If you’re new to welding, the wide array of products on the market may appear mind-blowing at first. Just like Ford, Toyota and Mercedes Benz in the auto industry, there are several major welding manufacturers. The big boys are Lincoln, Miller, Hobart (now owned by Miller), ESAB and Thermadyne.
And just as automakers turn out sedans, pickups, sports coupes and SUV’s, there are several “makes” of welding machines, each serving a different purpose. The most common are called MIG, TIG, Stick and Oxyacetylene welders. There are also more expensive but versatile multi-process machines, as well as engine-driven (fuel-powered) welders for work off the electrical grid. If you’re unfamiliar with the different welding processes, check out Skills to Learn before proceeding here.
As a new or aspiring welder, your prospects for employment will increase if you understand the features of many different types of equipment. Being able to decide which model works best for a particular assignment, and which filler rod, wire or stick electrode best meets code requirements will help qualify you to work as a supervisor, project assistant, weld technician or purchaser at your company. This article starts with the basics of how to choose a machine, then shows you how to read spec sheets included in the product sales literature.
Step 1: Determine the type(s) of metal you’ll be welding on.
Most welding is done on carbon steel, in the form of either pipe or sheet metal. Carbon steel (which is ordinary steel) can handle a lot of heat. Unlike the other metals listed below, this one is very forgiving when too much heat gets applied by a novice welder. Nearly all welding processes accommodate carbon steel. And you don’t need a lot of features on the machine to produce a good-looking weld.
Stainless steel is much more finicky in how it deals with heat. Composed of steel, chromium and nickel, this alloy steel is used for food/beverage vessels and many other products, largely because of its anti-corrosion properties. It’s typically welded using MIG or TIG machines and requires less current than carbon steel. You can also find stainless steel stick electrodes. This allows you to use a stick welding machine to get the job done. Of course, the base metal must be thick enough to stand the heat.
Aluminum is on another planet entirely. As a non-ferrous metal, aluminum conducts heat so well that you constantly need more of it to keep your puddle molten. At the same time, the work piece distorts easily if it gets too hot. Consequently, aluminum frequently requires more complex equipment to get the job done. You can use a MIG machine (especially one with a pulse welding feature), but many wirefeed mechanisms have trouble feeding the aluminum filler wire, so a special spool feeder must also be purchased. A good TIG welding machine is designed to weld aluminum. An AC power option is standard. An inverter, square wave, balance control and pulse feature are also helpful for welding aluminum. Naturally, these features add to the product cost.
Although it’s not the preferred choice, a stick welding machine can also weld aluminum. Like stainless steel, the base metal must be thick enough to stand the heat.
Titanium (used on custom bicycles and airplanes), chromoly (used on motorcycles and automobiles), and other alloy steels and exotic metals have their own thermal sensitivity issues that welders must take into account. Because these metals are so expensive, you don’t want to be making mistakes when you weld on them. Hence, they generally require a sophisticated TIG machine, along with plenty of set-up and fit-up, and a seasoned veteran at the controls.
Step 2: Establish a current range that covers all possible metal thicknesses.
The thicker the metal, the more current needed to weld a joint with good penetration. Since the cost of a welding machine is based in part on how much juice it generates, you’ll have to determine in advance the maximum thickness of base metals and fixtures you’re going to be working on in your shop.
Thick structural steel and pipe thicker than a half inch requires the use of a heavy duty MIG welding machine or a Stick welder. According to Miller Electric, you need one amp of power for every one-hundredth inch of mild steel thickness. For example, a 1/8″ (.125 in) sheet of mild steel requires approximately 125 amps. Stainless steel needs about 10% less juice than carbon steel, while aluminum needs about 25% more. Current settings are also tied to the diameter of welding rods, as explained in this Miller tutorial for setting machine parameters.
