Automated control system can play an influential role in the cycle time of a deep drawing press. Contributed by David Chia, MD, Beckhoff Automation.
With its Advanced Deep Drawing Press (ADP), Denmark-based Kiermar Technology developed a press that is characterised by the horizontal movement of the upper tools. The actual pressing procedure takes place from bottom to top. The upper tool only has to move 5 mm in a vertical direction before it drives horizontally out of the press and the finished product is placed on the conveyor belt by means of an ejector.
The deep drawing press is said to challenge traditional concepts of size, speed and energy efficiency. It has a significant pressing force but it weighs only 26 tons. Its overall height, including the crane for tool handling, is 4 m. Fast cycle times is also one of the characteristics of the machine that is based on fast tool and integrated material handling.
As a result, the press cycle for the production of a sink takes less than 15 seconds. “A complete pressing cycle is around 30 percent faster than other hydraulic deep drawing presses,” explains Martin Hansen, MD of the company. The electrical and hydraulic servo drives are controlled by a Beckhoff C6920 Industrial PC with TwinCAT automation software and the EtherCAT communication system.
The Reason Behind The Speed
The speed of the press can be attributed to the automation system working in the background. One Beckhoff C6920 Industrial PC is required to handle the PLC and motion control. PC-based control ensures that both the pressing procedure and the horizontal tool movements operate precisely and smoothly. The press is equipped with three electrical and three hydraulic servo axes. As they are controlled differently, this poses a challenge.
Hans Christian Pallesen, application engineer from Beckhoff Denmark says: “In the case of electrical axes, a certain operating profile can be created in advance on the basis of ramps, position and speed. That is not possible with hydraulically-controlled axes, since they change their profile during operation. In addition to that, the hydraulics behaves very differently, depending on the valve type, oil flow, oil temperature, etc.”
The hydraulic axes are ‘path controlled’, ie: the position controller is active only when at a standstill. The set value generator controls the cylinder according to ramp and speed, while its current position is constantly checked via the encoder signal. Once the set value position is reached, the position controller is activated again in order to maintain the current position.
While the electrical axes are controlled by the automation software, the hydraulic axes are controlled via the TwinCAT Hydraulic Library.
It is said that with the aid of the standard software library, the engineers were able to master the challenges of the ADP deep drawing press, such as the movement of 2,000 kg horizontally by 2 m for discharging the work piece — in less than two seconds and with an accuracy of ± 0.1 mm.
The automation software forms the cornerstone for the execution of the PLC program. The PLC data performance enables fast execution while at the same time handles demanding travel movements. The entire PLC program is updated every 2 ms, ie: 500 times per second. To do this, EtherCAT is used for communication with the servo drives and I/O components. The fast update rate gives rise to a fast control system, which contributes to the precise positioning.