Hybrid tooling by a combination of high speed cutting and electrochemical milling with ultrashort voltage pulses

Abstract

Electrochemical machining with ultra short voltage pulses (ECF) is an innovative technique to machine electrochemically active materials at micrometer feature size, particularly hard materials like stainless steel. Because ECF is an electrochemical process the workpiece as well as the tool are submerged in an appropriate electrolyte. The workpiece is electrochemically etched by a galvanic current. Therefore no mechanical forces, no thermal load and no tool wear occurs. Due to the use of short voltage pulses in the range of 10-200 ns the electrochemical process is confined to a small area around the tool. The ability to manufacture microstructures even in stainless steel makes ECF the ideal technique for the processing of micro moulds. For a higher through-put and a reasonable size of the moulds it is useful to manufacture the micro moulds in two steps. First conventional high precision milling is used to manufacture the main structure. Afterwards the structure is finished by the ECF process. Since these two steps are carried out on two different machines, the workpiece has to be aligned in the ECF machine after the milling process. Using a matching strategy alignment errors like rotation to the xy-plane, errors in scaling of the length of the axis and translation in the xy-plane can be corrected automatically by transforming the CAD/CAM data in a way that they match the two co-ordinate systems. It is shown by test-pattern that this strategy works very accurately. There is almost no mismatch between the HSC pre-milled structure and the ECF added microstructure in the different examples shown here. This investigation shows that hybrid tooling with ECF is a time saving approach to add microstructures with the ECF-process into pre-milled moulds. Therefore hybrid tooling has a high potential to become one of the leading techniques to manufacture cavities, e.g. for micro moulds in stainless steel.