1. Use rapid prototyping technology and three-dimensional software to establish a reasonable casting shape, and initially determine the parting surface, pouring system position and mold heat balance system. Convert the two-dimensional casting drawing into three-dimensional solid data according to the requirements, determine the reasonable shrinkage rate according to the complexity and wall thickness of the casting (usually 0.05%~0.06%), determine the position and shape of the parting surface, and determine the position and shape of the parting surface according to the die casting The data of the machine selects the position and diameter of the injection punch and the number of die-casting parts per die, makes a reasonable layout of the die-casting parts, and then carries out three-dimensional modeling of the gating system and the overflow system.
2. Carry out flow field and temperature field simulation to further optimize the mold pouring system and mold heat balance system. After processing the data of the casting, pouring system and overflow system, input the boundary condition data such as the jade casting process parameters, the physical parameters of the alloy, and the simulation software can simulate the filling process of the alloy and the trend of the liquid alloy inside the mold cavity It can also perform solidification simulation and temperature field simulation to further optimize the gating system and determine the location of the mold cooling point.
The results of the simulation express the information of the orientation of the liquid alloy and the distribution of the temperature field in the entire filling process in the form of pictures and images, and the parts that may have defects can be found through analysis. In the subsequent design, measures such as changing the position and orientation of the inner gate and adding a slag collecting bag are adopted to improve the filling effect and prevent and eliminate the occurrence of casting defects.
3. Design the overall structure of the mold according to the 3D model. While the simulation process is in progress, we can design the general layout of the mold, including the following aspects:
(1) Carry out the general layout design of the mold according to the data of the die-casting machine.
It is the first task to determine the injection position and punch diameter in the general layout design. The injection position should be determined to ensure that the die-casting part is located in the center of the die-casting machine plate, and the four pull rods of the die-casting machine cannot interfere with the core-pulling mechanism. The injection position is related to whether the die-casting part can be ejected from the cavity smoothly. ; The punch diameter directly affects the injection ratio, and thus the clamping force required for the die-casting mold. Therefore, determining these two parameters is the first step in our design.
(2) Design forming inserts and cores.
The main consideration is the strength and rigidity of the forming insert, the size of the sealing surface, the splicing between the inserts, the arrangement of push rods and cooling points, etc. The reasonable combination of these elements is the basic requirement to ensure the life of the mold. For large molds, it is especially necessary to consider the matching method of the vulnerable parts and the sealing surface. This is the key to prevent the early damage of the mold and the aluminum escape during the die-casting process. It is also the need for large mold exhaust and mold processing technology.
(3) Design the mold base and core pulling mechanism.
Small and medium-sized die-casting molds can directly choose standard mold bases. Large-scale molds must calculate the stiffness and strength of the mold base to prevent the elastic deformation of the mold base from affecting the dimensional accuracy of the die-casting part during the die-casting process. The key to the design of the core-pulling mechanism is to grasp the fit gap between the movable components and the positioning between the components. Considering the influence of thermal expansion on the sliding gap during the working process of the mold base, the fit gap of the large mold should be between 0.2~0.3mm, and the butt gap of the forming part should be between 0.3~0.5mm, which is selected according to the size of the mold and the heating condition. The square key is used for positioning between the formed slider and the slider seat. The lubrication of the core-pulling mechanism is also the focus of the design. This factor directly affects the reliability of the continuous work of the die-casting mold. An excellent lubrication system is an important part of improving the labor productivity of die-casting.
(4) The arrangement of heating and cooling channels and the selection of heat balance components.
Because the high temperature liquid enters the mold cavity at high speed under high pressure, it brings a lot of heat to the mold insert. How to remove this heat is a problem that must be considered when designing the mold, especially for large die-casting molds. The heat balance system directly affects the size of the die-casting part. And internal quality. Quick installation and accurate flow control are the development trend of modern mold heat balance systems. With the development of modern processing industry, the selection of heat balance components tends to be directly selected design modes, that is, component manufacturing companies directly provide component two-dimensional and three-dimensional data, design The user is on-demand, which can not only ensure the quality of the components but also shorten the design cycle.
