CN110976992A

CN110976992A - Cutting tool

Info

Publication number: CN110976992A
Application number: CN201911300046.4A
Authority: CN
Inventors: 蒋益民; 徐龙; 安彦杰; 龚学武; 王文宝; 邹淋合; 杨海涛; 李军旗
Original assignee: Shenzhen Jingjiang Yunchuang Technology Co Ltd
Current assignee: Shenzhen Jingjiang Yunchuang Technology Co Ltd
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2020-04-10

Abstract

The invention provides a cutting tool. The cutting tool includes a cutting edge and a coating layer formed on the cutting edge. The cutting edge includes a rake surface, a relief surface and a cutting edge connected between the rake surface and the relief surface. The cutting edge comprises an exposed portion which is not covered by the coating. The coating includes a thickness gradient. The thickness of the thickness-varied portion becomes thinner as it is closer to the exposed portion and becomes thicker as it is farther from the exposed portion, and the thickness-varied portion satisfies Tmin/Tmax of not more than 0.58, where Tmin is the thickness at the thinnest end of the coating in the thickness-varied portion where the thickness of the coating is thinner, and Tmax is the thickness at the thickest end of the coating in the thickness-varied portion where the thickness of the coating is thicker. The width W of the exposed part is k Tmax, and k is more than or equal to 0.2 and less than or equal to 20.

Description

Cutting tool

Technical Field

The invention relates to the field of mechanical finish machining, in particular to a cutting tool capable of realizing super-finishing.

Background

With the continuous development of science and technology, the precision machining requirement on various workpieces is higher and higher. For example, metal cutting machining has been gradually developed from ordinary rough and finish machining to super-finish machining, a nano-scale machining stage. Even the cutting of the surface of a metal workpiece is expected to be able to achieve the mirror effect directly without subsequent polishing treatment.

Conventionally, a bare tool without a coating layer can be used for cutting a metal workpiece requiring relatively low machining accuracy and surface roughness. However, when high smoothness, high brightness of the cut surface, or super-finishing is required, it is necessary to perform machining using a tool protected by a hard coating. Because the uncoated bare cutter is used for processing metal materials, the cutting edge of the cutter is easy to stick scraps, and the cutting edge can be quickly worn during quick milling, so that the cut metal surface is fogged and not bright, and even transverse grains are generated, and the uncoated bare cutter can not be applied to the high-precision cutting processing of metals.

The hard coating has the characteristics of high hardness, oxidation resistance, wear resistance and the like, is widely applied to cutters, dies and mechanical wear-resistant parts, and can effectively meet the requirements on the performance and the service life of the cutters. However, the cutting tools protected by the coatings in the prior art also tend to have the following disadvantages: the surface finish of the coating of the cutting edge of the cutter is low, the consistency is poor, and the defects of liquid drops, pits, sawteeth and the like exist at the cutting edge; the coating of the cutting edge often has a broken film with the size of micron or more in the cutting process, which is easy to cause chip sticking. The practical trial of various coated cutters shows that the existing various coated cutters have low yield, high performance randomness and low yield on a machine, and cannot be applied in large quantities.

Aiming at the problem, many enterprises and research institutions at home and abroad continuously develop optimization and improvement on the coating process, and the main directions are the following two aspects:

firstly, aiming at the sputtering deposition process, the main defect is that the low energy of deposited particles leads to low bonding strength between a coating and a substrate and between coating grains and grains, so that the phenomena of breaking a film on a cutting edge and sticking chips during cutting processing are difficult to avoid. The improvement direction is to adopt high-energy pulse sputtering, which improves the particle bonding strength, but brings new problems, the furnace chamber has serious ash falling, and the surface smoothness is deteriorated because of the appearance of point-shaped particles on the surface of the coating, and simultaneously, the internal stress of the coating is increased, and the coating is cracked on the cutting edge. Currently, there is no suitable coating process for application to solve the above problems.

Secondly, aiming at the cathodic arc deposition process, the main problems are poor surface finish caused by liquid drops and local broken film caused by high stress of the film layer during cutting. The improved method is to reduce the liquid drop and stress by adjusting the speed of arc flow and arc spot, magnetic filtering, coating time, etc. to reduce the liquid drop and stress, and to reduce the liquid drop on the cutting edge by polishing after coating. The proposal improves the broken film caused by the liquid drops and the stress, but still has larger yield and service life problems, and has no obvious effect, so that the broken film caused by the liquid drops and the stress still has great improvement space.

