Application Of Numerical Simulation In Sand Casting And Die Casting

In order to obtain high quality castings, a reasonable set of process parameters must be determined. The purpose of numerical simulation or numerical test is to analyze the influence of process parameters on the process implementation results by numerical calculation of the filling and solidification process of castings, so that technicians can verify and optimize the designed casting process and seek process problems as soon as possible. The process of numerical simulation is to establish a mathematical model, adopt a more scientific and reasonable solution method, and finally realize the casting under the production conditions, predict the liquid filling and solidification process, obtain the defect situation, and optimize the casting process.

Since casting is a solid-to-liquid to solid-state process, this process is full of uncontrollable factors, especially the liquid filling process and solidification process, but with the development of numerical simulation technology, we can preset some the parameters of the control factors (for example, sand casting, such as: various parameters of the sand, the temperature and chemical composition of the metal liquid), according to these parameters set in the numerical simulation software (such as procast), to carry out flow and solidification simulation, process optimization is performed based on the results of the simulation. Casting filling and solidification process and the development of computer simulation has entered the practical stage of engineering, and casting production is guided by scientific theory. The numerical simulation of the casting filling solidification process can help the staff to effectively predict the various defects, the size, location and time of occurrence of the casting before the actual casting, and take countermeasures to ensure the quality of the casting before pouring. Shorten the trial cycle and reduce production costs.

1. Vertical boxless shape (sand type)

Before the mold is made, gravity casting can be carried out according to the actual production conditions of the site, various parameters of the molding sand, the pouring temperature and chemical composition of the metal liquid, and the casting process scheme is simulated and analyzed.

Optimized process solutions can be obtained in a shorter period of time, reducing costs and development time, eliminating casting defects and improving product quality.

The main contents of the casting simulation include:

(1) Liquid flow simulation (filling);

(2) Solidification simulation;

(3) Microscopic simulation;

(4) Defect analysis and prediction (shrinkage, shrinkage porosity, sand washing, insufficient pouring).

It can be seen from the flow simulation that there is a vortex phenomenon, which may form defects such as bubbles and dross, and the solution can be adjusted to make the filling stable. Temperature field changes occur in the solidification simulation, and risers are set according to these changes and adjusted to optimize the solution, and the yield can be increased to maximize the benefits.

2. Low pressure die casting (wheel)

In the low pressure die casting process of wheel castings, low pressure casting is now using bottom injection casting. Air cooling and water cooling methods are used to control the mold temperature, which is important to prevent shrinkage, coarse structure and prolonged production cycle. Now taking water cooling as an example, the calculation and water cooling controller are simulated in the metal mold design, and a reasonable cooling system is designed by simulating the flow and solidification of the hub casting during the cycle. The heat loss or accumulation of the mold is controlled by using a water cooled controller. Productivity can be increased by reducing cycle times and casting defects on the foundry's low pressure casting wheel casting line.

The simulation calculation first performs pre-processing. The main work of the preprocessing is to perform mesh analysis on the 3D solid modeling of the casting mold, then import the solid modeling file into the simulation software, and input the actual setting conditions, including the inflow boundary, initial temperature, and thermoelectricity. Even position setting, pouring temperature, chemical composition of aluminum liquid, pouring time etc.. After the pretreatment is completed, the numerical simulation calculation is started, including the forming and opening process in one cycle. The forming process considers filling and solidification, and the opening process only considers the heat transfer of the mold cavity. The numerical simulation calculation section can consider a plurality of cyclic processes in order to observe whether the production process is stable.

After the simulation calculation is completed, it is a post-processing process, which is mainly to visually analyze the simulation calculation results and adjust the casting process parameters.

Through this simulation analysis, the influence of temperature and filling on the wheel defect can be predicted. As a reference, the process personnel can optimize the solution according to the result and control the temperature to improve the quality of the product. Finally, the actual results can be compared with the simulation results for further verification.

3. Progress in numerical simulation of die casting process

High pressure die casting production process is a dynamic cycle process. During the die casting process, the mold temperature rises or falls periodically with the die casting cycle. In a very short time after the molten metal is pressed, the temperature of the mold rises to the highest point and then decreases rapidly. The change thereafter is smooth and the magnitude and speed of the change in the temperature of the mold gradually decrease as the distance from the casting increases. These periodic changes cause periodic thermal expansion, shrinkage, and thermal stress on the mold surface, which ultimately leads to thermal fatigue failure of the mold. Therefore, the numerical simulation method is used to predict the temperature distribution and variation of casting parts and mold parts, which can achieve the purpose of optimizing the process control and ensuring the quality of castings, shortening the trial production cycle, reducing production costs and improving economic benefits.

Die casting molds have high cost, difficult production and high precision, which has high requirements for designers. The best result is a success and maximize the benefits. Numerical simulation provides a good platform for the inspection process to be performed before the mold is produced, so that the die casting process is digitally represented.

4. Conclusion

Through the above introduction, the application process of numerical simulation technology in sand casting and die casting actual production is described. The results show that the casting numerical simulation technology can help designers to predict the defects that may occur in the casting process, and use different methods to compare and develop the optimal process. The solution ultimately optimizes the casting process. In terms of mold cost, it can reduce the cost of mold production and repair costs caused by process reasons, and shorten the product development cycle. At the same time, it saves the cost of the test and has significant results in terms of cost CI. With the development of computer software and hardware software technology, numerical simulation technology will be more widely used in foundry production, making the uncontrollable flow and solidification process gradually become a controllable factor.

来源：科技论坛  作者：付立宾 白云鹏 张 磊