Small-diameter liquid expansion clamp, method for manufacturing same, and expansion amount control method

Abstract

The present application relates to the field of machine tool accessories, and particularly discloses a small-diameter liquid expansion clamp, a manufacturing method thereof and an expansion amount control method, aiming to enhance the strength of a thin-walled structure and ensure the uniformity of expansion thereof. The diameter of the expansion part of the small-diameter liquid expansion clamp is less than or equal to 4 mm, which can meet the demand of high-precision positioning and clamping of micro parts. The expansion part is in a cylindrical structure, and the side cavity wall of the expansion cavity is in a continuous and closed wave ring structure composed of alternating thickening parts and thinning parts. The thickening parts are used as reinforced inner ridges to improve the rigidity and fatigue resistance of the expansion part. The thinning parts are used as elastic connection zones to ensure that the expansion part can produce uniform radial expansion under the action of hydraulic pressure. Not only is the clamping force sufficient, but also the problem of local stress concentration can be avoided, and high-precision positioning and clamping can be achieved. In addition, by setting the closed end of the expansion part as a solid growth part, the axial elongation effect of the entire expansion part under the action of internal hydraulic pressure can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of machine tool accessories, specifically relating to a small-diameter hydraulic expansion clamp, its manufacturing method, and its expansion amount control method. Background Technology

[0002] Hydraulic expansion clamps, as tools that utilize hydrostatic expansion technology to achieve high-precision clamping, are commonly used for clamping and machining gears, thin-walled parts, and other similar components. Although hydraulic expansion clamps have been applied in precision machining scenarios such as semiconductor wafer transport equipment, traditional hydraulic expansion clamps are mostly designed for workpieces of standard sizes, and still have significant limitations when facing miniaturized machining scenarios such as harmonic reducers. Harmonic reducers, as core transmission components of robot joints, have advantages such as small size, high transmission accuracy, and large torque; their precision machining places extremely high demands on clamping tools.

[0003] Traditional hydraulic expansion clamps include a clamp body with an expansion section. To ensure structural strength, the expansion section is generally composed of a solid body and a thin-walled structure surrounding the solid body, forming an expansion cavity between the solid body and the thin-walled structure. For example, Chinese invention patent application CN109482923A discloses a harmonic flexible gear hobbing hydraulic tooling, including a mandrel body, a locking block, and a variable diameter expansion sleeve. The mandrel body has a flange located on its surface. The variable diameter expansion sleeve is connected to the mandrel body by screws and is located on one side of the flange. The locking block is engaged with the variable diameter expansion sleeve. The mandrel body includes a main oil passage, at least two branch oil passages, and an oil cavity. The main oil passage is axially located in the middle of the mandrel body. The branch oil passages include a first branch oil passage and a second branch oil passage, which radially pass through the main oil passage and penetrate the mandrel body. The oil cavity is located on one side of the mandrel body and connected to the second branch oil passage.

[0004] The problems with traditional hydraulic clamps include:

[0005] 1) Size limitations: The machining requirements for the inner holes of micro parts such as the flexible wheel and rigid wheel of the harmonic reducer are approaching the 2 mm level. Due to the presence of solid bodies, the diameter of the expansion part of the traditional hydraulic expansion clamp is usually greater than 4 mm, which cannot meet the high-precision clamping and positioning requirements of ultra-small holes.

[0006] 2) Miniaturization bottlenecks and insufficient rigidity: For expansion parts smaller than 4 mm, the wall thickness must be extremely thin to achieve hydraulic expansion, resulting in axial elongation. Limited by materials and processing technology, the strength and expansion uniformity of thin-walled structures are difficult to guarantee, easily leading to insufficient clamping force or localized stress concentration. Uneven clamping force often causes deformation during the processing of miniature parts, affecting the gear meshing accuracy of harmonic reducers, thereby reducing their transmission efficiency and lifespan.

[0007] 3) Poor dynamic stability: The harmonic reducer parts of the robot need to withstand high-frequency dynamic loads during the processing. Traditional hydraulic clamps are prone to micro-displacement in high-speed rotation or vibration environments, which affects the consistency of processing.

[0008] 4) Insufficient process adaptability and integration compatibility: The machining of harmonic reducer components involves ultra-precision turning, grinding, and inspection. Traditional hydraulic clamps are difficult to balance high repeatability (e.g., end face runout <2 μm) with rapid clamping. Moreover, the machining equipment for harmonic reducers is becoming more compact, and traditional hydraulic clamps are difficult to integrate with micro CNC machine tools or modular assembly equipment for robot joints. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a small-diameter hydraulic expansion clamp with high strength of thin-walled structure and good uniformity of expansion.

[0010] The technical solution adopted by the present invention to solve its technical problem is: a small-diameter hydraulic expansion clamp, including a clamp body, a hydraulic cavity formed in the clamp body, and a pressurizing mechanism for pressurizing the hydraulic cavity;

[0011] The fixture body has an expansion portion for clamping the workpiece;

[0012] The expansion section is a cylindrical structure that is connected to the hydraulic cavity at one end and closed at the other end. Its outer wall profile is cylindrical and its outer diameter is ≤4 mm. Its inner cavity is the expansion cavity.

[0013] The sidewall of the expansion cavity consists of at least three thickened portions spaced apart in the circumferential direction, and thinned portions connecting adjacent thickened portions;

[0014] On the cross-section of the expansion cavity, the thickened part is an arc shape that bulges toward the axis of the expansion part, and the thinned part is an arc shape that is concave away from the axis of the expansion part. The thickened and thinned parts that are adjacent to each other are smoothly connected, so that the inner wall profile of the expansion part is a continuous and closed wave ring.

[0015] Furthermore, the number of thickened sections is 3 to 8.

