Punch tool and sheet processing

While the mould tool shapes plastic under heat and pressure, the cutting tool works cold: it cuts, punches and bends sheet metal into finished parts in one or more operations. Cutting and stamping tool technology is one of the two main directions of the education, and the profession places great demands on precision because even one tenth of a millimetre too much clearance between punch and die gives burrs and skewed parts.

§Stamp, die, and the eccentric press that forms the metal plate

A stamping tool consists basically of two parts: the punch (upper tool) which has the shape you want to cut or press out and the die (lower tool) which fits precisely to the punch. When the punch is pressed down through the plate and further down into the die the item is cut or formed. The distance between punch and die — the cutting gap — must fit precisely to the plate's thickness and material; too large a gap gives a rough edge with burrs too small a gap wears the tool down quickly.

§Eccentric press.

Punching operations are typically performed on an eccentric press. An electric motor drives a flywheel around an eccentric shaft, and the flywheel's kinetic energy is converted to the straight, powerful movement that presses the stamp down through the plate. Press force and strike rate must match the tool and material so neither plate nor tool is overloaded.

§From single operation to progressive tool

The simplest punch tools make one operation at a time — for example one hole. In a progressive tool the sheet metal band is moved step by step through multiple punch and die stations in the same tool so the object is completely finished when it leaves the last station. This requires that each station is carefully aligned with the previous ones so the plate is fed precisely forward with each stroke.

• 01Cutting — separates the finished piece from the sheet strip
• 02Punching — creates holes or recesses
• 03Bending — forms the plate at an angle
• 04Deep drawing — forms the plate into a bowl or cup shape.

§Cut-off gap and material choice

The right cutting gap depends on the plate's material and thickness — harder and thicker material typically requires a larger gap than thin, soft material. If the gap is chosen wrongly, it shows immediately on the item's edge: too large a gap gives a rough, torn edge with visible burrs, while too small a gap gives unnecessary wear on both punch and die.

§Quality in the stamped workpiece

A well-tuned punch die gives parts with clean edges, minimal burrs, and uniform dimensions stroke after stroke. Wear on the punch and die first shows up as increasing burring—it's a sign the tool soon needs sharpening or replacement of wear parts before quality becomes unacceptable.