Method for polishing the inner wall of a metal part having a hollow cavity

Abstract

The application provides a metal part inner wall polishing method with a hollow cavity, comprising the following steps: S1, electrode design: designing a workpiece, and simultaneously, designing an electrode piece matched with the shape and size of the inner cavity in the inner cavity, the electrode piece having a gap with the inner cavity wall of the inner cavity; S2, additive printing; S3, electrochemical polishing: filling solid particles in the gap, and setting a blocking piece for restraining the solid particles in the gap at the opening, then connecting the electrode piece with the negative pole of a power supply, connecting the workpiece with the positive pole of the power supply, after the connection, introducing an electrochemical polishing liquid into the inner cavity, and starting the power supply to electrochemically polish the inner cavity wall; and S4, removing the electrode piece: destroying the structure of the electrode piece to complete the polishing of the inner cavity wall. The application has the advantages that the solid particles are arranged to avoid the overlap of the workpiece and the electrode piece in the electrochemical polishing process, the inner wall roughness is reduced, and the surface quality of the inner wall is improved.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing polishing technology, and in particular to a method for polishing the inner wall of a metal part with a hollow cavity. Background Technology

[0002] Additive manufacturing, or 3D printing, is a technology that directly prints three-dimensional solid parts by accumulating materials layer by layer. By eliminating the constraints of traditional manufacturing techniques on the design of part shapes, additive manufacturing can create monolithic components with various complex structures. However, due to inherent problems in laser additive manufacturing, such as the step effect, powder adhesion, and spheroidization effect, the surface roughness of additively formed parts is relatively high, generally reaching Ra 10μm to 50μm, while many practical applications require lower surface roughness, such as Ra below 3.2μm. Therefore, if effective subsequent surface polishing treatment is not performed on additively manufactured parts, the high surface roughness will severely limit the widespread application of this technology, especially for structural parts with complex internal features.

[0003] For the surface polishing requirements of additively manufactured metal parts, various polishing technologies are currently available, such as mechanical blasting, vibratory finishing, chemical dissolution leveling, or electrochemical polishing. These technologies can relatively easily reduce the surface roughness of parts, obtaining a relatively bright and smooth surface. They can even be machined to achieve the same quality level as traditional machining. However, for the inner surfaces of metal parts with complex hollow cavities, there are currently few satisfactory internal polishing technologies. Common internal polishing technologies include abrasive flow polishing and chemical polishing. Abrasive flow processing technology uses an abrasive medium flowing under pressure over the inner surface of the part, where the abrasive grains perform microscopic mechanical grinding to achieve a polishing effect. However, for metal parts with complex hollow cavities, abrasive flow processing suffers from uneven polishing removal and the existence of machining dead zones. Chemical polishing technology is based on the principle of chemical reaction between dissolution and metal to remove material from the inner wall of metal parts. The solution has good accessibility, but its leveling ability is limited. It cannot polish and level the inner surface of laser additive parts with high roughness. It generally suffers from problems such as long polishing time and limited polishing effect.

[0004] Electrochemical polishing is a relatively effective method for polishing the interior of additively manufactured parts. In electrochemical polishing, the part being polished acts as the anode, and another metal component acts as the cathode. Both electrodes are simultaneously in contact with the electrolyte, and a current is passed through them to produce selective anodic dissolution, thereby achieving the effect of polishing the inner surface of the part. To achieve good polishing consistency, the shape of the cathode needs to be similar to the shape of the surface to be processed on the workpiece. For current additive printing technology, it is not difficult to print the internal conformal cathode along with the part. However, how to ensure that the cathode does not overlap and short-circuit with the inner wall of the part during the polishing process, thus causing electrochemical polishing failure, and how to completely remove the cathode from the complex cavity afterwards, are still problems that need to be solved by those skilled in the art. Summary of the Invention

[0005] To address the aforementioned deficiencies, the present invention aims to provide a method for polishing the inner wall of a metal part with a hollow cavity. By adding solid particles between the electrode and the inner cavity wall of the workpiece, the overlapping short circuit between the electrode and the inner cavity wall of the workpiece is avoided without affecting the electrochemical polishing effect, thereby solving the above-mentioned technical problems.

[0006] This invention provides a method for polishing the inner wall of a metal part with a hollow cavity, comprising the following steps:

[0007] S1. Electrode Design: Design a workpiece having several openings and an inner cavity connected to the openings. Simultaneously, design an electrode component in the inner cavity that matches the shape and size of the inner cavity, with a gap between the electrode component and the inner cavity wall.

