Application of virtual assembly technology to establish three-dimensional model of auto body press line, and through the simulation in the virtual assembly environment to achieve reasonable planning of the assembly line of the press line, can effectively improve the assembly process of the press line, and shorten the assembly cycle of the press line, Improve the assembly quality of the press line and reduce the assembly cost of the press line. Virtual assembly is based on a computer-generated virtual environment, simulates the assembly process of a solid model, and analyzes and validates the assembly process and assembly results. Because the components of the press line of the automobile body are not only bulky and numerous in number, but also their mutual movements are very complicated, the assembly sequence of the stamping equipment and the assembly size between each other are difficult to determine. According to the traditional manual test assembly method, not only time-consuming and labor-intensive, prolonged the assembly cycle of the press line, directly affecting the press production line to put into production on schedule, and sometimes even due to the interference between components can not be completed successfully. In view of the above problems, taking into account the actual situation of the company, this paper applies virtual assembly technology to solve the problem of assembly of body press lines. On the basis of establishing a three-dimensional model library of automotive body stamping lines, a virtual environment was constructed to complete the assembly process of the parts of the stamping line, and simulation results were used to verify the assembly results. Therefore, through real-time information feedback and interaction with the assembly process, the operator can intuitively see his own assembly results, and on this basis, perform interference inspection and layout adjustments among various components, so that real use of virtual reality means to achieve stamping Reasonable planning of line assembly routes. Press line solid modeling The core problem of solid modeling of press lines is to solve how to express and store the data information of parts of the press line in the virtual environment so that it can fully support assembly process planning, assembly analysis and evaluation, and provide the required information data for assembly simulation. . Therefore, the assembly model is the information foundation and prerequisite for virtual assembly. 1. Basic modeling work of stamping line All the computer model formats generated by the modeling work mainly use CATIA V5 files, and can also be created using other CAD systems (such as Pro/E, AutoCAD, UG), etc., and use the neutral file format for conversion. The basic modeling work of the virtual stamping line is shown in Table 1. 2. Establish a virtual stamping line model library Based on the basic work of the stamping line in Table 1, a model library such as a press line assembly library, a stamping library, a mold library, and a terminal pickup library was established. The compositional structure is shown in FIG. 1 . Each model library corresponds to the physical address stored in a folder on the computer. (1) Press Line Assembly Library The press line component library is the main body of the entire virtual press line, including presses, destackers, cleaning machines, centering stations, rotary units, loading and unloading robots, and intermediate trolleys. Because the press structure and space layout are relatively fixed, the size, shape, and relative position are provided by the press manufacturer, and therefore are relatively stable in the subsequent assembly process. (2) Stamping Parts Library Stampings are the object of press work. CAD drawings are provided from the body design department. Typical stampings include exterior body panels and large liners. (3) mold library The mold is determined by the stamped parts. The CAD drawing of the mold is provided by the mold design department. The corresponding mold data file is selected according to the stamping parts. (4) Suction cups, structural parts, etc. of the end-collector magazine constitute the vacuum chuck-type end picker parts. The press units of the adjacent two presses are mainly composed of the following mechanisms: â–¡ A reclaimer manipulator with a vacuum chuck-type end picker that is placed centrally and arranged in the shape of the workpiece and is responsible for removing the workpiece from the last press and placing it on the shuttle car. â–¡ A shuttle car that moves on fixed rails between presses and is responsible for moving the workpiece from the discharge position of the pick-up robot to the pick-up position of the loading robot. â–¡ A loading robot, with the same end picker as the picker, picks up the workpiece from the shuttle and feeds it to the next press station. It can be seen that the end picker is an important actuator for picking and placing stampings. Press line virtual assembly Based on the establishment of each model library of the press line, the three-dimensional space coordinates and structural layout of each component model are adjusted by calling each parameter file and performing virtual assembly, and whether each part model design has a defect is determined by Boolean calculation (whether There is a spatial interference or gap). The space structure of the press structure and the press line is relatively fixed. The mold is embedded in the press. The stamping part is directly called from the stamping part library. According to the dot line constraints, point constraints, face constraints and the like provided by CATIA Axis constraints and other conditions are performed one by one until the assembly is completed. Therefore, this part of the assembly work is simple, and use CATIA macro command to record the assembly process, to achieve a one-time assembly reuse, that is, when starting a new assembly task, directly through the macro command playback complete the assembly of the part, necessary It is appropriate to modify some of the assembly details during playback. The assembly work of the end picker is very complicated. Because the stamping parts are frequently changed according to the requirements of the production plan, different stamping parts need to be picked up by different end pickers. Therefore, secondary development of CATIA is needed to intelligently assist The production line technicians quickly complete the assembly of their corresponding end-user parts for different stampings. This article uses CATIA's VBA secondary development technology to achieve the automatic assembly of the end picker. The flow chart is shown in Figure 2. 1. The operator pulls out the stamping data file from the stamping stock and sets the sucker type and model. 2. The software gives the number of suction cups, the reference size and the position of the suction cup on the workpiece according to the stamping part geometry. The operator adjusts based on the reference size and placement point of the suction cup given by the software. 