In addition, in order to solve the influence of the liquid droplets in the coating layer on the surface of the processed product and improve the processing effect of the coated cutting tool, various methods for post-treating the cutting tool coating layer have been explored in recent ten years.

For example: japanese patent No. 2105396, No. 2825693 discloses a method of mechanically polishing a coating at a cutting edge.

For example: chinese patent 200210082479.9 discloses a method for passivating the coating by shot blasting the rake face of the coated edge.

For example: chinese patent application publication No. 201910133238.4 discloses another tool coating passivation method. The method selects the walnut sand of 160- & ltSUB & gt and 1000- & ltSUB & gt, and the coating passivation is carried out at the rotating speed of 10-80r/min for 10-15 min.

For example: the application published by the Chinese patent application No. 201711443229.2 also discloses a method for removing coating particles by using a drag type polishing passivation machine to polish a coating part for 30min in a forward rotation mode and 30min in a reverse rotation mode.

For example: US7090914B2 also discloses that the surface roughness of the coating is preferably limited to 0.2 microns or less.

Although the liquid drops on the coating can be reduced or removed or the surface roughness of the coating can be optimized to a predetermined range by the various coating post-treatment processes, no matter which coating passivation process is adopted, the coating on the cutting edge of the tool after the coating passivation treatment is extremely easy to locally peel off after the tool is used for a period of time, so that the processed surface forms scratches or cutting lines, and the tool tip is easy to be sticky. In summary, the performance of the various coating process optimization methods and the coated cutting tools after coating treatment cannot meet the practical requirements, the yield on the machine is very low, and mass production and application cannot be performed at all.

Disclosure of Invention

In view of this, it is necessary to provide a cutting tool with low coating internal stress, good consistency of cutting edge, and being not easy to stick chips, and capable of realizing super-finishing.

Preferably, the length L of the gradual change in the thickness of the coating is m Tmax, where cot60 DEG m DEG cot3 deg.

Preferably, the coating includes a uniform thickness portion connected to the end of the thickness gradient portion where the thickness of the coating is thicker, the uniform thickness portion having a thickness equal to the thickness of the thickest end of the coating.

Preferably, the thickness of the coating layer at the end of the coating layer having the thinner thickness gradually changing part is 0.

Preferably, the thickness gradually-varying portion includes a thickness gradually-varying portion located on the rake face side and a thickness gradually-varying portion located on the flank face side, and a length Lrear of the thickness gradually-varying portion coating located on the flank face side is greater than a length Lfront of the thickness gradually-varying portion coating located on the rake face side.

Preferably, the thickness gradually varying portion includes a thickness gradually varying portion on the rake face side and a thickness gradually varying portion on the flank side, and a thickness Tmax _ rear at the thickest end of the thickness gradually varying portion coating on the flank side and a thickness Tmax _ front at the thickest end of the thickness gradually varying portion coating on the rake face side satisfy | Tmax _ rear/Tmax _ front-1| ≦ 0.15.

Preferably, Lrear/Tmax _ rear of the thickness gradation portion coating on the flank side is larger than Lfront/Tmax _ front of the thickness gradation portion coating on the rake face side.

Preferably, the cutting edge comprises an intermediate region. The cutting edge middle area comprises a convex curved surface. The curvature of the convex curved surface is larger than the curvatures of the front cutter surface and the rear cutter surface. The edge center region includes the above-described exposed portion.

The prior art generally considers that the cutting edge is more easily worn in high-speed cutting because the closer the cutting edge is to the cutting edge, the smaller the angle is, the thinner the structure is, and therefore a hard coating must be used to cover the cutting edge, and a certain thickness of the coating of the cutting edge is ensured after the subsequent passivation treatment, so that the sufficient protection of the 'fragile' cutting edge can be provided.

However, the applicant has found that if the cutting edge is covered with a coating, a two-phase structure of the cutting edge substrate and the coating material is formed at the cutting edge of the cutting edge. Therefore, the consistency of the microstructure of the cutting edge of the cutter is difficult to ensure no matter what coating deposition process and what coating material are adopted. Therefore, the tool yield is low and the performance randomness is high.

