CN103920877A - Design method of easily-removable support structure for SLM-manufactured metal parts - Google Patents

Abstract

A support structure design method for easy removal of metal parts manufactured by SLM is applied to the support design of structures such as suspended planes and curved surfaces in the process of manufacturing metal parts by laser selective melting SLM technology, so as to ensure that the surface can be formed, the structural stability above the surface and Forming quality meets technical requirements. This method designs a grid-shaped thin-walled structure support, and designs a zigzag structure in the support and solid connection part. The purpose of the grid-shaped thin-walled structure is: 1. Reduce the weight of the support and even the amount of powder used; 2. Satisfy the requirements of the support The strength of the suspension surface is easy to remove by mechanical means; 3. The processing time of the support is accelerated and the efficiency is improved. The purpose of the jagged shape is to reduce the strength of the connecting part between the support and the entity, and after removal, the surface quality of the molding surface will not be affected due to too many supports. The support structure is easy to realize and generate, and it is easy to remove and minimize the surface roughness of the support surface during post-processing, which is suitable for mass production.

Description

A design method of easy-to-remove support structure for metal parts manufactured by SLM

technical field

The invention proposes an easy-to-remove support structure design method applied in the process of SLM manufacturing metal parts, which is mainly used to select the support of the suspended plane and curved surface in the melting manufacturing process, so as to ensure the forming of the surface and the stability of the structure above the surface to achieve forming Quality and technical requirements, belonging to the field of rapid prototyping in laser advanced manufacturing.

Background technique

At present, 3D printing technology is very hot and has become the development trend of advanced manufacturing. In fact, it belongs to the category of rapid prototyping technology. It integrates modern scientific and technological achievements such as CAD technology, numerical control technology, laser technology and material technology, and is an important part of advanced manufacturing technology.

Rapid prototyping technology is developing in the direction of direct manufacturing of metal parts. Selective laser melting (SLM) is a new rapid prototyping technology that can directly form high-density and high-precision metal parts. The schematic diagram of its main principle is shown in Figure 6. During the manufacturing process, the platform in the powder supply bin 20 rises to a certain height according to the set layer thickness of powder, and the horizontal movement of the scraper clamp 15 drives the scraper 21 to spread the metal powder evenly on the On the substrate of the forming chamber 19; the laser scans and melts the area to be melted under the control of the vibrating mirror 14; then, the substrate descends by one layer thickness, and the processing of the lower layer is repeated, and so on, and the metal parts 17 are processed layer by layer. Powder collection bin 18 can recycle unused powder.

Compared with the current rapid prototyping technology for other commonly used forming metal parts, the selective laser melting technology overcomes the shortcomings of other sintering technologies that cannot use pure metal powder, poor forming compactness and mechanical properties, and complicated post-processing technology. Rapid design and automatic manufacturing of prototypes Fast manufacturing of tools is guaranteed. Without CNC milling, without EDM, without any special tooling and tools, complex tools and cavities are manufactured directly according to the prototype. Generally speaking, the manufacturing time and cost of molds are 1/3 of traditional transmission technology. The material used can be extended to a variety of pure metal or alloy materials (such as stainless steel, tool steel, iron alloy, etc.) The relative density of the formed parts is close to or reaches 100%, and the overall mechanical properties are better than those made by casting methods, such as As shown in Figure 7, the aluminum alloy samples manufactured by SLM have higher tensile strength and yield strength, and the overall performance is higher than that of samples manufactured by traditional methods. Moreover, the dimensional accuracy and surface roughness are good, and it can be directly put into practical use with or without simple post-processing (such as sandblasting, polishing, etc.).

There are many bottlenecks in the development of new technologies. Since selective laser melting (SLM) technology is a fusion of modern advanced technologies such as CAD technology, numerical control technology, laser technology and material technology, it is the product of the intersection of multiple disciplines, and the forming process problems to be solved are also multi-faceted. , mainly focusing on material preparation, process optimization, molding post-processing and precision control, etc.