[0016] Furthermore, the closed end of the expansion section is a solid growth section, the length of which is 1.5 to 2 times the outer diameter of the expansion section;

[0017] The solid growth section is constructed to reduce the axial elongation effect of the expansion section under hydraulic pressure.

[0018] Furthermore, the pressurizing mechanism includes a pressurizing channel disposed within the clamp body and connected to the hydraulic chamber, a pressurizing piston disposed within the pressurizing channel and in sliding sealing cooperation therewith, and a pressurizing screw threadedly connected to the pressurizing channel and capable of pressing the pressurizing piston toward the inner end of the pressurizing channel.

[0019] Furthermore, the small-diameter hydraulic expansion clamp also includes a sealing structure;

[0020] The sealing structure includes a sealing channel disposed within the fixture body and coaxially connected to the hydraulic chamber. A sealing ring platform is formed at the inner end of the sealing channel. A sealing ball that blocks the inner hole of the sealing ring platform and a sealing screw that tightens and fixes the sealing ball are disposed within the sealing channel.

[0021] Furthermore, the small-diameter hydraulic expansion clamp also includes a clamp base connected to the clamp body;

[0022] The fixture base has a piston chamber, which is equipped with a push rod piston that divides it into a first chamber and a second chamber; the fixture base has a liquid supply channel that communicates with the first chamber and is used to connect to the hydraulic system of the machine tool.

[0023] The pressurizing mechanism includes a pressurizing channel disposed within the fixture body and connected to the hydraulic chamber, a sealing element disposed at one end of the pressurizing channel near the fixture base, and a pressurizing push rod disposed through the sealing element; one end of the pressurizing push rod extends into the pressurizing channel, and the other end extends into the second chamber and abuts against the push rod piston.

[0024] Furthermore, the small-diameter hydraulic expansion clamp also includes a hydraulic compensation mechanism, which includes a compensation channel with a one-way valve structure.

[0025] The inlet of the compensation channel is located on the fixture base and is used to connect to the machine tool's hydraulic system;

[0026] The outlet of the compensation channel is connected to the pressurization channel and / or the hydraulic chamber.

[0027] Furthermore, the compensation channel includes a valve chamber, and a compensation inlet channel and a compensation outlet channel respectively connected to the valve chamber;

[0028] A valve seat is formed at the connection between the valve cavity and the compensation inlet channel;

[0029] The one-way valve structure includes a one-way valve core, a valve core spring, a sealing piston, and an adjusting screw;

[0030] The one-way valve core is axially movable in the valve cavity and together with the valve seat forms an opening and closing mechanism that can control the opening and closing of the compensation inlet channel and the compensation outlet channel;

[0031] The sealing piston is located in the valve cavity and on the side of the one-way valve core away from the valve seat;

[0032] The valve core spring is positioned between the one-way valve core and the sealing piston and is in a pre-tightened state.

[0033] The adjusting screw is threaded into the valve chamber and can push the sealing piston toward the one-way valve core.

[0034] Furthermore, the small-diameter hydraulic expansion clamp also includes a diameter measuring sensor for detecting the outer diameter of the expansion section.

[0035] Furthermore, the diameter measuring sensor includes a sensor body with a measuring hole, and at least four strain gauges evenly distributed circumferentially are provided on the wall of the measuring hole.

[0036] The present invention also provides a method for manufacturing a small-diameter hydraulic expansion fixture, including a preform preparation step;

[0037] Initial blank fabrication steps: Use 3D printing technology to create the initial blank of the fixture; or, use 3D printing technology to create the expansion part with the connecting seat, and machine the rest of the initial blank of the fixture.

[0038] The fixture blank is the aforementioned small-diameter hydraulic expansion fixture blank.

[0039] Furthermore, the manufacturing method also includes the steps of heat treatment, turning and grinding of the fixture blank in sequence;

[0040] The grinding process involves: first, rough grinding to remove excess material from the expanded part; then, aging treatment to release processing stress; and finally, fine grinding to achieve a circular runout accuracy of 0.003 mm, resulting in the finished product of a small-diameter hydraulic expansion fixture.

[0041] The present invention also provides a method for controlling the expansion amount of a small-diameter hydraulic expansion clamp, for controlling the aforementioned small-diameter hydraulic expansion clamp, comprising the following steps:

[0042] Step A: Install the small-diameter hydraulic expansion fixture onto the machine tool and set the initial hydraulic pressure in the machine tool's CNC system;

[0043] Step B: The machine tool supplies hydraulic oil to the first cavity of the small-diameter hydraulic expansion fixture, and then pushes the pressurizing push rod to compress the hydraulic medium in the hydraulic cavity through the push rod piston, so as to drive the expansion part to expand radially and clamp and fix the workpiece.

[0044] Step C: Process the workpiece and measure its dimensions after processing;

[0045] Step D: Compare the measured workpiece dimensions with the dimensions required by the drawing to determine the direction and degree of dimensional deviation, which will serve as the basis for adjusting the expansion amount.

[0046] Step E: Feedback the expansion amount adjustment data to the machine tool's CNC system. Based on the expansion amount adjustment data and the outer diameter data of the expansion part measured by the diameter measurement sensor, the machine tool's CNC system sends control commands to the controller.

[0047] Step F: The controller controls the machine tool's oil pump to work and adjusts the oil pressure supplied to the small-diameter hydraulic expansion fixture, thereby adjusting the expansion diameter of the expansion section.

