsten provides welders with greater stability and powerful arcs.

Tungsten Inert Gas (TIG) welders depend on tungsten electrodes to carry the alternating current (AC) or the direct current (DC) to the welding arc. Tungsten is a rare, metallic element that has the highest melting point of (3,410 degrees Celsius) of any metal on earth. Electrodes range from 1mm to 6mm in diameter with standard lengths from three to 24 inches. Easy arc starts, stability and bead length depend on using the proper electrode tip.

Pure Tungsten

Welders use pure tungsten mostly for AC sin wave welding and other less critical, low-current applications. Pure tungsten contains 99.5 % tungsten, costs less than other electrodes, has a clean, balled tip and gives good arc stability. It falls under AWS classification EWP and is colour-coded green.

2% Thoriated

Electrodes contain a minimum of 97.3 % tungsten and 1.7 to 2.2 % thorium. Most welders prefer 2% since the electrodes are easy to use, the pointed end lasts longer, arc starts are strong and there is a high current capacity. Stable and are designed for DC welding on nonferrous materials. 2% thoriated tungsten electrodes have a red tip. Thorium is a radioactive material and the storage and use of this class of electrodes requires special consideration. The main concern is the sharpening of the electrode where the dust can be inhaled. Tungsten’s should be sharpened on an enclosed wheel grinder.

2% Ceriated

This welding electrode contains a minimum of 97.3 % tungsten, with 1.8 to 2.2 % cerium. It's used for low current settings, has a low-amp arc and works well for either AC or DC processes. Ceriated electrodes provide a safe alternative to thoriated electrodes, and many welders can't tell the difference. These electrodes are colour coded by a grey tip.

Lanthanated

This stable electrode disperses evenly, provides excellent arc starts, low burn-off rates and reignites readily like ceriated. Lanthanated 1.5% electrodes


http://www.ehow.co.uk/list_7416764_types-tungsten-electrodes.html




have a 50 % greater carrying capacity than pure tungsten, and contain minimum 97.8 % tungsten and 1.3 to 1.7 % lanthanum. It conducts like thoriated and can replace it without significant program change. Colour-coded gold.

Zirconiated

Zirconiated tungsten electrodes contain a minimum of 99.1 % tungsten and 0.15 to 0.4% zirconium. It produces an extremely stable arc and resists spitting. Highly contamination resistant, its current rivals thoriated tungsten. Not recommended for DC welding but the preferred choice for AC welding of aluminium. Colour coded white.



Unit 215: Welding by TIG process Handout 4: TIG process Process

• An arc is produced between a non-consumable tungsten electrode and the work piece.

• The arc burns within a shield of gas to protect the molten weld pool and electrode from atmospheric attack.

• Additional metal needs to be added to produce the weld reinforcement. • Welding without additional weld metal is possible on close fitting joints and is

termed autogenous.

• Depending on the shielding gas being used this welding process can be: TIG – Tungsten Inert Gas

TAG – Tungsten Active Gas • Principles are the same, the only difference is the shielding gas being used.

Electrode polarity

• Direct current (DC) is used for the welding of the majority of metals • Alternating current (AC) is used for welding aluminium. • Electrical polarity has a great influence on the heat distribution of the arc. • The polarity of the electrode can be changed when using DC



• Electrode negative will produce a deep penetration weld as 66% of the heat is in

the plate. • Electrode positive will produce a shallow penetration weld as 66% of the heat is

in the electrode. The electrode will melt away.

AC welding

• Aluminium and its alloys have an oxide layer that has a higher melting point than the metal itself.

