CN114131045A

CN114131045A - 3D printing method and system for hole structure

Info

Publication number: CN114131045A
Application number: CN202111392461.4A
Authority: CN
Inventors: 金学军; 刘延卿; 刘仕龙
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2021-11-23
Filing date: 2021-11-23
Publication date: 2022-03-04
Anticipated expiration: 2041-11-23
Also published as: CN114131045B

Abstract

The application discloses a 3D printing method of a hole structure, which is characterized in that a laser selective melting method is utilized to perform scanning and printing layer by layer, when each layer is scanned and printed, the edge of the layer is firstly scanned and printed for at least one circle to form a closed area, and then the inside of the closed area is printed; when the inside of the closed area is printed, at least one circle of the edge of the hole inside the closed area is printed, and then the rest positions are printed. The product obtained by the method can greatly improve the energy absorption performance of the structure by only changing the process method during printing on the basis of not changing the original design and parameters.

Description

3D printing method and system for hole structure

Technical Field

The application relates to the field of material manufacturing, in particular to a method for preparing a hole structure material by selective laser melting.

Background

Selective Laser Melting (SLM) is one of the main techniques in additive manufacturing of metallic materials. The technical method uses laser as an energy source, and scans layer by layer on a metal powder bed according to a path after three-dimensional model CAD slicing, so that metal powder on the scanning path is melted and solidified to finally obtain a part designed by a model.

With the recent trend of light weight of automobiles, the part of the automobile interlayer for anti-collision protection is gradually replaced by a hole structure prepared by 3D printing. Although these pore structures may function, their energy absorption properties are yet to be improved.

Disclosure of Invention

The embodiment of the application provides a 3D printing method of a hole structure, and aims to at least solve the problem that the energy absorption and energy absorption of the existing 3D printing formed hole structure are still to be improved.

According to one aspect of the application, a 3D printing method of a hole structure is provided, scanning and printing layer by layer is carried out by utilizing a laser selective melting method, when each layer is scanned and printed, scanning and printing are carried out for at least one circle around the edge of the layer to form a closed area, and then the inside of the closed area is printed; when the inside of the closed area is printed, at least one circle of the edge of the hole inside the closed area is printed, and then the rest positions are printed.

Further, the scanning speed when the layer is firstly scanned and printed around the edge of the layer is lower than the scanning speed when the inside of the closed area is printed.

Further, the scanning speed of the layer around the edge of the layer is 1700mm/s-2000mm/s, and the scanning speed of the closed area inside the layer is 2000mm/s-2700 mm/s.

Further, the laser power when the layer is firstly scanned around the edge of the layer for printing is larger than that when the laser power is printed inside the closed area.

Further, the laser power during scanning and printing around the edge of the layer is 300W-340W, and the laser power during printing inside the closed area is 230W-300W.

Further, said first scanning at least one revolution around the edge of the layer comprises: the layers were printed around the edge in an outside-in order for 3 weeks.

Further, the printing at least one circle around the edge of the layer in the order from outside to inside includes printing for 2 or more circles with a degree of overlap of 20% to 30% between each circle and an adjacent circle in the width direction of the printing path.

Further, when the inside of the closed area is printed, taking an end point when scanning and printing are performed around the edge of the layer as a starting point, and calculating the hole with the shortest distance from each point of the edge of each hole in the current closed area to the starting point as the initial printing hole of the closed area.

Further, when the inside of the closed area is printed, the end point surrounding the hole which is printed before is taken as a starting point, and the hole with the shortest distance from each point of the edge of each unprinted hole in the current closed area to the starting point is calculated as the next hole to be printed.

According to another aspect of the present application, there is provided a 3D printing system of a hole structure, comprising an optical path unit, a mechanical unit, a control unit and a protective gas sealing unit, and software for implementing printing according to the method of the first aspect.

The invention provides a 3D printing method and a system of a hole structure, which utilize a laser selective melting method to perform scanning and printing layer by layer, when each layer is scanned and printed, the layer is scanned and printed for at least one circle around the edge of the layer to form a closed area, and then the inside of the closed area is printed; when the inside of the closed area is printed, at least one circle of the edge of the hole inside the closed area is printed, and then the rest positions are printed. The product obtained by the method can greatly improve the energy absorption performance of the structure by only changing the process method during printing on the basis of not changing the original design and parameters.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. In the drawings:

fig. 1 is a schematic flow chart of a 3D printing method according to an embodiment of the present application;

fig. 2 is a diagram showing the relationship between deformation and load obtained by performing a quasi-static compression test on a product obtained by printing different numbers of turns on the edge of each layer according to an embodiment of the present application.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.

