Magnetic field auxiliary fixed-point polishing device and method for additive manufacturing fine runner

Abstract

The invention discloses a magnetic field-assisted fixed-point polishing device and method for an additive manufacturing fine runner, and the magnetic field-assisted fixed-point polishing device and method are characterized in that a magnetic abrasive flowing through the interior of a workpiece is regulated and controlled through a magnetic field generation device capable of moving and rotating in multiple directions: under the condition of no magnetic field, polishing liquid is driven by high pressure to form a high-shear flow field; uniform cutting of the whole runner is realized through a shear thinning effect; when a specific area needs to be emphatically treated, the permanent magnet is accurately moved and positioned to a target area, magnetic particles can rapidly form a chain structure, liquid is locally solidified, and therefore the shearing force of the liquid is increased, and specific positions such as adhering slag and an under-throwing area of a bent pipe are efficiently and accurately removed; high efficiency and high precision are both considered, flow blockage and thermal runaway risks caused by runner defects can be effectively eliminated, and the reliability and safety of key components in the fields of aerospace, high-energy equipment and the like are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of precision polishing technology, and in particular to a magnetic field-assisted spot polishing device and method for additive manufacturing of fine flow channels. Background Technology

[0002] Additive manufacturing (AM) technologies, such as selective laser melting (SLM) and electron beam melting (EBM), have provided revolutionary solutions for manufacturing lightweight monolithic components with complex internal flow channels in fields such as aerospace and medical devices. However, their forming principles also bring inherent challenges: the surface of the internal channels of parts is prone to defects such as powder adhesion, step effects, and molten droplet splashing. These surface defects in the internal flow channels of additive manufacturing can not only lead to foreign matter shedding and flow channel blockage, but when the detached metal powder or slag particles migrate with the fluid to critical parts such as bends, valves, or nozzles in the system, they may also cause increased local flow resistance, system jamming, or abnormal pressure, and in severe cases, even cause system malfunction, directly threatening the reliability and safety of equipment operation. In high-speed emission equipment, high-power lasers, and other cutting-edge equipment that requires instantaneous heat dissipation, the internal cooling channels undertake the critical heat exchange task. Defects such as slag buildup on the flow channel walls can significantly disrupt the flow of the cooling medium, creating localized eddies and "heat transfer dead zones." Under extreme conditions, the walls in these areas cannot be effectively cooled, causing a rapid temperature increase that can quickly reach a critical state where the material glows red, softens, or even burns, leading to structural failure. This risk of instantaneous thermal runaway poses a serious threat to the operational safety of high-energy equipment.

[0003] Currently, post-processing polishing of such internal channels remains a significant technical challenge. Traditional mechanical and chemical polishing methods struggle to handle deep, thin, or complex internal channels, resulting in poor accessibility, uneven removal, secondary damage, and environmental pollution. Magnetorheological polishing (MRP) is an advanced intelligent polishing method. It utilizes the rheological properties of magnetorheological fluids under a magnetic field, causing magnetic particles to rapidly form chain-like structures, leading to localized solidification of the liquid and enabling targeted precision grinding of the workpiece. However, existing MRP, as a finishing solution, inherently limits its material removal rate, particularly when polishing high-roughness (Ra > 10μm) slender internal channels generated by additive manufacturing. When polishing slender internal channels, a spindle motor typically drives the workpiece to rotate, actively sweeping across the Bingham plastic solidified in a magnetic field, achieving micro-grinding through the generated shear force. While this mechanism is highly efficient for high-precision polishing, its low polishing efficiency when directly applied to large-scale removal of the substantial amount of material from initially rough surfaces fails to meet actual production needs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, a dual-mode magnetic field-assisted abrasive flow polishing apparatus and method for additive manufacturing of slender metal channels is provided. This method enables both overall channel polishing in the absence of a magnetic field and precise point-to-point removal when a magnetic field is applied, significantly improving polishing efficiency and flexibility. This invention is particularly suitable for the direct polishing of surfaces with high initial roughness, significantly enhancing polishing efficiency and process flexibility.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A magnetic field-assisted spot polishing device for additive manufacturing of fine flow channels, comprising: the device is a double-sided symmetrical feeding, magnetic field-assisted structure for spot polishing of workpieces, including a central workpiece processing unit, a symmetrically structured double-sided abrasive supply unit, and a shared power and control unit, specifically: The central workpiece processing unit includes a workpiece fixing device and a magnetic field applying device. The workpiece fixing device is located in the central area inside the magnetic field applying device and is used to fix the workpiece to be processed. The left and right ends of the workpiece fixing device are each connected to the abrasive cylinder outlet on the left and right sides through a rubber tube, respectively. The magnetic field applying device is located on the outermost side and achieves horizontal / vertical displacement through a lead screw guide rail to form an enclosed or semi-enclosed structure. The magnetic field applying device achieves circumferential adjustment so that the magnetic field accurately covers the target area of ​​the workpiece. The dual-sided abrasive supply unit includes a hydraulic pump, a check valve, a one-way valve, a throttle valve, a hydraulic cylinder, an abrasive cylinder, a positioner, a pressure gauge, a rubber hose, a relief valve, and a directional valve. The abrasive cylinder stores the abrasive mixture and is connected to one end of the workpiece fixing device via a rubber hose. The hydraulic cylinder is driven by the hydraulic pump, and the front end of the hydraulic cylinder piston rod is mechanically connected to the piston of the abrasive cylinder. The hydraulic cylinder linearly pushes the piston inside the abrasive cylinder, extruding the abrasive. Its outlet is connected to the rubber hose, and its inlet is connected to the hydraulic cylinder. The directional valve is connected to both hydraulic cylinders and positioned in the middle of the inlet path of both cylinders. The flow rate of the hydraulic cylinder is controlled by the throttle valve, and its return path is regulated by the relief valve. The throttle valve is connected in series in the inlet path of the hydraulic cylinder to control the flow rate of hydraulic oil entering the cylinder, thereby regulating the abrasive output speed. The one-way valve is connected in series in the pipeline between the outlet of the hydraulic pump and the throttle valve to prevent backflow of oil and protect the hydraulic pump and... The system includes: a motor; a check valve connected in series in the pipeline between the outlet of the hydraulic pump and the check valve to prevent backflow of the medium; a relief valve connected in series in the main oil line between the check valve and the check valve to limit the maximum pressure and protect the hydraulic module; a rubber hose connected at one end to the outlet of the abrasive cylinder and at the other end to the corresponding port of the workpiece fixing device for flexible conveying of abrasive to the workpiece; a positioner connected at one end to and controlled by the control console, and at the other end located between the abrasive cylinder and the oil cylinder; when the control console is in automatic mode, it controls the piston rods of both abrasive cylinders to automatically reverse direction, i.e., when the piston rod at the bottom of one abrasive cylinder advances first, touches the positioner inside and then retracts to the bottom, then the piston rod at the top of the other abrasive cylinder begins to advance, touches the positioner inside and then retracts to the top, and so on, achieving automatic reversal; a pressure gauge installed above the abrasive cylinder to monitor the abrasive supply pressure. The power and control unit includes a motor and a control console; the motor drives the hydraulic pump to provide pressurized oil to the hydraulic modules on both sides; the outlet pipeline of the hydraulic pump is divided into two lines to supply the abrasive supply units on both sides, and each line passes through its own check valve; the control console is an operation panel independent of the mechanical structure, used to centrally control the operation of the entire device, including the start and stop of the hydraulic pump, the start and stop control of the motor, and the opening and closing of the directional valve.

