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Automated die positioning

Since production in the metalworking industry has become faster and faster, parts must be produced in smaller lot sizes and at a faster pace. This change also concerns bending machines.

Exact, automated die positioning below the punch (Photo: Halstrup-Walcher)

Press brakes bend metal by vertically pushing a punch into a v-shaped die. This deforms the sheet metal located between the punch and die, thus creating an angular bend. Taking a piece of sheet metal that has previously been bent to a 30° angle and placing it between two flat punches creates a fold. A typical production application will require dies to be repositioned to change between the bend and the fold function. Repositioning dies quickly is not the only concern – positioning must also be as accurate as possible to maintain the quality of the produced parts.

Trumpf’s (Germany) Tru-Bend Series 5000 bending machine is a press brake that includes an optical positioning aid making it easier to switch to a new part geometry. This machine includes an automatic angle measurement system that helps operators maintain desired geometries, beginning with the very first part. It also achieves quick and precise positioning with LPE positioning systems from Halstrup-Walcher (Germany).
Two of these precision powerhouses (“powerhouses” because they have to generate up to 1000 N of lifting power) position the heavy lower tools to within 0,05 mm – and in just seconds. Keeping the die from tipping is crucial, which is achieved by the parallel positioning systems being well synchronized.

Exact, automated die positioning below the punch (Photo: Halstrup-Walcher)

How does this kind of linear positioning system actually work? The control system sends the desired target position to the system via bus communication. The positioning system always has up-to-date position data (even after a power failure or when a unit is replaced) thanks to the integrated, absolute measuring system. The regulated stepping motor then moves the linear cylinder and its precise ball screw to the desired target position with no backlash. The actual position is continuously reported back to the control system along with countless control parameters, in Tru-Bend applications via CANopen. CANopen, as well as other bus systems, are developed and supported in-house by the company.

Harald Böck, engineer and a product manager at Trumpf Maschinen Austria, describes one example from practical experience: Oxide scaling occurs during the metal bending process, producing an oil-metal mixture that slows down positioning. Due in no small part to the robust linear drive, this does not cause the machine to shut down.
Besides precision and efficiency, long product life is always a goal as well, ensuring reliability of the entire machine as it turns out precise metal bending products even after 10 or 15 years.

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