The question, how certain surface layer properties (for example, hardness or roughness) can be specifically influenced in different manufacturing processes, is of great economic interest. A prerequisite for the investigation of the formation of surface layer properties is the metrological assessment of the material stresses during processing. Up to now, no commercial in-process measuring system exists, which is able to determine material stresses in the form of mechanical strains in high-dynamic manufacturing processes with sufficient accuracy. A detailed analysis of the resolution limits shows that speckle photography enables deformation measurements with a resolution in the single-digit nanometer range. Thus, speckle photography basically offers the potential to measure material stresses during processing. Using the example of single-tooth milling, the applicability of speckle photography for in-process stress measurements is demonstrated. Even in such highly dynamic manufacturing processes with cutting speeds up to 10 m/s, the absolute measurement uncertainty of the strain is less than 0.05%. This is more than one order of magnitude lower than the occurring maximal strain. Therefore, speckle photography is suitable for characterizing the dynamic stresses and the material deformations in manufacturing processes.

The knowledge of the loads occurring during a manufacturing process (e.g., grinding) and of the modifications remaining in the material is used in the concept of process signatures to optimize the manufacturing process and compare it with others (e.g., laser processing). The prerequisite for creating a process signature is that the loads can be characterized during the running process. Due to the rough process conditions, until now there is no in-process technique to measure the loads in the form of displacements and strains in the machined boundary zone. For this reason, the suitability of speckle photography is demonstrated for in-process measurements of material loads in a grinding process without cooling lubricant and the measurement results are compared with finite element method (FEM) simulations. As working hypothesis for the simulation it is assumed, that dry grinding is a purely thermally driven process. Despite the approximation by a purely thermal model with a constant heat source, the measured displacements differ only by a maximum of approximately 20% from the simulations. In particular, the strain measurements in feed speed direction are in good agreement with the simulation and support the thesis, that the dry grinding conditions used here lead to a primarily thermally affecting process.

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.

In order to study the mechanical loads of a workpiece in manufacturing processes such as single-tooth milling, in-process measurements of workpiece deformations are required. To enable the resolution of shock waves due to the mechanical impact of the tool, a novel measurement system based on speckle photography is introduced to measure the dynamic deformations and strains with a high temporal and spatial resolution. The measurement results indicate deformations and strains propagating through the workpiece with the speed of sound triggered by the tool impact (i.e., the tool impact is shown to induce shock waves during milling). Finite element simulations of the workpiece behavior are performed in addition, which support the experimental findings. In the considered case, the dynamic excitation subsides after 300 ms. Hence, in processes with even shorter cyclic multiple loads, the tool encounters an already excited initial state during machining, which needs to be taken into account when precisely modeling the milling process and the resulting workpiece quality. Finally, the measurement results demonstrate that speckle photography in combination with modern high-speed cameras and compact short-pulse lasers provides a deeper understanding of individual manufacturing processes.

Zusammenfassung: Die Kenntnis der zum Beispiel während des Schleifprozesses auftretenden thermomechanischen Werkstückbeanspruchungen und der im Material verbleibenden Veränderungen lässt sich gemäß dem Konzept der Prozesssignaturen nutzen, um den Fertigungsprozess zu optimieren und mit anderen zu vergleichen (z. B. mit der Laserbearbeitung). Voraussetzung für die Erstellung einer Prozesssignatur ist, dass die Beanspruchungen während des laufenden Prozesses charakterisiert werden können. Aufgrund der rauen Prozessbedingungen gibt es beim Schleifen bisher keine prozessbegleitende Technik zur Messung der thermomechanischen Beanspruchungen in Form von Verschiebungen und Dehnungen in der bearbeiteten Randzone. Aus diesem Grund wird die Eignung der Speckle-Fotografie für prozessbegleitende Messungen von Werkstückbeanspruchungen in einem laufenden Schleifprozess ohne Kühlschmierstoff nachgewiesen und ein Konzept für eine Messung unter dem Einsatz von Kühlschmierstoffen vorgestellt.

The production of microstructures is becoming increasingly flexible in terms of geometry and material, requiring precise and versatile applicable geometry measurement methods. However, current optical methods depend on the optical surface response and need optically cooperative surfaces. Therefore, the indirect determination of the object geometry is proposed as a universally applicable innovative measurement method. In this method, it is not the object itself that is measured, but its imprint in a fluorescent medium. In this article, the object is therefore surrounded by a flow of fluorescent microparticles. A confocal microscope scans the space around the measurement object and the surface geometry can then be reconstructed from the fluorescence signal using model-based signal processing. Step geometries 200 µm high made of three different, optically uncooperative plastics were measured: white, slightly translucent polytetrafluoroethylene (PTFE), deep black polymethyl methacrylate (PMMA) and green polyethylene (PE). All three materials are challenging for direct measurement using standard optical reference methods. The indirect geometry measurement presented here, on the other hand, delivers measurement uncertainties of less than 5 µm, even at steep observation angles of up to 83°.