Hole making tool for aramid fiber-reinforced plastic and design method thereof

Abstract

The present invention belongs to the technical field of composite material processing, and relates to a hole making tool for aramid fiber-reinforced plastic and a design method thereof. The drill bit has a step reversed point angle structure, which can reduce a trust force during drilling and effectively cut off a high toughness aramid fiber, thus to improve the hole making quality of an AFRP-related component. It is proved that the new tool can significantly improve the hole making quality of an AFRP component, improve the service life and safety degree, and greatly reduce the processing cost. Therefore, the present invention has a broad application prospect in the fields of aerospace, military industries and civil application.

Claims

1. A design method of a hole making tool for aramid fiber-reinforced plastic, wherein the hole making tool for aramid fiber-reinforced plastic, comprising four regions: a multiple point angle drill tip region, a reversed point angle reaming region, a reaming region and a shank clamping region; the multiple point angle drill tip region comprises a twist drill, and has a tool diameter of D1; the width of a chisel edge 1 is b.sub.1, a major cutting edge is divided into a major cutting edge first part and a major cutting edge second part to form a double point angle structure which comprises a major cutting edge first point angle N.sub.1 and a major cutting edge second point angle N.sub.2, corresponding radial widths are respectively a first part radial length b.sub.2 of the major cutting edge first part and a second part radial length b.sub.3 of the major cutting edge second part, and a width ratio is determined according to actual processing requirements; a rake face and a flank face of the tool are ground to form a major cutting edge rake angle .sub.1 and two major cutting edge relief angles which are respectively a major cutting edge primary relief angle .sub.1 and a major cutting edge secondary relief angle .sub.2; the reversed point angle reaming region comprises a reversed point angle structure, a second step part of the tool is ground to obtain a reversed point angle which is P, a drill margin width is b.sub.4, a drill margin depth is b.sub.5, the maximum length of the reversed point angle structure is b.sub.6, a major cutting edge rake angle of the reversed point angle structure is .sub.2, and a major cutting edge relief angle of the reversed point angle structure is .sub.3; as a first step diameter and a second step diameter are different, a helix angle N.sub.3 of a chip groove and the width b.sub.7 of the chip groove in the two steps shall be appropriate; the tool diameter of the reaming region is the second step diameter D.sub.2, the reaming region has a drill margin and a taper of 3:1000, and the diameter near a minor cutting edge is large; the diameter of the shank clamping region is a shank diameter D.sub.3, and a clamping length is determined according to actual clamping requirements; the design method of the hole making tool for aramid fiber-reinforced plastic, which optimizes a step diameter ratio and point angles of the tool; first, the attribute parameters of a material to be processed, including an AFRP bonding interface equivalent modulus k.sub.b, a bonding strength .sub.b, an elastic modulus E.sub.f of a lower surface material, a moment of inertia of the section I.sub.f of the lower surface material, a single-layer fiber thickness t, a feed per tooth v, an end hole design diameter D.sub.2, the step diameter ratio n, a bottom layer debonding fiber length L, a half point angle of the tool, and a fiber deflection change z are determined; and the design method comprises the following specific steps: step 1: inputting the single-layer fiber thickness t and the feed per tooth v to calculate the relationship of a radial component force F.sub.X and an axial component force F.sub.Z with the half point angle of the tool; step 2: inputting the bonding interface equivalent modulus k.sub.b, the bonding strength limit .sub.b, the elastic modulus E.sub.f and the moment of inertia of the section I.sub.f according to the criteria for judging fiber material debonding to calculate a fiber deflection deformation equation: $\begin{array}{cc}z=e^{\sqrt[-4]{k_b/4E_f{I}_f}x}\left(K_1\cos \sqrt[4]{k_b/4E_f{I}_f}x+K_2\sin \sqrt[4]{k_b/4E_f{I}_f}x\right)+e^{\sqrt[4]{k_b/4E_f{I}_f}x}\left(K_3\cos \sqrt[4]{k_b/4E_f{I}_f}x+K_4\sin \sqrt[4]{k_b/4E_f{I}_f}x\right)& \left(1\right)\end{array}$ where K.sub.i is an integral constant, and i=1, 2, 3, 4; step 3: inputting the end hole design diameter D.sub.2 and primarily selecting the step diameter ratio n to calculate an expression of the bottom layer debonding fiber length L: $\begin{array}{cc}L=\left(n-1\right)D_2/2n& \left(2\right)\end{array}$ step 4: substituting the expression of the radial component force F.sub.X and the axial component force F.sub.Z about the half point angle of the tool and the expression of the debonding fiber length L into the debonding fiber deflection equation to obtain an equation of the half point angle and the deflection z: $\begin{array}{cc}z=\left(e^{-\sqrt{\frac{\mathrm{tv}.Math.\sin }{E_f{I}_f}}.Math.\left(n-1\right)D_2/2n}-e^{\sqrt{\frac{\mathrm{tv}.Math.\sin }{E_f{I}_f}}.Math.\left(n-1\right)D_2/2n}-\left(n-1\right)/n.Math.D_2\right)\tan & \left(3\right)\end{array}$ step 5: determining the deflection change range of the material according to processing quality requirements, calculating the corresponding ranges of the point angles according to equation (3) to guide the design of the tool, and judging and checking whether the structure of the tool is reasonable; if not reasonable, going back to step 3 and selecting the step diameter ratio n again.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a main view of a tool for drilling aramid fiber composite material.

