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Home> Industry Information> Process control of precision machining of mold parts

Process control of precision machining of mold parts

May 26, 2020

Process control of precision machining of Mold Parts
Grinding of mold parts
  For the processing of mold parts, the general guiding ideology is to adapt to different mold parts, different materials, different shapes and different technical requirements. There are many options. However, through the control of the processing process, to achieve good processing results and economy is our focus. According to the appearance and shape of the mold parts, the parts can be divided into three categories: shafts, discs, plates and molding heterogeneous parts. The process of these three types of parts is generally: roughing-semi-finishing-(quenching, quenching and tempering)-Precision Grinding-electrical machining-fitter trimming-assembly processing.

  (1) Heat treatment of mold parts

  To obtain the required heat treatment hardness of the mold parts, it is necessary to control the internal heat stress of the parts, so that the dimensional tolerance and geometric tolerance can be stabilized during and after processing of the parts. There are different heat treatment methods for the role of different material parts. The process should consider economics, material hardenability, hardenability, overheat sensitivity and decarburization sensitivity.

  After quenching, the internal stress generally remains in the workpiece, which can easily lead to subsequent finishing or cracking in the work. After the part is quenched, it should be tempered while hot to eliminate the quenching stress. For workpieces with complex shapes and many internal and external corners, tempering is sometimes not enough to eliminate the quenching stress. Before finishing, stress relief annealing or multiple aging treatments are required to fully release the stress. Take different methods according to different requirements.

  (2) Grinding of mold parts

  There are three main types of machine tools used for grinding: surface grinders, internal and external grinders and tool forming grinding machines. When finishing grinding, it is necessary to strictly control the appearance of grinding deformation and grinding cracks, even microscopic cracks on the surface of the workpiece, otherwise it will gradually show up in subsequent work. Therefore, the amount of feed during precision grinding should be small, cooling should be sufficient during grinding, the coolant medium should be selected as much as possible, and the parts with machining allowance within 0.01mm should be ground as constant as possible.

  When grinding the workpiece, be sure to choose the grinding wheel carefully. During grinding, the grinding wheel should be repaired in time to keep the grinding wheel sharp. When the grinding wheel is passivated, it will slip, score, squeeze on the surface of the workpiece, causing burns, micro cracks or grooves on the workpiece surface Most of the parts are processed by surface grinders. When processing long and thin sheet metal parts, there are certain processing difficulties. Before processing, under the strong attraction of the magnetic table of the grinding machine, the workpiece originally had some kind of bending to produce a straight deformation, which was close to the surface of the worktable. However, when there are strict requirements for the thickness of the board, the thickness must be appropriately added according to the comprehensive factors of the workpiece material, shape, cutting processing method, heat treatment method, etc. in the preparation.

  (3) Electrical processing of mold parts

  Modern mold companies have almost no shortage of electrical machining, because electrical machining can effectively process all kinds of special-shaped, various types of cavity or high-hardness parts, so it has become an indispensable processing method in the mold manufacturing and metal processing industries.

  According to the feedback information from the enterprise, the slow-moving wire cutting technology: the accuracy has reached ± 0.002mm, and the roughness Ra = 0.4μm. In order to pursue machining accuracy, after rough machining is completed, machining stress needs to be released. The method of dealing with stress concentration can use the principle of vector translation. Before finishing, leave a margin of 0.8-0.9mm, pre-process the approximate shape of the cavity, and then heat-treat, so that the processing stress is released as much as possible before finishing to ensure heat stability.

  For EDM processing, coarse and fine electrodes are made separately. The precision machining electrode requires that the shape conforms to the cavity, and the good precision electrode has been processed with CNC machine tools. For different mold parts, electrode materials should be selected appropriately. When designing electrodes, calculate the amount of electrode gap and the number of electrodes. When performing large-area or heavy-electrode machining, the clamping of the workpiece and the electrode should be stable and have a certain strength to prevent loosening during the machining process. However, the surface after EDM is more difficult to grind than the surface after ordinary machining or heat treatment. Therefore, precise finishing should be used before the end of EDM to remove the hardened thin layer formed on the surface.

  (4) Surface treatment of mold parts

  The content of the molding surface treatment includes no pores on the surface of the steel, uniform hardness, small difference in anisotropic characteristics, low inclusions, and parts where stress concentrations such as knife marks and wear marks are left during processing. Therefore, after the processing is completed, the surface of the parts needs to be strengthened, and the hidden troubles of the processing are dealt with by mechanical polishing, fitter grinding and polishing. Invert blunt edges, sharp angles and orifices of the workpiece. In general, the electro-machined surface will have a metamorphic hardened layer of about 6-10 μm, with an off-white color. The layer is brittle and has residual stress. Before use, the hardened layer must be fully eliminated by surface polishing and polishing off the hardened layer. In order to obtain a high-quality polishing effect, the material, shape, hardness of the workpiece and the surface quality of the cutting process must be fully considered. There must be high-quality polishing tools, high-quality polishing materials, correct polishing procedures, and rigorous personnel Quality, good clean environment.

  Conclusion: Numerous practices have proved that mold companies pay attention to the control of the precision machining process of mold parts, which is the long-term and effective way for mold companies to survive and develop. Through process control, it is possible to reduce the excessive tolerance and scrap of parts to a great extent, thereby effectively improving the service life of molds in production and use, and stabilizing product quality has far-reaching significance.

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