CN112364449B - Method for predicting surface roughness of additive manufactured part - Google Patents
Method for predicting surface roughness of additive manufactured part Download PDFInfo
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- 230000003746 surface roughness Effects 0.000 title claims abstract description 182
- 238000000034 method Methods 0.000 title claims abstract description 34
- 239000000654 additive Substances 0.000 title claims abstract description 31
- 230000000996 additive effect Effects 0.000 title claims abstract description 31
- 238000013461 design Methods 0.000 claims abstract description 37
- 238000013178 mathematical model Methods 0.000 claims abstract description 33
- 238000004519 manufacturing process Methods 0.000 claims abstract description 18
- 239000000843 powder Substances 0.000 claims description 23
- 239000002245 particle Substances 0.000 claims description 14
- 239000000155 melt Substances 0.000 claims description 6
- 238000010586 diagram Methods 0.000 description 11
- 238000002844 melting Methods 0.000 description 10
- 230000008018 melting Effects 0.000 description 10
- 230000000694 effects Effects 0.000 description 8
- 238000012545 processing Methods 0.000 description 5
- 239000002184 metal Substances 0.000 description 4
- 239000007787 solid Substances 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
- 238000009825 accumulation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000013499 data model Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/10—Geometric CAD
- G06F30/17—Mechanical parametric or variational design
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y50/00—Data acquisition or data processing for additive manufacturing
- B33Y50/02—Data acquisition or data processing for additive manufacturing for controlling or regulating additive manufacturing processes
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2111/00—Details relating to CAD techniques
- G06F2111/10—Numerical modelling
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/10—Additive manufacturing, e.g. 3D printing
Abstract
A method for predicting surface roughness of an additive manufactured part belongs to the technical field of additive manufacturing. The method for predicting the surface roughness of the additive manufactured part comprises the following steps: setting a placement angle and a slice layer thickness to obtain the inclination angles of the upper surface and the lower surface of each inclined area of the part, calculating the theoretical values of the upper surface roughness and the lower surface roughness of each inclined area of the part through a mathematical model of the surface roughness, judging whether the surface roughness of the part meets the design requirement, if so, manufacturing the part according to the current placement angle and slice layer thickness, and if not, adjusting the placement angle or slice layer thickness until the surface roughness of the part meets the design requirement, and manufacturing the part according to the current placement angle and slice layer thickness. The method for predicting the surface roughness of the additive manufactured part can predict the roughness of the part under different placing angles and different slice thicknesses, provides process guidance for SLM forming, reduces the workload and improves the working efficiency.
Description
Technical Field
The invention relates to the technical field of additive manufacturing, in particular to a method for predicting surface roughness of an additive manufactured part.
Background
Additive manufacturing (Additive Manufacturing, AM) is based on the discrete-stacking principle, part models are subjected to layered slicing by using layered slicing software, powder layer-by-layer melting, solidification and layer-by-layer accumulation are completed through data processing and numerical control system control, and finally rapid part forming is completed. The selective laser melting (selective laser melting, SLM) technology has been attracting attention in recent years as a newly developed additive manufacturing technology, because it can directly process powder into parts with complex shapes and high precision. As shown in figure 1, in the selective laser melting process, under the protection of inert atmosphere, a computer is used for controlling the laser to selectively scan the powder bed so as to selectively melt powder particles, solidify the powder particles into a solid layer, then a layer of powder is paved on the solid layer formed before, the laser is used for selectively scanning the powder bed again, and the processes of powder paving and laser selective powder melting are circulated until the part processing is completed.
The SLM technology can theoretically form any complex metal part, but in the actual production and processing process, the dimensional accuracy of the part cannot be guaranteed, and the problems of high surface roughness and the like are easy to occur. In order to reduce defects in the process of forming the sample by the SLM, the forming quality of the sample is improved, a researcher adopts a mode of adding a support to improve the forming quality of the part, and the support is removed after forming. While adding support can improve the quality of the forming of a portion of the part, for more complex samples, the support inside the formed sample is difficult to remove, affecting the surface roughness of the part and even the assembly of subsequent parts.
