rus
Issue #1/2016
A.Saprykin, N.Saprykina, E.Ibragimov, E.Babakova, Yu.Sharkeev
Influence Of Conditions Of Layerwise Laser Sintering (Melting) On The Quality Of Product Surface
Influence Of Conditions Of Layerwise Laser Sintering (Melting) On The Quality Of Product Surface
The influence of argon protective atmosphere, prior mechanical activation and operating conditions of laser sintering (speed of laser beam travel V, laser power P, scanning pitch S and preheating temperature of powder material t) on the quality of sintered surface layer obtained from the copper powder, cobalt-chromium-molybdenum powder and composite powder titanium+niobium is studied.
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he influence of argon protective atmosphere, prior mechanical activation and operating conditions of laser sintering (speed of laser beam travel V, laser power P, scanning pitch S and preheating temperature of powder material t) on the quality of sintered surface layer obtained from the copper powder SCP-1, cobalt-chromium-molybdenum powder of the alloy DSK-F75 and composite powder titanium+niobium TiNb (mass. 40%) is studied.
At the present time, the additive technologies are being implemented in industry at fast pace. Layerwise laser sintering (melting) of metal-powder compositions based on 3D CAD-model, which allows manufacturing the functional products, refers to one of the priority areas [1]. Layerwise shaping forms the basis of additive technologies. In other words, the formation of quality unit layer is the foundation. One of the problems of the quality assurance of surface layer includes the presence of tensions in sintered unit layer, which prevent the homogeneous application of the following layer of powder material and deform the product [2]. The objective of this paper consists in the consideration of the factors, which influence on the quality of sintered surface and internal structure, study of the influence of protective atmosphere of argon gas and prior mechanical activation of the powder SCP-1, cobalt-chromium-molybdenum powder of the alloy DSK-F75 and composite powder of titanium+niobium TiNb (mass. 40%) at the various ranges of operating conditions of sintering (melting) on the quality of sintered surface layer. The experiments were conducted using the technological laser complex consisting of ytterbium fiber laser LK-100-V, three-axis table, vacuum chamber, numerical control system and original software [3].
In order to get the idea in relation to the behavior pattern of powder materials during the laser sintering (melting), the powder compositions having different melting temperatures and particles size were selected in the capacity of process materials.
Stabilized copper powder SCP-1 with the content of copper of 99.5%. Melting temperature range of the powder: 1030–1070 °C. Bulk density: 1.25–1.9 g/cm 3. Average powder size: 0.07 mm. The powder is commonly used in metallurgy for manufacturing of sintered products and in instrument engineering.
The powder of cobalt-chromium-molybdenum alloy DSK-F75 with the content of cobalt – 66.4%, chromium – 28%, molybdenum – 3%. Melting temperature range: 1350–1450 °C, bulk density: 8.4 g/cm 3. Powder size: 0.1 mm. The alloy is commonly used in mechanical engineering for design of the products functioning at high temperatures and in dentistry for the production of prosthesis.
The powder composition of titanium+niobium TiNb with the content of titanium – 60%, niobium – 40%. Melting temperature of titanium powder: 1668°C, niobium powder: 2469°C. Bulk density of composite powder: 2.23 g/cm 3. Average size of titanium initial powders: 0.05–0.07 mm, niobium powder: 0.005–0.01 mm. Titanium-niobium alloys are widely used in electronics, energy sector and for the production of implants due to good mechanical properties, excellent biocompatibility and high corrosion stability.
In order to assure the quality of sintered surface layer of powder materials with different ranges of melting temperatures, the variation of the level of deformations and sintering thickness was studied depending on the sintering conditions [4].