It should be noted that the steps illustrated in the flowcharts of the figures may be performed in a computer system such as a set of computer-executable instructions and that, although a logical order is illustrated in the flowcharts, in some cases, the steps illustrated or described may be performed in an order different than presented herein.

As shown in fig. 1, an embodiment of the present invention provides a 3D printing method of a hole structure, including the following steps:

s102, scanning and printing layer by using a selective laser melting method, wherein when each layer is scanned and printed, scanning and printing at least one circle around the edge of the layer to form a closed area, and then printing the inside of the closed area;

s104, when printing is carried out on the inside of the closed area, firstly, at least one circle of printing is carried out around the edge of a hole in the closed area;

s106, printing the rest positions.

In accordance with conventional methods, the internal path is scanned 67 ° for each rotation relative to the previous layer. The above process also involves the preparation of the material and the use of software for printing, and therefore, at least a typical preparation process like the following is included:

s002: selecting and drying 17-4PH stainless steel powder as a raw material, wherein the drying temperature is 70 ℃, and the drying time is 3 hours;

s004: importing a three-dimensional model of a hole structure to be formed into 3D printing processing software in an STL format, and adding necessary support for a more complex model; slicing the model to obtain two-dimensional section data information, and importing the two-dimensional section data information into 3D printing equipment;

s006: and 3D printing and forming according to a preset scanning strategy and process parameters.

The metal powder 17-4PH stainless steel provided in certain preferred embodiments comprises the following chemical components in percentage by mass: c is less than or equal to 0.07 percent; mn is less than or equal to 1.00 percent; si is less than or equal to 1.00 percent; 15.5 to 17.5 percent of Cr; 3.0 to 5.0 percent of Ni; p is less than or equal to 0.04 percent; s is less than or equal to 0.03 percent; 3.0 to 5.0 percent of Cu; 0.15 to 0.45 percent of Nb and Ta; the balance being Fe. The 17-4PH stainless steel powder is spherical powder, the weight percentage of the grain diameter less than or equal to 60 mu m is not less than 95 percent, and the weight percentage of the grain diameter more than 60 mu m is less than 5 percent; the 17-4PH stainless steel powder had a minimum particle size of 15 μm and a maximum particle size of 75 μm, and an average particle size of 50 μm.

The method changes the printing process of the traditional selective laser melting method, distinguishes the edge of each layer from the inside, and prints the edge to form a closed area, so that the materials on the edge of each layer are higher in the degree of connection, stronger in structure and more compact in energy transfer; correspondingly, the hole edge and the rest part are also distinguished in the closed area, and the edge part limited to the hole is printed, so that the connection degree of materials on the hole edge in the closed area is higher, the hole structure is more stable, and the energy transfer is tighter. No matter the edge of the hole in the sealed area in the sea at the edge of each layer, the microstructure obtained during scanning is isometric crystal with smaller size relative to the internal scanning structure, so that the overall strength and toughness of the sample can be improved, and the overall energy absorption performance of the product obtained by the method provided by the embodiment is obviously superior to that of the traditional method. Compared with the prior art, when the hole structure is printed by the process, the proportion of fine grains in the structure of the finally-formed part is relatively high due to the fact that the surface of the hole structure is large, and therefore the strength and the toughness of the part are integrally improved, the metal hole structure printed by the technical scheme is used for anti-collision protection, the original part design and size are not changed, the process is improved through 3D printing, and the performance of the metal hole structure in the aspect of energy absorption can be remarkably improved.

In the implementation process of the method, because the scanning position is located at the periphery during edge scanning, each non-intersected scanning area of the layer is not subjected to path scanning, the heat dissipation condition is better, the molten metal on the laser scanning path can be rapidly cooled, and the heat is accumulated to assist the melting of the metal powder due to relatively insufficient heat dissipation during internal scanning.

Therefore, when scanning is performed inside the closed region in the scanning process, the outer region has more heat dissipation, and in order to effectively melt the material, an effective method is to reduce the scanning speed and give more melting time, so that the scanning speed when scanning and printing around the edge of the layer is lower than the scanning speed when printing inside the closed region. Preferably, the scanning speed when the layer is firstly scanned and printed around the edge of the layer is 1700mm/s-2000mm/s, and the scanning speed when the closed area is internally printed is 2000mm/s-2700 mm/s.

Also for reasons of material melting which is affected by too rapid heat dissipation, it is also useful to increase the laser power, which is greater when printing around the edge of the layer than when printing inside the enclosed area, by applying more power to make the material more easily melt. Preferably, the laser power for printing by scanning around the edge of the layer is 300W-340W, and the laser power for printing inside the closed area is 230W-300W.