For a part without a supporting structure, according to the discrete principle of SLM forming, after slicing treatment, the outer surface of a solid model is composed of a series of contour surfaces of slicing layers, as shown in fig. 2, when a certain angle exists between the model surface and the forming direction of the part, a step effect is generated, in the figure, an X sitting axis represents the laser scanning direction, a Z sitting axis represents the growth direction of additive manufacturing, the longitudinal section contour of the part is a circular curve, the included angle between the surface of the part and the forming direction is continuously changed, so that the overhanging surface of the part presents a step appearance, the step width w can be represented as w=h cot alpha, h is the layering thickness, alpha is the inclined angle between the inclined plane (the inclined plane on the left side of the part) of the part and the horizontal plane (X axis), and the larger the layer thickness is, the more obvious the step effect is when the inclined angle is fixed; the smaller the α, the more pronounced the step effect, when the layer thickness is constant, and the step width is 0 when α is 90 °, i.e. the step effect disappears. As can be seen from fig. 2, the width of the step effect is affected by the thickness of the slice layer and the inclination angle, and the wider the width is, the larger the surface roughness is. The surface roughness refers to the unevenness of the tiny peaks and valleys of the surface of the formed sample, which belongs to microscopic geometric errors, and the smoother the surface of the sample, the smaller the surface roughness. Since SLM is a layer-by-layer superposition process based on three-dimensional data model slicing processing, it is difficult to avoid layer-to-layer stair-step effects that directly affect surface roughness when shaping overhanging samples.
As shown in fig. 3, the sticky powder is also one of the main factors affecting the roughness of the surface roughness during SLM. The part may have overhang portions without physical support during delamination. In the SLM process, the laser penetration depth needs to be greater than the slice thickness in order to better form the metallurgical bond between layers. Therefore, a powder sticking phenomenon occurs in the formed part, thereby affecting the surface roughness. The size of the inclination angle determines the size of the overhang part without solid support when the thickness of the slice layer is fixed, and the smaller the inclination angle alpha is, the smaller the constraint of the entity on the overhang part is, and the overhang part with high freedom degree is more easy to deform due to the expansion and contraction of the volume of metal powder in the solid-liquid conversion process in the SLM forming process. In addition, the larger the overhang part is, the more laser energy is directly irradiated on the powder bed, and the heat in the molten pool cannot be timely transferred to the periphery due to relatively poor heat conduction capability of the powder, so that the liquid phase state time of the molten pool is prolonged, overhang is easy to generate, the lower surface roughness is increased, and the forming precision is influenced.
Disclosure of Invention
In order to solve the technical problems of step effect and the like of SLM formed parts in the prior art, the invention provides a method for predicting the surface roughness of additive manufactured parts, which can predict the roughness of the parts under different placing angles and different slice layer thicknesses, provide process guidance for SLM forming, reduce the workload and improve the working efficiency.