During the experiment, the samples of SCP-1 sintered unit layer with the length of 20 mm, width of 5 and 10 mm, DSK-F75 with the length of 20 mm, width of 10 mm and TiNb with the length and width of 10 mm were obtained. The ranges of process conditions of layerwise laser sintering were determined as a result of search experiments. In order to obtain the samples of copper powder SCP-1 the following parameters were used: Р = (14–30) W, V = (200–3000) mm/min, S = (0.1–0.3) mm, t = (26–200)°C. Rational conditions for the powder DSK-F75 are: Р = (10–20) W, V = (100–300) mm/min, S = (0.1–0.15) mm, t = (26–200)°C. Rational conditions for the composite powder TiNb (mass. 40%) in argon protective atmosphere and vacuum are: Р = (68–106) W, V = (1000–3000) mm/min, S = (0.1–0.2) mm, t = (200–400)°C. The power of laser radiation varies depending on the melting temperature of powder material and coefficient of thermal diffusivity, shape and size of particles. In order to obtain the surface, the increase of laser radiation and decrease of the speed of laser beam travel are typical for the refractory powder material DSK-F75 with the powder size of 0.1 mm. In order to obtain the surface of refractory powder composition TiNb, the powder was previously subjected to 15-minutes mechanical activation; sintering process took place in argon after vacuum treatment. Analysis of geometric state of sintered surface was performed in accordance with the specifically developed methods using the toolmaker digital microscope [5].
The influence of laser radiation power on the quality of sintered surface layer is shown in Fig. 1–3. The lack of power during the samples sintering causes their dispersion and, vice versa, the excess of power causes deformation, occurrence of longitudinal and transverse cracks, powder ignition.
The influence of power on the appearance of sintered surface of copper powder SCP-1 is shown in Fig. 1. Power variation from 15 to 30 W at V = 200 mm/min, t = 200 °C, S = 0.3 mm causes the change of Rz from 475 to 975 µm. The samples turned out to be solid but with the formation of longitudinal and transverse cracks. In case of power increase, the size of cracks increases as a result of growth of thermal stresses and high heat conductivity of the powder SCP-1.
The influence of power on the appearance of sintered surface of DSK-F75 is shown in Fig. 2. During sintering of this powder the occurrence of coagulation was observed. Coagulation means the consolidation of fine particles of disperse systems into larger particles under the influence of cohesion forces. The variation of power from 10 to 20 W at V = 300 mm/min, t = 26 °C, S = 0.1 mm causes the increase of roughness of the surface layer from 425 to 625 µm, diameter of coagulated particles from 175 to 325 µm and thickness of sintered layer from 0.65 to 1.0 mm. The sample given in Fig. 2 has low mechanical strength.
The influence of power on the appearance of sintered surface of TiNb (mass. 40%) is shown in Fig. 3. The sintered surface of this powder composition has typical uneven relief. The variation of power from 68 to 106 W at V = 3000 mm/min, t = 260 °C, S = 0.1 mm causes the decrease of roughness of the surface layer, and the thickness of sintered layer practically did not change.
The photographs of the appearance of studied powder materials are shown in Fig. 4–8 depending on the speed of laser beam travel. The photographs of change of the appearance of sintered surface of the powder TiNb are given in Fig. 8 depending on the speed of laser beam travel. The increase of the speed of laser beam travel from 1000 to 3000 mm/min at Р = 68 W, t = 200 °C, S = 0.1 mm causes the decrease of thickness of sintered layer from 1.55 to 1.33 mm.
The samples of copper powder SCP-1 obtained under the conditions P = 15 W, t = 200 °C, S = 0.3 mm are shown in Fig. 5. When V = 200 mm/min, the defects located along and across the formation of tracks occur on the sample. At V = 3000 mm/mi, n there is not enough time for the powder sintering. In case of increase of the speed, the thickness of sintered layer decreases from 1.700 to 0.7 mm. The defects are stipulated by high heat conductivity of the powder material and steep gradient of temperatures in the process of sintering and after sintering. The sample shown in Fig. 5b has low mechanical strength and is dispersed after touching it.
At V = 200 mm/min and Р = 15 W, t = 200 °C, S = 0.1 mm, sintering causes the combustion of powder material, Figure 6. The defects located along and across the formation of tracks occur on the sample. At the speed of 3000 mm/min, the sample becomes solid, without defects. The thickness of sintered layer becomes lower with the increase of the speed from 1.0 to 0.7 mm and roughness – from 590 to 225 µm.
The samples obtained under the conditions Р = 22 W, t = 114 °C, S = 0.2 m, at V = 200 mm/min and 3000 mm/min form the strong sintered surface, Fig. 7. The speed increase results in the variation of thickness of sintered layer from 0.9 to 0.41 mm, Rz – from 930 to 550 µm. The sample shown in Figure 7a has the structure of molten metal and black color due to the formation of copper oxide.
