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1
2015, 36(9): 87-90.
Abstract：
Four multi-layer single aluminum alloy beads using the same welding parameters were formed on substrates with four kinds of thickness by TIG arc. It is found that deposited metal width in stable region of different samples was basically unchanged. Based on this phenomenon, the experimental samples were designed using quadratic general rotary unitized design method and the model between process parameters (welding current, welding speed, wire feed speed and inter-layer temperature) and deposited metal width of stable region was established. The validation results show that the model has good prediction accuracy. Furthermore, it also reveals that the welding current, welding speed and inter-layer temperature were the main influential factors on deposited metal width. Among them, the welding current had the most influential effect, and then the welding speed and inter-layer temperature, successively. In addition, the welding speed and inter-layer temperature had interactive effects on deposited metal width.
Four multi-layer single aluminum alloy beads using the same welding parameters were formed on substrates with four kinds of thickness by TIG arc. It is found that deposited metal width in stable region of different samples was basically unchanged. Based on this phenomenon, the experimental samples were designed using quadratic general rotary unitized design method and the model between process parameters (welding current, welding speed, wire feed speed and inter-layer temperature) and deposited metal width of stable region was established. The validation results show that the model has good prediction accuracy. Furthermore, it also reveals that the welding current, welding speed and inter-layer temperature were the main influential factors on deposited metal width. Among them, the welding current had the most influential effect, and then the welding speed and inter-layer temperature, successively. In addition, the welding speed and inter-layer temperature had interactive effects on deposited metal width.
2
2018, 39(8): 123-128.
DOI: 10.12073/j.hjxb.2018390214
Abstract：
With the development of additive manufacturing (AM) technology, a variety of AM technologies, such as arc, laser and electron beam AM technologies, have been extensively researched in their respective sectors. The characteristics of electron beam freeform fabrication (EBF3) were summarized in this paper. The research on EBF3 technology and the latest achievements on the equipment and technique of EBF3 in domestic and foreign were introduced. Research work of EBF3 which should be launched was analyzed. Finally, EBF3 technology should be developed along refractory metals and composite materials, preparation of gradient materials and complex component additive manufacturing was prospected.
With the development of additive manufacturing (AM) technology, a variety of AM technologies, such as arc, laser and electron beam AM technologies, have been extensively researched in their respective sectors. The characteristics of electron beam freeform fabrication (EBF3) were summarized in this paper. The research on EBF3 technology and the latest achievements on the equipment and technique of EBF3 in domestic and foreign were introduced. Research work of EBF3 which should be launched was analyzed. Finally, EBF3 technology should be developed along refractory metals and composite materials, preparation of gradient materials and complex component additive manufacturing was prospected.
3
2015, 36(5): 25-28,32.
Abstract：
In this paper, the software SYSWELD was used to simulate the single track and overlapped laser cladding process. The results show that the molten pool undergoes a rapid heating and cooling process with high superheat degree during the laser cladding. During the single track laser cladding, the peak temperature of the center point on the molten pool surface is highest, reaching 2 589 ℃. In addition, the peak temperature decreases as the distance is far away from the molten pool center. After the single track laser cladding, the cladding coating is in the tensile stress status and the maximum value locates at the interface between the cladding coating and the matrix, while the heat affected zone is in compressive stress. During the laser overlapped cladding process, the first cladding layer experiences tensile stress, but the tensile stress value decreases obviously and the maximum stress locates at the heat affected zone. Furthermore, because of the preheating from the first track to the second one, the peak temperatures of the points on the second cladding coating are higher than those of the single track The maximum tensile stress appears at the bottom of the cladding coating while the heat affected zone is in compressive stress.
