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.

Shadow-Imaging-Based Triangulation Approach for Tool Deflection Measurement

“…Another approach to measure 3D displacement fields using only a single camera is based on laser speckles. Using speckle photography, Tausendfreund et al [19] measured 3D displacement fields during the deep rolling process. To achieve a high spatial resolution, the field of view of the camera is less than 10 mm wide, which is a too-small measurement range to cover a sufficient part of the machining volume in ISF.…”

Digital speckle photography in the presence of displacement gradients

“…The measurand is an in-plane displacement and the optical axis of the camera should be aligned to be perpendicular to the sample surface. While this study focuses on measuring in-plane displacement with a single-camera setup, the measurement setup can be expanded to also detect out-of-plane displacement, for instance by means of speckle decorrelation [10,11] or by integrating a stereomicroscope [12] or shearography [13]. With DSP, rigid-body displacements can be measured with single-digit nanometer resolution, while the achievable measurement uncertainty with fully developed speckle is only limited by Heisenberg's uncertainty principle, if a large number of speckles is evaluated to minimize the speckle noise [14,15].…”

“…In particular, an SLM allows the generation of multiple uncorrelated speckle patterns and thus a reduction of the random error by an order of magnitude through ensemble averaging [15]. DSP was applied in various manufacturing processes and material tests: In hole drilling to measure residual stress [18], in high temperature tensile tests [19], during singletooth milling [20], grinding [21], electro-hydraulic extrusion [16] and deep rolling [11]. In these practical applications higher-order displacement gradients generally occur due to localized loads, inhomogeneous material properties, holes, or notches.…”