1. Introduction
Lost foam casting is a new type of casting process that has developed rapidly in recent years. It has the advantages of low pollution, flexible process, low labor intensity, and good repeatability. It is especially suitable for the production of complex shell parts. However, in the actual production process, there are still some defects, such as sand sticking, porosity, and sand washing, which affect the quality of the castings. Therefore, it is necessary to analyze the causes of these defects and take corresponding countermeasures to improve the quality of the castings.
2. Analysis and Countermeasures of Sand Sticking Defects in Castings
2.1 Cause Analysis of Sand Sticking Defects
Sand sticking defect is a kind of defect formed by the adhesion of molten metal and molding sand on the surface of the casting during the pouring process. The 不合理 placement method, structure design or process design of the flywheel housing casting will lead to the inability to vibrate the mold cluster in the sand box, resulting in sand sticking defects.
2.2 Control Measures for Sand Sticking Defects
- Adjust the placement method of the white mold: According to the product structure, adjust the placement method of the white mold, with the motor hole of the flywheel housing facing upward, to facilitate the filling of molding sand and ensure that there is enough molding sand at the top of the flywheel housing.
- Increase the distance between two flywheel housings: Increase the distance between two flywheel housings from the original 80 mm to 120 mm to ensure that there is enough distance between the two mold clusters, thereby ensuring the compactness of the molding sand.
2.3 Production Verification of Sand Sticking Defects
After the analysis of the causes of the sand sticking problem of the flywheel housing and the implementation of the two measures of adjusting the product placement method and the combination spacing of the existing combination process, under the premise of ensuring that the variable factors such as the dipping process, pouring temperature, and vacuum pumping remain unchanged during the normal production process, production verification was carried out from small batches to large batches again. The sand sticking defect was 0, achieving the purpose of completely solving the sand sticking defect at the top of the flywheel housing.
3. Analysis and Countermeasures of Porosity Defects in Flywheel Housing Castings
3.1 Cause Analysis of Porosity Defects
When the molten iron enters the mold cluster, the white mold gasifies and decomposes to generate a large amount of gas and residues. If these gases cannot be discharged in time, porosity will be formed on the surface of the casting. The appearance of porosity is related to factors such as pouring temperature, coating permeability, and pouring speed.
3.2 Control Measures for Porosity Defects
- Increase the pouring temperature: Increase the pouring temperature from 1430 – 1440 °C to 1450 – 1460 °C.
- Reduce the coating thickness: Reduce the coating thickness at the motor hole from 2.0 mm to 0.5 mm.
- Increase the vacuum degree: Increase the vacuum degree from -0.025 MPa to -0.045 MPa.
- Add an exhaust sheet at the motor hole: Add an exhaust sheet with a size of 50 mm (length) × 30 mm (height) × 5 mm (width) at the motor hole.
3.3 Production Verification of Porosity Defects
After the analysis of the causes of the porosity problem of the flywheel housing and the implementation of the four measures of adjusting the product pouring temperature, coating thickness, pouring vacuum degree, and adding an exhaust sheet of the existing process parameters, in the process of the process test, by adopting the control variable method to test while ensuring that the other three process parameters remain unchanged. The results show that the scheme of adding an exhaust sheet is the best. Through subsequent small-batch to large-batch verification, all are processed normally, achieving the purpose of completely solving the porosity of the motor hole.
4. Analysis and Countermeasures of Sand Washing Defects in Connecting Rod Bracket Castings
4.1 Cause Analysis of Sand Washing Defects
During the pouring process, if the gating system of the mold cluster is not completely closed, especially the straight runner, it is easy to form a siphon, resulting in sand washing defects. In addition, the 不合理 design of the product gating system, unsmooth filling, and large local pressure in the inner runner can also cause the coating to crack due to the scouring of the molten iron, resulting in sand washing defects.
4.2 Control Measures for Sand Washing Defects
- Increase the coating thickness of the inner runner: The existing process is to dip the coating twice with a thickness of 1.5 mm. Add one more dip coating process for the inner runner, and the coating thickness is 2.2 mm.
- Increase the number of inner runners: Add one more inner runner of the same size at the bottom two points.
4.3 Production Verification of Sand Washing Defects
After the analysis of the causes of the sand washing problem of the connecting rod bracket and the implementation of the two measures of adjusting the coating thickness and the number of inlets of the existing process parameters, under the condition of ensuring that the influencing parameters such as pouring temperature and vacuum degree remain unchanged, production verification was carried out from small batches to large batches. The results show that the scheme of adding one inner runner at the bottom is the best. Through subsequent small-batch to large-batch verification, all are processed normally, achieving the purpose of completely solving the sand washing defect of the connecting rod bracket.
5. Conclusion
In the process of developing new products, casting defects should be avoided 巧妙 through process design. In the process of promoting process verification, the number of products should be increased gradually from small batches to large batches to avoid large losses due to insufficient consideration of the process. In the process of process verification, the five aspects of grasping the current situation, analyzing the causes, formulating plans, implementing countermeasures, and confirming the effects should be promoted step by step to ultimately achieve the purpose of completely solving the problem.
