Fooke has specially developed a turnkey milling method to produce specific wall-thickness sheet material that doesn’t require the use of massive amounts of chemicals - and reduces the processing time to a fraction.
In aerospace, weight is crucial: every pound saved, helps to reduce fuel consumption, improve aircraft efficiency, and ultimately reduce CO2 emissions. That's why fuselage segments for aircraft and missiles, outer shells of turbines and other aluminium sheets are designed in a specific thickness profile according to their structural load. In stressed areas, higher plate thicknesses are used. In areas not subject to high stress, the sheets are reduced to lower residual thicknesses to save weight.
Within a stretch forming process, flat, rolled raw sheets are shaped into spherically curved plates. The subsequent manufacturing of the pockets and thus achievement of the defined residual wall thickness can be realised by various removal technologies.
A complex, but still widely used process for example is chemical milling, in which sheets are immersed in chemical baths to obtain the desired thicknesses. While this technology is well-controlled and established, it has enormous drawbacks due to the high use of chemicals and the relatively long process time.
Although many companies aim to reduce environmental impact and shorten cycle times, the mechanical processing of the sheets is highly complex, due to a variety of influencing factors. Since the thickness tolerance and also the specified geometry is decisive for the final result, special attention is already paid during the inspection and processing of the input dimension of the pre-formed sheet. Deviations caused by handling or forming processes must be reliably detected. Furthermore, a correct clamping technique, the insertion of the sheets into a fixture and the quality of the clamping must always be ensured.
Machines made to endure
With focus on these challenges, Fooke has specially developed a milling method for this application that does not require the use of massive amounts of chemicals and reduces the processing time to a fraction.
The pre-shaped sheets are vacuum-fixed in negative contour - so-called ‘hard tooling’ and the pockets are machined by a high-speed machine. It’s not the depth of the pocket that is critical here but the particularly tight tolerance of the residual wall thickness.
Fooke offers a holistic solution: besides its state-of-the-art Endura 600LINEAR overhead gantry machine with linear drives, it also includes the hard tooling and the entire process of component measurement and compensation.
Manufacturing large, precise and highly dynamic milling machines has been part of Fooke's success story for decades. But the process of component measurement and compensation - which is based on different measurement methods with associated data processing and visualisation - can be highlighted as a decisive core competence of Fooke.
Various measuring routines and complex data processing algorithms for component correction ensure maximum accuracy. Deviations and e.g., deformations of the fixture can be reliably detected and compensated. The application includes the fully-automated integration of ultrasonic component measurement into the machine control. Temperature influences are also detected and considered accordingly in the machining process. Time-consuming adjustments of CNC programs are simply eliminated. A rigid and continuous quality control and documentation comply with the extremely stringent demands of the aerospace industry.
All these combined competencies enable Fooke to provide the customer with a turnkey solution that offers significantly higher process reliability compared to other methods, such as ‘mirror milling’ for example, at a considerably lower investment cost.
This turnkey solution has been developed, validated and has been in production at a large, well-known aircraft manufacturer in northern Germany since 2020, where the weight of a 10m x 2m fuselage is cut down to 50% with pocket milling.
