Manufacturing and machining method for deep-cavity small-structure part

Abstract

The invention discloses a deep-cavity small-structure part manufacturing and machining method, and belongs to the technical field of machining. Comprising turning, polishing and cleaning; for a structure with an arc surface in a deep cavity of the part, a tool for turning is a tool with a front angle of 5-15 degrees; polishing is conducted after turning, rough polishing, semi-fine polishing and fine polishing are sequentially adopted for polishing, and cleaning is conducted after each time of polishing; in the polishing step, a polishing rod with cloth fixed at the front end is adopted, an abrasive is sprayed on the cloth, and the polishing rod and the center of the part are staggered and rotate oppositely for polishing; according to the invention, turning-polishing-cleaning full-closed-loop manufacturing is realized; the precision of a deep-cavity small-structure part is improved, the problem of sealing failure of an aerospace / medical valve body under the extreme working condition (-80 DEG C) is solved, and the one-time delivery inspection percent of pass is improved to be larger than or equal to 98%.

Description

Technical Field

[0001] This invention belongs to the field of machining technology, and relates to precision mechanical manufacturing and ultra-precision surface treatment technology; specifically, it is a method for manufacturing and processing deep cavity small structure parts. Background Technology

[0002] Valve body parts (such as) Figure 1 Because they operate in extreme environments (working temperature -80℃), the performance requirements are extremely stringent, necessitating high precision in dimensions, position, and surface roughness, especially for critical components that function as sealing surfaces. For example, a valve body part made of 1Cr18Ni10Ti, with external dimensions of φ30×68mm and a minimum inner diameter of φ6mm, requires stringent machining quality control. This is reflected in two aspects: firstly, the control of tool marks: the precision of the tool marks between the milling and turning processes on the external end face boss must be strictly controlled to ≤0.01mm; secondly, the precision of the tool marks on the internal cavity "valve" (see...) Figure 1 (Partial view on the left) During turning, the tool joint dimension at the tangent point of the two arcs should be ≤0.01mm. Second, surface roughness control: the "gate" area of ​​the inner cavity is formed by the tangential connection of small arcs with R0.2mm and R0.3mm, and Ra≤0.1μm (mirror grade); third, after machining, the inner cavity of the part is cleaned until there are no residual foreign objects.

[0003] However, the existing technology has the following drawbacks regarding the machining of the aforementioned valve body parts: 1. Insufficient machining contour accuracy The part has a 10mm boss on a 22mm cylindrical body. Machining begins with a turning sequence to machine the pre-reserved process ring, followed by a milling sequence using a five-axis machine tool with vertical-horizontal conversion. On one hand, the milling sequence removes a large amount of allowance from the turning sequence, easily causing part deformation and making it difficult to control tool marks. On the other hand, the tool interpolation trajectory differs during the vertical-horizontal conversion of the milling sequence, making longitudinal and axial tool marks difficult to control. The critical "valve" part, a φ8mm×0.6mm boss located between the inner cavity and the sealing surface, has a narrow space where the upper and lower R0.2mm and R0.3mm arcs intersect, requiring two tools for two interpolation operations. The tool joint at the tangent point is prone to tool defects.

[0004] 2. Inappropriate tool angle in narrow areas leads to large errors in the tangential arc. When inspecting the internal cavity of a part by sectioning it, it was found that the tangent of the two circular arcs at the "gate" was not complete. The cause was the tool setting error (including radial and axial) between the two tools. Since the tool tip radius is perpendicular to the base plane, when cutting a small radial arc radius, the actual tool tip radius involved in the cutting is elliptical. Therefore, tools with the same rake angle, inclination angle, and tool tip radius will produce different machining trajectories for small and large tools. For example, if the tool rake angle is too large (>10°), the elliptical effect of the tool tip is amplified when cutting micro-arcs of R0.2mm and R0.3mm, resulting in a collapse of >0.02mm at the tangent point (100% out of tolerance) and a tool mark fluctuation of ±0.015mm (target ≤0.01mm). The strength of the tool shank is also a critical factor; therefore, the accuracy of this technique is insufficient.

