mem05018c - vetres

MEM05 Metal and EngineeringTraining Package

Learner guideVersion 2

Training and Education SupportIndustry Skills Unit

Meadowbank

Product Code: 5768

MEM05018CPerform advanced welding

using gas metal arc welding process

(aluminium edition)

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MEM05018C Perform advanced welding using gas metal arc welding process (Aluminium)

© TAFE NSW (Training & Education Support Industry Skills Unit, Meadowbank) 2013

Acknowledgments

The TAFE NSW Training and Education Support, Industry Skills Unit Meadowbank would like to acknowledge the support and assistance of the following people in the production of this resource package:

Bernard WeldingBOC Gases AustraliaCIGWELDLincoln Electric AustraliaSilverwater Welding SuppliesStandards AustraliaWelding Industries of Australia (WIA)

Writer:Updated from existing TAFE resources.

Reviewer:Stephen Davies (TES Industry Skills Unit)TAFE NSW

Project Manager:Stephen DaviesEducation Programs ManagerTraining and Education Support, Industry Skills Unit, MeadowbankTAFE NSW

Enquiries

Enquiries about this and other publications can be made to: Training and Education Support, Industry Skills Unit Meadowbank Meadowbank TAFE Level 3, Building J, See Street, MEADOWBANK NSW 2114 Tel: 02-9942 3200 Fax: 02-9942 3257

© TAFE NSW (Training and Education Support, Industry Skills Unit Meadowbank) 2013

Copyright of this material is reserved to TAFE NSW Training and Education Support, Industry Skills Unit Meadowbank. Reproduction or transmittal in whole or in part, other than subject to the provisions of the Copyright Act, is prohibited without the written authority of TAFE NSW Training and Education Support, Industry Skills Unit Meadowbank.

ISBN 978 1 74236 476 6

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MEM05018C Perform advanced welding using gas metal arc process (Aluminium)


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Contents

Introduction .................................................................................. 7

1. General introduction ............................................................................7

2. Using this learner guide ......................................................................7

3. Prior knowledge and experience ............................................................9

4. Unit of competency overview ................................................................9

Topic 1: GMAW safety .................................................................. 13

Review questions .................................................................................. 18

Topic 2: Aluminium ..................................................................... 21


Topic 3: GMAW aluminium ........................................................... 29


Topic 4: GMAW consumables ....................................................... 39


Topic 5: Pulse GMAW ................................................................... 47


Topic 6: Welding symbols ............................................................ 53


Topic 7: Destructive weld tests ................................................... 59


Topic 8: Welding aluminium structures ...................................... 67


Practical jobs .............................................................................. 72

JOB 1: Pad weld - Flat (Plate) ................................................................. 76

JOB 2: Horizontal/Vertical (Plate/sheet) ................................................... 78

JOB 3: Corner fillet - Horizontal/vertical (Plate) ......................................... 80

JOB 4: T-Fillet - Vertical (Plate) ............................................................... 82

JOB 5: T-Fillet - Overhead (Plate/sheet) ................................................... 84

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MEM05018C Perform advanced welding using gas metal arc process (Aluminium)


JOB 6: Butt weld - Flat - (Plate/sheet)) .................................................... 86

JOB 7: Butt weld - Horizontal (Plate) ....................................................... 88

JOB 8: Butt weld - Vertical (Plate) ........................................................... 90

Resource Evaluation Form ........................................................... 93

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© TAFE NSW (TES, Industry Skills Unit Meadowbank) 2013 Page 33 of 96

Care must be taken when installing nylon or teflon conduit liners, that they are cut to the correct size and not pinched or damaged by the holding screws. Conduits must be inspected and cleaned regularly especially when engaged with high volume production work.

Welding techniquesAluminium and its alloys can be readily welded providing appropriate precautions are taken. With some minor variations, welding techniques and joints used for welding aluminium are similar to those used for low carbon, low alloy and stainless steel.

Aluminium and its alloys possess a range of different properties from steel. For this reason, operators, must be aware of some of the difficulties associated with the material. Some key precautionary measures include:

Weld metal supportAluminium has poor structural stability when elevated to welding temperatures, especially when making butt welds on thin metal sections. This may lead to excessive penetration, possible “burn through” and/or collapse of the weld pool.