[0048] Furthermore, the machine tool's CNC system generates control commands based on the following formula;

[0049] Formula 1: ;

[0050] Formula 2: ;

[0051] Formula 3: ;

[0052] Where D is the diameter of the push rod piston;

[0053] d is the diameter of the pressure push rod;

[0054] Pg is the pressure at the inlet of the liquid supply channel;

[0055] P is the pressure inside the hydraulic chamber;

[0056] Δy(x) is the amount of expansion of the expansion portion;

[0057] R is the radius of the outer wall profile of the expansion section;

[0058] E1 is the elastic modulus of the expanded portion;

[0059] t is the minimum wall thickness of the expansion section;

[0060] l is the length of the expansion cavity;

[0061] μ1 is the Poisson's ratio of the expansion section;

[0062] λ is a dimensionless intermediate variable;

[0063] x is the axial coordinate of the expansion cavity length direction with the connection between the expansion section and the hydraulic cavity as the origin.

[0064] The beneficial effects of this invention are as follows: The diameter of the expansion part of this small-diameter hydraulic expansion clamp is less than or equal to 4 mm, which can meet the high-precision positioning and clamping requirements of micro parts. It is particularly suitable for clamping and processing components such as flexible wheels and rigid wheels of micro harmonic reducers. Compared with traditional hydraulic expansion clamps, in order to achieve a smaller diameter expansion part, this small-diameter hydraulic expansion clamp eliminates the solid structure inside the expansion part and designs it as a cylindrical structure. At the same time, in order to prevent the problems of insufficient expansion due to excessive wall thickness and insufficient rigidity and difficulty in ensuring expansion uniformity due to excessive wall thinness, the side cavity wall of the expansion chamber is set as a continuous and closed wave-shaped annular structure composed of alternating thickened and thinned parts. The thickened part is used as a reinforcing ridge to improve the rigidity and fatigue resistance of the expansion part, and the thinned part is used as an elastic connection area to ensure that the expansion part can generate uniform radial expansion under hydraulic action. This not only provides sufficient clamping force but also avoids the problem of local stress concentration, enabling high-precision positioning and clamping, and helping to ensure the processing accuracy of the clamped workpiece. In addition, by setting the closed end of the expansion section as a solid growth section, the axial elongation effect of the entire expansion section under the action of internal hydraulic pressure can be reduced, and the internal hydraulic pressure can be used as much as possible to make the expansion section radially expand, thereby effectively clamping the workpiece.

[0065] The technical effects brought about or directly generated by other technical features of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0066] Figure 1 This is a cross-sectional structural schematic diagram of one embodiment of the clamp of the present invention;

[0067] Figure 2 It is along Figure 1 Sectional view of line AA in the middle;

[0068] Figure 3 This is a cross-sectional view of another embodiment of the clamp of the present invention;

[0069] Figure 4 yes Figure 3 A magnified view of a section at point P in the middle;

[0070] Figure 5 yes Figure 3 The fixture shown is shown in the labeled diagram;

[0071] Figure 6 This is a schematic diagram of the implementation structure of the diameter measuring sensor in this invention;

[0072] Figure 7 This is a schematic diagram of the implementation structure of the fixture of the present invention after mounting the diameter measuring sensor;

[0073] Figure 8 This is a schematic cross-sectional view of the initial blank of the fixture;

[0074] Figure 9 This is a schematic diagram of the working state of the blank in the turning fixture;

[0075] Figure 10 This is a schematic diagram illustrating the working state of grinding the initial blank of the fixture into a finished product;

[0076] Figure 11 This is a radial deformation distribution curve of the small-diameter hydraulic expansion clamp in Example 1 under different working oil pressures;

[0077] Figure 12 This is a cross-sectional schematic diagram of an expansion cavity with 3 to 6 thickened sections;

[0078] Figure 13 This is a schematic diagram of the pressure-bearing state of the expansion cavities, which consist of five thickened sections.

[0079] Figure 14 This is a cloud map showing the expansion diameter of a small-diameter hydraulic expansion clamp with three thickened sections in Example 2.

[0080] Figure 15 This is a cloud diagram of the expansion diameter test of a small-diameter hydraulic expansion clamp with four thickened sections in Example 2;

[0081] Figure 16 This is a cloud map showing the expansion diameter of a small-diameter hydraulic expansion clamp with five thickened sections in Example 2.

[0082] Figure 17 This is a cloud map showing the expansion diameter of a small-diameter hydraulic expansion clamp with six thickened sections in Example 2.

[0083] Figure 18 This is a cloud map showing the expansion diameter of the small-diameter hydraulic expansion fixture with a thickness increase of 0.05 mm in Example 3.

[0084] Figure 19 This is a cloud map showing the expansion diameter of the small-diameter hydraulic expansion fixture with a thickness increase of 0.10 mm in Example 3.

[0085] Figure 20 This is a cloud map showing the expansion diameter of the small-diameter hydraulic expansion fixture with a thickness increase of 0.15 mm in Example 3.

[0086] Figure 21 This is a cloud map showing the expansion diameter of the small-diameter hydraulic expansion fixture with a thickness increase of 0.20 mm in Example 3.

[0087] The markings in the diagram are as follows: 100-Clamp body, 110-Hydraulic chamber, 120-Expansion section, 121-Expansion chamber, 122-Thickened section, 123-Thinned section, 124-Solid growth section, 131-Pressure channel, 132-Pressure piston, 133-Pressure screw, 134-Seal, 135-Pressure push rod, 136-Push rod head, 141-Sealing channel, 142-Sealing ball, 143-Sealing screw, 200-Clamp Base, 201-Second cavity, 210-Sealing cover, 220-Push rod piston, 230-Liquid supply channel, 241-Valve cavity, 242-Compensation inlet channel, 243-Compensation outlet channel, 244-One-way valve core, 245-Valve core spring, 246-Sealing piston, 247-Adjusting screw, 300-Diameter measuring sensor, 311-Measuring hole, 400-Clamp blank, 500-Turning tool, 600-Grinding tool. Detailed Implementation

[0088] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the drawings, the same reference numerals denote components with the same or similar functions.