In certain preferred embodiments, in order to integrate the material absorption properties with the time-consuming and performance-enhancing limitations of excessive edge printing passes, the number of passes of the initial pass around the edge of the layer needs to be controlled within a reasonable range, so that the 3 passes are printed in an outside-in order around the edge of the layer.

As shown in fig. 2, the relationship between deformation and load obtained by performing quasi-static compression test on the product obtained by printing different numbers of turns on the edge of each layer is shown as 3 curves, namely 3 curves for printing 3 weeks, 1 week and no curve for printing the edge from top to bottom. By comparison, the yield load of the latter is increased by about 50% and the energy absorption performance is increased by about 25% in the quasi-static compression test for the specimens without edge path scan and with 1 peripheral edge path scan. Wherein the energy absorption properties are obtained by integrating the area under the curve and between the axis of abscissa.

Meanwhile, as can be seen from the figure, the curves printed for 3 weeks and 1 week both have significantly more energy absorption effect than the curves printed for no, and the curves printed for 3 weeks have stronger energy absorption effect than the curves printed for 1 week, but the increase is not significant, and particularly after the displacement is greater than or equal to 12mm, the two curves almost coincide, which shows that the energy absorption effect is equivalent to the energy absorption effect thereafter. But when the displacement is between 2mm and 12mm, the energy absorption effect is still slightly better than that of printing for 1 week when the printing is carried out for 3 weeks, and the number of printing weeks can be reasonably selected according to the use requirement.

During the scanning process, the scanning pitch and the layer thickness can be kept the same on the inner part and the outer part, for example, the scanning pitch is 0.08-0.12mm, and the layer thickness is 0.02-0.04 mm. But it also provides a preferred embodiment that, in order to be able to further strengthen the material strength of the periphery, the printing at least one turn around the edge of the layer in an outside-in order comprises printing for 2 turns or more, and the overlap ratio between each turn and the adjacent turn in the width direction of the printing path is 20% to 30%. Through the coincidence in the width direction for the circle layer of edge is better in the hookability in the interior outside direction, can provide stronger support when impacting to the material inside.

Therefore, in some embodiments, when the inside of the closed area is printed, the end point when the inside of the closed area is scanned and printed around the edge of the layer is taken as the starting point, and the hole with the shortest distance from each point of the edge of each hole in the closed area to the starting point is calculated as the initial printing hole of the closed area. By the method, unnecessary laser head idle time is reduced, and scanning efficiency can be improved.

Similarly, the path planning between the holes inside also affects the scanning efficiency, and in the above embodiment, when the inside of the closed area is printed, the hole with the shortest distance from each point of the edge of the unprinted hole inside the current closed area to the starting point is calculated as the next hole to be printed, with the ending point of the hole around the previous printed hole as the starting point.

The embodiment of the invention also provides a 3D printing system of a hole structure, which adopts the scanning strategy on the basis of a traditional selective laser melting device (SLM), so that the system comprises a light path unit, a mechanical unit, a control unit, a protective gas sealing unit and software, wherein the software is used for realizing printing according to the scanning strategy method.

The optical path unit mainly comprises an optical fiber laser, a beam expanding lens, a reflecting mirror, a scanning galvanometer, a focusing lens and the like. The laser is the most central component in the laser selective zone melting device and directly determines the forming quality of the whole device. Because the quality of the laser beam is good, the laser beam can be gathered into a very fine beam, and the output wavelength of the laser beam is short, the optical fiber laser has very obvious advantages in selective laser melting and rapid forming of precise metal parts. The beam expander is an optical component essential for adjusting the quality of the light beam, and the beam expander is adopted in a light path to enlarge the diameter of the light beam, reduce the divergence angle of the light beam and reduce the energy loss. The scanning galvanometer is driven by a motor and is controlled by a computer, so that laser spots can be accurately positioned at any position of a processing surface. In order to overcome the distortion of the scanning galvanometer unit, a special flat field scanning lens is needed, so that the focusing light spot obtains consistent focusing characteristics in a scanning range.

The mechanical unit mainly comprises a powder spreading device, a forming cylinder, a powder cylinder, forming chamber sealing equipment and the like. The powder paving quality is a key factor influencing the SLM forming quality, and two types of powder paving devices, namely a powder paving brush and a powder paving roller, are mainly arranged in the SLM equipment at present. The forming cylinder and the powder cylinder are controlled by a motor, and the forming precision of the SLM is also determined by the control precision of the motor.

