Powder bed preheating device, powder bed and SLM printing method
By arranging the powder bed preheating device of electrodes along the height of the forming chamber during the SLM printing process, the problems of thermal gradient, thermal stress and thermal deformation in SLM printing are solved, and uniform preheating of the upper, middle and lower powders and improving the mechanical properties of the finished product are achieved.
Patent Information
- Application Number
- CN202411891219.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-20
- Publication Date
- 2025-04-04
AI Technical Summary
During the selective laser melting (SLM) printing process, local temperature changes and rapid cooling caused by laser heating are prone to occur thermal gradients, thermal stress and thermal deformation of the material, which affects the printing quality and the mechanical properties of the finished product.
A powder bed preheating device is designed, including a positive electrode, a negative electrode, a temperature sensor and a temperature control module. The electrodes are arranged at intervals along the height direction of the forming chamber. The powder and metal parts are heated by current to achieve uniform preheating of the upper, middle and lower powders and reduce the thermal stress of the finished product.
By preheating the powder bed and metal parts, the temperature gradient between the molded body and the molten pool layer is significantly reduced, thermal stress and thermal deformation are reduced, and the printing quality and mechanical properties of the finished product are improved.
Smart Images
Figure CN119747696A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of selective laser melting, and in particular relates to a powder bed preheating device, a powder bed and a SLM printing method. Background Art
[0002] As an important method in metal additive manufacturing, selective laser melting (SLM) technology has been widely used in high-end manufacturing fields such as aerospace, medical, and automobile in recent years. SLM technology selectively melts metal powder through a laser beam to build parts of complex shapes layer by layer, with high design freedom and manufacturing accuracy.
[0003] However, during the SLM printing process, due to local temperature changes and rapid cooling caused by laser heating, thermal gradients, thermal stresses, and thermal deformation of materials are easily generated. These factors directly affect the printing quality and the mechanical properties of the finished product. In order to solve this problem, powder bed preheating technology has become one of the effective means to improve the quality of SLM printing. Powder bed preheating can make the metal powder bed reach a suitable temperature before printing, reduce the temperature difference between different areas during laser scanning, and thus reduce thermal stress and thermal deformation. At present, infrared heating and laser-assisted heating are commonly used to preheat the powder bed. These methods can only preheat the surface powder in the powder bed, and there is a problem of uneven heating. Summary of the invention
[0004] The present application provides a powder bed preheating device to solve related technical problems.
[0005] The present invention is achieved through the following technical solution: a powder bed preheating device, comprising: Positive electrode, negative electrode, temperature sensor and temperature control module; The positive and negative electrodes are arranged at equal intervals along the height direction of the molding cavity of the powder bed, and the positive electrode and the negative electrode are respectively arranged on two opposite side walls of the molding cavity; The temperature sensor is used to be alternately arranged on the same side wall of the molding cavity at equal intervals with the positive electrode or the negative electrode; The temperature sensor is used to collect the powder temperature of the corresponding height area in the powder bed and send it to the temperature control module; The temperature control module is used to control the output current of the corresponding paired electrode according to the difference between the powder temperature of the height area covered by the paired positive and negative electrodes and the target temperature until the powder temperature is consistent with the target temperature.
[0006] Furthermore, a negative electrode located on the same horizontal line is provided for each positive electrode.
[0007] Furthermore, the temperature sensor is a contact temperature sensor, and the temperature sensor is arranged in a groove of the side wall of the molding cavity and is flush with the surface of the cavity wall of the molding cavity.
[0008] Furthermore, the positive electrode and the negative electrode in the electrode pair are both arranged in the groove of the side wall of the molding cavity, and are both flush with the surface of the cavity wall of the molding cavity.
[0009] The present invention also provides a powder bed, comprising the above-mentioned powder bed preheating device.
[0010] The present invention also provides an SLM printing method, in which a metal part is printed layer by layer in a powder bed as described above, and during the printing process, current is passed through paired electrodes to the metal powder and the molded body of the metal part, and the metal powder and the molded body are preheated by utilizing the resistance characteristics of the metal powder and the molded body under the action of the current. The molded body refers to the formed part of the metal part.
