**2. Materials and Methods**

*2.1. Process Setup and Process Parameters*

For the analysis of the warping and springback, bending experiments are conducted. The experimental set-up is executed as a kinematic three roll push-bending process (Figure 2). The process is divided in three phases: pre-bending, kinematic push bending, and unloading. In pre-bending (Figure 2a), the profile is clamped between guide roll, counter roll, and bending roll. Between guide and counter roll the profile is only guided so no force is implied in profile thickness direction. To initiate the bending force between bending and counter roll, the bending roll is rotated until the desired bending radius is reached. During the kinematic push-bending phase (Figure 2b) the profile is pushed forward with the feed velocity *ν*<sup>f</sup> to reach the desired bending angle. The profile is partially heated by induction in one profile area and consequently cooled by a water jet to keep the heated zone small with a length of the heated zone of 95 mm during this phase. Heating and cooling are deactivated for the unloading phase (Figure 2c). The bending roll is retracted, and the profile will spring back. *ν*

**Figure 2.** Process concept for (**a**) prebending phase, (**b**) kinematic push-bending phase, and (**c**) unloading phase.

The experiments are performed on a rotatory drawbending machine DB 2060-CNC-SE-F, built by transfluid, Schmallenberg, Germany (Figure 3). The temperature is measured by a pyrometer M318 produced by Sensortherm, Steinbach, Germany. The temperature

is measured at the center of the profile width after the profile passes the induction coil. Based on the measured temperature, the power output of the induction generator is controlled. Heating of the profiles is achieved through an induction generator TruHeat 7040 manufactured by Trumpf Hüttinger, Freiburg, Germany with a power of 40 kW. The heating and cooling zones are divided by a sheet of Dotherm D800-M, produced by Moeschter group, Dortmund, Germany, which possesses high temperature stability and low conductivity, to prevent water from reaching the cooling area. The geometry of the unloaded profiles is digitalized through the 3D scanning system ATOS, manufactured by GOM, Braunschweig, Germany, to quantify springback and warping.

**Figure 3.** Experimental setup, (**a**) frontal view, (**b**) top view between the rolls.

L-profiles with a width *b* of 40 mm and a thickness *t* of 2.5 mm are analyzed. The loaded bending radius is set to 600 mm. The profile feed velocity is varied between 4 mm/s and 8 mm/s to show the influence of feed velocity on springback. The temperatures for the partial heating of a single profile area are room temperature and varying temperatures between 200 ◦C to 600 ◦C in 100 ◦C steps. Higher temperatures are not investigated as material recrystallization mechanisms are not considered in this work. The term partial heating always refers to the heating of the area of the L-profile parallel to the force as depicted in Figure 2b).
