Tuomas Purtonen

Quality aspects in remote laser cutting

The new single-mode fibre lasers have made it possible to work with long working distances and high power densities in new ways. This enables a process called remote laser cutting, which is still quite new a process in the field of laser cutting but is now already proven to be a successful process for cutting various materials and forms. Process parameters of remote laser cutting differ from those of traditional laser cutting because of differences in basic process principles. Process parameters and performance also vary significantly between different materials and equipment. Parameters have to be optimized for each system in order to achieve the best cut quality. This study focuses on defining the possible quality of the remote laser-cut edge and its comparison to that of conventional CO2 laser cutting with equivalent materials. In this study, various metals were cut with the remote laser cutting process. The quality of the cut kerfs was measured by kerf surface roughness and perpendicularity, kerf width, 90° inner corner cut edge sharpness and burr height. When applicable, the comparison was carried out according to the quality standard for thermal cutting.

A study on the effect of cutting position on performance of fiber laser cutting of stainless steel tubes

Laser fusion cutting is a widely used process to cut stainless steel sheets and plates. In best cases, it provides such a good quality that it can be used instead of machining, e.g., for manufacturing tube systems and components where accurately cut holes and sections are required. The flexibility of fiber lasers provides a fast and affordable way to accomplish these demands. This paper examines the effect of cutting position on fiber laser cutting of stainless steel. The tests consist of flat sheet bevel cutting, cutting of tubes in vertical and nonvertical positions and orbital cutting. The effect of different cutting positions and parameters to the final quality of the cut edge are studied. The parameters were, e.g., material thickness, focal length, cutting speed, and laser power. The cutting tests were performed as high-pressure nitrogen cutting using a 5-kW multi-mode fiber laser. It was shown that the changed angle of incidence in the cutting direction had affected the cutting result. With a pushing cutting position, both the cutting quality and performance were improved. The results indicated clearly that orbital cutting is possible with the same parameters that are suitable for cutting in vertical position.

Quality of remote cutting

Remote cutting is stated to be a very fast laser cutting process for the cutting of thin materials. As the main characteristics of remote cutting have been studied only in past couple years, the quality of the cut is still not well compared and specified against other processes. Process parameters of remote cutting differ from the traditional laser cutting because of the multi-pass and vaporizing characteristics of the process. Process parameters and performance also vary depending on the used equipment and processed material. Parameters have to be optimized for each set up to achieve the best cut quality.Quality of laser cut kerf can be measured in various ways. In this study, various metals were processed using remote cutting. The quality of the cut kerfs were measured by burr height, kerf width, perpendicularity tolerance, surface roughness, 90 degree corner sharpness, and heat affected zone. The quality of the cut kerf is also compared to those of conventional CO2 laser cutting and remote fusion cutting with multimode fiber laser. When possible the comparison was carried out according to valid standard of thermal cutting.Remote cutting is stated to be a very fast laser cutting process for the cutting of thin materials. As the main characteristics of remote cutting have been studied only in past couple years, the quality of the cut is still not well compared and specified against other processes. Process parameters of remote cutting differ from the traditional laser cutting because of the multi-pass and vaporizing characteristics of the process. Process parameters and performance also vary depending on the used equipment and processed material. Parameters have to be optimized for each set up to achieve the best cut quality.Quality of laser cut kerf can be measured in various ways. In this study, various metals were processed using remote cutting. The quality of the cut kerfs were measured by burr height, kerf width, perpendicularity tolerance, surface roughness, 90 degree corner sharpness, and heat affected zone. The quality of the cut kerf is also compared to those of conventional CO2 laser cutting and remote fusion cutti...

A study about suitability of different welding processes for the production of aluminum stiffeners for ship structure

The use of laser in welding has ever growing role in manufacturing technology. Among the different laser welding processes the keyhole welding and keyhole welding combined with arc welding to form a so called hybrid welding are the most important laser welding process for metal industry. This process is commonly used in welding of aluminum car body parts, but not often seen in manufacture of larger aluminum products. Laser welding of aluminum is of high interest among the industrial production. High reflectivity and high thermal conductivity, high vapor pressure of alloying elements as well as low liquid surface tension and low ionization potential, make laser welding of aluminum and its alloys a demanding task for any welding method. The boats for use of authorities are often made from the aluminum. The manufacture of those is boats are usually carried out with manual welding processes. This study is concentrating on evaluation the suitability of laser welding to the manufacture of aluminum boat. This was carried out by welding a set of actual products with different welding methods and comparing those.The use of laser in welding has ever growing role in manufacturing technology. Among the different laser welding processes the keyhole welding and keyhole welding combined with arc welding to form a so called hybrid welding are the most important laser welding process for metal industry. This process is commonly used in welding of aluminum car body parts, but not often seen in manufacture of larger aluminum products. Laser welding of aluminum is of high interest among the industrial production. High reflectivity and high thermal conductivity, high vapor pressure of alloying elements as well as low liquid surface tension and low ionization potential, make laser welding of aluminum and its alloys a demanding task for any welding method. The boats for use of authorities are often made from the aluminum. The manufacture of those is boats are usually carried out with manual welding processes. This study is concentrating on evaluation the suitability of laser welding to the manufacture of aluminum boat. This wa...