[0011] Further, the following steps are included: When the metal part to be printed is a positive axis part, the positive axis part refers to the workpiece axis being parallel to the axis of the molding cavity. As the substrate gradually descends in the molding cavity, the positive and negative electrodes in the high, middle and low layers are paired in sequence.
[0012] Furthermore, when the metal part to be printed is an oblique-axis part, the oblique-axis part refers to the workpiece axis being inclined relative to the axis of the molding cavity. As the substrate gradually descends in the molding cavity, the corresponding positive and negative electrodes are paired according to the height area spanned by the molded body of the metal part.
[0013] Furthermore, the positive and negative electrodes are paired according to the electrodes corresponding to the highest point and the lowest point of the formed body.
[0014] Furthermore, after the substrate is preheated, metal powder is laid on the substrate and printing begins.
[0015] Compared with the prior art, the beneficial effects of the present invention include: 1. The prior art can only preheat the top layer of powder, but cannot preheat the middle and lower layers of powder, let alone directly preheat the metal parts in the printing process. However, the present invention can preheat the upper, middle and lower layers of powder by arranging the electrode pairs along the height direction of the molding cavity. At the same time, the present invention utilizes the conductivity and resistance characteristics of the powder and the metal parts. When the electrode pairs are energized, they can form a current loop with the powder and the metal parts, and the powder and the metal parts are directly heated by the current.
[0016] 2. In the prior art, the temperature of the powder layer being printed, i.e., the molten pool layer, is above 1000°C, and the farther the formed part of the metal part is from the molten pool layer, the lower its temperature is, and the bottom layer is even below 100°C. Such a huge temperature gradient causes the metal parts to generate great thermal stress during the printing process, with obvious thermal deformation and large dimensional errors. However, the present invention can greatly reduce the temperature gradient between the formed body and the molten pool layer after preheating the metal parts, thereby greatly reducing thermal stress. At the same time, the preheated powder has a heat-insulating effect on the formed body, and the preheated powder can be more fully melted under the action of the laser, and a more uniform shape is formed after the molten pool is cooled.
[0017] 3. When printing the positive shaft, the positive and negative electrodes on the same horizontal line are paired in sequence along the descending direction to preheat the molded body synchronously: according to the powder temperature in different height areas, the output current of the paired electrodes in the corresponding area is adjusted to ensure uniform temperature in each area and eliminate the adverse effects of temperature gradients.
[0018] 4. When printing the oblique axis parts, pair the corresponding positive and negative electrodes according to the height area spanned by the molded body. Since the resistance of the molded body is smaller than that of the metal powder, the current can flow more concentratedly along the axial direction of the molded body to heat the molded body, which has a higher preheating efficiency for the oblique axis parts. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0020] Figure 1 is a schematic diagram of the structure of the powder bed in this specific embodiment; Figure 2 is a finite element modeling diagram of powder and workpiece in the molding cavity in this specific embodiment; Figure 3 is a diagram of the current distribution in the molding cavity when a pair of electrodes is turned on in this specific embodiment; Figure 4 is a current distribution diagram in the molding cavity when three pairs of electrodes are turned on in this specific embodiment; Figure 5 It is a finite element simulation diagram of the oblique shaft member in this specific implementation manner. DETAILED DESCRIPTION
[0021] The existing technology can only preheat the top layer of powder, but cannot preheat the middle and lower layers of powder, let alone directly preheat the metal parts in the printing process.
[0022] In order to preheat the metal parts, this embodiment provides a powder bed preheating device. Since the powder bed preheating device is installed in the powder bed, this embodiment is described by taking the powder bed as an example.
