DE102013212122A1 - Drill bit i.e. double cutting twist drill, has first surface connecting second and third surfaces and exhibiting curvature that is smaller than radii of second and third surfaces, and flank and chip surfaces crossing each other - Google Patents

Abstract

The bit (1) has a thinning section profile edge (2a) whose outer end is outwardly extended such that a hone cut edge comprises a sectional shape. A first curved surface leads to a flank surface (9) and exhibits a radius. A second curved surface leads to a chip surface (10) and exhibits a radius that is smaller than the radius of the first surface. A third curved surface connects the first and second surfaces and exhibits a curvature that is smaller than the radii of the first and second surfaces. The flank and chip surfaces cross each other at a negative axial rake angle.

Description

Technical area

The present invention relates to a drill having a thinning portion at a rotational center portion, and more particularly, to a drill having an improved effect of protecting a cutting edge and capable of adapting to a wide range of cutting conditions.

background

In a drill having a plurality of cut edges, the width of a chisel edge formed between the cut edges has effects on the thrust during processing, and thinning is therefore performed to reduce the width of the chisel edge ) to reduce.

A conventional example of a drill to be thinned is, for example, the drill disclosed in PTD 1 below.

A cutting edge of the drill of the disclosure in this document is provided with a constant width nega-land formed by performing a chamfer honing to reinforce the cut edge. A thinning portion cutting edge is connected to a peripheral cutting edge located outside in the radial direction of the drill by a curved line when the drill is viewed from the front.

The reinforcement of the cut edge has also been implemented by a Rundhonverfahren instead of the negative elevation (nega-land). Alternatively, moreover, a method of connecting the thinning portion cutting edge to the peripheral cutting edge at an angle when the drill is viewed from the front has been widely employed.

CITATION

Patent Document

• PTD 1: Japanese Patent No. 4471894

Summary of the invention

Technical problem

In particular, in such a drill in which the thinning portion cutting edge is connected to the peripheral cutting edge at an angle, a stress concentrates at a portion where a groove surface of the thinning portion is bonded to a groove surface of a groove, the radially outer peripheral side of the cutting edge where the cutting speed increases, and thus the cutting edge is easily damaged at these sections.

Moreover, in a conventional drill, chamfer honing for cutting edge enhancement is performed to make a slant angle constant a chamfered surface at each section of the slicer, and round honing is performed to make a radius R constant at each section of the slit. There is therefore a problem with regard to limited cutting conditions.

An object of the present invention is to develop a shape of the cutting edge of a drill having a thinning portion at a mid-point, thereby suppressing damage to the cutting edge and allowing the drill to conform to a wide range of cutting conditions.

the solution of the problem

In order to solve the above-described problem, a drill having a thinning portion at a rotational center portion in the present invention is formed as follows. More specifically, a thinning portion cutting edge is formed by a sharp ridge line formed at a portion where a flank face and a rake face having a negative axial rake angle intersect each other.

A honing for cutting edge reinforcement is performed on an outer peripheral cutting edge extending radially outward from an outer end of the thinning section cutting edge such that the honed cutting edge has a cross sectional shape formed by a combination of a first curved surface leading to the flank surface and a radius R1, a second curved surface leading to the rake face and having a radius R2 that is smaller than the radius R1 after curvature, and a third curved face connecting the first curved face and the second curved face, and the curvature is smaller than the radii R1 and R2. The third curved surface may be a surface having a gradually changing curvature as long as it satisfies the above-described conditions.

Preferably, in this drill, the axial rake angle of the rake face of Thinning section selected within a range of -15 ° to -40 °. Preferably, a ratio of the radius R1 when a radius of the third curved surface (radius of a surface of constant curvature) is assumed to be 1 is selected to be 0.1 to 0.3, and a ratio of the radius R2 to the radius of the third curved surface is assumed to be 1, selected as 0.4 to 0.6. The radius R1 of the first curved surface is chosen to be the smallest to maintain the sharpness and reduce the flank area contact area during processing. The radius R2 of the second curved surface connecting the rake surface and the third curved surface is made smaller (the curvature greater) than the radius R3 of the third curved surface so as to maintain the cross-sectional area of the cut edge. The radius R2 is chosen to be larger (the curvature to smaller) than the radius R1 of the first curved surface to facilitate the guidance of chips to the direction of the rake face.