[0006] Specifically, the workpiece fixing device of the central workpiece processing unit includes a 316L stainless steel straight pipe, which is integrally formed by selective laser melting (SLM) technology; and is fixed to the breadboard by a pipe clamp.

[0007] Furthermore, the magnetic field application device of the central workpiece processing unit is fixedly mounted on the breadboard. This magnetic field application device specifically includes: a workpiece, a permanent magnet, a slider, a rotating platform, a small motor, a handwheel, a frame, a lead screw transmission structure, and a bearing assembly. The magnetic field generating device is fixedly mounted on the breadboard. The permanent magnet moves horizontally and vertically via the lead screw transmission structure and can be driven to rotate via the handwheel, converting rotational motion into linear motion, thereby causing the slider and permanent magnet to adjust their positions synchronously. Simultaneously, the rotating platform is connected to the frame via the bearing assembly and can rotate around the central axis. Combined with the adjustment of the moving mechanism, it is used to adjust the direction of the magnetic field, allowing the magnetic field of the permanent magnet to accurately cover the target area of ​​the workpiece. Once the position is determined, the permanent magnet is fixed by the magnet clamping device, thereby forming a localized strong magnetic field area on the workpiece surface. This causes the magnetic abrasive particles in the polishing fluid to chain and aggregate under the action of the magnetic field, forming a magnetorheological polishing rod for precise polishing of specific locations.

[0008] Specifically, the dual-sided abrasive supply unit has a symmetrical structure on both sides, and is connected to both ends of the workpiece flow channel through a sealed joint to form a closed loop; it also supports bidirectional flow. Furthermore, the dual-sided abrasive supply unit enables forward and reverse circulation of the polishing fluid via a control console.

[0009] Specifically, in the above steps, the permanent magnet 23 is an N52 neodymium magnet with an adjustable magnetic field strength of 200-4000 Gauss.

[0010] The present invention also provides a magnetic field-assisted spot polishing method for fine flow channels in additive manufacturing. This method is based on the aforementioned magnetic field-assisted spot polishing device for fine flow channels in additive manufacturing, and includes the following steps: Step S1: Before polishing, the workpieces in the same batch are cut by wire cutting and their initial surface roughness is measured under a confocal microscope and recorded as the reference data before polishing. Then, the overall polishing mode or the fixed-point polishing mode is selected according to the polishing requirements, and the parameters are optimized by orthogonal experimental method. Step S2: Start the magnetic field-assisted fixed-point polishing device. Under the drive of the hydraulic pump, the oil flows into the oil cylinder through the reversing valve, pushing the piston in the abrasive cylinder on one side to move. The polishing liquid in the abrasive cylinder is transported to the workpiece fixing device through the rubber tube under the monitoring of the pressure gauge. The polishing liquid polishes the inner channel of the workpiece under the push of the oil cylinder. At the same time, the flow direction of the abrasive is controlled by the control console. Each pipeline is connected in series with an overflow valve, a check valve and a one-way valve to prevent system overpressure and prevent medium backflow. Step S3: The used abrasive is transported through a rubber tube to the abrasive cylinder on the other side. The hydraulic pump is controlled by the positioner and the control console. Bilateral polishing can form a complete closed loop and ensure that the abrasive can continuously circulate throughout the process, so as to achieve continuous polishing of the workpiece.

