Electrical Discharge Machining and Waterjet Cutting of Nitinol Orthopedic Products

Traditionally, biomedical Nitinol orthopedic devices have been cut from plate/ thick sheet, or hot rolled bar using electrical discharge machining (EDM) techniques. This has been the preferred cutting method for these products due to speed, cost efficiencies, and the difficulty of traditional machining methods with Nitinol. After cutting, parts can be further treated with tumbling and chemical processing to remove any heat affected zone (HAZ) and recast material. Additionally, these post processing techniques help to create a consistent side wall and improve corrosion resistance. Concurrently, waterjet cutting of hard metals has been in use since the 1970’s and has continued to develop and improve its capabilities with time.

The purpose of this study is to provide a comprehensive comparison of representative Nitinol orthopedic device geometries manufactured using both EDM and waterjet. Microstructure of the as cut samples will be examined to compare surface finish, material recast layer, and HAZ created by these cutting techniques. Microstructural analysis will be performed using scanning electron microscopy (SEM) and electron channeling contrast imaging (ECCI). Understanding the surface conditions of these as-cut parts may help elucidate the benefits and detriments of each manufacturing technique when applied to size, speed, post processing and cost. The complete comparison gives customers and manufacturers the ability to better optimize cutting practices and deliver high quality orthopedics to patients.