Considerations for Switching to Pulsed MIG and Pulsed TIG Welding in Thin Gauge Aluminum Applications
Pulsed welding equipment has been around for a long time. However, technical advancements have made pulsed welding equipment much easier to use and, consequently, better for training operators to make quality welds. Some of the new Pulsed MIG and Pulsed TIG welding technologies provide excellent welding performance on thin gauge aluminum.
Upgrading to modern Pulsed MIG or Pulsed TIG inverter technology could potentially help you increase productivity, improve weld quality, reduce weld costs, and boost operator efficiency. That being said, you will need to study your particular application in detail to determine which, if any, of these processes is appropriate for you. Remember, pulse welding is not the answer to all aluminum welding-related problems.
When considering a move to pulse welding technology, evaluate these factors:
- Modern TIG inverters, such as models found in Miller’s Dynasty® product line, can pulse as fast as 5,000 pulses per second, produce a narrower heat-affected zone, provide increased arc stability, improved penetration, and faster travel speeds than older conventional TIG machines. These enhancements may improve the mechanical properties of the as-welded joint, improve overall weld quality, boost productivity, and cause less distortion.
- Modern Pulsed MIG inverters have replaced conventional spray transfer MIG welders for many thin gauge aluminum applications, and they may also be a viable alternative in some conventional AC TIG applications. The Pulsed MIG process makes this possible by providing tighter control of heat input, faster travel speeds, reduced potential for burn-through on thin gauge aluminum, and better control of the weld bead profile. Some of the new Pulsed MIG programs have been designed to produce welds with cosmetic profiles that are almost identical to characteristic TIG weld profiles (see Figures 1 and 2). This can be seen, for instance, in the Profile Pulse™ program featured in Miller’s AlumaFeed™ Synergic Pulsed MIG Aluminum Welding System.
The challenge of welding thin gauge aluminum efficiently involves obtaining good fusion while simultaneously controlling:
- Heat input
- Weld bead profile
- Arc starts/stops
- Arc performance
- Activities that do not add value (grinding, rework)
The key word here is control. Conventional and old pulsed welding technology cannot provide the advanced control capabilities of the new technology. Today’s control algorithms, software, and microprocessors operate much more efficiently than those developed five or ten years ago. While thicker sections of aluminum might not need advanced control and are often welded successfully with conventional MIG spray transfer, thin gauge aluminum offers little room for error but can often provide substantial room for improvement. Consider these weld characteristics when evaluating the Pulsed MIG process as a replacement for conventional MIG or AC TIG:
- The ability to control heat input. The pulses of peak current (which occur above the transition point) provide the good fusion associated with spray transfer, while the lower background current cools the weld puddle and allows it to freeze slightly to help prevent burn-through (see Figure 2).
- Much higher travel speeds. When switching from conventional AC TIG to Pulsed MIG, travel speeds usually increase substantially. This can result in a significant reduction of heat input to the welded component, a decrease in residual stress, and a lower probability for distortion.
- The ability to control bead profile. Using a function called arc control, operators can adjust the width of the arc cone which lets them tailor the bead profile to the application. A wider bead can help tie-in both sides of a joint and a narrow bead helps provide good fusion at the root of a joint. A bead of the right size helps to eliminate excess heat input, over-welding, and post-weld grinding.
- Superior arc starts. A good Pulsed MIG program for aluminum provides more energy at the start of the weld (which helps ensure good fusion) and then reduces energy to normal parameters for optimal welding characteristics.
- Superior arc stops. Today’s Pulsed MIG equipment provides the technology to ramp down to a cooler welding parameter to fill in the crater at the end of a weld. This helps to eliminate termination cracking which can be a serious issue when welding aluminum.
- The ability to use a larger diameter wire to weld thin gauge material. This can increase the deposition rate and aid feeding by using a stiffer wire, and can also save money on filler wire. The difference in price between a 0.030 wire and a 0.045 wire, for instance, can be considerable.
If you also consider the reduction in time and materials wasted on rejected parts, Pulsed MIG may look like an attractive alternative for welding thin gauge aluminum. Depending on the types of joint designs, joint fit-up characteristics, and joint consistency, Pulsed MIG or Pulsed TIG may be more suitable for your application than the other. Both processes may have a place in helping you improve your welding operation. Pulsed MIG may provide the greatest potential for major improvement as this process is capable of faster travel speeds, which could improve productivity. As always, work with a reputable welding equipment supplier who works with this type of equipment to determine if pulse welding is right for you.
Figure 1: Some of the new Pulsed MIG programs have been designed to produce welds with cosmetic profiles that are almost identical to the characteristic TIG weld profiles.
Figure 2: MIG or TIG? It’s hard to tell with Pulsed MIG, which is what was used for this weld. Pulsed MIG has come a long way in recent years. It has become very easy to use and very easy to train operators to make quality welds—much easier than training a TIG operator. Plus, the appearance of some Pulsed MIG welds can rival that of a TIG weld.
Figure 3: Shown here is a burn-through on the backside of an aluminum weld. Depending on the chemistry of the base alloy being welded, this can be a serious problem that can promote base alloy cracking and be susceptible to propagation.