rus
Issue #3/2023
D. O. Chukhlantsev, D. A. Shipikhin, E. S. Shishkin, V. P. Umnov
Diode Lasers and Its Use in the Robotic Systems
Diode Lasers and Its Use in the Robotic Systems
DOI: 10.22184/1993-7296.FRos.2023.17.3.176.183
The high-power diode lasers required for many laser industrial processes have conventionally been the bulky floor devices. However, the laser manufacturers have responded to the industrial need for compact systems that take full advantage of the miniaturization inherent in the diode lasers. This makes it possible to successfully integrate the diode lasers as the service tools into the actuating systems of multipurpose industrial robots, including the mobile robots for processing the large-dimensioned items. The article presents a laser-robot produced by the ThermoLaser LLC company, designed for processing large parts for energy and transport purposes.
The high-power diode lasers required for many laser industrial processes have conventionally been the bulky floor devices. However, the laser manufacturers have responded to the industrial need for compact systems that take full advantage of the miniaturization inherent in the diode lasers. This makes it possible to successfully integrate the diode lasers as the service tools into the actuating systems of multipurpose industrial robots, including the mobile robots for processing the large-dimensioned items. The article presents a laser-robot produced by the ThermoLaser LLC company, designed for processing large parts for energy and transport purposes.
Теги: beam quality diode lasers robotic systems ultrashort pulses диодные лазеры качество пучка робототехнические системы ультракороткие импульсы
Diode Lasers and Its Use in the Robotic Systems
D. O. Chukhlantsev, D. A. Shipikhin, E. S. Shishkin, V. P. Umnov
TermoLaser LLC, Vladimir, Russia
The high-power diode lasers required for many laser industrial processes have conventionally been the bulky floor devices. However, the laser manufacturers have responded to the industrial need for compact systems that take full advantage of the miniaturization inherent in the diode lasers. This makes it possible to successfully integrate the diode lasers as the service tools into the actuating systems of multipurpose industrial robots, including the mobile robots for processing the large-dimensioned items. The article presents a laser-robot produced by the ThermoLaser LLC company, designed for processing large parts for energy and transport purposes.
Keywords: diode lasers, ultrashort pulses, robotic systems, beam quality
Article received on: 10.04.2023
Article accepted on: 04.05.2023
Among the various laser radiation sources used in the production process, the diode lasers are gradually winning the first place, displacing the gas and other solid-state lasers, including the optical fiber ones [1–3]. This is due to the following undeniable advantages of diode lasers:
Due to the advantages noted, the diode lasers with high efficiency are used in various industrial engineering processes, such as surface hardening of metal products, building-up and alloying, soldering, and surface cleaning.
A constraint on an applicability of diode lasers is the relatively large size of the focused spot on the treated surface. The power on the target cannot be efficiently focused into a micron-sized spot, therefore, most applications for the high-power diode lasers involve heating of a specific area, usually measured in millimeters.
When evaluating the possible application of a diode laser, the specialists are usually concerned about the output beam quality obtained by the stepwise summarization of the power of arrays and modules. In this case, many separate beams of asymmetric quality are generated. They must be brought together into one beam with a symmetrical section. Such a problem corresponds to the concept of a diode-pumped solid-state crystal laser. However, this process requires additional energy costs, and this fact leads to a decrease in the laser efficiency.
Another solution is to sum the laser beams from several diodes in an optical fiber. However, when directing the light radiation from an array or, moreover, from a module through a fiber optic cable, it is necessary to face another problem, namely an attempt to direct a beam with a square section through a circular waveguide. In this case, part of the light beam energy that passes outside the tube, will be lost. In addition, there is a significant “dead’ area on the end surface of the optical bus. Its occurrence is caused by the absence of radiation from the space between the emitters. When these dark spots are projected onto an optical fiber, the power and brightness of the resulting beam is reduced. Another key problem occurs when combining the diode radiation within a fiber optical channel. The higher the output beam quality and the smaller the number of emitters projected onto the optical fiber, the higher the specific absorption of light energy from the fiber surface per unit of channel diameter. Moreover, the current achievements in the construction of high-power diode lasers make it possible to obtain a high quality of the resulting laser beam by using the developed homogenizing modules produced in the form of micro-optical gratings.
