Page 278 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 263

importantly, WPSs are not simply pieces of documentation to be filed
away—they are intended to be communication tools for maintenance
of weld quality. It is essential that all parties involved with the fabri-
cation sequence have access to these documents to ensure confor-
mance to their requirements.
Effect of welding variables. A variety of welding variables determine
the quality of the deposited weld metal. These variables are a function
of the particular welding process being used, but the general trends
outlined below are applicable to all welding processes.
Amperage is a measure of the amount of current flowing through
the electrode and the work. It is a primary variable in determining
heat input. An increase in amperage generally means higher deposi-
tion rates, deeper penetration, and more melting of base metal. The
role of amperage is best understood in the context of heat input and
current density, which are described below.
Arc voltage is directly related to arc length. As the voltage increases,
the arc length increases. Excessively high voltages may lead to weld
metal porosity, while extremely low voltages will result in poor weld
bead shapes. In an electric circuit, the voltage is not constant but is
composed of a series of voltage drops. For this reason, it is important
to monitor voltage near the arc.
Travel speed is the rate at which the electrode is moved relative to
the joint. All other variables being equal, travel speed has an inverse
effect on the size of weld beads. Travel speed is a key variable used in
determining heat input.
Polarity is a definition of the direction of current flow. Positive
polarity (or reverse) is achieved when the electrode lead is connected
lo the positive terminal of the dc power supply. The work lead would
be connected to the negative terminal. Negative polarity (or straight)
occurs when the electrode is connected to the negative terminal. For
most welding processes, the required electrode polarity is a function
of the design of the electrode. For submerged arc welding, either
polarity could be utilized.
Heat input is generally expressed by the equation
60 EI
H =
1000 S

where E represents voltage, I is current, and S is the travel speed in
inches per minute. The resultant computation is measured in kilo-
joules per inch. The heat input of welding is also directly related to
the cross-sectional area of the weld bead. High heat input welding is
automatically associated with the deposition of large weld passes.
The AWS D1.1 code does not specify heat input limits but does

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