Gradient material wear-resistant micro drill bit and preparation method thereof

Abstract

The application relates to the field of microfabrication technology and discloses a gradient material wear-resistant micro drill bit and a preparation method thereof. A plurality of tungsten foil laminates are stacked, and a plurality of micro drill bit blanks are processed by electric spark wire cutting; the blank is placed in a cavity formed by a high-carbon steel plate, high-carbon steel powder is filled around the blank, then another high-carbon steel plate with a smooth surface is pressed on the blank to form a sandwich structure; the structure is subjected to pressure and high-temperature diffusion treatment in a protective atmosphere, so that carbon atoms are diffused from the high-carbon steel to the surface of the tungsten foil to form a metallurgical bonding gradient tungsten carbide wear-resistant layer; finally, the residual is removed through pickling to obtain a finished product. The tungsten carbide gradient layer with high hardness and high bonding force is formed on the surface of the tungsten foil through the heat diffusion method, and the technical problems of low yield and short service life of the micro drill bit, especially the drill bit with a diameter less than 80 microns, caused by the easy breakage of the grinding processing and the easy peeling of the surface coating are fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of microfabrication technology, specifically to a wear-resistant micro drill bit made of gradient material and its preparation method. Background Technology

[0002] With the rapid development of precision instruments, electronic information, biomedicine and other fields, the demand for processing micro-holes is increasing. As a key processing tool, the performance of micro-drills is of paramount importance. Currently, micro-drills are mainly manufactured using grinding processes. First, the material diameter is machined to the target size, and then chip grooves are machined and the cutting edges are ground.

[0003] However, traditional grinding processes have significant limitations for micro drills with diameters below 80 μm. Due to the grinding force, extremely fine drill bits are prone to breakage during the machining of the working part, leading to a sharp drop in yield and hindering mass production. Furthermore, the cutting edge of micro drills experiences immense stress due to its tiny size during drilling, resulting in extremely rapid wear. To enhance wear resistance, current methods typically employ physical vapor deposition (PVD) wear-resistant coatings or electroplated diamond abrasive grains. However, these surface modification layers are mechanically bonded to the drill bit substrate, resulting in weak adhesion. They are prone to peeling off during high-speed, high-load drilling, failing to provide a sustained and effective improvement in the lifespan of micro drills.

[0004] Therefore, there is an urgent need in this field to develop a new method for efficiently preparing micro-drill bits with extremely fine dimensions and high wear resistance and high reliability wear-resistant layers. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a gradient material wear-resistant micro drill bit and its preparation method, which solves the problems of low yield due to easy breakage during grinding of micro drill bits with a diameter of less than 80μm, and short service life due to weak adhesion and easy peeling of the surface wear-resistant coating.

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

[0007] In a first aspect, this application provides a method for preparing a wear-resistant micro drill bit made of gradient material, comprising the following steps:

[0008] S1. Billet preparation:

[0009] Multiple layers of tungsten foil sheets with a thickness of 15–70 μm are stacked, aligned, and fixed. Then, a micro-electrical discharge wire cutting process is used to process the micro-drill blanks along the designed path, obtaining multiple micro-drill blanks with rectangular or parallelogram cross-sectional shapes in one go.

[0010] S2, Assemble the diffusion structure:

[0011] Prepare a high-carbon steel substrate and process a cavity on it with a depth equal to the thickness of the micro drill bit blank; place the micro drill bit blank in the center of the cavity and fill it with high-carbon steel powder as a solid carbon source around it, and then cover it with a high-carbon steel cover plate to create a closed diffusion environment that completely encapsulates the micro drill bit blank in high-carbon steel material.

[0012] S3, Thermal diffusion reaction:

[0013] The assembled structure in step S2 is placed in an atmosphere furnace with a protective atmosphere. An axial pressure of 1-10 MPa is used to make the contact surfaces fit tightly together. Then, the structure is heated to 900-1200°C according to the set heating program and held for 2-10 hours. This promotes the directional diffusion of carbon atoms in the high-carbon steel to the surface of the tungsten foil blank and the metallurgical reaction therewith, generating a tungsten carbide wear-resistant layer that has a gradient transition with the substrate and is metallurgically bonded.

