A flexible adaptive magnetic particle lapping device and method for a profiled hole

Abstract

The present application relates to the technical field of workpiece processing, and discloses a flexible self-adaptive magnetic particle grinding device and method for special-shaped holes, the grinding device comprising a machine body assembly, a machining table inside the machine body assembly for clamping and fixing a machining workpiece, a concave corner grinding unit for grinding a concave corner of the special-shaped hole and a rotary grinding unit for grinding a convex corner and an inner wall of the special-shaped hole movably arranged on the machining table; through a sliding block and a movable rod self-adaptive mechanism pre-tightened by a spring, passive, flexible and self-adaptive fitting of the concave corner grinding magnetic pole to the concave corner of the special-shaped hole is realized, a complex active drive and control system is not needed, the structure is simple and reliable, and the device is especially suitable for high-speed rotating working conditions; corresponding N-S magnetic poles are designed, a strong focusing closed magnetic circuit is formed in the concave corner area, the problem of magnetic field attenuation in the area is effectively solved, and the grinding efficiency and uniformity of the concave corner are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of workpiece processing, and more specifically, to a flexible adaptive magnetic particle grinding apparatus and method for irregularly shaped holes. Background Technology

[0002] With the increasing demand for high-performance components in aerospace, precision hydraulics, and medical devices, extremely high requirements are being placed on the surface quality of parts with irregularly shaped internal holes (such as polygonal holes, keyway holes, and internal splines). The concave corner areas (i.e., inner edges) of the inner surfaces of irregularly shaped holes are prone to stress concentration, microcracks, and surface roughness deterioration during traditional machining due to abrupt structural changes, severely impacting the fatigue life, sealing performance, and hydrodynamic characteristics of the parts. Therefore, achieving efficient, uniform, and controllable finishing of the inner surfaces of irregularly shaped holes, especially the hard-to-reach concave corner areas, has become a key technical challenge urgently needing to be solved in the field of precision manufacturing.

[0003] Currently, the finishing processes for the inner surfaces of irregularly shaped holes mainly involve the following technical approaches and their limitations:

[0004] Traditional mechanical grinding and electrochemical machining employ rigid abrasives or utilize electrochemical dissolution principles. Rigid abrasives struggle to adapt to complex, irregular contours, easily creating blind spots or overcutting at concave corners. Conventional magnetic abrasive technology, on the other hand, uses a magnetic field to control magnetic abrasive particles, forming a flexible "magnetic brush," offering advantages such as good adaptability and no tool wear. However, in machining irregular holes, the magnetic field strength of conventional axial or radial magnetic fields significantly decreases in concave corner areas, resulting in insufficient magnetic force on the abrasive particles in these regions, weak or even ineffective grinding, and severely uneven machining results between concave and planar areas.

[0005] To overcome the magnetic field attenuation problem at concave corners in conventional magnetic abrasive grinding, existing technologies have proposed integrating actively driven auxiliary magnetic poles into the device. For example, a servo motor drives a lead screw mechanism, or a cylinder drives a piston rod to advance or extend the auxiliary magnetic pole into the concave corner, aiming to locally enhance the magnetic field. While these solutions address the need for magnetic field strengthening to some extent, their inherent defects are amplified in practical applications, especially in core operating conditions where the workpiece must rotate at high speed to improve processing efficiency. Specifically, these defects manifest as poor dynamic stability and severe self-interference in the magnetic circuit.

[0006] Therefore, there is an urgent need for a method that can enable the auxiliary magnetic poles to autonomously and reliably adapt to different concave angles and maintain a pure and stable strong magnetic field under high-speed rotation conditions without the need for a complex active drive and electronic control system, thereby achieving efficient and uniform magnetic particle grinding of concave corner areas of irregular holes. Summary of the Invention

[0007] This invention provides a flexible adaptive magnetic particle polishing device and method for irregular holes, which solves the technical problem in related technologies that it is impossible to reliably and autonomously fit the concave corner of irregular holes and maintain a stable and effective polishing effect without a complex electronic control system in a high-speed dynamic and highly polluted polishing environment.

[0008] The present invention provides a flexible adaptive magnetic particle grinding device for irregular holes, including a body assembly and a processing table inside it for clamping and fixing the workpiece. The processing table is movably arranged with a concave corner grinding unit for grinding the concave corner of the irregular hole and a rotary grinding unit for grinding the convex corner and inner wall of the irregular hole.

