A drill bit based on segmented design and a design method for its structural parameters

Abstract

The present invention discloses a drill bit based on segmented design and a design method for its structural parameters. S1: Divide the cutting edge of the drill bit into multiple segments; S2: Analyze hole machining defects to extract machining defect information; S3: Classify the machining defects; S4: Establish an axial force calculation model and a prediction model for the horizontal component force of each segment of the cutting edge; S5: Analyze the influence of each segment of the cutting edge on the machining defects; S6: Adjust the structural parameters of each segment of the cutting edge; S7: Grind the drill bit according to the structural parameters of each segment of the cutting edge in S6; S8: Perform a drilling test on the drill bit obtained in S7 to verify its effectiveness. The present invention proposes a design method for drill bits for different materials, which can shorten the drill bit development cycle and improve the hole-making quality.

Description

Technical Field

[0001] The present invention relates to the field of drilling tools, and particularly to a drill bit based on segmented design and a design method for its structural parameters, belonging to the field of machining technology. Background Art

[0002] Carbon fiber reinforced composite material (CFRP) is a composite material with anisotropic properties formed by bonding high-strength brittle carbon fibers and low-strength plastic resin matrix. Due to its many excellent properties such as light weight, high specific modulus, high specific strength, low coefficient of thermal expansion, high corrosion resistance and fatigue resistance, and strong designability, it has been widely used in aerospace, automotive, military and other cutting-edge fields and has become increasingly important in various industrial applications. When assembling CFRP components, mechanical processing is required, and the most common one is drilling. During the drilling process of CFRP, due to the characteristics of CFRP such as inhomogeneity, anisotropy and low interlaminar properties, drilling defects such as delamination, burrs and tearing are likely to occur, seriously affecting the service performance of CFRP structural parts. Especially during the drilling process, the axial force is too large, exceeding the interlaminar bonding strength, resulting in delamination defects; on the other hand, during the drilling process, the tool wears and the cutting edge becomes dull, and the cutting edge cannot effectively cut off the fiber bundle to form burrs. These two defects mainly appear at the exit of the drilled hole. In order to suppress the processing defects, the structure of the twist drill is improved to improve the processing quality of the hole. Summary of the Invention

[0003] The present invention aims to solve at least one of the above-mentioned technical problems, and provides a drill bit based on segmented design and a design method for its structural parameters. By obtaining basic data through experiments, according to the distribution of cutting forces of each cutting edge segment and the influence of each cutting edge segment on the formation of key and important defects during the hole-making process, the geometric parameters of the cutting edge are optimized accordingly, so as to reduce the generation of quality defects in hole-making drilling.

[0004] Provide a drill bit based on segmented design to reduce the generation of quality defects in hole-making drilling.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A design method for the structural parameters of a drill bit based on segmented design includes the following steps:

[0007] S1. Divide the cutting edge of the drill bit into multiple segments, and the cutting edge of the drill bit includes a negative rake face main cutting edge segment, a positive rake face main cutting edge segment, and a main cutting edge at the outer edge corner;

[0008] S2. Analyze the hole processing defects to extract processing defect information, and the processing defects include burrs, overcut, hole diameter deviation, and edge nibbling;

[0009] S3. Classify the machining defects into critical defects, important defects, and general defects according to the degree of influence of the defects on the performance of the machined parts.

[0010] S4. Establish an axial force calculation model and a prediction model for the horizontal component force of each cutting edge segment.

[0011] Axial force calculation formula: F Z = l1 * k1 + 2 * l2 * k2 + 2 * l3 * k3 + 2 * l4 * k4 + 2 * l5 * k5, Equation (1), where l i is the length of each cutting edge segment in Figure 2, and k i is the axial component force coefficient per unit length, i = 1, 2, 3, 4, 5.

[0012] Horizontal component force formula for the i-th cutting edge: F ci = l i * k i / tanθ i , i = 2, 3, 4, 5, Equation (2), where θ i is the drill point angle of the i-th cutting edge.

[0013] S5. Analyze the influence of each cutting edge segment on the machining defects.

[0014] S6. Adjust the structural parameters of each cutting edge segment, where the structural parameters include the length, angle, and edge radius of each cutting edge segment.

[0015] S7. Grind the drill bit according to the structural parameters of each cutting edge segment in S6.

[0016] S8. Conduct a drilling test on the drill bit obtained in S7 to verify its effectiveness.

[0017] As an improvement to the above technical solution, the positive rake face main cutting edge segment includes several sub-segments.

[0018] As an improvement to the above technical solution, the drill bit cutting edge further includes one or more of a chisel edge, a chisel edge grinding segment, and a secondary cutting edge segment.