[0011] Furthermore, in step (1), either the overall polishing mode or the spot polishing mode is selected according to the polishing requirements. Specifically, the overall polishing mode does not apply a magnetic field and relies on the shear thinning effect of the polishing fluid under high-speed flow to achieve uniform micro-cutting throughout the flow channel. The spot polishing mode applies a magnetic field to the target area, causing the polishing fluid to form a magnetorheological polishing rod, thereby achieving localized and efficient material removal.

[0012] Further, in step S1, orthogonal experimental design is used for parameter optimization. Polishing pressure, magnetic field strength, abrasive particle size, abrasive concentration, and number of cycles are used as factors, and the reduction in surface roughness is used as the evaluation index. A process prediction model is established and the optimal parameter combination is verified. The parameter optimization, with the reduction in surface roughness as the evaluation index, requires first cutting the polished inner hole with wire cutting, and then measuring its surface roughness under a confocal electron microscope. Range analysis, variance analysis, and correlation analysis are performed on the measured data. Based on the results of the range analysis and variance analysis, significant process parameters are selected. Based on the selected significant process parameters, a prediction model for surface quality is constructed. The prediction model is then experimentally verified.

[0013] Specifically, the polishing slurry in step S2 is an emulsion-based carrier liquid with magnetic molten alloy powder as polishing abrasive. When the polishing slurry flows through the area where a magnetic field is applied, it forms a solidified structure with high yield stress through chaining of magnetic abrasive particles under the action of the magnetic field. Specifically, when the polishing slurry flows through the area where a magnetic field is applied, the magnetic composite abrasive particles are rapidly magnetized and arranged into a chain structure along the direction of the magnetic field lines to form a magnetorheological polishing rod. The magnetorheological polishing rod is closely attached to the inner wall of the flow channel and generates local shear stress under the drive of the fluid.

[0014] The beneficial effects of this invention are as follows: By employing single-component magnetic abrasives that combine soft magnetic properties with cutting capabilities, and utilizing high-pressure driven polishing slurry to create a high-shear-rate flow field within microchannels, a revolutionary dual-mode polishing is achieved: In the absence of a magnetic field, the polishing slurry maintains high fluidity and high shear force due to the shear-thinning effect, allowing the abrasives to uniformly micro-cut the entire channel wall under high-speed scouring, providing basic and effective overall removal capabilities. When a magnetic field is applied, the abrasives chain together to form a "gradient stiffness magnetic brush," significantly increasing local shear stress and achieving efficient targeted removal. Its inherent soft magnetic properties further ensure that it does not easily scratch the substrate while efficiently cutting, resulting in a smooth surface morphology. This synergistic effect enables the device to efficiently process surfaces with high initial roughness while achieving final precision finishing. Polishing an additively manufactured stainless steel straight tube with an inner diameter of 1 mm and a length of 105 mm can reduce the surface roughness from the original Ra10-20 μm to Ra0.4 μm within 50 minutes. The beneficial effects of the magnetic field-assisted spot polishing method for fine flow channels in additive manufacturing provided in this application are as follows: The experiment is designed using an orthogonal experimental method to efficiently analyze the significant impact of different experimental parameters on surface quality. A process prediction model is established based on experimental data, and the stability and effectiveness of the optimized parameter combination are verified, providing clear process guidelines for different polishing requirements. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a magnetic field-assisted polishing device. Figure 2 Schematic diagram for additive manufacturing of 1mm straight pipe; Figure 3 Schematic diagram for additive manufacturing of 1mm bends; Figure 4 Diagram of the device for applying a magnetic field; Figure 5 The images show the surface morphology of the flow channel before and after polishing using SEM. Figure label: 1-Hydraulic pump; 2-Motor; 3-Check valve; 4-One-way valve; 5-Throttle valve; 6-Oil cylinder; 7-Abrasive cylinder; 8-Positioning device; 9-Pressure gauge; 10-Rubber hose; 11-Workpiece fixing device; 12-Magnetic field applying device; 13-Control console; 14-Relief valve; 15-Directional control valve; 21-Breadboard; 22-Workpiece; 23-Permanent magnet; 24-Slider; 25-Rotating platform; 26-Small motor; 27-Handwheel; 28-Frame; 29-Screw drive structure; 210-Bearing assembly; 31-Augmented 1mm stainless steel pipe upper surface; 32-Augmented 1mm stainless steel pipe lower surface; 33-Polished stainless steel pipe upper surface. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0017] This invention provides a magnetic field-assisted spot polishing device and method for fine flow channels in additive manufacturing. The device aims to solve the polishing problems caused by defects such as powder adhesion and slag buildup in the fine flow channels (1-3mm aperture, aspect ratio >50:1) inside additively manufactured metal components. A multi-directionally movable and rotating magnetic field generator controls the flow of magnetic abrasive through the workpiece: in the absence of a magnetic field, high pressure drives the polishing fluid to form a high-shear flow field, achieving uniform cutting of the entire flow channel through shear thinning effect; when specific areas require focused treatment, a permanent magnet is precisely moved and positioned to the target area, causing the magnetic particles to rapidly form a chain structure, locally solidifying the liquid and increasing its shear force, thus efficiently and accurately removing slag, underpolished areas in bends, and other specific locations.

