A high-sharpness strong self-sharpening core drill for ceramic matrix composite small hole machining
By setting a grooved structure and diamond abrasive grains of different sizes on the substrate skeleton of the die-casting drill, the problems of rapid wear and poor quality in the machining of small holes in ceramic matrix composites are solved, achieving high sharpness and self-sharpening effect, and improving machining quality and service life.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
- Filing Date
- 2023-04-17
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies are insufficient for efficiently machining small holes in ceramic matrix composites. Traditional drilling tools wear out quickly, suffer severe tearing at the hole exit, and produce poor machining quality, failing to meet the demands for high-quality and low-cost machining.
A high-sharpening, self-sharpening nesting drill is designed by setting a groove structure on the tool matrix skeleton, with diamond abrasive grains of different sizes evenly distributed in a cross pattern, which enhances cutting ability and self-sharpening effect, and ensures hole-making accuracy and the rigidity of the nesting drill.
It significantly improves the machining quality and tool life of small holes in ceramic matrix composites, maintains hole diameter accuracy, and extends the service life of the nesting drill.
Smart Images
Figure CN116728614B_ABST
Abstract
Description
Technical Field
[0001] This invention proposes a high-sharpness, self-sharpening bushing drill for machining small holes in ceramic matrix composite materials, belonging to the field of drilling technology. Background Technology
[0002] Ceramic matrix composites have been widely used in aerospace, automotive and new energy fields due to their excellent physical and chemical properties such as high strength, low density, high temperature resistance and corrosion resistance. ([1] M'Saoubi R, Axinte D, Soo SL, Nobel C, Attia H, Kappmeyer G, et al. High performance cutting of advanced daerospace alloys and composite materials. CIRP annals. 2015;64(2):557-80. [2] Li L. Synergistic effects of interface slip and fiber fracture on stress-dependent mechanical hysteresis of SiC / SiC minicomposites. Compositeinterfaces. 2020;27(10):937-51). Due to the high brittleness, high hardness and anisotropy of the matrix and fiber reinforcement phase of this material, traditional drilling tools, such as cemented carbide and PCD tools, are prone to problems such as rapid wear of the casing drill, poor surface quality of the machined material and severe tearing at the hole exit during the machining process. ([3] Hrechuk A, Bushlya V, M'Saoubi R, et al. Experimental investigations into tool wear of drilling CFRP. Procedia Manuf 2018; 25: 294–301. 24. [4] Jia Z, Bai Y, Wang F, et al. Effect of tool wear on drilling unidirectional CFRP laminates indifferent fiber cutting angles. Int J Adv Manuf Technol 2020; 110: 89–99. 25. [5] Zhang B, Sui T, Lin B, et al. Drilling process of C fThe paper, titled "SiC ceramic matrix composites: Cutting force modeling, machining quality and PCD tool wear analysis. J Mater Process Technol 2022; 304: 117566," cannot meet the requirements for high-quality and low-cost machining of small holes in ceramic matrix composites.
[0003] Brazed diamond bushing drills offer advantages such as large abrasive grain exposure height, large chip space, and strong wear resistance, overcoming the drawback of rapid wear of bushing drills when drilling ceramic matrix composites. They are widely used in drilling ceramic matrix composites. The drilling capability of brazed diamond bushing drills primarily depends on the diamond abrasive grains attached to the substrate surface. The sum of the diamond abrasive grain diameter, the outer diameter of the substrate, and the thickness of the brazing filler metal determines the borehole diameter. In small-hole machining, due to limitations in tool rigidity, the substrate size cannot be too small, and the abrasive grains attached to the substrate surface must be relatively small to ensure drilling accuracy. Therefore, during drilling, once the abrasive grains at the tip wear away, the thicker sections of the bushing drill wall remain without abrasive grains during rotation, resulting in continuous friction with the material and causing sudden drill failure. Traditional small-hole bushing drills have low lifespan and poor machining quality, failing to meet the requirements for small-hole machining of ceramic matrix composites.
