JPS6158245B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drill that has increased torsional rigidity to prevent vibration during cutting and to smoothly discharge chips.

Conventional drills have a helical groove uniformly formed from the cutting edge to the base of the shank, and as a result, the cross-sectional area of the shank is reduced by the helical groove, resulting in weak torsional rigidity, especially during high-feed cutting. The disadvantage was that vibrations were likely to occur when the load became large. It has also been proposed to change the depth of the helical groove, that is, the core thickness of the drill.
The amount of change is approximately 1 mm per 100 mm of shank length, which increases the core thickness as it approaches the base of the shank, and at this level, the effect of increasing torsional rigidity is negligible. In particular, increasing the core thickness only increases the area of the center in the cross section of the shank, and since the increase in the polar moment of inertia is small, the contribution to the torsional moment is small. In addition, chips formed at the cutting edge rise along the helical groove and are discharged, but if the helical groove is formed gradually shallower, the chips will flow onto the inner surface of the machined hole or the inner surface of the helical groove while rising. There is a problem in that a large movement resistance is generated due to being pushed, and the evacuation of chips is obstructed.

In view of these points, the present invention dramatically improves the torsional rigidity by improving the shape of the helical groove, and also enables smooth discharge of chips.

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2, 1 is a shank, 2 is a twisted groove formed in the shank, 3, 3
is a chip with a pair of cutting edges. The head of the drill is conical and has cutting edges that are symmetrical to each other with a starting point at a center point 11 serving as the apex. The cutting edge has a curve that is convex in the rotational direction when viewed from the bottom, and is a spiral curve whose curvature increases as it approaches the center from the outer periphery.
When such a cutting edge shape is adopted, the chips are thinner at the center than at the outer periphery, and the cutting resistance is also small.
In addition, chips are not pressed against the cutting blade, so they are smoothly discharged.

The helical groove 2 is formed in a spiral along the shank, but its cross-sectional shape is not constant along the shank, and in the side view, the width of the opening of the helical groove is shown by the ridge line 6 in Fig. 1. is formed so that it gradually becomes narrower. In a conventional helical groove having a uniform shape, the width of the opening of the helical groove is constant, as shown by the imaginary line 7 in FIG. On the other hand, in the present invention, the depth of the helical groove becomes gradually deeper toward the base of the shank.

Further, referring to FIG. 2, the wall 50 at the rear in the direction of rotation at the cutting edge almost coincides with the curve of the cutting edge, but as you move toward the base of the shank, the wall 50 curves along imaginary lines 51, 52, 53, As shown at 54, the wall 40 at the front in the rotational direction is gradually displaced forward, and the wall 40 at the front in the rotational direction follows the curve 4.
Although the curvature becomes slightly smaller as shown in , the cross-sectional area of the twisted groove decreases as a whole. That is,
As shown in FIG. 3, the cross-sectional area of the helical groove 2 gradually narrows from the cutting edge toward the base of the shank.

The cross-sectional area of the shank 1 increases by the approximately triangular area between the walls 5 and 50, while the wall 4 at the front in the direction of rotation is set back from the wall 40 near the cutting edge, so the area decreases. However, the amount of decrease is very small, so the overall increase is. Furthermore, this increase is greater at the outer circumference than at the center of the shank, resulting in a large increase in the polar moment of inertia and a dramatic improvement in torsional rigidity.

The chips formed by cutting are caused by the curvature of the helical groove near the cutting edge, that is, the curve 40 in FIGS. 2 and 3.
After being bent along the curve, the chip rises along the helical groove, but since the curvature of the helical groove is smaller than the curvature of the bent chip, as shown by curve 4, the resistance when rising in the helical groove is It is very small and therefore chips can be discharged very smoothly. Note that the area of the entire helical groove is reduced by moving the rear wall 5 of the helical groove 5 forward in the rotational direction relative to the wall 50 at the cutting edge, but the chips are curved to a radius of curvature R. Since the helical groove is formed with a larger R′, there is no problem with chip evacuation. In addition, since the generated chips are bent with the radius of curvature R, it is also possible to form a twisted groove with the radius of curvature R to the base of the shank and only deepen the groove depth. There is an advantage in that the curvature of the helical groove is constant and that machining is easy. However, if the groove depth is increased and the radius of curvature of the groove is also increased as in the above embodiment, the movement of chips in the twisted groove becomes easier, and therefore the discharge of chips becomes easier. Furthermore, by forming such a groove shape, the rear wall 5 in the rotational direction
The angle θ formed by the inner surface of the hole of the work material is
Since the angle .alpha. is larger than the angle .alpha., there is no risk that chips rising along the groove will be caught between the outer surface of the shank and the inner surface of the hole, and the chips can be reliably discharged.

Note that the shape of the cutting edge is not limited to the spiral shape described above, and various shapes can be adopted, and the degree of change in the groove shape is not limited to the example shown in the figure, but may vary depending on conditions such as the shape of the cutting edge and the type of workpiece material. It may be selected as appropriate.

As explained above, the present invention increases torsional rigidity by improving the shape of the torsion groove,
This prevents vibrations during cutting and allows for smooth removal of chips, resulting in extremely high finishing accuracy and surface roughness of the machined hole. .

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the present invention, FIG. 2 is a bottom view thereof, and FIG. 3 is a sectional view taken along the line -- in FIG. 1...Shank, 2...Twisted groove, 3...Cutting blade, 4, 40...Wall in front of rotation direction, 5, 50...
...The rear wall in the direction of rotation.

Claims (1)

[Claims] 1 In a drill with a helical groove, the wall of the helical groove on the rear side in the rotational direction is formed so as to gradually approach the other wall of the helical groove from the cutting edge toward the base of the shank, and the depth of the helical groove is equal to the depth of the shank base. A drill characterized by being formed so as to increase toward .