Problems of the process of manufacturing precision forgings in multiple systems on a hot hydraulic hammer

Abstract

The article presents the results of a complex analysis referring to a periodical occurrence of forging defects in the form of twisting of pin-type elements (perpendicular to the main forging axis) as well as lack of total filling of these areas on the forgings in the process of hot precision forging on a hammer. The studies included: an analysis of the forging technology, advanced numerical simulations of the process and dynamic tests of the mutual shifting of the tools with the use of a high-speed measurement camera. The hot precision forging process was realized on a double operation hydraulic hammer with the maximal energy of 16 kJ, as a result of which, a so-called leaf is formed in the dies in two operations, which has 6 relatively small forgings (the mass of one is about 40 g), characterizing in a narrowed scope of dimension-shape tolerance (0.1–0.2 mm and 0.5–1°). The performed preliminary process analysis showed that, for this type of forgings made in a dynamic manner on a hammer, the key role is played by elastic deformations as well as the construction of the dies (application of guide locks) and the impression geometry. Additionally, during the forging process, in the case of pin-type elements (shape of a truncated cone with the convergence of 1°), their twisting was observed as well as small underfills caused by “closed volumes”, connected with the non-vaporized lubricant and the formation of air pockets. The mentioned problems relating to this process significantly affect the quality and precision of the forgings and cause defects. For this reason, based on the results of the conducted tests and analyses, a different approach to the design of dies was applied than in standard hammer forging technologies. It was introduced the necessary changes in the technology as well as modify the construction and geometry of the tools (in the lower die a negative slope was applied) in order to eliminate joggle and twisting of the forging elements, which disqualify such items.