[0089] In the description of this invention, the diameter of the expansion portion 120 refers to the outer diameter of the expansion portion 120. When the term "many" indicates a quantity, it generally refers to three or more; for example, "multiple" usually means three or more. The term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone.

[0090] Combination Figure 1 and Figure 2 As shown, the small-diameter hydraulic expansion clamp includes a clamp body 100, a hydraulic cavity 110 formed in the clamp body 100, and a pressurizing mechanism for pressurizing the hydraulic cavity 110.

[0091] The clamp body 100 has an expansion portion 120 for clamping the workpiece;

[0092] The expansion section 120 is a cylindrical structure with one end connected to the hydraulic cavity 110 and the other end closed. Its outer wall profile is cylindrical and its outer diameter is ≤4 mm. Its inner cavity is the expansion cavity 121. That is, the diameter of the expansion section 120 is less than or equal to 4 mm, preferably 3 mm. The length of the expansion section 120 is usually 30 to 50 mm.

[0093] The sidewall of the expansion cavity 121 is composed of at least three thickened portions 122 spaced apart circumferentially along the expansion cavity 121, and thinned portions 123 connecting adjacent thickened portions 122. The thickened portions 122 are locally thickened areas of the sidewall of the expansion cavity 121, and are usually arranged along the axial direction of the expansion cavity 121 to form a reinforcing inner ridge, thereby improving the rigidity and fatigue resistance of the expansion portions 120. The thinned portions 123 are locally thinned areas of the sidewall of the expansion cavity 121, and are usually arranged along the axial direction of the expansion cavity 121 to form an elastic connection area, thereby connecting the thickened portions 122 and achieving uniform elastic deformation.

[0094] On the cross-section of the expansion cavity 121, the thickened portion 122 is an arc shape that protrudes toward the axis of the expansion portion 120, and the thinned portion 123 is an arc shape that is recessed away from the axis of the expansion portion 120. The thickened portions 122 and thinned portions 123 that are adjacent to each other are smoothly connected, so that the inner wall profile of the expansion portion 120 is a continuous and closed wave ring.

[0095] The expansion section 120 of this small-diameter hydraulic expansion jig has a diameter of less than or equal to 4 mm, which can meet the high-precision positioning and clamping requirements of micro parts. It is particularly suitable for clamping and machining components such as flexible wheels and rigid wheels in micro harmonic reducers. Compared with traditional hydraulic expansion jigs, in order to achieve a smaller diameter for the expansion section 120, this small-diameter hydraulic expansion jig eliminates the solid structure inside the expansion section 120 and designs it as a cylindrical structure. At the same time, to prevent the problems of insufficient expansion due to excessively thick walls and insufficient rigidity and difficulty in ensuring expansion uniformity due to excessively thin walls, the side cavity walls of the expansion chamber 121 are set as a continuous and closed wave-shaped annular structure composed of alternating thickened sections 122 and thinned sections 123. In this way, on the one hand, the strength of the thin-walled structure of the expansion section 120 is improved, which is beneficial to manufacturing and processing, and the stability of clamping the workpiece is higher and the service life is longer. On the other hand, it can ensure the uniformity of expansion, which is beneficial to improving the clamping and positioning accuracy.

[0096] The hydraulic chamber 110 is typically filled with hydraulic medium (such as hydraulic oil). When a workpiece needs to be clamped and positioned, pressure is applied to the hydraulic chamber 110 via a pressurizing mechanism, causing the hydraulic medium to compress the wall of the expansion chamber 121. Because the thinned portion 123 is relatively thin and has relatively low rigidity, it is compressed by the hydraulic medium in a direction away from the axis of the expansion portion 120. Simultaneously, it is pulled by multiple evenly distributed thickened portions 122, resulting in elastic deformation and extension. Due to the extension of the thinned portion 123, the thicker thickened portions 122 move away from the axis of the expansion portion 120 under the compression of the hydraulic medium, thereby effectively clamping the workpiece. Although the wall thickness of the expansion chamber 121 is uneven, due to the rotational symmetry of the wave-ring structure and its continuous and smooth construction, it can convert the pressure of the hydraulic medium into uniform radial expansion of the expansion portion 120. This helps ensure the clamping force and accuracy, avoids local stress concentration problems, and achieves high-precision positioning and clamping of the workpiece.

[0097] To reduce processing difficulty and ensure that the expanded portion 120 possesses both excellent rigidity and elastic deformation capability, preferably, the number of thickened portions 122 is 3 to 8, and the corresponding number of thinned portions 123 is equal to the number of thickened portions 122. For example: Figure 2 In this embodiment, the expansion portion 120 has eight thickening portions 122 and eight thinning portions 123.

[0098] In some embodiments, the closed end of the expansion portion 120 is a solid elongation portion 124, the length of which is 1.5 to 2 times the outer diameter of the expansion portion 120. The solid elongation portion 124 is configured to reduce the axial elongation effect of the expansion portion 120 under hydraulic action. By providing a solid elongation portion 124 with a length of 1.5 to 2 times the outer diameter, the axial rigidity of its solid structure can be used to effectively resist the axial tensile force generated during the hydraulic compression process, thereby reducing the axial elongation effect of the expansion portion 120, and making full use of the internal hydraulic action to make the expansion portion 120 radially expand, thereby ensuring that the expansion portion 120 has sufficient force to clamp and position the workpiece.

