TECH A V GMAW Manuel utilisateur

GAS METAL ARC WELDING

(GMAW)

Learner Guide

TABLE OF CONTENTS

INTRODUCTION PAGE 1

LEARNERS INSTRUCTIONS (HOW TO USE THIS PROGRAMME) PAGE 2

PROGRAMME 1 - THE GMAW PROCESS

INTRODUCTION PAGE 3

RESOURCE NOTES PAGE 4

SELF-TEST NO. 1 PAGE 12

GLOSSARY OF TERMS PAGE 14

PROGRAMME 2 - EQUIPMENT PARTS AND FUNCTIONS

PART 1 - EQUIPMENT PARTS AND FUNCTIONS PAGE 19

RESOURCE NOTES PAGE 20

SELF-TEST EXERCISE 2.1 PAGE 26

PART 2 - WELDING EQUIPMENT PREPARATION PAGE 28

SELF-TEST EXERCISE 2.2 PAGE 36

PRACTICAL EVALUATION - EXERCISE 2.2 PAGE 37

PROGRAMME 3 - WELDING PRACTICES AND PROCEDURES

INTRODUCTION PAGE 38

RESOURCE NOTES PAGE 39

PART1 - BASIC SKILLS PAGE 39

PART 2 - PRACTICAL EXERCISES PAGE 44

PRACTICAL EXERCISE NO. 1 PAGE 49

EXERCISE NO. 2PAGE 50

PRACTICAL EXERCISE NO. 2 PAGE 52

EXERCISE NO. 3PAGE 53

PRACTICAL EXERCISE NO. 3 PAGE 55

EXERCISE NO. 4PAGE 56

PRACTICAL EXERCISE NO. 4 PAGE 57

CONCLUSION PAGE 58

SOME USEFUL GMAW TIPS PAGE 59

WELDING CHART 1 PAGE 60

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GAS METAL ARC WELDING

INTRODUCTION

This learning aid, consisting of your "Learners Guide" and video programmes, has been

designed to assist you to learn the BASIC SKILLS and KNOWLEDGE involved in "Gas Metal

Arc" welding processes.

OBJECTIVES: (PURPOSE OF THIS MATERIAL)

This series serves to assist you, the "Learner", in achieving a "Learnership" in any of the

engineering fields where GMAW welding is stated as being a "unit of learning".

PURPOSE STATEMENT (WHAT YOU WILL LEARN)

During this learning programme you will learn:

oTo describe basic GMAW welding processes.

oTo identify, by name, the equipment, components, accessories and consumables

used in typical processes.

To set up and prepare for welding.

To use GMAW equipment in flat weld position.

LEARNING ASSUMED TO BE IN PLACE (WHAT YOU SHOULD ALREADY KNOW / BE ABLE TO

DO)

oA working knowledge of Industrial Safety and Arc welding PPE.

oIdentify common metals and "alloys".

oAn understanding of AC and DC current.

oUse SMAW equipment.

LEARNING OUTCOMES (WHAT YOU WILL BE ABLE TO DO AFTER COMPLETING THE GMAW

MODULE)

oPrepare a typical MIG/MAG welding unit for operation.

oProduce "down-hand" welds, utilising both "Short-Circuit" and "Spray Transfer"

modes, on mild steel plates.

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LEARNERS INSTRUCTIONS (HOW TO USE THIS LEARNING AID)

Step 1 - Read the Resource Notes and follow any written instructions.

Step 2 - View the relevant video section (where applicable).

Step 3 - Complete any "Self-Test Exercise" (as applicable).

Step 4 - Perform a practical exercise (as applicable).

Step 5 - Have your Mentor/Instructor assess your work.

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PROGRAMME 1

THE GMAW PROCESS - AN INTRODUCTION

THE BASIC "GAS METAL ARC WELDING" PROCESS

In this section you will learn:

oTo describe the concept I principles of Gas Metal Arc Welding processes.

oDescribe/Identify by name, typical equipment constituting a GMAW system.

oExplain in basic terms how MIG/MAG/FCAW processes operate.

oExplain in basic terms the modes of metal transfer (Short arc, globular, spray and

pulsed).

BEGIN THIS SECTION OF LEARNING BY READING THE NOTES THAT BEGIN ON THE

NEXT PAGE.

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RESOURCE NOTES

PROGRAMME 1

1. PRINCIPLES OF GAS METAL ARC WELDING

Gas metal arc welding, or GMAW, is a welding process that involves the "continuous

feeding" of filler material into a weld-pool.

Gas Metal Arc Welding has become the most popular welding process, especially in

fabrication industries. Although the majority of GMAW is performed "manually" (by

hand skill) much is also performed using "robotic equipment" (Automobile

manufacturing is a major user of such systems).

In this series of programmes we will concentrate upon "manual practices".

GMAW is a very easy process to operate, and anyone having had experience

with other "traditional welding processes such as "gas welding" and "stick

welding (Shielded Metal Arc) will find the GMAW process a "pleasure" to use!

Although the term GMAW has been used several times already in this text, you will

rarely hear this in the "work-place". Other common terms used to describe this

process include:

oMIG or Metal Inert Gas.

oMAG or Metal Active Gas.

oFCAW or Fluxed Cored Arc Welding, also known as CO2 Welding.

These terms are based primarily on the method in which the weld pool (molten

metal) is protected or "shielded" from the atmosphere. In order to understand these

terms you need to first understand how a GMAW process works, in principle. There

is a lot of science involved in welding, especially in the GMAW process, and more

especially in the process of "metal transfer". We shall in this module explain those

issues that affect the "weld quality" and the manner in which you, the welder,

prepare and use the equipment. In this programme you will learn all that is

necessary to understand the process, however let us start at the beginning and get

to know what equipment is used in GMAW.

2. AN OVERVIEW OF BASIC GMAW EQUIPMENT

The main parts of any GMAW system typically comprise the following:

oA "Power Supply" that delivers DC welding current at Constant Voltage.

oA "Wire Feeder" -either fixed speed or variable speed.

oFiller-wire, also called "electrode wire". This is a "consumable item".

oShielding gas -either "inert" or "active". This too is a "consumable item".

oA "welding gun" and its connecting "power cable" and supply lines.

oA work lead or "ground-lead" (cable).

oSome systems include a "liquid cooling system" that cools the welding gun.

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3. HOW DOES GMAW WORK?

It is important that you understand the operating principles of your GMAW

equipment as this knowledge will assist you to set-up and operate your equipment

more efficiently.

In any arc welding process metal parts are locally heated to "melting temperatures"

using the "heat" generated from an electrical arc.

Causing an electrical current to "jump across a gap" produces an ARC. In "arc

welding", the arc is deliberately created between an "electrode" and the metal to

be welded (base metal). It must be understood that an arc is established through

voltage, but the "intensity' (heat power) is generated through current (amps).

A welding machine or "power source" provides electrical energy to create an arc

(electric equivalent of flame from a gas torch). The arc is directed onto the work

(base metal) to be joined (welded) where the "heat energy" produces "local melting"

of the metal.

The arc is created at the tip of the electrode wire that is constantly being fed

into the "weld pool". The electrode, in effect, "melts" into the weld adding "filler

material" into the molten pool. In this regard the electrode is also the filler-

material and is therefore a "consumable" item in the process.

Electrodes are produced in the form of "wire" and supplied on reels or spools

(Like fishing line). The wire is normally very thin, ranging in size (diameter) from

about 0.76mm -2.38mm (0.030 inch -0.090 inch). In "common language" the

electrode is known as "wire".

There are many TYPES of wire in terms of the "material" from which they are

produced and the "wire-size" or diameter.

Note: It must be understood that when you put metal into a weld, the filler

material must be "compatible" with (the same as or "similar to) the base metal.

(Base metal is sometimes called the "parent metal"). You must be aware there are

many types of metal and "alloys" on the general market and most of these need to

be "welded" in fabrication processes. Selecting the correct "wire" for the type of

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metal, and for the weld-process, is vital as a mistake could result in catastrophic

damage, and possible loss of life. For this reason the "responsible welder" will seek

advice on the correct wire type for any given task if he or she is in any doubt.

As a rule the wire type is provided in a "welding specification" for a given task, and

this in turn is given by the designing engineer or welding authority.

