WO2021212448A1

WO2021212448A1 - Compression mold and method for forming carbide tip of drill bit by widthwise pressing

Info

Publication number: WO2021212448A1
Application number: PCT/CN2020/086589
Authority: WO
Inventors: Xu Fang; Massimo Anghileri; Haifeng Ji; Zhenglin Yang; Hongkai BAI; Xiao CAI; Shunli SHI
Original assignee: Robert Bosch Gmbh
Priority date: 2020-04-24
Filing date: 2020-04-24
Publication date: 2021-10-28
Also published as: CN115443197A; CN115443197B

Abstract

A compression mold for forming a carbide drill tip (4) is disclosed. The mold comprises a die (1), an upper punch (2) and a lower punch (3). The die comprises an inner wall (11) defining a die hole. The upper punch is inserted into the die hole from the upper side of the die. The lower punch is inserted into the die hole from the lower side of the die. A part of the die hole defines a filling cavity. The filling cavity is defined by at least the top surface of the lower punch and the inner wall. A powdered material is fed into the filling cavity. The upper and lower punches are configured to compress the powdered material filled in the filling cavity in a vertical direction corresponding to the width direction of the drill tip formed by the powdered material. A compression method for forming a carbide drill tip is also disclosed. It is easy to form a drill tip with a sharp head.

Description

Compression Mold and Method for Forming Carbide Tip of Drill Bit by Widthwise Pressing

Technical Field

The disclosure relates to a compression mold and a method for forming a carbide tip of a drill bit by widthwise pressing.

Background Art

Carbide drill tips of drill bits for drilling hard materials are generally formed by powder metallurgy. A powdery material is pressed in a mold to form a semi-finished drill tip. A traditional mold for forming a semi-finished drill tip is schematically shown in Figure 1. The compression mold comprises a die 1, and an upper punch 2 and a lower punch 3 which are inserted into the die to define a filling cavity into which a powdery material is filled. The upper and

lower punches

2 and 3 compress the powdery material substantially in the heightwise direction of a drill bit 5 to be formed, that is, parallel to the rotational axis of the drill bit. A problem found in the compression molding process using the compression mold shown in Figure 1 is that the material in the head portion the drill bit has a smaller compression rate than other portions of the drill bit so the head portion has a low density, and thus such a mold cannot be used for forming a drill bit having a sharp head. In addition, the upper punch 2, which has two sharp portions, is worn more quickly than the lower punch 3. Further, the filling cavity defined in the compression mold shown in Figure 1 has a fixed width, which is not adjustable, so the compression mold cannot be used for forming drill bits which have different widths.

Figure 2 schematically shows another type of mold for forming a semi-finished drill tip. In a die 1, upper and

lower punches

2 and 3 comprise a powdery material substantially in the thicknesswise direction of the drill bit 4 to be formed. By using such a mold, only drill tips having the same shape and dimensions can be formed. In addition, all portions of the drill tip thus formed have nearly the same compression rate and thus have nearly the same strength.

Summary of the Disclosure

The disclosure is aimed at providing a new technique for forming a carbide tip of a drill bit to address at least one problem found in prior art.

According to one aspect of the disclosure, a compression mold is disclosed, the compression mold comprising:

a die formed with a vertical die hole therein, the die hole being defined by an inner wall;

an upper punch configured to be inserted into the die hole from above; and

a lower punch configured to be inserted into the die hole from below;

wherein a portion of the die hole forms a filling cavity which is defined at least by a top surface of the lower punch and the inner wall and into which a powdery material can be filled; and

wherein the upper and lower punches are configured to compress the powdery material filled in the filling cavity in a vertical direction which corresponds to the widthwise direction of the drill tip to be formed by the powdery material.

According to an embodiment of the compression mold, the upper punch has a bottom surface which comprises a transverse face and an oblique face, and the lower punch has a top surface which comprises a transverse face and an oblique face, the transverse faces being configured to form a base portion of the drill tip, while the oblique faces being configured to form an edge portion of the drill tip.

According to an embodiment of the compression mold, the filling cavity is defined by the top surface of the lower punch, the inner wall, and an upper surface of the die.

According to an embodiment of the compression mold, at least a portion of the upper surface of the die is formed as an oblique upper surface portion, at least a portion of the die hole being opened upwardly through the oblique upper surface portion.

According to an embodiment of the compression mold, the oblique upper surface portion is oblique with respect to a horizontal direction by an angle, the angle being equal to or not equal to the oblique angle of the oblique face of the upper punch .

