An approach to countersink depth control in the drilling of thin-wall stacked structures with low stiffness

摘要

The deformation of thin-wall stacked structures with low stiffness has been a common problem in the aircraft assembly process, making it difficult to achieve tight tolerance of the countersink depth in one-shot stack drilling. This difficulty is attributed to the complex tool position relative to the workpiece during the machining process. In this paper, an approach to countersink depth control composed of real measurement of the workpiece deformation and compensation of the tool position is presented. The deformation of the workpiece is divided into the following two categories: the rotation angle perpendicular to the feed direction and the deformation along the feed direction. These types of deformation are analysed regarding their influence on the countersink depth error. Effective measures are taken to ensure the countersink depth accuracy; such measures include the adjustment of the normal vector of the drilling position after the clamping process, the error monitoring of the normal vector during machining, and the multi-level compensation during machining. Theoretical analysis and validation of the proposed solution via comparative experiments showed a clear understanding of the coupled interaction of the thrust force with the workpiece deformation and corresponding reduction in the countersink depth error. The compensation solution requires simple computation and is straightforward to implement in industrial automatic drilling applications.