[0004] CN207432521U relates to a nesting drill bit for sapphire rod extraction, and discloses a nesting drill bit with a similar slotted structure. The slotted structure of the nesting drill bit is mainly to address the problem of poor chip removal ability during processing. The slotting improves the chip removal and drainage ability of the nesting drill bit. The purpose of the nesting drill bit is to use the nesting drill bit to extract sapphire from the crystal pillar to form individual sapphire pillars. Summary of the Invention
[0005] Objective: This invention addresses the problems of poor drilling quality and low tool life in small-hole machining of ceramic matrix composites. It proposes a high-sharpness, self-sharpening bushing drill for small-hole machining of ceramic matrix composites, significantly improving drilling quality. By incorporating a grooved structure on the inner and outer surfaces of the bushing drill's working end, the cross-sectional area of the tool matrix skeleton is reduced. This increases the effective number of abrasive grains on the bushing drill's cross-section while maintaining its overall rigidity, giving the bushing drill strong self-sharpening and high sharpness. The grooved structure and the different abrasive grain sizes on the inner and outer surfaces of the bushing drill's working end enhance the cutting capability of the bushing drill while ensuring drilling accuracy.
[0006] Technical solution: To achieve the above-mentioned objectives, the present invention adopts the following technical solution:
[0007] This invention discloses a high-sharpness, self-sharpening abrasive drill for machining small holes in ceramic matrix composites, comprising: a tool matrix skeleton with a grooved structure, and composite-size diamond abrasive grains brazed onto the matrix skeleton, the abrasive grain size being designed according to the machining process requirements; the tool matrix skeleton is a hollow cylindrical structure, with multiple grooved structures at the working end to accommodate the abrasive grains, the grooved structures being evenly distributed across the inner and outer circular surfaces of the working end; the inner and outer circular surfaces of the working end of the abrasive drill are arranged with diamond abrasive grains of a first size selected based on the drilling size, and the grooved structures of the abrasive drill are arranged with diamond abrasive grains of a second size selected based on the groove size.
[0008] The groove structure includes an outer groove on the outer circular surface of the working end of the tool base skeleton and an inner groove on the inner circular surface.
[0009] The groove structure has a trapezoidal or arc-shaped cross-section, and the number of outer and inner grooves is N (N≥2). The depth of the groove structure is less than the thickness of the base wall but greater than 0.5 times the thickness of the base wall, ensuring that the diamond abrasive grains in the inner and outer grooves intersect each other in the axial direction. The width of the groove structure is greater than the diameter of the diamond abrasive grains, and the length is less than the length of the working end of the die. The inner and outer grooves are not connected to each other.
[0010] The diamond abrasive grain size in the groove structure is greater than or equal to the abrasive grain size of the inner and outer circular surfaces of the die. The size of the first diameter diamond abrasive grain is equal to the diameter of the hole to be processed minus the outer circular surface diameter of the tool matrix skeleton and the thickness of the brazing layer. The size of the second diameter diamond abrasive grain is greater than the size of the first diameter diamond abrasive grain and less than or equal to the size of the first diameter diamond abrasive grain plus the depth of the groove structure.
[0011] The diameter of the high-sharpening self-sharpening die is 0.7 ~ 2 mm.
[0012] Beneficial effects:
[0013] 1. The skeleton structure design of the high-sharpening self-sharpening drill in this invention reduces the cross-sectional area of the tool matrix skeleton and increases the abrasive grain accommodating space of the drill. On the one hand, it ensures the rigidity and strength of the drill matrix, and on the other hand, it ensures that a sufficient number of effective abrasive grains participate in the processing.
[0014] 2. After the abrasive wear on the end face causes a decrease in drill bit sharpness, the hard and brittle ceramic matrix composite material removes the matrix and blunt abrasive grains, and then the abrasive grains inside the groove structure begin to fall out and participate in the machining. This design enhances the self-sharpening effect of the nested drill bit, ensuring its high sharpness.
[0015] 3. The grooved structure and the inner and outer circular surfaces of the working end of the casing drill use diamond abrasive grains of different sizes. The large-diameter abrasive grains in the grooved structure can enhance the cutting ability, while the small-diameter abrasive grains on the inner and outer circular surfaces can ensure the hole making accuracy. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of a high-sharpness, self-sharpening bushing drill for machining small holes in ceramic matrix composite materials according to the present invention.
[0017] Figure 2 This is a schematic diagram of the tool base skeleton in this invention.
[0018] Figure 3 This is a schematic diagram of the bore diameter after drilling in this invention.
[0019] Figure 4 This is the aperture measurement result of the present invention.
[0020] Figure 5 This is a schematic physical diagram of the tool base skeleton in this invention.
[0021] Explanation of main reference numerals in the attached drawings: 1-Tool matrix skeleton; 2-First diameter diamond abrasive grain; 3-Second diameter diamond abrasive grain; 4-Groove structure; 5-Outer groove; 6-Inner groove. Detailed Implementation
[0022] To enable those skilled in the art to better understand the technical solutions in this patent application, the technical solutions in this application 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 this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort should fall within the scope of protection of this application.
