An Introduction to Pulsed GMAW
February 1, 2017
Pulsed gas metal arc welding (GMAW) can offer companies quality and productivity advantages, including for welding operators of varying skill levels. In some cases, companies may be hesitant to adopt the process, but it can offer distinct advantages.
Changing welding processes can improve operator training
Companies are always looking for ways to become more productive, create higher quality parts and generate greater profitability. In some cases, reaching these goals is a matter of improving operator training, implementing lean practices or taking on other continuous improvement initiatives. Changing welding processes can make a significant difference.
While not new to the industry, pulsed gas metal arc welding (sometimes referred to as GMAW-P) is still being adopted for the first time by many companies as a means to drive improvements in the welding operation. The process is an excellent alternative to constant voltage (CV) GMAW, and may be a good option for companies looking to boost their efficiencies, especially since it can help improve the quality of welds across varying welding operator skill levels.
Why the hesitation?
In some cases, companies have been slow to adopt pulsed GMAW in their operations and the reasons for that vary.
It may be that companies are simply unfamiliar with the process, or that welding supervisors or operators are hesitant to change technologies since they fear extensive training may be involved. Some companies may be concerned that the cost will be significantly higher.
Fortunately, the transition from a spray process to learning pulsed GMAW is not difficult. Changing from a standard GMAW or a short circuit transfer process requires operator training, but the learning curve is typically much shorter than expected. It is true, however, that the process produces a different sound, which may be unsettling or intimidating to some, and the technology often costs more.
That said, the long-term benefits the process offers can produce a solid return on investment, and a bit of practice and knowledge can easily put common concerns to rest.
How it works
Pulsed GMAW is a modified spray transfer process in which the power source switches between a high peak current or voltage and a low background current or voltage between 30 to 400 times per second. During this switch, the peak current pinches off a droplet of wire and propels it to the weld joint. At the same time, the background current maintains the arc but produces such a low heat input that metal transfer can’t occur, allowing the weld puddle to freeze slightly and to help prevent burn-through.
This action differs from a traditional spray transfer process, which continuously transfers tiny droplets of molten metal into the weld joint.
Synergic vs. non-synergic
There are two different types of pulsed GMAW processes: synergic and non-synergic. In a synergic pulsed GMAW system, the power level automatically adjusts to the wire speed as it changes. This is the most common method in welding equipment today, as it is the easiest for welding operators to set and achieve good welding parameters.
For example, if the wire feed speed changes from 200 inches per minute (ipm) to 400 ipm, the arc length or power on the wire will remain the same relative to the power level that was on the 200 ipm setting.
On the other hand, using a non-synergic pulsed GMAW process requires the welding operator to adjust the power to match the wire feed speed.
Consider these key benefits impacting productivity, quality and ease of use offered by the pulsed GMAW process:
- Exceptional directional control over the weld pool makes it easier for new welding operators to learn the pulsed GMAW process and create welds with good bead appearance. In addition, most pulsed waveforms have a built-in “adaptive function” technology that allows more inexperienced welding operators with less steady hands to produce more consistent welds.
- Improved control over arc starts and stops helps reduce weld defects and improve appearance. When the welding operator initiates the arc, the process delivers higher energy, which offers good fusion. It then reduces the amount of energy going into the weld to prevent burn-through and provide greater control over the weld bead appearance. When stopping the arc, a pulsed GMAW process with a crater function is ideal, as it allows the operator to ramp down to a cooler welding parameter to fill in the crater at the end. This helps eliminate the potential for termination cracking that can easily occur when welding materials such as aluminum.
- Faster wire feed and travel speeds can occur in many applications with pulsed GMAW. This helps increase productivity while simultaneously reducing heat input, to decrease residual stress and reduce the opportunity for distortion or burn-through. Consider stainless steel. This material cannot handle too much heat or the welding operator may promote a phenomenon known as sensitization, which can result in the loss of corrosion resistance. Pulsed GMAW is a good solution for welding this material and avoiding such pitfalls.
- Prevent over-welding and poor fusion. Some pulsed GMAW power sources allow welding operators to adjust the width of the arc cone, which helps them tailor the bead profile to the application. Wider beads help improve tie-in on both sides of a joint, while narrower beads provide good fusion at the joint’s root.
- Reduced spatter generated during the pulsed GMAW process results in reduced time and money spent on associated grinding and post-weld cleanup.
- Easy setup of the process means the welding operator uses a single knob to set the wire feed speed. Since the arc length number or voltage automatically adjusts with pulsed GMAW, the arc becomes longer or shorter accordingly, for greater ease of use and productivity.
Applications that are prone to weld defects such as lack of fusion or porosity, or problems like burnthrough, spatter or warping are good candidates for pulsed GMAW. The lower heat input generated by the process offers similar advantages found when using a process like gas tungsten arc welding (GTAW), along with the good penetration, deposition and fusion associated with a traditional spray transfer process.
Pulsed GMAW can be used to weld thick or thin materials. On thicker sections, it helps minimize downtime for repositioning parts because it generates a cooler weld puddle than a traditional spray transfer process, which makes it usable in all positions. On thinner sections, it minimizes the opportunity for burn-through and reduces the risk of warping by controlling the heat input. This control often allows operators to use a larger diameter wire (up to 3/64 inch), which in turn increases deposition rates and productivity. It also allows the welding operator to put more weld metal in the joint in less time without the risk of adding excessive amounts of heat.
Welding operators who are new to pulsed GMAW should be aware of a few pitfalls and common mistakes, the most common of which is assuming the arc length is the same as the voltage.
In fact, on a pulsed GMAW power source, the arc length is a function of voltage, but the actual number is arbitrary. These power sources often have a zero to 100 scale that is nominal 50. If the welding operator wants less power, for example, he or she would adjust below 50 for less power or above 50 for more power.
Taking a limited look at the possibilities of pulsed GMAW is another common pitfall. There are advanced pulsed GMAW processes available with multiple programs, each of which possesses different attributes. Welding operators should always check to make sure they have the right program for the job in order to achieve the best results.
As always, companies should consult with a trusted welding distributor with questions about pulsed GMAW to determine the best power source for the application and to ensure they gain the best results.