• This oxide layer must be removed before welding can take place. • The AC current removes the oxide during the positive half cycle and welding

during the negative cycle. • Damage to the tungsten is prevented as it is cooling during the negative half

cycle. © 2015 City and Guilds of London Institute. All rights reserved. www.SmartScreen.co.uk


Electrical characteristics

• The distance from the electrode to the plate is known as the arc length. • As the arc length increases more volts are required to maintain the arc. • If the voltage increases, amperage will drop (Ohm’s law) • If amperages drop too much due to arc length, poor welds will result. • TIG machines use a drooping characteristic electrical form to reduce the effect of

variable arc length

Oxide removal

Welding and electrode cooling


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 4 Shielding gases In addition to providing a protective environment, the shielding gas and flow rate also have a pronounced effect on the following: • arc striking • arc stability • penetration and weld bead profile • speed of welding • cleaning action Gas flow • Gas flow is measured in litres per minute (Lp/m) • Low gas flow will not protect the molten pool from the atmosphere. • Too high a gas flow will cause turbulence and drag the surrounding air into the weld,

again causing defects. • Gas flow rates can vary depending on the gas, material thickness and joint type. • Gas flow is regulated by a flow meter. • As a general guide flow rates should be: • 1 - 3mm thick - 4 -9 lp/m • 4mm and above - 10 -20 lp/m Shielding gases

• Argon and helium are both inert gases. • Hydrogen is an active gas. • Hydrogen and helium increase the heat input, producing a hotter weld with

deeper penetration. • Helium is a light gas, so flow rates will need to be increased.



Unit 215: Welding by TIG process Handout 5: TIG welding Process variables The variables associated with TIG welding are:

– Shielding gas selection – Gas flow – Tungsten electrode type – Filler wire – Electrical polarity – Amperage

Shielding gas

• Argon and helium are both inert gases. • Hydrogen is an active gas. • Hydrogen and helium increase the heat input, producing a hotter weld with

deeper penetration. • Helium is a light gas, so flow rates will need to be increased.

Gas flow rate

• Flow rates are measured in litres per minute (L/pm) • Too high a flow rate will cause turbulence and draw surrounding air into the weld

pool causing defects. • Too low a flow rate will not protect the molten pool from the surrounding

atmosphere. • The diameter of the ceramic shroud influences the flow. • The correct diameter shroud should be selected to suit. • Ceramic shrouds are often identified by a number. This number should be

multiplied by 1.6 to give the outlet diameter in mm.


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 5 Tungsten electrodes • The diameter of the electrode will limit its current (amps) carrying capacity. • Too small an electrode will overheat. • Too large an electrode will limit arc heat and lead to poor penetration.

Current capacity • Current is measured in amps • Amperage ranges shown are only a guide

Electrode sharpening

• It is important to sharpen tungsten electrodes correctly. • Incorrectly ground electrodes can cause arc wander. • Machines are available to ensure accurate grinding.



TIG torch


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 5 TIG wire selection

• TIG electrode wire is selected to suit the joint • Material of the wire matches the material being welded • Various diameters are available

– Ø1, Ø1.6, Ø2.4, Ø3.2 • As a guide, the diameter of the wire should be slightly smaller than the metal

thickness being welded. Distortion

• As a weld cools it can cause distortion. • Being aware of distortion and trying to reduce it can save a lot of work. • One way to reduce the effects of distortion is called pre-setting.


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 5 Pre-setting

The amount of pre-setting can’t be calculated, it comes with experience. Distortion control

• Distortion can also be controlled by restraint. • Restraint means holding the metal and not letting it move.

Jigs and fixtures not only hold the pieces to be welded in the correct position they also help restrain distortion



Welding positions



Torch angles

Arc striking Striking the arc can be achieved in 3 ways:

• Scratch start: – The electrode is scratched against the surface of the plate and then

pulled away to form the arc. – This method can contaminate the weld and damage the electrode.

• Lift start: – The electrode is placed against the plate, power button pressed and then

lifted to start the arc. No contamination of the weld metal occurs. • High frequency (HF) start:

– When the power button is pressed a high frequency spark ionises the air gap. Ionisation causes the air to conduct electricity and the arc is formed. No contamination to the weld metal occurs.


SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 5 Welding techniques



Post welding

• Visually check welds for any defects • Welds should be wire brushed on completion. • The weld itself shouldn’t be cleaned up using a grinder. • Spatter needs to be removed, usually with a hammer and chisel.

