Die - casting mold finishing method

In most of the domestic die-casting mold manufacturing enterprises, finishing the method used in general grinding, electrical processing and fitter processing. At this stage to control the parts deformation, internal stress, shape tolerance and dimensional accuracy and many other technical parameters, in the specific production practice, the operation more difficult, but there are still many effective experience is worth learning. ª¥
       1. Die-casting mold finishing process control ª¥
       Die casting mold parts processing, a general guiding ideology is for different materials, different shapes, different technical requirements for adaptive processing, it has a certain plasticity, through the control of processing, to achieve good processing results. ª¥
       According to the appearance of different parts of the shape, the parts can be divided into three categories: shaft, plate and shaped parts, the common process is roughly: rough processing - heat treatment (quenching, quenching and tempering) Processing - fitter (surface treatment) - with processing. ª¥
       1.1 parts heat treatment ª¥
       Parts of the heat treatment process, so that parts required to obtain the required hardness at the same time, the need for internal stress control to ensure that the size of parts processing stability, different materials have different treatment. With the development of mold industry in recent years, the use of the types of materials increased, in addition to Cr12, 40Cr, Cr12MoV, carbide, the work of some of the high strength, stress harsh convex, die, optional new material powder alloy steel , Such as V10, ASP23, etc., such materials have a high thermal stability and good state of the organization. ª¥
       For Cr12MoV as the material of the parts, after the roughing of the quenching process, quenching after the workpiece there is a lot of retention stress, easily lead to finishing or working in the crack, parts quenching should be hot after tempering to eliminate quenching stress. Quenching temperature control at 900-1020 ¡æ, and then cooled to 200-220 ¡æ baked air-cooled, followed by rapid return 220 ¡æ tempering, this method is called a hardening process, you can get a higher strength and wear resistance, for wear As the main failure form of the mold effect is better. Production encountered some corner of the more complex shape of the workpiece, tempering is not enough to eliminate the quenching stress, finishing before the need for stress annealing or multiple aging treatment, the full release of stress. ª¥
       For V10, APS23 and other powder alloy steel parts, because it can withstand high temperature tempering, quenching can be used secondary hardening process, 1050-1080 ¡æ quenching, and then high temperature tempering at 490-520 ¡æ and carried out several times, you can get more High impact toughness and stability, to chipping the main form of failure for the mold is very applicable. The cost of powder alloy steel is higher, but its performance is good, is the formation of a wide range of trends. ª¥
1.2 parts of the grinding process ª¥
       There are three main types of machine tools for grinding: surface grinder, internal and external grinder and tool abrasive. Finishing grinding to strictly control the grinding deformation and grinding cracks, even a very small crack, in the subsequent processing will be used to reveal. Therefore, the grinding of the feed to be small, not large, coolant to full, size tolerance within 0.01mm parts to try to constant temperature grinding. It can be seen from the calculation, 300mm long steel parts, the temperature difference of 3 ¡æ, the material has about 10.8¦Ìm change, 10.8 = 1.2 ¡Á 3 ¡Á 3 (per 100mm deformation of 1.2¦Ìm / ¡æ), the finishing process must be fully considered this A factor of influence. ª¥
       Fine grinding when the choice of a good grinding wheel is very important for high-molybdenum steel mold high molybdenum situation, the choice of GD single crystal corundum grinding wheel is more applicable, when processing carbide, quenching high hardness of the material, the preferred use of organic bonding In recent years, with the application of new materials, CBN grinding wheel, that is, cubic boron nitride grinding wheel show that the diamond grinding wheel, organic binder grinding wheel self-grinding, grinding out the workpiece rough up to Ra = 0.2¦Ìm, Very good processing effect, in the NC molding mill, coordinate grinding machine, CNC internal and external grinder finishing, the effect is better than other types of grinding wheel. Grinding, we should pay attention to the timely repair of grinding wheel, to maintain the sharp wheel, when the wheel passivation, the workpiece surface will be rubbed, squeezed, causing the workpiece surface burns, reduced strength. ª¥
       Most of the processing of plate parts using surface grinding machine processing, often encountered in the processing of a long thin sheet parts, such parts of the processing more difficult. Because of the processing, the magnetic force of the adsorption, the workpiece deformation, close to the table surface (see Figure 1), when you win the workpiece, the workpiece will produce a deformation, the thickness of the same measurement, but parallelism (See Figure 2), grinding with an equal height of the pad in the workpiece below the four-dimensional block to death, when the processing of small infeed, multi-beam knife, after processing a good side, can be Do not have to wait for high block, direct adsorption processing, which can improve the grinding effect, to achieve parallelism requirements.
