?

Die casting molds are important process equipment in die casting production. The metal liquid cools and solidifies in the die casting mold, and then forms a die casting. The shape, size, quality, and smoothness of die-casting production are closely related to die-casting molds. Therefore, it is crucial to design die-casting molds correctly and reasonably.

1、 Basic structure of die-casting molds

The commonly used die-casting molds consist of two half molds, called fixed molds and moving molds. There are also more complex die-casting molds, with more than two and a half molds.

The components of the die-casting mold are shown in Figure 1.

?

?

The functions of the components of the die-casting mold are as follows:

(1) The sprue is connected to the pressure chamber or to the transverse sprue, including the sprue sleeve and diversion cone.

(2) The channel through which the alloy liquid enters the mold cavity in the pouring system, including the internal sprue, transverse sprue, and vertical sprue.

(3) The cavity is formed on the insert, forming the geometric shape of the die casting.

(4) The core pulling mechanism completes the extraction and insertion of the movable core, including slides, sliders, oil cylinders, slashes, etc.

(5) The overflow system discharges gases and stores cold metal residues.

(6) The temperature control system controls the temperature of the die-casting mold, including cooling water pipes and heating oil pipes.

(7) The ejection mechanism ejects the die-casting part from the mold cavity, including the ejector rod.

(8) Connect and fix the dynamic mold components, including sleeve plates, support plates, etc.

2、 Design of Die Casting Mold

The design of die-casting molds should pay attention to the following key points:

(1) It is necessary to adopt advanced and simple structures as much as possible to ensure stable and reliable operation, as well as daily maintenance and repair.

(2) To consider the modifiability of the pouring system, necessary modifications can be made during the debugging process.

(3) Reasonably select various tolerances, scales, and machining allowances to ensure reliable mold fit and required die casting accuracy.

(4) Select appropriate mold materials and reliable heat treatment processes to ensure the service life of die-casting molds.

(5) It should have sufficient stiffness and strength to withstand mold locking pressure and expansion force, without deformation during the die-casting production process.

(6) Use standardized die-casting mold parts as much as possible to improve economy and interchangeability.

When designing die-casting molds, it is also necessary to calculate the total projected area and injection specific pressure during die-casting production based on the projected area of the casting, in order to select a suitable tonnage die-casting machine.

The formula is as follows:

F expansion force=100 P injection specific pressure × S projected area.

F locking force=F expansion force/K coefficient.

In the equation, the K coefficient is generally selected as 0.85.

After selecting the die-casting machine, design the size, center position, reset rod hole position, and other dimensions of the mold that are connected to the die-casting machine based on the dynamic and static plates of the die-casting machine and the eccentric position of the injection.

?

With the development of China's automotive manufacturing industry, more and more automotive components are made of aluminum alloy materials, such as the cylinder block, cylinder head, oil pan, and various connecting brackets of automotive engines. With the increasing maturity of die-casting technology, various automobile manufacturers have increasingly high internal quality requirements for die-casting, especially the strict requirements of Volkswagen in Germany. Each engine die-casting product of a vehicle model has a corresponding set of technical requirements, and the requirement for product porosity is a necessary requirement for every component.

Some components are very complex in structure and require corresponding structures to be made on the mold in order to achieve mass die-casting production. For example, there are multiple angle threaded holes on the components. To ensure the quality of the processed product, it is necessary to make a core at the corresponding position of the die-casting mold.

The core pulling mechanism can be divided into two types according to the driving method: mechanical and hydraulic. Mechanical core pulling mainly achieves core pulling and resetting through diagonal pins, bent pins, gears, racks, etc. during the mold opening and closing process. The working principle of the hydraulic core pulling mechanism is relatively simple, and the hydraulic cylinder is directly used for core pulling and resetting actions. The hydraulic core pulling mechanism can select the size of the hydraulic cylinder based on the size of the core pulling force and the length of the core pulling distance.

In the continuous production process, the core pulling hole of the die casting mold will deform due to multiple sliding and pulling operations. In the middle and later stages of the mold's lifespan, the phenomenon of core pulling and grinding often occurs. To solve this problem, an insert sleeve can be added to the core pulling hole. If there is deformation of the core pulling hole, the insert sleeve can be replaced to solve the problem. This method can also be applied to the top rod of the mold, as long as a sleeve can be added, this structure can be made.

According to the requirements of some component drawings, some areas on the casting require the placement of irregular top rods of specified sizes.

Some complex products with thick and large areas cannot guarantee internal quality through die-casting process parameters. Therefore, when designing die-casting molds, it is necessary to consider adding a local extrusion mechanism. The principle of this mechanism is to insert the core within a short period of time after the injection is completed, making this area compact and reducing porosity. The forming part of the extrusion mechanism for core pulling does not have a die inclination, so it is only suitable for short distance structures.

3、 Design of Die Casting Process System

After the design of the mold frame was completed, we entered the design of the pouring system. Previously, we used to do this part based on practical experience by looking at two-dimensional or three-dimensional drawings. Adjust the position and direction of the inner runner during the production process based on the internal quality of the product. In the past decade, with the continuous development of numerical simulation technology for casting filling and solidification processes and the market demand of the casting industry, commercial software for casting process simulation has been constantly emerging. Many host manufacturers also require to see the die-casting simulation process before designing the mold, so many die-casting mold manufacturers use two simulation software, MAGMASoft or ANYCASTING, to import the designed 3D into this program at the beginning of the design. After setting the die-casting process parameters, the simulation software undergoes certain calculations to produce simulation animations that are close to the actual production effect.

The simulation results required for the die-casting process are as follows:

(1) The alloy liquid should reach the inner runner more or less simultaneously.

(2) During the filling process, the alloy liquid should be filled smoothly.

(3) During the filling process, there should be no effect of entrainment or turbulence.

(4) Before the filling is completed, the alloy liquid cannot seal the passage of the slag collection bag tightly.

(5) The cold metal generated during the filling process should not be present in the casting and should be completely driven into the slag collection bag.

According to the filling simulation and particle tracking simulation, as well as the requirements of the die-casting process, the position and size of the runner and slag collection ladle of the die-casting mold must be optimized accordingly; Based on solidification simulation and the wall thickness of the casting, the positions of cooling water and heating oil pipes in the mold, as well as point cooling, can be determined; Based on the simulation of mold erosion, it can be determined which areas of the mold require key spraying. Through simulation analysis, the manual optimization process of the gate and slag collection bag was solved during the design process, which saved the mold modification process caused by deviations based on experience during die casting mold manufacturing.

In order to further improve the quality of castings, some companies use vacuum technology to reduce the scrap rate and create higher value. Japan's vacuum pumping technology is very mature, and China has also borrowed some of their experience. The vacuum technology requires that the area of the mold exhaust duct be 1:100 of the punch area. Start the vacuum pump 0.4 seconds before the start of rapid injection. When designing the mold, the number of vacuum exhaust plates or vacuum valves can be determined based on the complexity of the product and the size of the mold.

If vacuum technology is well applied, the scrap rate of castings should be reduced to at least 20% of the original scrap rate. However, due to the high price of vacuum equipment, some die-casting mold factories only use it on product molds with high scrap rates.

For more information on die-casting molds, please follow Fenda Mold.