[0099] For example Figure 1As shown, in some embodiments, the pressurizing mechanism includes a pressurizing channel 131 disposed within the clamp body 100 and communicating with the hydraulic chamber 110, a pressurizing piston 132 disposed within the pressurizing channel 131 and slidably sealed therewith, and a pressurizing screw 133 threadedly connected to the pressurizing channel 131 and capable of pressing the pressurizing piston 132 toward the inner end of the pressurizing channel 131. The pressurizing piston 132 is generally provided with a sealing ring, which slidably seals with the pressurizing channel 131. When operating the pressurizing mechanism, tightening the pressurizing screw 133 compresses the pressurizing piston 132, causing it to move toward the inner end of the pressurizing channel 131, thereby compressing the hydraulic medium and increasing the pressure generated, thus causing the expansion portion 120 to expand radially; conversely, loosening the pressurizing screw 133, under the pressure of the hydraulic medium, compresses the pressurizing piston 132, causing it to move toward the pressurizing screw 133, thereby depressurizing and reducing the pressure generated by the hydraulic medium, thus causing the expansion portion 120 to retract radially.

[0100] For example Figure 1 As shown, in some embodiments, the small-diameter hydraulic expansion clamp also includes a sealing structure. The sealing structure includes a sealing channel 141 disposed within the clamp body 100 and coaxially connected to the hydraulic cavity 110. A sealing ring is formed at the inner end of the sealing channel 141. A sealing ball 142 is disposed within the sealing channel 141 to block the inner hole of the sealing ring, and a sealing screw 143 is provided to tighten and fix the sealing ball 142. By providing a sealing channel 141 coaxially connected to the hydraulic cavity 110, it is not only convenient to process the internal structure of the clamp body 100, but also convenient for later maintenance. Through the cooperation of the sealing ring and the sealing ball 142, the hydraulic cavity 110 can be effectively sealed to ensure its sealing performance. At the same time, by providing the sealing screw 143 to tighten and fix the sealing ball 142, it can be ensured that the hydraulic cavity 110 can withstand a large hydraulic pressure.

[0101] like Figure 3As shown, in order to be compatible with micro CNC machine tools or modular assembly equipment for robot joints, in some embodiments, the small-diameter hydraulic expansion fixture also includes a fixture base 200 connected to the fixture body 100; the fixture base 200 is provided with a piston chamber, and a push rod piston 220 is provided in the piston chamber to divide it into a first chamber and a second chamber 201; the fixture base 200 is provided with a liquid supply channel 230 communicating with the first chamber, and the liquid supply channel 230 is used to connect to the hydraulic system of the machine tool; the pressurizing mechanism includes a pressurizing channel 131 disposed in the fixture body 100 and communicating with the hydraulic chamber 110, a seal 134 disposed in the pressurizing channel 131 near one end of the fixture base 200, and a pressurizing push rod 135 disposed through the seal 134; one end of the pressurizing push rod 135 extends into the pressurizing channel 131, and the other end extends into the second chamber 201 and abuts against the push rod piston 220. When this small-diameter hydraulic expansion clamp is installed on a machine tool, the inlet of the fluid supply channel 230 is usually connected to the machine tool's hydraulic system. When the machine tool operates the pressurizing mechanism to pressurize, the control hydraulic system supplies hydraulic oil to the first chamber through the fluid supply channel 230. The hydraulic oil flowing into the first chamber pushes the push rod piston 220 to move, and then the push rod piston 220 pushes the pressurizing push rod 135 to move, so that the push rod 135 extends more into the rod part of the pressurizing channel 131. This causes the pressurizing push rod 135 to compress the hydraulic medium in the pressurizing channel 131, the hydraulic chamber 110, and the expansion chamber 121, increasing the pressure it generates. Then, it squeezes the wall of the expansion chamber 121, causing the expansion part 120 to expand radially and clamp the workpiece.

[0102] For example Figure 3 As shown, based on the previous embodiment, the piston chamber is a structure that passes through the clamp base 200, with one end closed by the sealing cover 210 and the other end closed by the clamp body 100.

[0103] For example Figure 3 As shown, based on the previous embodiment, the end of the pressure push rod 135 that extends into the pressure channel 131 is provided with a push rod head 136 so as to compress the hydraulic medium more effectively.

[0104] For example Figure 3As shown, in some embodiments, the small-diameter hydraulic expansion fixture also includes a hydraulic compensation mechanism, which includes a compensation channel with a one-way valve structure. The channel inlet of the compensation channel is located on the fixture base 200 and is used to connect to the hydraulic system of the machine tool. The channel outlet of the compensation channel is connected to the pressurization channel 131 and / or the hydraulic chamber 110. When the small-diameter hydraulic expansion fixture is installed on the machine tool, the channel inlet of the compensation channel is usually connected to the hydraulic system of the machine tool, and the pressure at the channel inlet of the compensation channel is controlled so that it is insufficient to open the one-way valve structure. Thus, during the operation of the small-diameter hydraulic expansion fixture, if the hydraulic medium in the hydraulic chamber 110 is lost due to poor sealing, internal air being expelled due to temperature rise, etc., and the expansion part 120 is unable to clamp the workpiece, the hydraulic system of the machine tool can open the one-way valve structure by supplying hydraulic medium, thereby compensating the hydraulic medium in the hydraulic chamber 110.