In this paper, the software SYSWELD was used to simulate the single track and overlapped laser cladding process. The results show that the molten pool undergoes a rapid heating and cooling process with high superheat degree during the laser cladding. During the single track laser cladding, the peak temperature of the center point on the molten pool surface is highest, reaching 2 589 ℃. In addition, the peak temperature decreases as the distance is far away from the molten pool center. After the single track laser cladding, the cladding coating is in the tensile stress status and the maximum value locates at the interface between the cladding coating and the matrix, while the heat affected zone is in compressive stress. During the laser overlapped cladding process, the first cladding layer experiences tensile stress, but the tensile stress value decreases obviously and the maximum stress locates at the heat affected zone. Furthermore, because of the preheating from the first track to the second one, the peak temperatures of the points on the second cladding coating are higher than those of the single track The maximum tensile stress appears at the bottom of the cladding coating while the heat affected zone is in compressive stress.
4
2016, 37(2): 89-93.
Abstract：
An approach is put forward to extract image feature points of fillet weld with the assistance of laser line. It overcomes the influence of the reflective stripes in the surface of fillet weld and identifies the feature points effectively. Firstly, the actual stripes and reflective stripes were distinguished by local contrast, then the actual stripes were divided by combination of morphological method and threshold segmentation, and the region of interest was determined. Secondly, the center points in light stripes were extracted according to the intensity distribution of the cross-section of light stripe. Finally, the iterative least-squares fitting method was applied to fit the piecewise centerline equations and to determine the fillet feature points. The experimental results show that this method can extract the sub-pixel image feature points from fillet weld with bright surface rapidly and accurately. It costs about 0.35s running on a PC whose CPU is clocked at 3.4 GHz, which can meet the real-time requirements of ordinary welding equipment with welding speed of 0-25 mm/s.
An approach is put forward to extract image feature points of fillet weld with the assistance of laser line. It overcomes the influence of the reflective stripes in the surface of fillet weld and identifies the feature points effectively. Firstly, the actual stripes and reflective stripes were distinguished by local contrast, then the actual stripes were divided by combination of morphological method and threshold segmentation, and the region of interest was determined. Secondly, the center points in light stripes were extracted according to the intensity distribution of the cross-section of light stripe. Finally, the iterative least-squares fitting method was applied to fit the piecewise centerline equations and to determine the fillet feature points. The experimental results show that this method can extract the sub-pixel image feature points from fillet weld with bright surface rapidly and accurately. It costs about 0.35s running on a PC whose CPU is clocked at 3.4 GHz, which can meet the real-time requirements of ordinary welding equipment with welding speed of 0-25 mm/s.
5
Abstract：
When convolution neural network (CNN) is applied to weld flaw detection image recognition, the target area is small, the local information is redundant, and the hard saturation region of activation function is less than zero, which makes the model sensitive to input change and difficult to train the network parameters. The super pixel segmentation algorithm (SLIC) and the improved ELU activation function are used to construct CNN model for weld flaw detection image defect recognition. First, the ELU activation function is used in the CNN model to generate better robustness to the input noise when the response gradient disappears, At the same time, the SLIC algorithm is used to deal with the pixels of the image, which increases the proportion of the region of interest in the weld flaw detection image, reduces the local redundant information, and improves the feature extraction ability of the model in the training process. Through the extraction of the region of interest of weld flaw detection image and the establishment of the CNN model described in this paper, the results show that the proposed method has better performance than the traditional convolution neural network in feature extraction, training time and recognition accuracy of weld flaw detection image.
When convolution neural network (CNN) is applied to weld flaw detection image recognition, the target area is small, the local information is redundant, and the hard saturation region of activation function is less than zero, which makes the model sensitive to input change and difficult to train the network parameters. The super pixel segmentation algorithm (SLIC) and the improved ELU activation function are used to construct CNN model for weld flaw detection image defect recognition. First, the ELU activation function is used in the CNN model to generate better robustness to the input noise when the response gradient disappears, At the same time, the SLIC algorithm is used to deal with the pixels of the image, which increases the proportion of the region of interest in the weld flaw detection image, reduces the local redundant information, and improves the feature extraction ability of the model in the training process. Through the extraction of the region of interest of weld flaw detection image and the establishment of the CNN model described in this paper, the results show that the proposed method has better performance than the traditional convolution neural network in feature extraction, training time and recognition accuracy of weld flaw detection image.
6
2017, 38(2): 23-27.
