Irregular profile precision milling method

Abstract

This application relates to the field of precision special machining technology, specifically disclosing a method for precision milling of irregularly shaped parts. The process sequentially completes the following steps: workpiece surface passivation treatment, preparation of a thermo-induced reversible complexing cutting fluid, workpiece clamping and immersion, assembly of special cutting tools, five-axis pulse machining path programming, point-to-point dissolution machining, layer-by-layer contour forming, and final cleaning and drying. The machining process relies on a ball-end tool with a micro-protrusion array and internal cooling structure to generate localized frictional heat, triggering point-to-point dissociation of the cutting fluid to achieve chemical removal. This method can be applied to the machining of irregularly shaped thin-walled parts made of titanium alloys, carbon steel, and aluminum alloys in the aerospace and medical device fields. It can effectively reduce machining forces, decrease workpiece deformation and internal residual stress, significantly improve contour forming accuracy and workpiece surface quality, and the entire machining process does not require a protective mask. It has a wide range of applicability and the overall operation is stable and reliable.

Description

Technical Field

[0001] This application relates to the field of precision special machining technology, and more specifically, it relates to a method for precision milling of irregularly shaped parts. Background Technology

[0002] Irregularly shaped parts are widely used in high-end equipment fields such as aerospace, medical devices, and automobile manufacturing. Their structures typically include complex curved surfaces and thin-walled features, requiring high machining accuracy and surface integrity. Precision milling is currently the mainstream process for machining such parts, enabling the forming of complex contours and meeting the basic requirements of industrial production for part size and shape.

[0003] Traditional mechanical milling removes material through the mechanical shearing action between the tool and the workpiece, inevitably generating cutting forces and residual stresses during the process. For irregularly shaped parts with thin walls and low rigidity, cutting forces can easily cause elastic deformation of the workpiece and tool deflection errors. The residual stress remaining after machining can also lead to dimensional changes in the parts during subsequent use. Existing technologies mostly improve machining results by optimizing cutting parameters and adding auxiliary supports, but they cannot fundamentally eliminate the adverse effects of cutting forces. Machining deformation remains a major technical bottleneck restricting the precision machining of thin-walled irregularly shaped parts. Summary of the Invention

[0004] To address the problem that traditional mechanical milling cannot fundamentally alleviate deformation during the machining of thin-walled irregular parts, this application provides a method for precision milling of irregular parts.

[0005] A method for precision milling of irregularly shaped parts includes the following steps: S1. Surface passivation treatment: The workpiece is pretreated to generate a uniform and dense sacrificial passivation film on its entire surface by chemical or electrochemical methods. S2. Preparation of cutting fluid: Prepare a thermo-induced reversible complexing self-passivating cutting fluid. The cutting fluid is chemically inert at room temperature and dissociates and releases active chelating anions when the temperature rises to its dissociation threshold. S3. Workpiece clamping and wetting: The passivated workpiece is clamped on the worktable of a multi-axis CNC machine tool by point contact positioning or vacuum suction cup adsorption, so that the area of ​​the workpiece to be processed is continuously completely wetted by the cutting fluid. S4. Tool configuration and installation: A ball-end tool is selected. The ball end of the tool is provided with a uniformly distributed array of micron-level micro-protrusions. The tool is machined with a fine internal cooling channel that extends to the vicinity of the tool tip. A constant temperature coolant is continuously introduced into the internal cooling channel. S5. Machining path compilation: Generate a five-axis linkage machining toolpath based on the three-dimensional contour model of the workpiece, and convert the toolpath into a pulse feed program; S6. Localized Dissolution Machining: The tool contacts the workpiece surface with a set contact force, causing the ball-end micro-protrusion to rub against the workpiece and generate heat until the temperature of the contact spot reaches the dissociation threshold of the cutting fluid, thereby triggering the dissociation of the cutting fluid and localized dissolution of the workpiece matrix material; after the tool is removed, the contact spot cools down, and the cutting fluid returns to chemical inertness. S7. Layer-by-layer scanning forming: Repeated pulse processing is performed, and the tool dissolves the material layer by layer and point by point along the contour of the part; S8. Finished product cleaning and inspection: After processing is completed, stop the cutting fluid supply, take out the workpiece for cleaning and drying, and obtain the finished product.

[0006] By adopting the above technical solution, a maskless machining system for thermally induced reversible complexation localized dissolution was constructed, which transforms the traditional shearing material removal method of mechanical milling into temperature-triggered chemical dissolution removal. The tool only provides a micro-friction heat source and scraping effect of dissolution products, which greatly reduces the mechanical force during the machining process. At the same time, combined with global passivation protection and micron-level thermal gradient control technology, the material removal area can be precisely defined without the need to make an additional machining mask.

[0007] Preferably, in step S1, the thickness of the sacrificial passivation film is 0.1 μm to 2 μm. Specifically, this step involves immersing the titanium alloy workpiece in a pretreatment solution containing fluorotitanate and a corrosion inhibitor, generating a fluorotitanate conversion film in situ at a temperature of 20°C to 30°C, for a treatment time of 5 min to 30 min.

[0008] By adopting the above technical solution, a barrier layer that is firmly bonded to the substrate is formed on the surface of the workpiece, which can isolate the cutting fluid from direct contact with the substrate metal and avoid chemical corrosion in non-processed areas. At the same time, the passivation film has moderate chemical stability and can be selectively penetrated by the active chelating anions generated by the dissociation of the cutting fluid. Moreover, the dissolution rate matches the substrate material and does not affect the material removal efficiency in the processed area.

[0009] Preferably, in step S2, the cutting fluid is chemically inert at a temperature not exceeding 30°C and reaches a dissociation threshold when the temperature rises to 45°C to 70°C; the cutting fluid is prepared by uniformly mixing the following components in parts by mass: 5-15 parts of reversible complex precursor, 2-8 parts of stabilizer, 0.5-3 parts of pH buffer, 0.6-1 parts of passivating film-forming agent, 5-20 parts of extreme pressure heat transfer medium, and the balance being deionized water.

