Additive / subtractive / equal-material composite machining and manufacturing method for high-yield-strength stainless steel

Abstract

The invention relates to an increase / decrease / equal-material composite machining and manufacturing method for high-yield-strength stainless steel. The method comprises the steps that S1, a base plate is selected and pretreated; s2, laser additive manufacturing; s3, milling and cutting materials; s4, performing ultrasonic rolling and equal-material processing; and S5, layer-by-layer composite machining is conducted till part forming is achieved, specifically, the step S2 to the step S4 are repeated on the rolled surface obtained in the step S4 till part preparation is completed, and the high-performance stainless steel is obtained. According to the invention, through the combination of an additive manufacturing technology, a traditional milling technology and an ultrasonic rolling technology, a brand-new additive / subtractive / equal material composite processing and manufacturing method is formed; the inherent thinking of single-process manufacturing is broken through, the limitation of a single process is broken through, advantage complementation and defect avoidance among different processes are achieved, and the effect that 1 + 1 + 1 is larger than 3 is achieved, so that the microscopic structure is improved, internal defects are eliminated, and the mechanical properties such as yield strength and hardness are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of additive manufacturing, in particular to a high-yield-strength stainless steel additive / subtractive / isometric composite machining manufacturing method. BACKGROUND

[0002] 316L stainless steel has been widely used in aerospace and marine facilities due to its excellent corrosion resistance and mechanical properties, but the yield strength and hardness of the 316L stainless steel manufactured by conventional process are low, which limits its application in modern industrial fields, therefore, how to improve its mechanical properties is a problem to be solved.

[0003] Additive manufacturing technology, as a new manufacturing technology, mainly melts the metal powder and inert gas dynamically sent into the laser beam spot together with the previous deposition layer to form a product with complex geometry. Due to its high material utilization, strong processing flexibility, few processing procedures and high design freedom, it is widely used in aerospace, automobile industry and medical devices. However, the products produced by this technology also have some drawbacks that cannot be ignored: due to the characteristics of powder melting / solidification, the surface roughness Ra of the workpiece is as high as 60 μm; the poor surface quality will directly affect the deposition of the next layer, and the spatter and spheroidization effect of the powder will lead to the formation of defects such as pores, cracks and un-melted powder, which will ultimately affect the mechanical properties of the product. In addition, due to the uneven distribution of temperature field, coarse columnar grains will inevitably form inside the workpiece along the temperature gradient, which will affect the mechanical properties, especially the reduction of yield strength. Therefore, it is urgent to solve the problem of reducing or even eliminating these defects and improving the mechanical properties. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a high-yield-strength stainless steel additive / subtractive / isometric composite machining manufacturing method, which combines additive manufacturing technology, traditional milling technology and ultrasonic rolling technology to form a new additive / subtractive / isometric composite machining manufacturing method; break the inherent thinking of single process manufacturing, break through the limitation of single process, realize the complementary advantages and defect avoidance among different processes, achieve the effect of "1+1+1 greater than 3", so as to improve the microstructure, eliminate internal defects and improve the mechanical properties such as yield strength and hardness.

[0005] The technical scheme adopted by the present application is as follows: The high-yield-strength stainless steel additive / subtractive / isometric composite machining manufacturing method proposed by the present application specifically includes the following steps: S1, substrate selection and pretreatment; S2, laser additive manufacturing: clamp the substrate obtained in step S1 to the machine tool, use additive manufacturing technology to perform additive deposition on the substrate to form a first layer of additive manufacturing surface; specifically comprising: S21, clamp the stainless steel substrate obtained in step S1 to the machine tool to ensure the levelness of the substrate; S22, pour the stainless steel powder into the powder feeder, open the protective gas, adjust the position of the laser head, make the powder spot coincide with the light spot, set the parameters of laser additive, run the laser processing path machine tool program, and complete the first layer of additive deposition according to the program; The parameters of laser additive are: laser power is 400-500W, powder feeding rate is 3.85-3.90g / min, and scanning speed is 680-720mm / min; S3, subtractive machining by milling: the additive manufacturing surface obtained in step S2 is machined by subtractive manufacturing technology to remove surface oxide layer, porosity and unmelted defects, and obtain a subtractive machining surface with better surface quality; S4, equal material machining by ultrasonic rolling: the subtractive machining surface obtained in step S3 is treated by ultrasonic rolling to obtain a rolling machining surface; S5, layer-by-layer composite machining until the part is formed: the rolling machining surface obtained in step S4 is repeated steps S2-S4 until the part is prepared, and a high-performance stainless steel is obtained.

