Hollow thin-walled ceramic insulating parts and their finishing methods

Abstract

This invention belongs to the field of ceramic technology, specifically relating to hollow thin-walled ceramic insulating parts and their finishing methods. The finishing method is characterized by the following steps: selecting high-purity alumina powder; cold isostatic pressing; graded debinding and high-temperature sintering; and obtaining a bulk density ≥3.95 g / cm³ after cooling. 3 The ceramic sintered parts are ground with low-damage reference plane grinding and CNC precision chamfering to achieve a smooth transition of sharp corners. The hollow thin-walled ceramic insulating parts and their finishing methods provided by this invention are suitable for slender hollow insulating parts with a large aspect ratio and a single wall thickness of ≤3mm, and can balance processing efficiency, processing quality and yield.

Description

Technical Field

[0001] This invention belongs to the field of ceramic technology, specifically relating to hollow thin-walled ceramic insulating parts and their finishing methods. Background Technology

[0002] Slender, hollow, thin-walled components generally refer to slender rectangular structures with a length of 300-1000 mm, a width of 30-80 mm, and a height of 20-50 mm, with an aspect ratio greater than 10:1. They are hollow internally, with the hollow portion measuring 294-994 mm in length, 24-74 mm in width, and 17-47 mm in height, and a single wall thickness ≤3 mm. These hollow, thin-walled ceramic insulators are typically used as key components in vacuum tubes, high-voltage insulators, spark plugs, and semiconductor equipment, requiring them to withstand high-voltage electrical impulses and possess long-term resistance to electrical breakdown. These insulators usually have a slender, hollow structure with a single wall thickness ≤3 mm. Currently, the processing route for these ceramic components mainly adopts a near-net-shape forming, sintering, and precision machining method. This involves first obtaining a green body through isostatic pressing, slip casting, or injection molding, then sintering at high temperature to obtain a dense ceramic, and finally precision machining of the sintered hard and brittle ceramic to meet the final dimensional accuracy and surface quality requirements.

[0003] For slender, hollow, thin-walled ceramic parts sintered after isostatic pressing, the common practice is to directly glue and bond them using rigid metal fixtures or to clamp the outer wall with a large area for ordinary grinding. Furthermore, relying solely on spray cooling fluid during processing can lead to thermal stress cracks and micro-damage on the ceramic surface. However, when producing long ceramic parts with an aspect ratio greater than 10:1 and an internal hollow single-wall thickness ≤3mm after isostatic pressing, the following specific problems arise after hollow precision milling and sintering: the ceramic material has extremely low fracture toughness, and the point or line clamping method of rigid fixtures can cause localized stress concentration on the ceramic surface, potentially inducing micro-cracks or even overall breakage before processing. Simultaneously, due to coaxiality errors in the blank, a large grinding allowance is required, resulting in significant material removal and low processing efficiency. More importantly, for hollow thin-walled parts with a large aspect ratio, the lack of sufficient radial support during grinding can easily lead to "tool tremor" when the grinding amount is too large or the grinding wheel speed is too fast, resulting in micro-cracks at the edges or overall breakage.

[0004] To alleviate the problem of excessive clamping force, some processes employ a wax-filling reinforcement method, which involves pouring a layer of molten adhesive wax into the hollow interior of the ceramic part before clamping. However, this method suffers from a significant hardness difference between the adhesive wax layer and the ceramic, interfering with accurate positioning and easily adhering to the cutting tool. Furthermore, it does not effectively improve the fracture toughness of the ceramic, and cleaning the adhesive wax layer after machining is extremely inconvenient. Another alternative method is sealing wax bonding, which has lower positioning accuracy, the sealing wax softens easily during the grinding temperature rise, and is difficult to clean after use.

[0005] Chinese patent CN113070740A discloses an efficient machining method and negative pressure fixture for thin-walled alumina ceramic structural parts. This method uses a negative pressure fixture for bottom adsorption positioning of the thin-walled structural part, combined with a diamond grinding head to grind the sides, central grooves, and through holes in stages. Negative pressure adsorption can distribute the adsorption force evenly, avoiding the stress concentration problem of traditional mechanical clamping, resulting in high clamping efficiency. However, this negative pressure fixture requires precise design of multiple positioning cavities according to the workpiece shape, and different specifications of workpieces require different fixtures, resulting in insufficient flexibility. For hollow thin-walled parts with a large length-to-width ratio, bottom adsorption cannot provide radial support in the middle section. When grinding the outer wall of slender tubes or performing deep hole machining, the rear part of the workpiece will still experience chatter due to lack of support, affecting machining accuracy and surface quality.

[0006] CN103072081A discloses a self-referenced positioning and clamping device and grinding method for thin-walled ceramic tubes. This technology employs a pneumatically-driven self-referenced positioning device for the support journal, directly grinding the support journal onto the long tube blank. This journal serves as the positioning reference for subsequent grinding processes, and a pneumatically adaptive clamping device enables floating clamping, avoiding the forced increase in grinding allowance due to blank coaxiality errors. However, this device is mainly suitable for external cylindrical grinding of support journals. Its self-centering jaws and clamping piston head apply radial force from the outer wall of the tube. For slender, hollow, thin-walled parts with a single wall thickness ≤3mm, even with pneumatically controlled clamping force, it is still difficult to completely avoid the risk of radial stress concentration inducing microcracks. Furthermore, this device has a complex structure, high equipment cost, and poor adaptability to non-circular cross-sections or insulating parts with complex internal cavities.

[0007] Regarding grinding process parameters, diamond grinding heads are commonly used in existing technologies for high-speed grinding of alumina ceramics. However, for thin-walled structural parts, if high speed and large feed rate are used throughout the process, the ceramic is prone to chipping or thermal stress cracking due to heat accumulation and excessive axial force when machining through holes and thin-walled areas. In addition, diamond grinding heads experience severe wear, further deteriorating the machining quality. Besides grinding, laser processing can form a modified layer and a reconstituted layer on the ceramic surface, and thermal stress can easily induce microcracks; ultrasonic processing has low efficiency, severe tool wear, and significant energy attenuation for long pipes; electrical discharge machining requires conductive pretreatment and poses a risk of contamination; diamond wheel cutting has low precision, the surface is easily broken, and it cannot be used for irregularly shaped machining. Summary of the Invention

[0008] The technical problem this invention aims to solve is overcoming the limitations of existing finishing techniques for hollow thin-walled ceramic insulators, which struggle to simultaneously address the challenges of radial support, chatter suppression, and surface microcrack control during high-speed grinding of slender hollow thin-walled components. This invention provides a hollow thin-walled ceramic insulator and its finishing method, specifically designed for slender hollow insulators with a large aspect ratio and a single-wall thickness ≤3mm, achieving a balance between processing efficiency, processing quality, and yield.

[0009] The precision machining method for hollow thin-walled ceramic insulating parts according to the present invention includes the following steps: Step 1: Raw Material Preparation: Select alumina powder with a purity ≥99.8wt%, controlling its D90 ≤1μm to ensure particle fineness and uniform distribution, facilitating subsequent densification during molding. To remove adsorbed water and residual volatiles from the powder, a hot air drying process is adopted, drying the powder at 100~130℃ for 1~3 hours. After treatment, the moisture content of the powder is controlled to ≤0.03%, with uniform moisture distribution, effectively preventing the powder from becoming damp and clumping together during pressing, and ensuring that the powder can flow fully and pack tightly during pressing and sintering stages, thereby achieving a stable bulk density of 3.95g / cm³ for the sintered ceramic green body. 3 The above provides a foundation for obtaining finished products with high dielectric strength and high insulation performance.

[0010] Step 2, Cold Isostatic Pressing: The dried powder is filled into a combined mold for cold isostatic pressing. After demolding, an alumina green body is obtained. Specific process parameters are: pressing pressure 100~120MPa, holding time 300s~600s. If the pressure is too high, the powder particles are prone to elastic compression and rebound, and microcracks are likely to occur after the pressure is released. The above parameter range ensures uniform stress distribution and consistent density within the green body. To reduce mold manufacturing costs and improve adaptability and process flexibility, this process addresses the pain points of high mold opening costs, large density gradients, and easy surface wrinkling faced by slender hollow ceramic sintered parts with large aspect ratios in small-batch production. A combined mold system based on a rigid frame, composite sealing, and regular forming is designed in the isostatic pressing stage.

[0011] Step 3: Hollow Precision Milling and Staged Sintering: The inner cavity is first formed through hollow precision milling, followed by staged variable-temperature sintering. The formed green body undergoes degreasing and densification sintering through staged heating to reduce internal stress and porosity, resulting in a high-density ceramic body. Specific sintering curves are as follows: The first stage involves heating the temperature to 700℃ at a rate of 15~25℃ / h and holding it at that temperature for 3~4 hours to degrease the material. This stage is mainly used to completely decompose and remove organic binders and molding aids from the green body, preventing incomplete decomposition at high temperatures that could lead to porosity or cracking.

[0012] Second stage: Continue heating at a rate of 30~50℃ / h to 900℃ to remove residues and obtain intermediate green body; ensure that all organic components are removed, and at the same time promote the initial bonding of grains and the homogenization of structure to form a defect-free intermediate green body.

