RU2807099C1 - Method for pre-fabrication of pore defects using slm process control - Google Patents

Abstract

FIELD: pre-fabrication of pore defects.

SUBSTANCE: invention is related to a method for pre-fabrication of pore defects by controlling the process of selective laser melting. According to the method, laser scanning is carried out on the specified metal melting layer according to the first scanning path and the second scanning path. The first scanning path and the second scanning path have a path overlap area. The path overlap area has a specified width. The supply of laser energy applied in the path overlap area is controlled to achieve a predetermined energy value, whereby keyholes are formed at a plurality of positions in the longitudinal direction of the path overlap area. This metal melting layer is considered as a defect layer, and keyholes in the path overlap area are considered as pore defects.

EFFECT: method can use the "keyhole effect" to form pore defects to characterize additive manufacturing metallurgical defects in an SLM part.

6 cl, 10 dwg

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

This invention relates to a method for prefabrication of pore defects by controlling a selective laser melting (SLM) process, which for example can be used for non-destructive testing of SLM parts, assessing the impact of defects on component production, etc.

BACKGROUND OF THE ART

Additive manufacturing (AM), also referred to as 3D printing, is a manufacturing technology by molding a component by melting virgin materials layer by layer based on the principle of discrete stacking. SLM technology is considered as one of the most promising AM technologies. Since a laser beam with a small focal spot is adopted as the forming energy source, a high-speed and high-precision scanning galvanometer is adopted as the processing beam control unit, and a thinner layer thickness control technology is adopted, compared with other AM technologies, SLM technology has additional advantages in obtaining high-density and high-precision molding, allows direct molding of complex cavity, complex profile, thin-walled and variable cross-section components, and is widely used, for example, in the aerospace field, such as pre-swirl injectors, fuel injectors and aircraft engine turbine blades.

Due to the complex phase change process involving the rapid melting and solidification of metal powder material during the SLM process, SLM parts tend to have typical defects such as pores, cracks and lack of fusion. Nowadays, non-destructive testing methods, such as industrial CT testing, ultrasonic testing, radiographic testing, fluorescence penetrating testing, etc., are widely applied to SLM parts in the aerospace industry to detect component characteristics such as defect position and size. , analyzing and assessing whether the components meet the requirements for use. However, due to different characteristics of structures and defects between AM parts and traditional parts, such as inhomogeneity and anisotropy, as well as complex geometries, traditional non-destructive testing processes may face problems such as low availability and large detection blind spots. This makes it difficult to use non-destructive testing technology for traditional parts. It is necessary to re-analyze the correspondence between structure characteristics and non-destructive test signals, clarify the non-destructive test signal characteristics of typical defects, and select applicable non-destructive testing methods and process parameters according to the complexity of the geometric structure. For example, industrial CT can detect defects such as pores, cracks and lack of fusion in AM parts and can produce tomographic images of the detected instances. Before CT testing, a sample must be prepared for comparative analysis of the defects contained, by combining material, structure, expected size of the detected defect, etc. detected instance, and then it is necessary to set acceptable parameters for the discovery process. Comparative analysis of the sample influences the setting of the parameters of the detection process, and affects the detection of defects in subsequent detected samples. The closer the material, molding process, defects, etc. sample to the detected instance, the better the detection effect can be obtained. Therefore, for a detected AM part, its benchmark sample should also be prepared through the AM process, and the associated defects should be prefabricated.

Currently, the method for prefabrication of pore defects inside an AM part mainly involves designing pores of specific sizes at specific positions in the 3D model construction stage, and then additively molding the part with the pore features. However, due to limitations of the AM technology itself, the engineered pore features are easily filled with liquid, molten metal during molding. This makes it difficult to use this method to successfully prefabricate pore defects. In view of the shortcomings of existing methods, this invention provides a method for prefabricating pore defects by controlling the SLM process.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for prefabrication of pore defects that can use the "keyhole effect" to prefabricate pore defects in an SLM part by controlling the SLM process.

It is a further object of this invention to provide a pore defect prefabrication method that can form pore defects with the characteristics of additive manufacturing metallurgical defects in an SLM part by controlling the SLM process.

This invention provides a method for prefabricating pore defects by controlling an SLM process, comprising: performing laser scanning on a specified metal melting layer according to a first scanning path; and performing laser scanning on said metal melting layer according to a second scanning path; wherein the first scanning path and the second scanning path have a path overlap zone, the path overlap zone has a predetermined width, and the supply of laser energy applied in the path overlap zone is controlled to achieve a predetermined energy value, whereby keyholes are formed at a plurality of positions in the longitudinal direction path overlap zones, wherein said metal melting layer is considered as a layer of defects, and keyholes in the path overlap zone are considered as pore defects.