Abstract：
According to the evolution of fatigue cracks in welded structures, the fatigue life of welded structures was defined as the sum of crack initiation life Ni and crack propagation life Np, and the SN curve and fracture mechanics combined with fatigue life evaluating method was proposed. Equivalent structural stress method and the lower 99% boundary of master SN curve were utilized to evaluate the crack initiation life, and cracks at the end of the initiation stage was regarded as semi-elliptical surface crack. Paris Equation and the stress intensity factor range of semi-elliptical surface cracks were utilized to evaluate the crack propagation life. Fatigue test data of 5 crane runway girder specimens from a reference were utilized to the comparisons and Validation investigation. Result showed that equivalent structural stress can characterize the crack initiation state of complex welded structures well, and there is a good consistency between the calculating fatigue life and the test life.
According to the evolution of fatigue cracks in welded structures, the fatigue life of welded structures was defined as the sum of crack initiation life Ni and crack propagation life Np, and the SN curve and fracture mechanics combined with fatigue life evaluating method was proposed. Equivalent structural stress method and the lower 99% boundary of master SN curve were utilized to evaluate the crack initiation life, and cracks at the end of the initiation stage was regarded as semi-elliptical surface crack. Paris Equation and the stress intensity factor range of semi-elliptical surface cracks were utilized to evaluate the crack propagation life. Fatigue test data of 5 crane runway girder specimens from a reference were utilized to the comparisons and Validation investigation. Result showed that equivalent structural stress can characterize the crack initiation state of complex welded structures well, and there is a good consistency between the calculating fatigue life and the test life.
7
Abstract：
Based on the characteristics of the friction stir welding and Coulomb friction work theory, 7075-T7315 aluminum alloy flats with thickness of 6 mm were chosen as the study objects. Based on ANSYS code, a three dimensional numerical model with two heat flux inputs of friction stir welding were established. Moreover, the effect of welding speed and rotation speed on temperature and residual stress distributions were investigated.
Based on the characteristics of the friction stir welding and Coulomb friction work theory, 7075-T7315 aluminum alloy flats with thickness of 6 mm were chosen as the study objects. Based on ANSYS code, a three dimensional numerical model with two heat flux inputs of friction stir welding were established. Moreover, the effect of welding speed and rotation speed on temperature and residual stress distributions were investigated.
8
Abstract：
316L austenitic stainless steel thin-walled samples were formed by cold metal transfer (CMT) based on wire arc additive manufacturing (WAAM) method. The forming width, side forming error, deposition efficiency and microstructure of the samples under different welding parameters were investigated. The results show that when the parameters are consistent, the width of the formed specimen increases with the decreasing of the welding speed. The side forming error reduces firstly and then increases with the increasing of the heat input. The deposition efficiency increases firstly and then reduces, and the side forming error and the deposition efficiency trend are the opposite. The more the deposition efficiency, the lower the side forming error, and the forming efficiency can reach more than 90%. The microstructure of the formed parts consists of γ-Fe phase and δ ferrite phase. The microhardness tests show that the hardness along the vertical and the deposition direction did not change significantly, which is related to the uniform microstructure of the sample.
316L austenitic stainless steel thin-walled samples were formed by cold metal transfer (CMT) based on wire arc additive manufacturing (WAAM) method. The forming width, side forming error, deposition efficiency and microstructure of the samples under different welding parameters were investigated. The results show that when the parameters are consistent, the width of the formed specimen increases with the decreasing of the welding speed. The side forming error reduces firstly and then increases with the increasing of the heat input. The deposition efficiency increases firstly and then reduces, and the side forming error and the deposition efficiency trend are the opposite. The more the deposition efficiency, the lower the side forming error, and the forming efficiency can reach more than 90%. The microstructure of the formed parts consists of γ-Fe phase and δ ferrite phase. The microhardness tests show that the hardness along the vertical and the deposition direction did not change significantly, which is related to the uniform microstructure of the sample.
9
2015, 36(7): 43-46,50.
