Finishing process of mould manufacturer

A mold shell is composed of multiple parts, and the quality of the parts directly affects the quality of the mold shell, and the Z final quality of the parts is also guaranteed by finishing. Therefore, the finishing operation is closely related to the finishing. For most die and mould processing enterprises in China, grinding, electric machining and milling are generally adopted for finishing. In this link, many performance parameters, such as part deformation, thermal stress, dimension tolerance and specification accuracy, should be well controlled. In real life practice, the actual operation is difficult, but there are still many practical work experience methods that are very worthy of reference.

The processing of mold parts can be divided into three categories according to the appearance of the parts: seat, special-shaped parts and shaft parts. The whole process of the same processing technology is roughly rough machining - heat treatment process (quenching, heat treatment) - finishing - milling (surface treatment) - assembly processing.

1、 It is the heat treatment process of parts.

While making the parts reach the specified strength, it is also necessary to operate the thermal stress to ensure the reliability of the specifications when the parts are processed. Different materials have different treatment methods. With the development trend of the die industry in recent years, more and more raw materials are used. In addition to Cr12,40Cr, Cr12MoV and cemented carbide tools, new materials such as V10, ASP23 can be used for some convex cavities with high working strength and strong bearing capacity. These materials have high heat resistance and good mechanical conditions.

Parts made of Cr12MoV shall be quenched after rough machining. After quenching, the workpiece has a lot of residual ground stress, which is very easy to cause cracks in finishing or work. After quenching, the quenching ground stress shall be removed while the parts are hot quenched. The quenching temperature is controlled at 900-1020 ℃, and then it is cooled to 200-220 ℃ for air cooling, and then it is quenched at 220 ℃ quickly. This method is called one time hard primer processing technology, which can obtain high compressive strength and wear resistance. For the mold shell with damage as the main ineffective method, the actual effect is good. In the production and manufacturing process, some workpieces with many corners and complex appearance are encountered, and the ground stress cannot be removed after quenching. Before finishing, the ground stress shall be removed and quenched or tempered for many times to fully release the ground stress.

For V10, APS23 and other powder carbon steel parts, they can withstand high temperature quenching. During quenching, the secondary hardening process can be used, 1050-1080 ℃ quenching, and then several times of high temperature quenching at 490-520 ℃, which can obtain high fracture toughness and reliability, and is very suitable for the mold shell with the broken edge as the key invalid mode. Powdered carbon steel has high engineering cost but good characteristics, which has produced a development trend of wide application.

2、 It is the grinding of parts.

There are three key types to choose CNC lathe for grinding: tool grinder, internal grinder and special tool mould. During finishing grinding, the grinding deformation and grinding cracks shall be strictly controlled. Even very small cracks may occur in the subsequent processing and application. Therefore, the cutting tool for fine polishing shall be small, not large, and the refrigerant shall be sufficient. The parts with standard tolerance within 0.01mm shall be ground at the temperature as far as possible. According to the measurement, when the temperature difference is 3 ℃, the raw material of 300 mm long cast iron is 10.8 μ Change of m, 10.8=1.2 × three × 3 (1.2 per 100mm shape change μ M/℃), each finishing process needs to consider the hazard of this factor.

It is very important to choose a suitable grinding wheel during finishing. In the case of high vanadium and high molybdenum die materials, GD single crystal jadeite wheels can be used. When machining cemented carbide tools and materials with high quenching strength, diamond saws with organic chemical adhesives are preferred. The grinding wheel with organic chemical adhesives has good self grinding performance, and the ground workpiece is not smooth up to Ra=0.2 μ m. In recent years, with the application of new materials, CBN grinding wheel, that is, boron nitride grinding wheel, has shown a very good actual machining effect. The actual effect is better than that of other types of grinding wheels, which are formed grinding on CNC machine tools and finishing machining on coordinate CNC grinding machines and CNC internal grinding machines. During the grinding process, it is necessary to repair the grinding wheel immediately to keep it sharp. After the grinding wheel is passivated, it will be rubbed and extruded on the surface of the workpiece, causing burns on the surface of the workpiece and reducing the compressive strength.