[0018] like Figure 1 As shown, this invention provides a magnetic field-assisted spot polishing device for fine flow channels in additive manufacturing. This device is a double-sided symmetrical feeding, magnetic field-assisted spot polishing device used for spot polishing of workpieces. Specifically, it includes a hydraulic pump 1, a motor 2, a check valve 3, a one-way valve 4, a throttle valve 5, a hydraulic cylinder 6, an abrasive cylinder 7, a positioner 8, a pressure gauge 9, a rubber hose 10, a workpiece fixing device 11, a magnetic field application device 12, a control console 13, an overflow valve 14, and a reversing valve 15. The device comprises three units: a central workpiece processing area, a symmetrically structured double-sided abrasive supply system, and a shared power and control system. I. Central Workpiece Processing Unit: The workpiece fixing device 11 is located in the central area inside the magnetic field applying device 12 and is used to fix the workpiece to be processed. The left and right ends of the workpiece fixing device 11 are each connected to the outlet of the abrasive cylinder 7 on the left and right sides through a rubber tube 10, respectively. The magnetic field applying device 12 is located on the outermost side and is fixed on the breadboard 21. It is used to establish a magnetic field in the processing area and affect the distribution and movement of the abrasive. Specifically, horizontal / vertical displacement is achieved through the lead screw guide rail to form an enclosed or semi-enclosed structure. The circumferential adjustment is achieved through the magnetic field applying device 12 so that the magnetic field accurately covers the target area of ​​the workpiece.

[0019] II. Dual-sided abrasive supply unit (The dual-sided abrasive supply unit has a symmetrical structure on both sides; taking one side as an example, the other side is exactly the same; and it is connected to both ends of the workpiece flow channel through a sealing joint to form a closed loop;): The abrasive cylinder 7 is used to store the abrasive mixture and is connected to one end of the workpiece fixing device 11 through the rubber tube 10. The oil cylinder 6 is driven by the hydraulic pump 1. The front end of the piston rod of the oil cylinder 6 is mechanically connected to the piston of the abrasive cylinder 7 and pushes the piston in the abrasive cylinder 7 linearly through the oil cylinder 6 to press out the abrasive. Its outlet is connected to the rubber tube 10 and its inlet is connected to the oil cylinder 6. The reversing valve 15 is connected to the oil cylinders 6 on both sides and is set in the middle of the oil inlet of the oil cylinders 6 on both sides. The reversing valve 15 is the core of the entire oil circuit direction control. Its valve body has four clearly marked ports: P (pressure oil port, connected to the output end of the hydraulic pump 1, receiving high pressure oil from the hydraulic pump 1), A (working oil port, connected to the rodless chamber or extended chamber of one side oil cylinder 6, outputting pressure oil to one side of the actuator), B (working oil port, connected to the rod chamber or retracted chamber of the right side oil cylinder 6, outputting pressure oil to the other side of the actuator), and T (return oil port, connected to the oil tank, leading the low pressure oil back to the oil tank). After the system starts, hydraulic oil is drawn from the oil tank by the hydraulic pump 1, pressurized, and flows into the P port of the directional valve 15. The oil then flows into the cylinder 6 through the A port of the directional valve 15, pushing the abrasive cylinder 7 to move. Simultaneously, the oil in the other cylinder 6 flows out from the B port of the directional valve 15 and returns to the oil tank through the T port of the directional valve 15, completing the return oil stage. The flow rate of the cylinder 6 is controlled by the throttle valve 5, and its return oil path is regulated by the relief valve 14. The throttle valve 5 is connected in series in the oil inlet of the cylinder 6 to control the flow rate of hydraulic oil entering the cylinder 6, thereby regulating the abrasive output speed. The check valve 4 is connected in series in the pipeline between the outlet of the hydraulic pump 1 and the throttle valve 5 to prevent backflow of oil and to protect the hydraulic pump 1 and the motor 2. The check valve 3 is connected in series in the pipeline between the outlet of the hydraulic pump 1 and the check valve 4 to prevent backflow of the medium. The relief valve 14 is connected in series in the main oil line between the check valve 3 and the check valve 4 to limit the maximum pressure and protect the hydraulic module. One end of the rubber tube 10 is connected to the outlet of the abrasive cylinder, and the other end is connected to the corresponding port of the workpiece fixing device 11, for flexibly conveying abrasive to the workpiece; one end of the positioner 8 is connected to and controlled by the control console 13, and the other end is located between the abrasive cylinder 7 and the oil cylinder 6. When the control console 13 is in automatic mode, it controls the piston push rods of both abrasive cylinders 7 to automatically reverse direction. That is, when the piston push rod at the bottom of one abrasive cylinder 7 advances first, touches the positioner 8 inside it, and then retracts to the bottom, then the piston push rod at the top of the other abrasive cylinder 7 begins to advance, touches the positioner 8 inside it, and then retracts to the top, and so on, to achieve automatic reversal. The pressure gauge 9 is installed above the abrasive cylinder 7; it is used to monitor the abrasive supply pressure.