According to an embodiment of the compression mold, the upper surface of the die further comprises a horizontal upper surface portion, a portion of the die hole being opened upwardly through the horizontal upper surface portion.

According to an embodiment of the compression mold, the upper surface of the die comprises a combination of at least one oblique upper surface portion and at least one horizontal upper surface portion, the least one oblique upper surface portion and the least one horizontal upper surface portion being designed to achieve desired densities of various portions of the drill tip to be formed.

According to an embodiment of the compression mold, at least one of the upper and lower punches is a split-type punch which comprises two or more punch parts that can be moved in the widthwise direction of the drill tip to be formed independently with respect to each other.

According to another aspect of the disclosure, a compression method for forming a carbide drill tip of a drill bit by using the compression mold described above is disclosed, the compression method comprising the steps of:

moving the lower punch upwards into the die to form a filling cavity inside the die;

filling a powdery material into the filling cavity ; and

moving the upper punch downwards into the die to compress the powdery material filled in the filling cavity in a vertical direction which corresponds to the widthwise direction of the drill tip to be formed by the powdery material.

The compression method of claim may further comprises further moving the lower punch upwards when the upper punch is being moved downwards or after the upper punch has finished its downward movement.

The compression method of claim may further comprises controlling the downward moving of the upper punch and/or the further upward moving of the lower punch to control the dimension of an head portion of the drill tip in the widthwise direction.

According to the disclosure, the upper and lower punches compress the powdery material substantially in the thicknesswise direction of the drill bit to be formed, that is, in a direction parallel to the major surfaces of the drill bit and perpendicular to the rotational axis of the drill tip, thus it is easy to form a drill tip with a sharp head. Further, drill bits having different widths can be formed by using the same die and by changing upper and lower punches. Furthermore, the head (apex) portion of the drill tip may have a different (generally higher) compression rate, and thus a different (generally higher) strength, than other portions of the drill tip. Furthermore, the difference in the wear rates of the upper and lower punches can be reduced compared with the prior art shown in Figure 1.

Brief Description of the Drawings

Figure 1 is a schematic view of a traditional mold for forming a drill tip;

Figure 2 is a schematic view of another traditional mold for forming a drill tip;

Figures 3 and 4 are schematic front views of drill tips that can be formed by using a technique of the disclosure;

Figure 5 is a schematic cross sectional view of a compression mold according to an embodiment of the disclosure;

Figures 6 and 7 are respectively schematic views of upper and lower punches of the compression mold shown in Figure 5;

Figures 8 and 9 are schematic views showing different stages of a molding process for forming a drill tip by using the compression mold shown in Figure 5;

Figure 10 is a schematic side view showing a configuration of the upper and lower punches of the compression mold shown in Figure 5;

Figure 11 is a schematic top view of a drill tip formed by using the upper and lower punches shown in Figure 10;

Figure 12 is a schematic side view showing another configuration of the upper and lower punches of the compression mold shown in Figure 5;

Figure 13 is a schematic top view of a drill tip formed by using the upper and lower punches shown in Figure 12;

Figure 14 is a schematic cross sectional view of a compression mold according to another embodiment of the disclosure;

Figures 15 and 16 are schematic views showing different stages of a molding process for forming a drill tip by using the compression mold shown in Figure 14;

Figure 17 is a schematic cross sectional view of a compression mold according to yet another embodiment of the disclosure;

Figure 18 is a schematic cross sectional view of a compression mold according to yet another embodiment of the disclosure; and

Figure 19 is a schematic cross sectional view showing a molding process for forming a drill tip by using the compression mold shown in Figure 18.

Detailed Description of Preferred Embodiments

Now some embodiments of the compression mold and the method for forming a carbide drill tip of a drill bit of the disclosure will be described with reference to the drawings.

Figures 3 and 4 schematically show two forms of a semi-finished carbide drill tip 4 or powder compact that can be formed by using the technique of the disclosure. The drill tip 4 is a single piece formed by pressing a powdery material. The drill tip 4 is then to be sintered to form a finished drill tip and the finished drill tip is fixed to a shank, for example by welding, to form a drill bit.

The drill tip 4 is composed of a base portion 41 and an edge portion 42 extending from the base portion 41. The base portion 41 is to be fixed to a shank (not shown) , and the edge portion 42 is used for cutting into a workpiece.

