Die casting mold is an important process equipment in die casting production. The liquid metal is cooled and solidified in the die casting mold to form the final die casting. The shape, size and quality of die casting, as well as the smoothness of die casting production are closely related to the die casting mold, so it is very important to design the die casting mold correctly and reasonably.
Basic structure of die casting mold
The commonly used die casting die is composed of two half dies, which are called fixed die and moving die. There are also more complex die casting dies, not just two halves.
The roles of die casting die components are as follows：
- The straight runner connects to the pressure chamber or to the cross runner, including the gate sleeve and the shunting cone.
- The channel through which the alloy liquid enters the mold cavity includes inner runner, cross runner and straight runner, etc.
- The cavity is formed on the insert to form the geometry of the die cast.
- The core pulling mechanism can pull out and insert the movable core, including slide, slider, cylinder, slash, etc.
- The discharge system discharges gas and stores cold metal residue.
- The temperature control system controls the temperature of the die casting mold, including the cooling water pipe and heating oil pipe.
- The ejector mechanism ejects the die casting from the cavity, including the ejector rod, etc.
- Moving die frame is connected and fixed with moving die parts, including sleeve plate, support plate, etc.
Design of die casting mold
The design of die casting mold should pay attention to the following points:
- As far as possible to use advanced simple structure, to ensure stable and reliable operation and daily maintenance, repair.
- The modifiability of the gating system should be considered and necessary modifications can be made during debugging.
- Reasonable selection of various tolerances, scale and machining allowance to ensure reliable mold fit and required die casting accuracy.
- Suitable die material and reliable heat treatment process are selected to ensure the service life of die casting die.
- Should have enough stiffness and strength, can withstand the clamping pressure and expansion force, die casting production process does not produce deformation
- Use standardized die casting parts whenever possible to improve economy and interchangeability.
In the design of the mold, but also according to the projected area of the casting to calculate the total projected area of the die casting production, injection specific pressure, to choose the appropriate tonnage of the die casting machine.
After the die casting machine is selected, according to the size of the die casting machine, the moving and static plate and the eccentric position of the injection, the size of the mold, the center position, the hole position of the reset rod and the size of the connected part of the die casting machine are designed.
With the development of Chinese automobile manufacturing industry, more and more aluminum alloy materials are used for automobile parts, such as engine cylinder block, cylinder head, oil pan and various kinds of connecting support. With the increasing maturity of die casting technology, automobile manufacturers have higher and higher requirements on the internal quality of die casting parts, especially the German Volkswagen. Each type of engine die casting product has a set of corresponding technical requirements, and the product porosity requirement is a necessary requirement for each kind of parts.
The structure of some parts is very complex, need to do some corresponding structure in the mold to achieve batch die-casting production, for example, there are a variety of angles of threaded holes on the parts, to ensure the quality of the product after processing, must be made in the corresponding position of the mold core.
The core-pulling mechanism can be divided into mechanical type and hydraulic type according to the driving mode. Mechanical core-pulling is mainly achieved through the process of opening and closing die, such as oblique pin, bending pin, gear, rack and so on. The working principle of hydraulic core pulling mechanism is relatively simple, which directly uses hydraulic cylinder to pull core and reset. The hydraulic core pulling mechanism can choose the size of hydraulic cylinder according to the size of the core pulling force and the length of the core pulling distance. The product in the mold design first consider C, D three holes to cast out, can respectively use hydraulic core pulling mechanism to take the way of angular slide in the production to achieve the shape of the hole. Is the guide rail mechanism of hole D. In this way, the hydraulic cylinder can be designed on the outside of the mold. The advantage of this design is that the mold can be thinner and easy to maintain in the continuous production process.
In the process of continuous production, the mold core pulling hole will because many thrusting slide core-pulling hole deformation, in the mid-late die life, often can appear core-pulling research the phenomenon of death, in order to solve this problem, may be increased at the site of the core-pulling hole a set set, if there is a core pulling hole deformation, can change the set set to solve. This method can also be applied to the top rod of the mold, as long as you can add inserts, you can do this structure.
Die casting process system design
Mold frame design, into the design of the pouring system, early are to see two-dimensional or three-dimensional pattern according to practical experience to do this part. The position and direction of the inner runner are adjusted according to the internal quality of the product in the production process. In recent decades, with the development of numerical simulation technology of casting mold filling and solidification process and the market demand of casting industry, commercial software of casting process simulation has been appearing continuously. Many Oems also require to see the simulation process of die-casting before designing the mold, so many mold manufacturers use MAGMAsoft or ANYCASTING simulation software. At the beginning of the design, they import the designed 3D into this program, and after setting the process parameters of die-casting, Simulation software through a certain calculation to get close to the actual production effect of simulation animation.
Die casting process requirements simulation results are as follows:
- The alloy liquid should arrive at the inner gate more or less simultaneously.
- The alloy liquid should be filled smoothly during the filling process.
- The filling process can not appear gas or turbulence effect.
- Before filling is completed, the alloy liquid can not seal the slag collecting bag aisle.
- The cold metal produced from the filling process cannot be stored in the casting, and should be all driven to the slag collection bag.
According to the filling simulation and particle tracking simulation, as well as the requirements of the die casting process, the location and size of the mold runner and slag collection bag should be optimized accordingly. According to the solidification simulation and the wall thickness of the casting, the cooling water and heating pipe in the mold, and the position of the point cooling can be determined; According to the mold erosion simulation, we can determine which parts of the mold need to be sprayed. Through simulation analysis, the process of manual optimization of gate and slag-collecting bag is solved in the design, so as to save the mold modification process caused by the deviation of experience in the mold manufacturing.
In order to further improve the quality of castings, some companies use vacuum technology to reduce the rejection rate and create higher value. Japanese vacuum technology is very mature, our country has also used some of their experience. The vacuuming technology requires that the area of the die exhaust is 1:100 of the punch area. Start the vacuum pump 0.4s before the start of fast injection. The number of vacuum exhaust plate or vacuum valve can be determined according to the complexity of the product and the size of the mold when designing the mold. Figure 11 shows the structure of vacuuming on the mold.
If the application of vacuum technology is better, the casting rejection rate should be reduced to less than 20% of the original rejection rate. However, due to the high price of vacuuming equipment, some die casting plants only use it in the product mold with high rejection rate.