[0020] III. Power and Control Unit: The control panel 13, independent of the mechanical structure, is used for centralized control of the entire device's operation, including starting and stopping the hydraulic pump 1, controlling the start and stop of the motor 2, opening and closing the directional valve 15, moving the two positioners 8, monitoring the pressure of the two pressure gauges 9, and controlling the magnetic field strength and switching of the magnetic field application device 12. The motor 2 drives the hydraulic pump 1, providing pressurized oil to the hydraulic modules on both sides. After the outlet of the hydraulic pump 1, the pipeline splits into two lines, each supplying the abrasive supply units on both sides (each line passes through its own check valve 4).

[0021] The present invention also provides a magnetic field-assisted spot polishing method for fine flow channels in additive manufacturing, as detailed below: The magnetic field-assisted point polishing device is activated. Driven by the hydraulic pump 1, the oil flows into the oil cylinder 6 through the reversing valve 15, pushing the piston in the abrasive cylinder 7 on one side to move. Under the monitoring of the pressure gauge 9, the polishing fluid in the abrasive cylinder 7 is delivered to the workpiece fixing device 11 through the rubber hose 10. The polishing fluid polishes the inner flow channel of the workpiece under the push of the oil cylinder 6. At the same time, the flow direction of the abrasive is controlled by the control console 13. Each pipeline is connected in series with an overflow valve 14, a check valve 3, and a one-way valve 4 for safety protection to prevent system overpressure and media backflow. After use, the abrasive is delivered to the abrasive cylinder 7 on the other side through the rubber hose 10. The operation of the hydraulic pump 1 is controlled by the positioner 8 and the control console 13. Bilateral polishing can form a complete closed loop cycle. Throughout the process, it is ensured that the abrasive can continuously and stably circulate in the system to achieve continuous polishing of the workpiece.

[0022] The workpiece fixing device 11 includes a 316L stainless steel straight tube, such as... Figure 2 and bends Figure 3 As shown, the 316L stainless steel workpiece is fixed in the breadboard 21 by a pipe clamp; the workpiece is integrally formed by selective laser melting (SLM) technology; before polishing, the workpieces to be processed in the same batch are cut by wire cutting, and their initial surface roughness is measured under a confocal microscope and recorded as the reference data before polishing.

[0023] The specific structure of the magnetic field applying device 12 is as follows: Figure 4As shown, the specific components include: workpiece 22; permanent magnet 23; slider 24; rotating platform 25; small motor 26; handwheel 27; frame 28; screw drive structure 29; and bearing assembly 210. Since the sealing joint of the workpiece connecting pipe in the workpiece fixing device 11 uses a compression fitting, the workpiece 22 is connected to the rubber tube 10 via the compression fitting. The permanent magnet 23 can move horizontally (left and right) and vertically (up and down) via the screw drive structure 29—the handwheel 27 drives the screw to rotate, converting the rotational motion into linear motion, thereby causing the slider 24 to adjust its position synchronously with the permanent magnet 23. Simultaneously, the rotating platform 25 is connected to the frame 28 via the bearing assembly 210 and can rotate around its central axis. Combined with the adjustment of the moving mechanism, the magnetic field of the permanent magnet 23 can accurately cover the target area of ​​the workpiece 22. Once the position is determined, the permanent magnet 23 is fixed by the magnet clamping device, thereby forming a local strong magnetic field area on the surface of the workpiece 22. This causes the magnetic abrasive particles in the polishing fluid to chain and aggregate under the action of the magnetic field, forming a "magnetorheological polishing rod" with high shear stress, thus achieving precise polishing of specific positions and ultimately achieving precise surface finishing.

[0024] The polishing slurry uses an emulsion as the base fluid and magnetic fused alloy powder as the polishing abrasive. It combines magnetic responsiveness with cutting ability. Under no magnetic field conditions, it achieves low-viscosity flow through shear thinning. Under a magnetic field, the magnetic abrasives chain together to form a solidified structure with high yield stress. The polishing slurry needs to maintain high viscosity under static or low-shear conditions to suppress the sedimentation of functional powders. During high-shear polishing, the viscosity decreases to ensure good fluidity, thus giving the polishing slurry both good sedimentation stability and rheological properties. The overall polishing mode does not apply a magnetic field, relying on the shear thinning effect of the polishing slurry under high-speed flow to achieve uniform micro-cutting throughout the flow channel. The targeted polishing mode applies a magnetic field to the target area, causing the polishing slurry to form a "magnetorheological polishing rod," achieving localized and efficient material removal.

