Title

Drill insert and drill bit

Technical Field

The present application relates to a drill insert and a drill bit using the drill insert, which are particularly suitable for drilling a hard material.

Background Art

Drill bits for drilling hard materials, such as rock, typically have forward impact and rotary cutting capacities. For example, Fig. 1 schematically illustrates a conventional drill bit for drilling a hard material, the drill bit comprising a cemented carbide insert 1 and a drill shank 2 holding the insert 1 . A chisel edge 5a is formed in the middle of the front end face of the insert 1 , and a pair of cutting edges 5z are formed on the two main surfaces of the insert 1 . The chisel edge 5a extends between the two main surfaces and is connected between inner ends of the two cutting edges 5z. The chisel edge 5a is mainly used for forward impact, and the two cutting edges 5z are mainly used for rotary cutting. The chisel edge 5a and the two cutting edges 5z are all straight. Regardless of the specific form taken, there is a significant geometrical abrupt change (included angle) formed between the straight chisel edge 5a and each of the two straight cutting edges 5z, so that the transition part between the chisel edge 5a and each of the two cutting edges 5z is easily broken due to stress concentration, which may even lead to breakage of the entire insert. In addition, when drilling of a hard material starts, the chisel edge 5a is pushed against the surface of the hard material, a line contact is formed between the chisel edge 5a and the surface of the hard material, which causes the forward impact pressure of the insert to be spread over the en- tire chisel edge 5a, and thus the forward impact fracture capacity is insufficient Moreover, it is not easy to accurately centre the insert on the hard material.

For the drill bit for drilling a hard material, it is necessary to ensure its machining capacity and also improve the durability of the insert. It is difficult for the drill inserts in the prior art to have excellent performance in both of these aspects.

Summary of the Invention

The present application aims to provide a drill insert and a drill bit using the drill insert, which can improve both the machining capacity and the durability.

According to an aspect of the present application, provided is a drill insert for drilling a hard material, the drill insert defining a rotation axis and having two main surfaces opposite to each other in a thickness direction, two side surfaces opposite to each other in a width direction, a front end face, and a rear end face, the front end face being provided with a blade, which comprises a chisel edge in the centre in the width direction and cutting edges joined to two end points of the chisel edge, wherein the blade is manufactured such that the chisel edge is in the form of a curve that axially bulges forwards, and there is a smooth transition between each of the end points of the chisel edge and a start point of the cutting edge joined thereto, without forming a significant corner.

In an embodiment, in the projection in a reference plane containing or parallel to the rotation axis, an included angle between each of the end points of the chisel edge and the start point of the cutting edge joined thereto is less than 10 degrees, preferably less than 5 degrees, and most preferably the tangent lines thereof are the same.

In an embodiment, each of the cutting edges comprises at least one straight segment joined to the corresponding end point of the chisel edge, and the straight segment forms the tangent line of the corresponding end point of the chisel edge in the projection in a reference plane containing or parallel to the rotation axis. In an embodiment, the reference plane is a plane parallel to the two main surfaces, and the chisel edge is a quadratic curve in the projection in the reference plane.

In an embodiment, the reference plane is a plane tangent to the chisel edge at the centre of the chisel edge, the rotation axis is located in the reference plane, and the chisel edge is a quadratic curve in the projection in the reference plane.

In an embodiment, the blade is rotationally symmetrical at 180° about the rotation axis.

In an embodiment, each of the cutting edges comprises a first cutting edge segment and a second cutting edge segment, wherein the first cutting edge segment is joined between the chisel edge and the second cutting edge segment, and the second cutting edge segment is formed by a line of intersection of the front end face and the corresponding main surface.

In an embodiment, in the projection in a reference plane containing or parallel to the rotation axis, an included angle between the first cutting edge segment and the second cutting edge segment is less than 10 degrees.

In an embodiment, each of the cutting edges extends from the corresponding end point of the chisel edge to the corresponding side surface of the insert, without any portion located on the corresponding main surface; or each of the cutting edges is partially formed by the line of intersection of the front end face and the corresponding main surface; or each of the cutting edges is entirely formed by the line of intersection of the front end face and the corresponding main surface.

In an embodiment, the blade is at least partially defined by a line of intersection of a datum plane and a ruled surface.

In an embodiment, the blade is at least partially defined by a line of intersection of a datum plane and a large curved surface, the large curved surface is formed by rotating a generatrix about a revolution axis, and the generatrix consists of two straight segments and a rounded corner located between the two straight segments.

In an embodiment, the datum plane is positioned such that the revolution axis is located in or intersects with the datum plane.

In another aspect of the present application, provided is a drill bit, comprising a drill shank and a drill insert mounted on the drill shank, the drill insert being a drill insert described above, wherein a blade of the drill insert is preferably formed by means of machining, such as grinding, after the drill insert is mounted to the drill shank, so as to form various features related to the blade.

