Prototyping of Injection EVA Foam Footwear Midsoles

Abstract

During the research and development (R&D) process for new footwear, prototypes of various components are made for functional testing and analysis. Nike makes prototypes at its World Headquarters Product Creation Center (PCC) and also outsources to suppliers at several development centers across Asia (ADC). One important component is the midsole, often made from a type of ethylene-vinyl acetate (EVA) foam called injection-phylon (IP). IP midsole prototyping is currently exclusively outsourced, however there is a desire for a supplementary internal capability at the PCC. This thesis develops a plan for how the PCC could achieve that.

A study was conducted to test the PCC’s current capabilities with the entire IP development process, benchmark a top ADC partner, and identify any gaps. It can be difficult to make IP parts that meet specifications due to the significant scale and non-uniform nature of how they expand after molding. Dealing with this expansion requires certain steps in the IP process and this study isolated three key aspects: expansion ratio (ER) grading, mold design, and part-making. The PCC then developed mold tools and three sets of midsoles to compare its capabilities in each of these aspects to a mold tool and set of midsoles sent from the ADC partner.

Results showed that the PCC was able to make IP midsoles that met many of the part specifications. The PCC also acquired new mold design, injection molding, and stabilization best practices. An ER grading method was also developed, with initial results proving it has promise and should be tested further.

The results also highlighted some gaps and additional research studies that could be conducted to bridge them including further analysis of these mold tools, testing the ER grading method on more midsole varieties, and thoroughly mapping the PCC’s upstream stakeholders’ requirements. The PCC should then undertake complete IP projects specifically chosen to test its IP capabilities in various midsole design complexities, formulations, development speeds, and quality levels. All of these efforts will help the PCC effectively implement an IP prototyping capability that is able to effectively supplement existing ADC capabilities.