One of the key tasks in the development of high-power diode lasers is the issue of an efficient cooling system [4]. As a rule, the microchannel cooling is used, when water flows through the channels with a minimum cross section in a copper radiator soldered to a diode laser rod. To minimize the current leakage and electrochemical corrosion, the deionized water that has a low electrical conductivity, is commonly used. The need for deionized water or water cartridges leads to increase in the operating costs and is a significant disadvantage. Recently, the cooling circuits have been developed based on the use of contact conductive cooling directly next to the rods and current contacts with the filtered tap water [5, 6].
TermoLaser LLC has developed and successfully operated a MEL‑3.0 mobile robotic laser, the operating tool of which is a small-sized, highly efficient diode laser with a nominal output power of 3.0 kW. The mobile robotic laser is equipped with a special controlled trolley with a standard process manipulator, having 6 degrees of freedom with an executive kinematic chain up to 3 meters long, designed mainly for processing the large-dimensioned long items, sequentially performing operations in various work cells or performing operations in various structural subdivisions of the same enterprise. As an additional option, the robotic laser can be equipped with a manipulator base stabilization system in relation to the trolley that ensures stability and rigidity of the stationary trolley position. This feature expands the operational and process capabilities of the mobile robot and provides the required processing accuracy and quality for the large-dimensioned long items on the non-rigid and uneven surfaces, for example, the ground surface in the case of field operations.
Figure 1 demonstrates a view of a mobile robotic laser. Table 1 shows its main technical specifications. Figure 2 provides a view of a diode laser (in Fig. 1 it is covered with a casing).
The emitting system of a diode laser consists of eight separate modules, while each of which generates a homogeneous beam through the special micro-optical elements. To direct all beams from all eight modules to the output beam profiler, four mirrors with an interference coating to combine the beams of two orthogonally located modules and a special lens are used. The generated output beam is directed to a focusing lens protected against external influences by two glasses. The laser provides the possible individual adjustment of the laser spot energy profile in the treatment area by setting the output power of the optical laser radiation of each laser module by a programmable computer control device. Each module consisting of diode arrays contains a copper base. The main parameters of the laser used in the robotic laser and being the final link of the kinematic robot chain are given in Table 2.
The basic component of each laser module is a radiation source, the technical specifications of which are given in Table 3.
One usage sample of the MEL‑3.0 robotic laser is the laser surface hardening of the car boss spline joint. Moreover, the requirements for hardness and depth of the hardened layer for projections, depressions and side surfaces of the splines are different. The boss material is cast iron VCh 50, GOST 7293-85, initial hardness is 170–207 HB. A view of the spline section hardened by a diode laser is shown in Fig.3. When performing the laser hardening procedure, the speed of the laser beam moving by the robot was changed from 1 mm/s to 5 mm/s, the power in the spot on the hardened surfaces was changed from 1200 to 1600 W by changing the laser power and various spot sizes for various surfaces: 2 × 16 mm for the side surfaces of the spline and 3 × 6 mm for depressions and projections. The hardness of hardened surfaces is 240–304 HB with a depth of more than 0.5 mm. At the same time, the spline profile distortion did not exceed 0.15 µm and the boss body heating temperature did not exceed 20 °C of the ambient temperature.
Fig. 4 shows an implementation scheme of the MEL‑3.0 robot for a more comprehensive hardening process of the working edge of a steam turbine blade made of alloy steel with a curvilinear shape of a hardening area along the part length with simultaneous usage of two diode lasers [7].
The laser beams 6 and 9, emitted by the diode radiation sources 4 and 7 through the optical heads 5 and 8, mounted on a bracket and moved by the robot along the working edge, have an impact on the front part 2 and end part 3 of the blade 1 leading edge. In this case, the required radiation power of each laser and the dimensions of the beam spots on the treatment surface are determined, and simultaneous hardening of the front part 2 and the end part 3 of the leading edge of the blade 1 is performed. The angular position of each bean (angles α and β) is selected in such a way that to provide the closest to normal incidence angle of radiation on the hardened surfaces 2 and 3 along the entire profile of the heated area and uniform exposure throughout the entire processing area. The installation angles α and β of the optical heads 5 and 8 are also selected with due regard to the prevention of direct and reflected radiation of the part in the optical head holes. When moving the laser beams 6 and 9 along the treated area, their angular position shall be programmatically changed when the transverse profile of the edge is changed and set as described above. To ensure the material hardening to the required depth, two conditions must be met: the material temperature in the layer to the full depth during the heating process shall reach or exceed the value of Ac3 + 50 °C, or 1 050 °C (for steel), during the cooling process, the material shall be cooled down at a maximum speed to prevent the troostite development.
