Process development of CNC machining

Hard cutting is an application field of high-speed cutting technology, that is, single-edged or multi-edged tools are used to process hardened parts. Compared with traditional grinding, it has the advantages of higher efficiency, better flexibility, simple technology, and less investment. It has been used in some applications. The field produces better results. In the automobile industry, the inner hole of 20crmo5 hardened gear (60hrc) is processed with CBN tools instead of grinding. The surface roughness can reach 0.22μm, which has become a new technology promoted by the automobile industry at home and abroad.

The current development of new cutting technology such as high-speed cutting to promote the development of manufacturing technology is a new task facing modern cutting technology. Contemporary high-speed cutting is not a partial increase in cutting speed. It is a cutting speed and advancement that can be achieved only by major advancements in technologies such as CNC machine tools, tool materials, coatings, and tool structures based on overall progress and further innovation in manufacturing technology. Only by doubling the speed can the overall cutting efficiency of the manufacturing industry be significantly improved. Practicing the current level of high-speed cutting, increasing the overall cutting efficiency of my country's machining by 1 to 2 times, and narrowing the gap with industrialized countries, is the goal and face of my country's professionals engaged in cutting and tool technology in the new century. A major challenge.

In the developed countries such as the United States, Germany and Japan, the mold industry is undergoing a large-scale technological revolution in recent years. This is to gradually replace electrical processing equipment with high-speed cutting machine tools to perform precision machining on mold cavities. These machine tools mainly include various high-speed CNC milling machines, machining centers, etc.

At present, the mold processing and manufacturing process mainly focuses on ordinary machining and EDM. Ordinary machine tool processing mold cavity is generally rough machining, semi-finishing and finishing before heat treatment, and then grinding, polishing and polishing, which is time-consuming and laborious. EDM is cutting after annealing, then heat treatment, EDM, and then grinding and polishing.

With the acceleration of the upgrading of consumer products, higher and higher requirements are put forward for the production efficiency and manufacturing quality of molds, and the shortcomings of low production efficiency and unstable quality of EDM molds are gradually exposed. To shorten the manufacturing cycle and reduce costs, mold companies must widely adopt advanced cutting processing technology. The emergence of high-speed cutting technology, which represents advanced manufacturing technology, has met the requirements and characteristics of modern mold processing.

The advantages of high-speed cutting technology for machining molds are mainly reflected in:

(1) The machining efficiency is greatly improved. Not only the machine speed is high, the feed is fast, but the rough and finishing machining can be completed at one time, which greatly improves the production efficiency. Combined with the numerical control technology, the mold manufacturing cycle can be shortened by about 40%.

(2) High-speed cutting molds do not require electrodes, nor subsequent grinding and polishing, and it is easy to automate the processing process, which improves the development speed of molds.

(3) The use of high-speed cutting technology can process hardened steel, and can obtain high surface quality. The surface roughness is lower than Ra0.6μm, and the processing effect of milling instead of grinding is obtained. This not only saves a lot of time, but also improves Finished surface quality.

In order to realize high-speed machining of mold cavity and related parts, the machine tool needs to have the following characteristics:

(1) Large load-bearing and high rigidity. This is because the mold is developing in the direction of large-scale, and the processing equipment must have a large enough table size and working stroke to adapt to it. Nowadays, molds of several tons to dozens of tons are very common, and the work surface of the machine tool is required to bear heavy weight. The strength and hardness of the mold material are high, and the mold cavity is often processed with a small-diameter end mill with a large elongation, so chattering is prone to occur during the processing process. In order to ensure the machining accuracy and surface quality of parts, high-speed machine tools used for mold manufacturing must have high dynamic and static stiffness to improve the positioning accuracy, tracking accuracy and vibration resistance of the machine tool.

(2) High-speed and high-power high-speed machining is the development direction, and high-speed milling has shown great advantages in mold processing. In order to adapt to the processing of the mold cavity surface, the radius of the tool should be smaller than the radius of the small circumference of the cavity surface to avoid "interference" between the tool and the workpiece during the processing. Due to the small diameter of the tool, the spindle speed is required to be very high. The spindle speed of foreign high-speed machining machine tools has reached 40,000 to 100,000 r/min, and the rapid feed rate can reach 30,000 to 60,000 min. The roughing and finishing of cavity and other parts of mold parts are often completed in one clamping of the workpiece, so the spindle power must be large. The spindle power of medium-sized mold milling machines and machining centers is often 10-40kW, and some are even higher.

(3) Multi-axis linkage and good deep cavity comprehensive cutting ability. Most mold cavities are composed of complicated space 6 curved surfaces and grooves, and many molds have deep cavities. In order to achieve high-precision, high-speed and high-stability machining of 3D curved surfaces, the machine tool requires multi-axis linkage and has a good comprehensive cutting ability for deep holes. A five-axis linkage machining center can be used. In addition to the linear motion of the three coordinates, there are also two feed motions of the rotating coordinates. The milling head or worktable can continuously rotate and feed in multi-axis linkage, which is suitable for processing mold parts with complex cavity surfaces.

Composite processing is one of the development directions of mold processing. Although the machining center has been able to combine many machining processes on one machine tool, it is still not fully adaptable to mold processing. It combines machining with electrical, chemical, ultrasonic and other different principles of processing methods, and has more than two process characteristics. The combined processing of the dies will have broad prospects in the future mold manufacturing.