An ultra precision micro grinding process using PCD tools trued by micro EDM

Mr. Toshihiko Wada and Mr. Takeshi Masaki of Matsushita Electric Industrial Co., Ltd. together with Mr. David W. Davis and Mr. Mark Walter have been selected to make an oral presentation to the American Society for Precision Engineering at the17th Annual Meeting in St. Louis October 20-25, 2002. An abstract of their presentation follows:

An ultra precision micro grinding process using PCD tools trued by micro EDM

Broadband digital networks require micro mechanical components and optical devices. These devices require ultra precision shapes. With such optical devices as optical wave-guides and micro lens arrays, the machining accuracy required is in the sub-micron regime and surface roughness in the nanometric regime. The shapes are not only simple plano surfaces but often three-dimensional microstructures.

There are many technologies for fabricating microstructures such as etching, LIGA and micro EDM. However, the drawbacks to these technologies are limits in materials utilized, shape/form and machining accuracy.

The authors developed a 3-axis machine platform for micro grinding of the above-described devices. The feature and capabilities of the micro grinding method are described along with the Poly Crystalline Diamond (PCD) tool utilized and the micro EDM process implemented to shape and true the PCD tool. When micro grinding, the tool rotation accuracy is critical. By truing the micro tool on the same machine and same linear motion system, it is much easier to achieve high accuracy tool rotation, even if the tool diameter is under 1mm.

The micro EDM process can make any shape tool, which allows one to utilize an optimized tool form thereby permitting fabrication of any three dimensional microstructure which has a tapered shape.

Using PCD as a tool material, it is expected tool wear would be negligible when machining hard materials such as Carbide. As a baseline for this fabrication method, a plano surface made from Carbide was ground using the bottom of a cylindrical PCD tool. Surface finishes were obtained down to Ry=7nm. Secondly, using the side of a cylindrical PCD tool, a cylindrical shape with a width of 84µm and depth of 35µm was machined into the Carbide. The authors further demonstrated that the grinding rate could be improved by controlling the discharge energy during the tool truing/shaping process.

Finally, using a cone shaped PCD tool, a micro V-groove with a width of 20µm was machined on an electro less nickel-plated aspherical surface and plano silicon wafer. Considering these results, the mechanics of this micro grinding process will be compared to general grinding applications and limitations will be discussed.

©2002 Precitech Inc.