Andre Streek

High-rate laser microprocessing using a polygon scanner system

This paper discusses results obtained in high-rate laser microprocessing by using a high average power high-pulse repetition frequency ultrashort pulse laser source in combination with an in-house developed polygon scanner system. With the recent development of ultrashort pulse laser systems supplying high average power of hundreds watts and megahertz pulse repetition rates, a significant increase of the productivity can potentially be achieved in micromachining. This permits upscaling of the ablation rates and large-area processing, gaining increased interest of the ultrashort pulse laser technology for a large variety of industrial processes. However, effective implementation of high average power lasers in microprocessing requires fast deflection of the laser beam. For this, high-rate laser processing by using polygon scanner systems provide a sustainable technological solution. In this study, a picosecond laser system with a maximum average power of 100 W and a repetition rate up to 20 MHz was used. I...

Laser microsintering of tungsten in vacuum

Laser microsintering of tungsten powder is investigated as a function of laser output power, pulse interval and vacuum level. The intensities are calculated for the evaporation thresholds of tungsten powder particles of various sizes. In addition, the powder layer generation and the resulting layer thicknesses are calculated. The powder abrasion occurring during the process was taken into consideration. Polished sections and REM images were prepared in order to analyse the experimental outcomes. The dependence of sinter density on the parameters is discussed.

Laser micro sintering of SiO2 with an NIR-laser

Many materials have already been investigated for laser micro sintering. Nearly all technical metals can be processed with this rapid prototyping technology. A new field of investigation is the sintering of ceramics. For industrial and also for medical, especially dental, application silicon dioxide is a multiply applicable material. One of its interesting features is that the properties of the resulting material can be varied between ceramic on the one and vitreous on the other side, depending on the extent of crystalline or amorphous character of the nano-scale structure. A special problem with laser micro sintering of ceramics is the poor absorption of Nd:YAG laser radiation by most of the materials. Besides that, laser micro sintering of ceramics, in contrary to the process with metals, is not merely a series of aggregational transitions. A solution for the micro part generation of SiO2 is reported. Typical laser sintering results from this material are presented. Material specific behaviors during laser micro sintering are discussed.

High-throughput machining using a high-average power ultrashort pulse laser and high-speed polygon scanner

Abstract. High-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (aluminum, copper, and stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high-average power picosecond laser in conjunction with a unique, in-house developed polygon mirror-based biaxial scanning system. Therefore, different concepts of polygon scanners are engineered and tested to find the best architecture for high-speed and precision laser beam scanning. In order to identify the optimum conditions for efficient processing when using high-average laser powers, the depths of cavities made in the samples by varying the processing parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. For overlapping pulses of optimum fluence, the removal rate is as high as 27.8  mm3/min for aluminum, 21.4  mm3/min for copper, 15.3  mm3/min for stainless steel, and 129.1  mm3/min for Al2O3, when a laser beam of 187 W average laser powers irradiates. On stainless steel, it is demonstrated that the removal rate increases to 23.3  mm3/min when the laser beam is very fast moving. This is thanks to the low pulse overlap as achieved with 800  m/s beam deflection speed; thus, laser beam shielding can be avoided even when irradiating high-repetitive 20-MHz pulses.

Laser micro sintering - Upgrade of the technology

Laser micro sintering, a modification of selective laser sintering for the freeform fabrication of micro-parts, has been developed continuously since its first application. The main feature of the original regime was the application of non-overlapping q-switched pulses which was required because of the poor density of the powder layers and the concomitant need for a compacting effect during the laser sinter process. Next to some unanticipated positive side effects of this regime, poor compactness of the products had to be taken into account frequently as a detrimental consequence. Recently an upgraded coating routine has been developed that contains a compaction-step of the powder coating prior to the sintering of each layer. After appropriate adaption of the laser regime micro-parts with considerably higher densities can be achieved now. Process observations and the properties of the sintered solids give evidence that a different sinter mechanism takes place with its own negative and positive side effect...

