How much do you know about finishing in mold making?
A mold is made up of many parts, the quality of the parts directly affects the quality of the mold, and the final quality of the parts is guaranteed by finishing, so it is important to control the finishing. In most of the domestic mold manufacturing enterprises, the finishing stage of the method is generally grinding, electrical machining and fitter processing. In this stage, many technical parameters such as deformation, internal stress, shape tolerance and dimensional accuracy should be well controlled. In the concrete production practice, it is more difficult to operate, but there are still many effective experience methods worth learning from.
Mold parts processing, according to the appearance of the parts of different shapes, parts can be roughly divided into three categories: plate, special-shaped parts and shaft, its common process is roughly: rough machining - heat treatment (quenching, quenching and tempering) - fine grinding - electrical processing - fitter (surface treatment) - combined processing.
1 Heat treatment of parts
The heat treatment process of parts, in order to make the parts to obtain the required hardness at the same time, but also need to control the internal stress, to ensure the stability of the dimensions of parts processing, different materials have different processing methods. With the development of die and mould industry in recent years, the types of materials used have increased. In addition to Cr12, 40Cr, Cr12MoV and cemented carbide, new materials such as powder alloy steel, such as V10 and Asp23, can be selected for some convex and concave dies with large working intensity and harsh stress. This kind of material has high thermal stability and good organization state.
For parts made of Cr12MoV, quenching treatment is carried out after rough machining. There is a large residual stress in the workpiece after quenching, which is easy to lead to fine machining or cracking at work. After quenching, the parts should be tempered while hot to eliminate the quenching stress. The quenching temperature is controlled at 900-1020℃, and then cooled to 200-220℃, and then quickly returned to the furnace for 220℃ tempering. This method is called the primary hardening process, which can obtain higher strength and wear resistance, and the effect is better for the mold with wear as the main form of failure. In the production of some workpiece with many corners and complex shapes, tempering is not enough to eliminate the quenching stress. Before finishing, stress relieving annealing or multiple aging treatments are needed to fully release stress.
For V10, APS23 and other powder alloy steel parts, because of its ability to withstand high temperature tempering, quenching can adopt the secondary hardening process, 1050-1080℃ quenching, then using 490-520℃ high temperature tempering and repeated, can obtain higher impact toughness and stability, is very suitable for the collapse of the blade as the main form of failure of the mold. Powder alloy steel has a high cost, but its performance is good, and it is forming a trend of wide application.
Grinding of parts
There are three main types of machine tools used in grinding: surface grinders, internal and external cylindrical grinders and tool grinders. Grinding deformation and grinding cracks should be strictly controlled when finishing grinding. Even very small cracks will be exposed in the subsequent processing. Therefore, the feed of fine grinding should be small, not large, the coolant should be sufficient, and the parts with the size tolerance within 0.01mm should be kept at a constant temperature as far as possible. According to the calculation, when the temperature difference of 300mm long steel is 3℃, the material changes about 10.8μm, 10.8=1.2×3×3(the deformation is 1.2μm/℃ for every 100mm). The influence of this factor should be fully considered in each finishing process.
Fine grinding when it is very important to choose the appropriate grinding wheel, in view of the condition of the die steel with high vanadium high molybdenum, GD single crystal alumina grinding wheel is applicable, when processing hard alloy, high quenching hardness of the material, the first diamond grinding wheel using organic binder, organic binder grinding wheel from sharpen sex good, grinding the workpiece roughness of Ra = 0.2 mu m, in recent years, With the application of new materials, CBN grinding wheel, also known as cubic borax nitride wheel, shows very good processing effect. It is better than other kinds of grinding wheels when finishing on CNC forming grinder, coordinate grinder, CNC internal and external grinding machine. In the grinding process, attention should be paid to dressing the grinding wheel in time to keep the sharpness of the grinding wheel. When the grinding wheel is passivated, it will slip and squeeze on the surface of the workpiece, resulting in the surface burn of the workpiece and the reduction of its strength.
Plate parts processing most of the surface grinding machine processing, often encountered in the processing of a long and thin sheet parts, such parts of the processing is more difficult. Because when processing, under the effect of magnetic adsorption, the workpiece deformation, close to the surface of workbench, after winning artifacts, reply again will produce deformation of workpiece, thickness measurement is consistent, but the degree of parallelism can not meet the requirements, the solution can be used to separate magnetic grinding method, starting with a contour grinding block cushion below the artifacts, all stop darkly, small feed processing, laser scalpel, processing after good side, Can not pad such as high block, direct adsorption processing, which can improve the grinding effect, to meet the requirements of parallelism.
