When you put an item in the melting machine, it takes a ridiculous long time to melt. Sometimes clicking the focus in and out of the game itself helps, sometimes not.
It's not really frozen, but I can see how some people might think it is when you're waiting 5 minutes and nothing, but a few more minutes and you get your part.
This is especially annoying as it takes such a long time *if* you do everything right, so it'll take even longer if you get stuff wrong. How it should work is the melting machine immediately melts the part and gives you back the other part, no waiting for ridiculous amounts of time.