[0014] S4. Post-processing:

[0015] The micro drill bit processed in step S3 is taken out and acid-washed to remove the residual high-carbon steel material on the surface, thus obtaining the wear-resistant micro drill bit of the gradient material.

[0016] Preferably, in step S1, the electrical parameters of the micro-electrical discharge wire cutting process are: pulse width of 0.1 to 10 μs, pulse interval of 1 to 20 μs, and processing current of 0.5 to 5 A.

[0017] Preferably, in step S1, the cutting speed of the micro-electrical discharge wire cutting is 20-200 μm / min.

[0018] Preferably, in step S3, the protective atmosphere is argon or nitrogen, the gas flow rate of the protective atmosphere is 100-500 ml per minute, and the pressure inside the furnace is maintained slightly higher than atmospheric pressure, in the range of 105-110 kPa.

[0019] Preferably, in step S3, the set heating program is as follows: heating from room temperature to 800°C at a rate of 5-15°C / min; and then heating from 800°C to the target temperature of 900-1200°C at a rate of 3-8°C / min.

[0020] Preferably, in step S2, the particle size of the high-carbon steel powder is 10-50 μm, and the carbon mass fraction of the high-carbon steel substrate, the high-carbon steel cover plate, and the high-carbon steel powder is not less than 0.7%.

[0021] Preferably, in step S4, a dilute hydrochloric acid solution with a concentration of 5% to 15% is used to perform ultrasonic cleaning at a temperature of 40 to 60°C, with an ultrasonic power of 100 to 300W and a cleaning time of 5 to 20 minutes.

[0022] Secondly, this application provides a gradient material wear-resistant micro drill bit, which is prepared by any of the preparation methods described in the foregoing embodiments.

[0023] Preferably, the working part of the micro-drill bit has a rectangular or parallelogram cross-section, the length of its diagonal is the diameter of the micro-drill bit, and the diameter is less than or equal to 80 μm.

[0024] Preferably, the diameter of the micro drill bit is less than or equal to 20 μm, and the thickness of its surface tungsten carbide gradient layer is 1–5 μm, with a Vickers hardness HV≥2200.

[0025] This invention provides a wear-resistant micro-drill bit made of gradient material and its preparation method. It has the following beneficial effects:

[0026] 1. This invention utilizes a high-temperature thermal diffusion reaction to induce a metallurgical reaction between carbon atoms and tungsten, generating a tungsten carbide gradient layer in situ on the surface of a tungsten foil. This gradient layer is metallurgically bonded to the substrate, with a bonding force far stronger than that of physical deposition or electroplating coatings. This significantly improves the wear resistance and service life of the micro-drill bit during drilling, avoiding the problem of coating peeling.

[0027] 2. This invention uses a micro-electro-electric wire cutting process to process multi-layer foil blanks in one go, avoiding the grinding force generated by traditional grinding processes when processing extremely fine dimensions. This effectively prevents the breakage of micro drill blanks and significantly improves the manufacturing yield and production efficiency of micro drills with diameters less than 80μm, or even 20μm.

[0028] 3. The micro drill bit prepared by the present invention has a gradient transition from tungsten carbide with high surface hardness to tungsten with high core toughness. This structure not only ensures the extremely high wear resistance of the cutting edge, but also maintains the good toughness of the drill bit as a whole, resulting in excellent comprehensive performance. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the preparation of the tungsten foil micro-drill bit blank according to the present invention;

[0030] Figure 2 This is a schematic diagram of the thermal diffusion welding process for the gradient material tungsten foil micro-drill bit of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a gradient material wear-resistant micro drill bit and its preparation method. The core of the method lies in forming an extremely fine micro drill bit blank through non-contact micro-electro-discharge wire cutting technology to avoid fracture caused by mechanical force; then, through sandwich structure solid-state thermal diffusion technology, a metallurgically bonded tungsten carbide gradient wear-resistant layer is generated in situ on the surface of the tungsten substrate, fundamentally solving the problem of easy coating peeling.

