Machining method of ceramic shaft part

Abstract

The invention discloses a machining method of a ceramic shaft part. The machining method comprises the steps that a tool system comprises a base clamp and a positioning mandrel; the ceramic shaft workpiece is arranged outside the positioning mandrel in a sleeving mode, an annular gap is formed between the ceramic shaft workpiece and the positioning mandrel, a meltable medium in a molten state is poured into the gap, and a rigid assembly is formed after cooling and solidification; the ceramic shaft workpiece is clamped on a machine tool workbench in a vertical posture, finish machining is conducted on the top end of the workpiece to form a datum plane under one-time clamping and positioning, and the part, not covered with the meltable medium, in the inner cavity of the ceramic shaft workpiece is machined; after machining is completed, the medium is melted, and the ceramic shaft workpiece is separated; and clamping on a machine tool in a horizontal posture, taking the processed reference surface and the inner cavity as positioning references, and carrying out milling forming processing on the outer shaft curved surface of the ceramic shaft workpiece by using a T-shaped forming milling cutter of which the shape of a cutter head is matched with the target outline of the outer shaft of the workpiece. Rigid connection between the workpiece and the tool is achieved through the meltable medium, so that the datum plane and the inner cavity can be machined under the same clamping, and repeated positioning errors are eliminated.

Description

Technical Field

[0001] This invention belongs to the field of machining technology and relates to a machining method for ceramic shaft parts. Background Technology

[0002] Ceramic materials possess irreplaceable advantages in manufacturing precision shaft parts due to their excellent comprehensive properties, including high hardness, high rigidity, high temperature resistance, and corrosion resistance. With the development of high-end equipment towards higher speeds and precision, extremely stringent requirements are placed on the dimensional accuracy and surface quality of ceramic shaft parts. Currently, for precision machining of ceramic shafts with complex internal cavities and external shaft structures, the industry generally uses vertical four-axis CNC machining centers, coupled with diamond grinding wheels for grinding. A typical traditional process route requires three clamping operations to complete: the first clamping operation to machine the reference plane; the second clamping operation to machine the internal cavity features; and the third clamping operation to machine the external shaft surface. Although existing technologies have explored ways to achieve "multiple processes in a single clamping operation" by optimizing tooling to avoid repetitive positioning errors, and have researched using special tools to improve the machining efficiency of ceramic outer diameters, existing solutions still have the following technical shortcomings that urgently need to be addressed for ceramic shafts with both precision internal cavities and complex external shapes:

[0003] Repeated clamping leads to cumulative errors, making it difficult to guarantee coaxiality and perpendicularity. Multiple disassembly and repositioning of the workpiece inevitably introduce clamping errors. Positional tolerances (especially perpendicularity) between the datum surface and the inner cavity, and between the inner cavity and the outer shaft curved surface, accumulate with each clamping, making it difficult to consistently achieve the high precision requirement of less than 0.01mm. Even with tooling assistance, traditional mechanical clamping can still cause microscopic deformation or positioning drift due to contact stress. Machining strategies are inefficient; complex outer shaft curved surfaces typically employ four-axis simultaneous grinding, resulting in complex machine tool motion trajectories, long single-point cutting times, and overall low machining efficiency, failing to meet the demands of mass production. Grinding conditions are harsh, resulting in short tool life. When grinding the side of a workpiece in a vertical position, the grinding wheel mainly relies on its bottom edge (end face) for cutting. The small chip space makes it difficult to remove grinding chips, and coolant cannot effectively wet the cutting zone, easily leading to wheel surface dulling and clogging, exacerbating abrasive grain shedding, thus significantly shortening wheel life and increasing machining costs.

