Coordinate Measuring Machine Guarantees Required Precision for Manufacturing Parts for Wind Turbines

Three-M Tool and Machine Incorporated, a small manufacturing company located in Wixom, Michigan, wanted to expand their business into the growing market for wind energy. They quickly realized that when you have a tool to edge out your competition, that tool quickly becomes a key to your company’s long-term vision.

In 2008, Three-M acquired a contract to manufacture gearbox and forward housings for Clipper Windpower. Until then, they had been using an older DEA gantry system for quality inspection of other large parts. The machine’s limited speed and size meant that the new housings could not be measured assembled. Production would have slowed to three units per month instead of the required 16. The search began for a more efficient and capable measuring system.

Three-M did some research with ZEISS since they had positive previous experience with them and were still using their first ZEISS system, a UMC 850, purchased in 1975. In 2005 they bought an additional CMM, a ZEISS CONTURA with a VAST XT active scanning sensor.

They chose a ZEISS MMZ G gantry machine in a configuration that could measure 3 meters vertically; an optimal solution for the inspection of gearbox housings standing upright. The CMM is equipped with the VAST gold probe which is capable of speeds up to 300 points per second. The VAST gold probe also allows scanning with styli up to 800 millimeters long weighing up to 600 grams. Not only did ZEISS have the right machine for the job, but Three-M found them to be very competitive on cost and delivery.

Three-M invested in some of the most accurate, state-of-the-art milling machines to handle the new Clipper project. “These are some of the best milling machines in the USA, but they still are not accurate enough to hold the required tolerances on these parts. We can’t just machine the part to the print right off the milling machine,” states Michael Medwid. True position tolerances on these larger parts are about 25 microns. These new parts, typically made of cast iron, are rough-machined, undersized as three separate castings, assembled together and sent through in-process inspection, making sure screw holes are lined up, then re-machined to print as separate castings and assembled one last time for final inspection. In-process inspection is performed on every 10th part with 100 percent final inspection. The casting would warp out of shape if this process wasn’t followed.