JPH026971Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a two-blade drilling tool such as a drill or a counterbore cutter that performs drilling by cutting down in the axial direction of the tool.

In general, this type of drilling tool is provided with a chip discharge groove along the axis of the tool body, and a large chip discharge groove is provided in consideration of smooth chip discharge. Therefore, it cannot be denied that the rigidity is poor. Moreover, since a large thrust load is generated in the chisel, problems such as tool breakage and poor hole accuracy often occur.

In this respect, the applicant proposed earlier that the cutting blade was placed at the center.
In other words, with a drilling tool without a chisel, it is possible to reduce the thrust load by threading the cylindrical core generated at the center of rotation at the width of the gap groove (Japanese Patent Application No. 127046/1986). That is, as shown in FIG.
are fixed by brazing, and the cutting blades 3 of each cutting blade tip 2, 2 are arranged point-symmetrically with respect to the rotation center 0, and the inner edge 3a of the cutting blade 3 is located at the rotation center 0.
A gap with a groove width of 0.2 to 2.5 mm is provided so that a core is not formed in the center. Therefore,
When such a drill is used as a drilling tool, there is no chisel and the cylindrical core generated in the gap groove is threaded, so the thrust load can be reduced accordingly, thereby increasing the rigidity of the drill. In addition, since each inner edge 3a is pressed during the drilling process, the so-called "misosuri" movement and the rifling caused by it can be prevented, and as a result, Tool breakage can be prevented and holes can be drilled with good accuracy.

By the way, in the case of such a drill, since the thrust load can be reduced and the rigidity of the drill can be relatively improved as described above, high-feed cutting is possible. However, when high-feed cutting is performed, the following new problem arises. In other words, when such a drill is used to cut a sticky workpiece material such as stainless steel at a high feed rate, thick chips are generated continuously, and these chips wrap around the drill and break the drill or damage the wall of the hole. Scraping worsens the surface roughness, and the chips discharged from the hole are thrown around by the drill, making drilling work extremely dangerous.Additionally, the chips scatter, worsening the working environment. Further, since the vicinity of the inner end edge 3a of the cutting blade tip 2 receives a large thrust load due to high-feed cutting, a problem has arisen in that the vicinity of the inner end edge 3a of the cutting blade tip 2 is easily damaged.

This idea was made in view of the above circumstances,
When the cutting edge is viewed from the bottom, the cutting edge consists of a smooth convex curved part with a relatively large curvature on the rotation center side of the tool body and a smooth concave curved part with a relatively large curvature on the outer periphery side of the tool body. Stainless steel, etc. is formed into a sine curve shape, and the convex curved part and the concave curved part are located on the same rotational direction side, and the convex curved part projects ahead of the concave curved part in the cutting rotation direction. The purpose of the present invention is to provide a two-blade drilling tool that can break up chips even when cutting a sticky workpiece material at a high feed rate and can prevent chipping near the inner edge of the cutting tip. shall be.

An embodiment of this invention will be described below with reference to FIG. Note that the same parts as in the conventional example described above are denoted by the same reference numerals, and the explanation thereof will be omitted.

As shown in FIG. 2a, the cutting edge 13 has a smooth convex curved portion 13b and a smooth concave curved portion 13b, which are sequentially formed from the rotation center 0 side toward the outer circumferential side in the same rotation direction side when viewed from the bottom. It is composed of a curved part 13c and a short straight part 13d. Double cutting edge 1
3 and 13 convex curved portions 13b and 13b, and
The concave curved portions 13c, 13c have the same shape and are located at the same position in the radial direction. Moreover, the convex curved portion 13b and the concave curved portion 1
3c are formed as if they were sine curves by drawing arcs of relatively similar shapes with relatively large curvatures, and the convex curved portion 13b is rotated in the cutting rotation direction with respect to the concave curved portion 13c and the straight portion 13d. , that is, it is projected forward in the direction of the arrow.
Further, the rake surface 14 of the cutting blade tip 12 corresponds to the convex curved section 13b, the concave curved section 13c, and the straight section 13d, respectively, and is formed along the chip discharge groove 15. and a flat portion 14d. Note that 16 in the figure is an oil hole for flowing cutting oil.

Next, when drilling with such a drill, chips are generated at the convex curved section 13b, concave curved section 13c, and straight section 13d of the cutting blade 13, and chips are generated at the convex curved section 14b, concave curved section 14c, and flat section, respectively. Part 1
4d. Since the growth rate of chips is approximately proportional to the cutting speed, the growth rate of chips is faster on the outer circumference side than on the inner circumference side, and therefore the chips tend to extend toward the center of the drill.

