3D Analysis of Combined Extrusion-Forging Processes

Abstract

Combined extrusion-forging processes are now getting importance for its abilities to give improved material properties, high production rate and less material waste when compared with that produced by machining, casting or by assembling the individual parts produced by different manufacturing processes. In its simplest form of combined extrusion-forging process, a billet is forged by punch and dies with punch/die or both containing an opening for extrusion. This tooling arrangement permits the simultaneous lateral spread due to forging, and backward/forward extrusion or both forward and backward extrusion simultaneously through the die/punch opening(s). The flow pattern of the material is dependent on a number of factors, including the frictional conditions at the work piece/tooling interface; the geometry of the dies, particularly the size of the dies hole; the material type; and the percentage area reductions. Due to the complexity of the analysis, and because of the large number of process variables, it is difficult to estimate the forming force required to manufacture a given component. In this direction, the present work emphasizes on estimation of forming force for forward and forward-backward extrusion-forging process of regular shapes and different tooth spur gear shapes.
Though technological barriers exist, as in most manufacturing areas, it is important to overcome them by developing proper understanding of the process with related attributes. In this direction, present work emphasis on the forward and forward-backward extrusion-forging process analysis of different methodology applied to different section heads with circular shaft. Based on these guiding principles, the methodology applied are upper bound analysis (particularly reformulated spatial elemental rigid region (SERR) technique), finite element analysis (commercial package DEFORM®-3D codes), and experimentation.
The understandings generated in this work not only properly explain the complex material flow mechanism but also presents in detail the upper bound analysis. The results of UBA are well validated with that of finite element analysis and experimental results. The achievements realized from the present work can be summarized as follows:
 Experimental studies are carried out with a view to compare some of the theoretical results predicated using the upper bound method in general, modified SERR technique in particular, with that obtained from the experiment. SERR technique is used to analysis the last stage of the combined extrusion forging process, which requires maximum load.
 A computational model for forward and forward-backward extrusion-forging process with and without considering friction is developed by incorporating all special features for all the section extrusions. Three formulations for forward extrusion-forging process and six formulations for forward-backward extrusion-forging processes are analyzed and the optimal solution for non-dimensional extrusion pressure is found out for further computation. The model is developed using FORTRAN code.
 Experiments are performed for triangle, square, pentagon, hexagon, 4-tooth, 6-tooth, 8-tooth and 12-tooth spur gear (involutes profile and pressure angle 14½º) is form using flat / square dies. Both forward and forward-backward extrusion-forging processes are carried out.
 FEM based commercial package DEFORM®-3D code is used for finite element analysis of the processes.
 The results obtained from experimental investigation are found to be in good agreement with the similar one predicted by theoretical analysis using the proposed modified SERR technique and finite element analysis.