Welding to the Frame
by Scott Simmons and Lance Williams

This is a short generic description that I would use in describing an auto repair. I deal with welding techniques in the context of my job as an automobile appraiser.

The application of heat, in any fashion, is important when dealing with any metal work. The knowledge of the "tempering" of each material used in an automobile is necessary in performing even the basic of body repairs. Mild steel, high strength steel, and super high strength steel all have a different yield strength and to allow this yield strength to remain after the repair, the knowledge of what can be done in the repair process is important. Heat can be generated by welding, use of a torch, or the simple application of force. Heat also can change the yield strength and therefore the ability for the metal to perform as designed. A good example on an automobile is when an inexperienced technician applies heat to a unibody frame rail when he is realigning the inner structure of a vehicle. Yes they can heat it, how much without changing the high strength steel's yield strength is the
concern. Yes the metal looks the same but are the molecules aligned in the same fashion as before. If not done correctly and the vehicle is involved in another collision, the forces applied in the areas of repair may not react in the correct fashion in handling the forces of the collision. This can affect anything from air bag deployment to increased damages. This is the type of information used when making a decision to repair or replace a weld in part.

A ladder or parameter frame is normally not HSS or SHSS and the tempters that can be applied are greater. This does not imply that you should get out the torch and glow you frame red and think it is all ok. If you look under your vehicle you will see attachment points for suspension, body, and engine components. Most are serviceable and available from Toyota. If they can be removed, and replaced at Toyota recommendations it would imply that welding with proper technique is approved by Toyota.

Now for a more specific response from Lance.

Thanks for the forward Scott. Please express to Mike, and the 80's cool list, that their concerns with regard to welding on the frame are completely valid, though maybe there's room for a better understanding of why.

First of all it's good to understand what Tempering is used for. In layman terms tempering is used to strengthen metal (improve it's yield strength). Tools make a good example of tempering. Tools are hardened so they don't just go to mush when you apply torque to loosen that rusted bolt. Hardening is accomplished by heating to a prescribed (high) temperature and cooling rapidly (by submerging in water or oil or some other coolant). This hardening process makes the metal brittle and tempering is often used to make the metal less brittle. One way to temper our now brittle tool is to heat it evenly to a certain temperature and allow it to cool at a particular rate. (temperatures and cooling rates vary depending on the material you're working with and the desired results) From a scientific perspective what you're doing is adjusting the alignment of the molecules. By re-aligning the molecules into an even and more stable structure, the piece remains hard but is not brittle. (that's why your ratchet doesn't deform _or_ shatter as
you curse and beat on stuck bolts with it)

As I alluded to above, tempering can be done using different methods (heat, vibration, chemical, etc) and to various degrees. For example, the steel used in the frame of an over the road trailer (semi) may be tempered to 115,000 psi yield strength where the steel used in an automobile frame may be tempered to 36,000 psi. Each has its own requirements for proper welding technique. (usually the difference is in pre-heating time/temp, electrode and cool down time/temp.) The term "proper technique" in this context refers to welding the pieces together without sacrificing the tempering.

Also, the entire frame system could be tempered after assembly or before. I think you'll find that in the case of an automobile frame the steel is tempered prior to assembly, though I defer to Toyota Motor Corp on that one. Why temper steel if you know you're going to bend it and weld on it later anyway? When you
increase yield strength you (by definition) increase the psi it will withstand before plastic deformation. (?engineering term?) The steel distributors I work with call this "higher notch strength" steel. This harder, stronger steel saves on materials and though subsequent weld areas collect stress it's normally
engineered with that consideration. Case in point: even properly tempered work pieces will collect stress at attachment points because these areas are more rigid due to the extra buttressing of the attachment. In this illustration it's the engineering, regardless of tempering, that makes the difference.

So the frame of our Land Cruisers is constructed of tempered steel, but just as with other forms of tempered steel it's completely safe to weld when proper techniques are employed. Need more evidence? Order a replacement trailing arm mount from Toyota. This is the piece to which your suspension is connected, it welds onto the (tempered) frame, clearly a practice supported by the engineers at Toyota.

Now is a good time to point out where much of the confusion on this topic comes from. Next time you're at a truck stop, take a look at the labels on the frame of an over the road trailer. You'll probably find a sticker that reads, "STOP: Do NOT weld to this trailer frame in any way." Most trailer frames are designed
to act as part of the suspension (notice the convex shape when empty vs. flat when loaded) and are also tempered to a much higher yield strength. Different tempering, different engineering, though similar in theory, it's not directly transferable to your automotive application. So if tempering isn't the issue, what is? Proper electrode selection for the materials you are welding. Some metals require different shielding and filler materials - cast iron is the obvious example, but stainless steel is another more likely to be
encountered in our sport. Proper heat and penetration. You've probably heard of "overheating" a weld and that comes from poor technique. When you are running the right amp setting, electrode diameter and employ the correct travel speed and angle for the material and position you're welding you won't have this problem. (generally it happens when a less experienced welder pools and fills because he/she/it has made a mistake in one of the other areas outlined above.) Finally, structural design should be considered. Knowing that stress will collect at your attachment points, take care not to compromise your frame section.
Substantial strength can be obtained by welding just to the outside vertical face. It is not necessary to weld entirely around the circumference of the box frame. With the right design full seam welding is also unnecessary in most cases.

Yes, there is a concern with welding on the frame. You should make sure it's done only by a skilled technician with the proper equipment. It will NOT harm your vehicle if done properly. Can welded on sliders be repaired if damaged? Of course. Does the repair have to mean more welding on the frame? Not at all.

These trucks are not cheap, neither is doing something twice because you didn't do it right the first time. Do your homework and build a relationship with your local fab shop. Professional welding services are not cheap (roughly $65/hr or more), you're paying a premium so don't be afraid to ask to see samples or
photos of their work. Most 4x4 shops cannot afford to keep a skilled welder on staff so be very cautious when contracting for them to provide welding services.

As expected in a forum of this nature there's always someone more expert that's reading on. I'm a welder, not a mechanical engineer, so please clarify or correct if I have not adequately conveyed the topics discussed above.

Hopefully this will help dispel the mystery behind metalwork.

Lance Williams
lwilliams@cov.com
Lobster Fabrication
Oakton, VA

PS - This link offers a good layman definition of tempering:
http://www.encyclopedia.com/printablenew/45975.html