Here, the chips generated at the convex curved portion 13b also tend to extend toward the center as described above. However, since the chips generated at the concave curved section 13c immediately press against the convex curved section 14b after being generated, they cannot proceed any further toward the center, and instead move toward the base end of the drill along the concave curved section 14c. extend. For this reason, the elongation of chips generated at the concave curved portion 13c is inhibited by the chips generated by the convex curved portion 13b, and as a result,
Tensile stress is generated between both chips. Then, this tensile stress causes cracks to occur on the sides of both chips that are connected to each other, and then the chips are separated.

In particular, in this drill, since the convex curved section 13b and the concave curved section 13c are formed in a sinusoidal shape (sine curve shape), the volumes of chips generated in both curved sections 13b and 13c in the cross section are almost equal. This makes it possible to more reliably cause separation due to the interference of chips as described above. In other words, the above-mentioned chip interference occurs when a tensile force is applied to one chip in a direction perpendicular to its traveling direction (chip width direction) from the other chip, and the tensile force is , the larger the difference in the volume of the cross section near the part where the chips are cracked and separated, the smaller it becomes. This is because, if the volume of chips from the concave curved portion 13c in the cross section is significantly larger than the other, the chips from the convex curved portion 13b will be pulled back toward the outer circumferential side by the chips from the concave curved portion 13c. Conversely, if the volume of chips in the cross section due to the convex curved portion 13b is large, the chips due to the concave curved portion 13c are
This is because the chips are pulled toward the center by overcoming this, and the directions of elongation of both chips become the same. In the former case, the elongation direction of the chips as a whole becomes closer to the outer periphery and the chips tend to stretch, and in the latter case, the chips end up reaching the bottom of the chip discharge groove 15. In this way, when the volumes in the cross section of both chips are different, the elongation direction of one chip is closer to the elongation direction of the other chip, the tensile force generated between the two chips becomes smaller, and the above-mentioned crack separation occurs. It becomes difficult.

On the other hand, in the above drill, the convex curved portion 13
Since the concave curved portion 13c and the concave curved portion 13c are formed in a sinusoidal shape, the volumes of chips generated in both the curved portions 13b and 13c in the cross section are approximately equal. As a result, both chips tend to extend in their respective extension directions, and a large tensile stress is generated between both chips, so that the chips can be reliably cracked and separated.

As a result, it is possible to prevent chips from wrapping around the drill and causing the drill to break, or from scraping the wall of the hole and worsening the surface roughness of the hole. The safety of the drilling work can be improved because the drill does not get swung around by the drill, and the work environment can be improved because there are no chips flying around.

Note that the finely divided chips are quickly discharged to the outside of the hole by the cutting oil flowing from the oil hole 16. Further, since the cutting blade 13 itself has a chip breaker function for the reason mentioned above, there is no need to form a chip breaker every time the drill is re-grinded, and the drill can be re-grinded easily. Furthermore, since the vicinity of the inner edge 13a of the cutting blade 13 is formed into a convex curved portion 13b,
The thickness of the cutting blade tip 2 near the inner edge 13a of the cutting blade 13 is increased, and by further increasing the thickness, the radius of curvature of the convex curved portion 13b can be increased,
As a result, the strength near the inner edge 13a of the cutting blade tip 2 can be improved, and damage to the area near the inner edge 13a of the cutting blade tip 2 can be prevented. Furthermore, the convex curved portion 13 of both cutting edges 13, 13
Of course, the concave curved portions 13c and 13c are formed in the same shape.
Because they are located at the same radial position,
It is possible to prevent the drill from swinging when biting into or penetrating the work. That is, the cutting edge 13 has a convex curved portion 1
3b and the concave curved portion 13c, the cutting edge 1
A radial load as a component of the cutting load acts on the drill bit 3, and this radial load causes the drill to swing during biting and penetration. In particular, both cutting edges 13,1
3 convex curved portions 13b, 13b, concave curved portion 1
When the radial positions of 3c and 13c are shifted from each other, the radial load acting on one cutting edge 13 and the radial load acting on the other cutting edge 13 are added, increasing the runout of the drill. . In this regard, in the above drill, both cutting edges 13, 13
Convex curved portions 13b, 13b comrades and concave curved portion 1
Since the radial positions of 3c and 13c are made to coincide with each other, the radial load acting on one cutting edge 13 and the radial load acting on the other cutting edge 13 cancel each other out. Therefore, it is possible to prevent the drill from swinging.

Moreover, since the portion of the cutting edge 13 located on the outermost peripheral side is the straight portion 13d, breakage of the cutting edge 13 can be prevented. That is, if the concave curved portion 13c is located at the outermost edge, the rake angle in the radial direction at the outer edge of the cutting blade 13 will become excessive, and the strength of that portion will decrease, making it more likely to break. However, if the straight portion 13d is formed, the radial rake angle can be set so that that portion has sufficient strength, and therefore the cutting edge 1
It is possible to prevent the loss of 3.