The control system consists of a computer and a plurality of control cards, and the laser beam scanning control is realized by the computer sending control signals to the scanning galvanometer through the control cards to control the X/Y scanning galvanometer to move. The equipment control system completes the machining operation of the parts. The method mainly comprises the following functions: (1) system initialization, state information processing, fault diagnosis and man-machine interaction functions; (2) various controls are carried out on the motor system, and motion control of the forming piston, the powder supply piston and the powder spreading roller is provided; (3) controlling the scanning galvanometer, and setting the movement speed, the scanning delay and the like of the scanning galvanometer; (4) setting various parameters of automatic molding equipment, such as adjusting laser power, ascending and descending parameters of a molding cylinder and a powder spreading cylinder, and the like; (5) provides the coordination control of five motors of the molding equipment to finish the processing operation of parts.

According to yet another aspect of the application, a processor is provided for executing software for performing the 3D printing method. According to the requirements of the SLM process, professional software involved in the SLM process mainly comprises three types: slicing software, scan path generation software, and device control software. The slicing processing implemented by the slicing software is one of key contents of the rapid prototyping software, and the function of the slicing software is to convert a three-dimensional CAD model of a part into a two-dimensional slicing model to obtain layer-by-layer section contour data. In the SLM process, the most basic operation is to control the laser to scan. Since the cross-sectional information obtained by layering is contour data, it is necessary to perform internal filling. The function of the scan path generation software is to generate a fill scan path from the profile data. The master control software mainly controls the forming process, displays the processing state and further realizes human-computer interaction.

According to yet another aspect of the present application, there is provided a memory for storing software for executing the 3D printing method.

It should be noted that the 3D printing performed by the software is the same as the 3D printing described above, and is not described herein again.

In this embodiment, an electronic device is provided, comprising a memory in which a computer program is stored and a processor configured to run the computer program to perform the method in the above embodiments.

These computer programs may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks, and corresponding steps may be implemented by different modules.

The programs described above may be run on a processor or may also be stored in memory (or referred to as computer-readable media), which includes both non-transitory and non-transitory, removable and non-removable media, that implement information storage by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), Read Only Memory (ROM), Electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), Digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information that can be accessed by a computing device. As defined herein, a computer readable medium does not include a transitory computer readable medium such as a modulated data signal and a carrier wave.

The above are merely examples of the present application and are not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A3D printing method of a hole structure is characterized in that: scanning and printing layer by using a selective laser melting method, wherein when each layer is scanned and printed, scanning and printing at least one circle around the edge of the layer to form a closed area, and then printing the inside of the closed area; when the inside of the closed area is printed, at least one circle of the edge of the hole inside the closed area is printed, and then the rest positions are printed.

2. The method of claim 1, wherein: the scanning speed when scanning around the edge of the layer for printing is lower than that when printing inside the closed area.

3. The method of claim 1, wherein: the scanning speed of the layer is 1700mm/s-2000mm/s when the layer is firstly scanned and printed around the edge of the layer, and the scanning speed of the closed area is 2000mm/s-2700mm/s when the layer is printed inside the closed area.

4. The method of claim 2, wherein: the laser power when scanning around the edge of the layer for printing is larger than that when printing inside the closed area.

5. The method of claim 1, wherein: the laser power during scanning and printing around the edge of the layer is 300W-340W, and the laser power during printing inside the closed area is 230W-300W.

6. The method of claim 1, wherein: said first scanning at least one revolution around the edge of the layer comprises: the layers were printed around the edge in an outside-in order for 3 weeks.

7. The method of claim 1, wherein: the printing at least one circle around the edge of the layer in the order from outside to inside comprises printing for 2 or more circles, and the contact ratio between each circle and the adjacent circle in the width direction of the printing path is 20-30%.

8. The method of claim 1, wherein: when the inside of the closed area is printed, the end point when the edge surrounding the layer is scanned and printed is taken as the starting point, and the hole with the shortest distance from each point of the edge of each hole in the current closed area to the starting point is calculated as the initial printing hole of the closed area.

9. The method of claim 6, wherein: when the inside of the closed area is printed, the end point surrounding the hole which is printed before is taken as the starting point, and the hole with the shortest distance from each point of the edge of each unprinted hole in the current closed area to the starting point is calculated as the next hole to be printed.

10. The utility model provides a 3D printing system of hole structure which characterized in that: comprising an optical path unit, a mechanical unit, a control unit and a protective gas sealing unit, and software for implementing printing according to the method of any of the preceding claims 1-9.