Due to their high specific strength and lightweight Carbon Fibre Reinforced Plastics (CFRP), as they are called in aerospace technical jargon, are predestined for the manufacture of relevant lightweight components. The use of CRP and even GRP is rising continuously in civil aviation and all premium manufacturers in the car industry use fibre-reinforced plastics for the production of key structural components. In the wind energy sector, too, all aerodynamic components are already being produced from composite materials. However, there is also a sustained demand for an automated, economical machining option for the maintenance, repair and overhauling (MRO) of damaged fibre composite components, in addition to the actual production of new items. The use of ULTRASONIC technology combined with the integral process approach of SAUER enables a groundbreaking technological solution for the highly efficient machining of these high-performance materials in optimum component quality for both categories. And DMG MORI offers a cross-application machining solution – mobile as well as stationary – for the two sectors production and MRO.

Efficient ULTRASONIC machining of high-end COMPOSITE components

Conventional machining processes for the machining of fibre composite materials often show potential of optimization due to their high degree of tool wear, frequently inadequate component quality and insufficient feed rates. It is precisely here that the innovative ULTRASONIC technology of DMG MORI comes into play. The targeted transmission of an ultrasonic vibration into the longitudinal axis of the tool results in a significant reduction of feed force, lengthening of tool life and improved chip break which in turn optimises chip removal. Targeted overlaying of the cutting direction with ULTRASONIC combined with the high cutting speed enables clean cutting of the fibres of the material and thus meet the high demands on productivity and component quality. Reduction of the effective process forces by up to 40 percent also results in clean edges thus eliminating fibre pull-out and delamination. This applies to both typical machining tasks such as trimming, the placement of pockets or drilling of CRP / GRP / ARP components for serial production as well as the placement of stepped mountings, for example, by means of accurate exposure of the individual laminate layers.

In its development of the new machining solution DMG MORI has consistently optimised mechanical machine components and integrated application-specific technologies (reconstrution and measurement of surfaces by means of laser, surface cleaning and activation using atmospheric pressure plasma etc.). This has resulted in a mobile milling unit and stationary machining centres that enable the highly effective and flexible machining or repair of COMPOSITE components for serial production and damaged surfaces in the MRO sector.

Stationary ULTRASONIC high-performance cutting of fibre composites with an integral machine concept

The ULTRASONIC technology is already integrated into DMG MORI products by SAUER GmbH. Based on a standardised HSK tool holder the company developed a special actor with integrated piezo technology. This innovative actor system also enables flexible integration of other fibre composite-compatible manufacturing steps. Laser measuring systems, for example, for surface reconstruction or atmospheric pressure plasma for surface cleaning and activation can be used as independent tools which can be changed over in the machine automatically.

DMG MORI has equipped the DMF 260 linear and the DMF 360 linear, among others, with this path-breaking ultrasonic technology. As ULTRASONIC 260 and ULTRASONIC 360 versions these models also profit from the rigidity, long-term stability and thermo-symmetric concept of the machine that ensures a high level of precision in continuous operation. DMG MORI has included the ULTRASONIC 85 with proven monoBLOCK® construction in its range for the machining of smaller fibre composite parts measuring up to 700 x 700 x 500 mm. For stationary ULTRASONIC high-performance cutting DMG MORI uses the so-called technology frame – based on the gantry design of the A-axis combined with the B-axis swivel head. This allows dynamic 5-axis machining of complex workpieces such as rotor blade segments. In addition the machines are equipped with a machining area with adequate air extraction and integrated fine particulate monitoring. The explosion-proof high-performance filter system always guarantees a stable filtering performance.

Mobile milling unit for MRO as well as demanding production tasks // small, light, mobile – with top performance

The use of fibre composite materials for primary structures is already increasing in the latest generations of aircraft. Whole wings and fuselage segments are today being produced using ultra-light carbon fibres. This in turn confronts service companies with completely new challenges, because conventional repair processes are no longer economically viable. To date the repair of damaged fibre composites is normally carried out in complex and expensive manual processes. This often involves moving the aircraft back into the hangar for it be repaired manually. Such repair work takes anything from a few days to several weeks. The aerospace industry is looking for adequate solutions that would enable fast, high-quality repair of their CFRP planes – because even in the age of carbon continuous operation inevitably leads to damage of the skin of the aircraft.

The focus of the new ULTRASONIC mobileBLOCK from DMG MORI and SAUER is just such sophisticated applications. For the very first time these mobile 5-axis milling units enable structured handling of the actual repair tasks in a few minutes while at the same guaranteeing 100 percent consistent quality, precision and repeatability. Sophisticated +/- 95° machining is possible thanks to the 5-axis kinematics of the integrated rotary swivel axis. Its lightweight design means that the ULTRASONIC mobileBLOCK can be docked simply and flexibly by means of vacuum suction feet. In addition to repair work this innovative mobile milling unit can be just as effectively integrated in demanding production tasks (e.g. the placement of boreholes or pockets in CRP components).

The adjustable vacuum suction feet of the ULTRASONIC mobileBLOCK generate a suction force of up to 400 N per foot. 16 vacuum suction feet are included in the standard version. Moveable ball joints (+/- 45°) and mounting arms that can be pivoted enable fast and simple adjustment to even surfaces (e.g. wings) and especially to components with radii and complex contours (e.g. frame elements on the fuselage of the aircraft). Thanks to its extremely compact and lightweight design and low overall weight of just 130 kg this mobile 5-axis milling unit is more than predestined for fast and simple docking directly onto the damaged area. The frame, X-axis gantry, adjustment arms and the Z-axis slide of the ULTRASONIC mobileBLOCK are all made of CRP making them especially insensitive to thermal expansion. This construction design also highlights the intelligent lightweight concept.

The standard version of the ULTRASONIC mobileBLOCK can be adapted quickly and simply by crane. This allows the mobile milling unit to be docked onto many different surfaces in a question of a few minutes. A new design study is looking at a possible scenario for automatic positioning of the
ULTRASONIC mobileBLOCK using a mobile transport carriage on wheels or rails. This will enable universal, automatic adaptation for both MRO and production tasks.

The 5-axis Beckhoff TwinCAT 3 NC control ensures simple, PC-based operation via a 21.5" (multi-)touch screen for the user. The integral operator guidance is extremely user-friendly offering the operator expedient support starting from the component drawing, on to definition of the damaged area, the machining task, laser surface measurement of the workpiece and on to include creation of the final NC file. Possible integration into an existing company network and continuous Internet access are possible.

The use of two different CRP-optimised lasers is possible for actual machining preparation. The point laser scanner is used to detect the workpiece surface in Z, while the integrated line scanner is used for reworking the surface of 3D shapes with up to 640 individual pixels. Both components can be installed and removed in just a few seconds depending on the different machining tasks. The intelligent kinematic design with X, Y, C, Z and A-axis allows unlimited 5-axis simultaneous machining and top dynamics thanks to optimised positioning of the centre of gravity. The ULTRASONIC technology is in this case integrated in the high-performance (up to 35,000 rpm) spindle with up to 35,000 rpm.