rus
Issue #3/2018
A. G. Sukhov, M. M. Malysh, M. O. Leder, S. V. Lednov
Laser cutting of titanium alloys
Laser cutting of titanium alloys
The results of the experiments are given in the article. They have shown the possibility of using laser cutting for the manufacture of parts with complex shape and small elements from titanium alloys, and also for cutting large-thickness parts.
Теги: gas laser cutting laser cutting microstructure research slanting thermal impact zone titanium alloys газолазерная резка зона термического влияния исследование микроструктуры лазерная резка резка с наклоном титановые сплавы
At present, methods of cutting metal using highly concentrated energy sources are widely used [1]. One of the promising processes is gas-laser cutting, based on the mechanism of destruction of metals by melting or evaporation with the blowing of melt products from the cutting zone by means various gases. Laser cutting has several advantages in comparison with other cutting methods, the main ones being the following:
• possibility of cutting large-volume products;
• locality of exposure, absence of contact with the workpiece;
• small zone of thermal influence;
• absence of deformation and warping of details;
• high speed and accuracy of processing;
• energy saving, waste minimization;
• no need for finishing operations;
• versatility, possibility of processing various materials.
The processes of laser cutting of titanium alloys have been underexplored, and concern mainly cutting with the use of inert gases [2,3]. Below are the results of a laser cutting of VST‑2 titanium alloy with a thickness of 3 mm, 6.5 mm, 9 mm and 12 mm. Cutting was performed on laser complexes TRUMPF TruLaser 5030 Classic, equipped with a CO2-laser with a power of 6 kW and TLC1005 with a CO2-laser with a power of 5 kW. Cutting gas is helium; output diameter of a nozzle is 2.3 mm. Cutting modes for samples are shown in Table 1. In order to minimize the experimental laser cutting with various geometries and subsequent study of samples with the zones of interest, the cutting was carried out according to the scheme shown in Fig. 1.
For thicknesses of 9 mm and 12 mm, the zone of p.6 – cutting with tilt, is absent. Figures 2 and 3 show the appearance of the samples under study: a – laser radiation input surface; b – laser radiation output surface. The input surfaces of the laser beam for different thicknesses are identical. The state of the surface at the exit of the beam for different thicknesses differs in the different degree of formation of the burr.
Surface of cut for samples 3, 6 and 9 mm thick is even without expressed roughness (Figures 4 and 5a), there are vertical strokes on the cutting surface of a sample 12 mm thick (Figure 5b) formed by a jet of cutting gas.
To study the macro- and microstructures of the zones of interest, the corresponding samples were cut out and the polished sections were manufactured. The macrostructure analysis was performed using OLYMPUS SZX 7 binocular, the microstructure analysis was carried out using OLYMPUS GX 71 optical microscope, the measurements of the zone of thermal influence were made using AnalySIS program. The results of the study of the heat-affected zone (HAZ) are given in Table 2. The results of geometrical measurements of the samples are shown in Table 3.
Measurements of the cutting geometry in the examined zones showed the following results:
• zone No. 1: the diameter of the insert is 0.7 mm, the width of the cut is from 0.4 to 0.6 mm (depending on the thickness of the metal being cut),
• zones Nos. 2 and 3: the technique of performing laser cutting of the minimum possible radii with a stop and without a stop does not affect the quality of the cut. The minimum cutting radius is 0.5 mm (zone No. 2),
• zone No. 4: the minimum thickness of the technological jumper cut by laser cutting is 1 mm for thicknesses of 3.0 and 6.5 mm and – from 3 to 4 mm for thicknesses of 9 and 12 mm. The laser beam is heat-affecting technological jumper across the entire thickness,
• zone No. 5: the minimum diameter of the cut hole is 2 mm for thicknesses of 3.0 and 6.5 mm, 4.3 mm for thicknesses of 9.0 mm and 3.3 mm – for a thickness of 12.0 mm.
Characteristic microstructure of the base metal of samples of different thicknesses is shown in Fig. 6. The value of the heat-affected zone was determined by means of metallographic method and microhardness measurement. The microhardness was measured with DuraScan50 hardness gauge with a load of 100 g from a distance of 50 µm from the surface of the cut in increments of 100 µm before reaching the base metal. The microhardness of the base metal of a sample 3.0 mm thick is 364–380 HV01; that of a sample 6.5 mm thick – 364–386 HV01; that of a sample 9.0 mm thick – 390–405 HV01; that of a sample 12.0 mm thick – 380–405 HV01. Determination of the value of the heat-affected zone by the method of measuring the microhardness was carried out selectively on several samples, since the results when measuring the value of the heat-affected zone by the metallographic method and the method of measuring the microhardness have a slight discrepancy (20–60 µm).
