A turning tool for engine cylinder block machining and machining application thereof

Abstract

The application belongs to the technical field of numerical control blades, and discloses a turning tool for machining an engine cylinder block and machining application thereof, which comprises a tool shank, a tool body and a blade, and is characterized in that the blade is made of the following materials according to the percentage by weight: tungsten carbide 75% to 85%, cobalt 8% to 12%, titanium carbide 3% to 6%, tantalum carbide 1% to 3%, and aluminum oxide dispersion strengthening phase 2% to 5%; the average particle size of the aluminum oxide dispersion strengthening phase is 0.1 μm to 0.5 μm, and the aluminum oxide particles are uniformly distributed in the tungsten carbide-cobalt hard alloy matrix to form a dispersion strengthening structure; the application reduces the cutting temperature, inhibits tool wear, prolongs the tool life, and improves the machining quality.

Description

Technical Field

[0001] This invention belongs to the field of CNC cutting tool technology, specifically relating to a lathe tool for machining engine cylinder blocks and its machining application. Background Technology

[0002] The engine cylinder block is the core load-bearing component of an internal combustion engine, and its machining accuracy and surface quality directly affect the engine's operating efficiency, service life, and reliability. Cylinder blocks are typically made of gray cast iron, ductile iron, or aluminum alloy. During turning, the tool tip area is subjected to extremely high cutting forces and temperatures; therefore, the hardness, wear resistance, red hardness, and chemical stability of the cutting tool material become key factors limiting machining efficiency and tool life.

[0003] Currently, the mainstream tool material used for turning engine cylinder blocks is WC-Co cemented carbide. WC-Co cemented carbide consists of a tungsten carbide hard phase and a cobalt binder phase. Tungsten carbide provides hardness and wear resistance, while cobalt imparts toughness. This type of material suffers from a performance bottleneck determined by its intrinsic properties: when the cutting temperature rises above 600℃, the cobalt binder phase softens, the ability of tungsten carbide grains to transfer loads through the binder phase decreases sharply, dislocation movement resistance decreases significantly, and the overall hardness and wear resistance of the material deteriorate rapidly. At 800℃, the hardness retention rate of traditional WC-Co cemented carbide is typically less than 60%. This degradation directly restricts further increases in cutting speed and effective extension of tool life.

[0004] Existing technologies form materials containing chemical vapor deposition or physical vapor deposition methods. A hard coating scheme for a dispersion layer. The crystals are distributed in a columnar crystalline morphology within the coating, with a total coating thickness ranging from 5 μm to 30 μm. In this scheme... The reinforced area is limited to the depth of the coating on the tool surface. After the coating fails due to wear or chipping, the substrate is exposed, and the high-temperature mechanical properties are equivalent to those of traditional cemented carbide.

[0005] Regarding the tool structure, European patent EP3623083A1 discloses a turning tool with an internal fluid channel. The coolant is sprayed from the channel outlet to the side clearance surface of the insert. The spray target is the gap between the flank face of the insert and the machined surface, not the area where the rake face with the highest cutting temperature contacts the chip. There is still room for improvement in the targeting of the coolant.

[0006] Chinese patent CN210648551U relates to a cemented carbide insert for a lathe tool body. Its improvements focus on the structure and installation method of the insert protective shell, but do not make any improvements at the material formulation level for the high-temperature working conditions of engine cylinder block machining.

[0007] In terms of materials, existing technologies lack a cemented carbide material that inherently possesses excellent high-temperature hardness retention capabilities, and coating solutions cannot fundamentally overcome the problem of intrinsic high-temperature softening of the substrate. In terms of cooling structure, there is a lack of an internal cooling structure that uniformly and targetedly delivers the cooling medium to the highest temperature region of the cutting zone. Summary of the Invention

[0008] The purpose of this invention is to provide a lathe tool for machining engine cylinder blocks and its machining application, which solves the technical problems of insufficient hardness retention due to high-temperature softening of the cobalt binder phase in existing lathe tool materials, poor cooling targeting of the cooling structure, and failure to form a systematic and synergistic configuration of the edge strengthening characteristics.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0010] A lathe tool for machining engine cylinder blocks includes a tool holder, a tool body, and a cutting insert, wherein the cutting insert is made of the following materials by weight percentage;

[0011] It includes: 75% to 85% tungsten carbide, 8% to 12% cobalt, 3% to 6% titanium carbide, 1% to 3% tantalum carbide, and 2% to 5% alumina dispersion strengthening phase;

[0012] The alumina dispersion strengthening phase has an average particle size of 0.1 μm to 0.5 μm, and the alumina particles are uniformly distributed in the tungsten carbide-cobalt cemented carbide matrix to form a dispersion strengthening structure.

[0013] The material has a Vickers hardness of not less than 75% of the room temperature Vickers hardness at 800℃±10℃, a flexural strength of 1800 MPa to 2000 MPa, and a room temperature Rockwell hardness HRA of 92.0 to 94.0.

[0014] Furthermore, the average particle size of the tungsten carbide is from 0.5 μm to 1.2 μm.

[0015] Furthermore, the average particle size of the cobalt is 1.0 μm to 2.0 μm.

[0016] Furthermore, the average particle size of the alumina dispersion-reinforced phase is 0.2 μm to 0.35 μm.

[0017] Furthermore, the composition of the cutting tool material also includes titanium carbonitride, with a weight percentage of 1% to 3% for titanium carbonitride, which partially replaces titanium carbide.

[0018] Furthermore, in at least 10 randomly selected observation areas with a cross-sectional area of ​​100 μm², the standard deviation of the number of alumina particles does not exceed 20% of the average number of alumina particles in these at least 10 observation areas.

[0019] Furthermore, the preparation method of tungsten carbide-cobalt cemented carbide is as follows:

[0020] Step 1: Weigh out tungsten carbide powder, cobalt powder, titanium carbide powder, tantalum carbide powder and alumina powder by weight percentage, and put all the weighed powders into a ball mill for wet ball milling and mixing. The ball milling medium is ethanol, and the ball milling time is 24 to 36 hours.

