Molds are more than just a sandbox used by humans to cast coins and inner casings. Today, it combines all kinds of high technology, can quickly form, weld, and assemble materials into parts, components or products with high efficiency, precision, streamline, ultra-miniature, energy saving, environmental protection, and product performance. , appearance, etc., are unparalleled in traditional craftsmanship. Looking into the 21st century, no matter which industry, such as electronics, biology, materials, automobiles, home appliances, etc., is not equipped with a production line made up of computers, molds and machining centers, it is impossible to take the pillar industry in the manufacturing industry. Mold is an important part of modern manufacturing technology, and its level marks the manufacturing level and production capacity of a country or enterprise. In the coming period, the key to the product quality, batchization cost and technological advancement of the five pillar industries in China is the mold. At present, the global total output value of molds has already exceeded the sum of the output value of the traditional machinery industry - machine tools and tools.
First, the modular design of the mold shortening the design cycle and improving the design quality is one of the keys to shorten the entire mold development cycle. The modular design is to use the similarity in structure and function of the product components to achieve standardization and combination of products. A large number of practices have shown that modular design can effectively reduce product design time and improve design quality. Therefore, this paper explores the use of modular design methods in mold design.
The implementation of the modular design of the mold.
1. Establishing a module library The module library is built in three steps: module partitioning, constructing feature models, and generating user-defined features. Standard parts are special cases of modules and exist in the module library. The definition of a standard part requires only the last two steps. Module partitioning is the first step in modular design. Whether the module division is reasonable or not directly affects the function, performance and cost of the modular system. The module division of each type of product must undergo technical investigation and repeated argumentation to obtain the division result. For molds, functional modules and structural modules are mutually tolerant. The structural module can have a large structural change in a local range, so that it can contain functional modules; and the functional structure of the functional module may be relatively fixed, so that it can contain structural modules. After the module design is completed, the feature model of the required module is manually constructed in the Pro/E Part/Assembly space, and the user-defined feature function of Pro/E is used to define two variable parameters of the module: Variable size and assembly relationships form User-Defined Features (UDFs). Generate a user-defined feature file (a file with a suffix of gph) and store it by grouping technology, that is, complete the creation of the module library.
2. The system realizes the module determination through two inferences, structure selection reasoning and automatic modeling of the module. The first reasoning gives the general structure of the module, and the second reasoning finally determines all the parameters of the module. In this way, the module "plasticity" goal is achieved. In the structure selection reasoning, the system accepts the module name, function parameters and structural parameters input by the user, performs inference, and obtains the name of the applicable module in the module library.
If the result is not satisfactory, the user can specify the module name. The module obtained in this step is still undefined, and it lacks definitions of dimensional parameters, precision, material characteristics, and assembly relationships. In the automatic modeling reasoning, the system uses the input size parameters, precision features, material features and assembly relationship definitions to drive the user-defined feature model, dynamically and automatically construct the module feature model and automatically assemble. The automatic modeling function was developed using Pro/TOOLKIT, a secondary development tool for C and Pro/E. The mold design can be completed quickly by the call of the module. The mold design cycle is significantly shortened after applying this system. Since the quality of the module is carefully considered in the design of the module, the quality of the mold is guaranteed. The module library stores mutually independent UDFs, so the system is extensible.Second, the defects in the mold manufacturing process and preventive measures 1. Forging processing High-carbon, high-alloy steel, such as Cr12MoV, W18Cr4V, etc., is widely used in the manufacture of molds. However, such steels have various defects such as segregation of components, uneven carbides, and uneven structure. To make molds from high-carbon and high-alloy steels, a reasonable forging process must be used to form the module blanks. On the one hand, the steel can reach the size and specifications of the module blanks, and on the other hand, the microstructure and properties of the steel can be improved. In addition, the high-carbon, high-alloy die steel has poor thermal conductivity, the heating speed can not be too fast, and the heating should be uniform. In the forging temperature range, a reasonable forging ratio should be adopted.
2. Cutting processing The cutting of the mold should strictly ensure the radius of the fillet at the transition of the dimension, and the intersection of the arc and the straight line should be smooth. If the cutting quality of the mold is poor, it may cause damage to the mold in the following three aspects: 1) The sharp corner or the radius of the fillet is too small due to improper cutting, which may cause serious stress during the working of the mold. concentrated. 2) The surface after cutting is too rough, there may be defects such as knife marks, cracks, and slits. They are both stress concentration points and the origin of cracks, fatigue cracks or thermal fatigue cracks. 3) The cutting process fails to completely and evenly remove the decarburized layer generated during the rolling or forging of the mold. It is possible to produce an uneven hardened layer during heat treatment of the mold, resulting in a decrease in wear resistance.
3. Grinding The mold is usually ground after quenching and tempering to reduce the surface roughness. Due to excessive grinding speed, excessive grinding wheel size or poor cooling conditions, the surface of the mold is locally overheated, causing local microstructure changes, or causing surface softening, hardness reduction, or high residual tensile stress. Such phenomena will reduce the service life of the mold, select appropriate grinding process parameters to reduce local heat generation, and perform stress-relieving treatment under possible conditions after grinding to effectively prevent the occurrence of grinding cracks. There are many measures to prevent overheating and grinding cracks. For example, use coarse grinding wheels with strong cutting force or grinding wheels with poor adhesion to reduce the grinding feed of the mold; select suitable coolant; grinding After 250 to 300 ° C tempering eliminates grinding stress and the like.
4. EDM When the mold is processed by EDM, the current density in the discharge zone is very large, and a large amount of heat is generated. The temperature of the processed area of ​​the mold is as high as 10000 °C. Due to the high temperature, the metallographic structure of the heat affected zone is bound to When the change occurs, the surface of the mold melts due to the high temperature, then quenches and solidifies quickly, forming a resolidified layer. It can be seen under the microscope that the re-solidified layer is white and bright, and there are many micro-cracks inside. In order to extend the life of the mold, the following measures can be taken: adjusting the EDM parameters by electrolysis or mechanical grinding to grind the surface after EDM, removing the white layer in the abnormal layer, especially to remove microcracks. After EDM A low temperature tempering is arranged to stabilize the anomalous layer and prevent microcrack propagation.
According to the method described above, the development cycle can be shortened and mold manufacturing defects can be effectively prevented, the mold manufacturing quality can be improved, and the production cost can be reduced.
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