It has been established that for a metal thickness of 3 mm, no burr is available for various cutting configurations (Figure 2). For the remaining thicknesses, the burr is observed when cutting the holes and technological jumpers. The cutting surface does not require any additional processing, except stripping from the burr.
The heat-affected zone depends on the thickness of the metal and is 6–8% of the thickness of the cut sample for cutting modes No. 1 to 3. When cutting holes (mode No. 5) and technological jumpers (mode No. 4), starting from a thickness of 6.5 mm, the value of the heat-affected zone increases as it approaches the exit surface of the laser beam. The HAZ is almost uniform in the thickness of the product (Figures 7 and 8). When cutting titanium alloys, changes in the structure of the metal in the HAZ do not affect the mechanical properties of the laser beam-cut parts under optimal conditions. This is confirmed by the results of mechanical and fatigue tests, as well as general corrosion tests carried out for parts cut with a laser beam and using guillotine shears.
The width of the cut increases with the thickness of the sample and ranges from 0.4 to 0.6 mm. The quality of the cut does not depend on the radius of the cut and the possible stop of the beam (Figure 9). The minimum cutting radius was 0.5 mm. Using the obtained experimental results, we performed an experimental laser trimming of a casting material for two stamped forgings made of ВТ6 alloy: cover (Fig. 10) and blade (Fig. 11).
Typically, argon is used as a process gas for gas-laser cutting of titanium. However, the quality of the edges of the cut may be unsatisfactory because of the formation of the burr, especially when the metal thickness is over 3 mm. In our case, the thickness of the stamp forgings along the perimeter of the cutting varies from 6 to 12 mm, therefore helium was used as the cutting gas. The work was performed on a 5-axis laser technological complex TRUMPF Laser Cell 1005. The both parts were processed at a laser power of 4.0 kW with a nozzle with a diameter of 2.3 mm. When cutting the "Cover" part, the cutting speed was 2.1 m / min, the cutting gas pressure was 17 bar, when processing the "Blade" part, the cutting speed was 1.0 m / min, the cutting gas pressure was 20 bar. The processing results are shown in Figures 12 and 13.
Furthermore, an estimation was made of the possibility of gas-laser cutting of titanium alloys of large thickness – the samples made of VST‑2 alloy with a thickness of 55 and 80 mm were cut (Figure 14). The cutting was carried out on a robotic complex FLW‑10-01 at a power of 10 kW with the use of helium. The surface of the cut in both cases is of satisfactory quality and does not require additional processing.
Thus, the experiments have shown the possibility of using laser cutting for the manufacture of parts from titanium alloys of complex shape with small elements, and also its application for cutting large-thickness parts.
• possibility of cutting large-volume products;
• locality of exposure, absence of contact with the workpiece;
• small zone of thermal influence;
• absence of deformation and warping of details;
• high speed and accuracy of processing;
• energy saving, waste minimization;
• no need for finishing operations;
• versatility, possibility of processing various materials.
The processes of laser cutting of titanium alloys have been underexplored, and concern mainly cutting with the use of inert gases [2,3]. Below are the results of a laser cutting of VST‑2 titanium alloy with a thickness of 3 mm, 6.5 mm, 9 mm and 12 mm. Cutting was performed on laser complexes TRUMPF TruLaser 5030 Classic, equipped with a CO2-laser with a power of 6 kW and TLC1005 with a CO2-laser with a power of 5 kW. Cutting gas is helium; output diameter of a nozzle is 2.3 mm. Cutting modes for samples are shown in Table 1. In order to minimize the experimental laser cutting with various geometries and subsequent study of samples with the zones of interest, the cutting was carried out according to the scheme shown in Fig. 1.
For thicknesses of 9 mm and 12 mm, the zone of p.6 – cutting with tilt, is absent. Figures 2 and 3 show the appearance of the samples under study: a – laser radiation input surface; b – laser radiation output surface. The input surfaces of the laser beam for different thicknesses are identical. The state of the surface at the exit of the beam for different thicknesses differs in the different degree of formation of the burr.
Surface of cut for samples 3, 6 and 9 mm thick is even without expressed roughness (Figures 4 and 5a), there are vertical strokes on the cutting surface of a sample 12 mm thick (Figure 5b) formed by a jet of cutting gas.
To study the macro- and microstructures of the zones of interest, the corresponding samples were cut out and the polished sections were manufactured. The macrostructure analysis was performed using OLYMPUS SZX 7 binocular, the microstructure analysis was carried out using OLYMPUS GX 71 optical microscope, the measurements of the zone of thermal influence were made using AnalySIS program. The results of the study of the heat-affected zone (HAZ) are given in Table 2. The results of geometrical measurements of the samples are shown in Table 3.
