Discussion on mold manufacturing methods
First, the modular method of the mold
Shortening the design cycle and improving design quality is one of the keys to shortening 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.
Implementation of modular design of the mold:
1, build 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 relationship. , forming user-defined features. After the user-defined feature file is generated and stored by the grouping technology, the module library is created.
2, module library management system development
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 and preventive measures in the mold manufacturing process
1. Forging and casting processing
High-carbon, high-alloy steels, such as Cr12MoV, W18Cr4V, etc., are 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, the mold loss may be caused 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 concentration during the working of the mold. . 2) The surface after cutting is too rough, there may be defects such as tool marks, cracks, slits, etc. They are not only stress concentration points, but also 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, CNC grinding processing
The mold is generally ground after fire and tempering to reduce the surface roughness value. 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.
When the mold is processed by the electric spark process, the current density in the discharge zone is very large, and a large amount of heat is generated. The temperature of the processed region 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 change, and the surface of the mold is changed. Melting occurs due to high temperature, then quenching, solidifying quickly, forming a re-solidified 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 bright layer in the abnormal layer, especially to remove the microcrack. After the electric discharge machining, a low temperature tempering is arranged to stabilize the abnormal layer and prevent the microcrack propagation.