[0010] By adopting the above technical solution, the cutting fluid has precise temperature response characteristics. At room temperature, the complex maintains a stable coordination structure and will not corrode the workpiece. When the local temperature rises to the dissociation threshold, the coordination bonds break and release active ions, achieving localized chemical dissolution. The synergistic effect of each component can maintain the performance stability of the cutting fluid during long-term processing, ensuring the continuity and consistency of the processing process.

[0011] Preferably, the reversible complex precursor is a pre-coordinated titanium-citric acid complex or an iron-oxalate complex, the stabilizer is an excess of free citrate ions or oxalate ions, the pH buffer is a borax-boric acid buffer, the passivating film-forming agent is selected from at least one of molybdate, tungstate, or hydrogen peroxide, and the extreme pressure heat transfer medium is a water-soluble polyalkylene glycol.

[0012] By adopting the above technical solutions, suitable complex precursors are selected for workpieces of different materials, improving the efficiency and selectivity of chemical dissolution. Excess free ligands inhibit the room-temperature dissociation of complexes through the common ion effect. The borax-boric acid buffer system can stably maintain the pH of the cutting fluid within the range where the complexes are stable. The passivating film-forming agent can quickly form a dense protective film on the fresh metal surface. The water-soluble polyalkylene glycol can quickly transfer the heat generated by friction, ensuring the stable formation of the thermal gradient.

[0013] Preferably, in step S3, the adsorption pressure of the vacuum suction cup is controlled between 0.02 MPa and 0.08 MPa, and the cutting fluid is supplied by pouring or immersion, with the circulating flow rate of the cutting fluid controlled between 5 L / min and 20 L / min.

[0014] By adopting the above technical solutions, the low-stress clamping method avoids workpiece deformation, point contact positioning reduces the contact area with the workpiece, and the vacuum chuck provides uniform adsorption force. While ensuring stable workpiece positioning, it will not cause squeezing damage to the thin-walled structure. The continuous supply of cutting fluid can ensure that the machining area is always fully wetted, and the circulating cutting fluid can promptly remove dissolved products and excess heat, maintaining the uniformity of cutting fluid concentration and temperature.

[0015] Preferably, in step S4, the ball end mill is made of graphite or cemented carbide with a thermal conductivity of not less than 100 W / (m·K), and the height of its surface micro-protrusions is 5 μm to 20 μm, with a spacing of 20 μm to 100 μm; the diameter of the internal cooling channel is 0.5 mm to 2 mm, and the temperature of the constant temperature coolant is 15°C to 25°C.

[0016] By adopting the above technical solutions, the high thermal conductivity of the tool material can quickly conduct heat, and the micro-protrusions on the surface can concentrate the frictional heat in a very small area at the tip, improving the local heat generation efficiency. Combined with the forced heat dissipation of the constant temperature coolant that runs through the tool tip, a steep temperature gradient is formed between the contact point and the surrounding area, ensuring that only the cutting fluid in the contact spot reaches the dissociation temperature, thus achieving micron-level localized machining accuracy.

[0017] Preferably, in step S5, the pulse feed program sets the dwell time of each machining point to 0.05s to 0.5s, the point spacing matches the size of the contact spot of the tool micro-protrusion, and the tool posture is adjusted in real time according to the surface normal to ensure that the ball head micro-protrusion is always in stable contact with the workpiece surface.

[0018] By adopting the above technical solution, the amount of material removed from a single point can be independently controlled by the dwell time. Matching the point spacing with the contact spot size can ensure the continuous connection of the processing area and avoid missed processing or overlapping processing. The real-time adjustment of the tool posture can adapt to the curvature changes of complex surfaces, ensuring that the micro-protrusions maintain normal contact with the workpiece surface and maintain the stability of frictional heat generation.

[0019] Preferably, in step S6, the set contact force is no greater than 0.1N, the rotation speed of the tool is 1000r / min to 5000r / min, and the diameter of the contact spot is 10μm to 100μm; the tool rotates to scrape off the generated dissolution products; the active chelating anions released after the cutting fluid dissociates first penetrate and dissolve the sacrificial passivation film generated in step S1, and then dissolve the exposed workpiece substrate material; after the tool is removed and the contact spot cools, the passivating film-forming agent in the cutting fluid generates a repassivation film in situ on the newly exposed workpiece surface.

[0020] By adopting the above technical solution, the extremely low contact force is only used to maintain effective contact between the micro-protrusion and the workpiece, and will not cause macroscopic elastic deformation of the workpiece. The appropriate rotation speed can scrape off the viscous complex generated by dissolution in time, avoid the accumulation of products to hinder the subsequent dissolution process, and at the same time refresh the cutting fluid in the contact area. The order of active ions penetrating the passivation film first and then dissolving the substrate can ensure the accuracy of the machining. The repassivation film formed quickly after machining can protect the fresh surface from corrosion by the subsequent cutting fluid.

[0021] Preferably, in step S7, the thickness of each material layer removed is controlled between 0.1 μm and 5 μm. During the processing, the cutting fluid circulation system filters in real time to remove metal complex precipitates, with a filtration accuracy of not less than 1 μm.

[0022] By adopting the above technical solution, the complex three-dimensional contour can be formed by dissolving layer by layer. The fine control of the thickness of each layer can ensure the overall machining accuracy and avoid heat diffusion and accuracy loss caused by excessive removal in a single process. Real-time filtration can remove the micron-level metal complex precipitates generated during the machining process, prevent the precipitate particles from scratching the workpiece surface or clogging the tool's micro-protrusion structure, and maintain the activity of the cutting fluid and the stability of the machining process.

[0023] Preferably, in step S8, the cleaning steps are as follows: ultrasonic cleaning is performed using deionized water and anhydrous ethanol, with each ultrasonic cleaning lasting 3 to 10 minutes and the ultrasonic frequency being 20 kHz to 40 kHz. After cleaning, the water is allowed to air dry naturally at room temperature.

[0024] By adopting the above technical solutions, deionized water can remove residual water-soluble cutting fluid and inorganic salt impurities from the workpiece surface, anhydrous ethanol can remove organic residues and replace surface moisture, ultrasonic cleaning can penetrate into the fine grooves and gaps of complex contours to ensure thorough cleaning, and room temperature air drying can avoid oxidation damage and thermal deformation caused by high temperature drying to the workpiece surface.

