PSI - Issue 42

Martin Killmann et al. / Procedia Structural Integrity 42 (2022) 66–71 Killmann, Merklein / Structural Integrity Procedia 00 (2022) 000 – 000

70

5

0% 10% 20% 30% 40% 0% 10% 20% 30% 40%

0% 10% 20% 30% 40%

Gap size 0.01 mm

Gap size 0.02 mm

Wear Wear

75

113

150

75

113

150

Elastomer wear 2000 cycles n = 3

Gap size 0.03 mm

F

1 Hz 5 Hz 10 Hz

75

113

150

Maximum Force F (kN)

Fig. 4: Influence of gap size, test frequency and force on elastomer wear

4.2. Influence on die stress The die stress is characterized experimentally by measuring the strains occurring on the most highly stressed point at the major axis of the ellipse. For this purpose, a strain gauge HBM 1-XY11-3/350, which measures the die strains in the critical tangential direction, is placed on the lower side of the die. The strains over 2000 test cycles with a gap of 0.02 mm, a force of 150 kN and a frequency of 10 Hz are shown in Fig. 5. These parameters are chosen because they induce the highest wear, which should show the highest impact on the die strains.

0 500 1000 µm/m 2000

Die Strains n = 3 Gap

0.02 mm

Force 150 kN Frequency 10 Hz Strain gauge HBM 1-XY11-3/350

strain

0

500 1000

-

2000

Cycle number

Fig. 5: Die strain over 2000 cycles

After a short increase in the beginning, the measured strains decrease continuously over the 2000 cycles. During this time, elastomer wear occurs, which leads to a lower volume being compressed. While the force and pressure is being kept constant by a force-controlled approach, the height over which the pressure is applied, decreases. The experimental results indicate that this causes a lower tool stress. To ensure stable test conditions, the elastomer specimen would have to be exchanged regularly. The size of the measured strains is hard to interpret, as it depends on the distance of the point of measurement to the area where the pressure is applied. The application of strain gauges is only possible on the lower side of the die. Therefore, a numerical analysis of the die stresses should be carried out in the future to determine the comparability of the stress state to cold forging and the time of elastomer change.