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High-precision inline measuring technology for laser structuring systems

Final report of the BMBF joint research project ERANET-MNT-scan4surf
 
: Schmitt, Robert; Mallmann, Guilhemme

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Aachen: Apprimus-Verlag, 2013, 71 pp.
ISBN: 978-3-86359-150-2
Bundesministerium für Bildung und Forschung BMBF
02PO2860 - 02PO2864; ERANET-MNT-scan4surf
English
Report
Fraunhofer IPT ()

Abstract
Within this Project an optical measurement system for the surface inspection of micro and macro structures with sub-micron accuracy within a laser structuring machine was developed and evaluated. The usage of the system as a tool to the development of an adaptive process initialization, an adaptive manufacturing and an inline quality inspection was also evaluated. The developed measurement system reached in its prototype status a standard deviation for distance measurements in the z-axis of fewer than 200 nm and a non-linearity of less than 1% for a measurement range of 1 mm was determined. Measurements on standards and laser structured surfaces are presented, which validate the potential of this technique for a telecentric surface inspection within laser structuring machines. The machine-integrated measurement solution for the surface inspection allows upon other possibilities the system alignment based on the actual shape and position of the workpiece. Hereby position dependent focus errors or structure overlaps can be avoided. Based on the in-line inspection production error, which are caused due to manufacturing tolerances and material defects, it can be detected and corrected at an early stage. These features are for laser micro machining systems of great advantage, since the achievable improvements lead to a reduction in the overall process time and increase of process stability and product quality. Consequently an increase in production rate and a reduction in production costs and committees are reached. An adaptive laser micro machining is particularly suitable for the laser structuring process. In this technique complex surface structures are produced on a workpiece by removal of material layer by layer with a laser beam. The in-line measuring system is used in this case before the machining of a next layer, in order to record the results of the removal process and the current surface texture. Based on these values, the current laser processing parameters can be adjusted to maintain the process stability and product quality constant. Due to the direct measurement of the removal depth in the ongoing process, the measuring system is also suitable for applications in process monitoring and control of other laser-based methods, such as laser cutting (distance control and measurement of the penetration depth), joining or welding (distance control to the component). The developed measurement principle allows this operation in the micro laser machining of various materials such as composites, plastics and glass. The developed measurement system based on the low coherence interferometry leads to a significant improvement of in situ monitoring in laser micro production technologies. The laser micro-machining of a workpiece can be controlled with high accuracy and corrected or adapted if necessary during machining process in real time. The measurement method can be integrated into existing machines and also shows no material dependence, as is often the case with today's sensors. In addition, the method allows an automated adjustment of process parameters, a precise alignment of components as well as a quality control directly after processing.

: http://publica.fraunhofer.de/documents/N-300294.html