MIG/MAG Training Programme

Learning & Assessment Package

Welding terms

MAGSMetal Arc Gas Shielded (covers all shielding gases MIG & MAG)

MIGMetal Inert Gas (covers totally inert gases e.g. Argon and/ or Helium)

MAGMetal Active Gas (covers gas mixtures that are not totally inert e.g. Argon + CO2, or Argon + Hydrogen or Argon + Oxygen etc)

GMAWGas Metal Arc Welding (American term for MAGS welding)

TAGSTungsten Arc Gas Shielded (covers all shielding gases TIG & TAG)

TIGTungsten Inert Gas (covers totally inert gases e.g. Argon and/ or Helium)

TAGTungsten Active Gas (covers gas mixtures that are not totally inert e.g. Argon + Hydrogen or Nitrogen or Nitrogen + Argon etc)

GTAWGas Tungsten Arc Welding (American term for TAGS welding)

MAGS Welding

The MAGS welding process was first developed in 1948 for the purpose of welding aluminium plates. This type of welding is a refinement of the TAGS process and uses a consumable wire electrode, which replaces the fixed Tungsten electrode of the TAGS process.

In 1953, the introduction of the constant potential type-welding machine opened up brand new welding applications for the MAGS process.

The advent of the constant potential type welding machines was a significant advancement for the MAGS process. For the first time the amperage could be changed over wide ranges with very little change in the arc voltage. This led to the development of wire feed equipment with constant speed drive motors. Instead of the wire feed speed varying, as it had to do with the conventional type welding machines. The constant potential welding machines make the amperage correction to maintain the pre-set voltage. The power supply unit must be the constant potential type.

Units normally comprise of a D.C. generator or A.C. rectified transformer. The rectified transformer is a device that permits current flow in one direction only. Its main function is to change A.C. to D.C. It is usual with units to provide a voltmeter and ammeter for voltage and amperage adjustment purposes, and voltage and wire feed controllers. The volt and ammeters purpose is primarily to assist the operator in setting up the correct welding conditions for the welding applications.

The voltmeter is read in different ways depending on the conditions. For example, the voltmeter will read 'O' when the welder is energised but not being used. It will read open circuit voltage (OCV) when the trigger is actuated but no arc struck. It will read the 'load voltage' when the arc is initiated. The 'arc' voltage is only measured at the arc.

This type of welding is a refinement of the TAGS process and uses a consumable wire electrode, which replaces the fixed Tungsten electrode of the TAGS process. In the MAGS process, the heat generated by an arc formed between the end of a consumable filler wire and the workpiece is used to fuse the joint area. The filler wire is fed continuously through a contact tube or tip. The arc is formed in an inert gas, which prevents oxidation of the weld, assists in cleaning, and determines the heating characteristics of the arc and the mode of transfer.

MAGS Welding Equipment

The component parts of a MAGS system are: -

Power supply unit.

Wire feeder unit.

Flexible lead (tube) assembly and return cable.

Welding gun.

Gas supply system

The Power Supply Unit

The power supply unit must be of the Constant Potential type.

For free flight or spray transfer the unit should be capable of delivering up to 400 amp (1.2mm wire) or 600 amp (for 1.6mm wire or flux-cored electrodes). The open voltage circuit should be high enough to provide a satisfactory arc length and voltage at the maximum operating current.

For dip transfer the unit should be capable of delivering up to 200 amps at an operating voltage of 21 volts. The unit should be fitted with a tapped or variable inductance control to govern the rate of rise and current during short circuit.

For pulse transfer, special power supply units should be used.

Wire Feeder Unit

The electrode wire reel or coil is mounted onto a spindle or spider hub, either horizontally or vertically as required. The hub is free to rotate as the wire drive unit draws off the wire.An adjustable braking device is incorporated in the assembly to prevent overrun of the electrode wire when the motor of the wire drive unit is switched off. To protect the electrode wire from dust and contamination, the reel assembly is usually enclosed by a cover or placed within the control unit cabinet. A cover is essential when using aluminium alloy wires.

Wire Feeder

This may either be a push or a pull type or combined.

Push Type

In the push type, the mechanism consists of two or more feed rolls where the grip or pressure can be adjusted. This method of feeding is used for base soft wire or a diameter not less than 1.2mm and of not less than 0.6mm in the case of hard wires.

Pull Type

The pull type consists of a drive usually built into the handle of the welding gun. Feed rolls pull wire off a small reel attached to the gun. In the combined method, push and pull feed units are used. One is mounted near the electrode wire reel assembly, and the other in the welding gun.

Spool On Gun

Flexible Lead Assembly

This will depend upon the type of equipment used. It normally contains: -

Cable for the welding current.

Control cable to link the switch on the gun with the control unit.

Hose to convey shielding gas.

Conduit to convey electrodes wire (except in the case of the reel on gun arrangement).

Hoses to convey cooling water (if used).

Hose to convey air to drive wire feed turbine (if used)

Welding Torch

For dip transfer and pulse transfer welding, the electrode holder normally has a curved neck. It is known as a welding gun since it resembles the shape of an oxy-acetylene welding nozzle and incorporates a button or lever-operated switch. Where a water-cooled gun or gun is required, there is usually a mechanism that cuts off electrical power should the water flow cease.

For free flight transfer welding (spray transfer) with flux-cored wires 1.2mm diameter or larger, or where a pull feed unit is incorporated, the equipment is generally pistol shaped, has a trigger type switch and is referred to as a welding gun. It can be water cooled when required for use with currents in excess of 300/400 amps.

The Constant Potential Welding Machine

The constant potential type-welding machine has a relatively flat volt-ampere curve and much lower maximum open circuit voltage than a conventional welder. It permits the welding machine to reach welding voltage without the delay in time involved with a higher open circuit voltage. The response time of the constant potential welding machines with the flat voltage-ampere curve is very fast. The lower open circuit voltage used with this type of welder reduces the possibility of a 'blast' of high voltage current at the weld start. Such a blast of current could cause burn back of the electrode into the contact tube of the gun.

Constant Potential Type Power Source (having a flat characteristic) used in MAGS welding

Contactor Control

All constant potential welding machines have built in primary contactors as standard equipment. The function of the primary contactor is that of a switch. It blocks the flow of current to the primary coil of the main welding transformer when in the 'open' position. When the contactor coil is energised it 'closes' and completes the circuit in the primary section of the welding machine. Something must trigger the primary contactor so that its coil will energise and cause the contactor to close. This function is performed when the trigger switch is actuated on the gun.

Wire Feed Mechanism

Locate the reel of wire on hub or spindle so that wire will be drawn off in the correct direction. Do not release the reel binding at this stage.

Loosen braking mechanism so that reel runs freely. Then tighten just sufficiently to prevent overrun of spool when wire is drawn off.

Fit correct size inlet guide to wire feed mechanism.

Release the end of the wire from the reel binding, but do not allow wire to become loose on the reel.

