BTA deep hole drill guide key and preparation method thereof

Abstract

This invention discloses a BTA deep hole drill guide key and its preparation method, belonging to the field of deep hole machining tool technology. The guide key comprises an alloy steel substrate and a PCBN composite sheet fixed thereon. The PCBN composite sheet sequentially comprises a cemented carbide base layer, a gradient transition layer with progressively increasing CBN content, and a polycrystalline cubic boron nitride working layer. This invention also discloses the preparation method of the guide key and a BTA deep hole drill incorporating the guide key. This invention solves the problem of high thermal stress and easy cracking at the PCBN-cemented carbide interface through a gradient transition layer design. Applying the PCBN composite sheet to the guide key of the BTA deep hole drill significantly improves the wear resistance and service life of the guide key. In deep hole machining of difficult-to-machine materials, the guide key life is more than 15 times longer than traditional cemented carbide products. Simultaneously, it significantly improves drilling straightness and surface quality, reduces tool change downtime, and is suitable for high-speed cutting and deep hole machining of various difficult-to-machine materials.

Description

Technical Field

[0001] This invention belongs to the field of deep hole tool processing technology, and particularly relates to a BTA deep hole drill guide key and its preparation method. Background Technology

[0002] BTA deep hole drills are currently the mainstream cutting tools for deep hole machining in the field of machining. Their structure mainly consists of a drill body and at least two guide keys (also called guide bars) mounted on the drill body. During deep hole drilling, the guide keys perform three core functions: first, they support the drill body, maintaining the drilling direction and ensuring the straightness of the hole; second, they directly contact the workpiece hole wall, bearing the radial cutting force during drilling; and third, they act as vibration dampers, reducing machining vibration and improving the surface finish of the hole wall.

[0003] Currently, BTA deep hole drilling guide keys in the industry are generally made of cemented carbide materials such as YG8 and YG6X. Some high-end products are coated with wear-resistant coatings such as TiN and TiAlN on the surface of the cemented carbide to improve its wear resistance. In conventional deep hole machining of ordinary steels such as 45# steel, the service life of the above-mentioned cemented carbide guide keys can basically meet the machining requirements. However, in deep hole machining of difficult-to-machine materials such as hardened steel, titanium alloys, and nickel-based alloys, there are insurmountable technical defects: Rapid wear and short service life: When machining hardened steel with HRC50 or higher, traditional cemented carbide guide keys usually need to be replaced after machining 5-10 meters; their overall lifespan is only 1 / 3-1 / 5 of the lifespan of the drill bit's cutting edge, becoming the core shortcoming restricting the overall lifespan of BTA deep hole drills.

[0004] Poor machining quality stability: After the guide key wears down, the radial support force of the drill bit becomes unbalanced, the straightness of the drill hole drops rapidly, and the surface roughness of the hole wall deteriorates, failing to meet the machining requirements of high-precision deep holes.

[0005] High processing costs and low efficiency: The short lifespan of the guide keys leads to frequent tool changes, which significantly increases the downtime for tool changes, seriously affecting the processing efficiency of the production line and increasing the cost of tool consumables.

[0006] Limited material compatibility: Cemented carbide has limited high-temperature hardness and high-temperature stability. In the machining of titanium alloys and nickel-based alloys, the temperature in the cutting zone is high, the hardness of cemented carbide drops rapidly, and wear is aggravated. At the same time, cemented carbide has a strong affinity with titanium alloy materials, which easily leads to adhesive wear, making it unsuitable for high-speed cutting and machining of difficult-to-machine materials. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a BTA deep hole drilling guide key and its preparation method. This guide key has high wear resistance, impact resistance, and high temperature stability, significantly improving its service life. It is suitable for deep hole machining of difficult-to-machine materials such as hardened steel, titanium alloys, and nickel-based alloys, thus solving the problems in the background technology.

[0008] This invention provides the following technical solution: A BTA deep hole drilling guide key includes an alloy steel substrate and a polycrystalline cubic boron nitride (PCBN) composite sheet fixed on the alloy steel substrate. The PCBN composite sheet sequentially includes a cemented carbide base layer, a gradient transition layer, and a polycrystalline cubic boron nitride working layer. The gradient transition layer is disposed between the cemented carbide base layer and the polycrystalline cubic boron nitride working layer, and the CBN content in the gradient transition layer increases in a gradient from the cemented carbide base layer to the polycrystalline cubic boron nitride working layer.

[0009] Preferably, the gradient transition layer includes at least two sub-transition layers, and the CBN quality fraction of each sub-transition layer is increased by 20% to 30% along the gradient increasing direction.

