Predictive shimming of frame-panel assemblies using FEM and laser scanning

This paper presents a predictive shimming methodology based on finite element analysis modeling (FEM) and laser scanning metrology. The aim of the predictive shimming methodology is to provide the geometry of the necessary shims for an assembly beforehand, so the shims can be manufactured in advance and placed on the exact location reducing ergonomic harmful conditions for plant personnel, improving accuracy, reducing the components assembly time and lowering manufacturing cost. The case study for the predictive shimming method is an aircraft torque box assembly (TBA). The interface of interest is the mating surface of the skin and the rib shear ties. A FEM model of the skin was developed to calculate the skin deformation under prescribed displacements at the shimming locations. The FEM model was successfully verified and validated. Using the FEM deformation data, the geometry of the shims needed for an assembly can be calculated. Laser scanning metrology is used to get a point cloud of the assembly, fine-tuning the shims geometry.