A gradient self-sharpening honing oilstone and a preparation method and a use method thereof

Abstract

The application discloses a gradient self-sharpening honing oilstone and a preparation method thereof, relates to the technical field of inner hole processing of superhard abrasive tools, and comprises a supporting base body and a sintered working layer fixed on the supporting base body. The sintered working layer comprises a surface cutting layer and a toughness transition layer adjacent to the supporting base body along the thickness direction. The sintered working layer comprises diamond main abrasive, auxiliary film-breaking abrasive and metal binder. The diamond main abrasive is 12%-32%, the auxiliary film-breaking abrasive is 3%-16%, and the volume ratio of connected pores is 1%-8% based on the volume of the surface cutting layer being 100%. The average particle size D50 of the diamond main abrasive is 1.3-4.0 times the average particle size D50 of the auxiliary film-breaking abrasive. The gradient self-sharpening honing oilstone improves the precision and stability of abrasive tool processing.

Description

Technical Field

[0001] This invention relates to the field of machining and manufacturing technology of internal holes in superhard material abrasives, and more specifically to a gradient self-sharpening honing stone and its preparation and application methods. Background Technology

[0002] Metal-bonded diamond grinding wheels are widely used in the grinding of hard and brittle materials such as ceramics, glass, cemented carbide, crystalline materials, and semiconductor materials due to their high shape retention, wear resistance, and dimensional stability. For diamond grinding wheels, grinding rods, or grinding discs with perforated structures, the dimensional accuracy, roundness, cylindricity, and coaxiality with the working layer of the inner hole directly affect clamping runout, grinding pattern, life stability, and batch consistency.

[0003] Existing methods for internal hole finishing typically include grinding, lapping, honing, or electrical discharge machining (EDM). Ordinary honing stones are generally designed for workpieces such as steel, cast iron, hydraulic cylinders, ceramics, or cemented carbide, with abrasive grit size, bond hardness, and self-sharpening mechanism primarily focused on a single workpiece material. However, when the workpiece is a metal-bonded diamond abrasive, the internal hole surface not only contains a copper-based, iron-based, bronze-based, or nickel-based metal matrix but also exposed or partially exposed diamond particles. This composite surface can lead to the following problems with ordinary honing stones:

[0004] (i) If the size of the oilstone is close to that of the diamond in the workpiece, it is easy to form slip and rolling between the diamond particles, making it difficult to stably cut into the metal matrix.

[0005] (ii) Under pressure and heat, the metal matrix is ​​prone to forming a coating layer, which covers the cutting edge area of ​​the whetstone or workpiece surface, resulting in a decrease in cutting force and clogging.

[0006] (iii) Although a single high-strength binder is wear-resistant, it is not self-sharpening enough, and the surface of the whetstone becomes dull after long-term processing; although a single brittle binder is sharp, thin strips of whetstone are prone to chipping, delamination, or insufficient shape retention.

[0007] (iv) The processing powder contains metal powder, broken abrasive particles and fine carbonaceous matter. If the chip removal and cooling are insufficient, it is easy to cause scratches, dimensional drift and fluctuations in the roughness of the inner hole.

[0008] Therefore, a special honing stone is needed for the composite surface characteristics of the inner hole of metal-bonded diamond abrasives, so that it can continuously destroy the matrix coating layer and expose the effective cutting edge while maintaining sufficient shape stability and anti-delamination ability, thereby stably obtaining high-precision inner holes. Summary of the Invention

[0009] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a gradient self-sharpening honing stone for finishing the inner hole of metal-bonded diamond abrasives, and its preparation and use method, so as to solve the problems of difficulty in cutting, matrix coating, stone clogging, scratches, delamination and insufficient dimensional stability of ordinary honing stones when processing the inner hole of metal-bonded diamond abrasives.

[0010] The present invention first provides a gradient self-sharpening honing stone, the gradient self-sharpening honing stone comprising: a support substrate and a sintered working layer fixed on the support substrate, the sintered working layer comprising a surface cutting layer and a tough transition layer adjacent to the support substrate along the thickness direction;

[0011] The sintered working layer includes diamond main abrasive, auxiliary film-breaking abrasive and metal binder and has interconnected pores. The working surface of the sintered working layer is provided with micro chip removal grooves.

