Constant-pressure grinding and polishing method for small-diameter thin-wall non-magnetic pipe

Abstract

The invention relates to a constant-pressure grinding and polishing method for a small-diameter thin-wall non-magnetic pipe, and belongs to the technical field of precision pipe machining. According to the method, a ferromagnetic grinding rod is arranged in an inner hole of a pipe in a penetrating mode, a uniform magnetic field is arranged around the ferromagnetic grinding rod, and the grinding rod and a magnet exert constant pressure on the inner surface and the outer surface of the pipe under interaction. Meanwhile, by controlling relative rotation of the pipe and the grinding rod, flowing spherical grinding liquid is continuously injected into the pipe, a water grinding abrasive belt is arranged on the outer wall of the pipe to form a friction pair, and synchronous grinding and polishing of the inner surface and the outer surface of the pipe are achieved. According to the method, the diameter of the grinding rod, the magnetic field intensity, the rotating speed and grinding material parameters can be accurately adjusted, the grinding and polishing amount control range is 0-1 mm, and the roughness Ra of the inner surface and the outer surface can be smaller than or equal to 0.8 micrometer. The method is suitable for thin-diameter straight pipes made of non-magnetic materials such as austenitic stainless steel, titanium alloy and high-temperature alloy, and has the advantages of being simple in structure, convenient to operate, high in applicability and excellent in surface quality and size control capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precision metal pipe machining, in particular to a constant pressure grinding and polishing method for small-diameter thin-walled non-magnetic pipe. BACKGROUND

[0002] Small-diameter thin-walled non-magnetic metal pipes are widely used in high-end manufacturing fields such as aerospace, medical devices and precision instruments. The commonly used materials include austenitic stainless steel, titanium alloy and high-temperature alloy. Such pipes have the characteristics of small diameter, thin wall, long length and large length-diameter ratio. The limitations of existing pipe preparation processes and equipment cause defects such as wrinkles, scratches and pits on the inner and outer surfaces of the pipes, which seriously affect the mechanical properties, dimensional accuracy and subsequent processing performance of the pipes.

[0003] For example, seamless small-diameter pipes used for manufacturing vascular stents usually require that the dimensional tolerance be controlled within ±5 μm and the inner and outer surface roughness be Ra≤0.8 µm. However, the existing traditional pipe manufacturing processes such as cold rolling and cold drawing are difficult to meet the above requirements due to the limitations of equipment precision and deformation process. At present, such high-precision pipes still rely on imports in China, which has problems such as high manufacturing cost, long supply cycle and supply source strangulation.

[0004] Therefore, it is a key to solve the technical bottleneck to develop a controllable grinding and polishing method for the inner and outer surface finishing of non-magnetic small-diameter thin-walled pipes under the existing equipment conditions. SUMMARY

[0005] The purpose of the present application is to provide a constant pressure grinding and polishing method for small-diameter thin-walled non-magnetic pipes, which utilizes a magnetic field to control the constant pressure between a ferromagnetic spiral thread grinding rod and the pipes, and realizes high-precision and high-consistency dimensional control and surface finishing of the pipes through synchronous grinding and polishing of the inner and outer surfaces.

[0006] The present application provides a constant pressure grinding and polishing method for small-diameter thin-walled non-magnetic pipes, which comprises the following steps: (1) a ferromagnetic grinding rod is arranged in the inner hole of the pipe; (2) the grinding rod and the pipe are placed in a uniform magnetic field with a magnetic field strength of 0.2 T to 1.6 T, so that the grinding rod applies a constant pressure to the inner wall of the pipe under the action of the magnetic force, and the magnet assembly applies a constant pressure to the outer wall of the pipe, the axis of the grinding rod and the pipe is parallel to the direction of the magnetic force line and perpendicular to the direction of the magnetic force line; (3) the relative uniform rotation of the pipe and the grinding rod is controlled, and the rotation speed ranges from 30 rad / min to 600 rad / min, so as to form a friction force between the inner wall of the pipe and the grinding rod; (4) continuously injecting the flowable abrasive into the inner hole of the pipe with a particle size of W0.5~W10, a concentration of 5 g / L~200 g / L, and a flow rate of 10 mL / min~100 mL / min; (5) arranging a friction pair between the outer surface of the pipe and the magnet, the friction pair being a water abrasive belt with a particle size in the range of 120Cw~2000Cw, and the abrasive belt and the pipe forming an outer surface polishing friction force in the rotating process; (6) realizing synchronous polishing of the inner and outer surfaces of the pipe through the action of the inner and outer surface friction of the above pipe, and realizing accurate control of the surface roughness Ra≤0.8 μm and the polishing amount 0~1 mm by adjusting the parameters such as the diameter of the polishing rod, the magnetic field strength, the rotating speed and the abrasive.