[0021] Step 2: The slurry obtained after ball milling is dried and granulated, and then the dried and granulated powder is pressed into shape at a pressure of 150 MPa to 200 MPa.

[0022] Step 3: The pressed blank is placed in a sintering furnace for graded heating and sintering. First, the temperature is raised to 800°C at a heating rate of 5°C / min, and then raised to 1400°C to 1500°C at a heating rate of 3°C / min. The temperature is held for 1 to 2 hours to obtain a tungsten carbide-cobalt-based cemented carbide with a uniform alumina dispersion reinforced structure.

[0023] Furthermore, in step one, the ball-to-material ratio of the ball milling mixture is 5:1, the grinding balls are WC-6Co cemented carbide balls with a diameter of 6 mm, the ball milling speed is 200 rpm to 300 rpm, the alumina powder is treated by ultrasonic dispersion for 20 to 40 minutes before ball milling, and the machine is stopped and the material is turned over every 4 to 8 hours during the ball milling process.

[0024] Furthermore, in step three, during the liquid phase sintering stage where the temperature is raised from 800℃ to 1400℃ to 1500℃, high-purity hydrogen gas with a flow rate of 0.3 L / min to 0.8 L / min is introduced into the sintering furnace as a protective atmosphere.

[0025] Furthermore, the tool body is provided with a coolant channel inside, and an annular diffusion cavity is provided at the outlet end of the coolant channel. The annular diffusion cavity is located in the area below the tool mounting seat. Multiple liquid outlet holes are evenly distributed on the side wall of the annular diffusion cavity. The diameter of each liquid outlet hole is 0.3 mm to 0.8 mm, and the axial direction of each liquid outlet hole points towards the cutting edge area of ​​the tool.

[0026] Furthermore, the number of liquid outlet holes is 6 to 12, and each liquid outlet hole is evenly arranged circumferentially along the side wall of the annular diffusion cavity. The ratio of the total cross-sectional area of ​​the liquid outlet holes to the cross-sectional area of ​​the coolant channel is 1.5:1 to 3:1.

[0027] Furthermore, the blade is an indexable blade, and a positioning boss is provided at the bottom of the blade. A positioning groove that matches the positioning boss is provided on the blade mounting surface of the blade body. The fitting accuracy between the positioning boss and the positioning groove is IT6 to IT7 grade.

[0028] Furthermore, the cutting face of the blade is provided with a chip breaker groove, the cross-sectional shape of the chip breaker groove is a polygonal shape, the polygonal chip breaker groove includes a first inclined section and a second inclined section, the angle between the first inclined section and the cutting face of the blade is 15° to 20°, and the angle between the second inclined section and the first inclined section is 25° to 35°.

[0029] Furthermore, the cutting edge of the blade is provided with a negative chamfer, the width of which is 0.1 mm to 0.3 mm and the angle of which is -5° to -15°.

[0030] Furthermore, the back face of the blade is provided with a titanium aluminum nitride coating, the thickness of which is 2 μm to 5 μm.

[0031] In addition, the present invention also discloses a machining application of a lathe tool for machining engine cylinder blocks, wherein machining is performed using the lathe tool for machining engine cylinder blocks as described above, including the following steps:

[0032] The engine cylinder block is clamped onto the lathe and aligned.

[0033] Fix the cutting tool on the tool post of the lathe and adjust the position of the cutting tool so that there is an initial gap between the tool tip and the surface of the cylinder block to be machined;

[0034] Start the coolant supply device to deliver coolant to the cutting area through the coolant channel and the annular diffuser chamber;

[0035] Start the lathe spindle and cut the cylinder block surface according to the preset cutting parameters. After roughing to remove 70% to 80% of the blank material, the cylinder block is then finished after dimensional measurement and cutting depth adjustment to complete the machining.

[0036] Furthermore, the cutting speed is adjusted according to the cylinder block material: when the cylinder block material is gray cast iron, the cutting speed is 120 m / min to 180 m / min; when the cylinder block material is ductile iron, the cutting speed is 100 m / min to 150 m / min; when the cylinder block material is aluminum alloy, the cutting speed is 300 m / min to 500 m / min.

[0037] Furthermore, during the cutting process, the cutting force and cutting temperature are monitored in real time. When the cutting force exceeds the preset threshold of 3000 N, the feed rate is automatically reduced by 15% to 25%; when the cutting temperature exceeds 600℃, the coolant flow rate is automatically increased by 25% to 35%.

[0038] Furthermore, a microtexture array is provided on the surface of the second inclined section of the chip breaker groove, the microtexture array being composed of multiple hemispherical micro-pits; the diameter of the hemispherical micro-pit is defined as... The depth of a hemispherical micro-pit is defined as The depth of the hemispherical micro-pit With respect to the diameter of the hemispherical micro-pit satisfy On the local surface of the second inclined segment, the area occupancy of micro-pits The area occupancy rate is 10% to 25%. The calculation formula is: in, This represents the total number of micro-pits. This represents the projected area of ​​a single micro-dimple on the surface of the second inclined segment. The total area of ​​the microtexture array distribution region; wherein the center line of the jet trajectory of the liquid outlet intersects with the second inclined segment region where the microtexture array is located.

[0039] Furthermore, the inner bottom surface of the annular diffusion cavity is provided with multiple turbulence microribs arranged alternately along the flow direction of the coolant, and the cross-sectional shape of the turbulence microribs is an isosceles trapezoid; the height of the turbulence microribs is defined as... The height of the turbulence microrib The value ranges from 0.2 mm to 0.5 mm; the spacing between adjacent perturbation microribs is defined as... ,spacing Height of the micro-ribs Satisfying the relation The hydraulic diameter of the flow channel in the annular diffuser cavity is defined as follows: Hydraulic diameter of the flow channel The calculation formula is:

[0040] ;

[0041] in Let be the flow cross-sectional area of ​​the annular diffusion cavity. The wetted perimeter of the annular diffuser cavity; the height of the turbulence microrib. With the hydraulic diameter of the flow channel satisfy .