[0105] Combination Figure 3 and Figure 4 As shown, based on the previous embodiment, the compensation channel includes a valve chamber 241, and a compensation inlet channel 242 and a compensation outlet channel 243 respectively connected to the valve chamber 241; a valve seat is formed at the connection between the valve chamber 241 and the compensation inlet channel 242; the one-way valve structure includes a one-way valve core 244, a valve core spring 245, a sealing piston 246, and an adjusting screw 247; the one-way valve core 244 is axially movable in the valve chamber 241, and together with the valve seat, forms an opening and closing mechanism that can control the opening and closing of the compensation inlet channel 242 and the compensation outlet channel 243; the sealing piston 246 is disposed in the valve chamber 241 and is located on the side of the one-way valve core 244 away from the valve seat; the valve core spring 245 is disposed between the one-way valve core 244 and the sealing piston 246 and is in a pre-tightened state; the adjusting screw 247 is threadedly connected to the valve chamber 241 and can press the sealing piston 246 toward the one-way valve core 244. The sealing piston 246 is used to pre-tighten the valve core spring 245 and seal the valve chamber 241. The adjusting screw 247 is used to squeeze or loosen the sealing piston 246 to adjust the pre-tightening force of the valve core spring 245, thereby controlling the pressure required to open the one-way valve structure. The specific compensation process is as follows: The machine tool's hydraulic system supplies hydraulic medium through the inlet of the compensation channel. When the pressure reaches the set threshold, the hydraulic medium in the compensation inlet channel 242 pushes the one-way valve core 244 away from the mating conical surface with the valve seat, forming a gap. Then, the hydraulic medium flows into the valve chamber 241 and along the compensation outlet channel 243 into the pressurization channel 131 and / or the hydraulic chamber 110, completing the compensation action. Afterwards, the machine tool's hydraulic system stops supplying fluid. The pressure in the compensation inlet channel 242 is insufficient to open the one-way valve structure. The one-way valve core 244, under the action of the valve core spring 245, re-mates with the valve seat, controlling the disconnection of the compensation inlet channel 242 and the compensation outlet channel 243.

[0106] like Figure 7As shown, in some embodiments, the small-diameter hydraulic expansion clamp also includes a diameter measuring sensor 300 for detecting the outer diameter of the expansion section 120. The diameter measuring sensor 300 can be of various types, such as a laser diameter measuring sensor, an ultrasonic diameter measuring sensor, a mechanical diameter measuring sensor, etc.

[0107] like Figure 6 As shown, in some embodiments, the diameter measuring sensor 300 includes a sensor body having a measuring hole 311, and at least four strain gauges uniformly distributed circumferentially along the wall of the measuring hole 311 are provided.

[0108] The present invention also provides a method for manufacturing a small-diameter hydraulic expansion fixture, including a preform preparation step;

[0109] Initial blank fabrication steps: The initial blank 400 of the fixture is fabricated using 3D printing technology; alternatively, the expanded portion 120 with a connecting seat is fabricated using 3D printing technology, and the remaining parts of the initial blank 400 of the fixture are machined to save costs, such as... Figure 8 As shown;

[0110] Among them, the fixture blank 400 is the blank of the small-diameter hydraulic expansion fixture mentioned above.

[0111] This manufacturing method uses 3D printing technology to create the fixture blank 400 or the expansion part 120 with a connecting seat, which ensures the uniformity of hydraulic medium pressure distribution in ultra-small apertures (less than 3 mm), further avoids local deformation of the expansion part 120, and improves the clamping repeatability of the small-diameter hydraulic expansion fixture to the sub-micron level.

[0112] To further improve the strength of small-diameter hydraulic expansion fixtures, in some embodiments, the fixture blank 400 is made of high-strength titanium alloy or special steel.

[0113] Specifically, the above manufacturing method also includes the steps of heat treatment, turning and grinding of the fixture blank 400 in sequence;

[0114] During the initial blanking process, the 3D-printed thickened portion 122 enhances the rigidity of the thin-walled structure of the expanded portion 120, which helps to ensure the machining accuracy in subsequent turning and grinding processes.

[0115] Considering heat treatment deformation, a larger allowance is usually reserved at the expansion section 120.

[0116] The purpose of turning is to remove excess material from the outer shape using a turning tool 500, such as... Figure 9 As shown;

[0117] Grinding process: First, rough grinding with a 600 grinding tool removes the excess material from the expansion portion 120. Then, aging treatment is performed to release machining stress. Finally, finish grinding is performed until the circular runout reaches an accuracy of 0.003 mm, resulting in the finished small-diameter hydraulic expansion fixture. Figure 10 As shown.

[0118] The present invention also provides a method for controlling the expansion amount of a small-diameter hydraulic expansion clamp, for controlling the aforementioned small-diameter hydraulic expansion clamp, comprising the following steps:

[0119] Step A: Install the small-diameter hydraulic expansion fixture onto the machine tool and set the initial hydraulic pressure in the machine tool's CNC system;

[0120] Step B: The machine tool supplies hydraulic oil to the first cavity of the small-diameter hydraulic expansion fixture, and then pushes the pressurizing push rod 135 through the push rod piston 220 to compress the hydraulic medium in the hydraulic cavity 110, so as to drive the expansion part 120 to expand radially and clamp and fix the workpiece.

[0121] Step C: Process the workpiece and measure its dimensions after processing;

[0122] Step D: Compare the measured workpiece dimensions with the dimensions required by the drawing to determine the direction and degree of dimensional deviation, which will serve as the basis for adjusting the expansion amount; the direction of dimensional deviation includes two directions: the size is too large and the size is too small.

[0123] Step E: Feedback the expansion amount adjustment data to the machine tool's CNC system. Based on the expansion amount adjustment data and the outer diameter data of the expansion part 120 measured by the diameter measuring sensor 300, the machine tool's CNC system sends control commands to the controller; the controller is usually a PLC controller.

[0124] Step F: The controller controls the machine tool's oil pump to work and adjusts the oil pressure supplied to the small-diameter hydraulic expansion fixture, thereby adjusting the expansion diameter of the expansion section 120.