[0023] refer to Figure 1 As shown, a powder bed is provided, and a powder bed preheating device is installed in a molding cavity 4 of the powder bed, and the powder bed preheating device includes: a positive electrode 101, a negative electrode 102, a temperature sensor 2 and a temperature control module 3; The positive and negative electrodes are arranged at equal intervals along the height direction of the molding cavity 4 of the powder bed, and the positive electrode 101 and the negative electrode 102 are respectively arranged on two opposite side walls of the molding cavity 4; The temperature sensor 2 and the positive electrode 101 or the negative electrode 102 are alternately arranged at equal intervals on the same side wall of the molding cavity 4; The temperature sensor is used to collect the powder temperature of the corresponding height area in the powder bed and send it to the temperature control module; The temperature control module is used to control the output current of the corresponding paired electrode according to the difference between the powder temperature of the height area covered by the paired positive and negative electrodes and the target temperature until the powder temperature is consistent with the target temperature.
[0024] The electrode pairs arranged along the height direction of the molding cavity can be used to preheat the powders in the upper, middle and lower layers. At the same time, the present invention utilizes the conductivity and resistance characteristics of the powder and the metal parts. When the electrode pairs are energized, they can form a current loop with the powder and the metal parts, and the powder and the metal parts are directly heated by the current.
[0025] Preferably, a negative electrode located on the same horizontal line is provided for each positive electrode.
[0026] After the positive and negative electrodes on the same horizontal line are paired, the current can flow along the horizontal lines in different height areas to form a partitioned current to achieve partitioned preheating.
[0027] In order to verify the current flow path, the finite element software was used to simulate the current influence of the preheating device on the powder bed and the workpiece. First, a geometric model including the electrode, powder bed and workpiece was constructed, such as Figure 2 As shown in the figure, the left electrode is supplied with current, and the right electrode is set to be grounded. The current density distribution in the molding cavity during the process of the electrode being energized is solved. Figure 3 and Figure 4 The current density distribution cloud diagram of the powder bed and workpiece after the electrode is turned on is shown.
[0028] Figure 3It is shown that when only electrode pair ① is turned on, the current mainly flows through the upper part of the workpiece, indicating that the flow of current is directional and directional heating of the local area can be achieved.
[0029] Depend on Figure 4 It can be seen that after all three pairs of electrodes are turned on, the current flows out from the left electrode, flows through the workpiece to generate a uniformly distributed current, and then flows into the right ground electrode. This process can achieve uniform heating of the entire workpiece.
[0030] In this specific embodiment, the temperature sensor is a contact temperature sensor (such as a thermocouple), which is arranged in a groove of the side wall of the molding cavity and is flush with the surface of the cavity wall of the molding cavity. The contact temperature sensor is small in size and high in accuracy. The contact temperature sensor needs to be flush with the surface of the cavity wall of the molding cavity to ensure contact with the powder and avoid motion interference with the substrate in the molding cavity.
[0031] In this specific embodiment, the positive electrode and the negative electrode in the electrode pair are both arranged in the groove of the side wall of the molding cavity and are flush with the surface of the cavity wall of the molding cavity to ensure contact with the powder and avoid movement interference with the substrate in the molding cavity.
[0032] This specific embodiment also provides an SLM printing method, in which a metal part is printed layer by layer in a powder bed as described above, and during the printing process, current is passed through paired electrodes to the metal powder and the molded body of the metal part, and the metal powder and the molded body are preheated by utilizing their resistance characteristics under the action of current. The molded body refers to the formed part of the metal part.
[0033] The powder bed in this specific embodiment can be used to print both positive shaft parts and oblique shaft parts, but the pairing methods of the positive and negative electrodes are different, which are explained below respectively.
[0034] When the metal part to be printed is a positive axis part, the positive axis part refers to the workpiece axis being parallel to the axis of the molding cavity. As the substrate gradually descends in the molding cavity, the positive and negative electrodes on the same horizontal line are paired in sequence along the direction of descending height.
[0035] When printing the positive shaft, the positive and negative electrodes on the same horizontal line are paired in sequence along the descending direction to preheat the molded body synchronously: according to the powder temperature in different height areas, the output current of the paired electrodes in the corresponding area is regulated to ensure uniform temperature in each area and eliminate the adverse effects of temperature gradients.
