PSI - Issue 38

Martin Killmann et al. / Procedia Structural Integrity 38 (2022) 212–219 Killmann / Structural Integrity Procedia00 (2021) 000 – 000

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additional tensile stresses. These can be seen on the outer surface of the die as well as at the base of the functional elements and in the middle of the ellipse. The following section will focus on how to adequately design the gaps, so that the compressive stress is effectively increased without creating critical tensile stresses.

Effect of gaps

Prestress Effect

Die Reinforcement

Geometry scaled x40

Geometry scaled x25

σ t

Reinforcement pressure

250

Tensile stress Compressive stress Bending effect

MPa

-500

Fig. 3: Mechanism of local prestressing by gaps

3.1 Gap parameters In the scope of this research, the gaps in the dies are modeled as shown in Fig. 4 using the CAD-system PTC Creo Parametric 5.0. At the position of the maximum tensile stresses, the gap has the highest distance a. Moving toward the start of the interference fit, this distance decreases, as the gap is modelled elliptically. After reaching a defined distance b the outer wall of the die is modelled as a spline, connecting the elliptical gap contour with the circular area of constant interference. The point, at which die and reinforcement first have contact is defined by the angle α . After that, the interference is increasing until the maximum interference is reached and kept constant. The shape of the spline, i.e. the distance from the point of contact to the gap and the area of constant interference is defined by the angles β and γ .

Die setup with gap

α

β

a

γ

Start of interference

b

constant inter ference

Outer die countour modelled as: Ellipse

Interference Reinforcement Die

Spline

Circle

Fig. 4: Modelling and parameters of the gaps