[0010] Preferably, the gradient transition layer includes three sub-transition layers, which are sequentially a first transition layer, a second transition layer, and a third transition layer along the direction from the cemented carbide base layer to the polycrystalline cubic boron nitride working layer; wherein the CBN mass fraction of the first transition layer is 20%, the CBN mass fraction of the second transition layer is 40%, and the CBN mass fraction of the third transition layer is 60%.

[0011] Preferably, the thickness of the cemented carbide base layer is 1-3 mm; the thickness of each sub-transition layer is independently 0.1-0.3 mm; and the thickness of the polycrystalline cubic boron nitride working layer is 0.5-1 mm.

[0012] Preferably, in the polycrystalline cubic boron nitride working layer, the mass fraction of CBN is 60% to 95%, and the balance is a binder; the binder includes two or more combinations of TiN, Al, Co, and Ni.

[0013] Preferably, the surface of the CBN micropowder in the polycrystalline cubic boron nitride working layer is coated with a W coating or a Ti coating.

[0014] Preferably, the cemented carbide base layer is a WC-Co series cemented carbide; the alloy steel substrate is 42CrMo alloy steel or DC53 alloy steel.

[0015] Preferably, the PCBN composite sheet is fixed to the alloy steel substrate by vacuum brazing, and the brazing is performed using Ag-Cu-Ti active solder.

[0016] Preferably, a BTA deep hole drill includes a drill body on which at least two BTA deep hole drill guide keys as described in any one of claims 1-8 are mounted.

[0017] Preferably, a method for preparing a BTA deep hole drill guide key includes the following steps: S1, Preparation of PCBN Composite Sheet: A PCBN composite sheet with a cemented carbide base layer, a gradient transition layer, and a polycrystalline cubic boron nitride working layer is prepared, wherein the CBN content of the gradient transition layer increases in a gradient from the cemented carbide base layer to the polycrystalline cubic boron nitride working layer; the PCBN composite sheet is formed by high temperature and high pressure sintering. S2, Guide key assembly: Fix the sintered PCBN composite sheet onto the alloy steel substrate to obtain the BTA deep hole drilling guide key.

[0018] Preferably, step S1 specifically includes: S11, Mixing: CBN micro powder is surface coated. The raw materials of the hard alloy base layer, each sub-layer of the gradient transition layer and the polycrystalline cubic boron nitride working layer are weighed according to the ratio, and ball milled, dried and sieved to obtain the mixture of each layer. S12, Assembly: Gradient transition layer mixture and polycrystalline cubic boron nitride working layer mixture are sequentially laid on a cemented carbide substrate. Each layer is evenly laid and pre-pressed to obtain a composite billet. S13, High-temperature and high-pressure sintering: The composite blank is loaded into a high-pressure synthesis block and sintered at a pressure of 5.0-6.0 GPa and a temperature of 1400-1500℃ for 15-30 minutes to obtain PCBN composite sheets.

[0019] Preferably, in step S11, the CBN micro powder surface coating treatment is performed by mixing CBN micro powder with W powder or Ti powder and heat-treating it in a vacuum furnace to form a W coating or Ti coating on the surface of the CBN micro powder.

[0020] Preferably, in step S12, the pre-pressing molding adopts a step-by-step pre-pressing method: first, each sub-layer mixture of the gradient transition layer is pressed into a single-layer blank, and then each single-layer blank and the working layer mixture are stacked in the order of the layers and pre-pressed as a whole; or a continuous pre-pressing method is adopted: the mixture is laid layer by layer on the cemented carbide substrate and pre-pressed one by one, and finally the overall pre-pressing molding is completed.

[0021] Preferably, step S2 specifically includes: S21, Post-processing: Cut the sintered PCBN composite sheet into a preset size and machine a positioning groove matching the PCBN composite sheet on the alloy steel substrate. S22, Brazing Fixing: Using Ag-Cu-Ti active brazing filler metal, the PCBN composite sheet is brazed into the positioning groove of the alloy steel substrate in a vacuum furnace. The brazing temperature is 820-880℃ and the holding time is 8-15min, thus obtaining the BTA deep hole drill guide key.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention relates to a BTA deep hole drill guide key and its preparation method, which significantly improves service life and processing efficiency. By using polycrystalline cubic boron nitride as the working surface material of the guide key and combining it with a gradient transition layer structure design, the service life of the guide key in deep hole machining of difficult-to-machine materials is increased by more than 15 times compared with traditional cemented carbide guide keys, and can be as high as 80 times. It can realize the one-time machining of ultra-long deep holes without the need for intermediate tool changes, greatly reducing downtime for tool changes, improving production efficiency, and reducing tool consumable costs.

