Ralf Hellmann
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View article: In situ high-speed milling and thermal post-processing for the optimization of fatigue behaviour of additive-manufactured IN718 components
In situ high-speed milling and thermal post-processing for the optimization of fatigue behaviour of additive-manufactured IN718 components Open
We report on the optimization of tensile properties and fatigue behaviour of Laser Powder Bed Fusion (PBF-LB/M)-built IN718 components employing an innovative hybrid additive-subtractive technology and various heat treatments. The hybrid a…
View article: Evaluation of the Impact of Heat Treatment Processes and Surface Conditions on the Mechanical Properties of PBF-LB/M-Built Inconel 718 Components
Evaluation of the Impact of Heat Treatment Processes and Surface Conditions on the Mechanical Properties of PBF-LB/M-Built Inconel 718 Components Open
A study of the mechanical properties of hybrid additive manufactured IN718 components is presented, optimising mechanical properties due to an in-situ high-speed milling and different heat treatment processes. At first, the impact of diffe…
View article: On the Impact of Process Parameters and Ambient Temperature on Tensile Strength and Fatigue Behaviour of SLS-Built Polyamide-12
On the Impact of Process Parameters and Ambient Temperature on Tensile Strength and Fatigue Behaviour of SLS-Built Polyamide-12 Open
We report on a comprehensive study of tensile strength and fatigue behaviour depending on process parameters and ambient temperature. For this, Polyamide-12 components are fabricated using Selective Laser Sintering. Firstly, different proc…
View article: Fabrication and analysis of through-glass vias for glass-based electronic packaging using an ultrashort pulsed laser
Fabrication and analysis of through-glass vias for glass-based electronic packaging using an ultrashort pulsed laser Open
View article: Development of a dynamic beam stabilization system for a six-axis ultrashort pulsed laser robot
Development of a dynamic beam stabilization system for a six-axis ultrashort pulsed laser robot Open
We report on the evaluation of a beam stabilization system mounted on a six-axis articulated ultrashort pulsed laser robot system for real 3D micromachining. The system integrates a discrete beam guiding system along the robot links and an…
View article: Full penetration detection in fiber laser remote cutting of electrical steel sheets from <i>in situ</i> monitored images using convolutional neural networks
Full penetration detection in fiber laser remote cutting of electrical steel sheets from <i>in situ</i> monitored images using convolutional neural networks Open
In laser remote cutting, a cut through is usually realized by repeating a scanning process for several ablation cycles. The material removal rate depends primarily on the laser power, feed rate, and number of cycles. Too few cycles will no…
View article: Layer detection in ultrashort pulsed multilayer laser ablation by analyzing ultrasonic process emission
Layer detection in ultrashort pulsed multilayer laser ablation by analyzing ultrasonic process emission Open
We report on the capability of an ultrasonic sensor, consisting of a membrane-free optical microphone, to distinguish material transitions in ultrashort pulsed laser ablation of multilayer material systems for electronic applications. The …
View article: Design Guide for Hybrid-Additive Manufacturing of Inconel 718 Combining PBF-LB/M and In Situ High-Speed Milling
Design Guide for Hybrid-Additive Manufacturing of Inconel 718 Combining PBF-LB/M and In Situ High-Speed Milling Open
As the correlation between design rules and process limitations is of the upmost importance for the full exploitation of any manufacturing technology, we report a design guide for hybrid-additive manufacturing of Inconel 718. Basic limitat…
View article: Fractographic Analysis and Fatigue Behavior of Additively Manufactured Ni‐Superalloy Components with Post Processing Heat Treatment and Hot Isostatic Pressing
Fractographic Analysis and Fatigue Behavior of Additively Manufactured Ni‐Superalloy Components with Post Processing Heat Treatment and Hot Isostatic Pressing Open
A report is made on a study of mechanical properties and fractographic characteristics of laser powder bed fusion (PBF‐LB/M)‐built Inconel 718, performing heat treatments and hot‐isostatic pressing. For this, tensile components are heat‐tr…
View article: Vision transformer based cut interruption detection and prediction of laser fusion cutting from monitored melt pool images