The invention overcomes the inherent technical bias of the prior art, exposes the middle area of the cutting edge and arranges the coating with gradually changed thickness. Because the exposed cutting edge is completely made of one-phase material of the cutting edge base material, the consistency of the cutting edge is naturally ensured, and the problems of different thicknesses, liquid drops, stress concentration and the like of the cutting edge coating in the prior art are thoroughly avoided. When cutting, the workpiece is cut by mainly utilizing the exposed cutting edge base material, and the exposed cutting edge is completely made of a single material and has better consistency, so that the cutting performance is obviously improved. Meanwhile, the invention mainly utilizes the functions of lubrication, chip guiding and chip removal of the coating with gradually changed thickness instead of the functions of increasing wear resistance and assisting cutting of the hard coating, reduces the adhesion of chips and the cutter by reducing the friction in the cutting process so as to inhibit the generation of accumulated chips, thereby reducing the abrasion of the cutter, improving the quality of the processed surface and prolonging the service life of the cutter. Through the combination of the exposed structure of the cutting edge and the coating with a gradual thickness variation, a technical effect which is not expected by the person skilled in the art is obtained.

Meanwhile, the coating near the cutting edge is designed to be gradually changed in thickness, the gradually changed thickness part is ensured, and the condition that Tmin/Tmax is less than or equal to 0.58 is met (wherein Tmin is the thickness of the thinnest part of the coating at the gradually changed thickness part, and Tmax is the thickness of the thickest part of the coating at the gradually changed thickness part). The thickness of the thickness gradient part is thinner and thicker as the thickness of the thickness gradient part is closer to the exposed part, and the width W of the exposed part is k Tmax, wherein k is more than or equal to 0.2 and less than or equal to 20. Such design can avoid or reduce the liquid drop of near blade coating to a great extent and reserve, has solved the garrulous membrane problem that collapses that blade position stress too high leads to simultaneously.

In addition, the invention designs the coating structure of the cutting tool into the concept that the cutting edge part is exposed and the coating thickness at the cutting edge is gradually distributed, thereby greatly expanding the application scene of the cutting tool compared with the conventional coating tool, not only realizing the highlight and high-mirror surface cutting of metal, but also realizing the superfinishing and nanofabrication of other metal alloys, plastics and composite materials thereof.

For example, the cutting tool designed by the coating structure can be directly applied to the processing of a die, and the die steel can be directly cut into a high-finish mirror surface die cavity surface without subsequent polishing treatment.

In addition, the cutting tool with the coating structure has unexpected processing effect on processing plastic materials, for example, the processing with high dimensional precision can be realized on the processing of holes and grooves of a PCB, and importantly, the directly processed groove holes are clean and are not easy to generate rough edges and burrs of the groove holes.

Drawings

Fig. 1 is a schematic perspective view of a chamfer milling cutter for processing a chamfer structure of an earphone according to an embodiment of the present invention.

Fig. 2 is a schematic view of a processing state of the chamfer milling cutter shown in fig. 1 for processing the chamfer of the earphone.

Fig. 3 is a partially enlarged schematic view of the cutting edge of the chamfer cutter shown in fig. 1 at circle III.

Fig. 4 is a schematic perspective view of a contour milling cutter for processing a mobile phone housing according to an embodiment of the present invention.

Fig. 5 is a schematic view illustrating a state of the contour milling cutter shown in fig. 4 processing the mobile phone housing.

Fig. 6 is a cross-sectional view of the contour cutter of fig. 4 taken along the direction VI-VI.

Fig. 7 is a partially enlarged schematic view of the cutting edge of the contour cutter shown in fig. 6 at circle VII.

FIG. 8 is a micro-topography of the cutting edge of the magnetron sputtering coating tool A before coating treatment in the comparative test of the present invention.

FIG. 9 is a micro-topography of the cutting edge of a cathodic arc evaporation coated cutting tool B before coating treatment in a comparative test of the present invention.

FIG. 10 is a microscopic view of the edge of magnetron sputtering coated tool A after coating treatment to make the coating thickness uniform (i.e. tool set A1).

