A process for optimizing deformation of complex components in metal additive manufacturing

Abstract

The application discloses a process for optimizing deformation of a complex component in metal additive manufacturing, which comprises the following steps: layering a complex component by using slicing software of an additive manufacturing system and marking layers with large cross-section changes; accumulating and additive forming layer by layer by additive manufacturing at layers without large cross-section changes; increasing the speed of a scraper for spreading powder before starting the additive marking layers, and then sintering; performing laser shock peening on the current layer after completing the additive of the current layer; performing rapid powder spreading, additive and laser shock peening on the next layer of material until the additive reaches the unmarked layer, returning the speed of the scraper for spreading powder to the initial speed and sintering; continuing the additive until completion; and the application combines laser shock peening with metal additive manufacturing, and adjusts the deformation degree and defects of the area with large cross-section changes in the additive process by adjusting the powder spreading speed, so as to adjust the interlayer cooling speed and reduce the temperature gradient, and the application has the advantages of good forming quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal additive manufacturing, and in particular to a process for optimizing deformation of a complex component in metal additive manufacturing. BACKGROUND

[0002] Metal additive manufacturing has the characteristics of fast cooling and fast heating. Such repeated and severe thermal cycles result in large residual stress in the interior and surface of the component, and the component is prone to warping, cracking and other phenomena after additive manufacturing. At the same time, due to the deformation in additive manufacturing, the powder spreading is uneven, and the forming quality of the part is also greatly reduced, with defects such as pores and delamination at the interlayer bonding.

[0003] The parts manufactured using metal additive manufacturing technology often have the characteristics of complex shape. After computer slicing, the cross-sectional area difference between the upper and lower layers is large, which makes the support body below the forming layer be solidified layer or powder at times during the sintering of the forming layer in the additive manufacturing process. Due to the order of magnitude difference in thermal conductivity between the powder and the solidified layer, the different shrinkage rates after heating result in stress accumulation and crack formation, so in complex components, the forming quality is poor and defects are many at places with large cross-sectional area changes.

[0004] Currently, some scholars use laser shock peening to reduce internal stress during additive manufacturing. A Chinese patent with application number 202210703365.5 discloses a method of metal additive manufacturing combined with laser shock and laser annealing. During the metal forming process, the metal deposition layer formed from metal powder raw materials is subjected to laser shock and / or laser annealing according to the number of layers and / or the material of the metal deposition layer. A Chinese patent with application number CN202011080732.8 discloses a laser shock adjustable electric arc additive manufacturing method, which combines numerical simulation to obtain the stress field distribution of the additive in real time, sets the laser shock path and performs laser shock processing. The above-mentioned existing methods focus on the combination of single laser shock peening and additive manufacturing. If limited surface laser shock peening is performed during additive manufacturing, the influence layer depth is about 1mm, and the stress regulation effect on the interior of the component is limited. If laser shock peening is performed multiple times during additive manufacturing, it will prolong the interlayer cooling time, which will lead to an increase in temperature gradient and an intensification of thermal cycles, and the stress regulation effect on complex components is limited. At the same time, the deformation of complex components during additive manufacturing is more severe than that of simple components, and the interlayer powder spreading flatness will be greatly reduced, which will exacerbate the deformation of the component. Therefore, it is necessary to select appropriate additive strategies to regulate the residual stress of complex components. SUMMARY

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a process for optimizing the deformation of complex components in metal additive manufacturing, which combines laser shock peening with metal additive manufacturing, and at the same time, by adjusting the powder spreading speed, the deformation degree and defects of the region with large cross-sectional variation in the additive process are regulated, so as to adjust the interlayer cooling speed to reduce the temperature gradient, and has the advantage of good forming quality.

