CN118385632B - Cutting blade with convex coating unit on rear surface - Google Patents

Abstract

The invention discloses a cutting blade with a convex coating unit on the back face, comprising a plate-like substrate, the plate-like substrate comprising an upper surface, a lower surface and a side surface connecting the upper surface and the lower surface, the side surface and the upper surface intersecting to form a plurality of cutting edge units, the cutting edge unit comprising a main cutting edge, an angle cutting edge and a secondary cutting edge, the side surface comprising a first back face and a second back face, the first back face being located above the second back face, the first back face being provided with a non-cutting area and a back cutting area involved in cutting, the first back face being provided with two layers of cutting coatings, namely a first coating and a second coating located outside the first coating, the first coating having the same microscopic composition at various locations and completely covering the first back face, the second coating being composed of more than one convex coating unit arranged in the back cutting area, the thickness of the convex coating unit being h1, and satisfying the following requirements: 1µm≤h1≤5µm, the blade has the advantages of high cutting performance, high matching degree of performance of each cutting edge, long service life and the like.

Description

A cutting insert with a convex coating unit on the back face

Technical Field

The invention mainly relates to the field of metal cutting tools, and in particular to a cutting blade with a convex coating unit on the back surface.

Background Art

In order to ensure the cutting performance of the cutting blade during cutting, cemented carbide with good strength is generally used as the substrate of the cutting blade. The industry has found that using pure cemented carbide as the blade material will cause greater friction during cutting and easily generate built-up edge during cutting. It can only be used in processing occasions that do not require high cutting speeds, and the blade life is short. However, a certain thickness of refractory hard compounds such as carbides, nitrides, oxides, etc. are coated on the surface of cemented carbide, so that the surface of the cutting blade has higher hardness, wear resistance, high heat resistance, low friction coefficient and eliminates built-up edge. It also allows the cutting blade cutting speed to be increased by more than 70%, which can greatly improve the cutting performance and service life of the cutting blade. The temperature required to prepare the coating is high and the control process is complex. In order to reduce the difficulty of manufacturing, the surface of the cutting blade usually uses a coating with the same structure and thickness.

During the cutting process of the blade, the area that is squeezed and rubbed against the processed surface is the back cutting area of the blade. When processing ordinary materials, as the wear value of the back cutting area increases, the cutting resistance increases, which can easily lead to the shedding of the coating in the back cutting area, that is, the back cutting area of the blade is prone to collapse and failure, especially for drilling blades. The rapid wear of the back tool surface mainly occurs in the key area of the back cutting area. If the service life of the cutting blade is to be guaranteed, the back cutting area must have a certain coating thickness. However, during the coating preparation process, the cutting edge stress is large, and the coating at the cutting edge where the side and the upper surface intersect is too thick, which can easily cause the coating to peel off at the cutting edge, affecting the qualified rate of blade production.

Summary of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a cutting blade with a convex coating unit on the back face having high cutting performance, high matching degree of performance of each cutting edge and long service life.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

A cutting blade with a convex coating unit on the back cutting surface, comprising a plate-like substrate, the plate-like substrate comprising an upper surface, a lower surface and a side surface connecting the upper surface and the lower surface, the side surface and the upper surface intersecting to form a plurality of cutting edge units, the cutting edge unit comprising a main cutting edge, an angle cutting edge and a secondary cutting edge, the side surface comprising a first back cutting surface and a second back cutting surface, the first back cutting surface being located above the second back cutting surface, the first back cutting surface being provided with a non-cutting area and a back cutting area involved in cutting, two layers of cutting coatings being provided on the first back cutting surface, namely a first coating and a second coating located outside the first coating, the first coating having the same microscopic composition at various locations and completely covering the first back cutting surface, the second coating being composed of more than one convex coating unit arranged in the back cutting area, the thickness of the convex coating unit being h1, which should satisfy the following: 1µm≤h1≤5µm.

As a further improvement of the above technical solution:

The thickness of the first coating is h, which should satisfy: h1≤h≤2h1.

The convex coating unit has a different microstructure from the first coating.

The convex coating unit has a different color from the outer surface of the first coating.

