Page 35 - MetalForming-Feb-2018-issue

New Enhanced S-6
Premium S-6
Min
Max
Min
Max
C
0.07
0.10
0.07
0.11
Mn
1.40
1.50
1.40
1.60
Si
0.80
0.90
0.80
0.95
Fabrication: Welding
Fig. 4—Enhanced wires have even more tightly controlled ranges than other pre- mium wires.
results does the perfect filler provide? With weld integrity as a prerequisite, these experts overwhelmingly said, “We want a GMAW wire that eliminates rework.”
Filler-metal manufacturers have responded to customer demand for such materials with S-6 filler wires that combine enhanced compositions and innovative coating technologies. The enhanced metallurgy reduces overall formation of silica islands, and creates a slag that self-releases or easily brush- es off (Fig. 2). As a result, users spend more time engaged in productive activ- ities and less time cleaning. For exam- ple, a construction-equipment OEM reduced arc-ignition errors by 66 per- cent in multipass applications (Fig. 3) using an enhanced S-6 wire. Previously, excess silica islands prevented positive arc ignition. When this occurred, the manufacturer needed to shut down a robotic-welding station and spend an average of 3 min. to clean the silica islands. With a rate of $280/hr. in the station, each stop cost $14.
Batch-to-batch consistency, espe- cially in robotic applications, also can be an issue. To address this, wires with enhanced metallurgy use a tightly con- trolled range for the primary alloying elements of a mild-steel wire (carbon, manganese and silicon), as well as tightly controlled amounts of as many as 17 raw elements (Fig. 4).
By way of comparison, the accept- able range for alloying elements is fair- ly broad (Fig. 5). As a result, standard
Enhanced S-6 wire
S-6 wires open themselves up to sig- nificant variations in batch-to-batch performance, which in turn can create the need for constant fine-tuning of welding parameters. If spatter levels increase, one culprit could be a change in metallurgy.
Enhanced S-6 wires also provide good puddle fluidity. As Fig. 6 shows, these wires provide a flat bead profile and excellent tie-in at the weld toe. They can reduce or eliminate the need for gas-tungsten-arc dressing or grinding to remove stress concentrations, which may be required in other situations.
Coating Considerations
In addition to enhancing the wire formulation, the next generation of GMAW wires uses innovative wire-coat- ing technologies that stabilize the weld process and provide superior arc sta- bility. As a result, tests show that they can reduce spatter by as much as 30 percent.
Coated or Not?
Most standard S-6 wires use a cop- per coating, and many in the industry incorrectly believe that the coating improves current transfer, reduces tip wear and protects against rust. In fact, manufacturers use a copper coating as one of their options to improve wire- feed performance. One downside of a copper-coated wire is that particles flake off and clog the gun liner and contact tip. Left unchecked, this clog- ging creates a drag on the wire and
Standard mild-steel wire
G3Si1
ER70S-6
Min
Max
Min
Max
C
0.06
0.14
0.06
0.15
Mn
1.30
1.60
1.40
1.85
Si
0.70
1.00
0.80
1.15
Fig. 5—S-6 wire composition standards as set by EN/ISO and AWS.
Historically, the drawback to using an S-6 wire was that it generated silica islands, or gold-brown glassy spots that result from bringing impurities to the surface of the weld (Fig. 1). Painting over a silica island may cause the paint to flake off. Often called a “pop out,” such defects cause aesthetic and rust issues. When using an S-6 wire, and especially in multipass welding appli- cations, manufacturers must stop pro- duction to deslag. Further, excessive buildup of silica islands creates a risk of arc-ignition issues. Erratic arc starts might lead to poor fusion with the wire burning back to the contact tip and excess spatter. As a result, some weld- ing procedures specify an S-3 wire, which generates fewer silica islands, even though it has poorer wetting action that can lead to other issues.
Because S-3 wires contain lower amounts of alloys, some believe that its use saves money when, in fact, its poorer wetting action and the resulting issues may add to overall costs.
The Perfect Wire
As part of voice-of-customer indus- try research projects in 2015 and 2016, Esab interviewed welding, production and manufacturing engineers at dozens of companies in Europe, Asia and North America. They were asked: What
Note the smooth weld face and transition.
Fig. 6
Bead shows high crown with potential for undercut.
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