[0025] In summary, this application has the following beneficial effects: 1. Because this application uses a thermally induced reversible complexing self-passivating cutting fluid in conjunction with a machining method with extremely low contact force, the material is removed through chemical dissolution. The tool only plays the role of thermal triggering and scraping off the dissolution products, which significantly reduces the cutting force and residual stress during the machining process and effectively alleviates the machining deformation problem of thin-walled irregular parts.

[0026] 2. The method of this application constructs a steep micron-level thermal gradient field by the synergistic effect of the micron-level micro-protrusion array on the surface of the ball end mill and the internal internal cooling channel, which precisely controls the dissolution reaction within the contact spot range. Combined with pulsed feed to precisely control the thickness of each layer removed, high contour machining accuracy can be obtained.

[0027] 3. In this application, a protection mechanism combining a pre-placed sacrificial passivation film and dynamic repassivation is preferred. The entire workpiece is passivated and protected before processing, and a repassivation film is quickly generated on the fresh surface after processing, forming a complete protective closed loop, which can effectively reduce stray chemical corrosion in non-processed areas.

[0028] 4. Since this application adopts a material removal method mainly based on chemical dissolution, it greatly reduces the work hardening and plastic deformation caused by mechanical cutting. A beneficial compressive stress state can be formed on the machined surface. At the same time, the rotation of the tool removes the dissolution products in time, which helps to improve the surface integrity of the machined product. Attached Figure Description

[0029] Figure 1This is a flowchart of the preparation process of a precision milling method for irregularly shaped parts, as provided in this application. Detailed Implementation

[0030] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0031] Technical Concept: Currently, the precision machining of irregularly shaped parts, especially thin-walled parts, mainly relies on traditional mechanical milling processes. This process removes material through mechanical shearing and compression between the tool and the workpiece. Its core drawback is that cutting forces and frictional heat are inevitably generated during the machining process. Thin-walled irregularly shaped parts have low structural rigidity and weak resistance to deformation. Cutting forces can easily cause problems such as workpiece clamping deformation and tool deflection errors, while frictional heat can lead to thermal deformation of the workpiece. At the same time, residual mechanical stress can also affect the stability of the workpiece in subsequent use. Conventional methods such as optimizing cutting parameters and adding auxiliary supports cannot fundamentally eliminate the above-mentioned machining defects caused by mechanical forces, making it difficult to meet the needs of high-end fields for precision machining of irregularly shaped parts.

[0032] To address the aforementioned issues, this technical solution employs a thermally induced reversible complexation-localized dissolution processing approach. First, the workpiece undergoes surface passivation treatment, generating a uniform and dense sacrificial passivation film on its surface to protect non-machined areas from corrosion. Then, a thermally induced reversible complexation-type self-passivating cutting fluid with temperature-responsive characteristics is formulated and paired with a ball-end tool featuring a micron-level array of micro-protrusions and built-in micro-cooling channels. Through extremely low contact force, the micro-protrusions generate heat through friction with the workpiece, precisely triggering the cutting fluid to dissociate and localize at the contact points, dissolving the workpiece material locally. Simultaneously, pulsed feed and layer-by-layer scanning are used to control machining accuracy. Combined with cutting fluid circulation filtration, post-machining passivation, and standardized cleaning and drying techniques, a precision machining system with minimal mechanical cutting force is constructed. This fundamentally improves machining deformation issues and enhances the machining accuracy and surface integrity of irregularly shaped parts.

[0033] Example 1: This example provides a method for precision milling of irregularly shaped parts, used for machining thin-walled titanium alloy parts with a wall thickness of 0.3 mm. The method includes the following steps: S1. Surface passivation treatment: The workpiece is pretreated on the surface, and a uniform and dense sacrificial passivation film is generated on its entire surface by chemical methods.

[0034] The thickness of the sacrificial passivation film is 1.05 μm. The workpiece pretreatment first involves ultrasonic degreasing with acetone for 5 min, then rinsing with deionized water 3 times. The titanium alloy workpiece is then immersed in a pretreatment solution containing fluorotitanate and benzotriazole corrosion inhibitor. A fluorotitanate conversion film is generated in situ at 25°C for 17.5 min. After treatment, the workpiece is rinsed twice with deionized water and dried with nitrogen.

[0035] S2. Preparation of cutting fluid: Prepare a thermo-induced reversible complexing self-passivating cutting fluid. The cutting fluid is chemically inert at room temperature. When the temperature rises to its dissociation threshold, it dissociates and releases active chelating anions.

[0036] The cutting fluid is chemically inert at temperatures not exceeding 30°C and reaches the dissociation threshold at temperatures rising to 57.5°C. The cutting fluid is prepared by uniformly mixing the following components in parts by mass: 10 parts of reversible complex precursor, 5 parts of stabilizer, 1.75 parts of pH buffer, 0.8 parts of passivating film-forming agent, 12.5 parts of extreme pressure heat transfer medium, and the balance being deionized water. The reversible complex precursor is a pre-coordinated titanium-citric acid complex, the stabilizer is excess free citrate ions, the pH buffer is borax-boric acid buffer, the passivating film-forming agent is sodium molybdate, and the extreme pressure heat transfer medium is water-soluble polyalkylene glycol. The pre-coordinated titanium-citric acid complex is prepared as follows: analytical grade titanium tetrachloride is slowly added dropwise to a 25% (w / min) citric acid aqueous solution at a rate of 1.5 mL / min, and the reaction temperature is controlled to never exceed 30℃. After the addition is completed, the pH of the solution is adjusted to 3.75 with 10% (w / min) ammonia. The reaction is carried out at a constant temperature of 25℃ and stirred at 400 r / min for 3 h, finally obtaining a clear and transparent pre-coordinated titanium-citric acid complex solution, in which the titanium ion concentration is 0.75 mol / L and the free citrate ion concentration is 1.35 times the titanium ion concentration. After mixing the components, the mixture is stirred at 400 r / min for 30 min and allowed to stand for 10 min to remove bubbles.