Advantageous Effects of the Invention

In the drill according to the present invention, the thinning portion cutting edge is formed by the sharp ridge line formed at the portion where the rake face with the negative rake angle and the flank face cross each other. Therefore, the drill according to the present invention is excellent in stability in penetrating a material to be cut.

Moreover, honing is performed on the outer peripheral cutting edge where the rotation speed increases and the cutting angle (wedge angle) thereof also increases, so that the outer peripheral cutting edge has a shape corresponding to the combination of the first to third curved surfaces having the aforementioned curvature relationship is formed. Therefore, as compared with a drill subjected to normal chamfering, the stress concentration at the portions of the third curved surface connecting the first and second curved surfaces is reduced, and damage to the cut edges is less likely occurs. On the other hand, compared to a drill subjected to round honing, blunting of the cut edge is reduced, and sharpness is also ensured.

Brief description of the drawing

1 Fig. 10 is a side view showing a main part of an example of a drill according to the present invention.

2 is an enlarged end view of the drill of 1 ,

3 is an enlarged cross-sectional view at a position along the line III-III of 2 ,

4 is an enlarged cross-sectional view at a position along the line IV-IV of 2 ,

5 FIG. 12 is a schematic view illustrating a comparison between a concentration of stress on a reinforced cutting edge subjected to bevel honing and a concentration of stress on a reinforced cutting edge of the drill according to the present invention. FIG.

Description of exemplary embodiments

An embodiment of a drill according to the present invention will be described below with reference to the attached 1 to 5 described. A drill 1 who in 1 and 2 is shown is a double-cutting spiral drill. The drill 1 has a cutting edge 2 and a groove 3 with a torsion angle. The drill 1 also has a thinning section 4 at a tip center portion and further has a main edge portion 6 and a minor margin section 7 on an outer periphery of a land portion 5 , The reference character "C" in FIG 1 denotes a centerline.

The cutting edge 2 , the groove 3 , the thinning section 4 , the survey section 5 , the main edge section 6 and the minor margin section 7 are all arranged centrally symmetrical. The reference numeral " 8th "Denotes an oil hole serving to supply a cut oil, which is in a flank surface 9 drilled at a point. The oil hole 8th is provided as needed.

The reference numeral " 10 "Denotes a rake face along the cutting edge 2 , The rake surface 10 is from a curved groove surface of the groove 3 educated.

The thinning section 4 of the drill shown in the figures is implemented by a single-phase thinning in which the rake face is formed by a flat surface. The thinning section 4 however, can also be implemented by a two-phase thinning, in which a rake face 10a of the thinning portion is formed by two surfaces which cross each other at an angle when the drill is viewed from the front. In the event that the drill has a two-phase thinning is used, an effect to improve the Spanbehandelbarkeit is expected.

The cutting edge 2 is from a thinning section cutting edge 2a and an outer peripheral cutting edge 2 B leading to an outer end of the cutting edge 2a leads, formed. As in 3 is shown, the thinning section cutting edge 2a is formed by a sharp ridge line formed at a portion where the rake face of the thinning portion and the flank face 9 cross each other (ridge line which is not subjected to honing for cutting edge reinforcement).

A honing to the cutting edge reinforcement becomes at the outer peripheral cutting edge 2 B carried out. As in 4 is shown, this honing is performed such that the cutting edge has a longitudinal vertical cross-sectional shape formed by a combination of a first curved surface 11a leading to the flank area 9 leads and has a radius R1, a second curved surface 11b leading to the rake face 10 leads and has a radius R2, and a third curved surface 11c that the first curved surface 11a and the second curved surface 11b combines.

A curvature of the second curved surface 11b is smaller than a curvature of the first curved surface 11a (that is, radius R2> radius R1), and a curvature of the third curved surface 11c is smaller than the curvature of the second curved surface 11b , As described above, in view of the relationship between the first curved surface 11a , the second curved surface 11b and the third curved surface 11c a ratio of the first curved surface 11a when a radius R3 of the third curved surface 11c is assumed to be 1 as 0.1 to 0.3, and there may be a ratio of the second curved surface 11b when the radius R3 of the third curved surface 11c is assumed to be 1, than 0.4 to 0.6. In the embodiment, the choice is made within these ranges.

The third curved surface 11c of the drill shown in the figure is a surface of constant curvature. The third curved surface 11c however, it may be a surface having a gradually changing curvature as long as the curvature in the entire area is smaller than those of the first and second curved surfaces 11a and 11b is.