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...

Orbital cutting and welding of stainless steel tubes with a fiber laser

Orbital welding is used in pipeline manufacturing and prefabrication, most common welding processes are semiautomatic GTA-, GMA- and GMA-tandem but also MMA welding is still in use. These traditional welding processes have limitations concerning welding speed and penetration. Modern laser technology allows the use of high power with small focal point, which results in deep penetration and high welding speed. Modern solid state lasers generate a beam with wavelength around 1 µm which can be transported with a flexible optical fibre. This simplifies the beam delivery in comparison to older CO2 laser technology. With a modern solid state laser it is possible to perform cutting and welding with the same laser and change of the processing head can be done relatively fast. Orbital system with possibility to use two processing heads can perform joint edge cutting as well as welding with a single laser source and with same orbital tractor. This could improve weld quality and decrease cycle time in tube to tube welding. This paper presents orbital cutting and orbital welding processes, parameters and test results altogether with the principle of an orbital system.Orbital welding is used in pipeline manufacturing and prefabrication, most common welding processes are semiautomatic GTA-, GMA- and GMA-tandem but also MMA welding is still in use. These traditional welding processes have limitations concerning welding speed and penetration. Modern laser technology allows the use of high power with small focal point, which results in deep penetration and high welding speed. Modern solid state lasers generate a beam with wavelength around 1 µm which can be transported with a flexible optical fibre. This simplifies the beam delivery in comparison to older CO2 laser technology. With a modern solid state laser it is possible to perform cutting and welding with the same laser and change of the processing head can be done relatively fast. Orbital system with possibility to use two processing heads can perform joint edge cutting as well as welding with a single laser source and with same orbital tractor. This could improve weld quality and decrease cycle time in tube to tube we...

Effect of variable power control in quasi-simultaneous fiber laser welding of polymers

In transmission laser welding of polymers, the process nature is dependent on rapid melting of the absorbing part. This melting creates the heat transfer to the transmissive part which is then melted and after the cooling period, a weld is created. Typically in quasi simultaneous laser welding (QSLW) material heats up towards the end of the welding cycle. With this new variant, the idea is to heat the material as fast as possible to the molten state and then keep it there for the rest of the welding time. With variable power control during the welding, the power level can be adjusted to melt the material effectively, and keep it molten during the whole welding time without overheating the material. This way the weld is given a longer time at melt so that more material would be mixed. Optimal power curve can be extracted with a pyrometer and then used in production.This paper presents the basic design variable of the power control system and shows how the quality of the weld is affected with its utilization. Welding results are compared to traditional QSLW and also to samples which are welded with only three power steps during welding.In transmission laser welding of polymers, the process nature is dependent on rapid melting of the absorbing part. This melting creates the heat transfer to the transmissive part which is then melted and after the cooling period, a weld is created. Typically in quasi simultaneous laser welding (QSLW) material heats up towards the end of the welding cycle. With this new variant, the idea is to heat the material as fast as possible to the molten state and then keep it there for the rest of the welding time. With variable power control during the welding, the power level can be adjusted to melt the material effectively, and keep it molten during the whole welding time without overheating the material. This way the weld is given a longer time at melt so that more material would be mixed. Optimal power curve can be extracted with a pyrometer and then used in production.This paper presents the basic design variable of the power control system and shows how the quality of the weld is affected with its utilizatio...

Effect of arc parameters in high brightness hybrid laser arc welding of low alloyed steel

In some laser welding cases, the low heat input results in a weld which has a high hardness compared to the base material. This can create problems in some cases, where higher fatigue life for the weld is required. One method to improve this problem is to increase the heat input by using hybrid laser arc welding (HLAW). This type of process has several advantages over conventional laser beam welding, including a better gap bridging ability and the possibility to use filler metal to modify weld metallurgy. There are also some disadvantages with HLAW, and the one most prominent is the vast amount of different process parameters. The arc parameters can have a significant effect to the heat input in HLAW. By altering the heat input, the toughness properties of the weld can be improved significantly by decreasing the maximum hardness of the weld. This paper describes, what can be accomplished with HLAW when using moderately high laser power in welding of medium thickness (8–10 mm) structural steel. The paper concentrates especially on the effect of arc parameters.In some laser welding cases, the low heat input results in a weld which has a high hardness compared to the base material. This can create problems in some cases, where higher fatigue life for the weld is required. One method to improve this problem is to increase the heat input by using hybrid laser arc welding (HLAW). This type of process has several advantages over conventional laser beam welding, including a better gap bridging ability and the possibility to use filler metal to modify weld metallurgy. There are also some disadvantages with HLAW, and the one most prominent is the vast amount of different process parameters. The arc parameters can have a significant effect to the heat input in HLAW. By altering the heat input, the toughness properties of the weld can be improved significantly by decreasing the maximum hardness of the weld. This paper describes, what can be accomplished with HLAW when using moderately high laser power in welding of medium thickness (8–10 mm) structural steel. The paper c...

