APPLETON, Wis., April 8, 2003 –Miller Electric Mfg. Co. has introduced Accupulse™, a new process technology for pulsed MIG welding (GMAW-P) that monitors controls and modifies pulsing parameters hundreds of times faster than previous pulsing technology. This benefits semiautomatic, automatic and robotic welding in manufacturing autos, trucks, trailers, railcars, agricultural and construction equipment and piping applications.

Accupulse provides shorter arc lengths along with a more focused arc column, which in turn provides significantly improved puddle control and arc stability. Accupulse also improves welding in tight corners without arc wandering as well as welding over tack welds without short circuits that produce spatter.

"Miller's next generation of technology better fulfills the productivity and problem-solving expectations of pulsed MIG welding. It will deliver an even faster return on investment," says Randy Broadwater, product manager, Miller Electric. "For those who found their expectations of pulsed MIG welding in the past did not live up to industry promises, the control, simplicity and operator appeal of Accupulse now gives them a compelling reason to look at it again."

Accupulse works by specifying key variables–wire type, diameter, shielding gas, wire feed speed and arc length control–for the application at hand. The welding power source then chooses from a vast library of data and selects the optimum pulsing parameters for the selected variables. The first Miller GMAW power sources with Accupulse technology will be available nationally in the summer of 2003.

What Is Pulsed MIG?

Pulsed MIG is a modified spray transfer process. Spray transfer continuously propels drops of molten metal across the arc. In pulsed spray transfer, the power source rapidly switches the welding output from high peak current to low background current. The peak current pinches off a spray-transfer droplet and propels it toward the weldment for good fusion. The background current maintains the arc but is too low for metal transfer to occur. With no metal transfer, the weld puddle gets a chance to cool. Figure 1 summarizes the benefits of pulsed MIG welding with old technology.

Figure 1–Old Technology–Standard Pulsed GMAW compared to GMAW

- Faster travel speeds (compared to GMAW Short Circuit Transfer)

- Higher deposition rates and deposition efficiency (compared to GMAW SCT)

- Reduced spatter for less clean-up time (compared to GMAW SCT)

- Minimized distortion (compared to GMAW spray transfer)

- Flexibility to weld thick or thin sections

- Lower fume emissions

- All-position welding (compared to GMAW spray transfer)

Old Technology

To fully appreciate Accupulse improvements, it is necessary to understand older technology. Older technologies developed in the early 1990s were limited to the electronics that were available and cost effective at the time. As part of their process control feedback loop, the machines of the past sampled the voltage value once per period (a period being one cycle of peak and background current). If a short circuit occurs the detection may not happen for nearly a full period (Fig. 2). During that time, the wire electrode becomes buried in the puddle and takes a fair amount of current to clear. To clear the short circuit and restart the arc, an increased current level is used. This tends to "punch" the puddle and cause excessive puddle agitation, adding to arc instability and spatter.

An ideal pulsed MIG welding system, such as Accupulse, maintains consistent arc length where as older technology uses a slower control scheme technology. Older technology does this by averaging the voltage observed during a given time period. Unfortunately, any change in conditions, such as encountering a tack weld, cannot be acted on until the next pulse cycle.

"With older technology most manufacturers attempted to react to future conditions by monitoring events that have already occurred. This was due to the speed limitation of previous electronics systems," says Broadwater. "It was a bit like driving down the road and trying to adjust your direction by looking in the rearview mirror and only opening your eyes once every minute. ...Sometimes the results aren't what you had hoped to achieve."

Faster Is Better

The new software-driven controls in the next generation of Miller inverters operate faster than 50 microseconds (a microsecond is one millionth of a second). Accupulse samples the arc voltage 10,000 times per second during the peak and background time (Fig. 3). Thus, Miller's new pulsing technology adapts hundreds of times faster than other systems.

"Accupulse monitors arc conditions almost continuously, and with its faster response rate it can detect and clear a short before it becomes a major problem or causes spatter," says Broadwater.

Accupulse

In addition to using speed for improvement, Accupulse adjusts the current to a predetermined level at the beginning of each peak and background phase.

"Accupulse ramps the current up or down to stay 'within the range' of the proper level for a specific wire diameter and type, wire feed speed and gas combination, which means a proper arc condition is much more likely," says Broadwater. Accupulse control scheme ramps the current. Once the target current is reached at the beginning of each phase, the CC control of the current turns off and the CV control loop turns on. The CV loop modulates the current to achieve the target voltage, allowing Accupulse to create the desired wave shapes with arc characteristics that optimize desired arc performance.

Figure 3. Accupulse wave form

- Improved travel speed

- Colder less heat input

- Reduced undercut

- Better puddle control

- Reduced distortion

- Less spatter

- Improved arc stability

- Reduced overwelding

- Better overall operator appeal

Solving Problems

With the ability to better regulate pulsing parameters, Accupulse enables operators to hold a shorter arc length, regardless of stick out, with a more focused arc column. In the past operators were forced by the limits of available technology to weld with a longer arc length to help prevent short circuits, resulting in spatter. Doing this also had a tendency to produce undercut if travel speeds were not reduced to compensate. This in turn has led to a great deal of overwelding on many parts.

"Accupulse gives operators superior control over the weld puddle compared to the performance of older pulse MIG technologies," says Broadwater. "In automatic applications, Accupulse improves welding over tack welds where the arc length can adapt rapidly without stumbling and causing spatter or a tip burnback. Accupulse reacts so quickly that it increases power immediately and keeps the arc above the tack to maintain productivity and weld quality."

In most applications, holding a shorter arc length reduces overall heat input, improves control and increases travel speeds. This may enable welding on thinner materials or using the next larger diameter electrode. For example, Accupulse permits welding steel out of position with a .052-in. diameter wire instead of the .045-in. wire commonly used (larger diameter wires cost less and offer improved feeding performance).

For more information on Accupulse, contact Randy Broadwater at rbroad@MillerWelds.com or 920-954-3814

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