[0033] First, refer to Figure 1 The diagram shows the preparation of micro drill bit blanks. Multilayer tungsten foil sheets with a thickness of 16-70 μm are stacked, aligned and fixed by a fixture. A micro-electrical discharge wire cutting device is used, and the electrode wire is cut and discharged along the pre-designed micro drill bit outline path under the control of the CNC system, so as to obtain multiple micro drill bit blanks at one time, with a rectangular cross-sectional shape.

[0034] Next, refer to Figure 2 The diagram illustrates a sandwich structure prepared by thermal diffusion. This structure includes a high-carbon steel substrate with a cavity whose depth is equal to the thickness of the tungsten foil blank. After placing the blank in the center of the cavity, high-carbon steel powder is filled around it as a solid carbon source. Subsequently, an upper high-carbon steel cover plate is placed on top, thus forming a diffusion environment that completely seals and encapsulates the tungsten blank.

[0035] The sandwich structure was placed in an atmosphere furnace and subjected to high-temperature thermal diffusion treatment under the action of a protective atmosphere and axial pressure, ultimately obtaining a gradient material micro-drill bit with a tungsten carbide surface and a tungsten core.

[0036] To enable those skilled in the art to fully understand and implement the present invention, several embodiments and comparative examples are listed below.

[0037] Example 1: Fabrication of a rectangular cross-section micro-drill bit with a diameter of 40 μm

[0038] S1. Blank Preparation: Ten tungsten foils with a thickness of 25μm and a purity ≥99.95% were selected, ultrasonically cleaned with alcohol, dried, and neatly stacked. They were then clamped and fixed with a special fixture. A Sodick AP250L micro-wire EDM machine (Japan) was used, with a copper wire of 0.05mm diameter as the electrode. The EDM parameters were set as follows: open circuit voltage 90V, pulse width 1.2μs, pulse interval 5μs, peak current 1.5A, and cutting speed 55μm / min. Cutting was performed in deionized water working solution along a set rectangular path with a final diagonal length of 40μm. Ten micro-drill blanks with an overall size of 15mm×5mm were obtained in one pass. Microscopic inspection showed that the blanks had neat edges and no defects such as curling or tearing, with a yield of 100%.

[0039] S2. Assemble the diffusion structure: Select a T10 high-carbon steel plate with a carbon mass fraction of 1.0% and a size of 40mm×40mm×5mm as the substrate and cover plate. Use a precision CNC milling machine to precisely machine a rectangular cavity with a depth of 40±2μm and a size of 20mm×10mm on the lower substrate. Precisely place a tungsten foil blank obtained in step S1 in the center of the cavity. Then, use a precision powder spreading device to uniformly fill the gaps around it with T10 high-carbon steel powder with a particle size of D50=20μm. Slight vibration is used during the powder filling process to ensure dense filling. Finally, cover it with the upper cover plate 90 with a surface finish Ra≤0.4μm to form a tight sandwich structure.

[0040] S3. Thermal diffusion treatment: The assembled sandwich structure is transferred to a tubular atmosphere furnace filled with high-purity argon gas (≥99.999%). The gas flow rate is adjusted and stabilized at 300 sccm, and the furnace pressure is maintained at approximately 108 kPa. A constant pressure of 5 MPa is applied to the component vertically through the pressurization mechanism above the furnace. The heating program is set as follows: the temperature is increased from room temperature to 800℃ at a rate of 10℃ / min; then increased from 800℃ to 1050℃ at a rate of 5℃ / min; and held at 1050℃ for 5 hours. After the holding period, the structure is cooled to below 200℃ with the furnace before being removed.

[0041] S4. Post-processing: Carefully separate the components, remove the micro drill bit, place it in a beaker containing 10% vol. dilute hydrochloric acid solution, put it in a 50℃ water bath, and ultrasonically vibrate it for 10 minutes in an ultrasonic cleaner with a power of 200W and a frequency of 40kHz. After removing it, rinse it three times with deionized water, dehydrate it with anhydrous ethanol, and dry it in an 80℃ vacuum oven for 1 hour to obtain the final graded material wear-resistant micro drill bit product.

