Technological heads of leading world manufacturers, which are intended for the implementation of technologies of laser and arc augmented laser welding, laser cutting, thermal treatment and cladding, are considered in the review article.
Technological heads of leading world manufacturers, which are intended for the implementation of technologies of laser and arc augmented laser welding, laser cutting, thermal treatment and cladding, are considered in the review article.
INTRODUCTION More than 55 years have passed since the moment of first laser invention . During this period of time the laser sources of different types have been created: gas, solid-state, semiconductor, diode, fiber, chemical lasers etc. As of today, the laser industry is one of fast growing sectors of world economy, with the average increase of about 12.5% from 1970 to 2015 . The volume of world market of laser sources was about 10 billion US dollars in 2015 with the market share of industrial lasers of about 4 billion US dollars  (Fig. 1). The largest market segment includes the laser sources, which are applied for laser cutting of metal, laser (arc augmented laser) welding, laser thermal hardening, laser cladding, labeling and engraving. Analysis of laser source market showed that in 2015 СО2-lasers and fiber lasers approximately had 40% and 39% market share, respectively. In comparison with 2014 with the decrease of market share of СО2-lasers, the growth of sales of fiber lasers used in all types of technologies (labeling – by 6%, moderate power lasers used in microworking – by 10%, high power lasers – by 22%) is observed. In comparison with 2014, the share of solid-state lasers has not changed but inside the segment the growth of sales of disk lasers is noticed. Also, the increase of demand with regard to the diode lasers, which are now used not only for surface thermal hardening, cladding and welding but also for metal cutting, is observed. The expansion of technological capabilities of diode lasers, which are produced by the leading company LaserLine, became possible due to the increase of maximum output power and enhancement of laser radiation quality from 20 kW with the spot diameter in focal plane of 3 mm (2013) to 25–40–100 kW with the spot diameter of 0.6–2 mm (2015) [2, 3].
The increase rate of the market of technological laser systems is also significant; it is equal to 10% at average for the period from 1993 to 2013. For comparison it should be noted that the average increase rate of the market of metalworking machines is about 1.3% for the same period (Fig. 2). Depending on the tasks, which must be solved, the laser technological complexes are equipped with different operating tools – laser technological head, optical system of which provides required spatial characteristics of laser radiation in working area (Fig. 3). In addition to focusing of laser radiation, the technological heads supply associated gases and materials to the treatment area: shielding gases – in case of welding, operating gases – in case of cutting, powders – in case of cladding, electrode wire – in case of arc augmented laser welding or laser welding with additive. Also, the technological heads can be equipped with the systems of video surveillance and monitoring of technological process, including the systems of control of technological head position in relation to workpiece. Let us consider the technological heads of leading world manufacturers, which are intended for the implementation of technologies of laser and arc augmented laser welding, laser cutting, thermal treatment and cladding. TECHNOLOGICAL LASER HEADS FOR LASER (ARC AUGMENTED LASER) WELDING Narrow and deep welding joint, which is typical for laser welding and can be obtained at the expense of high density of laser radiation power (106–107 W/cm 2) on the surface of welded workpieces, together with high welding speed (up to 20 m/min) provide the significant reduction of welding deformations, increase of technological efficiency of welded joints and productivity of welding process. Advantages of laser welding make this technology practically irreplaceable in case of mass production of critical welded structures. The further development of laser welding technologies is associated with the increase of maximum radiation power (Fig. 4) of used lasers. The occurrence of high-power fiber and diode lasers made it possible to implement a number of new technologies of laser and hybrid arc augmented laser welding. The most interesting of them is the welding of metals with large thickness, in particular modern complex alloyed dual – and three-phase steel used for the construction of pipelines, ship hulls, high-pressure vessels and other critical structures . Use of such high-power laser sources in the structure of welding technological complexes poses a number of requirements to the optical system of laser heads. First of all, these requirements include the provision of thermal resistance of mirrors and lenses. Secondly, they include provision of reliable protection of the optical system against condensed particles and vapors emerging from steam-gas channel with near-sonic speed. Also, small diameter of heating spot (≤ 600 µm) determines the requirements to accuracy of laser beam pointing on joint and limits the allowable gap between workpieces. The companies IPG , HighYAG , ScanSonic  and Precitec  offer the heads, which are intended for welding with