CN117216962A - Temperature field numerical simulation method for multilayer multi-channel shaping of SLM (selective laser deposition) - Google Patents
Temperature field numerical simulation method for multilayer multi-channel shaping of SLM (selective laser deposition) Download PDFInfo
- Publication number
- CN117216962A CN117216962A CN202311105400.4A CN202311105400A CN117216962A CN 117216962 A CN117216962 A CN 117216962A CN 202311105400 A CN202311105400 A CN 202311105400A CN 117216962 A CN117216962 A CN 117216962A
- Authority
- CN
- China
- Prior art keywords
- layer
- forming
- slm
- laser
- temperature field
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 238000000034 method Methods 0.000 title claims abstract description 128
- 238000004088 simulation Methods 0.000 title claims abstract description 46
- 230000008021 deposition Effects 0.000 title abstract description 4
- 238000007493 shaping process Methods 0.000 title description 3
- 230000008569 process Effects 0.000 claims abstract description 91
- 239000000843 powder Substances 0.000 claims abstract description 56
- 238000004458 analytical method Methods 0.000 claims abstract description 17
- 230000035945 sensitivity Effects 0.000 claims abstract description 13
- 238000003892 spreading Methods 0.000 claims abstract description 5
- 230000007480 spreading Effects 0.000 claims abstract description 5
- 239000010410 layer Substances 0.000 claims description 66
- 239000000463 material Substances 0.000 claims description 53
- 239000000758 substrate Substances 0.000 claims description 26
- 230000008859 change Effects 0.000 claims description 21
- 230000008018 melting Effects 0.000 claims description 14
- 238000002844 melting Methods 0.000 claims description 14
- 239000002245 particle Substances 0.000 claims description 9
- 238000012545 processing Methods 0.000 claims description 8
- 238000004364 calculation method Methods 0.000 claims description 7
- 238000001816 cooling Methods 0.000 claims description 6
- 238000011156 evaluation Methods 0.000 claims description 6
- 239000011229 interlayer Substances 0.000 claims description 6
- 125000004122 cyclic group Chemical group 0.000 claims description 4
- 230000004907 flux Effects 0.000 claims description 3
- 239000000155 melt Substances 0.000 claims description 3
- 230000005855 radiation Effects 0.000 claims description 3
- 230000004927 fusion Effects 0.000 claims description 2
- 238000005457 optimization Methods 0.000 claims description 2
- 239000000654 additive Substances 0.000 abstract description 3
- 230000000996 additive effect Effects 0.000 abstract description 3
- 238000007639 printing Methods 0.000 abstract description 3
- 238000012546 transfer Methods 0.000 abstract description 3
- 238000004519 manufacturing process Methods 0.000 abstract description 2
- 238000005516 engineering process Methods 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000011343 solid material Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 238000012886 linear function Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 230000035882 stress Effects 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Landscapes
- Powder Metallurgy (AREA)
Abstract
The invention discloses a temperature field numerical simulation method for multilayer multi-channel forming of an SLM (selective laser deposition), which comprises the steps of establishing a temperature field simulation model, simulating a multilayer multi-channel forming process of SLM laser additive manufacturing, applying a heat source to each layer, taking time as a node, ensuring the continuity of a moving heat source, and controlling the layer-by-layer powder spreading of the heat source to realize the layer-by-layer movement of the heat source by establishing a heat source model, setting an analysis step and a death unit; by adopting the method, the temperature history of the formed part and the relation among the channels and the layers can be analyzed, and the sensitivity degree of a molten pool relative to each parameter can be deeply compared by adjusting different process parameters, so that a reasonable process parameter range is screened. The invention is more true than single-channel and single-channel multilayer numerical simulation heat transfer, and provides theoretical support for actual printing.
Description
Technical Field
The invention relates to the technical field of additive processing, in particular to a temperature field numerical simulation method for SLM multilayer multi-channel forming.
Technical Field
The Selective Laser Melting (SLM) additive manufacturing technology has wide application prospect in the aspect of preparing high-performance complex metal components. The processing of shaped parts by SLM technology involves a complex series of physical metallurgical bonding phenomena, the quality of organization and performance being directly dependent on the choice of shaping process parameters. Therefore, in order to obtain the formed part with complete shape, compact structure and excellent performance, the change rule of the temperature of each point of the metal part along with time in the SLM process must be deeply known, and the optimal forming process parameters must be reasonably selected according to the material characteristics.
The forming process in which laser energy is absorbed and converted into heat energy is complicated, and excessive heat may cause problems such as deformation, cracks, and residual stress of parts, while too little heat may cause incomplete melting and bonding of metal powder. Therefore, heat is one of the key factors in the SLM forming process, but the conventional method is difficult to accurately measure, so that a numerical simulation method is adopted to analyze the temperature field in the forming process, and the method is an effective way for solving the problem.
