In the aerospace industry, composite materials have emerged on the fuselage, wings, vertical tail and control surfaces to a much greater degree over the last few years. Coast Composites Inc., part of the UK-based Hampson Industries Plc, supplies Invar tooling, as well as resin transfer molds and mandrels used in the composite lay-up and manufacture of today’s advanced flight critical aerospace structures. On the large, long bed CNC gantry mills used at its main facility in Irvine, California, the company claims high accuracy on even the longest wing skins. On its largest CNC mill, a German-built Handtmann five-axis machine that uses twin Siemens Sinumerik 840D numerical controls, accuracies are to +/- 0.003 in. on the longest runs. The Handtmann gantry mill can accommodate structures to 22 ft wide x 75 ft long x 84 in. high.

“Even though Invar tooling is the industry standard for composite lay-up, owing to its low coefficient of thermal expansion, you still get thermal growth over the long distance runs we process,” said Paul Walsh, president, Coast Composites.

To maintain accurate machining even with thermal growth, Coast engineers developed a temperature compensation system to adjust the go-to points from the control for real-time temperature on the machine and the work piece. The data covered all aspects of machining, from material composition to acceleration/deceleration mapping and the temperature variations over the largest pieces and longest machine cycles.

In the temperature compensation system, laser tracking operates in tandem with Valisys inspection software. A Siemens CNC engineer wrote the machine tool inspection interface software. The CNC runs real-time inspections and data analysis, essentially turning every machine tool into its own coordinate measuring machine. The laser tracker is now used primarily for final checking.

http://www.designworldonline.com/articles/6963/10/Custom-CNC-Turns-Every-Machine-into-a-CMM.aspx