[0023] By designing a gradient transition layer with progressively increasing CBN content, a continuous transition of composition between the cemented carbide base layer and the polycrystalline cubic boron nitride working layer is achieved. This effectively alleviates the interfacial thermal stress between the two materials, solves the industry pain point of easy delamination and cracking of PCBN composite sheets, and ensures the structural stability of the guide keys under strong radial cutting forces and high-frequency vibration conditions.

[0024] It has excellent wear resistance, with minimal wear during processing, and can maintain stable radial support force for a long time, effectively ensuring the straightness of the drilled hole. At the same time, it reduces the surface roughness of the hole wall by more than 50%, significantly improving the accuracy and surface quality of deep hole machining.

[0025] It breaks through the hardness and high-temperature performance limits of traditional cemented carbide, and can process low-hardness materials such as ultra-low carbon steel, as well as hardened steel with HRC60 and above. At the same time, it is compatible with high-speed cutting of various difficult-to-machine materials such as titanium alloys, nickel-based alloys, and non-magnetic steel, achieving one-click universality and greatly reducing tool selection and management costs.

[0026] By employing stepwise mixing, gradient material spreading, and high-temperature and high-pressure integrated sintering, combined with vacuum brazing for fixation, the process exhibits strong stability, enabling stable mass production of guide keys with high product performance consistency, making it suitable for industrial application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the assembly structure of the BTA deep hole drilling guide key of the present invention.

[0029] Figure 2 This is a schematic diagram of the overall structure of the BTA deep hole drill including the guide key of the present invention.

[0030] Figure 3 This is a schematic diagram of the overall structure of the guide key of the present invention.

[0031] Figure 4 This is a schematic diagram of the layer structure of the PCBN composite sheet of the present invention.

[0032] Figure 5 This is a comparison curve of the wear amount of the guide key of the present invention when machining HYT2 material with traditional cemented carbide guide keys.

[0033] Figure 6 This is a physical image of the guide key of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 a part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0036] Example 1 refer to Figure 1-4 A BTA deep hole drilling guide key includes an alloy steel substrate 3 and a polycrystalline cubic boron nitride (PCBN) composite sheet 4 fixed on the alloy steel substrate 3. The PCBN composite sheet 4 sequentially includes a cemented carbide base layer, a gradient transition layer, and a polycrystalline cubic boron nitride working layer 44. The gradient transition layer is disposed between the cemented carbide base layer and the polycrystalline cubic boron nitride working layer 44, and the CBN content in the gradient transition layer increases in a gradient from the cemented carbide base layer to the polycrystalline cubic boron nitride working layer 44.

[0037] The gradient transition layer includes at least two sub-transition layers, and the CBN quality fraction of each sub-transition layer is increased by 20% to 30% along the gradient increasing direction.

[0038] The gradient transition layer includes three sub-transition layers, which are, in sequence, a first transition layer 41, a second transition layer 42, and a third transition layer 43 along the direction from the cemented carbide base layer to the polycrystalline cubic boron nitride working layer 44; wherein the CBN mass fraction of the first transition layer 41 is 20%, the CBN mass fraction of the second transition layer 42 is 40%, and the CBN mass fraction of the third transition layer 43 is 60%.

[0039] The thickness of the hard alloy base layer is 1-3 mm; the thickness of each sub-transition layer is 0.1-0.3 mm; and the thickness of the polycrystalline cubic boron nitride working layer 44 is 0.5-1 mm.

[0040] Preferably, in the polycrystalline cubic boron nitride working layer 44, the mass fraction of CBN is 60%-95%, and the balance is a binder; the binder includes two or more combinations of TiN, Al, Co, and Ni.

[0041] The surface of the CBN micropowder in the polycrystalline cubic boron nitride working layer 44 is coated with a W coating or a Ti coating.

[0042] The cemented carbide base layer is a WC-Co series cemented carbide; the alloy steel substrate 3 is 42 chromium-molybdenum alloy steel or DC53 alloy steel.

[0043] The PCBN composite sheet 4 is fixed to the alloy steel substrate 3 by vacuum brazing, and the brazing is performed using Ag-Cu-Ti active brazing filler metal.

[0044] A BTA deep hole drill includes a drill body 1, on which at least two BTA deep hole drill guide keys as described in any one of claims 1-8 are mounted.

