摘要
数控技术诞生50多年来,已经取得了很大的发展。传统的数控程序是基于ISO 6983标准,即采用G&M代码描述如何加工,其本质是面向过程的,传递到CNC的数控程序丢失了高层信息,如被加工零件的三维几何信息,公差信息和表面粗糙度等,使得CNC系统与上游的CAD/CAPP/CAM系统之间不能实现完整的信息传递。STEP-NC是STEP在制造领域的扩展,具有STEP相同的几何描述形式。STEP-NC的出现打破了数字化制造过程中CAX与CNC之间信息传输的瓶颈,使从设计到现场制造之间的信息双向高速传输成为可能,为集成制造技术的发展提供了基础。
本论文首先描述了STEP标准的体系结构和分析了STEP-NC标准的数据模型。对STEP-NC程序生成技术进行了研究,包括EXPRESS数据类型与C++和SQL Server数据类型之间映射规则的建立、STEP AP 203文件特征识别技术、宏观工艺规划方法、STEP-NC文件输出等,并探索与CAD/CAPP集成。
基于开放式体系和模块化的思想,建立了STEP-NC数控系统的功能结构模型,包括数控程序解释器、微观工艺规划、运动控制等模块。解释器将程序中的实体实例信息映射到内存中;微观工艺规划对工艺参数、机床功能进行显示、匹配和具体化,并智能在线生成刀具轨迹;运动控制根据刀位文件并调用插补算法控制机床按工步运行。
研究了基于STEP-NC二轴半制造特征的平面、孔和型腔的刀具路径生成算法。基于.NET平台,采用Visual C++编程语言开发了STEP-NC数控铣削系统原型软件。结合具体实例,展示了原型软件读取STEP-NC程序、语法检查、微观工艺规划和刀轨仿真等功能。在三轴数控铣床上进行了加工试验,结果验证了原型软件的可行性和CAPP/CNC之间的集成。
NC technology has achieved great development since it was born more than 50 years ago. Conventional programming for numerical controlled machine tools is based on ISO 6983( G&M Codes) which is process-oriented, so high level information such as 3D geometry, tolerance information and surface roughness, will lose when NC program is transferred to the CNC. Information can not be completely transferred between CNC system and CAD/CAPP/CAM. STEP-NC is an extension of STEP standard in manufacturing field, which has the same geometric description as STEP. STEP-NC has broken the bottle-neck of the information transmission between CAX and CNC in digital manufacturing, and become the foundation of CIMS(computer integrated manufacturing system).
Firstly, the architecture of the STEP standard was described, and STEP-NC data model was analysed. Then the techniques to generate STEP-NC programs were researched, which included the establishment of mapping rules from EXPRESS data types to C++ language and SQL Server data types, feature recognition technology of STEP AP 203 files, macro process planning methods, STEP-NC file output, and CAD / CAPP integration.
Based on open architecture and modular methodology, functional framework of STEP-NC standard-based milling CNC system was proposed, which included NC program interpreter, micro process planning module, motion control module. The interpreter mapped the information in the entity instances of program into memory. The micro process planning module was used to display, match and specify process parameters, machine tool functions, and on-line generate tool path intelligently. The motion control module called the interpolation algorithm according to the cutter location file,and drove machines in steps.
Tool paths for planar faces, holes and cavities based on two5D manufacturing features in STEP-NC were investigated. Based on .NET platform, STEP-NC-compliant CNC milling system prototype was developed in Visual C++ language. STEP-NC file read, syntax check, micro process planning and tool path simulation were illustrated for the prototype software by examples. Tests were carried out in a three-axis CNC milling machine, and the feasibility of the prototype software and CAPP / CNC integration were verified.
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