Cut off the kinked end of wire cleanly, making sure that the cut end is not jagged or burred.

Thread the wire through the opened wire feed mechanism.

Close the wire feed rolls so that the wire is gripped and adjust pressure in accordance with manufacturers instructions.

With the reel-on-gun assembly, the wire can now be 'inched' through the gun nozzle when the current is switched on.

After making sure that all hose assembly connections other than the wire conduit connections have been made, fit the correct size outlet guide to the wire conduit.

Thread the outlet guide over the electrode wire protruding from the wire feed mechanism and lock the guide in position.

The wire can now be 'inched' through the conduit to the gun contact tube when the current is switched on.

Adjust the position of contact tube end/tip and fit gas nozzle.

Welder-Manipulator Controlled Variables

The main difference between MAGS and TAGS welding is that a wider range of shielding gasses is available with MAGS

The main variables (applicable to MAGS welding techniques) are: -

Welder controlled variables. (Speed of travel, technique and angle, joint setup)

Machine-controlled variables (arc voltage, welding current, wire feed speed, self adjusting arc length)

Welder controlled variables

These include protrusion of electrode wire, nozzle and wire speed feed. The welder can adjust all of these variables, but in doing so, the need for machine-controlled variables adjustments occurs.

The three main gun angles determine the penetration of the arc column. If significant change needs to be made in penetration characteristics, machine variables of amperage or voltage control should be used, or the original selection of electrode size should be reviewed.

In the drag pattern, which is the standard movement, the gun is moved in a straight line without oscillation, and without touching the workpiece.Note: This pattern is mainly applicable to workpieces in the flat position.

For out-of-position work the whip pattern, weaving pattern, or 'U' pattern may be preferred.

The whip and 'U' patterns are particularly suitable for weld pool manipulation.

To make a cover pass, the figure-of-eight pattern is used. This pattern is not suitable for tack welding.

Workpiece Variables

These are dictated by the composition of the parent metal which determines the type and amount of shielding gas, the electrode wire type and size, the welding position and the mechanical properties of the finished weld.

We can also use backing bars and other aids mainly for welding and butt joint.

Control of the Process

The main controlling parameters in MAGS welding with a constant potential power source and continuous wire feed system are: -

Wire Feed Speed

Arc Voltage

Inductance

The rate of wire feed must match the rate at which the filler is melted, and this burn off rate is related to current.

If a constant potential power source is used, the working voltage is preset and the current obtained varies to suit the arc characteristics. If the preset voltage is too high, or the wire feed speed is too low, the arc length may become excessive, and the filler wire may burn back onto the contact tip. If the wire feed speed is too high, or the arc voltage is too low, the unmelted filler wire short circuits the arc gap causing an effect known as stubbing.

The inductance control enables the amount of inductance in the output circuit of the power source to be varied, to minimise spatter and give a smoother arc when welding in the dip-transfer mode. As welding current is increased, it will be necessary to use more inductance.

Dip transfer, or short-circuiting arc technique is a mode of metal transfer in which the arcing period and short circuiting period alternate rapidly. The rate of this sequence is known as the dip transfer rate, or dip frequency, is normally between 50 and 200 cycles per second.

If there is insufficient inductance in the circuit, the rate of current rise when the wire has short circuited against the work piece will cause violent detachment of the weld metal and excessive spatter. Too much inductance will reduce the rate of burn off, lowering the dip frequency and causing the wire to stab into the work piece (stubbing).

The correct inductance setting for a given wire, current and voltage is characterized by a high-pitched buzz, and minimum, light spatter. The inductance also controls heat input to the weld, and around the optimum setting an increase in inductance will result in a hotter weld, and vice versa.

The low inductance, characterized by a crisper sound arc, gives minimum heat input and well-defined ripples on the cooled weld.

Control of the inductance thus enables the operator to select the best conditions for each application, from very thin sheet where low inductance is used to limit the heat input to prevent burning through, to heavier steel plate where the high inductance can minimise spatter and ensure adequate fusion.

Correct Stubbing

Shielding Gasses and Metals

There are several types of shielding gases and shielding gas mixtures in general use with the MAGS process. Some of the gases have a broad range of application while others are restricted in their use. This section will deal with the various shielding gases and their uses with weldable metals.

Argon

Argon is a chemically inert gas that will not combine with the products of the weld zone. Argon has a low thermal conductivity. The arc plasma is constricted with the result that high arc densities are present. The high arc density permits more of the available energy to go into the work as heat. The result is a relatively narrow bead width with deep papillary penetration at the weld centre. Argon causes a more concentrated arc than any of the other commonly used gases employed with the MAGS process. It is this reason that argon has a reputation for cleaning the work area. Actually, it is the concentration of the arc plasma, and therefore heat energy, that causes the refractory oxides to be loosened. This phenomenon is particularly noticeable when welding aluminium.

Argon is in abundant supply since it comprises almost 1% of the earth's atmosphere. The gas is obtained as a by-product in the manufacture of oxygen.

Argon is used as the shielding gas when welding many types of metal. Its primary use is in the welding of non-ferrous metals and alloys such as aluminium, magnesium, alloys of the two, and copper. In some metals applications, argon does not provide the penetration characteristics required for heavier weldments.In these cases, argon-helium mixtures are sometimes used. This gas mixture will be discussed under a separate heading.

Helium

Helium is also an inert gas and may be compared to argon in that respect. There the similarity ends. It is lighter than air and has high thermal conductivity. The Helium arc plasma will expand under heat (thermal ionization) reducing the arc density. With Helium there is simultaneous change in arc voltage where the gradient of the arc length is increased by the discharge of heat from the arc stream or core. This means that more arc energy is lost in the arc itself, and is not transmitted to the work. The result is that, with Helium there will be a broader weld bead with relatively shallower penetration than with argon. This also accounts for the higher arc voltage, for the same arc length that is obtained with helium as opposed to argon.Helium is derived from natural gas. The process by which it is obtained is similar to that of argon. First the natural gas is compressed and cooled. The hydrocarbons are drawn off, then nitrogen, and finally the helium. This is a process of liquidifying the various gases until at 253 0C the helium is produced.

Helium has sometimes been found in short supply due to governmental restrictions, and therefore has not been used as much as it might have been for welding purposes.

Helium is used primarily for the non-ferrous metals such as aluminium, magnesium and copper. It is also used in combination with other shielding gases.

Carbon Dioxide (CO2)

Carbon dioxide is a compound gas. The primary elements are carbon monoxide and oxygen. CO is not an inert gas such as helium or argon. CO has a feature that neither argon or helium has, and that is it's ability to dissociate and recombine. It is this factor that permits more heat energy to be absorbed in the gas. It also uses the free oxygen in the arc area to superheat the weld metal transferring from the electrode to the work. CO has a wider arc plasma than argon but less than helium. Depending on the type of metal transfer used, the weld deposit cross section will show an arc CO welding techniques. So that gas entrapment and interbead cracking do not occur.The penetration characteristics and/or globular transfer of metal could cause such faults in the weld across the arc.

