2.2.1. Turning

Analogy experiments with a three-step variation of cutting speed, *v*c, and feed, *f*, were carried out on cylindrical shafts with a material transition in axial direction. Coated indexable cemented tungsten carbide inserts DNMA150612 WAK20 with a symmetric cutting-edge rounding of *S*α/*S*γ = 30/30 μm, as well as *S*α/*S*γ = 75/75 μm, were used. Depth of cut, ap, and cutting direction were kept constant. Process parameters from the analogy investigations that have a significant influence on the subsurface properties were then used for the production of hybrid shafts for fatigue tests. All turning experiments were conducted on a Gildemeister CTX420 linear machine tool (DMG Mori Aktiengesellschaft, Bielefeld, Germany). A rake angle of γ = 3◦ was chosen for the longitudinal turning process. Analogy experiments with different feed directions (machining from hard–soft or soft–hard) on friction welded shafts revealed worse quality for the feed direction from SAE5140 (hard) into SAE1020 (soft) in the machining process. The reason is that clamping of the shaft with the SAE1020 side is inconvenient due to the lower strength of this material. This leads to slight chatter vibrations during machining. Therefore, in the following investigations, only the feed direction SAE1020 into SAE5140 was selected. The cutting parameters are summarized in Table 1. The choice of cutting parameters for the production of shafts for fatigue-life investigations is based on the lowest achieved roughness.


**Table 1.** Process parameters of the cutting operation.