[0045] A method for preparing a BTA deep hole drill guide key includes the following steps: S1, Preparation of PCBN composite sheet 4: A PCBN composite sheet 4 having a cemented carbide base layer, a gradient transition layer and a polycrystalline cubic boron nitride working layer 44 is prepared, wherein the CBN content of the gradient transition layer increases in a gradient from the cemented carbide base layer to the polycrystalline cubic boron nitride working layer 44; the PCBN composite sheet 4 is formed by high temperature and high pressure sintering. S2, Guide key assembly: Fix the sintered PCBN composite sheet 4 onto the alloy steel substrate 3 to obtain the BTA deep hole drilling guide key.

[0046] Step S1 specifically includes: S11, Mixing: CBN micro powder is surface coated. The raw materials of the cemented carbide base layer, each sub-layer of the gradient transition layer, and the polycrystalline cubic boron nitride working layer 44 are weighed according to the ratio, and ball-milled, dried, and sieved to obtain the mixture of each layer. S12, Assembly: Gradient transition layer sub-layer mixture and polycrystalline cubic boron nitride working layer 44 mixture are sequentially laid on the cemented carbide substrate. Each layer is evenly laid and pre-pressed to obtain a composite billet. S13, High-temperature and high-pressure sintering: The composite blank is loaded into a high-pressure synthesis block and sintered at a pressure of 5.0-6.0 GPa and a temperature of 1400-1500℃ for 15-30 minutes to obtain PCBN composite sheet 4.

[0047] In step S11, the CBN micro powder surface coating treatment is as follows: CBN micro powder is mixed with W powder or Ti powder, and heat-treated in a vacuum furnace to form a W coating or Ti coating on the surface of CBN micro powder.

[0048] In step S12, the pre-pressing can be performed in stages: specifically, the first step is to press the prepared first transition layer 41 (20% cBN + 80% YG8 cemented carbide raw material micro powder with a differential particle size of 20-80 μm) using a 500-ton hydraulic press to form a pressed blank of the first transition layer 41; the pressed blank is then removed for later use. The second step is to press the prepared second transition layer 42 (40% cBN + 60% YG8 cemented carbide raw material micro powder with a differential particle size of 20-80 μm) using a 500-ton hydraulic press to form a pressed blank of the second transition layer 42; the pressed blank is then removed for later use. The third step is to press the prepared third transition layer 43 (60% cBN + 40% YG8 cemented carbide raw material micro powder with a differential particle size of 20-80 μm) using a 500-ton hydraulic press to form a pressed blank of the third transition layer 43; the pressed blank is then removed for later use. Step 4: The prepared working layer 44, consisting of 85% cBN + 15% YG8 cemented carbide raw material micro powder with a micro-particle size of 20-80μm, is pressed using a 500-ton hydraulic press to form the pressed blank of working layer 44; the pressed blank is then removed for later use. Step 5: The pressed blanks of the first transition layer 41, the second transition layer 42, and the third transition layer 43 are stacked sequentially from bottom to top and pressed using an 800-ton hydraulic press to form a guided composite blank.

[0049] In step S12, the pre-pressing can also be performed using a continuous pre-pressing method. Specifically, it includes the following steps: First, the proportioned 20% cBN + 80% YG8 cemented carbide raw material micro powder of the first transition layer 41, with a differential particle size of 20-80 μm, is pressed using a 500-ton hydraulic press to form a pressed blank of the first transition layer 41. Second, without removing the pressed blank of the first transition layer 41, the 40% cBN + 60% YG8 cemented carbide raw material micro powder of the second transition layer 42 is directly laid on top of the pressed blank of the first transition layer 41, and pressed using a 500-ton hydraulic press to obtain a blank. Third, without removing the blank obtained in the second step, the 60% cBN + 40% YG8 cemented carbide raw material micro powder of the second transition layer 42 is laid on the blank pressed in the second step, and pressed using a 500-ton hydraulic press to obtain a blank. The fourth step involves not removing the billet obtained in the third step. On top of the billet pressed in the third step, a working layer of 85% cBN + 15% YG8 cemented carbide raw material micro-powder is laid, and then pressed using an 800-ton hydraulic press to obtain a composite billet. By employing a special pressing method, the cBN and YG8 cemented carbide powders can be fully pressed together.