[0012] With the volume of the surface cutting layer as 100%, the main diamond abrasive accounts for 12%-32%, the auxiliary film-breaking abrasive accounts for 3%-16%, and the volume percentage of the interconnected pores is 1%-8%.

[0013] The average particle size D50 of the diamond primary abrasive is 1.3-4.0 times that of the auxiliary film-breaking abrasive. The metal binder is a Cu-Sn-Ni based metal binder. The diamond volume fraction in the surface cutting layer is 3-15 percentage points higher than that in the toughness transition layer.

[0014] In one embodiment, the diamond primary abrasive has a particle size of 45-125 μm, and the auxiliary film-breaking abrasive has a particle size of 10-45 μm.

[0015] In one embodiment, the volume ratio of interconnected pores in the surface cutting layer and the toughness transition layer is the same.

[0016] In one embodiment, the auxiliary abrasive for breaking the film includes one or more of white corundum, green silicon carbide, and zirconium corundum, the auxiliary abrasive for breaking the film has a Mohs hardness of not less than 9, and the abrasive for breaking the film has a fracture toughness lower than that of the diamond main abrasive.

[0017] In one embodiment, the metal binder comprises, by weight: 40%-67% Cu, 10%-30% Sn, 3%-22% Ni, 0%-20% Fe, 0.2%-5% P, 0%-8% Ag, and 0.2%-5% solid lubricating phase.

[0018] In one embodiment, the thickness of the toughness transition layer is 0.2-1.5 mm, and the Ni and / or Fe content in the toughness transition layer is 3-20 percentage points higher than the Ni and / or Fe content in the surface cutting layer.

[0019] In one embodiment, the micro chip removal groove has a groove width of 0.10-0.80 mm, a groove depth of 0.05-0.40 mm, a spacing of 1-6 mm between adjacent micro chip removal grooves, and an angle of 20°-70° between the micro chip removal groove and the length direction of the oilstone.

[0020] The present invention also provides a method for preparing a gradient self-sharpening honing stone, the method comprising: providing a support substrate; forming a toughness transition layer on the support substrate; and forming a surface cutting layer on the toughness transition layer to obtain the gradient self-sharpening honing stone.

[0021] In one embodiment, the preparation method includes: preparing surface cutting layer mixed powder and toughness transition layer mixed powder respectively; loading the toughness transition layer mixed powder and surface cutting layer mixed powder into a mold in sequence and performing layered pre-pressing followed by hot pressing and sintering.

[0022] In one embodiment, the parameters of the hot pressing sintering include: hot pressing sintering is carried out under vacuum or a protective atmosphere, the sintering temperature is 620-760℃, the pressure is 15-35 MPa, and the holding time is 8-30 min.

[0023] In one embodiment, a removable pore-forming agent is further added to the surface cutting layer mixture powder, the removable pore-forming agent including one or more of polymethyl methacrylate microspheres, graphite particles, starch particles, and carbonate particles.

[0024] In one embodiment, the removable pore-forming agent is removed by thermal decomposition, oxidation, or dissolution to form the interconnected pores.

[0025] The present invention also provides a method for using a gradient self-sharpening honing stone, the method comprising:

[0026] The gradient self-sharpening honing stone is mounted on a radially expandable honing head for machining the inner hole of a metal-bonded diamond abrasive.

[0027] During processing, the gradient self-sharpening honing stone rotates relative to the inner hole to be processed and reciprocates axially, and the grinding debris is discharged from the micro chip removal groove and the connecting hole by the coolant.

[0028] In one embodiment, the metal-bonded diamond abrasive tool includes a diamond grinding wheel, a diamond grinding rod, or a diamond grinding disc.

[0029] In one embodiment, the primary diamond abrasive is selected based on the average particle size of the diamond abrasive in the metal-bonded diamond abrasive being processed, such that the average particle size D50 of the primary diamond abrasive is 1.4-3.2 times that of the average particle size D50 of the diamond abrasive in the metal-bonded diamond abrasive, and the average particle size D50 of the auxiliary film-breaking abrasive is 0.25-0.75 times that of the average particle size D50 of the primary diamond abrasive.

