October 6, 2008
by Jeff Herb
The newest generation of pulsed MIG welders is user-friendly and compact. As an added benefit, they use energy very efficiently, draw much less amperage than older welders and use single- or three-phase power ranging from 190 to 630 VAC.
Photo: Miller Electric
High volume manufacturers and fabricators applying lean principles to reduce waste should consider new pulsed MIG welding technology. Is it the right process for your application? Here are eight points to consider.
Do you pay people to chip spatter or apply and remove anti-spatter compound? Just add up the labour costs. Chances are a new pulsed MIG system could pay for itself in a matter of months. New welding systems monitor arc conditions thousands of times per second. With such a fast response rate, they detect and clear a short before it becomes a major problem or causes spatter. Pulsing technology also adjusts the current to a pre-determined level at the beginning of each peak at the background phase, and it adjusts the current up or down to generate optimum arc conditions for a specific wire diameter and type, wire-feed speed and gas combination.
No slag to chip
If you use flux-cored wire because its deoxidizers compensate for mill scale, or for high deposition rates, consider pulsed MIG welding with metal-cored wire.
Lower fume emissions
Many manufacturers of construction and agricultural equipment have switched from flux cored welding to the pulsed MIG process to reduce fume emissions. Pulsed MIG helps them with regulatory compliance and it creates a more comfortable atmosphere for the operator.
Less burn-through and distortion
If you staff a welding repair station to deal with burn-through, or if distortion causes part fit-up or other tolerance issues, you’re a good candidate for pulsed MIG. The power source switches output from high peak current to low background current several hundred times per second. The peak current pinches off a spray-transfer droplet, while the background current is set at a level that maintains the arc but is too low for metal transfer to occur. The background current lowers overall heat input, addressing the burn-through and warping issues commonly associated with spray transfer MIG. Note the pulse of peak current helps ensure good fusion, overcoming concerns related to cold lap. It also provides faster travel speeds, which improves productivity.
Don’t flip that weldment
The spray transfer process is only suitable for welding in flat and horizontal positions because the weld puddle is so fluid it would otherwise roll out of the joint. However, because the background portion of the pulsed MIG cycle allows the puddle to freeze slightly, you can weld out of position. By not repositioning the weldment (especially for just a few short welds) you can reduce cycle time.
One wire, one gas, one process
Many manufacturers weld a root pass with short circuit MIG (solid wire, C25 gas), then switch to flux cored for the fill passes (tubular wire, 100% carbon dioxide gas). Pulsed MIG welds thin to thick sections with a single wire and a single gas. One company says it saves more than $2,000 per day after switching to pulsed MIG because it eliminated the downtime from changing processes and simplified its consumables supply.
Decreased training time
New pulsed MIG operators make production-quality welds in less time, while experienced operators have even more control over bead appearance. Pulsed technology feels similar to traditional wire welding processes: operators hold a short (3/8- to 1/2-in.) stick out for better control over the weld puddle, and it automatically compensates for contact tip-to-work-distance variations.
Systems, such as Miller’s Invision 350 MPa, are also simple to use: turn on the welding machine, select the process (MIG or pulsed MIG), select the correct wire gas combination the pre-set menu, set wire feed speed and start welding. To weld faster or run hotter, simply increase wire feed speed. To weld slower or cooler, simply decrease wire feed speed. The system adjusts all other variables to maintain optimum arc conditions. To fine tune the arc, two additional functions are available. The arc control adjusts the arc from a wider cone with increased fluidity and flatter bead profile to a stiffer puddle with a narrower bead profile and a length control adjusts the arc to the operator’s preference.
Better bead appearance
The bead profile can be tailored to match the application, and even apprentice operators will produce great looking welds.
New pulsed MIG technology monitors controls and modifies pulsing parameters hundreds of times faster than previous pulsing technology. Some systems sample arc parameters up to 10,000 times per second. As a result, operators hold shorter arc lengths. Pulse MIG also creates a more focused arc column, which in turn provides significantly improved puddle control and arc stability. It improves welding in tight corners without arc wandering and welding over tack welds without short circuits that produce spatter.