[0006] In order to achieve the above-mentioned purpose, the present application is realized by the following technical solutions:

[0007] A process for optimizing the deformation of complex components in metal additive manufacturing, comprising the following steps:

[0008] 1) Layering the complex component by the slicing software of the additive manufacturing system, and marking the number of layers with large cross-sectional variation on the upper and lower layers;

[0009] 2) Starting the additive manufacturing process, at the non-marked layers with large cross-sectional variation, through additive manufacturing, the doctor blade spreads the powder and sinters, and the layers are accumulated and additive formed;

[0010] 3) Before starting the additive marking layers, the speed of the doctor blade spreading the powder is increased by more than 30%, and then sintering is performed;

[0011] 4) After the additive of the current layer is completed, laser shock peening is performed on the current layer, and the depth of the laser shock peening affected layer is ensured to be greater than 0.5mm;

[0012] 5) Rapid powder spreading and additive of the next layer of material is performed until the additive height is increased by 0.5mm, and laser shock peening is performed on the current layer of material again, and the depth of the laser shock peening affected layer is ensured to be greater than 0.5mm;

[0013] 6) Repeat steps 3) to 5) until the additive reaches the unmarked layer, and then the speed of the doctor blade spreading the powder is restored to the speed in step 2) and sintering is performed;

[0014] 7) Repeat steps 2) to 6) until the additive is completed, and the cross-sectional area of the complex component is suddenly changed, and the residual tensile stress on the surface of the component is partially neutralized by the introduced compressive stress, so that the deformation degree is reduced, and the pore defects in the entire region are improved.

[0015] The additive manufacturing refers to laser selective melting (L-PBF), electron beam melting (EBM) and other additive manufacturing technologies using metal powder as raw material.

[0016] The laser shock peening applies a Q-switched Nd:YAG pulse laser, and the laser shock peening parameters are as follows: spot diameter 1-4 mm, wavelength 1064 nm, longitudinal overlap rate 1-90%, transverse overlap rate 1-90%, pulse energy 1-100 J, pulse width 3-30 ns, and repetition frequency 0.5-10 Hz.

[0017] The laser shock peening affects a layer depth of 0.5-2 mm, which ensures that the adjacent layers have the laser shock peening effect while avoiding the extension of the interlayer cooling time caused by frequent laser shock peening.

[0018] The specific value of the large cross-sectional area change in the step 1) is selected according to actual needs, and the area change percentage is greater than 5%.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] (A) Compared with the conventional additive manufacturing technology, the present application is aimed at the characteristics that the cross-sectional area of the complex component changes greatly during additive manufacturing, and large deformation is easily generated. The laser shock peening is performed every 0.5 mm in this part of the region, and the residual compressive stress is introduced in sections to control the deformation and reduce the influence on the extension of the interlayer cooling time, thereby preventing the extension of the interlayer cooling time caused by the layer-by-layer shock peening, and the thermal cycle is aggravated.

[0021] (B) Compared with the conventional additive manufacturing technology, the powder spreading speed is increased in the region with a large change in the cross-sectional area, and the cooling time is reduced, so that the thermal cycle amplitude is reduced. At the same time, the increase in the powder layer thickness leads to an increase in the fusion ratio, so that the sintering area reaches the stable state faster, thereby reducing the accumulation of internal stress and improving defects such as pores.

[0022] (C) After the laser shock peening weakens the deformation degree, the powder is quickly spread, which can greatly reduce the powder shrinkage degree and improve the powder spreading uniformity, thereby effectively controlling the deformation of the complex component caused by the uneven powder spreading in the additive manufacturing, and improving the success rate of the additive complex component.

[0023] (D) Compared with the conventional layer-by-layer laser shock peening additive manufacturing technology, the additive manufacturing process is customized for the regions with a large change in the cross-sectional area and a small change in the cross-sectional area, the additive manufacturing time is reduced, and the additive manufacturing cost is saved. At the same time, it has strong flexibility, the number of dislocations is changed by adjusting the laser shock peening parameters, and the appropriate number of dislocations is selected to improve the microstructure performance of the component for subsequent processes. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The flowchart of the method of the present application is shown.

[0025] Figure 2 The schematic diagram of the target complex component in the embodiment of the present application is shown.

[0026] Figure 3 A specific diagram of an additive manufacturing process of an embodiment of the present application. DETAILED DESCRIPTION

[0027] The method of the present application will be described in detail below in conjunction with the accompanying drawings and embodiments.

