Abstract
In this paper, we present a system to compensate for the light deflection effect during the optical geometry measurement of a wrought-hot object. The acquired 3D data can be used to analyze the formed geometry of a component directly after a hot forging process without waiting for the needed cooling time to room temperature. This may be used to parameterize the process and to detect defect components early in the production process, among others. The light deflection as the deviation from the linear path of the light is caused by an inhomogeneous refractive index field surrounding the hot object. We present the design and setup for a nozzle-based forced air flow actuator, which suppresses the light deflection effect. The design process includes a simulation of the developing field, as well as of the interaction of the field with an external forced air flow. The cooling effect of the air flow is evaluated, and conclusions are drawn from the conflicting interests of good measurement conditions against the forced cooling of the hot object. The findings are then implemented in the physical setup of the suppression system. The system is evaluated using a previously established method based on optical triangulation and fringe projection. Other occurring effects and their influence on the evaluation are considered and discussed.
Highlights
The increasing technical and economical requirements for components have led to mono material bulk metal components reaching the limits of their performance due to the material used
The system presented in this paper aims to close that gap by adding a suppression device for the light deflection effect based on formed and forced air flow to an optical 3D geometry measurement system
The content includes the concept of the background-oriented Schlieren (BOS) method to reconstruct a refractive index field, as well as a presentation of a multi-camera fringe projection system (FPS) to quantify the influence of refractive gradients on triangulation measurements
Summary
The increasing technical and economical requirements for components have led to mono material bulk metal components reaching the limits of their performance due to the material used To extend those limits, the use of hybrid components is the subject of current research [1,2]. The background-oriented Schlieren method was introduced to estimate density differences in a transparent medium from a set of images [12]. To this end, a contrast-rich and unique background was set up in front of a camera. The estimation of the density gradient through the refractive index gradient required extensive knowledge about the measurement setup [14], e.g., the size and position of the refractive index field. This knowledge might be difficult to obtain in changing or unknown measurement conditions
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