CONDITIONS FOR OBTAINING SATISFACTORY WELDS

19 февраля, 2014 Oleg Maloletnikov

To obtain satisfactory welds it is desirable to have:

• a source of energy to create union by FUSION or PRESSURE

• a method for removing surface CONTAMINANTS

• a method for protecting metal from atmospheric CONTAMINATION

• control of weld METALLURGY

1.2.1 Source of Energy

Energy supplied is usually in the form of heat generated by a flame, an arc, the resistance to an electric current, radiant energy or by mechanical means (friction, ultrasonic vibrations or by explosion). In a limited number of processes, pressure is used to force weld region to plastic condition. In fusion welding the metal parts to be joined melt and fuse together in the weld region. The word fusion is synonymous with melting but in welding fusion implies union. The parts to be joined may melt but not fuse together and thus the fusion welding may not take place.

1.2.2 Surface Contaminants

Surface contaminants may be organic films, absorbed gases and chemical compounds of the base metal (usually oxides). Heat, when used as a source of energy, effectively removes organic films and adsorbed gases and only oxide film remains to be cleaned. Fluxes are used to clean the oxide film and other contaminants to form slag which floats and solidifies above the weld bead protecting the weld from further oxidation.

atomic hydrogen welding..........

....AHW

bare metal arc welding...............

....BMAW

carbon arc welding.....................

....CAW

-gas.......................................

....CAWG

-shielded..............................

.... CAWS

-twin......................................

.... CAW. T

electrogas welding....................

....EGW

flux cored arc welding...............

..... FCAW

Solid

state

welding

ISSWI

coextrusion welding............

.... CEW

cold welding.......................

.... CW

diffusion welding.................

.... DFW

explosion welding...............

....EXW

forge welding.......................

....FOW

friction welding...................

.... FRW

hot pressure welding...........

.... HPW

roll welding.........................

..... ROW

ultrasonic welding...............

.... USW

arc brazing......................

..... AB

block brazing.................

..... BB

carbon arc brazing..........

..... CAB

diffusion brazing.............

..... DFB

dip brazing.......................

..... DB

flow brazing.....................

....FLB

furnace brazing...............

..... FB

induction brazing............

.... IB

infrared brazing...............

..... IRB

resistance brazing..........

.... RB

torch brazing...................

.... TB

Oxyfuel

gas

welding

(OFW)

dip soldering.........................

.... OS

furnace soldering...................

.... FS

induction soldering...............

..... IS

infrared soldering..................

.... IRS

iron soldering.........................

....INS

resistance soldering.............

..... RS

torch soldering.......................

... TS

wave soldering.....................

... WS

flash welding..........................

.FW

projection welding................

.PW

resistance seam welding.

.RSEW

-high frequency................

RSEWHF

-induction..........................

..RSEW. I

resistance spot welding...

..RSW

upset welding........................

..UW

-high frequency.................

.UW. HF

-induction..........................

..UW. I

Adhesive

bonding

(ABD)

Thermal

spraying

(THSP)

Allied

processes

electric arc spraying........

... EASP

flame spraying..................

... FLSP

plasma spraying..............

... PSP

chemical flux cutting..............

..FOC

metal powder cutting..............

.POC

oxyfuel gas cutting.................

..OFC

-oxyacetylene cutting...

..OFC. A

-oxyhydrogen cutting..........

.OFC. H

-oxynatural gas cutting.

.OFC. N

-oxypropane cutting...........

..OFC. P

oxygen arc cutting...................

.AOC

oxygen lance cutting..............

.LOC

Other

cutting

gas metal arc welding................

..GMAW

-pulsed arc.............................

..GMAWP

-short circuiting arc................

...GMAWS

gas tungsten arc welding...........

...GTAW

) ^^

-pulsed arc.............................

..GTAW. P

plasma arc welding....................

...PAW

shielded metal arc welding..

...SMAW

1 Brazing

stud arc welding.........................

...SW

(B) 1

submerged arc welding..............

...SAW

-series....................................

... SAWS

Oxygen

Thermal

Arc

oxyacetylene welding..

...OAW

I cutting і—

—I cutting J—

—I cutting J '

oxyhydrogen welding...

..OHW

V (OC) J

(TC)

(AC)

pressure gas welding..

...PGW

Soldering

/ Weldina ^

f Other ^

V (S) /

1 processes I

1 welding J

electron beam welding..

...EBW

-high vacuum..................

...EBWHV

-medium vacuum............

...EBW. MV

-nonvacuum....................

. . EBW NV

electrostag welding.............

...ESW

flow welding.........................

...FLOW

induction welding................

...IW

laser beam welding.............

...LBW

percussion welding.............

...PEW

thermit welding....................

... TW

air carbon arc cutting..............

..AAC

carbon arc cutting...................

..CAC

gas metal arc cutting..............

.GMAC

gas tungsten arc cutting...

.GTAC

metal arc cutting.....................

..MAC

plasma arc cutting.................

.PAC

shielded metal arc cutting..SMAC

electron beam cutting..........

.... EBC

laser beam cutting...............

.... LBC

-air....................................

.... LBC. A

-evaporative....................

....LBC. EV

-inert gas.........................

...... LBC. IG

-oxygen............................

.... LBC. O

Resistance

welding

(RW)

Fig. 1.1 Master Chart of Welding and Allied Processes

1.2.3 Protecting Metal From Atmospheric Contamination

To protect the molten weld pool and filler metal from atmospheric contaminants, specially the oxygen and nitrogen present in the air, some shielding gases are used. These gases could be argon, helium or carbon-dioxide supplied externally. Carbon dioxide could also be produced by the burning of the flux coating on the consumable electrode which supplies the molten filler metal to the weld pool.

1.2.4 Control of Weld Metallurgy

When the weld metal solidifies, the microstructures formed in the weld and the heat-affected - zone (HAZ) region determines the mechanical properties of the joint produced. Pre-heating and post welding heat-treatment can be used to control the cooling rates in the weld and HAZ regions and thus control the microstructure and properties of the welds produced. Deoxidants and alloying elements are added as in foundry to control the weld-metal properties.

The foregoing discussion clearly shows that the status of welding has now changed from skill to science. A scientific understanding of the material and service requirements of the joints is necessary to produce successful welds which will meet the challenge of hostile service requirements.

With this brief introduction to the welding process let us now consider its importance to the industry and its applications.

Опубликовано в Introduction to Welding Technology
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