[0008] S2. Additive printing: The workpiece and electrode are printed simultaneously using a 3D printer;

[0009] S3. Electrochemical polishing: The gap is filled with solid particles made of insulating material, and a baffle is set at the opening to constrain the solid particles in the gap. Then, the electrode is connected to the negative terminal of the power supply, and the workpiece is connected to the positive terminal of the power supply. After the connection is completed, electrochemical polishing liquid is introduced into the inner cavity. After the flow of the electrochemical polishing liquid is stable, the power supply is turned on to perform electrochemical polishing on the inner cavity wall.

[0010] S4. Remove the electrode components: Destroy the structure of the electrode components, remove the baffle, drain the liquid and solid particles in the inner cavity, remove the electrode components, and complete the polishing of the inner cavity wall.

[0011] Preferably, in step S1, the electrode is configured as a porous structure.

[0012] Preferably, in step S1, the porosity of the middle part of the electrode is greater than the porosity at the opening.

[0013] Preferably, in step S4, the structure of the electrode is destroyed by introducing a chemical solution for dissolving or corroding the electrode into the inner cavity.

[0014] Preferably, in step S2, different printing parameters are used to print the workpiece and the electrode, so that the workpiece has a microstructure different from that of the electrode.

[0015] Preferably, in step S4, the electrode is connected to the positive terminal of the power supply, and the workpiece is connected to the negative terminal of the power supply. After the connection is made, the electrochemical polishing liquid is introduced into the inner cavity. After the flow of the electrochemical polishing liquid is stable, the power supply is turned on to destroy the structure of the electrode.

[0016] Preferably, the solid particles are made of ceramic material.

[0017] Preferably, the ceramic material is any one of Al2O3, Si3N4, ZrO2, and SiC.

[0018] The advantages of this invention are: 1. Adjusting the structural strength of the electrode at different positions to avoid large deformation of the electrode due to its own gravity;

[0019] 2. Insulating solid particles are added between the electrode and the inner wall of the workpiece. The solid particles can support and limit the electrode without affecting the electrochemical polishing effect, thus preventing the electrode from overlapping with the inner wall of the workpiece and causing a short circuit during the electrochemical polishing and electrochemical removal process.

[0020] 3. Electrochemical or chemical methods can be selected to remove the electrode components as needed, meeting the polishing requirements of various complex-shaped cavities. This helps to obtain metal parts with ideal internal polished surfaces, effectively improving the feasibility and practicality of electrochemical polishing methods in polishing the inner walls of metal parts with hollow cavities, and expanding the application prospects of electrochemical polishing methods in the polishing of the inner walls of additive metal parts. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method for polishing the inner wall of a metal part with a hollow cavity according to the present invention;

[0022] Figure 2 This is a schematic diagram of the relative position of the electrode and the workpiece in Embodiment 1 / 2, and a schematic diagram of the microstructure at different positions;

[0023] Figure 3 These are schematic diagrams of four three-period minimal surface porous structures for electrode components;

[0024] Figure 4This is a schematic diagram of filling solid particles between the electrode and the workpiece in Embodiment 1 / 2;

[0025] Figure 5 This is a schematic diagram of removing the electrode component in the inner cavity of the workpiece using a chemical solution in Example 2;

[0026] Figure 6 This is a schematic diagram of the microstructure of the workpiece printed using the first printing parameters in Example 2;

[0027] Figure 7 This is a schematic diagram of the microstructure of the electrode printed using the second printing parameters in Example 2.

[0028] Component designation explanation:

[0029] 1. Workpiece

[0030] 11. Inner cavity

[0031] 12 First Opening

[0032] 13 Second opening

[0033] 2 Electrode components

[0034] 3. Solid particles

[0035] 4 chemical solutions Detailed Implementation

[0036] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0037] Example 1

[0038] like Figure 1 As shown in Example 1, a method for polishing the inner wall of a metal part with a hollow cavity is provided. This method includes four main steps: electrode design, additive printing, electrochemical polishing, and electrode removal. The specific details are as follows:

[0039] S1. Electrode design: such as Figure 2 As shown, a workpiece 1 is first designed, which includes a first opening 12, a second opening 13, and an inner cavity 11 that communicates with the first opening 12 and the second opening 13 respectively. When designing workpiece 1, an electrode 2 matching the shape and size of the inner cavity 11 is designed within the inner cavity 11, with a uniform gap between the electrode 2 and the inner wall of the inner cavity 11. Furthermore, a fixing fixture is designed according to the shape and size of the first opening 12 and the second opening 13. This fixture can be used to fix the electrode 2 and workpiece 1 after printing.