[0013] The third stage involves heating the material to 1540-1560℃ at a rate of 20-30℃ / h and holding it at that temperature for 3-4 hours to achieve dense sintering. After cooling, a bulk density ≥3.95 g / cm³ is obtained. 3 The ceramic sintering process involves crystal rearrangement and diffusion and recrystallization, resulting in tight grain boundary bonding and controlled grain growth, thus preventing abnormal grain enlargement. The optimized staged sintering process effectively improves the bulk density of the green body, obtaining a dense sintered body with uniform internal structure, fine grains, and extremely low porosity, providing structural assurance for achieving high dielectric strength and excellent insulation performance.

[0014] In step two, the combined mold includes four insulating plates wrapped around the perimeter and a base plate locked to the four insulating plates by a pin-type self-locking structure. The four insulating plates have honeycomb-shaped venting micropores, and the inner surface of the insulating plates is fixed with a non-woven fabric layer by pressure-resistant adhesive to form a laminar flow venting barrier. It also includes an inner layer and an outer layer directly wrapped around the outside of the powder, as well as waterproof sealing tape for sealing the two layers of bags. The inner layer is vacuumed after filling. A buffer layer is filled between the insulating plates and the outer layer.

[0015] The pore size of the honeycomb-shaped exhaust micropores is φ2~φ5mm.

[0016] According to the length specifications of the ceramic sintered part, segmented polytetrafluoroethylene (PTFE) blocks are used to fill the inner cavity with vibration-damping support. The axial length of the PTFE blocks used is 40-50mm, and the initial radial dimension is 2-4mm smaller than the actual corresponding inner dimension of the cavity (1-2mm on each side). During filling, 5wt%-8wt% of talc powder is mixed with a molten adhesive wax layer at 60-70℃ to fill the radial gap of 1-2mm on each side between the PTFE blocks and the inner wall of the cavity. After cooling and solidification, a full contact coating is formed. After all the surface grinding and chamfering are completed, the ceramic sintered part is placed in an oven at 120-130℃ to melt and flow out the adhesive wax layer. The PTFE blocks are then removed, and the ceramic sintered part is immersed in dewaxing water for ultrasonic cleaning.

[0017] The polytetrafluoroethylene block is machined with vibration damping through holes running through its axis. There are 1 to 2 through holes with a diameter of φ3 to φ5 mm per square centimeter, and the edges of the through holes are ground and deburred.

[0018] The L-shaped and T-shaped clamping fixtures, with their surfaces precisely ground, are wrapped with a single layer of elastic gaskets with a Shore hardness of 80A to 90A. L-shaped clamping fixtures are used at the four corners of the ceramic sintered part, and T-shaped clamping fixtures are used every 150 to 200 mm on both outer walls of the ceramic sintered part. During clamping and fixing, a digital torque wrench is used for multi-step symmetrical pre-tightening: First, all fixtures are pre-tightened to 0.3 to 0.5 times the rated clamping torque M; second, a symmetrical tightening method is adopted, extending from the center to both ends, symmetrically clamping from the T-shaped clamping fixture at the center to both sides to 0.6 to 0.8 times the rated clamping torque M; third, all fixtures are locked to the full-load rated clamping torque M. M is 15 to 20 N·m.

[0019] During surface grinding, a liquid soft support vibration absorption system is also used: a circulating coolant tank with a height of 1 / 2 to 1 / 3 of the ceramic part's height is installed on the magnetic worktable of the surface grinder. Four to six magnetic steel pads are attached to the outer bottom of the circulating coolant tank. The circulating coolant tank is fastened to the magnetic worktable by the magnetic switch of the surface grinder. The clamped and fixed ceramic sintered part is placed horizontally at the bottom of the circulating coolant tank, and the long axis of the ceramic sintered part is aligned with the grinding forward direction. Coolant is injected into the circulating coolant tank until the liquid level submerges the tank, so that the ceramic sintered part is in a liquid-enclosed state.

[0020] In step five, the diamond-coated chamfering tool has a grit size of 120#; the spindle speed of the CNC machining center is controlled at 15,000~20,000 rpm, and the feed rate is 50~100 mm / min.

[0021] To further improve the dielectric strength and surface integrity of ceramic insulators, two steps, steps four and five, are required.

[0022] Step 4: Precision surface grinding with low damage: A multi-stage grinding system is used to perform fine grinding on the ceramic sintered parts. The system consists of three stages: rough grinding, semi-fine grinding, and fine grinding. Liquid cooling and chip control are used throughout the process. After processing, the surface roughness Ra of the ceramic sintered parts is ≤0.5μm, flatness ≤0.03mm, and parallelism ≤0.03mm. A near-mirror-level surface is obtained, avoiding electric field concentration caused by surface defects, eliminating residual stress and potential microcracks on the surface of the sintered body, and preventing the formation of breakdown channels under high voltage electric fields. This significantly improves the electric field reliability and stability of the ceramic sintered parts.

[0023] Step 5: Perform CNC precision chamfering on the product after precision surface grinding. Using a diamond-coated chamfering tool on a CNC machining center, perform micro-angle chamfering on the edges of the precision-ground ceramic sintered part. Liquid cooling is used during the process to achieve a smooth transition at sharp corners. This is because the edges of sintered alumina ceramics tend to form near-90° right angles, which are prone to charge concentration in a high-voltage electric field, leading to locally excessively high electric field strength and a higher risk of breakdown. Micro-angle chamfering on the CNC machining center effectively disperses the electric field stress at the sharp corners, improving the uniformity of the overall electric field distribution.

[0024] In step one, a hot air drying process is used to dry the powder at 100~130℃ for 1~3 hours, so that the moisture content of the dried powder is controlled to be ≤0.03%.

[0025] In step two, the cold isostatic pressing pressure is 100~120MPa, and the holding time is 300~600s.

[0026] The specific process parameters for the multi-stage grinding wheel system in step four are as follows: Rough grinding stage: Select a ceramic-bonded parallel grinding wheel with a grit size of 80#, set the grinding wheel speed Vs=18~20m / s, the table speed Vw=15~18m / min, and the single grinding depth ap=0.05~0.08mm; In this stage, a large grinding amount is mainly used to quickly remove sintered skin, burrs and irregular protrusions. After grinding, control the surface roughness Ra≤1.6μm, initially establish the reference flatness and parallelism, and lay the foundation for macroscopic dimensional accuracy.

[0027] Semi-finish grinding stage: A resin-bonded parallel grinding wheel with a grit size of 600# is selected. The grinding wheel speed Vs is set to 20~22 m / s, the table speed Vw to 15~18 m / min, and the depth of cut per pass ap to 0.03~0.05 mm. The grinding wheel hardness is relatively soft to reduce grinding stress and improve the surface quality. In this stage, the synergistic effect of higher grit size and flexible bond can effectively remove deep scratches formed in the rough grinding stage, ensuring that the surface roughness Ra ≤ 0.8 μm after grinding and significantly reducing residual surface stress.

[0028] Fine grinding stage: A resin-bonded parallel grinding wheel with a grit size of 1200# is used for final fine grinding. The grinding wheel speed Vs is set to 23~25m / s, and the table speed Vw is set to 18~20m / min. The depth of grinding per pass is gradually reduced from 0.005mm to 0.002mm, and a final 1~2 passes of feedless polishing surface grinding are performed. In this stage, the combination of high linear speed, low grinding force, and extremely small grinding depth completely eliminates surface subsurface cracks and damaged layers, achieving a surface roughness of Ra≤0.5μm and a uniform mirror gloss, providing physical protection for improved dielectric strength.

[0029] In the above-mentioned flat grinding stage, when producing long ceramics with an aspect ratio of 10:1 or greater and an internal hollow single-wall thickness of ≤3mm, the following problems exist after pressing, hollow precision milling, and sintering: During the later precision grinding process, due to the lack of radial support, excessive grinding amount or excessive grinding wheel speed can easily trigger a "chattering" phenomenon, leading to micro-cracks at the edges or overall breakage. To improve the structural stability of hollow ceramic sintered parts during the grinding process, the following anti-chatter, anti-clamping damage, and multi-dimensional support combination schemes are adopted: First, for thin-walled products with a single wall thickness of ≤3mm after sintering, segmented polytetrafluoroethylene block internal cavity anti-vibration support is implemented according to their length specifications. Second, a distributed clamping system is adopted. Traditional rigid clamps (such as metal vises or chucks) easily cause point stress concentration on the ceramic surface, even inducing internal micro-cracks before processing. Finally, a liquid soft support vibration absorption system is used in conjunction.

[0030] The chamfering angle and depth are determined comprehensively based on the geometric dimensions, dielectric strength requirements, and operating voltage level of the ceramic sintered part. The preferred chamfering angle is 30°±2°, and the chamfering depth is 1.0~2.0mm. This angle effectively reduces the electric field concentration effect at the sharp edges of the ceramic sintered part while ensuring the stability of structural strength and assembly accuracy. Customized 120# electroplated diamond-coated chamfering tools are used during processing to ensure their sharpness and wear resistance. Chamfering is performed on a high-precision CNC machining center, with the spindle speed controlled at 15000~20000rpm and the feed rate at 50~100mm / min. To avoid thermal stress cracks and micro-damage on the ceramic surface, a pouring liquid cooling method is used during processing to maintain a stable temperature in the cutting area and promptly remove debris. In actual machining, by optimizing the cutting path and controlling the depth of cut of the diamond-coated chamfering tool, a smooth transition of ceramic sharp corners and uniform electric field distribution can be achieved, significantly improving the dielectric stability and breakdown voltage withstand capability of the ceramic sintered parts. After machining, the surface is inspected under a special observation lamp and no obvious chipping, cracks, or secondary damage is found, ensuring that it meets the requirements for use in high-voltage insulation structures.