       Shaft parts with a rotating surface, the processing of widely used internal and external grinder and tool grinder. In the process of processing, the head frame and the top of the equivalent of the bus, if there is a beating problem, the work of the workpiece will also produce this problem, affecting the quality of parts, so before processing to do the top frame and the top of the detection work. When the hole grinding, the coolant to be fully poured into the grinding contact position, in order to facilitate the smooth discharge of grinding. Processing thin-walled shaft parts, it is best to use clamping platform, clamping force can not be too large, or easy in the workpiece circumference on the "inner triangle" deformation. ª¥
      1.3 electric processing control ª¥
       Modern mold factory, can not lack of electrical processing, electrical processing can be all kinds of special-shaped, high hardness parts for processing, it is divided into two kinds of wire cutting and spark. ª¥
       Thread cutting speed up to ¡À 0.003mm, roughness Ra = 0.2¦Ìm. Processing start, we must first check the status of the machine to see the water deionization, water temperature, silk verticality, tension and other factors to ensure good processing status. Wire cutting is a piece of material to remove the processing, which undermines the original stress balance of the workpiece, it is easy to cause stress concentration, especially at the corner, so when R <0.2 (especially sharp corners), should The design department makes suggestions for improvement. Processing of stress concentration method, can use the principle of vector translation, finishing before the first margin of about 1mm, pre-processing of the general shape, and then heat treatment, so that the processing stress in the first release before finishing to ensure thermal stability. ª¥
       When machining the punch, the wire cutting position and the path selection should be carefully considered. As shown in Figure 3, the left side of the workpiece clamping, processing route selection ¢Ù better than the route ¢Ú, because the line ¢Ù workpiece and material clamping parts of the tight connection, processing stability, if the use of route ¢Ú, the first time after the feed Into a wall-like, poor force, affecting the subsequent processing several times. Route ¢Û, with perforated wire processing, the best results. High-precision wire cutting processing, usually cut four times, can guarantee the quality of parts. When processing a taper with a taper, see Figure 4, in the fast and efficient position, the first roughing straight edge, the second side of the taper processing, and then re-processing straight edge, so do not need X section vertical Finishing, only finishing cutting edge straight edge, both to save time and cost savings.
       EDM production of the first electrode, the electrode has a thick, fine of the points. Finishing electrode requirements shape good, the best CNC CNC machine tools to complete. Electrode material selection, the copper electrode is mainly used for general steel processing. Cu-W alloy electrode, the overall performance is good, especially in the process of consumption is significantly smaller than the copper, with a sufficient amount of scouring liquid, it is suitable for difficult processing of materials and cross-sectional shape of complex parts finishing. Ag-W alloy electrode than Cu-W alloy electrode performance is better, but its high price, less resources, generally less used. When the electrode is made, it is necessary to calculate the amount of the gap between the electrode and the number of electrodes. When the large area or heavy electrode is machined, the workpiece and the electrode are clamped firmly to ensure sufficient strength to prevent the machining from loosening. For deep step processing, the loss of the electrode and the discharge due to poor discharge caused by the arc discharge, to be noted.
       1.4 surface treatment and composition ª¥
       Parts of the surface in the processing of leaving a knife marks, wear marks is the stress concentration of the place, is the source of crack propagation, so after the end of the processing, the need for surface hardening parts, grinding through the fitter, handle processing risks. Some of the edges of the workpiece, acute angle, orifice blunt, R. In general, the electroformed surface will produce about 6-10¦Ìm degaussing hardening layer, the color is gray, hardened layer of brittle and with residual stress, before use to fully eliminate the hardening layer, the method for surface polishing, grinding to remove the hardened layer. ª¥
       In the grinding process, the electrical processing process, the workpiece will have a certain magnetization, with a weak magnetic force, very easy to suck some small things, so before assembly, to the workpiece for demagnetization, and use acetic acid to clean the surface. During the assembly process, refer to the assembly drawing, find the parts, and then list the parts of each other between the equipment sequence, list the items should be noted, and then proceed with the assembly of the mold, the general assembly of the first guide column guide sleeve, Frame and convex and concave mold, and then on the gap, in particular, convex and concave mold gap configuration adjustment, the assembly is completed after the implementation of mold testing, write the overall situation report. On the discovery of the problem, you can use the reverse thinking method, that is, from the post-process forward process, from finishing to roughing, one by one inspection, until the crux, to solve the problem