The importance of test welds goes beyond providing a quality repair

Feb. 26, 2018
Proper destructive testing must be verified through two party inspections. It is imperative to have a good standard process for performing the tests and enforcing their completion.

Within the collision industry there is a lot of discussion about the need for and the importance of doing test welds prior to performing the actual welding of components. It should be more apparent than ever that it is necessary to perform them based on the liability of the work we do.

Destructive test welds should be performed, verified and signed off on. Once completed, test welds should be bagged and left on the dash until the vehicle is washed to allow anyone to verify.

On Aug. 3, 2016, MOTORS manuals made a change to their database that states, “Due to the different types of welding equipment used in the collision repair industry, labor times for welded replaced parts do not include equipment manufacturer procedural steps for welder setup and/or welding tests and preparation. Each welding machine manufacturer may have its own unique configurations and setup processes. Additionally, there may be vehicle-specific variables that may increase or decrease the amount of welding machine set-up time and pre-weld preparation. MOTORS suggests using an on-the-spot evaluation to determine an appropriate set-up and preparation time.” So why is it now that this is coming up? Why has it been a part of 16 different manufactures’ position statements but only now it is becoming so prevalent? Major injury cases from poor welds and lack of welds are a huge driver of this industry wake-up call.

Paint departments in body shops for decades have been a prime example of proper test procedures. It is not standard practice to read a color code, go to the mix computer, type in the code, select the first variant, mix the paint and paint the vehicle, expecting it to match. Instead we look up the code, search for the chip that matches most closely, mix that variant and perform a letdown panel to ensure it is the right color. We do all of this before putting a few hundred dollars of material on the vehicle. Before that process begins, the painter has cleaned and prepped his spray gun thoroughly. The painter then resets his pressures, needle settings and ensures the paint is going to atomize just as he wants before applying anything, even before applying paint to his test panel. This is an extensive process that is done before every paint job.

A poor paint job has never killed anyone, and yet an extensive process and proper equipment maintenance is expected. I’ve seen shop welders that are museum pieces, guns that haven’t been cleaned or maintained in years and overall dirty, mistreated equipment. This is the same equipment used to put vehicles back to pre-loss condition. “The welds look great and I’ve been welding for years.” “This welder is a part of me — I’d know if there is something wrong.” Some form of those statements have been uttered by body men around the world. The scary part is that poor paint jobs will lead to a visual issue. Bad welds do not have to look bad! An I-CAR instructor even discussed a body shop he visited where every weld each person did looked beautiful, but failed the destructive test every time. They replaced the wire, the gas bottle and adjusted every setting in every direction. They ended up having the building power tested and the current was not enough. They would have never known had they not done destructive testing.

How about that $40,000 spot welding machine? The one that you bought because the rep told you “it can’t do a bad weld.” After all, it gives a fault warning when it doesn’t perform a good weld. It must be performing proper welds if it doesn’t say they are bad, right? Wrong! Spot welds can look great and can be popped apart with little to no effort. The fact is the machine will give a warning only when it knows the weld is bad, but it can do a bad weld and not know it. Tips that have been overly used get a small bit of porosity in them and that can be one reason why the weld fails. That invisible porosity doesn’t allow the electricity to flow correctly and therefore doesn’t completely fuse the metal between the tips. It makes a beautiful burn mark on the outsides of the panels but since the metal wasn’t properly welded and fused, it will pop apart with no effort. The machines don’t recognize that and won’t display a fault.

The only way to ensure that a weld is good is with first a visual inspection and then the critical step of a destructive test. What is important to look for? Visual inspections are fairly easy. Proper heat rings, proper backside penetration, consistent shape, and zero porosity are all things that once you know what to look for are easy to inspect. Unfortunately, visual inspection is not even half the battle. Proper destructive testing is crucial. Different welds, different material, different material thickness all require performing a different destructive test.

I-CAR has a Squeeze-Type Resistance Spot Welding Hands-On Skills Development offering (ST015L01) that helps techs develop their spot welding skills and knowledge. Spot welding, weld bonding, visual inspection and destructive testing are all covered in a hands-on environment.