In order to achieve the above object, the technical scheme of the present invention is as follows:
a method for predicting the surface roughness of an additive manufactured part comprises the following steps:
s1, setting a placement angle of additive manufacturing of parts and setting a slice thickness;
s2, obtaining the inclination angles of the upper surfaces and the lower surfaces of all inclination areas on the part according to the placement angles;
s3, calculating theoretical values of the upper surface roughness of each inclined area of the part through a mathematical model of the upper surface roughness, and simultaneously calculating theoretical values of the lower surface roughness of each inclined area of the part through a mathematical model of the lower surface roughness;
the mathematical model of the upper surface roughness is as follows:
wherein R is ai1 Is the theoretical value of the surface roughness alpha of the ith inclined area of the part i1 The inclination angle of the upper surface of the ith inclination area of the part, h is the slice thickness, a i1 The width of the melt channel is the upper surface of the ith inclined area of the part; i is a positive integer greater than or equal to 1;
the mathematical model of the lower surface roughness is:
wherein R is ai2 Is the theoretical value of the lower surface roughness of the ith inclined area of the part, alpha i2 The inclination angle of the lower surface of the ith inclination area of the part, h is the slice thickness, a i2 Is a partThe bottom width of the melt pool at the lower surface of the ith inclined area;
s4, judging whether the surface roughness of the part meets the design requirement or not:
if the surface roughness of all inclined areas of the part meets the design requirement, namely, the theoretical value of the upper surface roughness of each inclined area of the part is respectively smaller than or equal to the standard value of the upper surface roughness, and meanwhile, the theoretical value of the lower surface roughness of each inclined area of the part is respectively smaller than or equal to the standard value of the lower surface roughness, the part is additionally manufactured according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, that is, the theoretical value of the upper surface roughness of one or more inclined areas of the part is greater than the standard value of the upper surface roughness, or the theoretical value of the lower surface roughness of one or more inclined areas of the part is greater than the standard value of the lower surface roughness, executing step S5;
s5, keeping the thickness of the slice layer unchanged, adjusting the placement angle of the part, and repeating the steps S2 and S3 to obtain the theoretical value of the upper surface roughness of each inclined area of the part and the theoretical value of the lower surface roughness of each inclined area;
s6, judging whether the surface roughness of the part obtained in the step S5 meets the design requirement:
if the surface roughness of all inclined areas of the part meets the design requirement, the part is manufactured in an additive mode according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, executing a step S7;
s7, keeping the placing angle of the part unchanged, reducing the thickness of the slice layer, and repeating the steps S2 and S3 to obtain the theoretical value of the upper surface roughness of each inclined area of the part and the theoretical value of the lower surface roughness of each inclined area;
s8, judging whether the surface roughness of the part obtained in the step S7 meets the design requirement:
if the surface roughness of all inclined areas of the part meets the design requirement, the part is manufactured in an additive mode according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, repeating the step S5 until the surface roughness of all the inclined areas of the part meets the design requirement, and additively manufacturing the part according to the current placement angle and slice layer thickness.
Further, in the step S5, the specific way of adjusting the placement angle of the parts is as follows: the angle of the smallest inclination angle among the inclination angles of the upper surfaces and the lower surfaces of the respective inclination areas of the part is increased.
Further, in the step S7, when the slice layer thickness is reduced, the slice layer thickness is not smaller than the minimum particle diameter of the powder particles.
The invention has the beneficial effects that:
1) The invention provides a mathematical model of the upper surface roughness and a mathematical model of the lower surface roughness of a part manufactured by SLM additive, which are used for predicting the roughness theoretical values of the upper surface and the lower surface of the part, wherein the establishment of the mathematical model mainly considers three technological parameters of a part placement angle, a melt channel width and a slice layer thickness, and the melt channel width is the diameter of a laser spot;
2) According to the invention, the roughness of the upper surface and the lower surface of the part manufactured by SLM additive can be rapidly predicted according to the placement angle of the part and the thickness of the slice layer;
3) The invention provides guidance for subsequent precision measurement, namely, a part with the largest roughness value is found by predicting the surface roughness of the part, the part only needs to detect the roughness value of the part, the workload is reduced, the manpower and the time are saved, and the working efficiency is improved;
4) According to the invention, according to the roughness requirement of the workpiece, the theoretical roughness value is estimated through the upper and lower surface roughness mathematical models, the part placement angle and the slice layer thickness are timely adjusted, the expected surface roughness is achieved, and theoretical guidance is provided for optimization of SLM additive manufacturing process parameters.
Additional features and advantages of the invention will be set forth in part in the detailed description which follows.