The patent 201911360583.8 discloses a temperature field numerical simulation method in an SLM forming process, which is based on a finite difference principle and adopts a unit nesting method to simulate the temperature field, wherein the method only considers a heat transfer strategy, does not consider a forming strategy, does not simultaneously know the relation between channels and layers, and is difficult to determine a reasonable process parameter range.
Disclosure of Invention
The invention provides a temperature field numerical simulation method for an SLM multi-layer multi-channel forming process, which comprises the steps of carrying out temperature process and relation among channels, layers on a forming piece in the SLM multi-layer multi-channel forming process, and deeply comparing sensitivity degree of a molten pool relative to each parameter by adjusting different process parameters so as to screen out reasonable process parameter ranges.
In order to achieve the above purpose, the invention discloses a temperature field numerical simulation method for an SLM multilayer multipass forming process, which is characterized in that: the method comprises the following steps:
step S1, a temperature field simulation model is established: establishing a three-dimensional model of a forming part and a substrate in three-dimensional modeling software, respectively endowing the forming part and the substrate with material properties, and setting boundary conditions;
step S2, dividing the unit refinement grid: dispersing the three-dimensional model of the formed piece and the three-dimensional model of the substrate into a regular hexahedral unit E according to three directions of length X, width Y and height Z 1 Wherein the width of the Y direction and the single channel are consistent with the diameter of the laser spot of the heat source; the hexahedral unit of the substrate is finely divided to obtain a grid unit E 2 The length of the thinned grid unit is x, the width is y, and the height is z, wherein the x, y and z directions are consistent with the X, Y, Z directions.
Step S3, a heat source model is established: firstly, a process parameter range is drawn up through pre-simulation, then, a time step and a scanning strategy of each channel are determined, a Gaussian movement heat source equation of each channel is established, the equation establishes a relation between a position function and time, a space domain is scattered to the time domain, laser heat sources are loaded to different positions at different moments through cyclic loading, then, the maximum allowable calculation time step is calculated by combining the sizes of hexahedral units E1 and E2 and the thermal physical parameters of a forming part material property, a substrate material property and a powder material;
step S4, calculating a temperature field: according to the Gaussian moving heat source equation and the scanning strategy, starting to simulate the SLM forming process, and obtaining a numerical simulation result of a temperature field in the SLM forming process, wherein the calculation result comprises a temperature change process of each node unit in the whole forming process;
step S5, temperature field analysis: according to the temperature change process of each node unit in the whole forming process, key nodes in the process are selected to analyze and compare the sensitivity degree of each parameter to a temperature field, and reasonable technological parameters of laser forming power and scanning speed of materials used for forming the part and the substrate are obtained according to analysis and comparison results.
The above scheme is further defined, in the step S1, the substrate material property is a thermal property parameter that varies with temperature, including a thermal conductivity coefficient, a density, a specific heat capacity, and an enthalpy, the formed member is in a powder form, and the material property is represented by the formulaAnd->Calculating to obtain the corresponding powder material property, wherein rho is the density of the powder state,for the porosity between powder particles ρ g Is of gas phase density ρ s Is of solid density, K e Is the heat conductivity coefficient in the powder state; k is the heat conductivity coefficient in the physical state; phi is the porosity of the powder; n is a macroscopic coordination coefficient; c is the average contact radius between particles; r is the average radius of the particles in the powder.
The above scheme is further defined, in the step S1, the boundary conditions include that during the SLM processing, heat convection is arranged between the side surface of the substrate, the upper surface except the powder bed and the upper surface of the powder bed and the surrounding environment, and the heat convection exchange condition is represented by the formula-Representation, where k e Is the coefficient of thermal conductivity of the powder bed; alpha is the thermal convection coefficient of the surface of the workpiece; t (T) a Is the ambient medium temperature; t (T) s The surface temperature of the workpiece; sigma is the bostein constant; epsilon is the heat radiation coefficient; q is the laser heat flux density.
The above scheme is further defined, in the step S3, the method of defining the process parameter range by pre-simulation includes determining the approximate forming power and scanning speed of the material used for forming the part and the substrate, calculating the scanning time step by speed, simulating the preliminary input parameters, and then performing the key observation and evaluation on the simulation result, wherein when the laser scanning reaches the second layer, the forming state of the first layer is taken as the evaluation standard, when the laser heat source of the selected process parameter scans the second layer, the forming layer surface temperature at the same position is the lower limit of the process parameter if the material melting point is not reached, the laser power is lower or the scanning speed is faster, the forming layer is not molten pool, the interlayer lap joint is seriously affected, the upper limit of the process parameter is selected by 20% -40% of the interlayer lap joint rate, the depth of the molten pool is judged, the lap joint rate is the upper limit of the process parameter when the lap joint rate exceeds 40%, the laser power is higher or the scanning speed is lower, the forming layer is excessively melted, and the forming quality and efficiency are seriously affected.