[0040] In step S1 above, the workpiece 1 and the electrode 2 can be made of iron-based, nickel-based, titanium-based, aluminum-based, or copper-based materials, preferably Ti6Al4V alloy. Within the inner cavity 11, the gap between any point on the outer surface of the electrode 2 and the inner cavity wall is relatively uniform, ranging from 2.5mm to 3mm.

[0041] When designing electrode 2, a more porous, easily broken section can be incorporated, or the entire electrode 2 can be designed as a porous structure to increase its surface area and facilitate subsequent removal. When the internal cavity shape of the workpiece 1 is complex, the deformation due to gravity must be considered when using a porous electrode 2. Adjusting the porosity at different locations can alter the structural strength of the electrode 2 at those locations, preventing it from overlapping with the internal cavity wall in localized areas and causing short circuits during subsequent electrochemical polishing. Figure 2 As shown, preferably, in step S1, the porosity of the middle part of the electrode 2 is set to be greater than the porosity of the electrode 2 located at the first opening 12 / second opening 13, that is, the microstructure of the electrode 2 changes from the first opening 12 to the second opening 13 in a dense-loose-dense trend. This setting helps to improve the structural strength of the electrode 2 located at the first opening 12 / second opening 13 and reduce the amount of gravitational deformation. Furthermore, the distribution of pores in the electrode 2 gradually changes from sparse to dense from the middle part of the electrode 2 to the first opening 12 / second opening 13, and the size of the pores is selected according to the size of the inner cavity 11.

[0042] The microstructure of electrode 2 can be as follows: Figure 2 The mesh structure shown can also be as follows: Figure 3 The three-period minimal surface porous structures shown in (a)-(d) are described. The three-period minimal surface porous structures can be accurately described by mathematical expressions. The basic properties such as porosity and specific surface area can be directly controlled by the parameters of the function expression. At the same time, their surfaces are very smooth, without sharp turns or connection points of lattice porous structures, and the overall structure is interconnected.

[0043] S2. Additive printing: Using a 3D printer, workpiece 1 and electrode 2 are printed simultaneously.

[0044] S21. Support Treatment and Fixture Fixing: Use a fixture to fix workpiece 1 and electrode 2, ensuring their relative positions remain consistent and unchanged during the printing process. Maintain a uniform gap between them, avoiding direct contact at any point to ensure electrical insulation. Part or all of the fixture material is made of electrically insulating material to further ensure electrical insulation between workpiece 1 and electrode 2. Remove all auxiliary support structures from the additive printing process described in step S2, and then perform a simple ultrasonic water wash on workpiece 1 and electrode 2 to remove residual metal powder from the workpiece 1, electrode 2, and fixture.

[0045] S22. Pre-polishing treatment: Before electrochemical polishing in step S3, the workpiece 1 and electrode 2 are subjected to ultrasonic-assisted chemical cleaning and water washing, followed by drying. Specifically, the fixed workpiece 1 and electrode 2 are first placed together in an ultrasonic bath for ultrasonic treatment. The cleaning solution formula is: sodium hydroxide 50g / L, sodium carbonate 20g / L, trisodium phosphate 20g / L, OP emulsifier 3g / L; the temperature of the cleaning solution is 70℃; after ultrasonic cleaning for 3 minutes, the workpiece 1 and electrode 2 are removed, the cleaning solution in the inner cavity 11 is drained, most of the residual liquid is simply rinsed off with room temperature distilled water, and then the workpiece 1 and electrode 2 are immersed in 85℃ distilled water for ultrasonic cleaning for 3 minutes. The workpiece 1 and electrode 2 are ultrasonically cleaned twice with room temperature distilled water, 3 minutes each time, and then dried with compressed air.

[0046] S3, Electrochemical polishing: such as Figure 2 and Figure 4 As shown, firstly, cleaned solid particles 3 are placed in the gap between workpiece 1 and electrode 2. Baffles are installed at the first opening 12 and the second opening 13 to confine the solid particles 3 within the gap. Then, electrode 2 is connected to the negative terminal of the polishing power supply, and workpiece 1 is connected to the positive terminal. An electrochemical polishing solution is pumped from the solution tank and the first opening 12 (or the second opening 13) into the inner cavity 11. The electrochemical polishing solution flows through the inner cavity 11 at a certain speed and then flows out from the second opening 13 (or the first opening 12), returning to the solution tank via a pipe, thus achieving the circulation of the electrochemical polishing solution. After the flow of the electrochemical polishing solution stabilizes, the polishing power supply is turned on to perform electrochemical polishing on the inner cavity wall.