(2) FIG. 2 is an enlarged view of a multiple point angle drill tip region A in FIG. 1.

(3) FIG. 3 is an enlarged view of a reversed point angle structure E in FIG. 1.

(4) FIG. 4 is a flow chart of an optimal design method for a step diameter ratio and point angles of a tool.

(5) In the figures: Amultiple point angle drill tip region, Breversed point angle reaming region, Creaming region, Dshank clamping shank region, and Ereversed point angle structure; 1chisel edge, 2major cutting edge first part, 3major cutting edge second part, 4minor cutting edge, 5major cutting edge of reversed point angle structure, 6minor cutting edge of reversed point angle structure, 7drill margin of tool, 8axis of tool, 9chip groove, 10rake face, 11ground rake face, 12flank face, and 13ground flank face; b.sub.1width of chisel edge, b.sub.2first part radial length of major cutting edge second part, b.sub.3second part radial length of the major cutting edge second part, b.sub.4drill margin width, b.sub.5drill margin depth, b.sub.6maximum length of reversed point angle structure, and b.sub.7width of chip groove; D.sub.1first step diameter, D.sub.2second step diameter, and D.sub.3shank clamping diameter; Psecond step reversed point angle, N.sub.1major cutting edge first point angle, N.sub.2major cutting edge second point angle, N.sub.3helix angle of chip groove, .sub.1major cutting edge rake angle, .sub.2major cutting edge rake angle of reversed point angle structure, .sub.1major cutting edge primary relief angle, .sub.2major cutting edge secondary relief angle, and .sub.3major cutting edge relief angle of reversed point angle structure.

DETAILED DESCRIPTION

(6) The technical solution in the embodiments of the present invention will be clearly and fully described below in combination with the drawings in the embodiments of the present invention. Apparently, the described embodiments are merely part of the embodiments of the present invention, not all of the embodiments.

(7) As shown in FIGS. 1, 2 and 3, a tool for drilling aramid fiber composite material, which has a double step structure and consists of four parts, namely a multiple point angle drill tip region A, a reversed point angle reaming region B, a reaming region C and a shank clamping region D. A double step and multiple point angle structure can reduce the trust force. The reversed point angle reaming region B comprises a reversed point angle structure E, which can convert an axial compression effect on a composite material into an axial tension effect, so as to effectively remove fibers and reduce the processing loss. In the embodiment, an ultimate goal is to process an end hole with a diameter of 6 mm.

(8) The multiple point angle drill tip region A is located at the utmost front end of the tool and has a diameter of D.sub.1=4 mm, and X-type grinding is used to make the length of a chisel edge b.sub.1=0.4 mm. When the chisel edge is shorter, the trust force can be reduced, and the delamination damage of AFRP can be reduced. A first step major cutting edge of the tool is divided into two parts which are respectively a major cutting edge first part 2 and a major cutting edge second part 3 to form a double point angle structure, the corresponding radial widths are respectively b.sub.2=1.3 mm and b.sub.3=1.5 mm, a major cutting edge first point angle is N.sub.1=90, and a major cutting edge second point angle is N.sub.2=120; a rake face 10 and a flank face 12 are ground to reduce the friction between the tool and the material, obtain a better heat dissipation effect, and obtain a ground rake face 11 and a ground flank face 13, wherein a major cutting edge rake angle is .sub.1=20 and two major cutting edge relief angles are respectively .sub.1=12 and .sub.2=45.

(9) The reversed point angle reaming region B comprises a first step end section and a second step initial section, a drill margin of the tool at steps is ground to form a reversed point angle, i.e., the reversed point angle structure E, wherein the reversed point angle is P=60; the axial compression on an aramid fiber is converted into axial tension, which reduces the deformation degree of the aramid fiber, wherein a drill margin width is b.sub.4=0.6 mm, a drill margin depth is b.sub.5=0.2 mm, and the maximum length of the reversed point angle structure is b.sub.6=1.2 mm. The reversed point angle structure E comprises a major cutting edge 5 of the reversed point angle structure and a minor cutting edge 6 of the reversed point angle structure, wherein a major cutting edge rake angle of the reversed point angle structure is .sub.2=25, and a major cutting edge relief angle of the reversed point angle structure is .sub.3=15. As a first step diameter and a second step diameter are different, a helix angle N.sub.3 of a chip groove 9 and the width b.sub.7 of the chip groove in the two steps shall be appropriate to meet the requirements of discharging chips smoothly, not causing chip blocking, and ensuring the rigidity of the structure in each step of the tool. Therefore, the helix angle of the chip groove is selected as N.sub.3=30, and the width of the chip groove is generally 0.8-0.9 times the diameter of the tool. A second step end hole tool diameter is D.sub.2=6 mm, so the width of the chip groove is selected as b.sub.7=5 mm, and in order to ensure the strength of the tool, the thickness of a drill core is selected as 2 mm.