Vision transformer based cut interruption detection and prediction of laser fusion cutting from monitored melt pool images Open
Incomplete cuts during laser fusion cutting result in a closed kerf, preventing the workpiece from detaching from the sheet and resulting in rework or rejection. We demonstrate the approach of a vision transformer, used for image classific…
View article: Holographic freeform micro hole processing using Bessel beams
Holographic freeform micro hole processing using Bessel beams Open
View article: Optimization of Mechanical Properties and Evaluation of Fatigue Behavior of Selective Laser Sintered Polyamide-12 Components
Optimization of Mechanical Properties and Evaluation of Fatigue Behavior of Selective Laser Sintered Polyamide-12 Components Open
In this paper, a comprehensive study of the mechanical properties of selective laser sintered polyamide components is presented, for various different process parameters as well as environmental testing conditions. For the optimization of …
View article: Rheological Investigation of Highly Filled Copper(II) Oxide Nanosuspensions to Optimize Precursor Particle Content in Reductive Laser-Sintering
Rheological Investigation of Highly Filled Copper(II) Oxide Nanosuspensions to Optimize Precursor Particle Content in Reductive Laser-Sintering Open
In this article, the particle concentration of finely dispersed copper(II) oxide nanosuspensions as precursors for reductive laser sintering (RLS) is optimized on the basis of rheological investigations. For this metallization process, a s…
View article: Spatially Resolved, Real-Time Polarization Measurement Using Artificial Birefringent Metallic Elements
Spatially Resolved, Real-Time Polarization Measurement Using Artificial Birefringent Metallic Elements Open
Polarization states define a fundamental property in optics. Consequently, polarization state characterization is essential in many areas of both field industrial applications and scientific research. However, a full identification of spac…
View article: Surface roughness optimization of hybrid PBF-LB/M-built Inconel 718 using in situ high-speed milling
Surface roughness optimization of hybrid PBF-LB/M-built Inconel 718 using in situ high-speed milling Open
We report on the optimization of the surface roughness of hybrid additive manufactured Ni superalloys, combining a conventional laser powder bed fusion process with in situ high-speed milling. This remarkable hybrid approach has only recen…
View article: Birefringence in Injection-Molded Cyclic Olefin Copolymer Substrates and Its Impact on Integrated Photonic Structures
Birefringence in Injection-Molded Cyclic Olefin Copolymer Substrates and Its Impact on Integrated Photonic Structures Open
This contribution quantifies the birefringence within injection-molded cyclic olefin copolymer plates and discusses its impact on the mechanical properties of the plates. It also focuses on the impact of birefringence on integrated wavegui…
View article: Femtosecond reductive Laser Sintering under multiple focus conditions for rapid production of conductive copper layers
Femtosecond reductive Laser Sintering under multiple focus conditions for rapid production of conductive copper layers Open
View article: Lattice-Like Waveguides With Integrated Bragg Gratings in Planar Cyclic Olefin Copolymers
Lattice-Like Waveguides With Integrated Bragg Gratings in Planar Cyclic Olefin Copolymers Open
This contribution demonstrates femtosecond laser direct writing of lattice-like waveguides in planar cyclic olefin copolymer substrates. Based on numerical simulation and experimental near-field analysis, stable single-mode waveguiding aro…
View article: Preparation of Dispersed Copper(II) Oxide Nanosuspensions as Precursor for Femtosecond Reductive Laser Sintering by High-Energy Ball Milling
Preparation of Dispersed Copper(II) Oxide Nanosuspensions as Precursor for Femtosecond Reductive Laser Sintering by High-Energy Ball Milling Open
This contribution demonstrates and discusses the preparation of finely dispersed copper(II) oxide nanosuspensions as precursors for reductive laser sintering (RLS). Since the presence of agglomerates interferes with the various RLS sub-pro…
View article: Fundamental Considerations and Analysis of the Energy Distribution in Laser Turning with Ultrashort Laser Pulses
Fundamental Considerations and Analysis of the Energy Distribution in Laser Turning with Ultrashort Laser Pulses Open
This article discusses the process of the laser turning of rotational symmetric, cylindrical components using ultrashort laser pulses with respect to the geometrical conditions and the resulting energy distribution during the laser turning…