[0005] 3. Loss of uniformity in high-speed polishing Traditional handheld power tool polishing suffers from vibration and tilting (amplitude ±0.1mm), resulting in inconsistent quality: quadrants 1 and 3 of the circumference are polished to a satisfactory level, but quadrants 2 and 4 are not polished properly. Therefore, the polishing method needs improvement, and this technology lacks flexibility.

[0006] 4. Micro-residue cleaning failure The original design of the traditional vertical nozzle only achieved laminar flow within a 6mm deep cavity, and its 90° orifice cleaning was incomplete, resulting in: diamond microparticle residue ≥20 particles / piece (particle size >5μm); 100% water stain adhesion rate; and a 35% increase in rework costs. 5. Low detection compatibility A 50x microscope cannot detect scratches ≤2μm, masking the true defects, resulting in: a first-pass yield of <70%; and a 300% increase in the risk of seal failure (verified under extreme conditions -80℃).

[0007] As can be seen from the above analysis, the numerous drawbacks of graded polishing and vertical cleaning technology for deep cavity small structure parts limit its widespread application.

[0008] Currently, domestic and international research on the machining of deep-cavity small-structure valve bodies mainly focuses on: 1. The main processing challenges are: turning with a depth-to-diameter ratio > 5:1 using a vibratory cutter (amplitude ≥ 5 micrometers) and hand-held polishing vibration (pressure fluctuation ± 15N); 2. Machining sequence: The mainstream method adopts a segmented process: turning - offline polishing - independent cleaning (cumulative error from repeated clamping ≥ 0.03mm); 3. Machining accuracy and efficiency of internal holes; 4. Arrange the processing sequence and explore the process parameters; 5. The three major challenges of deep cavity turning contour control, polishing uniformity, and residual cleaning are solved in a coordinated manner; 6. How to meet the standard of "zero defects under 200x microscopy + sealing under extreme working conditions" (Ra≤0.1μm). Summary of the Invention

[0009] This invention overcomes the shortcomings of the prior art and proposes a manufacturing method for deep cavity small structure parts; realizes a closed-loop manufacturing process of turning-polishing-cleaning; improves the precision of deep cavity small structure parts, so as to solve the sealing failure problem of aerospace / medical valve bodies under extreme conditions (-80℃), and improves the first-pass yield rate to ≥98%.

[0010] This invention is achieved through the following technical solution: A method for manufacturing deep-cavity small-structure parts includes turning, polishing, and cleaning. For parts with arc surfaces inside deep cavities, the turning tool is a tool with a rake angle of 5° to 15°. Polishing is performed after turning, and the polishing process consists of rough polishing, semi-finish polishing, and finish polishing. Cleaning is performed after each polishing step. The polishing process involves using a polishing rod with a cloth fixed at the front end. The cloth is sprayed with abrasive, and the polishing rod rotates in opposite directions relative to the center of the part to perform polishing. The speed for rough polishing is 280~320 r / min, the speed for semi-fine polishing is 2800~3200 r / min, and the speed for fine polishing is 3800~4200 r / min.

[0011] Preferably, the tool holder of the turning tool is made of cemented carbide and has a hardness of 89HRA~94HRA.

[0012] Preferably, the fabric surface has a nap.

[0013] More preferably, the coarse polishing and semi-fine polishing use suede fabric, and the fine polishing uses flannel fabric.

[0014] Preferably, the abrasive particles on the cloth used for coarse polishing have a particle size of 2~3μm, the abrasive particles on the cloth used for semi-fine polishing have a particle size of 1~1.2μm, and the abrasive particles on the cloth used for fine polishing have a particle size of 0.3~0.5μm.

[0015] Ideally, the coarse polishing time should be 2.5 to 3 minutes, the semi-fine polishing time should be 1 to 1.5 minutes, and the fine polishing time should be 25 to 35 seconds.

[0016] Preferably, the cutting tool used for turning is a tool with a 5° rake angle.

[0017] Preferably, high-pressure rinsing is used for cleaning after rough polishing and semi-fine polishing, and ultrasonic cleaning is used for cleaning after fine polishing.

[0018] Even better, the nozzle of the high-pressure water gun used for high-pressure rinsing is connected to the part, and the nozzle is set with a 20~25° inclined water outlet.