According to an embodiment, laser scanning along the first scanning path and the second scanning path applies a stripe type laser scanning mode; the first scanning path is located in the first strip zone, the second scanning path is located in the second strip zone, the first strip zone and the second strip zone form a lap joint zone, the lap joint zone forms a path overlap zone, and the lap joint amount of the lap joint zone is equal to width of the track overlap zone.

According to an embodiment, the first scan path includes a plurality of first scan lines oriented parallel and spaced equidistantly, the second scan path contains a plurality of second scan lines oriented parallel and spaced equidistant, and the scan steps of the first scan path and the second scan path are the same.

According to an embodiment, laser scanning along the first scanning path and the second scanning path employs a stripe-type reciprocating laser scanning mode.

According to an embodiment, laser scanning along the first scanning path and the second scanning path applies a laser pulse exposure mode.

According to an embodiment, the SLM process parameters are controlled as follows: Hastelloy X is used as the molding material; laser scanning power P=180-210 W; spacing of points on the scanning line D=80-100 µm; scanning line exposure time t=70-90 µs.

According to an embodiment, the SLM process parameters are further controlled as follows: layer thickness d=30 μm; scanning step h =70-100 µm; the size of the lap joint of the strips is δ=0.5-0.9 mm.

According to an embodiment, the position, size and length of the lap joint zone of the strips in the defect layer are controlled by changing the laser scanning direction and strip width values of the first strip zone and/or the second strip zone, thereby controlling the proportion of pore defects of the defect layer.

According to an embodiment, the pore defect fraction a of the defect layer is determined with reference to the following formula:

a =(N×(πR ² )×L/h)/S

where N is the size of the lap joint zone, R is the pore radius, L is the length of the lap joint zone, h is the scanning step, and S is the cross-sectional area of the defect layer.

The above pore defect prefabrication method uses the keyhole effect to prefabricate pore defects in the SLM part, where the keyhole effect can be created by controlling the parameters of the molding process, prefabricating a closed group of pores at a specified position of the SLM part; and the position of the pore defect and the proportion of pore defects can also be controlled by the parameters of the molding process.

By implementing the above pore defect prefabrication method, pores can be successfully produced in an SLM part, and the shape and size of the pores are characteristics of additive manufacturing metallurgical defects. The above method for prefabrication of a pore defect does not destroy the structure of the SLM part and preserves its characteristics, for example, heterogeneity and anisotropy. When an SLM part in which defects are prefabricated by the above pore defect prefabrication method is used for comparative analysis, it is useful to analyze the actual correspondence between the pore defects of the SLM part and the signals of non-destructive testing or part production, so as to obtain a better detection effect.

In addition, through the above pore defect prefabrication method, pores can be prefabricated at key positions of an SLM part or a representative sample thereof to carry out strength evaluation tests such as tensile strength, strength and fatigue. The obtained production evaluation results can be used to actually analyze and investigate the relationship between pore defects and part production, providing strong theoretical support for the application of SLM parts.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features, properties and advantages of this invention will appear from the following description taken in conjunction with the accompanying drawings and embodiments, wherein:

fig. 1 is a schematic view of a conventional melt bath.

Fig. 2 is a schematic view of a melt pool formed with a keyhole.

Fig. 3 is a schematic view of an exemplary laser scanning strategy.

Fig. 4 is a schematic view of another exemplary laser scanning strategy.

Fig. 5 is a schematic view of an exemplary laser scanning strategy according to the first example.

Fig. 6 - pore distribution diagram obtained in the first example.

Fig. 7 is a schematic view of an exemplary laser scanning strategy according to the second example.

Fig. 8 - pore distribution diagram obtained in the second example.

Fig. 9 is a schematic view of an exemplary laser scanning strategy according to the third example.

Fig. 10 is a pore distribution diagram obtained in the third example.

DETAILED DESCRIPTION OF IMPLEMENTATION OPTIONS

This invention will be further described below in connection with specific embodiments and the accompanying drawings. Additional details are set forth in the following description to facilitate a thorough understanding of this invention, but it will be appreciated that this invention can be practiced in many other ways that differ from those described herein. Those skilled in the art can make similar suggestions and conclusions according to the actual application situation without departing from the spirit of this invention. Therefore, the contents of this particular embodiment are not intended to limit the scope of protection of this invention.