[0047] In step S3 above, the solid particles 3 are made of insulating material and will not react with the electrochemical polishing solution. Specifically, the solid particles 3 are ceramic particles with a diameter of 0.2-2 mm, and the material is any one of Al2O3, Si3N4, ZrO2, and SiC. The specific diameter is selected according to the size of the inner cavity 11 and the electrode 2. Preferably, Al2O3 solid particles with a diameter of 1.5 mm can be used. The form of the baffle is not limited and can be a mesh baffle, filter screen, or membrane, which can constrain the solid particles 3 within the gap without affecting the flow of the electrochemical polishing solution. The electrochemical polishing solution is selected according to the material used in the workpiece 1. Preferably, based on the total mass of the electrochemical polishing solution, the electrochemical polishing solution includes the following components by mass percentage: 10% aminosulfonic acid, 87% formamide, and 3% brightener. The temperature of the electrochemical polishing solution is controlled at 55-60℃. The power supply for polishing is a rectangular pulse power supply with a peak current density of 10 A / cm. 2 The pulse width was 0.1ms, the pulse interval was 0.4ms, and the polishing duration was 10min.

[0048] S4. Remove the electrode: Continue to confine the solid particles 3 within the gap using the baffle. Connect the electrode 2 to the positive terminal of the polishing power supply, and connect the workpiece 1 to the negative terminal of the polishing power supply. Then, pump the electrochemical polishing solution with the same composition as in step S3 from the solution tank and the first opening 12 (or the second opening 13) into the inner cavity 11. The electrochemical polishing solution flows through the inner cavity 11 at a certain speed and then flows out from the second opening 13 (or the first opening 12), returning to the solution tank through a pipe, maintaining a continuous circulation. After the flow of the electrochemical polishing solution stabilizes, start the polishing power supply. The peak current density of the polishing power supply is 20 A / cm². 2 The pulse width is 0.2ms and the pulse interval is 0.2ms. During the gradual dissolution of electrode 2, the average current of the circuit is monitored online. The current gradually decreases as electrode 2 dissolves. When the average current curve of the circuit is basically flat, the areas with larger porosity in electrode 2 have been dissolved, and the initial structure of electrode 2 has been destroyed. At this time, the polishing power supply and pump are turned off, the baffle is removed, the solid particles 3 and liquid in the inner cavity 11 are discharged, electrode 2 is removed, and then pure water is pumped into the inner cavity 11 to dilute and wash away the electrochemical polishing liquid remaining in the inner cavity 11, thus completing the polishing of the inner cavity wall.

[0049] S41. Cleaning after polishing: Drain the liquid from the workpiece 1 and rinse its inner cavity 11 simply. Then place the workpiece 1 in 85°C distilled water and clean it with ultrasound for 3 minutes. Next, clean it with distilled water at room temperature twice with ultrasound for 3 minutes each time, and then dry it with compressed air.

[0050] Example 2

[0051] The difference between Example 2 and Example 1 is that in Example 2, step S4 is: the solid particles 3 are further constrained within the gap by the baffle, and a chemical solution 4 with a different composition from the electrochemical polishing solution is introduced into the inner cavity 11. This chemical solution 4 dissolves or corrodes the electrode 2 at a rate greater than its rate of dissolving or corroding the workpiece 1, and can even be one or two orders of magnitude higher. Figure 5 During the process of dissolving or corroding electrode 2 into numerous fragments, the chemical solution 4 causes minimal corrosion or dissolution to the inner wall of workpiece 1. Afterwards, the baffle is removed, the solid particles 3 and liquid in the inner cavity 11 are drained, electrode 2 is removed, and then the inner cavity 11 is repeatedly rinsed with clean water to remove any remaining electrode fragments and chemical solution 4, completing the polishing of the inner cavity wall. The chemical solution 4 can be selected based on the materials used for workpiece 1 and electrode 2, as well as their microstructures.

[0052] In step S2 of Example 2, nickel-based alloy DZ125 spherical powder is selected to print workpiece 1 and electrode 2. Correspondingly, the specific formula of the chemical solution 4 used in step S4 is as follows: every 100g of solution consists of 20g CuSO4, 8g HNO3, 8g HCl, 10g FeCl3, and 54g distilled water. After preparation, the temperature of the chemical solution 4 is maintained at 70°C, allowing the chemical solution 4 to continuously flow through the inner cavity 11 to continuously dissolve the electrode 2. After 60 minutes, the flow of the chemical solution 4 is stopped, completing the removal of the electrode 2.