[0031] The hollow thin-walled ceramic insulator has an alumina purity of ≥99.8wt% and a bulk density of ≥3.95g / cm³.3 The surface roughness Ra≤0.5μm, flatness≤0.03mm, parallelism≤0.03mm, the edge has a small chamfer transition surface of 30°±2°, and the electrical breakdown strength>20kV / mm.

[0032] The hollow thin-walled ceramic insulator has a length of 300~1000mm, a width of 40~65mm, a height of 20mm~50mm, an inner cavity size of 294mm~994mm, and a wall thickness of 2.5mm~3mm.

[0033] The finishing method of the present invention is applicable to hollow thin-walled ceramic insulating parts with an aspect ratio of 6:1 to 25:1, thin-walled and hollow, with a single hollow wall thickness of ≤3mm and an opening in the length direction.

[0034] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention solves the problem of forming quality of slender green bodies by combining a mold with laminar flow venting. A rigid frame, composite sealing, and regular forming mold are adopted. The powder filling height is quantified by a scale. Honeycomb micropores combined with non-woven fabric achieve surface venting and eliminate air holes. The middle layer is filled with closed-cell polyethylene to buffer the pressure and avoid isostatic pressing wrinkling and uneven density. The mold adopts a pin self-locking structure, which shortens the disassembly and assembly time, significantly reduces the mold opening cost, and combines high forming quality with industrial economy.

[0035] (2) The precision protection process for the ultra-thin-walled hollow component designed in this invention overcomes the problem of easy breakage when the aspect ratio is >10:1 and the single wall thickness is ≤3mm. It adopts segmented PTFE internal support combined with adhesive wax layer filling to compensate for deformation and eliminate resonance; elastic buffer layer clamps combined with multi-step pre-tightening to achieve linear stress distribution; circulating coolant wraps the component to absorb high-frequency vibration. This system makes the entire process free of tool chatter and micro-breakage, and the yield rate reaches 96%~100%, while traditional processes almost all fail.

[0036] (3) This invention constructs a low-damage fine grinding and micro-chamfering linkage process to optimize surface and electric field distribution. Graded grinding with 80#→600#→1200# resin grinding wheels, combined with decreasing grinding depth and feedless surface grinding, reduces surface microcrack density by more than 85%, Ra≤0.5μm, and flatness and parallelism≤0.03mm. CNC chamfering is performed directly after fine grinding to eliminate sharp corner charge concentration and ensure uniform electric field distribution. The PTFE internal support can be heated for demolding and reused, providing high process tolerance. Attached Figure Description

[0037] Figure 1 These are schematic diagrams of the top view, front view, and left view of the combined mold of the present invention; Figure 2 This is a schematic diagram of the structure of the vibration-damping support filling of the present invention; Figure 3 This is a top view schematic diagram of the liquid soft support vibration absorption system of the present invention; Figure 4 This is a cross-sectional schematic diagram of the liquid soft support vibration absorption system of the present invention; Figure 5 This is a schematic diagram of the product of the present invention.

[0038] Figure 1 In the middle: 101, alumina powder; 102, inner layer; 103, outer layer; 104, buffer layer; 105, insulating board; 106, micropores; 107, non-woven fabric layer; 108, base plate; 109, pin-type self-locking structure; 110, waterproof sealing tape; 111, visual ruler.

[0039] Figure 2 In the middle: 201, outer wall of ceramic sintered part; 202, inner wall of ceramic sintered part; 203, polytetrafluoroethylene block; 204, vibration damping through hole; 205, adhesive wax layer; 206, L-shaped wrapping clamp; 207, elastic gasket; 208, T-shaped wrapping clamp.

[0040] Figure 3 , Figure 4 In the middle: 301, magnetic worktable; 302, circulating coolant tank; 303, magnetic steel pad; 304, coolant; 305, parallel grinding wheel; 306, chamfer; 307, ceramic sintered part; 308, coolant inlet; 309, coolant outlet. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments.

[0042] like Figure 1 As shown, the combined mold used in step two of this invention includes a rigid structure, a composite sealing system, and a buffer structure. The rigid structure consists of a hollow cuboid shape formed by four insulating plates 105 surrounding and fixed, with a bottom plate 108 fixed at the bottom. The bottom plate is fixed to the insulating plates by a pin-type self-locking structure 109. The bottom plate 108 has symmetrically arranged L-shaped positioning self-locking slots on its outer edges, and the bottoms of the four insulating plates 105 are correspondingly provided with right-angle folded edge locking plates that match the self-locking slots. During assembly, physical locking is achieved by pushing the locking plates at the bottom of the insulating plates 105 horizontally or vertically into the self-locking slots of the bottom plate 108, eliminating the need for threaded connectors.

[0043] An inner layer 102 and an outer layer 103 are placed inside the square structure formed by the insulating plate 105 and the base plate 108. The inner layer 102 is a PE vacuum heat-sealed bag, and the outer layer 103 is a woven bag, which serve as a support to resist the compression of the mold assembly and prevent collapse. A buffer layer 104 is provided between the outer layer 103 and the inner wall of the insulating plate 105. The buffer layer 104 is made of pearl cotton sheets to eliminate the defect of ceramic parts with large length-to-width ratios being too thick in the middle and too thin at both ends during isostatic pressing. The buffer layer 104 is constructed by overlapping and bonding multiple layers of pearl cotton sheets with gradually changing axial length from the inside to the outside. Its specific configuration and installation structure are as follows: (1) Full height fit of the base layer: The first layer of pearl cotton sheet closest to the inner wall of the insulation board 105 has an axial length that is completely consistent with the height of the internal cavity of the insulation board 105. This layer of pearl cotton sheet is completely laid flat and bonded to the entire inner wall surface of the insulation board 105 from top to bottom with high-adhesion pressure-resistant double-sided adhesive tape to achieve reference fixation; (2) Gradual shortening of the axial length of subsequent layers: Starting from the first layer of pearl cotton sheet, the axial length of each subsequent layer of pearl cotton sheet decreases sequentially towards the outer layer 103. Each layer of pearl cotton sheet is aligned with the center line of the insulation board axial direction as a reference and is symmetrically stacked and bonded to the outside of the previous layer of pearl cotton sheet; (3) Gradient thickness molding: As the axial length of each outer layer of cotton sheet decreases sequentially, the total number of layers in the central region of the buffer layer 104 is the largest, with a total thickness of 6-8 mm in the middle. As the mold extends towards the upper and lower ends, the number of layers of pearl cotton decreases, with only a single base layer remaining at the two ends, and the thickness decreasing to 1.5-2 mm. Thus, an axial gradient buffer structure with a thick middle and thin ends, resembling an arc-shaped protrusion, is constructed inside the mold.

[0044] Under cold isostatic pressing high pressure environment, the thickest pearl cotton sheet in the middle provides the largest elastic compression displacement and pressure unloading, while the pearl cotton at both ends gradually thins out to provide a smaller unloading buffer. Thus, the thickness gradient can reverse the stress attenuation in the isostatic pressing isotropic mass transfer process, completely eliminating the dimensional defects of the billet being too thick in the middle and too thin at both ends.

[0045] Multiple micro-holes 106 are formed on the insulating plate 105, each with a diameter of φ3mm. The number of micro-holes is similar to a honeycomb pattern. A non-woven fabric layer 107 is attached to the inner wall of the insulating plate 105. A visual scale is provided on the insulating plate 105. The perforated parts of the insulating plate 105 are made visible. The visual scale 111 is a scale drawn from bottom to top on the outer insulating plate 105, which facilitates observation of the amount of material filled and facilitates standardization of dimensional pressing.

[0046] Both the inner layer 102 and the outer layer 103 are sealed with waterproof sealing tape 110. The inner layer 102 and the outer layer 103 are sealed independently. After the inner layer 102 is filled with alumina powder 101 in a PE vacuum heat-sealed bag and vacuumed, the opening of the inner layer is sealed with waterproof sealing tape 110 to prevent the leakage of fine granulated powder. Then, the entire inner layer 102 is inserted into the outer layer 103, and the opening of the outer layer is sealed again with waterproof sealing tape 110. Through this double-layer independent sealing, a double waterproof barrier is constructed during the high-pressure cold isostatic pressure mass transfer process, preventing both the infiltration of high-pressure water media into the powder and vacuum leakage.