[0023] Example 1
[0024] In this embodiment, 1.4 mm holes are machined in the ceramic matrix composite material.
[0025] Figure 1 This is a schematic diagram of a high-sharpness, self-sharpening bushing drill for machining small holes in ceramic matrix composite materials according to the present invention. Figure 2 This is a schematic diagram of the tool base skeleton in this invention.
[0026] like Figure 1 As shown, a high-sharpness, self-sharpening die for machining small holes in ceramic matrix composites includes a high-capacity space tool matrix skeleton 1 with a grooved structure and diamond abrasive grains of various sizes selected according to the characteristics of the matrix structure. The abrasive grain size is designed according to the requirements of the machining process;
[0027] like Figure 2As shown, the tool base frame 1 is a hollow cylindrical structure with multiple groove-shaped structures 4 at the working end to increase the space for abrasive grains. This structure can effectively reduce the volume of material removed and increase the space for abrasive grains. The first diameter diamond abrasive grain 2 on the outer surface of the working end of the bushing drill is 80 / 100 mesh. Selecting a smaller diameter grinding wheel on the outer surface can improve drilling accuracy. Combining the machining hole diameter and the abrasive grain size, the outer diameter of the base frame 1 is equal to the machining hole diameter minus the thickness of the abrasive grains and the brazing layer, which is 0.9 mm. Considering that a certain space should be left in the middle hole of the bushing drill, the bushing drill wall thickness is set to 0.25 mm, and the inner cylindrical surface diameter is 0.4 mm.
[0028] The groove structure 4 includes an outer groove 5 and an inner groove 6 on the outer circular surface of the working end of the tool base skeleton. All groove structures have trapezoidal or arc-shaped cross-sections. Six groove structures are evenly distributed along the circumference of the working end of the bushing drill, with three inner and three outer grooves. Considering that the groove depth should be less than the wall thickness, and to accommodate more abrasive grains, the depth of all groove structures is set to 0.2 mm. The grooves are not connected; therefore, the maximum width of the outer groove is set to 0.4 mm, the maximum width of the inner groove is 0.35 mm, and the length is 5 mm.
[0029] The use of large-grained diamond abrasive grains 3 in the outer groove structure 4 (outer groove) ensures strong cutting capability of the die-casting drill. The drop height of the diamond abrasive grains in the outer groove is less than that on the outer circular surface, ensuring that the hole diameter is determined by the abrasive grains on the outer circular surface. With a groove depth of 0.2 mm, the second-size diamond abrasive grains in the groove are set to 40 / 45 mesh, achieving greater cutting capability without compromising hole accuracy. The abrasive grain arrangement length should be greater than the groove length; a 7 mm arrangement is set. The first and second diamond abrasive grains 2 and 3 are bonded to the matrix skeleton 1 using a vacuum high-temperature brazing process.
[0030] Comparative Example 1 (without slots)
[0031] Traditional small-hole machining drill bits typically use hollow cylindrical bars as the base material. To ensure a certain level of tool rigidity, the base diameter is 0.9 mm, and the abrasive grain size is 80 / 100 mesh, brazed onto the inner and outer cylindrical surfaces and end faces of the tool base. Due to the small abrasive grain size, they are easily worn during drilling. Furthermore, once the end face abrasive grains fail, the drill bit loses its drilling capability, resulting in short tool life and poor machining quality.
[0032] Example 2
[0033] The high-sharpness, self-sharpening drill prepared in Example 1 was used for drilling small holes in ceramic matrix composite materials. The machining parameters were set as follows: spindle speed 30,000 r / min, feed rate 5 mm / min, and drilling depth twice the plate thickness (6 mm). During the machining process, the machine tool spindle drove the high-sharpness, self-sharpening drill to rotate and feed downwards at a uniform speed to drill holes in the workpiece.
[0034] After machining a certain number of small holes, the diamond abrasive grains at the very tip of the high-sharpness, self-sharpening drill bit wear down and fail. Because the hardness and wear resistance of the tool matrix 1 are much lower than those of the ceramic matrix composite material, wear occurs at the top of the drill bit during continuous drilling. The second-diameter diamond abrasive grains 3, embedded within the groove structure 4, begin to emerge, allowing the drill bit to maintain its sharpness and creating a strong self-sharpening effect. A new image of the small holes was taken after machining was completed. Figure 3 The diameter of the small hole after processing was measured. Figure 4 During the drilling stroke of 20 holes, the hole diameter can maintain good consistency, indicating that the nesting drill of the present invention has a longer nesting drill life compared with traditional PCD drill bits and carbide drill bits.
