Research On Key Technologies Of Reconfigurable Automatic Programming System In WEDM

Intelligence and green machining, reconfigurable and open architecture will be the development trends for WEDM machine tools, its controlling system and automatic programming system in the future decades. Based on the home market research of the low-speed WEDM machine tools, a research project, named Research and Development of Reconfigurable WEDM Machine Tools, was brought forward under the support of Suzhou Changfeng Co. Ltd in May 2001. As an important sub-project of the research project, a reconfigurable automatic programming system for WEDM, named NH-WAPS1.0, has been developed based on a famous geometric modeling engine, i.e. ACIS, from Spatial Technology Inc. In this dissertation, some key technologies used in NH-WAPS1.0 are summarized as follows: 1. Based on the research of the previous architectures of CAD/CAM systems, a component-based, double-bus architecture, aiming at openness, integration and efficiency of CAD/CAM system for WEDM is proposed. In the architecture, the ACIS geometry bus is in charge of ACIS geometry transfer between different components, and the other bus deals with non-geometry data transfer such as process parameters, code type of NC program, etc. With the separation of non-geometry data from ACIS geometry data and the effective communication between the two buses, CAD/CAM system with the proposed architecture has higher running efficiency, more reconfigurability and maintainability, which has been proved in NH-WAPS1.0. 2. With the WEDM used in more and more fields, much more demands of cutting Chinese characters in WEDM rise up increasingly. But the wide application of WEDM in Chinese characters cutting is heavily restraint by the outline cross of some extracted Chinese character glyphs. Based on the use of geometry topology between various ACIS geometric entities, an algorithm, which can trim the cross outlines automatically in the extracted Chinese character glyphs, is given to meet the process characteristics of traditional WEDM that only continuous ruled surface patches without self-intersection can be machining. 3. In the generation of the toolpath for commercially available 4-axis WEDM system, both the directrices of each ruled surface must be approximated by a series of line segments synchronously. As long as the line segments are sufficiently small, the resulting shape can approximate the desired cut ruled surface to an acceptable accuracy. It is however more efficient if we can produce the toolpath such that few larger subpatches are generated in the flat regions of a ruled surface while many smaller subpatches are generated in the curved regions. In order to achieve this, a subdivision algorithm, named Equal-error Synchro-linear Approximation, is presented in this dissertation, which can reduce the number of approximating line segments and improve the cutting efficiency of ruled surfaces significantly. 4. Ellipse-offset method is often used for calculation of the wire trajectory from the programmed paths for intricate ruled surfaces in 4-axis WEDM. But the premise that the wire axis parallel to the ruling of ruled surface is not suitable for the non-developable or twisted ruled surface, which is an important type ruled surface machined in 4-axis WEDM. An algorithm, named Virtual Wire Model, is put foreword in this dissertation. With the algorithm, not only can the wire trajectory be calculated accurately, but the over-cutting error of profile, which is inevitable in twisted ruled surface WEDM machining, can also be reduced easily to some extent. 5. Much more efforts are focused on how to show the machining process simultaneously and the machined workpiece vividly in computer simulation, but little attentions are paid on the verification of processability of workpiece in WEDM simulation. Based on the motion analysis of 4-axis WEDM system, a conclusion is drawn that all the maximum inclining angle of wire and the maximum displacements of the machining table and the wire guiding head occur on the vertex of the boundary lines during machining intricate ruled surfaces with...