[0047] In use, the above-mentioned combined mold is surrounded by four insulating plates 105, each engraved with a precise visual scale 111. The base plate 108, made of high-strength insulating material, forms a rigid frame using a pin-type self-locking structure 109. This mold eliminates traditional threaded connections, reducing assembly and disassembly time by more than 50%. It not only avoids frame wobbling caused by thread wear but also transforms uncontrollable powder compressibility into quantifiable powder loading height control through the visual scale 111, ensuring high consistency in green body dimensions. The four insulating plates, connected by micropores 106 and internally bonded with a non-woven fabric layer 107, create an efficient venting mechanism. The insulating plates 105 are machined with honeycomb-shaped venting micropores 106, and the non-woven fabric layer 107 is fixed to the inner wall of the insulating plates 105 with adhesive. The nonwoven fabric layer 107 is a medical-grade nonwoven fabric, which is laid flat and bonded to completely cover the entire inner surface of the insulating plate 105, forming a uniform laminar flow venting barrier. Compared to isolated venting holes, the nonwoven fabric layer 107 transforms point venting into surface venting, allowing gas deep within the powder to be rapidly guided laterally along the fiber gaps, ensuring no residual pores inside the green body. The inner layer 102 uses a PE bag, and the outer layer uses a woven bag layer for support, supplemented by waterproof sealing tape 110. The inner layer 102 is directly filled with alumina powder 101 as a direct contact layer. After filling, vacuum negative pressure is used to completely eliminate the risk of liquid media seeping in and contaminating the granulating powder, and significantly reduces surface crease defects caused by bag wrinkles, resulting in a smoother surface and reduced allowances in subsequent processing. The outer layer 103 provides mechanical strength to prevent sharp powder or mold edges from puncturing the sealing layer. Both layers are sealed with dedicated waterproof sealing tape. By constructing a multi-level waterproof protection system, the powder material is protected from contamination and water ingress under high pressure conditions of over 100MPa.

[0048] All of the following embodiments use the above-described combined mold, and the mold size is set to correspond to the size of the ceramic part. Honeycomb micropores 106 are formed on the insulating plate 105, and the diameter of the micropores 106 is set to φ3mm.

[0049] like Figure 2As shown, the ceramic sintered part of the present invention includes an outer wall 201 and an inner wall 202. The vibration-damping support filling structure includes a polytetrafluoroethylene block 203, and L-shaped wrapping clamps 206 at the four corners of the outer wall of the ceramic sintered part and T-shaped wrapping clamps 208 along the length of the outer wall. The number of T-shaped wrapping clamps 208 is arranged every 150~200mm on both sides of the outer wall. An elastic gasket 207 is also provided between the L-shaped wrapping clamps 206 and the outer wall 201 of the ceramic sintered part.

[0050] The elastic gasket 207 is made of a single layer of polyurethane elastomer material with a Shore hardness of 80A~90A. Its geometry matches and fully adheres to the inner workpiece contact surfaces of the L-shaped wrapping clamp 206 and the T-shaped wrapping clamp 208, and is fixed to the inside of the clamps by wear-resistant double-sided adhesive. Its thickness is 1.5~2.5mm. During clamping, it utilizes its own lateral and axial elastic deformation to discretize the concentrated stress of traditional rigid clamps, automatically compensate for the small deformations on the surface of the ceramic sintered parts, and prevent the generation of pre-added seamless internal cracks due to point stress concentration.

[0051] A polytetrafluoroethylene block 203 is placed in the inner cavity of the ceramic sintering part. An adhesive wax layer 205 is provided between the polytetrafluoroethylene block 203 and the inner wall 202 of the ceramic sintering part. Multiple vibration damping through holes 204 are opened on the polytetrafluoroethylene block 203.

[0052] The axial length of the PTFE block 203 is 40-50mm, and its radial height needs to be cut according to the actual internal cavity size of the product, leaving a 2-4mm allowance (i.e., a radial gap of 1-2mm on each side). The allowance is then filled with the adhesive wax layer 205. Before use, the PTFE block 203 is drilled with vibration-damping through holes 204 and deburred. One to two φ3-φ5mm vibration-damping through holes 204 (through holes) are drilled per square centimeter. This structure can further release stress, change the natural frequency of the support system, avoid resonance between the excitation force generated by the grinding wheel speed and the workpiece, and prevent the edges of the through holes from being too sharp, which would transmit non-uniform pressure to the inner wall of the ceramic and cause internal cracks.

[0053] Based on the shape and internal cavity dimensions of the ceramic sintered part 307, when filling the internal cavity with polytetrafluoroethylene blocks 203, the number and spacing of these blocks can be flexibly adjusted according to the actual length of the ceramic part. By adjusting the rigidity in segments, edge chipping defects during grinding can be eliminated.

[0054] First working condition: When the total length of the ceramic part is in the range of 300~500mm (corresponding to an inner cavity length of 294~494mm and a single side wall thickness of ≤3mm), the arrangement of the support blocks is denser in the front and sparser in the back. 1. Grinding wheel cutting-in end (within the initial 100 mm range): Since the impact load at the moment when the grinding wheel first cuts into hard and brittle ceramics is the largest, it is extremely easy to cause strong local chatter and edge disintegration. Dense support needs to be implemented in this area. The spacing between the polytetrafluoroethylene blocks (denoted as L1) is reduced to 30 - 50 mm to provide sufficient rigid limitation for the thin-walled part with weak rigidity at the cutting-in end; 2. Conventional support area in the middle and rear part: When the grinding wheel cuts in smoothly and enters the normal grinding stage, the cutting force significantly tends to be stable. At this time, the support density can be appropriately relaxed, and the spacing between the polytetrafluoroethylene blocks (denoted as L2) is expanded to 60 - 80 mm.

[0055] Through this non-uniform distribution with dense front and sparse rear (i.e., spacing L1 < L2), the internal cavity support stiffness is matched with the processing stress.

[0056] The second working condition: When the total length of the ceramic part is in the ultra-long part range of 500 - 1000 mm (corresponding internal cavity length is 494 - 994 mm, and the single-side side wall thickness ≤ 3 mm). Due to the excessive length-width ratio of such ultra-long parts, overall resonance and brittle fracture are extremely likely to occur during machining on a surface grinder. Therefore, the arrangement of the internal polytetrafluoroethylene blocks 203 must adopt a three-segment asymmetric support structure with dense ends and uniform distribution in the middle: 1. Initial cutting-in area (within the first 150 mm range): As the impact surface that first bears the impact of the grinding wheel, the support spacing L1 is reduced to the minimum, strictly controlled within 30 - 45 mm, and the amplitude at the initial stage of processing is forcibly suppressed through high-density close arrangement; 2. Middle stable area (middle part): The middle axial area after deducting both ends. The grinding system has entered a stable state, and the support spacing L2 is expanded to 80 - 100 mm to ensure the basic support stiffness.

[0057] 3. Final cutting-out area (within the last 100 mm range at the rear end): At the moment when the grinding wheel is about to cut out the ceramic part, since there is no support from the base material at the rear, the edge is extremely likely to occur tearing-type corner breakage. Therefore, local encryption is carried out again at the end, and the support spacing L3 is reduced to 45 - 60 mm to provide sufficient anti-tearing rigid support for the edge at the cutting-out end.

[0058] Under the working condition of processing ultra-long parts, the polytetrafluoroethylene blocks 203 in the entire internal cavity finally show a gradient arrangement state with dense ends and sparse middle (i.e., spacing L1 < L3 < L2), thus forming a rigid protection network in the internal cavity that can dynamically resist grinding impact.

[0059] During use, Figure 2Polytetrafluoroethylene (PTFE) block 203 is filled into the inner cavity of the ceramic sintered part, making the radial dimension of PTFE block 203 2-4 mm smaller than the actual inner cavity dimension. A 1-2 mm radial gap on each side is filled using an adhesive wax layer 205 (molten adhesive wax at 60-70℃ with 5%-8% talc powder added by weight of the adhesive wax). The addition of talc powder enhances lubrication, reduces friction, and prevents stress scratches on the inner wall caused by thermal expansion or grinding friction. The fluid properties of the adhesive wax layer achieve full-contact conformal support, perfectly compensating for minor internal cavity tapers or irregular deformations of the ceramic after sintering, ensuring a uniform mixed coating.

[0060] After filling, the ceramic sintered parts undergo precision surface grinding and CNC precision chamfering. The ceramic sintered parts are first fixed using a distributed clamping system. This system, employing a rigid frame and elastic interface, specifically involves wrapping the surfaces of the L-shaped and T-shaped clamps 206 with elastic gaskets of the same material on their contact surfaces with the ceramic. This hardness range provides both flexible protection and automatic compensation for minor surface irregularities in the blank, while also possessing sufficient static rigidity to prevent micro-displacement of the workpiece under grinding pressure, which could affect its flatness and straightness. L-shaped clamps 206 are clamped at the four corners of the ceramic sintered parts, and T-shaped clamps 208 are wrapped around the outer walls on both sides every 150-200 mm. During clamping, a multi-step pre-tightening method is adopted in conjunction with a digital torque wrench: The rated clamping torque is set to M. First, all clamps are pre-tightened to 0.3~0.5M. The second step involves a symmetrical tightening method extending from the center to both ends, starting from the central T-clamp and tightening towards both ends to 0.6~0.8M. The third step reaches the full load torque M. This multi-step symmetrical pre-tightening effectively prevents pre-existing arched displacement during clamping, ensuring that the parallelism and straightness after fine grinding achieve a linear stress distribution.