[0030] This invention provides a gradient self-sharpening honing stone for finishing the inner holes of metal-bonded diamond abrasives, and its preparation and use methods, which specifically include the following advantages:

[0031] By appropriately coarsening the diamond abrasive in the oilstone relative to the diamond abrasive in the workpiece, the probability of slippage between diamonds of the same grit size can be reduced, thereby improving the ability to penetrate the metal matrix.

[0032] By incorporating finer and brittle auxiliary abrasive particles, the coating layer and compacted powder layer can be continuously broken down, reducing surface clogging of the oilstone. The gradient design between the surface cutting layer and the toughness transition layer ensures a sharp working surface while giving the thin oilstone good resistance to bending, chipping, and delamination.

[0033] By combining interconnected pores and micro-chip removal channels, the ability of coolant to enter and wear debris to be removed is improved, reducing the risk of internal hole scratches, burns, and dimensional drift. By using a rule-based combination to protect the formulation, structure, preparation method, and particle size, the technical integrity of this invention compared to simple metal-bonded formulations or ordinary diamond petroleum stone is enhanced. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the gradient self-sharpening honing stone of the present invention;

[0035] Figure 2 This is a schematic diagram of the thickness gradient structure and microstructure of the sintering working layer of the present invention;

[0036] Figure 3 This is a schematic diagram showing the application of the honing stone of the present invention in the finishing of the inner hole of a metal-bonded diamond abrasive.

[0037] Figure 4 This is a schematic diagram of the process flow of the preparation method of the present invention;

[0038] Figure 5 This is a schematic diagram of the working surface arrangement of the micro chip removal groove of the present invention.

[0039] Reference numerals: 1-Supporting substrate; 2-Surface cutting layer; 3-Toughness transition layer; 4-Micro chip removal groove; 5-Fixing hole; 6-Length direction of honing stone; 7-Main diamond abrasive; 8-Auxiliary film-breaking abrasive; 9-Connecting pores; 10-Thickness gradient; 11-Metal-bonded diamond abrasive tool; 12-Inner hole to be machined; 13-Honing honing stone; 14-Honing head; 15-Radial feed direction; 16-Raw material weighing; 17-Mixing; 18-Layered loading; 19-Hot pressing sintering; 20-Dressing and sharpening; 21-Installation and use; 22-Angled groove; 23-Transverse groove; 24-Hinged groove. Detailed Implementation

[0040] Please see Figures 1 to 5 .

[0041] like Figure 1 As shown, the present invention provides a gradient self-sharpening honing stone 13, the gradient self-sharpening honing stone 13 includes a support base 1, the support base 1 may be provided with a fixing hole 5, the fixing hole 5 can be used for mounting on a machine tool, the support base 1 has a toughness transition layer 3, the toughness transition layer 3 has a surface cutting layer 2, and the surface cutting layer 2 has a micro chip removal groove 4.

[0042] like Figure 5 As shown, the micro chip removal groove 4 has structures such as inclined groove 22, transverse groove 23 and herringbone groove 24.

[0043] like Figure 2 As shown, the raw materials of the surface cutting layer 2 include diamond main abrasive 7 and auxiliary film-breaking abrasive 8, and the surface cutting layer 2 has interconnecting pores 9.

[0044] like Figure 3 As shown, the gradient self-sharpening honing stone 13 can be used to process the metal-bonded diamond abrasive 11, and the inner hole 12 of the metal-bonded diamond abrasive 11 to be processed can be processed by the gradient self-sharpening honing stone 13.

[0045] The processing may include mounting the honing stone 13 of the present invention on a radially expandable honing head 14, so that the working surface of the honing stone contacts the inner hole 12 to be processed in the metal-bonded diamond abrasive tool 11. Before processing, the honing stone 13 can be briefly sharpened using a scrap part of the same material or a soft steel ring to form an initial cutting edge of the diamond abrasive 7. During processing, the coolant is controlled to fully enter the inner hole 12 to be processed, and the abrasive chips are discharged along the micro chip removal groove 4 and the connecting hole 9.

