Ok listen up , it is not the heat that causes the warpage in sand balsting.!
SO why all the problems? if you actually use sand , there is a certain amount of ABRAISION that happens.. and that my PALS will cause just the slightest amount of metal to be removed on that side of the panel.
NOW if you remove metal than haven't you just made the surface area just a little bit BIGGER?
MMM less see here , how do i illustrate this ?
OK pay attention say you have some landsacpe.
now you have a hill that is 500 feet tall. the hill being a rusty bump in the sheet metal..
NOw you take a bulldoser and take off 10 feet of top soil.
the hill in now 490 feet tall. but look again it is also not so steep. you have increased the surface area. and it slopes less gradually . now the other side of the panel is still the same size , right? So you are going to get a warp. because you have ABRADED off some of the surface and made more surface area.... that is why most olks now adays will use a media blast .. it will cut the rust and paint , but not ABRADE any metal. thus increasing the surface area.
OF course this will not affect many of the parts on a car , but sure it will in thin sheet metal. and it has nothing to do with heat.