[0061] like Figures 3 to 4As shown, the liquid soft support vibration absorption system includes a magnetic worktable 301 for ceramic sintering parts, a circulating coolant tank 302, and magnetic steel pads 303. A circulating coolant tank 302 is mounted on the magnetic worktable 301. The circulating coolant tank 302 has coolant inlets 308 and coolant outlets 309 at both ends. The depth of the hollow interior of the circulating coolant tank 302 is 1 / 2 to 1 / 3 of the height of the ceramic sintering part 307. The circulating coolant tank 302 is an open, rigid tank structure with an open top and a hollow interior. The cross-section of the circulating coolant tank 302 is rectangular. The internal cavity dimensions of the tank are designed to follow the external dimensions of the ceramic sintering part to be processed and its fixture assembly: the length and width of the internal cavity are 20-50 mm larger than the overall structure after assembly and clamping, ensuring that the ceramic sintering part can be completely submerged in the tank, with sufficient fluid circulation clearance around it. The height is 1 / 2 to 3 of the height of the ceramic part, and the tank is filled with coolant. The circulating coolant tank 302 has an integrated coolant inlet and outlet at both ends of its longitudinal direction. To ensure rigidity and corrosion resistance, the tank body of the circulating coolant tank 302 is made of high-density polyethylene.

[0062] The ceramic sintered part 307 is placed at the bottom of the circulating coolant tank 302. The sintered part is fixed by the magnetic L and T-shaped clamps mentioned above. The long axis of the sintered part is consistent with the grinding forward direction.

[0063] The circulating coolant tank 302 is fixed to the magnetic worktable 301 on its outer bottom surface by magnetic steel pads 303. The magnetic steel pads 303 are bonded to the outer bottom surface of the circulating coolant tank 302. The circulating coolant tank 302 is filled with coolant 304. The coolant is a conventional coolant in the art and will not be explained further. Multiple equilateral triangular magnetic steel pads 303 (made of Q235 steel) with a side length of 50mm and a thickness of 10mm are fixed to the outer bottom surface of the circulating coolant tank 302. Utilizing their excellent magnetic conductivity, the entire circulating coolant tank 302 is firmly electromagnetically adsorbed and positioned on the magnetic worktable of the surface grinder.

[0064] In operation, a circulating coolant tank 302, with a height of 1 / 2 to 1 / 3 of the ceramic sintered part's height, is installed on the magnetic worktable of the precision surface grinder. The ceramic sintered part, encased in a clamp, is fixed to the bottom of the circulating coolant tank 302, ensuring that the long axis of the ceramic sintered part is aligned with the grinding direction. Four to six magnetic steel pads 303 are adhered to the outer bottom of the circulating coolant tank 302. The tank is then firmly attached to the magnetic worktable using the surface grinder's magnetic attraction switch, ensuring the ceramic part remains horizontal. The circulating coolant tank 302 is then filled with coolant 304. This liquid soft support changes the physical environment of the ceramic sintered part from air contact to liquid encapsulation, enhancing heat conduction while absorbing mechanical vibrations generated during grinding from all directions. This protects fragile parts such as 90° sharp corners from micro-chipping, significantly reducing grinding damage.

[0065] Throughout the entire surface grinding process, a flowing coolant cooling system is used. During grinding, the coolant pressure is maintained at 0.25~0.35MPa, the flow rate is controlled at no less than 10L / min, and the coolant temperature is strictly controlled at 15~25℃. This system can quickly remove grinding heat, preventing micro-cracks caused by heat in the ceramic, and effectively flush away grinding debris, preventing wheel clogging and secondary scratches. After surface grinding, the surface roughness, parallelism, and flatness of the ground product are measured using a contact roughness meter and a coordinate measuring machine. To avoid scratching the product, an ultra-fine diamond probe and extremely light measuring force are required when measuring roughness. Appearance: Visually inspect the product at a specific angle under high-brightness white light or a dedicated observation lamp to ensure there are no scratches, color differences, impurities, or other macroscopic defects. Through the above-mentioned multi-stage low-damage surface grinding process, the density of microcracks on the ceramic surface is reduced by more than 85%, and the electrical breakdown strength is increased by more than 20%, ensuring the long-term stable operation of ceramic sintered parts under high voltage and high frequency electric fields.

[0066] When performing CNC machining, the following methods are used: Figure 4 The ceramic sintered part 307 is machined using a parallel grinding wheel 305. The chamfer on the chamfer is an electroplated diamond-coated chamfer 306 to ensure the sharpness and wear resistance of the electroplated diamond-coated chamfering tool. The chamfering is performed on a high-precision CNC machining center with a spindle speed controlled at 15,000~20,000 rpm and a feed rate of 50~100 mm / min.

[0067] After all the above processing is completed, taking advantage of the low melting point of the adhesive wax layer 205, the entire assembly is placed in an oven at 120~130℃ to melt and flow out the adhesive wax layer. The polytetrafluoroethylene block 203 is recycled and reused, achieving non-destructive demolding. Subsequently, the ceramic part is immersed in dewaxing water at approximately 60℃ for ultrasonic cleaning, which removes residual microscopic thermal stress formed on the ceramic surface due to thermal expansion and contraction while cleaning. The adhesive wax layer is an industrial adhesive wax with a certain amount of talc added.

[0068] Example 1 The ceramic insulating part processed in this embodiment has a length of 300mm and a width of 50mm, i.e., a length-to-width ratio of 6:1, a height of 20mm, an inner cavity dimension of 294mm and a width of 44mm, and a parallel thin wall thickness of 3mm. Its finishing method includes the following steps: Step 1: Raw material preparation: Select alumina granulated powder with a purity of 99.8wt% and a D90 of 0.8μm. Use hot air drying process to dry the powder at 110℃ for 2 hours. After treatment, the moisture content of the powder is 0.02%.

[0069] Step 2, Cold Isostatic Pressing: The dried powder is filled into... Figure 1 The alumina green billet is cold isostatically pressed in a combined mold with a pressing pressure of 110 MPa and a holding time of 450 s. After demolding, the green billet is obtained.

[0070] Step 3: Graded Degreasing and High-Temperature Sintering: The alumina green blank is hollowly milled to form an internal cavity, with a rough parallel wall thickness of 3.6mm. It then undergoes graded variable-temperature sintering. The formed green blank is degreased and densified through graded heating. The specific sintering curves are as follows: First stage: Heat to 700℃ at a rate of 20℃ / h and hold for 3.5h for degreasing; Second stage: Continue heating at a rate of 40℃ / h to 900℃ to remove residues and obtain intermediate billet; The third stage: the temperature was increased to 1560℃ at a rate of 25℃ / h and held at that temperature for 3.5h for dense sintering. After cooling, a bulk density of 3.96 g / cm³ was obtained. 3 Ceramic sintered parts.

[0071] Step 4, adopt as follows Figure 2 The vibration-damping support filling structure shown is a ceramic sintered part, with T-shaped wrapping clamps 208 installed every 150mm on both outer walls. Based on the arrangement pattern of the first working condition, the polytetrafluoroethylene blocks 203 in the inner cavity are arranged in a two-stage non-uniform pattern, denser at the front and sparser at the back. 1. Grinding wheel cutting end (within 100mm of the beginning): The placement spacing between the polytetrafluoroethylene blocks 203 is set to the first spacing L1=35mm, and local dense support is implemented; 2. Rear-Middle Conventional Support Area: The spacing between the PTFE blocks 203 is increased to a second spacing L2 = 65mm. The axial length of each PTFE block 203 is uniformly 42mm, and its radial height is cut according to the actual dimensions of the inner cavity, with a 2mm filling allowance reserved on each side. A 3mm diameter vibration-damping through hole is opened within each square centimeter and deburred. After the support blocks are arranged, a molten adhesive wax layer at 65℃ (containing 5wt% talc powder of industrial adhesive wax) is injected into the reserved 2mm allowance and allowed to solidify naturally. When clamping, a multi-step pre-tightening method is adopted in conjunction with a digital torque wrench: set the rated clamping torque to M (15 N·m), first pre-tighten all clamps to 0.3 M (4.5 N·m); the second step is to adopt a symmetrical tightening method extending from the middle to both ends, starting from the central T-shaped wrapping clamp and clamping to both ends to 0.6 M (9 N·m); the third step is to reach the full load torque M (15 N·m).

[0072] Precision surface grinding with low damage is achieved through a multi-stage grinding system for fine grinding of the ceramic sintered parts. This system consists of three stages: rough grinding, semi-fine grinding, and fine grinding. The entire process is coordinated with liquid cooling and chip control. The coolant pressure is maintained at 0.3 MPa, the flow rate at 10 L / min, and the temperature at 20℃. After processing, the surface roughness Ra of the ceramic sintered parts is ≤0.5 μm, flatness ≤0.03 mm, and parallelism ≤0.03 mm. Specifically: Rough grinding stage: Select a ceramic bonded parallel grinding wheel with a grit size of 80#, set the grinding wheel speed Vs=18m / s, the table speed Vw=15m / min, the single grinding depth ap=0.05mm, and control the surface roughness to Ra≤1.6μm after grinding; Semi-finish grinding stage: Select a resin-bonded parallel grinding wheel with a grit size of 600#, set the grinding wheel speed Vs=20m / s, the table speed Vw=18m / min, the single grinding depth ap=0.03mm, and control the surface roughness to Ra≤0.8μm after grinding; Fine grinding stage: A resin-bonded parallel grinding wheel with a grit size of 1200# is selected for final fine grinding. The grinding wheel speed is set to Vs=23m / s and the table speed is set to Vw=20m / min. The depth of grinding in a single pass is gradually reduced from 0.005mm to 0.002mm. Finally, a no-feed polishing surface grinding is performed to make the surface roughness Ra≤0.5μm.

