Editor's Choice


Milling machines for the aircraft industry

Third Quarter 2020 Editor's Choice Electrical switching & drive systems & components

In aircraft construction, exceptional component quality and precision are crucial. However sheet-metal aircraft parts are often very large, making machining and handling problematic. Harmuth CNC-Frästechnik has built large-format milling machines that use PC-based control technology from Beckhoff to successfully overcome these challenges. The company works closely with CNC specialist, Penta-Tec and with milling specialist, A&T – a company that supplies structural components to an Airbus subsidiary.

In aircraft construction, exceptional component quality and precision are crucial. However sheet-metal aircraft parts are often very large, making machining and handling problematic. Harmuth CNC-Frästechnik has built large-format milling machines that use PC-based control technology from Beckhoff to successfully overcome these challenges. The company works closely with CNC specialist, Penta-Tec and with milling specialist, A&T; – a company that supplies structural components to an Airbus subsidiary.

Penta-Tec, headquartered in Austria, began developing complete CNC machine solutions in the 1990s and has adopted PC-based control technology from Beckhoff. “Their unique control solution had become increasingly popular, both in mechanical engineering and among CNC machine builders and was constantly evolving,” says managing director Dieter Köni.

One of these machine builders was Harmuth CNC-Frästechnika, a German company that makes 3D milling machines. With large-format milling machines, the dimensions and rigidity are critical factors. The machines range in type from light duty systems capable of operating dynamically at high speed, to heavy duty systems with large cutting heads for high precision face milling. “We can be extremely flexible with the machines we build, largely due to the open Beckhoff control technology, which lets us easily scale the computing power or the number of axes to suit our needs,” says managing director, Andreas Harmuth. “At the same time, PC-based control offers us options for remote maintenance.” The advantages of Harmuth’s milling systems come to the fore in applications such as the fabrication of large sheet-metal parts for the Airbus A320 series of aircraft. The parts are supplied by A&T.

In 2010, Penta-Tec found that rising functionality demands were pushing the performance of its proprietary control system to the limit and a new, flexible control system capable of delivering higher performance was needed. PC-based control technology from Beckhoff stood out as the ideal solution.

This was because Beckhoff drive technology – such as the EL7047 stepper motor terminal, AX5000 Servo Drives and AM8000 servomotors – covered every conceivable requirement, from simple auxiliary stepper axes and servo axes to the ability to incorporate linear and hydraulic axes. The exceptional range of EtherCAT terminals available also offered solutions to support any kind of application on the I/O side, particularly given the breadth of specialty hardware available from third-party vendors due to global acceptance of the EtherCAT standard.

Roman Felber, technical director at Penta-Tec, says that TwinCAT provides an affordable platform for a diverse range of CNC applications. With its ability to incorporate auxiliary tangential or gantry axes, for example, it supports economical solutions, even for complex CNC tasks. Its immense flexibility is another benefit. Also, highly advantageous are the master/slave coupling feature and the ability to flexibly configure individual axes to form interpolation groups. These allow complex systems to use multiple z-axes for other tasks.

A&T; uses large-format milling machines from Harmuth to fabricate aircraft fuselage panels milled from aviation grade sheet metal for the Airbus A320 series of aircraft. For Felber, one of the big challenges with machines of this size is maintaining precision: “With machining surfaces as much as 16 x 4 metres, it’s near impossible for machine builders to achieve precision in the tenth of a millimetre range,” he says. “We use software to enhance the precision. The machine is set up on site and measured up with a laser tracking system. This takes account of any machine-dependent tolerances and workpiece-dependent parameters. On machines this size, several components are often clamped in place at the same time, which also means adjusting for individual tolerances in position and form. This way we can keep the absolute positioning precision to within ±0,01 mm.”

Vacuum clamping offers a simple and hugely flexible means of fixing sheet metal in place in milling systems but it can require 15 to 20 kW or more of suction power. However, significant energy savings can be achieved by ramping the suction power up or down as needed. The clamping area is divided into 32 sections so that it can adjust the pressure specifically to match a given metal part to be machined. Also, the amount of suction needed to safely secure a given part is calculated according to the material parameters and surface area. An EM3701 pressure measuring terminal records the current suction level and passes it to the PLC as a control value and once the machining process is complete, the suction power falls back automatically to a pre-set stand-by level that prevents the part from slipping. Compared to simply switching the vacuum control system on and off, annual energy savings are around 50% to 60%.


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