*3.1. Initial Geometry*

Hybrid designs can be beneficial for all technical components that experience di fferent loads throughout the part. Accordingly, it is favorable to place high-performance materials in highly stressed areas, while the remaining structural areas can be made of lightweight or low-cost materials. In the following, the Tailored Forming of a bevel gear combining two di fferent steel grades is discussed. For the contacting tooth flanks exposed to rolling loads under operating conditions, a high-strength steel 41Cr4 (1.7035–AISI 5140) and a martensitic valve steel X45CrSi9-3 (1.4718–AISI HNV3) were used. The core of the bevel gear consisted of the low-alloyed steel C22.8 (1.0460–AISI 1022M). According to the assumed load collective, the coaxially arranged hybrid workpieces were produced by two di fferent types of weld cladding: plasma transferred arc deposition welding (PTAW) and laser hotwire cladding (LHC). The corresponding cladded preforms are shown in Figure 1a,b.

**Figure 1.** Cladded preforms produced with plasma transferred arc deposition welding (PTAW) (**a**) and laser hotwire cladding (LHC) (**b**) using a substrate with a diameter of 27 mm; geometry of the turned workpiece (**c**) and bevel gear (**d**).

For both methods, the cladding was welded onto a rotating cylinder of the C22.8 substrate. Due to the simultaneous axial movement of the cylinder, the weld seams formed a spiral pattern, which resulted in a wavy contour of the joining zone and non-uniform thickness of the clad layer as shown in a longitudinal cross section in Figure 2. Its thickness depends on the width of the sealing seams and the welding penetration depth, which di ffer according to the cladding method. Based on recommended thickness values determined in prior investigations on the compound forging of cylindrical gears, the diameter of the substrate cylinders was set to Ø 27 and Ø 28 mm for PTAW [18]. A smaller diameter is not suitable due to the high heat input during cladding. For these specimens, the material combination C22.8 (substrate)/41Cr4 (cladding) was used. For the LHC process, a substrate diameter of Ø 27 mm was favorable to achieve the minimal required thickness of the clad layer but prevent a cladding with several overlapping layers. In this case, a combination of C22.8 (substrate)/X45CrSi9-3 (cladding) was investigated. In order to ensure a constant diameter of the part, the cladded workpieces were additionally turned to a diameter of Ø 30 mm and shortened to a length of 78 mm (Figure 1c). The geometry of the hybrid bevel gear is illustrated in Figure 1d).

**Figure 2.** Material distribution in plasma transferred arc (PTA) cladded workpiece for a 41Cr4/C22.8 combination with an initial substrate diameter of Ø 27 mm along the cutting line A-A (longitudinal cross section).