The convex coating unit on the second coating is arranged on the rear cutting area.

The convex coating unit on the second coating layer is arranged on the non-cutting area.

The rear cutting area includes a main wear surface, an angle wear surface and an auxiliary wear surface corresponding to the main cutting edge, the angle cutting edge and the auxiliary cutting edge respectively.

The convex coating unit is arranged on the main wear surface and/or the corner wear surface and/or the secondary wear surface.

The non-cutting area includes a non-main wear surface, a non-corner wear surface and a non-secondary wear surface corresponding to the main cutting edge, the corner cutting edge and the secondary cutting edge respectively.

The convex coating unit is arranged on the non-primary wear surface and/or the non-corner wear surface and/or the non-secondary wear surface.

The convex coating unit on the main wear surface is a main front convex coating unit, and the main front convex coating unit extends to be adjacent to the angular wear surface. The maximum length of the main front convex coating unit in the cutting depth direction of the corresponding main cutting edge is y1, and the maximum cutting length of the main cutting edge is y, which should satisfy: 0.4y≤y1≤0.6y.

The convex coating unit on the secondary wear surface is a secondary front convex coating unit, which extends to be adjacent to the angular wear surface. The maximum length of the secondary front convex coating unit in the cutting depth direction of the corresponding secondary cutting edge is x1. The maximum cutting length of the secondary cutting edge is x, which should satisfy: 0.2x≤x1≤0.5x.

The convex coating units on the main wear surface, the angular wear surface and the secondary wear surface are respectively the main front convex coating unit, the angular front convex coating unit and the secondary front convex coating unit, and the heights of the main front convex coating unit, the angular front convex coating unit and the secondary front convex coating unit on the side are respectively D1, D2 and D3, which should satisfy: 0.3mm≤D1≤0.8mm, 0.3mm≤D2≤0.8mm, 0.3mm≤D3≤0.8mm.

The minimum clearances between the main convex coating unit, the corner convex coating unit and the secondary convex coating unit and the main cutting edge, the corner cutting edge and the secondary cutting edge on the side are d1, d2 and d3 respectively, and should satisfy: 0.01mm mm≤d1≤0.2mm, 0.01mm mm≤d2≤0.2mm, 0.01mm mm≤d3≤0.2mm.

Compared with the prior art, the advantages of the present invention are:

The cutting blade of the present invention has a convex coating unit on the back face, and two layers of cutting coatings are provided on the first back face, namely a first coating and a second coating located outside the first coating, the first coating has the same microscopic composition at all places and completely covers the first back face, the second coating is composed of more than one convex coating unit arranged in the back cutting area, the thickness of the convex coating unit is h1, and satisfies: 1µm≤h1≤5µm, and by arranging the convex coating unit on the back cutting area of the first back face, the overall thickness of the coating in the back cutting area where the convex coating unit is provided is greater than that in other areas, that is, the convex coating unit is arranged in the key area where the back cutting area contacts the chips, the overall thickness of the cutting coating in the key area is increased, the coating peeling problem is solved, and the cutting process is avoided. Avoid rapid wear and chipping in the rear cutting area. In particular, according to the difference in cutting function of each cutting edge, the thickness of the convex coating unit and the material (friction coefficient, etc.) can be optimized to reduce the deformation of chips on the first rear tool face and reduce the cutting force, so that the performance and service life of each cutting edge can be matched, and the performance stability and service life of the tool can be improved. In addition, the convex coating unit is set on the rear cutting area, and it can be set to have a certain gap between the edge of the convex coating unit and the cutting edge of the cutting edge unit, that is, there is only the first coating on the first rear tool face adjacent to the cutting edge, which can better control the overall thickness of the cutting coating at the cutting edge, avoid the chipping of the cutting edge due to the large stress deformation at the cutting edge when preparing the coating, and improve the qualified rate of blade production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a perspective structural diagram of a first embodiment of a cutting insert having a convex coating unit on the flank surface of the present invention;

FIG2 is a top view of a first embodiment of a cutting insert having a convex coating unit on the flank surface of the present invention;

3 is a front view of a first embodiment of a cutting insert having a convex coating unit on the flank surface of the present invention;

