CN112207330B

CN112207330B - Drilling method for austenitic stainless steel thin-wall substrate

Info

Publication number: CN112207330B
Application number: CN202010993856.9A
Authority: CN
Inventors: 张胜; 袁超; 姜建; 漆滔; 常文卫; 龚晓彬; 周超; 吴宪宏; 李胜强; 王盛; 陈刚
Original assignee: CRRC Zhuzhou Locomotive Co Ltd
Current assignee: CRRC Zhuzhou Locomotive Co Ltd
Priority date: 2020-09-21
Filing date: 2020-09-21
Publication date: 2022-06-14
Anticipated expiration: 2040-09-21
Also published as: CN112207330A

Abstract

The invention discloses a drill bit, wherein the main body of the drill bit is of a multi-drill structure and comprises a chisel edge, and a chamfering edge, an inward concave arc edge and an inward straight edge which are symmetrically arranged about the axis of a drill point and are sequentially connected, wherein the two inward straight edges are respectively connected with two ends of the chisel edge, and the chamfering edge angle delta of the chamfering edge is 40-45 degrees; the height k from the drill point to the bottom of the concave arc blade is 1.3-1.5mm, and the height mu from the drill point to the chamfered blade point is 0.8-1 mm; the chisel edge bevel phi is 0 deg., and the inner straight edge bevel tau is 60 deg. -65 deg.. Through regrinding the phi 8 drill bit angle, when 3mm thin-wall stainless steel is drilled, the phenomena of unqualified drilling roundness, hole position deformation and poor position precision are obviously improved, and the effect is very obvious. Through sampling detection on the processed product, the positioning size of the two phi 8 holes which are most difficult to control is reduced from the original 0.2mm to 0.1 mm.

Description

Drilling method for austenitic stainless steel thin-wall substrate

Technical Field

The invention relates to a drilling method for an austenitic stainless steel thin-wall substrate, and belongs to the technical field of drill bits for drilling processing.

Background

The substrate of the AC vacuum circuit breaker is arranged on the top of the electric locomotive and is required to be suitable for requirements and working conditions of electric traction, so that the selected material belongs to austenitic stainless steel, and the AC vacuum circuit breaker has the characteristics of good environmental stability, long mechanical life and the like. However, the thin-wall austenitic stainless steel belongs to a material difficult to process, and the processing difficulty is as follows:

(1) the austenitic stainless steel has large cutting force, insufficient cutter rigidity and high cutting difficulty, thus causing the tipping of the milling cutter.

(2) Due to thin-wall laser blanking, the drilling process cannot conduct heat and dissipate heat in time and is difficult to oxidize, so that the processing hardening is serious. Further increases the strength and hardness of the raw material, and makes the processing difficult.

(3) The cutting tool is easy to stick, the cutting force is not uniform during drilling, the plasticity and the toughness are reduced, and cutting heat is generated, so that chips are cold-welded on the front cutter face of the drill.

(4) The tool wear is accelerated. In the cutting process, the processing part of the drill point is worn, the edge is broken, and the dimensional stability is difficult to ensure, so that the processing is unsmooth.

(5) Since the austenitic stainless steel is difficult to drill, it is necessary to perform two operations in drilling, that is, first drilling the positioning recess on the substrate and then drilling the hole on the basis of the positioning recess, which significantly reduces the machining efficiency and increases the rejection rate.

As shown in fig. 1, when a conventional twist drill bit is used for processing a thin plate, the abrasion form of the drill bit is mainly rear abrasion, the drill tip penetrates through a workpiece, the centering of cutting edges on two sides is unstable, the stress is uneven, the workpiece is extruded, and stainless steel is subjected to plastic deformation to form an extrusion drill mark, so that an irregular deformed hole which is elliptical and has unqualified roundness is formed.

Cutting heat is generated in the drilling process of a common drill bit, and the main reason of abrasion of the high-speed steel drill bit is phase change abrasion. Because the stainless steel has poor heat dissipation performance, the cutting edge forms a heat accumulation high-temperature area at the drill tip to form a chip accumulation lump, the cutting edge is bonded by fusion welding, and finally the cutting edge and the stainless steel are fused together to ablate the drill.

