MIG Welding Basics for Farm and Automotive Repair
January 14, 2015
When it comes to keeping farm and ranch equipment and autos in good repair, MIG welding offers numerous benefits. Because MIG welding is an easy-to-learn process that offers flexibility in welding light-gauge to thick materials, it's a good choice for quick repairs around the farm, ranch or garage.
MIG welding can be used to weld all common metals, including carbon steel, stainless steel and aluminum, and the process is much more forgiving on thin metals than Stick welding. MIG welding enables the farmer, rancher or DIY welder to make most types of maintenance and repair welds on material from 24-gauge up to 1/2-inch thick.
Also, greater speeds can be achieved with MIG welding compared to Stick welding, which reduces the time spent on repairs. The continuous wire feed of MIG welding also minimizes stops and starts, which contributes to more consistency and efficiency in the process.
Following some basic tips can help users achieve a good quality weld with MIG welding in farm and auto repair application.
It’s a good idea to get comfortable with the welder and complete some practice welds on scrap metal that is similar to the material and project type to be worked on. That way, the operator can optimize technique to best achieve a proper weld.
It’s also important to clean the surface of the base material and clean the joint as well as possible, then check to make sure there is a good ground clamp connection. If the material is 1/4 inch or thicker, bevel the joint to ensure proper penetration of the base metal. This is especially important for butt joints.
Before tackling any project, make sure to have the appropriate safety gear, including eye protection and a welding helmet. The Miller Arc Armor® line of welding protection offers a wide range of helmet options, apparel, safety glasses and accessories.
There are numerous tips to keep in mind when selecting the proper equipment and consumables for the welding application. This includes choosing the most appropriate wire and gas and knowing power needs and capabilities.
To select the proper wire, be sure to match the wire type to the base material. Therefore, an operator would want to use aluminum wire with aluminum base material, and stainless steel wire with stainless steel base material, for example.
Some wires are better suited for welding dirty or rusty steel because they contain more oxidizers, so read the manufacturers’ recommendations for each type of wire.
When it comes to selecting gas, a shielding gas with a 75 percent argon/25 percent CO2 blend (also called 75/25 or C25) gives the best overall performance for MIG welding. It produces the least amount of spatter, best bead appearance and won’t promote burn-through on thinner metals. A 100 percent carbon dioxide shielding gas will provide deeper penetration, but it also increases spatter, and the bead will be rougher than that produced when using 75/25.
It’s important to know the requirements and capabilities for the application. How much voltage and amperage a weld requires depends on a number of variables, including metal thicknesses, type of metal, joint configuration, welding position, shielding gas, wire diameter and speed. Miller machines provide a convenient reference chart, located on the inside of the door housing the wire feed system, to help determine voltage and amperage.
Miller machines with the Auto-Set™ feature, found on several Millermatic® models, offer a simpler process for setting proper voltage and amperage. Simply select the wire diameter and dial in the thickness of metal. Auto-Set will then select the proper voltage, amperage and wire feed speed.
Once the proper wire and shielding gas are selected, there are some basic welding techniques to keep in mind to help achieve the best results.
The proper wire stickout for MIG welding should be around 1/4 to 3/8 of an inch from the contact tip, possibly a little longer for tight joint access. Stickout refers to the length of unmelted wire that extends from the end of the contact tip. One good rule of thumb is to listen for the “sizzling bacon” sound; if the arc sounds irregular, one common culprit could be too long of a wire stickout.
Also keep in mind that changing the distance of the contact tip to the workpiece causes voltage to vary and changes the shape of the weld bead, so don’t hold the gun too far away from the material being welded.
Push or pull?
The push technique involves pushing the gun away from (ahead of) the weld puddle. Pushing usually produces lower penetration and a wider, flatter bead because the arc force is directed away from the weld puddle.
With the pull or drag technique, the welding gun is pointed back at the weld puddle and dragged away from the deposited metal. Dragging typically produces deeper penetration and a narrower bead with more buildup.
In considering gun travel for MIG welding, the push technique is the most recommended, since it gives the operator a good view of the weld puddle and allows them to better direct wire into the joint.