4 is a left side view of a first embodiment of a cutting insert having a convex coating unit on the flank surface of the present invention;

Fig. 5 is an enlarged view of point A in Fig. 1;

6 is a perspective structural diagram of a second embodiment of a cutting insert having a convex coating unit on the flank surface of the present invention;

7 is a top view of a second embodiment of a cutting insert having a convex coating unit on the flank surface of the present invention;

8 is a schematic diagram of the thickness of the first coating and the second coating of the cutting blade having a convex coating unit on the flank surface of the present invention;

FIG. 9 is a schematic diagram of a cutting insert having a convex coating unit on the back face of the present invention when cutting a workpiece.

The symbols in the figure represent:

1. Plate-like substrate; 2. Upper surface; 3. Lower surface; 4. Side surface; 41. First flank surface; 42. Second flank surface; 411. Flank cutting area; 4111. Main wear surface; 4112. Angular wear surface; 4113. Secondary wear surface; 412. Non-cutting area; 4121. Non-main wear surface; 4122. Non-angular wear surface; 4123. Non-secondary wear surface; 5. Cutting edge unit; 51. Main cutting edge; 52. Angular cutting edge; 53. Secondary cutting edge; 6. Cutting coating; 61. First coating; 62. Secondary coating; 7. Convex coating unit; 711. Main front convex coating unit; 712. Angular front convex coating unit; 713. Secondary front convex coating unit; 721. Main rear convex coating unit; 722. Angular rear convex coating unit; 723. Secondary rear convex coating unit; 8. Workpiece.

DETAILED DESCRIPTION

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

In the description of the present invention, it should be noted that terms such as "center", "up", "down", "horizontal", "inside", "outside", "top", and "bottom" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

Figs. 1 to 5 show a first embodiment of a cutting blade having a convex coating unit on the back face of the present invention. The cutting blade having a convex coating unit on the back face of the embodiment comprises a plate-like substrate 1, the plate-like substrate 1 comprises an upper surface 2, a lower surface 3 and a side surface 4 connecting the upper surface 2 and the lower surface 3, the side surface 4 and the upper surface 2 intersect to form a plurality of cutting edge units 5, the cutting edge unit 5 comprises a main cutting edge 51, an angle cutting edge 52 and a secondary cutting edge 53, the side surface 4 comprises a first back face 41 and a second back face 42, the first back face 41 is located at the second back face Above the surface 42, the first back cutting surface 41 is provided with a non-cutting area 412 and a back cutting area 411 involved in cutting. Two layers of cutting coatings 6 are provided on the first back cutting surface 41, namely a first coating 61 and a second coating 62 located outside the first coating 61. The first coating 61 has the same microscopic composition at all locations and completely covers the first back cutting surface 41. The second coating 62 is composed of more than one convex coating unit 7 arranged in the back cutting area 411. The thickness of the convex coating unit 7 is h1, which should satisfy: 1µm≤h1≤5µm. A convex coating unit 7 is arranged on the rear cutting area 411 of the surface 41, so that the overall thickness of the coating in the rear cutting area 411 where the convex coating unit 7 is arranged is greater than that in other areas. That is to say, the convex coating unit 7 can be arranged in the key area where the rear cutting area 411 contacts the chips, and the overall thickness of the cutting coating in the key area is increased, thereby solving the problem of coating peeling and avoiding rapid wear and chipping in the rear cutting area 411. In particular, according to the difference in cutting functions of the cutting edges at various locations, the thickness and material (friction coefficient, etc.) of the convex coating unit 7 can be optimized to reduce the deformation of the chips on the first rear tool face 41 and reduce the cutting force, so that the performance and service life of the cutting edges at various locations are matched, thereby improving the performance stability and service life of the tool. In addition, the convex coating unit 7 is arranged on the rear cutting area 411, and it can be arranged that there is a certain gap between the edge of the convex coating unit 7 and the cutting edge of the cutting edge unit 5, that is, there is only the first coating 61 at the cutting edge, which can better control the overall thickness of the cutting coating at the cutting edge, avoid the chipping of the cutting edge due to the large stress deformation at the cutting edge when preparing the coating, and improve the qualified rate of blade production.

