Design of Experiments for Ruggedness Testing: Case Study on Paraffin Therapy Bath

Design of experiments (DOE) has become an essential tool for validation of medical manufacturing processes. Kim and Kalb provided a good overview of the techniques. They say “the process should be challenged to discover how outputs change as variables fluctuate within allowable limits.” This article shows how we challenged our durable medical device – a paraffin heat-therapy bath. We first ran a highly-fractionated 2-level factorial design. This minimal-run DOE showed a significant degree of sensitivity amongst a panel of users. Therefore, we then ran a follow-up design called a “foldover” to find out what really caused the effects. By combining data from both phases of the DOE we revealed some surprising interactions. This ultimately led to redesign of the product for better performance at lower cost.