the radiation power from 0.25 kW (head µ (HighYAG)) up to 50 kW (FLW-D50HP (IPG)) with the wavelength of 900–1080 nm at the market of laser equipment. Laser welding heads consisting of collimator, focusing lens, protective glass and system of feed of compressed air can be optionally equipped with CCD camera for the accurate pointing on joint and tracking the welding process on a real-time basis, system of supply of welding wire (heads PDT and PDT-B (HighYAG); ALO1 and ALO3 (ScanSonic)), contact (ALO1 and ALO3) or optical (FSO (ScanSonic)) sensor, holding down device in the form of "fingers’ or disks (FSO and RSK (HighYAG)) providing not only tight adjoining of welded samples but also control of the distance of laser head to workpiece surface. The variant of welding system FormWelder Plus (Precitec)  made on the basis of laser head YW30 or YW52, which are intended for the welding by radiation with micron wavelength and power up to 6 kW and 20 kW, respectively, and moved along the axes X and Y by 50 mm, is of interest (Fig. 5). ScanSonic product range also contains the simplest variant of laser head (VO) consisting of collimator and focusing lens, which are rated at the radiation power up to 6 kW. The head can be optionally completed with CCD camera, cartridge with protective glass, module of curtain gas-dynamic protection, system of automatic variation of focal distance and shock-proof sensor; it has straight and L-shaped execution. The variant of laser head BO-SF, which is intended for the welding with laser radiation power up to 30 kW and made on the basis of VO head, is of interest. Laser radiation with micron wavelength is formed practically with homogeneous distribution in cross-section with the efficiency factor of more than 98%. The head, which is optionally equipped with focusing mirror and collimator with different focal distances, is intended for laser welding of metal structures with large thickness in pipe building, ship building and other branches of industry (Fig. 6) . IPG company produces the laser heads FLW-D30 (up to 6 kW) and FLW-D50 with the modifications L (up to 10 kW), S (up to 30 kW) and HP (up to 50 kW) in L-shaped, straight and standard (without CCD camera) configuration. In addition to protective shield cup, cross-jet module, temperature sensor and focusing lens contamination sensor, optical sensor of joint tracking and device for wire supply, the heads can be optionally equipped with the modules of laser radiation scanning by trajectories in the form of line, circle and figure-eight (Wobble), radiation splitter into two beams with the same power (Dual Spot Module) and module providing the homogeneous distribution of laser radiation (Beam Shaper Module), which are intended for the transmission of radiation with the power up to 10 kW . Laser welding heads produced by LaserLine company for the use with diode laser differ in homogeneous distribution of laser radiation power in cross-section in the form of circle or rectangle . The heads are additionally equipped with the components, which are similar to ScanSonic and HighYAG. Kugler company makes the welding heads (LK190W, LK390F and LK390W), last-mentioned head is intended for the work with radiation with the power of more than 40 kW. The heads can be completed with focusing mirrors with the focal distance of 150 mm to 600 mm, system of variation of focal distance in automated mode and mirror-radiation splitter into two beams. The head for arc augmented laser welding LK390H is made on the basis of the head LK390W. Also, the company produces laser heads for microwelding with the diameter of laser radiation spot in focal plane less than 10 µm . Laser welding heads АР44 and АР54 (Fig. 7) produced by Reis company, which have quick-detachable fastener for the fixation to manipulating robot, are intended for the operation with laser radiation power up to 6 kW and up to 12 kW, respectively. The main differences of these heads from above-mentioned heads consist in the presence of diode illumination and quick-detachable magnetic fasteners of some modules: contact-measuring module, optical sensor of joint tracking and module of diode illumination. Also, the heads can be optionally equipped with the system of wire feed, nozzles for non-coaxial and coaxial joint protection. The head for arc augmented laser welding based on the laser head AP54 is offered by Reis company . When making the products for mechanical engineering (heat exchangers, air-tight units of pumps etc.), the tasks associated with the treatment in hard-to-reach places occur. For this reason, several companies (Nutech, GTV, IWS, RPM etc.) develop the special technological tool . The laser head with allowable radiation dose up to 3 kW and accessibility depth in basic configuration up to 1000 mm developed at the Institute of Laser and Welding Technologies serves as the instance of such technological tool . The head has fasteners for the installation on linear manipulators, industrial robots and other delivery systems. Layouts of the heads for welding of roll and non-roll joints (and surface thermal treatment) and examples of their use during welding of thin-wall shell ring to pump casing are given in Fig. 8. The general view of the head with rotating deflecting mirror for welding of internal non-roll joints installed on robotized delivery module is given in Fig. 9. Such concept practically does not have restrictions by accessibility