[0053] Furthermore, in step S2 of Example 2, different printing parameters can be used to print workpiece 1 and electrode 2, so that workpiece 1 has a different microstructure than electrode 2, thereby making the dissolution rate or corrosion rate of workpiece 1 in chemical solution 4 lower than that of electrode 2 in chemical solution 4. For example, printing parameters for producing a thoroughly melted and dense microstructure can be used when printing workpiece 1, while printing parameters for producing an incompletely melted and loosely structured microstructure can be used when printing electrode 2. Under the same chemical solution environment, the different microstructures of the two will lead to different dissolution or corrosion properties, thereby achieving selective removal of electrode 2.

[0054] Specifically, nickel-based alloy DZ125 spherical powder was used for additive printing to simultaneously print workpiece 1 and electrode 2. During laser printing, the first printing parameters (peak laser power of 350W, laser head scanning speed of 1200m / s, and scanning layer thickness of 0.03mm) were used to print workpiece 1. The microstructure of workpiece 1 is as follows: Figure 6 As shown; the electrode 2 is printed using the second printing parameters (laser peak power of 200W, laser head scanning speed of 900m / s, and scanning layer thickness of 0.03mm). The microstructure of the electrode 2 is as follows. Figure 7 As shown. After comparison Figure 6 and Figure 7 It can be seen that the density of the workpiece 1 printed using this method is significantly higher than that of the electrode 2. Thus, in step S4, the dissolution rate or corrosion rate of the workpiece 1 in the chemical solution 4 will be lower than that of the electrode 2 in the chemical solution 4, thereby achieving precise removal of the electrode 2.

[0055] Those skilled in the art can apply the inner wall polishing method of the present invention for metal parts with hollow cavities to workpieces 1 with only one opening or three or more openings as needed, and change the porosity at different positions of the electrode 2 according to the specific shape of the inner cavity 11 to ensure that the electrode 2 does not deform and overlap with the workpiece 1 due to gravity.

[0056] The solid particles used in this invention can fix and support the electrode 2 without affecting the electrochemical polishing process, constraining the electrode 2 in the middle of the inner cavity 11, and preventing the electrode 2 from overlapping with the inner cavity wall during the electrochemical polishing process and the removal of the electrode 2 by electrochemical methods, thus affecting the internal polishing process of the workpiece 1.

[0057] The electrochemical method described in Example 1 is fast in removing electrode 2 and can avoid dissolving or corroding workpiece 1; the chemical solution method described in Example 2 is more conducive to completely removing electrode 2 from the complex internal cavity 11.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for polishing the inner wall of a metal part with a hollow cavity, characterized in that, Includes the following steps: S1. Electrode Design: Design a workpiece having several openings and an inner cavity connected to the openings. Simultaneously, design an electrode component in the inner cavity that matches the shape and size of the inner cavity, with a gap between the electrode component and the inner cavity wall. S2. Additive printing: The workpiece and electrode are printed simultaneously using a 3D printer; S3. Electrochemical polishing: The gap is filled with solid particles made of insulating material, and a baffle is set at the opening to constrain the solid particles in the gap. Then, the electrode is connected to the negative terminal of the power supply, and the workpiece is connected to the positive terminal of the power supply. After the connection is completed, electrochemical polishing liquid is introduced into the inner cavity. After the flow of the electrochemical polishing liquid is stable, the power supply is turned on to perform electrochemical polishing on the inner cavity wall. S4. Remove the electrode components: Destroy the structure of the electrode components, remove the baffle, drain the liquid and solid particles in the inner cavity, remove the electrode components, and complete the polishing of the inner cavity wall.

2. The polishing method according to claim 1, characterized in that, In step S1, the electrode is configured as a porous structure.

3. The polishing method according to claim 2, characterized in that, In step S1, the porosity of the middle part of the electrode is greater than the porosity at the opening.

4. The polishing method according to any one of claims 1-3, characterized in that, In step S4, the structure of the electrode is destroyed by introducing a chemical solution into the inner cavity to dissolve or corrode the electrode.

5. The polishing method according to claim 4, characterized in that, In step S2, different printing parameters are used to print the workpiece and the electrode, so that the workpiece has a microstructure different from that of the electrode.

6. The polishing method according to any one of claims 1-3, characterized in that, In step S4, the electrode is connected to the positive terminal of the power supply, and the workpiece is connected to the negative terminal of the power supply. After the connection is made, the electrochemical polishing liquid is introduced into the inner cavity. After the flow of the electrochemical polishing liquid is stable, the power supply is turned on to destroy the structure of the electrode.

7. The polishing method according to claim 1, characterized in that, The solid particles are made of ceramic material.

8. The polishing method according to claim 7, characterized in that, The ceramic material is any one of Al2O3, Si3N4, ZrO2, and SiC.

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