(5) Design the launch mechanism.
The ejection mechanism can be divided into two forms: mechanical ejection and hydraulic ejection. Mechanical ejection uses the equipment’s own ejection mechanism to achieve the ejection action, and hydraulic ejection uses the hydraulic cylinder equipped with the mold itself to achieve the ejection action. The key to designing the pushing out mechanism is to try to make the center of the pushing out resultant force and the center of the releasing resultant force concentric as much as possible, which requires the pushing out mechanism to have good pushing out orientation, rigidity and reliable working stability. For large molds, the weight of the ejection mechanism is relatively large. The components of the ejection mechanism and the frame are likely to deflect the push rod due to the weight of the mold, causing the ejection jam to occur. At the same time, the thermal expansion of the mold also affects the ejection mechanism. It is extremely large, so the positioning between the ejector element and the mold frame and the fixed position of the pusher guide post are extremely important. The pusher guide post of these molds is generally fixed on the template, and the template, the shim and the mold frame Use a round pin or square key with a larger diameter for positioning, which can minimize the effect of thermal expansion on the ejection mechanism. If necessary, rolling bearings and guide plates can be used to support the ejection element. At the same time, pay attention to the lubrication between the elements when designing the ejection mechanism. . Mold designers in North America usually add a special grease plate to lubricate the push rod on the back of the movable mold frame to enhance the lubrication of the ejected components. A lubricating oil plate is added to the bottom of the movable mold frame, and there is an oil passage communicating with the through hole of the push rod. Lubricating oil is added during work to lubricate the ejection mechanism and prevent jamming.
(6) Design of guiding and positioning mechanism.
In the entire mold structure, the guiding and positioning mechanism is the factor that has the greatest impact on the stability of the mold, and it also directly affects the dimensional accuracy of the die casting. The guide mechanism of the mold mainly includes: mold closing guide, core pulling guide, and push guide. Generally, the guide element should adopt the friction pair of special material to reduce wear and anti-wear. At the same time, good lubrication is also indispensable. The necessary lubricating oil circuit must be set up between each friction pair. It should be particularly pointed out that the guiding structure of the extra-large sliding block generally adopts the guiding form of a copper guide sleeve and a hard guiding column, and a good positioning form is used to ensure the smooth running of the sliding block and accurate positioning.
The mold positioning mechanism mainly includes: positioning between dynamic and static molds, push-reset positioning, positioning between forming slider and slider seat, positioning between the push part of the frame and the mold frame, etc. The positioning between dynamic and static molds is a kind of movable positioning, and the accuracy of coordination is higher. Small molds can directly use the convex and concave surfaces between the forming inserts. Large die-casting molds must use special positioning mechanisms to eliminate thermal expansion. The positioning accuracy is affected by the other types of positioning structures, which are positioning between components, which are fixed positioning, and generally use round pins and square keys for positioning. the positioning of the convex and concave surfaces between the forming inserts ensures accurate positioning between the dynamic and static shapes and prevents the mold from wrong edges.
(7) Other designs such as vacuum, extrusion and exhaust mechanism.
In addition to the above-mentioned structure, some molds have special requirements such as vacuum system, extrusion mechanism, and corrugated plate exhaust. The design of the vacuum system is mainly the design of the sealing form. In order to maintain good sealing performance between the mold forming parts at the normal mold working temperature, silicone rubber is generally used for sealing. The key to the design of the extrusion mechanism is to control the timing and amount of extrusion to ensure the extrusion effect. Wave plate exhaust is a centralized exhaust form. The wave plate exhaust method is more commonly used, especially for aluminum alloy die-casting parts with thin wall thickness, pressure-resistant parts with high compactness requirements, and magnesium alloy die-casting parts. ; The wave plate gap should be large enough, but can not make the alloy liquid splash during the die-casting process, the wave plate gap is generally controlled at 0.3~0.6mm.