depth. Scientific and Technical Center "Electroresurs’ is one of few domestic manufacturers of laser heads; its workers produce the laser head VF001MA for the operation with fiber lasers with the power up to 3 kW. The head has capability of variation of focal distance in automatic mode and it can be equipped with the modules based on magnetic fastening with the sensor of control of distance to treated workpiece . Also, we should mention the scanning systems, use of which allows enhancing the productivity of welding approximately by 25%. The following scanning systems which are offered at the market can be marked out: IntelliWeld PR and IntelliWeld II FT (with F-theta lens) (ScanLab) intended for the operation with laser radiation with the power up to 8 kW. The company ScanLab also produces scanning systems IntelliScan III 10 and IntelliScan III 20, which are intended for the operation with different types of lasers (diode, fiber, solid-state and СО2-lasers) with the power of 150 W and 1000 W and working areas 120Ч120 mm 2 (f=163 mm, d=32 µm) and 60Ч60 mm 2 (f=160 mm and d=16 µm), respectively. The company Trumpf produces the scanning systems PFO, which are intended for laser welding, cutting and micro-working. The systems PFO of modifications 14, 20 and 33 are used for 2D treatment of workpieces by laser radiation with the power of 2 to 8 kW (diode, fiber, solid-state laser) with the speed of 22 to 78 m/s in working area 286Ч230 mm 2 (f=420 mm; PFO 14, PFO 20) and 320х190 mm 2 (f=450 mm, PFO 33). The scanning system for 3D treatment (PFO 3D) is also offered in PFO product range; it can be used in the structure of the complex based on diode laser with maximum output power of 8 kW. In the process of treatment, PFO 3D moves the laser beam in focal plane (f=1200 mm) with the speed up to 22 m/sec and dimensions of working area 780х530 mm 2, with the capability of variation of focal plane position along vertical axis at the distance ±475 mm . The scanning system made by Reis company is intended for welding with maximum power of laser radiation up to 15 kW and produced with focal distance of 300 mm to 1000 mm depending on configuration. The scanning system RLSK (HighYAG) equipped with quick-change glasses for the protection of mirrors and collimator, cross-jet system, system of integrity control of glass and RLSK head scanning system, CCD camera and system of apertures for fixation is intended for laser radiation with the power of 8 kW and wavelength of 1020–1080 nm. The scanning system is used for 3D welding with the working area 200Ч300Ч200 mm (WЧLЧH). The movement of laser radiation in working area is implemented at the speed and positioning accuracy: up to 5 m/sec (1 m/sec in the process of treatment) and ±0.2 mm (along the axes X and Y) and ±0.5 mm (along the axis Z), respectively. TECHNOLOGICAL LASER HEADS FOR LASER CUTTING Due to high density of laser radiation power, which exceeds 107 W/cm 2, the technology of laser cutting has following advantages in comparison with other thermal methods of cutting: high efficiency, low rate of energy input, narrow cutting width and heat-affected area, high quality of treated surface and capability of process automation; it is used in blank production when making the elements of metal sheets and sections (СО2, fiber, solid-state lasers) and plastics (СО2-lasers) in various sectors of industry. The use of modern laser sources in the structure of technological complexes poses certain requirements to laser heads: provision of high thermal resistance of optical system components, capability of focusing of laser radiation with minimum spot diameter, control of working gas pressure, integrity of optical system elements and distance to treated surface. For the purpose of implementation of laser cutting, the company Precitec makes the heads, which are intended for the operation in the structure of complexes based on СО2, diode, solid-state and fiber lasers . The laser heads operating in the structure of complexes based on СО2-lasers with the maximum power of 3 to 8 kW depending on configuration can be equipped with the sensors of control of working gas pressure, temperature, contamination or damage of focusing lens (models HP1,5" and HP2"); they are supplied in standard configuration without sensors (CM2" and M1,5"). All heads have the capability of adjustment of focal distance. The heads intended for laser cutting by diode, solid-state and fiber lasers with the maximum power of 500 W to 8 kW are equipped with the cartridge with quick-change protective glass and they have the capability of adjustment of focal distance. Depending on arrangement, the heads can be equipped with the sensor of control of focusing lens temperature (MiniCutter, SpeedCutter and LightCutter) and CCD camera for the monitoring of cutting process (FineCutter). The universal laser head FineCutter intended for the transmission of laser radiation with the wavelength of 255, 355, 515 nm; 1.064, 1.552 and 10.6 µm should be mentioned separately. The variant of laser cutting system FormCutter Plus is of interest; it is equipped with the guide ways with working field along the axes X and Y 50х50 mm 2 and it provides high accuracy of cutting even in case of use in the structure of robotized complex. The system of laser cutting is based on the head SolidCutter used at the maximum radiation power with the wavelength 900–1080 nm up to 4 kW; it can be made with the focal