[0019] As an improvement to the above technical solution, the length l1 of the chisel edge ranges from (0.1 - 0.17) * D, Equation (3), where D is the drill bit diameter, and the chisel edge grinding angle β ranges from 130° to 150°.

[0020] As an improvement to the above technical solution, the rake angle of the chisel edge grinding segment l2 is 0° to 5°.

[0021] As an improvement to the above technical solution, the range of l5 is 0.3 mm - 0.6 mm; when θ5 is greater than 180 °, the range of θ5 is 240 ° - 270 °.

[0022] As an improvement to the above technical solution, delamination defects and tearing defects are critical defects, burrs are important defects, and edge chipping is a general defect.

[0023] As an improvement to the above technical solution, the coefficient k i is obtained as follows:

[0024] Drills with diameters of l1, l1 + 2l2, l1 + 2l2 + 2l3, and l1 + 2l2 + 2l3 + 2l4 are designed, and the drill numbers are T1, T2, T3, and T4 respectively; the target drill T5 with a diameter of l1 + 2l2 + 2l3 + 2l4 + 2l5 is ground, and a dynamometer is used to measure the axial force during the drilling process;

[0025] k5: Drill the bottom hole with the T4 drill, and then ream the hole with the T5 drill under the corresponding machining parameters. At this time, the measured axial force F z5 is generated by the l5 segments on the two main cutting edges of the drill, and k5 = F z5 / (2 * l5), Equation (4);

[0026] k4: Drill the bottom hole with the T3 drill, and then ream the hole with the T5 drill under the corresponding machining parameters. At this time, the measured axial force F z4 is generated by the l4 and l5 segments on the two main cutting edges of the drill, and k4 = (F z4 -F z5 ) / (2 * l4), Equation (5);

[0027] k3: Drill the bottom hole with the T2 drill, and then ream the hole with the T5 drill under the corresponding machining parameters. At this time, the measured axial force F z3 is generated by the l3, l4, and l5 segments on the two main cutting edges of the drill, and k3 = (F z3 -F z4 -F z5 ) / (2 * l3), Equation (6);

[0028] k2: Drill the bottom hole with the T1 drill, and then ream the hole with the T5 drill under the corresponding machining parameters. At this time, the measured axial force F z2 is generated by the l2, l3, l4, and l5 segments on the two main cutting edges of the drill, and k2 = (F z2 -F z3 -F z4 -F z5) / (2*l2), Equation (7);

[0029] k1: Axial force F z2 Generated by the l2, l3, l4, and l5 segments on the two main cutting edges of the drill bit except for the chisel edge l1, k1 = (F z5 -F z2 ) / l1, Equation (8).

[0030] A segmented-designed drill bit, the cutting edge of the drill bit includes one or more segments of a chisel edge, a chisel-edge grinding segment, a main cutting edge segment with a negative rake angle, a main cutting edge segment with a positive rake angle, a main cutting edge segment at the outer edge corner, and a secondary cutting edge segment.

[0031] As an improvement of the above technical solution, the length l1 of the chisel edge ranges from (0.1 - 0.17)*D, Equation (3), D is the diameter of the drill bit, the chisel-edge grinding angle β ranges from 30° to 50°, the rake angle of the chisel-edge grinding segment l2 is 0° - 5°, the range of l5 is 0.3 mm - 0.6 mm; when θ5 is greater than 180°, the range of θ5 is 240° - 270°.

[0032] The beneficial effects of this application compared with the prior art are:

[0033] The present invention proposes a drill bit design method for CFRP, which can shorten the drill bit development cycle and improve the hole-making quality. Description of the Drawings

[0034] The following further details the specific embodiments of the present invention in conjunction with the accompanying drawings, where:

[0035] Figure 1 is a schematic structural diagram 1 of an embodiment of the present invention;

[0036] Figure 2 is a schematic structure of an embodiment of the present invention Figure 2 ;

[0037] Figure 3 is a logic block diagram of an embodiment of the present invention. Specific Embodiments

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] It should be noted that when a component is referred to as "fixed to" another component, it can be directly on the other component or there can also be an intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be an intermediate component at the same time. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time. When a part is referred to as "disposed in the middle", it is not only disposed at the exact middle position, as long as it is not disposed at the two end parts, it belongs to the range defined by the middle. The terms "vertical", "horizontal", "left", "right" and similar expressions used in this article are only for the purpose of illustration.

[0040] Unless otherwise defined, all technical and scientific terms used in this article have the same meaning as those commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the specification of this invention in this article are only for the purpose of describing specific embodiments, and are not intended to limit this invention. The term "and / or" used in this article includes any and all combinations of one or more of the related listed items.

