This is an example of a lapped sheetmetal joint inside a Dodge pickup cab. Read below to l
Q: Hi Ron, great column you have in Classic Trucks! I'm doing the initial brainstorming on my '67 Dodge truck, and some things have me confused. There are multiple areas inside the cab that I would like to make smooth, but they have different surface heights- the cab corners above the windshield, and the area where the rockers will meet the cab, for instance. How do you go about making all the surface planes meet each other, and get it to all flow together nicely? I haven't seen many of these Dodges built with anything other than stock bodywork, so I'm kind of breaking new ground here.DevilBradVia the Internet
A:Fortunately, this job is fairly straightforward. First, the joints must be cleaned to remove all traces of paint and rust in preparation for welding. When welding joints like this, it is best to make a series of very small blobs of weld and skip around quite a bit so the metal is always at room temperature when you are adding more weld to it-this will keep the distortion to a minimum. After welding, sand off any projections of weld bead, then use plastic filler to make the joint completely smooth.
Q:In many articles and projects I've seen, and in discussions with people about the high-strength steels employed on late-model vehicles, mention is made of the problems with welding this material. Some have even said not to weld it at all. In a discussion with a body shop owner, he suggested that the weld area would need to be heat-treated-cooled at a specific rate with a misting device like that used on milling machines for spraying coolant.
Still, I see late-model stretch limos and older cars and trucks customized with late-model parts. So apparently it is possible to join new metal to old. One example is the late-model Cadillac taillights used on Cadzilla.
I'm specifically interested in customizing my Dodge pickup, and in using late-model parts on other old cars and trucks. Is it possible to join the new high-strength steels to older metal, and if so, how can it be done properly?
Norman Park, GA
A:As you mentioned, some (but not all) of the sheetmetal on new cars is High Strength Low Alloy steel (HSLA), and there are some special considerations that must be observed when welding it. In the collision-repair industry, this material is welded every day, but there are certain techniques used when welding this material so that its special properties aren't compromised in areas where high strength is necessary.
Let's begin by making a distinction between structural and non-structural auto body panels. Back in the days when cars had a separate frame, all the body panels were non-structural. When unibody cars became the norm, the major body panels were designed to be stressed, and the welded body shell took the place of the frame. On new cars, most of the parts that are welded together are made of HSLA steel, while most of the parts that can be unbolted (front fenders, doors, hoods, and deck lids) are regular drawing-quality steel. Some parts are a composite, such as doors, which often have an "anti-intrusion" beam going across them made of HSLA steel.
HSLA steel is alloyed with materials that allow it to be heat-treated, and the heat treatment is what increases its yield and tensile strength. The problem with welding this material is that the heat from welding takes the heat treatment away, leaving the heat-affected zone (HAZ) softer than the undisturbed metal next to it. If parts HAVE to be replaced during a collision repair, MIG welding or spot welding are the only techniques allowed. Both of these processes have a very small HAZ, so the strength of the structure is not compromised to a huge degree. Gas or TIG welding is NOT approved for this work, since the larger HAZ will make the area next to the weld considerably softer.
While it is true that steel is heat-treated by chilling it at a prescribed rate, I DO NOT recommend trying to do this by quenching with water, compressed air, or with a misting device. The problem is that quenching the metal quickly can harden it too much, making it glasslike and liable to fracture under impact rather than bend. In industry, metals are heat-treated by putting them into huge ovens so they can be heated slowly at a carefully prescribed rate. They usually have to "soak" at a specific temperature for some time, and then they are cooled at a carefully controlled rate (which is different for each alloy of steel). You simply don't have enough control of these parameters in a shop environment to know what the results will be, and with structural elements, this could be deadly!
As long as any welding is in areas that aren't highly stressed (like the taillights you mention), losing the HSLA steel's heat treatment won't be a problem, and any welding technique can be used. There is no problem joining regular cold-rolled steel to HSLA steel, and after welding, the strength of the metal in the HAZ will be pretty similar for both types of metal. Nearly all pickups have body panels that are non-structural, so this issue is less important on trucks than on passenger cars.
You can e-mail your questions to Professor Hammer at email@example.com, or mail to: Professor Hammer c/o CLASSIC TRUCKS Magazine, 774 S. Placentia Ave., Placentia, CA 92870. We'll print your name and city unless you request otherwise. Ron Covell has made several metalworking videos and offers an ongoing series of workshops across the nation covering all aspects of metalworking. Check them out online at www.covell.biz, or call for a current schedule of workshops or their free catalog of videos, books, and fine-quality metalworking tools. Phone 831-747-4631 or 800-768-0705. You can send a request by mail to: Covell Creative Metalworking, 106 Airport Blvd., #105, Freedom, CA 95019.