CO is used primarily for low carbon steel welding. It has also found application in the formulation of some shielding gas mixtures.

It is suitable for dip transfer at low currents and can be used at high currents for spray transfer. There are two types of internal fittings to the cylinders, one that allows gas, which might contain moisture, to be ejected on opening the valve, and the other called the syphon tube, which only allows liquid carbon dioxide to be ejected.

Syphon type cylinders should be used in which the liquid is drawn from the bottom of the cylinder. To prevent the regulator freezing as liquid carbon dioxide expands into gas, it is necessary to fit an electric heater-vaporizer unit between they cylinder valve and the regulator when using syphon type cylinders.

BS EN 1089-3 Cylinder Colour Codes

Note that the new CO2 Liquid withdrawal cylinders have a GREY shoulder in addition to being painted Black with a white stripe.

Argon-Oxygen

Argon is an excellent shielding gas for the MAGS process because it allows the use of spray type metal transfer. When depositing flat or horizontal fillet welds however, the typical deep central penetration does not allow the weld metal to 'wet out' at the toes of the weld. This is particularly noticeable when welding steel or stainless steel. These phenomena will invariably cause undercut at the edges of the weld bead. The tendency to undercut may be prevented by the addition of 1-5% oxygen to the argon. The oxygen permits a controlled oxidation to take place, as well as increasing the temperature of the molten metal transferred across the arc. The additional time at liquidus allows the hot molten metal to 'wet out' at the toes of the weld. This action produces a featheredge at the junction of the weld and parent metal.

Argon-oxygen mixtures are very common for welding stainless steels. They may be used for low carbon and low alloy steels, but the cost is usually prohibitive. Argon-oxygen shielding gases are usually purchased as pre-mixed gases.

Argon- CO2

For some applications of low carbon steel welding, welding grade CO2 does not provide the arc characteristics needed for the job. This will usually manifest itself where surface appearance is a factor, in the form of intolerable spatter in the weld area. In such cases a mixture of argon- CO2 has usually eliminated the problem. Some welding authorities believe that the mixture should not exceed 25% CO2.

The reason for wanting to use as much CO2 as possible in mixture is primarily the cost. By using a cylinder of each type of gas, argon and CO2, the mixture percentages may be varied by the use of flow meters. This method precludes the possibility of gas separation such as may occur in pre-mixed cylinders. The price of CO2 is 15% cheaper that that of argon in most areas.

Argon CO2 shielding gas mixture are employed for welding low carbon steel, low alloy steel and in some cases for stainless steel.

Argon-Helium- CO2

This mixture of shielding gases is used primarily for welding austenitic stainless steels. The combination of gases provides a unique characteristic to the weld. It is possible to make a weld with very little build up of the top bead profile. The result is excellent for those applications where a high crowned weld is detrimental rather than help. This gas mixture has found considerable use in the welding of stainless steel pipes.

The shielding gas will also have a pronounced effect upon the following aspects of the welding operation and the resultant weld:

Arc characteristics

Mode of metal transfer

Penetration and weld bead profile

Speed of welding

Undercutting tendency

Cleaning action

The Inert Shielding Gases - Argon and Helium

Argon and helium are inert gases. These gases and mixtures of the two are necessarily used in the welding of non-ferrous metals and also widely used to weld stainless steel and low alloy steels. Basic differences between argon and helium are:

Density

Thermal conductivity

Arc characteristics

The density of argon is approximately 1.4 times that of air (heavier) while the density of helium is approximately 0.14 times that of air (lighter). The heavier the gas the more effective it is at any given flow rate for shielding the arc and blanketing the weld area in flat position (down hand) welding. Therefore, helium shielding requires approximately two or three times higher flow rates that argon shielding in order to provide the same effective protection.

Helium possessed a higher thermal conductivity that argon and also produces an arc plasma in which the arc energy is more uniformly dispersed. The argon plasma is characterised by a very high-energy inner core and an outer mantle of lesser heat energy. This difference strongly affects the weld bead profile. The helium arc produces a deep broad profile.

Industrial Gases

A new standard governing the colour coding of transportable gas cylinders is coming into force across Europe. As a result many UK industrial gas cylinders will be repainted.

The aim of the new standard (EN 1089-3), which replaces the old colour scheme (BS349), is to help improve safety standards within the gases industry.

What does this mean?

The new system means that the shoulder colours for all gas cylinders from all gas companies in the UK will adopt a standard colour scheme.

During the changeover period, both old and new cylinders will be in circulation. So it is important to read the label.

The cylinder label or collar should be the primary means of identifying the cylinder. The colour of the cylinder itself should only be the secondary means for identifying the cylinder and used when the label or collar is not visible or accessible.

Cylinder Shoulder Colours

FlammableREDInertBRIGHTGREENOxygenWHITEArgonDARK GREENNitrogenBLACKCarbonDioxideGREYHeliumBROWNAcetyleneMAROON

In an emergency and when cylinder label is not clearly visible this will quickly help you identify the main chemical hazard of the gas.

New Industrial Identification Chart

Gases used in MAGS welding

Gas Cylinder used for MAGS Welding

Cylinders for MAGS welding are filled to a pressure of either 230 bars or 300 bars.

GasesNew Colour Coding

Argon + Carbon DioxideBlue with a light green shoulder

Carbon Dioxide (vapour)Black with a Grey shoulder

Carbon Dioxide (liquid)Black with a white stripe and a Grey shoulder

Pure ArgonDark Green (for aluminium and other non-ferrous)

Pure HeliumBrown (for aluminium and other non-ferrous)

Argon + Helium Blue with a brown shoulder (non-ferrous metals)

Argon + Oxygen Blue with a white shoulder (for stainless steel)

Spray Transfer

Flat position (butt)Because of the high heat input and high welding speeds possible when using spray arc, it is important to maintain adequate gas coverage to the solidifying weld area trailing the gun. Forehand welding (most right handed welders move left to right with the gun inclined towards the body is preferable and weaving is permitted allowing an even further spread of shielding gas.

Horizontal/vertical filletForehand welding is desirable for good gas cover and optimum weld shape.

Techniques

Dip Transfer

Vertical DownAdequate gas cover is important - stick out length should be kept constant for an even weld contour. By controlling stickout, poor 'fit up' can be tolerated by depositing a much cooler weld. Vertical down is not recommended for heavier sections because of the risk of cold lapping and lack of fusion particularly in the root run.

Vertical UpGenerally gives a convex weld contour and it is suggested that a slight weaving technique be used, even on smaller passes. This weaving produces a weld of good appearance.Larger fillets require a triangular movement, with slight pauses at either side to eliminate under cutting and to deposit enough metal at the edges to avoid a convex bead shape. Illustrated are various joint configurations using dip transfer.

