In-Process Measurement of Three-Dimensional Deformations Based on Speckle Photography

Abstract

In the concept of the process signature, the relationship between a material load and the modification remaining in the workpiece is used to better understand and optimize manufacturing processes. The basic prerequisite for this is to be able to measure the loads occurring during the machining process in the form of mechanical deformations. Speckle photography is suitable for this in-process measurement task and is already used in a variety of ways for in-plane deformation measurements. The shortcoming of this fast and robust measurement technique based on image correlation techniques is that out-of-plane deformations in the direction of the measurement system cannot be detected and increases the measurement error of in-plane deformations. In this paper, we investigate a method that infers local out-of-plane motions of the workpiece surface from the decorrelation of speckle patterns and is thus able to reconstruct three-dimensional deformation fields. The implementation of the evaluation method enables a fast reconstruction of 3D deformation fields, so that the in-process capability remains given. First measurements in a deep rolling process show that dynamic deformations underneath the die can be captured and demonstrate the suitability of the speckle method for manufacturing process analysis.

Influence of displacement gradients on laser speckle photography

“…From the simulation, we estimate a maximum systematic error of around 60 nm with 𝑊 ev = 10 Pixel. The maximum cumulative uncertainty of the measurement reported in [6] is 22 nm. Thus, systematic errors due to displacement gradients are a significant and previously not considered contribution to the measurement uncertainty budget, which deserve further attention.…”

“…Decreasing the DIC evaluation window size 𝑊 ev reduces the systematic error, but in turn increases the random error. In order to demonstrate the relevance of the systematic errors studied here, an in-process measurement during a single tooth milling process from [6] is considered. Fig.…”