When making butt welds on aluminium it is important to support the weld pool. Temporary copper or ceramic backing materials are sometimes used to support the weld joint to prevent weld metal “drop through” and to assist alignment and fit-up. An alternative is to use a permanent backing strip (if design permits) which are composed of the same material as the main joint.

Backing strip supporting butt joint

Crater controlGas metal arc welding aluminium generally leaves a crater at the end of the weld.On solidification of the weld crater, cracking can sometimes occur.

Crater at the end of a weld seam

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of 96 © TAFE NSW (TES, Industry Skills Unit Meadowbank) 2013


Techniques used to eliminate crater cracking include:

• Modern GMAW power sources are equipped with a “crater fill” function to allow operators to change current values at the end of the weld run to fill the crater

• Reversing the direction of welding at the end of the weld will allow the weld crater to be filled

• Use of “run-on” and/or “run-off” tabs will avoid craters forming in the completed weld

• Breaking the arc and “re-striking” after the weld pool has solidified.

Welding issuesIn contrast to welding plain carbon steels, some common difficulties associated with GMAW aluminium include:

• Weld cracking. This occurs in aluminium alloys because of high stresses generated across the weld due to high thermal expansion (twice that of steel) and substantial contraction on solidification

• Solidification cracks. Cracks are sometimes caused by the use of an incorrect wire, wire/parent metal combination or inappropriate weld geometry

Solidification crack in a weld

• Porosity. is caused by the absorption of hydrogen in the weld pool. Sources of hydrogen are moisture on the parent material, wire surfaces and water vapour from the shielding gas atmosphere. Aluminium is most at risk to porosity when welding is taking place in relatively high humidity. Operators need to allow wire spools to “stabilise” to the temperature in the welding area prior to use. Wire electrode packaging should remain unopened in the welding area for 24 hours after entry from a cooler storage area.

• Pre-weld cleaning of aluminium. It is essential to remove all traces of oil, grease, lubricant, dust, stencil markings and heavy oxidation from material surfaces before welding. Weld joints should be cleaned with a stainless steel wire brush, dedicated only for the purposes of cleaning aluminium. Edges should then be wiped with a clean cloth dipped a petroleum based solvent such as acetone or toluene, and then allowed to dry thoroughly. Cleaning between weld runs can be done with a stainless wire brush.

• Oxide layer. Aluminium has a tenacious layer of oxide that forms rapidly on its surface in the presence of air. The melting point of this oxide is approximately 2050ºC compared to pure aluminium’s melting point of 660ºC. To successfully weld aluminium, this refractory oxide must be temporarily removed. The GMA welding process breaks up the oxide by the action of the arc. It is achieved by the electrode being connected to the positive (+) terminal, which allows the electron flow to lift the oxide from the weld zone during welding to allow fusion to take place without oxide interference.

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• No colour change when heated. Unlike carbon steel aluminium displays no visible colour change when heated. As a result there is little warning to the operator that the material is approaching its melting point. Because of aluminium’s low melting point and lack of colour change, care must be taken avoid overheating the material when welding.

• Electrical/thermal conductivity. Aluminium is about one-third the density of steel and has much higher thermal/electrical conductivity rates. The co-efficient of linear expansion is about twice that of steel. Cold starts on thicker metal sections can occur due to its higher thermal conductivity and preheating may be necessary on heavier metal sections.

• Black “sooty” weld deposits. Ideally welds should be bright and shiny after welding. However, a common occurrence when GMAW aluminium is to sometimes find a black “sooty” coating on the weld. The soot is actually aluminium and magnesium oxides. Black soot or smut as it sometimes referred to, is due to the lower boiling points of both aluminium and magnesium as they are lower than the temperature of a welding arc. As a result, some of the aluminium and magnesium in the wire evaporates during welding, alloys such as 5356 and 6061 contain relatively high amounts of magnesium which present this problem. Black “sooty” welds can be minimised by: - Using a push technique, don’t pull the gun - Increase argon gas flow rate - Ensure all gas connections are tight and not leaking - Ensure you don’t use too long a stick-out or nozzle to work distance.

Black “sooty” weld deposit

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Review questions

These questions have been included to assist you revise what you have learned in Topic 3: GMAW aluminium.

Q1. List two (2) metal transfer modes recommended for GMAW aluminium.

