Plastic mold for the lower cover of the main body of the computer bionic device
Causes of mold quenching cracks:
1. Improper grinding process for mold heat treatment.
2. There are high tensile stresses and microcracks in the hardened layer during EDM machining after the heat treatment of the mold.
3. Improper operation of mold heat treatment (heating or cooling too fast, improper selection of quenching cooling medium, too low cooling temperature, too long cooling time, etc.).
4. The complex shape of the mold, uneven thickness, sharp corners and threaded holes, etc., make the thermal stress and organizational stress too large.
5. Excessive heating temperature of mold quenching will cause overheating or overburning.
6. After the mold is quenched, the tempering is not timely or the tempering holding time is insufficient.
7. When the mold is reworked and quenched, it is reheated and quenched without intermediate annealing.
8. There is serious network carbide segregation in the mold material.
9. There is mechanical processing or cold plastic deformation stress in the mold.
Preventive measures for mold quenching cracks:
1. Improve the EDM machining process of the mold, and carry out stress relief and tempering.
2. Improve the forging and spheroidizing annealing process to eliminate the mesh, band, and chain carbides, and improve the uniformity of the spheroidizing structure.
3. After mechanical processing or cold plastic deformation, the mold should be subjected to stress relief annealing (>600℃, then heating and quenching).
4. For molds with complex shapes, asbestos should be used to plug the threaded holes, to wrap dangerous sections and thin walls, and to adopt hierarchical quenching or austempering.
5. Annealing or high temperature tempering is required when reworking or refurbishing molds.
6. The mold should be preheated during quenching and heating, and pre-cooling measures should be taken when cooling, and suitable quenching medium should be selected.
7. After the mold is quenched, it should be tempered in time, and the holding time should be sufficient, and the high-alloy complex mold should be tempered 2-3 times.
8. Strictly control the quenching heating temperature and time to prevent the mold from overheating and overburning.
9. Strictly control the internal quality of mold raw materials
10. Choose the right grinding process and the right grinding wheel.
How long is the service life of plastic mold steel
There are many types of plastic mold steels, and they involve a wide range. From the price point of view, they range from ten to several hundred yuan. There are imported and domestic ones, so their quality, characteristics, and use environment are all Not the same, so the service life is very different. In addition, the service life of the plastic mold steel is calculated when the mold is made and the production is started. The mold manufacturing is put into use after the steps of design, processing, assembly, and debugging. Therefore, due to the design of the processing personnel during the mold processing The difference in level and manufacturing process will greatly affect the service life of the mold. Let's analyze the factors that affect the service life of the injection mold.
۞ Quality of mold steel
The decisive factor of steel quality, choosing the right mold steel is the top priority. For example, if the injection materials are different, the corresponding mold steel materials will not be the same, such as high polishing requirements, corrosion resistance requirements, and so on. In addition, the quality will vary depending on the origin. Generally, the life of 718 mold steel produced by large factories is about three to five million mold times, NAK80 mold steel is about 1 million mold times, and H13 mold steel and SKD61 mold steel are usually 1 million. About the mold time, you can choose to use large or small steel materials according to the situation.
۞ Steel surface treatment
The surface treatment of the mold steel is also very important. Nitriding can enhance the surface hardness of the steel and effectively extend the life of the mold; electroplating can effectively modify the mold steel, and some plastic parts that require high brightness and corrosion resistance can be enhanced by electroplating. And improve the performance of steel.
۞ Structural design of mold
The mature mold structure not only considers the product material properties, shrinkage rate, molding temperature, elastic tensile deformation coefficient, etc., but also considers the cooling water circuit and the speed of mold opening and closing. A reasonable mold structure can effectively extend the life of the mold and ensure the smooth production of the mold.
۞ Mold processing technology
If a worker wants to do his job well, he must first sharpen his tools. The arrangement of the plastic mold process is particularly important. A reasonable process arrangement can speed up the production cycle, shorten the processing time, and effectively save costs. And more importantly, accurate and reasonable processing can ensure the stability of the mold in the production process and prolong the life. Some processing errors will cause mold welding, no matter how good the welding is, it is a loss to the mold; in addition, poor processing may also affect the mold operation, reduce the mold life, and cause the plastic mold to pull during the production process. Crack or even break.
۞ Mould accessories
It is the shortest piece of wood that determines the capacity of the bucket. Everyone understands this principle, but it is often not noticed when doing it. The same is true for the mold. Although the standard parts of mold accessories do not directly participate in the molding, they control the operation of the entire mold. The standard parts with excellent quality should have the characteristics of wear resistance, hard enough, high precision, and not suitable for deformation.
۞ Flying model or butt
The confrontation mainly relies on the experience of the mold fitter. The seemingly simple job is the most technical job. The main focus of complex molds is this effort. The flat mold is the simplest, as long as the fractal surface does not have flashing, it is basically fine. For example, auto parts molds are very troublesome, not only the fractal surface is relatively irregular, but also often includes multiple sliders and top blocks. At the same time, other problems of the mold can be improved and perfected through the collision. So it is a comprehensive job.
۞ polished or dermatoglyph
The polishing of the mold is the last link in the manufacture of the mold. Polishing is directly reflected on the plastic parts, so this is the most face-to-face job. Polishing can also help and supplement the action of the mold, especially for demolding. Often the production of some molds is not smooth because of improper lighting, excessive resistance, difficulty in demolding, and even whitening and cracking.
۞ Mold assembly
Mold assembly is just like assembling a machine. Every component and every screw cannot be wrong, otherwise the consequences will be very serious, from the slightest to the product defect, affecting the production, and the other to completely damaging the mold and causing scrap. Therefore, the assembly work must be very meticulous. During the assembly process, pay special attention to the cleaning of the mold, especially the waterway and screw holes. The iron filings must be blown out, otherwise the customer will be very angry.
۞ Mold hot runner system
This actually has the least impact on mold quality, because hot runners are generally designated by customers, especially some large customers. Well-known foreign brands are very good in quality and after-sales service, so there is generally no problem in quality. It's just that the quality of some domestic hot runners is quite different. In order to save costs and strive for price advantages, individual small companies use unreliable heating and conduction accessories, which are prone to problems. The main problem of cold runner is how to ensure the balance of injection molding, gate size, injection pressure and so on.
۞ Cooling water circuit
Anyone who has mold experience knows how important cooling is to a mold. Due to the increase in prices and human wages, when mass production of products, the profit that does not reduce the injection cycle of one second is unimaginable. However, while accelerating the production cycle, the temperature of the mold will rise. If it is not effectively controlled, the mold will be too hot to form, and even cause the mold to deform and fail. Therefore, a good waterway design is particularly important, including the arrangement density, diameter, interconnection of the waterway, and so on.
۞ Mold maintenance
Maintenance is one of the important factors in the service life of the mold. Therefore, every time the mold is used, a comprehensive maintenance must be carried out, especially the rust prevention of the forming part and the rust prevention of the main moving parts. The mold is more or less due to the production process. It will be exposed to water, especially water or sweat stains on the mold during installation or disassembly. Therefore, the mold must be dry when the shutdown period is long. After cleaning the mold, it must be brushed with protective oil or anti-rust oil.
Pure plastic mold steel is set according to the use and grade and order requirements before refining. The subsequent series processing and human factors are not considered. The theoretical service life of general plastic mold steel is 250,000 to 800,000 times. Medium plastic mold steel 800 to 1 million times, good brand plastic mold steel and patented steel will exceed 150 times or even higher.