Choosing the right MIG gun consumables — and using and maintaining them properly — can make a big difference in gun performance and in weld quality. The liner is especially crucial to good gun performance, and proper liner installation is critical. Nothing else goes right if the liner doesn’t properly guide the wire through the welding cable and out to the contact tip.
Improper liner installation sounds like an incidental issue, but it can create a real mess that costs time and money. Even trimming the liner too short or leaving the liner too long can lead to numerous problems, such as birdnesting and wire feeding issues. These problems can result in costly rework and operator downtime for maintenance and repairs. And wasted wire due to birdnesting can drive up costs.
Various types of liners
There are numerous liner types available that can be used for both semi-automatic and robotic applications. Choosing one is often up to the preference of the welding operator or maintenance personnel. The three main categories are conventional liners, front-loading liners and front-loading liners with a spring-loaded module, which provides up to 1 inch of forgiveness for improperly trimmed liners.
• Are installed through the back of the gun
• Frequently are used in the industry, so many welding operators are familiar and comfortable installing this type of liner
• Often require a lengthy changeover process, since liner replacement may require the welding operator to climb over robotic tooling or transfer systems to remove the gun from the feeder, or to climb several feet into the air to change liners on a boom-mounted feeder
• Can’t account for changes in length as the cable grows and shrinks with twisting
• Are installed from the front of the gun
• Can reduce downtime and offer time saving advantages, since changeover doesn’t require leaving the front of the gun
• Are unable to grow or shrink as the cable twists and moves
Front-loading liners with a spring-loaded module inserted into the power pin:
• Allow for up to 1 inch of motion as the cable twists
• Tend to be more forgiving if the liner is trimmed incorrectly
The installation process is somewhat similar for all three liner types, with some variations. Here are some general steps to take when installing a new MIG gun liner. These steps are the same for both semi-automatic and robotic MIG guns:
1. Before removing the consumables, make sure the gun is straight and the cable is flattened. Trim the wire at the front of the gun to remove the molten wire bead that often forms after welding.
2. Remove all front-end consumables.
3. For a conventional liner installation, remove the power pin from the feeder at the back of the gun and cut the wire. This allows the wire and a conventional liner to be removed from the back of the gun.
4. If using a conventional liner, feed the liner through the back of the gun, threading it into the power pin. Reinsert the power pin into the feeder, and feed a few inches of wire through the back of the power pin. (See below for variations for front-load liners and front-load liners with spring-loaded modules)
5. Because the liner is longer than the gun assembly, there will be a foot or so of liner sticking out the front of the gun, so it’s necessary to trim the liner. Liners often come with a plastic liner gauge with a 3/4 in. stick-out that can be fed over the top of the liner and pressed flush against the neck, so the liner can be trimmed precisely.
6. Hit the trigger to pull the wire up and at the same time purge the gun with shielding gas.
There are some variances in installation, depending on liner type. Here are some differences to note:
• When installing a front-loading liner, unravel the liner and stick the brass end over the wire and through the neck. Feed the liner through the front of the gun using short strokes, to avoid kinking. The liner will click or snap into place once it hits the receiver in the power pin. After that, put the liner gauge on top of the liner and follow the standard installation steps.
• When installing a front-loading liner with the spring-loaded module, the only difference is that the receiver is built into the module pin, rather than the back of the power pin. While feeding the liner using short strokes, the liner will engage with the receiver inside of the module’s power pin. The welding operator can feel the liner spring back toward the front of the gun, meaning the liner is properly engaged.
Place the liner trim gauge over the front-loading liner until it is flush against the neck. Push the liner back into the gun until it bottoms out against the spring-loaded module, then trim the liner flush to the end of the liner trim gauge. After trimming, remove the liner trim gauge and release the liner. Note that the liner will spring back and stick out of the neck by approximately 1-3/4 inch, which is normal, as installing the consumables will compress the liner into its proper position.
Installation also varies when retrofitting a gun to a front-loading liner, or when completing a liner changeover. When it’s not the first time the liner is being installed, there are some additional things to remember:
• When retrofitting from a conventional liner to a front-loading liner, the first installation will be from the back of the gun, since a receiver is needed in back to accept the front-loading liner.
• After following the standard steps and removing the conventional liner and wire, install the end of the front-loading liner into the receiver and unravel the liner. Feed the front-loading liner in, just as with a conventional liner, through the back of the gun, and thread the receiver into the power pin.
Proper liner installation can help optimize performance
While liners may seem like a small part of the welding operation, it’s important to be mindful of the impact they can have on quality, performance and costs. Liners perform a vital function in the MIG welding process, and proper liner installation can help reduce costly rework, operator downtime and wasted wire.