The optimization of laser selective melting forming process is mainly the optimization of processing parameters and the optimization of forming structure. The optimization of processing parameters is mainly to ensure that the density of the solid part is close to 100%, there are as few holes as possible, the surface roughness is as small as possible, and there is no need for over-burning to cause fusion tumors, etc. The optimization of the molding structure is mainly reflected in the quality of the molding and the guarantee of dimensional accuracy. It is necessary to ensure that the structural design is suitable for SLM, and to optimize the structural design of the auxiliary molding of certain part structures.

Although SLM technology can form metal parts of any complex shape in principle, it cannot perfectly form all geometric features, including thin plates, sharp corners, especially the overhang surface structure, etc. The overhang surface structure makes the local shape accuracy and size of SLM formed parts The accuracy cannot meet the requirements, and in serious cases, the processed parts will be scrapped, or the molding process will fail. For the processing of the overhanging surface, at present, it is mainly to add a large amount of metal supports to ensure the stability of the forming process, and then remove the supports and surface grinding methods to ensure the forming surface. There are also a few cases where the overhanging surface is obtained by machining after SLM forming. But when the workpiece is fine and complex, or the overhanging surface is inside the part, adding support or subsequent machining is no longer suitable. Therefore, in the design of the forming structure, the overhanging surface can be formed smoothly without adding support as much as possible, or the overhanging surface can be avoided or minimized during the design stage. It is necessary to design and add support to ensure the quality and stability of the molding.

Fig. 7 is a schematic diagram of arbitrary curved surface parts after layering. Among them, sections a~b and sections c~d will meet the overhanging structure during the SLM forming process, and will form a suspended part without self-support when layered and sliced. The length of the suspended part between layers is S=H× ctgθ, where H is the thickness of the slice, and the inclination angle θ is the angle between the profile of the slice layer and the horizontal plane. In SLM molding, the larger the S value, the easier it is to cause overhangs and warping deformation, which is very unfavorable to molding. The S value is closely related to the layer thickness h and the inclination angle θ. The larger the value of h, or the smaller the θ, the S will increase. At present, the layer thickness of the process used by SLM is generally determined by the powder particle size of the material, and the optimized layer thickness range is 20-50 μm. Therefore, the S value is mainly related to the inclination angle θ. The inclination angle θ1 of section a~b is significantly greater than the inclination angle θ2 of section c~d, so defects are more likely to occur in section c~d. In the SLM forming process, there is a limit tilt angle. The so-called limit inclination angle means that when the inclination angle is less than a certain value, the overhanging structure will collapse, affecting continuous processing. Through a large number of experiments, it can be concluded that the limit inclination angle is 40 to 45 degrees. If the angle between the part surface and the horizontal plane is greater than this inclination angle, it can support itself without auxiliary support. If the angle is smaller than this angle, it must be supported to prevent overhangs and warping. There are two defects of bending and deformation.

Figure 8 and Figure 9 are schematic diagrams of typical round hole overhang structures and square hole overhang structures encountered during SLM processing. In Figure 8, the area (h1+h2) belongs to the stable forming area, which can be well formed as its own support, while the h3 area needs to add auxiliary support under this area to ensure the forming of the surface when forming a round hole with a diameter of more than 6mm. The key to forming the round-hole overhang structure by SLM is how to judge the position limits of h2 and h3. The main basis is that the tangent angle α at the limit is consistent with the critical forming angle discussed in Figure 7. All need to add support below the 31 faces during the square hole formula suspension structure among Fig. 9.

The addition of support and the ease of removal after support determine the surface quality of the molding surface and the ease of subsequent processing. At the same time, it must be ensured that the removal of the support will not affect the structure of the molded part. Therefore, it is easy to melt the support structure in the laser selection area. Removing the design is of great significance to the improvement of the SLM process and the expansion of the application range.

Contents of the invention

The purpose of the present invention is to provide an easy-to-remove support design method applied in the data processing process of laser selective melting metal parts manufacturing, so that the support can be easily removed after the parts are taken out so that the impact on surface quality is minimized.

