Defect suppression method for additive manufacturing of high-specific-gravity tungsten alloy thick-wall hemispherical component

Abstract

The invention discloses a defect suppression method for additive manufacturing of a high-specific-gravity tungsten alloy thick-wall hemispherical component, and belongs to the field of laser powder bed melting additive manufacturing. High-specific-gravity tungsten alloy powder is molten layer by layer through a double-laser powder bed melting technology to form the high-specific-gravity tungsten alloy hemispherical thick-wall component. Two beams of laser, namely a first laser and a second laser, are arranged in the double-laser powder bed melting process; in the forming process, the technological parameters of the first laser are kept unchanged all the time, the laser energy density of the second laser is linearly and progressively decreased after the second laser is deposited to the mth layer in the stacking direction until the second laser is deposited to the last layer, the surface temperature value of a formed component is detected in real time, and the preset energy density value of each layer is dynamically calibrated to eliminate interlayer heat accumulation; in the forming process, the forming quality of the component obtained when the m layer is deposited in the stacking direction is good, and the requirement for the forming quality of the component is met. Therefore, the method can achieve the purposes of controllable process parameter layering, linear performance change and effective defect suppression.

Description

Technical Field

[0001] The invention relates to a defect suppression method for additively manufacturing a high-density tungsten alloy thick-walled hemispherical component, and belongs to the field of laser powder bed melting additive manufacturing. Background Art

[0002] Laser powder bed fusion (L-PBF) is an advanced material forming method that uses a computer to design a part model and then uses a laser beam to selectively melt metal powder in a layered manner to directly form complex components. Compared with traditional methods, it has advantages such as no need for molds and a shorter process route. Dual laser powder bed fusion (DL-PBF) has obvious advantages in forming high-melting-point, highly brittle W alloys. Switching the high-energy input mode of a single laser to the low-energy input mode of a dual-beam laser, and using the same forming trajectory for the dual-beam lasers, can delay the solidification of the molten pool and reduce the temperature gradient, thereby effectively suppressing the generation of cracks in the W alloy. Chinese patent CN118893219A uses the DL-PBF process to prepare a highly dense, extremely low-defect 98W alloy block specimen. The process parameters of the dual-beam lasers in this process are the same, but for the formation of large-scale W alloy complex components, heat accumulation is a huge challenge during the forming process. Severe heat accumulation can induce defects such as cracks and warping. Combined with the characteristics of the DL-PBF process, if the energy density of the first laser is too low, the probability of unmelted W alloy powder will increase, affecting the forming quality. The second laser is mainly used to delay the solidification of the molten pool. If the energy density of the second laser is too high, the effect of suppressing thermal stress will deteriorate when forming large-scale complex components. Therefore, the first laser is fixed at a higher laser power, and the laser power of the second laser decreases linearly along the stacking direction. However, the preset linear energy density will be adjusted in real time due to excessive heat accumulation during the actual printing process. Therefore, it is necessary to calibrate the preset energy density in real time to eliminate interlayer heat accumulation, so as to achieve the purpose of layered controllable process parameters and uniform performance changes.

[0003] Tungsten alloy hemispherical components are widely used in military, aerospace and other fields due to their high density, high strength and excellent radiation shielding properties. Traditional processing methods are complex and costly. At the same time, high-density tungsten alloy thick-walled hemispherical components (wall thickness 10-20mm) are more difficult to form than thin-walled hemispherical components (wall thickness 1-5mm). On the one hand, the increase in wall thickness will increase the weight of the top of the hemisphere and extend the printing time. Therefore, the use of conventional supports will cause the top to collapse due to the low support strength, or the addition of high-density supports will increase damage to the scraper. On the other hand, the extended printing time will increase the degree of heat accumulation. Therefore, it is of great significance to explore a DL-PBF process suitable for the high-precision forming of high-density tungsten alloy thick-walled hemispherical components and an effective method to suppress defects such as cracks and warping. Summary of the Invention

[0004] The present invention provides a defect suppression method for additively manufacturing high-density tungsten alloy thick-walled hemispherical components, so as to achieve the goals of layered controllable process parameters, linear performance changes, and effective defect suppression.

