Deep Drawing Press

In the conventional type the upper side is the active one: the main cylinder drives the upper die down and the lower side holds against it. The counter-holding force comes from the cushion cylinder beneath the bolster and is carried to the underside of the blank holder in the die by the cushion pins supported on the cushion plate. The sheet is thus held between two surfaces at a measured pressure; it does not wrinkle as it flows through the die opening.

To say “the force is constant throughout the stroke” is not correct. As the resistance of the material being formed changes, so does the force; the cushion force too varies with the flow resistance of the sheet. The advantage of the hydraulic press over the eccentric one is not constancy but control: the nominal force can be obtained at any desired point of the stroke — on an eccentric press full tonnage is reached only close to bottom dead centre — the speed is profiled to suit the part, the stroke can be stopped wherever wanted, and the blank holder force is set independently of the drawing force.

The result is determined as much by the die, the quality of the sheet, the lubrication and, where needed, intermediate annealing as by the press; the press alone does not make up for these. As the depth approaches the diameter the draw is split into stages, and between the stages the work-hardened sheet is softened again. ÖZKOÇ carries out the frame, the hydraulics, the electrics and the PLC/HMI software under one roof, from design through to commissioning; the drawing recipe is stored in the machine’s control.

• The upper side is active: the main cylinder drives the die.
• The lower side holds against it: the cushion plate feeds the blank holder through the cushion pins.
• Blank holder pressure too low → the sheet wrinkles; too high → the part tears.
• The force is not constant; it changes with the resistance of the material and is controlled.
• As the depth approaches the diameter the draw is split into stages, and annealing may be needed in between.

When the form and the embossing do not come out, the toolmaker is blamed at once. More often than not the die is not the cause: the press frame deflects under load and the die halves do not seat properly on one another. The frame’s share in this is usually unknown to the buyer, because it is written in no catalogue.

When ÖZKOÇ builds the frame as a welded construction, it joins the crossbeams and the plates BY PREPARING A WELD BEVEL. There are many firms in the industry that join without preparing a bevel; the seam then stays on the surface only. With the bevel prepared, the seam works into the section and the frame resists deflection under load.

This holds for every frame type, monoblock or column-type — it is not an option that depends on the type of press, it is ÖZKOÇ’s manufacturing discipline.

• The crossbeams and the supporting plates are joined with a prepared weld bevel.
• The seam does not stay on the surface, it works into the section; the frame does not deflect under load.
• The same discipline is applied whether the frame is monoblock or column-type.