Insufficient pouring and cold shuts are the most common defects in the forging process of precision castings. In many cases, these two defects may lead to complete scrapping of the castings, so attention should be paid to avoiding them during the forging process. Underpouring refers to the incomplete casting caused by the inability of molten metal to fill the mold cavity. The characteristic of this defect is the smooth circular edge perforation on the casting wall or the inability of one or more ends of the casting to fill with metal fluid. Cold shut refers to a casting where two strands of metal are not fully fused and exhibit obvious discontinuous defects. This defect usually manifests as cracks or wrinkles with smooth circular edges.

The characteristics of these two types of defects are: firstly, they are easy to detect during casting inspection; Secondly, apart from the cleaning process, there are reasons for almost every casting process. Based on years of production practice and relevant materials, the author will discuss the reasons and preventive measures for casting and cold isolation.

Casting and shape design

(1) Due to uneven thickness of the casting section, metal flow is interrupted. In some casting designs, the thin-walled parts are located in areas that are difficult for molten metal to reach, making it difficult to properly set up the pouring system. Where possible, this design should be modified, and in cases where it is impossible to change the design, a fairly complex gating system should be used to avoid such defects.

(2) The cross-section of the casting is relatively thin, and this design did not take into account the flow and solidification laws of the metal. If the designer cannot make the cross-section thicker, the only remedy is to increase the pouring temperature of the metal or change its chemical composition to improve its fluidity. A better remedy is to use castings (cores), which do not produce sudden cooling but increase production costs, so the design should be changed as much as possible.

2. Casting shape

(1) Appearance or core box wear causes the casting section to be too thin. Sand is a material with high wear force, which can cause appearance wear, resulting in thinning of the casting cross-section, insufficient casting, and cold insulation defects. An effective preventive measure is to establish a regular inspection system to inspect the appearance of defects.

(2) Poor shape strength! Under the pressure of forming or core making, the shape may deform due to insufficient strength. This shape and core box can cause deformation of the casting and core. This not only causes the metal liquid to flow as expected, but also results in the casting section being too thin. The method of correction is to enhance the appearance.

(3) The appearance or positioning of the core box is incorrect, due to wear on the positioning pins and sleeve. Too few positioning pins or too small positioning pin size are prone to wear. When the upper and lower molds of the bottom plate are installed in half according to the centerline, there may also be dislocation defects. If the sample casting is not cast, it is difficult to verify whether the two halves installed on the upper and lower mold bottom plates are aligned. The primary measure to prevent such defects is to strengthen inspections.