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This invention addresses the problems of high-temperature performance degradation, insufficient cooling targeting, and lack of functional feature synergy in existing turning tools by introducing alumina dispersion strengthening phase into the body material, constructing a targeted cooling structure with an integrated annular diffusion cavity in the tool body, and systematically and synergistically configuring the cutting edge characteristics of the insert. These solutions address the issues of material, cooling, and cutting edge strengthening in the prior art.

[0044] At the material level, alumina particles are uniformly dispersed in the tungsten carbide-cobalt cemented carbide matrix as an independent second phase. Through the Orowan bypass mechanism, they stably hinder dislocation movement at high temperatures, significantly improving the high-temperature hardness retention of the cutting tool material from an intrinsic matrix perspective. This overcomes the defect of rapid matrix softening after wear or chipping, a common problem with traditional coating solutions. At the cooling level, the combination of coolant channels and annular diffusion chambers inside the tool body guides the cooling medium to the cutting edge region of the tool through multiple uniformly distributed outlet holes. This directly exchanges heat with the highest temperature region in the cutting zone, effectively reducing the cutting temperature and suppressing the high-temperature softening process of the cobalt binder phase.

[0045] At the edge strengthening level, the zigzag chip breaker groove regulates the chip curling and fracture morphology, preventing long chips from entangled and damaging the machined surface; the negative chamfer optimizes the stress distribution of the cutting edge, disperses the peak stress under intermittent cutting conditions, and reduces the probability of chipping; the titanium aluminum nitride coating on the flank provides a low coefficient of friction surface and generates a self-lubricating alumina protective film, reducing cutting friction heat and tool wear. These three features work synergistically to address the intermittent cutting conditions of engine cylinder blocks, jointly improving machining quality and tool life. Attached Figure Description

[0046] 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.

[0047] Figure 1 This is a flowchart of the method for preparing tungsten carbide-cobalt cemented carbide according to the present invention.

[0048] Figure 2 This is a flowchart of the engine cylinder block machining method of the present invention. Detailed Implementation

[0049] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0050] The following disclosure provides many different implementations or examples for carrying out different structures of the embodiments of the present invention. To simplify the disclosure of the embodiments of the present invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the embodiments of the present invention. Furthermore, reference numerals and / or reference letters may be repeated in different examples of the embodiments of the present invention; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed.

[0051] The following is in conjunction with the appendix Figures 1-2 The embodiments of the present invention will be described in detail below.

[0052] Example 1: This example provides a turning tool material for machining engine cylinder blocks, which, by weight percentage, consists of: 78% tungsten carbide, 10% cobalt, 5% titanium carbide, 2% tantalum carbide, and 5% alumina dispersed reinforcing phase. The average particle size of the tungsten carbide is 0.8 μm, the average particle size of the cobalt is 1.5 μm, and the average particle size of the alumina dispersed reinforcing phase is 0.3 μm.

[0053] The mechanisms of action and synergistic relationships of each component are as follows:

[0054] Tungsten carbide, as the framework phase of cemented carbide, constitutes the main load-bearing structure of the material in an ultrafine grain morphology. The average grain size of tungsten carbide is controlled in the range of 0.5 μm to 1.2 μm. According to the Hall-Petch relationship, refining the grains can improve the room temperature hardness of the material. At the same time, finer tungsten carbide grains have a higher recrystallization temperature at high temperatures, which helps to delay the degradation of high-temperature performance. Thus, a finer grain structure is maintained at high temperatures, and a higher grain boundary strengthening effect is maintained.

[0055] During liquid-phase sintering, cobalt melts and fills the spaces between tungsten carbide particles, connecting them into a continuous whole upon cooling. A cobalt content window of 8% to 12% was optimized: below 8%, liquid-phase sintering is insufficient, resulting in decreased material density and inadequate flexural strength; above 12%, the binder phase volume fraction is too high, leading to a decrease in overall material hardness, and the negative impact of binder phase softening at high temperatures on performance is more pronounced.

[0056] During sintering, titanium carbide and tantalum carbide partially dissolve in the cobalt binder phase, resulting in a solid solution strengthening effect and improving the high-temperature strength of the binder phase itself. Titanium carbide and tungsten carbide can form (W,Ti)C composite carbides, which have a higher hardness than pure tungsten carbide, thus helping to improve the overall wear resistance of the material.

[0057] Tantalum carbide has excellent resistance to diffusion wear, which can effectively suppress the diffusion and adhesion of workpiece material to the cutting tool during the cutting process.

[0058] The alumina dispersion strengthening phase content is 5%, with an average particle size of 0.3 μm. During sintering, the alumina particles do not undergo significant interfacial chemical reactions with tungsten carbide or cobalt, maintaining chemical inertness and uniformly distributed as independent second-phase particles within the tungsten carbide-cobalt matrix. Its dispersion strengthening effect is based on the Orowan bypass mechanism: when dislocations move in a high-temperature stress field and encounter unshearable alumina particles, the dislocation lines bend, eventually leaving dislocation loops around the particles, thus the particles effectively hinder dislocation movement. Alumina has a high melting point of 2050℃, and at 800℃, the particles neither grow nor soften, and the dispersion strengthening effect hardly diminishes with increasing temperature; in contrast, the solid solution strengthening effect of the cobalt binder phase weakens sharply with increasing temperature. The selection of the alumina particle size window from 0.1 μm to 0.5 μm is based on the following criteria: When the particle size is less than 0.1 μm, the particles tend to agglomerate during ball milling, making it difficult to achieve uniform dispersion; when the particle size is greater than 0.5 μm, the interparticle spacing increases, the Orowan bypass stress decreases, and the dispersion strengthening effect weakens. Under the condition of alumina particle size of 0.3 μm and content of 5%, the average interparticle spacing is approximately 0.8 μm to 1.2 μm. This distribution density ensures sufficient dislocation hindering effect without compromising the overall toughness of the material due to excessive second-phase particles disrupting the continuity of the binder phase.

