Petri Laakso

Sintering of printed nanoparticle structures using laser treatment

Printed intelligence is a promising new technology to produce low-cost electronics. Non-conductive circuits can be printed using nanoscale metal particle inks. Due to the nanoscale size of the particles, the typical sintering temperatures of 100–300 °C are only a fraction of the macroscopic melting point of the corresponding materials, thus allowing the use of paper or plastic substrates.Sintering of printed nanoparticle structures using laser treatment has been investigated at VTT. Laser sintering can be utilized in manufacturing of printed conductor structures such as antennas, circuits and sensors. A drop-on demand printer was used to print patterns with metallo-organic silver nanoparticles on a flexible polyimide substrate. Laser sintering was made with a 940 nm CW fiber coupled diode laser. Process was optimized using different laser power levels, line separation and repetition rounds. Conductivity of laser sintered samples was compared to conductivity of samples sintered in convection oven.Printed intelligence is a promising new technology to produce low-cost electronics. Non-conductive circuits can be printed using nanoscale metal particle inks. Due to the nanoscale size of the particles, the typical sintering temperatures of 100–300 °C are only a fraction of the macroscopic melting point of the corresponding materials, thus allowing the use of paper or plastic substrates.Sintering of printed nanoparticle structures using laser treatment has been investigated at VTT. Laser sintering can be utilized in manufacturing of printed conductor structures such as antennas, circuits and sensors. A drop-on demand printer was used to print patterns with metallo-organic silver nanoparticles on a flexible polyimide substrate. Laser sintering was made with a 940 nm CW fiber coupled diode laser. Process was optimized using different laser power levels, line separation and repetition rounds. Conductivity of laser sintered samples was compared to conductivity of samples sintered in convection oven.

Adaptive multibeam laser cutting of thin steel sheets with fiber laser using spatial light modulator

Laser cutting with multibeam diffraction pattern using an adaptive optics is studied. Infrared (IR) continuous single-mode fiber laser with maximum power of 200 W is applied to laser cutting of thin metal sheets, together with liquid crystal on silicon spatial light modulator (SLM). SLM can be used as the adaptive diffractive optical element, which can modify intensity profile of the laser beam almost arbitrary. In studies single Gaussian laser beam was divided into multiple spots. It was found out that with this way it is possible to enhance the cutting quality and also decrease pressure of the needed assist gas. Multibeam configuration enabled to laser cut burr free with 50% less protection gas pressure compared to single beam laser cutting with conventional optics.

Laser cutting of paper

It is commonly known that CO2 laser beam is suitable for paper and board cutting. However there exists quite little published research work about paper cutting with laser. Lasers at paper industry are mainly used to different perforating and scoring applications. There exists only few paper slitting applications. Water jet cutting is widely used edge trimming applications at paper plants. Laser cutting could be substation process for water jet cutting.This paper concentrates on understanding parameters that are characteristic to the laser cuttability of coated and uncoated papers. Also economical aspects, for edge trimming of paper web, are studied. This study was performed within a national project in Finland about laser cutting of pulps, papers and boards. The research was carried out with a Trumpf 2.7 kW HQ laser and a work cell designed and manufactured for the project.The cutting experiments contained the cutting tests of how different laser parameters like power, focal point position, and focal length affected the cutting speed and the cut edge quality. Papers used in study could be laser cut with acceptable quality. Highest cutting speeds were noted with 127 mm focal length. It was also found that the cut edge quality and kerf width were stable for each grammage and paper types produced with parameter combinations on cutting limit (laser power/cutting speed).It is commonly known that CO2 laser beam is suitable for paper and board cutting. However there exists quite little published research work about paper cutting with laser. Lasers at paper industry are mainly used to different perforating and scoring applications. There exists only few paper slitting applications. Water jet cutting is widely used edge trimming applications at paper plants. Laser cutting could be substation process for water jet cutting.This paper concentrates on understanding parameters that are characteristic to the laser cuttability of coated and uncoated papers. Also economical aspects, for edge trimming of paper web, are studied. This study was performed within a national project in Finland about laser cutting of pulps, papers and boards. The research was carried out with a Trumpf 2.7 kW HQ laser and a work cell designed and manufactured for the project.The cutting experiments contained the cutting tests of how different laser parameters like power, focal point position, and focal leng...

Parallel femtosecond laser processing using intensity modulated diffraction pattern produced with spatial light modulator

