Highest precision and speed in watch manufacturing

Highest precision and speed in watch manufacturing
Marginal Column

3 x faster than conventional machine tools

July 2016


The new milling center for watch components of the Swiss machine tool manufacturer Bumotec works quickly and accurately. The drive and control technology for the company was developed in close partnership with Bosch Rexroth.

With the new NC milling center s100multi, the Swiss company Bumotec has developed a machine that combines precision with impressive production speed − with acceleration values of 3g and an operating speed of 60,000 rpm. It consists of four workstations in a square formation that edit the workpieces simultaneously. For example, watch plates, which are the basis for each mechanical clock mechanism. Different sized holes are usually drilled into these for components, such as bearings or shafts. A process that requires a lot of tool changes and thus entails productivity losses caused by idle time.

Therefore, Bumotec has taken a different approach and mills the holes with exact diameters into the plates, rather than drilling them. This approach reduces the need for tool changes, however it requires the cutter to travel in precise curves – which places high demands on the drive and control technology. Prior to the development of the machine, Bumotec considered the solutions offered by different vendors involving a defined test structure with two axes. “For each path we set a time that had to be reached,” says Dr. Patric Pham, Director of Development at Bumotec. With a special measurement setup, the company subsequently identified the degree of precision. “When certain dynamic values were exceeded, an explosion of errors occurred,” Dr. Pham recalls. “The system comprising the IndraMotion MTX CNC controller and IndraDrive servo drives remained accurate and could even surpass our very demanding specifications.”

Bumotec closely involved Bosch Rexroth in the engineering project throughout the entire development process. One result of this direct cooperation: a drive-technical implementation, which enabled accurate 3-D interpolation in the three linear axes. A prerequisite for this was the combination of high production speed and precision. Thus, both round and oval cutouts or holes can be milled without changing tools and the smallest watch parts processed. With the s100multi, watch manufacturers can economically manufacture small batch sizes without having to make compromises in terms of flexibility.