[0028] As shown in Figure 1 Embodiment 1, a process for optimizing deformation of a complex component in metal additive manufacturing, comprising the following steps:

[0029] 1) Layering the complex component by slicing software of the additive manufacturing system, and marking the layers with cross-section changes of more than 5% between the upper and lower layers, as shown in Figure 2 part of the layers are marked, and the initial speed of the scraper at low speed is set;

[0030] 2) Start the additive manufacturing process, for example, selective laser melting, as shown in Figure 3 (a), at the layers with small cross-section changes, the scraper runs at low speed to spread powder, and accumulates and sinters layer by layer until the marked layers are reached; in the selective laser melting process, the laser power is 200 W, the laser scanning speed is 800 mm / s, the scanning pitch is 0.12 mm, the layer thickness is 0.03 mm, and the scraper spreading powder speed is 25 mm / s;

[0031] 3) Before the marked layers, the speed of the scraper spreading powder is increased by 30%, and then sintering is performed;

[0032] 4) After sintering the current layer, as shown in Figure 3 (b), laser shock peening is performed on the current sintered layer, and the laser shock peening affected layer depth is ensured to be greater than 0.5 mm; the specific parameters of laser shock peening are: spot diameter 2 mm, wavelength 1064 nm, longitudinal overlap rate 50%, transverse overlap rate 50%, pulse energy 10 J, and repetition frequency 5 Hz;

[0033] 5) Rapid powder spreading and sintering of the next layer of material is performed, as shown in Figure 3 (c), until the additive height increases by 0.5 mm, laser shock peening is again performed on the current layer of material, and the laser shock peening affected layer depth is ensured to be 1 mm;

[0034] 6) Repeat steps 3) to 5) until the cross-section changes of the upper and lower layers are less than 5%, i.e. the unmarked layers in step 1), the speed of the scraper spreading powder is restored to the speed in step 2) and sintering, as shown in Figure 3 (d), after sintering, laser shock peening is no longer performed;

[0035] 7) Repeat steps 2)~6) until the additive is completed. The cross-sectional area mutation region of the complex component is partially neutralized by the residual tensile stress on the surface of the component due to the introduction of compressive stress, which greatly reduces the degree of deformation. At the same time, due to the higher powder spreading speed, the thermal cycle is smaller, and the defects such as porosity in the entire region are improved.

[0036] Example 2, the specific parameters of laser shock peening in step 4) of example 1 are changed to spot diameter 4mm, wavelength 1064nm, longitudinal overlap rate 90%, transverse overlap rate 90%, pulse energy 100J, repetition frequency 10Hz; step 5) ensures that the laser shock peening affected layer depth is greater than 0.5mm, and the additive height is increased by 0.5mm; the other steps are the same as example 1.

[0037] Example 3, the specific parameters of laser shock peening in step 4) of example 1 are changed to spot diameter 1mm, wavelength 1064nm, longitudinal overlap rate 1%, transverse overlap rate 1%, pulse energy 1J, repetition frequency 0.5Hz; step 5) ensures that the laser shock peening affected layer depth is greater than 2mm, and the additive height is increased by 2mm; the other steps are the same as example 1.

[0038] Comparative example 1, without laser shock peening process in steps 4)-5) of example 1, the other steps are the same as example 1.

[0039] Comparative example 2, the powder is always kept at the slow speed at the beginning of example 1 during the additive process, and the other steps are the same as example 1.

[0040] Table 1

[0041]

[0042] Examples 1-3 use the scheme of fast powder laying and laser shock peening at the same time, and the porosity and surface roughness are lower, which shows that the scheme described in this patent can maximize the surface quality, reduce the temperature gradient to optimize the density, and reduce the porosity. Comparative examples 1 and 2 cancel the laser shock peening process and the fast powder laying process respectively, and the porosity and surface roughness are improved.