(10) The tool end hole diameter of the reaming region C is D.sub.2=6 mm, the reaming region C has a drill margin 7 and a taper of 3:1000, and the diameter near a minor cutting edge 4 is large, so that the friction can be reduced, and the drilled and reamed holes can be further processed to improve the smoothness of hole walls. The helix angle of the chip groove 9 in the multiple point angle drill tip region A, the reversed point angle reaming region B and the reaming region C is N.sub.3=3430, and an escape is reserved at an end section of the reaming region C to facilitate processing by the tool.

(11) The diameter of the shank clamping region D is D.sub.3=5 mm, and a clamping length is determined according to actual clamping requirements.

(12) When the optimal design method taking into account the step diameter ratio and point angles of the tool proposed by the present invention is adopted, the specific design steps are as follows: Step 1: inputting the single-layer fiber thickness t=0.2 mm and the feed per tooth v=0.03 mm to obtain the relationship of a radial component force F.sub.X and an axial component force F.sub.Z with the half point angle of the tool by calculation; Step 2: inputting the bonding interface equivalent modulus k.sub.b=115 GPa/m, the bonding strength limit .sub.b=30 MPa, the elastic modulus E.sub.f=15 GPa and the moment of inertia of the section I.sub.f=m.sup.4 according to the criteria for judging fiber material debonding to obtain a fiber deflection deformation equation by calculation; Step 3: inputting the end hole diameter D.sub.2=6 mm and primarily selecting the step diameter ratio n=6:4 to obtain the bottom layer debonding fiber length L=1 mm and obtain a debonding fiber deflection equation by calculation; Step 4: substituting the expression of the radial component force F.sub.X and the axial component force F.sub.Z about the half point angle of the tool into the debonding fiber deflection equation to obtain an equation of the half point angle and the deflection z; Step 5: obtaining the value range of point angle P (P=60) according to the deflection change range, checking whether the structural strength of the tool meets design and processing requirements to complete the design of the tool in the embodiment, and using a 3D software to model and manufacture the tool.

(13) A three-axis vertical high-speed machining center is adopted as an experimental platform, an ordinary twist drill with a diameter of 6 mm commonly used in engineering and the new tool designed in the embodiment are used as drill bits, and the drill bits are made of cemented carbide without coating and without cooling during processing. A workpiece processed is an AFRP laminate, the size of the laminate is 1501804 mm, the mass of aramid fibers accounts for 60% of the total mass of the laminate, and the fiber layup directions are 0 and 90 cross layup directions. With respect to cutting parameters, a spindle speed of 3000 r/min and a feed speed of 90 mm/min are used. The AFRP laminate is processed with the ordinary twist drill and the new tool designed in the embodiment, and the processing qualities are compared. It is measured that the peak value of the drilling trust force of the new tool designed in the embodiment is only 36% of that of the twist drill. The processing damages at the inlet and the outlet of the processed material are quantified and compared, which shows that the material processed by the twist drill has a burr area of 3.6 mm.sup.2 and a delamination factor of 1.45, and the material processed by the new tool designed in the embodiment has a burr area of 0.4 mm.sup.2 and a delamination factor of 1.06; compared with the twist drill, the burr area is reduced by more than 80%, and the delamination factor is reduced by more than 25%, i.e., the tool designed by the present invention has a good inhibition effect on the damages such as delamination and burrs at the outlet of AFRP.

(14) A tool structure for drilling aramid fiber composite material and a design method thereof proposed by the present invention mainly relates to a step reversed point angle structure, and a design method is proposed to optimize the step diameter ratio and point angles of the tool. Compared with ordinary twist drill, the peak value of the drilling trust force of the new tool is only 36% of that of the twist drill, the burr area after processing is reduced by more than 80%, and the delamination factor is reduced by more than 25%, which can prove that the tool designed by the present invention can significantly improve the hole making quality of an AFRP component, improve the service life and safety degree, and greatly reduce the processing cost. The tool structure and design method proposed by the present invention are not limited to the structure of the embodiment, and can be changed and modified in a variety of ways. In conclusion, all changes and modifications without departing from the innovation scope of the present invention shall fall within the protection scope of the present invention.