Process improvement of LY1 flat-cone threaded hollow rivet black impression

Material 2A01 (LY1) flat-cone threaded hollow rivets (see Figure 1), mainly used in the aerospace industry, the demand for this product in the aerospace field is large. The appearance of the product requires that the surface should be smooth and burr-free, and cracks, scars, scratches, crushing and other mechanical damage are not allowed. Therefore, for the flat-cone threaded hollow rivets produced by the company, the vertical black mark on the surface of the raw material 2A01 cannot meet the appearance quality requirements of the product.

Fig.1 Schematic diagram of the structure of the flat cone threaded hollow rivet

1. Cause analysis

The product is mainly made by cold head forming → heat treatment → mechanical processing → surface treatment process. Since the shape of the product is mainly cold-formed, the surface deformation of the product is caused by the cold extrusion force during the cold head forming, which requires high quality of the appearance of the raw material, and no cracks, scars, scratches or pressures are allowed. Intrinsic surface defects that injure other mechanical damage. However, due to various reasons, the raw materials before the actual product processing, such as the indentation of the materials in the transportation, the management of the warehouse is not in place to produce defects such as black marks on the surface, so that the inherent defects of the raw materials before processing can not be avoided. Such inherent raw material defects are subjected to cold head forming, heat treatment, and mechanical processing, which are difficult to ensure the appearance quality of the product - scars that are not allowed. Therefore, in order to ensure the final appearance requirements of the product under the premise of actual raw material defects, the existing process must be improved to meet and guarantee.

2. Process improvement results

According to the analysis of the above reasons, in order to obtain the quality requirements of the product without scars, it is necessary to ensure that the raw materials must not have black mark defects before the cold heading is formed. In view of the inherent defects of the black marks of the actual raw materials, it is necessary to remove the method before cold heading. The black marks cause surface defects to be free from the inherent defects of the raw materials on the extruded belt (see Figure 2). Therefore, it is possible to remove the black mark on the surface of the original 2A01 aluminum wire by performing alkaline washing on the raw material coil 2A01 aluminum wire before cold head forming (see Fig. 3). Because the outer diameter of the raw material is only 0.02~0.05mm in the alkaline washing process, it does not affect the outer diameter size requirement of the wire before cold heading. After the material was subjected to cold head forming, heat treatment, mechanical processing, and surface treatment, the scar after processing of the original product did not exist (see Fig. 4).

Figure 2 2A01 wire before alkaline washing

Figure 3 LY1 wire after alkaline washing

Figure 4 Flat cone threaded hollow rivet

3. Conclusion

After the process test and its batch verification, the material 2A01 flat-cone threaded hollow rivet is completely guaranteed and meets the appearance quality requirements of the product after the surface alkali washing process is improved before the cold head forming. Therefore, the improved process method is: cutting→alkaline washing→cold forming→heat treatment→machining→surface treatment.

　　 About the author: Yang Yuxi, Wang Feng, Guizhou Aerospace Precision Manufacturing Co., Ltd.