FIG. 11 is a microscopic view of the cutting edge of the cathodic arc evaporation coated tool A after coating treatment to provide uniform coating thickness distribution (i.e., B1 sets of tools).

Fig. 12 is a cross-sectional microscopic view of the cutting edges of the tool of group a1 shown in fig. 10.

Fig. 13 is a cross-sectional microscopic view of the cutting edges of the B1 set of cutters shown in fig. 11.

FIG. 14 is a microscopic view of a partially exposed edge of magnetron sputtering coating tool A coated with a graded coating thickness (i.e., tool set A2).

Fig. 15 is a microscopic topography of the partially exposed edges of the coated cathodic arc evaporation coated tool B with a coating treatment having a gradual coating thickness distribution (i.e., B2 sets of tools).

Fig. 16 is a cross-sectional microscopic view of the cutting edge of the tool of group a2 shown in fig. 14.

Fig. 17 is a cross-sectional microscopic view of the cutting edges of the B2 set of cutters shown in fig. 15.

Description of the main elements

Knife handle 10

Cutting

part

20, 50

Earphone 30

Mobile phone outer frame 60

Cutting

edge

21, 51

Chip groove 23

Rake face

211, 511

Flank surface

212, 512

Cutting

edges

213, 513

Near

rake surface area

216, 516

Near

relief area

218, 518

Intermediate areas

219, 519

Near

rake edge coating

252, 552

Near-

relief edge coating

254, 554

Homex coating

257, 259, 557, 559

The following detailed description will further illustrate the invention in conjunction with the above-described figures.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. When an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Referring to fig. 1, an embodiment of the present invention is applied to a chamfer milling cutter. It should be noted, however, that the application of the inventive concept of the graded thickness coating structure of the present invention is not limited to milling cutters, but can also be applied to other cutting tools, such as: taps, drills, reamers, boring cutters, and the like. Such cutting tools applying the inventive concept should be considered within the scope of the present invention.

The chamfer milling cutter comprises a cutter handle 10 and a cutting part 20 arranged at one end of the cutter handle 10. The shank is integrally formed with the cutting portion 20. In other applications, the milling cutter may also be a combined cutter of a cutter head and an insert, in which case the cutting edges 20 are provided on the insert. Whether a unitary cutter or a gang cutter is considered to be within the scope of the present invention.

In the present embodiment, the chamfer cutter is used to machine a chamfer structure of the earphone 30 (see fig. 2). The earphone chamfer structure matrix is made of stainless steel (SUS316-Li), the tool holder 10 and the cutting part 20 are made of hard alloy, and the material of the cutting part 20 can be replaced by other suitable materials according to different cutting materials, such as carbon tool steel, alloy tool steel, high-speed steel, ceramic and the like, which should be considered as being within the protection scope of the present invention.

The cutting part 20 includes a plurality of cutting edges 21, a plurality of chip flutes 23 provided corresponding to the cutting edges, and a coating layer formed on the cutting edges 21. In the present embodiment, the material of the coating is an AlCrN coating, but the inventive concept is not limited to a specific material, and the material of the coating may be replaced by other materials, such as DLC coating, cubic boron nitride coating, TiN coating, TiC coating, TiCN coating, TiAlN coating, CrN coating, TiSiN coating, a12O3 coating, etc., or various composite coatings, such as nitride/nitride coating, nitride/carbide coating, nitride or carbide/metal coating, nitride/oxide coating, etc., which should be considered to be within the protection scope of the present invention. The chip groove 23 plays a role in guiding metal chips, so that the metal chips generated during cutting can be smoothly discharged from the chip groove 23.

Each cutting edge 21 includes a rake surface 211 and a flank surface 212, and an edge 213 where the rake surface intersects the flank surface (see fig. 3). Referring to fig. 3, fig. 3 is an enlarged view of the cutting edge 213 of the cutting blade 21. The edge 213 comprises a near rake region 216 that adjoins the rake face 211, a near relief region 218 that adjoins the relief face 212, and an intermediate region 219 that connects between the near rake region 216 and the near relief region 218. The intermediate region 219 has an exposed area that is not covered by the coating.

In this embodiment, the edge mid-region 219 includes a convex curved surface (also referred to as an R-angle) having a curvature greater than the curvatures of the rake surface 211 and the flank surface 212. The helix angle of the chamfer cutter in this embodiment is 0, and the rake face 211 and the flank face 212 are substantially flat near the cutting edge 213, and each point has a curvature of 0, i.e., smaller than that of the convex curved surface.