[0059] To determine the effect of alumina content on the high-temperature performance of materials, seven groups of samples with the same basic composition (tungsten carbide, cobalt, titanium carbide, and tantalum carbide) but alumina contents of 0%, 1%, 2%, 3%, 4%, 5%, and 6%, respectively, were prepared.

[0060] All samples were subjected to the same ball milling parameters (ball-to-material ratio 5:1, rotation speed 250 rpm, ball milling time 30 hours), pressing parameters (pressing pressure 180 MPa), and sintering parameters (staged heating sintering: heating to 800℃ at 5℃ / min, heating to 1450℃ at 3℃ / min, holding for 1.5 hours, vacuum degree ≤ ).

[0061] Hardness testing was performed according to GB / T 7997 Vickers Hardness Test Method for Cemented Carbide and GB / T 3849.1 Rockwell Hardness Test Method for Cemented Carbide. High-temperature hardness testing was conducted at 800℃±10℃ for 30 minutes under a load of 10 kgf. The correspondence between room temperature Vickers hardness and Rockwell hardness (HRA) is shown in the conversion table in the appendix of GB / T 3849.1. The room temperature Rockwell hardness, room temperature Vickers hardness, 800℃ Vickers hardness, and the calculated 800℃ hardness retention rate for each sample are listed in Table 1.

[0062] Table 1. Comparison of performance parameters of cutting tool materials with different alumina contents;

[0063] 1 0 89.5 1400 2150 742 53 2 1 90.2 1470 2120 911 62 3 2 92.0 1580 2080 1122 71 4 3 93.0 1650 2050 1254 76 5 4 93.5 1720 2020 1359 79 6 5 93.8 1760 1950 1408 80 7 6 93.2 1680 1720 1310 78

[0064] As shown in Table 1, when the alumina content increases from 0% to 5%, the 800℃ hardness retention rate of the cutting tool material monotonically increases from 53% to 80%. When the alumina content further increases to 6%, the hardness retention rate decreases from 80% to 78%, and the room temperature flexural strength drops from 1950 MPa to 1720 MPa. The decrease in flexural strength is attributed to the excessive alumina particles disrupting the continuity of the cobalt binder phase and increasing stress concentration points within the material. The alumina content range of 2% to 5% thus constitutes the optimal window for overall performance: at the lower limit of 2%, the 800℃ hardness retention rate has increased from 53% in the comparative example (0% alumina content) to 71%; at the upper limit of 5%, the hardness retention rate reaches 80%, and the flexural strength remains at an engineering-acceptable level of 1950 MPa.

[0065] The lathe tool in this embodiment includes a handle, a tool body, and a cutting blade.

[0066] The tool holder and the tool body can be fixed together using a method such as an M12×1.25 fine thread connector, providing a clamping base for the entire cutting tool. A coolant channel is provided axially inside the tool body, and the inlet end of the coolant channel is connected to an external coolant supply device.

[0067] The outlet end of the coolant passage is in fluid communication with an annular diffusion chamber located below the blade mount. The annular diffusion chamber is constructed as a closed-loop channel extending along the contour of the blade mount, and its internal flow channel cross-section can be rectangular, circular, or other shapes that achieve uniform liquid distribution. Eight liquid outlet holes, each with a diameter of 0.5 mm, are evenly distributed on the cavity wall of the annular diffusion chamber and are uniformly arranged circumferentially along the blade mounting area.

[0068] The angle between the axis of each coolant outlet and the flank face of the cutting edge is 35°, allowing the coolant jet to directly cover the high-temperature area of ​​the cutting edge. The ratio of the total cross-sectional area of ​​the coolant outlet to the cross-sectional area of ​​the coolant channel is approximately 1.8:1. This area ratio creates back pressure in the annular diffusion chamber, ensuring uniform coolant flow from each outlet and preventing uneven pressure drop that could lead to insufficient cooling in certain areas.

[0069] The insert is an indexable insert with a regular square shape and four indexable cutting edges. A locating boss is located at the center of the bottom of the insert. The locating boss has a square cross-section with a side length of 6 mm and a height of 3 mm.

[0070] The blade mounting surface has a positioning groove. The cross-sectional shape of the positioning groove is square, with a side length of 6.02 mm and a depth of 3.5 mm. The fit between the two achieves an IT6 level accuracy, with an installation gap of approximately 0.02 mm. The fit between the positioning boss and the positioning groove enables the blade to self-center during installation.

[0071] The cutting edge of the insert has chip-breaking grooves arranged along the direction of the cutting edge.

[0072] The chip breaker groove is zigzag-shaped and includes a first inclined section and a second inclined section.

[0073] The first inclined section slopes downwards from the inside of the cutting edge towards the center of the insert, with an angle θ1 of 18° between it and the plane containing the insert's rake face. The second inclined section continues to extend from the end of the first inclined section towards the center of the insert, with an angle θ2 of 30° between it and the plane containing the first inclined section. The length of the first inclined section is 2 mm, the length of the second inclined section is 1.5 mm, the total depth of the chip breaker groove is 0.8 mm, and the radius of the fillet at the bottom of the groove is 0.2 mm.

[0074] During the cutting process, the chip rises along the first inclined section and its curl radius decreases sharply when it touches the second inclined section. The chip breaks after the bending strain exceeds the fracture limit of the chip material. In a machining test cycle of continuously turning 20 gray cast iron cylinder blocks, the average chip length remained in the range of 20 mm to 30 mm, and no long chip entanglement occurred.

[0075] Furthermore, the cutting edge of the insert has a negative chamfer with a triangular cross-section, the width b of which is 0.2mm, and the negative chamfer angle is... (That is, the angle between the negative chamfer and the cutting edge of the blade is 10°, and the negative chamfer is inclined to the outside of the blade).