[0037] S3. Workpiece clamping and wetting: The passivated workpiece is clamped on the five-axis CNC machine tool table by point contact positioning and vacuum suction cup adsorption, so that the workpiece area to be processed is continuously and completely wetted by the cutting fluid.

[0038] The vacuum chuck's adsorption pressure is controlled at 0.05 MPa, and the cutting fluid is supplied by pouring. The circulating flow rate of the cutting fluid is controlled at 12.5 L / min. During clamping, three point contact positioning blocks are evenly distributed on the edge of the workpiece, with a positioning accuracy of ±0.01 mm, to avoid workpiece deformation during clamping.

[0039] S4. Tool configuration and installation: Select ball end mills. The ball end mill surface of the tool is provided with a uniformly distributed array of micron-level micro-protrusions. The tool is machined with a fine internal cooling channel that extends to the vicinity of the tool tip. Constant temperature coolant is continuously introduced into the internal cooling channel.

[0040] The ball end mill is made of cemented carbide with a thermal conductivity of not less than 100 W / (m·K). The height of the micro-protrusions on its surface is 12.5 μm and the spacing is 60 μm. The diameter of the internal cooling channel is 1.25 mm, and the temperature of the constant-temperature coolant is 20 °C. The tool installation torque is 5 N·m. Before the coolant is introduced into the internal cooling channel, compressed air is purged for 30 seconds to ensure that the channel is unobstructed.

[0041] S5. Machining Path Compilation: Generate a five-axis linkage machining toolpath based on the three-dimensional contour model of the workpiece, and convert the toolpath into a pulse feed program.

[0042] The pulse feed program sets the dwell time of each machining point to 0.275s, and the point spacing matches the size of the tool micro-protrusion contact spot. The tool posture is adjusted in real time according to the surface normal to ensure that the ball head micro-protrusion is always in stable contact with the workpiece surface. The tool path is generated using an equal residual height strategy, and the residual height is controlled at 0.05μm.

[0043] S6. Localized Dissolution Machining: The tool contacts the workpiece surface with a set contact force, causing the ball-end micro-protrusion to rub against the workpiece and generate heat until the temperature of the contact spot reaches the dissociation threshold of the cutting fluid, thereby triggering the dissociation of the cutting fluid and localized dissolution of the workpiece matrix material; after the tool is removed, the contact spot cools down, and the cutting fluid returns to chemical inertness.

[0044] The contact force was set to 0.05 N, the tool rotation speed to 3000 r / min, and the diameter of the contact spot to 55 μm. The tool rotated to scrape away the generated dissolution products. The active chelating anions released after the cutting fluid dissociated first penetrated and dissolved the sacrificial passivation film generated in step S1, and then dissolved the exposed workpiece substrate material. After the tool was removed and the contact spot cooled, the passivating film-forming agent in the cutting fluid generated a repassivation film in situ on the newly exposed workpiece surface. The machining environment temperature was controlled at 22℃±2℃ to avoid the ambient temperature affecting the stability of the cutting fluid.

[0045] S7, Layer-by-layer scanning forming: Repeated pulse processing is performed, and the tool dissolves the material layer by layer and point by point along the contour of the part.

[0046] The thickness of each material layer removed is controlled at 2.55μm. During the processing, the cutting fluid circulation system filters in real time to remove metal complex precipitates with a filtration accuracy of 2μm. The filter element of the cutting fluid circulation system is replaced every 2 hours to ensure the filtration effect.

[0047] S8. Finished product cleaning and inspection: After processing is completed, stop the cutting fluid supply, take out the workpiece for cleaning and drying, and obtain the finished product.

[0048] The cleaning steps are as follows: ultrasonic cleaning with deionized water and anhydrous ethanol, each ultrasonic cleaning time is 6.5 minutes, ultrasonic frequency is 30 kHz, and after cleaning, air dry at room temperature; after cleaning, blow dry the surface residual ethanol with clean nitrogen, and then air dry for 30 minutes to avoid dust contamination.

[0049] Example 2: This example provides a method for precision milling of irregularly shaped parts, used for machining 45 steel irregularly shaped parts. The method includes the following steps: S1. Surface passivation treatment: The workpiece is pretreated on the surface, and a uniform and dense sacrificial passivation film is generated on its entire surface by chemical methods.

[0050] The thickness of the sacrificial passivation film is 0.1 μm. The workpiece pretreatment first uses acetone for ultrasonic degreasing for 3 min, then rinses twice with deionized water, and then immerses the 45 steel workpiece in a pretreatment solution containing fluorotitanate and hexamethylenetetramine corrosion inhibitor. A fluorotitanate conversion film is generated in situ at 20°C for 5 min. After treatment, it is rinsed once with deionized water and dried with nitrogen.

[0051] S2. Preparation of cutting fluid: Prepare a thermo-induced reversible complexing self-passivating cutting fluid. The cutting fluid is chemically inert at room temperature. When the temperature rises to its dissociation threshold, it dissociates and releases active chelating anions.

[0052] The cutting fluid is chemically inert at temperatures not exceeding 30°C and reaches the dissociation threshold at temperatures rising to 45°C. The cutting fluid is prepared by uniformly mixing the following components in parts by mass: 5 parts of reversible complex precursor, 2 parts of stabilizer, 0.5 parts of pH buffer, 0.6 parts of passivating film-forming agent, 5 parts of extreme pressure heat transfer medium, and the balance being deionized water. The reversible complex precursor is a pre-coordinated iron-oxalate complex, the stabilizer is excess free oxalate ions, the pH buffer is a borax-boric acid buffer, the passivating film-forming agent is sodium tungstate, and the extreme pressure heat transfer medium is water-soluble polyalkylene glycol. The preparation method of the pre-coordinated iron-oxalate complex is as follows: analytical grade ferric chloride solid is added in batches to an oxalic acid aqueous solution with a mass fraction of 15%, and the amount added in each batch does not exceed 10% of the total mass. After stirring until completely dissolved, the pH of the solution is adjusted to 4.0 with an 8% sodium hydroxide solution. The reaction is carried out at a constant temperature of 30℃ and a stirring speed of 200 r / min for 1 h. Finally, a clear pre-coordinated iron-oxalate complex solution is obtained, in which the iron ion concentration is 0.8 mol / L and the free oxalate ion concentration is 1.1 times the iron ion concentration. After mixing the components, the mixture is stirred at 300 r / min for 20 min and allowed to stand for 5 min to remove bubbles.