Cooling is performed mainly due to the heat transfer to the unheated part area, and to a much lesser extent, due to the heat transfer in the form of electromagnetic radiation into the external environment and into the gas masses being in contact with the surface. To ensure constant values of heat fluxes leaving the material area during the hardening procedure, two flows of cooled gases are used. The first flow 11 is directed by a nozzle 12 with a dispersed jet to the part surface o at some small distance from the edge of the hardening area from the side of the laser impact zone 7. This flow shall remove heat from the part, while compensating for its heating due to the heat influx from the hardening area from the side opposite to the laser radiation impact zone 4. The second flow containing an inert gas is directed by a nozzle 14 with a dispersed jet 13 to the rib of the leading edge, so that the flow generates an area with an inert gas atmosphere, displaces air and volatile products of the hardening process from the surface being treated and simultaneously removes heat from the hardened layer surface. The power of the lasers 4 and 7 is regulated by the control system according to the information from the temperature sensor 10 of the hardened surface.
Fig. 5 shows the hardening results of the blade working edge in one of the cross sections. The hardness of the top in the section (area 1 on Fig. 5) is 48.15 HRC. The hardness at a distance of 14 mm from the top (area 2 on Fig. 5) is 49.5 HRC. The depth of the hardened layer at the top is 3.0 mm, at a distance of 14 mm from the top – 1.6 mm.
TermoLaser LLC has developed an engineering design of a mobile robotic laser for processing the large-dimensioned items using a diode laser and an original robot with a total link length of up to 15 meters. The developed robotic laser can be used for mounting or processing, for example, for the ship hulls, large land and air transport vehicles or large tanks.
AUTHORS
Chukhlantsev Dmitriy O., Cand. of Sciences (Econom), CEO of TermoLaser LLC, Vladimir, Russia.
Shipikhin Dmitriy A., deputy director general of TermoLaser LLC for manufacturing, Vladimir, Russia.
Shishkin Evgeniy S., process engineer, TermoLazer LLC, Vladimir, Russia.
Umnov Vladimir P., Cand. of Sciences (Eng.), associate professor, deputy director general of TermoLaser LLC for science, Vladimir, Russia.
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest and they supplemented the manuscript in part of their work.
D. O. Chukhlantsev, D. A. Shipikhin, E. S. Shishkin, V. P. Umnov
TermoLaser LLC, Vladimir, Russia
The high-power diode lasers required for many laser industrial processes have conventionally been the bulky floor devices. However, the laser manufacturers have responded to the industrial need for compact systems that take full advantage of the miniaturization inherent in the diode lasers. This makes it possible to successfully integrate the diode lasers as the service tools into the actuating systems of multipurpose industrial robots, including the mobile robots for processing the large-dimensioned items. The article presents a laser-robot produced by the ThermoLaser LLC company, designed for processing large parts for energy and transport purposes.
Keywords: diode lasers, ultrashort pulses, robotic systems, beam quality
Article received on: 10.04.2023
Article accepted on: 04.05.2023
Among the various laser radiation sources used in the production process, the diode lasers are gradually winning the first place, displacing the gas and other solid-state lasers, including the optical fiber ones [1–3]. This is due to the following undeniable advantages of diode lasers:
- narrow emission line of the laser diodes;
- possible processing of not only metals, as when using an optical fiber laser, but also non-metals, such as wood, acrylic, stone, etc.;
- lack of fiber optic cable;
- unequalled electrical and optical efficiency (efficiency up to 50% and above);
- higher power-to-size ratio compared to any other industrial laser technology, as well as the solid-state stability and reliability;
- high (over 10 thousand hours in a continuous mode and 109 pulses in a quasi-continuous mode) service life of the high-power laser diodes used.
Due to the advantages noted, the diode lasers with high efficiency are used in various industrial engineering processes, such as surface hardening of metal products, building-up and alloying, soldering, and surface cleaning.