[0009] The concave corner grinding unit includes a mounting shaft slidably disposed inside the workpiece. The mounting shaft has several mounting grooves on its circumferential side, and a connecting rod is disposed in each groove. Two sliders are slidably disposed on the circumferential side of each connecting rod. The top of each slider is movably connected to a movable rod. The other ends of the two movable rods are connected via concave corner grinding magnetic poles. The top of each concave corner grinding magnetic pole has a V-shaped guide groove extending along its length. An outer magnetic pole is disposed on the outer wall of the workpiece, and the position of the outer magnetic pole corresponds to the concave corner grinding magnetic pole located at the concave corner inside the workpiece.

[0010] The rotary grinding unit includes a rotary grinding magnetic pole for rotary grinding, and the peripheral surface of the rotary grinding magnetic pole is provided with a threaded groove.

[0011] In a preferred embodiment, the body assembly includes a machine tool for supporting and mounting the remaining components of the grinding device, the machine tool surface being fitted with a protective cover and an operation panel, the protective cover being slidably disposed on the outer surface of the machine tool.

[0012] In a preferred embodiment, the machining table includes a spindle box installed inside the machine tool. A gripper for clamping and fixing one end of the workpiece is installed on one side of the spindle box, and a slide rail is fixedly installed at the bottom of its side. A slide block and a slide box are slidably arranged on the surface of the slide rail, and a slender shaft is connected to one end of the slide box.

[0013] In a preferred embodiment, a rectangular groove is provided on the top of the slide block, and an annular fixing frame is installed inside the rectangular groove. The concave corner grinding unit is slidably sleeved on the outside of the workpiece through the slide block. A sliding groove is provided inside the annular fixing frame, and a number of mounting blocks are installed inside the sliding groove. The number of mounting blocks is the same as the number of concave corners of the irregular hole, and their installation positions correspond to the positions of the concave corners of the irregular hole. The top of the mounting block is connected to one end of the external magnetic pole.

[0014] In a preferred embodiment, one end of the slender shaft is connected to one end of the mounting shaft. The slider is slidably disposed in the mounting groove inside the mounting shaft. The two sliders are movably connected by a spring, and the spring is sleeved on the circumferential side of the connecting rod. At the same time, the outside of the spring is sealed by a corrugated sleeve. The other side of each slider is fixedly connected to one end of a damper. The other end of the damper is connected to the groove wall of the mounting groove. One end of the connecting rod located directly above the damper is also connected to a corrugated sleeve to seal the connecting rod.

[0015] In a preferred embodiment, the rotary grinding unit further includes a motor, which is mounted on the other end of the mounting shaft, and the output end of the motor is fixedly connected to one end of the rotary grinding magnetic pole.

[0016] In a preferred embodiment, the magnetic poles of the threaded groove and the concave angle grinding magnetic pole are of the N-level, and the magnetic poles of the outer magnetic pole are of the S-level.

[0017] In a preferred embodiment, the concave-angle grinding magnetic pole moves back and forth along the axial direction of the irregular hole inside the workpiece, and the corresponding position of the concave-angle grinding magnetic pole moves synchronously and always corresponds to the position of the concave-angle grinding magnetic pole.

[0018] A method of using a flexible adaptive magnetic particle polishing device for irregularly shaped holes includes the following steps:

[0019] S1. Fill the inner cavity of the workpiece with magnetic abrasive and fix one end of it with a clamp.

[0020] S2. The slender shaft and the concave corner grinding unit and rotary grinding unit installed at its front end are fed into one end of the irregular hole inside the workpiece through the slide box. Each concave corner grinding magnetic pole is aligned with a concave corner of the irregular hole. At the same time, the same number of mounting blocks as the concave corners of the irregular hole are installed in the slide groove inside the ring fixed frame. The position of the external magnetic pole on each mounting block corresponds to the concave corner grinding magnetic pole at the concave corner of the irregular hole inside the workpiece.

[0021] S3. Start the slide box and motor. The slide box pushes the concave corner grinding unit and the rotary grinding unit to move along the workpiece axis. The concave corner grinding magnetic pole moves at the concave corner of the irregular hole and forms an NS closed magnetic circuit with the external magnetic pole to grind the concave corner. The motor drives the rotary grinding magnetic pole to rotate and drive the abrasive to form a magnetic brush to grind the protruding corner and inner wall of the irregular hole.