Overhead (thicker sections)A circular movement can be used to flatten the weld face and lessen the risk of a convex weld.

Horizontal butt joint Use forehand technique for good gas cover and use weaving as shown.

Techniques Applications

Low Carbon Steel

It has been estimated that approximately 80% of all welding performed today is on some type of steel material. Probably 90% of the steel that is welded is classed as low carbon or 'mild' steel. In the past few years, the MAGS process has successfully competed for the right to be used in place of other processes for a good share of this work. The reason is that it is faster, cleaner and does a better job. The MAGS process has found applications in practically every type of industry where welding is done.

Short Circuiting or Dip Transfer

The process has been discussed as far as the principles are concerned. This portion of the text will discuss the uses to which the process may be put.

The process is primarily designed for the welding of light gauge metals. The method of welding may be used on steel up to 5mm thick with one pass. It can be used on thicker plate for positional welding. Normally, either welding grade CO2 gas mixture is used as the shielding gas with this process.

Applications include all types of sheet metal fabrications, angle iron frames, and stators for electric motors, root pass for pipe welding, maintenance work and many others.

Spray Transfer

For spray transfer on steel, the shielding gas usually used is argon-oxygen mixtures with a 5% oxygen content being the most popular. Spray transfer of steel, using solid wire and argon-oxygen gas is not widely used due to the high cost of the shielding gas. Argon- CO2 with up to 20% CO2 is now mainly used.

In any type of welding there are always failures. A weld failure can cause rework of the part, and in some cases can actually cause scraping of the part. Since rework is always expensive (sometimes it can cost more than the original weld!), it is to be avoided whenever possible. Some of the items that cause rework are slag inclusions, porosity, lack of penetration and lack of fusion. Of these the most common fault is porosity.

Porosity is one of the recurring problems faced in welding any metal. There are several general rules that will help to minimize porosity problems. The following data are not intended to answer all the reasons that porosity occurs, but it will certainly help to decrease the possibility of porosity if due notice is made of the suggestions.

Welding speeds that are too fast will cause either partial or complete loss of shielding gas pattern in the arc area and will cause porosity.

Current densities that are too high will often cause porosity due to excessive heat of the molten metal from the electrode. In some cases alloying and deoxidising elements have excessive burnout across this type of arc. It is probable that the electrode wire is too small in diameter for the application and the next larger diameter should be used. If the smaller wire size must be used then decrease the current value by decreasing wire speed feed.

Shielding gases used with the MAGS process must be of the right type for the metal being welded, and must have the right flow in litres per hour (LPH), or unsatisfactory results will occur. Shielding gas flows are usually above 10 LPH but not more than 30 LPH. It is imperative that the shielding has to be clean and dry. Argon and helium purities are approximately 99.99+%.

It is very important that the welding electrode be kept centred in the flow of shielding gas. If the wire is off centre it can cause an erratic arc as well as porosity.

In all steel welding there is the possibility that a silicate residue will be left on the surface of the weld bead. This is particularly true when welding steels that have a high silicon content, or when the electrode has a substantial silicon content. The residue appears as a glassy substance that is extremely hard. The silicate residue should be removed during multi-pass welding or prior to painting or plating operations. It can usually be removed by chipping or with a power wire brush.

Welding

Principles of Semi-Automatic Welding

Description of the Process

Semi-automatic MIG/MAGS welding consists of a D.C. arc burning between a thin bare metal wire electrode and the workpiece. The arc and weld zone are enveloped in a protective gas shield. The wire electrode is fed automatically from a spool, through a torch, which is connected to the positive terminal and is moved by hand.

The arc is self-adjusting. This means that any variation in the arc length made by the welder produces a change in the burn off rate of the electrode and the arc rapidly re-establishes its original length.

Applications

This process is a development of TIG (tungsten-insert-gas) welding, but the tungsten electrode replaced by a continuously fed wire and was first used only on aluminium with argon as the shielding gas. The price of argon restricted its application until the use of carbon dioxide (CO2) was successfully developed as a much cheaper shielding gas for carbon steels. Semi-automatic welding is now employed on steels of all thicknesses, aluminium, copper and many of their alloys, also nickel and stainless steel.

Safety precautions

The general safety precautions concerning metal are welding which appear in previous notes are applicable to MIG welding. Good ventilation is essential with gas shielding processes and overhead fume extractors may be ineffective where the heavier the air gases, especially CO2, are employed. CO2 is heavier than air and will accumulate at a low level in confined spaces, reducing the oxygen content and raising the danger of suffocation.

Equipment

The basic equipment consists of: -

Power SourceA direct current unit is essential. This may be a motor generator, but for shop use a rectifier is the normal unit. The design and capacity varies according to the particular application.

Wire Feed UnitThe continuous wire electrode is fed to the arc by feed rolls connected to a variable speed motor.

Torch or gun (Water or air cooled)Connected to the wire feed unit by a flexible hose assembly through which pass the wire electrode and shielding gas.

Shielding GasCO2 (carbon dioxide) for steels argon for aluminium and argon mixtures for stainless steel and special applications.

Electrical Conditions

Welding Current and Wire Feed Speed

Wire feed speed and amperage are generally set by the same control i.e. higher wire speed means higher amperage and lower wire speed means amperage. An ammeter is normally fitted to the power source.

Voltage

Open circuit voltages may be varied by stepped or stepless control and a voltmeter is normally provided as standard equipment. Means are generally provided for reading the arc voltage, i.e. by press button, switch or first pressure on the torch trigger.

Metal transfer

The various MIG welding techniques known as dip, spray, pulsed arc fall into various ranges of application and are distinguishable mainly by the method of transfer or type of wire.

Dip Transfer

Dip transfer, known also as short arc welding is carried out using currents below 200 amperes and voltages below 25 volts with a relatively small gauge electrode wire. Under these conditions the arc is so short that the molten globules at the electrode tip short circuit to the workpiece at rapid, regular intervals. The rise in current during short-circuiting melts off the electrode tip and allows re-establishment of the arc. This cycle occurs at a frequency in the range of 100 times per second.

Effect of inductance on dip transfer

Too rapid a current rise during short-circuiting will cause globules to explode out of the arc at the current peak, resulting in excessive spatter. Too slow a current rise will result in stubbing or freezing of the electrode tip in the molten pool. A means of control is provided in power sources designed for dip transfer in the form of a variable choking coil or inductance. The higher the inductance the lower the speed at which the short-circuiting current builds up. Varying inductance values will also produce the following effects: -

Low inductance setting will give higher short circuiting frequency and relatively cold welding.

High inductance setting will give lower short circuiting frequency and relatively hot welding due to longer arcing periods between short circuits.

Once the wire feed speed (amperage) and voltage are set the circuit may be timed to produce a tranquil arc.

The effect of inductanceThe effect of arc voltage

Applications and advantages of dip transfer

Thin sheet may be easily welded with dip transfer even with faulty fit up i.e. varying gap size, with minimum heat input and distortion. Positional welding and root runs on butt welds on thick plate are also carried out by this technique.