According to the present application, the chisel edge of the drill insert is in the form of a curve that bulges forwards, and when drilling of a hard material starts, a point contact is formed between the chisel edge and the surface of the hard material, so that the forward impact fracture capacity of the drill bit is improved. Moreover, the curved chisel edge makes it easier to accurately centre the insert on the hard material. In addition, there is a smooth transition between the chisel edge and the cutting edge, and thus there is no significant geometrical abrupt change (included angle) in the transition part between the chisel edge and each of the cutting edges, so that the transition part is not easily damaged during drilling, which can prolong the service life of the entire drill bit.

Brief Description of the Drawings

The foregoing and other aspects of the present application will be more fully understood from the following detailed description in conjunction with the accompanying drawings, in which:

Fig. 1 is a partial schematic diagram of a drill bit in the prior art;

Figs. 2 to 5 are respectively a front view, a top view, a side view and a perspective view of a drill insert according to an embodiment of the present application; Figs. 6 to 9 are respectively schematic diagrams illustrating a blade of the drill insert shown in Figs. 2 to 5;

Figs. 10 and 11 are respectively a front view and a top view of a drill insert according to another embodiment of the present application; and Figs. 12 and 13 are respectively a front view and a top view of a drill insert according to another embodiment of the present application.

Detailed Description of Embodiments

Various feasible implementations of a drill bit and a drill insert according to the present application are described below with reference to the drawings. It should be noted that the drawings herein are intended to show the principles of the present application clearly, so that some details are omitted, and the drawings are not drawn to scale and in actual shape.

The present application generally relates to a drill bit and a drill insert, which are used for drilling a hard material, especially stone.

Figs. 2 to 5 illustrate a drill bit according to an embodiment of the present application.

As shown, the drill bit comprises a drill insert (hereafter referred to as an insert) 1 . The insert 1 is made of cemented carbide, is substantially plate-shaped, and is fixedly mounted (e.g., welded) to a drill shank (not shown).

The insert 1 has a height direction (an axial direction) X, a width direction (a transverse direction) Y and a thickness direction Z. The insert 1 has a rotation axis O in the direction X.

The insert 1 is flat, and has two main surfaces 1 a parallel to each other and two side surfaces 1 b parallel to each other. The side surfaces 1 b may be arranged obliquely (not perpendicular) to the main surfaces 1 a as shown, or may be perpendicular to the main surfaces 1 a.

A front end face of the insert 1 (the face that faces the drilled material during drilling) axially bulges forward in the middle in the width direction. A line of intersection of the front end face and each of the side surfaces 1 b is defined by a front corner point A and a rear corner point B in a rotation direction. The line AB is preferably a straight line. The height of the front corner point A is greater than that of the rear corner point B, measured axially from the rear end face of the insert 1 .

The front end face of the insert 1 is provided with a blade 5. The blade 5 is rotationally symmetrical at 180° about the rotation axis O. Each point on the blade 5 is the axially frontmost point among all the points on the insert at the same widthwise distance from the rotation axis O. The blade 5 divides the front end face into two rotationally symmetrical tool faces 7. Each of the tool faces 7 is defined in the thickness direction by the blade (a main edge) 5 and a rear edge (a secondary edge) 6.

The blade 5 comprises: a chisel edge 5a in the centre, and cutting edges respectively extending from end points of the chisel edge 5a.

The chisel edge 5a is a smooth curved segment, the centre of which is preferably on the rotation axis O and forms the axially frontmost point of the entire insert 1 . The chisel edge 5a is substantially inclined relative to the two main surfaces 1 a, viewed from the axial direction. Specifically, the chisel edge 5a has two end points, each of which is offset, relative to the centre of the chisel edge 5a, towards the corresponding main surface 1 a and side surface 1 b, viewed from the axial direction.

Each of the cutting edges in this example comprises a first cutting edge segment 5b extending obliquely from the corresponding end point of the chisel edge 5a to the corresponding main surface 1 a and a second cutting edge segment 5c formed by a line of intersection of the corresponding tool face 7 and the main surface 1 a. Each first cutting edge segment 5b starts from the corresponding end point of the chisel edge 5a and ends at an intersection point C of the first cutting edge segment 5b and the corresponding main surface 1 a. Each second cutting edge segment 5c starts from the corresponding intersection point C and ends at the corresponding front corner point A.

