Pulsed MIG May Solve Aluminum Fabrication Problems -- Q&A
March 1, 2007
Questions and answers for Pulsed MIG aluminum welding.
Q: What's the difference between spray transfer and pulsed spray transfer?
A: Pulsed spray transfer, commonly called pulsed MIG, puts less heat into the work yet maintains many benefits of spray transfer, such as good fusion, high deposition rates and/or fast travel speeds. In pulsed spray transfer, the power source switches between a high peak current and a low background current. The peak current pinches off a spray transfer droplet and propels it toward the weldment. The background current maintains the arc, but is too low for metal transfer to occur. This is unlike spray transfer, which continuously transfers tiny drops of molten metal.
Q: What aluminum applications are good candidates for pulsed MIG?
A: Good applications include those now prone to such problems as lack of fusion, warpage, burn through, spatter, lack of puddle control and poor bead appearance. Any fabricator currently using the short circuit process on thinner metal might want to examine pulsed MIG. Short circuit transfer can be prone to poor fusion (especially at the toes of the weld) and porosity. Pulsed MIG can solve these problems because it lowers heat input to levels associated with short circuit transfer, yet maintains the good fusion of spray transfer. For example, pulsed welding a 1/8 in. thick section of aluminum with a 3/64 in. diameter wire reQuires an average of 140 amps. In the program for this application, a 90 amp background current eliminates worries about burn through or warping, while a 350 amp pulse of peak current provides good penetration and wet out.
Q: I've heard that pulsed MIG weld beads look good. Why is that?
A: Pulsed MIG provides good bead appearance because the tiny molten droplets being transferred do not create spatter. Also, because the weld puddle cools in-between pulses, it freezes faster. The puddle is less likely to sag or look excessively convex when welding out-of-position. Operators have so much control over the weld pool with pulsed MIG that they can create beads with a TIG-like appearance. In fact, manufacturers currently TIG welding might consider pulsed MIG as a way to increase out-put while satisfying bead appearance and Quality control demands.
Q: Can pulsed MIG increase productivity?
A: Yes, in many applications. Compared to short circuit or spray transfer, pulsed MIG often permits using a larger diameter wire and/or faster wire feed speeds without adding excess heat. This increases travel speed and/or deposition rates. For example, one fabricator welding lap joints on thin gauge aluminum increased travel speed from 105 to 144 in./min. after switching from short circuit transfer to pulsed MIG.
Q: Are pulsed MIG systems a good investment?
A: For Qualified applications, absolutely. If you weld a lot of aluminum, you may experience a very Quick payback. Consider that pulsed MIG welding permits using larger diameter wires. Recall that you can pulse MIG weld a 1/8 in. section of aluminum with 3/64 in. wire. A major manufacturer's list price for this wire is $4.85/lb. Welding the same aluminum section with short circuit transfer typically calls for .035 in. wire, which lists for $5.16/lb. Thus, switching to pulsed MIG can provide a wire savings of $0.31 per lb.
Q: Isn't pulsed MIG equipment too complicated?
A: Not necessarily. As an easy way to try pulsed MIG welding, consider an inverter like Miller's Invision™ 354MP or Invision 456MP. These affordable power sources feature built-in pulsing programs for 4043 and 5356 series aluminum wire and work with standard feeders for aluminum like Miller's XR-Edge.™ You do not need a pulsing pendant or programmable wire feeder for pulsing. Finally, this system sets up almost like a "regular" MIG aluminum system, so operators feel very comfortable using it.