Spray Transfer

In the higher current range of approximately 250-500 amperes and over 25 volts the metal is transferred across the arc in small free flight droplets in the form of a fine spray. Positional welding is not practicable due to the highly fluid state of the molten pool, but aluminium is successfully welded in all positions by the spray transfer technique.

Applications and advantages of spray transfer

The high deposition rate makes spray transfer welding heavy steel sections a very economical proposition.

Globular transfer (transition stage)

Transition from dip to spray transfer and vice versa does not take place at a clearly defined point. This will depend upon wire size and type also type of gas i.e. with aluminium wire and argon shielding gas spray conditions can be obtained at a much lower amperage. Between the dip and spray ranges are a transitional area, which is neither dip nor spray, but an undesirable condition in which large globules are transferred in free flight, resulting in a very unsatisfactory deposit. This transition stage is generally unsuitable for practical welding.

Pulsed Arc (controlled spray transfer)

Pulsed arc equipment combines two power sources in one unit. One side supplies a background current to keep the wire tip in a molten condition, while the other side produces pulses of higher current at regular intervals, which detach and accelerate the droplets of metal into the molten pool.

Advantages of Pulsed Arc

Lower currents are used than with spray transfer technique thereby extending the range of the plant. Positional welding is possible with the high deposition rate of spray transfer.

Flux cored wire (tubular)

Hollow wires filled with flux and CO2 shielding gas is used with this process. The current range is between 350 and 550 amperes.

Advantages of Fluxed Cored Wire

Higher currents and deposition rates are possible on down hand welding of heavy steel sections with good transfer conditions, low spatter and excellent penetration. This process is also used for hard facing applications. The slag covering prevents rapid heat radiation heat from the weld.

Shielding Gases for MIG/MAGS Welding

Gas or gas mixtureMetalTransferCharacteristics

Pure CO2Low carbon steelDip and sprayAll positions and thicknesses.

Argon with 5% or 20% CO2 plus 2% OxygenLow carbon and low alloy steelsDip spray and pulsed arcAll positions and thicknesses. Used also with flux cored wire

Pure Argon

Or

Pure HeliumAluminium and alloys, copper and alloysDip spray and pulsed arcTotally inert. Completely prevents oxidation of the weld pool.

Argon with 1% oxygenStainless steelsDip spray and pulsed arcReduces surface tension of weld pool. Provides good wetting action.

Argon with 5% oxygen High alloy steelsDip and sprayReduces surface tension of weld pool

Argon with 2% oxygen and 5% CO2Low carbon and low allow steelsDip spray and pulsed arcSuitable for all positions, gives optimum pulsed arc transfer.

Argon-Helium-CO2 mixturesAustenitic stainless steelsDip spray and pulsed arcMost suitable for stainless steel pipes.

Argon with 2% oxygen and 2 % CO2Low carbon and low alloy steelDip and sprayMost suitable alternative to CO2. Can be used for stainless steel where corrosion is not a hazard.

Arc voltage

The open circuit voltage setting should be the lowest that will give the required arc voltage. Too high an arc voltage will give a tendency for the arc to be long with a blobby transfer and excessive spatter. Too low an arc voltage may lead to stubbing of the electrode wire into the weld pool or excessive penetration. These faulty effects are more noticeable with dip transfer.

Welding current

Welding current is set with the wire feed control the calibrations of which vary from one power source to another.

Electrode wire size

Smaller diameter wires will give faster deposition rates than the large wires, due to the greater current density resulting in a faster burn off rate. Smaller wires also tend to give deeper penetration.

Edge Preparations

Edge Preparations Continued

Fabrication Welding & Foundry, BMC

1Centre for Fabrication, Welding & Foundry - BMC

Inductance setting

When using dip transfer technique the effect of increasing inductance at any given open circuit voltage setting is to produce a hotter arc giving quieter welding conditions with less spatter and a smoother finish to the weld. Decreasing inductance has the opposite effect; the arc is cooler with a more crackling sound and the weld surface has a more pronounced ripple. Therefore high inductance is required on thick plate and low inductance on very thin sheet.

Welding Nozzle and Contact Tip

The relatively positions of the ends of the welding nozzle and contact tip play an important part in the different applications. On torches where the nozzle is adjustable the following settings should be used.

Mode of transferPosition of contact tip

Dip3.25 mm to 10 mm beyond end of nozzle for greater visibility and accessibility.

Spray (steel)6 mm to 10 mm within the nozzle for improved gas shielding.

Spray (aluminium)10 mm to 12 mm within the nozzle.

Spray (flux cored wire)15 mm to 20 mm within the nozzle.

Correct size contact tips should be used. The nozzle and tip should be cleaned regularly during use to remove spatter and dirt. A silicone spray should be used on nozzles and contact tips before use and at intervals thereafter.

Gas purging

The gas hose should be purged of air before use if the equipment has been left unused for any length of time. This is achieved by allowing shielding gas to flow through the hose assembly and nozzle for approximately 15 seconds, usually by a gas purge button on the wire feed unit or by light pressure on the torch trigger.

Gas heater

Pure carbon dioxide is supplied in steel cylinders as a liquid under pressure, the liquid occupying about two thirds of the capacity. Heat from the atmosphere raises the liquefied gas to its boiling point and the gas formed above the liquid prevents further boiling when a certain pressure is reached. Vaporization recommences when gas is drawn from the cylinder. The moisture content of the gas rises as the cylinder is emptied. To prevent this moisture being carried to the weld area and causing porosity syphon type cylinders should be used.

Carbon dioxide tends to cause freezing up of the regulator as a result of the refrigeration effect of the expansion into gaseous form. To prevent this freezing and to convert the liquid to gas an electric heater-vaporizer is fitted between the regulator and cylinder. The heater-vaporizer must always be switched on before starting to weld when using carbon dioxide but is not necessary with argon.

Extension of Electrode Wire

The length of electrode wire extending beyond the contract tip has a bearing upon the results. The arc current will be reduced with increased length of wire protruding, which will result in less penetration. Wire extension is measured from the contact tip to the weld pool surface and be approximately follows: -

For dip transfer3.25 mm to 6 mm

For spray transfer20 mm to 30 mm

For flux cored wire30 mm to 44 mm

Burn Back

Burn backs are the result of some obstruction of the electrode wire either in the feed hose or on the wire reel, which in turn causes fusion of the electrode wire to the contact tip. No attempt should be made to clear the fault by operating the torch or gun; the obstruction should be traced and cleared.

Welding Speed

Too fast a welding speed may cause spatter and undercut. There may also be a tendency to porosity due to gas being trapped in the solidifying weld metal. Too slow a welding speed will cause excessive penetration. Optimum speeds for various material thicknesses and wire diameters will come instinctively with experience and increasing skill.