[0007] The constant-pressure polishing method for the small-diameter thin-wall non-magnetic pipe provided by the application sets the diameter of the ferromagnetic polishing rod to be between 0.25 mm and 0.45 mm smaller than the inner diameter of the pipe, and the magnetic field strength is 0.2 T~1.6 T, so as to adapt to the pipe wall thickness of 0.1 mm~10 mm.

[0008] The constant-pressure polishing method for the small-diameter thin-wall non-magnetic pipe provided by the application sets the magnetic field to be composed of a plurality of strip-shaped permanent magnets arranged in the same direction and spliced, the length of the magnet is adjusted according to the length of the pipe, and a uniform magnetic field section with an effective length of 100 mm~5000 mm is formed.

[0009] The constant-pressure polishing method for the small-diameter thin-wall non-magnetic pipe provided by the application sets the pipe to be arranged in a limiting groove, the width of the limiting groove is greater than the outer diameter of the pipe by 0.3 mm~0.5 mm, and the limiting groove is used to prevent the pipe from being axially deviated or bent due to the centrifugal force or friction force in the rotating process.

[0010] The constant-pressure polishing method for the small-diameter thin-wall non-magnetic pipe provided by the application sets the surface of the ferromagnetic polishing rod to be provided with a thread-shaped groove, and the helical rise angle is 15°~75°, which is used to guide the flowable abrasive and the polishing scraps generated in the polishing process to flow to the outside of the pipe along the axial direction.

[0011] The constant-pressure polishing method for the small-diameter thin-wall non-magnetic pipe provided by the application sets the abrasive grains of the abrasive to be spheroidized, so as to avoid that the sharp abrasive causes local scratches on the inner and outer surfaces of the pipe in the polishing process.

[0012] The constant-pressure polishing method for the small-diameter thin-wall non-magnetic pipe provided by the application sets the abrasive to be a water-soluble suspension liquid composed of spherical hard particles, a fat-soluble paste material, or a composite mixture thereof, and the flowability of the abrasive is adjusted according to the gap (0.25 mm~0.45 mm) between the polishing rod and the pipe, so as to be stored in the thread-shaped groove and flow out along the axial direction of the pipe together with the polishing scraps during the polishing.

[0013] Compared with the prior art, the present invention has the following advantages: (1) A uniform and constant inner wall polishing pressure is formed by the action of a magnetic field to achieve consistent force during the polishing process of the pipe; (2) Through the bidirectional action of the ferromagnetic grinding rod and the abrasive belt, the inner and outer surfaces are polished simultaneously, improving processing efficiency and consistency; (3) By adjusting parameters such as the magnetic field and grinding rod, it can be adapted to pipes of different materials and sizes, and has strong process adaptability; (4) It can achieve precise control within the range of Ra≤0.8μm and polishing amount 0~1mm, meeting the high-end needs of medical devices and precision manufacturing. (5) The equipment has a simple structure, low cost, and safe and convenient operation, making it suitable for large-scale promotion and application. Attached Figure Description

[0014] Figure 1 This is a schematic front view of the structure of the method described in this invention; Figure 2 This is a left-side view of the structure of the method described in this invention; Figure 3 The image shows the actual appearance of the L605 cobalt-chromium alloy pipe after processing by the method described in this invention. The nominal outer diameter of the pipe is 1.8 mm and the wall thickness is 0.11 mm. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0016] Example 1: The polished tube is made of 304 austenitic stainless steel. The tube diameter before drawing was 3.5 mm, which was then cold-drawn to 2.75 mm in two passes. The tube length is 1100 mm. The surface roughness Ra of the inner surface of the tube before polishing is >1.6 μm, and the inner diameter of the tube before polishing is 2.45 mm. In this embodiment, only the inner surface of the stainless steel tube is polished. Figure 1As shown: A strip-shaped magnetic field is formed along the length of the pipe using 26 permanent magnets measuring 40 mm × 10 mm × 30 mm. The uniform magnetic field length is greater than 1000 mm, and the magnetic field strength is 0.3 T. Limiting grooves are installed above the magnets. The grinding rod with helical grooves has a diameter of 2.10 mm, a thread groove depth of 0.3 mm, and a helix angle of 60°. The grinding rod material is medium carbon steel. The abrasive selected is W2.5 corundum abrasive, which is treated and then added to a solution to prepare a 10... wt.% polishing fluid; both ends of the tube are fixed to the tube rotation device of the calibrated polishing equipment, which ensures that the tube axis is perpendicular to the magnetic field lines; the grinding rod passes through the tube and is fixed to the grinding rod rotation device of the calibrated polishing equipment, which ensures that the tube and grinding rod axes are nearly coincident. One end of the rotation device can be translated along the length of the tube to put the grinding rod in a loaded and locked state; the tube is filled with a fluid paste-like abrasive from one end; the tube rotates at a constant speed of 300 rpm; the grinding rod rotates in the opposite direction at a constant speed of 100 rpm, and the relative rotation direction of the two is related to the removal of abrasive debris (e.g., ...). Figure 2 (As shown); during the polishing process, polishing fluid is continuously injected into the pipe from one end at a flow rate of 30 mL / min, and the mixture of polishing shavings and abrasives is continuously discharged from the other end of the pipe.

