Low pressure casting defects of aluminum alloy flywheel housing

The structure of the flywheel housing is relatively complex and belongs to a typical thin-walled shell structure. Due to the need to install a variable displacement pump on the flywheel housing, one side of the flywheel housing is suspended outside, which has a great impact on the structural stiffness and is prone to deformation during processing. In particular, the connection between the outer part of the suspension and the bottom positioning surface has a sudden change in the cross-sectional area, Unreasonable structure will lead to stress concentration at this position. When subjected to abnormal vibration and turbulence, the stress is easy to exceed the material limit, resulting in cracking. The connection position between the flywheel housing and the frame body belongs to the engine mounting point, which directly bears the engine load and the overturning torque during power output. It is a large load bearing point. When the design strength is insufficient, it is easy to crack, which directly affects the driving safety of the road sweeper. Usually, this kind of flywheel housing is made by bending and welding of steel plate. Complex welding tooling is required to ensure the welding deformation. Machining is carried out after welding. The manufacturing cycle is long and the flywheel housing is heavy.

The structure of flywheel housing is shown in Figure 1. It is a thin-walled part with an average wall thickness of only 6mm, a weight of 4.5kg, a contour dimension of 354mmx434mmx97.6mm, and the material is alsi7mg0.3 alloy.

The flywheel housing is produced by low-pressure casting process. After the mold is opened, the parts are trial cast. After the trial casting, internal defects are found during the processing of the connecting hole, and the defect positions are wire cut. The defects of the parts after cutting are shown in Figure 2.

According to the analysis results, the liquid metal temperature is controlled at (725 ± 5) ° C, the mold temperature is controlled at (325 ± 20) ° C, the mold filling time is controlled at 15s, and the holding pressure is set at 1.5bar. The casting site pictures and blank pictures are shown in Figure 3.

Conduct wire cutting for area a and area B of trial cast parts, and the section after cutting is shown in Figure 4. It can be observed that the shrinkage problem in area a and area B has been well solved, and the tissue of the section plane is good and dense.