[0053] S3. Workpiece clamping and wetting: The passivated workpiece is clamped on the five-axis CNC machine tool table by point contact positioning and vacuum suction cup adsorption, so that the workpiece area to be processed is continuously and completely wetted by the cutting fluid.

[0054] The vacuum chuck's adsorption pressure is controlled at 0.02 MPa, and the cutting fluid is supplied by pouring. The circulating flow rate of the cutting fluid is controlled at 5 L / min. During clamping, two point contact positioning blocks are distributed diagonally on the workpiece, with a positioning accuracy of ±0.02 mm.

[0055] S4. Tool configuration and installation: Select ball end mills. The ball end mill surface of the tool is provided with a uniformly distributed array of micron-level micro-protrusions. The tool is machined with a fine internal cooling channel that extends to the vicinity of the tool tip. Constant temperature coolant is continuously introduced into the internal cooling channel.

[0056] The ball end mill is made of graphite with a thermal conductivity of not less than 100 W / (m·K). The height of the micro-protrusions on its surface is 5 μm and the spacing is 20 μm. The diameter of the internal cooling channel is 0.5 mm, and the temperature of the constant temperature coolant is 15 °C. The tool installation torque is 3 N·m, and the internal cooling channel is purged with compressed air for 20 seconds before the coolant is introduced.

[0057] S5. Machining Path Compilation: Generate a five-axis linkage machining toolpath based on the three-dimensional contour model of the workpiece, and convert the toolpath into a pulse feed program.

[0058] The pulse feed program sets the dwell time of each machining point to 0.05s, the point spacing matches the size of the contact spot of the tool micro-protrusion, and the tool posture is adjusted in real time according to the surface normal to ensure that the ball head micro-protrusion is always in stable contact with the workpiece surface; the tool path is generated using an equal step strategy with a step size of 10μm.

[0059] S6. Localized Dissolution Machining: The tool contacts the workpiece surface with a set contact force, causing the ball-end micro-protrusion to rub against the workpiece and generate heat until the temperature of the contact spot reaches the dissociation threshold of the cutting fluid, thereby triggering the dissociation of the cutting fluid and localized dissolution of the workpiece matrix material; after the tool is removed, the contact spot cools down, and the cutting fluid returns to chemical inertness.

[0060] The contact force was set to 0.01N, the tool rotation speed to 1000r / min, and the diameter of the contact spot to 10μm. The tool rotated to scrape away the generated dissolution products. The active chelating anions released after the cutting fluid dissociated first penetrated and dissolved the sacrificial passivation film generated in step S1, and then dissolved the exposed workpiece substrate material. After the tool was removed and the contact spot cooled, the passivating film-forming agent in the cutting fluid generated a repassivation film in situ on the newly exposed workpiece surface. The processing environment temperature was controlled at 20℃±2℃.

[0061] S7, Layer-by-layer scanning forming: Repeated pulse processing is performed, and the tool dissolves the material layer by layer and point by point along the contour of the part.

[0062] The thickness of each material layer removed is controlled at 0.1 μm. During the processing, the cutting fluid circulation system filters in real time to remove metal complex precipitates with a filtration accuracy of 1 μm. The filter element of the cutting fluid circulation system is replaced every 1 hour.

[0063] S8. Finished product cleaning and inspection: After processing is completed, stop the cutting fluid supply, take out the workpiece for cleaning and drying, and obtain the finished product.

[0064] The cleaning steps are as follows: ultrasonic cleaning is performed using deionized water and anhydrous ethanol, with each ultrasonic cleaning lasting 3 minutes and the ultrasonic frequency being 20 kHz. After cleaning, the surface is allowed to air dry naturally at room temperature. After cleaning, the surface is dried with clean nitrogen to remove any residual ethanol, and then allowed to air dry naturally for 15 minutes.

[0065] Example 3: This example provides a method for precision milling of irregularly shaped parts, used for machining irregularly shaped aluminum alloy parts. The method includes the following steps: S1. Surface passivation treatment: The workpiece is pretreated on the surface, and a uniform and dense sacrificial passivation film is generated on its entire surface by electrochemical methods.

[0066] The thickness of the sacrificial passivation film is 2μm. The workpiece pretreatment first uses acetone for ultrasonic degreasing for 8 minutes, then rinses with deionized water 4 times, and then immerses the aluminum alloy workpiece in a pretreatment solution containing fluorotitanate and sodium phosphate corrosion inhibitor. The fluorotitanate conversion film is generated in situ at 30℃ for 30 minutes. After the treatment, it is rinsed with deionized water 3 times and dried with nitrogen.

[0067] S2. Preparation of cutting fluid: Prepare a thermo-induced reversible complexing self-passivating cutting fluid. The cutting fluid is chemically inert at room temperature. When the temperature rises to its dissociation threshold, it dissociates and releases active chelating anions.

[0068] The cutting fluid is chemically inert at temperatures not exceeding 30°C and reaches the dissociation threshold at temperatures rising to 70°C. The cutting fluid is prepared by uniformly mixing the following components in parts by mass: 15 parts of reversible complex precursor, 8 parts of stabilizer, 3 parts of pH buffer, 1 part of passivating film-forming agent, 20 parts of extreme pressure heat transfer medium, and the balance being deionized water. The reversible complex precursor is a pre-coordinated titanium-citric acid complex, the stabilizer is excess free citrate ions, the pH buffer is borax-boric acid buffer, the passivating film-forming agent is 3% hydrogen peroxide by mass, and the extreme pressure heat transfer medium is water-soluble polyalkylene glycol. The preparation method of the pre-coordinated titanium-citric acid complex is as follows: analytical grade titanium tetrachloride is slowly added dropwise to a 30% citric acid aqueous solution at a rate of 2 mL / min, and the temperature of the reaction system is controlled to not exceed 30℃. After the addition is completed, the pH of the solution is adjusted to 4.0 with 10% ammonia. The reaction is carried out at a constant temperature of 25℃ and stirred at 500 r / min for 4 h. Finally, a clear and transparent pre-coordinated titanium-citric acid complex solution is obtained, in which the titanium ion concentration is 1.0 mol / L and the free citrate ion concentration is 1.5 times the titanium ion concentration. After the components are mixed, the mixture is stirred at 500 r / min for 40 min and allowed to stand for 15 min to remove bubbles.