Hot metal

• Hot metal is a common hazard in the welding workshop. • To protect yourself and others make sure:


unless you are sure its cool! Good housekeeping At the end of the shift or lesson it is important to leave the work area in a safe state.



Unit 215: Welding by TIG process Handout 6: Inspection and testing Completed welds are often subjected to a system of inspection and testing to ensure its quality. • Testing has two main categories:














Limitations



SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 6 Magnetic particle testing









SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 6 Types of etchant

Metal Etchant





Nick break test



SmartScreen 2850 Level 2 in Engineering Unit 215 Handout 6 Bend testing






Cupping test




Unit 215: Welding by TIG process Worksheet 1: TIG welding Joint Material Electrode type &

diameter Current range Current polarity Shielding gas

Open corner 3mm stainless steel

Tee fillet 2mm aluminium

Lap joint 4mm LCS

Butt weld 6mm aluminium

Tee fillet 1mm LCS

Lap joint 3mm stainless steel

Open corner 4mm aluminium

Butt weld 4mm LCS

Tee fillet 3mm stainless steel



Unit 215: Welding by TIG process Worksheet 2: Weld defects Identify the following defects and their likely cause by selecting one of the 3 options. Defect Description Cause


1. No shielding


1. Uneven leg

length 2. Underfill 3. Lack of

fusion


gas

1. Excessive


penetration 3. Overfill

1. Poor

technique 2. High amps 3. Dirty metal



prep 3. Wrong

electrode material




fusion

1. Wrong

electrode material

2. Poor cleaning

3. Porosity

1. Overlap 2. Overfill 3. Excess weld

metal

1. Dirty metal 2. Incorrect

weld prep 3. Wrong

electrode

1. Excess weld

metal 2. Overlap 3. Cracking


1. Excessive




SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 3 Task title: Open corner joint PA Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


Amperage Electrode type

Filler wire diameter Weld joint type















Good fusion


Bend or cupping test (if applicable) Weld acceptable y/n



No cracking

List 3 problems you had when completing this task and then explain how you overcame them.





Assessor feedback


Candidate: _________________________________ date: __________________ Assessor: _________________________________ date: ___________________ _

SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 4 Task title: Lap joint PB Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used

SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 4 Task planning sheet


PPE






Good fusion





No cracking






Assessor feedback


Candidate: _________________________________ date: __________________


Assessor: _________________________________ date: ___________________

SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 5 Task title: Tee joint PB Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


















Good fusion





No cracking






Assessor feedback



SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 6 Task title: Lap joint PC Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


















Good fusion





No cracking






Assessor feedback



SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 7 Task title: Butt weld PA Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


















Good fusion





No cracking






Assessor feedback



SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 8 Task title: Butt joint PC Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


















Good fusion





No cracking






Assessor feedback



SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 9 Task title: Open corner PF (vertical up) Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


















Good fusion





No cracking






Assessor feedback



SmartScreen 2850 Level 2 in Engineering Unit 215 Worksheet 10 Task title: Tee joint PF (vertical up) Date started: __________________ Date completed: ___________________ Approved stages Tutor signature Risk assessment Tick when checked Planning sheets completed Work area clean and tidy before starting Name stamped Tools in good condition Marking out within tolerance Electrical leads in good condition Tacked ready for welding Other people at risk protected Weld completed Guards fitted to machines Task cleaned up and de-burred Tools returned to storage Weld tested Scrap material removed Paperwork complete Work area clean and tidy when finished Task completed List the tools you used List the machines you used List the PPE you used



PPE


















Good fusion





No cracking






Assessor feedback



Please bring your completed workbook with you when you attend class.

When you have studied this material please contact us to makearrangements for your practical training.

2850 DIPLOMA IN ENGINEERING FABRICATION … Joint Butt joints are generally produced where the edges...

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Transcript of 2850 DIPLOMA IN ENGINEERING FABRICATION … Joint Butt joints are generally produced where the edges...