distance of collimator of 75 mm and 100 mm and focusing lens of 75 mm, 100 mm and 125 mm (Fig. 10). The head ProCutter deserves the special attention; it is intended for laser cutting of metals and alloys at the power of laser radiation up to 8 kW and wavelength 1030–1090 nm. The head has the function of automatic or manual (depending on configuration, Fig. 11) adjustment of focal distance, LED display for visual control of pressure, temperature, contamination of optical system and movement in the working process, and it has capability of data transmission from control sensors to cell phone or tablet through Bluetooth . The laser head Bimo FSC (HighYAG) intended for cutting with the power of laser radiation up to 8 kW (fiber, solid-state laser) with the efficiency factor of radiation transmission of more than 97% (1064 nm) is of interest. The head has the capability of variation of focal distance and diameter of laser radiation (Fig. 12). Also, HighYAG company produces the head for laser cutting at maximum power up to 0.25 kW and wavelength 900–1080 nm. The head is equipped with CCD camera and it has capability of variation of focal plane position relative to nozzle along the axis Z at ±5 mm. The heads for laser cutting with the radiation power up to 1 kW (D30 Compact) and up to 12 kW (FLC-D30) are produced by the company IPG. The laser head FLC-D30 is equipped with protective glass with control system, nozzle with the sensor of height control, it has capability of manual and automatic movement of focusing lens along the vertical axis, Ethernet connection and collimator with diaphragm and cooling system; this head is intended for laser cutting of steel, aluminum, copper alloys and brass. The laser head can be optionally equipped with coaxial camera. LaserLine company offers the laser head for cutting of stainless steel and galvanically treated sheets with the thickness up to 3 mm with the diameter of radiation spot generated by diode laser, which is equal to 150 µm at the market. The head is equipped with protective glass, capacitance or contact sensor and sensor of control of focusing lens damage. Also, the technological laser heads LK190C and LK390C presented by Kugler, which operate with the radiation power up to 8 kW, are of interest. The heads are equipped with capacitance sensor of control of the distance to treated workpiece and they have capability of nozzle alignment along the axes X, Y and Z in manual or automatic mode. TECHNOLOGICAL LASER HEADS FOR O CLADDING In case of laser cladding, high-concentration laser radiation generated by modern laser sources has the following advantages in comparison with other heating sources: high efficiency, low coefficient of diffusion of the basic metal with cladded metal, minimum heat-affected area, low rate of energy input, residual deformations and locality of workpiece treatment. The laser heads produced for the implementation of technology of laser cladding must have the optical system with high thermal resistance, system of precise supply of cladded material into the zone of laser radiation impact, which provides high material utilization rate, and capability of variation of heating spot diameters and powder jet in focal plane within wide range in order to ensure high-precision and effective cladding. Precitec company presents the variants of heads for laser cladding with coaxial powder feed through four nozzles and ring nozzle (YC30 and YC52) (Fig. 13) and non-coaxial (Fig. 14) powder feed. The heads differ in maximum power of transmitted laser radiation: 2 kW and 6 kW, respectively, with micron wavelength. Minimum diameter of powder jet in the area of constriction in case of powder supply through four nozzles and in case of non-coaxial supply (heads YC30 and YC52) is equal to 2 mm, in case of jet ring feed of powder – 0.7 mm. Laser heads with coaxial powder feed presented by the company LaserLine are intended for the operation with diode lasers; they have homogeneous distribution of laser radiation in cross-section in the form of circle or rectangle. Depending on arrangement, the laser cladding heads produced by Reis can be equipped with the nozzles with coaxial ring or jet (through three nozzles) feed made by the company ILT (Fraunhofer). The heads are intended for the integration into laser complexes based on diode, fiber and solid-state lasers with maximum output power of 5 kW providing the width of cladded layer of 0.2 mm to 4 mm depending on the feed scheme and used laser source (Fig. 15). The workers of IWS (Fraunhofer) produce the nozzles of Coax series for coaxial ring powder feed in case of cladding with the power of laser radiation of 3–8 kW and efficiency of 10–150 g/min depending on configuration. Also, IWS produces the nozzles for non-coaxial feed and slot symmetric powder feed Coax 11, with the capability of variation of slot width (Fig. 16). The nozzle provides cladding of the bead with the width of 8–22 mm. The heads are intended for use in the structure of technological complexes made on the basis of СО2, diode, fiber, solid-state lasers with the power up to 10 kW. Also, the variant of the laser head for laser cladding with coaxial wire feed CoaxBrazer (Precitec)  and CoaxWire (IWS, Fraunhofer) is of interest. In case of use of CoaxBrazer head cladding is performed with ring-type distribution of laser radiation power providing the prior heating of substrate for the purpose of enhancement