[0076] The transition between the negative chamfer and the rake face of the main cutting edge is connected by an arc with a radius of 0.05 mm. In the intermittent cutting conditions commonly encountered in engine cylinder block turning, the introduction of this negative chamfer helps to reduce the peak stress in the cutting edge region, thereby reducing the probability of cutting edge chipping.

[0077] The cutting edge has a reinforcing layer on its flank face. This reinforcing layer is a titanium aluminum nitride coating formed by physical vapor deposition, with a coating thickness of 3 μm and a titanium to aluminum atom ratio of 3:7 (i.e., ...). The coating has a microhardness of HV 3300 and a scratch adhesion strength between the coating and the substrate of 65 N. Under high-temperature cutting conditions, a dense alumina protective film can be formed on the surface of the titanium nitride aluminum coating, which has a lower coefficient of friction than uncoated cemented carbide, thereby reducing frictional heat and tool wear during the cutting process.

[0078] The manufacturing method of the lathe tool in this embodiment is carried out according to the following steps.

[0079] Step 1: Weigh out tungsten carbide powder (average particle size 0.8 μm), cobalt powder (average particle size 1.5 μm), titanium carbide powder (average particle size 1.0 μm), tantalum carbide powder (average particle size 1.0 μm), and alumina powder (average particle size 0.3 μm) by weight percentage. Place all raw material powders into a planetary ball mill for wet ball milling and mixing. The ball milling media is anhydrous ethanol, the ball-to-powder ratio is 5:1, the grinding balls are 6 mm diameter WC-6Co cemented carbide balls, the ball milling speed is 250 rpm, and the ball milling time is 30 hours. To improve the dispersibility of alumina powder in the slurry, 0.5 wt% polyethylene glycol can be added as a dispersant.

[0080] Step 2: The slurry obtained after ball milling is spray-dried to granulate, resulting in a uniformly mixed and highly flowable granulated powder. The spray drying outlet temperature is set so that the powder moisture content is below 0.1 wt%.

[0081] Step 3: The granulated powder is loaded into a mold for bidirectional pressing. The pressing pressure is 180 MPa, the holding time is 45 seconds, and the pressing speed is 3 mm / s. The relative density of the formed green body is 92% of the theoretical density.

[0082] Step 4: Place the formed preform into a vacuum sintering furnace for staged heating and sintering. The sintering regime is as follows: heat from room temperature to 800℃ at a rate of 5℃ / min, hold at 800℃ for 30 minutes to fully remove residual binder, polyethylene glycol dispersant, and gases; then heat to 1450℃ at a rate of 3℃ / min, hold at 1450℃ for 1.5 hours. The sintering atmosphere is vacuum, and the vacuum degree is maintained below 10⁻²Pa. After the holding period, slowly cool to 1000℃ at a rate of 2℃ / min, and then cool to room temperature in the furnace. The staged heating was designed based on the following considerations: a faster heating rate (5℃ / min) was used in the low-temperature stage below 800℃ to improve efficiency and shorten the time window for abnormal grain growth; after entering the liquid phase sintering stage above 800℃, a slower heating rate (3℃ / min) was used to ensure that the cobalt binder phase fully melted and uniformly filled the gaps between tungsten carbide particles, while giving alumina particles sufficient time to achieve uniform distribution in the liquid phase through diffusion, avoiding local agglomeration of alumina particles caused by excessively rapid heating. After sintering, the relative density of the material reached over 98.5%.

[0083] Step 5: Perform grinding on the sintered material;

[0084] For rough grinding, a silicon carbide grinding wheel is used with a feed rate of 0.5 mm; for finish grinding, a diamond grinding wheel is used with a feed rate of 0.05 mm; and the surface is polished with diamond polishing paste until the surface roughness Ra ≤ 0.2 μm. The ground material is cut into square insert blanks, which are then ground to form the cutting edge, flank face, rake face, chip breaker groove, and negative chamfer. Diamond grinding wheels are used; the surface roughness Ra of the rake face after grinding is 0.4 μm, and the surface roughness Ra of the flank face after grinding is 0.2 μm. The cutting edge radius is no greater than 0.01 mm.

[0085] Step 6: Deposit a titanium aluminum nitride coating on the back face of the cutting tool using magnetron sputtering physical vapor deposition.

[0086] Deposition parameters: The target material was an alloy target with a titanium-aluminum atomic ratio of 3:7; the deposition temperature was 250℃; the deposition pressure was 0.8 Pa; the argon flow rate was 50 sccm; the nitrogen flow rate was 20 sccm; the deposition time was 60 minutes; a -100 V DC bias voltage was applied to enhance the ion bombardment effect and improve the coating density and adhesion. After deposition, the coating was vacuum annealed at 400℃ for 1 hour to eliminate internal stress.

[0087] Step 7: Install the coated cutting tool onto the tool body using the locating boss and locating groove, and tighten the fixing screws with a torque of 15 N·m to 20 N·m. Secure the tool body and tool holder together with the threaded connector to complete the cutting tool assembly.

[0088] This embodiment also provides a method for machining engine cylinder blocks using the above-described lathe tool.

[0089] The gray cast iron engine cylinder block is clamped on the three-jaw chuck of a CNC lathe and aligned with a dial indicator. The coaxiality error between the cylinder block axis and the lathe spindle axis is controlled within 0.02 mm.

[0090] The cutting tool is fixed to the lathe tool post, and the initial distance between the tool tip and the surface to be machined is set to 0.8 mm.

[0091] Start the coolant supply device. The coolant is an 8% water-based cutting fluid. It is delivered to the cutting area through the coolant channel and the annular diffusion chamber. The coolant flow rate is set to 8 L / min.

[0092] During the roughing stage, the spindle speed is 900 rpm, the feed rate is 0.2 mm / r, and the depth of cut is 1.5 mm; during the finishing stage, the spindle speed is 1100 rpm, the feed rate is 0.15 mm / r, and the depth of cut is 0.2 mm. The corresponding cutting speed is 150 m / min, which is within the recommended machining speed range for gray cast iron.