[0073] A circulating coolant tank 302, with a height equal to half the height of the ceramic part, is installed on the magnetic worktable of a precision surface grinder. Figures 3 to 4 As shown, the circulating coolant tank 302 is filled with coolant, and two magnetic steel pads 303 are attached to each side of the bottom outer side of the circulating coolant tank 302.

[0074] Step 5: Perform CNC precision chamfering on the product after precision surface grinding. Use a 120# diamond chamfering tool on a CNC machining center; control the spindle speed of the CNC machining center at 15000 rpm, the feed rate at 50 mm / min, the chamfer angle at 30°, and the chamfer depth at 1.0 mm. Use a pouring liquid cooling system during machining.

[0075] After all the above processing is completed, the integral ceramic part with the internal vibration-damping support filling structure is placed in a 130℃ oven to melt and flow out the adhesive wax layer. The polytetrafluoroethylene block 203 is recycled and reused. Then, the ceramic part is immersed in 60℃ dewaxing water for ultrasonic cleaning and natural drying to obtain a hollow thin-walled ceramic insulation part.

[0076] Example 2 The ceramic insulating part processed in this embodiment has a length of 780mm and a width of 65mm, i.e., a length-to-width ratio of 12:1, a height of 40mm, an inner cavity size of 775mm × 60mm, and a parallel thin wall thickness of 2.5mm. Its finishing method includes the following steps: Step 1: Raw material preparation: Select alumina granulated powder with a purity of 99.8wt% and a D90 of 0.8μm. Use hot air drying process to dry the powder at 100℃ for 3 hours. After treatment, the moisture content of the powder is controlled to be 0.01%.

[0077] Step 2, Cold Isostatic Pressing: The dried powder is filled into... Figure 1 The alumina green billet is formed by cold isostatic pressing in a combined mold with a pressing pressure of 100 MPa and a holding time of 600 s. After demolding, the green billet is obtained.

[0078] Step 3: Graded Degreasing and High-Temperature Sintering: The alumina green blank is hollowly milled to form an internal cavity, with a rough parallel wall thickness of 3mm. Graded variable-temperature sintering is then performed. The formed green blank undergoes degreasing and densification sintering through graded heating. The specific sintering curves are as follows: First stage: Heat to 700℃ at a rate of 15℃ / h and hold for 4 hours for degreasing; Second stage: Continue heating at a rate of 30℃ / h to 900℃ to remove residues and obtain intermediate billet; The third stage: the temperature was increased to 1540℃ at a rate of 20℃ / h and held for 4 hours for dense sintering. After cooling, a bulk density of 3.95 g / cm³ was obtained. 3 Ceramic sintered parts.

[0079] Step 4, adopt as follows Figure 2The vibration-damping support filling structure shown is for ceramic sintered parts. The T-shaped wrapping clamps 208 are installed every 200mm on both outer walls. Because this part is an extra-long component, the polytetrafluoroethylene blocks 203 in the inner cavity are arranged in a three-section structure with denser ends and evenly distributed in the middle. 1. Initial cutting area (within the first 150mm): The support spacing between the polytetrafluoroethylene blocks is set to the minimum first spacing L1=40mm; 2. Middle stable zone (the middle section after deducting the two ends): The support spacing between the polytetrafluoroethylene blocks is enlarged to a second spacing L2=90mm; 3. End Cut-out Area (Last 100mm of the rear section): The support spacing between the PTFE blocks is tightened to a third spacing L3 = 50mm to suppress edge tearing during cutting. The axial length of the PTFE block 203 is uniformly 40mm, and its radial height is cut according to the actual size of the inner cavity, with a 1.5mm gap on each side. A 3mm diameter vibration-damping through hole is opened within each square centimeter and deburred. After the support blocks are arranged, a molten adhesive wax layer (containing 5wt% talc) at 65℃ is injected into the 1.5mm gap on each side and allowed to solidify naturally. When clamping, a multi-step pre-tightening method is adopted in conjunction with a digital torque wrench: set the rated clamping torque to M (18 N·m), first pre-tighten all clamps to 0.3 M (5.4 N·m); the second step is to adopt a symmetrical tightening method extending from the middle to both ends, starting from the central T-shaped wrapping clamp and clamping towards both ends to 0.7 M (12.6 N·m); the third step is to reach the full load torque M (18 N·m).

[0080] Precision surface grinding with low damage is achieved through a multi-stage grinding system for fine grinding of the ceramic sintered parts. This system consists of three stages: rough grinding, semi-fine grinding, and fine grinding. The entire process is coordinated with liquid cooling and chip control. The coolant pressure is maintained at 0.3 MPa, the flow rate at 10 L / min, and the temperature at 20℃. After processing, the surface roughness Ra of the ceramic sintered parts is ≤0.5 μm, flatness ≤0.03 mm, and parallelism ≤0.03 mm. Specifically: Rough grinding stage: Select a ceramic bonded parallel grinding wheel with a grit size of 80#, set the grinding wheel speed Vs=18m / s, the table speed Vw=15m / min, the single grinding depth ap=0.06mm, and control the surface roughness Ra≤1.6μm after grinding; Semi-finish grinding stage: Select a resin-bonded parallel grinding wheel with a grit size of 600#, set the grinding wheel speed Vs=22m / s, the table speed Vw=18m / min, the single grinding depth ap=0.04mm, and control the surface roughness Ra≤0.8μm after grinding; Fine grinding stage: A resin-bonded parallel grinding wheel with a grit size of 1200# is selected for final fine grinding. The grinding wheel speed is set to Vs=25m / s and the table speed is set to Vw=20m / min. The depth of grinding in a single pass is gradually reduced from 0.005mm to 0.002mm. Finally, three passes of non-feed polishing surface grinding are performed to achieve a surface roughness of Ra≤0.5μm.

[0081] A circulating coolant tank 302 with a height of 20mm is installed on the magnetic worktable of the precision surface grinder. Figures 3 to 4 As shown, the circulating coolant tank 302 is filled with coolant, and four magnetic steel pads 303 are attached to the bottom outside of the circulating coolant tank 302.

[0082] Step 5: Perform CNC precision chamfering on the product after precision surface grinding. Use a 120# electroplated diamond-coated chamfering tool on a CNC machining center; control the spindle speed of the CNC machining center at 15000 rpm, the feed rate at 80 mm / min, the chamfer angle at 30°, and the chamfer depth at 2.0 mm. Use a pouring liquid cooling system during machining.

[0083] After all the above processing is completed, the integral ceramic part with the internal anti-vibration support filling structure is placed in a 120℃ oven to melt and flow out the adhesive wax layer. The polytetrafluoroethylene block 203 is recycled and reused. Then, the ceramic part is immersed in 60℃ dewaxing water for ultrasonic cleaning and natural drying to obtain a hollow thin-walled ceramic insulation part.

[0084] Example 3 The ceramic insulating part processed in this embodiment is 600mm long × 40mm wide, with an aspect ratio of 15:1 and a height of 35mm; its internal cavity dimensions are 594mm long × 34mm wide, and the thickness of the parallel thin walls on both sides is 3.0mm. Figure 5 As shown, its finishing method includes the following steps: Step 1: Raw material preparation: Select alumina granulated powder with a purity of 99.8wt% and a D90 of 0.8μm. Use hot air drying process to dry the powder at 130℃ for 1 hour. After treatment, the moisture content of the powder is controlled to be 0.015%.

[0085] Step 2, Cold Isostatic Pressing: The dried powder is filled into... Figure 1 The alumina green billet is formed by cold isostatic pressing in a combined mold with a pressing pressure of 120 MPa and a holding time of 300 s. After demolding, the green billet is obtained.

[0086] Step 3: Graded Degreasing and High-Temperature Sintering: The alumina green blank is hollowly milled to form an internal cavity, with a rough parallel wall thickness of 3.6mm. It then undergoes graded variable-temperature sintering. The formed green blank is degreased and densified through graded heating. The specific sintering curves are as follows: First stage: Heat to 700℃ at a rate of 25℃ / h and hold for 3 hours for degreasing; Second stage: Continue heating at a rate of 50℃ / h to 900℃ to remove residue and obtain intermediate billet; The third stage: the temperature is increased to 1560℃ at a rate of 30℃ / h and held at that temperature for 3h to achieve dense sintering. After cooling, a bulk density of ≥3.97g / cm³ is obtained. 3 Ceramic sintered parts.