A section of the thinning section 4 for connection with the groove 3 has such a shape that an edge remains when the drill is viewed from the front. The outer diameter side of the chip surface 10a the thinning section 4 (Section corresponding to the outer diameter side of the thinning section cutting edge 2a ), however, may be formed by a surface R having a small radius R for connection to the groove 3 having.

As described above, the thinning portion cutting edge becomes 2a formed by the ridge line which is not subjected to honing. Therefore, excellent penetration into a material to be cut can be ensured.

In addition, honing at the outer peripheral cutting edge 2 B performed such that the outer peripheral cutting edge 2 B has a cross-sectional shape formed by the combination of the first to third curved surfaces having different curvatures. Therefore, as compared with a drill subjected to normal chamfering, a concentration of stress at the portions of the cutting edge for connecting the flank surface and the rake face is reduced (the stress is distributed). As a result, damage to the cut edge is less likely to occur. Moreover, blunting of the cut edge is suppressed, as well as sharpness, as compared with a drill subjected to round honing.

5 Figure 3 shows schematically a concentration of stress on a reinforced cutting edge which is subjected to bevel honing and the reinforced cutting edge of the drill according to the present invention. The reference character "W" in the figure indicates a material to be cut. In the reinforced cutting edge, the chamfer honing as shown in 5 (a) is subjected to an edge on portions of a negative bump surface 12 (nega-land surface) for connecting the flank surface 9 and the rake surface 10 generated, and it focuses the stress at the edge portions. Therefore, chip formation of the cut edge, which starts at the edge portions, is less likely to occur.

In contrast, in the shape of the reinforced cut edge as shown in FIG 5 (b) the section corresponding to the nega-land surface of 5 (a) through the third curved surface 11c and furthermore, the portions of the third curved surface are replaced 11c for connecting the flank surface 9 and the rake surface 10 through the first and second curved surfaces 11a and 11b educated. Therefore, the stress applied to each curved surface is distributed and less likely to cause chipping of the cut edge as compared to the reinforced cut edge associated with chamfer honing, as shown in FIG 5 (a) is subjected occurs.

With regard to the axial rake angle AR of the thinning section 4 For example, a small negative angle is preferable for improving the sharpness and ensuring excellent penetration into the material to be cut, whereas a large negative angle is preferable when the main focus is on the thickness of the thinning section cutting edge. In view of a balance between the penetration ability and the thickness of the thinning portion cutting edge, the suitable axial rake angle AR of the rake face of the thinning portion is within a range of -15 ° to -40 °.

Moreover, a drill in which a negative thinning is selected is inferior in the sharpness of a thinning portion cutting edge over a drill in which a positive thinning is selected. Therefore, a radial runout tends to easily occur during processing.

To cope with this problem, the drill shown by way of example is a double edge type drill with a minor edge portion 7 , Therefore, compared to a single edge type drill, it is less likely that a radial runout will occur during the processing, and deterioration of the characteristics in the processed hole surface (generation of a feed mark) will result of the radial impact (radial runout) suppressed.

Claims (3)

Drill with a thinning section ( 4 ) at a rotational center portion, wherein a thinning section cutting edge (FIG. 2a ) is formed by a sharp ridge line which is generated at a portion where a flank surface ( 9 ) and a chip surface ( 10 ) at a negative axial rake angle, wherein: honing for cutting edge reinforcement at an outer peripheral cutting edge (FIG. 2 B ) extending radially outward from an outer end of the thinning portion cutting edge such that the honed cut edge has a cross-sectional shape formed by a combination of a first curved surface (Fig. 11a ) leading to the flank surface ( 9 ) and has a radius R1, a second curved surface ( 11b ) leading to the chip surface ( 10 ) and has a radius R2 which is smaller in radius of curvature than the radius R1 and a third curved surface (FIG. 11c ), which has the first curved surface ( 11a ) and the second curved surface ( 11b ) and the curvature is smaller than the radii R1 and R2. A drill according to claim 1, wherein: the third curved surface ( 11c ) is formed by a surface of constant curvature having a radius R3 and a ratio of the radius R1 when the radius R3 of the third curved surface (FIG. 11c ) is assumed to be 1, chosen to be 0.1 to 0.3, and a ratio of the radius R2, if the radius R3 of the third curved surface ( 11c ) is assumed to be 1, chosen as 0.4 to 0.6. A drill according to claim 1 or 2, wherein: the axial rake angle (AR) of the rake face of the thinning section (FIG. 4 ) within a range of -15 ° to -40 °.

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