Where Pulse Waveforms Meet Excellence

I thought that others might benefit from this Q&A on pulse GMAW welding.

Brian:

I have a cell that I am working on that has a pulse capable power supply.  It currently runs .035″ solid lincoln wire.

If I was to experiment with pulse, somewhere in the back of my mind I thought you always taught us to go up to .045″.  Is that correct or am I getting confused with some other application?

Thanks, N.

N –

Thanks for the question. You are correct.  This is the reason why various welding “experts” say that going to pulse causes a reduction in penetration that is often a problem. Going up one wire size is the “trick” that puts you back in the same ballpark on penetration, while gaining the benefits that pulse can bring – such as a longer arc length for lower spatter, spatter that is cooler and much less tenacious in adhering, and a different bead profile that often brings advantages.

Basic Variables of the Pulse Waveform

Basic Variables of the Pulse Waveform

Now, once you’re in pulse, then the window of opportunity opens in terms of waveform selection/alteration to optimize your weld characteristics for most advantage. Some say that “a factory waveform is already optimized and pulse is pulse”. That’s the voice of ignorance.  The Pulse-GMAW process is the waveform, which produces specific results. Repeatability of the results hinges on the consistency of that waveform’s reproduction and stability.  Each and every waveform produces a unique balance in target criteria such as travel speed, deposition rate, resistance to burn-through, spatter production, out of position capability, fit-up gap variations, sidewall penetration, bead width/depth, etc.  Sure, the “factory waveform” was optimized, but probably not for your factory or specific application. Odds are that the “canned” waveform does not have the target balance you need to get highly optimized results like fast cycle times, zero rework, and no quality concerns.   

One new launch application I worked on made 14 welds on an assembly, and included joints such as .020″ to .020″, and .050″ to 10 mm, and 6-layer edge welds, with fit-up gaps to 1.5 and 2 x material thickness.  After a major integrator programmed Motoman robots for 6 weeks using their best programmers including 3 BSWE’s who were OSU graduates, they were still unable to weld even one assembly that did not require weld repair.  Not very impressive for having around a dozen weld joints. They proclaimed that the original agreed goal of max 10% weld repair was unprecedented and was not achievable due to fitup gaps and comp0nent part variations – and from their imposed limitations, they were correct. Since it was running a very nice waveform with a low-spatter stable arc, they were adamant that a custom waveform would be useless.

Fortunately, while they insisted it would do nothing, they allowed me 4 hours to develop a custom waveform. The very first assembly we  welded looked 100% better and required no weld repair whatsoever. Production ran well below the launch goal of 3% combined weld scrap/repair, and appeared to run at or below my 1% personal goal.  The launch proved to be a marvel to all the OEM representatives that visited. Visitors always assumed (and I suspect the integrator claimed) that our excellent tooling and other superb aspects of the manufacturing design approach were the key – not suspecting that the pulse waveform design was the critical make-or-break essential which I had banked on from the beginning. I was content to allow that misconception for a competitive advantage, but it only lasted for two or three years before our competitors were running waveforms based on similar design objectives… but that’s a separate story.

A waveform is not limited to the nine lives of a cat, or to picking a basic color like blue, yellow or red.  Constructing a waveform is like working with a weaving machine with hundreds of colors to choose from, and patterns limited by your imagination.  To me all of that is very obvious, so I remain stunned at how few WE’s and welding industry experts and OEM factory reps seem to understand this.

This is why the welding engineers, in one remarkable plant I visited, said that “the pulse waveform is everything”, and every product they welded had its’ own custom optimized waveform (or several).  No waveform was the same.  As you can imagine, this approach opens the door for a high value of optimization potential by being able to change waveforms from weld to weld or even within the same weld as joint orientation/fitup-gap/thickness/design change. And such a high level of optimization brings a degree of profitability, efficiency, and quality that is very difficult for competitors to match.

Once you know that you can accomplish a balance that is optimized for your application, then it becomes a matter of having the knowledge/theory training and the tools to be able to do it with some reasonable cost and efficiency. Of course the waveform toolsets, as well as waveform consistency, go back to system design – which 95% of the time is whatever it is and no amount of intelligent discussion or request on your part is going to impact much at the OEM design level. (Admittedly I am a glutton for punishment and try to find the 5%, because the results have been fantastic when the OEM is open to such a partnership effort.) As an afterthought, I prefer welding system designs that allow me to hold my developed waveforms close to my chest – rather than easily being copied in a few moments (or openly accessible) to spread to all my competitors.

Fronius, like everyone else, has their own unique blend in approach.  One of their advantages – and I’m skimpy on personal experience with this – is that you can work with them to select from among thousands of different waveforms in their database to get the results you’re looking for… and if nothing is doing the trick, they will develop a waveform for you to get the results you need.

Finally, the welding system design makes a huge difference – if I forgot to mention that. The Digipulse systems – even the ancient ones – are great performers because they were robustly and exhaustively designed for high performance from their beginning in the mid 1980’s. If you have one of those you won’t have any inherent performance problems, but you’ll be limited in interfacing and flexibility: you cannot change arc transfer modes or pulse waveforms except through manual selection. However, most of the previous generations of the famous Red and Blue guys and popular imports are – frankly – rarely high performance possibilities and are sometimes like opening a can of ugly attack worms when you activate pulse mode.  That’s exactly why my friend Ed Craig, famous welding engineering consultant, was adamantly opposed to Pulsed-GMAW for many years (except for certain special applications).

Whenever stepping into the potential advantages of pulsed-GMAW (pulsed MIG/MAG), you need to exercise caution to avoid stepping into a nightmare and unleashing a costly disease on your company, and be aware that you may have to explore welding system retrofits as a first step.

Brian Dobben

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