Shaft parts with rotary surface, its processing is widely used inside and outside cylindrical grinder and tool grinder. In the process of processing, the head frame and the top are equivalent to the bus. If there is a jump problem, the workpiece processed will also produce this problem, which affects the quality of the parts. Therefore, the head frame and the top should be tested well before processing. When grinding the inner hole, the coolant should be fully poured to the grinding contact position to facilitate the smooth discharge of the grinding. Processing thin-walled shaft parts, the best use of clamping process table, clamping force should not be too large, otherwise it is easy to produce "inner triangle" deformation on the circumference of the workpiece.
Electrical machining control
Modern die factory, can not lack of electrical processing, electrical processing can be processed on all kinds of special-shaped, high hardness parts, it is divided into two kinds of wire cutting and electric spark.
The machining accuracy of slow wire cutting is up to ±0.003mm, and the roughness is Ra0.2μm. At the beginning of processing, we should first check the condition of the machine tool, check the deionization degree of water, water temperature, vertical degree of silk, tension and other factors, to ensure a good processing state. Wire cutting processing is the removal of a whole piece of material processing, it destroys 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 be put forward to the design department to improve the suggestion. Processing of stress concentration method, can use the principle of vector translation, finishing before leaving a margin of about 1mm, pre-processing a rough shape, and then heat treatment, so that the processing stress in the finishing before the first release, to ensure thermal stability.
When machining punch, the choice of wire cutting position and path should be carefully considered. The best effect is achieved by drilling and thread processing. High precision wire cutting processing, usually cutting times for four times, can ensure the quality of parts. When machining the die with taper, in the position of fast and efficient, the first rough machining straight edge, the second taper machining, and then finishing straight edge, so that there is no need for vertical finishing of section X, only finishing straight edge of the edge section, which saves time and cost.
EDM first to make electrodes, electrodes are coarse, fine points. Finishing electrodes require good shape conformity, and it is best to complete the machining with CNC CNC machine tools. The material selection of the electrode, the red copper electrode is mainly used for general steel processing. Cu-W alloy electrode, the comprehensive performance is good, especially in the process of processing consumption is significantly smaller than that of copper, with sufficient amount of scour fluid, is very suitable for processing difficult materials and complex section shape finishing. When making electrodes, it is necessary to calculate the amount of electrode gap and the number of electrodes. When large area or heavy electrode processing is carried out, the workpiece and electrode clamping should be firm to ensure that it has enough strength to prevent loosening during processing. When deep step machining is carried out, attention should be paid to the electrode loss and arc discharge caused by poor discharge.
Surface treatment and assembly
The tool marks and abrasion marks left on the surface of parts during processing are the place where the stress is concentrated and the source of crack expansion. Therefore, after processing, the surface of parts needs to be strengthened and the processing hidden trouble is dealt with through grinding by the fitter. Some of the workpiece edge, acute Angle, orifice for blunt, R. Generally, the electromachining surface will produce about 6-10μm of metamorphic hardening layer, the color is gray and white, the hardening layer is brittle and has residual stress, before use to fully eliminate the hardening layer, the method is surface polishing, grinding to remove the hardening layer.
In the grinding process, electrical processing, the workpiece will have a certain magnetization, with weak magnetic force, very easy to suck some small things, so before assembly, to the workpiece for demagnetization treatment, and ethyl acetate cleaning surface. Assembly process, the first to see the assembly drawing, checking the parts, then list the parts order between equipment, list all the matters should be paid attention to, and then to proceed mold assembly, assembly loading first commonly guide pin, guide sleeve, then pretend to die set and convex concave die, and then with the clearance, especially the convex concave die clearance adjustment, equipping assembly should implement the mold after the completion of testing, Write an overall situation report. To the problem that discovers, can adopt the reverse thinking method, namely from the later working procedure to the working procedure, from the fine processing to the rough processing, one by one inspection, until finds out the crux of the problem, solves the problem.
Practice has proved that good finishing process control can effectively reduce the parts out of tolerance and scrap, and effectively improve the first success rate and service life of the die.
The above information is provided by clicking on the open link Mold Manufacture