It is intended in this publication to present the basic concepts of the gas metal arc welding (GMAW) process that will enable the reader to obtain a fundamental understanding of the process and its variations.1 This knowledge@ combined with basic information about other welding processes@ should be helpful to the reader in the selection of the best welding process for metals to be joined. In addition@ the reader will find specific technical data which will be a guide in establishing optimum operation of this process. Historically@ the GMAW process was developed and made commercially available in 1948@ although the basic concept was actually introduced in the 1920's. In its early commercial applications@ the process was used to weld aluminum with an inert shielding gas@ giving rise to the term MIG (metal inert gas) which is stilI in common usage when referring to the process. As time went on@ variationswere added to the process@ among which was the use of active shielding gases@ particularly CO2@ for welding certain ferrous materials. This eventually led to the?formally accepted AWS term of gas metal arc welding (GMAW) for the process. Further developments to the process included the following: the short circuiting mode of metal transfer (GMAW-S)@ a lower heat energy variation of the process that permits welding in all positions and also on sheet metal thicknesses; a method using molding shoes to confine the molten weld metal for vertical welding electrogas welding (EGW); and a method of controlled pulsating current (GMAW-P) to provide a uniform spray droplet metal transfer from the electrode at lower average current levels. The GMAW process uses either semiautomatic@ machine@ or automatic equipment and is principally applied in high production welding. Most metals can be welded with this process and may be welded in all positions with the low energy variations of the process. GMAW is an economical process that requires little or no cleaning of the weld metal. Warpage and metal finishing are minimal. Each of the variations of GMAW provides specific advantages@ and standard process equipment is normally designed to permit the use of severa1 of these Variations. However@ some equipment is designed for one specific mode only. Other variations@ such as pulsed current or other processes such as electrogas@ require essentially special units which are unique for these variations. The Committee has prepared these recommended practices as guidelines with the hope that they will serve as an incentive for industry to further develop the GMAW process@ The Committee is continuing its activities to provide data for additional materials@ designs@ and equipment@ and these recommended practices will be revised as new information becomes available.l . Gas metal arc welding is defined as an arc welding process that produces coalescence of metals by heating them with an arc between a continuous filler metal electrode and the workpieces. Shielding is obtained entirely from an externally supplied gas.Abstract This standard is a recommended practice on the gas metal arc welding (GMAW) process. This document presents the basic concepts of this process and should enable the reader to obtain a fundamental understanding of this process and its variations@ such as short circuit@ spray@ and pulse modes of metal transfer. It provides the specific technical data which will act as a guide in establishing optimum operation of the process.