Both the first cutting edge segment 5b and the second cutting edge segment 5c are preferably straight segments. There is a smooth transition between a start point of each first cutting edge segment 5b and the corresponding end point of the chisel edge 5a. The smooth transition herein may be considered as, in the projection in a reference plane containing the rotation axis O or parallel to the rotation axis O, an included angle between the start point of the first cutting edge segment 5b and the corresponding end point of the chisel edge 5a being less than 10 degrees, preferably less than 5 degrees, and most preferably the tangent line at the start point of each cutting edge segment 5b being the same as the tangent line at the corresponding end point of the chisel edge 5a, so that no significant corner, or even no corner is formed between the start point of each first cutting edge segment 5b and the corresponding end point of the chisel edge 5a, viewed from any direction. The reference plane is selected from a plane (the plane XY) which is parallel to the main surface and a plane which contains the rotation axis and is tangent to the chisel edge at the midpoint of the chisel edge.

Each rear edge 6 is formed between the rear corner point B and the intersection point C on the corresponding main surface 1a.

Each part of each rear edge 6 has a shape following substantially the shape of the corresponding portion of the blade 5 towards which the rear edge faces in the thickness direction, so that the height of each point on the rear edge 6 in the axial direction is lower than that of the corresponding point on the blade 5 towards which the rear edge faces in the thickness direction.

Each rear edge 6 has a straight segment in the thickness direction corresponding to the second cutting edge segment 5c, i.e., the part connected to the rear corner point B, and has a curved segment in the thickness direction corresponding to the chisel edge 5a, and has a straight or curved segment in the thickness direction corresponding to each first cutting edge segment 5b.

Optionally, the portion of each tool face 7 that faces the second cutting edge segment 5c in the thickness direction is a flat portion, the portion that faces the chisel edge 5a in the thickness direction is a curved portion, and a transition portion is formed between the flat portion and the curved portion. Each second cutting edge segment 5c is at an angle a relative to a straight line parallel to the width direction of the rear end face of the insert 1.

The portion of each rear edge 6 that is connected to the rear corner point B is at an angle [3 relative to a straight line parallel to the width direction of the rear end face of the insert 1. The angle [3 is preferably equal to the angle a.

Each first cutting edge segment 5b forms a small angle y with the corresponding main surface 1 a, and the angle y is less than 20 degrees, preferably less than 15 degrees, and most preferably less than 10 degrees, viewed from the axial direction.

Optionally, referring to Fig. 6, the chisel edge 5a, the first cutting edge segment 5b and the second cutting edge segment 5c of the blade 5 are presented as line segments 5a', 5b' and 5c', respectively, in the projection in the plane XY as a reference plane (i.e., in the projection in the main surface 1 a), where the line segment 5a' is a quadratic curve segment, each line segment 5c' is preferably a straight segment (but may also be a curved segment), and each line segment 5b' is a straight segment that is smoothly joined between the line segments 5a' and 5c' and is preferably co-linear or forms a small included angle (e.g., less than 10, preferably less than 5 degrees) with the line segment 5c' connected thereto.

Measured in another way, referring to Fig. 7, an imaginary plane P is taken as the reference plane, the rotation axis O lies in the imaginary plane P, and the imaginary plane P is tangent to the chisel edge 5a at the midpoint of the chisel edge 5a. The chisel edge 5a, the first cutting edge segment 5b and the second cutting edge segment 5c of the blade 5 are presented as line segments 5a", 5b" and 5c", respectively, in the projection in the imaginary plane P, where the line segment 5a" is a quadratic curve segment, each line segment 5c" is preferably a straight segment (but may also be a curved segment), each line segment 5b" is smoothly joined between the line segments 5a" and 5c" and is preferably co-linear or forms a small included angle (e.g., less than 5 degrees) with the line segments 5c" connected thereto. It should be understood by those skilled in the art that, due to various types of popularly used design software available, it is not difficult to design the trajectory of the blade 5 formed by a combination of straight and curved lines in a three- dimensional space, so other ways of defining the segments of the blade 5 are also possible. In the simplest case, the designer can even determine the trajectory of the blade 5 directly in three-dimensional design software by point-by-point adjustment, provided that the trajectory of the blade 5 broadly conforms to the requirements of the present application.

To be more precise, the chisel edge 5a and the first cutting edge segment 5b of the blade 5 can be defined as a line of intersection of a datum plane and a ruled surface. The ruled surface is a curved surface created by the motion (revolution or non-revolution) of a straight generatrix.

In practical design, the chisel edge 5a and the first cutting edge segment 5b of the blade 5 can also be defined by a line of intersection of a datum plane and an approximate ruled surface. For example, in the example shown in Fig. 9, the chisel edge 5a and the first cutting edge segment 5b of the blade 5 can be defined as a line of intersection of a datum plane and a large curved surface. Here, a generatrix R rotates about a revolution axis Oc to form a large curved surface, the generatrix R consisting of two straight segments Rb and Rc and a rounded corner Ra located between the straight segments Rb and Rc. A datum plane P' crosses the large curved surface, and a line of intersection of the datum plane P' and the large curved surface forms the first cutting edge segments 5b at both ends and the chisel edge 5a joined between the two first cutting edge segments 5b. The datum plane P' may be selected on demand and is adjustable during design. For example, the revolution axis Oc may be located in the datum plane P' or intersect with the datum plane P' (the plane P' may be inclined at any of onedimensional, two-dimensional or three-dimensional inclination angles relative to the revolution axis Oc in three dimensions).