The base portion 41 is defined by a base face 43 and two side surfaces 44 extending upwards from the base face 43. The edge portion 42 is defined by two oblique cutting edges 45 that extend from upper ends of the two side surfaces 44 respectively. The two cutting edges 45 are joined at an head (apex) portion 46. An head angle θ is defined between the two cutting edges 45 at the head portion 46. The drill tip 4 is generally flat and has two opposite major surfaces 47.

In the configuration that the head angle θ is smaller than about 120°, especially smaller than about 90°, the drill tip 4 may be categorized as having a sharp head.

The drill tip 4 has a width W measured between the two side surfaces 44, a height H measured between the head portion 46 and the base face 43, and a thickness measured between the two major surfaces 47. The width W of the drill tip 4 corresponding to the diameter of the hole to be drilled by the drill bit.

It should be noted that the head portion 46 may either be substantially in the form of an intersecting line between the two cutting edges 45, as schematically depicted in Figure 3, or be substantially in a form of a plane having a small width in the width W, as schematically depicted in Figure 4.

The drill tip 4 also has a rotation axis O around which the drill tip 4 is rotated when the drill bit is driven to rotate. The drill tip 4 may be symmetrical about the rotation axis O, in which condition the head portion 46 is centered on the rotation axis O; alternatively, the drill tip 4 may be asymmetrical about the rotation axis O, in which condition the center of the head portion 46 may be offset from the rotation axis O.

The key principle of the disclosure is to compress the powdery material for the drill tip 4 in the widthwise direction, that is, in a direction substantially parallel to the major surfaces 47 and perpendicular to the rotation axis O. In other words, the powdery material is compressed from the two side surfaces 44 of the drill tip 4 to be formed.

An embodiment of a compression mold for forming the drill tip 4 is schematically shown in Figure 5. The compression mold comprises a die 1 which has a vertical die hole formed therethrough and defined by an inner wall 11, an upper punch 2 configured to be inserted into the die hole from above, and a lower punch 3 configured to be inserted into the die hole from below. The upper punch 2 has a bottom surface 21 and the lower punch 3 has a top surface 31. The bottom surface 21, the top surface 31 and the inner wall 11 define a filling cavity (mold cavity) inside the die 1.

As shown in Figure 6, the bottom surface 21 comprises a transverse face 22 corresponding to one of the side surfaces 44 of the drill tip 4 to be formed, and an oblique face 23 corresponding to one of the cutting edges 45 of the drill tip 4. The oblique face 23 extends from an end of the transverse face 22 and ends at a sharp edge 24. The oblique face 23 forming an oblique angle α with the horizontal direction. The upper punch 2 also has opposite major surfaces 25.

As shown in Figure 7, the top surface 31 comprises a transverse face 32 corresponding to the other one of the side surfaces 44 of the drill tip 4 to be formed, and an oblique face 33 corresponding to the other one of the cutting edges 45 of the drill tip 4. The oblique face 33 extends from an end of the transverse face 32 and ends at a sharp edge 34. The oblique face 33 forming an oblique angle β with the horizontal direction at the sharp edge 34. The lower punch 3 also has opposite major surfaces 35. The sum of the oblique angle α and the oblique angle β equals to the head angle θ.

As shown in Figure 8, for forming a semi-finished carbide drill tip 4, the lower punch 3 is inserted into the die hole from below, and a powdery material 5 is filled into die hole on top of the lower punch 3. The filling amount of the powdery material depends on the compression rate of the powdery material 5. Then, the upper punch 2 is inserted into the die hole from above.

Then, as shown in Figure 9, the upper punch 2 is moved downwards to compress the powdery material. The lower punch 3 may either move upwards or remain stationary. Under the compression of the upper and

lower punches

2 and 3 in a widthwise direction of a drill tip 4 to be formed, the powdery material forms the drill tip 4. The drill tip 4 is now a semi-finished product. After the drill tip 4 undergoes a sintering process, it becomes a finished product.

In the compression mold, the drill tip 4 is in the orientation shown in Figure 9. The head portion 46 of the drill tip 4 is pointed in a substantially horizontal direction. One side surface 44 and the corresponding cutting edge 45 of the drill tip 4 are compressed by the bottom surface 21 of the upper punch 2 and the other side surface 44 and the corresponding cutting edge 45 are compressed by the top surface 31 of the lower punch 3. For this reason, the compression molding process described above may be called “widthwise pressing” or “widthwise compression” .

