Welding Processes

Welding Processes
James Vela
Welding Engineer
In The Twenty First Century
 SMAW: Shielded Metal Arc welding (stick)
 GTAW: Gas Tungsten Arc Welding (tig)
 GMAW: Gas Metal Arc Welding (mig)
 FCAW: Flux Core Arc Welding (flux core)
 SAW: Submerged Arc Welding ( sub-arc)

Manual: SMAW, GTAW

Semi-Automatic: GMAW, FCAW

Machine: GMAW, FCAW, SAW

Automatic: Robotic, Orbital

Cost reduction through increased productivity
1.
Deposition rates
2.
Heat input
3.
Process limitations: IE Material thickness
position etc.
4.
Repeatability
5.
Operator comfort

Increasing deposition rates while improving
quality, maintaining code compliance, and
improving operator comfort has a numerous
benefits for your business.

Manual Processes have generally lower
deposition rates and higher heat inputs.

Examples:
Based on information obtained from the Lincoln Electric
website. Using welding parameters in the upper range. 80% of max

Manuel SMAW and GTAW 1/8” typically
deposit 2 to 4 Lbs./Hr. of electrode/rod.
Based on a 20%-40% operating factor.

Semi-Automatic FCAW GMAW 0.045” typically
deposits 5 to 9 Lbs. /Hr. Based on a 50% to
80% operating factor.

Machine SAW 3/32” typically deposits 10 to
14 Lbs./Hr. based on 80% to 90% operating
factor.

Weaving/Oscillation slows the travel speed
significantly and makes a large bead deposit.

Many welders and welding operators mistakenly
believe that the larger bead will fill the joint faster.

The deposition rate is unaffected by the travel speed
it is based on the electrical parameters.

IE The hotter the parameters the higher the
deposition rate.

Heat input is an important factor in process
selection. Excessive heat input can have an
adverse effect on the micro structure of the
welded joint and subsequently the
mechanical properties.




Heat input calculation Amps X Volts X 60 / Travel
Speed = J/in.
GTAW 180A X 14.6V X 60 / 3 IPM = 52,560
J/in.
GMAW/ spray transfer. 240A X 27V X 60 / 12
IPM = 32,400 J/in.
SAW Machine 520 Amps X 31V X 60 / 19.5
IPM = 49,600 J/in.



Size, diameter, material thickness, type of
weld, and position are an important
consideration in process selection.
Small dimeter valves and but joints in pipe
are generally welded with manual processes.
SAW and GMAW-spray transfer are limited to
flat and horizontal positions only.

Understanding the process will increase your
chances of repeatability and help with
process selection.

Process control documents such as Welding
Procedure Specifications (WPS) can be a
valuable tool to ensure repeatability.

Getting the most out of GMAW

Understanding how the process works is key
to optimizing productivity and quality
objectives simultaneously.

Short Circuit (short arc)

Globular Transfer

Spray Transfer

Pulsed Spray Transfer

Short circuit: 90-150 Amps 16-19 Volts

Globular Transfer:155-195 Amps 22-24Volts

Spray Transfer: 200-260 Amps 26-29 Volts

*Pulsed Spray: 175-260 Amps 23-29 Volts
*Requires a Pulse Spray power source
The Electrode makes contact
The arc ignites.
The electromagnetic field causes
a pinch effect the arc is extinguished
The wire advances and the
Arc reignites.
20 to 200 times per second.
Advantages:

Ideal for sheet applications

Open root butt joints.
Disadvantages:

Limited Penetration

Limited thickness

ASME IX limits range qualified
to 1.1t in lieu of 2t.

The electrode is melted across an open arc
and the electrode is transferred to the molten
puddle in droplets larger in than the diameter
of the wire.
Advantages:

All position welding

Shallow wide penetration that
is good for overlay and hot pass.
Disadvantages:

Excessive spatter

Fusion discontinuities in
multi-layer welding

Arc instability = operator discomfort

The electrode is melted across an open arc
and the electrode is transferred to the molten
puddle in droplets smaller in than the
diameter of the wire.
Advantages:
No Spatter
 High deposition rates for
build up and repair welds.
 Deep Penetration profile less
chance of fusion discontinuities.

Disadvantages:

Requires 85% to 95% Argon for best results.

Flat and Horizontal only

Thicker materials to prevent burn through.


The current vacillates between spray and
globular transfer.
The background current provides short
intervals of globular transfer.




Advantages:
All position welding.
High deposition rate.
Arc stability



Disadvantages:
+
=
Operators often find it difficult to balance the
amperage/ wire feed speed, with the voltage,
and adjust the background current to an
appropriate setting.




Knowledge of optimum process parameters and
capabilities can be profitable for the following
reasons:
1) Maximum deposition rates give us faster weld
times
2) Controlling heat input reduces stress, warpage,
and harmful grain growth.
3) Understanding the process capabilities can save
thousands of dollars by avoiding expensive and
unnecessary “advanced” Equipment
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