[0050] Because stable bonding of cBN (cubic boron nitride) and YG8 cemented carbide micropowder is difficult to achieve, subsequent delamination and cracking are prone to occur. The above method can effectively solve this problem. cBN has a zincblende crystal structure, dominated by strong covalent bonds (BN bonds, with bond energies as high as 410 kJ / mol), resulting in extremely strong interatomic bonding and very high atomic diffusion activation energy at both room and high temperatures. This makes it almost impossible for cBN to form chemical bonds through atomic interdiffusion with dissimilar materials. YG8 cemented carbide, with WC (a mixture of covalent and metallic bonds) as the hard phase and Co as the binder phase, relies on the metallic bonds of Co to achieve liquid-phase sintering and bonding. This bonding depends on the diffusion, wetting, and fusion of metal atoms. The fundamental difference in bond types between the two materials prevents effective chemical bonding at the interface. Even with physical bonding, it is only a mechanical adhesion with extremely weak bonding force, making interface debonding highly likely. Furthermore, when pure cBN comes into direct contact with pure YG8, the material properties undergo a precipitous change. During the sintering and cooling process, the shrinkage of the two materials differs greatly, and tensile / shear stresses exceeding the material strength limit are generated at the interface, eventually leading to interface cracking and delamination. This is the core reason why PCBN composite sheets are prone to failure in the industry.

[0051] This solution addresses the core challenges mentioned above by using a gradient mix ratio of 20%→40%→60% cBN, combined with a layered pre-compression / layer-by-layer pressing process, thereby achieving dual optimization of performance and process. The core of the gradient mix ratio is to transform the "cliff-like abrupt change" in material properties into a "continuous gradual change," fundamentally solving the interfacial mismatch problem while taking into account both the wear resistance of the working surface and the toughness of the matrix.

[0052] By gradually increasing the cBN content from 20% to 40% to 60%, the thermal expansion coefficient, elastic modulus, and hardness of the composite sheet all show a linear and continuous change, unlike the abrupt jump between pure cBN and pure YG8, where the thermal expansion coefficient of pure YG8 is 8×10. -6 / ℃→20%cBN layer 7×10 -6 / ℃→40%cBN layer 6×10 -6 / ℃→60%cBN layer 5×10 -6 / ℃→85%cBN working layer 443.5×10 -6 / ℃.

[0053] The cBN content in the gradient layer gradually increases, and each layer retains a sufficient amount of WC-Co phase. The Co binder phase can fully wet the cBN particles in the same layer, solving the problem of poor wettability between pure cBN and Co. The cBN content of adjacent layers differs by only 20%, with minimal compositional differences. During high-temperature and high-pressure sintering, Co and W elements can diffuse upwards, while B and N elements can diffuse downwards, forming a continuous element diffusion band between layers. This achieves true metallurgical bonding rather than mechanical bonding, and the interfacial bonding strength is more than 3 times higher than that of direct bonding. The transition layer with low cBN content is equivalent to a "bonding buffer layer," which not only achieves perfect bonding with the bottom YG8 hard alloy base layer but also provides a stable bonding substrate for the top high cBN working layer 44, solving the compatibility problem between the high-hardness wear-resistant layer and the high-toughness support layer. The performance difference between adjacent layers is minimal. During the heating / cooling process, the difference in shrinkage / expansion between layers is gradually dispersed and offset, reducing the interfacial thermal stress by more than 90%. This fundamentally solves the problem of delamination and cracking caused by thermal stress, and significantly improves the impact resistance and structural stability of the composite sheet.

[0054] From the YG8 base layer to the 20% cBN layer, and then to the 40% and 60% cBN layers, the plasticity of the material gradually decreases while the hardness gradually increases, thus avoiding direct contact between the hard and brittle cBN and the plastic YG8.

[0055] During cold pressing, the transition layer with low cBN content still has excellent plastic deformation capacity and can achieve stable pressing with the base layer. At the same time, it provides plastic buffer for the upper high cBN layer to avoid stress concentration. The brittleness of the high cBN layer is gradually dispersed, and overall brittle fracture will not occur. The density and strength of the green body are greatly improved, providing a defect-free qualified green body for subsequent high temperature and high pressure sintering.

[0056] Addressing the density difference of over four times between cBN and WC, layered lamination employs a step-by-step process of pressing the lower layer, then laying the upper layer, and pressing the upper layer again. This process completely fixes the composition and thickness of each layer, thoroughly avoiding the mixing of components caused by the settling of heavy particles and the floating of light particles. It precisely achieves the preset gradient ratio, ensuring structural consistency in every batch of products—something that cannot be achieved with a single-layer lamination process. Different cBN contents require different optimal lamination pressures: low-cBN layers have good plasticity and can be densified under low pressure; high-cBN layers are brittle and require high pressure to achieve particle rearrangement and densification. Layered lamination allows for individual setting of lamination pressure and holding time for each layer, ensuring that each layer reaches optimal density. This avoids the uneven density problem of "over-pressed bottom layer and under-pressed top layer" that occurs with single-layer lamination, completely eliminating defects such as interlayer porosity and looseness. The overall density of the sintered composite sheet can reach over 99.5%, significantly improving impact resistance and wear resistance. The lower layer of blank, which is pressed first, already has a certain strength and surface micro-roughness. When the upper layer of powder is laid and pressed, the powder particles of the upper layer will be embedded in the surface micro-pores of the lower layer of blank, forming a very strong mechanical anchoring effect. The interlayer bonding force is more than twice that of pressing with powder in one go. At the same time, pressing layer by layer can gradually remove the air in the powder, avoiding the problem of air being trapped between layers during one-time pressing, which would lead to bulging and delamination after sintering.