[0006] Further, the step S1 comprises: selecting the same type of stainless steel substrate according to the material of the part to be formed, polishing the stainless steel substrate with sandpaper to remove the surface oxide film, and wiping the surface with anhydrous ethanol to obtain a bright machining surface and ensure good metallurgical bonding.

[0007] Further, in step S3, the subtractive manufacturing technology is milling, the cutting speed of milling is 93-95m / min, the axial cutting depth is 0.14-0.16mm, the radial cutting depth is 4.8-5.2mm, and the feed speed is 280-320mm / min.

[0008] Further, the step S4 specifically comprises: S41, clean the residual powder and milling chips on the subtractive machining surface to ensure the surface quality of subsequent rolling machining; S42, start the ultrasonic rolling equipment, move the rolling tool head to the starting position, and perform rolling calibration; S43, set the ultrasonic frequency, ultrasonic rolling amplitude, static pressure, rolling feed speed, rolling interval parameters, perform multi-pass ultrasonic rolling treatment, select appropriate oil output of lubricating oil, cool and lubricate the machining surface and ultrasonic rolling tool head, and run the program to complete the ultrasonic rolling process.

[0009] Further, in the step S43, the ultrasonic frequency of the ultrasonic rolling device is 25-35 kHz, the ultrasonic rolling amplitude is 14-16 mu m, the static pressure is 1000-1400 N, the rolling feed speed is 1400-1600 mm / min, and the rolling interval is 0.04-0.06 mm.

[0010] Further, the ultrasonic rolling tool head is a hard alloy ball.

[0011] Compared with the prior art, the present application has the following beneficial effects: 1. The additive / subtractive / isometric composite machining manufacturing method of high yield strength stainless steel breaks the inherent thinking of single process manufacturing, breaks through the limitation of single process, realizes the complementary advantages and defect avoidance among different processes, and achieves the effect of "1+1+1 greater than 3".

[0012] 2. The additive / subtractive / isometric composite machining manufacturing method of high yield strength stainless steel adopts laser directional energy deposition technology, which has high material utilization, strong processing flexibility, few processing procedures, and high design freedom, and can be combined with milling subtractive machining and ultrasonic rolling isometric machining processes.

[0013] 3. The additive / subtractive / isometric composite machining manufacturing method of high yield strength stainless steel adopts milling process to perform subtractive machining on the surface of additive manufacturing, which can effectively remove the pores, oxidation layer and unmelted defects on the surface of additive manufacturing, and provides a good surface quality for subsequent ultrasonic rolling.

[0014] 4. The additive / subtractive / isometric composite machining manufacturing method of high yield strength stainless steel adopts ultrasonic rolling technology to process the subtractive surface, which belongs to isometric machining, and after ultrasonic rolling strengthening, the method has the effects of closing small pores, improving organization, refining grains and introducing high-density dislocations.

[0015] In summary, compared with single additive manufacturing processing, the additive / subtractive / isometric composite machining manufacturing method of high yield strength stainless steel strengthens the whole part by layer-by-layer strengthening treatment. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The figure is a flowchart of the method of the present application; Figure 2 The figure is a schematic diagram of the pore characteristics of 316L stainless steel of Comparative Example 1 and Example 1; wherein (a) is the pore characteristics of 316L stainless steel obtained by additive manufacturing of Comparative Example 1, and (b) is the pore characteristics of 316L stainless steel obtained by additive / subtractive / isometric composite machining manufacturing of Example 1; Figure 3Fig. 1 is a schematic diagram of the metallographic structure of the 316L stainless steel of Comparative Example 1 and Example 1; wherein (a) is the metallographic structure of the 316L stainless steel obtained by using additive manufacturing in Comparative Example 1, and (b) is the metallographic structure of the 316L stainless steel obtained by using additive / subtractive / isometric composite machining in Example 1; Figure 4 Fig. 2 is a schematic diagram of the grain EBSD image of the 316L stainless steel of Comparative Example 1; Figure 5 Fig. 3 is a schematic diagram of the grain EBSD image of the 316L stainless steel of Example 1; Figure 6 Fig. 4 is a schematic diagram of the internal microhardness of the 316L stainless steel of Comparative Example 1 and Example 1; Figure 7 Fig. 5 is a schematic diagram of the tensile property comparison of the 316L stainless steel of Comparative Example 1 and Example 1. DETAILED DESCRIPTION

