JP2001322018A - Drill - Google Patents

Abstract

(57) [Problem] To provide a drill which has high rigidity and whose core thickness does not change even by regrinding. A chip length (L) of a chip discharge groove (2) in a drill (1) is provided.
A parallel groove 4 having a substantially constant core thickness W1 from the tip toward the rear end, a _first cut-up portion 5 formed by cutting up the parallel groove 4, and a _first cut-up portion 5 larger than the axis O of the drill 1. And the second cut-up portion 6 raised with an inclination smaller than the tangent line at the contact point P, to provide a portion having a constant thickness which does not change even by re-grinding, and to gradually increase the thickness. A portion is provided to prevent a decrease in rigidity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drill and, more particularly, to a core thickness of a cutting portion in a solid drill.

[0002]

2. Description of the Related Art Conventionally used drills are shown in FIG.
As shown in FIG. 5, a parallel groove portion 4 having an equal thickness W by providing a chip discharge groove parallel to the axis O from the tip of the tool body, and a first groove formed by cutting up the parallel groove.
The cut-up portion 5 forms an appropriate groove length L, which is used as the blade portion of the drill 1, and the rear end side thereof is used as a shank. Such a drill with a constant core thickness has a core thickness W
However, since the thrust is small, the thrust is kept small and good sharpness is obtained, but the rigidity is reduced, so that bending or breakage is likely to occur. If the core thickness W is increased, the rigidity is enhanced, but the cross section of the chip discharge groove is reduced, so that the chip discharge performance is reduced.

[0003] As a means for satisfying both the rigidity and the chip discharge property, there is a method of changing the core thickness. For example drill 1 shown in FIG. 9 are progressively thicker in a tapered shape toward the rear end side from the distal end comprising web thickness W ₁ W ₂
This is a so-called web taper type drill in which a core thickness is formed. In such a drill 1, a decrease in rigidity is suppressed, and at the same time, chip discharge is less hindered.

[0004]

In general, when a cutting edge is worn out and its life has expired, the solid drill is reclaimed and reused by performing grinding to drive in from the front end side.
This regrind is repeated many times. However,
A drill such as the web taper type has a problem that the performance of the drill is not constant because the core thickness changes each time grinding is performed. Since the core thickness becomes gradually thicker, the cutting force increases and the sharpness becomes gradually worse.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has an outer peripheral portion of a round rod-shaped drill body, which extends from a tip to a rear end side and has a predetermined groove. The drill has a chip discharge groove that is designed to be cut up at a long length, and the tip length of the chip discharge groove is provided with a cutting edge. In the drill, the groove length forms a substantially constant core thickness from the front end toward the rear end side. Formed by a parallel groove portion, a first cut-up portion obtained by cutting up the parallel groove portion, and a second cut-up portion raised with an inclination larger than the axis of the drill and smaller than a tangent to the first cut-up portion. It is characterized by the following.

[0006] The tip side of the drill is formed so that the core thickness is constant, so that the core thickness does not change by re-grinding. Since the effective groove length is formed from the tip of the drill to the intermediate portion of the second cut-up portion, it functions as an outer peripheral cutting edge having the length, and the first cut-up portion and the second cut-up portion are formed of a web taper type. Since it is formed as a drill having a core thickness gradually increasing like a drill, it has an effect of preventing a decrease in rigidity. In addition, a chip pocket of a sufficient size is secured in the vicinity of the cutting edge at the tip, so that generation and outflow of chips are not hindered.

[0007]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the appearance of a drill 1 of the present invention, and FIGS. 2 and 3 show a partial cross section thereof. A pair of twisted chip discharge grooves 2 extend from the front end toward the rear end side, and form a groove length L at the outer peripheral portion of the round drill body. A cutting edge 3 is provided at a leading edge of the chip discharge groove 2 to form a so-called solid type twist drill.

By the way, in the present invention, chip discharge grooves 2, parallel grooves 4 of the groove length L ₁ having a web thickness W ₁ substantially constant toward the rear end side of the tip, forming the parallel groove 4 at a grinding A first round-up portion 5 formed by round-up with a circular grindstone, and a second round-up portion 5 subsequently described below.
It is formed by synthesizing with the round-up portion 6. That is, the second cut-up portion 6 moves the axis O of the drill 1 at the intermediate point P before the first cut-up portion 5 reaches the outer peripheral surface of the drill 1.
It has a shape having a larger inclination and rising with an inclination smaller than a tangent at the intermediate point P of the first cut-up portion 5. In this case, the effective flute length In the length of L _2, the outer peripheral cutting edge 7 is formed between the effective groove length L _2.

