Small shops are evaluating how they can use semiautomatic GMAW to get the productivity and quality they need.

Tim Nacey, Panasonic Factory Solutions Company of America, edited by Ron Lucas, managing editor

Panasonic's GB2 inverter CV and companion HM-III pulse machines team with a robot to manage arc characteristics and communications using a new encoder-controlled wire feeder.

New Windows CE-controlled teach pendants let operators set welding parameters with more efficiency, speed, and accuracy.

Digital technology makes wire feed speed control more uniform than conventional technology and lowers spatter levels.

Oscilloscope tracings of arc voltages during the first 40 msec of arc starting cycles compare the Panasonic HM-III inverter with a traditional analog power source.

Devices equipped with 32-bit processing speed can eliminate wire burn-back and stubbing during arc starting even on extremely small fillet welds.

In the past, major manufacturers relied almost exclusively on Tier One suppliers for assemblies and parts. Today, that ball has beenpassed down the supply chain to small fabricators and job shops. These operations, in turn, are finding that rapid changes and short deadlines dictate the use of semiautomatic GMAW. The high-speed repeatability and versatility of these systems tackle the challenges of inaccessibility to weld joints, inconsistent joint prep, fit-up of raw materials, and frequent design changes.

Several new technologies place in the welder's hands the required capabilities of automatic welding along with its high levels of precision and consistency. The technologies also raise the consistency and quality of manual welding to levels approaching automatic. The result is often excellent bead quality, arc consistency, and minimum spatter when welding thin or thick-mild steel, stainless steel, or aluminum alloys.

Ultrahigh-speed performance, soft-ware-controlled welding machines now let operators, no matter what their skill levels, easily set up welding conditions for different wire materials and parts of varying sizes and shapes. The machines new Windows CE-controlled teach pendants simplify operation and allow operators to set welding parameters with great efficiency, speed, and accuracy.

Superfast, all-digital circuits
Advanced power sources incorporate all-digital circuitry powered by super-fast 32-bit RISC processors. Such power sources function semi-or fully automatically, depending on the application. They also operate 3,000 faster than typical 16-bit processors.

Older technology uses slower 16-bit or partial-digital, partial-analog circuitry to communicate procedural information among the power source, robot, wire-feed motor, and other equipment. Equipment such as Panasonic's GB2 inverter CV and companion HM-III pulse machines, on the other hand, manage arc characteristics and communications using anencoder-controlled wire feeder teamed with a robot. Together, they improve performance.

Directly addressing smaller fabricators' specific needs for flexibility, two independent databases store optimum arc characteristics for both manual and fully automatic MIG welding. These databases hold arc characteristics specific to each process, helping welders improve bead appearance and arc control, minimize spatter, and boost productivity in both semi-automatic and automatic welding.

We're only human
Humans can't maintain a perfectly uniform contact tip-to-work distance as robots do, or travel as fast. The special database for manual welding, however, adjusts for such differences once a wire feeder is connected.

The technology also provides truly uniform wire-feed-speed (WFS) control, which delivers almost-perfect consistent arc characteristics. The result is better bead appearance and virtually zero spatter level, particularly with respect to large ball spatter that can stick to the plate.

Additionally, WFS is independent of input voltage fluctuations, a major concern in many fab shops. Newly designed encoder feedback circuits driven by the high-speed capabilities of the 32-bit RISC processor yield virtually instantaneous and consistent control of the WFS. For example, a preset WFS of 590.6 in./min typically varies only ± 0.79 in./min or ±0.13%. With older technology, a variance of ±6-8% of the set speed is often the case.

Wire motion savings add up
Wire motion also halts more quickly at the arc ending time for a much shorter arc-end sequence. In a shop making large numbers of short "stitch" welds — often the case in automotive or other high-volume sheetmetal welding applications — savings of only a second per weld adds up.

For example, one automotive application on aluminum required about 10,000 welds/shift. Annualized on a one-shift basis, faster wire-stopping time yields a savings of about 150 hr, or three weeks of production time.

Accurate, consistent WFS conditions prevail even when considerable force, frequently exceeding the low force level of the NEMA standard, is needed to feed the wire.

Such situations occur in fab shops under certain circumstances:

• When the wire source is located far from the wirefeeder.
• When wire is pulled from large reels often weighing 500 to as much as 1,000 lb.
• As the wire path coils, twists, turns, and follows other non-linear paths. These happen when welders move around complex weldments, greatly increasing friction in the feeding liner.
• When awkward access makes it difficult to complete a weld.

For arc-response control, the 32-bit RISC processor yields an extremely stable waveform. This provides repeatable short-circuiting transfer of weld metal, in which all short circuits are virtually identical and emit an audibly uniform sound. Experienced welders listen for a distinct, crisp sound, which tells them the process is running just right. Excellent arc stability is achieved at low currents (less than 100 amp), while miniscule spatter results at moderate currents (175 to 275 amp).

Arc-starting reliability
An often-ignored factor critical to welding quality and productivity is arc-starting reliability. Should the arcinitiation sequence fail, end users can end up with costly problems such as spatter, wire burn-back to the contact tip, or wires fused to the base material. As a result, users may have to clean up spatter or cut the wire and grind off the fused stub.

Arc ignition at the first touch of wire to base materials is far more reliable, R&D shows, when the wire end from the prior arc-end sequence is small and uniformly elliptical. These characteristics can be achieved repeatedly only with a uniform WFS enabled by the faster 32-bit control of the encoder feeder.

For example, take 0.045-in.-diameter steel wire combined with CO2 shield gas. With all-digital, 32-bit RISC control, the wire end is small with an optimum elliptical shape and a diameter ranging from 0.05 to 0.06 in. Under analog-digital control, the wire end is larger and circular (approx. 0.08-in. diameter). With typical all-digital, 32-bit controls, arc-starting success rates increase from 91% to almost 98%, at 150 amp, and at 250 amp, they go from 94% to 99%.

Devices equipped with 32-bit processing speed can eliminate wire burn back and stubbing during starting. They use a two-energy-level starting sequence applying energy at precise millisecond intervals to ensure near-perfect arc starts. The first burst of energy from a capacitor begins arc ignition. The inverter provides the second, higher level of energy. This action is only made possible because of the 32-bit processor's fast control.

Tight control is necessary. If the starting energy is excessive, wire burns off more quickly than the wire-feed speed can replenish it. In turn, this creates an arc flare and melted contact tip and significant productivity loss. Insufficient starting energy, on the other hand, will fail to ignite the arc and cause stubbing or wire fusion at the contact tip.

About the author Mr. Nacey is Industrial Group Manager, Panasonic Factory Solutions Company of America, Elgin, Ill., 1-888-PANWELD, naceyt@us.panasonic.com, panasonicfa.com