Welding conditions

The following tables are intended only as a guide-

Low carbon steel, Dip transfer, Butt welds with Argon- CO2 shielding gasGas Pressure 30 1b/sq in (2.0 Bar)

Plate thickness (m/m)Edge PreparationPositionCurrent (amps)Arc VoltsWire feed (m/min)Gas flow1tr/minWire size (mm)

1.0

Square edge, no root gap All45-6514-153.5-4.0120.8

1.6Square edge, no root gapAll130-16017-184.7-6.0140.8 or 1.0

3.0Square edge, 1mm root gapAll120-16017-193.0-4.3151.0

6.060 single vee, 1mm root face & 1mm root gapAll140-16017-183.2-4.0151.0

10.060 single vee, 2mm root face & 2mm root gapAll140-16017-183.2-4.0151.0 or 1.2

Above 10.060 double vee, 2mm root face & 2mm root gapAll140-16017-183.2-4.0151.0 or 1.2

Low carbon steel, Dip transfer; Fillet welds with Argon- CO2 shielding gasGas Pressure 30 1b/sq in (2.0 Bar)Plate thickness (m/m)PositionCurrent (amps)Arc VoltsWire feed (m/min)Gas flow(1tr/min)Wire size (mm)

1.0Flat & horizontal/ vertical45-6514-153.5-4.0120.8

1.6Flat & horizontal/ vertical130-16017-184.7-6.0140.8 or 1.0

3.0Flat & horizontal/ vertical120-16017-193.0-4.3150.8 or 1.0

6.0Flat & horizontal/ vertical250-27026-276.6-7.3161.0or1.2

10.0Flat & horizontal/ vertical270-31026-287.0-7.8161.0or1.2

Inductance adjusted as necessary

Aluminium Butt welds, flat position with Pure Argon shielding gas.

Metal thickness (mm)Wire Dia (mm)Current (amps)Arc VoltsWire feed(m/min)Gas flow(1ltr/min)Welding positionEdgepreparation

1.61.070-10017-184.0-6.014AllSquare edge

3.01.2105-12017-205.0-7.014`AllSquare edge, root gap 1mm, no root face

6.01.2120-14020-246.5-8.514Overhead&vertical up60 single vee, root gap 2mm, root face 2mm

6.01.2160-20027-308.0-10.014Flat filletNo gap

10.01.2120-14020-246.5-8.516Overhead&vertical up60 single vee, root gap 2mm, root face 2mm

10.01.6240-30029-327.0-9.016Flat filletNo gap

Above 10.01.6130-20020-266.5-8.018Overhead&vertical up60 double vee, root gap 2mm, root face 2mm

Above 10.01.6300-50032-409.0-14.018Flat fillet

No gap

No inductance requiredFault Finding

Weld DefectCauseRemedy

Scattered Porosity

Heavy visible porosity

Cold lapping

Over-penetration in rootTorch at wrong startingAngle.

Build-up of silicate slag

Oil or other deposit on pipe

Windy conditions blowing away shielding gas

Insufficient shielding gas

No shielding gas

Too much gas causing turbulence

Welding current low, hence deposition rate too high

Arc voltages too low

Welding speed too low

Excessive electrode extension

Arc not on leading edge of weld pool

Heavy deposition

Wrong direction of welding

Miss-use of hot start device

Torch angle

Root gap too wideCorrect the angle

Remove slag

Clean the pipe

Erect wind shields

Increase gas flow rate

Check for torch and line blockageEnsure that CO2 heater is workingCheck gas cylinder contents

Reduce gas flow rate

Reduce wire feed speed

Increase voltage

Increase welding speed

Decrease torch distance

Keep arc forward of the pool-on the base metal

Keep welding runs thin

Use upwards method

Do not use hot start for the first side of root run

Use torch at a shallower angle

Reduce root gap to 3.25 max oscillate torch

Stainless SteelsStainless Steel is a name given to a group of Steel Alloys with many differences in properties and behaviour having one property in common resistance to corrosion.

When an Alloy of Steel contains more than approximately 10% Chromium it can be classed as a Stainless Steel. This is due to the fact that Chromium has a high affinity for Oxygen and forms a tenacious, stable Oxide film which is resistant to further chemical or physical change. This film, known as the passive film, forms practically instantaneously in ordinary atmospheres and has the remarkable property of being self-healing and rebuilding when it has been removed.

This large group of Stainless Steels can be divided into four major groups, namely Austenitic, Ferritic, Martensitic and Duplex.

Martensitic

This group contains a minimum of 12% Chrome and usually a maximum of 14% with Carbon 0. 08%-2.00%. Due to the high Carbon content of the Steel it is heat treatable. Types include 410, 416 and 431. Martensitic steels are magnetic.

Ferritic

Contains a minimum of 17% Chrome and Carbon 0.08%-0.20%. The Ease in Chromium imparts increased resistance to corrosion at elevated temperatures, but the lack of mechanical properties due to the fact that it cannot be heated treated, limits its applications. Like Martensitic steels they are magnetic and the welding of this group should be carried out with the necessary precautions. 430 is the most common type of Martensitic Stainless Steel.

Austenitic

Contains Chromium normally in the range 17-25% and Nickel in a range with various additional elements. In the fully annealed they exhibit a useful range of mechanical and physical properties. The mechanical properties can be increased with cold working. Welding of this group must be carried out with the correct methods but the low Carbon content results in fewer welding problems than with the Ferritic and Martensitic grades. Normally these steels are non-magnetic. The most commonly used Austenitic Stainless Steel was the 302 grade or 18/8 st/st (18% chromium, 8% nickel). The nearest available equivalent is now the 304 grade. Note that NIOBIUM is added to st/st electrodes in order to prevent weld decay.

Type 304

An economic balance of alloying elements ensures good formability, corrosion resistance, toughness and mechanical properties. Its corrosion resistance in unpolluted atmospheres and freshwater environments is excellent but some attack may occur in coastal/marine locations and damp industrial atmospheres. Not recommended for use in seawater environments.

Type 304L

A low carbon form of 304 with 0.030-0.035% carbon maximum, designed primarily to avoid intercrystalline corrosion after welding. The tensile strength is somewhat lower than type 304.

Type 321

A variation of 304 with titanium added in proportion to the carbon content to avoid intercrystalline corrosion and improve high temperature properties. Corrosion resistance is similar to 304. Not recommended for bright or mirror polishing.

Type 347

Very similar to 321 but uses Niobium (Columbium) as the stabilising element instead of Titanium.

Type 316

The addition of 2-3% Moybdenum in this grade confers increased corrosion resistance in industrial and coastal environments, together with improved elevated temperature properties. The resistance to pitting when actually immersed in cold seawater is limited. A higher nickel content of 1 2% is used to maintain an austenitic structure.

Type 316L

Similar to 316 but with a lower carbon content of 0. 030-0.035% maximum to avoid intercrystalline corrosion after welding.