The blade angles on two sides of the common drill bit have the largest bearing torque, the largest cutting force and the small back angle of the drill bit, so that the phenomenon of blade breakage caused by insufficient drill point strength is caused.

The cutter grinding of the phi 8 common group drill bit is slightly small in diameter, and the common grinding machine is difficult to grind and mold; influenced by the material of the workpiece, the austenitic stainless steel has high strength, large plastic deformation and poor thermal conductivity, and easily causes the drill bit to have difficult chip removal and abrade and ablate the drill bit.

Aiming at the problem of high difficulty in drilling thin-wall stainless steel, a drill bit capable of improving the drilling quality and reducing the abrasion of the drill bit is urgently needed.

Disclosure of Invention

In order to improve the drilling precision of the thin-wall stainless steel and prolong the service life of the drill bit, the invention provides the drill bit, and the specific technical scheme is as follows.

The utility model provides a drill bit, its drill bit main part is ni zhifu drill structure, its characterized in that: the drill comprises a chisel edge, and a chamfering edge, an inner concave arc edge and an inner straight edge which are symmetrically arranged about the axis of a drill point and are sequentially connected from the radial outer side to the inner side, wherein the two inner straight edges are respectively connected with two ends of the chisel edge, and the chamfering edge angle delta of the chamfering edge is 40-45 degrees; the height k from the drill point to the bottom of the concave arc blade is 1.3-1.5mm, and the height mu from the drill point to the chamfered blade point is 0.8-1 mm; the transverse cutting edge bevel psi is 0 DEG, and the inner straight cutting edge bevel tau is 60 DEG-65 deg.

Further, the drill bit main body is of a phi 8 group drilling structure.

Further, the vertex angle 2 phi of the inner edge of the drill is 130-132 degrees; the vertex angle 2 eta of the outer edge is 123-125 degrees.

Further, the inclination angle gamma of the drill chisel edge is 89-90 degrees; the length omega of the transverse edge is 0.15-0.2 mm.

Furthermore, the back angle alpha of the arc edge is 11-12 degrees, and the radius chi of the arc edge is 2-3 mm.

Furthermore, the back angle beta of the chamfered edge is 6-7 degrees; the width v of the chamfering edge is 0.3-0.45 mm.

A method for drilling a thin-walled substrate using the drill bit described above, the drill bit being a Φ 8 drill bit and being connected to a spindle, the thin-walled substrate being a thin-walled substrate of austenitic stainless steel having a thickness of about 3mm, characterized in that: the working state of the drill in which the drill drills a hole directly in the substrate by a single operation is set such that the rotation speed of the spindle is 350-450rpm and the feed per revolution at the time of drilling is 0.122-0.128 mm.

Through making the drill bit set to including the chisel edge and radial consecutive edge chamfering, indent circular arc sword and interior straight sword to through the edge chamfering angle that sets up the edge chamfering, the height of drill point to indent circular arc sword bottom, the height of drill point to the edge chamfering, chisel edge oblique angle and interior straight sword oblique angle, can increase drill point department and hold the bits space, and keep the intensity of drill point, consequently be favorable to chip removal and heat dissipation, still do benefit to the centering of drill bit simultaneously, thereby improve form and position tolerance and machined surface roughness.

Through regrinding of the angle of the phi 8 drill bit, when 3mm thin-wall stainless steel is drilled, the existing phenomena of unqualified drilling roundness, hole position deformation and poor position precision are obviously improved, and the effect is very obvious. Through sampling detection on the processed product, the positioning size of two phi 8 holes which are most difficult to control is reduced from 0.2mm to 0.1 mm. And the number of the through holes which can be processed after the drill bit is polished each time is greatly increased.

For the drill bit, the spindle rotating speed and the feeding amount per revolution during drilling are properly set, so that chips can be well removed and heat can be well dissipated when an austenitic stainless steel substrate with the thickness of 3mm is drilled, the qualification rate of products is greatly improved, and the rejection rate of raw materials is reduced.