[0125] In order to precisely control the supply hydraulic pressure, in some implementations, the machine tool's CNC system generates control commands based on the following formula;

[0126] Formula 1: ;

[0127] Formula 2: ;

[0128] Formula 3: ;

[0129] Combination Figure 3 and Figure 5 As shown, D is the diameter of the push rod piston 220;

[0130] d is the diameter of the pressure push rod 135;

[0131] Pg is the pressure at the inlet of the liquid supply channel 230;

[0132] P is the pressure inside the hydraulic chamber 110;

[0133] Δy(x) is the expansion amount of the expansion section 120;

[0134] R is the radius of the outer wall contour of the expansion section 120;

[0135] E1 is the elastic modulus of the expansion portion 120;

[0136] t is the minimum wall thickness of the expansion section 120;

[0137] l is the length of the expansion cavity 121;

[0138] μ1 is the Poisson's ratio of the expansion portion 120;

[0139] λ is a dimensionless intermediate variable;

[0140] x is the axial coordinate of the length of the expansion cavity 121 with the connection between the expansion section 120 and the hydraulic cavity 110 as the origin.

[0141] Example 1

[0142] Based on formulas 1-3, an expansion control test was conducted on the small-diameter hydraulic expansion clamp provided by the present invention.

[0143] The expansion part 120 of the small-diameter hydraulic expansion clamp has a diameter of 3 mm, the number of thickened parts 122 is 8, and the length of the expansion cavity 121 is 40 mm.

[0144] The deformation of the expansion section 120 was tested under working oil pressures of 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, and 80 MPa in the hydraulic chamber 110, respectively. Figure 11 As shown.

[0145] pass Figure 11 It can be seen that the deformation of the expansion part 120 is positively correlated with the working oil pressure, that is, as the working oil pressure increases, the radial expansion of the expansion part 120 increases linearly; on the x-axis, the deformation curve shows the largest deformation at 0 mm and 40 mm, and the smallest deformation at the middle position of 20 mm, showing a concave arc symmetrical distribution, indicating that the expansion part 120 can generate effective radial expansion within the test pressure range, and can clamp and fix the workpiece at both ends, which is beneficial to improving the bending resistance and rotation accuracy of the workpiece.

[0146] Example 2

[0147] An expansion diameter measurement test was conducted on the small-diameter hydraulic expansion clamp provided by this invention.

[0148] The expansion diameter of small-diameter hydraulic expansion fixtures with equal diameter expansion sections 120 and 3, 4, 5, and 6 thickened sections 122 were respectively measured. Figure 12 As shown.

[0149] The diameter measuring sensor 300 used for testing includes a sensor body with a measuring hole 311. The inner diameter of the measuring hole 311 matches the diameter of the expansion part 120. At least four strain gauges are provided on the hole wall of the measuring hole 311, which are evenly distributed in the circumferential direction, and can output a 24V digital signal to measure the diameter value.

[0150] Taking a small-diameter hydraulic expansion fixture with five thickened sections 122 as an example, under pressure P in the hydraulic chamber 110, the deformation δ of the outer diameter of its expansion section 120 exhibits a radial trend, such as... Figure 13 As shown.

[0151] The expression for the inner curve is as follows:

[0152] X(α)=(R_in+Amp*sin(N*α))*cos(α);

[0153] Y(α)=(R_in+Amp*sin(N*α))*sin(α);

[0154] α:[0,2*pi];

[0155] Where R_in: the radius of the inscribed circle of the thickened part 122;

[0156] Amp: The thickness of the thickened part 122, that is, the radius of the outer circle of the thickened part 122 minus the radius of the inner circle of the thickened part 122;

[0157] N: The number of thickened portions 122;

[0158] α: The starting angle of the thickened portion 122;

[0159] pi: Pi (the mathematical constant in Chinese)

[0160] In this embodiment, R_in = 1.25 mm, Amp = 0.1 mm, resulting in:

[0161] X(α)=(1.25+0.1*sin(N*α))*cos(α);

[0162] Y(α)=(1.25+0.1*sin(N*α))*sin(α);

[0163] α:[0,2*pi];

[0164] N: [3, 4, 5, 6];

[0165] The expansion diameter test results correspond to respectively Figures 14 to 17 As can be seen from the results, the outer diameter deformation δmax gradually decreases as N increases, and the difference between the outer diameter deformation δmax and the outer diameter deformation δmin also gradually decreases. Therefore, from the perspective of the uniformity of outer diameter deformation, the optimal number of thickened parts 122 N in the test group is 6.

[0166] Example 3

[0167] Based on Example 2, when the number of thickened portions 122 is 6, an expansion diameter size detection test is conducted under different thickening ranges.

[0168] In this embodiment, R_in = 1.25 mm, N = 6, resulting in:

[0169] X(α)=(1.25+Amp*sin(6*α))*cos(α);

[0170] Y(α)=(1.25+Amp*sin(6*α))*sin(α);

[0171] α:[0,2*pi];

[0172] Amp:[0.05, 0.10, 0.15, 0.20];

[0173] The expansion diameter test results correspond to respectively Figures 18 to 21 As can be seen from the results, the outer diameter deformation δmax gradually increases with the increase of Amp, and the difference between the outer diameter deformation δmax and the outer diameter deformation δmin also gradually increases. Therefore, in terms of the uniformity of outer diameter deformation, when the number of thickened parts 122 is 6, Amp of 0.05 mm is optimal.

[0174] Based on the above embodiments, it can be concluded that, in some embodiments of the present invention, a set of preferred parameters for the thickened portion 122 are:

[0175] X(α)=(1.25+0.05*sin(6*α))*cos(α);

[0176] Y(α)=(1.25+0.05*sin(6*α))*sin(α);

[0177] α:[0,2*pi];

[0178] That is: R_in is 1.25 mm, Amp is 0.05 mm, and N is 6.