View article: Picosecond laser microvia drilling of ABF material using MHz burst mode
Picosecond laser microvia drilling of ABF material using MHz burst mode Open
We report on a comprehensive study of laser percussion microvia drilling of Ajinomoto build-up film (ABF) material using an ultrashort pulsed laser in MHz burst mode. After laser processing, microvia drilling quality is being evaluated by …
View article: Drilling Sequence Optimization Using Evolutionary Algorithms to Reduce Heat Accumulation for Femtosecond Laser Drilling with Multi-Spot Beam Profiles
Drilling Sequence Optimization Using Evolutionary Algorithms to Reduce Heat Accumulation for Femtosecond Laser Drilling with Multi-Spot Beam Profiles Open
We report on laser drilling borehole arrays using ultrashort pulsed lasers with a particular focus on reducing the inadvertent heat accumulation across the workpiece by optimizing the drilling sequence. For the optimization, evolutionary a…
View article: Static and Dynamic Mechanical Behaviour of Hybrid-PBF-LB/M-Built and Hot Isostatic Pressed Lattice Structures
Static and Dynamic Mechanical Behaviour of Hybrid-PBF-LB/M-Built and Hot Isostatic Pressed Lattice Structures Open
We report on a comprehensive study of the mechanical properties of maraging steel body-centred cubic lattice structures fabricated by a hybrid additive manufacturing technology that combines laser powder bed fusion with in situ high-speed …
View article: Multi-Bessel Beams Generated by an Axicon and a Spatial Light Modulator for Drilling Applications
Multi-Bessel Beams Generated by an Axicon and a Spatial Light Modulator for Drilling Applications Open
We report on an optical setup to generate multi-Bessel beam profiles combining a refractive axicon and a spatial light modulator. Based on their particular beam profile, Bessel beams offer advantageous properties for micro drilling process…
View article: Evaluation of a Cut Interruption Algorithm for Laser Cutting Steel and Aluminum with a High-Speed Camera
Evaluation of a Cut Interruption Algorithm for Laser Cutting Steel and Aluminum with a High-Speed Camera Open
We report on a monitoring system based on a high-speed camera for fiber laser fusion cutting. The monitoring system is used without an external illumination retrofit on a conventional cutting head, with the optical path aligned coaxially t…
View article: Dual-color single molecule localization microscopy on transparent polymer waveguide chips
Dual-color single molecule localization microscopy on transparent polymer waveguide chips Open
Photonic waveguide chips offer near-field excitation of biological samples, which enables cost-effective, large field-of-view super-resolution microscopy without the need for high numerical aperture (NA) objective lenses. Single molecule l…
View article: Mechanical Properties of LPBF-Built Titanium Lattice Structures—A Comparative Study of As-Built and Hot Isostatic Pressed Structures for Medical Implants
Mechanical Properties of LPBF-Built Titanium Lattice Structures—A Comparative Study of As-Built and Hot Isostatic Pressed Structures for Medical Implants Open
We compare different lattice structures with various elementary cell sizes built by laser powder bed fusion with and without hot isostatic pressing as post treatment. Cylindrical lattice structures are mechanically tested upon static and d…
View article: Evaluation of SLS 3D-Printed Filter Structures Based on Bionic Manta Structures
Evaluation of SLS 3D-Printed Filter Structures Based on Bionic Manta Structures Open
We report on additively manufactured filter systems based on bionic manta ray structures and evaluate their filter performance. The filters are periodic lamella structures produced by selective laser sintering using PA12 polyamide powder. …
View article: Function Integration in Additive Manufacturing: Design and Realization of an LPBF Built Compressed Air Motor
Function Integration in Additive Manufacturing: Design and Realization of an LPBF Built Compressed Air Motor Open
We present a compressed air motor, completely built by laser powder bed fusion. To highlight the fully functional integration by additive manufacturing, the rotor, stator, bearings, turbine, gas inlet and outlet were all built in a single …
View article: Femtosecond Laser-Based Micromachining of Rotational-Symmetric Sapphire Workpieces
Femtosecond Laser-Based Micromachining of Rotational-Symmetric Sapphire Workpieces Open
Sapphire is a robust and wear-resistant material. However, efficient and high-quality micromachining is still a challenge. This contribution demonstrates and discusses two novels, previously unreported approaches for femtosecond laser-base…