What Is The Relationship Between Die Casting Simulation And Die Casting Production?

Die casting simulation refers to the simulation analysis of die casting filling, heat conduction and solidification process before the actual die casting. With the development of die flow analysis software, most die casting enterprises have realized that CAE technology can bring practical benefits to enterprises. How does die casting simulation technology reflect its value in daily die casting production? The author believes that at this stage, the value of die casting simulation is mainly reflected in the design of die casting die, the calculation and setting of die casting process parameters. This paper will analyze the relationship between die casting production and simulation analysis from the following aspects and provide new ideas for everyone to better understand die flow analysis, so as to better use die flow analysis tools to serve to die casting production. Here is everything you know about the relationship between casting simulation and die casting production.

 

The difference between theory and practice of die casting process conditions.

Perhaps many die-casting workers find that even though they have done many die-casting simulations before the completion of the die-casting mold, and have obtained a relatively satisfactory mold scheme through the comparison of simulation results, such problems will still occur in the actual production process.

 

The author thinks that the combination of theory and practice is insufficient.

In high-pressure die-casting, specific die-casting parts have specific geometry. Based on the classic theory of high-pressure die-casting, these geometry parameters are substituted into the mathematical model related to high-pressure die-casting process, and key parameters such as punch critical speed, ingate speed and punch speed can be quickly calculated. The main function of the pre-processing module of the die-casting simulation software in the industry now is to substitute these key parameters as boundary conditions into the built-in solver of the software, carry out numerical calculation through a high-performance computer, and complete the simulation of the die-casting process.

Usually, after we analyze and compare the mold flow of the known castings, if we get a satisfactory die-casting mold scheme and die-casting process scheme, we will start to introduce the actual die-casting production. However, in actual production, due to the close cooperation between members or the stability level of equipment performance, the conditions that should have been prepared according to the data in the pre-processing module of the simulation software may be changed in the actual operation process, resulting in unsatisfactory results.

 

Here is an example of exception resolution:

In the process development stage of the casting, according to the calculation results of the injection process parameters, the high-speed speed of the punch set in the simulation process is 4m / S. The gas trapping simulation results show that there is no gas trapping inside the product, so it can be considered that the casting pouring design is reasonable.

However, during the commissioning production stage, the on-site process commissioning personnel continuously produced 3-5 molds. It was found that the inside of the cast after cutting. Obviously, the distribution of these holes on the cutting plane was not the result we wanted.

 

Through careful inspection of the actual die casting process curve fed back by the die casting machine, at least two problems are found:

① The measured punch speed is 3.1m/s, 20% lower than the set speed of 3.9m/s;

② Since the pressurization is started before the filling of the cavity is completed, the pressurization is premature, and the pressurization is actually invalid.

After shutdown, it was found that the energy storage pressure of the accumulator of the die-casting machine was too small, so an appropriate amount of nitrogen was injected into the accumulator. Meanwhile, it was found that the punch resistance continued to increase during the injection process (usually more than 100bar is abnormal), and the punch was replaced in time. After debugging and replacement, the final pressure injection process curve tends to be normal: the measured speed (3.8-4.12) m / s has approached the set speed of 3.9m/s, and the pressurization curve also tends to be normal. The final purpose of the above operation is to make the measured punch speed tend to the set punch speed.

 

After the equipment is adjusted, the quality of the castings produced after commissioning gradually reaches the standard and tends to be stable.

In addition to the above reasons, the measured ejection velocity value is lower than the set value may also be due to:

① There is friction resistance between the surface of the pressure chamber and the surface of the punch;

② The viscosity of the hydraulic oil in the injection cylinder of the die casting machine will change with the temperature, causing the speed of the injection rod pushing the punch to be unstable.

It can be seen that the actual die-casting process is complex and changeable, and the parameters used for simulation are relatively ideal and fixed. We should try our best to take the simulation results as the guide, and constantly adjust the equipment parameters during the die-casting process, so as to make the actual parameters fully close to the ideal process parameters.

 

The environmental factors of the actual die casting process are complex and changeable, and the simulation process cannot be considered one by one.

For example, the release agent sprayed in the die-casting mold before the die-casting machine closes the mold, especially the water-based release agent, often generates a large amount of gas after the mold is closed, making the actual situation in the mold cavity more complicated than the setting of simulation analysis parameters, and also leading to a large difference between the actual production results and the simulation results.

For another example, the initial mold temperature set in the mold flow analysis may be different from the actual measured mold temperature. In the cycle of die casting production, the temperature of the mold cavity surface fluctuates greatly. When the molten metal flows through the mold cavity, the temperature of the mold cavity surface rapidly jumps from the set initial temperature to the peak temperature. The temperature set by simulation is usually defined as the mold temperature close to the stable production of die casting. This temperature difference will also lead to a large difference between the simulation and the actual. The surface temperature of the mold cavity changes with time, so it is difficult to obtain accurate measurement results in practice. As a general guiding principle, the mold temperature set in the simulation software should be higher than the surface temperature that people may expect, because the heat loss of the mold temperature before the molten metal is poured into the pressure chamber should be considered.

 

Selection of actual operation mode of simulation software.

In the form of die-casting simulation, the current die-casting simulation software can provide various forms of simulation, such as: Gate filling mode, multi gate filling mode, belt filling mode, etc. the simulation results of the same casting with different modes will be different.

In actual work, in order to save development time, multi gate filling simulation is usually carried out first, and then gate filling simulation is carried out after appropriate adjustment according to the results. Finally, after having a clear idea, the material pipe filling method is used again for simulation, so that the accuracy of the results obtained is higher.

Although the quality of die-casting products is closely related to the on-site work experience of die-casting practitioners, can we do a good job of die-casting only by relying on on on-site experience? Even if we can do it well, I’m afraid the process will not be so easy. However, if the die casting simulation technology can be scientifically and fully combined with the actual production, it will certainly get twice the result with half the effort.

Nevertheless, we should also look at this issue dialectically. The die casting simulation technology is based on the powerful computing power of modern computers, fully combines the known knowledge of computational fluid mechanics, heat transfer, materials science and applied mathematics, and displays the actual die casting process in the form of cloud pictures (pictures or videos) through virtual means, so as to help engineers predict some possible adverse factors. However, there are errors in the process of virtual die casting, which depends on the accuracy of the simulation software, the treatment of the initial boundary conditions, and the experience of the die casting simulation operators. Therefore, in die-casting production, we should combine practice, be familiar with theory, not blindly operate, and pay attention to the guiding significance of simulation technology to die-casting production.