[0042] Example 2: Fabrication of a rectangular cross-section micro-drill bit with a diameter of 20 μm

[0043] S1. Blank preparation: Select 20 high-purity tungsten foils with a thickness of 15 μm. The electrical discharge parameters are set as follows: pulse width 0.8 μs, pulse interval 3.5 μs, peak current 0.9 A, and cutting speed 35 μm / min. Other steps are the same as in Example 1.

[0044] S2. Assembly diffusion structure: The cavity depth is machined to 15±1μm, and the high carbon steel powder filled in has a particle size D50=10μm.

[0045] S3. Thermal diffusion treatment: Adjust the argon flow rate to 200 sccm. Apply a pressure of 3 MPa. Heating program: Increase the temperature to 800℃ at 8℃ / min, then increase it to 1000℃ at 4℃ / min, and hold for 8 hours.

[0046] S4. Post-treatment: Use 8% vol. dilute hydrochloric acid and ultrasonically clean for 15 minutes at 40℃ and 150W power. Other steps are the same as in Example 1.

[0047] Example 3: Fabrication of a parallelogram-shaped micro-drill bit with a diameter of 80 μm

[0048] S1. Blank Preparation: Five high-purity tungsten foils with a thickness of 55 μm were selected. The electrical discharge parameters were set as follows: pulse width 4.5 μs, pulse interval 16 μs, peak current 3.2 A, and cutting speed 125 μm / min. The cutting path was a parallelogram.

[0049] S2. Assembled diffusion structure: Cavity depth is 80±3μm. The particle size of the high-carbon steel powder filled in is D50=45μm.

[0050] S3. Thermal diffusion treatment: Adjust the argon flow rate to 450 sccm. Apply pressure to 8 MPa. Heating program: Increase the temperature to 800℃ at 12℃ / min, then increase it to 1120℃ at 6℃ / min, and hold for 3 hours.

[0051] S4. Post-treatment: Use 12% vol. dilute hydrochloric acid for ultrasonic cleaning at 60℃ and 280W power for 7 minutes. Other steps are the same as in Example 1.

[0052] Example 4: Fabrication of a rectangular cross-section micro-drill bit with a diameter of 100 μm

[0053] S1. Blank preparation: Select 4 pieces of high-purity tungsten foil with a thickness of 70μm. Set the electrical discharge parameters as follows: pulse width 6μs, pulse interval 20μs, peak current 4.0A, and cutting speed 150μm / min.

[0054] S2. Assembled diffusion structure: Cavity depth is 100±4μm. The particle size of the high-carbon steel powder filled in is D50=50μm.

[0055] S3. Thermal diffusion treatment: Argon flow rate is 500 sccm, and the applied pressure is 10 MPa. Heating program: Increase the temperature to 800℃ at 15℃ / min, then increase it to 1150℃ at 8℃ / min, and hold for 2 hours.

[0056] S4. Post-processing: Same as Example 3.

[0057] Comparative Example 1: Traditional Grinding Process

[0058] An attempt was made to grind a 0.5 mm diameter cemented carbide (YG8) bar using a Swiss Studer S141 high-precision CNC internal and external cylindrical grinder, with the goal of preparing a 40 μm diameter micro-drill bit blank. A W5 diamond grinding wheel was used at a rotation speed of 40,000 rpm. The drill bit fractured under grinding force when the diameter reached approximately 60 μm. The experiment was repeated 10 times, with a success rate of 0% and a yield of 0%.

[0059] Comparative Example 2: PVD-coated micro drill bits

[0060] A commercially available 40μm diameter pure tungsten micro-drill bit was procured and fabricated using a drawing process. A titanium nitride (TiN) wear-resistant coating with a thickness of approximately 2.0±0.2μm was deposited on its surface using a Leybold Sypro T-type magnetron sputtering coating machine. Deposition parameters: argon atmosphere, bias voltage -80V, temperature 450℃, deposition time 120min.

