Any welders on the board?

You have a couple of things that may cause this. The most likely cause is not enough shielding gas while you are welding. You may think it is doing alright but you will have the results you are getting. Give me a little more info on what you are welding with. What type of welder is it? How old is It?( may seem like a silly question but it helps in figuring out possible problems) What type of gas are you using?