[0004] Therefore, there is an urgent need for a ceramic shaft machining method that can fundamentally reduce the number of clamping operations, improve machining conditions, and optimize cutting strategies. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of error accumulation caused by repeated clamping in the machining of ceramic shafts in the prior art, and to provide a machining method for ceramic shaft parts.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A method for machining ceramic shaft parts includes the following steps:

[0008] A ceramic shaft workpiece to be processed and a tooling system are provided. The tooling system includes a base fixture and a positioning mandrel that matches the inner cavity shape of the ceramic shaft workpiece. The positioning mandrel is fixed on the base fixture.

[0009] The ceramic shaft workpiece is sleeved on the outside of the positioning mandrel, so that an annular gap is formed between the inner wall of the ceramic shaft workpiece and the outer wall of the positioning mandrel. Molten fusible medium is poured into the annular gap. After it cools and solidifies, the ceramic shaft workpiece, fusible medium, positioning mandrel and base clamp are fixedly connected into a rigid assembly.

[0010] The rigid assembly is clamped vertically on the machine tool table. In one clamping and positioning, the top end face of the ceramic shaft workpiece is first precision machined to form a reference surface, and then the part of the inner cavity of the ceramic shaft workpiece that is not covered by the fusible medium is machined.

[0011] After processing, the ceramic shaft workpiece is separated from the tooling system by heating to melt the fusible medium.

[0012] The separated ceramic shaft workpiece is re-clamped on the machine tool in a horizontal position, and the machined reference surface and inner cavity are used as positioning references. A T-shaped forming tool with a cutting head shape that matches the target contour of the outer shaft of the workpiece is used to turn the outer shaft surface of the ceramic shaft workpiece.

[0013] The width of the annular gap between the inner wall of the ceramic shaft workpiece and the outer wall of the positioning mandrel is 0.02 mm to 0.1 mm.

[0014] The base clamp and / or positioning mandrel are preheated before the molten, meltable medium is poured in.

[0015] The vertical posture refers to the clamping state in which the axis of the ceramic shaft workpiece is perpendicular to the axis of the machine tool spindle; the horizontal posture refers to the clamping state in which the axis of the ceramic shaft workpiece is parallel to the axis of the machine tool spindle.

[0016] When machining the internal cavity and reference surface in the vertical orientation, a diamond grinding wheel is used for grinding.

[0017] The T-shaped forming milling cutter is a polycrystalline diamond tool.

[0018] When clamping ceramic shaft workpieces in a horizontal position, a precision spring collet or two-end centers are used for positioning and clamping.

[0019] The perpendicularity of the reference plane to the inner cavity axis is no greater than 0.01 mm.

[0020] The fusible medium is industrial paraffin or a low-melting-point alloy.

[0021] The melting point of the low-melting-point alloy is below 150°C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention provides a method for machining ceramic shaft parts. By using a fusible medium to achieve a rigid connection between the workpiece and the tooling, the datum surface and the inner cavity can be machined in the same clamping operation, eliminating repeated positioning errors. The perpendicularity of the datum surface and the inner cavity axis can therefore be stably controlled to a high standard of ≤0.01mm, providing a precise and reliable reference for subsequent processes.

[0024] This invention optimizes external spindle machining from complex four-axis simultaneous grinding to efficient vertical T-shaped milling. It simplifies machine tool movement and employs continuous forming cutting, resulting in higher material removal rates. This method combines datum surface and internal cavity machining into a single operation, reducing the number of setups and improving overall machining efficiency by over 50% compared to traditional methods.

[0025] When machining external shafts, the horizontal turning method employed in this invention allows the T-slot milling cutter to cut with its side edge, resulting in better chip removal and cooling space. This avoids the rapid wear and burning problems of the grinding wheel bottom edge caused by difficult chip removal and insufficient cooling in traditional vertical grinding. This not only extends tool life and reduces costs but also improves the stability of the machining process and the consistency of workpiece surface quality. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the wax mold fixing and clamping device of the present invention;

[0028] Figure 2 This is a schematic diagram of the tool processing of the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of the part to be processed;

[0030] Figure 4 This is a schematic diagram of the machining and clamping process in the prior art.