In addition, in the above embodiment, when the cutting blade 13 is viewed from the side, the cutting blade 13 is straight, but it is not limited to this, and it may have various shapes as shown in FIGS. 3 to 5. Can be done. Hereinafter, the drill shown in FIGS. 3 to 5 will be explained. Note that the parts other than the cutting blade are the same as those in the above embodiment, so the same reference numerals are given to the parts other than the cutting blade, and the explanation thereof will be omitted. The one in FIG. 3 is a convex curved portion 23b.
The tip angle of the cutting blade 23 is made into two steps at the point of contact between the straight portion 23d and the straight portion 23d, which has the effect of further separating the chips generated from the convex curved portion 23b and the chips generated from the concave curved portion 23c. The one shown in Fig. 4 not only has a two-step tip angle, but also has a convex curved portion 33b recessed toward the tool body 1 side from a concave curved portion 33c, which makes chip separation more reliable and allows the cutting edge 33
The strength of the inner edge 33a of the cutting edge 2 can be increased by increasing the angle formed between the inner surface of the cutting edge 2 and the inner surface of the cutting edge 2, thereby preventing the cutting edge 2 from breaking. It is possible to reduce so-called core runout by moving it farther from the center of rotation. In the one shown in FIG. 5, the tip of the cutting edge 43 has a convex arc shape, and the tip angle on the center side is large and the tip angle on the outer periphery is small, so that the inner end of the cutting edge 2 is strengthened. In addition, the chip performance is improved by making the chips generated from the outer circumferential side thinner, and since there is no bending point on the cutting edge 43, there is an effect of preventing local wear.

Further, in the above embodiment, the cutting edge tip 2 is fixed to the tool body 1 by brazing, but the present invention is not limited to this, and the cutting edge tip 2 may be fixed with a bolt or the like. may be formed integrally with the tool body 1.

As explained above, according to the two-blade drilling tool of this invention, when the cutting edge is viewed from the bottom, the cutting edge has a smooth convex curve that is sequentially formed from the rotation center side to the outer circumference side. It consists of a smooth concave curved part that touches this convex curved part, and a narrow straight part, and the convex curved part and the concave curved part are formed in a substantially sinusoidal shape, and the convex part of both cutting edges is formed into a substantially sinusoidal shape. Since the curved portions and the concave curved portions are formed in the same shape and located at the same position in the radial direction, and the convex curved portions are made to protrude ahead of the concave curved portions in the cutting rotation direction, The volumes of chips generated in the convex curved portion and the concave curved portion in the cross section are approximately equal, and the elongation of the chips generated in the convex curved portion is inhibited by the chips generated by the convex curved portion. As a result, large tensile stress is generated between both chips, causing cracks to form on the sides of both chips that are connected to each other, making it possible to reliably separate the chips and greatly improving chip evacuation performance. can.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the previously proposed drill without a cutting edge in the center; a is a bottom view thereof, b is a side view thereof, and Figure 2 is a diagram showing an embodiment of this invention.
is a bottom view of the device, b is a side view thereof, FIGS. 3 to 5 are side views showing other embodiments of this invention, and FIG. 6 is a bottom view of FIG. 5. 1... Tool body, 2... Cutting blade tip, 13, 23,
33, 43...Cutting blade, 13a, 23a, 33a, 4
3a...Inner edge, 13b, 23b, 33b, 43b
...Convex curved portion, 13c, 23c, 33c, 43c...
Concave curved part, 13d... Straight line part, 14... Rake face, 1
5...Chip discharge groove, 0...Rotation center.

Claims (1)

[Scope of utility model registration request] Two cutting edges 13 are arranged at the tip of the tool body 1 symmetrically with respect to the rotation center 0 of the tool body 1.
and a chip discharge groove 15 located on the rake face 14 side of each cutting edge 13 and provided along the axial direction of the tool body 1. The inner edge 13a is spaced apart from the rotation center 0 of the tool body 1 and has a width d of both inner edges.
(d=0.2 to 2.5 mm), and when each of the cutting edges 13 is viewed from the bottom, the cutting edges 13
A smooth convex curved portion 13b with a relatively large curvature is formed sequentially from the rotation center 0 side of the tool body 1 toward the outer circumferential side, and a smooth convex curved portion 13b with a relatively large curvature continuous with this convex curved portion 13b. The concave curved portion 13c is formed in a substantially sinusoidal shape, and then consists of a narrow straight portion 13d continuous to this concave curved portion 13c, and convex curved portions 13b of both cutting edges 13, 13,
13b and the concave curved portions 13c, 13c have the same shape and are located at the same position in the radial direction, and the convex curved portion 13b protrudes ahead of the concave curved portion 13c in the cutting rotation direction. A two-blade drilling tool featuring: