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DASAR GMAWSumber naskah

Gas Metal Arc Welding

Metal Inert Gas

Wanda sue Benton

ESAB University & Florence-Darlington Technical College

DEP.TEKNIK MESIN

PPPPTK BMTI BANDUNG

2009

Prepared by:

Ahmad Nurdin

Yusuf Tinting Sirenden

Objectives

Gambaran umum pengoperasian GMAW

Gambaran umum cacat dalam pengelasan

GMAW

Mendemonstrasikan, menggunakan, dan

troubleshooting peralatan

Mendemonstrasikan teknik pengelasan

Mengelas pelat baja lunak pada berbagai

posisi

Introduction

GMAW adalah didefinisikan sebagai busur

cahaya menggunakan satu elektroda dapat

dimakan yang secara kontinyu memberi

makan dan satu gas pelindung.

GMAW adalah juga dikenal sebagai MIG

(Gas mulia Logam).

Hasil pengelasan kualitasnya lebih tinggi

Hasilkan produktivitas tinggi

KEUNTUNGAN

Mudah dalam pengisian celah atau

gap

Pengelasan dapat dilakukan dalam

semua posisi

Tidak ada / sedikit slag atau terak

Kecepatan las yang Tinggi

Kualitas tinngi

Lebih sedikit / kecil distorsi

Types of Metal Transfer

The basic GMAW process includes three

distinctive process techniques:

1. Short Circuit (Short Arc)

2. Globular Transfer

3. Spray Arc Transfer

Short Circuit (Short Arc)

Beroperasi pada tegangan dan arus rendah

Pembekuan-cepat . Kecil kubah genangan

(mengelas)

Cocok dalam pengelasan bahan tipis di/dalam

posisi apapun, demikian pula bahan tebal di/dalam

posisi vertikal dan posisi 'overhead’

Transfer Logam terjadi ketika hubungan singkat

listrik stabil

Globular Transfer

Arus dan kecepatan kawat las terjadi maksimum

diatas short arc .

Cairan logam terjadi lebih besar dari diameter

kawat yang sedang digunakan

Spater terjadi saat ini pengelasan lebih banyak

Cocok untuk Pengelasan terjadi secara efektif bila

dilakukan pada posisi flat ketika menggunakan

transfer berbentuk bulat

Spray Arc Transfer

Terjadi ketika arus dan setting tegangan

yang digunakan lebih tinggi dari Globular

Transfer

Cocok Digunakan pada material tebal, pada

posisi flat

Spater / Percikan sedikit

Manual GMAW Equipment

Three major elements are :

1.) Welding torch and accessories

2.) Welding control & Wire feed motor

3.) Power Source

GMAW equipment can be used either

manually or automatically

WIRE CONTROL

&

WIRE FEED MOTOR

POWER SOURCE

Welding Torch & Accessories

The welding torch guides the wire and

shielding gas to the weld zone.

Brings welding power to the wire also

Major components/parts of the torch are the

contact tip, shielding gas nozzle, gas

diffuser, and the wire conduit

TRIGGER

INSTALLED

COMPONENTS

NOZZLE

CONTACT TIP

GAS DIFFUSER

Welding Control & Wire

Feed Motor

Welding control & Wire feed motor are

combined into one unit

Main function is to pull the wire from the

spool and feed it to the arc

Controls wire feed speed and regulates the

starting and stopping of wire feed

Wire feed speed controls Amperage

WIRE FEEDER

Power Source

Almost all GMAW is done with reverse polarity also known as DCEP

Positive (+) lead is connected to the torch

Negative (-) lead is connected to the work piece

Provides a relatively consistent voltage to the arc

Arc Voltage is the voltage between the end of the wire and the work piece

22 - 17

Direct Current Electrode Positive (DCEP)

Generally used for gas metal arc welding

– Provides maximum heat input into work allowing

relatively deep penetration to take place

– Assists in removal of oxides from plate

– Low current values produce globular transfer of metal

from electrode

On carbon steel shielding gas must contain

minimum of 80% argon

Ferrous metals need addition of 2 to 5% oxygen to

gas mixture

22 - 18

Gas Metal Arc DCEP Welding: Wire Positive, Work Negative

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22 - 19

Direct Current Electrode Negative (DCEN)

Limited use in welding of thin gauge materials

Greatest amount of heat occurs at electrode tip

Wire meltoff rate great deal faster than DCEP

Penetration also less than with DCEP

Arc not stable at end of filler wire

– Corrected by use of shielding gas mixture of 5%

oxygen added to argon

– Meltoff rate reduced so benefit cancelled

22 - 20

Gas Metal Arc DCEN Welding: Wire Negative, Work Positive


22 - 21

Alternating Current

Jarang digunakan dalam GMAW

Busur tidak stabil oleh karena terjadi arus

balik

Kombinasi keduanya, yaitu polaritas DCEN

dan DCEP, terjadi polaritas pada penetrasi

Digunakan untuk pengelasan aluminium

POSITIVE

TERMINAL

NEGATIVE

TERMINAL

Shielding Gases

Purpose of shielding gas is the protect the weld area from the contaminants in the atmosphere

Gas can be Inert, Reactive, or Mixtures of both

Gas flow rate is between 25-35 CFH

Argon, Helium, and Carbon Dioxide are the main three gases used in GMAW

22 - 24

Shielding Gas Argon and helium first used for gas metal

arc

– Continue to be basic gases

Argon used more than helium on ferrous metals to keep spatter at minimum

– Also heavier than air so good weld coverage

Oxygen or carbon dioxide added to pure gases to improve arc stability, minimize undercut, reduce porosity, and improve appearance of weld

22 - 25

Shielding Gas

Helium added to argon to increase

penetration

Hydrogen and nitrogen used for only

limited number of special applications

Carbon dioxide has following advantages:

– Low cost

– High density, resulting in low flow rates

– Less burn-back problems because of its shorter

arc characteristics

22 - 26

Specific Metal Recommendations

Aluminum alloys: argon

Magnesium and aluminum alloys: 75

percent helium, 25 percent argon

Stainless steels: argon plus oxygen

Magnesium: argon

Deoxidized copper: 75 percent helium, 25

percent argon preferred

Low alloy steel: argon, plus 2 percent

oxygen

22 - 27

Specific Metal

Recommendations

Mild steel: 15 percent argon, 25 percent

carbon dioxide (dip transfer); 100 percent

CO2 may also be used with deoxidized wire

Nickel, Monel®, and Inconel®: argon

Titanium: argon

Silicon bronze: argon

Aluminum bronze: argon

FLOW METER

CYLCINDER

PRESSURE

GAUGE

CFH PRESSURE

ADJUSTMENT

KNOB

22 - 30


Aluminum alloys: argon

Magnesium and aluminum alloys: 75

percent helium, 25 percent argon

Stainless steels: argon plus oxygen

Magnesium: argon

Deoxidized copper: 75 percent helium, 25

percent argon preferred

Low alloy steel: argon, plus 2 percent

oxygen

22 - 31


Mild steel: 15 percent argon, 25 percent

carbon dioxide (dip transfer); 100 percent

CO2 may also be used with deoxidized wire

Nickel, Monel®, and Inconel®: argon

Titanium: argon

Silicon bronze: argon

Aluminum bronze: argon

22 - 32

Joint Preparation Joint design should provide for most

economical use of filler metal

Correct design for job depends on:– Type of material being welded

– Thickness of material

– Position of welding

– Welding process

– Final results desired

– Type and size of filler wire

– Welding technique

22 - 33

Joint Preparation

Arc in gas metal arc welding more penetrating

and narrower than arc in shielded metal arc

welding therefore, smaller root openings may

be used for groove welds

– Change in joint design increase speed of

welding

100% penetration may be secured in ¼" plate

in square butt joint welded from both sides

22 - 34

Joint Preparation

No root face recommended for 60º single-or double-V butt joints

– Root opening should range from 0 to 3/32"

– Double-V joints may have wider root openings than single-V

Plates thicker than 1 inch should have U-groove preparation

– Require less weld metal; root face thickness should be less than 3/32" and root spacing 1/32 and 3/32"

22 - 35

V-Groove, Butt Joint Comparison


Multipass mengelas lebih mudah karena sedikit terak,

memastikan pembersihan lebih mudah

Untuk Sambungan Fillet, permukaan deposit las lebih

sedikit/ kecil pada permukaan material

Jenis sambungan Tertentu ditarik mundur untuk

mencegah terjadinya penyumbatan pada torch

Joint Preparation

22 - 37

Joint Preparation

Multipass welding easier since absence of slag

ensures easier cleaning

For fillet welds deposit smaller weld beads on

surface of material

Certain types of joints backed up to prevent

weld from projecting through back side

– Blocks, strips and bars of copper, steel or ceramics

22 - 38

Comparison of Penetration in a Fillet Weld

Carbon dioxide shielded

MAG weld versus coated

electrode weld.


22 - 39

Electrode Diameter

Influences size of weld bead, depth of penetration, and speed of welding

General rule

– For same current, arc becomes more penetrating as electrode diameter decreases and deposition rate increases

To get maximum deposition rate at given current density, use smallest wire possible consistent with acceptable weld profile

Wire 0.045" and larger provide lower deposition rate and deposit wider beads than small wires

22 - 40

Electrode Diameter

Filler wires should be same composition as materials being welded

Position of welding may affect size of electrode

Welding thin material– Wires with diameters: 0.023/0.025, 0.030, 0.035"

Medium thick materials– Wires with diameters: 0.045" or 1/16"

Heavy materials– Wire with diameter: 1/8"

Small diameters recommended for vertical and overhead positions

22 - 41

Electrode Extension

Length of filler wire that extends pas contact tube

Area where preheating of filler wire occurs

Also called the stickout

Controls dimensions of weld bead since length of extension affect burnoff rate

Exerts influence on penetration through its effect on welding current– As extension length increased, preheating of wire

increases and current reduced which in turn decreases amount of penetration into work

Stickout distance may vary from 1/8 to 1 1/4"

22 - 42

Electrode Extension

Short electrode extensions (1/8–1/2 inch) used for short circuit mode of transfer, generally with smaller diameter electrodes (0.023–0.045 inches)

Stainless steel favors shorter electrode extension because of its higher resistivity (1/8–1/4 inch)– Longer and larger diameter electrode extensions used

for spray arcs (1/2–11/4 inches)

Excessive long arcs with active gases reduce the

mechanical properties in weld

– Various alloys being burned out as metal transferred

across longer arc

22 - 43

Electrode Extension Tests indicated that when electrode extension

increased from 3/16 to 5/8 inch, welding current then drops approximately 60 amperes

Current reduced because of change in amount of preheating that takes place in wire

– As electrode extension increased, preheating of wire increases

– Thus less welding current required from power source at a given feed rate

– Because of self-regulating characteristics of constant voltage power source, welding current decreased

– As welding current decreased, depth of penetration also decreases

22 - 44

Nomenclature of Area Between Nozzle and Workpiece


22 - 45

Position of the Gun

Expressed by two angles: travel and work

Bead shape changed by changing direction of wire as goes into joint in line of travel

Gun Angle

– Can be compared to angle of electrode in shielded metal arc welding

– Drag technique results in high narrow bead with deeper penetration (10º drag angle)

– As drag angle reduced, bead height decreases, width increases

– Increased travel speeds characteristic of push technique

22 - 46

Travel and Work Gun Angles


22 - 47

Travel and Work Gun Angles


Travel Angle

(T.A.)(Drag) Travel Direction

(Push) Travel DirectionWork Angle

(W.A.)

22 - 48

Drag and Push Gun angles


22 - 49

Drag and Push Methods

Produces large wide beads Produces flatter bead shape


22 - 51

Work Angle

Position of wire to joint in plane perpendicular to line of travel

Filler weld joints: work angle normally half of included angle between plates forming joint

Butt welds: work angle normally 90º to surface of plate being joined

Utilizes natural arc force to push weld metal against vertical surface to prevent undercut and provide good bead contour

22 - 52

Work and Gun Angles


22 - 53

Arc Length Constant voltage welding machine used for gas

metal arc welding provides for self-adjustment of arc length

– Arc length shortened, arc voltage reduced

– Arc length lengthened, arc voltage increased

No change in wire-feed speed occurs

Corrected by automatic increase or decrease of burnoff rate of filler wire

Welder has complete control of welding current and arc length by setting wire-feed speed on wire feeder and voltage on welding machine

22 - 54

Arc Voltage

Decided effect upon penetration, bead height, and bead width

Chief function to stabilize welding arc and provide smooth, spatter-free weld bead

Higher or lower causes arc to become unstable

– Higher: produces wider, flatter bead and increases possibility of porosity and increases spatter and increases undercut in fillet welds

– Lower: causes bead to be high and narrow

22 - 55

Arc Voltage

High arc voltages result in globular transfer

– Spatter prone and reduces deposition efficiency

Has sharp crackling sound when proper arc

voltage for short circuit transfer

– Spray arc have hissing sound

Not set to control penetration

Better control of weld profile and arc

stability

22 - 56

Relationship of Arc Length to Weld Bead Width


High VoltageLow Voltage

Arc Length

Arc Length

Electrode

Electrode

22 - 57

Penetration Comparisons


Arc voltage too high

for travel speed.

Arc voltage too slow

for travel speed

Proper arc voltage

for speed

22 - 58

Wire-Feed Speed

Fixed relationship between rate of filler wire burn off and welding current

Electrode wire-feed speed determines welding current

– Current set by wire-feed speed control on wire feeder

Excessive speed, welding machine cannot put out enough current to melt wire fast enough

– Stubbing or roping of wire occurs

– Causes convex weld beads and poor appearance

Decrease in speed results in less electrode being melted

Generally – high setting of filler wire speed rate results in short arc, slow speed in long arc

22 - 59

Effect of Wire-Feed Speeds


22 - 60

Care of Nozzles

Keep the gun nozzle, contact tube, and wire-feeding system clean to eliminate wire-feeding stoppages

– Nozzle is natural spatter collector

If spatter builds up thick enough, it can actually bridge gap and electrically connect insulated nozzle to contact tube

To remove spatter, use soft, blunt tool for prying


22 - 61

Care of Nozzles

Spatter almost falls out by itself if nozzle

kept clean, shiny and smooth

Antispatter compound may be applied to

gun nozzle and contact tube end

Do not clean by tapping or pounding on

solid object

– Bends gun nozzles, damages threads and high

temperature insulation in nozzle can break

22 - 62

Care of Contact Tubes

Transfers welding current to electrode wire

Hole has to be big enough to allow wire with

slight cast to pass through easily

Wire wears hole to oval shape

– Wire slides more easily, but transfer of current not as

good and arcing in tub results

– Spatter flies up into bore and wire slows down because

of friction

– Must be replace; secure tightly in gun and check

periodically for tightness

22 - 63

Care of Wire-Feed Cables

Wire-feed conduit flexible steel tube that

does not stretch

Main source of friction in wire-feed system

Should be kept clean and straight as

possible

– Clean with dry compressed air

Lubricate with dry powdered graphite

reduces friction

Clean every time spool or coil changes

22 - 64

Bird Nesting

Wire coils sideways between wire-feed

cable and drive rolls

Prevent by accurate alignment of wire-feed

cable inlet guide

– Aligned exactly with rollers so wire does not

have to make reverse bend

– Notch in drive rolls must be in perfect

alignment to provide smooth passage for wire

22 - 65

Cleanliness of Base Metal

Clean area thoroughly before welding

Remove all rust, scale, burned edges and

chemical coatings

– Gas producers

– Porosity is result

Intense heat of arc burns away some of the

contaminants

22 - 66

Arc Blow

Arc blown to one side or other by condition of pull

and counter-pull as magnetic field is distorted

– Ionized gases carrying arc from end of electrode wire to

work act as flexible conductor with magnetic field

around it

– When placed in location such as corner of joint or end

of plate, magnetic field distorted and pulls in another

direction

– Magnetic field tries to return to state of equilibrium

Does not occur with a.c. welding arcs

– Forces exerted by magnetic field reversed 120 times per

second thus keeping magnetic field in equilibrium

22 - 67

Connecting Work to Minimize Arc Blow

Suggestions to shorten trial-and-error

process to correct or minimize arc blow

Attach work lead or leads directly on

workpiece if possible

Connect both ends of long, narrow

weldments

Use electrical conductors of proper length

Weld away from work connection

22 - 68


On parts that rotate, use rotating work connection or allow work cable to wind up no more than one or two turns

In making longitudinal welds on cylinders, use two work connections—one on each side of the seam as close as possible to point of starting

If multiple work connections necessary, make sure cables are same size and length and have identical terminals

22 - 69


On multiple-head installations, all heads should weld in same direction and away from work connection

Use individual work circuits on multiple-head installations

Do not place two or more arcs close to one another on weldments that are prone to magnetic disturbance with one arc such as tubes or tanks requiring longitudinal seams

22 - 70

Setting Up Equipment

Constant voltage d.c. power source

Wire-feeding mechanism with controls and spooled or reeled filler wire mounted on fixture

Gas-shielding system consisting of one or more cylinders of compressed gas, pressure-reducing cylinder regulator, flowmeter assembly

Combination gas, water, wire, and cable control assembly and welding gun of correct type and size

Connecting hoses and cables, work lead, and clamp

Face helmet, gloves, sleeves (if necessary), and assortment of hand tools

22 - 71

Assumed Safety Precautions

Welding equipment installed properly

Welding machine in dry location, and no

water on floor of welding booth

Welding booth lighted and ventilated

properly

All connections tight, and all hoses and

leads arranged so they cannot be burned or

damaged

Gas cylinders securely fastened so they

cannot fall over and not part of electrical

22 - 72

Starting Procedure

1. Check power cable connections; connect gun cable to proper welding terminal on welding machine and work cable end connected to proper terminal on welding machine

2. Start welding machine by pressing onbutton or, in case of engine drive, start engine

3. Turn on wire-feed unit

4. Check gas-shielding supply system

5. Check water flow if gun water cooled

22 - 73

Starting Procedure

5. Set wire-feed speed control for type and size of filler wire and for job

6. Voltage rheostat should be set to conform to type and thickness of material being welded, diameter of filler wire, the type of shielding gas, and type of arc

7. Adjust for proper electrode extension beyond contact tube

8. To start arc, touch end of electrode wire to proper place on weld joint, usually just ahead of weld bead, with current shut off; lower helmet and press gun trigger on torch

22 - 74

Shutting Down the Equipment

1. Stop welding and release gun trigger

2. Return feed speed to zero position

3. Close gas outlet valve in top of gas cylinder

4. Squeeze welding gun trigger, hold it down, and bleed gas lines

5. Close gas flowmeter valve until finger-tight

6. Shut off welding machine and wire feeder

7. Hang up welding gun and cable assembly

22 - 75

Starting the Weld

Running start

– Arc started at beginning of weld

– Electrode end put in contact with base metal

– Trigger on torch pressed

– Tends to be too cold at beginning of weld

Scratch start

– Arc struck approximately 1 inch ahead of beginning of

weld

– Arc quickly moved back to starting point of weld,

direction of travel reversed, and weld started

– Arc may also be struck outside of weld area on starting

tab

22 - 76

Finishing the Weld

Arc should be manipulated to reduce penetration

depth and weld pool size when completing weld

bead

– Decreases final shrinkage area

– Reduction accomplished by rapidly increasing speed of

welding for approximately 1 to 2 inches of weld length

– Trigger released, stopping wire feed and interrupting

welding current

Gun trigger can be turned on and off several times

at end of weld to fill crater

22 - 77

Gun Angle

Push angle of 5 to 15 generally employed when welding in flat position

– Take care push angle not changed as end of weld approached

Work angle equal on all sides when welding uniform thicknesses

Welding in horizontal position, point gun upward slightly

Thick-to-thin joints, direct arc toward heavier section

Slight drag angle may help when welding thin sections

22 - 78

Control of Arc

Arc voltage controls penetration, bead

contour, and such defects as undercutting,

porosity and weld discontinuities

Arc should be occasionally noisy for most

applications of spray arcs

22 - 79

Practice Jobs

Practice gas metal arc welding on mild

steel, aluminum, and stainless steel

Specifications given in Job Outline in order

assigned by instructor

Beyond these job, practice other forms of

joints in all positions

– Use various types and sizes of filler wire and

different shielding gases

22 - 80

MIG/MAG Welding of Carbon Steel

Bulk of all welding done on carbon steel

MIG/MAG welding on increase

– Welders find it relatively easy to master

– Consistently produces sound welds at high rate

of speed

22 - 81

Groove Welds: Jobs 22-J1 and J2

Plate up to 1/8" thick may be butt welded

with square edges with root opening of 0 to

1/16"

Heavier plate, 3/16 and 1/4 inch may be

welded without beveling edges if 1/16 to

3/32" opening provided

Bead should be wider than root spacing for

proper fusion

Two passes, one from each side usually

needed

22 - 82


For code welding, plate thicknesses from 3/16 to 1" should be beveled– 60º single- or double-V without root face

recommended

– Root opening of 0 to 1/16" should be maintained

– Wider root openings may be provided for double-V joints

– Single-V grooves backing pass from reverse side generally required

Less distortion when welding from both sides of joint

22 - 83


Open root joint should be run using short

circuit or pulse spray for ferrous metals

Practice 3G using both uphill and downhill

techniques

U-grooves used on plate thicker than 1 inch

– Root spacing between 1/32 and 3/32"

maintained

– Root face of 3/32" or less to assure penetration

– Requires less filler metal than V groove butt

joint

22 - 84


Argon-oxygen mixture containing 1-5% oxygen

recommended for spray arc welding

– Oxygen improves flow of weld metal and reduces

tendency to undercut

Argon with 10% CO2 sometimes used

Carbon dioxide at 100% used by arc not true spray

arc

– Popular for MAG small wire welding

Short arc welding of carbon steel uses mixture of

75% argon and 25% carbon dioxide

22 - 85

Fillet Welds: Jobs 22-J3-J10

Used in T-joints, lap joints, and corner joints

Deposit rate and rate of travel high with deep

penetration

Permits smaller fillet welds than with stick

electrode welding

Position of nozzle and speed of welding important

Welding may be single pass or multipass

– Multipass may be done with stringer or weave beads

Each pass must be cleaned carefully

22 - 86

Inspection and Testing


Outside corner joint in steel plate welded with gas metal

arc welding process in the flat position.

Penetration through back side of corner joint welded

in the flat position.

22 - 87


Fillet weld on lap joint in steel plate

welded with gas metal arc welding

process in 2F position.


Fillet weld on lap joint in steel plate welded

with gas metal arc welding process in 3F

position, downhill. Note porosity caused

by poor gas shielding.

22 - 88



Fillet weld on T-joint welded

in the 2F position with the

gas metal arc welding

process in steel plate.

Penetration through back side of a

V-groove butt joint welded

in the 1G position.

The first (root) pass of a V-groove

butt joint welded in the 1G position

with the gas metal arc welding

process in steel plate.

22 - 89

Fillet and Groove Welding Combination

Project:

Job Qualification Test 1

Purpose

– Ability to read print

– Develop bill of materials

– Thermally cut

– Fit components together

– Tack and weld carbon steel project

Follow instructions found in Fig. 22-26

22 - 90

Fillet and Groove Welding Combination

Project:

Job Qualification Test 1

Inspection and testing (visual inspection only)

– Shall be no cracks or incomplete fusion

– Shall be no incomplete joint penetration in groove welds except as permitted for partial joint penetration groove welds

– Undercut shall not exceed lesser of 10% of base metal thickness or 1/32 inch

– Frequency of porosity shall not exceed one in each 4 inches of weld length, and maximum diameter shall not exceed 3/32 inch

– Welds shall be free from overlap

– Only minimal weld spatter shall be accepted

22 - 91

Fillet and Groove Welding

Combination Project: Job Qualification

Test2

Purpose


– Develop bill of materials

– Thermally cut


– Tack and weld carbon steel project

– Use spray arc mode of metal transfer

– Note on Fig. 22-27

22 - 92

Fillet and Groove Welding

Combination Project: Job Qualification

Test2

Inspection and testing (visual inspection only)

– Shall be no cracks or incomplete fusion

– Shall be no incomplete joint penetration in groove welds except as permitted for partial joint penetration groove welds

– Undercut shall not exceed lesser of 10% of base metal thickness or 1/32 inch

– Frequency of porosity shall not exceed one in each 4 inches of weld length, and the maximum diameter shall not exceed 3/32 inch



22 - 93

Groove Weld Project: Job Qualification Test 3

Project



– Tack and weld carbon steel unlimited thickness

test plate

– Using spray arc mode of metal transfer

– Instructions in notes in Fig. 22-28

22 - 94


After tacking, have it inspected

After complete welding, use visual inspection and cut specimens for bend testing

Use side bend test procedures and check:

Testing criteria:

– No cracks or incomplete fusion

– No incomplete joint penetration in groove welds except as permitted for partial joint penetration groove welds

22 - 95


Testing criteria (cont.):

– Undercut shall not exceed lesser of 10 percent

of base metal thickness or 1/32 inch

– Frequency of porosity shall not exceed one in

each 4 inches of weld length and maximum

diameter shall not exceed 3/32 inch



22 - 96

Side Bend Acceptance Criteria as Measured

on Convex Surface of Bend Specimen

No single indication shall exceed 1/8 inch

measured in any direction on surface

Sum of greatest dimensions of all indications on

surface, which exceed 1/32 inch, but are less than

or equal to 1/8 inch, shall not exceed 3/8 inch

Cracks occurring at corner of specimens shall not

be considered unless there definite evidence that

they result from slag inclusions or other internal

discontinuities

22 - 97

MIG Welding of Aluminum Readily joined by welding, brazing, soldering,

adhesive bonding, and mechanical fastening

Lightweight

Alloyed readily with many other metals

Highly ductile and retains ductility at subzero temperatures

High resistance to corrosion, no colored salts, not toxic

Good electrical and thermal conductivity

High reflectivity to both heat and light

Nonsparking and nonmagnetic

22 - 98

MIG Welding of Aluminum

Easy to fabricate

May be given wide variety of mechanical, electrochemical, chemical and paint finishes

Needs high heat input for fusion welding

Aluminum and its alloys rapidly develop oxide film when exposed to air (melting point 3600ºF)

– Must be removed during welding

Removed by fluxes, action of arc in inert gas atmosphere or mechanical and chemical means

22 - 99

MIG Welding of Aluminum

MIG and TIG replaced stick electrode

welding for aluminum and its alloys

– Small percentage still using stick electrodes

Type of joint and position of welding

determines process to used on thicknesses

1/8 inch and under

22 - 100

Factors that Make Gas Metal Arc

Welding Desirable Joining Process for

Aluminum

Cleaning time reduced because there no

flux on weld

Absence of slag in weld pool eliminates

possibility of entrapment

Weld pool highly visible due to absence of

smoke and fumes

Welding can be done in all positions

22 - 101

Joint Preparation

Designed like those for steel

Narrower joint spacing and lower welding currents used

Foreign substances must be removed

– Wiped off or removed by vapor degreasing

– Oxide film removed by chemical and mechanical cleaning methods

Weld as soon as possible before oxide film has chance to form again

Sheared edges can also cause poor quality welds

22 - 102

Shielding Gas

Argon preferred for welding aluminum plate thicknesses up to 1 inch

Plate thicknesses 1-2 inches may use:– Pure argon, mixture of 50% argon and 50% helium, or

mixture of 75% argon and 25% helium

– Helium provides high heat and argon excellent cleaning action

Plate thicknesses from 2-3 inches– Mixture of 50% argon and 50% helium or 25% argon

and 75% helium

Plate thicknesses greater than 3 inches– Mixture of 25% argon and 75% helium

22 - 103

Spray Arc Welding

Weld metal deposited continuously

More arc energy and greater heat provided for

melting filler wire and base material

Helium, helium-argon mixtures and argon used as

shielding gases

– Choice dependent upon type of material, thickness and

welding position

Welding can be done in all positions

GMAW-P very effective when welding aluminum

22 - 104

Out-of-Position Welding

Horizontal position

– Care must be taken to penetrate to root of joint

when welding butt joints and T-joints

– Overheating in any one area causes sagging,

undercutting or melt-through to back of joint

– Weld metal should be directed against upper

plate

– In multipass welding, be sure fusion between

passes

22 - 105

Horizontal Position

Welding T-joint in aluminum

plate in 2F position

Welding V-groove butt joint

in aluminum plate in 2G position.


22 - 106

Out-Of-Position Welding

Vertical position

– Travel-up technique on fillet and groove welds

– Do not use too high welding current nor deposit too

large weld bead

– Slight side-to-side motion helpful

Overhead position

– No problem with fillet and groove welds

– Welding current and travel speed lower than flat

position

– Gas flow rate higher because gas has tendency to leave

area

– Somewhat awkward – assume relaxed position as

22 - 107

Out-Of-Position Welding


Welding V-groove butt joint in

aluminum plate in 3G position, uphill.

Welding T-joint in aluminum

plate in 3F position, uphill.

22 - 108

Butt Joints: Jobs 22-J11 and

J12

Easy to design

Require minimum of base material

Perform better under fatigue loading

Require accurate alignment and edge preparation

Usually necessary to bevel edge on thicknesses of ¼" or more to permit root pass penetration

– On heavier plate, chipping back side and welding back side with one pass

– Sections with different thicknesses should be beveled before welding

22 - 109

Lap Joints: Job 22-J13

More widely used on aluminum alloys than

on other materials

Use double-welded, single-lap joints in

thicknesses of aluminum up to ½"

Require no edge preparation

Easy to fit

Require less jigging than butt joints

22 - 110

T-Joints: Jobs 22-J14-J16

Seldom require edge preparation on material ¼" or

less in thickness

Fully penetrated if weld fused into root of joint

Easily fitted and normally require no back

chipping

Jigging usually quite simple

Better to put small continuous fillet weld on each

side of joint rather than one large weld on one side

Continuous fillet welding recommended over

intermittent welding for longer fatigue life

22 - 111

Edge and Corner Joints

Economical from standpoint of preparation,

base metal used, and welding requirements

Harder to fit up

Prone to fatigue failure

Edges do not require preparation

22 - 112


Inspect carefully for defects

Use same inspection and testing procedures

used previously

Look for surface defects

High quality welds in aluminum can be

produced only if proper welding conditions

and good cleaning procedures been

established and maintained

22 - 113

Effect of Current on Aluminum Welds


Aluminum weld bead

made with current

too high

Aluminum weld bead

made with current

too low

Aluminum weld bead

made with

correct current

Kaiser Aluminum & Chemical Corporation Kaiser Aluminum & Chemical Corporation Kaiser Aluminum & Chemical Corporation

22 - 114

Main Causes of Cracking in Aluminum Welds

Generally in crater or longitudinal form

Crater cracks

– Cause: arc broken sharply and leaves crater

– Cure: manipulate gun properly

Longitudinal cracks caused by

– Incorrect weld metal composition

– Improper welding procedure

– High stresses imposed during welding by poor joint design or poor jigging

22 - 115

Main Causes of Porosity in Aluminum Welds

Hydrogen in the weld area

Moisture, oil, grease, or heavy oxides in the weld

area

Improper voltage or arc length

Improper or erratic wire feed

Contaminated filler wire (Use as large a diameter

as possible and GMAW-P if lower heat is needed.)

Leaky gun

Contaminated or insufficient shielding gas

22 - 116

Major Causes of Incomplete Fusion

of Weld Metal with Base Metal

Incomplete removal of oxide film before

welding

Unsatisfactory cleaning between passes

Insufficient bevel or back chipping

Improper amperage (WFS) or voltage

22 - 117

Causes of Inadequate Penetration at

Root of Weld and Into Side Walls of

Joint

Low welding current (WFS)

Improper filler metal size

Improper joint preparation

Too fast travel speeds for the selected wire-

feed speed

22 - 118

Causes of Metallic and Nonmetallic

Inclusions in Aluminum Welds

Copper inclusions caused by burn-back of

electrode to contact tube

Metallic inclusions from cleaning weld with

wire brush which leaves bristles in weld

Nonmetallic inclusions from poor cleaning

of base metal

Always use push gun travel angle when

welding aluminum

22 - 119

Groove Weld Project: Job Qualification Test 4

Purpose



– Tack

– Weld aluminum test plates

– Using spray arc mode of metal transfer

Inspection and testing

– Visual inspection

– Perform side bend tests

22 - 120


Performance Qualification

Test GMAW Spray Transfer, Aluminum

3G and 4G Positions

AWS SENSE

Shown only to illustrate what a qualification test would

look like. Follow it and inspect and test as listed in text.

22 - 121

MAG Welding of Stainless Steel

Heat and corrosion resistant alloy

– Always contains high percentage of chromium in addition to nickel and manganese

Excellent strength-to-weight ratios

Many alloys possess high degree of ductility

Widely used in products such as tubing, piping, kitchen equipment, ball bearings

Supplied in sheets, strip, plate, shapes, tubing, pipe and wire extrusions

22 - 122

MAG Welding of Stainless Steel

Lower rate of thermal conductivity than carbon steel– Heat retained in weld zone longer

Thermal expansion greater than carbon steel– Causes greater shrinkage stresses and warpage

Has tendency to undercut

All standard forms of joints used in fabrications

Copper backing bars necessary for welding sections up to 1/16" thick

No air must be permitted to reach underside of weld while weld pool solidifying (air weakens it)– If no backing bar, argon should be used as purge gas

shield

22 - 123

Advantages of MAG Welding Stainless Steel

Absence of slag-forming flux reduces cleaning time and makes it possible to observe weld pool

Continuous wire feed permits uninterrupted welding

MAG lends itself to automation

Welding may be performed with short-circuiting, spray, or pulsed spray modes of transfer

22 - 124

Spray Arc Welding

Electrode diameters as large as 3/32" can be used for stainless steel– 1/16" wire used with high current to create spray arc

transfer of metal

DCEP used for most stainless-steel welding

Most common gas: mixture of Ar and 1 to 2% O– Recommended for single-pass welding

Push travel angle should be employed on plate ¼" thick or more

Gun should be moved back and forth in direction of travel and slightly from side to side

22 - 125

Short Arc Welding (GMAW-S)

Requires low current ranging form 20 to 175

amperes; low voltage of 12 to 20 volts, small

diameter wires

Metal transfer occurs when filler wire short

circuits with base metal

Ideally suited for most stainless-steel welding on

thicknesses from 16 gauge to 1/16"

– Also for first pass in which fitup is poor or copper

backing unsuitable

– Very desirable in vertical and overhead positions for

first pass

22 - 126

Short Arc Welding (GMAW-S)

For stainless steel in light gauges, triple

mixture of gas gives good arc stability and

excellent coalescence

– 90% helium, 7 ½% argon and 2 ½% carbon

dioxide

– Produces small heat-affected zone that

eliminates undercutting and reduces distortion

– Does not lower corrosion resistance

– Flow rates must be increased because of lower

density of helium

22 - 127

Pulse Spray Arc (GMAW-P)

Can be done with lower current levels and higher wire-feed speeds

Can be used on all thickness ranges

Spray-type gas: 1 and 2% oxygen with remainder being argon most common

Weld more fluid and flows well because arc on all the time

Spatter reduced on thin base metals as compared to short-circuiting mode of transfer

22 - 128

Hot Cracking

Tendency of some stainless steels

– More welding passes needed

– Stringer beads recommended instead of weave

Reduce contraction stresses and cooling more rapid

Can reduce when welding sections 1 inch or

thicker by preheating to 500ºF

– Also reduce by GMAW-S or P welding

22 - 129

Stainless-Steel Sensitization

Carbide precipitation

– Sensitizing chromium out of individual grains of

austenitic types of stainless steel

– Occurs most readily in 1,200ºF heat range

To reduce situation

– Use GMAW process with its rapid speed and high

deposition rate

– Use stabilized and low carbon grades of stainless steel

– Using proper filler metals such as ER308L which is low

in carbon

22 - 130

Inspection and Testing: Jobs 22-J17-J23

Inspect each weld carefully for defects

Fillet weld on lap joint in 3/8" stainless-steel plate welded

in the 1F position with the gas metal arc welding process.


22 - 131

Inspection and Testing: Jobs 22-J17-J23

Fillet weld on T-joint in 3/8" stainless-steel plate

welded in 1F position with gas metal arc welding process.

Fillet weld on T-joint in 3/8" stainless-steel plate

welded in 2F position with gas metal arc welding process.


22 - 132

Copper and Its Alloys May be welded successfully by gas metal arc process

Electrolytic copper can be joined by using special techniques, but weldability not good

Various grades of deoxidized copper readily weldable with MIG process– Deoxidized filler wires necessary

Filler wires of approximately matching chemistry used

Argon preferred shielding gas for material 1" and thinner– Flow of 50 cubic feet per hour sufficient

– Heavier material uses 65% and 35% argon

22 - 133

Copper and Its Alloys

Joint design like any other metal

– Steel backup necessary for sheets 1/8" or thinner

Welding currents on high side required

– Preheat not required when welding ¼" or less

Always provide good ventilation when welding copper and its alloys

– Beryllium-copper alloy dangerous

22 - 134

Copper and Its Alloys

GMAW-B

– Variation of GMAW process where B indicates

brazing or just MIG brazing

– Uses silicon-bronze type electrode with inert

shielding with Argon 100% most common

– Main application for coated carbon steel sheet

metal (light gauge)

– Zinc coating applied for corrosion resistance

– Base metal not melted (hence brazing operation)

22 - 135

Nickel and Nickel-Copper Alloys

Can be welded using gas metal arc process

Remove all foreign material in vicinity since susceptible to severe embrittlement and cracking when come in contact with foreign materials

Argon generally preferable for welding up to about 3/8 inch in thickness – Above that thickness, argon-helium mixtures

usually more desirable

Joint preparation like other metals

22 - 136

Magnesium

Silvery white metal, two-thirds weight of aluminum and one-quarter weight of steel

Melting point of 1,204ºF

Strength-to-weight ratio high when compared to steel

Welding techniques like aluminum

– Rate of expansion greater

– Care taken that surface clean before welding

Arc characteristics of helium and argon with magnesium different than with other metals

– Argon recommended in most cases

22 - 137

Titanium

Bright white metal that burns in air

Only element that burns in nitrogen

Melting point of about 3,500ºF

Most important compound titanium dioxide

– Used extensively in welding electrode coatings

Used as stabilizer in stainless steel

22 - 138

Zirconium

Bright gray metal

Melting point above 4,500ºF

Very hard and brittle and readily scratches

glass

Used in hard-facing materials

Often alloyed with iron and aluminum

Argon or helium-argon mixtures used for

gas shielding

139

ER70S-XElectrode

Rod

70,000 psi Min. Tensile Strength

Solid

Chemistry, Amount of Deoxidizers (Silicon,

Manganese and/or Aluminum, Zirconium and

Titanium) X=2,3,4,6,7 or G

AWS Classification of

GMAW Electrodes

142

GMAW Lesson #1

Objective: To run a stringer (straight) bead using short arc transfer and to fill the crater

Equipment:

– Single Process - Constant Voltage Power Source & Wire Feeder

Power MIG 215 or Power MIG 255C

– Multi-Process

Composite: Power MIG 350 MP

Combination: V-350/ LF-72 package

Material:

– Mild Steel Plate – 3/16” or thicker .035” SuperArc L-56 (ER70S-6)

100% CO2 or 25% CO2/ 75% Argon blend shielding gas

143

GMAW Lesson #2 Objective: To make a fillet weld on a lap joint in the horizontal position (AWS position

2F)

Equipment:



– Multi-Process



Material

– Mild Steel Plate – 10 gauge

– .035” SuperArc L-56 (ER70S-6)

– 100% CO2 or 25% CO2/ 75% Argon blend shielding gas

2F

144

GMAW Lesson #3 Objective: To make a fillet weld on a tee joint in the horizontal position

(AWS position 2F)

Equipment:


Power MIG 215 or Power MIG 255C– Multi-Process –


Combination: V-350/ LF-72 package Material:


– .035” SuperArc L-56 (ER70S-6)


2F

145

GMAW Lesson #4 Objective: To make a fillet weld on a lap joint in the vertical position welding down

(AWS position 3FD)

Equipment:



– Multi-Process –



Material:


– .035” SuperArc L-56 (ER70S-6)


3FD

146

GMAW Lesson #5 Objective: To make a fillet weld on a tee joint in the vertical position welding down (AWS position

3FD)

Equipment:






Material:


– .035” SuperArc L-56 (ER70S-6)


3FD

147

GMAW Lesson #6 Objective: To make a butt weld with a gap in the vertical position

welding down

Equipment:






Material:


– .035” SuperArc L-56 (ER70S-6)


3G

148

GMAW Lesson #7

Objective: To make a fillet weld on a tee joint in the overhead position (AWS position 4F)

Equipment:






Material:


– .035” SuperArc L-56 (ER70S-6)


4F

149

GMAW Lesson #8 Objective: To make a three pass fillet weld on a tee

joint in the horizontal position (AWS position 2F)

Equipment:

– Single Process - Constant Voltage Power Source

& Wire Feeder





Material:

– Mild Steel Plate – ¼”

– .035” SuperArc L-56 (ER70S-6)


2F

150

GMAW Lesson #9

Objective: To run a horizontal fillet weld on a tee joint using axial spray transfer (AWS position 2F)

Equipment:


Power MIG 225C



Combination: V-350/ LF-72 package Material:

– Mild Steel Plate – ¼”

– .045” SuperArc L-56 (ER70S-6)

– 90% Argon/ 10% CO2 blend shielding gas

2F

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