Further limiting the above scheme, in the step S3, the gaussian moving heat source equation is as follows
Wherein q is the power density of the laser, A is the absorptivity of the forming material to the laser; p is the input laser power; r is the radius of a laser spot; x is x 2 +y 2 Is the square of the distance from any point of the powder bed to the center of the light spot.
In step S3, the scanning strategy uses a cyclic scanning path, the analysis step length of each layer is the time when all forming channels are scanned currently plus the reserved powder spreading time for each layer, the corresponding time of each layer is adjusted after the speed is changed, the position change formula is optimized, any unit position in the space in the SLM multi-layer multi-channel forming process is represented by the point coordinates of the geometric center, namely F (x, y, z, t) =f (o±vt, y, nd, t), wherein o is the initial position of each forming channel, v is the scanning speed, n is the scanning layer number, and d is the powder layer thickness; after optimization, when the speed value is changed, the loading time of the heat source is related, and the heat source formula is 2 x A x P/(pi R) 2 )*exp((-2/R 2 )*(({X}-(x 0 )-v*{TIME})^2+({Y}-(y 0 ) 2), wherein A is the absorptivity of the forming material to the laser, P is the input laser power, R is the laser spot radius, x 0 For the scan at the start pointx coordinate, v is laser scanning speed, TIME is scanning TIME, y 0 Is the y-coordinate of the scanning process.
In step S5, the number of key nodes in each layer is 3, the positions of the key nodes are the midpoints of each channel, the analysis and comparison content is that the sensitivity degree analysis and comparison of each parameter to the temperature field are performed for the selected key nodes, and the midpoints of each channel of the formed part are selected and marked, including the temperature change under different powers and different speeds, the temperature and the existence time of a molten pool under different powers and different speeds, the fusion depth temperature gradient under different powers and different speeds, the overlap edges under different powers and different speeds, the cooling rates under different powers and different speeds and the width-depth ratio.
Compared with the prior art, the invention has the following advantages: the temperature field simulation is carried out by adopting the method, so that the time for manually updating the scanning distance is not needed when the scanning speed is changed as before, the workload is further reduced, and the error rate is reduced; the method can accurately simulate the temperature change of the heat source near the point, obtain the sensitivity degree of the molten pool to each technological parameter in the simulation, and purposefully adjust the parameters according to the specific molten pool state, so that the parameters in a small range are changed, the state of the molten pool is effectively improved, the forming process is helped to be optimized, and the printing quality and the part performance are improved.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a top view of a temperature field simulation model size division;
FIG. 3 is a front view of a temperature field simulation model sizing;
FIG. 4 is a diagram of a scanning strategy and special point markers;
FIG. 5 is a graph of temperature simulation results;
FIG. 6 is a temperature cloud plot at a power of 250W and a speed of 1000 mm/s;
FIG. 7 bath temperature and residence time at point 2 at different power levels;
FIG. 8 bath temperature and residence time at point 2 at different rates;
wherein: 1. a substrate, 2, a molded body.
Detailed Description
In order to make the purpose and technical scheme of the invention clearer and easier to understand. The present invention will now be described in further detail with reference to the drawings and examples, which are given for the purpose of illustration only and are not intended to limit the invention thereto.
Referring to fig. 1, a temperature field numerical simulation method for an SLM multilayer multipass forming process includes the steps of:
step S1: the method comprises the steps of establishing a temperature field simulation model, wherein the layers on the substrate are not less than 3 layers, the channels on the substrate are not less than 3 channels, the size of the formed part is 0.75mm multiplied by 0.225mm multiplied by 0.09mm and divided into 3 layers, each layer is 30 mu m, the size of the substrate is 1.6mm multiplied by 1mm multiplied by 0.4mm, corresponding material properties are given to the formed part and the substrate, and the material properties of the substrate are thermal physical parameters of the JMatPro software, such as heat conductivity, density, specific heat capacity, enthalpy and the like, which change along with the temperature. The material of the formed piece is powder, the material attribute is calculated to obtain the corresponding powder material attribute by the formulaAnd->Calculated, wherein ρ is the density of the powder state, < >>For the porosity between powder particles ρ g Is of gas phase density ρ s Is of solid density, K e Is the heat conductivity coefficient in the powder state; k is the heat conductivity coefficient in the physical state; phi is the porosity of the powder; n is a macroscopic coordination coefficient; c is the average contact radius between particles; r is the average radius of the particles in the powder.
