Pulsed MIG Welding Aluminum and Stainless Steel
- May 24, 2019
Tips to help shops optimize results
Welding operations are always looking for technologies and solutions to help improve productivity and get more parts out the door—without sacrificing quality. While operations may be hesitant to change the actual welding process, it’s a move that can yield significant results.
A switch to pulsed MIG welding can be especially beneficial for productivity and efficiency in the right applications. This process delivers high productivity on a variety of material thicknesses and a reduced risk of weld defects like burn-through and distortion. Pulsed MIG also allows great versatility for all-position welding.
The characteristics of aluminum and stainless steel make these metals well-suited for pulsed MIG welding. The controlled heat of the pulsed MIG process helps reduce distortion and burn-through on the materials. In addition, the lower heat of the process provides good weld puddle control and higher deposition rates.
How does pulsed MIG welding work?
Compared to a conventional spray transfer process, which continuously transfers tiny droplets of molten metal into the weld joint, pulsed MIG uses a modified spray transfer.
During this process, the power source switches between a high peak current and a low background current between 30 to 400 times per second. The peak current pinches off a droplet of wire and propels it to the weld joint, while the background current maintains the arc at a low enough power level so that metal transfer can’t occur.
Because of these differences in the transfer processes, pulsed MIG runs cooler than standard MIG, even at the same wire feed speed, and it allows the weld puddle to freeze slightly. It also maintains the good penetration and fusion associated with traditional spray transfer MIG.
The benefits of pulsed MIG
The increased deposition rates for pulsed MIG (compared to standard MIG) can be a good choice for operations looking to improve productivity. The pulsed process also typically offers a clean arc that results in minimal spatter — reducing the time and money spent on post-weld cleanup.
Choosing a power source that allows operators to tailor arc characteristics for pulsed MIG can deliver additional benefits. Operators can get a 28 per cent wider operating window and a more forgiving arc, which help compensate for variations in operator technique and skill level.
With some welding systems, the operator can adjust arc cone width and tailor the bead profile for pulsed MIG.
4 tips to optimize pulsed MIG
Even though the pulsed MIG process delivers substantial benefits for many applications, it’s important to follow some key best practices to help optimize results.
1) Proper cleaning: Always clean the base material thoroughly before welding. Any oxide on the aluminum surface should be removed with a wire brush
designed for use with stainless steel or aluminum.
2) Push technique: For the best results with pulsed MIG, use a slight push technique with the welding gun. A drag technique isn’t typically recommended for pulsed MIG.
3) Consider larger wires: Even on thin-gauge material, larger diameter welding wires can be used with pulsed MIG. Larger wires increase the deposition rate (and, therefore, productivity) and are less likely to become tangled.
4) Don’t forget training: Welders may have less experience with the pulsed welding process, so it’s important to implement proper training to get the most out of the investment.
Pulsing with aluminum
Aluminum is widely used in many industries and applications where corrosion resistance, strength and lighter weight are necessary. However, welding this material does present some challenges.
Working with aluminum is all about puddle control, as it acts like a huge heat sink and rapidly transfers heat away from the weld area much faster than other materials.
This can make it more difficult to establish the weld puddle and keep it under control. Operators must walk a fine line—providing enough heat to get proper fusion in the weld while still controlling the heat to prevent distortion or burn-through.
To address these challenges, pulsed MIG provides lower heat input and can offer greater control over the weld puddle, in addition to faster travel speeds and good fusion.
Because the welding wire used for aluminum is softer and can be prone to birdnesting, it’s important to use a push-pull gun for pulsed MIG welding the material. Motors in this type of gun help pull the wire through the liner.
Pulsing with stainless steel
Stainless steel offers corrosion resistance and high strength, in addition to good ductility for a wide range of applications. Like aluminum, it also comes with its own unique challenges for welding.
Stainless steel is prone to distortion because it’s a poor conductor of heat and may undergo thermal expansion during welding. Operators may also struggle with a sluggish weld puddle that doesn’t flow out of the weld toes as well.
Pulsed MIG provides the ability to run tighter arcs, allowing the weld bead to fill the toes faster. An operator can use the arc control feature to influence the tie-in at the weld toes for a more or less fluid weld puddle.
Another challenge operators may encounter when welding stainless steel is carbide precipitation, which occurs when carbon combines with the chrome that has been added to the steel for corrosion resistance.
Carbide precipitation lowers the metal’s resistance to corrosion, but this issue can be prevented by controlling heat input and optimizing travel speeds.
Since the welding wire used for stainless steel is stiffer and not as prone to feeding issues, a push-only standard MIG gun can be used.
Gain productivity with pulsed MIG
When compared to TIG welding and traditional spray transfer MIG, the pulsed MIG process can deliver much greater travel speeds, reduce downtime and increase productivity in the right applications—for a quick return on investment.
Pulsed MIG can be especially beneficial for overcoming the challenges presented when welding aluminum and stainless steel, helping operators reduce defects and produce high quality welds. SMT
Kodi Welch is a welding engineer with Miller Electric Mfg.