A method for designing a support structure that is easy to remove for SLM manufacturing metal parts, characterized in that: the designed support structure includes: a support grid thin-wall structure and a sawtooth connection structure on the edge of the support grid thin wall, forming a network of multiple through holes connected into one shape structure; the grid size in the supporting grid thin-walled structure is adjusted according to the required strength, including the length in the X direction and the length in the Y direction; in addition, the direction of the thin wall and the Y direction form a certain angle a, and the angle a is 30-45 degree; the thickness of the thin wall is 0.1-0.3mm; in the sawtooth connection structure, a part of the support extends into the entity.

Further, the sawtooth is divided into two parts, top and bottom, and the top and bottom parts are respectively two trapezoids with a common bottom, and the width of the bottom is smaller than that of the two trapezoids.

In order to achieve the above object, the present invention designs a grid-shaped thin-walled structure support, and a zigzag structure is designed at the support and the solid connection part. The purpose is to make it only satisfy the strength of the support suspension surface forming and be easy to remove by mechanical means, and also speed up the processing time of the support and improve the efficiency. The sawtooth structure is to minimize the strength of the connecting part between the support and the entity, so that the surface quality of the molding surface will not be affected by too many supports after removal.

The beneficial effect of the present invention is that: the support structure designed by the present invention can be easily realized and generated in the processing engineering, and can be easily removed and the surface roughness of the support surface can be minimized in the process of post-processing, and the method is simple The utility model has the characteristics of practicality and low cost, is suitable for mass production, and has great economic benefits.

Description of drawings

Fig. 1 is a schematic diagram of the external structure of the easy-to-remove support for metal parts manufactured by SLM of the present invention;

Fig. 2 is a schematic diagram of the internal structure of the easy-to-remove support for metal parts manufactured by SLM of the present invention;

Fig. 3 is a schematic diagram of the thin-wall structure of the easy-to-remove supporting grid for the SLM manufacturing of metal parts of the present invention;

Fig. 4 is a schematic diagram of the structure of the sawtooth connection part of the easy-to-remove support for metal parts manufactured by SLM of the present invention;

Fig. 5 is a schematic diagram of the partial structure of the sawtooth connection of the easy-to-remove support for metal parts manufactured by SLM of the present invention;

Fig. 6 is a schematic diagram of the principle of the SLM manufacturing metal parts forming process method of the present invention;

Fig. 7 is a comparison diagram of tensile mechanical properties of aluminum alloy parts manufactured by SLM of the present invention;

Figure 8 is a schematic diagram of the layered structure of the overhanging surface of the metal part manufactured by SLM of the present invention;

Fig. 9 is a schematic diagram of the structure of the overhanging surface of the round hole of the metal part manufactured by SLM of the present invention;

Fig. 10 is a schematic diagram of the structure of the overhanging surface of the square hole of the metal part manufactured by SLM of the present invention.

In the figure: 1. Part entity, 2. Support structure, 3. Laser melting zone, 4. Support grid thin-walled structure, 5. Zigzag connection structure, 6. Part entity part, 7. Support structure part, 8. Breakpoint Line length, 9, length into the entity, 10, tooth top width, 11, tooth bottom width, 12, tooth top height, 13, tooth bottom height, 14, laser system, 15, powder scraping system, 16, metal powder, 17. Forming parts, 18. Powder collection bin, 19. Forming bin, 20. Powder supply bin, 21. Scraper, 22. Tensile strength, 23. Yield strength, 24. Elongation, 25. Tensile strength and yield strength Ruler, 26. Elongation scale, 27. SLM manufacturing sample, 28. Casting sample, 29. Casting sample after aging, 30. Arc surface to be supported, 31. Plane to be supported.

Detailed ways

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

The structural diagram of this embodiment is shown in Figure 1. An example of such a hanging surface is given. The main part entity 1 has two bosses, and the size reaches the order of tens of millimeters. In this order of magnitude, an auxiliary forming structure must be added to ensure The forming quality and dimensional accuracy of the boss, etc. Therefore, it is necessary to make necessary supports under the overhanging surface of the boss to ensure the shape. Part 2 in the figure is the supporting structure. After the SLM process is completed, the parts are taken out, and then such supports are removed to obtain the boss and overhanging surface structure.

