Prediction of Cutting Interruptions for Laser Cutting Using Logistic Regression
Leonie Tatzel, Fernando Puente León

Cutting interruptions in 2D laser cutting are undesired for several reasons: They lead to an unnecessarily high material consumption and decrease the productivity of the laser cutting machine. Furthermore, they can contaminate the laser cutting head and thus influence subsequent processes negatively or cause long set-up times. Therefore, we developed a model to predict cutting interruptions, exemplarily for 3 mm stainless steel. We have set 1050 different combinations of the cutting parameters nozzle-sheet distance, gas pressure, nozzle-focus distance and speed on a state-of-the-art laser cutting machine. It was then determined whether separating the sheet was possible or not. The experimentally generated database was used to train a simple, interpretable machine learning model to predict cutting interruptions
reliably. An averaged accuracy and recall larger than 95 % could be obtained with a polynomial logistic regression
approach. In addition to that, it could be shown that speed and focal position are the most crucial parameters.

Keywords: laser macro processing; laser cutting; cutting interruptions; logistic regression

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Effects of Beam Power and Power Density Distribution on Process and Quality Issues during Fiber Laser Cutting of Stainless Steel Sheet Metal
Dirk Petring, Dennis Arntz, Stoyan Stoyanov, Frank Schneider

Sheet metal fabricating industry implemented fiber laser cutting promptly due to being a more cost-efficient alternative to CO2 laser beam cutting regarding investment as well as operation. Continuous technology improvements regarding available power levels as well as versatility in beam shaping provide further options for improved performance. However, with a lack of understanding of the underlying fundamentals, parameter optimization mainly takes place by trial and error. The multi-dimensional parameter space often impedes to find the real optimum and the associated rules. Process diagnostics and quality analyses combined with the simulation tool CALCut yield a deeper insight into the effects of beam properties on process and quality issues. Thereby, processing rules and their range of validity can be identified.

Using the example of stainless steel cutting with beam powers between 5 and 10 kW and different power density
distributions reveals how the cutting front and cut result can be deliberately affected.

Keywords: Laser beam cutting; fiber laser; process diagnostics; process simulation; process optimization; cut quality.

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Cutting of composite materials: a quality and processing time optimized scan strategy for GFRP and CFRP
Frank Schneider, Dirk Petring, Norbert Wolf

Glass fiber and carbon fiber reinforced plastics (GFRP, CFRP) play an important role in the material mix of automotive and aerospace components. Light weight design has to be consistent with the availability of an efficient production technology. Cutting of these materials with multi kW-fiber lasers enables the demanded cutting speeds in the range of meters per minute. An optimization procedure is presented for a multi-pass process in order to achieve high quality cut edges and short
processing times by appropriate setting of scan speed and interval times between scans. The process is demonstrated by trimming a car roof bow. Following a multi material approach, the part consists of two stacked layers of GFRP and CFRP at the cut path. Since the length of the cut is 800 mm at each side of the roof bow, the scan field (200x200 mm²) is moved continuously over the workpiece, demonstrating the applicability for bigger components.

Keywords: CFRP cutting, GFRP cutting, fiber laser cutting, multi-pass, scan strategy

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Tip-tilt piezo platform scanner qualifies dynamic beam shaping for high laser power in cutting applications
C. Goppold, P. Herwig, D. Stoffel, M. Bach

Dynamic beam shaping raises the cutting speed and increases the cut edge quality. This has been shown several times by the authors in previous publications. This innovative technology offers a large potential in process improvements, especially for laser cutting of thick plates. Commonly used galvanometer driven scanners require large integration space and do have limited lifetime compared to piezo based solutions. Physik Instrumente GmbH & Co. KG and Fraunhofer IWS are developing a piezo based tip-tilt platform scanner, which achieves the necessary dynamic beam shaping functionality, but saves installation space by the factor of eight.

The solution is small enough to substitute conventional deflection mirrors in the optical beam path and is therefore easy to integrate even into existing machines. The present paper introduces the advanced possibilities for the process using this new system technology and demonstrates a possible integration.

Keywords: dynamic beam shaping; oscillation; tip-tilt; piezo; laser cutting; high laser power

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Laser Drilling of Thermal Barrier Coated Nickel Alloy
S. Marimuthu, B. Smith, P. Hayward

Millisecond laser drilling is state-of-the-art for producing acute angle film-cooling holes over aero-engines. After the drilling, most of these components are covered with thermal barrier coating (TBC). The preferred manufacturing method would be to laser drill the cooling holes after TBC coating but is not practiced due to the issues associated with coating delamination. The recent introduction of millisecond pulse quasi-CW fibre lasers is having a significant impact on the laser drilling of metals and alloys. This paper investigates the millisecond-pulsed-quasi-CW-fibre laser drilling of angular holes over TBC coated aerospace nickel superalloy. The main investigation concentrates on understanding the quasi-CW-fibre laser parameters to control the TBC delamination. Apart from the investigation on traditional percussion and trepanning laser-drilling of acute angle holes over coated component, a new method of drilling called “laser drilling post laser scribing” was evaluated, to achieve delamination free millisecond laser drilling.

