Developing CAD/CAM Techniques for Machining Unexpanded Honeycomb Core

Composites parts manufacture is an increasingly important part of aerospace production. A wide range of techniques are in practice for fabricating composite structures. Structural fillers are commonly used, one of these being honeycomb core. In addition to providing the structural strength and stiffness, they also contribute to reducing weight and can impart other desirable properties such noise and vibration damping, and the ability to absorb impacts from equipment failure. When the shape of the core needs to be accurately controlled, it is fixtured in its expanded form and machined using 5-axis routers with specialized cutters. For large parts such as wing edges or helicopter rotor blades, this requires machines with larger tables to accommodate the size of the work piece. There are definite capital equipment savings, operation and maintenance savings, floor space reductions and possibly machining time reductions to be achieved by machining core in its unexpanded form, when it occupies a fraction of the expanded length. This is difficult to do for all but the simplest surfaces because of challenges predicting and controlling excess material and gouging of the part. The paper motivates the development of CAD/CAM techniques for this domain by introducing approaches for modeling the collapsed core of a part from its expanded form. It further investigates the machining errors that can occur from tool paths generated by common CAM systems using NC verification technology.