Under the conditions that the thickness h of the first coating 61 is set to 4µm and 8µm respectively, and the material of the first coating 61 is set to TiCN and TiAlSiN respectively, the thickness h1 of the convex coating unit 7 is set to satisfy: 1µm≤h1≤5µm. Through multiple actual cutting experiments, as shown in Table 1 below, it can be seen that compared with the comparative example (Table 2 below), the service life of the cutting blade (the time when the first flank surface 41 is scrapped due to wear and chipping) and the production qualification rate of the blade can be significantly improved at the same time:

Table 1

Comparative Example:

Table 2

In this embodiment, the thickness of the first coating 61 is h, as shown in Figure 8. In order to ensure the coating performance of the cutting blade, the first coating 61 is required to have good toughness, and the convex coating unit 7 has good wear resistance. If the thickness h1 of the convex coating unit 7 is greater than the thickness h of the first coating 61, due to the influence of the coating bonding force between the two coatings, the convex coating unit 7 is prone to peeling off from the first coating 61, which will reduce the product qualification rate and product performance. At the same time, if the thickness of the convex coating unit 7 is less than half of the thickness of the first coating 6, the performance improvement of the cutting area with the convex coating unit 7 is limited. Therefore, it should satisfy: h1≤h≤2h1. For example, if h=8µm and h1=0.8h are set, the production qualification rate of the blade can reach 93%, and the service life is increased by 25% compared with the cutting blade with only the first coating 6.

In this embodiment, the convex coating unit 7 and the first coating 61 have different microstructures to improve the wear failure of the flank and reduce the friction surface resistance.

In this embodiment, the outer surfaces of the convex coating unit 7 and the first coating 61 have different colors to improve the appearance recognition.

In this embodiment, the convex coating unit 7 on the second coating 62 is arranged on the rear cutting area 411 .

In this embodiment, the rear cutting area 411 includes a main wear surface 4111 , an angle wear surface 4112 , and an auxiliary wear surface 4113 corresponding to the main cutting edge 51 , the angle cutting edge 52 , and the auxiliary cutting edge 53 , respectively.

In this embodiment, convex coating units 7 are provided on the main wear surface 4111, the corner wear surface 4112 and the auxiliary wear surface 4113, and the three convex coating units 7 are independent of each other and can be provided with different microstructures.

In addition to the above embodiments, the convex coating unit 7 may be provided only on the main wear surface 4111 or only on the angular wear surface 4112 or only on the secondary wear surface 4113, or only on the main wear surface 4111 and the angular wear surface 4112, or only on the angular wear surface 4112 and the secondary wear surface 4113.

The convex coating unit 7 on the main wear surface 4111 is a main front convex coating unit 711, which extends to be adjacent to the angular wear surface 4112. The maximum length of the main front convex coating unit 711 in the cutting depth direction of the corresponding main cutting edge 51 is y1, and the maximum cutting length of the main cutting edge 51 is y. In order to ensure the contact area between the chips and the main front convex coating unit 711, the contact area with the first coating 61 on the main wear surface 4111 is reduced to ensure that the main front convex coating unit 711 and the first coating 61 have a long cutting service life during large cutting depth processing. The following should be satisfied: 0.4y≤y1≤0.6y. Specifically, in this embodiment, y =8mm, y1=3mm.

In this embodiment, the convex coating unit 7 on the secondary wear surface 4113 is a secondary front convex coating unit 713, and the secondary front convex coating unit 713 extends to be adjacent to the angular wear surface 4112. The maximum length of the secondary front convex coating unit 713 in the cutting depth direction of the corresponding secondary cutting edge 53 is x1, and the maximum cutting length of the secondary cutting edge 53 is x. In order to ensure the contact area between the chips and the secondary front convex coating unit 713 and reduce the contact area with the first coating 61 on the secondary wear surface 4113, and to ensure that the secondary front convex coating unit 713 and the first coating 61 have a longer cutting service life during large cutting depth processing, it should satisfy: 0.2x≤x1≤0.5x, specifically, x=5.5mm, x1=2mm.