When increasing the speed from 100 to 300 mm/min, at Р = 10 W, t = 26 °C, S = 0.1 mm, in Figure 8 the surface roughness reduces from 560 to 425 µm, thickness of sintered layer – from 0.88 to 0.65 mm.
When setting the speed of laser beam travel, it is necessary to take into account its significant influence on the quality of surface layer. The speed increase results in the reduction of layer thickness and roughness, and in some cases it is too high for the formation of sintered surface. Sometimes, the speed decrease results in the combustion of powder material, occurrence of defects due to the material overheating at the temperature higher than boiling temperature.
In Figure 9, with the scanning pitch S = 0.1 mm and at Р = 15 W, t = 200 °C, V = 3000 mm/min, the sintered surface has certain strength. The increase of S from 0.1 to 0.3 mm reduces the thickness of sintered layer from 0.7 to 0.66 mm increasing Rz from 225 to 425 µm.
When increasing the scanning pitch from 0.1 to 0.15 mm under sintering conditions Р = 10 W, t = 26 °C, V = 300 mm/min, in Figure 11 the surface roughness reduces from 425 to 300 µm, the thickness of sintered layer decreases from 0.65 to 0.4 mm, the diameter of coagulated particles reduces from 175 to 150 µm.
The scanning pitch does not significantly influence on the quality of surface layer. The different influence on powder materials is observed. When sintering the composite powder of TiNb (mass. 40%), the increase of scanning pitch causes the increase of thickness of sintered layer. When sintering cobalt-chromium-molybdenum composition, the increase of scanning pitch causes the decrease of thickness of sintered layer, Rz and diameter of coagulated particles. When sintering the copper powder SCP-1, the thickness of sintered layer decreases and roughness increases.
Performed studies allow drawing the conclusion about the significant influence of the power on the quality of sintered surface layer. In case of incorrect setting of power, the samples either were dispersed after touching them or deformed; in some cases the powder combustion occurs and the process gets beyond control. Also, the influence of the speed of laser beam travel has significant impact on the quality of surface layer. The increase of speed results in the reduction of thickness and roughness of sintered layer; in some cases it is not sufficient for the surface formation. Sometimes, the speed decrease results in the combustion of powder material and occurrence of defects. The scanning pitch does not significantly influence on the quality of surface layer. When sintering cobalt-chromium-molybdenum composition, the increase of scanning pitch causes the decrease of thickness of sintered layer, Rz and diameter of coagulated particles. Such studies will be needed in the process of setting the sintering conditions for new powder compositions.
The works were performed with the financial support from the Russian Scientific Fund, project 15–19–00191.
he influence of argon protective atmosphere, prior mechanical activation and operating conditions of laser sintering (speed of laser beam travel V, laser power P, scanning pitch S and preheating temperature of powder material t) on the quality of sintered surface layer obtained from the copper powder SCP-1, cobalt-chromium-molybdenum powder of the alloy DSK-F75 and composite powder titanium+niobium TiNb (mass. 40%) is studied.
At the present time, the additive technologies are being implemented in industry at fast pace. Layerwise laser sintering (melting) of metal-powder compositions based on 3D CAD-model, which allows manufacturing the functional products, refers to one of the priority areas [1]. Layerwise shaping forms the basis of additive technologies. In other words, the formation of quality unit layer is the foundation. One of the problems of the quality assurance of surface layer includes the presence of tensions in sintered unit layer, which prevent the homogeneous application of the following layer of powder material and deform the product [2]. The objective of this paper consists in the consideration of the factors, which influence on the quality of sintered surface and internal structure, study of the influence of protective atmosphere of argon gas and prior mechanical activation of the powder SCP-1, cobalt-chromium-molybdenum powder of the alloy DSK-F75 and composite powder of titanium+niobium TiNb (mass. 40%) at the various ranges of operating conditions of sintering (melting) on the quality of sintered surface layer. The experiments were conducted using the technological laser complex consisting of ytterbium fiber laser LK-100-V, three-axis table, vacuum chamber, numerical control system and original software [3].
In order to get the idea in relation to the behavior pattern of powder materials during the laser sintering (melting), the powder compositions having different melting temperatures and particles size were selected in the capacity of process materials.
Stabilized copper powder SCP-1 with the content of copper of 99.5%. Melting temperature range of the powder: 1030–1070 °C. Bulk density: 1.25–1.9 g/cm 3. Average powder size: 0.07 mm. The powder is commonly used in metallurgy for manufacturing of sintered products and in instrument engineering.