Microscopically, the rake face 211 and the flank face 212 extend in the direction of the cutting edge 213 and finally extend to the region of the cutting edge 213 where the cutting edge is cut for contact friction with the workpiece, as observed by a scanning electron microscope. In the region of the edge 213, the edge near rake region 216 and the edge near flank region 218 continue to connect finally to a curved surface, i.e., the R-angle, which is convex and has a large curvature. The convex curved surface is observed from the macro, namely the position of the sharpest edge point of the cutting edge is also the main action area for the contact friction with the processed product to cut. The region of the cutting edge containing the convex curved surface is defined as a cutting edge middle region 219.

It should be noted that the definition of the edge near rake region 216 and the edge near flank region 218 is merely to facilitate the reader's understanding of the relative positions of the thickness graded coating deposited thereon, and that there are no objective physical boundaries between the edge near rake region 216 and the rake face 211, and between the edge near flank region 218 and the flank face 212. The thickness gradient coating may extend from the edge exposure area to the rake face 211 or the flank face 212, or may be present only in the area of the edge 213.

The coating includes a near-rake edge coating 252 formed on the near-rake region 216 of the edge 213, and a near-relief edge coating 254 formed on the near-relief region 228 of the edge. The near-rake edge coating 252 and the near-relief edge coating 254 both decrease in thickness in a direction closer to the exposed region of the edge.

To reduce the stress at the edge and improve the uniformity at the edge, the thickness gradient, i.e., the near-rake edge coating 252 and the near-relief edge coating 254, both have a thickness Tmin/Tmax of less than or equal to 0.58, where Tmin is the thickness at the thinnest end of the coating at the thinner thickness gradient of the coating and Tmax is the thickness at the thickest end of the coating at the thicker thickness gradient of the coating.

In this embodiment, the near-rake edge coating 252 gradually decreases in thickness in a direction near the edge exposure region and finally decreases to 0 at the edge mid-region 219. The near relief edge coating 254 gradually decreases in thickness in the direction near the exposed edge region and finally decreases to 0 at the exposed edge region.

It should be noted that the cutting edge profile design will vary depending on the cutting needs of different machined workpieces, and therefore, in some cutting edge profile configurations, only either the near-rake edge coating 252 or the near-relief edge coating 254 may be designed to have a decreasing thickness in a direction near the edge exposure region, while the other edge coating remains uniform in thickness. Such cutting tools of varying designs are considered to be within the scope of the present invention.

The applicant has found that if the coating thickness is treated to be gradually distributed, and the thickness gradient portion is made to satisfy Tmin/Tmax ≦ 0.58, and a part of the region of the cutting edge 213 is completely exposed so as not to be covered with the coating, the cutting effect and the yield of the machining of the tool in which the cutting edge is completely covered with the coating are better. However, the term "exposed" in the present invention means not covered by the hard coating, but covered by other soft materials, such as polymer coating, organic material coating, and the like, and still considered to be exposed, and shall be considered to fall within the scope of the present invention.

To further obtain better edge uniformity, the width W of the exposed portion may preferably satisfy the following condition: w is k Tmax, wherein k is more than or equal to 0.2 and less than or equal to 20. The reason for optimizing the width W of the exposed portion to this range is on the one hand that the width W of the exposed portion cannot be too small. The width of the exposed part is too small, the structure is similar to that of a full-coating cutter, and the consistency of the cutting edge of the cutter is difficult to ensure. On the other hand, the width W of the exposed part cannot be too large, the exposed part is similar to a bare blade when the width W of the exposed part is too large, the blade edge of the bare blade is easy to stick scraps, the cutting effect can fog and fog, and transverse lines are generated. It should be noted that the thickness Tmax of the coating at the thickest end of the coating at the portion where the thickness of the coating is thicker in the thickness-varied portion of the coating of the present invention is not limited to a specific range, and a specific Tmax and the width W of the bare portion may be designed according to the cutting requirements of a specific product.

To further obtain better cutting performance, the length L of the coating thickness gradually-changing portion may preferably satisfy the following condition: l-m Tmax, wherein cot60 ° ≦ m ≦ cot3 °.