[0022] S4. The slide box pushes the concave corner grinding unit and the rotary grinding unit back and forth two to three times to grind the irregular holes inside the workpiece. After grinding, the concave corner grinding unit and the rotary grinding unit are taken out, and then the workpiece is rinsed and the magnetic abrasive is collected.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. This invention achieves passive, flexible, and adaptive fitting of the concave corner grinding magnetic pole to the concave corner of the irregular hole through an adaptive mechanism of a spring-preloaded slider and movable rod. It does not require a complex active drive and control system, and has a simple and reliable structure, especially suitable for high-speed rotation conditions.

[0025] 2. The corresponding NS magnetic pole design of the present invention forms a strongly focused closed magnetic circuit in the concave corner area, which effectively solves the problem of magnetic field attenuation in this area and significantly improves the grinding efficiency and uniformity of the concave corner.

[0026] 3. The rotary grinding magnetic pole and the adaptive concave angle grinding unit of this invention work together to achieve synchronous and composite grinding of the inner wall and concave angle of irregular hole, resulting in high processing efficiency and good surface quality consistency.

[0027] 4. The device of the present invention has a modular structure. By adjusting the number and position of the adaptive mechanism, it can adapt to different numbers and shapes of irregular holes with concave angles, and has strong versatility. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0029] Figure 2 This is a schematic diagram of the overall structure of the processing table of the present invention.

[0030] Figure 3 This is the present invention. Figure 2 Enlarged view of point A in the middle.

[0031] Figure 4 This is a schematic diagram of the internal concave corner grinding unit and rotary grinding unit of the workpiece of the present invention.

[0032] Figure 5 This is the present invention. Figure 4 Enlarged view of section B in the middle.

[0033] Figure 6 This is a front view of the workpiece being processed and the grinding assembly of the present invention.

[0034] Figure 7 This is a schematic diagram of the overall structure of the concave corner grinding unit of the present invention.

[0035] Figure 8 This is a schematic diagram of the overall structure of the concave-angled grinding magnetic pole of the present invention.

[0036] Figure 9 This is a schematic diagram of the overall structure of the rotary grinding unit of the present invention.

[0037] Figure 10 This is a flowchart of the method of using the present invention.

[0038] In the diagram: 1. Machine body assembly; 101. Machine tool; 102. Protective cover; 103. Control panel; 2. Machining table; 201. Spindle box; 202. Gripper; 203. Slide rail; 204. Slide box; 205. Slide seat; 206. Slender shaft; 3. Concave angle grinding unit; 301. Annular fixing frame; 302. Mounting block; 303. External magnetic pole; 304. Mounting shaft; 305. Connecting rod; 306. Slider; 307. Spring; 308. Damper; 309. Corrugated sleeve; 310. Movable rod; 311. Concave angle grinding magnetic pole; 4. Rotary grinding unit; 401. Rotary grinding magnetic pole; 402. Threaded groove; 403. Motor; 5. Machining workpiece. Detailed Implementation

[0039] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, features described in some examples may be combined in other examples.

[0040] refer to Figures 1-9 This embodiment provides a flexible adaptive magnetic particle grinding device for irregular holes. The device mainly includes: a body assembly 1, a processing table 2, a concave corner grinding unit 3, a rotary grinding unit 4, and a workpiece to be processed 5.

[0041] See Figure 1 The machine body component 1 constitutes the basic support structure of the device, including machine tool 101, protective cover 102 and operation panel 103. Machine tool 101 provides a rigid base for the whole. Protective cover 102 is installed on machine tool 101 to enclose the processing area and prevent abrasive splashing. Operation panel 103 is integrated on one side of machine tool 101 for setting and monitoring processing parameters.

[0042] See Figure 2The machining table 2 is used to clamp and drive the workpiece 5. Specifically, it includes a spindle box 201, grippers 202, a slide rail 203, an apron 204, a slide block 205, and a slender shaft 206. The spindle box 201 is fixed to the machine tool 101, and its output end is equipped with grippers 202 for clamping one end of the workpiece 5. These grippers can be driven to rotate by a built-in motor. The slide rail 203 is mounted on the upper surface of the machine tool 101. The apron 204 is slidably mounted on the slide rail 203 and can be driven to move along the axial direction of the workpiece 5 by a drive device. The slide block 205 is slidably mounted on the apron 204 via the slide rail 203 and can move in a direction perpendicular to the axis of the workpiece 5. One end of the slender shaft 206 is fixedly connected to the apron 204, and the other end extends into the workpiece 5 to support the concave angle grinding unit 3 and the rotary grinding unit 4.

