Wire feed is sticking when
Cleanliness is important when it comes to Mig welding. Any rust, dirt, dust, oil is liable to be deposited in the whip liner. If it's just a dirty liner you can try cleaning it with a solvent that doesn't leave an oil deposit (electric motor cleaner, brake cleaner, that sort of thing) compressed air and flexing of the whip.
Make sure your whip hasn't been crimped, if it has then no amount of cleaning will restore it to operation.. a new liner is the only reasonable answer.
It's possible that a bad tip can cause feed issues. Miller type tips are the worst, in my experience, sometimes you just get a tip that will weld to the wire when the current passes between them. I've worked in shops where I might go through three tips in five minutes and then hit one that would last all afternoon. If the wire sticks and you can hold the gun up and rotate your wrist and you feel a 'pop' and the wire jumps out of the tip then just change the tip out. Excessive roller pressure with a tip that's sticking to the wire can really make trouble for you. Nozzle dip is your friend sometimes with tip sticking issues.
Copper clad wire is not particularly friendly to liners, the copper is liable to flake off in the liner. I use bare wire, I bag the wire in a plastic bag on the feeder and I wrap a scratcher pad on the wire just before it goes into the feeder and I find that I have few feed issues. Wire that has even a trace of rust should be discarded as it will both fill your liner with rust and give poor quality welds.
on Nov 13, 2019