[0019] Even better, the ultrasonic cleaning frequency is 150~220kHz.

[0020] The beneficial effects of this invention compared to the prior art are as follows: 1. This invention employs a collaborative vibration damping model involving cutting tools, materials, and structure: establishing a matching design between carbide cutting tools and a depth-to-diameter ratio of 6:1 to overcome the challenge of vibration control during internal hole turning with a length-to-diameter ratio of 6:1 (depth 48.6mm / hole diameter ¢8mm). It innovatively selects carbide tool holders (with vibration damping performance up to 8 times the tool holder diameter) to replace traditional high-speed steel (≤5 times) and ordinary steel tool holders (≤3 times), completely resolving the dimensional deviation problem caused by vibration.

[0021] 2. This invention reveals the amplification mechanism of the tool rake angle on small arc contours: the smaller the rake angle (5° is better than 15°), the smaller the influence of the vertical cutting edge of the tool tip on the deformation of tangent arcs of R0.2mm and R0.3mm. By reducing the rake angle, the distortion effect of the vertical cutting edge on fine features can be suppressed. Optimizing the rake angle to 5° achieves a contour accuracy improvement of more than 40%, verified by sectioning electronic measurement. This fills the gap in the tool angle-contour accuracy correlation model in fine feature turning.

[0022] 3. This invention employs a three-stage adaptive polishing technology: Rough polishing (2.5μm abrasive + base coat, 300r / min) completely eliminates turning marks; Semi-polished finish: (1μm abrasive + chamois leather, 3000r / min) Eliminates scratches and enhances reflectivity; Fine polishing (0.5μm abrasive + flannel 4000r / min) achieves a scratch-free mirror finish under a 200x microscope.

[0023] Through seven systematic experiments with flannel, it was verified for the first time that flannel (long and resistant to shedding) is the best polishing medium, solving the defect of fuzz fusion and adhesion in high-speed polishing; making the surface roughness of the parts reach Ra≤0.01mm, meeting the ultra-precision machining standard.

[0024] 4. This invention adopts a non-contact vortex cleaning fixture: Through the inclined nozzle structure design, it achieves efficient cleaning in narrow spaces and avoids secondary damage: The 20° inclined water nozzle is designed, combined with a high-pressure water gun (2.5Mpa) to form a vortex in the φ16.5mm inner cavity, which removes polishing residue and detached particles, and eliminates water stain defects.

[0025] 5. This invention solves the common problem of integrated machining and polishing of microstructures in the field of aerospace / aviation precision instruments; the polishing process can be extended to high-end manufacturing fields such as medical devices and optical devices; it reduces the rework rate of precision parts and reduces the processing cost per piece by more than 30%. Attached Figure Description

[0026] Figure 1 For existing valve body parts drawings; Figure 2 This is a process route diagram for the present invention; Figure 3 Sectional view of machining a "thrust valve" with a 5° rake angle; Figure 4 Sectional view of machining a "thrust valve" with a 15° front angle; Figure 5 This is the result of roughness calculation; Figure 6 The tool marks are magnified 200 times for the unpolished surface; Figure 7 Photo of the power head being polished; Figure 8 This is a diagram showing the effect of the valve after semi-precision polishing. Figure 9 This is a rendering of the valve after precision polishing. Figure 10 Photographs of the four polishing media used in the experiment; Figure 11 Photographs of the flannel medium used in the experiment; Figure 12 Schematic diagram of a 20° tilted water nozzle; Figure 13 This is a diagram showing the effect of two circular arcs joining together. Detailed Implementation

[0027] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0028] This embodiment proposes a closed-loop manufacturing method for deep-cavity small-structure parts, encompassing turning, polishing, and cleaning, specifically addressing issues such as… Figure 1 The valve structure within the deep-cavity, small-structure valve body shown employs a machining strategy of "alternating turning and milling, roughing followed by finishing, multiple machining operations, and phased polishing and cleaning" to ensure that the surface roughness, shape, and cleanliness of key product elements meet requirements. For detailed process route information, please refer to [link to process route details]. Figure 2 Specifically, the steps are as follows: Step 1: Turning 1.1 Tool Material Selection: Since the critical machining element is located at the bottom surface of the φ16.5 inner hole, with a depth of 48.6mm and a minimum diameter of φ8mm, the required tool length-to-diameter ratio is 48.6 / 8≈6 times. The vibration damping effect of ordinary steel tool holders is ≤3 times the tool holder diameter, high-speed steel tool holders are ≤5 times the tool holder diameter, and carbide tool holders are ≤8 times the tool holder diameter. Therefore, carbide tool holders with a hardness of 94HRA are selected as the tool material.