Conversely, working with very thin metal requires different settings on a more sensitive welding machine. Now the objective is to provide just enough heat to get the job done. Sometimes a low current induces an unstable arc, and that’s a welder’s nightmare. Besides that, if too much heat enters the base metal, the area surrounding the weld weakens or melts. So many of the features described in the paragraph above about aluminum will also apply when welding on extremely thin stock for any metal type.
If you’re careful, you can use an oxyacetylene kit to weld thin ferrous material, but make sure the torch can accommodate a tiny three-ought (i.e. 000) sized welding nozzle. This form of welding is discussed further in the “Cutting and Grinding” section.
Step 3: Decide if your welding will take place inside a home shop, a warehouse or out in the field.
As mentioned earlier, knowing where you will be welding most of the time figures into what sort of equipment you should purchase. There are a couple of things to think about:
Power supply: If you’re plugging the machine into the wall (i.e. the power grid), your choices are as follows:
- 115 volt AC – This is the standard power provided to every customer of the utility company, residential and commercial. A few entry-level arc welding machines are rated for 115 volts input power, but not many.
- 220-240 volts AC – This is a high-power, 30-amp circuit used by most welding machines. Any industrial location will have this available. Residential wiring is another matter. Since most welding equipment requires a 30-amp circuit, you may have to hire a licensed electrician to wire a circuit from the control panel.
- Single-Phase vs. Three-Phase – Most electrical equipment is designed for normal “single phase” operation, drawing from the 220-240 voltage line coming off the grid. However, at many warehouses and other industrial locations, a “three phase” option is available. In this scenario, a third hot wire joins the circuit, making more amperage available to power large motors. This option also gives you better energy efficiency, so companies are willing to invest in three-phase machines to save a bundle on their electricity bill. You cannot, however, use a three-phase machine at home.
Offgrid Scenario: If you’re welding outdoors and don’t have access to the power grid, you’ll need an engine-driven welder, or welder-generator to complete the assignment. Farmers and welders who work in the field typically buy this type of machine. Depending on the model, the generators run on gasoline, diesel or liquid propane (not all three), and may accommodate a stick welding torch, a Tig torch, or a MIG/Flux-core wirefeed unit and gun. The low end of this product niche starts at about $2000 and is used only for stick welding. When reviewing product sales literature, look for the symbols CC (constant current) and CV (constant voltage). CV machines are costlier, but are the right choice if you’re plugging a MIG/flux cored welder into it. You’ll also need to know your power requirements (i.e. maximum watts) in order to choose the right sized generator. Beware, the state of California only permits the use of generators meeting low carbon emission standards, otherwise known as CARB-compliant.
Windy conditions: If you expect to be welding in unsheltered areas where a breeze is possible, this may negatively affect your welds. The CO2/argon gas used in MIG to shield the weld’s molten puddle until it solidifes will be ineffective, resulting in oxidation and porosity. Thus, you’ll want to be able to switch the MIG machine over to flux-cored mode (or use a straight flux-cored welder). Alternatively, a stick welder will work in a breezy environment (but not too breezy) . Both of these welding processes contain solid deoxidizers within the wire or rod. They vaporize directly over the puddle during welding, leaving a protective layer of slag behind.
Step 4: Read product spec sheets so you can compare similar machines and choose one with the power and features you need.
Here are a few key things to look at:
Duty Cycle: This spec tells you how much uninterrupted welding a machine can knock in ten-minutes. Traditionally, duty cycle is defined as the number of minutes out of a 10-minute period a welder can weld at the highest current the machine offers. After reaching the limit, the machine must be allowed to cool down.
Duty cycle is given as a percentage. So you have to do the math in your head, multiplying each percentage point by ten to get the number of minutes you can expect to weld per ten-minute interval. If you exceed the duty cycle, the machine heats up and the circuits inside may fry.
For example, a very inexpensive machine with a maximum current of 70 amps may have a 10 percent duty cycle. This means you can weld for 1 minute out of every 10 without the equipment overheating or burning out.
