The additive manufacturing of geometrically complex parts of pure copper using laser assisted powder bed fusion (LPBF) is demonstrated. The high thermal and electrical conductivity of pure copper combined with the geometric freedom of the LPBF process offers a wide range of applications. We demonstrate the fabrication of parts combining a high homogeneous density with complex geometries by adapting the laser power to the available thermal mass. This is done by applying a simple model which calculates the required laser power based on available thermal mass approximated by the local geometry.
Additive manufacturing (AM) of pure copper using laser assisted powder bed fusion (LPBF) at a wavelength of 1070 nm is demonstrated. The rapid drop of absorption at the melting point of pure copper hinders the identification of an appropriate processing window. With a combination of an extensive parameter study and a comprehensive analysis using a multiscale numerical model of the LPBF process different processing windows extending over a wide range of incident laser powers were verified. The model allows to investigate the sensitivity of single parameters, and thereby gives the opportunity to carefully adjust the strategy of the AM process.
Laser assisted powder bed fusion of pure Aluminum and hypereutectic Al-Si using ultra-short laser pulses at different pulse lengths is presented. The experiments were carried out with a fiber laser system delivering pulses from 500 fs to 600 ps at a wavelength of 1030 nm and a repetition rate of 20 MHz. Time dependent reflectance measurements indicate that the absorption is increased towards shorter pulse durations. In comparison to longer pulses and cw radiation, powder bed fusion using ultra-short laser pulses lead to uniform structures at lower average powers yielding a homogeneous microstructure that exhibits optimized mechanical properties.
During the last decade, laser assisted additive manufacturing evolved to a serious alternative to traditional manufacturing methods. The greatest benefit lies in the realization of almost any desired geometry impossible to create with common molding or cutting processes. Due to the lack of linear absorption in the visible and near infrared, transparent dielectrics like glass are challenging materials for laser powder bed fusion (LPBF). Here, a comparative study on the additive manufacturing of pure fused silica glass parts is presented. For the fusion process, either a common CO2 laser system working at 10.6 μm or an ultrashort pulse (USP) fiber laser system at 1030 nm were applied. While the mid-infrared laser radiation from CO2-lasers is absorbed linearly, ultrashort laser pulses benefit from their extremely high peak power leading to strong nonlinear absorption. In contrast to alternative approaches [1], there was no need for binding materials. For both systems, a comprehensive parameter study is presented, highlighting major differences like surface quality, resolution and processing time.
Here we present laser aided additive manufacturing of pure copper parts using ultrashort laser pulses. The process is based on the powder bed fusion of pure copper powder with grain sizes in the range of 5 μm – 15 μm. For processing, a fiber laser system delivering 500 fs pulses at a wavelengths of 515 nm was used. Robust 3D printed parts are generated featuring a high degree of resolution. The fabricated copper samples were characterized in terms of morphology, density distribution, thermal and electrical conductivity. The inner structure is revealed by x-ray computed tomography measurements.
Within the field of laser assisted additive manufacturing, the application of ultrashort pulse lasers for selective laser melting came into focus recently. In contrast to conventional lasers, these systems provide extremely high peak power at ultrashort interaction times and offer both the opportunity of nonlinear absorption and the potential to control the thermal impact at the vicinity of the processed region by tailoring the pulse repetition rate. Consequently, transparent materials like borosilicate glass or opaque materials with extremely high melting points like copper, tungsten or even special composites like AlSi40 can be processed. In this publication, we present the selective laser melting of glass by using 500 fs laser pulses at MHz repetition rates emitted at a center wavelength of 515 nm. In order to identify an appropriate processing window, a detailed parameter study was performed. We demonstrate the fabrication of porous bulk glass parts as well as the realization of structures featuring thicknesses below 30 μm, which is below typical achieved structural sizes using pulsed or CO2 laser [1]. In contrast to alternative approaches [2], due to the nonlinear absorption and therefore complete melting of the material, there was no need for binding materials. This work demonstrates the potential for 3D printing of glass using the powder bed approach.
Additive manufacturing gained increasing interest during the last decade due to the potential of creating 3D devices featuring nearly any desired geometry. One of the most widely used methods is the so-called powder bed method. In general, conventional cw and pulsed laser sources operating around 1030 nm and CO2 lasers at 10.6 μm are usually applied. Among other materials like polymers, these systems are feasible for several metals, alloys and even ceramics, but easily reach their limitation at a wide range of other materials, regarding required absorption and intensity. In order to overcome these limits, ultrashort pulse laser systems are one approach. Due to the increased peak power and ultrashort interaction times within the femtosecond and picosecond time range, materials with extraordinary high melting points, increased heat conductivity or new composites with tailored specifications are coming into reach. Moreover, based on the nonlinear absorption effect, also transparent materials can be processed.
Here, we present the selective laser melting of pure copper using ultrashort laser pulses. This work involves a comparative study using 500 fs pulses at processing wavelengths of 515 nm and 1030 nm. The repetition rate of the applied laser system was varied within the MHz range in order to exploit heat accumulation. By using the ultrashort interaction times and tailoring the repetition rate, the induced melt pool can be significantly optimized yielding robust copper parts revealing thin-wall structures in the range below 100 μm.
Glass processing with ultrashort laser pulses allow for different material modifications, ranging from smooth refractive index changes which can be used for the generation of waveguides up to large disruptions due to accumulates stress for glass separation. These disruptions, generated by a dense electron plasma, are favored for glass dicing applications. To tailor the resulting material response a fundamental understanding of the laser/material interaction is of interest. Therefore, we analyze the spatio-temporal evolution of free carriers induced by ultrashort laser pulses using a pump-probe setup with high temporal and spatial resolution and various probe wavelengths.
Single laser pulses with 1026nm wavelength, 6ps (FWHM) pulse duration and 200μJ pulse energy were applied to fused silica, Borofloat 33 and Gorilla glass. Electron densities around 1 x 1020cm-3 in the focal plane and 1 x 1019cm-3 in front of the focus are obtained, independent from the glass type used.
The free carriers slowly decay within several ns, while the decay time depends on both the maximum electron densities reached and glass species. In this process a part of the excited electrons relax within several 10ps into a long-living stage where a transient effect is observed. Here, various probe wavelengths show differences in the recorded signal.
A further carrier relaxation leads to permanent (stress, voids) and non-stable (color center) modifications crucial for precise glass dicing applications.
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