The machining of seat parts is mostly done by tool grinder. It is difficult to process long and thin metal sheet parts in daily cleaning. During processing, due to the magnetic adsorption effect, the workpiece is deformed. The surface close to the workbench is deformed. After the workpiece is obtained, the workpiece will react and deform. The thickness is correct and consistent, but the flatness is not specified. The magnetic grinding method can be selected as the processing method. When grinding, the contour block is placed under the workpiece, and the blocks on four sides are heavy. During processing, small knives and multiple laser knives are used. After processing, the contour block does not need to be placed, and the processing can be immediately adsorbed, Improve the actual grinding effect to meet the flatness requirements.

Shaft parts have rotating surfaces, and internal grinder and CNC grinder are generally selected for processing. In the whole processing process, the head frame is equivalent to the bus duct. If there is a vibration problem, the processed workpiece will also cause this problem and endanger the quality of the parts. Therefore, the head frame and inspection work should be done well before processing. When grinding the internal thread, the refrigerant shall be fully sprayed on the grinding contact part to facilitate smooth discharge of grinding. For processing thick wall shaft parts, a strong clamping processing platform shall be selected, and the clamping force shall not be too large, otherwise it is very easy to cause internal triangle deformation on the workpiece circle.

3、 It is electric machining operation.

Modern mold shell processing plants can not lack electric machining, which can process various special-shaped and high toughness parts, including wire cutting and spark discharge.

The machining accuracy of slow wire cutting can reach ± 0.003mm, and the surface roughness is Ra0.2 μ m。 When processing step by step, first check the condition of the CNC lathe, check the deionization degree of water, temperature, flatness of wire, support force and other elements to ensure good processing conditions. Wire cutting refers to the removal of a whole piece of raw material, which destroys the original geostress balance of the workpiece, and is very easy to generate stress, especially at the corners. Therefore, when R<0.2 (especially the bevel), the technical department should be given clear suggestions for improvement. The basic principle of vector material movement can be used to solve the stress in the process of processing. Before finishing, a capacity of about 1mm is reserved. After pre processing, a heat treatment process is carried out to make the treated geostress release preferentially before finishing to ensure heat resistance.

When processing the mold base, carefully consider the selection of wire entry position and mode. The actual effect is better when opening and threading are selected. High precision wire cutting processing, generally four times of laser cutting, can ensure the quality of parts. When machining the cavity with finish, rough the straight edge from a fast and efficient point of view, then rough the straight edge, and then finish the straight edge. In this way, there is no need to carry out vertical finishing of section X, and only finish the knife edge section, saving both time and cost.

The first step of spark discharge machining is to make electrical grade, which can be divided into rough and fine. The appearance of finish machining electrical grade shall meet the requirements, and CNC lathe shall be used for machining. In the selection of electrical grade materials, the red copper electrode is mainly used for the processing of general iron castings. Cu-W aluminum alloy is of electrical grade and has good comprehensive performance. Especially in the whole processing process, the amount used is obviously less than that of red copper. With a certain amount of flushing fluid, it is very suitable for raw material processing and finishing of parts with complex cross section appearance. When making electrical grade, the gap and total number of electrical grade must be measured. When large-scale or heavy electrical processing is carried out, the workpiece and electrical grade shall be clamped firmly to ensure sufficient compressive strength and avoid processing looseness. During deep processing, attention should be paid to the electric arc charge and discharge caused by the loss of each part of the electrode and the discharge obstruction.

4、 It is surface solution and assembly.

The tool lines and scratches left on the surface of the machined parts are stress areas and the root cause of crack growth. Therefore, after the machining is completed, the surface of the parts must be strengthened and polished according to the milling workers, so as to solve the potential processing safety problems. Some edges, obtuse angles and pipe orifices shall be blunted and R treated. Generally speaking, the machined surface will produce 6-10 μ The mouldy and hard bottom layer about m is grayish white in color. The hard bottom layer is brittle and contains residual stress. Before use, the hard bottom layer should be fully removed by surface polishing.

Practical experience has proved that excellent finishing process management can reasonably reduce part deviation and damage, and reasonably improve the initial pass rate and service life of the mold shell.

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