<title>Feature-based machining system using STEP</title>

Abstract

Discrete part manufacturing flows from a design phase in which product information is defined to a manufacturing phase in which the processes are planned and executed. Process planning typically culminates with the generation of numerical control (NC) programs for specific equipment, such as machining centers or turning centers. These NC programs are written in the dialects of the various equipment vendors, for the specific mechanical configuration of the target machine. As a result, porting programs between machines is difficult. Worse, NC programs contain little if any of the product design information. The lack of this information at run time limits any adaptive control that could direct the process so that final parts more closely conform to the original design. The authors have developed a prototype machining system in which product and process data replaces NC programs at run time. In this system, information models built in the EXPRESS information modeling language are used for all types of data, and data files are all in STEP Part 21 format; each Part 21 file is understandable by making reference to one of the EXPRESS models. The EXPRESS schemas of tool models proposed to ISO is used. An EXPRESS schema for ALPS (A Language for Process Specification, developed by NIST) is used for process planning. Ad hoc EXPRESS schemas are used for machining options, setup descriptions, shop and workstation operations, and tool usage rules. The system has been demonstrated on a three-axis machining center.