Abstract：
The finite element model for welding of a large-sized thin armor steel structure was developed based on the finite element software SYSWELD. The influence of welding sequence on the distortion of the thin plate structure was investigated by using Local-Global method. Using heat source fitting tool in SYSWELD, the double ellipsoid heat source models which were suitable for the site welding process were established through comparing the weld cross-sections of calculation and experiment. The welding procedures of both T-joint and butt joint were analyzed by the thermal elastic-plastic finite element method. The local plastic strain and the joint stiffness were obtained. Furthermore, the distortion behaviors of the thin plate structure in different welding sequences were simulated. The results show that the welding distortion of the medium plate is severe, and the maximum deformation is 9.6 mm. The calculated results agree well with the experimental ones. The distortion of the thin plates is improved effectively by using the optimized welding sequence. The maximum deformation is reduced by 75%.
The finite element model for welding of a large-sized thin armor steel structure was developed based on the finite element software SYSWELD. The influence of welding sequence on the distortion of the thin plate structure was investigated by using Local-Global method. Using heat source fitting tool in SYSWELD, the double ellipsoid heat source models which were suitable for the site welding process were established through comparing the weld cross-sections of calculation and experiment. The welding procedures of both T-joint and butt joint were analyzed by the thermal elastic-plastic finite element method. The local plastic strain and the joint stiffness were obtained. Furthermore, the distortion behaviors of the thin plate structure in different welding sequences were simulated. The results show that the welding distortion of the medium plate is severe, and the maximum deformation is 9.6 mm. The calculated results agree well with the experimental ones. The distortion of the thin plates is improved effectively by using the optimized welding sequence. The maximum deformation is reduced by 75%.
10
Abstract：
The selective laser melting technology shows great advantages in the field of manufacturing of complex parts, but the organization and the comprehensive performance of the specimens have yet to be further optimized. Specimens of 316L stainless steel were fabricated by selective laser melting technology, the microstructure characteristics of different regions were analyzed, the tensile mechanical properties were tested. The results showed that the micro-structure were mainly cell crystal. However, the grain growth direction were different in some "micro-melting pools", and almost perpendicular to each other, which showed a small typical columnar crystal in the same field of view (subgrain) and "hexagonal cellular crystal" coexistence of micro-structure characteristics. Compared with the traditional specimens, the tensile strength of had greatly improved, but the elongation decreased. This was mainly due to the fact that SLM was a process of rapid melting and solidification which maked the difference of laser incident angle, scanning strategy and heat dissipation conditions resulting in complex crystals at different regions and different microstructure. The fine columnar crystal formed by rapid cooling that was submicron order and densely distribute was the main reason of the increases in tensile strength. However, the obvious anisotropy of grain, which resulted in the uneven deformation of grain in different directions and restrained mutually during the tensile test, and the inevitable remarkable internal stress at the interface of fusion lines leaded to a decrease in elongation.
The selective laser melting technology shows great advantages in the field of manufacturing of complex parts, but the organization and the comprehensive performance of the specimens have yet to be further optimized. Specimens of 316L stainless steel were fabricated by selective laser melting technology, the microstructure characteristics of different regions were analyzed, the tensile mechanical properties were tested. The results showed that the micro-structure were mainly cell crystal. However, the grain growth direction were different in some "micro-melting pools", and almost perpendicular to each other, which showed a small typical columnar crystal in the same field of view (subgrain) and "hexagonal cellular crystal" coexistence of micro-structure characteristics. Compared with the traditional specimens, the tensile strength of had greatly improved, but the elongation decreased. This was mainly due to the fact that SLM was a process of rapid melting and solidification which maked the difference of laser incident angle, scanning strategy and heat dissipation conditions resulting in complex crystals at different regions and different microstructure. The fine columnar crystal formed by rapid cooling that was submicron order and densely distribute was the main reason of the increases in tensile strength. However, the obvious anisotropy of grain, which resulted in the uneven deformation of grain in different directions and restrained mutually during the tensile test, and the inevitable remarkable internal stress at the interface of fusion lines leaded to a decrease in elongation.
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