An Adaptive STEP-NC Interpreter for Feature-Based Machining on EMCO Mill

Abstract

Computer numerical controlled (CNC) machine tools have been developed for machining parts with complex shapes since the 1950s. The data model stipulated by ISO (International Organisation for Standardisation) 6983, otherwise known as G-code, was developed to program and control such machine tools. This standard has led to a bottle neck situation of total Computeraided Design (CAD)/Computer-aided Manufacturing (CAM) integration and data exchange between different parties. The development of ISO10303, commonly known as STandard of Exchange of Product model data (STEP), has shown true benefits and possibilities in terms of standard form of data exchange among the whole product process chain. However, this still left a gap of data transmission between CAD/CAM systems and CNCs in order to achieve a total interoperable manufacturing environment, hence, the development of ISO 14649 (STEP-NC). Unlike G-code, STEP-NC specifies the machining processes based on the machining features. The information contained in a STEP-NC file can be transferred to an intelligent controller in order to create the suitable tool-path based on the parameters available. Since the tool-path generation is achieved by the controller and STEP-NC provides high-level data in a formal standardized data format, it becomes totally transferable across different systems. Researchers have focused on different ways to enable deployment of STEP-NC standard on modern CNC architecture. The indirect programming environment was developed based on the lowest level of integration between STEP-NC and CNC machine which provided limited advantages over G-code. The interpreted programming environment integrates STEP-NC data with CNCs at a deeper level. Instead of using a G-code program, the controller takes cutter location (CL) commands directly in order to perform the required machining tasks. The adaptive programming environment is considered the ultimate solution for STEP-NC enabled CNC machining. In this case, the controller is intelligent enough to process STEP-NC files and generate the process data necessary to perform the machining. Based on the three levels of enabling integrations between STEP-NC and modern CNCs, the interpreted programming method was considered in this research. Because it is conducive to emerge the advantages of STEP-NC concept, and show how manufacturing industries can quickly adopt STEP-NC. In this research, an EMCO Concept Mill 105 with a remote control station was chosen. The CNC machine was connected with the remote control station by an Ethernet cable. The program running on the remote control station was WinNC running in a Windows XP environment. In order to directly program the EMCO Concept Mill 105 and prove STEP-NC data model’s capabilities for adaptive and intelligence control, investigation of STEP-NC data model was carried out and method of automatically processing a STEP-NC (Part 21) file was developed. The network communication management method between the CNC machine and the control station was inherited from previous research achievements. The outcome of this research was a “plug and play” software program called “Adaptive STEP-NC Interpreter” which was capable of processing STEP-NC (Part 21) files and generating tool-path data based on the available cutting tool information. The program was also capable to re-schedule the operation sequences to achieve a minimum machining time for machining some of the STEP-NC features, e.g. plannar_face, closed_pocket and round_hole. For further study, a more user-friendly interface is to be designed as well as algorithms to handle the rest of the STEP-NC features. In addition, the ability of automatically extracting and processing the available cutting tool information from the CNC machine is to be further investigated. It is a necessary input for the system to optimise tool-path generation and operation sequences with a goal of achieving the maximum manufacturing efficiency.