Industries always face severe crisis by increased scrap rate, so they are continually striving to improve process quality by reducing defective parts and controlling setup procedures for critical processes. This work concentrates on the thermoforming process of a bathtubs factory that consists of four processes: thermoforming, spray, refine and packaging. The main problem in the thermoforming process is the differences in the acrylic sheets thickness. So, this work presents a procedure applied on the thermoforming process to determine the best setup factors such as temperature, time and other independent factors of ovens, which effect on the acrylic sheets thickness. An algorithm was developed called the Best Setup (BS), is used to determine the process setup factors to eliminate the defective parts. BS combines orthogonal experimental design with ANOVA that is a suitable technique for testing the hypothesis about the mean. Also applies an optimization design for variables defined by quality control engineers.