In general, light industrial/hobbyist welding machines have a duty cycle of 20%, medium duty 40-60%, and heavy duty 60-80%. But nowadays manufacturers are playing with the formula. In order to boast a higher duty cycle, they base the percentage on a lower amperage setting. So with a machine that provides a maximum 140 amps with a 10% duty cycle, you might see a rating of 30% at 115 amps instead.
On the up side, you can use the same tactic to get around a low duty cycle for a machine that otherwise fits all your needs. Just buy the model with a higher maxiumum current than you expect to use. That way, you effectively increase your duty cycle.
Open-Circuit Voltage: This is the voltage emanating from an arc welding torch or gun when current is not flowing. On the one hand, it’s sort of dangerous to have a live circuit sitting around on the work bench with the potential to cause a serious injury. (That’s why OSHA limits OCV on equipment.) On the other hand, OCV affects the way a torch electrode will perform when striking an arc, so the extra punch you get at start-up is important in some types of welding.
In particular, E6010 and E7018 rods in stick welding require a reasonably high OCV. That enables a crisper arc start as the welder scratches the rod against the metal to begin the weld. A frequent problem for students is the inability to strike an arc, so a low OCV on a small welding machine may only aggravate the situation. So you should take note of this figure in the specs. An OCV of about 80 volts is considered normal in a stick welder. In a MIG welder, it can drop to about 35, but it’s not a big deal, since in MIG welding the arc usually starts without any fuss when you pull the trigger.
Thermal Overload Protection: Either a machine has it or doesn’t. And you should only buy a machine that has it. This feature automatically cuts output power to your torch or gun if the circuit inside starts overheating. The fan or other cooling mechanism will continue running to help disperse the heat (assuming you leave the machine turned on). In some specs, this feature is clearly stated. But with other products you have to check the equipment manual or ask a sales rep. (See the samples below for more.)
Step 5: Determine if you need to use compressed gases and how you will purchase, transport and store them.
A variety of gases (CO2, argon, oxygen, etc.) are used for different welding processes. In the case of MIG, the type of gas you need depends on the process, the base metal, welding position and environmental conditions. With oxy-fuel welding, you simply need oxygen and a fuel gas. And a TIG machine typically uses argon but on occasion may require helium. Besides reading the equipment literature carefully, you’ll want to consider a few other things:
- If you buy a welding machine that requires a compressed gas (i.e. gas stored in a tank under pressure), you’ll need to occasionally transport the tank to a supplier for refills. Hopefully, there’s a supplier in your area with a reasonable policy for exchanging and filling empty tanks.
- The tanks themselves can either be purchased or leased from the supplier. Cylinders come in a number of sizes, so you’ll have to research how big a tank you need based on how often you’ll be using it. As a rule, it doesn’t cost too much more to fill a large tank than it does to fill a small one.
- There are lots of safety issues and storage requirements associated with gas, so be sure you understand what’s involved before buying welding equipment that uses it. If you’re thinking of buying a used tank, be sure your gas supplier will agree to fill it before purchasing. Always keep your sales receipt and other documentation handy. OSHA requires that all tanks get inspected every two years.
- Most mild steel applications in MIG call for a combination of 75 % argon and 25 % CO2, although you can probably use 100% CO2 with good results. Welding aluminum in MIG and TIG usually calls for all argon gas. Stainless steel requires a tri-mix blend of 90% helium,7.5% Argon and 2.5% CO2. Don’t worry, you don’t have to mix the gases yourself. You just buy the blend you need.
- While having to use compressed gases with an arc welding machine adds to your costs, you save money on filler rod. MIG filler wire is cheaper and more efficiently used than stick electrodes. (Self-shielding flux core wire doesn’t require any gas.)
- Both acetylene gas and oxygen are nowadays extremely expensive. That’s why the oxy-acetylene process is generally used for torch cutting rather than welding.