The powder of cobalt-chromium-molybdenum alloy DSK-F75 with the content of cobalt – 66.4%, chromium – 28%, molybdenum – 3%. Melting temperature range: 1350–1450 °C, bulk density: 8.4 g/cm 3. Powder size: 0.1 mm. The alloy is commonly used in mechanical engineering for design of the products functioning at high temperatures and in dentistry for the production of prosthesis.
The powder composition of titanium+niobium TiNb with the content of titanium – 60%, niobium – 40%. Melting temperature of titanium powder: 1668°C, niobium powder: 2469°C. Bulk density of composite powder: 2.23 g/cm 3. Average size of titanium initial powders: 0.05–0.07 mm, niobium powder: 0.005–0.01 mm. Titanium-niobium alloys are widely used in electronics, energy sector and for the production of implants due to good mechanical properties, excellent biocompatibility and high corrosion stability.
In order to assure the quality of sintered surface layer of powder materials with different ranges of melting temperatures, the variation of the level of deformations and sintering thickness was studied depending on the sintering conditions [4].
During the experiment, the samples of SCP-1 sintered unit layer with the length of 20 mm, width of 5 and 10 mm, DSK-F75 with the length of 20 mm, width of 10 mm and TiNb with the length and width of 10 mm were obtained. The ranges of process conditions of layerwise laser sintering were determined as a result of search experiments. In order to obtain the samples of copper powder SCP-1 the following parameters were used: Р = (14–30) W, V = (200–3000) mm/min, S = (0.1–0.3) mm, t = (26–200)°C. Rational conditions for the powder DSK-F75 are: Р = (10–20) W, V = (100–300) mm/min, S = (0.1–0.15) mm, t = (26–200)°C. Rational conditions for the composite powder TiNb (mass. 40%) in argon protective atmosphere and vacuum are: Р = (68–106) W, V = (1000–3000) mm/min, S = (0.1–0.2) mm, t = (200–400)°C. The power of laser radiation varies depending on the melting temperature of powder material and coefficient of thermal diffusivity, shape and size of particles. In order to obtain the surface, the increase of laser radiation and decrease of the speed of laser beam travel are typical for the refractory powder material DSK-F75 with the powder size of 0.1 mm. In order to obtain the surface of refractory powder composition TiNb, the powder was previously subjected to 15-minutes mechanical activation; sintering process took place in argon after vacuum treatment. Analysis of geometric state of sintered surface was performed in accordance with the specifically developed methods using the toolmaker digital microscope [5].
The influence of laser radiation power on the quality of sintered surface layer is shown in Fig. 1–3. The lack of power during the samples sintering causes their dispersion and, vice versa, the excess of power causes deformation, occurrence of longitudinal and transverse cracks, powder ignition.
The influence of power on the appearance of sintered surface of copper powder SCP-1 is shown in Fig. 1. Power variation from 15 to 30 W at V = 200 mm/min, t = 200 °C, S = 0.3 mm causes the change of Rz from 475 to 975 µm. The samples turned out to be solid but with the formation of longitudinal and transverse cracks. In case of power increase, the size of cracks increases as a result of growth of thermal stresses and high heat conductivity of the powder SCP-1.
The influence of power on the appearance of sintered surface of DSK-F75 is shown in Fig. 2. During sintering of this powder the occurrence of coagulation was observed. Coagulation means the consolidation of fine particles of disperse systems into larger particles under the influence of cohesion forces. The variation of power from 10 to 20 W at V = 300 mm/min, t = 26 °C, S = 0.1 mm causes the increase of roughness of the surface layer from 425 to 625 µm, diameter of coagulated particles from 175 to 325 µm and thickness of sintered layer from 0.65 to 1.0 mm. The sample given in Fig. 2 has low mechanical strength.
The influence of power on the appearance of sintered surface of TiNb (mass. 40%) is shown in Fig. 3. The sintered surface of this powder composition has typical uneven relief. The variation of power from 68 to 106 W at V = 3000 mm/min, t = 260 °C, S = 0.1 mm causes the decrease of roughness of the surface layer, and the thickness of sintered layer practically did not change.