[0069] S3. Workpiece clamping and wetting: The passivated workpiece is clamped on the five-axis CNC machine tool table by point contact positioning and vacuum suction cup adsorption, so that the workpiece area to be processed is continuously and completely wetted by the cutting fluid.

[0070] The vacuum chuck's adsorption pressure is controlled at 0.08 MPa, and the cutting fluid is supplied by immersion. The circulating flow rate of the cutting fluid is controlled at 20 L / min. During clamping, four point contact positioning blocks are evenly distributed around the workpiece, with a positioning accuracy of ±0.005 mm.

[0071] S4. Tool configuration and installation: Select ball end mills. The ball end mill surface of the tool is provided with a uniformly distributed array of micron-level micro-protrusions. The tool is machined with a fine internal cooling channel that extends to the vicinity of the tool tip. Constant temperature coolant is continuously introduced into the internal cooling channel.

[0072] The ball end mill is made of cemented carbide with a thermal conductivity of not less than 100 W / (m·K). The height of the micro-protrusions on its surface is 20 μm and the spacing is 100 μm. The diameter of the internal cooling channel is 2 mm, and the temperature of the constant temperature coolant is 25 °C. The tool installation torque is 8 N·m, and the internal cooling channel is purged with compressed air for 40 seconds before the coolant is introduced.

[0073] S5. Machining Path Compilation: Generate a five-axis linkage machining toolpath based on the three-dimensional contour model of the workpiece, and convert the toolpath into a pulse feed program.

[0074] The pulse feed program sets the dwell time of each machining point to 0.5s, the point spacing matches the size of the tool micro-protrusion contact spot, and the tool posture is adjusted in real time according to the surface normal to ensure that the ball head micro-protrusion is always in stable contact with the workpiece surface; the tool path generation adopts an equal residual height strategy, and the residual height is controlled at 0.02μm.

[0075] S6. Localized Dissolution Machining: The tool contacts the workpiece surface with a set contact force, causing the ball-end micro-protrusion to rub against the workpiece and generate heat until the temperature of the contact spot reaches the dissociation threshold of the cutting fluid, thereby triggering the dissociation of the cutting fluid and localized dissolution of the workpiece matrix material; after the tool is removed, the contact spot cools down, and the cutting fluid returns to chemical inertness.

[0076] The contact force was set to 0.1N, the tool rotation speed to 5000r / min, and the diameter of the contact spot to 100μm. The tool rotated to scrape away the generated dissolution products. The active chelating anions released after the cutting fluid dissociated first penetrated and dissolved the sacrificial passivation film generated in step S1, and then dissolved the exposed workpiece substrate material. After the tool was removed and the contact spot cooled, the passivating film-forming agent in the cutting fluid generated a repassivation film in situ on the newly exposed workpiece surface. The processing environment temperature was controlled at 25℃±2℃.

[0077] S7, Layer-by-layer scanning forming: Repeated pulse processing is performed, and the tool dissolves the material layer by layer and point by point along the contour of the part.

[0078] The thickness of each material layer is controlled at 5μm. During the processing, the cutting fluid circulation system filters in real time to remove metal complex precipitates with a filtration accuracy of 3μm. The filter element of the cutting fluid circulation system is replaced every 3 hours.

[0079] S8. Finished product cleaning and inspection: After processing is completed, stop the cutting fluid supply, take out the workpiece for cleaning and drying, and obtain the finished product.

[0080] The cleaning steps are as follows: ultrasonic cleaning with deionized water and anhydrous ethanol, each ultrasonic cleaning time is 10 minutes, ultrasonic frequency is 40 kHz, and after cleaning, air dry at room temperature; after cleaning, blow dry the surface residual ethanol with clean nitrogen gas, and then air dry for 60 minutes.

[0081] Comparative Example 1: The only difference between this comparative example and Example 1 is that in step S2, the reversible complex precursor is replaced by a pre-coordinated titanium-citric acid complex with an equal concentration of ordinary ammonium fluorotitanate solution. This solution maintains constant chemical etching activity in the range of 30°C to 70°C and does not have thermally induced dissociation characteristics. The remaining cutting fluid components, process steps and parameters are exactly the same as those in Example 1.

[0082] Comparative Example 2: The only difference between this comparative example and Example 1 is that the surface passivation treatment in step S1 is omitted, and the workpiece is directly clamped and immersed in step S3 after being degreased with acetone and rinsed with deionized water. There is no sacrificial passivation film. The remaining process steps and parameters are exactly the same as in Example 1.

[0083] Comparative Example 3: The only difference between this comparative example and Example 1 is that the ball end mill used in step S4 has no internal cooling channel and no constant temperature coolant is introduced. The entire tool is at ambient temperature. The remaining structural parameters and surface micro-protrusions are exactly the same as in Example 1.

[0084] Comparative Example 4: The only difference between this comparative example and Example 1 is that in step S6, the set contact force between the tool and the workpiece is increased from 0.05N to 5.0N. The remaining process steps and parameters are exactly the same as in Example 1.

[0085] Comparative Example 5: This comparative example uses a traditional precision milling process for thin-walled parts. The differences between this comparative example and Example 1 are as follows: Step S1, surface passivation treatment, and Step S2, cutting fluid preparation are not performed; a common carbide ball end mill with the same diameter as in Example 1 is used, with no micro-protrusion array on the surface and no internal cooling channels; before machining, the workpiece is immersed in molten tin-bismuth low-melting-point alloy, and after cooling, a rigid filling support is formed; a conventional water-based emulsion is used as the cutting fluid, and the cutting parameters are: spindle speed 8000 r / min, feed rate 300 mm / min, and depth of cut 0.1 mm; after machining, the workpiece is heated to 180°C to melt and remove the low-melting-point alloy support, and then the same cleaning and drying steps as in Example 1 are performed.

