i got aproblem with apart i produce it is shaped by angle 90 degree after chemical treatment i found that 90 degree is decreased to 89.5 or 89
I may be reading the original text wrong, but it sounds like you are making a product out of right angle stock.
I'd question whether it was ever truly 90° to start with. Being off by a half, or full degree is very possible for a piece of raw material like angle stock.
Finished dimensions vs unfinished dimensions need to be controlled by the drawing. Be sure those are called out if you are the designer so the manufacturer will know what finished angular tolerances you will accept. If nothing is called out, then the manufacturer will assume the finishing has been taken into account and produce your part cut to spec and then finished. Don’t be surprised there is an iterative design process for finished parts, this is very common in set up where the process has not been previously ironed out.