of its cohesion with cladded material. CoaxWire head is equipped with the splitter of laser beam into three beams, which converge in the area of beam treatment, and in case of use of wire with the diameter of 0.4–1.6 mm and maximum radiation power of 4 kW it has the efficiency of 3 kg/h. The head can be optionally equipped with CCD camera and pyrometer. The technology of laser cladding with the use of wire has a number of advantages in comparison with the technology of laser cladding by metal powder due to the availability of welding wire at domestic market and wire utilization rate, which approximates to 100%. The head is intended for the use with fiber, solid-state and diode laser sources (Fig. 17). The laser head for recovery of internal, hard-to-reach surfaces produced by Nutech is shown in Fig. 18. The workers of CLA and IWS (Fraunhofer) produce the heads ID, ID-2 and Coaxid for cladding of internal cylindrical surfaces with the minimum diameter of 127 mm, 88.9 mm and 100 mm, respectively, and operating stroke in standard configuration of 1 m using the power of laser radiation up to 6 kW (diode laser; head ID) and up to 3 kW (disk, fiber, solid-state laser; heads ID-2 and Coaxid). The heads provide cladding with the productivity of 75 g/min, 60 g/min and 50 g/min at the width of cladded layer up to 8 mm, 6 mm and 4 mm, respectively. The head CoaxPowerLine should be specifically mentioned; it is intended for laser cladding by diode laser with the radiation power up to 15 kW and concurrent induction heating with inductor power from 20 to 50 kW. Use of induction heating increases the productivity of cladding up to 18 kg/hour. On the basis of estimations of manufacturers the use of induction heating of treated workpiece allows obtaining the productivity, which is comparable with cladding efficiency at the power of laser radiation of 8–10 kW, at the power of laser radiation of 4 kW (Fig. 19). TECHNOLOGICAL LASER HEADS FOR SURFACE THERMAL HARDENING Technology of laser thermal hardening is implemented at the expense of heating of workpiece surface layer upon its short-term interaction with high-concentration laser radiation up to the temperatures, which insignificantly exceed the temperatures of polymorphous transformation, and further cooling with high speed due to the heat transfer inside the workpiece. Cooling with high speed suppresses carbon diffusion upon polymorphous transformation forming the martensitic phase component in surface layer, which has high tribological characteristics. Fiber, solid-state and diode laser sources, which generate the laser radiation absorbed by workpiece material with higher absorption coefficient, are more suitable for the implementation of technology of laser thermal hardening in comparison with the radiation generated by СО2-laser . For the purpose of provision of high process efficiency and layer, which is homogeneously hardened by depth, it is more preferable to use the laser heads with homogeneous distribution of radiation in cross-section. Such type of heads primarily includes the laser welding heads IPG with the power up to 10 kW FLW-D50L with additionally built-in Beam Shape Module, heads Kugler with mirrors providing the homogeneous distribution of laser radiation and laser welding heads produced by LaserLine. Also, the homogeneous heating of surface can be implemented by oscillation of laser radiation in cross-section relative to the treatment direction. The laser heads of the company IPG FLW-D30 Wobble and FLW-D50 Wobble with maximum radiation power of 6 kW and 10 kW are successfully used for the implementation of such technology. In addition to galvanometric scanator providing the movement of laser radiation in transverse direction and forming hardened layer with the width up to 30 mm, the head RLH-A (ScanSonic) is also equipped with pyrometer, which is located coaxially in relation to laser radiation and which measures the temperature of treated area within the range from 800 to 1600 °C. The optical system of laser head is capable to transmit the laser radiation generated by fiber, solid-state and diode laser with maximum power up to 6 kW (Fig. 20). In order to implement the technology of laser thermal hardening, the company Precitec additionally produces ScanTracker system, which is capable to scan the radiation with frequency of 1 kHz. Workers of CLA company produce the laser head ID-H for thermal hardening of internal cylindrical surfaces with the diameter of not less than 76 mm and operating stroke of 1 m at the power of laser radiation up to 3 kW. CONCLUSION The results of performed analysis showed that the vast majority of laser heads is intended for the operation in the structure of technological complexes based on diode, fiber and solid-state lasers. The heads are made on the basis of module principle, which provides the capability of selection of required configuration depending on set tasks. The main efforts of the companies producing laser heads are aimed at the fabrication of components of optical systems with high thermal resistance and additional systems, which are supplied in the structure of laser heads and which provide the full automation of technological process. Authors express their gratitude to S.V. Smirnov (LLC "TsK SPA") and S. Shmelev (NTO "IRE-Polyus") for provided information on the technical characteristics of laser heads produced by Precitec, ScanSonic, Nutech and IPG Photonics.