Drawings

FIG. 1 is a schematic view of a conventional drill bit (twist drill) machining a thin-walled part;

FIG. 2 is a schematic view of a drill bit of the present invention;

FIG. 3 is a schematic view of a drill bit of the present invention (various angles labeled);

FIG. 4 is a top view of the drill bit of the present invention;

FIG. 5 is a first live shot of the drill bit of the present invention;

FIG. 6 is a second live shot of the drill bit of the present invention;

FIG. 7 is a schematic view of a prior art thin plate tri-point drill for machining thin wall parts.

Detailed Description

The present invention is described in further detail below with reference to the attached drawing figures.

Referring to fig. 2-6, the drill main body is a phi 8 group drill structure, which comprises a chisel edge 1, and two sets of sequentially connected chamfered edges 4, concave arc edges 3 and inner straight edges 2 symmetrically arranged about the drill point axis, wherein the two inner straight edges 2 are respectively connected with two ends of the chisel edge 1;

the key points of the shape and the angle of the phi 8 drill bit are as follows:

1. sharpening chisel edge

The novel inner straight edge is ground from the drill point, the length of the chisel edge is shortened, the front angle of the chisel edge is increased, the chip containing space at the drill point is enlarged, the strength of the drill point is kept, the cutting feed force can be reduced, and no strict requirement is imposed on the grinding wheel fillet grinding. The length of the phi 8 chisel edge is omega 0.15mm-0.25mm, the inner straight edge bevel tau is 60 degrees, the chisel edge bevel psi is 0 degrees, and the chisel edge bevel of the common drill is 133-125 degrees. The chisel edge oblique angle is an included angle between the chisel edge and the main cutting edge (concave arc edge) in the end surface projection of the drill; the trimmed chisel edge is parallel to the middle section, so that the chisel edge oblique angle psi is 0 DEG or 180 DEG, and the chisel edge oblique angle psi is in the same direction and symmetrical with the cutting edges formed by the chamfered edges at the two sides, thereby increasing the rigidity of the drill point and being beneficial to uniformly transmitting cutting force; the uniform torque transmission is facilitated; is beneficial to the centering stability in the processing process.

2. Coping main cutting arc edge

As shown in fig. 7, the conventional common thin-wall drill grinds a concave arc edge, the depth of the arc of the groove is greater than the thickness of the thin-wall part, and a circular ring of an outer edge and a drill core is formed to sleeve materials. However, the method is not suitable for the stainless steel material with high toughness and high strength and difficult chip breaking, because the sheet of the jacking material generates plastic deformation, the formed sheet is clamped in the concave arc and is not easy to fall off, and when the next hole is drilled, the drill bit is easy to be broken due to the fact that the blade is extruded and deflected. Therefore, in the embodiment, the arc edge extension is ground, and the 45 ℃ excessive chamfering edge is added. The chamfering edge angle is an included angle of the whole chamfering edge relative to the end plane of the drill bit, and the chamfering edge angle has the following functions: chip removal and chip breaking are facilitated; the smoothness of the processed hole wall is improved; the chamfering edge forms two symmetrical peak angles, which is beneficial to the centering action of the drill bit and improves the form and position tolerance and the processing surface roughness.

The arc groove is smoothly transited to the chamfering edges at two sides, so that chips can be conveniently removed, and the edge of the grinding wheel is used for grinding the R2.5 arc surface. And then grinding the chamfered edges at the two sides. In the processing of stainless steel having high toughness, it is first considered to increase the strength of the chamfered edge and to prevent the chipping of the chamfered edge. Properly reduce the relief angle, make the drill bit become sharp, roll out banded iron fillings when falling arris sword and arc sword drilling, be favorable to the chip removal, be favorable to the heat dissipation.

3. Grinding chamfered edge

The 45-degree chamfering edge is polished to be sharper, so that the friction between ligaments and the hole wall is reduced, and the form and position tolerance and the surface roughness of the hole are improved. The plastically deformed circular sheet iron filings are not embedded in the arc edge of the drill point any more, so that the iron filings are not stuck to the cutter any more. The back angle of the chamfering edge is beta, 7 degrees, and the width v of the chamfering edge is 0.4 mm.

