In the work developed in this paper, the model of the microstructural behavior of Inconel 718 for the rotary forging process is studied. This process is presented as an alternative to the conventional forging. The window process of Inconel 718 is very narrow, so the requirements for manufacturing Inconel are very restrictive. Optimization of the rotary forging process was carried out in order to manufacture Inconel pieces with good microstructural distribution. Microstructural specification was given by aeronautic sector. Numerical work was done in order to simulate the microstructural behavior during the forming process. This method was used: a) to understand the recrystallization mechanism that take place in rotary forging processes, b) to compare the microstructure between a piece done in conventional forging and another done in rotary forging and c) to study the influence of the initial grain size in the final piece.
Microstructural behaviour of Inconel 718 using rotary forging as forming process is presented in this paper. This work is the continuation of a previous one, presented in ESAFORM 2012, in which the numerical model was described and previous results about microstructural behaviour were shown. Several simulations are carried out in order to investigate the effect of initial grain size, temperature and strain rate in microstructure. Experimental tests are done in order to validate the numerical results, analyzing the final microstructure. Preparation of the experimental equipment is shown: heating tool system, thermal isolation technique, tool design for the integration of the heating and the isolation system. Heat loss during the transfer operation between furnace and rotary forging machine is measured experimentally, in order to obtain a precise initial temperature value of the part at the beginning of the process. The experimental tests allow validating the simulation work, obtaining the real input parameters for the numerical calculation. Two ways of forming are obtained depending on the initial grain size. The optimal combination of the rotary forging process parameters listed above is determined in achieving a fine and homogeneous microstructure.
The forging process plays an important role in the automotive industry thanks to the good mechanical properties of the forged parts. Nowadays, due to the European policy of increasing efficiency in raw material and energy usage, the metal forming sector is demanding new innovative technologies. In this context, rotary extrusion technology is a very promising metal forming alternative to the drilling techniques after forging processes.The presented work is focused on hollow shafts that are usually manufactured using a combination of forming and metal cutting techniques. Deep drilling is the most common technique to obtain internal holes in the automotive hollow parts, but it is an expensive process in terms of material usage. In this framework, rotary extrusion appears as an alternative technology that leads to the reduction of material usage and process time. The tubular shape is formed with the combination of two forming processes: flow forming and backward extrusion.This paper presents the development of a simulation methodology, the process design for a hollow part, the specifications of the experimental unit, and the manufactured prototypes in order to validate the simulation model. Also the incremental process is improved thanks to a sensitivity study of the rollers geometry. Rotary extrusion experiments are done using a modified flow forming machine and 20% material saving is achieved when obtaining the deep hole in comparison to the current deep drilling technology. The process design and numerical model tasks carried out try to provide the industry manufacturers an alternative technology to drilled parts considering the advantages of rotary extrusion parts.
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