The research focus on identifying possible product quality problems that adversely affect rate ofrnrework or recyclability by selecting case in EPI. By performing cause and effect analysis tornstrengthen and diagnose causes corresponding to the identified, prioritized quality problems.rnTaguchi and Response Surface Methodology design of experiment is systematically approachedrnfrom the existing EPI extrusion machine set- points to identify the possible response output valuesrnapproaching. rnTaguchi is used to screen the variables that have significant effects (were: Feed speed, vacuumrnpressure, Take-off speed, screw speed and die-temperature) and L27(3rn) orthogonal array by usingrnMinitab and know Response factor: Thickness and Width variation. RSM design experiment forrnprocess parameter optimization the selected response factor from Taguchi design experimentrnselected independent experimental factors: Feed drum, vacuum chamber, rotational screw speedrnand barrel temperature. The dependent response parameters: Feed speed, vacuum pressure, Takeoffrnspeed,rnscrewrnspeedrnandrndie-temperature.rnAfterrnthis,rnAnalysisrnofrnVariance(ANOVA)rnusedrntornrnintegraternTaguchi andrnResponsernSurfacernMethodologyrndesignrnexperiments.rnrn7rnAccordingly, in this research, to set possible parameter combinations and to reduce variationrnaround thickness and width pipe and control the factor with the biggest impact on the Signal tornnoise ratio is Screw speed. And for mean both show that the factor with the greatest effect on thernmean is Feed speed. Finally, the desired target thickness and width of pipe that means optimumrnparameter level for minimum value of thickness and width variation of the pipe is Feed speed-1,rnvacuum pressure-1, Take-off speed-1, screw speed-1, temperature one-2, temperature two-3 andrntemperature three-3 (A1, B1, C1, D1, E2, F3, G3). The S/N ratio optimum parameter level forrnminimum value of thickness and width variation of the pipe is Feed speed-1, vacuum pressure-2,rnTake-off speed-1, screw speed-1, temperature one-3, temperature two-1 and temperature three-2rn(A1, B2, C1, D1, E3, F1, G2).