Main technical issue
At present, aircraft manufacturing companies are heavily driven by weight and cost reduction initiatives. To that end, and specifically related to structural components, the use of highly slender ribbed parts made on newly developed aluminum alloys has been extensive developed over the last decade. However, due to the nature of the materials used and the asymmetrical geometries related to these slender ribbed components, the appearance of geometrical distortions after the manufacturing of these components is a major issue. Furthermore, non-repetitive residual stress fields on the stocks make the appearance of nonacceptable distortions on some parts when following the same manufacturing process. In order to overcome these distortion problems, the classic solutions have been based on the incremental removal of material from opposite sides of the machining stock, so the distortion could be balanced. While this solution could lead to a distortion-free part, it generates different inconveniences due to the difficulty to clamp the part on the already machined ribbed zone without damaging the fins, or the long machine and set-up times required to carry out the whole machining of the part.
Proposed technical solution
The present paper presents the work carried out for the development of an easy to implement solution for the manufacturing of distortion-free parts. On the one hand, an analytical model has been developed for the calculation of both the residual stress state of the aluminum stocks and the final distortion of the parts after the machining process. On the other hand, two fixturing solutions have been developed. The first one allows modification of the initial state of the stock in case it is required for the minimization of the final distortion of the part. The control of this fixture is coupled with the analytical model for the part distortion on a simpleto- use graphic user interface, so it can be used on the shop-floor without the need of a high power computer. Based on the calculation model developed, this interface indicates the best way to machine the component, bringing down the whole manufacturing process to only two machining steps and reducing the whole machine time significantly in comparison to solutions based on sequential passes. Finally, the second fixture helps on clamping the ribbed parts without damaging the fins. It is based on hydraulic clamps which apply the clamping force in a balanced way, so the fins are not deformed nor damaged during the clamping process.
Main advantages of the solution
The application of the present developments in comparison to the conventional machining process has:
- Improved the part accuracy from 2 mm distortion to 0.3 mm distortion thanks to the application of the distortion minimization procedure.
- Reduced machine time from 4 days to 2 days due to the avoidance of the sequential clamping procedures.
Thanks to the application of the present solution, it is possible to ensure the quality on ribbed slender structural components, avoiding the generation of defective parts and the material and energy waste associated to it. Furthermore, the machine time required for their manufacturing could be further reduced since the sequential machining is no longer needed, improving the competitiveness of the manufacturers on the market.