[0005] In order to achieve the above technical objectives, the present invention will adopt the following technical solutions:

[0006] A defect suppression method for additively manufacturing a high-density tungsten alloy thick-walled hemispherical component, wherein a dual-laser powder bed melting process is used to melt high-density tungsten alloy powder layer by layer to form the high-density tungsten alloy hemispherical thick-walled component; the dual-laser powder bed melting process is equipped with two laser beams, corresponding to a first laser and a second laser;

[0007] During the forming process, the process parameters of the first laser remain unchanged, while the process parameters of the second laser linearly decrease the laser energy density after depositing to the mth layer along the stacking direction until the last layer is deposited.

[0008] During the forming process, the component formed by depositing to the mth layer along the stacking direction has good forming quality and meets the component forming quality requirements.

[0009] Preferably, during the forming process, the process parameters of the second laser achieve a linear decrease in laser energy density by linearly decreasing its laser power.

[0010] Preferably, during the forming process, when the nth layer is deposited along the stacking direction and n>m, the laser power of the second laser in the current forming layer is preset by the following formula:

[0011] P n =P0-a(nm);

[0012] Where: P n represents the preset laser power value of the second laser at the nth layer, P0 is the initial laser power of the second laser, and a is the laser power change rate.

[0013] Preferably, the laser power variation rate a is set to 10%.

[0014] Preferably, during the forming process, when the n+1th layer is deposited along the stacking direction and n>m, the real-time temperature value T of the metal surface of the nth layer is determined. n Whether the laser power preset value of the current forming layer needs to be calibrated is determined by whether the standard temperature value T0 is exceeded:

[0015] When the judgment result shows that T n >T0, it is necessary to calibrate the preset value of the laser power of the second laser in the current shaping layer to obtain a corrected value of the laser power of the second laser in the current shaping layer.

[0016] Preferably, the laser power correction value of the second laser in the current forming layer is obtained specifically by the following method:

[0017] Calculate the laser power correction index k n+1 :

[0018] According to the calculated laser power correction index k n+1 Determine whether to suspend the powder spreading operation of the current forming layer: When the judgment result shows that k n+1 When the value is >50%, the powder spreading operation of the current forming layer is suspended until the calculated laser power correction index k n+1 When the value is less than or equal to 50%, the powder spreading operation of the current forming layer is carried out normally, and the laser power of the second laser in the current forming layer is corrected according to the following rules:

[0019] When k n+1 ∈(0,10%], P' n+1 =P0-a(n+1-m)-20;

[0020] When k n+1 ∈(10%,30%], P' n+1 =P0-a(n+1-m)-40;

[0021] When k n+1 ∈(30,50%], P' n+1 =P0-a(n+1-m)-60;

[0022] Where: P' n+1 Indicates the laser power correction value of the n+1th layer.

[0023] Preferably, the standard temperature value T0 is calculated as follows:

[0024]

[0025] Among them, T n is the real-time temperature value of the metal surface of the nth layer.

[0026] Preferably, the value of m is 100.

[0027] Preferably, the process parameters of the first and second lasers are: laser power P0 = 200 W, scanning speed v = 1000 mm / s; time interval Δt = 100 ms.

[0028] Preferably, the high-density tungsten alloy powder includes the following components: 98 wt.% W, 1.4 wt.% Ni, and 0.6 wt.% Fe.

[0029] Based on the above technical objectives, the present invention has the following advantages over the prior art:

[0030] 1. The defect suppression method for additively manufacturing high-density tungsten alloy thick-walled hemispherical components described in the present invention utilizes the unique advantages of the DL-PBF process for forming high-density tungsten alloys, re-optimizes the dual-laser energy distribution to adapt to the forming of large-sized high-density tungsten alloy thick-walled hemispherical components, fixes the energy density of the first laser, and sets the preset energy density of the second laser to linearly decrease along the stacking direction, thereby effectively reducing the severe heat accumulation caused by long-term high heat input in thick-walled hemispherical components, thereby effectively suppressing the formation of defects such as cracks and warping.

[0031] 2. To improve the applicability of preset process parameters, the present invention uses a thermal imager to collect surface temperature distribution data of the metal layer layer by layer and calculate the real-time temperature value, determine whether the real-time temperature value of the formed metal layer exceeds the standard temperature value, and quantitatively calibrate the preset energy density of the metal layer. This can achieve independent control of process parameters for different metal layers, uniform performance changes, precise response to heat accumulation, and rapid elimination. It should be pointed out here that the current method of forming large-scale complex components often uses simulation methods to obtain the temperature field characteristics of the component forming and then adjust the process parameters in real time. However, this method is relatively complex and has large simulation errors, resulting in poor practicality in industrial production.