[0036] When the metal part to be printed is an oblique axis part, the oblique axis part refers to the workpiece axis being inclined relative to the axis of the molding cavity. As the substrate gradually descends in the molding cavity, the corresponding positive and negative electrodes are paired according to the height area spanned by the molding. Specifically, the positive and negative electrodes are paired according to the electrodes corresponding to the highest point and the lowest point of the molding. Figure 5 As shown, the highest point A and the lowest point B of the formed body, the electrode corresponding to the highest point A should be at least at the same height as the highest point A and should not be lower than point A; the electrode corresponding to the lowest point B should be at least at the same height as the lowest point B and should not be higher than point B.
[0037] When printing the oblique axis parts, the corresponding positive and negative electrodes are matched according to the height area spanned by the molded body. Since the resistance of the molded body is smaller than that of the metal powder, the current can flow more concentratedly along the axial direction of the molded body to heat the molded body, which has a higher preheating efficiency for the oblique axis parts.
[0038] After the positive and negative electrodes are paired, the temperature control module controls the output current of the corresponding paired electrode according to the difference between the powder temperature in the height area covered by the paired electrode and the target temperature until the powder temperature is consistent with the target temperature.
[0039] For paired electrodes on the same horizontal line, the temperature sensors corresponding to the positive electrode and the negative electrode are consistent, that is, the corresponding powder temperatures are consistent. The powder temperature collected by the corresponding temperature sensor is taken as the powder temperature of the height area covered by the paired electrode. If multiple temperature sensors are provided in the height area, the average value can be taken.
[0040] For paired electrodes that are not on the same horizontal line, the temperature sensors corresponding to the positive electrode and the negative electrode are different. The powder temperatures collected by all temperature sensors in the height area covered by the positive and negative electrodes are taken, and the average value is calculated as the powder temperature of the height area covered by the paired electrode.
[0041] The temperature control module is implemented by a PID constant temperature controller, and its control principle belongs to the prior art and will not be described in detail here.
[0042] In this specific embodiment, metal powder is laid on the substrate 5 after the substrate 5 is preheated and printing begins. Printing begins after the substrate is preheated, which is conducive to the metal powder forming a metallurgical bond with the substrate during the laser melting process, and is convenient for fixing the metal parts during the printing process to prevent them from moving. Figure 1 As shown, the metal part 6 (arc-shaped arch column) is fixed on the substrate 5 through the metallurgical bonding layer during the printing process to avoid displacement when spreading or scraping powder.
[0043] In this specific embodiment, after printing is completed, the powder bed preheating device is turned off and the metal part is cooled naturally. Since the temperature uniformity of the entire powder bed is ensured during the entire printing process, no thermal stress concentration will occur during the natural cooling process, so no additional heat preservation and stress relief treatment is required, which greatly shortens the production cycle and reduces energy consumption.
[0044] The following is an example of SLM additive manufacturing of GH3625 alloy curved arch columns.
[0045] First, the arc column model was established using modeling software, and then the relevant parameters of laser forming were set as follows: laser power 380W, scanning speed 1000mm∙ s-1 , spot radius 50μm, powder thickness 60μm, scanning spacing 120μm, scanning path "S", interlayer angle 67°. The slicing software converts the 3D model of the part into a series of 2D slicing data and generates code. The code contains information such as laser scanning path, laser power, scanning speed, etc., which is used to control the laser head movement and heating parameter adjustment of the SLM equipment. Import the sliced data file into the SLM equipment to complete the equipment preparation, including: checking the equipment operation status and ensuring that the laser, scanning system, powder bed and other components are in normal working condition. Pre-powder preparation: evenly spread a layer of metal powder on the powder bed and prepare to start printing.
[0046] The substrate preheating temperature is set to 100°C to ensure that the powder bed reaches the appropriate preheating temperature at the beginning of the printing process. During the printing process, the substrate gradually descends, and the temperature of the corresponding area is monitored in real time through thermocouples in the high, middle and low layers to accurately detect the temperature changes in each area.