It should be noted that, in the end strokes of the upper and

lower punches

2 and 3, their

sharp edges

24 and 34 may either substantially contact each other in the vertical direction to form the head portion 46 in the form of substantially a line as described above with reference to Figure 4 or be separated by a small distance in the vertical direction to form the head portion 46 in the form of substantially a plane as described above with reference to Figure 5. The width of the drill tip 4, especially the width of the head portion 46, can be precisely controlled by precisely controlling the strokes of the upper and

lower punches

2 and 3.

According to the technique of the disclosure, all portions of the powdery material are fully compressed so the edge portion 42 (including the head portion 46) has a high density and strength. Thus, a drill bit having a sharp head can be formed by using the die 1.

In addition, the die 1 can be used with different upper and

lower punches

2 and 3. By adjusting the oblique angles α and β and the vertical levels of the transverse faces 22 and 32 of the upper and

lower punches

2 and 3, drill tips 4 with different widths and head angles can be formed.

It should be noted that the transverse face 22 and the oblique face 23 may be perpendicular to the major surfaces 25 of the upper punch 2 and the transverse face 32 and the oblique face 33 may be perpendicular to the major surfaces 35 of the lower punch 3, as shown in Figure 10, so that the side surfaces 44 and the cutting edges 45 of the drill tip 4 are perpendicular to the major surfaces 47, as shown in Figure 11. Alternatively, the transverse face 22 and the oblique face 23 may be oblique to the major surfaces 25 of the upper punch 2 and the transverse face 32 and the oblique face 33 may be oblique to the major surfaces 35 of the lower punch 3, as shown in Figure 12, so that the side surfaces 44 and the cutting edges 45 of the drill tip 4 are oblique to the major surfaces 47, as shown in Figure 13.

It should be noted that the compression mold may be modified in order that various portions of the drill tip 4 have desired density. For example, the die 1 and/or the upper punch 2 and/or the lower punch 3 may be modified to adjust the profile of the filling cavity.

As an exemplary embodiment, the die 1 of the compression mold shown in Figure 14 has an oblique upper surface portion 12 through which the die hole is opened. The lowest intersecting line between the oblique upper surface portion 12 and the inner wall 11 corresponds to the location of the

sharp edges

24 and 34. The oblique upper surface portion 12 forms an angle γ with the horizontal direction. The angle γ may be equal to the oblique angle α of the oblique face 23 of the upper punch 2. However, in order that the head portion 46 of the drill tip 4 has a higher density than the remaining portions of the edge portion 42, the angle γ may be smaller than the oblique angle α of the oblique face 23. Other aspects of the compression mold are the same or similar to that of the compression mold shown in Figures 5-9 and will not be described here.

When the compression mold shown in Figure 14 is used for forming a drill tip, the lower punch 3 is inserted into the die hole from below so that a filling cavity is defined by the top surface 31 of the lower punch 3, the inner wall 11 of the die 1 and the oblique upper surface portion 12 of the die 1. The powdery material 5 is filled into substantially the whole filling cavity as shown in Figure 15. It can be seen that, compared with the case shown in Figure 8, there is more powdery material in the portion of the filling cavity that corresponds to the base portion 41 of the drill tip 4. Then, as shown in Figure 16, the upper punch 2 is moved downwards into the die hole to compress the powdery material to form a drill tip 4.

According to the embodiment shown in Figures 14-16, the amount of the powdery material in the portion of the filling cavity that corresponds to the edge portion 42 of the drill tip 4 increases in a transverse direction away from the head portion 46 towards the base face 43, so the edge portion 42 may have a substantially constant compression density, or the changing rate of the density of the edge portion 42 in the transverse direction away from the head portion 46 towards the base face 43 is lower. As a result, there is no significant change in the density within the edge portion 42.

Further, for the reason that there is more powdery material in the portion of the filling cavity that corresponds to the base portion 41 compared with the case shown in Figure 8, the base portion 41 has a higher density compared with that formed in the compression mold shown in Figures 5-9. Thus, there is no big different between the density of the edge portion 42 and that of the base portion 41.

For further increasing the uniformity of the densities of various portions of the base portion 41, a compression mold shown in Figure 17 is proposed. The die 1 of the compression mold shown in Figure 17 has an oblique upper surface portion 12 substantially corresponding to the oblique face 23 of the upper punch 2 and a horizontal upper surface portion 13 substantially corresponding to the transverse face 22 of the upper punch 2. Through both the oblique upper surface portion 12 and the horizontal upper surface portion 13, the die hole is opened upwardly. The lowest intersecting line between the oblique upper surface portion 12 and the inner wall 11 corresponds to location of the

sharp edges

24 and 34. The oblique upper surface portion 12 forms an angle γ with the horizontal direction. The angle γ may be equal to or different from the oblique angle α of the oblique face 23 of the upper punch 2. Other aspects of the compression mold are the same or similar to that of the compression mold shown in Figures 5-9 or the compression mold shown in Figures 14-16 and will not be described here.

