Plane strain extrusion forging process
Hu, Weiping (1992) Plane strain extrusion forging process. PhD thesis, Dublin City University.
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Metal forming is one of the oldest materials processing techniques which are still playing important roles in modem life. In metal forming, as in any other manufacturing processes, the ultimate goal is to produce components of a selected material with a required geometrical shape and a structure optimised for the proposed service environment. Of the above production of the desired shape is a major part of the manufacturing process.
Extrusion forging is a metal forming process in which the billet is partially undergoing extrusion, thus forming a boss, and partially deformed laterally. The understanding of the metal flow and the prediction of forging load in such a process is important both for the die design and the product quality control.
Due to the complexity in deformation pattern and the inherent unsteadiness of the operation, it is at present very difficult to obtain a satisfactory analytical solution. In this work, an approximate analysis has been carried out by assuming that the deformation will go through three distinctive modes, and an over-estimation solution has subsequently been formed.
Numerical analysis has been performed using a commercial finite element analysis package. The plane strain extrusion forging of rectangular billets has been simulated using 8-noded elements. Results of deformation profile and forging load are obtained.
Experimental work has been carried out by deforming rectangular billets between two dies, with at least one of them grooved. The effect of material property, forming speed and the lubricating condition at the die-billet interface has been studied experimentally, by applying different billet materials, different forming speeds and different lubricants at the die/billet interfaces.
The analytical approach is capable of predicting the deformed profiles as well as the forging loads for certain die combinations, while for others the result is only valid within about 50% of axial deformation. The results from the finite element analysis give excellent correlation with the experimental results.
From the analytical, numerical and the experimental studies it has been found that the plane strain extrusion forging of rectangular billets between grooved dies takes place with significant inward barrelling. The deformed profile depends mainly on the relative geometry of the die/billet combination, which is characterized by the ratio of the groove width to billet width, and the cross-section aspect ratio of the billet. The material properties of the billet material have been found having little effect on the deformation patterns, though the forging load varied because of the change in the yield stress. The interfacial friction has been noted affecting the forging load as well as the deformed profiles. The effect of the forming speed is mainly on the forging load rather than the deformation geometry.
The present study provides a better understanding of the plane strain extrusion forging process, which is similar to the initial stages of closed the die forging. The results of the study can be applied to the product quality control and tool design in such metal forming operations.
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