FIG. 9 is a schematic diagram showing a cutting workpiece 8 being cut by a cutting insert having a convex coating unit on the flank surface of the present embodiment.

In order to avoid coating peeling at the main cutting edge 51, the secondary cutting edge 52 and the corner cutting edge 53 and improve the cutting efficiency and cutting life, in this embodiment, the convex coating units 7 on the main wear surface 4111, the angular wear surface 4112 and the secondary wear surface 4113 are respectively the main front convex coating unit 711, the angular front convex coating unit 712 and the secondary front convex coating unit 713, and the heights of the main front convex coating unit 711, the angular front convex coating unit 712 and the secondary front convex coating unit 713 on the side 4 are D1, D2 and D3 respectively, which should satisfy: 0.3mm≤D1≤0.8mm, 0.3mm≤D2≤0.8mm, 0.3mm≤D3≤0.8mm, specifically, D1=D2=D3=0.4mm.

In order to ensure that the cooling medium exists in the form of a dynamic thin film between the cutting edge unit 5 and the convex coating unit 7, and in order to avoid large coating stress at the cutting edge, the cutting coating adjacent to the cutting edge unit 5 should be evenly arranged and the overall thickness should not be too large, otherwise the production qualification rate of the blade will be low. Therefore, there should be a certain gap between the convex coating unit 7 and the cutting edge unit 5. In this embodiment, the minimum gaps between the main front convex coating unit 711, the corner front convex coating unit 712 and the secondary front convex coating unit 713 on the side 4 and the main cutting edge 51, the corner cutting edge 52 and the secondary cutting edge 53 are d1, d2, and d3, respectively, which should satisfy: 0.01mm mm≤d1≤0.2mm, 0.01mm mm≤d2≤0.2mm, 0.01mm mm≤d3≤0.2mm, specifically, d1=d2=d3=0.01mm.

Figures 6 and 7 show a second embodiment of a cutting blade having a convex coating unit on the back face of the present invention. The difference between this embodiment and the first embodiment is that: in this embodiment, the convex coating unit 7 on the second coating 62 is arranged on the non-cutting area 412, and the convex coating unit 7 is set in different colors to improve the appearance recognition of the cutting blade.

In this embodiment, the non-cutting area 412 includes a non-main wear surface 4121 , a non-corner wear surface 4122 , and a non-secondary wear surface 4123 corresponding to the main cutting edge 51 , the corner cutting edge 52 , and the secondary cutting edge 53 , respectively.

In this embodiment, the non-main wear surface 4121, the non-angle wear surface 4122 and the non-auxiliary wear surface 4123 are all provided with convex coating units 7, that is, the convex coating units 7 are arranged in the non-cutting area 412. Of course, the convex coating units 7 can also be arranged separately on the non-main wear surface 4121, the non-angle wear surface 4122 or the non-auxiliary wear surface 4123 according to actual needs.

Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should fall within the scope of protection of the technical solution of the present invention.

Claims (11)

1. The utility model provides a cutting insert that relief surface was equipped with convex coating unit, includes platy base member (1), platy base member (1) include upper surface (2), lower surface (3) and connect side (4) of upper surface (2), lower surface (3), side (4) and upper surface (2) intersect and form a plurality of cutting edge units (5), cutting edge unit (5) include main cutting edge (51), angle cutting edge (52) and minor cutting edge (53), side (4) include first relief surface (41) and second relief surface (42), first relief surface (41) are located second relief surface (42) top, first relief surface (41) are equipped with non-cutting area (412) and participate in back cutting area (411) of cutting, its characterized in that: the utility model discloses a cutting tool for the cutting of the metal sheet, including first back face (41), be equipped with two-layer cutting coating (6) on the first back face (41), be first coating (61) and be located respectively outside second coating (62) of first coating (61), the microcosmic composition of first coating (61) everywhere is the same and completely covers first back face (41), second coating (62) are by setting up more than one protruding coating unit (7) in back cutting region (411), the thickness of protruding coating unit (7) is h1, should satisfy: 1 [ mu ] m is less than or equal to h1 is less than or equal to 5 [ mu ] m, the rear cutting region (411) comprises a main wear surface (4111), an angular wear surface (4112) and a secondary wear surface (4113) which respectively correspond to the main cutting edge (51), the angular cutting edge (52) and the secondary cutting edge (53), the main wear surface (4111) and/or the angular wear surface (4112) and/or the secondary wear surface (4113) are provided with the convex coating unit (7), and the convex coating units (7) on the main wear surface (4111), the angular wear surface (4112) and the secondary wear surface (4113) are respectively a main front convex coating unit (711), an angular front convex coating unit (712) and a secondary front convex coating unit (713), and the heights of the main front convex coating unit (711), the angular front convex coating unit (712) and the secondary front convex coating unit (713) on the side surface (4) are respectively D1, D2 and D3, so as to meet the following conditions: d1 is less than or equal to 0.3mm D2 is 0.8mm or less and 0.3mm or less less than or equal to 0.8mm and less than or equal to 0.3mm d3 is less than or equal to 0.8mm.