[0087] Step 4, adopt as follows Figure 2 The vibration-damping support filling structure shown is a ceramic sintered part. The T-shaped wrapping clamps 208 are installed every 180mm on both outer walls. The axial length of the PTFE block 203 is 47mm. Because this part is an extra-long component, the PTFE blocks 203 in the inner cavity are arranged in a three-segment asymmetric gradient structure. 1. Initial cutting area (within the first 150mm): The support blocks are continuously and tightly filled, and the placement spacing is set to the first spacing L1=40mm; 2. Middle Stable Zone (Middle Section): The spacing between the support blocks is increased to a second spacing L2 = 90mm; 3. End Cut-out Area (Last 100mm of the rear section): The spacing between the support blocks is tightened again to a third spacing L3 = 55mm. The axial length of the polytetrafluoroethylene block 203 is uniformly 47mm, and its radial height is cut according to the actual size of the inner cavity with a 2mm filling allowance. Before use, two 4mm diameter vibration-damping through holes are opened per square centimeter and deburred. After the support blocks are arranged, a molten adhesive wax layer at 70℃ (containing 8wt% talc) is injected into the reserved 2mm allowance and allowed to solidify naturally. When clamping, a multi-step pre-tightening method is adopted in conjunction with a digital torque wrench: set the rated clamping torque to M (16 N·m), first pre-tighten all clamps to 0.4 M (6.4 N·m); the second step is to adopt a symmetrical tightening method extending from the middle to both ends, starting from the central T-shaped wrapping clamp and clamping towards both ends to 0.8 M (12.8 N·m); the third step is to reach the full load torque M (16 N·m).

[0088] Precision surface grinding with low damage is achieved through a multi-stage grinding system for fine grinding of the ceramic sintered parts. This system consists of three stages: rough grinding, semi-finish grinding, and finish grinding. The entire process is coordinated with liquid cooling and chip control. The coolant pressure is maintained at 0.3 MPa, the flow rate at 10 L / min, and the temperature at 18℃. After processing, the surface roughness Ra of the ceramic sintered parts is ≤0.5 μm, flatness ≤0.03 mm, and parallelism ≤0.03 mm. Specifically: Rough grinding stage: Select a ceramic bonded parallel grinding wheel with a grit size of 80#, set the grinding wheel speed Vs=20m / s, the table speed Vw=18m / min, the single grinding depth ap=0.05mm, and control the surface roughness Ra≤1.6μm after grinding; Semi-finish grinding stage: Select a resin-bonded parallel grinding wheel with a grit size of 600#, set the grinding wheel speed Vs=22m / s, the table speed Vw=18m / min, the single grinding depth ap=0.03mm, and control the surface roughness Ra≤0.8μm after grinding; Fine grinding stage: A resin-bonded parallel grinding wheel with a grit size of 1200# is selected for final fine grinding. The grinding wheel speed is set to Vs=24m / s and the table speed is set to Vw=20m / min. The depth of grinding in a single pass is gradually reduced from 0.005mm to 0.002mm. Finally, two feedless polishing-type surface grindings are performed to achieve a surface roughness of Ra≤0.5μm.

[0089] A circulating coolant tank 302 with a height of 20mm is installed on the magnetic worktable of the precision surface grinder. Figures 3 to 4 As shown, the circulating coolant tank 302 is filled with coolant, and four magnetic steel pads 303 are attached to the bottom outside of the circulating coolant tank 302.

[0090] Step 5: Perform CNC precision chamfering on the product after precision surface grinding. Use an electroplated diamond-coated chamfering tool on a CNC machining center with a grit size of 120#. The spindle speed of the CNC machining center is controlled at 18000 rpm, the feed rate is 70 mm / min, the chamfer angle is 30°, and the chamfer depth is 1.5 mm. Liquid cooling is used during machining.

[0091] After all the above processing is completed, the integral ceramic part with the internal vibration-damping support filling structure is placed in a 125℃ oven to melt and flow out the adhesive wax layer. The polytetrafluoroethylene block 203 is recycled and reused. Then, the ceramic part is immersed in 60℃ dewaxing water for ultrasonic cleaning and natural drying to obtain a hollow thin-walled ceramic insulation part.

[0092] Example 4 The ceramic insulating part processed in this embodiment is 1000mm long and 40mm wide, with an aspect ratio of 25:1 and a height of 50mm; its internal cavity dimensions are 994mm long and 34mm wide, and the thickness of the parallel thin walls on both sides is 3mm. Its finishing method includes the following steps: Step 1: Raw material preparation: Select alumina granulated powder with a purity of 99.8wt% and a D90 of 0.8μm. Use hot air drying process to dry the powder at 120℃ for 2 hours. After treatment, the moisture content of the powder is 0.02%.

[0093] Step 2, Cold Isostatic Pressing: The dried powder is filled into... Figure 1 The alumina green billet is cold isostatically pressed in a combined mold with a pressing pressure of 115 MPa and a holding time of 400 s. After demolding, the green billet is obtained.

[0094] Step 3: Graded Degreasing and High-Temperature Sintering: The alumina green blank is hollowly milled to form an internal cavity, with a rough parallel wall thickness of 3.6mm. It then undergoes graded variable-temperature sintering. The formed green blank is degreased and densified through graded heating. The specific sintering curves are as follows: First stage: Heat to 700℃ at a rate of 20℃ / h and hold for 3.5h for degreasing; Second stage: Continue heating at a rate of 40℃ / h to 900℃ to remove residues and obtain intermediate billet; The third stage: the temperature was increased to 1550℃ at a rate of 25℃ / h and held at that temperature for 3.5h for dense sintering. After cooling, a bulk density of 3.96 g / cm³ was obtained. 3 Ceramic sintered parts.

[0095] Step 4: Clamp the ceramic sintered part using a vibration-damping support filling structure. The T-shaped wrapping clamps are symmetrically arranged at equal intervals of 200mm on both sides of the outer wall of the ceramic sintered part. Due to the extremely large length-to-width ratio of this part, the risk of chatter during mechanical grinding is extremely high. Therefore, the internal polytetrafluoroethylene blocks 203 are precisely arranged in three sections along the entire length: 1. Initial cutting area (within the first 150mm): The placement spacing between polytetrafluoroethylene blocks is set to the minimum first spacing L1=35mm, and a high-density arrangement is implemented; 2. Middle Stable Zone (Middle Section): The spacing between the PTFE blocks is increased to a second spacing L2=85mm, leaving ample space for flexible support. 3. End Cut-out Area (Last 100mm of the Rear Section): The spacing between the PTFE blocks is set to a third spacing L3 = 50mm to enhance the rigidity against brittle fracture at the tail. The axial length of the PTFE blocks 203 is uniformly 50mm, and their radial height is cut according to the actual size of the inner cavity, with a 2mm filling allowance on each side. A 3mm diameter vibration damping through hole is opened within each square centimeter and deburred. After the arrangement is completed, a molten adhesive wax layer (containing 6wt% talc) at 60℃ is injected into the 2mm allowance area on each side and allowed to cool and solidify naturally, forming a combined rigid and flexible vibration damping layer. When clamping, a multi-step pre-tightening method is adopted in conjunction with a digital torque wrench: set the rated clamping torque to M (20 N·m), first pre-tighten all clamps to 0.3 M (6 N·m); the second step is to adopt a symmetrical tightening method extending from the middle to both ends, starting from the central T-shaped wrapping clamp and clamping to both ends to 0.6 M (12 N·m); the third step is to reach the full load torque M (20 N·m).

[0096] Precision surface grinding with low damage is achieved through a multi-stage grinding system for fine grinding of the ceramic sintered parts. This system consists of three stages: rough grinding, semi-fine grinding, and fine grinding. The entire process is coordinated with liquid cooling and chip control. The coolant pressure is maintained at 0.3 MPa, the flow rate at 10 L / min, and the temperature at 20℃. After processing, the surface roughness Ra of the ceramic sintered parts is ≤0.5 μm, flatness ≤0.03 mm, and parallelism ≤0.03 mm. Specifically: Rough grinding stage: Select a ceramic bonded parallel grinding wheel with a grit size of 80#, set the grinding wheel speed Vs=19m / s, the table speed Vw=16m / min, the single grinding depth ap=0.06mm, and control the surface roughness Ra≤1.6μm after grinding; Semi-finish grinding stage: Select a resin-bonded parallel grinding wheel with a grit size of 600#, set the grinding wheel speed Vs=21m / s, the table speed Vw=18m / min, the single grinding depth ap=0.04mm, and control the surface roughness Ra≤0.8μm after grinding; Fine grinding stage: A resin-bonded parallel grinding wheel with a grit size of 1200# is selected for final fine grinding. The grinding wheel speed is set to Vs=23m / s and the table speed is set to Vw=20m / min. The depth of grinding in a single pass is gradually reduced from 0.005mm to 0.002mm. Finally, three passes of non-feed polishing surface grinding are performed to achieve a surface roughness of Ra≤0.5μm.

[0097] A circulating coolant tank 302 with a height of 25mm is installed on the magnetic worktable of the precision surface grinder. Figures 3 to 4As shown, the circulating coolant tank 302 is filled with coolant, and six magnetic steel pads 303 are attached to the bottom outside of the circulating coolant tank 302.

[0098] Step 5: Perform CNC precision chamfering on the product after precision surface grinding. Use an electroplated diamond-coated chamfering tool on a CNC machining center with a grit size of 120#. The spindle speed of the CNC machining center is controlled at 20,000 rpm, the feed rate is 100 mm / min, the chamfer angle is 30°, and the chamfer depth is 2.0 mm. Liquid cooling is used during machining.

[0099] After all the above processing is completed, the integral ceramic part with the internal vibration-damping support filling structure is placed in a 130℃ oven to melt and flow out the adhesive wax layer. The polytetrafluoroethylene block 203 is recycled and reused. Then, the ceramic part is immersed in 60℃ dewaxing water for ultrasonic cleaning and natural drying to obtain a hollow thin-walled ceramic insulation part.

