Geometrically Adaptive Milling of Fan Blade Assembly Weld Fillets

Abstract

<p>Modern aeroengine design focuses on reducing overall weight and improving component service life. For fan blade assemblies, the blades and hub/shaft are attached by the most common dovetail (or fir tree) attachment design, which experiences fretting fatigue at the joint resulting in lower reliability and higher repair difficulty. A new joining design that connects blade /disk by welding and eliminates the attachment, has been implemented in military and commercial aeroengines. This joining design is most suitable for large diameter fan blades where single piece machining is impractical and time consuming. The joined blade requires post-process machining to remove excess weld material. However, because of varying assembly geometry, joints must be individually measured and tool paths consequently adjusted to match actual surface locations. The objective of this thesis is to develop an automated and geometrically adaptive post-process weld machining system.</p> <p>This thesis proposes a solution that integrates surface digitization, computer aided design (CAD) and computer aided manufacturing (CAM) systems, to accommodate the part-to-part variation issue. The integrated system includes precise laser digitizing, geometric modelling, tool path customizing, coordinate registration and CNC machining. The core algorithm was designed on the open and object-oriented C++ ACIS/HOOPS kernel. The customized tool paths are prepared based on the misalignment distance measured by laser digitizing, and a custom developed mathematical correction algorithm that can be implemented on a typical personal computer. At present, the machining process is designed for a three-axis machine tool. Suggested future works include implementation on a five-axis machine, and feed rate optimized tool paths.</p>