A laser additive manufacturing method for large-size structural parts based on residual stress release

Abstract

The present invention proposes a laser additive manufacturing method for large-size structural parts based on residual stress release. First, the clamping edge of the long edge of the structural part and the substrate is used as the rotation axis, and the bottom edge of the structural part is rotated along the additive manufacturing construction direction to lift the bottom of the short edge upward, and fill the gap between the bottom of the model and the substrate; according to the length of the bottom edge, the edge is rounded at the connection between the short edge and the substrate; the height of the intersection of the edge rounding and the short edge is the center height of the first stress release hole; the second stress release hole is set downward close to the rotation axis direction of the first stress release hole; the model of the component is introduced into the laser additive manufacturing equipment, and the structure is printed; the printed structure is heat treated to obtain the structure with the residual stress removed. The present invention can improve the yield rate of printed parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular to a laser additive manufacturing method for large-size structural parts based on residual stress release. Background Art

[0002] The rudder and wing structure is one of the main load-bearing components of the aircraft. The traditional preparation method is mainly through the welding of the skin and the skeleton structure. This method requires a lot of manpower and material resources to complete the machining and welding of parts, and its development cycle is long and the development cost is high. With the development of metal additive manufacturing technology, the size of the printer's forming cabin is getting larger and larger, and the effective forming length of the equipment exceeds 600mm, which makes additive manufacturing of large-sized structural parts such as rudders and wings possible. In the heating cycle of the laser additive manufacturing process, the thermal expansion of the material is restricted by the surrounding material at a lower temperature, thereby forming compressive stress in the heated area. In the cooling cycle, the heated area begins to cool, and the contraction of the material in this area is restricted by the plastic strain formed in the heating stage to form tensile stress. If the magnitude of the stress in the hot-cold cycle exceeds the yield strength of the material, even if the material cools to ambient temperature, residual stress will be formed and remain in the part. For large-sized structural parts such as rudders and wings, the residual stress at the bottom during the cooling process is large, especially at the short edge due to the lack of material constraints, the risk of fracture and deformation is doubled. Summary of the invention

[0003] The purpose of the present invention is to provide a laser additive manufacturing method for large-size structural parts based on residual stress release. For large-size metal structural parts such as rudders and wings, especially materials with higher strength such as titanium alloys and high-strength steel, the probability of printing cracks can be effectively reduced, and the one-time forming of complex copper alloy parts can be achieved.

[0004] The technical solution to achieve the purpose of the present invention is:

[0005] A laser additive manufacturing method for large-size structural parts based on residual stress release comprises the following steps:

[0006] Model construction:

[0007] With the long edge of the structural component and the clamping edge of the substrate as the rotation axis, the bottom edge of the structural component is rotated along the additive manufacturing construction direction to lift the bottom of the short edge upward, and fill the gap between the bottom of the model and the substrate;

[0008] According to the length of the bottom edge, the edge is rounded at the junction of the short edge and the base plate;

[0009] The height of the intersection of the edge chamfer and the short edge is the height of the center of the first stress relief hole;

[0010] A second stress release hole is arranged downwardly from the first stress release hole and close to the rotation axis;

[0011] Printing structural parts:

[0012] Import the component model into the laser additive manufacturing equipment and print it to obtain the structural part;

[0013] Heat treatment: The printed structure is heat treated to obtain a structural part with residual stress removed.

[0014] Compared with the prior art, the present invention has the following significant advantages:

[0015] (1) The present invention provides a laser additive manufacturing method for large-size structural parts based on residual stress release. The stress hole diameter, rotation angle, and number of stress holes of the structure are determined according to the bottom edge length of the model, and then the multiple stress holes are rearranged to obtain the required stress release structure. For products with a length of less than 500 mm, the product printing success rate can be increased to 95%, and for products with a size of more than 500 mm, the product printing success rate can be increased to 90%.

[0016] (2) The present invention has greatly improved the success rate of printing multiple parts in one cabin. For the printing of two products in one cabin, the product with a length less than 500 mm can increase the product printing success rate to 95% (except for stress relief holes and support structures, the part body is considered successful if it does not crack). For products with a size greater than 500 mm, the product printing success rate can be increased to 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the principle of the rudder wing component model.

[0018] Figure 2 for Figure 1 Top view of . DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0020] The present invention discloses a laser additive manufacturing method for large-size structural parts based on residual stress release. The method determines the stress hole diameter, rotation angle, and number of stress holes of the structure according to the bottom edge length of the model, and then rearranges the multiple stress holes to obtain the required stress release structure (see Table 1 for the specific relationship).

[0021] Table 1

[0022] Bottom length (mm) Stress hole diameter (mm) Rotation angle (°) Number of stress holes 100-200 3-4 2 1-2 200-300 3-5 2 1-2 300-400 4-6 1-2 2-3 More than 500 5-8 1-2 2-3

[0023] Two embodiments are taken from Table 1 for detailed description:

[0024] Example 1

[0025] In this embodiment, a laser additive manufacturing method for large-size structural parts based on residual stress release is used. When the bottom edge length of the model is 300 mm, one cabin and two parts are used for printing. First, the model is assembled, and then 3D printing is performed.

[0026] Model building steps:

[0027] Step 1: Under the premise of meeting the structural size requirements, use the clamping edge of the long edge of the structural component and the substrate as the rotation axis, rotate the bottom edge of the structural component by 2° along the additive manufacturing construction direction, raise the bottom of the short edge by about 10mm, and fill the gap between the bottom of the model and the substrate. Figure 1 and Figure 2 shown.

