*3.2. Die Forging*

The hybrid workpieces were used to form the near-net-shaped geometry of the bevel gear. The forging experiments were carried out on a screw press Lasco SPR 500 (LASCO Umformtechnik GmbH, Coburg, Germany) with a maximum capacity of 40 kJ per single step. The corresponding forming tool system depicted in Figure 3 was designed modularly. The lower die and the upper geared die are the main components, creating the mold. The geared die is located in the upper part of the tool. This ensures an appropriate detaching of the final forgings by their own weight. The height of the bevel gear is defined by limit stops. Before forming, the forging dies were heated up to a temperature of 200 ◦C. The maximum forging force was approx. 510 kN.

**Figure 3.** Forging tool system for manufacturing hybrid bevel gears.

The heating of the workpieces was carried out inductively. For an optimal die filling, an axially inhomogeneous heating profile was used (Figure 4). Details about the heating strategy are given in [19]. An axial temperature gradient of ca. 200 ◦C was achieved by off-center positioning of the workpiece inside the induction coil. By means of the electromagnetic end effect occurring in the workpiece areas located close to the edge of the induction coil, it was possible to set lower temperatures in the lower part of the workpiece [20]. In order to ensure high reproducibility of the forging tests, the pre-heated workpieces were automatically transferred from the induction coil to the forging tool system. After forging, the bevel gears were directly transported to the air-water spray cooling station and subsequently processed in an integrated heat treatment step. In the reference process route without heat treatment, the bevel gears were cooled in still air.

**Figure 4.** Thermographic image and axial temperature profile measured at the workpiece surface before forming.