[0041] As shown in FIGS. 1 to 3, the present invention provides a drill bit based on segmented design and a design method for its structural parameters, including the following steps:

[0042] S1. Divide the cutting edge of the drill bit into multiple segments, and the cutting edge of the drill bit includes a negative rake face main cutting edge segment, a positive rake face main cutting edge segment, and a main cutting edge at the outer edge corner.

[0043] In some embodiments of the present application, the cutting edge of the drill bit further includes one or more of a chisel edge, a chisel edge grinding segment, and a secondary cutting edge segment.

[0044] Referring to FIGS. 1 and 2, in the present application, based on the damage fracture mechanism of the material and the variation law of the rake angle of the main cutting edge, the spatial curve of the cutting edge of the drill bit is divided into a chisel edge, a chisel edge grinding segment, a negative rake face main cutting edge segment, a positive rake face main cutting edge segment, a main cutting edge segment at the outer edge corner, and a secondary cutting edge segment. The number of divided segments can be increased or decreased according to specific circumstances.

[0045] When the chisel edge has no influence on the exit quality, the chisel edge grinding segment can be reduced. When the outer edge corner has no influence on the exit quality, the main cutting edge segment at the outer edge corner can be reduced. When grinding a constant rake angle cutting edge, the negative rake face main cutting edge segment and the positive rake face main cutting edge segment can be combined into one segment for analysis.

[0046] When the drill bit is a multi-stage drill bit, the number of analysis segments of the main cutting edge can be increased to determine the influence of the cutting edge of each stage of the drill bit and perform subsequent analysis and design. When the main cutting edge segment has an important influence on the hole quality and it is difficult to optimize the drill bit structure by only dividing the main cutting edge segment with negative rake angle, the main cutting edge segment with positive rake angle, and the main cutting edge segment at the outer edge corner, the main cutting edge segment with positive rake angle can be further segmented to more precisely optimize the drill bit.

[0047] S2. Analyze the hole machining defects and extract the machining defect information. Specifically, the machining defects include burrs, tears, delamination, overcutting, hole diameter deviation, and edge nibbling. The machining defect information includes information such as defect morphology, size, and distribution.

[0048] S3. Classify the machining defects, and classify them into critical defects, important defects, and general defects according to the degree of influence of the defects on the performance of the workpiece to be machined.

[0049] In this application, according to the degree of influence of the defects on the performance of the workpiece to be machined, they are classified into critical defects, important defects, and general defects. Defects that seriously reduce the performance of the workpiece to be machined are critical defects, defects that partially reduce the performance of the workpiece to be machined are important defects, and defects that slightly reduce the performance of the workpiece to be machined are general defects. For example, in CFRP drilling, delamination and tear defects seriously affect the safety performance of the part and are critical defects; burrs can be removed later but the cost increases, so they are important defects; while when damage such as edge nibbling has little impact on the performance and service life of the part, it is a general defect.

[0050] S4. Establish an axial force calculation model and a horizontal component force prediction model for each segment of the cutting edge. The axial force calculation formula: F Z =l1*k1 + 2 *l2*k2+2* l3*k3+ 2*l4*k4+ 2*l5*k5, Equation (1).

[0051] Among them, l i is the length of each segment of the cutting edge in Figure 2, k i is the axial component force coefficient per unit length, i = 1, 2, 3, 4, 5, and the formula for the horizontal component force on the i-th cutting edge: F ci =l i *k i / tanθ i , i = 2, 3, 4, 5, Equation (2).

[0052] Among them, θ i is the drill point angle of the i-th cutting edge.

[0053] In the embodiment of this application, the average rake angle of each segment of the cutting edge is used for simulation and experiment to obtain the corresponding coefficient k i .

[0054] Specifically, the coefficient k i is obtained as follows:

[0055] Drills with diameters of l1, l1 + 2l2, l1 + 2l2 + 2l3, and l1 + 2l2 + 2l3 + 2l4 are designed, and the drill numbers are T1, T2, T3, and T4 respectively; grind the target drill T5 with a diameter of l1 + 2l2 + 2l3 + 2l4 + 2l5, and use a dynamometer to measure the axial force during the drilling process;

[0056] k5: Drill the bottom hole with drill T4, and then ream the hole with drill T5 under the corresponding machining parameters. At this time, the measured axial force F z5 is generated by the l5 segments on the two main cutting edges of the drill, and k5 = F z5 / (2 * l5), Equation (4);