[0061] Comparative Example 3: Non-optimal thermal diffusion parameters

[0062] Repeat the steps of Example 1, but in the S3 heat diffusion treatment, change the pressure to 0.5 MPa (lower than the lower limit required by the present invention), the heat preservation temperature to 850°C (lower than the lower limit required by the present invention), and the heat preservation time to 1 hour (lower than the lower limit required by the present invention).

[0063] Experimental Testing and Performance Analysis

[0064] The performance of the micro drill bits prepared in Examples 1 to 4 of the present invention and the samples of Comparative Examples 1 to 3 were tested, and the test results are shown in the table below.

[0065] Table 1: Comparison of Micro-Drill Bit Performance Test Results

[0066]

[0067]

[0068] Life test conditions: Continuous drilling of through holes on a 1.0mm thick 304 stainless steel plate, spindle speed 40000rpm, feed rate 5μm / s. After drilling 20 holes, the wear condition was checked under a microscope. The failure criterion was that the wear of the drill bit diameter exceeded 10% of the nominal diameter or the drill bit broke. The result is the average value of 5 samples.

[0069] "-" indicates that the test was not performed because the sample could not be successfully prepared or the sample did not meet the test conditions.

[0070] The yield of Comparative Example 1 (traditional grinding process) was 0%, which indicates that when machining extremely fine drill bits with a diameter of 40 μm or less, the traditional grinding process, due to the unavoidable macroscopic mechanical forces, causes the blank to fracture 100% during the machining process, making effective preparation impossible.

[0071] Examples 1-4 of this invention employ micro-wire electrical discharge machining, a non-contact processing method without macroscopic mechanical force, achieving a blank yield of over 98%. This directly demonstrates that the technical means employed in this invention successfully circumvents the fundamental defects of traditional processing methods, providing a key guarantee for the reliable preparation of ultra-fine drill bits.

[0072] Although the surface hardness (2400HV) of Comparative Example 2 (PVD coating) is comparable to that of the embodiments of the present invention, its coating has extremely low adhesion to the substrate, with a critical load of only 26N. This indicates that the coating formed by physical vapor deposition is only mechanically bonded to the substrate, and the interfacial bonding strength is weak.

[0073] The surface hardness (1650 HV) and bonding strength (45 N) of Comparative Example 3 (with non-optimal thermal diffusion parameters) are significantly lower than those of the embodiments of the present invention. This is because the thermal diffusion temperature, pressure and time are insufficient, resulting in insufficient diffusion of carbon atoms and failure to form a sufficiently thick and dense tungsten carbide gradient layer that can achieve metallurgical bonding with the substrate.

[0074] The surface hardness of Examples 1 to 4 of the present invention is maintained above 2250 HV, and the critical load of bonding force is greater than 80 N. This fully demonstrates that by using the sandwich structure described in the present invention and thermal diffusion under specific pressure, temperature and time, a tungsten carbide gradient layer with high hardness and high metallurgical bonding with the substrate can be generated in situ on the surface of the tungsten substrate. This gradient layer effectively overcomes the inherent disadvantage of weak bonding force of traditional coatings.

[0075] Comparative Example 2 had the shortest drilling life, averaging 320 holes, and its failure mode was "coating peeling and rapid substrate wear". This is completely consistent with the test results of its low adhesion, where premature coating peeling leads to the substrate losing protection and failing rapidly.

[0076] The lifespan of Comparative Example 3 was an average of 150 pores, even lower than that of Comparative Example 2. Its failure mode was "wear-resistant layer peeling and insufficient wear resistance". This confirms that its heat diffusion layer is not hard enough, has low hardness, is not strong enough, and has insufficient bonding force, so it cannot provide effective wear protection.