Claims

1. A process for optimizing the deformation of complex components in metal additive manufacturing, characterized in that, Includes the following steps: 1) Complex components are layered using additive manufacturing system slicing software, and the number of layers with large changes in cross-sectional area between upper and lower layers is marked; the specific value for large changes in cross-sectional area is an area change percentage greater than 5%; 2) The additive manufacturing process begins. In the number of layers with large changes in the non-marked cross-section, additive manufacturing is used to spread powder with a scraper and sinter it, then build up the layers one by one and add it into shape. 3) Before starting the additive manufacturing process and marking the number of layers, the speed at which the doctor blade spreads the powder is increased by more than 30%, followed by sintering; 4) After the current layer is completed by additive manufacturing, laser shock peening is performed on the current layer, and the depth of the laser shock peening layer is ensured to be greater than 0.5 mm; 5) Perform rapid powder spreading and additive manufacturing of the next layer of material until the additive height increases by 0.5mm. Then, perform laser shock peening on the current layer of material again, and ensure that the depth of the laser shock peening layer is greater than 0.5mm. 6) Repeat steps 3) to 5) until the additive reaches the unmarked layer, after which the speed of the doctor blade spreading the powder is restored to the speed in step 2) and sintering is performed; 7) Repeat steps 2) to 6) until the additive manufacturing is complete. In areas of abrupt changes in the cross-sectional area of ​​complex components, the introduced compressive stress partially neutralizes the residual tensile stress on the component surface, reducing the degree of deformation and improving the porosity defects in the entire area.

2. The process according to claim 1, characterized in that: The additive manufacturing process refers to selective laser melting or electron beam melting.

3. The process according to claim 1, characterized in that: The laser shock enhancement utilizes a Q-switched Nd:YAG pulsed laser with the following parameters: spot diameter 1–4 mm, wavelength 1064 nm, longitudinal overlap 1–90%, transverse overlap 1–90%, pulse energy 1–100 J, pulse width 3–30 ns, and repetition frequency 0.5–10 Hz.

4. The process according to claim 1, characterized in that: The depth of the laser shock reinforcement layer is between 0.5 and 2 mm.

5. The process according to claim 1, characterized in that, Includes the following steps: 1) Use the additive manufacturing system slicing software to divide complex components into layers, mark the number of layers where the cross-sectional difference between the upper and lower layers exceeds 5%, and set the initial speed of the scraper when running at low speed. 2) The additive manufacturing process begins with selective laser melting. In the layers with large changes in cross-section, a doctor blade moves at a low speed to spread powder, which is then deposited and sintered layer by layer until the layers for additive marking are reached. In the selective laser melting process, the laser power is 200W, the laser scanning speed is 800mm / s, the scanning interval is 0.12mm, the layer thickness is 0.03mm, and the doctor blade powder spreading speed is 25mm / s. 3) Before starting the additive manufacturing process and marking the number of layers, the speed at which the doctor blade spreads the powder is increased by 30%, followed by sintering; 4) After the current layer is sintered, laser shock peening is performed on the current sintered layer, and the depth of the laser shock peening layer is ensured to be greater than 0.5 mm. The specific parameters of laser shock peening are: spot diameter 2 mm, wavelength 1064 nm, longitudinal overlap rate 50%, transverse overlap rate 50%, pulse energy 10 J, and repetition frequency 5 Hz. 5) Perform rapid powder spreading and sintering of the next layer of material until the additive height increases by 0.5mm. Then, perform laser shock blasting on the current layer of material again, and ensure that the depth of the laser shock blasting layer is 1mm. 6) Repeat steps 3) to 5) until the cross-sectional change between the upper and lower layers is less than 5%, i.e., the number of layers not marked in step 1), the speed of the doctor blade spreading the powder is restored to the speed in step 2), and sintering is performed. After sintering is completed, laser shock strengthening is no longer performed. 7) Repeat steps 2) to 6) until the additive manufacturing is complete. In areas of abrupt changes in the cross-sectional area of ​​complex components, the introduced compressive stress partially neutralizes the residual tensile stress on the component surface, reducing the degree of deformation. At the same time, the high powder spreading rate leads to a small thermal cycle, improving the porosity defects in the entire area.

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