[0057] Step S2 specifically includes: S21, Post-processing: Cut the sintered PCBN composite sheet 4 into a preset size, and process a positioning groove on the alloy steel substrate 3 that matches the PCBN composite sheet 4. S22, Brazing Fixing: Using Ag-Cu-Ti active brazing filler metal, the PCBN composite sheet 4 is brazed into the positioning groove of the alloy steel substrate 3 in a vacuum furnace. The brazing temperature is 820-880℃ and the holding time is 8-15min, thus obtaining the BTA deep hole drill guide key.

[0058] Example 2: refer to Figure 6 A BTA deep hole drill guide key, the structure of which is as follows: It includes a 42CrMo alloy steel substrate 3 and a PCBN composite sheet 4 fixed to the alloy steel substrate 3 by vacuum brazing; PCBN composite sheet 4 comprises, in sequence, a cemented carbide base layer, a gradient transition layer, and a polycrystalline cubic boron nitride working layer 44, wherein: Hard alloy base layer: YG8 hard alloy, 2mm thick; Gradient transition layer: 3 sub-transition layers, each with a thickness of 0.2mm; along the direction from the cemented carbide base layer to the working layer 44, the first transition layer 41 is 20% cBN + 80% YG8 cemented carbide, the second transition layer 42 is 40% cBN + 60% YG8 cemented carbide, and the third transition layer 43 is 60% cBN + 40% YG8 cemented carbide; Polycrystalline cubic boron nitride working layer 44: 0.8mm thick, composed of 85% cBN + 15% binder, with a binder ratio of TiN:Al:Co=5:3:2; the cBN micro powder surface is treated with W plating.

[0059] The guide surface of the polycrystalline cubic boron nitride working layer features an asymmetric arc-shaped microtexture: arc-shaped recesses are 10 μm deep and 100 μm in diameter, spaced 200 μm apart along the feed direction; the flow-guiding microgrooves are 40 μm wide and 20 μm deep, communicating with the arc-shaped recesses. The alloy steel substrate and PCBN composite sheet contain a through-flow spiral internal cooling microchannel with a diameter of 0.8 mm. The inlet is connected to the BTA deep hole drilling internal cooling system, and the outlet is connected to the end of the flow-guiding microgrooves.

[0060] This embodiment also provides a method for preparing the above-mentioned BTA deep hole drill guide key, the steps of which are as follows: S1: Preparation of PCBN composite sheet 4 S11 Mixing: Mix cBN micro powder with W powder and heat treat in a vacuum furnace to form a W coating on the surface of cBN micro powder; weigh the raw materials of cemented carbide base layer, 3 transition layers and working layer 44 according to the above ratio, put them into ball mill jars, add anhydrous ethanol, ball mill and mix for 24 hours, dry the mixture and pass it through a 100-mesh sieve to obtain the mixture of each layer; S12 Assembly: On the YG8 cemented carbide substrate, a mixture of the first transition layer 41, the second transition layer 42, the third transition layer 43, and the working layer 44 is laid from bottom to top. Each layer is evenly laid and pre-pressed layer by layer using a 500-ton hydraulic press. Finally, an 800-ton hydraulic press is used for overall pre-pressing to obtain a composite billet. S13 High Temperature and High Pressure Sintering: The assembled composite blank is loaded into a high pressure synthesis block and placed in a six-sided top press. It is sintered at a pressure of 5.5 GPa and a temperature of 1450℃ for 20 minutes. After cooling, it is taken out to obtain PCBN composite sheet 4. S2: Guide key assembly S21: Post-processing: The sintered PCBN composite sheet 4 is processed into a size of 10mm×15mm×4mm by wire cutting, and a positioning groove matching the composite sheet is processed on the 42CrMo alloy steel substrate 3. S22 Brazing Fixing: Using Ag-Cu-Ti active brazing filler metal, the PCBN composite sheet 4 is brazed into the positioning groove of the alloy steel substrate 3 in a vacuum furnace at a brazing temperature of 850℃ for 10 minutes. After cooling, it is taken out and ground to obtain the BTA deep hole drill guide key.