[0032] Based on the above technical advantages, the present invention can effectively solve the problems of defects such as cracks and warping caused by heat accumulation in large-sized and high-density tungsten alloy components during the long-term forming process, and can achieve high-precision forming of high-density tungsten alloy thick-walled hemispherical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the forming principle diagram of the DL-PBF process;

[0034] Figure 2 A lattice support model used for forming thick-walled hemispherical components made of high-density tungsten alloy. (a) shows the front view of the lattice support model; (b) shows a partially enlarged schematic diagram of the lattice support in (a); and (c) shows a bottom view of the lattice support.

[0035] Figure 3 This is the surface state of the stainless steel substrate after wire cutting processing;

[0036] Figure 4 Schematic diagram of the process for forming high density tungsten alloy thick-walled hemispherical components using the DL-PBF process;

[0037] Figure 5 This is a flow chart for real-time monitoring of the metal layer surface temperature field and dynamic calibration of process parameters;

[0038] Figure 6The actual picture of the high-density tungsten alloy thick-walled hemispherical component with the initial process parameter P0=200W; in the figure: (a) is a schematic diagram of the printing process of the thick-walled hemispherical component; (b) is a physical picture of the formed thick-walled hemispherical component (before polishing); (c) is a physical picture of the formed thick-walled hemispherical component (after polishing).

[0039] Figure 7 Images of a high-density tungsten alloy thick-walled hemispherical component with initial process parameters P0 = 180W. (a) Schematic diagram of the printing process for the thick-walled hemispherical component; (b) a photo of the formed thick-walled hemispherical component (before polishing); (c) a photo of the formed thick-walled hemispherical component (after polishing); and (d) the bottom surface of the formed thick-walled hemispherical component. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way serves as any limitation on the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention. Unless otherwise specified, the relative arrangement of components and steps, expressions and numerical values described in these embodiments do not limit the scope of the present invention. Technologies, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the technologies, methods and equipment should be considered part of the specification. In all examples shown and discussed here, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of the exemplary embodiments may have different values.

[0041] The defect suppression method of the additively manufactured high density tungsten alloy thick-walled hemispherical component of the present invention is as follows: Figure 1 、 4 As shown, the following steps are included:

[0042] Step S1: Through a dual laser (i.e., DL-PBF) forming block test, the process window for forming a tungsten alloy block by melting 98W-Ni-Fe alloy powder by the DL-PBF process is obtained to determine the initial process parameters for forming the tungsten alloy block by the DL-PBF process.

[0043] Generally, the criteria for determining the initial process parameters are the compressive strength, metallographic structure, density and microhardness of the tungsten alloy block.

[0044] Step S2: Establish a three-dimensional model of the thick-walled hemispherical component to be formed and set a chamfer at its bottom to improve the bonding between the bottom of the thick-walled hemispherical component and the substrate. The outer diameter of the thick-walled hemispherical component is 64 mm, the inner diameter is 36 mm, and the wall thickness is 14 mm. A high-strength lattice support with low loss to the flexible scraper suitable for the forming of the thick-walled hemispherical component is added inside. The top of the lattice support is embedded in the hemispherical overhang surface of the thick-walled hemispherical component and the embedding depth is 1-2 mm, as shown in the attached figure. Figure 2 shown.

[0045] The thick-walled hemispherical component model with lattice support was imported into the slicing software for layered slicing, with a total of 1600 slices.

[0046] Step S3: assigning the initial process parameters of the tungsten alloy block formed by the DL-PBF process obtained in step S1 to the slicing process parameters to select the initial process parameters for forming the thick-walled hemispherical component by DL-PBF.

[0047] Step S4: Use wire cutting to process independent squares of 3.5cm×3.5cm on the surface of the stainless steel substrate to release thermal stress. The surface state of the stainless steel substrate after wire cutting is as shown in the attached figure. Figure 3 As shown, the depth of the individual squares is 2 mm.

[0048] Step S5: Add 98W-Ni-Fe alloy powder to the forming chamber, level the substrate, debug the powder spreading device, and introduce argon gas into the forming chamber to ensure that the oxygen content of the processing atmosphere is less than 500 ppm.

[0049] Step S6: Scan the laser beam across the substrate for preheating.

[0050] Step S7: The dual lasers start forming the thick-walled hemispherical component. The first laser maintains the initial process parameters unchanged, and the second laser adopts a linear decreasing energy density forming strategy to dynamically adjust the process parameters along the stacking direction.

