3 mold automatic control <br> <br> only established from product design, process planning, NC programming to the global concept of milling, ie, CAD / CAM technology are integrated to be able to provide a suitable surface for the free five-axis milling The way to achieve. Mold manufacturers with five-axis linkage machines have criticized the practice of using only CAM technology. In practice, it can be found that a small part of the automobile manufacturing supporting factory is directly processed by CNC milling using CAD data. Most of the workpiece geometry data is provided by the customer in the form of a prototype or design model. Not a few years ago, the automotive industry began to demand a complete abandonment of the use of prototypes and models to make molds, although this goal is not easy to achieve in a short time.
Compared with the average machining accuracy of copy milling of 0.6mm, CNC milling has higher precision and can be controlled within 0.2mm. Elimination of profiling and mold painting with scraping also prevents cumulative errors. For example, a change in temperature alone can cause a dimensional change of more than 0.1 mm on a large sample. If the finished model or its parts are not repairable and need to be replaced, the machining accuracy of the joint surface is required to be within 5 μm, which can only be obtained by direct CNC milling. Practical experience has shown that the surface generated in this way can reduce the amount of manual post-processing work by 50%. These practical advantages are decisive for mold manufacturing. Therefore, more and more manufacturers are directly applying digital control technology to manufacture all molds.
After hard work, like the three-axis linkage CNC, the five-axis NC system in modern mold manufacturing allows the operator to feed the machine through the console knob to increase the speed of the tool as much as possible. In the face of user complaints, when the NC machining program is normally generated via CAD data, CAM processor, NC processor and post-processor, the data required for subsequent editing and compensation no longer exists in the machine control system, and the control system is manufactured. Manufacturers are changing the way to transfer all CAD data directly to the CNC system for use. In this way, the NC system is capable of three-dimensional tool compensation even though the NC machining program does not include information data relating to the normal vector of the cutting point. In addition, it is also possible to easily change the process contents such as machining strategy, tool path, tool used, workpiece position, etc. directly next to the machine. Only this technical improvement can double the speed of the entire process of CNC machining.
In view of the speed and accuracy of the NC programming language affecting the operation of the process, there are manufacturers who put the improvement goal on the CAD description that allows the NC system to directly process the surface, that is, without intermediate programming of the NC programming language. As a result, the normal time of the NC system processing block is reduced to 2 ms, and the shortest time can be 0.5 ms. In this way, the speed of the NC system is no longer a bottleneck, and it is necessary to tow the heavy workpiece, that is, the feed drive system of the automobile mold to become a weak link.
Because CAD data is often flawed or incomplete, NC system manufacturers have tried to facilitate user intervention in the CAM process to find and correct incorrect data, but tool compensation is still done by the NC system. In addition to compensating for the tool length, the radius of the small, reground tool can be compensated for within tight tolerances and there is no need to adapt the tool path. The NC systems currently available from these manufacturers can compensate for tool length and workpiece position for 5-axis simultaneous milling.
In addition, the speed pre-control (forward-looking) function, which is important for mold manufacturing, has become a standard feature of modern CNC systems. This function is set up to allow the NC system to pre-process multiple upcoming blocks so that the feed acceleration and tool path speed are adapted to the contour of the workpiece being milled, so that the feed rate is not reduced at the end of each block. To zero. The free surface that is common in mold making often requires intermediate interpolation points during processing. At this time, the forward-looking function can be used to control the machine to produce smooth trajectory movement while maintaining a high cutting speed. Some manufacturers have further developed and successfully equipped with NC systems that are suitable for forward-looking functions, and can compensate for machine errors during operation. On the other hand, due to the large amount of calculation required, the current machine tool control system cannot find the processing interference through online calculation, and it is necessary to continue to improve in the future.
4 Conclusion <br> <br> five-axis high speed milling technology in automobile manufacturing molds used widely to promote the development of auto mold manufacturing. The application of five-axis milling requires attention to the applicable workpiece shape, advantageous machining options and suitable tools. Only through the comprehensive use of computer-aided design/computer-aided manufacturing technology, especially the efforts to strengthen the functions of the computer numerical control system of the machine tool, can the full advantage of the five-axis high-speed milling process be achieved.
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