A constraint on an applicability of diode lasers is the relatively large size of the focused spot on the treated surface. The power on the target cannot be efficiently focused into a micron-sized spot, therefore, most applications for the high-power diode lasers involve heating of a specific area, usually measured in millimeters.
When evaluating the possible application of a diode laser, the specialists are usually concerned about the output beam quality obtained by the stepwise summarization of the power of arrays and modules. In this case, many separate beams of asymmetric quality are generated. They must be brought together into one beam with a symmetrical section. Such a problem corresponds to the concept of a diode-pumped solid-state crystal laser. However, this process requires additional energy costs, and this fact leads to a decrease in the laser efficiency.
Another solution is to sum the laser beams from several diodes in an optical fiber. However, when directing the light radiation from an array or, moreover, from a module through a fiber optic cable, it is necessary to face another problem, namely an attempt to direct a beam with a square section through a circular waveguide. In this case, part of the light beam energy that passes outside the tube, will be lost. In addition, there is a significant “dead’ area on the end surface of the optical bus. Its occurrence is caused by the absence of radiation from the space between the emitters. When these dark spots are projected onto an optical fiber, the power and brightness of the resulting beam is reduced. Another key problem occurs when combining the diode radiation within a fiber optical channel. The higher the output beam quality and the smaller the number of emitters projected onto the optical fiber, the higher the specific absorption of light energy from the fiber surface per unit of channel diameter. Moreover, the current achievements in the construction of high-power diode lasers make it possible to obtain a high quality of the resulting laser beam by using the developed homogenizing modules produced in the form of micro-optical gratings.
One of the key tasks in the development of high-power diode lasers is the issue of an efficient cooling system [4]. As a rule, the microchannel cooling is used, when water flows through the channels with a minimum cross section in a copper radiator soldered to a diode laser rod. To minimize the current leakage and electrochemical corrosion, the deionized water that has a low electrical conductivity, is commonly used. The need for deionized water or water cartridges leads to increase in the operating costs and is a significant disadvantage. Recently, the cooling circuits have been developed based on the use of contact conductive cooling directly next to the rods and current contacts with the filtered tap water [5, 6].
TermoLaser LLC has developed and successfully operated a MEL‑3.0 mobile robotic laser, the operating tool of which is a small-sized, highly efficient diode laser with a nominal output power of 3.0 kW. The mobile robotic laser is equipped with a special controlled trolley with a standard process manipulator, having 6 degrees of freedom with an executive kinematic chain up to 3 meters long, designed mainly for processing the large-dimensioned long items, sequentially performing operations in various work cells or performing operations in various structural subdivisions of the same enterprise. As an additional option, the robotic laser can be equipped with a manipulator base stabilization system in relation to the trolley that ensures stability and rigidity of the stationary trolley position. This feature expands the operational and process capabilities of the mobile robot and provides the required processing accuracy and quality for the large-dimensioned long items on the non-rigid and uneven surfaces, for example, the ground surface in the case of field operations.
Figure 1 demonstrates a view of a mobile robotic laser. Table 1 shows its main technical specifications. Figure 2 provides a view of a diode laser (in Fig. 1 it is covered with a casing).
The emitting system of a diode laser consists of eight separate modules, while each of which generates a homogeneous beam through the special micro-optical elements. To direct all beams from all eight modules to the output beam profiler, four mirrors with an interference coating to combine the beams of two orthogonally located modules and a special lens are used. The generated output beam is directed to a focusing lens protected against external influences by two glasses. The laser provides the possible individual adjustment of the laser spot energy profile in the treatment area by setting the output power of the optical laser radiation of each laser module by a programmable computer control device. Each module consisting of diode arrays contains a copper base. The main parameters of the laser used in the robotic laser and being the final link of the kinematic robot chain are given in Table 2.
The basic component of each laser module is a radiation source, the technical specifications of which are given in Table 3.