2. The cutting insert provided with a relief coating unit according to claim 1, wherein: the thickness of the first coating (61) is h, and the following conditions are satisfied: h1 is less than or equal to h and the time is less than or equal to 2h1.

3. The cutting insert provided with a relief coating unit according to claim 1 or 2, characterized in that: the convex coating unit (7) has a microstructure different from that of the first coating (61).

4. The cutting insert provided with a relief coating unit according to claim 1or 2, characterized in that: the convex coating unit (7) has a different color from the outer surface of the first coating (61).

5. The cutting insert provided with a relief coating unit according to claim 1 or 2, characterized in that: a convex coating unit (7) on the second coating (62) is provided on the rear cutting region (411).

6. The cutting insert provided with a relief coating unit according to claim 1 or 2, characterized in that: the convex coating unit (7) on the second coating (62) is disposed on the non-cutting region (412).

7. The cutting insert provided with a relief coating unit according to claim 1 or 2, characterized in that: the non-cutting region (412) includes a non-primary wear surface (4121), a non-angular wear surface (4122), and a non-secondary wear surface (4123) corresponding to the primary cutting edge (51), the angular cutting edge (52), and the secondary cutting edge (53), respectively.

8. The cutting insert provided with a relief coating unit according to claim 7, wherein: the non-main wear surface (4121) and/or the non-angular wear surface (4122) and/or the non-auxiliary wear surface (4123) are provided with the convex coating unit (7).

9. The cutting insert provided with a relief coating unit according to claim 1 or 2, characterized in that: the convex coating unit (7) on the main wear surface (4111) is a main forward convex coating unit (711), the main forward convex coating unit (711) extends to be adjacent to the angular wear surface (4112), the maximum length of the main forward convex coating unit (711) in the cutting depth direction of the corresponding main cutting edge (51) is y1, and the maximum cutting length of the main cutting edge (51) is y, and the following conditions are satisfied: y is more than or equal to 0.4y and less than or equal to y1 less than or equal to 0.6y.

10. The cutting insert provided with a relief coating unit according to claim 1 or 2, characterized in that: the convex coating units (7) on the auxiliary wear surface (4113) are auxiliary forward convex coating units (713), the auxiliary forward convex coating units (713) extend to be adjacent to the angular wear surface (4112), the maximum length of the auxiliary forward convex coating units (713) in the cutting depth direction of the corresponding auxiliary cutting edge (53) is x1, and the maximum cutting length of the auxiliary cutting edge (53) is x, so that the following conditions are satisfied: x is more than or equal to 0.2 and less than or equal to x1 less than or equal to 0.5x.

11. The cutting insert provided with a relief coating unit according to claim 1 or 2, characterized in that: the minimum gaps between the main forward convex coating unit (711), the corner forward convex coating unit (712) and the auxiliary forward convex coating unit (713) and the main cutting edge (51), the corner cutting edge (52) and the auxiliary cutting edge (53) on the side surface (4) are d1, d2 and d3 respectively, and the following conditions are satisfied: d1 is less than or equal to 0.01mm d2 is 0.2mm,0.01mm is less than or equal to d2 less than or equal to 0.2mm, less than or equal to 0.01mm d3 is less than or equal to 0.2mm.