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0018] Referring to the drawings of the present application, Figure 1 The additive / subtractive / isometric composite machining method for high yield strength stainless steel provided by the present application specifically comprises the following steps: S1, substrate selection and pretreatment: according to the material of the to-be-formed part, a stainless steel substrate of the same type is selected, the stainless steel substrate is polished with sandpaper to remove the surface oxide film, and the surface is wiped with anhydrous ethanol to obtain a bright machining surface and ensure good metallurgical bonding.

[0019] S2, laser additive manufacturing: the substrate obtained in step S1 is clamped to the machine tool, and additive deposition is performed on the substrate by using additive manufacturing technology to form a first layer of additive machining surface; wherein the additive manufacturing technology is laser directional energy deposition technology, which specifically comprises: S21, the stainless steel substrate obtained in step S1 is clamped to the machine tool to ensure the levelness of the substrate; S22, the stainless steel powder is poured into the powder feeder, the protective gas is turned on, the position of the laser head is adjusted to make the powder spot coincide with the light spot, the parameters of laser additive are set, the laser machining path machine tool program is run, and the first layer of additive deposition is completed according to the program; The laser additive manufacturing related parameters are as follows: the laser power is 400-500 W, preferably 450 W; the powder feeding rate is 3.85-3.90 g / min, preferably 3.88 g / min; and the scanning speed is 680-720 mm / min, preferably 700 mm / min.

[0020] S3, subtractive machining by milling: the additive machining surface obtained in step S2 is machined by subtractive manufacturing technology to remove the surface oxide layer, pores and unmelted defects, and a subtractive machining surface with better surface quality is obtained; The subtractive manufacturing technology is milling machining, the cutting speed of milling is 93-95 m / min, preferably 94 m / min; the axial cutting depth is 0.14-0.16 mm, preferably 0.15 mm; the radial cutting depth is 4.8-5.2 mm, preferably 5 mm; and the feed speed is 280-320 mm / min, preferably 300 mm / min.

[0021] S4, equal-material machining by ultrasonic rolling: the subtractive machining surface obtained in step S3 is subjected to ultrasonic rolling treatment to obtain a rolling machining surface; specifically comprising: S41, cleaning the residual powder and milling chips on the subtractive machining surface to ensure the surface quality of subsequent rolling machining; S42, starting the ultrasonic rolling equipment, moving the ultrasonic rolling tool head to the starting position, and performing rolling calibration; the ultrasonic rolling tool head is a hard alloy ball; S43, setting the ultrasonic frequency, ultrasonic rolling amplitude, static pressure, rolling feed speed, rolling interval and other parameters, performing multi-pass ultrasonic rolling treatment, selecting appropriate oil output of lubricating oil, cooling and lubricating the machining surface and the ultrasonic rolling tool head, and running the program to complete the ultrasonic rolling process.

[0022] The ultrasonic frequency of the ultrasonic rolling equipment is 25-35 kHz, preferably 30 kHz; the ultrasonic rolling amplitude is 14-16 μm, preferably 15 μm; the static pressure is 1000-1400 N, preferably 1200 N; the rolling feed speed is 1400-1600 mm / min, preferably 1500 mm / min; and the rolling interval is 0.04-0.06 mm, preferably 0.05 mm.

[0023] S5, layer-by-layer composite machining until the part is formed: repeating steps S2-S4 on the rolling machining surface obtained in step S4 until the part is prepared, and obtaining high-performance stainless steel.