In the SLM processing process, the preheating temperature is set to be 100 ℃, the forming bin is filled with protective gas, the side surface of the matrix, the upper surface except the powder bed and the upper surface of the powder bed are in thermal convection with the surrounding environment, and the material at the boundary belongs to the third class of boundary conditionsThe material exchanges heat with the medium. Adding heat convection in ANSYS set boundary condition, and carrying out heat exchange between material and medium at boundary by the formula-Representation, where k e Is the coefficient of thermal conductivity of the powder bed; alpha is the thermal convection coefficient of the surface of the workpiece; t (T) a Is the ambient medium temperature; t (T) s The surface temperature of the workpiece; sigma is the bostein constant; epsilon is the heat radiation coefficient; q is the laser heat flux density.
Latent heat processing is based on SLM processing principles, and the temperature field considers that the powder material can undergo a state change from melting to solidification in the analysis simulation actual processing, and the change involves the problem of absorbing and releasing the latent heat of the phase change of the material itself, so that the latent heat needs to be processed. The latent heat of treatment of the invention adopts a heat enthalpy method, namely the latent heat is defined by the heat enthalpy of input changing along with the temperature, and can be calculated by a formula H= [ pi ] cdT, wherein H is the heat enthalpy, rho is the material density, c is the specific heat capacity of the material, and T is the temperature.
Step S2: dividing the unit refinement grid: dividing the three-dimensional model of the formed part and the substrate obtained in the step S1 according to the set unit size to obtain a plurality of hexahedral units E 1 The hexahedral cells in the set area are thinned and divided to obtain grid cells E with smaller size 2 The method comprises the steps of carrying out a first treatment on the surface of the As shown in fig. 2 and 3, the substrate adopts a hexahedral unit E 1 The mesh division is 0.08mm multiplied by 0.08mm, and the forming piece adopts a thinned hexahedral unit E 2 Meshing 0.025mm by 0.030mm.
Step S3: and (3) establishing a heat source model: first, the rough technological parameter range is planned through pre-simulation, and the specific operation is as follows by taking AI7075 as an example: the method comprises the steps of determining the approximate forming power and scanning speed of the material through inquiring data, calculating the scanning time step through speed, simulating preliminary input parameters, carrying out key observation and evaluation on simulation results, wherein when laser scanning reaches a second layer, the forming state of a first layer is taken as an evaluation standard, when a laser heat source of selected process parameters is used for scanning to the position of the second layer, if the surface temperature of a forming layer positioned at the same position at the moment can reach the melting point of the material, the lower limit of the process parameters is the lower limit of the process parameters, which means that the laser power is lower or the scanning speed is higher, the forming layer cannot be melted, the interlayer lap joint is seriously affected, the upper limit of the process parameters is selected, the upper limit of the process parameters can be judged through the depth of the melted pool by 20% -40% of the interlayer lap joint rate, and the lap joint rate is the upper limit of the process parameters when the lap joint rate exceeds 40%, which means that the laser power is higher or the scanning speed is lower, the forming layer is excessively melted, and the forming quality and the efficiency are seriously affected.
Selecting representative parameter collocation according to the screened technological parameter range, determining the time step and scanning strategy of each channel, enabling the laser energy of the laser to be more consistent with Gaussian distribution, enabling a plane Gaussian heat source model to be a heat source model with more use times, and inputting a formula in an ANSYS function editorGenerating an APDL command stream, wherein A is the absorptivity of the forming material to laser, P is the input laser power, R is the laser spot radius, and x 2 +y 2 Taking the time used by each track and the reserved powder spreading time of each layer into consideration for squaring the distance between any point of the powder bed and the center of the light spot, and calculating the maximum allowable calculation time step t according to the time required by the node temperature of the material to be reduced to the room temperature state from the highest in the simulation process so as to ensure convergence of heat transfer calculation.
Step S4: calculating a temperature field, and starting to simulate the SLM forming process according to the Gaussian moving heat source equation and the scanning strategy, so that a numerical simulation result of the temperature field in the SLM forming process can be obtained, wherein the calculation result comprises the temperature change process of each node unit in the whole forming process; the SLM forming process is that the materials are grown layer by layer, and in the temperature field analysis process, the materials participate layer by layer, which is different from the quantitative overall participation of the materials in the conventional finite element analysis process, and in order to accurately restore the actual technological process, a 'unit life-death' technology is introduced to effectively represent the layer-by-layer growth process of the powder materials.