[0093] Roughing stops after removing 75% of the blank material. After dimensional measurement and depth of cut adjustment, finishing begins.

[0094] After finishing, the coolant and spindle were shut off, and the machined cylinder block was removed for quality inspection. The surface roughness Ra after finishing reached 1.2 μm, and the dimensional tolerances met the design drawing requirements.

[0095] Example 2: Based on Example 1, this example further limits the uniformity of the alumina dispersion strengthening phase distribution in the cutting tool material and further improves the cooling structure.

[0096] The material composition and basic process parameters of the cutting tool in this embodiment are the same as those in Embodiment 1. The difference is that the ball milling process parameters are optimized to ensure that the uniformity of alumina particle distribution in the matrix meets the following quantitative standards:

[0097] Within at least 10 randomly selected observation areas with a cross-sectional area of ​​100 μm², the standard deviation of the number of alumina particles does not exceed 20% of the average number of alumina particles in these at least 10 observation areas.

[0098] The quantity and standard deviation of the alumina particles were obtained by image analysis and statistical analysis of 10 randomly selected 100 μm² fields of view using a scanning electron microscope in backscattered electron mode. Specifically, the alumina powder was pre-treated by ultrasonic dispersion for 30 minutes before ball milling to form a uniform suspension in ethanol before being mixed with other powders. During ball milling, a shutdown and material turning operation was performed every 6 hours to remove the powder adhesion layer on the wall of the ball mill and ensure that all powders participated uniformly in the mixing process.

[0099] After meeting the above standards, the hardness retention rate of the cutting tool material at different sampling locations under 800℃ conditions does not exceed ±2 percentage points, while for materials of the same composition without uniformity control measures, the fluctuation range can reach ±5 percentage points.

[0100] Regarding the cooling structure, Embodiment 2 adds a flow guide ring inside the annular diffusion cavity. The flow guide ring is an annular thin sheet with a thickness of 1 mm, on which guide grooves corresponding to the positions of each liquid outlet are formed. The bottom surface of the guide groove is a slope, which gradually rises at an angle of 3° from the side near the coolant channel outlet to the side near the liquid outlet, thereby guiding the coolant to flow towards the liquid outlet and improving the uniformity of the liquid outlet flow.

[0101] In Example 2, during the sintering process, high-purity hydrogen gas at a flow rate of 0.5 L / min was introduced into the furnace as a protective atmosphere during the liquid-phase sintering stage, which involved heating from 800°C to 1450°C. The reducing effect of hydrogen at high temperatures removes the oxide film on the surface of the powder particles, improves the wettability of the cobalt binder to the tungsten carbide particles, and is beneficial for increasing the sintering density and the uniformity of the binder phase distribution. In this step, the atmosphere inside the sintering furnace was switched from vacuum to flowing hydrogen gas, achieving atmosphere-protected sintering. After sintering, the relative density of the material reached 99.2%, higher than the 98.5% achieved under the pure vacuum sintering conditions in Example 1.

[0102] Example 3: This example is basically the same as Example 1, except that the material composition of the cutting tool is adjusted by weight percentage as follows:

[0103] The composition includes 76% tungsten carbide, 10% cobalt, 5% titanium carbide, 3% tantalum carbide, 4% alumina dispersion reinforcing phase, and 2% titanium carbonitride. The titanium carbonitride is introduced in a manner that partially replaces titanium carbide, and has an average particle size of 0.8 μm.

[0104] Titanium carbonitride provides a complementary solid solution strengthening method in addition to alumina dispersion strengthening:

[0105] During the sintering process, carbon and nitrogen atoms in titanium carbonitride partially dissolve in the cobalt binder phase, forming interstitial solid solution reinforcement, which further improves the high-temperature strength of the binder phase.

[0106] The cutting tool material of Example 3 retained 79% of its hardness at 800℃ (close to 80% in Example 1) and had a bending strength of 2100 MPa (higher than 1950 MPa in Example 1), exhibiting more balanced overall mechanical properties. These results demonstrate that, under the technical path of partial titanium carbide substitution, even reducing the alumina content from 5% to 4%, a similar high-temperature hardness retention rate can still be achieved by introducing carbonitride interstitial solid solution strengthening effects into the binder phase. Simultaneously, higher bending strength is obtained due to the reduced alumina content. This provides a feasible path for customized formulations based on different machining conditions; a lower alumina content combined with titanium carbonitride is used for rough machining, which emphasizes impact toughness, while a higher alumina content is used for finish machining, which emphasizes high-temperature wear resistance.

[0107] Regarding the machining method, the cutting speed is 120 m / min to 180 m / min when the cylinder block is made of gray cast iron; 100 m / min to 150 m / min when the cylinder block is made of ductile iron; and 300 m / min to 500 m / min when the cylinder block is made of aluminum alloy. During machining, the cutting force and cutting temperature are monitored in real time by a force sensor mounted on the tool body and an infrared temperature probe mounted near the cutting tool. When the cutting force exceeds a preset threshold of 3000 N, the feed rate is automatically reduced by 20%, and when the cutting temperature exceeds 600 °C, the coolant flow rate is automatically increased by 30%, achieving adaptive cutting control based on real-time feedback.

[0108] Table 2 lists the key performance indicators of the turning tools in Examples 1 to 3 compared with those of the comparative examples. The comparative examples used turning tools with the same geometry, coating, and cooling method as Example 1, the only difference being that the insert material was a WC-Co-TiC-TaC cemented carbide (basic composition: 78% tungsten carbide, 10% cobalt, 5% titanium carbide, and 2% tantalum carbide) without alumina dispersion strengthening phase. Engine cylinder block turning tests were performed under the same cutting conditions. All tests were completed on the same CNC lathe, with the workpiece material uniformly being HT250 gray cast iron engine cylinder block blanks, and an average machining allowance of 2.5 mm per piece.

