JPH0653010U - Hard-coated half-moon drill - Google Patents

Abstract

(57) [Summary] [Object] To provide a hard film-coated half-moon drill having a long life and high performance, which solves the problem of reduction in fracture resistance caused by coating a hard film on a cemented carbide. [Structure] A round bar 2 forming a half-moon drill made of cemented carbide is coated with a hard coating to prevent the occurrence of cracks 4.
One end of the round bar 2 is a cutting edge portion 7 having a semicircular cross section. The tip 1 of the cutting blade portion 7 is formed in a conical shape or a bowl shape, and the shank 2 is formed at the other end portion. Apply a hard coating on the surface of the cutting edge.
At least one of the main cutting edges 5 is chamfered with a width of 20 μm to 500 μm on the rake face 7 at an angle of 15 ° to 45 °, and a hard coating is further applied.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a hard film-coated half-moon drill coated with a hard film having a long life and high performance, which solves the problem of deterioration in fracture resistance caused by coating a hard film on a cemented carbide.

[0002]

[Prior art]

Half-moon drills are also used for drilling brass, small and relatively deep holes, or for grooving or engraving. Such a half-moon drill has, for example, as shown in FIG. 3 and FIG. The cutting edge is formed by removing one side of the plane passing through the center line AA so that the cross section becomes a half moon shape as shown in FIG. Further, conventionally, for the purpose of extending the life of the cutting tool, it has been practiced to coat the tool surface with a hard coating from hard ceramics such as titanium nitride and titanium carbide to diamond having the highest hardness. The bulk hardness of titanium nitride or titanium carbide is at least 1800 kgf / mm ^{2 in} Vickers hardness, and is generally higher than the tool base material. However, when these hard coatings were coated for the purpose of extending the life of the half-moon drill, there was a problem that the cutting edge was likely to be chipped.

However, when the hard coating is not applied, chipping of the cutting edge is usually not a big problem, but wear resistance is a problem. In order to solve such a problem, a twist drill, which is different from the present invention, is chamfered at the intersection of the rake face and the flank face as disclosed in Japanese Utility Model Laid-Open No. 60-175513. And, the chamfering angle 3 is set in the range of 10 ° to 45 ° with respect to the axis of the drill, and the chamfering width is set to 0.03 to 0.3 mm to improve wear resistance. Twist drills are also disclosed.

[0004]

[Problems to be solved by the device]

 However, it is known that when a base material is coated with a material having a lower toughness than that of the base material, the bending strength of the base material is lower than that of a base material that is not subjected to a coating treatment. growing. Therefore, depending on the type or application of the cutting tool, coating with a coating such as hard ceramics easily causes chipping or chipping, which may reduce the performance. In the case of a half-moon drill, the strength of the tip of the cutting edge is lower than that of a normal drill, so the strength is greatly affected by coating with a hard coating. Therefore, the conventional hard coating cannot be thickly coated with the half-moon drill.

The half-moon drill rotates a work piece clockwise or counterclockwise, and the main cutting edge receives a force in a direction perpendicular to the rake face 3 of the work piece, and at the same time, the main cutting edge moves in the direction of arrow a shown in FIG. It also receives power from the direction. The force in this direction causes tensile stress on the outer peripheral surface of the tip of the drill (the backside of the rake face 3), and if this exceeds the limit of material strength, cracks 4 will enter the cutting edge in the direction as shown in FIG. Causes shell-shaped chips. Materials such as cemented carbide, which are mainly composed of ceramics, have a low strength against tensile stress, and are therefore particularly prone to chipping. In addition, the smaller the tip angle θ of the half-moon drill, the more likely it is that chips will enter. Furthermore, when a half-moon drill is coated with a hard coating, its bending strength decreases, so this effect becomes more pronounced, and the use limit decreases with increasing film thickness.

The crack 4 enters the tip of the main cutting edge 5 because the tip is deformed by receiving stress due to cutting, and the maximum value of the elongation of the base material at this time is the limit value of the tensile strength of the material. This is because they can cross. When a hard coating is applied to the base material, cracks are more likely to occur because the amount of deformation of the cutting edge when stress is applied is determined by the strength of the base material. Since the coating deforms as much as the surface layer of the base metal, a hard coating with a large elastic constant is subject to a larger tensile stress, and it fractures before the base metal and progresses to the base metal. is there.

