TECHNICAL FIELD

The present invention relates to a drill, in particular, a drill preferably used for drilling holes by manpower using a hand drill, a drill press or the like.

BACKGROUND OF THE INVENTION

Recently, for drills for machine tools such as machining centers or the like, fully automatic machines allowing unmanned processing are becoming the mainstream and thus various kinds of drills corresponding to the fully automatic machines have been developed and sold.

However, drills used for devices requiring operator's power to drill holes, such as a hand drill or a drill press, have not been positively researched or developed. As a result, drills in almost same configurations have been used over several decades.

Since drills used for a hand drill, a drill press or the like employ operator's arm strength to drill holes, it is difficult to drill holes when drilling resistance is high.

However, manufacturers of drills have spent little time on research for decreasing the high drilling resistance. It is partly because they have prioritized strength and stiffness of the conventional drills, and because users of drills actually grind a drill in accordance with one's taste after purchasing it.

In Japanese Unexamined Patent Application Publication No. 2006-88267, the applicant proposes a drill preferably used for exfoliating a spot welding part of a car's body which is made of high hardness steel sheets.

This drill has two cutting blades which are symmetrical about an axis of rotation, has a tip part on which thinning is performed, and has 0.05 to 0.3 mm chisel width, and its thinning is performed at an inclined angle of 1 to 4 degrees toward the straight line joining blade edges of both cutting blades when seen from the drill's tip side.

This drill has less thrust resistance during drilling and requires less power applied by an operator, since its chisel width is narrow and thinning is performed at 1 to 4 degrees.

However, this drill has a rake angle of more than 90 degrees shaped by thinning in order to deal with steel sheets with high hardness.

Therefore, the drilling force of the central part is weak, and when drilling with a hand drill, a significant power would be required till the drilling from a central part reaches to a peripheral cutting blade.

Moreover, a tip has a risk of breakage during use because of a quite narrow width of a chisel, and particularly a tip of a drill made from powder high-speed steel is fragile and more easily chipped.

In Japanese Unexamined Patent Application Publication No. 2012-192514, the applicant proposes a drill capable of significantly reducing drilling resistance and allowing easy hole-drilling by manpower using a hand drill, a drill press or the like.

The drill has two cutting blades which are symmetrical about an axis of rotation, wherein thinning is performed on its tip part, and a rake angle θ1formed by a main cutting blade and a rake angle θ2formed by a thinning cutting blade satisfy θ1>θ2>0°, except for a part just below the chisel.

SUMMARY OF THE INVENTION

For a drill (101) described in Japanese Unexamined Patent Application Publication No. 2012-192514, a rake angle changes when drilling started by a thinning cutting blade (103) reaches a main cutting blade (104): the gentle rake angle allowing a stable drilling rapidly increases at an inner edge part (105) of the main cutting blade (104), further increases as a drilled part approaches the drill's peripheral side, and becomes equal to a flight angle at a peripheral part (106) (seeFIG. 17).

As a result, there are frequent problems upon penetrating with a drill such as cracks in an inner periphery of a drilled workpiece and deformation of a workpiece when it is a thin plate, acryl or the like.

When a workpiece is a laminated material, for example, a carbon fiber reinforced plastic (hereinafter referred to as CFRP), there are problems of inducing an interlayer peeling phenomenon (delamination) when drilling holes, or delamination when drilling CFRP by the conventional drill inFIG. 17.

Common drills having a flight angle of about 30 degrees (=rake angle/peripheral part) may cause the problems.

Though the problems can be solved by making a gentle flight angle of a drill, other problems such as discharged chips are brought and may deteriorate sharpness of a drill itself. Hence, it is impossible to solve the problems only by making a gentle flight angle.

As a result of zealous examination, the inventors found out that the problems can be solved by providing a main cutting blade of a drill with U-shaped grooves.

The present invention is made to solve the problems of the Prior-Arts, and provides a drill having less possibility of cracks in an inner periphery of a drilled workpiece and its deformation upon penetrating with a drill, as well as delamination.

The present invention according to first aspect relates to a drill comprising two cutting blades which are formed symmetrical about an axis of rotation,

wherein each of the cutting blades has a main cutting blade formed from a drill tip toward a peripheral side of the drill to become a shape with curves,

a thinning cutting blade formed in closer to the drill tip than the main cutting blade to become a shape with curves, and

an U-shaped cutting blade formed on the drill's peripheral part of the thinning cutting blade to become a shape with curves.

The present invention according to second aspect relates to the drill of first aspect, wherein the U-shaped cutting blade is formed near the peripheral part of the drill.

The present invention according to third aspect relates to the drill of first aspect, wherein the U-shaped cutting blade is formed to be adjacent to the thinning cutting blade and aligned at the outer peripheral side in a radial direction.

The present invention according to fourth aspect relates to the drill of any one of first to third aspects, having two clearance faces formed symmetrical to an axis of rotation,

wherein the clearance faces are provided with back grooves in a shape with curves so as to comprise a first margin part and a second margin part located at a heel side of the first margin part.

The present invention according to fifth aspect relates to the drill of fourth aspect, wherein a second margin cutting blade is provided at the second margin part.

The invention according to sixth aspect relates to the drill of fourth or fifth aspect, wherein multiple peripheral grooves are formed at a peripheral part of the main cutting blade and/or a peripheral part of the second margin cutting blade.

According to the invention of first aspect, there is provided a drill comprising a thinning cutting blade in a shape with curves formed in closer to the drill tip than the main cutting blade, and an U-shaped cutting blade in a shape with curves formed in closer to the periphery of the drill than the thinning cutting blade, such that drilling resistance can be significantly decreased and make it easier to drill holes using a hand drill, a manual drill press or the like, even if drilling a thin plate, soft materials, or a carbon fiber reinforced plastic (CFRP). Moreover, the reduction of drilling resistance improves drilling accuracy and reduces the time to drill holes, resulting in an improvement of working efficiency. It also allows for a significant increase in the drill's life span.

Therefore, provided herein is a drill having less possibility of cracks in an inner periphery of a drilled workpiece and deformation of a workpiece upon penetrating with a drill, as well as delamination.

According to the invention of second aspect, an U-shaped cutting blade is formed near the peripheral part of the drill, thereby enhancing a cutting force and reducing drilling resistance. In addition, it is possible to discourage the drill's wear and significantly increase the drill's life span.

According to the invention of third aspect, an U-shaped cutting blade is formed to be adjacent to the thinning cutting blade and aligned at the outer peripheral side in a radial direction, thereby enhancing a cutting force and reducing drilling resistance. In addition, it is possible to discourage the drill's wear and significantly increase the drill's life span.

According to the invention of fourth aspect, there are provided two clearance faces formed symmetrical to an axis of rotation, wherein the clearance faces are provided with back grooves in a shape with curves so as to comprise a first margin part and a second margin part located at a heel side of the first margin part, thereby more easily preventing cracks in an inner periphery of a drilled workpiece and deformation of a thin plate upon penetrating with a drill, and delamination.

According to the invention of fifth aspect, a second margin cutting blade is provided on the second margin part, thereby enabling to cut away a part which is difficult to cut due to a little elastic deformation during drilling, and more easily prevent delamination.

According to the invention of sixth aspect, there are formed multiple peripheral grooves at a peripheral part of the main cutting blade and/or a peripheral part of the second margin cutting blade, thereby enabling to suppress heat generation during drilling a workpiece, and solve problems such as deformation of drilled holes and a change of material quality of a workpiece due to heat generation during drilling.