In the range of the groove length L ₁ from the tip of the drill 1, the core thickness W ₁ is constant, and the core thickness does not change even after re-grinding, so that the sharpness of the drill at the beginning of the product is maintained. Until the effective groove length L ₂ greater than the groove length L _1, since the axial thickness is changing gradually increases from the web thickness W ₁ until the web thickness W _2, the bending rigidity is enhanced. In addition, since this tapered portion is provided at a position distant from the cutting edge 3 at the front end, the influence of the reduction in the cross-sectional area of the chip discharging groove 2 on the chip discharging performance is small. Such drill characteristics will be described more specifically below.

FIG. 4 shows the measurement results of the cutting force, and the thickness W of the core is shown.
A conventional drill was 30% certain drill diameter, 35 web thickness W ₂ of the drill diameter web thickness W ₁ is 25% of the drill diameter
7 is a graph showing measured values of thrust and torque when a stainless steel is drilled using the drill of the present invention in which the percentage is set to%. As a result, in the drill of the present invention, the torque value does not change and the thrust value increases only slightly as compared with the conventional drill.

FIG. 5 shows an analysis result by the electronic computer. In other words, a bending load is applied to the tip of the twist drill, and the maximum value of the maximum principal stress when a deflection of 0.2 mm occurs is obtained according to the distance from the tip. 25% of drill diameter constant,
Also those web thickness W is constant 30%, and in which the web thickness W ₁ which is the present invention drills 25% of the drill diameter and the web thickness W ₂ were analyzed for those 35% of the drill diameter. From this figure, it can be seen that the above-described drill has the largest maximum value of the maximum principal stress and the above-described drill has the smallest value. In other words, it can be said that the above-mentioned drill is most difficult to break.

As another embodiment, FIGS. 6 and 7 show examples applied to a straight groove drill. The same parts as those described above are denoted by the same reference numerals, and have the same configuration as that of the twist drill except that the chip discharge groove 2 is straight, and a detailed description thereof will be omitted.

According to the drill of the present invention, the core thickness at the tip side of the drill is made constant, so that the core thickness does not change even by re-grinding. Since the effective groove length is formed from the tip of the drill to the intermediate portion of the second cut-up portion, it functions as an outer peripheral cutting edge having the length, and the first cut-up portion and the second cut-up portion are formed of a web taper type. Since it is formed as a drill whose core thickness is similar to that of a drill,
Effective in preventing rigidity reduction. In the vicinity of the cutting edge at the tip, a sufficiently large chip pocket is ensured, so that generation and outflow of chips are not hindered.

[Brief description of the drawings]

FIG. 1 is a front view of a drill according to the present invention.

FIG. 2 is a sectional view taken along an axis O of a tip portion of the drill shown in FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 1;

FIG. 4 is a graph comparing measured values of cutting resistance with a conventional drill.

FIG. 5 is a diagram showing a result of stress calculation with respect to a bending load.

FIG. 6 is a front view of another embodiment of the drill of the present invention.

FIG. 7 is a sectional view taken along the line AA of FIG. 6;

FIG. 8 is a cross-sectional view taken along an axis O of a tip portion of a conventional drill.

FIG. 9 is a cross-sectional view along the axis O of the tip of another conventional drill.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Drill 4 Parallel groove part 5 First cut-up part 6 Second cut-up part L ₁ groove length L ₂ effective groove length L groove length W, W ₁ , W ₂ core thickness

Claims (1)

[Claims] 1. An outer peripheral portion of a drill body having a round bar shape,
A chip is provided with a chip discharge groove extending from the front end toward the rear end side so as to be cut up with a constant groove length, and in a drill having a cutting edge at a leading edge of the chip discharge groove, the groove length is A parallel groove portion that forms a substantially constant core thickness from the front end toward the rear end side, a first cut-up portion formed by cutting up the parallel groove portion, and an inclination larger than the axis of the drill and smaller than a tangent to the first cut-up portion. A drill formed by the second raised portion raised up.