Type 317

Similar to 31 6 but the 3-4% Moybdenum content gives adequate pitting resistance in cold seawater. Crevice corrosion can still occur and designs for seawater use should take this into account.

UNS S31254

Often known simply as 6 MoIy, this is a super-austenitic steel in which the high levels of Chromium, Molybdenum and Nitrogen give high resistance to seawater attack.

L Grades

With the exception of the stabilised varieties, most of the above grades can be obtained as low carbon or L versions, e.g. 304L. The carbon is usually restricted to a max. of 0.030 or 0.035% to avoid the risk of intercrystalline corrosion after welding and/or slow cooling. The tensile strength is somewhat lower then the standard grades.

H Grades

The late 1950s saw the development of the first H Grade, 321H, which had a specified 20000F minimum heat treatment and a restricted carbon content of 0.04-0.10%, to improve creep resistance at elevated temperatures.

N Grades

Several grades may have controlled high Nitrogen contents, e.g. 316N. Nitrogen is usually restricted to the range 0.08-0. 1 5% and gives higher tensile strengths than the standard grades. Resistance to pitting corrosion is improved.

Duplex

This group has a balance of Chromium, Nickel, Molybdenum and Nitrogen to give a near equal mix of austenite and ferrite. They combine high strength with excellent corrosion resistance. Tensile and yield.

Strengths are approximately double those of a straight austenitic steel and resistance to stress-corrosion cracking in chloride solutions is superior to Type 316.

UNS S31803

This is the most widely used of the duplex steels and typifies the standard description above. The nominal composition is 0.03% max. C, 22% Cr, 5.5% Ni, 3.0% Mo and 0.1 5% N.

UNS 532304

A low alloy duplex containing 0.03% max. C, 23% Cr, 4% Ni and 0. 1 % N. It has similar or slightly superior corrosion resistance to Type 31 6 in most acid environments, but with approximately double the tensile properties. Its primary use is as a structural stainless steel where mechanical strength is important.

UNS S32750

A super-duplex containing 0.03% max. C, 25% Cr, 7% Ni, 4% Mo and 0.28% N. The higher alloy content of this steel gives enhanced corrosion resistance in the same class as the super-austenitics and nickel base alloys but with much higher mechanical properties.

05 MIG/MAGS Welding (mc paper)

1. The heat source used in MAGS welding is:-

a) Oxygen and acetylene b) Argonc) An electric arcd) CO2

2. The shielding gas used for M.I.G. welding is: -

a) A flammable gasb) An active gasc) A reducing gasd) A totally inert gas

3. The purpose of a welding rectifier is to: -

a) Correct current changesb) Convert A.C. to D.C.c) Correct voltage charges d) Convert D.C. to A.C.

4. MAGS welding is a: -

a) Non fusion processb) Fusion processc) Surface adhesion processd) Friction process

5. The maximum recommended length of an integrated cable is: -

a) 2mb) 8mc) 6md) 4m

6. The power source normally used for MAGS welding is: -

a) An A.C. Transformer onlyb) A constant potential typec) A constant current typed) A D.C. battery 7. The term duty cycle refers to: -

a) The minimum output currentb) The maximum output current for a given period of timec) The minimum period of time the machine can be used d) The number of hours worked in a day

8. A 0.8 mm diameter wire should be used with: -

a) A one size smaller contact tipb) Any diameter contact tip providing that it is the correct length c) A 0.8 mm diameter contact tipd) A one size larger contact tip

9. A suitable shielding gas for the welding of aluminium would be: -

a) Pure nitrogen b) Pure argonc) Carbon dioxided) An argon / carbon dioxide mix (5 or 20% CO2)

10. Which one of the following elements is added to filler wire as a deoxident: -

a) Carbon b) Siliconc) Heliumd) Hydrogen

11. The contact tip is made from:

a) Steelb) Chromiumc) A copper alloyd) Plastic

12. When producing welds on low carbon steel using the MAGS process one purpose of the inductance control is to reduce: -

a) Porosity b) Penetrationc) Undercut d) Spatter

13. Which gas can be added to argon in order to improve the weldability or fluidity on stainless steel: -

a) Carbon dioxide b) Heliumc) Oxygend) Nitrogen

14. A lack of shielding gas coverage would cause which of the following defects

a) Oxidisationb) Penetrationc) Excess reinforcementd) Lack of one side wall fusion

15. Dip transfer is most suitable for welding in the flat position: -

a) Thick plate b) Sheet metal c) Aluminiumd) Galvanised steel

16. Inductance is a method of: -

a) Metal transfer b) Stabilising the arc to produce less spatterc) Explaining how the equipment works to new learnersd) Stopping porosity

17. Porosity during MAGS welding can be caused by: -

a) Using the wrong diameter wireb) Working in an enclosed space c) Draughts causing turbulenced) Using the wrong diameter contact tip

18. If the drive rolls on a wire feed unit are fastened too tight, which of the following faults could result?

a) An increase in wire feed speedb) A decrease in wire feed speed c) The electrode wire flattensd) Overheating of the wire

19. Spray transfer is used for welding: -

a) Thin sheet sectionsb) Overhead welding c) Steam pipe weldingd) Thick sections

20. Vessels that have contained flammable materials, prior to welding, should be

a) Flame cleaned b) Steam cleaned and then checked with an explosimeterc) Welded from a distance d) Thoroughly washed out with hot water and allowed to stand in the open air for one hour

21. The welding lead that forms the circuit during M.A.G.S welding is connected to the:

a) Negative terminal of a D.C. power sourceb) Secondary side of an A.C. transformerc) Primary side of an A.C. transformerd) Positive terminal of a D.C. power source

22. A suitable grade of filter lens for MAGS welding with a current of 120 amps would be: -

a) E.W. 11b) E.W. 14c) G.W.12 d) E.W. 8

23. Output voltages for most MAGS welding sets are more likely to be used in the range of: -

a) 10-12 voltsb) 14-50 volts c) 50-110 voltsd) 110-200 volts

24. Which of the following modes of transfer relies totally on semi-short circuiting:

a) Pulsedb) Globularc) Dipd) Spray

25. Which gas can be used for the welding of copper: -

a) Nitrogenb) Oxygenc) Carbon dioxided) Hydrogen

26. Which of the following standards covers wire electrodes and deposits for gas shielded metal arc welding of non-alloy and fine grained steels: -

a) BS EN 4872b) BS EN 287c) BS EN 288d) BS EN 440

27. What should be removed in order to ensure a good electrical contact when making welding repairs to steel gates?

a) The nuts and bolts that would form part of the welding circuit b) Paint and rustc) The handlesd) The hinges