[0035] Compared to the ordinary small-hole machining drill in Comparative Example 1, the high-sharpening self-sharpening drill has a specially designed groove structure and abrasive grain arrangement, which effectively improves the sharpness of the tool and thus results in slower wear during machining, effectively maintaining the hole diameter accuracy. The ordinary small-hole machining drill in Comparative Example 1 shows a significant decrease in hole diameter during drilling, and after drilling the fifth hole, the end-face abrasive grains are completely worn, causing the drill to lose its drilling ability and fail. Compared to the ordinary drilling drill, the drilling drill of this invention has strong self-sharpening capability, significantly improving tool life and ensuring machining quality, demonstrating the advantages of this invention.
[0036] Compared with the structure of CN207432521U, the present invention has the following differences: 1. The grooved structure of the present invention is designed to increase the abrasive grain accommodating space of the nesting drill and reduce the cross-sectional area of the matrix. The grooved structure is also not a through groove and cannot provide the chip removal and drainage capabilities described in the aforementioned patent. 2. The grooved structure design of the present invention increases the abrasive grain accommodating space of the nesting drill. After the end face abrasive wears down, causing a decrease in the sharpness of the nesting drill, the hard and brittle ceramic matrix composite material removes the matrix and blunt abrasive grains, and then the abrasive grains inside the grooved structure begin to emerge and participate in machining. This design enhances the self-sharpening effect of the nesting drill and ensures its high sharpness, while the slotted structure in the aforementioned similar patents cannot achieve a self-sharpening effect after tool wear.
Claims
1. A high-sharpness, self-sharpening bushing drill for machining small holes in ceramic matrix composite materials, characterized in that, include: (1) Tool matrix skeleton; (2) Composite-size diamond abrasive grains brazed onto the inner and outer surfaces of the working end of the tool matrix skeleton; The tool base frame is a hollow cylindrical structure with multiple groove structures at the working end. The groove structure includes an outer groove and an inner groove axially arranged on the outer circular surface and inner circular surface of the working end of the tool base frame. The inner and outer grooves are evenly distributed on the inner and outer circular surfaces of the working end and are not connected to each other to ensure the rigidity of the base. The diameter of the casing drill is 0.7 ~ 2 mm, and the length of the groove structure is less than the length of the working end; The composite-size diamond abrasive grains are brazed onto the inner groove, outer groove, outer circular surface of the working end, and inner circular surface of the working end; the diamond abrasive grains in the inner and outer grooves have the same grain size; the diamond abrasive grains on the inner and outer circular surfaces of the working end have the same grain size; the cross-section of the groove structure is trapezoidal or arc-shaped, and the number of outer grooves and inner grooves is N, where N≥2; The composite-size diamond abrasive grains brazed to the inner and outer circular surfaces of the working end are the first-size diamond abrasive grains, and their arrangement is based on the drilling size design to ensure the drilling accuracy. The diamond abrasive grains brazed into the inner and outer grooves are second-diameter diamond abrasive grains, and their arrangement is based on the groove size to enhance cutting ability. The first diameter diamond abrasive grain is smaller than the second diameter diamond abrasive grain. When the first-diameter diamond abrasive wears down and the drill bit's sharpness decreases, the abrasive grains inside the groove structure begin to fall out and participate in the processing, enhancing the self-sharpening effect of the nesting drill and ensuring its high sharpness. 0.5 times the base wall thickness < the depth of the groove structure < the base wall thickness, to ensure that the diamond abrasive grains inside the outer groove and on the outer circular surface of the working end intersect each other in the axial direction; The width of the groove structure is greater than the diameter of the diamond abrasive grain, and the length is less than the length of the working end of the casing drill.
2. The high-sharpness, self-sharpening bushing drill for machining small holes in ceramic matrix composite materials according to claim 1, characterized in that, The size of the first diameter diamond abrasive grain = the diameter of the hole to be processed - the outer diameter of the tool matrix skeleton - the thickness of the brazing layer; the size of the first diameter diamond abrasive grain < the size of the second diameter diamond abrasive grain ≤ (the size of the first diameter diamond abrasive grain + the depth of the groove structure).