Wherein the selection principle of the scanning strategy is to reduce the moving distance of the laser, maintain the continuity of scanning, and avoid the need of laser re-scanning after the single-channel scanningThe next scanning is started after the left end is moved, so that the forming efficiency is improved; and the reciprocating scanning strategy can more uniformly distribute energy in the whole construction structure, so that the thermal stress concentration and buckling deformation generated by repeated heat receiving of a single-side area are reduced. The scheme adopts a bad scanning path, and particularly referring to fig. 4, a first path is scanned from a left starting point to a right ending point, then a laser heat source is shifted by one track width, and a second path is scanned from the right starting point to the left ending point. The analysis step length of each layer is the time when all forming channels are scanned currently plus the reserved powder spreading time for each layer, a position change formula is optimized, and any unit position in a space in the multi-layer forming process of the SLM is represented by the point coordinates of the geometric center of the unit, namely F (x, y, z, t) =F (o+/-vt, y, nd, t), wherein o is the initial position of each forming channel, v is the scanning speed, n is the scanning layer number, and d is the thickness of the powder layer; starting to simulate the multilayer multi-channel forming process of the SLM according to the Gaussian moving heat source model and the scanning strategy in the step S3, and obtaining a numerical simulation result of a temperature field in the multilayer multi-channel forming process of the SLM, wherein the result comprises a temperature change process of each node unit in the whole forming process; the optimized heat source formula is 2 x A x P/(pi R) 2 )*exp((-2/R 2 )*(({X}-(x 0 )-v*{TIME})^2+({Y}-(y 0 ) 2), wherein A is the absorptivity of the forming material to the laser, P is the input laser power, R is the laser spot radius, x 0 For the x-coordinate at the scan start point, v { TI ME } is the distance travelled by the scan process, y 0 The method is characterized in that the method is a y coordinate of a scanning process, wherein when the distance travelled by the scanning process is changed from the original fixed input to a speed value in an APDL code, the loading time of a heat source can be related, the accuracy of parameters is ensured, the loading synchronism of the heat source can be maintained, the workload of process parameter replacement in the APDL code is reduced, and key elements of a temperature field such as node temperature, molten pool temperature and existence time, temperature gradient, molten pool width and depth and the like are calculated through an insertion module and a selected node position.
Step S5: temperature field analysis, namely, deriving a temperature cloud chart according to the forming process determined in the step S4, analyzing and summarizing the temperature change process of each node unit, and analyzing and comparing the sensitivity degree of each parameter to the temperature field as shown in figure 5; adjusting process parameters such as different laser powers and scanning speeds by changing corresponding values in the generated APDL code, reading a temperature curve graph of a key node by selecting a key position in the key node through an inserted node, and analyzing the sensitivity degree of the peak change of temperature and the required time to the parameters by comparing the temperature change; summarizing temperature field data under each process collocation parameter, drawing a graph of molten pool temperature and existence time under different process parameters, and comparing and analyzing the sensitivity degree of the highest value of the molten pool temperature and the existence time to the parameters; reading the temperature gradient of the key node of the molten pool, and comparing and analyzing the sensitivity degree of the temperature gradient to the parameters according to the variation amplitude of the temperature gradient under different parameters to obtain that the temperature gradient of the molten pool is more sensitive to power; reading the width of a key node molten pool and the temperature of the depth edge, comparing the melting point of a forming material, and ensuring the edge lap quality through the remelting rate of 20% -40%; and (3) reading the cooling rate of the key node and the width-depth ratio of the molten pool, and comparing and analyzing the sensitivity degree of the cooling rate and the width-depth ratio to parameters to obtain that the cooling rate is more sensitive to the scanning speed and the width-depth ratio of the molten pool is more sensitive to the power.
The temperature field simulation is carried out by adopting the method, the time for manually updating the scanning distance is not needed when the scanning speed is changed as before, and the workload is further reduced, and the error rate is reduced. The method can accurately simulate the temperature change of the heat source near the point, obtain the sensitivity degree of the molten pool to each technological parameter in the simulation, and purposefully adjust the parameters according to the specific molten pool state, so that the parameters in a small range are changed, the state of the molten pool is effectively improved, the forming process is helped to be optimized, and the printing quality and the part performance are improved.
Example 1
The material of the forming layer in the temperature field simulation is Al7075 powder, the main chemical components are shown in table 1, the thermophysical parameters of the Al7075 powder material are shown in table 2 through the thermophysical formulas, the laser adopts a reciprocating scanning strategy, the technological parameters are shown in table 3, and the simulation is carried out according to the method, and the results are as follows.
