PSI - Issue 77

Vasco Gomes et al. / Procedia Structural Integrity 77 (2026) 559–566 Gomes et al./ Structural Integrity Procedia 00 (2026) 000–000

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4.2. Pneumatic counterbalance (3D model) As aforementioned, using pneumatic cylinders to counterbalance the slide significantly affects the servo press, especially the motor’s torque. Compared to a system without pneumatic compensation, Fig.5-a) shows the peak torque decreasing from 1225 Nm to 230 Nm, an 81% reduction. Additionally, the torque curve profile changes, reflecting the cylinder’s behaviour. Fig. 5-b) shows pressure and, consequently, force initially increasing linearly during the chamber filling, and afterwards oscillating response, due to the cylinder’s piston movement which matches the slide’s displacement.

Fig. 5. (a) Motor torque with and without pneumatic compensation.; (b) Cylinder piston stroke, force and pressure.

4.3. Stamping load and contact (3D model) When applying the stamping loads in the 3D model system, local increase in the motor’s torque was observed, while the motor’s shaft rotational speed decreased in relation to the 800 rpm target (as a way to enable higher torque output). Fig. 6-a) shows these curves: blue curves for the system without stamping loads, and green with them. Regarding the contact groups, they allow the determination of factors, such as the normal/tangential forces and the power losses, shown in Fig. 6-b). One corner of the slide was selected to showcase its four contact regions. The power losses obtained were minimal, likely associated to idealized conditions: perfect gaps, tolerances, wear, and others.

Fig. 6. (a) Motor torque (above) and speed (below) with and without stamping loads; (b) Power losses in 4 of the 16 contact regions.

4.4. Journal bearing (1D model) In the 1D model, the key interest lies in the plain journal bearing and its variables, including the relative eccentricity, which starts at almost 1 (idle system) and decreases with time. Fig. 7-a) also shows that lubricant viscosity and temperature are inversely related. Over time (Fig. 7-b)), the lubricant’s viscosity and temperature, as well as the eccentricity stabilize, with the latter exhibiting low values due to a relatively moderate shaft speed (oscillating around 45 rpm). The model showcases the condition for hydrostatic lubrication, in which the fluid is injected pressurized (60 bar, for this specific scenario). The pressure distribution can be calculated using the short-bearing approximation, valid since the bearing’s length-to-diameter ratio is below 1 (Ocvirk, 1952), whose equation is shown below. ( ) = 2 � 6 ( ) �2+ ( ) � ( 2+ 2 ) �1+ ( ) � 2 � + 0 (1)