Exploring the Benefits of Magnetic Pulse Welding in Structural Steel Assemblies

Horsing Around with Acronyms

Early in my career, when fabrication tasks were added to the welding I had been doing, I sometimes saw senior co-workers using a yellow paint stick to write “NFG” on my work. Hmmm, I wondered, what does that mean? “Nice,” “Fine,” “Good,” or all of the above? After seeing this too many times and having no Wikipedia back then, my curiosity led me to the lead hand, who filled me in on the meaning of NFG. Turns out I was a good welder, not so good fabricator. If you have not seen that before, the “N” stands for “no,” the “G” for “good,” and the “F”… well, use your imagination.

A couple of years later, when my wife and I were expecting our first child, I decided it was time to get serious and buy an SLR camera to take proper photos. With the SLR acronym baffling this photo-neophyte, I put my blind faith in the good intentions of the camera shop salesman. With glazed eyes, I listened to him babble on about F-stops, aperture, and focal length. When he got to the shelves with Nikon cameras, I recognized that name as the most common make used by the photographers I had come across. My camera shopping became even easier when I laid my eyes on the Nikon model “FG” camera sitting on the shelf. With the shame of NFG hanging over my early fabrication work, I immediately recognized the Nikon FG must be a pretty darn good camera, so I bought it. True story, BTW – well, mostly true.

Optimizing Wire Feed Speed for Productivity

In looking at the 8 welds below, imagine they were made by different Welders on your shop floor. The application here was to use the FCAW process with an 0.045″ E70T-1 wire and 85/15 shield gas to make a 1/4″ fillet weld 6 inches long on the T-joint of 1/4″ mild steel assembly. Given no guidance or documented procedures to follow, the Welders could set up machines the way they see fit. Even when welding procedures do exist, my experience has been that some Welders prefer instead to set up weld machines with variables they are comfortable with.

My goal here is to show how different weld machine setups can influence the productivity and cost of welding operations. Lousy at keeping secrets, I will jump ahead to the conclusion and let you know that to optimize productivity, the goal should be to weld at the highest practical wire feed speed (WFS) setting. That was the primary adjustment in making these 8 welds.

In inspecting to evaluate compliance, there may be minor issues, but all welds come close to the specified size and met acceptance criteria of a common structural welding code. Close-up views of each of the 8 welds are shown below. In seeing that the 8 Welders all have the skills to produce acceptable welds, a Manufacturing Manager overseeing their work might make the mistaken assumption that all is good. Good welds, yes, but maybe not good productivity, as we will see in the next section.

Instead of the scenario of having 8 Welders make the welds shown above, in fact, they were all welded by yours truly. I did use a wide range of parameters, with the primary change being a consistent increase in wire feed speed accompanied by suitable adjustments in arc voltage and travel speed. The table below lists the parameters and the effect on productivity as measured with the deposition rate in lb/hr.

Back to the scenario of the welds representing production welds from 8 different Welders. Welder 8 will have done almost one and a half times MORE work in comparison to Welder 1 at the end of the day. I like to display weld optimization data on an annual basis for a more dramatic effect. The annual cost for the amount stated in the chart below is 8 Welders × 40 hrs/wk × 48 wks/yr × 25% arc on time, then factored by a combined labor/overhead rate of $80/hr. This welding cost-saving potential is not a minor incremental reduction – the annual welding time is reduced from 15,360 to 6,410 hours if the 127 WFS procedure were used instead.

So, if you are the Manufacturing Manager thinking that arcs and sparks make for productive welding, give your head a shake and learn to optimize, specify, and monitor WFS. Almost all of the GMAW/FCAW machines I used early in my career had only dial reference numbers to set WFS and arc voltage. Those machines usually had analog amp and volt meters, leading some to think those were the variables being adjusted with the two dials. Arc voltage, yes, but with a constant voltage (CV) power source, the amperage output is not adjusted but instead a by-product of the WFS, the electrode stickout (ESO), and wire diameter.

Standardizing Welding Procedures

I still see those analog machines out in the trenches, and setup requires one person to weld while the other adjusts the dials while looking at the analog meters. I have sometimes seen Welders use a marker or scriber to identify the 0-10 dial settings on the wire feeder with 150A, 200A, etc. That is not an accurate way to adjust WFS, as ESO fluctuations can easily cause amperage to change by 25% or more. Thinking a dial setting of 45 would produce amperage of 200A would result in a big surprise if there was a need to change from 0.035″ to 0.045″ diameter wire.