TABLE 1 main chemical composition of Al7075
| Element(s) | Si | Mg | Cr | Zn | Fe | Ti | Cu | Mn | Al |
| Content/wt.% | <0.01 | 2.46 | 0.22 | 5.45 | <0.10 | <0.05 | 1.62 | <0.10 | Allowance of |
TABLE 2 thermophysical parameters of Al7075 powder materials
TABLE 3 finite element numerical simulation parameters for SLM process
| Parameters (parameters) | Numerical value |
| Laser absorptivity A | 0.1 |
| Powder layer thickness, d (μm) | 30 |
| Spot radius, R (μm) | 37.5 |
| Scan pitch, s (μm) | 75 |
| Laser power, P (W) | 150,200,250,300 |
| Scan rate, v (mm/s) | 800,1000,1200,1600 |
| Initial temperature, T 0 (K) | 373.15 |
FIG. 6 is a temperature cloud plot at a power of 250W and a speed of 1000mm/s, wherein the central region of each layer at the same position is selected to minimize the edge interference, the circle enclosed by the black dotted line in FIG. 6 represents the melting line (910K) of Al7075, and the temperature cloud plot shows asymmetry as a result, because the formed solid material has obvious difference from the thermal physical properties of the material in the powder state, and the heat is more easily conducted to the solid material side. The temperature field isotherm distribution of the surface of the molten pool is similar to ellipse, the moving direction of the laser heat source, namely the front isothermal line of the molten pool is denser than the rear isothermal line, the width and the length of the molten pool of the first layer, the second layer and the third layer are increased, the width of the molten pool of the second layer is increased by 6.6 percent, the length is increased by 15.2 percent, and the depth is increased by 8.4 percent. The third layer has a bath width increased by 8.2% and a length increased by 20.6% and a depth increased by 9.3% over the second layer. The method is characterized in that obvious heat accumulation effect exists in the scanning process, the method is verified with the actual technological process and other similar temperature field simulation cases, along with the gradual lamination of the deposition layers, the heat loss caused by heat conduction is effectively weakened, the temperature of a molten pool generated by a higher powder layer is higher, the size is larger, the remelting rate has a larger influence on the lap joint proportion of the molten pool, excessive secondary heating of forming cooling melt channels is caused by overlarge proportion, the melting condition of metal powder is directly influenced by the overlarge proportion, and the reasonable range of the molten pool can be selected by controlling the remelting rate.
Referring to fig. 7, on the premise of keeping the speed, the power is increased from 150W to 300W, the temperature change curve almost shows a linear function proportional relationship, on the premise of keeping the scanning speed v=1000 mm/s, when the laser power is increased from 150W to 300W, the temperature of the molten pool is increased from 1 909.3k to 3.508.5 k, and the existence time of the molten pool is increased from 0.09ms to 0.19ms; referring to fig. 8, while maintaining the laser power p=250w, the temperature of the molten pool is reduced from 3 074.7k to 2 646k and the molten pool existing time is shortened from 0.19ms to 0.10ms when the scanning speed is increased from 800mm/s to 1600 mm/s. When lower speeds are used, the bath state is relatively stable, and heat can be more fully absorbed to maintain temperature and thus slow melting point temperature changes. With the increase of the speed, the molten pool becomes obviously dynamic, the heat supply cannot follow the demand, and the melting point temperature is rapidly reduced within a certain range. When the speed reaches a certain value, the molten pool forms a special flow mode, and the heat absorption efficiency is better than that of a dynamic transition stage, so that the descending trend of the melting point temperature is slowed down. When the laser power is low or the scanning speed is high, the formed molten pool temperature is low, and the existence time is short.