The point being made is that you simply cannot use "any old wire type" for any

job!

Filler-wire (the electrode) is carried to the weld-zone via a "welding-gun" or torch.

The welding gun is attached to the end of a cable assembly, sometimes known as a

"conduit:'. The cable serves many functions and strictly speaking it is a combination"

unit consisting of:

oA "liner" through which the electrode is fed.

oA conductor wire or "electrode lead", through which the "welding current"

passes.

oA "gas line" (or tube) through which the shielding gas flows.

o"Signal wires" (or sensor wires) through which the gun "communicates" with

the welding machine.

oAnd in some cases, "water lines" (hoses) through which "coolant' flows to

and from the welding-gun.

This cable is connected to an adapter (socket) at the wire-feeder outlet. With the

cable connected, and the machine is "powered up", upon operating the trigger on

the welding-gun (depending on make, type and design) the welding machines'

"contactor" is activated. A contactor is usually a "solenoid (or electronic) activated

switch" that "connects the welding current to the welding terminals of the machine

(In other words the welding -circuit is activated and the machine terminals are live!)

At the same time other circuits are activated that do the following:

oOpen the shielding gas valve (providing gas flow).

oOpen the coolant valve (providing coolant, where applicable).

oOperate the "wire feeder motor" and thereby drive the electrode-wire

through the gun.

In order for welding to happen the "welding circuit' must be "closed" (or

completed).

The circuit is complete as soon as an arc has been established. As already

mentioned, an arc is the "source of "heat" in a weld-zone. The resultant heat causes

local melting of the parent metal and the tip of the wire which "transfers" into the

melted "weld pool". The manner in which the electrode I filler metal enters or

"transfers" into the weld-pool is particularly important and we will deal with this in

more detail when we describe "metal transfer modes" in the next section, but first a

word about "shielding".

Most metals will, especially when in their molten state, readily "react" with the

gases in the atmosphere (notably with oxygen and nitrogen) to form "oxides" and

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"nitrides". Simply stated, the result of this "chemical combination" results in the

metal becoming "oxidised" or, in "welding language", porous. A "porous weld" is

extremely weak and cannot be tolerated in any joint that will carry load (or stress),

as the weld will fracture. To avoid "porosity" the weld zone must be protected or

"shielded" from the atmosphere and this is part of the reason we need "shielding

gas" in the system. In a pure Metal Inert Gas (MIG) process the shielding gas is an

INERT gas, such as ARGON or HELIUM. Inert gases will not react (mix or combine)

with heated metal (in the weld pool).

Note: Argon is the most widely used gas type in MIG processes, mainly because

helium is extremely costly.

Shielding gas, supplied in pressurised cylinders, is forced through the welding gun

and exits via a "gas nozzle" at the "nose" of the gun. This gas is directed onto (over)

the weld pool where it surrounds the weld zone and "drenches" the hot metal.

Atmospheric gases cannot penetrate the gas shield as a positive pressure is created

in the gas envelope. (Gas shield pressure exceeds atmospheric pressure).

Some "shielding gases" are "mixtures" of inert and reactive gases. The commonest

reactive gas used is "carbon dioxide" (C02). The addition of a reactive gas into the

"shielding gas cylinder' is not to improve shielding but to improve other factors such

as "arc stability", weld penetration and various other factors that are far too

technical to launch into right now! When a welding process makes use of "mixed

gases", that include an active gas such as C02, then that process should technically

be considered as Metal Active Gas (MAG) process.

Note: This distinction varies according to countries and many (including South

Africa) consider the MAG process to be one that uses purely "active gas", normally

C02 , as the total means of "shielding". In contrast to MIG and MAG processes that

use "solid wire electrodes", the FCAW process uses "hollow electrode wire" and the

hollow "core" of the wire is filled with "flux". Flux is a mixture of various substances

(chemicals and other compounds) which, when subjected to the heat of the welding

process, release shielding gas and, in some cases, add elements into the weld that

improve the quality of the weld material. The flux also acts to "clean" the metal

surfaces during the process. Conventional FCAW electrodes do not generate

sufficient shielding for the weld and additional shielding is provided, most usually,

with carbon dioxide. Some flux-cored wires, known as "self-shielding electrodes", do

not require additional shielding during the welding process.

