Development of a Design Tool for Fixtures for Milling Thin-Walled Structures Using Holonomic Constraints and Finite Stiffness Supports

One of the challenging manufacturing processes in the aerospace industry is the machining of the thin-walled structural components that are assembled into the load carrying members such as the spar, the rib, and the skin. For... [ view full abstract ]

One of the challenging manufacturing processes in the aerospace industry is the machining of the thin-walled structural components that are assembled into the load carrying members such as the spar, the rib, and the skin. For this process, the dynamics of the system is a major factor that greatly affects the accuracy of the milling process. This is compounded with the continuous change in the thickness of the workpiece, which leads to a system with varying dynamics. The non-linearity of the system is demonstrated by the coupling between the cutting forces and the dynamics of the system. Although the fixture design plays a crucial role in reducing the workpiece vibrations, it relies on the designer’s experience as there are no computationally efficient methodology for modelling the effect of the fixture on the vibration of thin-walled structures.

Thus, the objective of this work is to develop a computationally efficient model for the simulation of the effect of fixture layout (number, location and stiffness of the supports) on the workpiece dynamic response during machining operation. Two formulations are developed and compared for the simulation of the effect of fixture supports. The first formulation, which will be referred to as Perfectly Rigid Support formulation, is based on Holonomic constraints. The second formulation is based on translational springs with finite stiffness. A comparison between these two formulations is presented. A generalized element based on the dynamics of a 3D pocket is used to represent typical multi-pocket load-carrying aerospace structures. The dynamic response is calculated using the Rayleigh-Ritz method for an equivalent 2D multi-span plate. A new formulation was developed to represent the continuous change in thickness of the workpiece due to the material removal action.