CV power sources stand for constant voltage, constant arc length, constant melt-off rate. Based on the much larger cross-sectional area of the 0.045″ wire, that 45 WFS setting should result in a 65% increase in amps at the same ESO. Using wire feeders without digital controls or specifying amps in GMAW weld procedures in an industrial setting today is just plain sloppy. Yes, amperage has a big effect on heat input and needs to be controlled for heat-sensitive metals, but it is almost never a controlled variable.

For each application, it is beneficial to have a Welding Specialist experiment to find out what the highest or optimum WFS that produces acceptable results is. That will be dependent on variables, including base metal thickness, joint configuration, and desired weld profile. In optimizing WFS, the Welding Specialist will make other adjustments, such as arc voltage and/or work travel angle, and look for cause-effect as WFS increases are made. Too high on thin material, and melt-through is the negative consequence. WFS would need to decrease significantly in changing from 1F to 3F-D position as the vertical orientation causes gravity to influence the weld puddle while hot and liquid. Even a change from 1F to 2F may require lower WFS to minimize a tendency for undercut at the upper fillet toe.

Without this experimentation for each application, it is quite possible that the 250 WFS used in the earlier example could have been used for all welding – it made good-looking welds but at the sacrifice of productivity gains. Moving onto specifying the WFS that should be done with explicit and concise welding procedures. Instead of using the wide range of WFS that may appear on a wire spec sheet or from reference manuals, use the ideal value from the optimization experimentation with no more than a ±5% range.

A weld procedure document should be developed for each application and be front and center where they are used on the shop floor. If the concept is that procedures will produce the desired quality and productivity when used, why are they sometimes in binders stored in the Supervisor’s office or in the QA Dept filing cabinet, waiting to see the light of day during the next quality audit? To ensure all Welders do use the optimized WFS, a firm statement should be made that all welding must be in compliance with the variable ranges specified on welding procedures. Instead of having 8 Welders welding 8 ways, the goal is to have everyone use the ideal settings. Monitoring should be followed up with providing the Welders with the equipment, resources, instructions, and training so that they can all produce optimum welding.

Conclusion: Focus on Wire Feed Speed for Welding Productivity

Never more than a paragraph or two from goofing off, I will close back on my acronym podium. The NFG I started with really does need that ever-versatile F-word to find humor in my camera purchase. But I can’t cuss in the title of this article, so I have a new one for you, and I hope you have learned your lesson on Why The Focus on Wire Feed Speed to Optimize Welding Productivity.

Welder, I’m assuming that at 600 IPM, those welds were deposited flat. Thanks for this article – this is one of the concepts I spent the most time training for my tradesmen in the weld shop. A firm grasp of this concept and variation due to stick out, CTTWD, will give the average shop an unimaginable competitive advantage.

As a Robotic Welding Technology Leader at HDT Global, I can attest that a critical factor in controlling welding cost is controlling weld size to minimize the amount of overwelding. The article shows pictures of 1/4″ fillets on 1/4″ plates. Generally, this weld size on both sides of the plate is a bit of an overkill. Likewise, pictures showing welds made by different welders appear to vary significantly in fillet size. Consider that making a 1/4″ fillet where a 3/8″ fillet will do increases both filler metal consumption and arc on time by about 56% and increases the stress, distortion, and weight of the part. Also, overwelding a part increases the heat input, which may require a lower than optimum wire feed speed, further reducing productivity.

In contrast, faster wire feed speeds can be used in conjunction with faster welding travel speeds to make the same size weld faster with about the same amount of heat input. I see people designing parts who think that they have to specify fillet sizes in 1/16″ increments, so if 3/16″ is not big enough, the next logical step is to specify a 1/4″ fillet that requires 77% more filler metal. I recommend that very careful consideration is used to determine the optimum weld size, and both welders and inspectors use gauges to check weld size frequently.

As a Welding and Pressure Vessel Design Software expert at thinkCEI.com, I’ve seen people using our welding documentation software not realizing it sets the WPS to the maximum range allowed on the WPS created from the PQRs that support it. While this creation is quick, a good CWI can really do a lot to optimize the procedure in just a few minutes that will pay huge benefits over the life of the document.

So, there you have it, Welders – the power of wire feed speed optimization. Keep those arcs and sparks flying, but with an eye on productivity. And remember, if you ever see an “NFG” scribbled on your work, you know what it means – time to focus on those fabrication skills! Visit The Weld Fab to explore more insights on precision welding and metal fabrication.