Due to technical development of the adaptive optics, use of them in various laser processing applications has become possible. These techniques based on the adaptive optics have been applied with various lasers to generate diffraction patterns with equal intensity spots. In this paper ultrashort laser pulse ablation with intensity modulated diffraction pattern is presented. Diffraction patterns are generated with the Computer Generated Holograms (CGH) created using the Spatial Light Modulator (SLM). Applied CGHs are designed using method based on the Iterative Fourier Transform Algorithm (IFTA). Added to this Fresnel lenses are used to avoid problems with 0th-diffraction order. With this kind of designing procedure it is possible to generate diffraction patterns with intensity variation between diffracted spots. By intensity modulating the diffracted beams it is possible to ablate virtually arbitrary patterns with depth variation into the different materials. In this paper different kinds of CGHs are designed to generate various diffraction patterns with intensity modulation. These patterns are used to ablate greyscale images directly into the silicon using ultrashort pulses.Due to technical development of the adaptive optics, use of them in various laser processing applications has become possible. These techniques based on the adaptive optics have been applied with various lasers to generate diffraction patterns with equal intensity spots. In this paper ultrashort laser pulse ablation with intensity modulated diffraction pattern is presented. Diffraction patterns are generated with the Computer Generated Holograms (CGH) created using the Spatial Light Modulator (SLM). Applied CGHs are designed using method based on the Iterative Fourier Transform Algorithm (IFTA). Added to this Fresnel lenses are used to avoid problems with 0th-diffraction order. With this kind of designing procedure it is possible to generate diffraction patterns with intensity variation between diffracted spots. By intensity modulating the diffracted beams it is possible to ablate virtually arbitrary patterns with depth variation into the different materials. In this paper different kinds of CGHs are desi...

Quasi-simultaneous laser welding of transparent polymers by using beam off-setting scanning technique

Quasi-simultaneous laser welding (QSLW) of polymers is widely known laser joining technique. Traditionally joining of polymers has been done by using lasers of around 1 µm wavelength. With this wavelength the pair of polymers to be joined needs to be transparent and absorbing, usually clear and black. Joining of two transparent polymers with laser has been possible only by using laser absorbing additive between the samples or by doping the polymer with absorbing additive. During the last years lasers with new wavelengths between 1.4 to 2 µm have been developed. With this wavelength range welding of the transparent polymer to another transparent one without any absorbing additives has become possible.Only few studies of joining transparent polymers with new wavelength lasers are published. In this paper joining of transparent to transparent polymers with QSLW technique and 1.9 µm fibre laser is studied. Also a new scanning technique for QSLW is introduced. In this technique laser beam path is off- setting to a different place in every scanning round. This way the Gaussian beam shape of fibre laser can be smoothened to be more suitable for polymer welding and variation of the weld width is possible without changing the scanner optic. With this technique more flexibility on laser welding of polymers is achieved without losing the benefits of quasi-simultaneous laser welding.Quasi-simultaneous laser welding (QSLW) of polymers is widely known laser joining technique. Traditionally joining of polymers has been done by using lasers of around 1 µm wavelength. With this wavelength the pair of polymers to be joined needs to be transparent and absorbing, usually clear and black. Joining of two transparent polymers with laser has been possible only by using laser absorbing additive between the samples or by doping the polymer with absorbing additive. During the last years lasers with new wavelengths between 1.4 to 2 µm have been developed. With this wavelength range welding of the transparent polymer to another transparent one without any absorbing additives has become possible.Only few studies of joining transparent polymers with new wavelength lasers are published. In this paper joining of transparent to transparent polymers with QSLW technique and 1.9 µm fibre laser is studied. Also a new scanning technique for QSLW is introduced. In this technique laser beam path is off- setting ...

Laser cutting of pulps

Laser cutting offers unique possibilities for different production systems. So far the utilization has been most advanced in cutting of metal products. The laser has also been utilized for paper and board cutting in some specific applications. This study is performed within a national project in Finland about laser cutting of pulp, paper and board. The research is carried out with a Trumpf 2.7 kW HQ laser, with focal point diameter of 80 µm and a work cell designed and manufactured for the project. The study concentrates on the physical phenomena of laser cutting of different pulps. These experiments covered the effect of pulp type and weight per square meter (grammage g/m2). The experiments covered also the effect of laser parameters on the cutting speed and cut edge quality. By the experiments it can be seen that all of the variables have an effect on both the cutting speed and the cut quality.Laser cutting offers unique possibilities for different production systems. So far the utilization has been most advanced in cutting of metal products. The laser has also been utilized for paper and board cutting in some specific applications. This study is performed within a national project in Finland about laser cutting of pulp, paper and board. The research is carried out with a Trumpf 2.7 kW HQ laser, with focal point diameter of 80 µm and a work cell designed and manufactured for the project. The study concentrates on the physical phenomena of laser cutting of different pulps. These experiments covered the effect of pulp type and weight per square meter (grammage g/m2). The experiments covered also the effect of laser parameters on the cutting speed and cut edge quality. By the experiments it can be seen that all of the variables have an effect on both the cutting speed and the cut quality.

Rapid laser sintering of alkaline fuel cell substrates using integrating mirror

Nickel screens and foams are commonly used in alkaline fuel cell (AFC) as substrates to support electrodes. The methods used for fabrication of these substrates impact significantly on the viability, with the material and processing cost of nickel comprising almost one third of the total. Therefore, improvements to the manufacturing speed of substrates would increase affordability. Currently, state of the art commercial selective laser sintering systems are limited to a volumetric manufacturing speed of 1–3 mm3/s. This study describes a novel technique that multiplies the sintering speed of nickel AFC substrates. The novel technique is based on an integrating mirror, which creates a homogenized 60 mm wide and 0.3 mm long beam from a Nd:YAG laser, and a 0.8 mm thick nickel powder layer in a nitrogen environment. The influence of the nickel powder characteristics, and sintering parameters, as velocity, laser power, etc., and postsintering treatments of the samples on the mechanical properties of the substra...

