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Figure 1 Virtual CNC milling machine structure 
Figure 2 CNC milling machine model 
Figure 3 CNC code processing flow
Numerical Control Milling Simulation Processing Technology in Virtual Manufacturing
Virtual manufacturing uses information technology, simulation technology, and computer technology to comprehensively simulate people, materials, information, and manufacturing processes in real-world manufacturing activities to discover problems that may arise in manufacturing, and take precautionary measures before actual production of products. Achieve one-time manufacturing success, in order to reduce costs, shorten product development cycle and enhance product competitiveness. Due to the rapid development of computer technology and computer graphics, computer simulation technology has been widely used in manufacturing systems. The use of simulation machining to replace or reduce the actual trial cutting work is of great significance for CNC machining.
1. Virtual CNC milling machine architecture
In the establishment of the virtual CNC milling machine model, in order to pursue the immersive realism and surpass the reality of virtuality, the virtual CNC milling machine should meet the following requirements:
(1) A structure similar to a real machine tool to mimic any function of a real machine tool and allow the designer to design and modify the system in an intuitive manner.
(2) It can reflect the realistic processing environment and processing process in a comprehensive and realistic way, and can provide alarm information for collisions and interferences occurring during processing.
(3) has a complete graphical interface.
The perfect graphic interface allows the user to operate the virtual CNC machine as in the real environment, and can completely observe the various states of the machine operation and various machine operating parameters in the form of images, thus maximizing human-machine integration. degree. According to the above analysis, the architecture of the virtual CNC milling machine is analyzed, as shown in Figure 1.
The machining simulation platform of CNC milling machine mainly includes the construction of virtual environment and the motion control of each component of the milling machine. Add the OpenGL code of the milling machine model to the OpenGL application framework and add mouse and keyboard responses to control the overall model of the milling machine. In order to facilitate the user to interact with the virtual environment, you can also add other buttons or toolbars, thus forming a complete virtual environment. The control part of the movement mainly includes the motion control of the milling cutter and the table to achieve the relative movement of the tool and the workpiece.
2. Geometric Modeling Module
The machining simulation platform of CNC milling machine is completed by using VC++ 6.0 combined with OpenGL programming interface. Due to the characteristics of OpenGL itself, complex models like CNC milling machines cannot be created in this environment. In order to get a complete and clear CNC milling machine model in OpenGL environment, firstly build the CNC milling machine model with 3D modeling software Pro/ENGINEER Wildfire2.0, save it as WRL format, and then convert the file format to 3DS format with Deep Exploration. , you can directly read the 3DS file in the program and assemble it. The OpenGL display list technology is used when drawing the machine tool, and each component is generated with an OpenGL display list, which can greatly improve the redraw efficiency and meet the requirements of real-time drawing. Then in the OpenGL programming environment, the code can be recalled to reproduce the 3D model of the CNC milling machine. The complete model of the CNC milling machine is shown in Figure 2.
3. Process Simulation Module
The virtual machining process simulation will describe the analytical model of the machining process combined with the solid model of the workpiece and machine tool. Analytical models in virtual machining can express the physical process of machining, while solid models represent the geometry of the machining process. Therefore, given the process of designing the parts, the machine tools used and the parts used, the following work can be performed on the computer:
(1) Verify the correctness of the tool path obtained from the process specification. In this case, the solid model of the workpiece and the machine model are used to simulate the machining process, and the tool cuts the material on the workpiece along the designed trajectory, thereby making it easy to check where the tool trajectory is unreasonable and to improve it in time.
(2) Verify that the cutting parameters determined in the process specification are reasonable and feasible, and predict whether the selected cutting parameters will lead to some undesired results, such as dimensional tolerance, tremor, tool transition wear and surface roughness values.
(3) Accurately evaluate the merits of a process specification, and based on this evaluation, appropriate processing conditions can be determined to improve or even optimize the process specifications. With virtual machining, the accuracy of the calculation of machining time and machining costs can be improved.
4. NC code parsing module
Since the machining process simulation is driven by the NC program, in the simulation of the machining process, the NC program is first analyzed and interpreted, and the errors are found, the useful information during the simulation of the machining process is extracted, and the NC program is converted into the simulation. Drive data. The computer processing flow of the NC code is shown in Figure 3.
The process is as follows: First, the NC program is read into the computer memory, and the program is subjected to lexical error detection, syntax error detection and logic error detection by the NC code error detector. After the error correction NC program is corrected, it enters the numerical control code translator, calculates the displacement of each coordinate of the machine tool of each time segment, and drives the movement of the model to realize the NC code-driven machining process simulation.
5 Conclusion
The system realizes the simulation of the numerical control machining process through the graphic verification of the input NC machining code and has the following characteristics:
(1) On the basis of the verification and compilation of the NC code, the simulation of the actual CNC machining process is realized by the three-dimensional graphic display of the machine tool, the tool, the fixture and the workpiece.
(2) Simulating the process of tool, workpiece geometry, machining environment and material removal during simulation, eliminating the problems of machine tool cutters, fixture damage and scrapping of parts due to program errors.
(3) The current simulated program line can be displayed in real time during simulation, which is more convenient for the user to check the correctness of the code.
In addition, the system can be used as a manufacturing unit tool in virtual manufacturing to achieve digital production of products, and can also be used to train CNC programmers.