Cutting of a truck frame

By Lawrence (*****)

Date 09-15-2009 23:09

Welcome to the forum Kris!!!

You said:
"Take into account that the heat affected zone resulting from plasma is larger than that resulting from oxyacetilene and has a higher hardness."

I think this is a debatable statement at the least..

**In my experience** Oxy-Fuel is slower and this results in a larger HAZ (heat affected zone)... even though the Oxy-Fuel flame is not nearly as hot as a plasma arc, the resulting heat input from PAC is minimized because of the concentration of heat and the speed of the cut travel..

I would think whether Oxy-Fuel or plasma, the cut ends would need to have some minimal attention at the kerf edges that would remove any hardness that was a byproduct of the cut.

As far as the best method... The auto manufacturer's collision repair data will tell you exactly which process is preferred.

By RonG

Date 09-16-2009 01:52

I know you don't need to be 2nd'ed Lawrence but I have to but in. The Plasma is instant and the heat input is so slight the HAZ is almost non exsistent. We have cut 410 & 422 Turbine blades with plasma and you can still file cut it after words.

Granted you can't beat around the bush about it or leave Dross but it works.

Kris, stop to think about when you use the Oxy/Fuel torch the first thing you have to do is preheat before you even pull the trigger. Plasma goes straight through the instant you push the button.

By DaveBoyer (*****)

Date 09-16-2009 02:03

What sort of truck? Light and medium duty truck frames are not heat treated, and don't have any issues with either cutting method.

If the truck is new enough to have any computerized electronic parts, take the manufacturer's precautions with regard to protecting the electronics from the possible stray currents before using a plasma cutter or electric welding.

By Tommyjoking (****)

Date 09-17-2009 08:54

WTG DAVe I agree with Lawrence.....your statement of methods is contradictory with regards to HAZ. I have cut light and heavy truck frames with both methods with no ill effects concerning "the work being done". If you cut outside or beyond the spring hangers or "suspension mount points" you are pretty free to do what you want without affecting the original performance of the truck chassis itself. There are some DOT regs regarding this which i will not pretend to be able to quote.
Tommy

By 803056

Date 09-17-2009 20:18

Dicey business if the frame is quenched and tempered high strength low alloy steel.

What filler metal are you going to weld it with? What preheat temperaure are you going to use? What interpass temperature are you going to observe? What heat input limitations are you going to abide by? Do you have an insurance policy that will cover you should something go wrong and your weld fails?

Al

By bmaas1

Date 09-17-2009 22:29

I have done this once. I had to stretch a semi-tractor frame 18-20 inches or so. I don't think it's worth the risk messing with but it was fun to do.

Brian

By Paladin (***)

Date 09-18-2009 02:48

When Dodge first came out with the the Cummins Turbo diesel, a year or two before the big body style change, a Hot Shot driver wanted to put a 5 foot long sleeper behind his cab. Torch cut the frame, beveled frame, added fish plates, checked alignment about ten times, and welded it up with 5p stringer and 7018 fill. I had to add 5 ft. of drive shaft with idler, brake lines, electrical lines. Bigger job than I expected (as usual). Finding channel to match frame was not easy either. Well, that was one long One Ton Dodge. He drove it a year or two and asked me to take the five feet out. I did but only the welding part. He reconnected everything.

Like most, now I think I would pass due to liability, not to mention the pita of chasing all the parts and pieces to complete the job.