[0017] After 30 minutes of polishing, the inner surface roughness of the pipe is Ra=0.353 μm, the inner diameter of the pipe is 2.51 mm, the pipe size is uniform, and the surface quality is uniform. After removing the clamping parts at both ends, the uniform pipe length is 1000 mm.

[0018] Example 2: The polished tube is made of 316L austenitic stainless steel. The tube diameter before drawing was 3.0 mm, and it was cold-drawn to 2.0 mm in 6 passes. The tube length is 1700 mm. The surface roughness Ra of the inner tube before polishing is >1.6 μm, and the inner diameter is 1.74 mm. In this embodiment, only the inner surface of the stainless steel tube is polished. Figure 1As shown: A strip-shaped magnetic field is formed along the length of the pipe using 41 permanent magnets measuring 40 mm × 10 mm × 30 mm. The uniform magnetic field has a length greater than 1600 mm and a strength of 0.4 T. Limiting grooves are installed above the magnets. The grinding rod with helical grooves has a diameter of 1.40 mm, a thread groove depth of 0.2 mm, and a helix angle of 60°. The grinding rod material is medium carbon steel. The abrasive selected is W2.5 corundum abrasive, which is treated and then added to a solution to prepare a 10... wt.% polishing fluid; both ends of the tube are fixed to the tube rotation device of the calibrated polishing equipment, which ensures that the tube axis is perpendicular to the magnetic field lines; the grinding rod passes through the tube and is fixed to the grinding rod rotation device of the calibrated polishing equipment, which ensures that the tube and grinding rod axes are nearly coincident. One end of the rotation device can be translated along the length of the tube to put the grinding rod in a loaded and locked state; the tube is filled with a fluid paste-like abrasive from one end; the tube rotates at a constant speed of 350 rpm; the grinding rod rotates in the opposite direction at a constant speed of 150 rpm, and the relative rotation direction of the two is related to the removal of abrasive debris (e.g., ...). Figure 2 (As shown); during the polishing process, polishing fluid is continuously injected into the pipe from one end at a flow rate of 30 mL / min, and the mixture of polishing shavings and abrasives is continuously discharged from the other end of the pipe.

[0019] After 30 minutes of polishing, the inner surface roughness of the pipe is Ra=0.362 μm, the inner diameter of the pipe is 1.78 mm, the pipe size is uniform, and the surface quality is uniform. After removing the clamping parts at both ends, the uniform pipe length is 1600 mm.

[0020] Example 3: The polished tube is made of high-nitrogen, nickel-free austenitic stainless steel; the tube diameter before drawing is 3.2 mm; it is cold-drawn to a nominal outer diameter of 1.8 mm in 8 passes, and the tube length is 1300 mm; due to the high hardness of the material, the deformation is large and the number of deformation passes is high, the surface roughness of both the inner and outer surfaces of the tube before polishing is Ra>3.2 μm; the inner diameter of the tube before polishing is 1.53 mm; the outer diameter of the tube before polishing is 1.82 mm. Figure 1As shown: 31 permanent magnets with dimensions of 40mm×10mm×30mm are spliced ​​together along the length of the pipe to form a strip magnetic field. The effective length of the magnetic field is greater than 1200mm and the magnetic field strength is 0.5T. A limiting groove is installed above the magnet. A sanding belt is placed between the limiting groove and the magnet, and the sanding belt is flatly fixed to the magnet by the limiting groove. This embodiment is completed in two steps: (1) First, the outer surface abrasive is selected as 600Cw abrasive belt; the inner surface abrasive rod is selected as medium carbon steel, with a diameter of 1.2 mm, a thread groove depth of 0.15 mm, and a helix angle of 45º; the abrasive is selected as W10 corundum abrasive, which is processed and then added to a solution to prepare a 20 wt.% polishing liquid; both ends of the tube are fixed on the tube rotating device of the calibrated polishing equipment, which ensures that the tube axis is perpendicular to the magnetic line direction; the abrasive rod passes through the tube and is fixed on the abrasive rod rotating device of the calibrated polishing equipment, which ensures that the tube and the abrasive rod axis are nearly coincident, and one end of the rotating device can be translated in the length direction of the tube so that the abrasive rod is in a loaded and locked state; the tube is filled with fluid paste abrasive from one end; the tube rotates at a speed of 450 rpm; the abrasive rod rotates in the opposite direction at a speed of 250 rpm, and the relative rotation direction of the two is related to the discharge of abrasive chips (e.g. Figure 2 (As shown in the figure). During the polishing process, polishing fluid was continuously injected into the pipe from one end at a flow rate of 10 mL / min, and the mixture of abrasive chips and polishing materials was continuously discharged from the other end of the pipe. After 20 minutes of polishing, the inner surface roughness of the pipe was Ra=1.6 μm, the outer diameter of the pipe was 1.806 mm, the inner diameter of the pipe was 1.58 mm, and the pipe dimensions and surface quality were uniform. (2) Remove the pipe and grinding rod. Clean the pipe with solvent using ultrasonic cleaning to thoroughly remove residual abrasive from the surface. Replace the 600Cw abrasive belt with a 1200Cw abrasive belt. Select 201 stainless steel as the grinding rod material. The diameter of the grinding rod with spiral grooves is 1.3 mm, the depth of the thread groove is 0.15 mm, and the helix angle is 75º. Select W1.5 corundum abrasive, which is treated and then added to the solution to prepare a 15 wt.% polishing liquid. Re-fix both ends of the pipe to the pipe rotating device. The grinding rod passes through the pipe and is fixed to the grinding rod rotating device. Then increase the flow rate of the polishing liquid to 90 mL / min and repeat the operation in (1). After polishing for 30 minutes, the outer surface roughness Ra=0.278 μm, the inner surface roughness Ra=0.162 μm, the outer diameter of the pipe is 1.80 mm, the inner diameter of the pipe is 1.59 mm, the pipe size is uniform, and the surface quality is uniform. Remove the clamping parts at both ends, and the uniform pipe length is 1200 mm.

[0021] Example 4: The polished tube is made of L605 cobalt-chromium alloy; the tube length is 1200 mm; the surface roughness of both the inner and outer surfaces of the tube before polishing is Ra>0.8 μm; the inner diameter of the tube before polishing is 1.59 mm; the outer diameter of the tube before polishing is 1.81 mm.Figure 1 As shown: Along the length of the pipe, 28 permanent magnets with dimensions of 40 mm × 10 mm × 30 mm and one permanent magnet with dimensions of 20 mm × 10 mm × 30 mm are spliced ​​together to form a strip magnetic field. The effective length of the magnetic field is greater than 1100 mm, and the magnetic field strength is 0.5 T. A limiting groove is installed above the magnet. An abrasive belt is placed between the limiting groove and the magnet, and the abrasive belt is flatly fixed to the magnet by the limiting groove. The grinding rod with spiral pattern has a diameter of 1.2 mm, a thread groove depth of 0.15 mm, and a helix angle of 60º. The outer surface abrasive belt is selected as 1000Cw; the grinding rod material is 201 stainless steel; the abrasive is W1.0 corundum, which is treated and then added to a solution to prepare a 20 wt.% polishing slurry; both ends of the tube are fixed to the tube rotation device of the calibrated polishing equipment, which ensures that the tube axis is perpendicular to the magnetic field line; the grinding rod passes through the tube and is fixed to the grinding rod rotation device of the calibrated polishing equipment, which ensures that the tube and grinding rod axes are nearly coincident. One end of the rotation device can be translated along the length of the tube to put the grinding rod in a loaded and locked state; the tube is filled with a fluid paste-like abrasive from one end; the tube rotates at a constant speed of 500 rpm, and the grinding rod rotates in the opposite direction at a constant speed of 200 rpm. The relative rotation direction of the two is related to the removal of abrasive chips (e.g., Figure 2 (As shown in the figure) During the polishing process, polishing fluid is continuously injected into the pipe from one end at a flow rate of 60 mL / min, and the mixture of grinding debris and abrasive is continuously discharged from the other end of the pipe.