Generally, a hard coating applied to a cutting tool has a high hardness but a large elastic constant and a low toughness. Therefore, when stretched by the same amount as the base material of the cutting tool, the hard coating has a higher tensile stress than the base material. The hard coating breaks before the elongation limit of the base metal is reached. Therefore, this effect becomes more remarkable in the cBN film or the diamond film having a large elastic constant. Further, as the film thickness increases, cracks are more likely to occur in the hard coating tool, and the reason for the decrease in strength is that as the film thickness increases, the depth of cracks generated in the film increases, which is due to the hard coating. It is thought that this is because it is easier to propagate cracks generated in the base material to the base material.

[0008]

[Means for Solving the Problems]

 Therefore, we devised to coat the tool base material with a hard coating and chamfer the main cutting edge of the half-moon drill as a measure to prevent the occurrence of cracks. That is, according to this invention, one end is formed as a cutting blade having a semicircular cross section, and the tip of the cutting blade is formed in a conical shape or a bowl shape, and a shank is formed at the other end. A cemented carbide half-moon drill with a hard coating on the surface, chamfering a width of 20 μm to 500 μm at an angle of 15 ° to 45 ° to the rake face on at least one of the main cutting edges, Further, it relates to a half-moon drill having a hard coating.

[0009]

[Action]

 According to this invention, by chamfering the main cutting edge as described above, there is no thin portion with a large deformation amount on the cutting edge, which reduces the deformation of the hard coating and also reduces the deformation of the hard coating. It is possible to prevent the hard coating from cracking. Furthermore, by chamfering the main cutting edge, the force in the direction perpendicular to the chamfered surface is applied during cutting, which further reduces the deformation of the cutting edge and enhances the effect of preventing cracking. be able to.

[0010]

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. With a half-moon drill that does not have a hard coating, chipping of the cutting edge is not a major problem, but when a material harder than the base material is coated, this becomes a major problem, and titanium nitride or titanium carbide, or even the highest hardness. The present invention is applicable to the case where many hard coatings are applied up to a diamond having a diamond. As described above, these coatings all have a Vickers hardness of 1800 kgf / mm ² or more as the bulk hardness.

The structure of the meniscus drill according to the present invention has the same general structure as that shown in FIGS. 3 and 4. That is, approximately half of the entire length of the round bar 2 made of cemented carbide is cut in the longitudinal direction along the center line AA to form a shank 6 having a circular cross section and a cutting edge portion 7 having a semicircular cross section. To do. The cutting edge portion 7 is formed of a pair of main cutting edges 5 and 5 having a tip angle θ and an outer peripheral cutting edge 8 which extends parallel to the shank side following the main cutting edges.

The main cutting edge 5 and the outer peripheral cutting edge 8 of the cutting edge portion 7 are chamfered 9. Since the width of the chamfer 9 affects the cutting resistance of the half-moon drill, it can be narrowed with a small-diameter half-moon drill, which is easily broken, and can be selected up to a wide value with a large-diameter half-moon drill, but the range is 20 to 500 μm. Appropriate. The width w of the chamfer 9 is constant over the entire main cutting edge 5 as shown in FIG. However, the width w of the chamfer 9 does not necessarily have to be constant, and as shown in FIG. 2, the chamfer width of this portion is narrowed because chipping is unlikely to occur near the intersection of the main cutting edge 5 and the outer peripheral cutting edge 8. The outer peripheral cutting edge 8 may be chamfered by widening its width toward the tip.

Further, the angle of the chamfer 9 also has a great influence on the generation of cracks on the cutting edge and the cutting resistance, and the sharpness is reduced as the angle with respect to the rake face 3 is increased, but chipping is less likely to occur. The preferable range of the chamfer angle is 15 to 45 with respect to the rake face. In the half-moon drill, one of the two cutting edges acts on the cutting, but the blades on the opposite side can be used by reversing the rotation direction. Therefore, chamfering is only required on one side when used for unidirectional rotation only, and chamfering can be performed on both cutting edges when used on machines that can rotate in both directions.

