Welding On Motorhome

wildmanbaker wrote:
O.K.... Have any of you taken a factory tour? During the build process, have you seen the batteries, ECU, or the like, being disconnected? A gas chassis, never, a diesel, not after it is a rolling unit. Worry more about a fire, or melting something, than stray electrical damaging something.

electricity will find the weakest point to arc across and do damage. That is why it is so important that you have a good ground on the piece you are welding. If you do not have a good ground it will damage somewhere else.

O.K.... Have any of you taken a factory tour? During the build process, have you seen the batteries, ECU, or the like, being disconnected? A gas chassis, never, a diesel, not after it is a rolling unit. Worry more about a fire, or melting something, than stray electrical damaging something.

There was a post sometime in the last few years saying that Allison recommends that the wiring to the transmission be unplugged along with the batteries.

As a younger person I was certified to weld about anything you can think of even under water and in nuclear power plants etc.....Its a motor home frame, not a space ship, any compentent welder can weld it just by taking normal cautions (unhook the batteries and ground close to your work) Don't make it more complicated than it is.

I agree with rorr503, IF you do not know what you are doing, it is best to get a professional to do the job. It is true that bolts, hucks or heated rivets is better then welding. But in the industry where I worked there is a lot of welding. Rolled steel, Aluminum and even some cast iron. We used migs most of the time, but some stick for deeper penetration. I also agree with rorr that if holes are cut out, they are not as good as holes made with a drill or reamers. You can not put too much heat on rolled steel either because it will weaken it. Takes the tensile out of it.

But if you get a certified welder, he will know what to do.

Just a note about welding on or heating any steel. It's always good to know what you are welding on. I'm not sure I would ever ignore a do not weld, drill or heat sign on a MH frame.

At least in buildings, engineers say that bolted connections are the best, followed by properly riveted connections with welding being at the bottom of the list. That may be one reason welding in our trade must be done by all-position, certified personnel. And there are sooo many different methods of welding too.

We have had problems after blowing out, or making, holes and slots using gas torches on elevator counterweight frames. The holes and slot corners were no longer perfectly round, which caused fracture cracks years later that were easily identified with magnafluxing. These cracks eventually led to catastrophic frame failure. Now I know, you're not working on elevators, but the heat-related principles and risks remain.

Here again, where the connection is being made is very important. Adding an extension of the rear bumper of a MH is different than adding something at the motor or axle mount area of the frame.

Can welding be done on MH frames. Maybe, but use good judgement.

RayChez wrote:
Disconnect the batteries and get a good ground for the welding machine. Keep it as close as possible to what ever you are going to weld. Welded for many years.

LOL! Who said it would crystallize the frame? Some of you guys are funny with statements like that.

The only metal that has to be preheated before welded is cast iron and then treated after. If you do not preheat, it will break into hundreds of pieces.

How about HY80 or HY120. That has to be preheated to be welded.

On my 05 National MH the factory welded complete frame on the Workhorse frame ( it's called duraframe constuction)that raises the floor up about 10" and surounds the storage compartments. They also welded many other brackets to the frame so I don't beleave a couple of more welds would do anything to the itegrity of the frame.

There are many forms of steels that require a pre-heat and post weld heat treatment. The use of pre and post weld heat treatment can be based not only on material chemistry, but on the thickness of the material, service or process it will see, stress that is induced due to joint configuration, work hardening, or forming process.

In mild carbon steels the most common reasons to perform a pre-heat and post weld heat treat (PWHT) is material thickness, process it will be exposed to, or to relieve stress in the material due to work hardening or joint configuration.

Solution annealing or annealing can also be used to render certain properties back into the material.

Welding on materials that have seen PWHT should not be taken lightly. There are engineering design reasons for going to the extra time and expense to perform this.

There are many different types of carbon steel filler metals with chemical compositions that give certain properties to the weld metal in the as welded condition. As an example the increase Molybdenum (found in 7018-A1 and 7018-Mo for instance) will in part a slightly higher Moly content to the weld metal. This is used when added ductility is desired.

Some materials that have been PWHT'd can be welded on with the application of pre-heat, and then controlling the cooling rate after welding. These processes are spelled out in the qualified welding procedure and specified by the design engineer.

While this has been a long post it is just a brief and limited example that is not all inclusive.

While some have not had problems with grabbing the MIG gun and disconnecting the batteries. The area they have welded on may not have the stress' or they have just been very lucky.

While not in vehicle frames, I have seen material failures due to lack of or incorrect pre and pwht of carbon steel materials. Sometimes the failure is immediate and in the worst cases it has happened years after the welding. The worst cases are in my opinion because at the time of failure those injured had no clue that the failure was happening.

Sorry for the long post and rant.

RayChez wrote:


LOL! Who said it would crystallize the frame? Some of you guys are funny with statements like that.

The only metal that has to be preheated before welded is cast iron and then treated after. If you do not preheat, it will break into hundreds of pieces.

perhaps that is what was meant by crystallize?
bumpy