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5 Essentials to Complete Before Spot Welding a Vehicle

Pro Line Systems International-Auto Body Shop Equipment
Published by Giulio Valle in Informational · 20 March 2023
Tags: SpotWelding5TipsBeforeSpotWeldingAnyVehicle

Essential Things You Need To Do Before And After Spot Welding


Despite technological advancements with the introduction of "smart" welders, spot welding remains a complex process. Here are five essential tasks to ensure success before welding on a vehicle.

1. Clean The Electrodes

auto body technician using PTI.S7 Spot WelderSounds easy, but you would be amazed how many people need help understanding the importance of electrode shape. The new type inverters use a low beveled electrode, usually about 13mm in size, although the Weilander Schill GT Invertaspot, Pro spot, and Tecna Rhino also use 16mm.

This was chosen to achieve a large spot weld diameter without indenting into the steel too much and thinning it out in the HAZ (heat-affected zone ) area. Domed electrodes are frowned upon in modern vehicle repair precisely because of this problem.

The Elektron Mi100 Inverter spot welder is frequently utilized with one beveled cap and one domed electrode. This setup creates narrow, deep-penetrating spot welds with an increased likelihood of weld "splash out." Despite some manufacturers claiming that this is the recommended configuration, it is, in fact, misguiding information.

Historically, domed electrodes were used to facilitate welding Galvanized and coated steels. The dome shape of the electrodes enables penetration and melting of these layers at the weld's start, allowing the welding current to access the underlying steel. To weld Galvanized steels, a "pulsed mode" is often employed. The first pulse melts the galvanizing layer, which enables the electrodes to touch the steel layer below for the main welding current pulse to perform the weld.

Additionally, the domed shape of the electrodes reduces the chances of the molten Galvanizing layer sticking to the electrode cap. Galvanizing and copper are attracted to each other, so every time the welder is used, some Galvanizing may stick to the electrode cap, potentially leading to weld problems later on as this layer increases.

Using domed electrodes can help mitigate the problem of "splash out." However, it also has the effect of decreasing the size of the weld nugget. Furthermore, it is advised that the coatings on Galvanized and zinc-coated steels are removed before welding using a sander. This eliminates the need for domed electrodes and allows for the use of the appropriate beveled electrode, resulting in an optimal weld nugget diameter.

One issue with beveled electrodes is that they tend to wear down quickly. The angle's radius is shallow to prevent excessive indentation of the steel. However, this also makes them prone to wearing flats if not monitored closely. This creates two problems, one being that the worn-out electrode might not properly weld the steel, and second, it will increase the chances of "Splashing out" and decrease the size of the nugget.

  • The spot weld area has grown too large, which can lead to inferior weld nuggets due to insufficient welding current and pressure for the expanded surface area. Insufficient current for the larger surface area can result in inadequate welding and potential failure of the panel. A new beveled electrode cap typically has a contact area of around 4mm, while a worn electrode cap may have a contact area of up to 13mm.
  • The expanded contact area presents challenges for the proper function of "smart" or automatic modes and makes monitoring the weld more challenging.

2. Perform a Test Tag / And Tear Test


spot weld tear test exampleAlways perform a test weld, or "test tag," before welding on a vehicle, even if using a "smart" welder. Some individuals suggest welding a tag onto the vehicle and pulling it. However, this method is not recommended. The purpose of a test weld is two-fold:

  • Confirm that the settings on the welder are appropriate for the specific panel on the vehicle that will be welded.
  • To ensure the correct diameter of the nugget. You must do your tear or destructive test even if you use a smart welder. The nugget should be at least 5mm in diameter.

3. Adhere to the Guidelines and Procedures Recommended by the Auto Manufacturer.


What to do Before Completing a Spot Weld on a VehicleSome manufacturers, such as Vauxhall and Peugeot, provide detailed and thorough guidelines for the safe and effective use of their equipment. They give a set program for the panel to be welded or the correct welding parameters. Conversely, some manufacturer methods sheets can be less informative, offering only minimal information and a few diagrammatic representations.

I often use this example when training: "When you drill off ten spot welds on a vehicle, how many should you replace them with?" The answer is 10.

When working with spot welders, technicians often rely on settings measured in millimeters of thickness. They set the machine according to the thickness of the panel, as advised by the machine's suppliers. Therefore, technicians generally select settings between 1.0mm to 1.5mm.
These settings on most machines will produce a spot weld with a diameter of 5mm. It's always recommended to refer to the Manufacturer's guidelines and instructions to ensure that you are operating the equipment safely and effectively.

By replacing the ten spot welds with 5mm in diameter, the strength of that panel may be adequate. However, if the spot weld that was removed was 8mm in diameter, then replacing it with a 5mm weld would reduce that panel's strength by one-third.

In instances where manufacturer information is limited, it is advisable to replace the spot welds with an equivalent diameter and conduct a peel test. It's crucial not to rely solely on "smart" welding or thickness settings alone, as these may not consider all the variables that affect the strength of a weld.


4. Prep Spot Weld Areas


The welder is not to blame for an explosion of sparks; it's the fault of joint preparation or electrode preparation. A drilled indentation is left in an old panel, which causes an air gap when a new panel is placed on it. This "pip" causes splashout or blowup in the joint if you subsequently weld in the old weld spot (as some manufacturers recommend). Before beginning the welding process, you must attempt to remove this "pip" as much as possible.

We recommend that you place your new weld next to the old one for many reasons. This reduces the possibility of expulsion and panel damage. As a matter of course, technicians routinely clean off all of the edges of the new/old panels before welding and rustproofing them. This is a poor technique because it makes it harder to recognize where to weld. If you make this assessment, draw a line on the new panel where you found the old spot weld indentations. To make locating your welding equipment simpler, write a mark next to it.

Using this technique, you can significantly reduce the number of cathodic priming weld faults. I do not recommend removing all of the cathodic primings on the new panel. You should clean very well and leave as much of the primer between the welds as possible.

5. Watch Your Weld Performance.

The quality of your weld will increase significantly if you pay close attention to the appearance of the weld while you weld rather than relying exclusively on the weld indicator. Green lights, beeps, and OK displays are just a few indicators for welders. They do not mean that you have executed a good weld; they merely indicate that the welder's built-in programming has been met. Reducing the chance of splashout by adjusting welding pressure manually is advisable rather than relying on "smart" mode. For example, if you see splatter, you should increase the welding pressure to reduce it.

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              Article provided by, Giulio Valle
                        


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