[0014]

EXAMPLES Examples of the present invention will be shown below. In the first embodiment, a diameter of 5 mm, a total length of 50 mm, a working portion length of 15 mm, and a half-moon drill with a tip angle θ of 120 ° are chamfered 9 on both sides of the main cutting edge 5 with a width of 50 μm and an angle of 20 ° to the rake face 3. Further, a half-moon drill in which the chamfer 9 was coated with a titanium carbide film having a thickness of 8 μm was produced. FIG. 2 shows the action part. In addition, as a comparative product, a half-moon drill having the same dimensions as the drill of the present invention but having a titanium carbonitride film coating treatment without chamfering was manufactured. Using these half-moon drills, stamping of steel materials was performed. The processing conditions are as follows.

Work Material SKH51 Before Heat Treatment Rotational Speed 8000 rpm Movement Speed 3000 mm / min Character Depth 0.5 mm As a result, the chamfered half-moon drill of the present invention shows no wear and tear after cutting 200 workpieces. The comparative drill which was not chamfered, on the other hand, had a chip at the tip during the first work marking process.

As a second embodiment of the present invention, a diameter of 6 mm, a total length of 80 mm, a working portion length of 25 mm, and a cutting angle on both sides of a half-moon drill having a tip angle of 140 ° from the intersection of the main cutting edge 5 and the outer peripheral portion to the tip. Chamfering 9 was performed in which the width w was continuously changed from 0 to 150 μm. The outline of the action part is shown in FIG. A diamond film having a thickness of 12 μm was coated by plasma CVD within a range of 10 mm from the tip of the half-moon drill to manufacture the drill of the present invention. Further, a half-moon drill having the same dimensions as the half-moon drill of the present invention was coated with a diamond film in the same manner without chamfering, to obtain a comparative drill. In addition, as another half-moon drill for comparison, a half-moon drill without chamfering 9 or diamond film coating was prepared. Drilling of aluminum alloy was performed using these drills. The cutting conditions are as follows. Work material ADC12 Rotation speed 10000 rpm Feed rate 0.1 mm / rev Hole depth 12 mm

The results are shown in Table 1. As can be seen from the results, it was found that the coated half-moon drill of the present invention, which was chamfered 9, showed almost no wear on the cutting edge even after machining 10,000 holes, the hole dimensions were stable, and the performance was excellent. .

[0018]

[Table 1]

[0019]

[Effect of device]

 In the coated half-moon drill of the present invention, the cutting edge is chamfered, and the chamfer is coated with a hard coating such as titanium carbide film or diamond. Reduce the amount of deformation. It also exhibits stable drilling performance. As a result, the service life was significantly improved compared to the conventional half-moon drill.

[Brief description of drawings]

FIG. 1 is a plan view of a cutting edge portion of a half-moon drill used in a first embodiment of the present invention.

FIG. 2 is a plan view of a cutting edge portion of a half-moon drill used in a second embodiment of the present invention.

3A is a plan view of a conventional half-moon drill, and FIG. 3B is a side view of the same.

FIG. 4 is a side view of the conventional half-moon drill shown in FIG.

FIG. 5 is a side view of a cutting edge portion of the conventional half-moon drill shown in FIG. 4, showing a portion where a crack enters.

[Explanation of symbols]

 1 Tip 2 Round bar 3 Rake face 4 Crack 5 Main cutting edge 6 Shank 7 Cutting edge part 8 Peripheral cutting edge 9 Chamfer

Claims (2)

[Scope of utility model registration request] 1. A cutting edge portion having one end formed as a cutting edge portion having a semicircular cross section, a tip end of the cutting edge portion formed in a conical shape or a bowl shape, and a shank formed at the other end, and a cutting edge surface. Cemented carbide half-moon drill with hard coating on at least one of the main cutting edges, 15 ° to 45 ° to the rake face
A hard film-coated half-moon drill characterized by chamfering a width of 20 μm to 500 μm at an angle of ° and further coating a hard film on the chamfer. 2. The Vickers hardness of the hard coating is 1800 kg.
The hard coating half-moon drill according to claim 1, which has a f / mm ² or more.