[0109] Table 2. Comparison of performance parameters between the examples and comparative examples;

[0110] Alumina content (wt%) of lathe tool material 0 5 5 4 Room temperature flexural strength (MPa) 2150 1950 2000 2100 Room temperature hardness (HRA) 89.5 93.8 93.8 93.5 Hardness retention rate at 800℃ (%) 53 80 81 79 Tool life (pieces) for cutting gray cast iron cylinder blocks 42 85 92 80 Surface roughness Ra (μm) of the machined surface 1.8 1.2 1.1 1.3 Average temperature in the cutting zone (°C) 680 520 490 530 Average cutting force (N) 3200 2850 2780 2900

[0111] As can be seen from the data comparison in Table 2, the cutting tools of Examples 1 to 3 are superior to the comparative examples in all key performance indicators.

[0112] Regarding tool life, Example 1 achieved a single lathe tool machining 85 gray cast iron cylinder blocks, approximately 2.0 times that of the comparative example (42 blocks). Example 2, due to improved alumina distribution uniformity and the introduction of a flow guide ring, further extended tool life to 92 blocks. Although the alumina content in Example 3 was reduced to 4%, the tool life still reached 80 blocks thanks to the synergistic effect of titanium carbonitride, and its bending strength was the highest among the three. Regarding cutting temperature, the average cutting zone temperature of the examples was reduced by approximately 140°C to 190°C compared to the comparative example, a decrease of 22% to 28%. This effect stemmed from the efficient removal of heat from the cutting zone by the multi-point cooling structure of the annular diffusion cavity and the low-friction characteristics of the titanium nitride aluminum coating. Regarding surface roughness, the Ra value of the examples decreased from 1.8 μm in the comparative sample to 1.1 μm to 1.3 μm, a decrease of 28% to 39%, reflecting the direct contribution of the high-temperature wear resistance of the alumina dispersion-reinforced material to dimensional accuracy and surface morphology during the finishing stage.

[0113] Example 4: This example, based on Example 1, further discloses refined improvements to the local morphology of the chip breaker groove on the cutting edge rake face and the bottom structure of the annular diffusion cavity inside the tool body. Utilizing the jet interception and turbulence enhancement mechanisms in fluid mechanics, it overcomes the technical bottleneck in traditional turning where coolant cannot effectively penetrate to the chip layer and tool interface, thereby further improving the tool's service life under high-temperature and heavy-load conditions.

[0114] In practical implementation:

[0115] In a specific embodiment of the blade structure, a microtexture array is machined on the surface of the second inclined section of the chip breaker groove.

[0116] The microtexture array consists of multiple hemispherical micropits arranged in a matrix. The diameter of each hemispherical micropit... Set to 50 μm, depth Set to 10 μm, the ratio of the two It is 0.2, falling into The preferred range.

[0117] On the local effective stress surface of the second inclined section, the area occupancy of micro-pits The content was precisely controlled at 18%, falling within the preferred range of 10% to 25%. The aforementioned microtexture array was fabricated using a femtosecond laser processing system to ensure that there was no obvious heat-affected zone or remelted layer during the processing, thus maintaining the initial mechanical properties of the cemented carbide substrate and the titanium aluminum nitride coating.

[0118] The femtosecond laser processing parameters are: laser wavelength 1030 nm, pulse width 290 fs, repetition rate 100 kHz, single pulse energy 15 μJ, and scanning speed 500 mm / s. In terms of processing sequence, the femtosecond laser processing of the microtextured array is performed after the deposition of the titanium-aluminum nitride coating on the flank face of the cutting tool. The ultrashort pulse and cold processing characteristics of the femtosecond laser allow the cemented carbide matrix material in the chip breaker region to be directly removed in a vaporized form, resulting in a minimal heat-affected zone. Furthermore, this processed area does not overlap with the coating area on the flank face, thus ensuring the complete preservation of the coating's hardness, adhesion, and microstructure. After the tool is assembled, the axial deflection angle of each coolant outlet is pre-calibrated using a three-dimensional flow field to ensure that the high-pressure coolant jet ejected from the outlet accurately hits and covers the second inclined section region where the microtextured array is located.

[0119] The innovation of this microtextured array lies in the creation of targeted microhydrodynamic effects. In machining, the second inclined section is the core region where chips violently curl and experience extremely high normal pressure friction with the rake face. The ratio is set at... The hemispherical micro-concave pits in the interval avoid the defect that the fluid cannot overflow due to the formation of a closed vortex inside the pit because of excessive depth.

[0120] When the high-speed coolant sprayed from the outlet reaches this area, the micro-pits act as miniature high-pressure reservoirs. The bottom surface of the high-speed, high-temperature chip sweeps across the surface of the micro-pit, forcibly squeezing out the coolant trapped inside. This forms a localized hydrodynamic lubricating water film with extremely high load-bearing capacity between the chip and the rake face, physically transforming the solid-solid friction into solid-liquid-solid friction and significantly suppressing the crescent-shaped wear on the rake face.

[0121] In a specific embodiment, the inner bottom surface of the annular diffusion cavity has multiple isosceles trapezoidal cross-section turbulence microribs arranged alternately along the flow direction of the coolant. The turbulence microribs are integrally formed during the precision CNC milling or precision EDM machining stage of the tool body.

[0122] In this embodiment, the height of the turbulence microribs The spacing between adjacent perturbation microribs is set to 0.3 mm. Set to 1.5 mm, the ratio of spacing to height. It is 5, falling into The preferred range.

[0123] Hydraulic diameter of the flow channel in the annular diffuser cavity The cross-sectional parameters of the flow channel are calculated to be 2.5 mm, and the calculation formula is as follows: ,in Let be the flow cross-sectional area of ​​the annular diffusion cavity. Let be the wetted perimeter of the annular diffusion cavity. From this, the ratio of the microrib height to the hydraulic diameter can be calculated. It is 0.12, falling into The preferred range.

