Application of Design of Experiment Method for Thrust Force Minimization in Step-feed Micro Drilling

Micro drilled holes are utilized in many of today's fabrication processes. Precision production processes in industries are trending toward the use of smaller holes with higher aspect ratios, and higher speed operation for micro deep hole drilling. However, undesirable characteristics related to micro drilling such as small signal-to-noise ratios, wandering drill motion, high aspect ratio, and excessive cutting forces can be observed when cutting depth increases. In this study, the authors attempt to minimize the thrust forces in the step-feed micro drilling process by application of the DOE (Design of Experiment) method. Taking into account the drilling thrust, three cutting parameters, feedrate, step-feed, and cutting speed, are optimized based on the DOE method. For experimental studies, an orthogonal array L(27)(3(13)) is generated and ANOVA (Analysis of Variance) is carried out. Based on the results it is determined that the sequence of factors affecting drilling thrusts corresponds to feedrate, step-feed, and spindle rpm. A combination of optimal drilling conditions is also identified. In particular, it is found in this study that the feedrate is the most important factor for micro drilling thrust minimization.