In fig. 1 and fig. Figure 2 shows a schematic view of the keyhole effect. In this case, FIG. 1 schematically shows a conventional melt bath, and FIG. 2 schematically shows a keyhole formed in a melt bath.

As shown in FIG. 1, when the energy density of the incident laser beam 10 is in the desired operating range, the formed melt pool 20 is relatively stable, which results in metallurgical quality. The figure also shows the laser scanning direction D0 of the laser beam 10, wherein the metal melting layer 30 is melted and formed by SLM, and the base material 40 has already been melted and formed by SLM.

As shown in FIG. 2, when the energy density of the incident laser beam 10 increases to a critical energy value, the surface of the material evaporates and forms plasma 50. Under the action of the reaction force of the vapor, a keyhole 60 is formed inside the molten metal. Then the liquid metal moves under the influence of Marangoni convection and surface tension, etc. .d. in the melt bath, envelops and fills the keyhole 60. The gas that does not have time to escape is enclosed by the solidified part, forming pores.

When the laser 10 moves to the next position in the laser scanning direction D0, the laser energy at the critical energy value is still surrounded by the agglomerated plasma 50 at this time, so the energy of the laser beam 10 incident on the powder material is lower than the critical energy value and keyholes cannot form. After the laser 10 continues to move out of range of the agglomerated plasma 50, the energy density of the laser beam 10 will again reach a critical energy value and form a keyhole 60, which again acts as a pore defect in the part, i.e. the pore defect is prefabricated into the part. Therefore, pore defects formed by the keyhole effect have a certain periodicity.

This invention provides a method for prefabricating pore defects in an SLM part using a keyhole effect, also referred to as a method for prefabricating pore defects by SLM process control.

According to FIG. 3, in the method for prefabricating pore defects according to this invention, laser scanning is performed on said metal melting layer LY according to a first scanning path P1, and laser scanning is performed on said metal melting layer LY according to a second scanning path P2. Here, the first scanning path P1 and the second scanning path P2 have a path overlap zone A0, the path overlap zone A0 has a predetermined width, and the supply of laser energy superimposed in the path overlap zone A0 is controlled to achieve a predetermined energy value, due to which keyholes are formed in At a plurality of positions in the longitudinal direction of the path overlap zone A0, said metal melting layer LY is considered as a defect layer, and the keyholes in the path overlap zone A0 are considered as pore defects.

The SLM process consists of melting and solidifying a component layer by layer, in which the metallurgical structure of said metal melting layer LY can be changed by changing the parameters of the SLM process. Therefore, by setting the SLM process parameters for generating a keyhole for the specified metal melting layer LY, or by changing the height of the specified metal melting layer LY in the above pore defect prefabrication method, the position of the pore defect in the height direction can be controlled.

In the exemplary embodiment shown in FIG. 3, laser scanning along the first scanning path P1 and the second scanning path P2 may adopt a stripe type laser scanning mode. The first scan path P1 is located in the first strip zone Z1 (left in FIG. 3), and the second scan path P2 is located in the second strip zone Z2 (right in FIG. 3).

The first strip zone Z1 and the second strip zone Z2 form the lap joint zone Z0 of the strips. The lap joint area Z0 forms the path overlap area A0 of the first scanning path P1 and the second scanning path P2. The value δ of the overlap strip connection zone Z0 of the overlap strip connection zone is equal to the width of the track overlap zone A0. The lap joint length L of the lap joint zone Z0 is equal to the length of the track overlap zone A0.

The first scan path P1 may comprise a plurality of first scan lines L1 oriented in parallel and spaced equidistantly, and the second scan path P2 may comprise a plurality of second scan lines L2 oriented in parallel and spaced equidistantly. The scan steps of the first scan path P1 and the second scan path P2 are the same, and both are equal to the scan step h. Scan pitch h means the pitch between two adjacent first scan lines L1 (or two adjacent second scan lines L2).

Additionally, laser scanning along the first scanning path P1 and the second scanning path P2 may use a stripe-type reciprocating laser scanning mode. In other words, the scan directions indicated by the two adjacent first scan lines L1 are opposite, and the scan directions indicated by the two adjacent second scan lines L2 are opposite.

In particular, with reference to FIG. 3, in the pore defect prefabrication method, strip-type reciprocating laser scanning is carried out. The laser scans the first strip zone Z1 from the first start point B1 on the left to the first end point E1 according to the first scan path P1, and then scans the second strip zone Z2 from the second start point B2 on the right to the second end point E2 according to the second scan path P2.