Drawings
FIG. 1 is a schematic diagram of a prior art selective laser melting technique;
FIG. 2 is a schematic diagram of a prior art SLM forming process that produces a step effect;
FIG. 3 is a schematic diagram of the powder sticking phenomenon of a part in the prior SLM forming process;
FIG. 4 is a schematic diagram of a mathematical model of the surface roughness of a part during SLM forming according to an embodiment of the invention;
FIG. 5 is a schematic diagram of a mathematical model of the lower surface roughness of a part during SLM forming according to an embodiment of the invention;
FIG. 6 is a schematic diagram of an implementation step of adjusting a placement angle and a slice thickness of a part according to an embodiment of the present invention, wherein (a) is a schematic diagram of an initial placement angle and a slice thickness of the part; (b) a schematic diagram of the parts after the placement angles are adjusted; (c) a schematic view of the part after the thickness of the slice layer is reduced;
FIG. 7 is a schematic view of surface roughness corresponding to different inclination angles of upper and lower surfaces of a part according to an embodiment of the present invention;
fig. 8 is a schematic view of surface roughness corresponding to a region where the inclination angle of a part is minimum according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention.
In order to solve the problems in the prior art, as shown in fig. 1 to 8, the invention provides a method for predicting the surface roughness of an additive manufactured part, which comprises the following steps:
s1, setting a placement angle of additive manufacturing of parts and setting a slice thickness; specifically, selecting a slice layer thickness in a particle size range according to the particle size range of the metal powder;
s2, obtaining the inclination angles of the upper surfaces and the lower surfaces of all inclination areas on the part according to the placement angles; specifically, the inclination angle of the upper surface of each inclined area of the part and the inclination angle of the lower surface of each inclined area of the part are changed by adjusting the placement angle of the part;
s3, calculating theoretical values of the upper surface roughness of each inclined area of the part through a mathematical model of the upper surface roughness, and simultaneously calculating theoretical values of the lower surface roughness of each inclined area of the part through a mathematical model of the lower surface roughness;
the mathematical model of the upper surface roughness is:
wherein R is ai1 Is the theoretical value of the surface roughness alpha of the ith inclined area of the part i1 The inclination angle of the upper surface of the ith inclination area of the part, h is the slice thickness, a i1 The width of the melt channel is the upper surface of the ith inclined area of the part; i is a positive integer greater than or equal to 1;
the mathematical model of the lower surface roughness is:
wherein R is ai2 Is the theoretical value of the lower surface roughness of the ith inclined area of the part, alpha i2 The inclination angle of the lower surface of the ith inclination area of the part, h is the slice thickness, a i2 A bottom width of the molten pool for the lower surface of the ith inclined area of the part;
s4, judging whether the surface roughness of the part meets the design requirement or not:
if the surface roughness of all inclined areas of the part meets the design requirement, namely, the theoretical value of the upper surface roughness of each inclined area of the part is respectively smaller than or equal to the standard value of the upper surface roughness, and meanwhile, the theoretical value of the lower surface roughness of each inclined area of the part is respectively smaller than or equal to the standard value of the lower surface roughness, the part is additionally manufactured according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, that is, the theoretical value of the upper surface roughness of one or more inclined areas of the part is greater than the standard value of the upper surface roughness, or the theoretical value of the lower surface roughness of one or more inclined areas of the part is greater than the standard value of the lower surface roughness, executing step S5;
s5, keeping the thickness of the slice layer unchanged, adjusting the placement angle of the part, and repeating the steps S2 and S3 to obtain the theoretical value of the upper surface roughness of each inclined area of the part and the theoretical value of the lower surface roughness of each inclined area;
s6, judging whether the surface roughness of the part obtained in the step S5 meets the design requirement:
if the surface roughness of all inclined areas of the part meets the design requirement, the part is manufactured in an additive mode according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, executing a step S7;
s7, keeping the placing angle of the part unchanged, reducing the thickness of the slice layer, and repeating the steps S2 and S3 to obtain the theoretical value of the upper surface roughness of each inclined area of the part and the theoretical value of the lower surface roughness of each inclined area;
s8, judging whether the surface roughness of the part obtained in the step S7 meets the design requirement:
if the surface roughness of all inclined areas of the part meets the design requirement, the part is manufactured in an additive mode according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, repeating the step S5 until the surface roughness of all the inclined areas of the part meets the design requirement, and additively manufacturing the part according to the current placement angle and slice layer thickness.