[0046] like Figure 4As shown, in some embodiments, the preparation of the gradient self-sharpening honing stone 13 includes the steps of AF, specifically including the steps of raw material weighing 16-mixing 17-layer loading 18-hot pressing and sintering 19-sharpening and sharpening 20-installation and use 21.

[0047] Example 1

[0048] (1) Support base: 10mm thick, made of 45 steel;

[0049] (2) Toughness transition layer: 0.6 mm thick, raw materials: 18% 200 / 230# diamond main abrasive, 4% finer auxiliary film-breaking abrasive white corundum, 6% interconnected pores, the balance is Cu-Sn-Ni based metal binder, the metal binder includes 55% Cu, 13% Sn, 10% Ni, 13% Fe, 2% P, 6% Ag, the balance is solid lubricating phase.

[0050] (3) Surface cutting layer: 6mm thick. The raw materials include: 24% 200 / 230# diamond main abrasive, 10% finer auxiliary film-breaking abrasive white corundum, 6% interconnected pores, and the balance is Cu-Sn-Ni based metal binder, which includes 60% Cu, 18% Sn, 5% Ni, 8% Fe, 2% P, and 6% Ag, with the balance being a solid lubricating phase.

[0051] During loading, a toughness transition layer mixture powder is first laid in the mold on the supporting substrate, pre-pressed, and then a surface cutting layer mixture powder is laid for light pressing and positioning. Subsequently, it is hot-pressed and sintered for 8 minutes at 620℃ and 15MPa under vacuum or argon atmosphere. After cooling, the shape is trimmed, the working surface is grooved, and slightly sharpened to obtain a honing stone, which is used to machine the inner hole of 325#-500# metal-bonded diamond grinding wheels.

[0052] Example 2

[0053] (1) Support base: 10mm thick, made of 45 steel;

[0054] (2) Toughness transition layer: 0.6 mm thick, raw materials: 17% 200 / 230# diamond main abrasive, 10% finer auxiliary film-breaking abrasive white corundum, 2% interconnected pores, the balance is Cu-Sn-Ni based metal binder, the metal binder may include 40% Cu, 10% Sn, 21% Ni, 20% Fe, 2% P, 5% Ag, the balance is solid lubricating phase.

[0055] (3) Surface cutting layer: 6mm thick. The raw materials include: 28% 200 / 230# diamond main abrasive, 10% finer auxiliary film-breaking abrasive white corundum, 2% interconnected pores, and the balance is Cu-Sn-Ni based metal binder. The metal binder may include 41% Cu, 12% Sn, 17% Ni, 15% Fe, 2% P, 8% Ag, and the balance is solid lubricating phase.

[0056] During loading, a toughness transition layer mixture powder is first laid in the mold on the supporting substrate, pre-pressed, and then a surface cutting layer mixture powder is laid and lightly pressed for positioning. Subsequently, it is hot-pressed and sintered at 760℃ and 35MPa for 8 minutes under vacuum or argon atmosphere. After cooling, the shape is trimmed, the working surface is grooved, and slightly sharpened to obtain a honing stone.

[0057] Example 3

[0058] (1) Support base: 10mm thick, made of 45 steel;

[0059] (2) Toughness transition layer: 0.6 mm thick, raw materials: 12% 200 / 230# diamond main abrasive, 3% finer auxiliary film-breaking abrasive white corundum, 6% interconnected pores, the balance is Cu-Sn-Ni based metal binder, the metal binder may include 52% Cu, 13% Sn, 15% Ni, 12% Fe, 2% P, 3% Ag, the balance is solid lubricating phase.

[0060] (3) Surface cutting layer: 6mm thick. The raw materials include: 15% 200 / 230# diamond main abrasive, 3% finer auxiliary film-breaking abrasive white corundum, 6% interconnected pores, and the balance is Cu-Sn-Ni based metal binder. The metal binder may include 55% Cu, 15% Sn, 10% Ni, 8% Fe, 2% P, 5% Ag, and the balance is solid lubricating phase.