[0022] After 30 minutes of polishing, the surface roughness of both the inner and outer surfaces of the pipe is Ra < 0.4 μm. The outer diameter of the pipe is 1.795 mm, and the inner diameter is 1.60 mm. The pipe dimensions and surface quality are uniform. Figure 3 As shown. After removing the clamping parts at both ends, the uniform pipe length is 1100 mm.

[0023] Matters not covered in this invention are common knowledge.

[0024] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A constant pressure polishing method for small-diameter, thin-walled, non-magnetic pipes, characterized in that: The steps of this method are as follows: (1) Insert a ferromagnetic grinding rod through the inner hole of the pipe; (2) Place the grinding rod and the pipe in a uniform magnetic field with a magnetic field strength of 0.2 T to 1.6 T, so that the grinding rod applies a constant pressure to the inner wall of the pipe under the action of magnetic force, and the magnet assembly applies a constant pressure to the outer wall of the pipe. The axes of the grinding rod and the pipe are parallel and perpendicular to the direction of the magnetic field lines. (3) Control the pipe and the grinding rod to rotate at a constant speed relative to each other, with a rotation speed range of 30 rad / min to 600 rad / min, so as to generate friction between the inner wall of the pipe and the grinding rod; (4) Continuously inject a flowable abrasive with a particle size of W0.5~W10, a concentration of 5 g / L~200 g / L, and a flow rate of 10 mL / min~100 mL / min into the inner hole of the pipe; (5) A friction pair is provided between the outer surface of the pipe and the magnet. The friction pair is a water-jet abrasive belt with a particle size in the range of 120Cw to 2000Cw. The abrasive belt and the pipe form a polishing friction force on the outer surface during rotation. (6) Through the action of friction between the inner and outer surfaces of the pipe, the inner and outer surfaces of the pipe are simultaneously polished; thereby achieving precise control of surface roughness Ra≤0.8 μm and polishing amount 0~1 mm.

2. The constant pressure polishing method for small-diameter, thin-walled, non-magnetic pipes according to claim 1, characterized in that: The diameter of the ferromagnetic grinding rod is set to be between 0.25 mm and 0.45 mm smaller than the inner diameter of the tube, and the magnetic field strength is between 0.2 T and 1.6 T to adapt to the tube wall thickness of 0.1 mm to 10 mm.

3. The constant pressure polishing method for small-diameter, thin-walled, non-magnetic tubing according to claim 1 or 2, characterized in that: The magnetic field is composed of multiple strip-shaped permanent magnets arranged in the same direction. The length of the magnets is adjusted according to the length of the pipe to form a uniform magnetic field section with an effective length of 100 mm to 5000 mm.

4. The constant pressure polishing method for small-diameter, thin-walled, non-magnetic tubing according to any one of claims 1-3, characterized in that: The pipe is placed in a limiting groove, the width of which is 0.3 mm to 0.5 mm greater than the outer diameter of the pipe, to prevent the pipe from shifting axially or bending due to centrifugal force or friction during rotation.

5. The constant pressure polishing method for small-diameter, thin-walled, non-magnetic tubing according to claim 1 or 2, characterized in that: The surface of the ferromagnetic grinding rod is provided with threaded grooves to guide the fluid abrasive and the abrasive debris generated during the grinding and polishing process to flow axially to the outside of the pipe.

6. The constant pressure grinding and polishing method for small-diameter, thin-walled, non-magnetic pipes according to claim 5, characterized in that: The helix angle of the threaded groove is 15°~75°.

7. The constant pressure polishing method for small-diameter, thin-walled, non-magnetic tubing according to claim 1, characterized in that: The abrasive grains are spherical to prevent sharp-angled abrasive grains from causing localized scratches on the inner and outer surfaces of the pipe during the polishing process.

8. The constant pressure polishing method for small-diameter, thin-walled, non-magnetic tubing according to claim 1 or 7, characterized in that: The abrasive is a water-soluble suspension, a fat-soluble paste, or a composite mixture of spherical hard particles. Its fluidity is adjusted according to the gap between the grinding rod and the tube so that it can be stored in the threaded groove and discharged along the tube axis with the abrasive chips while being polished.

9. The constant pressure polishing method for small-diameter, thin-walled, non-magnetic tubing according to claim 8, characterized in that: The gap between the grinding rod and the tube is 0.25 mm to 0.45 mm.

Images