[0086] I. Contour Accuracy and Machining Deformation Test: The test standard is GB / T16857.2-2017 "Product Geometric Specification (GPS) - Acceptance and Re-inspection of Coordinate Measuring Machines - Part 2: Coordinate Measuring Machines for Measuring Dimensions and Shapes". A Zeiss CONTURAG2 coordinate measuring machine with a measurement accuracy of ±0.5μm was used. Full contour scanning was performed on all workpieces processed in Examples 1-3 and Comparative Examples 1-5. For each workpiece, 100 measurement points were evenly selected on the contour to be processed, including 20 feature points in the curvature abrupt change zone and 80 feature points in the smooth zone. The deviation values ​​between the actual coordinates and the coordinates of the three-dimensional theoretical model for all measurement points were calculated to obtain the maximum and average contour error. Simultaneously, the wall thickness before and after machining was measured at 5 typical locations on each workpiece, and the maximum and average changes in wall thickness were calculated to characterize the degree of machining deformation of the workpiece. All measurements were performed in a constant temperature measurement chamber at 20℃±1℃. Each workpiece was measured three times, and the average value was taken as the final result.

[0087] II. Comprehensive Surface Integrity Test: The test standards are GB / T6062-2009 "Geometric Specifications for Products (GPS) - Characteristics of Contact (Stylus) Type Surface Roughness Measuring Instruments Using the Surface Structure Profilometry Method" and GB / T7704-2017 "Non-destructive Testing - X-ray Stress Measurement Method". A Taylor-Hopson FormTalysurfi60 surface roughness meter was used to measure the roughness of the machined surfaces of all workpieces according to the standards in section I above. For each workpiece, three measurement positions were selected in both the smooth and abrupt change zones. The measurement length at each position was 4 mm, the sampling length was 0.8 mm, and the evaluation length was 4 mm. The surface roughness values ​​Ra and Rz were recorded. Subsequently, using an XSTRESS3000 X-ray stress analyzer, the residual stress on the machined surfaces of all workpieces was measured according to the second standard mentioned above. The side-tilt fixed ψ method was adopted, with a Cu target, tube voltage of 30kV, tube current of 20mA, and diffraction crystal plane of titanium alloy 213 crystal plane. The diffraction angle 2θ was approximately 142°. The residual stress values ​​were measured on the surface and at depths of 5μm, 10μm, and 20μm from the surface. Each location was measured three times, and the average value was taken as the final result.

[0088] Table 1: Test Results of Contour Accuracy and Machining Deformation Example 1 0.008 0.003 0.005 0.002 Example 2 0.010 0.004 0.006 0.003 Example 3 0.009 0.0035 0.0055 0.0025 Comparative Example 1 0.052 0.021 0.035 0.018 Comparative Example 2 0.045 0.018 0.030 0.015 Comparative Example 3 0.038 0.015 0.025 0.012 Comparative Example 4 0.025 0.010 0.018 0.008 Comparative Example 5 0.085 0.032 0.060 0.028 Note: All data are the average of three repeated measurements, and the ambient temperature was controlled at 20℃±1℃. A smaller profile error indicates higher machining accuracy, and a smaller wall thickness variation indicates less machining deformation. The wall thickness variation in Comparative Example 5 includes additional deformation generated during the introduction and removal of the low-melting-point alloy support; its actual machining deformation is greater than the measured value.

[0089] Table 2: Comprehensive Test Results of Surface Integrity Example 1 0.20 0.30 -120 -80 Example 2 0.25 0.35 -100 -65 Example 3 0.22 0.32 -110 -75 Comparative Example 1 1.80 2.50 -5 -3 Comparative Example 2 1.50 2.20 -8 -4 Comparative Example 3 1.20 1.80 -10 -6 Comparative Example 4 0.80 1.50 +150 +120 Comparative Example 5 1.60 3.20 +220 +180 Note: In the residual stress values, negative values ​​represent compressive stress, and positive values ​​represent tensile stress. Compressive stress is beneficial for improving the fatigue strength and corrosion resistance of the workpiece, while tensile stress will reduce the service life of the workpiece. The residual stress in Comparative Examples 1 to 3 is close to zero, indicating that no mechanical stress is introduced during the material removal process, but the surface roughness is poor. Comparative Examples 4 and 5 have significant tensile stress, which is caused by work hardening and plastic deformation generated during mechanical cutting.

[0090] As can be seen from Examples 1-3 and Comparative Example 1, and in conjunction with Tables 1 and 2, the thermally induced reversible complexation response mechanism is the core foundation for achieving localized chemical dissolution. When the cutting fluid loses its temperature-triggered activity switching capability, it cannot confine the dissolution reaction to the local area in contact with the tool, resulting in continuous global chemical corrosion, which leads to a significant decrease in machining accuracy and severe deterioration of surface integrity.

[0091] As can be seen from Examples 1-3 and Comparative Example 2, and from Tables 1 and 2, the pre-placed sacrificial passivation layer is a key element in constructing a protection system for non-machined areas. Without the protection of the initial passivation film, the workpiece will undergo uniform surface corrosion during the cutting fluid immersion process, the contour edges will become blurred, and a sharp feature structure cannot be formed. At the same time, the roughness of the machined surface will also increase significantly.

[0092] As can be seen from Examples 1-3 and Comparative Example 3, and from Tables 1 and 2, forced internal cooling of the tool is a necessary condition for constructing a micron-level extreme thermal gradient. Without an internal cooling system, the heat generated by friction diffuses into the tool and the workpiece, causing a significant expansion of the heat-affected zone, making it impossible to precisely control the melting range, and ultimately resulting in reduced contour accuracy and increased machining deformation.