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Q2. State three (3) types of wire feed systems used for GMAW aluminium.

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Q3. What is meant by the term “bird nesting”?

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Q4. What three (3) equipment checks can be done to prevent “bird nesting”?

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Q5. What type of welding gun is best suited for feeding aluminium wire over longer distances?

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Q6. List two (2) techniques used to eliminate craters at the end of a weld run.

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Q7. Explain why it is important to support aluminium weld joints during welding.

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Q8. Explain how aluminium can be pre-cleaned prior to welding.

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Q9. How is the oxide layer on aluminium temporarily removed during GMAW.

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True / False questions (Circle the correct response)

Q10. Highly polished knurled rolls should be used to feed aluminium wires. True False

Q11. Using a “drag” (backhand) welding technique can produce dirty weld deposits. True False

Q12. Short arc (dip) transfer is best suited for welding thick sections of aluminium. True False

Q12. Black “sooty” welds are caused by using too large a wire diameter. True False

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Topic 4: GMAW consumablesConsumable selectionIt is important to select the correct type of wire electrode and shielding gas to suita particular alloy type and job application if parts are to be joined successfully. A wire electrode must be capable of producing sound weld deposits that closely match the physical and mechanical properties of the parent metal.

When welding aluminium and its alloys it is critical that mechanical properties such as impact, yield and tensile strength of the weld metal match those of the parts being welded. Physical properties also need to be considered such as corrosion resistance and colour match.

In addition to mechanical and physical properties, other factors that influence the selection of a wire electrode include:

• Type of shielding gas used (see shielding gases)

• Composition of the parent metal (alloy type)

• Requirements the weld is expected to perform in service

• Standard or code requirements you are complying with

• Cost, dependable supply and availability of consumables

• Capacity of the power source (current range, duty cycle, pulse facilities etc.)

• Type of joint and weld positions likely to be encountered.

Large diameter wires are capable of producing high deposition rates and are used for welding thicker sections whereas smaller diameter wires are better suited for positional welding and joining thinner sections.

Wire electrodes are classified in accordance with AS/NZS ISO 18273:2006 Welding consumables-Wire electrodes, wires and rods for welding aluminium alloys – Classification. The purpose of this Standard is to provide specific requirements for consumable manufacturers to produce wires to a specified composition and quality for GMAW applications. The classification system also provides fabricators, the user of the product, with details relating to a wires mechanical properties and other information needed to select a wire for a given application.

Note: Fabricators should be aware that some wires may be supplied bearing American Welding Society (AWS) specifications to meet code AWS A5.18 and AWA A5.28 requirements or the superseded Standard AS 2717.2:1988. It is recommended to consult the manufacturer or consumable suppler for detailed information concerning applications for a given wire classification.

Classification of wiresIn accordance with AS/NZS ISO 18273:2006, classification of aluminium wires is divided into two (2) parts, these being;

Part 1 = indicates the product form which is either a solid wire or rodPart 2 = indicates a numerical symbol indicating the wires chemical composition.

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Example: ISO 18273 - S Al 4043 or it can be expressed as S ALSi5

- ISO 18273 refers to the Standard number- S – refers to product form (solid wire)- Al 4043 – refers to the chemical composition of the wire (see table 1 in the standard).The above wire may also be expressed in the following terms:- Al Si5 – refers to the chemical composition of the wire which indicates 4.5-6%Si) (see table 1 in the standard).

It can be seen from the above system, wire electrodes are classified similar to wrought products in that they are given the letters Al to indicate the wire is aluminium based followed by a four digit number to indicate the alloy type. For example, a Al 1070 wire is essentially pure aluminium, Al 4043 is an aluminium/silicon wire and Al 5356 is aluminium/magnesium wire. See table 1 in the Standard for detailed information.

Wires are precision wound onto spools and are supplied in hermetically sealed packaging. The most common being a 7 Kg spool, others are available in 2 and 0.5 Kg weighted spools. Wires used for large volume production work are available in sealed 70 kg bulk containers and should always be used on electrode positive (d.c.+).

Some examples of aluminium wires and applications are indicated in the table below.

Base metal Wire type and applications1000 series

pure aluminiumA soft, unalloyed, low strength aluminium wire for welding 1XXX series wrought aluminium products. These wires provide a good resistance to chemical corrosion and cracking.