[0029] 1.2 Tool Angle Selection: When machining stainless steel, increasing the rake angle can reduce cutting force and prevent chips from sticking to the tool. In the trial cutting process, tools with rake angles of 5° and 15° were selected respectively.

[0030] The machining method involves precisely setting the tool on the test piece and turning the inner hole with the same diameter as the "gate" element, compensating for diameter direction errors. The testing method involves radially sectioning the part and performing electronic measurements under a 200x microscope. The experimental machining results are as follows: Figure 3 and Figure 4 In this embodiment, a 5° tool rake angle is selected for machining the part.

[0031] In turning tools, due to the presence of rake angle, clearance angle, and secondary clearance angle, and the fact that the tool tip radius is ground perpendicular to the horizontal base surface, the actual cutting edge participating in cutting at the tool tip is a three-dimensional oblique line, which is an inclined elliptical shape. This three-dimensional oblique line has a smaller impact when turning larger parts, but when turning "gate" elements, the radial diameter of the "gate" is small, and after radial sectioning, it is tangent to R0.2mm and R0.3mm, with small arc radii. The influence of the three-dimensional cutting edge on machining elements is amplified, resulting in different machining profiles under the same tool path for different tool rake angles, and the smaller the tool rake angle, the smaller the impact on the machined profile.

[0032] Step 2: Polishing After machining the "gate" element, the surface of the part appears relatively bright to the naked eye. The surface roughness was achieved at a feed rate of 0.05 mm / r and a tool radius of R0.4 mm. The theoretical roughness calculated is Ra0.781 μm (see [reference]). Figure 5 However, when viewed under a 200x microscope (such as...), Figure 6 The part has obvious tool marks on its surface, and the process requires that this area have a mirror finish when viewed under magnification, with no scratches, water stains, or other defects allowed. Clearly, the surface roughness of this area does not meet the requirements and polishing is necessary.

[0033] The polishing equipment uses a CNC turning center, with the workpiece clamped in the chuck and a polishing nylon rod fixture (such as...) clamped in the tool post power head. Figure 7As shown in the image, a cloth is fixed at the front end, and a water-based abrasive is sprayed onto the cloth. The center of the power head is offset from the center of the part by 0.5mm, and they rotate in opposite directions to polish the part.

[0034] Experiments were conducted using different types of polishing cloth, different abrasive particles, and different polishing times. The following conclusions were drawn: 2.1 Coarse Polishing: Spray 2.5μm abrasive onto the chamois, power head speed 300r / min, polishing time 3 minutes. Perform multiple coarse polishing sessions until no tool marks are visible under a 200x microscope. Chamois is chosen as the polishing cloth because its high toughness and relatively hardness result in a longer lifespan during coarse polishing.

[0035] The speed of the power head is selected primarily to remove tool marks, resulting in a longer polishing time. At higher speeds, the grinding temperature increases, causing the abrasive to evaporate and resulting in dry grinding between the chamois and the parts, leading to an insignificant rough polishing effect.

[0036] High-pressure rinsing is performed after each rough polishing to prevent impurities from affecting the polishing effect of the next polishing.

[0037] 2.2 Semi-finish polishing: Spray 1μm abrasive onto the chamois, rotate the power head at 3000 rpm, and polish for 1 minute. Perform multiple semi-finish polishing sessions until no large scratches are visible under a 200x microscope.

[0038] The selected speed of the power head is to increase the reflectivity of the valve surface and remove larger scratches, such as... Figure 8 As shown, this prepares the surface for final polishing to enhance brightness.