In the invention, the specific mode of whether the surface roughness of the part meets the design requirement is as follows: comparing the theoretical value of the upper surface roughness of each inclined area of the part with the standard value of the upper surface roughness (according to the drawing requirements) respectively, and simultaneously comparing the theoretical value of the lower surface roughness of each inclined area of the part with the standard value of the lower surface roughness (according to the drawing requirements) respectively; if the theoretical values of the upper surface roughness of each inclined area of the part are respectively smaller than or equal to the standard value of the upper surface roughness, and meanwhile, the theoretical values of the lower surface roughness of each inclined area of the part are respectively smaller than or equal to the standard value of the lower surface roughness, namely, the surface roughness of all inclined areas of the part meets the design requirement; if the theoretical value of the upper surface roughness of one or more inclined areas of the part is greater than the standard value of the upper surface roughness, or the theoretical value of the lower surface roughness of one or more inclined areas of the part is greater than the standard value of the lower surface roughness, that is, only one of the theoretical values of the surface roughness of all the inclined areas of the part is greater than the standard value, that is, the surface roughness of the part does not meet the design requirement.
Specifically, in step S5, the specific manner of adjusting the placement angle of the parts is: the angle of the smallest inclination angle among the inclination angles of the upper surfaces and the lower surfaces of the respective inclination areas of the part is increased.
Specifically, in step S7, when the slice thickness is reduced, the slice thickness is not smaller than the minimum particle diameter of the powder particles. In the SLM forming process, slice layer thickness is an important parameter to ensure part surface roughness in addition to tilt angle. It is known from mathematical models of the upper and lower surface roughness of the part that the smaller the slice thickness, the smaller the surface roughness, with other parameters being determined. Therefore, after the inclination angle of the part is determined, the slice layer thickness is selected as small as possible according to the particle size of the metal powder, which is helpful for reducing the surface roughness of the part after SLM forming, that is, when the slice layer thickness is selected, the slice layer thickness is not smaller than the minimum particle size of the powder particles, for example, TC4 powder particle size ranges from 20 μm to 53 μm, and the slice layer thickness should be selected between 20 μm and 53 μm, and the minimum is not lower than 20 μm. However, the thickness of the sliced layer is as large as possible under the condition of ensuring the surface roughness to increase the processing speed.
The prediction method can be executed in additive manufacturing planning software to realize the prediction of the surface roughness of the additive manufactured part.