It should be noted that the cutting tool of the present invention is not limited to a specific size, and the length L of the coating thickness gradually varying portion, the thickness Tmax of the thickest coating portion at the thicker end of the coating thickness gradually varying portion, and the width W of the exposed portion of the cutting edge can be determined according to the actual cutting requirements and the above-mentioned relation, regardless of the blade diameter.

The chamfer cutter in this example had a blade diameter of 6mm, a thickness Tmax of the coating layer at the end of the coating thickness gradient portion where the coating thickness was thicker was about 0.6 to 0.8. mu.m, a length L of the coating thickness gradient portion was about 2.6 to 3.1. mu.m, and a width W of the bare portion was about 1.2. mu.m.

In the present embodiment, the length Lrear of the near-flank edge coating 254 on the flank side is greater than the length Lfront of the near-flank edge coating 252 on the rake side.

In this embodiment, the coating includes a uniform thickness coating 257 formed on the rake surface 211, and a uniform thickness coating 259 formed on the flank surface 212. It should be noted that the attachment location of the blanket coating 257 and the near-rake edge coating 252 is not limited to a fixed location and may be located on the rake surface 211 or the near-rake region 216 of the edge. Similarly, the location of the connection between the uniform thickness coating 259 and the near-flank edge coating 254 is not limited to a fixed location, and may be located in the near-flank region 218 of the flank 212 or edge. Such cutting tools of varying designs are considered to be within the scope of the present invention.

Preferably, the thickness Tmax _ real where the thicker one-side overcoat of the near-relief edge coating 254 on the flank side is thickest and the thickness Tmax _ front where the thicker one-side overcoat of the near-rake edge coating 252 on the rake face side is thickest satisfy | Tmax _ real/Tmax _ front-1| ≦ 0.15. In the present embodiment, the thickness Tmax _ real at the thickest end of the near-relief edge coating 254 on the flank side is substantially equal to the thickness Tmax _ front at the thickest end of the near-relief edge coating 252 on the rake side.

In the present embodiment, Lrear/Tmax _ ear of the near-flank edge coating 254 on the flank side is larger than Lfront/Tmax _ front of the near-flank edge coating 252 on the rake face side.

Referring to fig. 4, fig. 4 shows an embodiment of the present invention applied to a contour milling cutter. In this embodiment, the contour milling cutter is used for processing the contour of the handset casing 60 (see fig. 5). In order to cut and process the appearance contour of a product, the rotary projection of the cutting edge of the contour milling cutter is a semi-closed concave curved surface. In this embodiment, the material of the mobile phone casing is stainless steel (SUS316-Li) or aluminum alloy (AL7K03), and a part of the material includes super-hard engineering plastic and fiber composite material. The contour milling cutter adopting the coating structure concept of the invention not only can realize the cutting processing of the semi-closed concave curved surface with larger processing difficulty, but also can directly cut the metal outer frame into a high-gloss mirror surface effect without subsequent polishing treatment.

Referring to fig. 6, the contour milling cutter of the present embodiment includes a plurality of cutting edges 51 extending spirally and a coating layer formed on the cutting edges 51. In the present embodiment, the contour cutter has 4 cutting edges 51. It should be noted that the cutting edges of the present invention are not limited to a particular number, and cutting tools having at least one cutting edge should be considered within the scope of the present invention as long as the coating structure of the present invention is contemplated.

Fig. 7 shows a microscopic enlargement of one of the cutting edges. Although the rake face and the flank face are both macroscopically curved surfaces extending spirally, on a microscopic scale, the rake face and the flank face are both approximately planar in cross section, and have a curvature that is also significantly smaller than the convex curved surface at the cutting edge 513.

The cutting edge 51 includes a rake surface 511, a flank surface 512 and an edge 513 connected between the rake surface and the flank surface. Referring to fig. 8, the edge 513 includes a near rake region 516 adjoining the rake surface 511, a near relief region 518 adjoining the relief surface 512, and an intermediate region 519 connecting between the near rake and near relief regions. The central region 519 comprises an exposed area not covered by the coating described above.