[0124] The innovation of the turbulence-inducing microfin configuration lies in achieving the optimal balance between heat exchange efficiency and pumping pressure loss. (Ratio) This ensures that after the fluid separates at one micro-rib, it can re-attach before reaching the next micro-rib. Periodic boundary layer disruption and re-attachment force the coolant to generate intense vortex shedding and secondary flow, significantly increasing the turbulent kinetic energy within the fluid. The dramatic increase in fluid mixing allows heat transferred from the high-temperature blade to the blade body mounting base to be rapidly stripped away and carried away by the mainstream coolant flow, completely eliminating the risk of film boiling due to localized overheating within the annular diffuser chamber, thus ensuring the subcooling of the jet stream from the outlet.

[0125] It should be noted that even without a microtextured array on the cutting edge rake face, adding turbulence-enhancing microribs can still reduce the overall temperature of the tool body mounting base by strengthening the turbulence of the internal flow field, minimizing positioning accuracy loss due to thermal expansion, and increasing the subcooling of the coolant at the outlet, thus improving its cooling effect on the cutting area. When turbulence-enhancing microribs and microtextured arrays are used in combination, they respectively enhance heat transfer and trap lubrication within the coolant delivery channel and at the cutting zone interface, synergistically optimizing overall cooling efficiency and tool wear suppression.

[0126] In practice, the same workpiece material (HT250 gray cast iron engine cylinder block blank) and cutting parameters as in Example 1 were used to conduct a comparative test on the tool life and cutting temperature of Example 4.

[0127] The test results are as follows: the average temperature of the cutting zone of the lathe tool in Example 4 was significantly reduced to 410°C, which is 110°C lower than the 520°C in Example 1; the machining life of a single lathe tool in Example 4 reached 125 pieces, which is about 47% higher than the 85 pieces in Example 1.

[0128] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lathe tool for machining engine cylinder blocks, comprising a tool holder, a tool body, and a cutting insert, characterized in that, The blade is made of the following materials by weight percentage; It includes: 75% to 85% tungsten carbide, 8% to 12% cobalt, 3% to 6% titanium carbide, 1% to 3% tantalum carbide, and 2% to 5% alumina dispersion strengthening phase; The alumina dispersion strengthening phase has an average particle size of 0.1 μm to 0.5 μm, and the alumina particles are uniformly distributed in the tungsten carbide-cobalt cemented carbide matrix to form a dispersion strengthening structure. The material has a Vickers hardness of not less than 75% of the room temperature Vickers hardness at 800℃±10℃, a flexural strength of 1800MPa to 2000MPa, and a room temperature Rockwell hardness HRA of 92.0 to 94.

0.

2. The turning tool for machining engine cylinder blocks according to claim 1, characterized in that, The average particle size of the tungsten carbide is from 0.5 μm to 1.2 μm.

3. The turning tool for machining an engine cylinder block according to claim 1, characterized in that, The cobalt has an average particle size of 1.0 μm to 2.0 μm.

4. The turning tool for machining an engine cylinder block according to claim 1, characterized in that, The average particle size of the alumina dispersion-reinforced phase is 0.2 μm to 0.35 μm.

5. A turning tool for machining engine cylinder blocks according to claim 1, characterized in that, The material composition of the cutting tool also includes titanium carbonitride, which is 1% to 3% by weight.

6. A turning tool for machining an engine cylinder block according to claim 1, characterized in that, Within at least 10 randomly selected observation areas with a cross-sectional area of ​​100 μm², the standard deviation of the number of alumina particles does not exceed 20% of the average number of alumina particles in these at least 10 observation areas.

7. A lathe tool for machining engine cylinder blocks according to claim 1, characterized in that, The preparation method of tungsten carbide-cobalt cemented carbide is as follows: Step 1: Weigh out tungsten carbide powder, cobalt powder, titanium carbide powder, tantalum carbide powder and alumina powder by weight percentage, and put all the weighed powders into a ball mill for wet ball milling and mixing. The ball milling medium is ethanol, and the ball milling time is 24 to 36 hours. Step 2: The slurry obtained after ball milling is dried and granulated, and then the dried and granulated powder is pressed into shape at a pressure of 150 MPa to 200 MPa. Step 3: The pressed blank is placed in a sintering furnace for graded heating and sintering. First, the temperature is raised to 800°C at a heating rate of 5°C / min, and then raised to 1400°C to 1500°C at a heating rate of 3°C / min. The temperature is held for 1 to 2 hours to obtain a tungsten carbide-cobalt-based cemented carbide with a uniform alumina dispersion reinforced structure.

8. A turning tool for machining an engine cylinder block according to claim 7, characterized in that, In step one, the ball-to-material ratio of the ball milling mixture is 5:

1. The grinding balls are WC-6Co cemented carbide balls with a diameter of 6 mm. The ball milling speed is 200 rpm to 300 rpm. Before ball milling, the alumina powder is treated by ultrasonic dispersion for 20 to 40 minutes. During the ball milling process, the machine is stopped and the material is turned over every 4 to 8 hours.

9. A turning tool for machining an engine cylinder block according to claim 7, characterized in that, In step three, during the liquid phase sintering stage where the temperature is raised from 800℃ to 1400℃ to 1500℃, high-purity hydrogen gas with a flow rate of 0.3 L / min to 0.8 L / min is introduced into the sintering furnace as a protective atmosphere.

10. A machining application of a lathe tool for machining engine cylinder blocks, characterized in that: Machining an engine cylinder block using a lathe tool as described in any one of claims 1 to 9 includes the following steps: The engine cylinder block is clamped onto the lathe and aligned. Fix the cutting tool on the tool post of the lathe and adjust the position of the cutting tool so that there is an initial gap between the tool tip and the surface of the cylinder block to be machined; Start the coolant supply device to deliver coolant to the cutting area through the coolant channel and the annular diffuser chamber; Start the lathe spindle and cut the cylinder block surface according to the preset cutting parameters. After roughing to remove 70% to 80% of the blank material, the cylinder block is then finished after dimensional measurement and cutting depth adjustment to complete the machining.

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