One usage sample of the MEL‑3.0 robotic laser is the laser surface hardening of the car boss spline joint. Moreover, the requirements for hardness and depth of the hardened layer for projections, depressions and side surfaces of the splines are different. The boss material is cast iron VCh 50, GOST 7293-85, initial hardness is 170–207 HB. A view of the spline section hardened by a diode laser is shown in Fig.3. When performing the laser hardening procedure, the speed of the laser beam moving by the robot was changed from 1 mm/s to 5 mm/s, the power in the spot on the hardened surfaces was changed from 1200 to 1600 W by changing the laser power and various spot sizes for various surfaces: 2 × 16 mm for the side surfaces of the spline and 3 × 6 mm for depressions and projections. The hardness of hardened surfaces is 240–304 HB with a depth of more than 0.5 mm. At the same time, the spline profile distortion did not exceed 0.15 µm and the boss body heating temperature did not exceed 20 °C of the ambient temperature.
Fig. 4 shows an implementation scheme of the MEL‑3.0 robot for a more comprehensive hardening process of the working edge of a steam turbine blade made of alloy steel with a curvilinear shape of a hardening area along the part length with simultaneous usage of two diode lasers [7].
The laser beams 6 and 9, emitted by the diode radiation sources 4 and 7 through the optical heads 5 and 8, mounted on a bracket and moved by the robot along the working edge, have an impact on the front part 2 and end part 3 of the blade 1 leading edge. In this case, the required radiation power of each laser and the dimensions of the beam spots on the treatment surface are determined, and simultaneous hardening of the front part 2 and the end part 3 of the leading edge of the blade 1 is performed. The angular position of each bean (angles α and β) is selected in such a way that to provide the closest to normal incidence angle of radiation on the hardened surfaces 2 and 3 along the entire profile of the heated area and uniform exposure throughout the entire processing area. The installation angles α and β of the optical heads 5 and 8 are also selected with due regard to the prevention of direct and reflected radiation of the part in the optical head holes. When moving the laser beams 6 and 9 along the treated area, their angular position shall be programmatically changed when the transverse profile of the edge is changed and set as described above. To ensure the material hardening to the required depth, two conditions must be met: the material temperature in the layer to the full depth during the heating process shall reach or exceed the value of Ac3 + 50 °C, or 1 050 °C (for steel), during the cooling process, the material shall be cooled down at a maximum speed to prevent the troostite development.
Cooling is performed mainly due to the heat transfer to the unheated part area, and to a much lesser extent, due to the heat transfer in the form of electromagnetic radiation into the external environment and into the gas masses being in contact with the surface. To ensure constant values of heat fluxes leaving the material area during the hardening procedure, two flows of cooled gases are used. The first flow 11 is directed by a nozzle 12 with a dispersed jet to the part surface o at some small distance from the edge of the hardening area from the side of the laser impact zone 7. This flow shall remove heat from the part, while compensating for its heating due to the heat influx from the hardening area from the side opposite to the laser radiation impact zone 4. The second flow containing an inert gas is directed by a nozzle 14 with a dispersed jet 13 to the rib of the leading edge, so that the flow generates an area with an inert gas atmosphere, displaces air and volatile products of the hardening process from the surface being treated and simultaneously removes heat from the hardened layer surface. The power of the lasers 4 and 7 is regulated by the control system according to the information from the temperature sensor 10 of the hardened surface.
Fig. 5 shows the hardening results of the blade working edge in one of the cross sections. The hardness of the top in the section (area 1 on Fig. 5) is 48.15 HRC. The hardness at a distance of 14 mm from the top (area 2 on Fig. 5) is 49.5 HRC. The depth of the hardened layer at the top is 3.0 mm, at a distance of 14 mm from the top – 1.6 mm.
TermoLaser LLC has developed an engineering design of a mobile robotic laser for processing the large-dimensioned items using a diode laser and an original robot with a total link length of up to 15 meters. The developed robotic laser can be used for mounting or processing, for example, for the ship hulls, large land and air transport vehicles or large tanks.
AUTHORS
Chukhlantsev Dmitriy O., Cand. of Sciences (Econom), CEO of TermoLaser LLC, Vladimir, Russia.
Shipikhin Dmitriy A., deputy director general of TermoLaser LLC for manufacturing, Vladimir, Russia.
Shishkin Evgeniy S., process engineer, TermoLazer LLC, Vladimir, Russia.
Umnov Vladimir P., Cand. of Sciences (Eng.), associate professor, deputy director general of TermoLaser LLC for science, Vladimir, Russia.
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest and they supplemented the manuscript in part of their work.
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