I-CAR also offers Steel GMA Welding (WCS03) Welding Training and Certification and has a great reference sheet that outlines 10 of the most popular welds — not spot welds — and what their destructed weld should behave and look like. (Login to I-CAR’s website and search “test welds” to find their PDF.) They also have a great online class (WCS06e) that gets into the nuts and bolts of a weld. It is a great tool for non-techs to learn what to look for when verifying welds.

Trust but verify. That is the best principal for body shop owners and managers. They need to trust that their techs are doing the job right but they have to verify it for themselves. Once a tech performs a test weld, that he/she is happy with, he/she needs to have it verified BEFORE proceeding to weld on the car. A good process is to assign two people who are approved to sign off on test welds. The tech has to receive one of their signatures on the test weld panels, then bag the test welds and keep them with the car. This will allow anyone at any time to spot check that the tech has done the test welds and has had them approved. Once the vehicle is completed, those bagged test welds should be stored with the Repair Order file in the event the weld integrity is ever questioned.

A production manager or in-process quality control person should shoulder the responsibility of ensuring the right number of welds — or other attachment methods — have been performed before the vehicle can move on to the paint department. A great practice is for the person accepting the vehicle into paint to look for the bag with the signed panels. Whoever it is that accepts the vehicle into paint should also perform a visual inspection of all the welds on the car, ensuring that none of the welds look bad or are missing. Requiring a job to be performed a second time with 100 percent cost being assumed by the technician who failed to perform the test welds is a great way to ensure test welds are completed and the process is followed.

Which welds require destructive test? All of them! If you are doing a spot weld with a squeeze type resistant welder, you should do a destructive test. If you have a plug weld with a MIG, you should do a destructive test. Seam welds, brazed joints, all should get a test weld. If you have some welds over two panels and some through three, you should do a test weld for both. If you have a spot weld through adhesive and some without adhesive, you should do a test for both. Any weld performed on the car should have a destructive test that emulates the scenario to be performed. Use the same metal, same preparation, and same equipment. If you have to change the wire for each area of the car, make sure you use the correct wire for the destructive tests. If you run out of wire, or shielding gas you must perform another set of test welds. Test welds should be performed directly before the actual welds are done. This will ensure that no outside forces can alter the welds between the time the test was done and the actual welds are performed.

The best questions to ask techs, customers, and third-party payers are simple: How many welds are needed to install a part? How many of those welds should be good? The answer is just as simple: as many welds as were removed. The answer to how many should be good is of course a rhetorical question. We want them to all be good, of course, but how do we know that they are all good? While there may not be a way to be sure every single weld is good, we can make sure our training and equipment is good. With those two areas assured we increase our chances of success. Back to our painter comparison—we know that if the correct chip is selected, the gun is tuned, and the spray out looks good, the car, with reasonable certainty, will be painted correctly. If we perform proper test welds using the right metals, prepped just like the car will be prepped, the welder can be tuned and verified. Then with reasonable certainty we will know that the welds performed will be structurally sound.

Many manufactures have a very clear and strict process for performing spot welds. These can be found with their repair procedures. With a firm understanding of I-CAR’s best practices and each OEM’s repair procedures, a single standard operating procedure can be written and implemented for your shop. With so many variations in repair procedures between different OEMs, the SOP should be to follow OEM procedures and perform test welds. It is an imperative step in safe and proper repairs and should never be neglected.

Welds are just one form of structural attachment. Many manufactures utilize adhesive bonds as well as rivets. These joining methods are just as important as welds and just as susceptible to issues. It is a good practice to test those materials as you would test a weld. Rivets can be destructive tested just like a spot weld. While there are not as many guidelines as to the result of a destructive test for adhesive or rivets, common sense will let you know if something seems right or obviously wrong. The wrong length rivet, or wrong hole size are the most common cause for poor strength and need to be ensured are correct with a test. (Note that I-CAR offers Rivet Bonding Hands-On Skills Development (RVT01) to help techs develop skills and knowledge related to this.) Outdated adhesive, wrong application process, and poor preparation are all causes for a weak glue joint. Structural adhesive should be very hard to break apart and weak joints will be apparent. Like with welds any different rivet, different adhesive, or different scenario must be tested and verified for proper strength.

Like all processes, their proper implementation must be trained and verified. Proper destructive testing must be verified through two party inspections. It is imperative to have a good standard process for performing the tests and enforcing their completion — it is a life or death process! Your customer may crash test your work. How will they do?

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