The Approach To The CAD System Of The Typical Pipe Intersecting Curve Development

With the quick development of computer technology, computer aided design is widely applied to all kinds of fields. The intersectional pipe fittings are used in such industries as Chemical, water supply and drainage, petroleum and building, etc. For the development of intersecting curve, its traditional method is the geometry drawing method, which is not only complex but also time taking, in addition, the precision of the developed curve are low. With the second-development of AutoCAD, the development of the intersecting curve between the cylinders pipe and the conical pipe CAD (computer aided design) is established in this system, which is visible and parametric. The main contents covered by this paper are as follows.1. Base on the theory of analytical spatial geometry, this paper deduces mathematical models for the development of intersecting curve in relation to two cylinder pipes, cylinder and conical pipes as well as two conical pipes. Meantime, the mathematical model of the groove angle and the local dihedral is also deduced.2. This paper discusses how the weld groove and the plate thickness affect the sheet metal manufacture processing, and how to design with reasonable method. The method of weld groove angle is adopted in the system, leading to an improved welding quality and efficiency, and thus saving the welding materials.3. On the platform AutoCAD2004, the code of this system is programmed with Visual Lisp. This software can develop the intersecting curve between the cylinders pipe and the conical pipe. By this software, the coordinates of discrete points on the developed curve are calculated; further, these points are connected continuously so as to obtain a developed intersecting curve, which is up to the required precision. While the intersecting curve is drawn, the groove curve is generated at the same time.4. The interface between computer and operator is developed with DCL, and the meaning of every input parameter is illustrated with sketch map. In this way, data can be input easily and visually. After developed curve is generated, the software will mark with specified dimensions and output relevant curve data.On the basis of practice, this system is proved to have such features as parametric development drawing, fast drawing generation, high precision developed intersecting curves, easy operation and extensive application. According to the generated curves, the digital controlled cutter can produce accurate sheet metal parts efficiently. What is more, the sheet-metal drawing can be generated and dimensions be marked so as to facilitate the production.