Through the analysis, the size of the molten pool is gradually increased along with the increase of the laser power; as the scan speed increases, the size of the melt pool gradually decreases. The aspect ratio of the melt pool is more significantly affected by the laser power. On the premise that the melting depth of a molten pool is ensured to be larger than the thickness of a powder layer, the highest temperature of the molten pool is higher than the melting point (910K) of powder, and by comparing various parameters of temperature fields under different power matching different scanning speeds, reasonable technological parameters of the high-strength aluminum alloy Al7075 powder material prepared by adopting an SLM technology are 250-300W of laser power and 800-1000 mm/s of laser scanning speed.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (7)
1. A temperature field numerical simulation method for an SLM multi-layer multi-channel forming process is characterized by comprising the following steps of: the method comprises the following steps:
step S1, a temperature field simulation model is established: establishing a three-dimensional model of a forming part and a substrate in three-dimensional modeling software, respectively endowing the forming part and the substrate with material properties, and setting boundary conditions;
step S2, dividing the unit refinement grid: dispersing the three-dimensional model of the formed piece and the three-dimensional model of the substrate into a regular hexahedral unit E according to three directions of length X, width Y and height Z 1 Wherein the width of the Y direction and the single channel are consistent with the diameter of the laser spot of the heat source; the hexahedral unit of the substrate is finely divided to obtain a grid unit E 2 The length of the refined grid unit is x, the width of the refined grid unit is y, and the height of the refined grid unit is z, wherein the x, y and z directions are consistent with the X, Y, Z directions;
step S3, a heat source model is established: firstly, a process parameter range is drawn up through pre-simulation, then, a time step and a scanning strategy of each channel are determined, a Gaussian movement heat source equation of each channel is established, the equation establishes a relation between a position function and time, a space domain is scattered to the time domain, laser heat sources are loaded to different positions at different moments through cyclic loading, then, the maximum allowable calculation time step is calculated by combining the sizes of hexahedral units E1 and E2 and the thermal physical parameters of a forming part material property, a substrate material property and a powder material;
step S4, calculating a temperature field: according to the Gaussian moving heat source equation and the scanning strategy, starting to simulate the SLM forming process, and obtaining a numerical simulation result of a temperature field in the SLM forming process, wherein the calculation result comprises a temperature change process of each node unit in the whole forming process;
step S5, temperature field analysis: according to the temperature change process of each node unit in the whole forming process, key nodes in the process are selected to analyze and compare the sensitivity degree of each parameter to a temperature field, and reasonable technological parameters of laser forming power and scanning speed of materials used for forming the part and the substrate are obtained according to analysis and comparison results.
2. A method of temperature field numerical simulation of an SLM multilayer multipass forming process according to claim 1, characterized by: in the step S1, the substrate material properties are thermophysical parameters including thermal conductivity, density, specific heat capacity and enthalpy, and the formed part is powder, and the material properties are represented by the formulaAnd->Calculating to obtain corresponding powder material properties, wherein ρ is the density of the powder state, < >>For the porosity between powder particles ρ g Is of gas phase density ρ s Is a solid-state density of the material,K e is the heat conductivity coefficient in the powder state; k is the heat conductivity coefficient in the physical state; phi is the porosity of the powder; n is a macroscopic coordination coefficient; c is the average contact radius between particles; r is the average radius of the particles in the powder.
3. A method of temperature field numerical simulation of an SLM multilayer multipass forming process according to claim 1, characterized by: in the step S1, the boundary conditions include that heat convection is arranged between the side surface of the substrate, the upper surface except the powder bed and the upper surface of the powder bed and the surrounding environment in the SLM processing process, and the heat convection exchange condition is represented by the formulaRepresentation, where k e Is the coefficient of thermal conductivity of the powder bed; alpha is the thermal convection coefficient of the surface of the workpiece; t (T) a Is the ambient medium temperature; t (T) s The surface temperature of the workpiece; sigma is the bostein constant; epsilon is the heat radiation coefficient; q is the laser heat flux density.
4. A method of temperature field numerical simulation of an SLM multilayer multipass forming process according to claim 1, characterized by: in the step S3, the method of defining the process parameter range by pre-simulation includes determining the approximate forming power and scanning speed of the material used by the forming piece and the substrate, calculating the scanning time step by speed, simulating the preliminary input parameters, and then performing important observation and evaluation on the simulation result, wherein when the laser scanning reaches the second layer, the forming state of the first layer is used as an evaluation standard, when the laser heat source of the selected process parameters scans the second layer, if the surface temperature of the forming layer at the same position of the first layer fails to reach the melting point of the material, the lower limit of the process parameters is determined, the laser power is lower or the scanning speed is higher, the forming layer fails to melt pool, the interlayer lap joint is seriously affected, the upper limit of the process parameters is selected by 20% -40% of the interlayer lap joint rate, the lap joint rate is determined by the depth of the melt pool, and the upper limit of the process parameters is determined to be higher when the laser power is higher or the scanning speed is lower, the forming layer is excessively melted, and the forming quality and efficiency are seriously affected.
5. A method of temperature field numerical simulation of an SLM multilayer multipass forming process according to claim 1, characterized by: in the step S3, the Gaussian motion heat source equation is as follows
Wherein q is the power density of the laser, A is the absorptivity of the forming material to the laser; p is the input laser power; r is the radius of a laser spot; x is x 2 +y 2 Is the square of the distance from any point of the powder bed to the center of the light spot.