[0061] S3: Post-processing: 1. Remove the blank and extract the molybdenum wire core to form a through spiral internal cooling microchannel; 2. Use a femtosecond laser to process an asymmetric microtexture on the guide working surface of the PCBN working layer to connect the flow guide microchannel with the outlet of the internal cooling microchannel; 3. After precision surface grinding, external cylindrical grinding, and ultrasonic cleaning, the BTA deep hole drill guide key is obtained.

[0062] Example 3: This embodiment provides a BTA deep hole drilling guide key, the only difference in structure from Embodiment 1 is: The alloy steel matrix 3 is made of DC53 alloy steel; The cemented carbide base layer is made of YM40 cemented carbide with a thickness of 1mm; The gradient transition layer consists of three sub-transition layers, each with a thickness of 0.1 mm. The polycrystalline cubic boron nitride working layer 44 has a thickness of 0.5 mm. Its composition is 95% cBN + 5% binder, with the binder being TiN + Co. The cBN micropowder surface is treated with Ti plating.

[0063] The microtextured arc-shaped pits are 5μm deep and 80μm in diameter; the flow-guiding microchannels are 30μm wide and 10μm deep; and the internal cooling microchannels are 0.5mm in diameter.

[0064] The difference between the preparation method in this embodiment and that in Example 1 is only that: High temperature and high pressure sintering parameters: pressure 6.0 GPa, temperature 1500℃, holding time 15 minutes; Brazing parameters: Brazing temperature 880℃, holding time 8 minutes.

[0065] Example 4: This embodiment provides a BTA deep hole drilling guide key, the only difference in structure from Embodiment 1 is: The thickness of the cemented carbide base layer is 3mm; The gradient transition layer consists of three sub-transition layers, each with a thickness of 0.3 mm. The polycrystalline cubic boron nitride working layer is 44 with a thickness of 1 mm. Its composition is 60% cBN + 40% binder, with the binder being Al + Ni + Co. The cBN micropowder surface is treated with W plating.

[0066] The microtextured arc-shaped pits are 20 μm deep and 150 μm in diameter; the flow-guiding microchannels are 50 μm wide and 30 μm deep; and the internal cooling microchannels are 1.0 mm in diameter.

[0067] The difference between the preparation method in this embodiment and that in Example 1 is only that: The pre-compression molding adopts a step-by-step pre-compression method: first, the mixture of the three transition layers is pressed into single-layer blanks by a 500-ton hydraulic press, and then each single-layer blank and the mixture of the working layer 44 are stacked in the order of layer level and pre-compressed as a whole by an 800-ton hydraulic press. High-temperature and high-pressure sintering parameters: pressure 5.0 GPa, temperature 1400℃, holding time 30 minutes; brazing parameters: brazing temperature 820℃, holding time 15 minutes.

[0068] An embodiment provides a BTA deep hole drill, including a drill bit body 1, on which two BTA deep hole drill guide keys prepared in embodiment 2 are symmetrically mounted.

[0069] Comparative Example 1: This comparative example uses a commercially available conventional cemented carbide guide key, grade YG8X, with specifications identical to those in Example 2.

[0070] Comparative Example 2: This comparative example is a common single-gradient PCBN guide key, without a transition layer gradient, microtexture, or internal cooling channel. It is prepared using a traditional step-by-step process of "sintering first, then brazing". The remaining structure and raw material specifications are the same as in Example 1.

[0071] Cutting performance was tested using Example 2 and Comparative Example 1. The test conditions were as follows: machine tool: BTA deep hole drilling machine; workpiece material: HYT2; hole diameter: φ75.3 mm; hole depth: 1746 mm; cutting speed: 95 m / min; feed rate: 27 mm / min; cooling method: high-pressure internal cooling. The test samples were guide keys prepared in Example 1, Comparative Example 1, and Comparative Example 2. The test results are shown in the table below. The test samples were the guide keys prepared in Example 2 and the cemented carbide guide keys from Comparative Examples 1 and 2.

[0072] refer to Figure 5 The guide keys prepared in Examples 2 and 3 were simultaneously subjected to performance tests. The results showed that, in the processing of HYT2 material, the wear resistance of the guide keys in Examples 2 and 3 was more than 38 times that of Comparative Example 1 and more than 4 times that of Comparative Example 2. In the processing of HRC62 hardened steel, the service life was more than 18 times that of Comparative Example 1 and more than 5 times that of Comparative Example 2. Both demonstrated excellent wear resistance, impact resistance, and thermal fatigue resistance. The above test results fully demonstrate that this solution has unexpected technical effects compared to the prior art.

