1. Introduction
In the realm of modern manufacturing, the production of high – quality components is crucial. The moving coil skeleton, as the core component of the electric shaker, plays a vital role in various industries such as automotive and aerospace. It is used to transmit vibrations and carry test specimens, thus demanding characteristics like low weight, high stiffness, and high resonance frequency.
Traditional gravity casting for moving coil skeletons often leads to numerous defects, poor performance, and a low casting yield. Low – pressure casting, on the other hand, offers advantages such as smooth filling of liquid metal and sequential solidification. This process reduces the likelihood of gas entrapment, slag inclusion, and shrinkage defects, ultimately enhancing the mechanical properties of the castings.
With the development of computer – aided engineering, numerical simulation has become an essential tool in casting process design. Software like ProCAST enables engineers to analyze the casting process, predict defects, and optimize process parameters without the need for extensive physical trials. This paper focuses on using ProCAST to simulate the low – pressure casting process of ZL302 aluminium alloy moving coil skeletons, aiming to explore the impact of different process parameters on the casting quality.
2. Aluminium Alloy and Low – pressure Casting Basics
2.1 Aluminium Alloy ZL302
ZL302 is a commonly used aluminium alloy in the casting industry. Its chemical composition, as shown in Table 1, mainly consists of magnesium (Mg), silicon (Si), manganese (Mn), and aluminium (Al). The specific composition range of each element endows the alloy with certain mechanical properties, making it suitable for the production of moving coil skeletons.
| Element | Mass Fraction (%) |
|---|---|
| Mg | 4.5 – 5.5 |
| Si | 0.8 – 1.3 |
| Mn | 0.1 – 0.4 |
| Al | Balance |
| Table 1 Chemical Composition of ZL302 Aluminium Alloy |
2.2 Low – pressure Casting Process
Low – pressure casting is a casting method that fills the mold under counter – gravity and solidifies under a certain pressure. The process parameters that significantly affect the casting quality include pouring temperature, sand mold preheating temperature, and holding pressure.
During the low – pressure casting process, the liquid metal is forced to rise from the crucible into the mold through the riser tube under the action of pressure. Smooth filling is achieved, which reduces the risk of turbulence and gas entrapment. The holding pressure during solidification helps to feed the liquid metal to the areas with solidification shrinkage, minimizing shrinkage porosity and cavities.
3. Model Establishment for Moving Coil Skeleton
3.1 Geometric Modeling
The moving coil skeleton has a complex structure with an outer contour size of 320mm×360mm×320mm, a maximum wall thickness of 23mm, and a minimum wall thickness of only 8mm. To accurately simulate the casting process, a geometric model was first created using the 3D modeling software UG. In the model, all surface holes were set as non – cast holes, and 4mm machining allowances were added to the upper and lower surfaces.
3.2 Design of the Gating System
A slot – type gating system was adopted for the casting, as shown in Figure 1. The double riser openings and horizontal runners at the lower part of the casting determine the filling state of the liquid metal during the casting process. The connection between the casting and the slot – type inner runner ensures smooth filling of the liquid metal, reducing gas entrapment and slag inclusion. The riser at the top of the casting plays a role in feeding and slag collection, which helps to reduce the shrinkage porosity and cavity rate of the casting and improve the casting quality.
3.3 Mesh generation
After the geometric model was completed, it was imported into the ProCAST software in X_T file format for mesh generation. Mesh inspection was carried out on the casting model, and defective models were repaired. The cell sizes of the sand mold and casting parts were set to 10mm and 5mm respectively. Finally, the number of surface meshes and volume meshes reached 195,496 and 3,926,891 respectively, as shown in Figure 1d.
4. Numerical Simulation Scheme Design
4.1 Selection of Process Parameters
Based on the principles of low – pressure casting and production experience, the main process parameters selected for this simulation include pouring temperature, sand mold preheating temperature, and holding pressure. The pouring temperature was set in the range of 690 – 730°C, the sand mold preheating temperature was set between 30 – 100°C, and the holding pressure was set at 23 – 33kPa.
4.2 Orthogonal Experiment Design
An orthogonal experiment was designed to systematically study the influence of different process parameters on the low – pressure casting of aluminium alloy moving coil skeletons. The designed numerical simulation schemes are shown in Table 2.
| Scheme | Pouring Temperature (°C) | Sand Mold Preheating Temperature (°C) | Holding Pressure (kPa) |
|---|---|---|---|
| 1 | 690 | 30 | 23 |
| 2 | 710 | 30 | 23 |
| 3 | 730 | 30 | 23 |
| 4 | 750 | 30 | 23 |
| 5 | 730 | 30 | 28 |
| 6 | 730 | 30 | 33 |
| 7 | 730 | 100 | 23 |
| Table 2 Numerical Simulation Schemes |
5. Numerical Simulation Setup in ProCAST
5.1 Software Module Settings
In the ProCAST software, the CAST module was used for simulation. The gravity direction was set to be opposite to the filling direction of the liquid metal. The virtual sand box material was set as Resin Bonded Sand, which was defined as a solid with a linear – elastic mechanical type. The casting material was ZL302, with a rigid mechanical type.
5.2 Heat Transfer and Boundary Conditions
The heat transfer coefficient between the liquid metal and the sand mold was set to \(h = 500~W/(m^{2}\cdot K)\). The outer surface of the sand box was set as air cooling, and the inlet pressure was set at the riser tube opening. The value of this pressure parameter was 0.1MPa higher than the pressure value in the casting process parameters. In the Simulation Parameters, LPDC Filling was selected for the simulation.