[0024] Preferably, the stainless steel is 316L stainless steel.

[0025] The application is a kind of additive / subtractive / isometric composite machining and manufacturing method by synergistically integrating additive manufacturing technology, milling subtractive technology and ultrasonic rolling isometric technology. The additive manufacturing deposition layer is processed by milling and ultrasonic rolling. The purpose is to remove the surface oxide layer, pores and unmelted defects by milling process to obtain better surface quality and provide surface conditions for ultrasonic rolling. Then the ultrasonic rolling process is used to close small pores, improve the structure, refine the grains and introduce high-density dislocations to form a whole part with low defects, high yield strength and high hardness layer by layer.

[0026] The application will be further described by specific examples and comparative examples: Example 1 The substrate of this example is 316L stainless steel with a size of 200mmx200mmx20mm, which is treated by double-sided wire drawing. The surface of the substrate is wiped with anhydrous ethanol before the test to remove surface dirt. The powder selected is 316L stainless steel powder with a particle size of 15-53μm. The additive / subtractive / isometric composite machining and manufacturing method described in the application is used. The specific manufacturing process is as follows: S1, substrate selection and pretreatment: according to the material of the part to be formed, a stainless steel substrate of the same type is selected. The stainless steel substrate is polished with sandpaper to remove the surface oxide film, and the surface is wiped with anhydrous ethanol to ensure good metallurgical bonding and obtain a bright processing surface; S2, laser additive manufacturing: the substrate obtained in step S1 is clamped to the machine tool, and additive deposition is carried out on the substrate by additive manufacturing technology to form a first layer of additive processing surface; specifically including: S21: clamp the stainless steel substrate obtained in step S1 to the machine tool to ensure the levelness of the substrate; S22: pour 316L stainless steel powder into the powder feeder, open the protective gas, adjust the position of the laser head to make the powder spot coincide with the light spot, and set the parameters of laser additive as follows: laser power is 450W, powder feeding rate is 3.88g / min, and scanning speed is 700mm / min; run the program to complete the additive process.

[0027] S3, milling subtractive machining: the additive processing surface obtained in step S2 is processed by subtractive manufacturing technology to remove the surface oxide layer, pores and unmelted defects to obtain a better surface quality of the subtractive processing surface; the subtractive manufacturing technology is milling machining, the cutting speed of milling is 94m / min, the axial cutting depth is 0.15mm, the radial cutting depth is 5mm, and the feed speed is 300mm / min.

[0028] S4, ultrasonic rolling isometric machining: the subtractive processing surface obtained in step S3 is processed by ultrasonic rolling to obtain a rolling processing surface; specifically including: S41: Clean the residual powder and milling chips on the subtractive machining surface to ensure the surface quality for subsequent rolling machining.

[0029] S42: Turn on the ultrasonic rolling device, move the rolling tool head to the starting position, and perform rolling calibration.

[0030] S43: Set the ultrasonic frequency of the ultrasonic rolling device to 30 kHz, the ultrasonic rolling amplitude to 15 pm, the static pressure to 1200 N, the rolling feed speed to 1500 mm / min, and the rolling interval to 0.05 mm. Adjust the appropriate amount of lubricating oil, run the program to complete the rolling process.

[0031] S5, layer-by-layer composite machining until the part is formed: repeat steps S2-S4 for the rolling machining surface obtained in step S4 until the part is prepared, obtaining high-performance stainless steel.

[0032] Comparative Example 1 The substrate selection of this comparative example is a 316L stainless steel with a size of 200 mm x 200 mm x 20 mm, which has been subjected to double-sided wire drawing treatment, and before the test, the surface of the substrate is wiped with anhydrous ethanol to remove surface dirt. The powder selection is 316L stainless steel powder with a particle size of 15-53 pm. Laser directed energy deposition manufacturing method is used. The specific manufacturing process is as follows: Step S1, substrate selection and pretreatment: according to the material selection of the same type of stainless steel substrate for the shaped part, the stainless steel substrate is polished with sandpaper to remove the surface oxide film, and then wiped with anhydrous ethanol to ensure good metallurgical bonding and obtain a bright machining surface; Step S2, laser additive manufacturing: the substrate obtained in step S1 is clamped to the machine tool, and additive deposition is performed on the substrate using additive manufacturing technology to form a first layer of additive machining surface; specifically including: S21: clamp the stainless steel substrate obtained in step S1 to the machine tool to ensure the levelness of the substrate; S22: pour the 316L stainless steel powder into the powder feeder, turn on the protective gas, adjust the position of the laser head, and make the powder spot coincide with the light spot. Set the laser additive parameters as follows: laser power is 450 W, powder feeding rate is 3.88 g / min, and scanning speed is 700 mm / min; run the program to complete the additive process.