The drill bit disclosed by the invention has the following advantages in processing 3mm thin-wall stainless steel:

a: reducing the cutting face of the cutting area, thereby reducing the cutting force;

b: the cutting chips are convenient to rotate out, a large amount of cutting heat is brought out, and the cutter burning is prevented;

c: the three-point drill is automatically centered, the cutting force is symmetrical and uniform, the position degree of the positioning hole is ensured, and the product quality is ensured;

d: and the cutting amount is properly selected, so that the method is suitable for mass production. More than 1000 workpieces can be processed by grinding once.

The spindle rotation speed S350-450 is most suitable, and the feed amount F45-55 is most suitable. By calculating the feed per revolution Fz:

Fz＝F/S＝45/350＝0.128mm/r；

Fz＝F/S＝55/450＝0.122mm/r

therefore, the feeding amount per revolution during drilling is 0.122mm-0.128mm, the durability of the cutter per revolution is optimal, and the efficiency is best.

The statistics of the actual processing quality shows that the processing qualified rate of the product is improved by 99.8/100 compared with the original processing qualified rate. The economical processing causes the rejection rate of raw materials to be reduced to 99.8/100 from the original 95/100.

The structure drill point of the common drill bit is composed of a chisel edge, two side straight edges and an auxiliary back edge (edge zone) as shown in figure 1. The heat dissipation capability of the processed stainless steel is poor, and the stainless steel is easy to ablate; the thin-wall part is unstable in centering, cutting force is transmitted, and torque is unbalanced. The form and position tolerance of the hole is difficult to be accurate.

The common thin plate three-point drill structure is composed of a horizontal blade, two arc blades and two side blade bands as shown in figure 7, forms a three-point with a middle height and two sides slightly lower, the height from the drill point to the bottom of the concave arc is larger than the thickness of a thin plate workpiece, and three points and the concave arc blades on the two sides are matched for trepanning. However, thin-wall stainless steel has large plasticity variation, difficult chip breaking and easy knife sticking, and the iron chips are bonded in the concave circular arc, so that the continuous trepanning processing is difficult.

The thin-wall stainless steel drill bit is beneficial to transferring scrap iron and bringing cutting heat; high durability, stable centering and high form and position tolerance.

The embodiments of the present invention are described above with reference to the drawings, and the embodiments and features of the embodiments of the present invention may be combined with each other without conflict. The present invention is not limited to the above-described embodiments, which are only illustrative and not restrictive, and those skilled in the art can make many modifications without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A drilling method for an austenitic stainless steel thin-wall substrate is characterized in that a drill bit main body is of a phi 8 multi-drill structure, the drill bit comprises a chisel edge, and a chamfering edge, an inner concave arc edge and an inner straight edge which are symmetrically arranged relative to a drill tip axis and are sequentially connected from the radial outer side to the inner side, the two inner straight edges are respectively connected with two ends of the chisel edge, and the chamfering edge angle delta of the chamfering edge is 40-45 degrees; the height k from the drill point to the bottom of the concave arc blade is 1.3-1.5mm, and the height mu from the drill point to the chamfered blade point is 0.8-1 mm; the transverse edge bevel psi is 0 DEG, the inner straight edge bevel tau is 60-65 DEG, and the inner edge vertex angle 2 phi of the drill is 130-132 DEG; the vertex angle 2 eta of the outer edge is 123-125 degrees, and the inclination angle gamma of the cross edge of the drill is 89-90 degrees; the length omega of the cross edge is 0.15-0.2mm, the back angle alpha of the arc edge is 11-12 degrees, the radius chi of the arc edge is 2-3mm, and the back angle beta of the chamfered edge is 6-7 degrees; the width v of the chamfering edge is 0.3-0.45 mm; the thickness of the stainless steel thin-wall substrate is 3mm, the working state of the drill is set so that the rotating speed of the main shaft is 350-450rpm, and the feed per rotation during drilling is 0.122-0.128 mm, and the drill directly drills a hole on the substrate through a single operation in the working state.