[0061] During loading, a toughness transition layer mixture is first laid in the mold on the supporting substrate, pre-pressed, and then a surface cutting layer mixture is laid and lightly pressed for positioning. Subsequently, it is hot-pressed and sintered at 620℃ and 15MPa for 30 minutes under vacuum or argon atmosphere. After cooling, the shape is trimmed, the working surface is grooved, and slightly sharpened to obtain a honing stone.

[0062] Comparative Example 1

[0063] Comparative Example 1 uses ordinary diamond petroleum stone of the same grit size. The grit size of the diamond abrasive is basically the same as that of the diamond grit in the inner hole of the machine tool. It uses an ordinary homogeneous metal binder working layer and does not set up special auxiliary film-breaking abrasive and thickness gradient layer. The rest are the same as those in Example 1.

[0064] Comparative Example 2

[0065] Comparative Example 2 uses an oilstone without auxiliary film-breaking abrasive. Compared with Example 1, the white corundum auxiliary film-breaking abrasive is removed, and its volume fraction is made up by the metal binder. Other particle size mismatch, gradient layer and chip removal groove settings are kept the same.

[0066] Comparative Example 3

[0067] Comparative Example 3 uses a gradient-free transition layer oilstone. Compared with Example 1, the toughness transition layer is eliminated, and the sintered working layer has a single homogeneous formula along the thickness direction. The main abrasive, auxiliary film-breaking abrasive, and micro chip removal groove settings are kept consistent with Example 1.

[0068] evaluate:

[0069] To further illustrate the technical advantages of this invention compared to ordinary diamond oilstones of the same grit size, oilstones without auxiliary film-breaking abrasives, and oilstones without gradient transition layers, the above embodiments and comparative examples were used for verification. Each group of tests should be conducted under the same honing equipment, the same coolant, the same honing pressure or expansion amount, the same spindle speed, the same reciprocating speed, and the same cutting method to reduce the influence of non-structural factors on the evaluation results.

[0070] The test subject is a metal-bonded diamond grinding wheel for internal hole finishing. The diamond grit size in the inner hole of the workpiece can be selected in the range of 325#-500#. The binder is mainly copper-tin or copper-tin-nickel metal binder. The machining allowance for the inner hole is 0.20 mm, and the target dimensional tolerance is H7. The number of samples in each group should not be less than 10, preferably not less than 20.

[0071] Table 1 Evaluation Indicators, Test Methods, and Judgment Criteria

[0072] Evaluation indicators Test methods Recommended Recording Unit Determine the caliber Removal per unit time Record the inner hole diameters D1 and D2, effective hole length L, and actual processing time t before and after honing. The volume removal amount can be calculated using Q=πL(D2²-D1²) / (4t). The diameter removal rate can also be recorded simultaneously on the production site. mm³ / min;μm / min Under the same pressure and time, a higher Q and smaller fluctuations indicate better penetration ability and self-sharpening stability. Degree of clogging on the surface of the oilstone After a fixed processing time, remove the oilstone and photograph the working surface under a 50×-200× microscope to count the area percentage of areas with metal coating, compacted powder, or shiny clogging; manual rating of 0-5 levels can also be used as an aid. %; Level 0-5 The lower the area ratio or the lower the rating, the better. A rating of 0 is recommended as no significant clogging, and 5 as clogging exceeding 50%. Stability of inner hole size reaching H7 Each group should process no fewer than 10 pieces continuously, and record the actual inner hole size, dimensional range, standard deviation, and number of H7 qualified pieces. Pass rate; σ; Range A higher H7 pass rate and smaller size dispersion indicate better oilstone cutting stability. Roundness / Cylindricity A roundness meter, coordinate measuring machine, or pneumatic gauge, along with a roundness evaluation program, are used to record the roundness and cylindricity of the inner hole, respectively. μm The lower the value, the better. Pay close attention to whether there are any abnormal values ​​in the comparative model caused by elliptical shapes, conical holes, or localized strain. Surface scratch ratio Inspect the inner surface of the bore using a 50× microscope or endoscope, and record the number of workpieces with continuous scratches, deep scratches, or abnormal bright bands. If necessary, specify a scratch length threshold, for example, a scratch with a length ≥ 0.5 mm is considered a valid scratch. % The lower the ratio of scratched items to total items, the better. Oilstone mill consumption The height and mass of the whetstone or the contour of the working surface are measured before and after processing and converted into volumetric wear. At the same time, the grinding ratio G can be calculated as workpiece volume removed / whetstone wear volume. mm³ / piece; mm³ / h; G-value Wear should not be judged solely on the premise that the lower the better; it should be considered in conjunction with removal capacity, clogging, and dimensional stability. Excessively low wear may indicate insufficient self-sharpening. Grinding wheel runout after machining Install the machined grinding wheel or abrasive onto a standard mandrel or the target machine tool spindle, and measure the radial runout (TIR) ​​using a dial indicator, micrometer, or runout meter. μm The lower the runout and the smaller the fluctuation within the batch, the better the inner hole size, roundness, cylindricity and clamping consistency.