In order to increase the ease of removal of the support, the internal structure of the support is also designed, as shown in Figure 2, 1 is the part entity, 3 is one of the surfaces of the entity to be processed, which is the surface melted and then solidified by the laser, and 4 is the inside of the support Structure, the internal structure is designed as a grid thin-walled structure, which can not only reduce the amount of powder used for the support, but also reduce the strength of the support and increase the ease of removal. As shown in Figure 3, the size of the grid can be adjusted according to the required strength, such as the length in the X direction, the length in the Y direction, increasing the length, the grid will become larger, and the ease of removal will increase, but the strength will decrease. According to the actual situation of the part to make sure. In addition, the direction of the thin wall forms a certain angle a with the Y direction, and this angle is also adjustable, ranging from 30 degrees to 45 degrees. In this way, one direction of the thin wall is parallel to a certain side of the part, so that the force distribution of the thin wall in each direction is not uniform, resulting in poor forming. The thickness of the thin wall can be adjusted in the range of 0.1 to 0.3. Adjusting the thickness of the thin wall can adjust the strength of the support, making the removal of the support more flexible.

As shown in Figure 4, the 5-serrated connection structure further reduces the connection area between the support and the entity on the basis of the thin-walled grid structure, and further increases the ease of removal of the support. Under the action of the sawtooth, the suspension surface of the first layer can be formed And ensure that it will not be scraped off by the scraper and affect the forming of the next layer. Figure 5 shows a partial enlarged view of the support structure and the connection of the parts. 6 is the part entity, 7 is the support structure, and a part of the support extends into the entity. The length of this protruding entity is shown as 9, which can be set to change the bonding strength between the support and the entity in the longitudinal direction. The commonly used setting range is 0.05~0.3. The sawtooth is divided into two parts, the top and the bottom. Both the top width 10 and the bottom width 11 are adjustable parameters. The commonly used setting range is 0.1 to 0.4. The height of the top and bottom of the support is also an adjustable parameter. The commonly used setting range is 0.2 to 1.0. Changing the height of the teeth can change the difficulty of removing the support. The higher the teeth, the easier it is to remove, but the strength of the teeth decreases. The shorter the teeth, the opposite is true. 8 is the length of the breakpoint line, which means that there is a transverse cross-sectional contraction between the top and the bottom of the tooth. The length of the line here is also adjustable. The commonly used setting parameters are 0.1 to 0.2. Because the size here becomes smaller, the strength is also the smallest. , the breakage between the support and the entity also occurs here. Adjust the strength of the tooth by adjusting the width and height of the bottom of the tooth, adjust the width of the top of the tooth and the length of the protruding entity to adjust the bonding strength, adjust the length of the breakpoint line to adjust the fracture strength of the tooth and support the fracture strength.

The present invention proposes a method of grid thin-walled structure and zigzag connection structure by designing the internal structure and connection part structure of the columnar support, and adjusts the strength and ease of removal of the support by adjusting and setting the parameters of each part, according to different parts The size can be adjusted according to the size of different hanging surfaces, which not only simplifies the support but also ensures the strength, flexible handling, and increases the ease of removal of the support. After removal, a simple polishing treatment on the surface of the part can ensure the surface quality and reduce the influence of the support. It is suitable for mass production and has high economic value.

Claims (2)

1. A method for designing a support structure that is easy to remove for SLM manufacturing metal parts, characterized in that: the designed support structure includes: a support grid thin-walled structure and a sawtooth connection structure on the edge of the support grid thin wall, forming a plurality of through holes connected into one network structure; the grid size in the thin-walled structure of the support grid is adjusted according to the required strength, including the length in the X direction and the length in the Y direction; in addition, the direction of the thin wall and the Y direction form a certain angle a, and the angle a is 30 -45 degrees; the thickness of the thin wall is 0.1-0.3mm; part of the support in the sawtooth connection structure extends into the entity. 2. A method for designing a supporting structure for easy removal of metal parts manufactured by SLM according to claim 1, characterized in that: the sawtooth is divided into two parts, top and bottom, and the top and bottom parts are respectively two trapezoids with a common bottom , and the width of the base is smaller than the bases of the two trapezoids.