Butt welding of transparent polyamide (PA11) with 1.94µm fiber laser

Laser welding of polymeric products has been manufactured for more than 20 years. During that time polymer welding has developed a lot. In spite of that, there are still some limitations in applying the process to the industry. Typically welding has been made in lap joint configuration with black and clear parts because of optical properties of polymers. When using ∼1µm lasers, the absorbing and transparent partners are needed. Previously visually transparent materials have been welded in lap joint configuration using infrared absorbers with ∼1µm lasers. Recently new fiber lasers have introduced wavelengths which can have interesting optical properties for polymers. For example, 1.94µm laser has volume absorption through the whole material thickness on selected polyamide 11 (PA11) polymer material. This makes it possible to use butt joint for welding of polymeric components. When butt joint can be introduced, it will enable more possibilities in using polymer welding in the industry. A joint between two clear components without any additional absorbers can also be introduced with these new wavelengths and it will also decrease the costs and enable new applications when no infrared absorbing additives are needed or accepted. This paper presents results of butt welding of transparent PA11 using TWIST method with 1.94µm fiber laser. Weld quality is evaluated visually and by comparing weld tensile strength to base material tensile strength.Laser welding of polymeric products has been manufactured for more than 20 years. During that time polymer welding has developed a lot. In spite of that, there are still some limitations in applying the process to the industry. Typically welding has been made in lap joint configuration with black and clear parts because of optical properties of polymers. When using ∼1µm lasers, the absorbing and transparent partners are needed. Previously visually transparent materials have been welded in lap joint configuration using infrared absorbers with ∼1µm lasers. Recently new fiber lasers have introduced wavelengths which can have interesting optical properties for polymers. For example, 1.94µm laser has volume absorption through the whole material thickness on selected polyamide 11 (PA11) polymer material. This makes it possible to use butt joint for welding of polymeric components. When butt joint can be introduced, it will enable more possibilities in using polymer welding in the industry. A joint between two c...

Increasing the productivity of femtosecond laser using spatial light modulator

Spatial light modulator can be used to split the beam into several beams. Using this kind of approach one can utilize most of the laser power from the fs laser. Typically most of the power from fs laser has to be attenuated to be able to machine material in the gentle ablation regime. This regime will give the best quality but will take more time in processing. If multiple spots can be utilized the speed of processing can be multiplied. In this paper we demonstrate the usage of SLM together with scanhead to speed up the process. Processing speed is compared to the normal single spot processing. Quality of the processing is compared between techniques and is also evaluated using SEM and white light interferometer.Spatial light modulator can be used to split the beam into several beams. Using this kind of approach one can utilize most of the laser power from the fs laser. Typically most of the power from fs laser has to be attenuated to be able to machine material in the gentle ablation regime. This regime will give the best quality but will take more time in processing. If multiple spots can be utilized the speed of processing can be multiplied. In this paper we demonstrate the usage of SLM together with scanhead to speed up the process. Processing speed is compared to the normal single spot processing. Quality of the processing is compared between techniques and is also evaluated using SEM and white light interferometer.

TWINQUASI – A new method for quasi-simultaneous laser welding of polymers

Quasi-simultaneous laser welding (QSLW) of polymers has been studied, developed and used both in academia and industry for many years. The process has high flexibility and lot of advantages but it has some limitations especially when short welding time is required. The short welding time requires a scanner with extremely high speed and accuracy which usually limits the maximum dimensions of the joint and products to be welded. This paper presents a new method to utilize a QSLW-process with two lasers and optical scanners (TWINQUASI) for quasi-simultaneous laser welding of polymers which enables welding of larger components within a short welding time. The paper demonstrates TWINQUASI and compares its performance to those of traditional QSLW. Results show that with this method the length of the weld can be doubled within the same welding time while still keeping equal scanning frequency to that of the conventional QSLW-process. It is shown that with the TWINQUASI method, larger components can be welded with quasi-simultaneous method compared to shown earlier. Another advantage of the process is the ability to program scanning paths of both lasers individually. Because of this, the TWINQUASI method enables also variation of the weld width within one weld seam giving even more flexibility to the process.Quasi-simultaneous laser welding (QSLW) of polymers has been studied, developed and used both in academia and industry for many years. The process has high flexibility and lot of advantages but it has some limitations especially when short welding time is required. The short welding time requires a scanner with extremely high speed and accuracy which usually limits the maximum dimensions of the joint and products to be welded. This paper presents a new method to utilize a QSLW-process with two lasers and optical scanners (TWINQUASI) for quasi-simultaneous laser welding of polymers which enables welding of larger components within a short welding time. The paper demonstrates TWINQUASI and compares its performance to those of traditional QSLW. Results show that with this method the length of the weld can be doubled within the same welding time while still keeping equal scanning frequency to that of the conventional QSLW-process. It is shown that with the TWINQUASI method, larger components can be welded wit...