6. A method of temperature field numerical simulation of an SLM multilayer multipass forming process according to claim 1, characterized by: in the step S3, the scanning strategy adopts a cyclic scanning path, the analysis step length of each layer is the time when all the forming channels are scanned currently plus the reserved powder spreading time for each layer, the corresponding time of each layer is adjusted after the speed is changed, the position change formula is optimized, any unit position in the space in the SLM multi-layer multi-channel forming process is represented by the point coordinates of the geometric center, namely F (x, y, z, t) =f (o±vt, y, nd, t), wherein o is the initial position of each layer of forming, v is the scanning speed, n is the scanning layer number, and d is the powder layer thickness; after optimization, when the speed value is changed, the loading time of the heat source is related, and the heat source formula is 2 x A x P/(pi R) 2 )*exp((-2/R 2 )*(({X}-(x 0 )-v*{TIME})^2+({Y}-(y 0 ) 2), wherein A is the absorptivity of the forming material to the laser, P is the input laser power, R is the laser spot radius, x 0 The x coordinate of the scanning starting point is, v is the laser scanning speed, TIME is the scanning TIME, y 0 Is the y-coordinate of the scanning process.
7. A method of temperature field numerical simulation of an SLM multilayer multipass forming process according to claim 1, characterized by: in step S5, the number of key nodes in each layer is 3, the positions of the key nodes are midpoints of each channel, the analysis and comparison content is that the sensitivity degree analysis and comparison of each parameter to a temperature field are performed for the selected key nodes, and the midpoints of each channel of the formed part are selected and marked, including temperature changes under different powers and different speeds, molten pool temperatures and existence times under different powers and different speeds, fusion depth temperature gradients under different powers and different speeds, overlapping edges under different powers and different speeds, cooling rates under different powers and different speeds, and a width-depth ratio.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311105400.4A CN117216962A (en) | 2023-08-30 | 2023-08-30 | Temperature field numerical simulation method for multilayer multi-channel shaping of SLM (selective laser deposition) |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311105400.4A CN117216962A (en) | 2023-08-30 | 2023-08-30 | Temperature field numerical simulation method for multilayer multi-channel shaping of SLM (selective laser deposition) |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN117216962A true CN117216962A (en) | 2023-12-12 |
Family
ID=89045366
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202311105400.4A Pending CN117216962A (en) | 2023-08-30 | 2023-08-30 | Temperature field numerical simulation method for multilayer multi-channel shaping of SLM (selective laser deposition) |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN117216962A (en) |
-
2023
- 2023-08-30 CN CN202311105400.4A patent/CN117216962A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP5712306B2 (en) | Manufacturing method of three-dimensional body | |
| CN111283192B (en) | Laser powder bed melting additive manufacturing molten pool monitoring and pore control method | |
| CN105718690A (en) | Laser 3D printing molten bath solidification behavior numerical simulation method based on time and space active tracking | |
| CN105945284B (en) | The method and device of laser 3D printing metal works | |
| RU2450891C1 (en) | Method of part sintering by laser layer-by-layer synthesis | |
| CN105112708A (en) | Rapid manufacturing method for laser remelting scanning carbide dispersion strengthened aluminum alloy | |
| CN105710366B (en) | A kind of scan method for increasing material manufacturing three-dimensional body | |
| CN111595783B (en) | Material laser absorption rate measuring system and method | |
| CN113059188B (en) | Method for processing parts by using laser melting forming device | |
| CN111112621A (en) | Method for predicting and monitoring shape and size of laser directional energy deposition molten pool | |
| CN106529051A (en) | Method for determining heat source model parameters of single wire submerged arc welding numerical simulation | |
| CN109317675A (en) | A kind of pure molybdenum precinct laser fusion preparation method of high-compactness | |
| CN109571942B (en) | Three-dimensional object manufacturing apparatus, method thereof, and computer storage medium | |
| Long et al. | Numerical simulation of thermal behavior during laser metal deposition shaping | |
| Upadhya et al. | Modelling the investment casting process: a novel approach for view factor calculations and defect prediction | |
| CN110170652A (en) | A kind of molding face printing equipment of Variable Area and its Method of printing | |
| Cao | Numerical investigation on molten pool dynamics during multi-laser array powder bed fusion process | |
| CN117216962A (en) | Temperature field numerical simulation method for multilayer multi-channel shaping of SLM (selective laser deposition) | |
| CN115238605A (en) | Numerical simulation method for predicting surface quality of SLM (Selective laser melting) single melting channel | |
| CN109047759B (en) | Laser scanning method for improving interlayer strength and reducing warping deformation | |
| CN113523302B (en) | Method for inhibiting burning loss of selective laser melting formed magnesium alloy | |
| Lin et al. | Optimization of Surface Roughness and Density of Overhang Structures Fabricated by Laser Powder Bed Fusion | |
| US20200039145A1 (en) | Powder-Bed-Based Additive Manufacture of a Workpiece | |
| EP2918359A1 (en) | Sintering particulate material | |
| CN109885946B (en) | Method for determining energy distribution of composite heat source and welding simulation method |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |