Conference Agenda

Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).

Please note that all times are shown in the time zone of the conference. The current conference time is: 17th Oct 2021, 01:22:27am CEST

Program for LiM 2021
Micro: Micro Machining
Wednesday, 23/June/2021:
2:45pm - 4:00pm

Session Chair: Oliver Hentschel, Institute of Photonic Technologies (LPT), Germany
Location: Room 3
ICM Ground Floor 125

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2:45pm - 3:00pm

Laser machining of different steel grades with 10ps laser pulses: the influence of carbides onto the surface roughness and structures for different laser parameters

Stefan M. Remund, Severin N. Herren, Josef Zürcher, Beat Neuenschwander

Berner Fachhochschule Technik und Informatik, Switzerland

When steel is machined with ultra-short pulses the specific removal rate strongly depends on the pulse fluence, the wavelength and, in case of bursts, on the number of pulses whereas the steel grade has a minor influence. This situation changes for the surface roughness. Beside the laser parameters, the initial surface and the number of machined layers the obtainable surface roughness also depends on the carbides located in the steel as well as their size and distribution and therefore it is strongly influenced by the steel grade. E.g. for a given set of parameters a surface roughness (sq) value of 350nm, 410nm and 500nm was achieved for CK75 (no carbides), M390 (small carbides) and K100 (large carbides). We will present the results of a systematic study for different steel grades in the application of surface structuring and smoothening of surfaces machined by alternative technologies as e.g. electrical discharge machining (EDM).

3:00pm - 3:15pm

Scaling the throughput of high-quality silicon laser micromachining using a 1-kW sub-picosecond laser

Daniel Holder1, Rudolf Weber1, Christoph Röcker1, Gerhard Kunz2, David Bruneel3, Martin Delaigue4, Thomas Graf1, Marwan Abdou Ahmed1

1IFSW, University of Stuttgart, Germany; 2Robert Bosch GmbH, Germany; 3Lasea, Belgium; 4Amplitude Systemes, France

Recently, laser processing of silicon with ultrafast lasers has gained widespread attention for manufacturing of optics for THz radiation, an emerging topic with applications in medical imaging, security and communication. Such THz-optics require high-quality surfaces with low roughness in order to provide high transmission and low scattering. In the past, the low average power of ultrafast lasers limited the achievable throughput in silicon laser micromachining.

In this work a processing strategy for high-quality high-throughput micromachining of silicon with a 1-kW sub-picosecond laser is presented, which takes benefit of pulse bursts, low fluences and high feed rates.

As a result, laser micromachining could be demonstrated as a suitable technology for manufacturing of smooth structures on silicon while maintaining a high throughput. Surfaces with an appropriate roughness of Sa ≤ 0.6 µm were produced with a high material removal rate of 230 mm³/min and a machining depth of up to 313 µm.

3:15pm - 3:30pm

Ultra-short laser micro-machining by spatially shaped ps- and fs-pulses for depth-selective µ-TLM resistivity test structures in TCO contact layers

Stephan Krause1,2, Stefan Lange2, Gao Yiding2, Volker Naumann2, Christian Hagendorf2, Paul-Tiberiu Miclea1,2

1Fraunhofer CSP, Germany; 2Martin-Luther-University Halle/Wittenberg

We applied spatially shaped ultra-short pulse laser micro-machining for a new processing approach of µ-TLM test structures. These structures are used for resistivity measurements of multilayer systems with highly resistive interface layers, e.g. in TCO top contacts for solar cells. For precise measurements of the electrical sheet and contact resistivity of the individual layers, isolating trenches and homogenous ablation areas are required that can be fabricated by matching of pulse overlapping based on rectangular spots in µm-dimensions.

Ultrashort pulses by 10 ps and 200 fs (515/532/1030 nm) as well as optical beam shaping elements for redistribution to top-hat intensity profiles enables a selective removal of the top TCO. Thus, thermal damage is minimized in the underlying material and multilayer adjacent region of the laser trenches by ultrafast ablation mechanism. Morphology and microstructure of heat-affected zones were characterized by high-resolution transmission electron microscopy to optimize laser recipes for enhancing ablation selectivity.

3:30pm - 3:45pm

Automated cutting by water jet-guided laser machining using a break-through sensor

Falk Braunmüller, Jérémie Diboine, Amédée Zryd, Bernold Richerzhagen

Synova S.A., Switzerland

The Laser Micro-Jet® is now a well-established technology among others for micro-machining and high-quality machining of hard and composite materials, with the advantages of narrow parallel cut walls without focus adaptation, minimizing the heat-affected zone and the avoidance of burrs.
This contribution describes the development of a break-through sensor measuring light from the laser plasma through the water jet. By detecting a completed cut, additional safety cutting passes can be reduced and the cutting is stopped just in time.
The sensor enables an optimized, automatized cutting, which represents a significant step towards industry 4.0. The technology is now employed on an industrial scale by several customers, showing the high potential of the technology: The processing time is reduced by 5-20%.
Finally, first results of a cutting sensor with spectrally resolved plasma detection will be presented, which shall enable a targeted ablation by detecting various layers in a multi-layer material.

3:45pm - 4:00pm

Laser turning using ultra-short laser pulses and intensity distribution techniques

Julian Zettl1, Christian Bischoff2,3, Stefan Rung1, Cemal Esen3, Andrés Fabián Lasagni4, Ralf Hellmann1

1University of Applied Sciences Aschaffenburg, Germany; 2Topag Lasertechnik GmbH, Germany; 3Ruhr University Bochum, Germany; 4Technical University Dresden, Germany

We report on the fabrication of rotationally symmetric parts by using focused ultra-short laser pulses while impinging the rotating work piece tangentially. The use of ultra-short laser pulses enables this process to fabricate parts in a non-contact manner, even from materials that are hard to machine such as stellite or fused silica. The target geometry is realized by moving the constantly rotating specimen according to the specified geometry under the focused laser spot. In order to further enhance this manufacturing approach, a spatial distribution of the laser power on the work piece is investigated. Beam shaping techniques are applied to alter the shape of the focal spot and to study the effects on the resulting ablation rate, process efficiency and surface quality.

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