[0033] Step S3, layer-by-layer machining until the part is formed: repeat step S2 for the additive machining surface obtained in step S2 until the part is prepared, obtaining stainless steel.

[0034] The 316L stainless steel obtained in Comparative Example 1 and Example 1 is subjected to the following tests: 1. Porosity The porosity of the additive sample (Comparative Example 1) was 0.56%; the porosity of the additive / subtractive / isostatic sample (Example 1) was 0.02%, which was reduced by 96.4% compared with the additive sample. As can be seen, when the 316L stainless steel is manufactured by additive / subtractive / isostatic composite machining, the porosity is greatly reduced, as shown in Figure 2 .

[0035] 2. Metallographic structure The additive sample (Comparative Example 1) and the additive / subtractive / isostatic sample (Example 1) both contained equiaxed structures and columnar structures. The internal structure of the additive sample (Comparative Example 1) grew along the temperature gradient to form columnar structures, while the equiaxed structures were mainly distributed in the middle and upper parts of the molten pool where the temperature gradient was relatively low. The additive / subtractive / isostatic sample (Example 1) was affected by the ultrasonic vibration between the layers and rolling, and the length of the columnar structure was significantly shortened, and the columnar structure at the lap joint area of each layer tended to transform into an equiaxed structure, as shown in Figure 3 .

[0036] 3. Microstructure The average grain size of the additive sample (Comparative Example 1) was 49.2 μm; the average grain size of the additive / subtractive / isostatic sample (Example 1) was 20.2 μm, which was reduced by 58.9% compared with the additive sample. As can be seen, when the 316L stainless steel is manufactured by additive / subtractive / isostatic composite machining, the grain refinement effect is significant, as shown in Figure 4 and Figure 5 .

[0037] 4. Microhardness The average hardness value of the additive sample (Comparative Example 1) was 214.4 HV 0.1 ; the average hardness value of the additive / subtractive / isostatic sample (Example 1) was 269.1 HV 0.1 , which was increased by 25.5% compared with the additive sample. As can be seen, when the 316L stainless steel is manufactured by additive / subtractive / isostatic composite machining, the overall microhardness can be significantly improved, as shown in Figure 6 .

[0038] 5. Tensile properties The yield strength of the additive sample (Comparative Example 1) was 474.1 ± 4.2 MPa; the yield strength of the additive / subtractive / isostatic sample (Example 1) was 670.3 ± 6.2 MPa, which was increased by 41.4% compared with the additive sample. The ultimate tensile strength of the additive sample (Comparative Example 1) was 592 ± 5.7 MPa, and the ultimate tensile strength of the additive / subtractive / isostatic sample (Example 1) was 746.7 ± 5.8 MPa, which was increased by 26.1% compared with the additive sample, as shown in Figure 7 .

[0039] From the test results, the beneficial effects of the method are: the size and number of pores are greatly reduced compared to the additive sample; the solidification structure is transformed from columnar crystal to equiaxed crystal, and the overall grain is greatly refined; the density and uniformity of the material are improved; and the overall mechanical properties such as microhardness, yield strength and tensile strength are improved.

[0040] Finally, it should be noted that: the method proposed by the application is not only for stainless steel materials, but also for other types of additive manufacturing metals (nickel-based alloy, magnesium alloy, etc.), and the mechanical properties can be strengthened by adjusting the process parameters; in addition, the additive / subtraction / equal material composite manufacturing method is not limited to the process combination of laser additive, milling subtraction, ultrasonic rolling equalization, and can be applied to the process combination between other types of additive manufacturing (arc additive, electron beam additive, ultrasonic additive, friction stir welding additive, etc.), cutting subtraction (turning, grinding, etc.), and equal material strengthening (laser impact, ultrasonic impact, hammering, etc.).