The most usual (common) gases used in GMAW processes are:

oArgon -a fully inert gas -commonly used for welding aluminium.

oHelium -a fully inert gas -not commonly used alone, often mixed with argon

and CO2for high quality welds in stainless steel. Thick section aluminium

(over 25mm) requires at least 75% helium 25% argon mix to achieve the

desired heat input.

oCarbon Dioxide -Usually known by its "chemical designation, CO2'' This is a

"reactive gas" that, if permitted, will combine "chemically" with the metal in

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a weld-pool. This gas is used only with "ferrous metals" and, with the

exception of FCAW welding, is mixed in small quantities with inert gases.

oOxygen -a reactive gas and used only in minute quantities for purposes of

improving arc stability and heat transfer when welding steel using "spray

transfer". Oxygen is normally mixed with argon in quantities rarely exceeding

5% of total volume.

Note: Gas providers or suppliers usually have their own "brand names" for their

"commercial gas mixes". Ask your gas vendor for the information regarding the

proportions and suitability of gases for a particular application.

4. METAL TRANSFER MODES

We move now to a topic that is often misunderstood namely, metal transfer modes,

or "the way in which the electrode wire gets into the weld!"

There are 3 "modes of transfer" namely:

oShort-Circuit transfer, sometimes called "dip transfer", "short arc transfer"

and "buried arc".

oGlobular transfer, and

oSpray transfer.

4.1 SHORT CIRCUIT TRANSFER (SHORT ARC AND DIP TRANSFER)

Short Circuit Transfer is the "preferred mode" for welding the following:

oThin metal up to approximately 2 to 3mm thick.

oOut of Position welding.

oFilling large gaps.

oRoot runs in heavy gauge material (V-grooved).

The short circuit mode is considered to provide a "cool weld" owing to the "on and

off' nature of the arc.

In the short circuit mode the "cycle" begins when an arc jumps across the small gap

between the electrode wire and the work (base-metal). An instant later the

electrode-wire makes contact with the base metal or weld-pool as it is fed through

the gun by the wire feeder, and a "dead short" occurs in the circuit. The welding

machine (power source) tries to maintain the pre-set voltage and it does this by

increasing the amperage (current). As a result of the increased current a "pinch

force" is created at the electrode tip, and a small section of the wire fuses (breaks)

off into the weld-pool. At this instant the "arc gap" is recreated between the

electrode tip and the base metal and the arc is re-generated, due to the voltage

returning to its set value. The electrode wire is then fed back into the weld pool

creating a short circuit again, and so the cycle continues.

This "cycle" of shorting, wire tip pinching off and the arc re-establishing happens

between 80 and 200 times per second!

Table des matières

Manuels Système de soudage populaires d'autres marques

Berner

Berner PLASMACUT 54 Manuel utilisateur

Pro Spot

Pro Spot PR-155 Manuel utilisateur

Forney

Forney 210 Manuel utilisateur

Thermal Arc

Thermal Arc 400S Manuel utilisateur

Lincoln Electric

Lincoln Electric HANDYMIG 170I Manuel utilisateur

GYS

GYS PROTIG 201 AC/DC Manuel utilisateur

TAFA

TAFA 30*8B35 Manuel utilisateur

Lincoln Electric

Lincoln Electric INVERTEC V350-PRO CE Manuel utilisateur

ESAB

ESAB Buddy Arc 145 Manuel utilisateur

CIGWELD

CIGWELD 636804 Guide rapide

Red-D-Arc

Red-D-Arc DC-400 Manuel utilisateur

Hobart Welding Products

Hobart Welding Products Spool Gun DP 3035-10 Manuel utilisateur

Elettro

Elettro HI-MIG 3000 SYNERGIC Manuel utilisateur

WIA

WIA Weldmatic 270 CP132-2 Manuel utilisateur

Sonics

Sonics H520T Manuel utilisateur

Miller

Miller Big Blue 400D Manuel utilisateur

NewArc

NewArc RT2000 Guide de démarrage rapide

Hypertherm

Hypertherm powermax1000 Manuel utilisateur