Efficiency of mechanical presses

When deep drawing, power-bound hydraulic or ground-bound mechanical presses are mainly used. In a mechanical press, the force available on the ram varies with the ram travel depending on the kinematics of the drive (e.g. toggle lever or crank drive). In the case of a tied-away press with a standard design, the nominal force of the press F_N can only be used for 8% of the total stroke H.3

Mechanical and hydraulic presses — Fig. 1
Comparison of a hydraulic press with a mechanical press
F_N Nominal press force W Forming work H Press stroke h_z Forming stroke VP Full utilization point HP Hydraulic press MP Mechanical press

With a single stroke, the efficiencies are significantly lower than with continuous strokes due to the clutch work required.

Efficiency single stroke η_tot = 0.4... 0.51

Efficiency continuous stroke η_tot = 0.5... 0.66

The efficiencies depend heavily on the degree of utilization of the machine and the optimal design of the system. The press should be operated at the full utilization point VP.

Mechanical presses are insufficiently designed for deep draws. The bell-shaped curve of the force with deep draws exceeds the force limit curve, which is why hydraulic presses are predominantly used for such applications.

Overload of mechanical presses — Fig. 2
Overloading a mechanical press with deep pulls
F_N Nominal press force H Press stroke h_z Forming stroke HP Hydraulic press MP Mechanical press

Lange / Umformtechnik Grundlagen Studienausgabe / Springer Verlag / Berlin / 2002 / 2 . Auflage