Small-diameter drill bit

Patent metadata

Field	Value
Publication number	US-11413690-B2
Application number	US-201716090675-A
Country	US
Kind code	B2
Filing date	Apr 14, 2017
Priority date	Apr 15, 2016
Publication date	Aug 16, 2022
Grant date	Aug 16, 2022

Abstract

In this small-diameter drill bit, two cutting blades having main cutting blades, of which a difference between lengths are 0.04 mm or less, are formed on a tip of a double-margin drill bit body having a diameter of 2 mm or less and a margin length/diameter ratio of 3 or more. Two tip flank faces are formed such that a first extension line extending from a linear first intersecting ridgeline between a first tip flank face and a second tip flank face of one of the flank faces to the linear first intersecting ridgeline of the other flank face is located on a side in the drill bit rotation direction with respect to the other linear first intersecting ridgeline. A distance between the first extension line and the linear first intersecting ridgeline is in a range of 0.04 mm-0.08 mm.

First claim

What is claimed is:

1. A small-diameter drill bit in which two chip discharge grooves opening to two tip flank faces of a drill bit body and extending to a rear end side are formed symmetrically with respect to an axis at an outer periphery of a tip part of the drill bit body that is configured to rotate around the axis, cutting blades are respectively formed at intersecting ridgeline parts between wall faces of the chip discharge grooves that face a drill bit rotation direction and the tip flank faces, a first margin part adjacent to a side of each of the chip discharge grooves opposite to the drill bit rotation direction, and a second margin part adjacent to a side of the chip discharge groove in the drill bit rotation direction are formed on a land part between the chip discharge grooves, and a diameter D of the cutting blades is between 2 mm and 1 mm,
wherein a ratio L/D of each respective margin length L to the diameter D is 3 or more, the margin length L being in a direction of the axis from an outer peripheral end of each of the cutting blades to a rear end of each of the first and second margin parts,
wherein a thinning part is formed at an inner periphery of a tip part of the chip discharge groove,
wherein the thinning part has a thinning face that faces the side opposite to the drill bit rotation direction,
wherein each of the cutting blades includes a main cutting blade that linearly extends from an outer periphery of the drill bit body toward an inner periphery side thereof as seen from a tip side in the axis direction, and a thinning blade that is bent on the inner peripheral side of the main cutting blade and is formed at an intersecting ridgeline part between the thinning part and each of the tip flank face,
wherein a difference between lengths from outer peripheral ends of two main cutting blades as seen from the axis direction tip side is 0.04 mm or less,
wherein the tip flank faces each has a first tip flank face and a second tip flank face,
wherein the first tip flank face is connected to a side of the cutting blade opposite to the drill bit rotation direction,
wherein the second tip flank face is connected to a farther side of the first tip flank face opposite to the drill bit rotation direction, intersects the thinning face, wherein a first intersecting ridgeline between the first tip flank face and the second tip flank face and a second intersecting ridgeline between the second tip flank face and the thinning face are linear as seen from the axis direction tip side,
wherein as seen from the axis direction tip side, the two tip flank faces are formed such that a first extension line extending from the first intersecting ridgeline in one of the tip flank faces to the opposite tip flank face side is located on a side in the drill bit rotation direction side with respect to the first intersecting ridgeline of the opposite tip flank face,
wherein a distance between the first extension line and the first intersecting ridgeline as seen from the axis direction tip side is in a range of 0.04 mm to 0.08 mm,
wherein as seen from the axis direction tip side, the two tip flank faces are formed such that a second extension line extending from the second intersecting ridgeline in one tip flank face to the opposite tip flank face side is located on the side in the drill bit rotation direction with respect to the second intersecting ridgeline of the opposite tip flank face
wherein a distance between the second extension line and the second intersecting ridgeline is in a range of 0.08 mm or less as seen from the axis direction tip side, and
wherein succession in the drill bit rotation direction is as follows: the main cutting blade, the second intersecting ridgeline, the second extension line, the first intersecting ridgeline, and the first extension line.

2. The small-diameter drill bit according to claim 1 ,
wherein the second margin part is formed in a direction as extending from the second tip flank face to the thinning face in a circumferential direction.

3. The small-diameter drill bit according to claim 1 ,
wherein the wall faces of the chip discharge grooves are coated with a nitride film of Ti and Si.

4. The small-diameter drill bit according to claim 3 ,
wherein the wall faces of the chip discharge grooves are coated with the nitride film of Ti and Si by a sputtering method, and then, the wall faces of the chip discharge grooves are irradiated with abrasive power and subjected to smoothing machining.

5. The small-diameter drill bit according to claim 3 ,
wherein the wall faces of the chip discharge grooves are coated with the nitride film of Ti and Si by an arc ion plating method, and then, the surface of the chip discharge grooves are irradiated with abrasive power and subjected to smoothing machining.

Assignees

• Mitsubishi Hitachi Tool Eng Ltd
• Moldino Tool Engineering Ltd

Inventors

• Yoshioka Shogo

Classifications

• B23B51/011

  Micro drills · CPC title

• B23B51/06

  Drills with lubricating or cooling equipment {(B23B51/042 takes precedence)} · CPC title

• B23B2251/14

  Configuration of the cutting part, i.e. the main cutting edges · CPC title

• B23B51/02 Primary

  Twist drills · CPC title

• B23B2251/12

  Cross sectional views of the cutting edges · CPC title