August 2019 Volume 1

FORGING RESEARCH

flange and a tubular body whose dimensions are shown in Figure 2-2. The new forging process is composed of several stages. The principle behind this process is to transform a section of hollow structure to a solid rod by locally heating the tubular blank followed by upsetting. Then the solid rod is shaped to a flange in the same way as the conventional solid axle shaft is forged. The new forging process is cost effective as well as productive and has advantages over alternative forming processes discussed in the introduction chapter.

Admittedly, in order to further enhance dimensional accuracy of the flange diameter and mechanical performance of the part, a final machining and a heat treatment may be needed at the end of forging. The main objectives of this chapter are to present a) a conceived differential heating-based process for manufacturing of axle shaft. b) metal flow patterns, formability, forming loads and the geometric quality of the final part which were investigated with FEM. c) the validity of the proposed process for shafts of various inner diameters

Figure 2-1: Axle Shaft [11][10]

Figure 2-2: Dimensions of the Hollow Axle Shaft

create the flange. Meanwhile the bottom die is used to support the flange. Figure 2-6 shows configuration of the dies and the workpiece at the beginning (left) and the end (right) of the flanging step. After the forging operations, the circumferential surface of the flange is machined to final dimensions. A through hole can be drilled at the center of the flange.

2.2. Proposed Forging Sequence for Hollow Axle Shaft The differential heating-based formingprocess startswith a tube.The process is composed of the three operations: i) induction heating, ii) upsetting, and ii) flanging. The forging sequence is shown in Figure 2-3. Induction heating is used to create a differential temperature field within the workpiece which includes a hot, cold and warm regions. Figure 2-4 shows the desired temperature distribution in the workpiece after completion of the induction heating. The left side of the figure is the initial tubular blank at room temperature. The right side shows the temperature distribution after the induction heating. The upsetting operation is used to cause hot metal to flow inwards and fill the central hole. This is accomplished by using the top die to compress the workpiece, a die case to restrict outward radial flow, and the cold material to constrain the downwards metal flow. The cold metal region undergoes much less deformation than hot metal region due to its high flow stress and acts as a pseudo die. Figure 2-5 shows the configuration of the dies and the workpiece at the beginning (left) and the end (right) of the upsetting. In the flanging operation, the hot metal is further upset, but this time without the constraint of the die case, allowing the metal to flow radially to

Figure 2-3. Forging Sequence for the Hollow Axle Shaft

FIA MAGAZINE | August 2019 54