In another embodiment, the laser may scan the first stripe zone Z1 from the first start point B1 on the left to the first end point E1 in a stripe-type reciprocating laser scanning mode, and then continue to scan the second stripe zone Z2 from the third start point B3 on the right to the third end point E3 in stripline reciprocating laser scanning mode. Compared with the case where the laser returns to the second starting point B2 to start scanning the second strip zone Z2, the third starting point B3 is closer to the first end point E1, so to improve efficiency, it is useful to start scanning the second strip zone Z2 from the third starting point B3 .

At the location where the first strip zone Z1 and the second strip zone Z2 are lapped, a lap joint zone Z0 is formed having a certain lap joint amount (the lap joint value δ). The lap joint zone Z0 is melted twice by the laser: after the laser scans the first strip zone Z1, the lap joint zone Z0 quickly melts and solidifies as the temperature rises; when the laser scans the second strip zone Z2, the lap joint zone Z0 is rescanned, and melting again occurs in the lap joint zone Z0. For example, by controlling the parameters of the forming process to apply laser energy input to the lap joint zone Z0 twice, the specified energy value is achieved, or the evaporation condition of the metal material is achieved, at this time, keyholes will be formed in the lap joint zone Z0, thereby leaving pores defects.

The laser strip scanning mode is a zone scanning mode. Its principle is to divide a section of the component model into many strip zones, and then scan the laser zone by zone according to the information about the section of the component model, in which the scanned zone quickly melts and solidifies. The width of one strip zone may be referred to as the strip width. Preferably, the stripe widths of all stripe zones are the same, as shown in FIG. 3, fig. 4 and then FIG. 5, fig. 7, fig. 9. In FIG. 3 and fig. 4, the first strip zone Z1 is taken as an example to show the strip width w0.

In the method for prefabrication of a pore defect, the position, size and length of the lap joint zone Z0 of the strips in the above-mentioned defect layer can be controlled by changing the laser scanning direction and the width w0 of the strip (the strip width of the first strip zone Z1 and/or the second strip zone Z2), thereby , controlling the pore defect fraction a of the above-mentioned defect layer. For example, according to the embodiment shown in FIG. 3, the component model section is divided into two strip zones. Whereas, according to the embodiment shown in FIG. 4, for the same component model section, the strip width w0 is changed, the component model section is divided into four strip zones, and the laser scanning direction is changed.

As described above, the scanning steps of the first scanning path P1 and the second scanning path P2 are the same, and both are equal to the scanning step h. According to FIG. 3, the pore defect fraction a (or pore defect ratio) of the defect layer can be determined with reference to the following formula or approximately according to the following formula:

a =(N×(πR ² )×L/h)/S (1)

where N is the size of the lap joint zone Z0, R is the pore radius, L is the length of the lap joint zone Z0, h is the scanning pitch, and S is the cross-sectional area of the above defect layer.

The parameters can be adjusted according to the above formula (1) to obtain the desired pore defect fraction a of the defect layer.

Laser scanning along the first scanning path P1 and the second scanning path P2 may apply a laser pulse exposure mode. According to experiments, the inventor found that, compared with the continuous laser exposure mode, the keyhole effect is more likely to occur in the laser pulse exposure mode.

Below are specific examples of implementation of this invention. It will be appreciated that each subsequent example may use element reference numerals and portions of the content of the previous example, with the same reference numerals being used to represent the same or similar elements and description of the same technical content being selectively omitted. As for the description of the omitted part, reference may be made to the previous example, and the description of the subsequent example will not be repeated. Moreover, in the first to third examples, various process parameters of the first strip zone Z1 and the second strip zone Z2 are the same, and the second scan path P2 in the second strip zone Z2 may be substantially equivalent to the path formed by shifting the first scan path P1 in the first strip zone Z1 at a given distance.

First example

The laser scanning strategy in this example is shown in FIG. 5. The SLM molding equipment used in this example adopts laser pulse exposure mode, Hastelloy X alloy is used as the molding material, and the size of the SLM molded sample is 10mm * 10mm * 10mm.

Setting the SLM process parameters for pore defects also includes: laser scanning power P=200 W, scanning line point spacing D=80 μm, and scanning line exposure time t=80 μs, and scanning line point spacing D means the distance between two adjacent points when the laser pulse moves in the dotted mode, and the scanning line exposure time t means the time it takes to move between two adjacent points when the laser pulse moves in the dotted mode;

layer thickness d=30 µm, scanning step h=70 µm, and width of the overlap zone Z0 of the strips δ=0.5 mm;

strip width w0=5 mm, and the laser scanning direction is 90°, forming one horizontally extending lap joint zone Z0 of the strips with a length of 10 mm.