Tips for various positions
The travel angle in welding is defined as the angle relative to the gun in a perpendicular position. Normal welding conditions in all positions call for a travel angle of 5 to 15 degrees. Travel angles beyond 20 to 25 degrees can lead to more spatter, less penetration and general arc instability.
The work angle is the gun position relative to the angle of the welding joint. The recommended work angle varies with each welding position and joint configuration.
- For a butt weld (a 180-degree joint), hold the gun at a 90-degree angle to the workpiece, directing the filler metal straight into the joint with a travel angle of 5 to 15 degrees. A small, back and forth motion with the gun can help fill a large gap or when making multiple passes. A slight pause at the side of the weave bead can help avoid undercut.
- For a T-joint or fillet weld, keep the gun as a 45-degree angle, or equal distance from each piece. When making multiple passes, the work angles change slightly. This helps avoid uneven weld beads and undercuts.
- For a lap joint (also a fillet weld), angle the gun between 60 and 70 degrees. The thicker the metal being welded, the greater the angle.
- Because of the effects of gravity, the gun work angle must be dropped slightly by 0 to 15 degrees. Without changing the work angle, the filler metal may sag or rollover on the bottom side of the weld joint. The travel angle, whether using a push or pull technique, generally remains the same as for a weld joint in the flat position.
- Vertical welding, both up and down, can be difficult, which makes pre-weld setup important. Consider reducing the voltage and amperage 10 to 15 percent from the settings for the same weld in a flat position. The vertical down technique helps when welding thin metals, because there is less arc penetration due to the faster travel speed. When welding vertical down, keep the wire on the leading edge of the weld puddle. A slight weave may help flatten the weld crown. With vertical up welding, the travel angle of the gun is a 5 to 15 degree drop from the perpendicular position. A slight weaving motion can help control the size, shape and cooling effects of the weld puddle.
- This is the most difficult and should be avoided when possible. If you need to weld in the overhead position, reduce welding parameters a minimum of 10 to 15 percent and try to maintain fast travel speeds to avoid having the weld pool fall from the joint onto you.
Choosing a welder
When choosing a machine to meet farm, ranch and auto repair welding needs, consider the types and thicknesses of metal that will be welded most often. Also, if portability is an important need in many applications, keep in mind that some machines offer greater portability than others.
Numerous Miller MIG machines are suitable for these applications:
- The Millermatic® 141 with Auto-Set™ is an all-in-one wire welder that welds 24-gauge to 3/16-inch mild steel, in a 120V, easy-to-use package.
- The Millermatic® 190 with Auto-Set™ welds 24-gauge to 5/16-inch mild steel, and is one of the simplest Millermatic machines to setup and start welding. It weighs only 35 pounds, so it can be easily moved around the workspace.
- The Millermatic® 211 Auto-Set™ with MVP™ welds from 24-gauge to 3/8-inch thick material in a single pass and offers Miller’s Multi-Voltage Plug, which allows you to connect to common 120 or 230 V power receptacles without using any tools.
- The Millermatic® 212 Auto-Set™ welds from 22-gauge to 3/8-inch thick in a single pass, with 160 amps at 60 percent duty cycle.
- The Millermatic® 252 offers the highest duty output in its class and can weld material from 22-gauge to 1/2-inch thick in a single pass. The machine has no-tool, quick-change reversible drive rolls and an easy-to-set, scaled tension knob.
- It is important to know the proper voltage and amperage requirements for the application. Engine-driven welder/generators are a good option when you have power generation needs in addition to welding. Miller welder/generators that are good options for farm, ranch and auto repair applications include the Blue Star® 185, Bobcat™ 250 and Trailblazer® 325, which offer rugged durability, reliable outdoor power, stable arc performance and portability.
Choices to suit many applications
Most welding operators can create good, high quality MIG welds with a combination of practice and following the basic techniques and tips discussed.
For more information on machine options and accessories or to purchase any of the machines mentioned in this article, visit your local welding distributor or MillerWelds.com.