[0073] Table 2. Record of Actual Measurement Results for Examples and Comparative Examples

[0074] Group Removal per unit time degree of clogging H7 pass rate Roundness / Cylindricity Scratch ratio Oilstone mill consumption Jumping after processing Example 1 28.5 5% (Level 1) 98% 3.2 / 4.1 1.5% 1.2 4.5 Example 2 29.1 3% (Level 1) 99% 3.1 / 4.2 1 % 1.3 4.4 Example 3 27.4 6% (Level 1) 97% 2.9 / 4 2.3% 1.1 4.2 Comparative Example 1 14.2 45% (Level 4) 72% 8.5 / 10.2 6.5% 0.4 (Passivation slippage) 12.5 Comparative Example 2 18.6 65% (Level 5) 80% 6.4 / 8.3 14.5% 0.8 8.6 Comparative Example 3 25.4 8% (Level 1) 60% 18.5 / 22.4 12% 5.6 (Abnormal delamination and block falling) 28.4

[0075] As shown in Table 2, compared with Comparative Example 1, Example 1 demonstrates reduced friction between diamonds of the same grit size, increased removal amount per unit time, reduced clogging, and improved H7 size qualification rate; compared with Comparative Example 2, Example 1 demonstrates the effect of auxiliary film-breaking abrasive on destroying the metal coating layer, graphite film, or powder compaction layer; compared with Comparative Example 3, Example 1 demonstrates the effect of the toughness transition layer on preventing the thin strip oilstone from flaking, delamination, maintaining its shape, and improving the stability of the grinding wheel runout after processing.

[0076] When comparing the oilstone of the present invention with that of the comparative example using the above-mentioned test method, the oilstone of the present invention, due to the difference in particle size between the main diamond abrasive and the diamond abrasive in the workpiece, can reduce the slippage and rolling between diamond particles of the same particle size. Because the auxiliary film-breaking abrasive undergoes micro-fracture during processing, it can continuously destroy the metal coating layer and the powder compaction layer. Because the toughness transition layer improves the bonding reliability between the working layer and the support substrate, it can reduce oilstone chipping, delamination, and internal hole fluctuation caused by the deterioration of the oilstone shape.

[0077] It can be seen that the oilstone of the present invention can more stably obtain H7 dimensional accuracy in the inner hole finishing of metal bonded diamond abrasives, and improve roundness, cylindricity, surface scratch ratio and grinding wheel runout after processing.

[0078] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, devices, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of the present invention, any prior art methods, devices, and materials similar to or equivalent to those described, used, and materials in the embodiments of the present invention can be used to implement the present invention. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A gradient self-sharpening honing stone, characterized in that: It includes a support substrate and a sintered working layer fixed on the support substrate, wherein the sintered working layer includes a surface cutting layer and a tough transition layer adjacent to the support substrate along the thickness direction; The sintered working layer includes diamond main abrasive, auxiliary film-breaking abrasive and metal binder and has interconnected pores. The working surface of the sintered working layer is provided with micro chip removal grooves. With the volume of the surface cutting layer as 100%, the main diamond abrasive accounts for 12%-32%, the auxiliary film-breaking abrasive accounts for 3%-16%, and the volume percentage of the interconnected pores is 1%-8%. The average particle size D50 of the diamond primary abrasive is 1.3-4.0 times that of the auxiliary film-breaking abrasive. The metal binder is a Cu-Sn-Ni based metal binder. The diamond volume fraction in the surface cutting layer is 3-15 percentage points higher than that in the toughness transition layer.

