August 2019 Volume 1

FORGING RESEARCH

Figure 2-4: Temperature Distribution of the Workpiece in the Induction Heating Operation

Figure 2-5: Configuration of Dies and the Workpiece at the Beginning (left) and the End (right) of the Upsetting Operation

Figure 2-6: Configuration of the Dies and the Workpiece at the Beginning (left) and the End (right) of the Flanging Operation

2.3. Metal Flow Pattern and Process Feasibility As is shown in Figure 2-7, a defect-free hollow axle shaft is successfully forged. The metal flow, which is visualized by the flow net of FEM simulation, gives insights into the deformation characteristics. In order to explain the metal flow during the upsetting operation, the workpiece is divided into three zones, the deformed zone, the deforming zone and the undeformed zone. As is shown in Figure 2-8, effective stress of the deforming zone is higher than that of the other two zones. In the deforming zone, material is pushed outwards in the radial direction and compressed in the axial direction. The non-uniform temperature distribution in the deforming zone results in inhomogeneous deformation. For, example, the surface layer, which is in contact with the die is less

deformed than the core due to cooling by the die, hence higher stress is observed in this zone. Figure 2-9 shows strain concentration in the core and Figure 2-10 shows the temperature gradient from the contact layer to the core. As the top die moves down, the deforming zone shifts downwards and the central hole is filled. When the deforming zone approaches the warm zone, the upsetting operation stops and the flanging operation begins. As is shown in Figure 2-11, the hot material which lies between two die undergoes a larger stress than the warm and cold material surrounded by the bottom die. The cold material acts as a pseudo die to prevent the hot material from flowing into the central hole. Thus, the hot material forms the flange, while the warm and cold material deform very little and the tubular body remains hollow.

FIA MAGAZINE | August 2019 55