[0043] The concave corner grinding unit 3 is the core component of this invention for achieving adaptive concave corner grinding, such as... Figure 4 , Figure 7 and Figure 8 As shown, it mainly consists of a mounting shaft 304, a slider 306, a spring 307, a movable rod 310, and a concave-angle grinding magnetic pole 311. The mounting shaft 304 is a slender tubular structure that is slidably sleeved on the outside of the slender shaft 206 and can be driven axially by the slide box 204. On the circumferential side of the mounting shaft 304, several mounting grooves are spaced apart axially. The number of mounting grooves is the same as the number of concave angles of the irregular holes in the workpiece 5, and their positions correspond one-to-one. Each mounting groove is equipped with an adaptive mechanism: one end of each of the two movable rods 310 is connected to both sides of a concave-angle grinding magnetic pole 311 by hinges, and the other end is hinged to a slider 306. The two sliders 306 are slidably mounted on the connecting rod 305 in the mounting groove, and the two sliders 306 are connected by a spring 307. Under the preload of spring 307, the two sliders 306 tend to move closer together, causing the two movable rods 310 to retract and bringing the concave-angle grinding magnetic pole 311 into a "retracted" state. The top of the concave-angle grinding magnetic pole 311 has a V-shaped guide groove extending along its length, which helps it to more stably align and conform to the concave angle, while also preventing magnetic abrasive from entering. Furthermore, a corrugated sleeve 309 is fitted at the hinge of the movable rod 310 and on the outside of the guide rod to prevent abrasive intrusion. In some embodiments, a damper 308 may also be provided between the slider 306 and the wall of the mounting groove to suppress possible vibrations.

[0044] It should be further explained that, corresponding to the internal concave corner grinding magnetic pole 311, an external magnetic pole 303 is provided on the outside of the workpiece 5. The external magnetic pole 303 is mounted on an annular fixing frame 301 via a mounting block 302. The annular fixing frame 301 is slidably fitted onto the outside of the workpiece 5 via a slide block 205. By adjusting the position of the slide block 205, each external magnetic pole 303 can be precisely aligned with the position on the outer wall of the workpiece 5 corresponding to the internal concave corner. According to the magnetic field design, the magnetic pole of the concave corner grinding magnetic pole 311 is the N pole, and the magnetic pole of the external magnetic pole 303 is the S pole. The two correspond in space to form an N-S closed magnetic circuit, which strongly concentrates the magnetic field in the concave corner area.

[0045] The rotary grinding unit 4 is used to grind the protruding corners, i.e., the raised inner edges, and the inner wall surface of irregularly shaped holes. For example... Figure 4 and Figure 9 As shown, it mainly includes a rotary grinding magnetic pole 401 and a motor 403 that drives its rotation. The rotary grinding magnetic pole 401 is also sleeved on the mounting shaft 304, and its peripheral side is machined with threaded grooves 402. The motor 403 is fixedly mounted on one end of the mounting shaft 304, and its output shaft is fixedly connected to the rotary grinding magnetic pole 401, which can drive it to rotate at high speed. The magnetic pole of the rotary grinding magnetic pole 401 is also a north pole.

[0046] See Figure 10 This embodiment also provides a method for using a flexible adaptive magnetic particle polishing device for irregularly shaped holes, including the following steps:

[0047] S1. Fix one end of the workpiece 5 to be processed using the clamp 202. Pour a pre-mixed mixture of magnetic abrasive and grinding fluid into the inner cavity of the workpiece 5.

[0048] S2. Start the drive mechanism, and send the slender shaft 206 and the concave corner grinding unit 3 and rotary grinding unit 4 carried at its front end into the irregular hole inside the workpiece 5 via the slide box 204. During the feeding process, ensure that each concave corner grinding magnetic pole 311 is precisely aligned with the concave corner of an irregular hole. At the same time, externally, by moving the slide block 205, each outer magnetic pole 303 on the annular fixing frame 301 is moved to align with the corresponding concave corner position on the outside of the workpiece 5, ensuring that the inner and outer magnetic poles correspond one-to-one.