[0025] The experimental procedure is as follows: The magnetic field generating device 12 is fixed on the breadboard 21. Whether to add a permanent magnet 23 is adjusted according to the polishing requirements. The workpiece 22 (straight or bent) to be polished is passed through the magnetic field applying device 12, and both ends are connected to two high-pressure resistant rubber tubes 10 through compression fittings. The other end of the rubber tube 10 is connected to the inlet and outlet ports of the two abrasive cylinders 7, forming a closed loop: abrasive cylinder 7 → rubber tube 10 → workpiece 22 → other side rubber tube 10 → other side abrasive cylinder 7.

[0026] The prepared polishing liquid is slowly poured into the abrasive cylinder 7 through a funnel at the opening above the cylinder 7 until the entire circulation loop is completely filled.

[0027] A pressure gauge 9 is connected to the opening above the abrasive cylinder 7 to monitor the inlet and outlet pressures in real time while sealing the cylinder. The workpiece 22 and the rubber tube 10 are securely fixed to the optical breadboard 21 using pipe clamps to ensure no vibration or displacement during high-pressure cycling.

[0028] Inspect all connections to ensure they are well-sealed and can withstand the maximum operating pressure set for subsequent experiments.

[0029] Polishing method implementation: Mode 1: Overall uniform polishing mode. Condition setting: No external magnetic field is applied, that is, the permanent magnet 23 is moved to a position away from the workpiece.

[0030] Start polishing: Start the drive hydraulic pump 1 and set the target polishing pressure (pressure adjustment range 2-10Mpa).

[0031] The polishing slurry flows within the microchannels at a high shear rate under high pressure.

[0032] Polishing Mechanism: Due to the shear-thinning effect, the viscosity of the polishing slurry decreases significantly and its fluidity increases when flowing at high speed. The magnetic alloy abrasive grains within the slurry roll and slide freely within the flow channel, performing uniform and indiscriminate micro-cutting on the entire inner wall of the flow channel.

[0033] Process control: The flow rate for each polishing pass is set via positioner 8. After the preset number of polishing passes is reached, hydraulic pump 1 is stopped, ending the polishing process. Applicable scenarios: Primarily used for processing simple straight pipes, or for preliminary overall roughness reduction of complex internal flow channels.

[0034] Mode 2: Precision Polishing and Removal Mode Condition Settings: Based on the overall polishing mode, or directly activate this mode.

[0035] The permanent magnet 23 is fixed in the slider 24, and the permanent magnet 23 is placed in the target area of ​​the workpiece (such as the inner arc top of the bend or the location of the slag defect observed in advance by CT scan) through the lead screw transmission structure 29 and the rotating platform 25.

[0036] Start polishing: Start the drive hydraulic pump 1 and set the target polishing pressure.

[0037] Polishing Mechanism: When the polishing fluid flows through the area where a magnetic field is applied, the magnetic composite abrasive particles within it are rapidly magnetized (the magnetic composite abrasive particles simultaneously function as magnetic particles and abrasive particles, replacing the traditional two-component system of magnetic particles and abrasive particles). They align in a chain-like structure along the magnetic field lines, forming a flexible "magnetorheological polishing rod" or "gradient stiffness magnetic brush" with high yield stress. This "polishing rod" adheres closely to the inner wall of the flow channel, generating local shear stresses far exceeding those in areas without a magnetic field under fluid drive, achieving efficient and precise material removal at specific locations.

[0038] Process control: The position of the permanent magnet 23 can be moved as needed to treat different defects one by one. The polishing amount can also be controlled by the number of passes or time.

[0039] like Figure 5 The images shown are SEM images of the morphology of the 1mm additively manufactured stainless steel pipe before and after polishing, including the upper surface 31, the lower surface 32, and the upper surface 33 of the polished stainless steel pipe. Figure 5 As can be clearly seen, after polishing with this device, not only are local protrusion defects such as slag and molten droplets caused by additive manufacturing precisely removed, but the underpolishing problem caused by the abrasive inertial force on the inside of the bend is also corrected.

[0040] Parameter optimization: To obtain the optimal process window, orthogonal experimental design was used to optimize the core parameters. An orthogonal array was designed to conduct experiments using polishing pressure, magnetic field strength, abrasive particle size, abrasive particle concentration, and number of cycle passes as factors, with the reduction in surface roughness as the evaluation index.

[0041] After the experiment, the workpiece was cleaned, and workpiece 22 was cut open by wire cutting. The surface roughness 33 after polishing was measured and recorded. Through range analysis and variance analysis, the significance ranking of the influence of each factor on the index was determined, and the optimal parameter combination was preliminarily determined.

[0042] Based on the experimental data, a regression model was established between the process parameters and the polishing effect. Finally, the optimized parameter combination was used to conduct 3-5 repeated verification experiments to test the stability and repeatability of the process.

