Standard enables data flow between CNC, CAD/CAM

-- Control Engineering, 12/9/2004

Developed 40 years ago, the ISO 6983/RS274D language for computerized numerical control (CNC) programs was designed for an era when paper tape was the most popular medium for moving data between computers. Back then, the logic necessary to process simple commands was barely affordable for a CNC machine. Until now, even though the average microprocessor can easily process 3D data, NC programming remained the only function in the design-to-manufacturing process that didn’t use full fidelity 3D information.

To remedy this situation, AP-238—the official ISO STEP (STandard for the Exchange of Product model data) number for the STEP-NC standard—has been introduced. In AP-238, the information required to control a machine is linked to the information created by CAD and CAM systems to create an independent, fully documented CNC control file. This will make developing a CNC part program more efficient because the machining instructions can be defined more concisely. CNCs can also use this richer information to optimize and check a part program for the tooling available at the time of manufacturing, instead of having it fixed at the time of planning. An AP-238 data set describes all that the shop floor needs to know about the product and the process including all the required tolerances, so drawings will no longer be required on the shop floor.

The activity model and information requirements behind AP-238 have been standardized separately as ISO 14649. These models were originally developed by a joint European and Japanese project. The first model they produced was for the data necessary to control milling machines. The leading developers of the milling model represented Siemens, the Universities of Aachen and Stuttgart in Germany, Komatsu and Fanuc in Japan, and Heidenhein in Switzerland.

The Draft International Standard of AP-238 is now available on the TC184-SC4 documents Web site as wg3n1534, and will soon be circulated by the various national standards organizations. For those who do not have access to the SC4 site, you can view it courtesy of STEP Tools by clicking here.

—David Greenfield, editorial director, Control Engineering, dgreenfield@reedbusiness.com