[0051] Step S8: Collect the surface temperature distribution data of the formed component layer by layer, calculate the real-time temperature value of each layer, if the real-time temperature value is less than or equal to the standard temperature value, continue printing and monitoring, if the real-time temperature value is greater than the standard temperature value, quantitatively calibrate the laser power of the second laser, the specific steps are as shown in the attached figure. Figure 5 As shown:

[0052] Step S81: The thermal imager collects the temperature distribution data of the first m layers (the value of m can be 100) layer by layer and calculates its average temperature value T avg , as the standard temperature value T0, when the first m layers are solid formed, the first laser and the second laser both use the initial process parameters, specifically P0 = 200W, v = 1000mm / s, Δt = 100ms, and the standard temperature value T0 is calculated as follows:

[0053]

[0054] Among them, T n is the real-time temperature value of the metal surface of the nth layer.

[0055] Step S82: When the nth layer is formed and n>m layers, the laser power of the first laser is still 200W and is always fixed, and the laser power of the second laser is P n Decrease linearly according to the following formula:

[0056] P n =P0-a(nm);

[0057] Where: P n represents the preset laser power value of the second laser at the nth layer, P0 is the initial laser power of the second laser, and a is the laser power change rate (the laser power change rate a can be 10%).

[0058] Step S83: The thermal imager collects the temperature distribution data of the metal surface of the nth layer and calculates its temperature value T n , when T n When ≤T0, the n+1th layer is formed, and the laser power of the second laser does not need to be corrected. It can be calculated by the following formula: n+1 =P0-a(nm), when T n When >T0, calculate the laser power correction index k of the n+1th layer according to the following formula n+1 :

[0059] Among them, T n is the real-time temperature value of the nth layer, and T0 is the standard temperature value;

[0060] Step S84: Correct the index k according to the calculated laser power n+1 Determine whether to suspend the powder spreading operation of the current forming layer (n+1 layer): When the judgment result shows that k n+1 When the temperature is >50%, the powder spreading operation of the current forming layer (n+1 layer) is suspended, the formed metal layer is briefly cooled, and the thermal imager collects the surface temperature value of the nth layer of metal in real time until the calculated laser power correction index k n+1 When the value is less than or equal to 50%, the powder spreading operation of the current forming layer (n+1th layer) is carried out normally, and the laser power of the second laser in the current forming layer is corrected according to the following rules:

[0061] When k n+1 ∈(0,10%], P' n+1 =P0-a(n+1-m)-20;

[0062] When k n+1 ∈(10%,30%], P'n+1 =P0-a(n+1-m)-40;

[0063] When k n+1 ∈(30,50%], P' n+1 =P0-a(n+1-m)-60;

[0064] Where: P' n+1 Indicates the laser power correction value of the n+1th layer.

[0065] Step S9: After printing is completed, wait for the forming chamber to cool to room temperature and take out the component. Check whether there are defects such as cracks and warping on its surface. If there are, adjust the initial process parameters and reprint. If not, separate the substrate and the component by wire cutting, remove the internal support and grind and polish.

[0066] The present invention can achieve independent control of process parameters of different metal layers, uniform performance changes, precise response to heat accumulation, and rapid elimination by presetting the linearly decreasing energy density of the second laser and calibrating it in real time. The lattice support can effectively solve the problem of forming the overhanging surface on the top of the thick-walled hemispherical component of tungsten alloy. Based on the above processing steps, high-precision forming of thick-walled hemispherical components of high-density tungsten alloy can be achieved, which improves the intelligent level of laser additive manufacturing and enables real-time monitoring and real-time adjustment. It can be seen that the present invention provides technical support for the high-precision forming of thick-walled hemispherical components of high-density tungsten alloy, and provides a technical reference for the forming of large-scale complex components of other refractory alloys (molybdenum alloys, tantalum alloys).

[0067] The present invention will be further explained below in conjunction with embodiment:

[0068] Example 1

[0069] In this embodiment, the initial process parameters for forming a high-density tungsten alloy thick-walled hemispherical component by the DL-PBF process are P0=200W, v=1000mm / s, and Δt=100ms.