[0043] In summary, this invention can reduce the surface roughness of additively manufactured stainless steel flow channels with an inner diameter of 1mm from Ra 10-20μm to Ra 0.4μm (taking 50 minutes), balancing high efficiency and high precision. It effectively eliminates the risks of flow blockage and thermal runaway caused by flow channel defects, significantly improving the reliability and safety of key components in aerospace, high-energy equipment, and other fields. The above description is merely a preferred embodiment of this invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0044] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A magnetic field-assisted spot polishing device for fine flow channels in additive manufacturing, characterized in that, include: The device is a symmetrical, magnetically assisted abrasive feeding structure used for spot polishing of workpieces. It includes a central workpiece processing unit, a symmetrically structured symmetrical abrasive feeding unit on both sides, and a shared power and control unit. Specifically: The central workpiece processing unit includes a workpiece fixing device (11) and a magnetic field applying device (12). The workpiece fixing device (11) is located in the central area inside the magnetic field applying device (12) and is used to fix the workpiece to be processed. The left and right ends of the workpiece fixing device (11) are connected to the outlets of the abrasive cylinder (7) on the left and right sides respectively through a rubber tube (10). The magnetic field applying device (12) is located on the outermost side and is moved horizontally / vertically through the lead screw guide rail to form an enclosed or semi-enclosed structure. The magnetic field applying device (12) is used to achieve circumferential adjustment so that the magnetic field accurately covers the target area of ​​the workpiece. The dual-sided abrasive supply unit includes a hydraulic pump (1), a check valve (3), a one-way valve (4), a throttle valve (5), a hydraulic cylinder (6), an abrasive cylinder (7), a positioner (8), a pressure gauge (9), a rubber hose (10), an overflow valve (14), and a directional valve (15). The abrasive cylinder (7) is used to store the abrasive mixture and is connected to one end of the workpiece fixing device (11) via a rubber tube (10); the oil cylinder (6) is driven by a hydraulic pump (1), and the front end of the piston rod of the oil cylinder (6) is mechanically connected to the piston of the abrasive cylinder (7), and the piston inside the abrasive cylinder (7) is pushed linearly by the oil cylinder (6) to press out the abrasive. Its outlet is connected to the rubber tube (10), and its inlet is connected to the oil cylinder (6); the reversing valve (15) is connected to the oil cylinders (6) on both sides and is set at the inlet of the oil cylinders (6) on both sides. In the middle of the oil circuit, the flow rate of the oil cylinder (6) is controlled by the throttle valve (5), and the pressure of its return oil circuit is regulated by the overflow valve (14); the throttle valve (5) is connected in series in the oil inlet of the oil cylinder (6) to control the flow rate of hydraulic oil entering the oil cylinder (6), thereby regulating the abrasive output speed; the check valve (4) is connected in series in the pipeline between the outlet of the hydraulic pump (1) and the throttle valve (5) to prevent backflow of oil and to protect the hydraulic pump (1) and the motor (2); the check valve (3) is connected in series in the pipeline between the outlet of the hydraulic pump (1) and the throttle valve (5). The pipeline between the check valve (4) is used to prevent backflow of the medium; the relief valve (14) is connected in series in the main oil line between the check valve (3) and the check valve (4) to limit the maximum pressure and protect the safety of the hydraulic module; one end of the rubber tube (10) is connected to the outlet of the abrasive cylinder (7), and the other end is connected to the corresponding port of the workpiece fixing device (11) for flexible conveying of abrasive to the workpiece; one end of the positioner (8) is connected to the control console (13) and controlled by the control console (13), and the other end is located between the abrasive cylinder (7) and the check valve (4). Between the oil cylinders (6), when the control panel (13) is in automatic mode, it controls the piston push rods of the two abrasive cylinders (7) to automatically switch directions. That is, when the piston push rod at the bottom of one abrasive cylinder (7) advances first, touches the internal positioner (8) and then retracts to the bottom, the piston push rod at the top of the other abrasive cylinder (7) begins to advance, touches the internal positioner (8) and then retracts to the top. This cycle is repeated to achieve automatic switching. The pressure gauge (9) is installed above the abrasive cylinder (7) to monitor the abrasive supply pressure. The power and control unit includes a motor (2) and a control console (13); the motor (2) is used to drive the hydraulic pump (1) to provide pressure oil to the hydraulic modules on both sides; the outlet pipeline of the hydraulic pump (1) is divided into two lines to supply the abrasive supply units on both sides, and each line passes through its own check valve (4); the control console (13) is an operation panel independent of the mechanical structure, used to centrally control the operation of the entire device, including the start and stop of the hydraulic pump (1), the start and stop control of the motor (2), and the opening and closing of the directional valve (15).

2. The magnetic field-assisted spot polishing device for additive manufacturing fine flow channels according to claim 1, characterized in that, The workpiece fixing device (11) of the central workpiece processing unit includes a 316L stainless steel straight pipe, which is integrally formed by selective laser melting (SLM) technology; and is fixed to the breadboard (21) by pipe clamps.