[0031] Among them, 1-cutting tool; 2-top fixing component; 3-wax model; 4-base fixing fixture; 5-T-type turning tool; 6-workpiece to be processed; Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0034] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0035] A method for processing ceramic shaft parts according to the present invention includes the following steps:

[0036] A ceramic shaft workpiece to be processed and a tooling system are provided. The tooling system includes a base fixture and a positioning mandrel that matches the inner cavity shape of the ceramic shaft workpiece. The positioning mandrel is fixed on the base fixture.

[0037] Before pouring the molten, fusible medium, the base fixture and / or positioning mandrel are preheated. Ceramic and metal tooling have different thermal conductivity and coefficients of thermal expansion. If the temperature difference is too large, the molten medium will solidify rapidly upon contact with the cold tooling, potentially leading to incomplete filling, voids, or internal stress. Preheating (typically to slightly below the medium's melting point) slows the cooling rate of the contact surface, ensuring the medium smoothly and completely fills the entire annular gap, resulting in a uniform, dense, and well-bonded solid filler layer. This is crucial for achieving stress-free, high-rigidity fixation.

[0038] The ceramic shaft workpiece is sleeved over the positioning mandrel, forming an annular gap between the inner wall of the ceramic shaft workpiece and the outer wall of the positioning mandrel. Molten, fusible medium is poured into the annular gap. After cooling and solidification, the ceramic shaft workpiece, fusible medium, positioning mandrel, and base clamp are rigidly connected into a single assembly. The width of the annular gap between the inner wall of the ceramic shaft workpiece and the outer wall of the positioning mandrel is 0.05 mm to 0.5 mm.

[0039] The fusible medium is industrial paraffin wax or a low-melting-point alloy. The low-melting-point alloy has a melting point below 150°C. Industrial paraffin wax is inexpensive, easy to remove, and has a relatively stable shrinkage rate, making it suitable for most applications requiring high precision and operating at relatively low temperatures. Low-melting-point alloys offer higher strength and better thermal conductivity, providing stronger support rigidity. Furthermore, their slight volume expansion upon solidification allows for tighter encapsulation and positioning, making them suitable for applications with extremely high rigidity requirements or those generating significant heat during processing. The limitation of a melting point below 150°C ensures that the medium can be melted and removed using conventional and safe heating methods, avoiding any impact on the ceramic workpiece's properties or operational risks due to excessively high temperatures.

[0040] The rigid assembly is clamped vertically onto the machine tool table. In a single clamping and positioning operation, the top end face of the ceramic shaft workpiece is first precision-machined to form a reference surface. Then, the portion of the ceramic shaft workpiece's inner cavity not covered by the fusible medium is machined. Vertical orientation refers to the clamping state where the axis of the ceramic shaft workpiece is perpendicular to the machine tool spindle axis. When machining the inner cavity and reference surface in this vertical orientation, an end mill or diamond wheel is used for grinding. The perpendicularity of the reference surface to the inner cavity axis is no greater than 0.01 mm.

[0041] After processing, the fusible medium is melted by heating, separating the ceramic shaft workpiece from the tooling system. Utilizing the properties of the fusible medium, a phase change (from solid to liquid) is caused by gentle heating (the temperature is controlled within a range that is harmless to the ceramic workpiece and below its tolerance limit), thereby completely releasing the clamping force on the workpiece. This separation method avoids the bumps, scratches, or stress damage that may occur with mechanical disassembly, and is particularly suitable for brittle ceramic precision parts, ensuring the safety of the first half of the processing.

[0042] The separated ceramic shaft workpiece is re-clamped on the machine tool in a horizontal position. Using the machined reference surface and inner cavity as positioning references, a T-shaped forming tool with a tool tip shape matching the target contour of the workpiece's outer shaft is used to turn and shape the outer curved surface of the ceramic shaft workpiece. The horizontal position refers to the clamping state where the axis of the ceramic shaft workpiece is parallel to the axis of the machine tool spindle. When clamping the ceramic shaft workpiece in a horizontal position, a precision spring collet or two-pointed ends are used for positioning and clamping. The T-shaped forming tool is a polycrystalline diamond tool or a cubic boron nitride tool.