The coatings include a near-rake edge coating 552 formed on the edge 513 in the near-rake region 516 and a near-relief edge coating 554 formed on the edge near-relief region 518. The near-rake edge coating 552 and the near-relief edge coating 554 both decrease in thickness in a direction closer to the edge exposure area. In this embodiment, the lower thickness end coating of both the near-rake edge coating 552 and the near-relief edge coating 554 reduces the thickness to 0 near the edge exposure region. It should be noted that the thickness of the thinner end of the coating thickness gradually varying portion may be other than zero, but if not zero, Tmin/Tmax ≦ 0.58 should be satisfied.

In the present embodiment, the length Lrear of the near-relief edge coating 554 on the flank side is greater than the length Lfront of the near-rake edge coating 552 on the rake side. The thickness Tmax _ real at the thicker endmost coating of the near-relief edge coating 554 on the flank side is equal to the thickness Tmax _ front at the thicker endmost coating of the near-rake edge coating 552 on the rake side.

The blade diameter of the profile cutter in this example was 16mm, the thickness Tmax of the end coating at the thicker end of the coating thickness gradient was about 1.2 μm, the length L of the coating thickness gradient was about 4.0 to 4.6 μm, and the width W of the bare portion was about 2.2 μm.

Even for the concave semi-closed contour, the uncoated exposed area of the cutting edge can be cut lightly, and chips can smoothly slide out from the smooth and defect-free coated surface, so that the cutting edge is not easy to stick chips. Meanwhile, because the area of the uncoated region of the cutting edge is within a specific range, the front cutter face and the rear cutter face of the cutter are still coated, the cutting heat is not easy to transfer to the inside of the cutter, the abrasion degree of the cutter is greatly reduced, and the service life of the cutter can be greatly prolonged. Because the exposed area of the cutting edge without the coating has no unevenness and better consistency, a high-finish transitional surface is easy to obtain during cutting, thereby meeting the required product processing requirements.

To further illustrate the technical effects of the present invention which are unexpected to those skilled in the art by the concept of bare edge and gradient thickness coating configuration, comparative experiments of a gradient thickness coated tool with the existing uniform thickness coated tool are described below.

Coating scheme

Referring to table one, a coated cutting tool a (see fig. 8) and a coated cutting tool B (see fig. 9) are first manufactured by a magnetron sputtering apparatus and a cathode arc apparatus, respectively. As can be seen, the coating directly prepared by either the magnetron sputtering process or the arc evaporation process has droplets.

The prepared cutters A and B are divided into two groups, namely, the magnetron sputtering coating cutter A is divided into A1 groups and A2 groups, and the cathode arc evaporation coating cutter B is divided into B1 groups and B2 groups. Then, the two groups a1 and B1 go through conventional post-coating processes, such as: and the polishing and other processes reduce or remove the defects of liquid drops and the like on the surface of the coating. FIG. 10 is a microscopic view of the cutting edge of magnetron sputter coated tool A after conventional post-processing to remove droplets (i.e., tool set A1). Fig. 11 is a microscopic view of the cutting edge of the cathodic arc evaporation coated tool B after conventional post-processing to remove droplets (i.e., B1 sets of tools). Fig. 12 is a cross-sectional microscopic view of the cutting edges of the tool of group a1 shown in fig. 10. Fig. 13 is a cross-sectional microscopic view of the cutting edges of the B1 set of cutters shown in fig. 11. As can be seen from fig. 12 and 13, the thickness of the edge coating was substantially uniform for both the magnetron sputtering coating cutter group a1 and the cathodic arc evaporation coating cutter group B1 after conventional post-coating treatments.

The cutters of the A2 group and the B2 group are coated by a coating post-treatment process to become gradually thinner as the thicknesses of the cutters are closer to the middle area of the cutting edge. FIG. 14 is a microscopic edge profile of magnetron sputtering coating tool A after coating post-treatment to provide a graded coating thickness profile (i.e., tool set A2). Fig. 15 is a edge micro-topography of a cathodic arc evaporation coated tool B after post-coating treatment to provide a graded coating thickness profile (i.e., B2 sets of tools). Fig. 16 is a cross-sectional microscopic view of the cutting edge of the tool of group a2 shown in fig. 14. Fig. 17 is a cross-sectional microscopic view of the cutting edges of the B2 set of cutters shown in fig. 15. As can be seen, the tools of group a2 and group B2 had left a portion of the middle region at the edge exposed and uncovered by the coating after the coating post-treatment, and the thickness of the coating gradually decreased in a direction approaching the exposed region of the edge (see fig. 16, and fig. 17).