[0049] S3. Start the motor 403 inside the spindle box 201 to drive the workpiece 5 to rotate at the set speed. Start the motor 403 to drive the rotary grinding magnet 401 to rotate at high speed. The rotating magnetic field works together with the thread groove 402 to drive the magnetic abrasive to form a "magnetic brush" and efficiently grind the protruding corners and inner wall surfaces of irregular holes.

[0050] The motor 403 driving the slide box 204 is started, causing the mounting shaft 304 to slowly feed the concave corner grinding unit 3 and the rotary grinding unit 4 along the axis of the workpiece 5. During the feeding process, when the V-groove tip of the concave corner grinding magnetic pole 311 contacts the concave corner wall, it will be subjected to a reverse force. This force is transmitted through the movable rod 310, forcing the two sliders 306 to slide in opposite directions against the elastic force of the spring 307. This process allows the concave corner grinding magnetic pole 311 to passively and adaptively always conform to the concave corner surface and maintain appropriate contact pressure. At the same time, the internal concave corner grinding magnetic pole 311 (N pole) and the corresponding external magnetic pole 303 (S pole) form a stable and strong closed magnetic field, which firmly attracts and confines the magnetic abrasive to the concave corner area for precision grinding.

[0051] S4. Reciprocating Grinding and Finishing: The control slide box 204 drives the grinding assembly to perform several reciprocating axial movements within the hole of the workpiece 5 to ensure grinding uniformity. After grinding, the grinding assembly is removed from the workpiece 5, the workpiece 5 is unloaded, rinsed to remove residual abrasive, and the magnetic abrasive is recovered for recycling.

[0052] The embodiments of this example have been described above. However, this example is not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms based on the guidance of this example, and all of them are within the protection scope of this example.

Claims

1. A flexible adaptive magnetic abrasive grinding device for irregularly shaped holes, comprising a body assembly (1) and a processing table (2) therein for clamping and fixing the workpiece (5) to be processed, characterized in that, The processing table (2) is movably equipped with a concave corner grinding unit (3) for grinding the concave corner of the irregular hole and a rotary grinding unit (4) for grinding the protruding corner and inner wall of the irregular hole. The concave corner grinding unit (3) includes a mounting shaft (304) slidably disposed inside the workpiece (5). The mounting shaft (304) has several mounting grooves on its circumferential side, and a connecting rod (305) is provided in each mounting groove. Two sliders (306) are slidably disposed on the circumferential side of the connecting rod (305). The top of each slider (306) is movably connected to a movable rod (310). The other ends of the two movable rods (310) are connected through a concave corner grinding magnetic pole (311). The top of the concave corner grinding magnetic pole (311) is provided with a V-shaped guide groove extending along its length direction. An outer magnetic pole (303) is provided on the outer wall of the workpiece (5). The position of the outer magnetic pole (303) corresponds to the concave corner grinding magnetic pole (311) located at the concave corner inside the workpiece (5). The rotary grinding unit (4) includes a rotary grinding magnetic pole (401) for rotary grinding, and the peripheral side of the rotary grinding magnetic pole (401) is provided with a threaded groove (402). The inner surface of the irregular hole has a concave corner; during the grinding operation, the slender shaft (206) and the concave corner grinding unit (3) and the rotary grinding unit (4) installed at its front end are sent into the workpiece (5) through the slide box (204), and each concave corner grinding magnetic pole (311) is aligned with the concave corner of an irregular hole; the slide box (204) and the motor (403) are started, and the slide box (204) pushes the concave corner grinding unit (3) and the rotary grinding unit (4) to move along the axis of the workpiece (5). The concave corner grinding magnetic pole (311) moves to the concave corner of the irregular hole and forms an N-S closed magnetic circuit with the external magnetic pole (303) to grind the concave corner. The motor (403) drives the rotary grinding magnetic pole (401) to rotate and drive the abrasive to form a magnetic brush to grind the protruding corner and inner wall of the irregular hole.

2. The flexible adaptive magnetic particle polishing device for irregularly shaped holes according to claim 1, characterized in that, The machine body assembly (1) includes a machine tool (101) for supporting and mounting the other parts of the grinding device. A protective cover (102) and an operation panel (103) are mounted on the surface of the machine tool (101). The protective cover (102) is slidably disposed on the outer surface of the machine tool (101).