3. The software generates other structural parts of the end picker, automatically assembles the end picker components, and calculates the sucker force conditions. Sucker force analysis does not pass, repeat the above steps, manually adjust the sucker's reference size and layout. 4. The loading/unloading robot is a mechanism that connects the end picker and the press. The generated end picker is assembled with the loading/unloading robot and the press and Boolean calculation is performed to check if the end picker has spatial interference/gap with other components of the press line, thereby further adjusting the size of the end picker structural member. And space layout. 5. The operator saves the assembly program of the terminal pickup that is given by the software and is adjusted to prepare for further stamping line simulation. The assembly scheme of the end picker also needs to follow the overall simulation verification of the press line, that is, whether the end picker will interfere with other parts of the press line during the work. If no interference occurs during the subsequent stamping line simulation operation and the operation of the end picker, the assembly scheme of the end picker is finally determined. The effect of the automatic assembly process of the end picker is shown in Figure 3. The dialog box in the figure is a control for the operator to input and adjust the model of the suction cup of the end picker and the dimensional parameters of the structure. Simulation of virtual press lines 1, stamping line virtual assembly environment construction The virtual environment is a simulated three-dimensional space built on a computer. It is the basis for the entire virtual assembly system to function. The virtual assembly environment in this paper uses CATIA's Real Time Rendering (real-time modeling) environment module. Its content is shown in Figure 4. The stamping line model library is the main content of the virtual environment and is the process of digitizing the stamping line. In order to make the virtual environment system closer to reality, the digital model must be processed in terms of light, color, texture, sound, etc., so that the virtual assembly simulation can be visually realistic. For the rendering process of complex multi-shape entities such as automotive body stamping lines, the overhead of real-time rendering can be reduced by constructing a LOD method for modeling, thereby speeding up the browsing speed. LOD is the English abbreviation of Level of Detail. The main idea is to construct a set of three-dimensional models that can display the number of different polyhedrons based on their distance and visual characteristics in the virtual scene for the same entity. When the model is driven, according to the established rules, the corresponding display hierarchy is selected so as to simplify the model in real time without affecting the purpose of visual effects. 2, the assembly simulation driver The movement elements of the press line mainly include the movement of the slider inside/outside the slider; the movement of the up/down air cushion; the movement of the mold clamping device; the movement of the moving table; the movement of the demolition machine, the washing machine, and the center stage. Using the Kinematics Simulator module in the Digital Mockup function of CATIA, motion constraints are processed for each element of the press line, including the addition of a spherical high pair, a cylindrical high pair, a spherical low pair, and a spherical pin pair. Cylindrical sleeve pairs, rotation pairs, moving pairs and other movement constraints. The point that needs special explanation is, because of the numerous motion mechanisms on the whole press line, the entire press line movement system must be decomposed into many subsystems, and each subsystem must have one part fixed on the ground surface, and other parts and The components constitute various kinds of motion constraints, making the subsystem a spatial motion component whose degree of freedom should be greater than zero and equal to the number of primary motions, and can be checked by CATIA's Mechanism Analysis. When all subsystems pass the inspection, the stamping line assembly simulation is finally combined. To move the virtual press line, it is also necessary to give the movable mechanism a motion law that is consistent with the actual operating conditions. This can be driven by the Kinematics module adding the command operation to the press line motion mechanism. The content includes the time of each motion degree of motion, the size of the motion, and so on. For more complex motion laws, further detailed descriptions can be added by adding the Laws and Speed-Accelerations options so that their movement laws are closer to the actual operating conditions. The Play a Simulation interface in the CATIA Real Time Rendering environment visualizes the entire assembly process driven by the parts. Figure 5 shows the simplified simulation model running process of the assembled press line. 3, verification of virtual assembly results The virtual assembly process is implemented on the computer. The virtual reality is a mapping from the actual process to the computer. It visually simulates the actual process. Through virtual reality to achieve forward-looking predictions of the actual process. The main purpose of establishing a virtual press line is to perform a feasibility analysis of the assembly scheme prior to assembly of the actual press line. Therefore, the verification of the virtual assembly result, that is, the motion interference check between the components of the press line, is the main content of the virtual press line simulation operation. Each component model of the virtual press line is simulated and driven according to the set movement law. If there is interference between the motion units of the press line during the operation, the software will issue a warning and show the interference status in a striking color. If there is no motion interference between the component parts in the simulation run, the assembly result of the virtual press line is verified, and the overall assembly scheme of the press line is output, waiting for the arrival of the next press line assembly task. Conclusion In this paper, the virtual assembly technology is applied to establish the model library of the auto body stamping line, and the simulation of the virtual stamping line assembly is replaced by the original physical model pre-assembly. Press line assembly personnel can achieve reasonable planning of the press line assembly route by means of virtual assembly, which can effectively improve the assembly process of the press line. It has important theories for shortening the assembly cycle of the press line, improving the assembly quality of the press line, and reducing the assembly cost of the press line. Practical significance. PVC Self-Repair High Speed Zipper Door
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