Simultaneous sub second laser welding of polymers with diffractive optics

The paper presents a novel method for simultaneous transmission welding of polymers using a high power multimode fiber laser. The method utilizes a diffractive optical element which shapes the focused laser beam into the desired weld shape. This kind of optical device enables the use of high power multimode fiber laser which again gives a possibility to use sub-second welding times.Weld quality was assessed in terms of strength (pull test) and visual appearance. The diffractive optics provides an even powerd istribution and only small part of power is lost on the zeroth order.Design of diffractive element gives flexibility with the weld shapes and sizes but the drawback is that these parameters cannot be modified after the production of the element. Using the optics would be more advantageous if multiple parts could be welded at one shot because the part changing time will be a lot longer than the welding time. Results show good weld quality, superior welding speed and high weld strength compared to quasi-simultaneous laser welding of the same material.The paper presents a novel method for simultaneous transmission welding of polymers using a high power multimode fiber laser. The method utilizes a diffractive optical element which shapes the focused laser beam into the desired weld shape. This kind of optical device enables the use of high power multimode fiber laser which again gives a possibility to use sub-second welding times.Weld quality was assessed in terms of strength (pull test) and visual appearance. The diffractive optics provides an even powerd istribution and only small part of power is lost on the zeroth order.Design of diffractive element gives flexibility with the weld shapes and sizes but the drawback is that these parameters cannot be modified after the production of the element. Using the optics would be more advantageous if multiple parts could be welded at one shot because the part changing time will be a lot longer than the welding time. Results show good weld quality, superior welding speed and high weld strength compared to quasi...

Laser welding of micro-VLE-measurement device and its practical application

The knowledge of phase equilibrium is critical for the modeling and operation of reactors and separation units. The use of incorrect vapor-liquid equilibrium (VLE) data for distillation leads to tower malfunction with varying end results. The only reliable method for obtaining valid VLE data for a non-ideal system is to measure it. When studying components that are either very expensive or hazardous the amount of chemicals used is preferably minimized. Typical volume of chemicals used in a VLE-measurement is 100 cm3 or above. In a VLE-measurement the temperature, pressure and composition of both phases are determined for a range of concentrations.The laser micro/fine processing is one of the fastest spreading and developing areas of all laser processes in the world. The wide field of applications makes laser a novel tool for micro processing and gives lots of new ideas, solutions, opportunities and applications for designing these milli and micro scale process devices for chemical industry.In this study an exceptionally small VLE-measurement device was designed and manufactured by utilization of laser processing. Even though the application itself is in micro scale the laser processing used in fine processing scale gave opportunity to reach the minimum volume. Laser welding has unique possibilities for this kind of welding when heat input can be controlled and only small heat affected zone and thereby minor distortions are caused. Laser welding also enables welding of demanding structures, like this micro-VLE-device.The volume of the measurement cell of micro-VLE-device was approximately 2.5 cm3, which was made possible by using the pressure transducer cavity as the equilibrium cell. The chemical consumption is therefore reduced by up to a factor of 50. The valves were also welded to the structure. The welding would not have been possible with conventional methods due to overheating of the transducer electronics. The cell was initially tested by measuring pure component vapor pressures of alkanes.The knowledge of phase equilibrium is critical for the modeling and operation of reactors and separation units. The use of incorrect vapor-liquid equilibrium (VLE) data for distillation leads to tower malfunction with varying end results. The only reliable method for obtaining valid VLE data for a non-ideal system is to measure it. When studying components that are either very expensive or hazardous the amount of chemicals used is preferably minimized. Typical volume of chemicals used in a VLE-measurement is 100 cm3 or above. In a VLE-measurement the temperature, pressure and composition of both phases are determined for a range of concentrations.The laser micro/fine processing is one of the fastest spreading and developing areas of all laser processes in the world. The wide field of applications makes laser a novel tool for micro processing and gives lots of new ideas, solutions, opportunities and applications for designing these milli and micro scale process devices for chemical industry.In this study a...