Research On The STEP-NC-Based CNC System

Conventional Programming of numerical controlled machine tools is based on G-Codes (iso6983),no high level information( such as 3D geometry,Process technology and so on) has been included in the NC Program which will be transferred to the CNC. And no information can be feed back to the CAD/CAM/CAPP, so that the empirical knowledge of the workers can,t be used。ISO14649(STEP-NC) extends the current STEP standard into the application area of manufacturing。STEP-NC,which is based on the STEP standard and uses the same geometry description method , increases the efficiency and flexibility of NC Programming by means of a strucuterd,object-oriented machining description。Therefore,STEP-NC-based NC program will not only transfer the 3D geometry for the machined workpiece into CNC,but also the Process technology and machining information,which will overcome lots of disadvantage of the conventional ISO 6983-based NC Program。The outstanding characteristic of STEP-NC-based NC Program is that it is neutral and not specific to any CNC system。Based on the newest internationalstandard—STEP-NC,the author studies the key technology of NC mill machining,the main contents are described as follows:1.The shortcomings of conventional NC progrmaming data interface—ISO 6983 was pointed out.The develop course of product data exchange has been analyzed,and it was pointed out that STEP-NC would be used as new NC Programming data interface replacing ISO 6983, which has been used more than 50 years.2.The rationale and framework of STEP-NC data model was introduced,and the relationship between STEP-NC and STEP was analyzed.The principle difference of STEP-NC, which was used as Application Reference Model,and AP238,which was used as application Interpret Model,was pointed out.And the difficulty of using STEP-NC or AP238 as implementation method was studied.Three kinds of different implementation method were introduced and compared,and ISO Part21 physical file format was adopted as implementation method in this dissertation.3.The generating process of STEP-NC Part 21 Physical file was studied, which was composed of three Parts: feature recognition,macro process planning and mapping into Part21 Physical file.STEP-NC manufacture feature was recognized from the input AP203 Physical file, and was used as the input of macro process planning.4.STEP-NC numerical controlled Program interpreter was studied,including mapping from EXPRESS to C++,grammar and syntax analysis,etc. A kind of memory_based NC Program interpreting method was proposed. Workingstep was used as basic unit,arithmetic of generating Process sequence tree was studied.