[0039] High-pressure rinsing is performed after each semi-finish polishing to prevent impurities from affecting the polishing effect of the next polishing.

[0040] 3.3 Fine Polishing: Apply 0.5μm abrasive to the flannel fabric, rotate the power head at 4000 rpm, and polish for 30 seconds. Perform multiple fine polishing passes until no scratches are visible under a 200x microscope. Figure 9 As shown.

[0041] In the fine polishing process, experiments were conducted using different fabric materials. The first three types showed significant scratches after polishing, while the velvet fabric achieved a scratch-free finish. The conclusion is that fabrics with a napped surface are more suitable for fine polishing than those without. However, because the nap of the velvet fabric is not firmly bonded to the main body, the nap detaches after polishing for more than 20 seconds at a power head speed of 4000 rpm. Furthermore, the high temperature of polishing melts the nap, which then adheres to the "gate," resulting in excess material that is difficult to remove. A survey of the types of velvet fabrics on the market and their characteristics are shown in Table 1 below. ; After screening, thicker fabrics like corduroy and flannel were removed. Experiments revealed that coral fleece, polar fleece, and velvet, due to their short pile, were more prone to scratches. Therefore, flannel, with its long pile and resistance to shedding, was ultimately chosen as the polishing medium (see [link to experiment]). Figure 10 and Figure 11 ).

[0042] Step 3: Cleaning After polishing, the cavity of the part contains residual material, including alcohol (the main component of the abrasive), diamond particles, and polishing shavings. Cleaning is necessary after each polishing cycle to avoid affecting subsequent polishing. For example, a thorough cleaning is required between rough polishing and semi-finish polishing to prevent the presence of 2.5μm diamond abrasive particles during semi-finish polishing, which could negatively impact the polishing result. The same principle applies between semi-finish and finish polishing.

[0043] After the parts are polished, they still need to be precisely cleaned to ensure that there are no foreign objects present when they are delivered.

[0044] Based on the above two requirements, two experiments were arranged in the parts cleaning process: high-pressure rinsing and ultrasonic cleaning.

[0045] 3.1 High-pressure flushing: This experiment used the Worx WU633 high-pressure portable water gun. It can provide a pressure of 2.5 MPa and a flow rate of 4 L / min, which is sufficient for rinsing such small parts.

[0046] The high-pressure water gun is designed with interchangeable nozzles (such as...). Figure 12 (As shown) It is connected to the part with an M20×1.5 thread. One end of the nozzle thread is connected to the valve body part, and the other end is connected to the high-pressure water gun. In order to make the water flow form a vortex in the inner cavity, a 20° inclined water nozzle is designed at the water outlet.

[0047] Experiments have shown that high-pressure washing is effective at cleaning abrasives with alcohol as the main component, effectively removing excess material adhering to the surface of parts. However, due to impurities in the water and the presence of diamond particles as the abrasive medium in the abrasive, the "threshold" element can cause scratches under high-pressure washing. Therefore, high-pressure washing is only suitable after rough polishing and semi-fine polishing.

[0048] 3.2 Ultrasonic Cleaning The principle of ultrasonic cleaning is to generate a "cavitation effect" in the cleaning fluid. The generation and collapse of bubbles in the liquid produce a powerful impact force, which is used to remove impurities, dirt and grease from the surface of objects.

[0049] This experiment used the Dr. Crown GLS3230-200 ultrasonic cleaning equipment; When selecting equipment parameters, the core principle for considering ultrasonic frequency is: higher frequency results in more precise cleaning but weaker force; lower frequency provides stronger cleaning but may damage precision parts. Specific selection guidelines are shown in Table 2 below. ; The "threshold" element is easily damaged after fine polishing, so a 200kHz ultrasonic cleaning device was selected. This fills the functional gap that high-pressure water guns cannot clean after fine polishing.

[0050] Step 4: Testing The "gate" element has high surface roughness requirements and a small radius of curvature. Its shape and roughness inspection methods differ from those of common parts.

