Research On Tool Path Planning Approach For Five-Axis Machining Based On STEP-NC

As the times progress and society advances, modern manufacturing drives new requirements for numerical control technology. Prized for its special and irreplaceable advantage, five-axis NC machining has been promoted and caught redoubled attention from NC technology field. STEP-NC (STEP-Compliant Data Interface for Numeric Controls) is the extension of STEP (STandard for Exchange of Product model data) standard in manufacturing field, and denotes a new developing direction of NC technology. If we compare the NC technology to a huge ship, then STEP-NC would be its rudder and the five-axis machining technology would be one of its most powerful engines.Supported by the major mechanical and electrical equipment special project of zhejiang province: "Control system of superior grade NC machine tools (2006C11067)", this research theme combined STEP-NC and five-axis machining technology into an integrated whole, investigated the planning approach and application of five-axis machining technology under new technical conditions with STEP-NC. The goal of this investigation was groping a way to propel STEP-NC practicality and lower the difficulty of five-axis machining applications in future.STEP-NC is improving and developing as a Draft International Standard of ISO. Now, STEP-NC has no concrete data model for five-axis free-form surface machining and no research puts forward detailed approaches for five-axis machining application based on STEP-NC. Thus, defining corresponding data model for five-axis machining should be a precondition. Based on analyzing the three-axis machining data model of ISO 14649 Part 11 and studied the characteristics of five-axis machining, a new STEP-NC data model of five-axis milling was built and used as the foundation of five-axis machining application based on STEP-NC.Free-form surfaces and curves are familiar objects in five-axis machining and described as the uniform NURBS in STEP-NC. A new tool path planning method for five-axis milling called Machining Region Parallel Planning (MRPP) approach was proposed in this paper. The developed approach was devised to treat with part surfaces described as NURBS and aimed to improve the machining efficiency of the tool paths. MRPP method was different from other conventional five-axis tool paths generation methods in mode of tool path generation and calculation. Not working from any boundary of the part surface with sequencing each tool path, it used iterative-searching algorithm and hardware-level multithreading parallel algorithm to improve the calculated performance and quality of tool paths generated. Based on above work, the STEP-NC demonstrational application platform was built by following the principle of open architecture, modularization and extensibility. It was a part of primary work to design and implement the software system of this platform. By independently developing the XML drive module and the plug-in support system, our STEP-NC demonstrational application platform could work as an advanced experiment environment for STEP-NC technology with high degree of modularization and extensibility. This part of work also discussed the design and implement method of the STEP-NC program interpret module and the tool-path planning module.The experimental researches of MRPP algorithm performance characteristics and five-axis milling tool path planning application base on STEP-NC were carried out on the STEP-NC demonstrational application platform. The algorithm performance characteristics experiment analyzed and compared the running results of MRPP algorithm and a common serial algorithm. The experiment of five-axis milling tool path planning application verified the validity and practicability of STEP-NC data model for five-axis milling and STEP-NC demonstrational application platform. The comparative analysis of the quality and efficiency of tool paths generated by MRPP approach and tradition iso-parametric approach was also put up in the experiment.