[0057] k4: Drill the bottom hole with drill T3, and then ream the hole with drill T5 under the corresponding machining parameters. At this time, the measured axial force F z4 is generated by the l4 and l5 segments on the two main cutting edges of the drill, and k4 = (F z4 - F z5 ) / (2 * l4), Equation (5);

[0058] k3: Drill the bottom hole with drill T2, and then ream the hole with drill T5 under the corresponding machining parameters. At this time, the measured axial force F z3 is generated by the l3, l4, and l5 segments on the two main cutting edges of the drill, and k3 = (F z3 - F z4 - F z5 ) / (2 * l3), Equation (6);

[0059] k2: Drill the bottom hole with drill T1, and then ream the hole with drill T5 under the corresponding machining parameters. At this time, the measured axial force F z2 is generated by the l2, l3, l4, and l5 segments on the two main cutting edges of the drill, and k2 = (F z2 - F z3 - F z4 - F z5 ) / (2 * l2), Equation (7);

[0060] k1: The axial force F z2 is generated by the l2, l3, l4, and l5 segments on the two main cutting edges of the drill except for the chisel edge l1, and k1 = (F z5 - F z2 ) / l1, Equation (8).

[0061] S5. Analyze the influence of each segment of the cutting edge on the machining defects.

[0062] The applicant uses a method combining "addition" and "subtraction" through the above steps. According to the distribution of the above cutting forces and combined with the experimental results, the influence of each cutting edge segment on the formation of key and important defects during the hole-making process is studied, and the main cutting edge segments that lead to the formation of key and important defects are analyzed.

[0063] For example, pre-drill a bottom hole and then ream it. The diameter of the reamer is equal to the diameter of the bottom hole, which can eliminate the influence of the chisel edge and also calculate the axial force on the chisel edge. Collect information such as cutting force, cutting temperature, defect location and size during the machining process. Conduct experiments according to the above principle and supplement with cutting simulation to master the role of each cutting edge segment in the defect formation process one by one, and clarify the cutting edge segment or combination of cutting edge segments that lead to the formation of each key and important defect.

[0064] The applicant found that: for each cutting edge segment,

[0065] Chisel edge: During the drilling process, the chisel edge mainly extrudes the material and generates a large axial force.

[0066] Chisel edge grinding segment: Grinding the chisel edge can shorten the length of the chisel edge and increase the rake angle of the cutting edge in the grinding segment, which is beneficial to removing the material and makes the cutting force smaller.

[0067] Negative rake angle main cutting edge segment: The negative rake angle is not conducive to removing the material. Adjust the helix angle of the drill bit to reduce the length of this segment.

[0068] Positive rake angle main cutting edge segment: It has a longer length and generates a larger axial force.

[0069] Main cutting edge segment at the outer edge corner: It is mainly used to remove the damage to the entrance, hole wall and exit caused by the previous cutting edge segments (the first few cutting edge segments) during the early stage of drilling and plays a finishing role. Therefore, it cannot be too long.

[0070] Side edge: It is mainly used to finish the hole wall surface.

[0071] S6. Adjust the structural parameters of each cutting edge segment. The structural parameters include the length, angle and edge radius of each cutting edge segment. Control the magnitude, direction and acting point of the cutting force on the cutting edge to reduce the size and scope of key and important defects; on this basis, determine the size of the main cutting edge segment l5 at the outer edge corner according to the scope of key and important defects (around the hole) (the size of l5 is larger than the defect scope) to ensure that the defects caused in the previous stage can be removed during the cutting of the main cutting edge segment at the outer edge corner without bringing new key and important defects.

[0072] S7. Grind the drill bit according to the structural parameters of each cutting edge in S6. Specifically: the length l1 of the chisel edge ranges from (0.1 - 0.17) * D, formula (3), where D is the diameter of the drill bit; the grinding angle β of the chisel edge ranges from 130° to 150°; the rake angle of the chisel edge grinding section l2 is from 0° to 5°. The range of l5 is from 0.3 mm to 0.6 mm; when θ5 is greater than 180°, the range of θ5 is 240° - 270°. After the helix angle of the drill bit is determined, the length l2 of the chisel edge grinding section can be measured, and the lengths of the main cutting edge l3 with negative rake angle and the main cutting edge l4 with positive rake angle are also determined values, which can be calculated according to existing formulas.

[0073] S8. Conduct a drilling test on the drill bit obtained in S7 to verify its effectiveness.

[0074] The present invention proposes a design method for drill bits for different materials, which can shorten the drill bit development cycle and improve the hole-making quality.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered within the scope of the technical solutions of the present invention.

