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Down to the Wire

For metal fabricators, a healthy bottom line depends on quality weld wire and shielding gases.

The metal fabrication industry continues to develop new alloys for new applications and products at a quick pace. This rapid development of different base metals sometimes requires new filler metals, unique shielding gases and equipment.

The automotive industry, in an attempt to keep up with the changes in CAFE requirements, is one of the most active market segments in this regard. These new steel alloys are designed for very high strengths: They are thinner and therefore, reduce automobile weight and improve safety.

But that makes bending, forming and trimming more difficult. The new characteristics also make welding more challenging.

For business owners in this segment, the current material evolution is affecting power sources and procedures as well as filler metals and gases. Welding power sources must input less heat into these new thinner higher-strength alloys via wave form control and not just via the amperes and volts that were once the only power management we had.

By managing heat input, these businesses can reduce weld cracking and weld size as well as stress and distortion. As the automotive industry continues to use these alloys to meet the CAFE standards set by the EPA and the government, they will be able to leverage their greater strength and hopefully save lives.

With these changes, it is clear to see that robots will be more important than ever before to follow the more exacting weld procedures those standards and materials require. These more stringent procedures will help to manage weld width, depth and speed in order to manage the heat input and maintain the material’s composition.

We have yet to see, however, all of the changes that will occur with filler metals. Base metals will braze welded, GMAW welded, laser welded, spot welded and maybe some new processes that we have yet to apply to these new requirements. Filler metals, therefore, become part of the solution.

Chemistry is an obvious requirement, however, mechanical characteristics will also come into play. Filler metal precision will be a mandatory requirement for effectiveness and success, which means the welding wires of the past will need to improve in terms of consistency of diameter, cast, helix and surface condition.

wire surface conditions
Which of these wire surface conditions are you using to robotically weld your new alloy and your thinner metal parts?

Weld wire surface conditions

  • Chemistry – Typically, welders prefer wire surface conditions with the smallest chemistry range. The simple acceptance of an AWS spec might be suitable for welding A 36 steel, however, these new higher-strength base metal alloys require tighter filler metal specs to be successful. Also, be prepared to better manage your purchasing department, which might not understand your new tighter manufacturing requirements. A lack of proper oversight may cost hours and dollars of pain for your manufacturing team while purchasing thinks they did a good job reducing the price per pound of wire.
  • Filler metal surface condition – When was the last time that your filler wire supplier provided you with electron beam surface condition photos of the filler metal you are using? Probably never, but regardless, your supplier was still pleased with the fact that the wire cost was 5 cents less per pound than any other brand. The new cheap supplier gets the sale, but you’re left wondering why your rework rates climbed.

Cast, helix and twist

figure-2 If you take several feet of weld wire from the box, drum or spool and lay it on the floor, you will see the built-in weld wire defects that are making your manufacturing world more complicated. But when a business is more cognizant of those defects – the cast, helix and twist – the equation might not remain so complicated.

  • Cast – The cast of welding wire is essentially the diameter of the wire when you take it off of the spool. Average weld wire packaged on a spool has a cast of 26 inches whereas a true robotic weld wire does not have cast, but instead forms a sine-wave when laid on the floor. This permits a faster welding speed and less spatter because the weld wire is precisely melted into the joint.
  • Helix – The helix of welding wire is the distance the unspooled wire rises from the floor. The average wire might have a helix of 1 inch, which is acceptable for AWS but contributes to over-welding, more labor and more filler metal. The helix contributes to an oscillation of wire and therefore, makes the weld bead wider. This increases heat, distortion, time and weld cracking. Have you measured the helix of your welding wire lately?
    figure-3
    By consulting with a knowledgeable gas technician regarding your selection of shielding gas, you may see a very quick – and inexpensive – improvement in your bottom line.
  • Twist – Twist is more difficult to test than the helix and the cast, but it can be done in the field. To do so, pull 4 inches of wire out of the drum or from the spool. Bend the wire 90 degrees and hold the bent portion at the 12 o’clock position. Then, pull it out 30 feet and slowly release the wire so it can rotate. One rotation in 30 feet is too much and implies issues with wire binding in the torch and may lead to knots in the drum. Spooled wire generally has the biggest issue with cast and helix while twist is less common.

The expense of over-welding

figure-4Engineering requests a 1/8-in. weld and the cast and helix make that impossible. If the weld widens to 3/16 of an inch, some would think nothing of it. If one selects the over-welding expense or OWE of 0.072 for 3/16 of an inch through .032 for 1/8 of an inch, the difference is 0.042. That seems like a small number, right? So why worry about it?

The sketches above represent the issue of cast and helix when weld wire is supplied from a spool.
The sketches above represent the issue of cast and helix when weld wire is supplied from a spool.

You worry about it because 0.072/0.042 is a 225 percent increase in labor, wire, time or expense to make your product. You are already working hard trimming every expense you have to make a profit, and this one small detail is making it even more difficult while also reducing your bottom line.

figure-6The solution? Test your wire frequently. Measure your weld sizes and train your operators to look for wire issues. Simply making the weld bigger due to weld wire defects is an expense you can ill afford.

This excess consumption adds to every part of your fabrication expense, including labor and the time it takes to make the weld. It also can increase spatter, distortion and cracking. So don’t let your weld wire supplier be the only one benefitting from this expensive situation.

  • Labor – The weld speed is reduced when the weld is wider than engineering requested on the drawings.
  • Spatter – It is common to have excessive spatter when the wire is in and out of the puddle and impossible for your welder to control.
  • Time to make the weld – A wider weld is just plain expensive – get a stopwatch and time the process. A small crown or weld toes that display cold lap will show up as an issue when the parts are powder coated.
  • Distortion – You make the part and it does not fit because it is twisted like a banana due to the excessive heat input and later oversized weld shrinkage.
  • The sketch would look something like this
    The sketch would look something like this

    Cracking – This is not so much of an issue with a mild still, but it can be. The real problem is when you are welding on the more expensive LAHS steels. These steels are not very forgiving and may cost you the contract and a lot of money to find this issue.

Shielding gas’s impact

Does the selection of a shielding gas impact this situation?

You bet it does. Today, in American fabrication, 75 percent argon and 25 percent CO2 is still the most common shielding gas. This gas mixture was developed to bridge gaps and was also developed for use on very thin sheet metal. The common use of this gas mixture, when there are 8 to 10 mixtures that may more kindly impact your bottom line, can come as a surprise.

The good news is that if you investigate this with a knowledgeable gas technician, you may see a very quick – and inexpensive – improvement in your bottom line. A mixture of 75 percent Argon and 25 percent CO2 is a very fast freeze shielding gas, which can produce a high crown similar to CO2 but not quite as tall. This crown can easily cost you 7 to 15 percent in speed and grinding.

So how does one manage this in a very busy fab shop when manpower is limited?

Measure your weld size against the engineering drawings. Oversized welds are very expensive. And, look at the new gas mixtures from your gas supplier. In one case study, a recent change in shielding gas reduced reject rates from 20 percent to less than 1 percent.

In the end, something as simple as purchasing one welding wire over another can make a huge difference in the time spent producing parts and the quality in which they are produced. And for anyone in fabrication – and especially anyone fabricating automotive parts that must adhere to CAFE standards – the welding wire can have a big impact on your bottom line.

Praxair

© Copyright 2015 Praxair Technology, Inc. All rights reserved. The information in this article is believed to be correct. Praxair is not responsible for any use or misuse of any information contained herein.