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I was looking for information on tubular K members and ran into this site. I have read some of the forums in the past and decided to join. I retired a couple of years ago after working 45+ years in industrial construction. I worked as an "exotic metals welder" for much of that time. I was certified to weld on high pressure critical piping and pressure vessels. I also had certifications to weld on "space frames", aircraft frames, race car chassis and roll cages, and several others. I am just setting out my credentials for the comments I am going to make.

Welding on car frames, suspension components, roll cages, and other critical parts of a car is not for beginners. If any of the components were to fail from improper welding technique, preparation, post weld heat treatment, or any of dozens of other issues, you would be responsible and liable for any injuries or damage to others and their property. I have seen hundreds of weld failures due to poor welding or a complete lack of experience and metallurgy knowledge by the welder. Mig welding with the small units popular today has little to no penetration in the parent metal and offers very low strength in the finished weld. Especially when much of it is ground off after the weld is completed. Grease, oil products, paint, rust, lack of proper surface preparation, and other issues prevent a good weld from being performed in many cases. Using improper alloy welding wire, and incorrect settings on the machine, and other issues unrecognized by by inexperienced DIY'ers create a situation where many welds are doomed to fail - sooner or later. Most welds done by inexperienced people will not be obvious to them as to how weak they actually are. I strongly suggest that if you are going to weld on your or someone else's car, that you take real classes from a certified professional and learn to do it correctly. If you can't weld to a world class standard, take it to someone who can. Yours, and others lives may depend on it.

All that being said, I have seen many failures of the factory welds and base metal on the chassis and suspension of many cars. I welded up most of the factory seams and junctions of frame members on the cars I was racing or using for higher performance. In all cases the extra weld reinforcement and added weld area increased chassis stiffness and improved the dynamics of the working suspension components. Carefully plan and design any modifications.

Most all cars are built with a corporate eye strongly focused on the bottom line. Anything that can be left out during the production process, usually is. Any extra metal added to the car, or time spent welding the chassis or body is money lost from profits to shareholders. The bare minimum is often the maximum allowed. So, almost all cars will benefit greatly from judicious reinforcement of welded joints and added support from braces, stiffeners, extra crossmembers, and sub-frame connectors. Just be very carefull that you do it properly.

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So you are saying the plethora of 140Amp hobby machines are for hobbies and not car frames? They won't listen.

I would though like to hear your comments on post weld heat treatment, if/as it relates to this topic.