Typical 1XXX wire products include:

• CIGWELD Autocraft Al 1100• Lincoln Superglaze 1100

Operating data Electrode classification

Wire size(Ø mm)

Voltage range(volts)

Current range(amps)

Al 1100 1.62.02.4

23-2825-3125-31

200-350250-400250-400

4000 seriesaluminium/silicon alloy

An aluminium/silicon wire for welding a range of wrought and cast aluminium alloys. The Al 4043 can be used for welding some heat-treatable alloys and 6000 series aluminium/ silicon/magnesium alloys. Al 4043 wires are less sensitive to weld cracking with the 6XXX series base alloys.

Typical 4XXX wire products include:

• CIGWELD Autocraft Al 4043• Lincoln Superglaze Al 4043

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Wire size(Ø mm)

Voltage range(volts)

Current range(amps)

Al 4043 1.21.6

20-2523-28

150-250200-350

5000 series aluminium/ magnesium alloy

Al 5356 is the most popular aluminium/magnesium wire. Al 5356 is a general purpose alloy wire designed for welding 5000 series alloys. Applications include marine structures and ship/boat building.

Typical 5000 wire products include:

• CIGWELD Autocraft Al 5356• WIA Ausmig 5356• Lincoln Superglaze 5356


Wire size Voltage range Current range (amps)

Al 5356 0.80.91.01.2

14-2116-2217-2320-25

50-15080-180110-220150-250

Care and storage of wire electrodes

• Always store wire packages off the floor in a clean, dry, low humidity environment

• Store unpackaged wires for long periods in a heated cabinet at 10-15°C above ambient temperature

• Do not unseal wire spools from their packaging until such times as they are to be used

• Never remove classification codes, identification labels or trade names from either the storage box or spool. This can lead to an improper type of wire being used on a job

• Always replace and store partially used wire spools in the packaging (box) they were originally supplied in

• Never use badly contaminated wires as they will contaminate the weld and cause unnecessary wear and tear on conduit liners, drive rolls and contact tips

• Damaged spools should be discarded as they will cause irregular wire feed problems resulting in poor quality weld deposits

• Use dust covers on wire spools “loaded” on machines to avoid contamination from moisture and workshop dust.

Shielding gasesThe primary role of a shielding gas for GMAW is to exclude the damaging effects of oxygen and nitrogen in the surrounding air from entering the welding arc. Shielding gases are an essential consumable needed to produce a stable arc and prevent contamination from the atmosphere which is composed of approximately 80% nitrogen and 20% oxygen.

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The GMAW process produces sound quality welds by using a non-reactive, inert gas medium to shield the arc, wire and weld pool. Argon (Ar) and argon + helium (Ar/He) mixtures are inert gases extensively used for GMAW nonferrous metals such as aluminium and aluminium alloys. Choosing a gas or mixture needs carful consideration as different gases and gas mixtures will have a marked effect upon such features as:

• Weld bead contour, appearance (finish) • Level of penetration • Arc characteristics and stabilisation • Metal transfer characteristics• Surface cleaning action • Welding speeds• Strength of finished weld.

Mixtures contain varying quantities of argon and helium. Selection of a shielding gas or mixture is dependent on such factors as:

• Composition and thickness of material to be welded• Mode of metal transfer required (spray, pulse, short arc)• Application - automated, robotic welding• Weld profile and penetration levels required.

Argon (Ar) Argon is the most widely used inert shielding gas in Australia. It is the least expensive of the inert gases because it is obtained from separating air during the oxygen and nitrogen distillation process. Argon produces a moderately hot welding arc and is suitable for welding all aluminium alloys. It produces a “finger-like” penetration profile and slower welding speeds compared to helium. Argon is extensively used for welding aluminium because its relatively low cost and availability.

Helium (He) Helium is much more expensive than argon because it is mostly imported from other countries. In contrast to argon, helium produces a hotter arc, faster welding speeds and broader, but a slightly less deep penetration profile. Although it can be used as a standalone gas, it is most effective when combined with argon as a gas mixture.