[0070] The forming quality of the hemispherical component manufactured by the defect suppression method of the additive manufacturing of high-density tungsten alloy thick-walled hemispherical component of the present invention is as shown in the attached figure. Figure 6 As shown in the figure, it was found that the bottom of the hemispherical component had poor bonding with the substrate and severe warping occurred. A longitudinal crack appeared on the side of the hemispherical component, running upward along the bottom. However, the forming quality of the top of the hemispherical component was good, without obvious defects. This shows that the initial laser power P0 was too high, resulting in severe heat accumulation at the bottom of the hemisphere, which in turn induced cracks and warping defects. The initial laser P0 should be appropriately lowered and reprinted.

[0071] Example 2

[0072] In this embodiment, the initial process parameters for forming a high-density tungsten alloy thick-walled hemispherical component by the DL-PBF process are P0=180W, v=1000mm / s, and Δt=100ms.

[0073] The forming quality of the hemispherical component manufactured by the defect suppression method of the additive manufacturing of high-density tungsten alloy thick-walled hemispherical components of the present invention is as follows: Figure 7 As shown, it was found that the bottom of the hemispherical component had good bonding with the substrate, and the side forming quality of the hemispherical component was good, without defects such as warping and cracks. Wire cutting was used to separate the substrate and the component, and the internal support was removed and polished. The dimensional accuracy of the hemispherical component reached ±0.17mm.

[0074] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A defect suppression method for additively manufacturing a thick-walled hemispherical component of a high-density tungsten alloy, characterized in that: The double laser powder bed fusion process is used to melt the high density tungsten alloy powder layer by layer to form a high density tungsten alloy hemispherical thick-walled component; the double laser powder bed fusion process is equipped with two laser beams, corresponding to the first and second lasers; During the forming process, the process parameters of the first laser remain unchanged, while the process parameters of the second laser linearly decrease the laser energy density after depositing to the mth layer along the stacking direction until the last layer is deposited. During the forming process, the component formed by depositing to the mth layer along the stacking direction has good forming quality and meets the component forming quality requirements.

2. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 1, characterized in that: During the forming process, the process parameters of the second laser achieve a linear decrease in laser energy density by linearly decreasing its laser power.

3. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 2, characterized in that: During the forming process, when the nth layer is deposited along the stacking direction and n>m, the laser power of the second laser in the current forming layer is preset by the following formula: P n =P0-a(n-m); Where: P n represents the preset laser power value of the second laser at the nth layer, P0 is the initial laser power of the second laser, and a is the laser power change rate.

4. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 3, characterized in that: The laser power variation rate a is set to 10%.

5. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 3, characterized in that: During the forming process, when the n+1th layer is deposited along the stacking direction and n>m, the real-time temperature value T of the metal surface of the nth layer is determined. n Whether the laser power preset value of the current forming layer needs to be calibrated: If the judgment result shows that T n >T0, it is necessary to calibrate the preset value of the laser power of the second laser in the current shaping layer to obtain a corrected value of the laser power of the second laser in the current shaping layer.

6. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 5, characterized in that: The laser power correction value of the second laser in the current forming layer is specifically obtained by the following method: Calculate the laser power correction index k n+1 : According to the calculated laser power correction index k n+1 Determine whether to suspend the powder spreading operation of the current forming layer: When the judgment result shows that k n+1 When the value is >50%, the powder spreading operation of the current forming layer is suspended until the calculated laser power correction index k n+1 When the value is less than or equal to 50%, the powder spreading operation of the current forming layer is carried out normally, and the laser power of the second laser in the current forming layer is corrected according to the following rules: When k n+1 ∈(0,10%], P' n+1 =P0-a(n+1-m)-20; When k n+1 ∈(10%,30%], P' n+1 =P0-a(n+1-m)-40; When k n+1 ∈(30,50%], P' n+1 =P0-a(n+1-m)-60; Where: P' n+1 Indicates the laser power correction value of the n+1th layer.

7. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 5, characterized in that: The calculation formula of the standard temperature value T0 is as follows: Among them, T n is the real-time temperature value of the metal surface of the nth layer.

8. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 1, characterized in that: The value of m is 100.

9. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 1, characterized in that: The process parameters of the first and second lasers are: laser power P0 = 200 W, scanning speed v = 1000 mm / s; time interval Δt = 100 ms.

10. The defect suppression method for additively manufacturing a high density tungsten alloy thick-walled hemispherical component according to claim 1, characterized in that: The high-density tungsten alloy powder includes the following components: 98 wt.% W, 1.4 wt.% Ni, and 0.6 wt.% Fe.

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