[0028] Step 2: According to the length of the bottom edge, make a rounded edge at the connection between the short edge and the base plate, with a radius of 8mm.

[0029] Step 3: Take the height of the intersection of the chamfered edge and the short edge as the center height of the first stress release hole, and make a stress release hole with a diameter of 3mm.

[0030] Step 4: Make a second stress relief hole at the lower left of the first stress relief hole, with a diameter of 3 mm.

[0031] Step 5. Copy the model 30mm to the right of the structural model as the second product model.

[0032] Printing process steps:

[0033] Using TC4 powder as raw material, the selective laser melting equipment is used for printing. Before printing, argon protection is required to keep the oxygen content in the forming chamber below 1000ppm, and the substrate is preheated to 80°C. The scanning speed is set to 1200mm / s, the printing power is 350W, the powder diameter is 15-53μm, and the printing layer thickness is 50μm for printing. After printing, when the temperature in the forming chamber drops below 70°C, the substrate is removed, the residual powder is cleared, and the forming of the part is observed.

[0034] Heat treatment steps:

[0035] The heat treatment furnace was evacuated to 10 -3 Pa, heat to 800℃ and keep warm for 2h, cool the furnace to 500℃ and pass argon gas for cooling. After the heat treatment is completed, take out the sample, remove the support and observe the cracks of the parts.

[0036] The first stress release hole was broken along the center of the rounded edge, while the second stress release hole was not broken. After multiple tests, the success rate of the laser additive manufacturing equipment to obtain the structural parts was 95%. By setting the stress release hole at the filling position, the fracture position will not occur on the structural part body, but only at the filling position, which improves the yield rate.

[0037] Example 2

[0038] In this embodiment, a laser additive manufacturing method for a large-size structural part based on residual stress release is used. When the length of the bottom edge of the model is 500 mm, one cabin is used for printing:

[0039] Model building steps:

[0040] Step 1: On the premise of meeting the structural size requirements, use the clamping edge of the long edge of the structural component and the substrate as the rotation axis, rotate the bottom edge of the structural component by 2° along the additive manufacturing construction direction, raise the bottom of the short edge by about 20 mm, and fill the gap between the bottom of the model and the substrate.

[0041] Step 2: According to the length of the bottom edge, make a chamfer at the connection between the short edge and the base plate, with a radius of 20mm.

[0042] Step 3: Take the height of the intersection of the chamfered edge and the short edge as the center height of the first stress release hole, and make a stress release hole with a diameter of 8 mm.

[0043] Step 4: Make a second stress release hole at the lower left of the first stress release hole, with a diameter of 8 mm. Depending on the model size, make a third stress release hole at the lower right of the first stress release hole, with a diameter of 8 mm.

[0044] Printing process steps:

[0045] The model is imported into the software for slicing, and finally the structural parts are obtained through laser additive manufacturing equipment: TC4 powder is used as the raw material and printed by selective laser melting equipment. Before printing, argon protection is required to make the oxygen content in the forming chamber lower than 1000ppm, and the substrate is preheated to 80℃. Set the scanning speed to 1200mm / s, the printing power to 350W, the powder diameter to 15-53μm, and the printing layer thickness to 50μm for printing. After printing, when the temperature in the forming chamber drops below 70℃, take out the substrate, clear the residual powder, and observe the forming of the parts.

[0046] Heat treatment steps:

[0047] The heat treatment furnace was evacuated to 10 -3 Pa, heat to 800℃ and keep warm for 2h, cool the furnace to 500℃ and pass argon gas for cooling. After the heat treatment is completed, take out the sample, remove the support and observe the cracks of the parts.

[0048] After testing, the first stress release hole was broken at the height of the center of the chamfered circle, the second stress release hole was not broken, and the third stress release hole was broken. After multiple tests, the success rate of structural parts obtained by laser additive manufacturing equipment was 90%.

[0049] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A laser additive manufacturing method for large-size structural parts based on residual stress release, characterized in that: The following steps are involved: Model construction: With the long edge of the structural component and the clamping edge of the substrate as the rotation axis, the bottom edge of the structural component is rotated along the additive manufacturing construction direction to lift the bottom of the short edge upward, and fill the gap between the bottom of the model and the substrate; According to the length of the bottom edge, the edge is rounded at the junction of the short edge and the base plate; The height of the intersection of the edge chamfer and the short edge is the height of the center of the first stress relief hole; A second stress release hole is arranged downwardly from the first stress release hole and close to the rotation axis; Printing structural parts: Import the component model into the laser additive manufacturing equipment and print it to obtain the structural part; Heat treatment: Heat treatment is performed on the printed structure to obtain a structural part with residual stress removed; The bottom edge is rotated by 1-2° along the additive manufacturing construction direction; The bottom of the short edge is raised by 10-20 mm; The radius of the edge chamfer is 8-20mm; When the length of the bottom edge is not less than 300 mm, a third stress relief hole is also provided at the filling position, and the third stress relief hole is close to the edge chamfer; The diameter of the stress release hole is 3-8 mm.

2. The laser additive manufacturing method for large-size structural parts based on residual stress release according to claim 1 is characterized in that: During the printing process, protective gas was introduced to preheat the substrate, and the scanning speed, printing power, and printing layer thickness were set. The powder diameter was 15-53μm, and printing was performed.

3. The laser additive manufacturing method for large-size structural parts based on residual stress release according to claim 1 is characterized in that: Heat treatment furnace vacuum to 10 -3 Pa, heat to 800℃ and keep warm for 2h, cool the furnace to 500℃ and pass argon for cooling.

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