[0093] As can be seen from Examples 1-3 and Comparative Example 4, and from Tables 1 and 2, extremely low contact force is the core guarantee for achieving stress-free machining. When the contact force increases to the range of conventional cutting forces, even if material removal is still mainly chemical dissolution, significant mechanical stress and elastic deformation will be introduced, leading to tool deflection error and residual tensile stress in the workpiece, which seriously affects the dimensional accuracy and service life of the workpiece.

[0094] As can be seen from Examples 1-3 and Comparative Example 5, and from Tables 1 and 2, traditional mechanical milling processes cannot fundamentally solve the problem of machining deformation in thin-walled irregular parts. Even with the use of low-melting-point alloy fillers to increase rigidity, significant machining deformation and residual tensile stress still occur. Furthermore, the introduction and removal of supports introduce additional dimensional errors and surface contamination, resulting in an overall machining effect far inferior to the cutting force-free machining method of this application.

[0095] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for precision milling of irregularly shaped parts, characterized in that: Includes the following steps: S1. Surface passivation treatment: The workpiece is pretreated to generate a uniform and dense sacrificial passivation film on its entire surface by chemical or electrochemical methods. S2. Preparation of cutting fluid: Prepare a thermo-induced reversible complexing self-passivating cutting fluid. The cutting fluid is chemically inert at room temperature and dissociates and releases active chelating anions when the temperature rises to its dissociation threshold. S3. Workpiece clamping and wetting: The passivated workpiece is clamped on the worktable of a multi-axis CNC machine tool by point contact positioning or vacuum suction cup adsorption, so that the area of ​​the workpiece to be processed is continuously completely wetted by the cutting fluid. S4. Tool configuration and installation: A ball-end tool is selected. The ball end of the tool is provided with a uniformly distributed array of micron-level micro-protrusions. The tool is machined with a fine internal cooling channel that extends to the vicinity of the tool tip. A constant temperature coolant is continuously introduced into the internal cooling channel. S5. Machining path compilation: Generate a five-axis linkage machining toolpath based on the three-dimensional contour model of the workpiece, and convert the toolpath into a pulse feed program; S6. Localized Dissolution Machining: The tool contacts the workpiece surface with a set contact force, causing the ball-end micro-protrusion to rub against the workpiece and generate heat until the temperature of the contact spot reaches the dissociation threshold of the cutting fluid, thereby triggering the dissociation of the cutting fluid and localized dissolution of the workpiece matrix material; after the tool is removed, the contact spot cools down, and the cutting fluid returns to chemical inertness. S7. Layer-by-layer scanning forming: Repeated pulse processing is performed, and the tool dissolves the material layer by layer and point by point along the contour of the part; S8. Finished product cleaning and inspection: After processing is completed, stop the cutting fluid supply, take out the workpiece for cleaning and drying, and obtain the finished product.

2. The method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S1, the thickness of the sacrificial passivation film is 0.1 μm to 2 μm. Specifically, the titanium alloy workpiece is immersed in a pretreatment solution containing fluorotitanate and corrosion inhibitor, and a fluorotitanate conversion film is generated in situ at a temperature of 20°C to 30°C for a treatment time of 5 min to 30 min.

3. The method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S2, the cutting fluid is chemically inert at a temperature not exceeding 30°C and reaches the dissociation threshold when the temperature rises to 45°C to 70°C. The cutting fluid is prepared by uniformly mixing the following components in parts by mass: 5-15 parts of reversible complex precursor, 2-8 parts of stabilizer, 0.5-3 parts of pH buffer, 0.6-1 parts of passivating film-forming agent, 5-20 parts of extreme pressure heat transfer medium, and the balance being deionized water.

4. The method for precision milling of irregularly shaped parts according to claim 3, characterized in that: The reversible complex precursor is a pre-coordinated titanium-citric acid complex or an iron-oxalate complex; the stabilizer is an excess of free citrate or oxalate ions; the pH buffer is a borax-boric acid buffer; the passivating film-forming agent is selected from at least one of molybdate, tungstate, or hydrogen peroxide; and the extreme pressure heat transfer medium is a water-soluble polyalkylene glycol.

5. The method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S3, the adsorption pressure of the vacuum suction cup is controlled between 0.02 MPa and 0.08 MPa, and the cutting fluid is supplied by pouring or immersion, with the circulating flow rate of the cutting fluid controlled between 5 L / min and 20 L / min.

6. The method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S4, the ball end mill is made of graphite or cemented carbide with a thermal conductivity of not less than 100 W / (m·K). The height of the micro-protrusions on its surface is 5 μm to 20 μm, and the spacing is 20 μm to 100 μm. The diameter of the internal cooling channel is 0.5 mm to 2 mm, and the temperature of the constant temperature coolant is 15°C to 25°C.

7. The method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S5, the pulse feed program sets the dwell time of each machining point to 0.05s to 0.5s, the point spacing matches the size of the tool micro-protrusion contact spot, and the tool posture is adjusted in real time according to the surface normal to ensure that the ball head micro-protrusion is always in stable contact with the workpiece surface.

8. A method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S6, the set contact force is no greater than 0.1N, the rotation speed of the tool is 1000r / min to 5000r / min, and the diameter of the contact spot is 10μm to 100μm; The blade rotates to scrape away the generated dissolved products; The active chelating anions released after the cutting fluid dissociates first penetrate and dissolve the sacrificial passivation film generated in step S1, and then dissolve the exposed workpiece substrate material. After the tool is removed and the contact spot cools, the passivating film-forming agent in the cutting fluid generates a repassivation film in situ on the newly exposed workpiece surface.

9. A method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S7, the thickness of each material layer removed is controlled between 0.1 μm and 5 μm. During the processing, the cutting fluid circulation system filters in real time to remove metal complex precipitates, with a filtration accuracy of not less than 1 μm.

10. A method for precision milling of irregularly shaped parts according to claim 1, characterized in that: In step S8, the cleaning steps are as follows: ultrasonic cleaning is performed using deionized water and anhydrous ethanol, with each ultrasonic cleaning lasting 3 to 10 minutes and the ultrasonic frequency ranging from 20 kHz to 40 kHz. After cleaning, the water is allowed to air dry naturally at room temperature.

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