Keywords: Laser; Drilling; Thermal barrier coating; Delamination; Aero-engine;

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Influence of reinforcement materials in laser perforation of polymers
Martin Griebel, Jean Pierre Bergmann

The laser treatment of polymeric parts becomes more and more popular for the plastic processing industry. In order to increase the mechanical properties the used basic polymers (e.g. polypropylen PP) are typically reinforced by materials such as glass fibers or talc powder in different volume levels.. These specific material features affect the cutting or perforation process in a significant manner. First empirical test series of cutting with laser beam show, that an influence is present and build an initial data base, in order to set up a scientific model of the process, which is not fully understood till now. A systematic relationship in order to develop a decision support for the users of laser machines is the main goal of this study. The test results show a strong difference between particles filled (talc) and fiber filled (glass) compounds. While for the first type a wide linear behavior between depth and laser power can be detected, for the second a quick saturation can be pointed out. Effects are described in the paper

Keywords: laser drilling plastics, additives

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Determination of the 3D-Geometry of Cutting Fronts with High Temporal Resolution
Michael Sawannia, Peter Berger, Michael Jarwitz, Rudolf Weber, Thomas Graf

The geometry of the cutting front was determined with a high temporal and spatial resolution during cutting of 10 mm thick stainless steel with a solid-state laser. The geometry was reconstructed using the information of the polarization state of the thermal radiation emitted from the process zone. This reconstruction of the geometry makes it possible to investigate the influence of process parameters on the geometry of the cutting front, including structures on the front and the global angle of inclination.

Keywords: Cutting front geometry; 3D surface reconstruction; thermal process emission; process diagnostic; laser cutting; solid-state
laser

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High-speed X-Ray Imaging of the Cutting Process during Laser Beam Cutting of Aluminum
Jannik Lind, David Blazquez-Sanchez, Jens Weidensdörfer, Rudolf Weber, Thomas Graf

The online X-ray diagnostics system at the IFSW was modified for laser beam cutting allowing for the analysis of the temporal behavior of the local inclination of the cutting front. The cutting front of 10 mm thick aluminum samples was recorded during the process with a framerate of 1000 Hz. When increasing the feed rate, it was observed that the inclination of the cutting front with respect to the laser beam increased until loss of cut.

Keywords: laser beam cutting; cutting front; aluminium; online high-speed X-ray imaging

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Establishing optimal parameters for laser cutting of thin semi-transparent organic material
Wahyudin P. Syam, E.R. Britchford, A. Hopkinson, D.T Branson III, K.T. Voisey

The manufacturing challenge of laser cutting thin, light weight, semi-transparent, organic material is address in this work. A novel glass-sandwich fixturing method is developed. This increases the ease of material manipulation and permits cutting in a sterile environment. The transparency of the glass sandwich to fibre laser radiation (2kW IPG 200S fibre laser, λ = 1070nm) is exploited, allowing the sandwiched material to be cut. A process window is determined using powers and translation speeds of up to 600 W and 1200 mm/s respectively. An approximately linear relationship is observed for the maximum cutting speed at any given power. Cut width and heat affected zone dimensions are investigated as a function of cutting speed and power. The organic material has extensive site to site and sample to sample variations in material thickness and transparency. A process robustness analysis is carried out to determine optimal cutting parameters.

Keywords: cutting; organic material; semi-transparent; fibre laser; fiber laser; amniotic membrane;

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Cut Edge Structures and Gas Boundary Layer Characteristics in Laser Beam Fusion Cutting
Madlen Borkmann, Achim Mahrle, Eckhard Beyer, Christoph Leyens

Fiber laser fusion cutting trials on AISI 304 stainless steel sheets of 10 mm thickness were performed to gain further insight into the formation mechanisms of topographical features of cut edges. It is found that particularly the variation of focus position causes distinct processing regimes with completely different cut edge structures. Standard cut edges can be divided in six different structural zones. It has become obvious that particular details of the different cut edge zones can be only understood as a result of a rather complex cutting gas flow. Corresponding high-resolution CFD simulations of the cutting gas elucidate the structure of the supersonic flow field and particular boundary layer characteristics. The results strongly support the hypothesis that the cutting gas flow and particularly the stability of the gas boundary layer plays an important role for the generation of the final cut edge topography.

Keywords: laser beam fusion cutting; cut edge structure; gas flow characteristics; gas boundary layer; modelling and simulation

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Improving component cleanliness during laser remote ablation processes with high-power lasers by optimized emission blower and suction strategies
Tom Schiefer, Martin Sauer, Annett Klotzbach, Elke Schade, Michelle Wöllner, Gerrit Mäder, Beate Leupolt, Jens Standfuß, Stefan Kaskel

Laser remote processing with high-performance laser sources enables materials such as metals or fiber composites to be cut, welded or ablated flexibly and quickly. All these manufacturing processes produce process and material specific particulate as well as gaseous emissions. This must be recorded quantitatively and qualitatively in order to implement appropriate protective measures with regard to occupational health and safety as well as to minimize the cross-contamination of the component to be treated. Ideally, an additional cleaning step should be avoided by optimizing the arrangement of the process suction and blower. Particle distributions as well as gas phase analyses during the remote ablation process were recorded during ablation tests on metals or carbon-based composites. The structure quality and the contamination of the sample surface after laser material processing as well as after the additional cleaning process were determined. Subsequently, the samples were thermally joined to evaluate the influences.

Keywords: laser surface treatment; particle analysis; joining; occupational safety