Claims

1. A design method for the structural parameters of a drill bit based on segmented design, characterized in that: It includes the following steps: S1. Divide the drill bit cutting edge into multiple segments. The drill bit cutting edge includes a negative rake main cutting edge segment, a positive rake main cutting edge segment, and a main cutting edge at the outer edge corner; S2. Analyze the hole machining defects to extract machining defect information. The machining defects include burrs, tears, delamination, overcutting, hole diameter deviation, and edge nibbling; S3. Classify the machining defects. According to the degree of influence of the defects on the performance of the workpiece to be machined, they are divided into critical defects, important defects, and general defects; S4. Establish an axial force calculation model and a prediction model for the horizontal component force of each segment of the cutting edge; Axial force calculation formula: F Z =l1 *k1+ 2 *l2 *k2+2* l3 *k3+ 2*l4 *k4+ 2*l5 *k5, Equation (1), where, l i is the length of each cutting edge segment, k i is the axial component force coefficient per unit length, i = 1, 2, 3, 4, 5 Horizontal component force formula on the i-th cutting edge: F ci =l i *k i / tanθ i , i = 2, 3, 4, 5, Equation (2), where θ i is the drill point angle of the i-th cutting edge; S5. Analyze the influence of each segment of the cutting edge on the machining defects; S6. Adjust the structural parameters of each segment of the cutting edge. The structural parameters include the length, angle, and edge radius of each segment of the cutting edge; S7. Grind the drill bit according to the structural parameters of each segment of the cutting edge in S6; S8. Conduct a drilling test on the drill bit obtained in S7 to verify its effectiveness.

2. The design method of the drill bit structure parameters based on segmented design according to claim 1, characterized in that, The positive rake main cutting edge segment includes several sub-segments.

3. The design method of the drill bit structure parameters based on segmented design according to claim 2, characterized in that, The drill bit cutting edge further includes one or more of a chisel edge, a chisel edge grinding segment, and a secondary cutting edge segment.

4. A design method for the structural parameters of a drill bit based on segmented design according to claim 3, characterized in that, The length l1 of the chisel edge ranges from (0.1 - 0.17)*D, formula (3), where D is the drill bit diameter, and the chisel edge grinding angle β ranges from 130° to 150°.

5. A design method for the structural parameters of a drill bit based on segmented design according to claim 4, characterized in that, The rake angle of the chisel edge grinding segment is 0° - 5°.

6. A design method for drill bit structure parameters based on segmented design according to claim 2, characterized in that, The range of l5 is 0.3 - 0.6 mm; when θ5 is greater than 180°, the range of θ5 is 240° - 270°.

7. A design method for the structural parameters of a drill bit based on segmented design according to claim 1, characterized in that, Delamination defects and tear defects are critical defects, burrs are important defects, and edge nibbling is a general defect.

8. A design method for the structural parameters of a drill bit based on segmented design according to claim 1, characterized in that Coefficient k i The obtaining method is as follows: Design drill bits with diameters of l1, l1 + 2l2, l1 + 2l2 + 2l3, and l1 + 2l2 + 2l3 + 2l4. The drill bit numbers are T1, T2, T3, and T4 respectively; grind the target drill bit T5 with a diameter of l1 + 2l2 + 2l3 + 2l4 + 2l5, and use a dynamometer to measure the axial force during the drilling process; k5: Drill the bottom hole with a T4 drill bit, and then ream the hole with a T5 drill bit under the corresponding machining parameters. At this time, the measured axial force F z5 is generated by the l5 segments on the two main cutting edges of the drill bit, and k5 = F z5 / (2 * l5), Equation (4); k4: Drill the bottom hole with a T3 drill bit, and then ream the hole with a T5 drill bit under the corresponding machining parameters. The axial force F measured at this time z4 is generated by the l4 and l5 segments on the two main cutting edges of the drill bit. k4 = (F z4 - F z5 ) / (2 * l4), Equation (5); k3: Drill the bottom hole with a T2 drill bit, and then ream the hole with a T5 drill bit under the corresponding machining parameters. The axial force F measured at this time z3 is generated by the l3, l4, and l5 segments on the two main cutting edges of the drill bit. k3 = (F z3 - F z4 - F z5 ) / (2 * l3), Equation (6); k2: Drill the bottom hole with a T1 drill bit, and then ream the hole with a T5 drill bit under the corresponding machining parameters. The axial force F measured at this time z2 is generated by the l2, l3, l4, and l5 segments on the two main cutting edges of the drill bit. k2 = (F z2 - F z3 - F z4 - F z5 ) / (2 * l2), Equation (7); k1: Axial force F z2 Generated by the l2, l3, l4, and l5 segments on the two main cutting edges of the drill bit, except for the chisel edge l1, k1 = (F z5 -F z2 ) / l1, Equation (8).

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