CEMP-E
TI 809-26
1 March 2000
(2) Metal cored electrodes, previously classified as FCAW electrodes, are now listed in both A5.18
and A5.28. GMAW with metal cored electrodes is similar to FCAW, with a tubular electrode, but the core
contains metallic powders (alloy) rather than flux materials. Metal cored electrodes require less current to
obtain the same deposition rates, have better tolerance for mill scale and rust, and when used out-of-
position, are less likely to cold lap. Metal cored electrodes typically provide higher deposition rates
because higher currents may be used than with solid wire electrodes. Weld appearance is typically very
good, and the weld is essentially free of slag. The consistency of mechanical properties is typically better
with metal cored electrodes than with solid wire electrodes.
(3) Properties and usage for GMAW electrodes, up to 550 MPa (80 ksi), are summarized in Tables
C-12 and C-13. For higher strength electrodes, see AWS A5.28.
c. Advantages, Disadvantages and Limitations. The Gas Metal Arc Welding (GMAW) process
offers several advantages over Shielded Metal Arc Welding (SMAW), but also has some disadvantages
and limitations.
(1) The GMAW electrode is continuous, eliminating the numerous starts and stops necessary with
SMAW on longer and larger welds.
(2) Increased deposition rates are possible with GMAW because the current can be higher than
the electrode is passed through a contact tip usually 20 to 25 mm (3/4 to 1 in.) from the end of the
electrode, minimizing the buildup of heat from electrical resistance. This electrode extension distance,
commonly called "stickout," varies for each WPS, and may be considerably higher. Both factors provide
GMAW an economic advantage over SMAW.
(3) The number of arc starts and stops, a potential source of weld discontinuities, is also reduced.
(4) GMAW electrode wires do not need heated holding ovens. For critical welds requiring very low
hydrogen deposits, GMAW electrode wires are available in the lowest diffusible hydrogen category, H2.
(5) GMAW "operator appeal" is usually high because of good arc control and little fume generation.
(6) Because no flux is involved, GMAW is intolerant of high levels of mill scale, rust, and other
surface contaminants, and is limited to welding on relatively clean materials. Commonly, mill scale must
be removed by blast cleaning or power wire brushing prior to welding.
(7) GMAW is also seriously affected by wind because of the removal of the shielding gas from
around the weld puddle. For field work, it is often necessary to erect protective shielding from wind to
maintain the shielding gas around the molten weld puddle. Such shielding may be expensive, time-
consuming, require additional ventilation for the welder, and constitute a fire hazard. For shop
fabrication, wind is less of a problem than under field conditions. However, drafts from doorways and
windows, fans used to cool personnel and provide ventilation, and welding fume exhaust equipment can
create unacceptable wind speeds that degrade weld quality.
(8) The equipment required for GMAW is more expensive and complicated than SMAW, and more
difficult to maintain. This increased cost is offset by the higher productivity levels achieved using GMAW
compared to SMAW.
Table C-10. AWS A5.18 Classification System for Carbon Steel Electrodes for GMAW
Table
C-17
Previous Page
