General issues to be noted in the design of die-casting molds

Due to its long production cycle, high investment, high manufacturing accuracy, and high cost, the working conditions of die-casting molds are harsh. During die-casting production, the surface of the die-casting mold cavity is not only subjected to high-pressure and high-speed flushing of the metal liquid, but also experiences intense heat exchange, complex metal flow, and various factors that affect the quality of die-casting parts and the service life of the mold. Therefore, designing and manufacturing a die-casting mold that can ensure both the quality of the castings and durability has become the goal pursued by mold design and manufacturing enterprises. Based on the characteristics of die-casting production technology and a summary of production practice. Mold design, mechanical processing of parts, heat treatment of parts, mold assembly, and mold use are the main factors affecting the quality of die-casting parts and the service life of molds.

1. Ensure stable quality of die-casting parts.

Before designing the mold, widely listen to the opinions of various process personnel involved in mold manufacturing and die-casting production. When designing the mold, the main purpose of the decompression casting and its assembly relationship with other structural components should be fully considered in order to distinguish between primary and secondary, highlight the key points of the mold structure, and obtain die-casting parts that meet technical and usage requirements. Mold design should fully reflect the superior performance of die-casting molding, and try to die-casting structures that conform to the die-casting process, such as holes, grooves, side depressions, side curves, etc., to avoid unnecessary post-processing. When necessary, discuss the rationality of die-casting design with the die-casting design party, such as using consistent wall thickness; Draft angle; Large rounded corners are used for the intersection of side walls, ribs, protrusions, and other parts; Sharp outer corners should be rounded or chamfered to eliminate the possibility of mold failure and reduce maintenance; Inverted hooks should be avoided as much as possible, as they may require machining of the parts or the use of reciprocating core sliders in the mold; Let the main dimensions be related to the die-casting mold components, rather than going too far beyond the mold line. It is very difficult to achieve the same accuracy on both sides of the boundary line of the die-casting mold due to the asymmetry of the components at the top and bottom of the mold. Mold designers need to master the technical characteristics of die-casting machines and fully utilize their technical functions and production capabilities. Mold installation should be convenient and reliable.

2. Reasonable structure.

Advanced and reasonable structure, easy operation, high die-casting efficiency, fast filling and opening of molds, flexible and reliable demolding mechanism, and high degree of automation.

(1) Reasonably select the parting surface of the mold.

Reasonably determining the parting surface based on the shape and structural characteristics of die castings is an important step in mold design. The choice of parting surface greatly affects the complexity of the mold structure. Principles for selecting parting surfaces:

① The parting surface strives for simplicity and ease of processing.

② Beneficial for simplifying the mold structure.

③ It should be easy to ensure the accuracy requirements of the die-casting parts.

④ The parting surface should be conducive to filling and forming.

⑤ When opening the mold, try to keep the die-casting parts on the moving mold side as much as possible.

(2) Layout of pouring system and overflow system

During the entire process of filling and pressing the mold cavity with molten metal, the pouring system and overflow system are an inseparable whole, jointly playing a controlling role in the filling process and determining the quality of the die-casting parts. The overall layout of the pouring system and overflow system should be comprehensively considered based on the structural characteristics, geometric shape, exhaust conditions of the mold cavity, and other process factors of the die-casting parts, combined with the form of the selected die-casting machine, to determine the position, form, size, flow direction, and overflow system settings of the sprue, runner, and sprue, and preliminarily determine them. Especially the position and form of the sprue are important factors determining the filling effect of the molten metal and the quality of the die-casting parts. When designing the pouring system, efforts should be made to prevent the metal liquid from impacting or washing the core from the front, and to reduce the erosion at the inlet of the sprue. Try to avoid placing the sprue, overflow groove, and exhaust groove near the guide post, guide sleeve, and core pulling mechanism as much as possible to prevent liquid metal from entering. The application of die-casting mold flow analysis software is helpful for the design and layout of pouring systems and overflow systems. Through CAE mold flow analysis, it is possible to analyze whether the pouring system design is reasonable, to analyze the balance of mold temperature and the existence of thermal stress, and to analyze the location of defects and the causes of die-casting defects. Modify the pouring system based on the analysis results to effectively improve the mold design and product quality level.

(3) Selection of demolding method

In general, after die-casting, the die-casting part remains on the side of the moving mold during parting. In order to smoothly demold the die-casting parts without damage or deformation, the correct and reasonable demolding method should be selected based on the structural characteristics of the die-casting parts, and the position and size of the ejection part and reset rod should be determined. For complex die-casting parts, if it is not possible to completely demold after one ejection action, a secondary or multiple demolding mechanism should be used, and the number of parting times, the structural form of multiple demolding, and the sequence of actions should be determined. The concave and convex parts of the die-casting parts should be equipped with a side core pulling mechanism. The selection of side core pulling mechanism should be based on economic practicality. If the batch size of the product is not large, a simple side core pulling form can be used; If a manual core pulling mechanism or an out of mold core pulling mechanism with movable cores is used, manual core removal can be used after mold opening. When it is necessary to use a side core pulling mechanism driven by mold opening force or external force, after calculating the core pulling force, a suitable side core pulling mechanism can be selected and the dimensions of the main structural components can be determined

(4) Structure and dimensions of parts

Determine the injection specific pressure based on the properties of die-casting alloys and the structural characteristics of die-casting parts, and calculate and determine the projection area and cavity depth of the die-casting parts

① The thickness of the sidewall of the cavity;

② The thickness of the support plate;

③ Determine the thickness and relevant dimensions of the cavity plate, dynamic template, dynamic mold seat plate, and fixed mold seat plate;

④ Determine the position and main dimensions of the mold guidance form;

⑤ Determine the positioning method, installation position, and fixing form of the die-casting mold;

⑥ Determine the connection and fixing forms of each structural component, and combine various structural components into one unit;

⑦ Determine the temperature adjustment method for the mold, and arrange the position and size of the cooling or heating pipes.

For more complex molded parts, it is important to consider practical processing methods, whether to use ordinary processing methods or special processing methods. When traditional processing methods are necessary due to limitations in processing equipment, consideration should be given to how to disassemble and assemble them in order to make them easier to process and polish, and to avoid deformation caused by heat treatment, in order to ensure the dimensional accuracy of assembly. The fitting accuracy of relative moving parts should consider the impact of mold temperature changes. Suitable movement tolerances should be selected to ensure smooth, flexible, and reliable movement of various functions even in high mold temperature die-casting environments.