[0073] By simultaneously matching the gradients of CBN content, fracture toughness, and thermal conductivity, the interfacial thermal stress is reduced by more than 95% through continuous gradual changes in composition, completely solving the industry pain point of delamination and cracking in PCBN composite sheets. Furthermore, the toughness gradient achieves compatibility between impact resistance and high wear resistance, preventing the high CBN layer from being damaged by impact. At the same time, the thermal conductivity gradient rapidly and directionally removes cutting heat from the working surface, increasing thermal fatigue life by more than 4 times. This achieves a triple synergy of crack resistance, impact resistance, and heat resistance, an unexpected effect that cannot be achieved by a single CBN content gradient.

[0074] The asymmetric arc-shaped microtexture can store cutting fluid and accommodate wear debris, reducing the friction coefficient of the guide surface by more than 60% and significantly reducing adhesive wear. The through-type spiral internal cooling microchannel directly delivers high-pressure cutting fluid to the guide working surface, achieving fixed-point forced cooling and reducing the working surface temperature by more than 300°C. This completely avoids the hardness reduction and tool sticking problems caused by high temperature. The two work together to improve the wear resistance by 3-5 times compared to ordinary non-gradient PCBN guide keys.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A BTA deep hole drill guide key, characterized in that, The invention includes an alloy steel substrate and a polycrystalline cubic boron nitride (PCBN) composite sheet fixed on the alloy steel substrate. The PCBN composite sheet sequentially includes a cemented carbide base layer, a gradient transition layer, and a polycrystalline cubic boron nitride working layer. The gradient transition layer is disposed between the cemented carbide base layer and the polycrystalline cubic boron nitride working layer, and the CBN content in the gradient transition layer increases in a gradient from the cemented carbide base layer to the polycrystalline cubic boron nitride working layer.

2. A BTA deep hole drilling guide key according to claim 1, characterized in that, The gradient transition layer includes at least two sub-transition layers, and the CBN quality fraction of each sub-transition layer increases by 20%-30% along the gradient increasing direction.

3. A BTA deep hole drilling guide key according to claim 2, characterized in that, The thickness of the hard alloy base layer is 1-3 mm, the thickness of a single layer of the gradient transition layer is 0.1-0.3 mm, and the thickness of the polycrystalline cubic boron nitride working layer is 0.5-1 mm.

4. A BTA deep hole drilling guide key according to claim 1, characterized in that, In the polycrystalline cubic boron nitride working layer, the mass fraction of CBN is 60%-95%, and the balance is binder; the binder includes two or more combinations of TiN, Al, Co and Ni.

5. A BTA deep hole drilling guide key according to claim 4, characterized in that, The surface of the CBN micropowder in the polycrystalline cubic boron nitride working layer is coated with a W coating or a Ti coating.

6. A BTA deep hole drilling guide key according to claim 1, characterized in that, The cemented carbide base layer is a WC-Co series cemented carbide, and the alloy steel matrix is ​​42 chromium-molybdenum alloy steel or DC53 alloy steel.

7. A BTA deep hole drilling guide key according to claim 1, characterized in that, The PCBN composite sheet is fixed to the alloy steel substrate by vacuum brazing, and the brazing is performed using Ag-Cu-Ti active solder.

8. A BTA deep hole drill, comprising a drill bit body, characterized in that, The drill bit body is equipped with at least two BTA deep hole drill guide keys as described in any one of claims 1-7.

9. A method for preparing a BTA deep hole drilling guide key, used to manufacture the guide key as described in any one of claims 1-7, characterized in that, Includes the following steps: S1, Preparation of PCBN composite sheet: A PCBN composite sheet is prepared having a cemented carbide base layer, a gradient transition layer with increasing CBN content, and a polycrystalline cubic boron nitride working layer in sequence. The PCBN composite sheet is integrally formed by high temperature and high pressure sintering. S2, Guide key assembly: Fix the sintered PCBN composite sheet onto the alloy steel substrate to obtain the BTA deep hole drilling guide key.

10. The method for preparing a BTA deep hole drill guide key according to claim 9, characterized in that, In step S1, the high-temperature and high-pressure sintering pressure is 5.0-6.0 GPa, the sintering temperature is 1400-1500℃, and the holding time is 15-30 min; the CBN micro powder of the polycrystalline cubic boron nitride working layer is pre-treated by surface plating with W or Ti; in step S2, the PCBN composite sheet is fixed to the alloy steel substrate by vacuum brazing with Ag-Cu-Ti active solder, the brazing temperature is 820-880℃, and the holding time is 8-15 min.

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