6. Simulation Results and Analysis
6.1 Influence of Pouring Temperature on the Low – pressure Casting Process
6.1.1 Analysis of the mold filling process
By selecting Schemes 1 – 4 for numerical simulation analysis, it was found that the filling processes of the castings under the four groups of schemes were relatively consistent. The liquid metal smoothly filled the mold from the riser opening without gas entrapment or splashing. As the pouring temperature increased from 690°C to 750°C, the filling time of the casting decreased from 22s to 20s, as shown in Table 3. This indicates that the increase in pouring temperature improves the filling efficiency of the casting and shortens the filling time. The reason is that when the pouring temperature is low, the fluidity of the liquid metal deteriorates, making it difficult to fill the mold cavity and potentially resulting in cold shuts and misruns.
| Pouring Temperature (°C) | Filling Time (s) |
|---|---|
| 690 | 22 |
| 710 | 21 |
| 730 | 20.5 |
| 750 | 20 |
| Table 3 Filling Time at Different Pouring Temperatures |
6.1.2 Analysis of shrinkage cavities and porosity
Figure 2 shows the distribution of shrinkage porosity and cavities in the castings at different pouring temperatures. The distribution positions of shrinkage porosity and cavities in the four groups of schemes were relatively consistent, mainly concentrated at the connection between the rib plate and the base of the casting. This is because the wall thickness at this location is relatively large, which is prone to forming hot spots and independent liquid – phase regions. During the holding pressure solidification process, the pressure cannot effectively feed the liquid metal to the hot – spot areas, resulting in shrinkage porosity and cavity defects.
6.2 Influence of Sand Mold Preheating Temperature on the Low – pressure Casting Process
6.2.1 Analysis of the filling process
To explore the influence of the sand mold preheating temperature on the low – pressure casting process of the moving coil skeleton, Schemes 3 and 7 were selected for numerical simulation analysis. The results showed that the filling processes of the liquid metal at different sand mold preheating temperatures were stable without splashing. As the sand mold preheating temperature increased, the filling time of the liquid metal did not change significantly, indicating that at a relatively high pouring temperature, the sand mold preheating temperature had little effect on the filling rate.
6.2.2 Analysis of shrinkage cavity and porosity
Figure 3 shows the distribution of shrinkage porosity and cavities in the castings at different sand mold preheating temperatures. Although the distribution positions of shrinkage porosity and cavities were basically the same, when the sand mold preheating temperature reached 100°C, the volume of shrinkage porosity and cavities inside the casting decreased. The main reason is that as the sand mold preheating temperature increases, the temperature of the liquid metal at the end of filling is high. During the holding pressure stage, the liquid metal can be more effectively fed to the hot – spot areas under pressure, improving the feeding effect.
6.3.2 Analysis of shrinkage cavity and porosity
Figure 4 shows the distribution of shrinkage porosity and cavities in the castings after solidification at different holding pressures. As the holding pressure increased, the volume of shrinkage porosity and cavities in the casting decreased from 0.13 \(cm^{3}\) to 0.11 \(cm^{3}\). Therefore, appropriately increasing the holding pressure can improve the quality of the casting.
7. Optimization of Low – pressure Casting Process
7.1 Comprehensive Consideration of Process Parameters
Based on the above simulation results, in actual production, it is necessary to comprehensively consider the influence of various process parameters. When ensuring the strength of the sand mold, an appropriate increase in the holding pressure can effectively reduce shrinkage porosity and cavity defects. At the same time, an appropriate increase in the pouring temperature can improve the filling efficiency and reduce shrinkage porosity and cavity volume. Although the influence of the sand mold preheating temperature on the filling rate is small, increasing it appropriately can also improve the feeding effect of the liquid metal.
7.2 Verification of Optimized Process Parameters
After determining the optimized process parameters, it is necessary to verify them through physical experiments. By comparing the experimental results with the simulation results, further adjustments and optimizations can be made to ensure the accuracy and reliability of the process parameters. This iterative process helps to continuously improve the quality of the castings and the efficiency of the production process.
8. Conclusion
In this study, the low – pressure casting process of ZL302 aluminium alloy moving coil skeletons was numerically simulated using ProCAST software. The following conclusions were drawn:
- With the increase of pouring temperature, the fluidity of the liquid metal increases, the filling time decreases, and the volume of shrinkage porosity and cavities in the casting first decreases and then increases. Appropriate increase in pouring temperature can improve casting defects.
- The increase of sand mold preheating temperature has little effect on the filling rate of the casting, but when the sand mold preheating temperature increases from 30°C to 100°C, the volume of shrinkage porosity and cavities in the casting decreases.
- During the holding pressure solidification stage, with the increase of holding pressure, the fluidity and feeding performance of the liquid metal are enhanced, and the volume of shrinkage porosity and cavities in the casting decreases from 0.13 \(cm^{3}\) to 0.11 \(cm^{3}\). Therefore, in actual production, under the premise of ensuring the strength of the sand mold, appropriately increasing the holding pressure can improve the casting quality.
These research results provide a theoretical basis and technical support for the production of aluminium alloy moving coil skeletons, and can also be used as a reference for the low – pressure casting process design of other similar components. Future research can focus on further optimizing the process parameters, exploring new casting technologies, and improving the overall performance of the castings.