2. The gradient self-sharpening honing stone according to claim 1, characterized in that: The main diamond abrasive has a particle size of 45-125 μm, and the auxiliary film-breaking abrasive has a particle size of 10-45 μm.

3. The gradient self-sharpening honing stone according to claim 1, characterized in that: The auxiliary abrasive for breaking the film includes one or more of white corundum, green silicon carbide, and zirconium corundum. The auxiliary abrasive for breaking the film has a Mohs hardness of not less than 9, and its fracture toughness is lower than that of the diamond main abrasive.

4. The gradient self-sharpening honing stone according to claim 3, characterized in that: Based on the mass of the metal binder, the metal binder comprises: 40%-67% Cu, 10%-30% Sn, 3%-22% Ni, 0%-20% Fe, 0.2%-5% P, 0%-8% Ag, and 0.2%-5% solid lubricating phase.

5. The gradient self-sharpening honing stone according to claim 1, characterized in that: The thickness of the toughness transition layer is 0.2-1.5 mm, and the Ni and / or Fe content in the toughness transition layer is 3-20 percentage points higher than the Ni and / or Fe content in the surface cutting layer.

6. A method for preparing a gradient self-sharpening honing stone, characterized in that: The preparation method includes the following steps: Provide a support base; A tough transition layer is formed on the support substrate; The gradient self-sharpening honing stone is obtained by forming a surface cutting layer on the toughness transition layer; The gradient self-sharpening honing stone includes: a support substrate and a sintered working layer fixed on the support substrate, wherein the sintered working layer includes a surface cutting layer and a tough transition layer adjacent to the support substrate along the thickness direction; The sintered working layer includes diamond main abrasive, auxiliary film-breaking abrasive and metal binder and has interconnected pores. The working surface of the sintered working layer is provided with micro chip removal grooves. With the volume of the surface cutting layer as 100%, the main diamond abrasive accounts for 12%-32%, the auxiliary film-breaking abrasive accounts for 3%-16%, and the volume percentage of the interconnected pores is 1%-8%. The average particle size D50 of the diamond primary abrasive is 1.3-4.0 times that of the average particle size D50 of the auxiliary film-breaking abrasive, the metal binder is a Cu-Sn-Ni based metal binder, and the diamond volume fraction in the surface cutting layer is 3-15 percentage points higher than the diamond volume fraction in the toughness transition layer.

7. The preparation method according to claim 6, characterized in that: The formation of the toughness transition layer and the surface cutting layer includes: placing the mixed powder of the toughness transition layer on the support substrate, then placing the mixed powder of the surface cutting layer on the mixed powder of the toughness transition layer, and performing hot pressing sintering.

8. The preparation method according to claim 7, characterized in that: The parameters for hot pressing sintering include: hot pressing sintering is carried out under vacuum or a protective atmosphere, the sintering temperature is 620-760℃, the pressure is 15-35 MPa, and the holding time is 8-30 min.

9. A method of using a gradient self-sharpening honing stone according to any one of claims 1-5, characterized in that, The gradient self-sharpening honing stone is mounted on a radially expandable honing head for machining the inner hole of a metal-bonded diamond abrasive. During processing, the gradient self-sharpening honing stone rotates relative to the inner hole to be processed and reciprocates axially, and the grinding debris is discharged from the micro chip removal groove and the connecting hole by the coolant.

10. The method of use according to claim 9, characterized in that, The primary diamond abrasive is selected based on the average particle size of the diamond abrasive in the metal-bonded diamond abrasive being processed, such that the average particle size D50 of the primary diamond abrasive is 1.4-3.2 times that of the average particle size D50 of the diamond abrasive in the metal-bonded diamond abrasive, and the average particle size D50 of the auxiliary film-breaking abrasive is 0.25-0.75 times that of the average particle size D50 of the primary diamond abrasive.

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