[0043] Example

[0044] This embodiment uses a typical ceramic shaft part with a stepped outer contour and inner cavity structure as the processing object to illustrate the complete process flow of the present invention.

[0045] 1. Preliminary preparations

[0046] Workpiece: Provide pre-sintered ceramic blanks with machining allowances for both inner and outer diameters.

[0047] Tooling fabrication: Based on the target part drawing, design and machine a dedicated tooling. This tooling consists of a base fixture and a positioning mandrel. The contour of the positioning mandrel matches the designed shape of the workpiece's inner cavity, and its size is set to be smaller than the design size by a preset clearance on one side, 0.05mm-0.2mm. The upper end of the base fixture has a cavity to accommodate the workpiece, and the lower end is machined with a standardized positioning structure for connection with the machine tool table or spindle interface.

[0048] Medium preparation: Industrial-grade paraffin is selected as the fusible medium, and its melting point is suitable for heating to melt and cooling to solidify.

[0049] 2. Fusible medium-assisted clamping and assembly formation

[0050] Install and fix the positioning mandrel on the base fixture.

[0051] When the ceramic workpiece blank is inserted into the positioning mandrel, a uniform annular gap is formed between the inner wall of the workpiece and the outer surface of the mandrel.

[0052] Preheat the tooling components appropriately to reduce the temperature difference during the injection of the molten medium. Heat the solid paraffin until it is completely melted into a liquid.

[0053] Molten paraffin wax is poured smoothly into the aforementioned annular gap until it is completely filled. It is then allowed to stand or forced to cool completely to allow the paraffin wax to solidify. Once solidified, the paraffin wax firmly binds the workpiece, positioning mandrel, and base fixture into a rigid whole, providing circumferential, stress-free support and positioning for the workpiece's internal cavity.

[0054] 3. Vertical machining of the inner cavity and datum surface in a single clamping operation

[0055] The rigid assembly described above is clamped in a vertical position (workpiece axis perpendicular to machine tool spindle) on the worktable of a vertical CNC machining center using the positioning structure of the base fixture.

[0056] In this clamping process, the top surface of the workpiece is first milled using a finishing tool to produce a smooth and flat end face, which is defined as the process reference surface (A surface).

[0057] Subsequently, by changing to a suitable finishing tool, and under the same clamping condition, the internal cavity structure of the workpiece (except for the positioning section covered by paraffin wax) is precision machined according to the program. Thus, datum surface A and all features of the internal cavity are machined in a single positioning operation, ensuring extremely high geometric accuracy between them.

[0058] 4. Media removal and workpiece separation

[0059] The assembled unit with its internal cavity machined is removed from the machine tool.

[0060] A heating device is used to heat the assembly as a whole or in parts, so that the paraffin wax, which serves as a binding medium, melts.

[0061] Once the paraffin wax has melted, the ceramic workpiece with the machined inner cavity can be easily removed from the positioning mandrel, and then any remaining paraffin wax in the inner cavity of the workpiece can be cleaned.

[0062] 5. Secondary clamping and horizontal machining of the outer shaft contour

[0063] The workpiece is re-clamped in a horizontal position (workpiece axis parallel to machine tool spindle) onto another CNC lathe or mill-turn machining center. During clamping, a precision fixture is used, and the machined datum surface A and the inner cavity are used as positioning datums to ensure accurate positioning.

[0064] Select a PCD (polycrystalline diamond) T-slot forming tool specially designed for the outer contour shape of the workpiece. Install the tool and set the workpiece coordinate system.

[0065] The machine tool is started, and the spindle drives the workpiece to rotate. The T-shaped forming tool makes continuous feed motions along the workpiece axis. Utilizing its forming cutting edge, complex contours such as steps and curved surfaces on the outer circle of the workpiece can be turned efficiently and precisely in a single pass. This process uses wet cutting, with coolant fully poured in for chip removal and cooling.