28. The secondary lead connecting the work to the power source unit is called the welding:

a) Earthb) Mainsc) Returnd) Output

29. The glass tube situated adjacent to the regulator on MAGS unit is a

a) Contents gaugeb) Heater unitc) Filter unitd) Flowmeter

30. When using liquid CO for the MAGS welding process, which of the following should be connected to the cylinder?

a) A filterb) A heaterc) A coolerd) An explosimeter

31. A cylinder painted black with a grey shoulder and a vertical white line contains: -

a) Oxygen gasb) CO2 gas c) CO2 liquidd) Argon gas

32. The gas supplied in the blue cylinders with a light green shoulder contains a mixture of argon and: -

a) Oxygenb) Heliumc) Hydrogend) CO2

33. The filler wire used in MAGS welding is fed in to the weld pool from a: -

a) Spoolb) Heaterc) Regulatord) Solenoid

34. The slope angel of MAGS gun when making a bead in the flat position should be: -

a) 30 to 40 degb) 40 to 50 degc) 50 to 60 degd) 75 to 85 deg

35. Which of the following ancillary items of equipment would be most useful for using the MAGS welding process?

a) A spark lighterb) A powered fluxc) A pair of cuttersd) A pair of welding goggles

36. The abbreviation O.C.V. Stands for: -

a) Outlet current voltageb) Open current voltagec) Outlet circuit voltaged) Open circuit voltage37. The type of edge preparation most suited for use with MAGS welding of low carbon steel plate 20 mm thick is:

a) Square edge butt with a 3 mm root gapb) Single vee butt with no root gapc) Single vee butt with a broad root face and no root gapd) Double vee butt with a 3 mm root gap

38. Which one of the following 15 mm thick joints would require the minimum number of runs for the economy of materials and labour?

a) Single vee buttb) Double vee buttc) Single Vee butt with a broad root faced) Double U butt

39. A double vee preparation would be the most suitable when MAGS welding plate of thickness

a) 3 mmb) 6 mm c) 10 mmd) 20 mm

40. The best technique for joint surface cleaning to remove oil would be

a) Grindingb) Wire wool cleaningc) Degreasingd) Wire brushing

41. Porosity in a welded joint maybe caused by incorrect

a) Edge preparationb) Fit upc) Root faced) Material cleaning

42. A small amount of the weld metal deposited during MAGS welding maybe lost through

a) Spatterb) Faster welding speedsc) Poor joint preparationd) Low quality plate

43. Which of the following components would be found within the MAGS welding system:

a) Tungsten electrodeb) High Frequency Unitc) A DC constant potential type power sourced) Oxygen cylinder

44. Which one of the following materials produces a high melting point protective oxide layer on its surface:

a) Low carbon steelb) Low alloy steelc) Aluminiumd) Chrom-moly steel

45. Which of the following MAGS wires would be most suitable for a pull type system of wire feed:

a) Low carbon steelb) Aluminiumc) Stainless steeld) Low alloy steel

46. Argon gas is

a) Heavier than airb) A combustible gasc) Lighter than aird) A reducing gas

47. A constant potential type of power source can be used for

a) MIG onlyb) MIG and TIGc) MMA and MIGd) MMA and TIG

48. The term MIG welding could be used when welding with the shielding gas(es)

a) pure Argonb) Argon plus Carbon Dioxidec) Helium plus Carbon Dioxided) Pure Hydrogen

49. The term MAG welding could be used when welding with the shielding gas(es)

a) pure Argonb) pure Heliumc) Argon plus Heliumd) Argon plus Carbon Dioxide

50. Select the correct colour coding for an Argon cylinder

a) Brownb) Blackc) Greend) Red

51. Select the correct colour coding for a Helium cylinder

a) Brownb) Blackc) Greend) Red

52. Which shielding gas(es) can be used when MIG welding aluminium?

a) Argon or Heliumb) Argon or Hydrogenc) Nitrogend) Helium and Hydrogen

53. Backing bars are:

a) temporary, do not form part of the welded joint and are used to support the underside of the weldb) permanent and form part of the completed weldc) used to open up closed joints distorted during tack weldingd) used to support the welder when working above headheight

54. Argon can accumulate in an open tank and cause asphyxiation due to the fact that

a) Argon is lighter than airb) Argon is an inert gasc) Argon is heavier than aird) Argon

55. MAGS welding, for a given current, produces more:

a) ultra violet light than manual metal arc weldingb) heat than manual metal arc weldingc) spatter than manual metal arc weldingd) slag than manual metal arc welding

56. When working in confined spaces there is a greater risk of asphyxiation when using the shielding gas:

a) Nitrogenb) Heliumc) Hydrogend) Argon

57. A welding transformer:

a) steps up the voltageb) steps down the voltagec) steps down the currentd) steps down the current and the voltage

58. A rectifier

a) changes DC to ACb) changes DC positive to DC negativec) changes AC to DCd) steps down the voltage

59. Unequal leg lengths of a tee fillet welded in the horizontal/vertical position is most likely to be caused by:

a) incorrect tilt angle of torchb) too much spatterc) incorrect slope angle of torchd) too fast a welding speed

60. The Reportable Diseases and Dangerous Occurrences Regulations (RIDDOR) 1995 require that employers:

a) keep records for at least five yearsb) provide induction training for all new employeesc) notify authorities of the escape of radioactive materiald) assist in investigations by an enforcing authority.61. Which one of the following may be regarded as a hazard when carrying out a risk assessment on mechanical lifting equipment?

a) Maintenance schedule.b) Operator training.c) Defined gangways.d) Warning signs.

62. Signs indicating mandatory actions are:

a) circular on a blue backgroundb) triangular on a yellow backgroundc) triangular on a blue backgroundd) circular on a yellow background.

63. The Manual Handling Operations Regulations (1992) are concerned with

a) the training of personnelb) reducing the risk of injuryc) design and construction of rope slingsd) rules for the use of slings.

64. When should head protection be worn?

a) at all times unless there is no risk from falling objectsb) at all times unless you are working above head heightc) only when working on scaffoldingd) only when there is a risk of an explosion

65. What is the maximum safe voltage for mains operated portable electrical tools on site?

a) 12 voltsb) 420 voltsc) 230 voltsd) 110 volts

66. The COSHH regulations are MAINLY involved with the protection of the

a) environmentb) workplacec) persond) atmosphere Candidates Name ___________________

Candidates Answer Sheet: MIG/MAGS Welding

abcdabcdabcd

13365

23466

33567

43668

53769

63870

73971

84072

94173

104274

114375

124476

134577

144678

154779

164880

174981

185082

195183

205284

215385

225486

235587

245688

255789

265890

275991

286092

296193

306294

316395

326496

ASSESSORS NAME _________________________RESULT ______ %

ASSESSORS SIGNATURE _____________________________ DATE _______

CANDIDATES SIGNATURE ___________________________ DATE _______

ANSWERS

ANSWER SHEET: MIG/MAGS Welding

abcdabcdabcd

13365

23466

33567

43668

53769

63870

73971

84072

94173

104274

114375

124476

134577

144678

154779

164880

174981

185082

195183

205284

215385

225486

235587

245688

255789

265890

275991

286092

296193

306294

316395

326496