[0041] The details of the application are well known.

[0042] The above-described embodiments are merely preferred embodiments of the application, and are not intended to limit the scope of the application. Any modifications and improvements made by those skilled in the art to the technical solutions of the application without departing from the design spirit of the application shall fall within the protection scope of the claims of the application.

Claims

1. A method for manufacturing high-yield-strength stainless steel using a composite processing method involving increasing / reducing / equal material, characterized in that, The method includes the following steps: S1. Substrate selection and pretreatment; S2. Laser Additive Manufacturing: The substrate obtained in step S1 is clamped onto a machine tool, and additive manufacturing technology is used to deposit additive materials on the substrate to form the first additively processed surface; specifically including: S21. Mount the stainless steel substrate obtained in step S1 onto the machine tool and ensure the levelness of the substrate. S22. Pour stainless steel powder into the powder feeder, turn on the protective gas, adjust the position of the laser head so that the powder spot and the light spot coincide, set the parameters of laser additive manufacturing, run the laser processing path machine tool program, and complete the first layer of additive deposition according to the program. The parameters for laser additive manufacturing are: laser power of 400-500W, powder feeding rate of 3.85-3.90g / min, and scanning speed of 680-720mm / min. S3. Milling and sublimation: The additively processed surface obtained in step S2 is processed using subtractive manufacturing technology to remove the surface oxide layer, pores and unmelted defects, and obtain a subtractively processed surface with better surface quality. S4. Ultrasonic rolling and other material processing: The subtractive processing surface obtained in step S3 is subjected to ultrasonic rolling treatment to obtain the rolled surface. S5. Layer-by-layer composite processing until the part is formed: Repeat steps S2 to S4 on the roll-processed surface obtained in step S4 until the part is prepared and high-performance stainless steel is obtained.

2. The method for manufacturing high yield strength stainless steel using composite processing of added / subtracted / equal materials according to claim 1, characterized in that: Step S1 includes: selecting a stainless steel substrate of the same type according to the material of the part to be formed, polishing the stainless steel substrate with sandpaper to remove the surface oxide film, and wiping the surface with anhydrous ethanol to obtain a bright processed surface and ensure good metallurgical bonding.

3. The method for manufacturing high yield strength stainless steel using a composite processing method of increasing / reducing / equal material as described in claim 1, characterized in that: In step S3, the subtractive manufacturing technology is milling, with a cutting speed of 93-95 m / min, an axial depth of cut of 0.14-0.16 mm, a radial depth of cut of 4.8-5.2 mm, and a feed rate of 280-320 mm / min.

4. The method for manufacturing high yield strength stainless steel using composite processing of added / subtracted / equal materials according to claim 1, characterized in that: Step S4 specifically includes: S41. Clean the residual powder and milling chips on the surface of the subtractive processing to ensure the surface quality of the subsequent roll forming process; S42. Turn on the ultrasonic rolling equipment, move the rolling tool head to the starting position, and perform rolling calibration; S43. Set the ultrasonic frequency, ultrasonic rolling amplitude, static pressure, rolling feed speed, and rolling interval parameters, perform multiple ultrasonic rolling processes, select the appropriate lubricating oil output, cool and lubricate the machined surface and ultrasonic rolling tool head, and run the program to complete the ultrasonic rolling process.

5. The method for manufacturing high yield strength stainless steel using a composite processing method of increasing / reducing / equal material as described in claim 4, characterized in that: In step S43, the ultrasonic frequency of the ultrasonic rolling equipment is 25-35kHz, the ultrasonic rolling amplitude is 14-16μm, the static pressure is 1000-1400N, the rolling feed speed is 1400-1600mm / min, and the rolling interval is 0.04-0.06mm.

6. The method for manufacturing high yield strength stainless steel using a composite processing method of increasing / reducing / equal material as described in claim 5, characterized in that: The ultrasonic rolling tool head is a carbide ball bearing.

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