Abstract
We report on an optical sensor system attached to a 4 kW fiber laser cutting machine to detect cutting interruptions. The sensor records the thermal radiation from the process zone with a modified ring mirror and optical filter arrangement, which is placed between the cutting head and the collimator. The process radiation is sensed by a Si and InGaAs diode combination with the detected signals being digitalized with 20 kHz. To demonstrate the function of the sensor, signals arising during fusion cutting of 1 mm stainless steel and mild steel with and without cutting interruptions are evaluated and typical signatures derived. In the recorded signals the piercing process, the laser switch on and switch off point and waiting period are clearly resolved. To identify the cutting interruption, the signals of both Si and InGaAs diodes are high pass filtered and the signal fluctuation ranges being subsequently calculated. Introducing a correction factor, we identify that only in case of a cutting interruption the fluctuation range of the Si diode exceeds the InGaAs diode. This characteristic signature was successfully used to detect 80 cutting interruptions of 83 incomplete cuts (alpha error 3.6%) and system recorded no cutting interruption from 110 faultless cuts (beta error of 0). This particularly high detection rate in combination with the easy integration of the sensor, highlight its potential for cutting interruption detection in industrial applications.
Highlights
Laser cutting of metals with high power fiber lasers is an established and often-used manufacturing method in modern industry
The sensor signals look similar for a series of cuts when using constant laser parameters and no differences are observed between cutting stainless steel and mild steel
A variation of the nozzle-to-workpiece distance between 1 mm and 3 mm showed no influence on the detection rate. This impressive high detection rate highlights the qualification of this system and evaluation algorithm for cutting interruption detection using fiber laser cutting machines
Summary
Laser cutting of metals with high power fiber lasers is an established and often-used manufacturing method in modern industry. Potential variations of the material properties (e.g., impurities or sulfur inclusions), as well as the condition and performance of the laser cutting system (e.g., dirty optics or thermal lens effects), may negatively influence the cutting process in an unpredictable way [8]. These disturbances can lead to a cutting interruption, which in turn may necessitate re-work or even results in an increase of material waste. Whereas sensing and monitoring of laser welding processes is commonly in use [9,10,11], sensing solutions for laser-cutting processes are hardly in practice
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