Argon/helium mixtures Argon and helium are commonly mixed together in varying proportions to form a mixture suitable for welding a range of different metals. The greater proportion of helium in a mixture, the hotter the arc temperature. For example, three parts argon (75%) to one part helium (25%) produces a hot arc which is especially good for GMAW aluminium alloys. Mixed in opposite proportions, 75% He and 25% Ar produces a very hot arc, rapid melting of the metal (without the need for pre-heat) and broad deep penetration. achieved. These mixtures are an economic alternative to using pure helium. They are used for improving weld speeds, penetration and shape of the weld.

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Typical weld bead and penetration profiles for argon, helium and an argon/helium gas mixture are illustrated below.

Argon Argon/helium Helium

Advantages of using an argon based gas mixture as opposed to a single gas such as argon include:

• Improves weld bead profile and appearance • Depth of penetration can be controlled • Reduced spatter levels • Increased welding speeds – increased productivity • Reduces undercutting, lack of fusion. • Better edge wetting.

Identification of gases Shielding gases for GMAW are classified in accordance with AS 4882-2003 Shielding gases for welding. This Standard provides a designation system to identify welding gases. The table below reflects AS 4882 by providing a letter to indicate a type of gas.

Designator GasA ArgonC Carbon Dioxide (CO2 )He HeliumH HydrogenN NitrogenO Oxygen

Note: The chemical symbol for Argon is Ar, although only the letter A is used as the designator in AS 4882.

Shielding gases comprise of the following designator and numbering arrangement:

SG – B X - % 2 component mixSG – B XY - % % 3 component mixSG – B XYZ - % % % 4 component gas mix

Where:SG – identifies the product as a “shielding gas”;SG – B - Indicates the singular, or the base gas in the gas mixture

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Topic 5: Pulse GMAWThe mode of metal transfer is a highly controlled form of spray transfer requiring specially designed pulsing welding power sources. Pulse transfer involves using a welding current programmed to operate between a high energy peak current and a low background current.

When the welding current is in the background cycle it will operate in the globular transfer mode and when it reaches its peak current level it will operate in the spray transfer range. This action results in the arc constantly alternating back and forth between both current ranges.

During a single pulse cycle the arc will form a background current which keeps the arc “energised” and stable without actually depositing any filler metal. A droplet forms but is not transferred.

As the current reaches its high energy “peak”, the droplet is detached and trans-ferred across the arc into the weld pool. One metal droplet is transferred per pulse; the frequency per second is controlled by setting on the machine. Pulsed transfer technology offers control over several key variables. These include:

• Peak current - spray mode• Peak current time• Background current - a reduced current value lower than short arc transfer• Background current time• Period - the time the background and peak currents operate through one cycle• Frequency - refers to the number of times a period occurs per second.

Most modern machines have a range of factory set programs inbuilt to automatically adjust pulse parameters such as those mentioned above. This option takes a large proportion of guesswork out of setting up equipment to produce optimum welding conditions. Selecting a given program can be as simple as entering the type and thickness of metal that has to be welded.

Pulse sequenceA typical pulse sequence is explained in the diagram below.

1. Establishing the arc2. Heating the electrode and parent metal3. Droplet forms at the electrode tip4. Droplet is “nipped off” and transferred during the peak, spray mode5. Droplet joins parent metal to form the weld.

GMAW pulse sequence

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A graphical description of pulsed arc metal transfer illustrated below shows the pulse transfer in relation to current input.

Pulsecurrent

Pulse timetp

MeancurrentBack-

groundtime tb

Note: 0.9 to 1.6 mm diameter wires are most commonly used for pulsed arc transfer.

Advantages

Pulsed arc metal transfer offers a number of advantages compared to other GMAW modes of transfer. Some of these include:

• Greater control of weld penetration levels• Improved control of weld metal deposits• Smooth regular weld profiles and crater control• More resistant to lack of fusion defects than other modes of transfer• Excellent arc stability with very low spatter levels• Less distortion when welding thinner sections due to better controlled heat input• Root pass quality is comparable with GTAW• Lower fume outputs• Able to cope with poor joint fit-ups better than conventional GMAW.

Limitations

• Equipment is more expensive than conventional systems• More complex to set up for the operator• Higher arc energy requires the use of additional safety protection for operators

and those working nearby

Applications

Typical applications for pulse GMAW include:

• Welding pipes and tubes• Ship and boat building• Welding aluminium and stainless steels fabrications• Ideally suited for robotic, fully automated applications.

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