In this example, the above SLM process parameters for prefabrication of pore defects are set in layers 1500 to 1700 of the sample to mold the sample in SLM mode.

In fig. 6 is a pore distribution diagram of a sample with prefabricated pore defects obtained in this example, showing pores H1. The average radius R of the pore formed in this example is about 25 µm. According to formula 1) a =(N×(πR ² )×L/h)/S, the proportion a of pore defects of the resulting defect layer is approximately 0.34%.

Second example

The laser scanning strategy in this example is shown in FIG. 7. The SLM molding equipment used in this example adopts laser pulse exposure mode, Hastelloy X alloy is used as the molding material, and the size of the SLM molded sample is 10mm * 10mm * 10mm.

Setting the SLM process parameters for pore defects also includes: laser scanning power P=180 W, point spacing on the scanning line D=100 μm, and scanning line exposure time t=90 μs;

layer thickness d=30 µm, scanning step h=100 µm, and the overlap value of the strips δ=0.5 mm;

the width of the strip w0=7 mm, and the laser scanning direction is 45°, forming one lap joint zone Z0 of the strips with a length of 14.14 mm, running along the diagonal line.

In this example, the above SLM process parameters for prefabrication of pore defects are set in layers 1000 to 1100 of the sample to mold the sample in SLM mode.

In fig. 8 is a pore distribution diagram of a sample with prefabricated pore defects obtained in this example, showing pores H1. The average radius R of the pore formed in this example is about 25 µm. According to formula 1) a =(N×(πR ² )×L/h)/S, the proportion a of pore defects of the resulting defect layer is approximately 0.28%.

Third example

The laser scanning strategy in this example is shown in FIG. 9. The SLM molding equipment used in this example adopts laser pulse exposure mode, Hastelloy X alloy is used as the molding material, and the size of the SLM molded sample is 10mm * 10mm * 10mm.

Setting the SLM process parameters for pore defects also includes: laser scanning power P=210 W, point spacing on the scanning line D=90 μm, and scanning line exposure time t=70 μs;

layer thickness d=30 µm, scanning step h=90 µm, and the overlap value of the strips δ=0.5 mm;

the width of the strip w0=7 mm, and the laser scanning direction is -45°, forming one lap joint zone Z0 of the strips with a length of 14.14 mm, running along the other diagonal line.

In this example, the above SLM process parameters for prefabrication of pore defects are set in layers 1000 to 1100 of the sample to mold the sample in SLM mode.

In fig. 10 is a pore distribution diagram of a sample with prefabricated pore defects obtained in this example, showing pores H1. The average radius R of the pore formed in this example is about 25 µm. According to formula 1) a =(N×(πR ² )×L/h)/S, the proportion a of pore defects of the resulting defect layer is approximately 0.31%.

Experiments demonstrate that among the SLM process parameters, three parameters, namely laser scanning power P, scanning line point spacing D, and scanning line exposure time t, have a stronger influence on whether the keyhole effect is generated.

The SLM process parameters are controlled as follows: Hastelloy X alloy is used as the molding material; laser scanning power P=180-210 W; spacing of points on the scanning line D=80-100 µm; scanning line exposure time t=70-90 µs.

In addition, the SLM process parameters are further controlled as follows: layer thickness d=30 μm; scanning step h=70-100 µm; the size of the lap joint of the strips is δ=0.5-0.9 mm.

Controlling the SLM process parameters in the above range can create keyhole effects and obtain regular pore defects.

In practice, in connection with FIG. 3, the above method for pre-fabricating a pore defect can be carried out as follows:

The SLM process parameters are controlled as follows: laser scanning power P=180-210 W, point spacing on the scanning line D=80-100 µm, and scanning line exposure time t=70-90 µs; layer thickness d=30 µm, scanning step h=70-100 µm, and the overlap value of the strips δ=0.5-0.9 mm. The width w0 of the strip and the direction of laser scanning are set according to the specified position of the pore defect.

Then the position and proportion of pore defects in the SLM part are set: the position, size and length of the zone Z0 of the lap joint of strips in the defect layer are controlled by changing the laser scanning direction and the width of the strip, where the proportion a of pore defects of the defect layer can be approximately determined according to the formula (1) . Then, by selecting one or more of these metal fusion layers, the position of the pore defects in the height direction of the SLM part can be controlled.