[0100] Comparative Example 1 The ceramic insulating part machined in this comparative example is 500mm long and 50mm wide, with an aspect ratio of 10:1 and a height of 50mm. Its internal cavity dimensions are 444mm long and 34mm wide, with 3mm thick parallel thin walls on both sides. The finishing method includes the following steps: Step 1: Raw material preparation: Select alumina granulated powder with a purity of 99.8wt% and a D90 of 0.8μm. Use hot air drying process to dry the powder at 120℃ for 2 hours. After treatment, the moisture content of the powder is 0.03%.

[0101] Step 2, Cold Isostatic Pressing: The dried powder is filled into a traditional polyurethane mold for cold isostatic pressing. The pressing pressure is 110MPa and the holding time is 450s. After demolding, alumina green blanks are obtained.

[0102] Step 3: Graded Degreasing and High-Temperature Sintering: The alumina green blank is hollowly milled to form an internal cavity, with a rough parallel wall thickness of 3.6mm. It then undergoes graded variable-temperature sintering. The formed green blank is degreased and densified through graded heating. The specific sintering curves are as follows: First stage: Heat to 700℃ at a rate of 25℃ / h and hold for 3.5h for degreasing; Second stage: Continue heating at a rate of 45℃ / h to 900℃ to remove residues and obtain intermediate billet; The third stage: the temperature was increased to 1550℃ at a rate of 40℃ / h and held at that temperature for 3.5h for dense sintering. After cooling, a bulk density of 3.95g / cm³ was obtained. 3 Ceramic sintered parts.

[0103] Step 4: No internal support is built (the inner cavity is completely suspended). Without using a clamp with an elastic buffer layer and a circulating coolant tank, the hollow ceramic part is directly clamped onto a magnetic worktable using a hard metal vise and directly ground in an air-exposed environment.

[0104] Results: During the rough grinding stage, the ceramic part experienced severe high-frequency tremor when the grinding wheel cut in, due to the empty cavity and a wall thickness of only 3mm. The edge of the cutting end immediately fractured macroscopically over a large area. When grinding to the middle, under the superposition of mechanical vibration and local thermal stress, a transverse penetrating fracture occurred directly, resulting in a yield of 0%. Subsequent indicators could not be measured.

[0105] The products prepared in the above examples and comparative examples were subjected to performance testing, and the test results are shown in Table 1.

[0106] Bulk density and apparent porosity: Refer to GB / T25995-2010; Surface roughness (Ra): Refer to GB / T10610-2009; Flatness and parallelism: Refer to GB / T1182-2018; Electrical breakdown strength: Refer to GB / T5593-2015.

[0107] Table 1 Test Results

[0108] As can be seen from the above, the embodiments of the present invention, through combined mold forming and segmented internal support filling, completely eliminate the phenomena of green blank porosity, creases, and grinding chatter, achieving a yield rate as high as 96% to 100%. In contrast, Comparative Example 1, due to the lack of internal support and hard clamping, resulted in the complete breakage of the workpiece, with a yield rate of 0%. The graded grinding and liquid-encapsulated vibration absorption process of the present invention stably controls the surface roughness Ra at 0.31~0.48μm, with flatness and parallelism both better than 0.03 mm. In contrast, Comparative Example 1, due to breakage during processing, could not obtain any effective surface quality indicators. The ceramic insulation parts produced by the present invention have an electrical breakdown strength of 20.5~23.5kV / mm, far exceeding the requirements for high-voltage insulation. In contrast, Comparative Example 1, due to breakage during processing, could not undergo electrical performance testing, fully verifying the reliable processing capability of this process for slender, thin-walled hollow structures.

Claims

1. A method for precision machining of hollow thin-walled ceramic insulating parts, characterized in that, Includes the following steps: Step 1: Select alumina powder with a purity ≥ 99.8 wt%, and use a hot air drying process to control the moisture content of the dried powder to ≤ 0.03%; Step 2: Fill the dried powder into the combined mold and perform cold isostatic pressing. After demolding, obtain the alumina green blank. Step 3: The alumina green billet is first hollowed out by precision milling to form an inner cavity, and then subjected to staged variable-temperature sintering treatment. The specific curves are as follows: First stage: heating to 700℃ at a rate of 15~25℃ / h and holding for 3~4h for degreasing; Second stage: heating to 900℃ at a rate of 30~50℃ / h for residue removal, obtaining an intermediate billet; Third stage: heating to 1540~1560℃ at a rate of 20~30℃ / h and holding for 3~4h for densification sintering, obtaining a bulk density ≥3.95g / cm³ after cooling. 3 Ceramic sintered parts; Step 4: Use a multi-stage grinding wheel system to perform surface finishing on the ceramic sintered parts. The multi-stage grinding system consists of three stages: rough grinding, semi-finish grinding, and finish grinding. The entire process is combined with liquid cooling and chip control. After processing, the surface roughness Ra of the ceramic sintered parts is ≤0.5μm, flatness ≤0.03mm, and parallelism ≤0.03mm. Step 5: Using an electroplated diamond-coated chamfering tool on a CNC machining center, perform micro-angle chamfering on the edges of the ceramic sintered parts after surface grinding, using a pouring liquid cooling method during the process.

2. The finishing method for hollow thin-walled ceramic insulating parts according to claim 1, characterized in that, In step two, the combined mold includes an insulating plate wrapped around the four sides, and a base plate locked to the four insulating plates by a pin-type self-locking structure. The four insulating plates have honeycomb-shaped venting micropores, and a non-woven fabric layer is fixed to the inner surface of the insulating plate with glue. It also includes an inner layer and an outer layer directly wrapped around the outside of the ceramic powder, and waterproof sealing tape for the two layers. The inner layer is vacuumed after being filled with ceramic powder. A buffer layer is filled between the insulating plate and the outer layer.

3. The finishing method for hollow thin-walled ceramic insulating parts according to claim 2, characterized in that, The pore size of the honeycomb-shaped exhaust micropores is φ2~φ5mm.

4. The finishing method for hollow thin-walled ceramic insulating parts according to claim 1, characterized in that, The hollow thin-walled ceramic insulating component has an aspect ratio of 6:1 to 25:1, is thin-walled and hollow, and has a single hollow wall thickness of ≤3mm.

5. The finishing method for hollow thin-walled ceramic insulating parts according to claim 4, characterized in that, According to the length specifications of the ceramic sintered part, segmented polytetrafluoroethylene (PTFE) blocks are used to fill the inner cavity with vibration-damping support. The axial length of the PTFE blocks used is 40~50mm, and the initial radial dimension is 2~4mm smaller than the actual corresponding inner dimension of the cavity. During filling, a layer of adhesive wax melted at 60~70℃ is used. After filling and solidification, the surface is finely ground and chamfered. After all these processes are completed, the ceramic sintered part is placed in an oven at 120~130℃ to melt and flow out the adhesive wax layer. The PTFE blocks are then removed, and the ceramic sintered part is immersed in dewaxing water for ultrasonic cleaning.

6. The finishing method for hollow thin-walled ceramic insulating parts according to claim 5, characterized in that, The polytetrafluoroethylene block is machined with vibration damping through holes running through its axis. There are 1 to 2 through holes with a diameter of φ3 to φ5 mm per square centimeter, and the edges of the through holes are ground and deburred.

7. The finishing method for hollow thin-walled ceramic insulating parts according to claim 5, characterized in that, Elastic gaskets are added to the contact surfaces of the L-shaped and T-shaped wrapping clamps and the ceramic sintering parts. L-shaped wrapping clamps are used at the four corners of the ceramic sintering parts, and T-shaped wrapping clamps are used every 150-200mm on both outer walls of the ceramic sintering parts. During clamping and fixing, a digital torque wrench is used for multi-step symmetrical pre-tightening: First, pre-tighten all clamps to 0.3-0.5 times the rated clamping torque M; Second, adopt a symmetrical tightening method extending from the middle to both ends, symmetrically clamping from the T-shaped wrapping clamp at the center to both sides to 0.6-0.8 times the rated clamping torque M; Third, lock all clamps to the full-load rated clamping torque M.

8. The finishing method for hollow thin-walled ceramic insulating parts according to claim 5, characterized in that, During surface grinding, a liquid soft support vibration absorption system is also used: a circulating coolant tank is installed on the magnetic worktable of the surface grinder, and 4 to 6 magnetic steel pads are bonded to the outer bottom of the circulating coolant tank to secure the circulating coolant tank to the magnetic worktable; the clamped and fixed ceramic sintered part is placed horizontally at the bottom of the circulating coolant tank, and the long axis of the ceramic sintered part is aligned with the grinding forward direction; Fill the circulating coolant tank with coolant until the liquid level submerges the tank.

9. The method for precision machining of hollow thin-walled ceramic insulating parts according to claim 1, characterized in that, In step five, the diamond-coated chamfering tool has a grit size of 120#; the spindle speed of the CNC machining center is controlled at 15,000~20,000 rpm, and the feed rate is 50~100 mm / min.

10. A hollow thin-walled ceramic insulating component, characterized in that: It is prepared by the finishing method described in any one of claims 1-9.

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