3. The flexible adaptive magnetic particle polishing device for irregularly shaped holes according to claim 2, characterized in that, The machining table (2) includes a spindle box (201) installed inside the machine tool (101). A gripper (202) for clamping and fixing one end of the workpiece (5) is installed on one side of the spindle box (201), and a slide rail (203) is fixedly installed on the bottom of its side. A slide seat (205) and a slide box (204) are slidably arranged on the surface of the slide rail (203). A slender shaft (206) is connected to one end of the slide box (204).

4. The flexible adaptive magnetic particle polishing device for irregularly shaped holes according to claim 3, characterized in that, The top of the slide block (205) is provided with a rectangular groove, and an annular fixing frame (301) is installed inside the rectangular groove. The concave corner grinding unit (3) is slidably sleeved on the outside of the workpiece (5) through the slide block (205). The annular fixing frame (301) is provided with a sliding groove, and a number of mounting blocks (302) are installed inside the sliding groove. The number of mounting blocks (302) is the same as the number of concave corners of the irregular hole, and their installation positions correspond to the positions of the concave corners of the irregular hole. The top of the mounting block (302) is connected to one end of the external magnetic pole (303).

5. A flexible adaptive magnetic particle polishing device for irregularly shaped holes according to claim 4, characterized in that, One end of the slender shaft (206) is connected to one end of the mounting shaft (304). The slider (306) is slidably disposed in the mounting groove inside the mounting shaft (304). The two sliders (306) are movably connected by a spring (307), and the spring (307) is sleeved on the circumferential side of the connecting rod (305). At the same time, the outside of the spring (307) is sealed by a corrugated sleeve (309). The other side of each slider (306) is fixedly connected to one end of a damper (308). The other end of the damper (308) is connected to the groove wall of the mounting groove. The connecting rod (305) is located directly above the damper (308).

6. A flexible adaptive magnetic particle polishing device for irregularly shaped holes according to claim 5, characterized in that, The rotary grinding unit (4) also includes a motor (403), which is mounted on the other end of the mounting shaft (304), and the output end of the motor (403) is fixedly connected to one end of the rotary grinding magnetic pole (401).

7. A flexible adaptive magnetic particle polishing device for irregularly shaped holes according to claim 6, characterized in that, The magnetic poles of the threaded groove (402) and the concave-angle ground magnetic pole (311) are N-level, and the magnetic pole of the outer magnetic pole (303) is S-level.

8. A flexible adaptive magnetic particle polishing device for irregularly shaped holes according to claim 7, characterized in that, The concave grinding magnetic pole (311) moves back and forth along the axial direction of the irregular hole inside the workpiece (5). The outer magnetic pole (303) at the corresponding position of the concave grinding magnetic pole (311) moves synchronously and always corresponds to the position of the concave grinding magnetic pole (311).

9. A method of using a flexible adaptive magnetic particle polishing device for irregularly shaped holes as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Fill the inner cavity of the workpiece (5) with magnetic abrasive and fix one end of it with a clamp (202); S2. The slender shaft (206) and the concave corner grinding unit (3) and rotary grinding unit (4) installed at its front end are fed into one end of the irregular hole inside the workpiece (5) through the slide box (204). Each concave corner grinding magnetic pole (311) is aligned with the concave corner of an irregular hole. At the same time, the same number of mounting blocks (302) as the number of concave corners of the irregular hole are installed in the slide groove inside the ring fixing frame (301). The position of the outer magnetic pole (303) on each mounting block (302) corresponds to the concave corner grinding magnetic pole (311) at the concave corner of the irregular hole inside the workpiece (5). S3. Start the slide box (204) and motor (403). The slide box (204) pushes the concave corner grinding unit (3) and the rotary grinding unit (4) to move along the workpiece (5) axial direction. The concave corner grinding magnetic pole (311) moves to the concave corner of the irregular hole and forms an NS closed magnetic circuit with the external magnetic pole (303) to grind the concave corner. The motor (403) drives the rotary grinding magnetic pole (401) to rotate and drive the abrasive to form a magnetic brush to grind the protruding corner and inner wall of the irregular hole. S4. The slide box (204) pushes the concave corner grinding unit (3) and the rotary grinding unit (4) back and forth two or three times to grind the irregular hole inside the workpiece (5). After grinding, the concave corner grinding unit (3) and the rotary grinding unit (4) are taken out, and then the workpiece (5) is rinsed and the magnetic abrasive is collected.

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