Finally, 3D printing is carried out through the SLM process, setting the above SLM process parameters for the above mentioned metal fusion layer, and setting the conventional process parameters for the other metal fusion layers, to obtain SLM parts with prefabricated pore defects.

The above method for prefabrication of a pore defect can create a "keyhole effect" by controlling the parameters of the SLM process, thereby forming regular pore defects at a specified position of the SLM part. The above pore defect prefabrication method applies the preferred SLM process parameters, sets the position of the pore defects in the two-dimensional section of each layer of the SLM part by controlling the laser scanning direction and strip width, and then sets the corresponding SLM process parameters in the specified metal fusion layer of the SLM part, which allows you to achieve prefabrication of the desired pore defects in the SLM part.

The above pore defect prefabrication method can also determine the pore defect proportion a of the defect layer according to the formula, so each parameter can be easily adjusted to obtain the desired pore defect proportion.

Obviously, the above pore defect prefabrication method is applicable not only to the case of pore prefabrication in comparative samples for non-destructive testing, but also applies to other situations where the effect of pore defects on SLM parts is well understood. For example, at key locations of SLM parts or typical samples of their characteristics, pore defects can be prefabricated to perform tests to evaluate strength, such as elongation, durability, fatigue, etc. to evaluate the impact of pore defects on mechanical properties and predict the service life of components.

It is understood that the accompanying drawings are used as examples only, and are not necessarily drawn to scale, and are not intended to limit the scope of protection actually claimed in this invention. Moreover, variations in various embodiments can be made as appropriate.

Although this invention has been described above by way of preferred examples, they are not intended to limit this invention, and variations and modifications may be suggested by any person skilled in the art without departing from the spirit and scope of this invention. Therefore, any modifications, equivalent variations and embodiments of the above examples according to the technical essence of this invention, not beyond the scope of the technical solutions of this invention, all fall within the scope of protection given by the claims of this invention.

Claims (21)

1. A method for the preliminary formation of pore defects in metal by controlling the process of selective laser melting, in which laser scanning is carried out on a given metal melting layer along the first scanning path; And carry out laser scanning on a given metal melting layer along the second scanning path, wherein the first scanning path and the second scanning path have a path overlap zone, the path overlap zone has a predetermined width, and the supply of laser energy applied in the path overlap zone is controlled to achieve a predetermined energy value for forming keyholes at a plurality of positions in the longitudinal direction of the path overlap zone , and the given metal melting layer is a layer of defects, and keyholes in the track overlap area are pore defects, when laser scanning along the first scanning path and the second scanning path, strip-type laser scanning mode is used, and laser pulse exposure mode is applied, the first scanning path is located in the first strip zone, the second scanning path is located in the second strip zone, the first strip zone and the second strip zone forming an overlap zone, the overlap zone forms a path overlap zone, and the amount of overlap of the strips of the overlap zone equal to the width of the track overlap zone, wherein the SLM process parameters are selected as follows: Hastelloy X alloy is used as a forming material; laser scanning power P=180-210 W; spacing of points on the scanning line D=80-100 µm; scanning line exposure time t=70-90 µs. 2. The method of claim 1, wherein the first scanning path comprises a plurality of first scanning lines oriented in parallel and spaced at equal distances from each other, the second scanning path comprises a plurality of second scanning lines oriented in parallel and spaced at equal distances from each other, and the scanning steps of the first scanning path and the second scanning path are the same. 3. The method according to claim 1, in which when laser scanning along the first scanning path and the second scanning path, a strip-type reciprocating laser scanning mode is used. 4. The method according to claim 1, in which the parameters of the selective laser melting process are additionally selected as follows: layer thickness d=30 µm; scanning step h = 70-100 µm; the size of the lap joint of the strips is δ=0.5-0.9 mm. 5. Method according to any one of paragraphs. 1-3, in which the position, size and length of the lap joint zone of the strips in the defect layer are controlled by changing the laser scanning direction and the strip width values of the first strip zone and/or the second strip zone to control the proportion of pore defects of the defect layer. 6. The method according to claim 1 or 5, in which the proportion a of pore defects of the defect layer is determined by the following formula: a= (N×(πR ² )×L/h)/S where N is the size of the overlap zone, R is the pore radius, m, L is the length of the overlap zone, m, h is the scanning step, m, and S is the cross-sectional area of the defect layer, m ² .