Siemens’ machine error compensation scheme goes a step farther

  • 30-Jun-2008 09:57 EDT

Siemens’ Volumetric Compensation System accounts for linear and rotary errors.

As accuracy requirements increase in the aerospace manufacturing industry, machine tool builders and control providers are responding in different ways. For CNC control provider Siemens Energy & Automation, it means taking volumetric compensation to new heights.

Tim Shafer, the company’s Aerospace Industry Director, noted that tolerances are becoming especially tight for military programs. For Lockheed Martin's F-35 Joint Strike Fighter, for example, tolerance is about five thousands of an inch (compared to about 20 or 30 thousandths in the commercial sector), he said. “It’s created a huge manufacturing challenge for the F-35 program because, for machine tool manufacturers, mechanically it is extremely difficult to try to achieve the kind of tool tip and tool vector accuracy [required] on a large machine.”

Which is why Siemens’ Volumetric Compensation System (VCS) is an attractive solution. In addition to compensating for 21 possible linear errors in a given machine, the Siemens system addresses rotary errors. With this capability, VCS not only compensates so that a cutting tool meets the material at the right place, it also ensures that the spindle is in the correct orientation, according to Shafer.

Siemens’ VCS is integrated into the company’s control system. No mainline competitor can make that claim, according to Shafer. Non-integrated “black box” solutions are fraught with potential problems, he said.

Shafer noted that in doing the original research on volumetric compensation, the University of Huddersfield in the U.K. used the black box approach—and Siemens control.

Siemens has two pilot programs for VCS evaluation. One is at the National Center for Advanced Manufacturing (NCAM) based at NASAMichoud facilities in New Orleans. NCAM is a partnership of government, academia, and industry with the goal of fulfilling the technology needs of aerospace and commercial markets. A five-axis gantry-type machining center from Forest Liné will be used for the evaluation. Renishaw is assisting Siemens with calibration work. The other pilot program has been delayed. VCS also has been tested at one U.S. and two European OEMs, said Shafer.

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