The photographs of the appearance of studied powder materials are shown in Fig. 4–8 depending on the speed of laser beam travel. The photographs of change of the appearance of sintered surface of the powder TiNb are given in Fig. 8 depending on the speed of laser beam travel. The increase of the speed of laser beam travel from 1000 to 3000 mm/min at Р = 68 W, t = 200 °C, S = 0.1 mm causes the decrease of thickness of sintered layer from 1.55 to 1.33 mm.
The samples of copper powder SCP-1 obtained under the conditions P = 15 W, t = 200 °C, S = 0.3 mm are shown in Fig. 5. When V = 200 mm/min, the defects located along and across the formation of tracks occur on the sample. At V = 3000 mm/mi, n there is not enough time for the powder sintering. In case of increase of the speed, the thickness of sintered layer decreases from 1.700 to 0.7 mm. The defects are stipulated by high heat conductivity of the powder material and steep gradient of temperatures in the process of sintering and after sintering. The sample shown in Fig. 5b has low mechanical strength and is dispersed after touching it.
At V = 200 mm/min and Р = 15 W, t = 200 °C, S = 0.1 mm, sintering causes the combustion of powder material, Figure 6. The defects located along and across the formation of tracks occur on the sample. At the speed of 3000 mm/min, the sample becomes solid, without defects. The thickness of sintered layer becomes lower with the increase of the speed from 1.0 to 0.7 mm and roughness – from 590 to 225 µm.
The samples obtained under the conditions Р = 22 W, t = 114 °C, S = 0.2 m, at V = 200 mm/min and 3000 mm/min form the strong sintered surface, Fig. 7. The speed increase results in the variation of thickness of sintered layer from 0.9 to 0.41 mm, Rz – from 930 to 550 µm. The sample shown in Figure 7a has the structure of molten metal and black color due to the formation of copper oxide.
When increasing the speed from 100 to 300 mm/min, at Р = 10 W, t = 26 °C, S = 0.1 mm, in Figure 8 the surface roughness reduces from 560 to 425 µm, thickness of sintered layer – from 0.88 to 0.65 mm.
When setting the speed of laser beam travel, it is necessary to take into account its significant influence on the quality of surface layer. The speed increase results in the reduction of layer thickness and roughness, and in some cases it is too high for the formation of sintered surface. Sometimes, the speed decrease results in the combustion of powder material, occurrence of defects due to the material overheating at the temperature higher than boiling temperature.
In Figure 9, with the scanning pitch S = 0.1 mm and at Р = 15 W, t = 200 °C, V = 3000 mm/min, the sintered surface has certain strength. The increase of S from 0.1 to 0.3 mm reduces the thickness of sintered layer from 0.7 to 0.66 mm increasing Rz from 225 to 425 µm.
When increasing the scanning pitch from 0.1 to 0.15 mm under sintering conditions Р = 10 W, t = 26 °C, V = 300 mm/min, in Figure 11 the surface roughness reduces from 425 to 300 µm, the thickness of sintered layer decreases from 0.65 to 0.4 mm, the diameter of coagulated particles reduces from 175 to 150 µm.
The scanning pitch does not significantly influence on the quality of surface layer. The different influence on powder materials is observed. When sintering the composite powder of TiNb (mass. 40%), the increase of scanning pitch causes the increase of thickness of sintered layer. When sintering cobalt-chromium-molybdenum composition, the increase of scanning pitch causes the decrease of thickness of sintered layer, Rz and diameter of coagulated particles. When sintering the copper powder SCP-1, the thickness of sintered layer decreases and roughness increases.
Performed studies allow drawing the conclusion about the significant influence of the power on the quality of sintered surface layer. In case of incorrect setting of power, the samples either were dispersed after touching them or deformed; in some cases the powder combustion occurs and the process gets beyond control. Also, the influence of the speed of laser beam travel has significant impact on the quality of surface layer. The increase of speed results in the reduction of thickness and roughness of sintered layer; in some cases it is not sufficient for the surface formation. Sometimes, the speed decrease results in the combustion of powder material and occurrence of defects. The scanning pitch does not significantly influence on the quality of surface layer. When sintering cobalt-chromium-molybdenum composition, the increase of scanning pitch causes the decrease of thickness of sintered layer, Rz and diameter of coagulated particles. Such studies will be needed in the process of setting the sintering conditions for new powder compositions.
The works were performed with the financial support from the Russian Scientific Fund, project 15–19–00191.
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