Some Optimizing Methods of Design and Manufacture

1 Modular method of mold

Shortening the design cycle and improving design quality is one of the keys to shortening the entire mold development cycle. Modular design is to use the similarity in structure and function of product parts to realize the standardization and combination of products. A lot of practice shows 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 mold modular design.

1.1 Build a module library

There are three steps in the establishment of the module library: module division, construction of feature models and generation of user-defined features. A standard part is a special case of a module and exists in the module library. The definition of standard parts only needs to go through the last two steps. Module division is the first step in modular design. Whether the module division is reasonable will directly affect the function, performance and cost of the modular system. The module division of each type of product must go through technical research and repeated demonstrations before the division result can be obtained. For molds, functional modules and structural modules are mutually inclusive. Structural modules can have large structural changes in the local area, so it can contain functional modules; and the local structure of functional modules may be relatively fixed, so it can contain structural modules. After the module design is completed, manually construct the feature model of the required module in the Pro/E part/assembly (Part/Assembly) space, and use the user-defined feature function of Pro/E to define two variable parameters of the module: Change the size and assembly relationship to form User-Defined Features (UDFs). After generating the user-defined feature file (the file with the suffix of gph), it is named and stored according to the grouping technology, and the establishment of the module library is completed.

1.2 Development of module library management system

The system realizes the module determination through two inferences, structure selection inference and module automatic modeling. The first inference gets the rough structure of the module, and the second inference finally determines all the parameters of the module. This approach achieves the module "plasticity" goal. In the structure selection reasoning, the system accepts the module name, function parameters and structure parameters input by the user, performs reasoning, and finds the name of the applicable module in the module library.

If the result is not satisfied, the user can specify the module name. The module obtained in this step is still indeterminate, and it lacks the definition of dimension parameters, precision, material characteristics and assembly relationship. In automatic modeling reasoning, the system uses the input dimension parameters, precision features, material features and assembly relationship definitions to drive user-defined feature models, dynamically and automatically construct module feature models and automatically assemble them. The automatic modeling function is developed by using C language and Pro/TOOLKIT, the secondary development tool of Pro/E. The mold design can be completed quickly by calling the module. After applying this system, the mold design cycle is significantly shortened. Since the quality of the module is seriously considered in the design of the module, it plays a basic role in guaranteeing the quality of the mold. The UDFs files that are independent of each other are stored in the module library, so the system is scalable.

2 Defects and preventive measures in the mold manufacturing process

2.1 Forging process

High-carbon and high-alloy steels, such as Cr12MoV, W18Cr4V, etc., are widely used in the manufacture of molds. However, this kind of steel has defects such as composition segregation, coarse and uneven carbide, and uneven structure to varying degrees. When high-carbon and high-alloy steel is used to make molds, a reasonable forging process must be used to form the module blank, so that on the one hand, the steel can reach the size and specification of the module blank, and on the other hand, the structure and performance of the steel can be improved. In addition, high-carbon and high-alloy die steels have poor thermal conductivity, and the heating rate should not be too fast, and the heating should be uniform. Within the forging temperature range, a reasonable forging ratio should be adopted.

2.2 Machining

The cutting process of the mold should strictly ensure the fillet radius at the size transition, and the junction between the arc and the straight line should be smooth. If the cutting quality of the mold is poor, it may cause mold damage in the following three aspects. 1) Due to improper cutting, the sharp corner or the radius of the fillet is too small, which will cause serious stress concentration when the mold is working . 2) If the surface after cutting is too rough, there may be defects such as knife marks, cracks, and cuts. They are not only stress concentration points, but also initiation sites for cracks, fatigue cracks, or thermal fatigue cracks. 3) If the cutting process fails to completely and evenly remove the decarburization layer produced by the die hair damage during rolling or forging, an uneven hardened layer may be generated during the heat treatment of the die, resulting in a decrease in wear resistance.

2.3 Grinding

After the mold is fired and tempered, it generally needs to be ground to reduce the surface roughness value. Due to the influence of factors such as excessive grinding speed, too fine grinding wheel grain or poor cooling conditions, the local overheating of the mold surface will cause local microstructure changes, or cause surface softening, hardness reduction, or high residual tensile stress And other phenomena will reduce the service life of the mold, choose appropriate grinding process parameters to reduce local heating, and perform stress relief treatment under possible conditions after grinding, which can effectively prevent the occurrence of grinding cracks. There are many measures to prevent grinding overheating and grinding cracks, such as: use coarse-grained grinding wheels with strong cutting force or poorly bonded grinding wheels, reduce the grinding feed of the mold; choose a suitable coolant; grind After tempering at 250-300 ℃ to eliminate grinding stress and so on.

2.4 EDM

When the mold is processed by the EDM process, the current density in the discharge zone is very high, which generates a lot of heat. The temperature of the processed area of the mold is as high as 10,000°C. Due to the high temperature, the metallographic structure of the heat-affected zone will change, and the surface layer of the mold will change. Melting occurs due to high temperature, then quenched and solidified quickly to form a resolidified layer. It can be seen under the microscope that the resolidified layer is white and bright, and there are many microscopic cracks inside. In order to prolong the life of the mold, the following measures can be taken: adjust the EDM parameters and use electrolytic or mechanical grinding to grind the surface after EDM, remove the white and bright layer in the abnormal layer, especially to remove micro cracks. After EDM Arrange a low-temperature tempering to stabilize the anomalous layer and prevent micro-crack propagation.