The principle of the invention is as follows:
as shown in fig. 4The method is characterized in that the method is a schematic diagram of a mathematical model of the upper surface roughness of the part, the selective laser melting is that adjacent melting channels of the same layer are mutually overlapped, adjacent layers are mutually accumulated, and finally the rapid forming process of the part is realized. Based on the principle of SLM forming and combining the characteristics of laser energy density distribution, the longitudinal section of each melting channel is simplified into an arc, the highest point of the melting channel, namely the highest point in the Z coordinate direction of each arc, is the center point of laser, and the width a of the melting channel i1 Establishing a mathematical model of the surface roughness of the part for the diameter of the light spot;
as shown in fig. 5, which is a schematic diagram of a mathematical model of the lower surface roughness of a part, an overhang part without physical support appears in the process of layering and slicing, and in the process of laser scanning, the conditions of powder sticking, edge tilting and the like are easy to occur, so that the lower surface forming angle and the surface roughness are affected. Simplifying the longitudinal section of the bottom of the molten pool into an arc, and reducing the width a of the bottom of the molten pool i2 Establishing a mathematical model of the lower surface roughness of the part for the diameter of the light spot;
as shown in fig. 6, the implementation steps of the adjustment of the placement angle of the parts and the slice thickness are as follows:
as shown in FIG. 6 (a), the placement angle of the component is set to obtain a tilt angle β of the upper surface of a certain tilt region of the component, and the slice thickness is set to h 1 The method comprises the steps of carrying out a first treatment on the surface of the Calculating theoretical value R of upper surface roughness of certain inclined area of part through mathematical model of upper surface roughness of part a1 If the theoretical value R a1 Above the standard value Ra, i.e. the surface roughness of the part does not meet the design requirements, as shown in FIG. 6 (b), maintaining the slice thickness at h 1 The arrangement angle of the part is unchanged, so that the inclination angle of the upper surface of a certain inclined area of the part is increased, the inclination angle of the upper surface is alpha, (alpha & gt beta), and the theoretical value R of the upper surface roughness of the certain inclined area of the part is calculated through a mathematical model of the upper surface roughness of the part a2 If the theoretical value R a2 When the surface roughness of the part is larger than the standard Ra, namely the surface roughness of the part does not meet the design requirement, as shown in fig. 6 (c), the placing angle is kept unchanged, namely the inclination angle alpha of the upper surface is kept unchanged, and the slice layer thickness is reduced to h 2 ，(h 2 ﹤h 1 ) Through zeroCalculating theoretical value R of upper surface roughness of certain inclined area of part by mathematical model of upper surface roughness of part a3 If the theoretical value R a3 Smaller than the standard Ra, the slice layer thickness h is formed according to the current placement angle (namely the inclination angle alpha) 2 To additively manufacture the part.
As shown in fig. 7, the surface roughness of the upper and lower surfaces of the part is corresponding to different inclination angles. When the thickness of the slice layer is fixed, the corresponding inclination angles of the two points of the upper surface A, B are respectively alpha 1 And alpha 2 Comparing the surface roughness R of the two areas a1 And R is a2 (calculated by the mathematical model of the surface roughness on the part of the invention), the surface roughness obviously increases with decreasing inclination angle; the inclination angles corresponding to the two points of the lower surface C, D are respectively alpha 3 And alpha 4 Comparing the surface roughness R of the two areas a3 And R is a4 It is known (calculated from the mathematical model of the lower surface roughness of the part of the present invention) that the larger the angle of inclination, the smaller the surface roughness of the region. In summary, the smaller the inclination angle, the greater the surface roughness, whether the upper or lower surface of the part. By combining the schematic diagram with the mathematical models of the upper and lower surface roughness of the part, the theoretical surface roughness is zero when the surface roughness is smaller and the inclination angle reaches 90 degrees when the inclination angle of the sample is closer to 90 degrees.
Under the condition that the technological parameters and the inclination angle are the same, according to the mathematical model of the upper and lower surface roughness of the part, the roughness of the upper surface is better than that of the lower surface. For example, when the thickness of the slice layer is 50 μm, the diameter of the spot is 100 μm, and the inclination angle is 30 °, the roughness of the upper surface is 25 μm and the roughness of the lower surface is 34 μm, which are obtained from the mathematical model of the roughness of the upper and lower surfaces of the component. Therefore, in forming a complex portion of the structure or an inner cavity, the area should be formed as an upper surface in order to secure surface roughness.
In the process of forming each sample, the slice layer thickness is the same, so that the surface roughness corresponding to the area with the smallest inclination angle in the part is the largest. Therefore, in actual work, after the inclination angle and the slice thickness are optimized, the surface roughness of the area with the minimum inclination angle can be calculated through the mathematical model of the upper surface roughness and the lower surface roughness of the part, the maximum roughness of the whole part can be calculated, if the surface roughness of the area meets the requirement, other areas meet the requirement, and therefore, the prediction of the surface roughness provides help for guiding the subsequent detection work, reduces the workload and improves the work efficiency. As shown in fig. 8, the inclination angle corresponding to the point a is α, for a similar part, the smaller the included angle formed by the tangent line of each position and the X axis is, the larger the surface roughness of the part is, and if the surface roughness of the part corresponding to the minimum inclination angle can meet the requirement, that is, the surface roughness of the part meets the requirement.
