Why Spot Track?


This clip reports on the potential difficulties facing Repair Shops today http://workshop.search-autoparts.com/_Spot-Welding-Techniques/video/1776713/31710.html

Is there any way of identifying the different types of steel and their particular strength characteristics?

This question has been raised before. The simple answer is yes. The reality is somewhat different.

The tools used in cutting panels and removing spot welds will be dictated by the strength of the steels used e.g. normal drill bits (to drill out existing spot welds in panel removal) may be weaker than the metal the operator is trying to drill.

But if you mean can some international standard be reached is another matter.

For example, why do we have measurements in p.s.i. and MPa ? It is because Nations do not agree on a common method of measurement.

If an agreement on standard classifications could be reached, the steel manufacturers could stamp a number or code onto the steel blank. Would this be in the right place for a repairer to see it on strip down, probably not? The stamp may also create a structural weakness. It might be possible to stamp the individual panels and assemblies but the higher the strength the more difficult it would be to make an impression. Perhaps the car manufacturer could use a sticker label on each assembly. The problem here is that it would be covered over by electrocoat paint. After all that, what coding would be used, who would pay for this to happen, what quality standards would apply, how would this information get to the repairer around the world etc and finally what would be the benefit against the cost.

The manufacturer of the car knows what the car is made of, and a joint may consist of multiple layers of differing thicknesses and strengths, but this information does not necessarily communicate to the panel technician in the repair aftermarket.

Many high strength steels are so strong the entire section / part must be replaced. This is due to its resistance to cutting and to reshaping. Low strength steels may be heated to a condition where they become more easily worked e.g. frame correction using hydraulic rams and pulling attachments. This no longer an option as the heat used in this operation would compromise the material's performance in subsequent collisions. Even incorrect welding could bring about structural failure.

Is this all too complicated for the Repair Market?

What is the welding equipment manufacturer's opinion?

"FAN is working very closely with the automobile industry at manufacturing and repair levels. Together with the manufactures, we jointly test and define which welding machines and processes will be best suited to the new materials. In this way we offer Bodyshops only inverter welding-machines for new and old materials.

But there is still a real need for training in welding machine operator skills. True, the machines are smarter in technology, but the operator must also be able to recognise failures due to metal surface preparation like porocity and suchlike.

Repairers are not able to take destructive samples such as micrograph weld cross sections.

Training then, has to be vital, not necessarily in the identification of the metals but in identification of the weld quality. A trained operator can usually detect a bad weld, e.g weld spatter, but even he does not know if the actual weld point is good without destructive testing. Destructive testing is not possible on the repaired car of course"

Franz Mollner, FAN Austria GmbH. Manufacturer of Resistance Welding Machines for Body Repairers and other industries.

Spot Welding machines are available for the Repair Market. Their capacity for the job in no way matches the power and consistency of an automobile assembly plant.

The standard required for the repair market is around 6500 A, 3 phase inverter machine with transformer pincers delivering up to 15000 A and sufficient pressure / clamping force which is essential, when working on structural components.

Have repairs always been subject to weld failure?

Yes and No is the answer. Conscientious Repair Workshops with high quality tooling and skills levels will always endeavour to produce high quality welding standards. However, the Automotive Industry has design objectives in manufacturing which are major leaps forward for the benefit of Safety and Environment.

The need for fuel efficiency, occupant protection in the event of collisions and economical manufacturing amongst many other objectives has led to revolutionary new materials being introduced into Car Body manufacture.

The introduction of High Strength Steels has created new challenges for welding of motor body panels, specifically with structural components and high protection body zones.

What is weld failure?

What is weld failure?
Graphic courtesy ACT

The type of flaws can be categorised as:

  • Stick weld (or cold weld)
  • Burnt (or oversized) weld
  • Loose weld (no fusion has occurred).
  • Undersized nugget
  • Porosity

In all these cases the structural integrity of the weld and by implication the repair is affected.