And then carrying out comparison of the high-gloss cutting effect by taking the cutter groups A1, A2, B1 and B2 respectively, wherein the cutting parameters are shown in a table II.

Table two cutting plan parameters

The specific scheme data and result data are as follows:

table three comparison results

It should be noted that although the coating deposition processes selected as comparative in this comparative experiment were magnetron sputtering and cathodic arc evaporation, the inventive concept was not limited to the kind of coating deposition process nor to the kind of coating material as verified by various experiments. Compared with the practical application, the cutting edge is exposed, the coating thickness at the cutting edge is processed to be gradually distributed, and compared with the coating cutter with uniformly distributed thickness, the cutting performance and the on-machine yield of the coating cutter are greatly improved no matter which coating deposition process is adopted or different coating materials are changed.

In conclusion, the cutting tool of the present invention is used for cutting the exposed substrate at the cutting edge instead of the coating at the cutting edge. The coating structure of the present invention functions primarily to increase lubrication for chip guiding and chip removal, rather than covering and protecting the cutting edge as in the prior art, and to undertake cutting of the workpiece. The invention overcomes the technical prejudice that the high-precision machining cutting tool in the prior art must be covered with a coating at the cutting edge. By the structural design of the substrate of the exposed cutting edge part and the coating with gradually changed thickness, the cutting processing with high precision and high finish degree is realized.

Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A cutting tool comprising a cutting edge and a coating formed on the cutting edge, the cutting edge comprising a rake face, a flank face and a cutting edge connecting between the rake face and the flank face, the cutting edge comprising an exposed portion not covered by the coating, the coating comprising a thickness taper portion, the thickness taper portion being thinner the closer the thickness to the exposed portion and thicker the farther the thickness from the exposed portion, the thickness taper portion satisfying Tmin/Tmax ≦ 0.58, wherein Tmin is the thickness at the thinnest end of the coating in the thickness taper portion, Tmax is the thickness at the thickest end of the coating in the thickness taper portion, the width W ═ k ≦ Tmax of the exposed portion, and 0.2 ≦ 20.

2. The cutting tool of claim 1, wherein: the length L of the coating thickness gradient is m Tmax, wherein cot60 DEG-m DEG-3 deg.

3. The cutting tool of claim 1, wherein: the coating comprises a uniform thickness part connected with one end of the gradual thickness change part where the thickness of the coating is thicker, wherein the thickness of the uniform thickness part is equal to that of the thickest part of the thicker end of the coating.

4. The cutting tool of claim 1, wherein: the thickness of the coating layer at the end of the coating layer with the thinner thickness gradually decreases to 0.

5. The cutting tool of claim 1, wherein: the thickness gradually-varying portion includes a thickness gradually-varying portion located on the front blade surface side and a thickness gradually-varying portion located on the flank surface side, and a length Lrear of the thickness gradually-varying portion coating located on the flank surface side is greater than a length Lfront of the thickness gradually-varying portion coating located on the front blade surface side.

6. The cutting tool of claim 1, wherein: the thickness gradually varying portion includes a thickness gradually varying portion on the rake face side and a thickness gradually varying portion on the flank face side, and a thickness Tmax _ real at the thickest end of the thickness gradually varying portion coating on the flank face side and a thickness Tmax _ front at the thickest end of the thickness gradually varying portion coating on the rake face side satisfy | Tmax _ real/Tmax _ front-1| ≦ 0.15.

7. The cutting tool of claim 1, wherein: the thickness gradually varying portion includes a thickness gradually varying portion on the rake face side and a thickness gradually varying portion on the flank face side, and Lrear/Tmax _ ear of the thickness gradually varying portion coating on the flank face side is larger than Lfront/Tmax _ front of the thickness gradually varying portion coating on the rake face side.

8. The cutting tool of claim 1, wherein: the cutting edge comprises a middle region, the middle region of the cutting edge comprises a convex curved surface, the curvature of the convex curved surface is greater than the curvatures of the front cutter surface and the rear cutter surface, and the middle region of the cutting edge comprises the exposed part.