Welding

WHAT EVERY ENGINEER SHOULD KNOW ABOUT WELDING
From amperage to preheat, there’s more to welding procedures than meets the eye
By Duane K. Miller, P.E.

W

ITHIN THE WELDING INDUS TRY, THE TERM

“W E L D I N G P ROCEDURE S PECIFICATION ” (or WPS) is used to signify the combination of variables used to make a certain weld. At a minimum the WPS (or “Welding Procedure” or simply “Procedure”) consists of: process (Shielded Metal Arc Welding [SMAW], Flux Cored Arc Welding [FCAW], etc.); electrode specification (AWS A5.1, A5.20, etc.); electrode classification (E7018, E71T-1, etc.); electrode diameter; electrical characteristics ( (AC, DC+, DC-); base metal specification (A36, A572 Gr. 50, etc.); minimum preheat and interpass temperature; welding current (amperage)/wire feed speed; arc voltage; travel speed; position of welding; post weld heat treatment; shielding gas type and flow rate; and joint design details. The welding procedure is somewhat analogous to a cook’s recipe: It outlines the steps required to make a quality weld under specific conditions. EFFECTS OF WELDING VARIABLES The effects of the variables are somewhat dependent on the welding process being employed, but general trends apply to all the processes. It is important to distinguish the difference between constant current (CC) and constant voltage (CV) electrical welding systems. Shielded metal arc welding is always done with a CC system, while flux cored welding and gas metal arc welding generally are performed with CV systems. Submerged arc may utilize either. • 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. Generally, an increase in amperage means higher deposition rates, deeper penetration, and more admixture. The amperage flowing through an electrical circuit is the same, regardless of where it is measured. It may be measured with a tong meter or with the use of an electrical shunt. The role of