While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the spirit and principles of the invention, the scope of which is defined by the claims and their equivalents.
Claims (3)
1. The method for predicting the surface roughness of the additive manufactured part is characterized by comprising the following steps of:
s1, setting a placement angle of additive manufacturing of parts and setting a slice thickness;
s2, obtaining the inclination angles of the upper surfaces and the lower surfaces of all inclination areas on the part according to the placement angles;
s3, calculating theoretical values of the upper surface roughness of each inclined area of the part through a mathematical model of the upper surface roughness, and simultaneously calculating theoretical values of the lower surface roughness of each inclined area of the part through a mathematical model of the lower surface roughness;
the mathematical model of the upper surface roughness is as follows:
wherein R is ai1 Upper table for ith inclined area of partTheoretical value of surface roughness, alpha i1 The inclination angle of the upper surface of the ith inclination area of the part, h is the slice thickness, a i1 The width of the melt channel is the upper surface of the ith inclined area of the part; i is a positive integer greater than or equal to 1;
the mathematical model of the lower surface roughness is:
wherein R is ai2 Is the theoretical value of the lower surface roughness of the ith inclined area of the part, alpha i2 The inclination angle of the lower surface of the ith inclination area of the part, h is the slice thickness, a i2 A bottom width of the molten pool for the lower surface of the ith inclined area of the part;
s4, judging whether the surface roughness of the part meets the design requirement or not:
if the surface roughness of all inclined areas of the part meets the design requirement, namely, the theoretical value of the upper surface roughness of each inclined area of the part is respectively smaller than or equal to the standard value of the upper surface roughness, and meanwhile, the theoretical value of the lower surface roughness of each inclined area of the part is respectively smaller than or equal to the standard value of the lower surface roughness, the part is additionally manufactured according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, that is, the theoretical value of the upper surface roughness of one or more inclined areas of the part is greater than the standard value of the upper surface roughness, or the theoretical value of the lower surface roughness of one or more inclined areas of the part is greater than the standard value of the lower surface roughness, executing step S5;
s5, keeping the thickness of the slice layer unchanged, adjusting the placement angle of the part, and repeating the steps S2 and S3 to obtain the theoretical value of the upper surface roughness of each inclined area of the part and the theoretical value of the lower surface roughness of each inclined area;
s6, judging whether the surface roughness of the part obtained in the step S5 meets the design requirement:
if the surface roughness of all inclined areas of the part meets the design requirement, the part is manufactured in an additive mode according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, executing a step S7;
s7, keeping the placing angle of the part unchanged, reducing the thickness of the slice layer, and repeating the steps S2 and S3 to obtain the theoretical value of the upper surface roughness of each inclined area of the part and the theoretical value of the lower surface roughness of each inclined area;
s8, judging whether the surface roughness of the part obtained in the step S7 meets the design requirement:
if the surface roughness of all inclined areas of the part meets the design requirement, the part is manufactured in an additive mode according to the current placement angle and the slice layer thickness;
if the surface roughness of the part does not meet the design requirement, repeating the step S5 until the surface roughness of all the inclined areas of the part meets the design requirement, and additively manufacturing the part according to the current placement angle and slice layer thickness.
2. The method for predicting the surface roughness of an additive manufactured part according to claim 1, wherein in the step S5, the specific way of adjusting the placement angle of the part is: the angle of the smallest inclination angle among the inclination angles of the upper surfaces and the lower surfaces of the respective inclination areas of the part is increased.
3. The method according to claim 1, wherein in the step S7, the slice layer thickness is not smaller than the minimum particle diameter of the powder particles when the slice layer thickness is reduced.
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