Influence of EDM generator programs on shape and surface roughness of Ni-Ti sheets

In the last decades caloric cooling technologies received an increasing scientific and industrial interest as promising alternatives to conventional vapor compression technology. Theoretically, efficiency of caloric technologies is more than 40% higher than for the conventional vapor compression cycle. Particularly interesting is elastocaloric cooling, which is an emerging technology, occurring due to the uniaxial mechanical loading of active regenerators. These are made of shape memory alloys, such as Ni-Ti. The regenerators must have a high fatigue resistance to withstand multiple loading cycles and simultaneously possess excellent elastocaloric properties. Therefore, it is crucial to establish a manufacturing process that allows fabricating thin regenerator elements with profound surface quality and as little impact on their functionality as possible. Considering the challenges of conventional machining technologies due to the specific characteristics of Ni-Ti, electrical discharge machining (EDM) demonstrates a high potential to meet the requirements for micro-shaping surfaces for elastocaloric applications. This paper presents fundamental analyses of the influence of EDM generator programs on the resulting removal depth, removal width and surface roughness of Ni-Ti sheets. Based on the perspective application in elastocaloric applications, adequate EDM programs are selected with regard to the targeted precision, surface roughness and minimal surface roughness.