Surface characteristics of Invar alloy according to micro-pulse electrochemical machining

Invar is a 36 % nickel iron alloy that has a low thermal expansion, compared to other metals and alloys, at temperatures ranging from room temperature up to approximately 230 °C. Invar alloy is ductile, easily weldable and its machinability is similar to that of austenitic stainless steel. Due to the low thermal expansion of Invar, it is used for shadow masks for display devices such as UHDTV – organic light-emitting diode. In this study, micro-pulse electrochemical machining (MPECM), which is a non-contact ultra-precision machining method, was developed to manufacture Invar sheets; optimum parameters of MPECM were defined and the basic MPECM experiments were carried out on an Invar sheet. The optimum parameters were determined with pulse-on time and duty-ratio analysis. The experimental results show that MPECM is hard to control. Therefore, using ultrashort charging times and very high pulses, it is possible to achieve a successful anodic dissolution at a very small electrode gap. Hence, a longer pulse-on time and a small electrode gap may provide the scope for further improvement of the machining accuracy by controlling the localization effect. Furthermore, the machining depth and MPECM efficiency were investigated with respect to various parameters and pulse-on time, considering different duty-ratio conditions.