[0066] 6. Effect Verification

[0067] After processing is completed, the parts are inspected:

[0068] Accuracy: As measured by a coordinate measuring machine, the perpendicularity of the reference plane A to the inner cavity axis consistently meets the extremely high requirement of ≤0.01mm, and the accuracy of the outer contour also meets the design standards.

[0069] Efficiency: Compared with the traditional three-clamping, four-axis linkage grinding process, the method in this embodiment reduces the total processing time by about 40%-50%, and the efficiency is significantly improved.

[0070] Economic efficiency: T-shaped turning tools operate under good cooling and chip removal conditions, with a lifespan far exceeding that of traditional grinding wheels and bars, reducing the cost per tool. At the same time, the machining process is stable and the product consistency is high.

[0071] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for machining ceramic shaft parts, characterized in that, Includes the following steps: A ceramic shaft workpiece to be processed and a tooling system are provided. The tooling system includes a base fixture and a positioning mandrel that matches the inner cavity shape of the ceramic shaft workpiece. The positioning mandrel is fixed on the base fixture. The ceramic shaft workpiece is sleeved on the outside of the positioning mandrel, so that an annular gap is formed between the inner wall of the ceramic shaft workpiece and the outer wall of the positioning mandrel. Molten fusible medium is poured into the annular gap. After it cools and solidifies, the ceramic shaft workpiece, fusible medium, positioning mandrel and base clamp are fixedly connected into a rigid assembly. The rigid assembly is clamped vertically on the machine tool table. In one clamping and positioning, the top end face of the ceramic shaft workpiece is first precision machined to form a reference surface, and then the part of the inner cavity of the ceramic shaft workpiece that is not covered by the fusible medium is machined. After processing, the ceramic shaft workpiece is separated from the tooling system by heating to melt the fusible medium. The separated ceramic shaft workpiece is re-clamped on the machine tool in a horizontal position, and the machined reference surface and inner cavity are used as positioning references. A T-shaped forming tool with a cutting head shape that matches the target contour of the outer shaft of the workpiece is used to turn the outer shaft surface of the ceramic shaft workpiece.

2. The method for processing ceramic shaft parts as described in claim 1, characterized in that, The width of the annular gap between the inner wall of the ceramic shaft workpiece and the outer wall of the positioning mandrel is 0.02 mm to 0.1 mm.

3. The method for processing ceramic shaft parts as described in claim 1, characterized in that, The base clamp and / or positioning mandrel are preheated before the molten, meltable medium is poured in.

4. The method for processing ceramic shaft parts as described in claim 1, characterized in that, The vertical posture refers to the clamping state in which the axis of the ceramic shaft workpiece is perpendicular to the axis of the machine tool spindle; the horizontal posture refers to the clamping state in which the axis of the ceramic shaft workpiece is parallel to the axis of the machine tool spindle.

5. The method for processing ceramic shaft parts as described in claim 1, characterized in that, When machining the internal cavity and reference surface in the vertical orientation, a diamond grinding wheel is used for grinding.

6. The method for processing ceramic shaft parts as described in claim 1, characterized in that, The T-shaped forming milling cutter is a polycrystalline diamond tool.

7. The method for processing ceramic shaft parts as described in claim 1, characterized in that, When clamping ceramic shaft workpieces in a horizontal position, a precision spring collet or two-end centers are used for positioning and clamping.

8. The method for processing ceramic shaft parts as described in claim 1, characterized in that, The perpendicularity of the reference plane to the inner cavity axis is no greater than 0.01 mm.

9. A method for processing ceramic shaft parts as described in claim 1, characterized in that, The fusible medium is industrial paraffin or a low-melting-point alloy.

10. A method for processing ceramic shaft parts as described in claim 9, characterized in that, The melting point of the low-melting-point alloy is below 150°C.

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