Claims

1. A small-diameter hydraulic expansion clamp, comprising a clamp body (100), a hydraulic cavity (110) formed in the clamp body (100), and a pressurizing mechanism for pressurizing the hydraulic cavity (110); The fixture body (100) has an expansion portion (120) for clamping the workpiece. Its features are: The expansion section (120) is a cylindrical structure with one end connected to the hydraulic cavity (110) and the other end closed. Its outer wall profile is cylindrical and its outer diameter is ≤4 mm. Its inner cavity is the expansion cavity (121). The sidewall of the expansion cavity (121) is composed of at least three thickened portions (122) distributed circumferentially, and thinned portions (123) connecting adjacent thickened portions (122); In the cross-section of the expansion cavity (121), the thickened part (122) is an arc shape that protrudes toward the axis of the expansion part (120), and the thinned part (123) is an arc shape that is concave away from the axis of the expansion part (120). The thickened parts (122) and thinned parts (123) that are adjacent to each other are smoothly connected, so that the inner wall profile of the expansion part (120) is a continuous and closed wave ring. The closed end of the expansion portion (120) is a solid growth portion (124), the length of which is 1.5 to 2 times the outer diameter of the expansion portion (120); The solid growth section (124) is configured to reduce the axial elongation effect of the expansion section (120) under hydraulic action; The small-diameter hydraulic expansion clamp also includes a clamp base (200) connected to the clamp body (100) and a diameter measuring sensor (300) for detecting the outer diameter of the expansion part (120). The fixture base (200) is provided with a piston chamber, and a push rod piston (220) is provided in the piston chamber to divide it into a first chamber and a second chamber (201); the fixture base (200) is provided with a liquid supply channel (230) connected to the first chamber, and the liquid supply channel (230) is used to connect to the hydraulic system of the machine tool. The pressurizing mechanism includes a pressurizing channel (131) disposed in the clamp body (100) and connected to the hydraulic chamber (110), a seal (134) disposed at one end of the pressurizing channel (131) near the clamp base (200), and a pressurizing push rod (135) disposed through the seal (134); one end of the pressurizing push rod (135) extends into the pressurizing channel (131), and the other end extends into the second chamber (201) and abuts against the push rod piston (220); The diameter measuring sensor (300) includes a sensor body with a measuring hole (311), and at least four strain gauges are provided on the hole wall of the measuring hole (311) evenly distributed in the circumferential direction. The expansion amount control method for this small-diameter hydraulic expansion clamp is as follows: Step A: Install the small-diameter hydraulic expansion fixture onto the machine tool and set the initial hydraulic pressure of the hydraulic chamber (110) in the CNC system of the machine tool; Step B: The machine tool supplies hydraulic oil to the first cavity of the small-diameter hydraulic expansion fixture, and then pushes the pressurizing push rod (135) through the push rod piston (220) to compress the hydraulic medium in the hydraulic cavity (110), so as to drive the expansion part (120) to expand radially and clamp and fix the workpiece. Step C: Process the workpiece and measure its dimensions after processing; Step D: Compare the measured workpiece dimensions with the dimensions required by the drawing to determine the direction and degree of dimensional deviation, which will serve as the basis for adjusting the expansion amount. Step E: Feed back the expansion amount adjustment data to the CNC system of the machine tool. The CNC system of the machine tool sends control commands to the controller based on the expansion amount adjustment data and the outer diameter data of the expansion part (120) measured by the diameter measuring sensor (300). Step F: The controller controls the machine tool's oil pump to work and adjusts the oil pressure supplied to the small-diameter hydraulic expansion fixture, thereby adjusting the expansion diameter of the expansion section (120).

2. The small-diameter hydraulic expansion clamp according to claim 1, characterized in that: The number of thickened portions (122) is 3 to 8.

3. The small-diameter hydraulic expansion clamp according to claim 1 or 2, characterized in that: It also includes a hydraulic compensation mechanism, which includes a compensation channel with a check valve structure; The inlet of the compensation channel is located on the fixture base (200) and is used to connect to the hydraulic system of the machine tool; The outlet of the compensation channel is connected to the pressurization channel (131) and / or the hydraulic chamber (110).

4. The small-diameter hydraulic expansion clamp according to claim 3, characterized in that: The compensation channel includes a valve chamber (241), and a compensation inlet channel (242) and a compensation outlet channel (243) respectively connected to the valve chamber (241). A valve seat is formed at the connection between the valve chamber (241) and the compensation inlet channel (242); The one-way valve structure includes a one-way valve core (244), a valve core spring (245), a sealing piston (246), and an adjusting screw (247). The one-way valve core (244) is axially movable in the valve chamber (241) and together with the valve seat forms an opening and closing mechanism that can control the opening and closing of the compensation inlet channel (242) and the compensation outlet channel (243); The sealing piston (246) is disposed in the valve chamber (241) and is located on the side of the one-way valve core (244) away from the valve seat; The valve core spring (245) is disposed between the one-way valve core (244) and the sealing piston (246) and is in a pre-tightened state; The adjusting screw (247) is threaded into the valve chamber (241) and can press the sealing piston (246) toward the one-way valve core (244).

5. A method for manufacturing a small-diameter hydraulic expansion clamp, characterized in that: Including the steps for making the initial embryo; Initial blank making steps: Use 3D printing technology to make the initial blank of the fixture; or, use 3D printing technology to make the expansion part (120) with the connecting seat, and machine the rest of the initial blank of the fixture. Wherein, the fixture blank is the blank of the small-diameter hydraulic expansion fixture as described in any one of claims 1 to 4.

6. The method for manufacturing a small-diameter hydraulic expansion clamp according to claim 5, characterized in that: It also includes the steps of heat treatment, turning and grinding of the fixture blank in sequence; Among them, the grinding process is as follows: first, rough grinding is performed to remove the excess of the expansion part (120), then aging treatment is performed to release the processing stress, and finally fine grinding is performed until the circular runout reaches an accuracy of 0.003 mm, so as to obtain the finished product of the small diameter hydraulic expansion fixture.

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