Measurements of the cutting geometry in the examined zones showed the following results:
• zone No. 1: the diameter of the insert is 0.7 mm, the width of the cut is from 0.4 to 0.6 mm (depending on the thickness of the metal being cut),
• zones Nos. 2 and 3: the technique of performing laser cutting of the minimum possible radii with a stop and without a stop does not affect the quality of the cut. The minimum cutting radius is 0.5 mm (zone No. 2),
• zone No. 4: the minimum thickness of the technological jumper cut by laser cutting is 1 mm for thicknesses of 3.0 and 6.5 mm and – from 3 to 4 mm for thicknesses of 9 and 12 mm. The laser beam is heat-affecting technological jumper across the entire thickness,
• zone No. 5: the minimum diameter of the cut hole is 2 mm for thicknesses of 3.0 and 6.5 mm, 4.3 mm for thicknesses of 9.0 mm and 3.3 mm – for a thickness of 12.0 mm.
Characteristic microstructure of the base metal of samples of different thicknesses is shown in Fig. 6. The value of the heat-affected zone was determined by means of metallographic method and microhardness measurement. The microhardness was measured with DuraScan50 hardness gauge with a load of 100 g from a distance of 50 µm from the surface of the cut in increments of 100 µm before reaching the base metal. The microhardness of the base metal of a sample 3.0 mm thick is 364–380 HV01; that of a sample 6.5 mm thick – 364–386 HV01; that of a sample 9.0 mm thick – 390–405 HV01; that of a sample 12.0 mm thick – 380–405 HV01. Determination of the value of the heat-affected zone by the method of measuring the microhardness was carried out selectively on several samples, since the results when measuring the value of the heat-affected zone by the metallographic method and the method of measuring the microhardness have a slight discrepancy (20–60 µm).
It has been established that for a metal thickness of 3 mm, no burr is available for various cutting configurations (Figure 2). For the remaining thicknesses, the burr is observed when cutting the holes and technological jumpers. The cutting surface does not require any additional processing, except stripping from the burr.
The heat-affected zone depends on the thickness of the metal and is 6–8% of the thickness of the cut sample for cutting modes No. 1 to 3. When cutting holes (mode No. 5) and technological jumpers (mode No. 4), starting from a thickness of 6.5 mm, the value of the heat-affected zone increases as it approaches the exit surface of the laser beam. The HAZ is almost uniform in the thickness of the product (Figures 7 and 8). When cutting titanium alloys, changes in the structure of the metal in the HAZ do not affect the mechanical properties of the laser beam-cut parts under optimal conditions. This is confirmed by the results of mechanical and fatigue tests, as well as general corrosion tests carried out for parts cut with a laser beam and using guillotine shears.
The width of the cut increases with the thickness of the sample and ranges from 0.4 to 0.6 mm. The quality of the cut does not depend on the radius of the cut and the possible stop of the beam (Figure 9). The minimum cutting radius was 0.5 mm. Using the obtained experimental results, we performed an experimental laser trimming of a casting material for two stamped forgings made of ВТ6 alloy: cover (Fig. 10) and blade (Fig. 11).
Typically, argon is used as a process gas for gas-laser cutting of titanium. However, the quality of the edges of the cut may be unsatisfactory because of the formation of the burr, especially when the metal thickness is over 3 mm. In our case, the thickness of the stamp forgings along the perimeter of the cutting varies from 6 to 12 mm, therefore helium was used as the cutting gas. The work was performed on a 5-axis laser technological complex TRUMPF Laser Cell 1005. The both parts were processed at a laser power of 4.0 kW with a nozzle with a diameter of 2.3 mm. When cutting the "Cover" part, the cutting speed was 2.1 m / min, the cutting gas pressure was 17 bar, when processing the "Blade" part, the cutting speed was 1.0 m / min, the cutting gas pressure was 20 bar. The processing results are shown in Figures 12 and 13.
Furthermore, an estimation was made of the possibility of gas-laser cutting of titanium alloys of large thickness – the samples made of VST‑2 alloy with a thickness of 55 and 80 mm were cut (Figure 14). The cutting was carried out on a robotic complex FLW‑10-01 at a power of 10 kW with the use of helium. The surface of the cut in both cases is of satisfactory quality and does not require additional processing.
Thus, the experiments have shown the possibility of using laser cutting for the manufacture of parts from titanium alloys of complex shape with small elements, and also its application for cutting large-thickness parts.
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