High resolution laser micro sintering / melting using q-switched and high brilliant laser radiation

Since the discovery of selective laser sintering/melting, numerous modifications have been made to upgrade or customize this technology for industrial purposes. Laser micro sintering (LMS) is one of those modifications: Powders with particles in the range of a few micrometers are used to obtain products with highly resolved structures. Pulses of a q-switched laser had been considered necessary in order to generate sinter layers from the micrometer scaled metal powders. LMS has been applied with powders from metals as well as from ceramic and cermet feedstock’s to generate micro parts. Recent technological progress and the application of high brilliant continuous laser radiation have now allowed an efficient laser sintering/melting of micrometer scaled metal powders. Thereby it is remarkable that thin sinter layers are generated using high continuous laser power. The principles of the process, the state of the art in LMS concerning its advantages and limitations and furthermore the latest results of the recent development of this technology will be presented. Laser Micro Sintering / Laser Micro Melting (LMM) offer a vision for a new dimension of additive fabrication of miniature and precise parts also with application potential in all engineering fields.

Laser micro melting

Additive manufacturing (AM) offers a quick and efficient method for prototyping and small batch production with a short delivery time or even individual parts. Components of high geometrical complexity can be directly shaped from metals, metal-alloys, metal-matrix composites and from ceramic materials. By a suitable choice of the process parameters AM produced components can meet the demanding requirements of the aerospace, automotive and biomedical industries. Laser micro sintering (LMS) as a further development of selective laser sintering uses fine grained powders below 10 µm to produce high accuracy 3D structures (<25 µm) with a low surface roughness (∼3 µm). Up to now, sintering of different material was accomplished through laser radiation in a ns-pulse regime. Recent developments regarding the coating mechanism to achieve higher powder density allows the application of high brilliant continuous radiation for a direct laser micro melting of high resolution structures. This paper will present the principle of the process and the state of the art of laser micro sintering, its advances and limitations, views of the products and the newest results of the further development of this technology. The introduced laser micro melting technology opens up a new dimension for the freeform fabrication of miniature and precise parts with application potentialities in a multitude of engineering fields.Additive manufacturing (AM) offers a quick and efficient method for prototyping and small batch production with a short delivery time or even individual parts. Components of high geometrical complexity can be directly shaped from metals, metal-alloys, metal-matrix composites and from ceramic materials. By a suitable choice of the process parameters AM produced components can meet the demanding requirements of the aerospace, automotive and biomedical industries. Laser micro sintering (LMS) as a further development of selective laser sintering uses fine grained powders below 10 µm to produce high accuracy 3D structures (<25 µm) with a low surface roughness (∼3 µm). Up to now, sintering of different material was accomplished through laser radiation in a ns-pulse regime. Recent developments regarding the coating mechanism to achieve higher powder density allows the application of high brilliant continuous radiation for a direct laser micro melting of high resolution structures. This paper will present the pri...

High-throughput machining using high average power ultrashort pulse lasers and ultrafast polygon scanner

In this paper, high-throughput ultrashort pulse laser machining is investigated on various industrial grade metals (Aluminium, Copper, Stainless steel) and Al2O3 ceramic at unprecedented processing speeds. This is achieved by using a high pulse repetition frequency picosecond laser with maximum average output power of 270 W in conjunction with a unique, in-house developed two-axis polygon scanner. Initially, different concepts of polygon scanners are engineered and tested to find out the optimal architecture for ultrafast and precision laser beam scanning. Remarkable 1,000 m/s scan speed is achieved on the substrate, and thanks to the resulting low pulse overlap, thermal accumulation and plasma absorption effects are avoided at up to 20 MHz pulse repetition frequencies. In order to identify optimum processing conditions for efficient high-average power laser machining, the depths of cavities produced under varied parameter settings are analyzed and, from the results obtained, the characteristic removal values are specified. The maximum removal rate is achieved as high as 27.8 mm3/min for Aluminium, 21.4 mm3/min for Copper, 15.3 mm3/min for Stainless steel and 129.1 mm3/min for Al2O3 when full available laser power is irradiated at optimum pulse repetition frequency.