[0051] 4.1 Shape detection: Because the shape of the "gate" element directly affects the sealing condition, the shape requirements are high. However, measurement factors such as the fullness of the arc and the influence of tool marks on the shape cannot be measured using conventional methods. Therefore, the process requires destructive measurement. Specifically, out of 10 products, the first and last products are wire-cut and measured. If the arc radius, tool mark effect, and dimensions of the two products meet the requirements, it means that the middle 8 products meet the requirements.

[0052] The arc was marked and observed using an industrial camera with measurement capabilities at 200x magnification.

[0053] a) Mark the radius of the arc and the distance between the centers of the two arcs.

[0054] b) Observe whether the two arcs are fully tangent and whether the tool marks are obvious.

[0055] 4.2 Roughness Inspection: The process requires the use of a stereo microscope and an industrial camera to magnify the surface 200 times during roughness inspection. The "gate" area must be free of scratches on the entire observable annular arc as a criterion for judgment.

[0056] The microscope required a focal length ≥80mm, with sufficient magnification to meet usage requirements while maintaining adequate clarity. After evaluation, the Sunny Optical SZMN7045TR microscope, equipped with an MD-SS4K industrial camera and a dedicated microscope light source XD-301, was selected. Figure 13 The performance of the testing equipment is consistent with the process requirements. Technical specifications and achievements are shown in Table 3. .

[0057] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features.

[0058] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0059] To provide the public with a thorough understanding of the present invention, specific details have been described in detail in the above preferred embodiments. However, those skilled in the art can fully understand the invention even without these detailed descriptions. Several improvements and modifications can be made without departing from the principles of the invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for manufacturing and processing deep-cavity small-structure parts, comprising turning, polishing, and cleaning; characterized in that, For parts with arc surfaces inside deep cavities, turning tools with a rake angle of 5° to 15° are used; after turning, polishing is performed, with rough polishing, semi-finish polishing and finish polishing performed in sequence, and cleaning is performed after each polishing; The polishing process involves using a polishing rod with a cloth fixed at the front end. The cloth is sprayed with abrasive, and the polishing rod rotates in opposite directions relative to the center of the part to perform polishing. The speed for rough polishing is 280~320 r / min, the speed for semi-fine polishing is 2800~3200 r / min, and the speed for fine polishing is 3800~4200 r / min.

2. The method for manufacturing and processing a deep-cavity small-structure part according to claim 1, characterized in that, The tool holder of the turning tool is made of cemented carbide, and the hardness of the tool holder is 89HRA~94HRA.

3. The method for manufacturing and processing a deep-cavity small-structure part according to claim 1, characterized in that, The fabric surface has a nap.

4. The method for manufacturing and processing a deep-cavity small-structure part according to claim 3, characterized in that, The coarse polishing and semi-fine polishing use suede fabric, while the fine polishing uses flannel fabric.

5. A method for manufacturing and processing a deep-cavity small-structure part according to claim 1 or 4, characterized in that, The abrasive particles on the cloth used for coarse polishing have a particle size of 2~3μm, the abrasive particles on the cloth used for semi-fine polishing have a particle size of 1~1.2μm, and the abrasive particles on the cloth used for fine polishing have a particle size of 0.3~0.5μm.

6. The method for manufacturing and processing a deep-cavity small-structure part according to claim 5, characterized in that, The coarse polishing time is 2.5 to 3 minutes, the semi-fine polishing time is 1 to 1.5 minutes, and the fine polishing time is 25 to 35 seconds.

7. The method for manufacturing and processing a deep-cavity small-structure part according to claim 1, characterized in that, The cutting tool used for turning is a tool with a 5° rake angle.

8. The method for manufacturing and processing a deep-cavity small-structure part according to claim 1, characterized in that, High-pressure rinsing is used for cleaning after rough polishing and semi-fine polishing, while ultrasonic cleaning is used for cleaning after fine polishing.

9. A method for manufacturing and processing a deep-cavity small-structure part according to claim 8, characterized in that, The nozzle of the high-pressure water gun used for high-pressure rinsing is connected to the part, and the nozzle is equipped with a 20~25° inclined spray nozzle.

10. A method for manufacturing and processing a deep-cavity small-structure part according to claim 8, characterized in that, The frequency of ultrasonic cleaning is 150~220kHz.

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