3. The magnetic field-assisted spot polishing device for additive manufacturing fine flow channels according to claim 1, characterized in that, The magnetic field application device (12) of the central workpiece processing unit is fixedly mounted on the breadboard (21). The magnetic field application device (12) specifically includes: workpiece (22), permanent magnet (23), slider (24), rotating platform (25), small motor (26), handwheel (27), frame (28), lead screw transmission structure (29), and bearing assembly (210). The magnetic field generating device (12) is fixedly mounted on the breadboard (21). The permanent magnet (23) moves in the horizontal and vertical directions through the lead screw transmission structure (29) and can drive the lead screw to rotate through the handwheel (27), converting the rotational motion into rotational motion. The linear motion drives the slider (24) and the permanent magnet (23) to adjust their positions synchronously. At the same time, the rotating platform (25) is connected to the frame (28) through the bearing assembly (210) and can rotate around the central axis. Combined with the adjustment of the moving mechanism, it is used to adjust the direction of the magnetic field, so that the magnetic field of the permanent magnet (23) can accurately cover the target area of ​​the workpiece (22). When the position is determined, the permanent magnet (23) is fixed by the magnet clamping device, thereby forming a local strong magnetic field area on the surface of the workpiece (22), so that the magnetic abrasive particles in the polishing liquid will chain and aggregate under the action of the magnetic field to form a magnetorheological polishing rod for precise polishing of specific positions.

4. The magnetic field-assisted spot polishing device for additive manufacturing fine flow channels according to claim 1, characterized in that, The dual-sided abrasive supply unit has a symmetrical structure on both sides and is connected to both ends of the workpiece flow channel through a sealed joint to form a closed loop; and supports bidirectional flow.

5. The magnetic field-assisted spot polishing device for additive manufacturing fine flow channels according to claim 1, characterized in that, The dual-sided abrasive supply unit realizes the forward and reverse circulation of polishing fluid through the control console (13).

6. The magnetic field-assisted spot polishing apparatus for additive manufacturing fine flow channels according to claim 1, characterized in that, In step (2), the permanent magnet 23 is an N52 neodymium magnet with an adjustable magnetic field strength of 200-4000 Gauss.

7. A magnetic field-assisted spot polishing method for fine flow channels in additive manufacturing, characterized in that, This method is based on the magnetic field-assisted spot polishing apparatus for additive manufacturing fine flow channels as described in claims 1-6, and includes the following steps: Step S1: Before polishing, the workpieces in the same batch are cut by wire cutting and their initial surface roughness is measured under a confocal microscope and recorded as the reference data before polishing. Then, the overall polishing mode or the fixed-point polishing mode is selected according to the polishing requirements, and the parameters are optimized by orthogonal experimental method. Step S2: Start the magnetic field-assisted fixed-point polishing device. Under the drive of the hydraulic pump (1), the oil flows into the oil cylinder (6) through the reversing valve (15) and pushes the piston in the abrasive cylinder (7) on one side to move. The polishing liquid in the abrasive cylinder (7) is transported to the workpiece fixing device (11) through the rubber tube (10) under the monitoring of the pressure gauge (9). The polishing liquid polishes the inner flow channel of the workpiece under the push of the oil cylinder (6). At the same time, the flow direction of the abrasive is controlled by the control console (13). Each pipeline is connected in series with an overflow valve (14), a check valve (3) and a one-way valve (4) to prevent system overpressure and prevent medium backflow. Step S3: The used abrasive is transported through the rubber tube (10) to the abrasive cylinder (7) on the other side. The hydraulic pump (1) is controlled by the positioner (8) and the control console (13). The double-sided polishing can form a complete closed loop and ensure that the abrasive can continuously circulate throughout the process, so as to realize the continuous polishing of the workpiece.

8. The magnetic field-assisted spot polishing method for additive manufacturing fine flow channels according to claim 7, characterized in that, In step (1), the overall polishing mode or the spot polishing mode is selected according to the polishing requirements. Specifically, the overall polishing mode does not apply a magnetic field and relies on the shear thinning effect of the polishing fluid under high-speed flow to achieve uniform micro-cutting throughout the flow channel. The spot polishing mode applies a magnetic field to the target area, so that the polishing fluid forms a magnetorheological polishing rod to achieve localized and efficient material removal.

9. The magnetic field-assisted spot polishing method for additive manufacturing fine flow channels according to claim 7, characterized in that, In step (1), the orthogonal experimental method is used to optimize the parameters, with polishing pressure, magnetic field strength, abrasive particle size, abrasive concentration and cycle number as factors, and the amount of surface roughness reduction as the evaluation index, to establish a process prediction model and verify the optimal parameter combination. The parameter optimization uses the reduction in surface roughness as the evaluation index. It requires first cutting open the polished inner hole by wire cutting, and then measuring its surface roughness under a confocal electron microscope. The measured data are then subjected to range analysis, variance analysis, and correlation analysis. Based on the results of the range analysis and variance analysis, significant process parameters are selected. Based on the selected significant process parameters, a predictive model for surface quality is constructed. Finally, the predictive model is experimentally verified.

10. The magnetic field-assisted spot polishing method for additive manufacturing fine flow channels according to claim 7, characterized in that, The polishing slurry in step (2) is an emulsion-based carrier liquid with magnetic molten alloy powder as polishing abrasive. When the polishing slurry flows through the area where a magnetic field is applied, it forms a solidified structure with high yield stress through chaining of magnetic abrasive particles under the action of the magnetic field. Specifically, when the polishing slurry flows through the area where a magnetic field is applied, the magnetic composite abrasive particles are rapidly magnetized and arranged into a chain structure along the direction of the magnetic field lines to form a magnetorheological polishing rod. The magnetorheological polishing rod is closely attached to the inner wall of the flow channel and generates local shear stress under the drive of the fluid.

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