Everything on a car eventually needs to be assembled, including body and frame panels. That's where welding comes in and, because of the high costs of having major welding jobs done professionally, it is in your best interest to learn this skill and to purchase the equipment. Remember, sheet metal and welding supplies are cheap, labor isn't.
There is one (and only one) goal in welding: to produce a high-quality, high strength bond between two or more pieces of metal. The type of welder you buy must be capable of producing an acceptable weld on the materials you are likely to encounter. Let's look at the various types of welding systems available and try to narrow down the field to a few good choices...
We're going to spend very little time on the traditional gas welder, the oxy-acetylene torch. The reason is that its advantages are outweighed by its disadvantages.
Those include the unwieldiness and numerous safety precautions of the oxygen and acetylene tanks; difficulty in learning the skills required to produce an acceptable weld; the tendency to warp or cut through the metal being worked on; and the overall cost of the equipment.
The only significant advantages of the torch welder are its ability to cut metal and to work fast, but even in those cases the resultant edge requires additional cleanup and preparation steps and the "learning curve" is very steep.
The most common welders used in auto restoration, therefore, are MIG (metal arc welders, gas or flux-cored), TIG (tungsten arc welders using shielding gas) and Arc Welders (the traditional "stick" electrode). To choose the most appropriate one for your needs, you have to consider the following parameters:
— What is the maximum and minimum thickness of metal to be welded? Fortunately, automobiles use metals that fall into a relatively narrow range.
—What is the metal type? Again, automobiles generally are made of steel and, rarely, aluminum.
—What is the normal position the welding "head" will be put in? Do you need to do a lot of welding overhead? The answer is usually no here.
—How much current is available in your shop and do you have 220 volts? Check your circuits.
Let's be frank. Our overwhelming favorite type of welder is the MIG. We'll explain why shortly, but first we'll give an overview of the other contenders. Here we go!
Gas Tungsten Welders (TIG, for Tungsten Inert Gas) use a nonconsumable tungsten electrode and a shielding gas that protects the metal surface from contamination. It can be used in all positions because its heating effects are very precise and controllable. TIG welders have several advantages:
—Because there is no spatter of metal or flux materials, welds made by TIG are cosmetically excellent and generally of very high structural quality.
— The operator can adjust the heat density (current flow) as he is welding by using a foot or hand control.
—Welds most metals, including aluminum, with one shielding gas (argon).
—Because the welding process is so controlled, TIG welders can weld very thin materials with little distortion.
Before you run out and buy a TIG, bear in mind that there are some disadvantages associated with such welders:
—TIG welding is a relatively slow process, roughly half the practical speed of MIG.
—Most TIG welders require a water supply with inlet and outlet hoses.
—Learning to use a TIG welder takes a significant amount of practice.
—TIG welders are considerably more expensive than MIG, stick or torch welders.
Commonly called ARC welders, stick welders use a consumable, flux-coated electrode that contains the specific metal required for the weld being performed (steel, stainless, cast iron, etc.). The electrodes come in a variety of thicknesses that must be matched to the thickness of the metal being welded. The advantages of stick welding are:
—Welding can be performed in any position, but working overhead results in significant amounts of sputtered metal and flux.
—Unaffected by wind, drafts or humidity.
—Stick welders are the least expensive.
—They are less sensitive to the cleanliness of the metal being welded.
Stick welders do have disadvantages, however:
—They don't work well with thin metals (18 gauge or thinner).
—The finished weld needs additional steps to clean it up.
—It takes considerable time and practice to stick weld with any degree of expertise.
MIG (Metal Inert Gas) welders are arc welders that consist of a spool of welding wire (usually of .030 thickness) that is fed through a special tube that ends in the welding head. Inside that tube also flows the shielding gas, typically a 75% CO2/25% Argon mixture. At the welding head is a trigger that simultaneously turns on the current and flows the gas, and when the wire touches the metal it creates an arc that does the welding.
There is a host of advantages to MIG welding:
—MIG welding is the easiest process to learn. Generally, most people acquire the necessary skill within the first hour of practice.
—MIG welders weld most common metals, including aluminum and stainless, and can weld thin metals as well as those up to about 1/4 inch.
—Overhead welding can be done relatively easily.
—MIG welding is quite fast.
MIG welders that use flux cored wire are available as well. Flux-cored wires contain a welding flux inside, thus eliminating (except in certain situations) the need for a shielding gas. Some MIG welders can operate either with flux core wire or with shielding gas. The chief advantage of a MIG welder that uses flux-cored wire is its portability, since there's no need for gas cylinders, regulators and hoses.
Another great advantage of MIG welders is their cost. A very good quality MIG can be obtained for less than $400, although they run well into the thousands of dollars depending upon power capacity.
Not so fast, because first we have to discuss Duty Cycle. To do so we need to make it clear that a welder does its thing through the passage of great amounts of current, or amperage, through the connection between the wire and the metal, which is grounded to the welder to complete the electrical circuit.
Thinner metals (18 gauge up to 3/16ths) require current densities of at least 100 amps, up to 130 amps, to do acceptable work. Welding 1/4 inch steel requires roughly 180 amps of current in order to penetrate deeply enough into the metal to make a good weld.
The welder's power supply uses transformers and inverters to step down the 120 or 220 volt input in order to provide large amounts of current. Doing so, however, creates lots of heat in the windings of the circuitry. The heat must be dealt with in some way or otherwise the power supply will fail.
Welders deal with the heat through the "duty cycle." That means the welder can provide a specific amount of current for a certain percentage of the time, after which it must rest and cool down. A duty cycle of 20% means that a welder can deliver full current for two minutes of operation out of every ten minutes it is turned on. Obviously, the greater the duty cycle rating, the longer the welder can run without stopping.
Most welding operations are short-term events, wherein you might weld a one-inch bead and then stop and move to another point on the piece or take time to inspect the weld, etc. Therefore, duty cycles of greater than 40% aren't of importance to hobbyists.
Input voltage is of some concern, however. Most inexpensive MIG welders are 120 volt devices that can deliver high current but for only short duty cycles. 220 volt welders can deliver far more current for longer duty cycles, so it pays to purchase that type of MIG welder.
You get what you pay for when it comes to welders. More specifically, expenditure of money is directly proportional to ease of operation, reliability, availability of supplies, quality of welds and general peace of mind.
As said above, $400 will get you a decent, reliable welder that can operate with common wire spools available at home centers and welding supply shops. $500-$600 will get you a very easy-to-use MIG that will last many years without annoying problems.
If you plan to do a lot of welding often, spend the bucks for a professional grade, name-brand welder like a Lincoln or Miller. Higher priced welders offer features like reverse-polarity welding, longer duty cycles, easy replacement of wire spools, etc.
At the very least, make sure whatever you purchase has a range of current settings (sometimes labeled as "heat ranges") and wire speeds, and that you are absolutely sure you can obtain replacement nozzles, tips, spools and general parts. There are many, many welders available for prices less than $200, but most are difficult to use, limited in weld quality and hard to find parts for.
Since you're buying the welder, spend the money on an instant-darkening face shield. These devices cost as little as $100 and work incredibly well. Also, you need to spend some money on safety equipment, such as heavy gloves and fire-resistant shop coats or shirts and pants.
Welders throw off molten metal globs that love to land on your bare skin or flammable clothing, so make sure the right safety equipment is being used and there's a good fire extinguisher handy.