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Abstract: this paper introduces the implementation of Open Inventor in the design and development of sheet metal CAD / CAM software system, and some key technologies in the design and development of the software system, mainly solving the problems of sheet metal unfolding design, optimal layout, NC machining simulation and so on.

With the development of information industry, the design and manufacture of sheet metal parts are also undergoing changes. But at present, the design and manufacture of sheet metal parts depend to a large extent on the manual completion of process designers. Due to the diversity and low efficiency of manual labor, it is difficult to achieve the standardization, efficiency and optimization of sheet metal process, and it is difficult to meet the requirements of shortening the replacement cycle of new products. According to our own needs, the development of sheet metal CAD / CAM integrated software system has become an urgent problem to be solved. This paper mainly introduces the implementation of Open Inventor in software system and some key technologies.

A brief introduction to Open Inventor

Users have to have a lot of man-machine conversation when using CAD / CAM software system, and the medium of man-machine dialogue is graphics, so it is very important to choose a suitable graphics development tool. The graphic development tool chosen in this article is Open Inventor from Mercury. Open Inventor is a graphic tool library developed on the basis of Open GL, which has comprehensive and powerful components for rapid product development, so as to help users shorten the development cycle, optimize development costs and resources, and bring greater development efficiency to users.

Open Inventor is an object-oriented and efficient 3D graphics production system, it also provides a variety of file format interface methods, users can use these methods to read or output graphic objects. Open Inventor encapsulates the information of graphic objects and the operation of graphic objects. In this way, it is easy for users to change color, size, texture, moving position, change perspective, animation, mouse selection, high brightness display and other operations on the created graphic objects.

Second, the overall structure design and key technologies of the system.

1. Graphics processing

The main work of graphics processing is to unfold and loft the input sheet metal graphics to prepare for the following layout and machining simulation. The formation of three-dimensional graphics is obtained by the movement of a two-dimensional section on a certain trajectory. According to this principle, the complex sheet metal graphics are divided into several single shapes, and the data of each body is read, including the section data, the corresponding trajectory data and the topological relation data of the body, which are recorded separately. Unfolding lofting is to find the real length of the trajectory, and then according to the recorded section data, use SoExtrusion0 in Open Inventor to generate the unfold drawing of the split body, and then lay the unfold drawing of the split body on the same plane according to the topological relation data to form the unfold drawing of the original sheet metal figure.

Fig. 1 overall structure diagram of the system

2. Layout treatment

The layout and blanking algorithm of sheet metal is the cutting problem (Cutting Stock Problem, CSP), that is, how to arrange the plane graphics of different shapes on one or more rectangles without overlap to make the area utilization of these graphics the highest. This problem belongs to NP-complete problem, and it is also a difficult problem of NP. It is very difficult to find the optimal solution, and approximate algorithms are mainly used to solve some problems.

At present, the common approximate algorithms are genetic algorithm, ant algorithm, simulated annealing algorithm, greedy algorithm and so on. These algorithms are complex and inefficient by conventional methods, so we can use the powerful numerical calculation function of Matlab and mixed programming with VC + +. The m file is converted into C / C++ code file by the Maflab compiler and the necessary libraries are generated, and then the application program that can be executed independently is generated by the VC++ compiler. In this way, the library functions in it can be directly called to generate and distribute the executable file which does not depend on Matlab.

3. Simulation processing module

Simulation machining is mainly divided into machining process simulation and NC instruction output. The machining process is the process of removing materials. Using the subtraction operation of Boolean operation and setting the time function with So Timer Sensor () in Open Inventor, the Boolean subtraction operation can be completed in every time period. The Boolean operation can use So Bool Operation (), and each action is connected to form the whole processing process. The output NC code can only be machined in accordance with the requirements of the CNC system in the CNC machine tool. Different CNC systems have different requirements for writing NC code, but the tool path is the same. For this reason, the post-processing program is set to read the tool path data, and then converted into the corresponding NC code according to the requirements of the CNC system.

III. Concluding remarks

In practical application, the system improves the design efficiency, optimizes layout and blanking, enhances the predictability of product manufacturing, and shortens the cycle of products from design to manufacturing. it has important practical significance and application value for popularizing digital design and manufacturing of products and improving the competitiveness of products in the market. And other software platforms (such as Pro / e) can import the graphic files output by the system for other analysis, and the NC code generated by the system can be input to the corresponding CNC machine tools for NC machining. This article is from Yuyun sheet Metal Software. For more details, please click: www.bjmes.cn

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