[0047] In the middle and lower layers of the powder bed, when the temperature is detected to be lower than the preset value, the temperature control system will automatically adjust the current and turn on the electrodes in the corresponding area. Based on the real-time feedback of temperature information, the system dynamically adjusts the heating power of the heating element by adjusting the power output of the current to ensure that the temperature of each area of the powder bed rises evenly.
[0048] For high-rise areas: Since the laser scanning process will make the upper area higher in temperature, the temperature control system will reduce the heating power of the upper electrode to avoid overheating. Middle and bottom areas: These areas are farther away from the laser scanning area and usually have lower temperatures, so the system will increase the heating power of these areas to ensure that the temperature gradually rises and reaches a stable preheating state.
[0049] As SLM printing progresses, the laser head scans and melts the powder according to the preset path, and the temperature of each layer is monitored and adjusted in real time during the melting and cooling process. The temperature control module continuously adjusts the heating power based on the information fed back by the thermocouple to ensure that the temperature of the powder bed of each layer is always kept within the ideal range.
[0050] After printing is completed, the machine automatically stops the laser scanning and slowly cools the part in a protective atmosphere. Since the hierarchical control system of the resistance heating has ensured the temperature uniformity of the entire powder bed, there will be no thermal stress concentration during the cooling of the part. After cooling is completed, the support structure is removed and the necessary heat treatment is performed to further optimize the mechanical properties of the material. Finally, surface treatment is performed to remove possible surface defects.
[0051] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection created by this application.
Claims
1. A powder bed preheating device, characterized in that: include: Positive electrode, negative electrode, temperature sensor and temperature control module; The positive and negative electrodes are arranged at equal intervals along the height direction of the molding cavity of the powder bed, and the positive electrode and the negative electrode are respectively arranged on two opposite side walls of the molding cavity; The temperature sensor is used to be alternately arranged on the same side wall of the molding cavity at equal intervals with the positive electrode or the negative electrode; The temperature sensor is used to collect the powder temperature of the corresponding height area in the powder bed and send it to the temperature control module; The temperature control module is used to control the output current of the corresponding paired electrode according to the difference between the powder temperature of the height area covered by the paired positive and negative electrodes and the target temperature until the powder temperature is consistent with the target temperature.
2. The powder bed preheating device according to claim 1, characterized in that: A negative electrode located on the same horizontal line is provided for each positive electrode.
3. The powder bed preheating device according to claim 1, characterized in that: The temperature sensor is a contact temperature measuring sensor, which is arranged in a groove of the side wall of the molding cavity and is flush with the surface of the cavity wall of the molding cavity.
4. The powder bed preheating device according to claim 1, characterized in that: The positive electrode and the negative electrode in the electrode pair are both arranged in the groove of the side wall of the forming cavity and are both flush with the surface of the cavity wall of the forming cavity.
5. A powder bed, characterized in that: It comprises a powder bed preheating device as described in any one of claims 1 to 4.
6. A SLM printing method, characterized in that: The metal part is printed layer by layer in the powder bed as described in claim 4, and during the printing process, current is passed through the metal powder and the metal part's molded body through paired electrodes, and the metal powder and the molded body are preheated by utilizing the resistance characteristics of the metal powder and the molded body under the action of current. The molded body refers to the formed part of the metal part.
7. The SLM printing method according to claim 5, characterized in that: The following steps are involved: When the metal part to be printed is a positive axis part, the positive axis part refers to the workpiece axis being inclined relative to the axis of the molding cavity. As the substrate gradually descends in the molding cavity, the positive and negative electrodes on the same horizontal line are paired in sequence along the direction of descending height.
8. The SLM printing method according to claim 5, characterized in that: When the metal part to be printed is an oblique-axis part, the oblique-axis part refers to the workpiece axis being inclined relative to the axis of the molding cavity. As the substrate gradually descends in the molding cavity, the corresponding positive and negative electrodes are paired according to the height area spanned by the molding.
9. The SLM printing method according to claim 8, characterized in that: The positive and negative electrodes are paired according to the electrodes corresponding to the highest point and the lowest point of the formed body.
10. The SLM printing method according to claim 6, characterized in that: After the substrate is preheated, metal powder is laid on the substrate and printing begins.