Other ways of precisely defining the chisel edge 5a and the first cutting edge segment 5b of the blade 5 can also be used herein. Various modifications can be made to the previously described embodiment of the insert 1 by those skilled in the art. For example, in the modified embodiment shown in Figs. 10 and 11 , the blade 5 is only composed of the chisel edge 5a and the first cutting edge segments 5b on two sides, with a smooth transition between the chisel edge 5a and each first cutting edge segment 5b. Each first cutting edge segment 5b extends as far as the corresponding side surface 1 b. In this example, the cutting edge of the insert 1 comprises only the first cutting edge segments 5b, without the second cutting edge segment 5c described previously, where the first cutting edge segments 5b do not have any portion located on the corresponding main surface 1a. Other aspects of the modified embodiment shown in Figs. 10 and 11 are the same as or similar to the embodiment shown in Figs. 1 to 9, which will not be repeated.

As another example, in the modified embodiment shown in Figs. 12 and 13, the blade 5 comprises only the chisel edge 5a and the second cutting edge segments 5c on two sides. In this example, the cutting edge of the insert 1 comprises only the second cutting edge segments 5c, without the first cutting edge segment 5b described previously. The chisel edge 5a is joined to and forms a smooth transition with each second cutting edge segment 5c, so that in the projection in a reference plane containing the rotation axis O or parallel to the rotation axis O, an included angle between a start point of each second cutting edge segment 5c and the corresponding end point of the chisel edge 5a is less than 10 degrees, preferably less than 5 degrees, and most preferably the tangent lines thereof are the same (or the tangent lines at the start point of each second cutting edge segment 5c and the corresponding end point of the chisel edge 5a are co-linear). The reference plane is selected from a plane (the plane XY) which is parallel to the main surface and a plane which contains the rotation axis and is tangent to the chisel edge at the midpoint of the chisel edge. In this way, no significant corner, or even no corner is formed between the start point of each second cutting edge segment 5c and the corresponding end point of the chisel edge 5a, viewed from any direction. Other aspects of the modified embodiment shown in Figs. 12 and 13 are the same as or similar to the embodiment shown in Figs. 1 to 9, which will not be repeated. It should be understood that the cutting edge of the insert 1 may be in other forms, such as three or more segments, to enable the insert 1 to achieve different functions. Each of the cutting edges of the insert 1 is preferably in the form of a straight line or a curve with a large bending radius, and forms a smooth transition with the chisel edge 5a, so that in the projection in a reference plane containing the rotation axis O or parallel to the rotation axis O, the included angle between the start point of each of the cutting edges and the corresponding end point of the chisel edge 5a is less than 10 degrees, preferably less than 5 degrees, and most preferably the tangent lines thereof are the same (or the tangent lines at the start point of each of the cutting edges and the corresponding end point of the chisel edge 5a are co-linear). The reference plane is selected as previously described. In this way, no significant corner, or even no corner, is formed between each cutting edge and the chisel edge 5a, viewed from any direction. The cutting edges of the insert 1 also preferably have a smooth transition therebetween.

The cutting edge segment (the second cutting edge segment described previously) located on the main surface may be composed of a plurality of line segments (straight and/or curved segments).

With regard to the blade and the tool faces on the insert, the insert can be machined (e.g., ground) after being fixed (e.g., welded) to the drill shank, to form the blade and the tool faces. It is also possible to machine (e.g., grind) the insert to form the blade and the tool faces and then fix the insert to the drill shank.

According to the present application, the chisel edge of the drill insert is in the form of a curve that bulges forwards, and when drilling of a hard material starts, a point contact is formed between the chisel edge and the surface of the hard material, so that the pressure applied by the insert to the hard material can be increased, the forward impact fracture capacity of the drill bit can be improved, and the drilling speed can be increased. Moreover, the curved chisel edge makes it easier to accurately centre the insert on the hard material. In addition, there is no sharp corner on the curved chisel edge, so that stress concentration is not likely to occur. In addition, there is a smooth transition between the chisel edge and the cutting edge, so that there is no significant geometrical abrupt change (included angle) in the transition part between the chisel edge and the cutting edge, the stress concentration at the transition part is alleviated or even eliminated during drilling, and the transition part is not easily damaged, which can prevent fracture of the entire insert so as to prolong the service life of the entire drill bit Although the present application is described herein with reference to the specific exemplary embodiments, the scope of the present application is not limited to the details as shown. Various modifications can be made to these details without departing from the basic principles of the present application.