Methods for Monitoring of Laser Cutting by Means of Acoustic and Photodiode Sensors

Abstract

Laser cutting is a well-established sheet metal processing method. Nowadays a trend towards the cutting of thick plates (> 15 mm) can be observed. However for these thick plates the process window in which good cutting results can be obtained is more narrow compared to that for thin sheets due to the very difficult balance to be found between the different process parameters. Even after determination of the process window, a good cutting quality cannot always be guaranteed. Therefore cutting of thick plates is still characterized by a large scrap percentage, which impedes a breakthrough to large scale industrial use. A solution to this problem is to incorporate a sensor system in the laser cutting machine that monitors the cut quality on-line. This monitoring system could then be integrated in a process control system, which adapts the process parameters in function of the observed cut quality in real time. In this way a good cut quality could always be guaranteed. In this study, the first step in this direction, the determination of an appropriate monitoring system, is dealt with. The applicability for monitoring purposes of two types of sensors is investigated: a microphone and a photodiode. For both types, correlation between the sensor output and the cut quality is investigated in a qualitative way. The scope of the reported research was not limited to contour cutting, also piercing is covered in the study.

Development of a real time monitoring and adaptive control system for laser flame cutting

“…In previous publications the authors of this paper reported on the use of acoustic and photodiode based systems for process monitoring of higher power CO 2 flame cutting [14,15,16]. In line with observations made by the researchers referred to above, the authors concluded that photodiodes can provide useful information for quality assurance purposes with a very limited time delay.…”

Monitoring of CO₂ Laser Cutting of Thick Steel Plates by Means of a NIR Camera Based System

“…Although the relay distance proved to have no influence on the image quality, it was decided to keep this distance as small as possible. It was also observed that at optimum image quality (maximum sharpness), D cutting 1 and D camera 2 are approximately linearly correlated (Fig. 7).…”

“…-The optimal position D camera,opt at which the sharpness of the image is optimal 1 Distance between the image plane and the cutting lens. 2 Distance between the camera lens and the camera plane.…”

“…Since the dichroic mirror is logically the only component of the monitoring system that might influence the properties of the laser beam, a detailed analysis has been performed to identify this probable influence. 1 The window of interest is a virtual rectangular area within the camera image of which the pixel values are classified by the camera as thermal images. The dimensions and the position of the WOI is determined in the software of the camera.…”

“…This optical system uses photodiodes and a NIR camera as sensors. The concepts and results of the photodiode-based monitoring system have already been reported [1,2]. This paper is dedicated to the development of the optical set-up for camera-based monitoring of the laser cutting process.…”