[0077] The drilling life of Examples 1-4 of this invention is significantly extended, ranging from 980 to 2500 holes, and the failure mode is "uniform wear" in all cases. This indicates that the gradient wear-resistant layer prepared by this invention remains intact throughout the drilling process, without peeling off, and only gradually wears down due to normal friction until it reaches the end of its life. The significant improvement in life is directly due to the durable and stable wear-resistant protection provided by the high-hardness gradient layer with high-strength metallurgical bonding.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a wear-resistant micro-drill bit made of gradient material, characterized in that, Includes the following steps: S1. Billet preparation: Multiple layers of tungsten foil sheets with a thickness of 15–70 μm are stacked, aligned, and fixed. Then, a micro-electrical discharge wire cutting process is used to process the micro-drill blanks along the designed path, obtaining multiple micro-drill blanks with rectangular or parallelogram cross-sectional shapes in one go. S2, Assemble the diffusion structure: Prepare a high-carbon steel substrate and process a cavity on it with a depth equal to the thickness of the micro drill bit blank; place the micro drill bit blank in the center of the cavity and fill it with high-carbon steel powder as a solid carbon source around it, and then cover it with a high-carbon steel cover plate to create a closed diffusion environment that completely encapsulates the micro drill bit blank in high-carbon steel material. S3, Thermal diffusion reaction: The assembled structure in step S2 is placed in an atmosphere furnace with a protective atmosphere. An axial pressure of 1-10 MPa is used to make the contact surfaces fit tightly together. Then, the structure is heated to 900-1200°C according to the set heating program and held for 2-10 hours. This promotes the directional diffusion of carbon atoms in the high-carbon steel to the surface of the tungsten foil blank and the metallurgical reaction therewith, generating a tungsten carbide wear-resistant layer that has a gradient transition with the substrate and is metallurgically bonded. S4. Post-processing: The micro drill bit processed in step S3 is taken out and acid-washed to remove the residual high-carbon steel material on the surface, thus obtaining the wear-resistant micro drill bit of the gradient material.

2. The method for preparing a gradient material wear-resistant micro drill bit according to claim 1, characterized in that, In step S1, the electrical parameters of the micro-electrical discharge wire cutting process are: pulse width of 0.1 to 10 μs, pulse interval of 1 to 20 μs, and processing current of 0.5 to 5 A.

3. The method for preparing a gradient material wear-resistant micro-drill bit according to claim 2, characterized in that, In step S1, the cutting speed of the micro-electrical discharge wire cutting is 20-200 μm / min.

4. The method for preparing a gradient material wear-resistant micro drill bit according to claim 1, characterized in that, In step S3, the protective atmosphere is argon, nitrogen, or a mixture of the above gases and trace amounts of hydrogen. The flow rate of the protective atmosphere is 100-500 ml per minute, and the pressure inside the furnace is maintained slightly higher than atmospheric pressure, ranging from 105 to 110 kPa.

5. A method for preparing a gradient material wear-resistant micro-drill bit according to claim 1 or 4, characterized in that, In step S3, the set heating program is specifically as follows: heating from room temperature to 800°C at a rate of 5-15°C / min; and then heating from 800°C to the target temperature of 900-1200°C at a rate of 3-8°C / min.

6. The method for preparing a gradient material wear-resistant micro-drill bit according to claim 1, characterized in that, In step S2, the particle size of the high-carbon steel powder is 10-50 μm, and the carbon mass fraction of the high-carbon steel substrate, the high-carbon steel cover plate, and the high-carbon steel powder is not less than 0.7%.

7. The method for preparing a gradient material wear-resistant micro drill bit according to claim 1, characterized in that, In step S4, a dilute hydrochloric acid solution with a concentration of 5% to 15% is used to perform ultrasonic cleaning at a temperature of 40 to 60°C, with an ultrasonic power of 100 to 300W and a cleaning time of 5 to 20 minutes.

8. A wear-resistant micro drill bit made of gradient material, characterized in that, The wear-resistant micro drill bit is prepared by any one of the methods described in claims 1 to 7.

9. The wear-resistant micro drill bit made of gradient material according to claim 8, characterized in that, The working part of the micro-drill bit has a rectangular or parallelogram cross-section, and its diagonal length is the diameter of the micro-drill bit, wherein the diameter is less than or equal to 80 μm.

10. A gradient material wear-resistant micro drill bit according to claim 9, characterized in that, The micro drill bit has a diameter of less than or equal to 20 μm, and the thickness of its surface tungsten carbide gradient layer is 1–5 μm, with a Vickers hardness HV≥2200.

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