When the compression mold shown in Figure 17 is used for forming a drill tip, the lower punch 3 is inserted into the die hole from below so that a filling cavity is defined by the top surface 31 of the lower punch 3, the inner wall 11 of the die 1 and the oblique upper surface portion 12 and the horizontal upper surface portion 13 of the die 1. The powdery material 5 is filled into the whole filling cavity as shown in Figure 17. It can be seen that, compared with the case shown in Figure 15, the powdery material in the portion of the filling cavity that corresponds to the base portion 41 of the drill tip 4 has an even height. Then, the upper punch 2 is moved downwards into the die hole to compress the powdery material to form a drill tip. Thanks for the even distribution of the powdery material in the portion of the filling cavity that corresponds to the base portion 41, the base portion 41 has a substantially constant density, or at least there is no significant change in the density within the base portion 41.

In another embodiment, the upper surface of the die may have a curved upper surface portion. In yet another embodiment, the upper surface of the die may have a combination of one or more oblique upper surface portions and one or more horizontal upper surface portions. The oblique upper surface portion (s) and/or the horizontal upper surface portion (s) may be either planar or curved.

Other modifications to the die 1 for adjusting the profile of the filling cavity, especially by modifying the upper surface of the die, can be made by those skilled in the art under the teaching of the disclosure.

Alternatively or in addition, the adjustment of the density of portions of the drill tip 4 can be achieved by modifying one or both of the upper and

lower punches

2 and 3. For example, in the embodiment shown in Figure 18, the lower punch 3 is of split-type, that is, it comprises a first punch part 3a and a second punch part 3b. The first punch part 3a has a horizontal top surface 32 that corresponds to one of the side surfaces 44 of the drill tip 4 to be formed, and the second punch part 3b has an oblique top surface 33 that corresponds to one of the cutting edges 45 of the drill tip 4. The die 1 has an oblique upper surface portion 12 and a horizontal upper surface portion 13, similar to that shown in Figure 17. Alternatively, the die 1 may have a single oblique upper surface portion 12 like that shown in Figures 14-16.

When the compression mold shown in Figure 17 is used for forming a drill tip, the first and

second punch parts

3a and 3b of the lower punch 3 are inserted into the die hole from below, but the first and

second punch parts

3a and 3b do not move upwards by the same distance. For example, as shown in Figure 18, the second punch part 3b moves upwards by a distance smaller than the first punch part 3a so that the lowest edge of the oblique top surface 33 is lower than the horizontal top surface 32. Then, the powdery material 5 is filled into the whole filling cavity as shown in Figure 18.

Then, as shown in Figure 19, the upper punch 2 is inserted into the die hole and moves downwards to compress the powdery material 5. After the upper punch 2 is fixed, or at the meantime when the upper punch 2 is moving, the second punch part 3b moves upwards further to reach its final position.

It is understood that the upper punch 2 can also be of a split-type so that different pieces of the upper punch 2 moves downwards individually.

By using a split-type upper punch 2 and/or a split-type lower punch 3, possibly in combination with a die 1 with a specifically designed upper surface portion, desired densities in various portions of the drill tip 4 can be achieved.

It can be seen that, by using the widthwise pressing technique disclosed here, drill bits having a sharp head can be formed. Of course, drill bits having a blunt head can also be formed using the technique disclosed here.

In addition, by using different upper and lower punches, drill bits having different widths can be formed with the same die.

Further, the difference in the wear rates of the upper and lower punches can be reduced compared with the prior art shown in Figure 1.

In some embodiments, desired densities of various portions of the drill tip can be achieved by specifically designed filling cavity and/or upper and lower punches. Especially, the head portion of the drill tip may have a high density and strength, while the base portion of the drill tip may have an evenly distributed density and strength. Alternatively, densities of each portion of the drill tip may be determined based on the expected using condition of the drill bit.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. The attached claims and their equivalents are intended to cover all the modifications, substitutions and changes as would fall within the scope and spirit of the disclosure.

Claims

A compression mold for forming a carbide drill tip of a drill bit comprising:

a die (1) formed with a vertical die hole therein, the die hole being defined by an inner wall (11) ;

an upper punch (2) configured to be inserted into the die hole from above; and

a lower punch (3) configured to be inserted into the die hole from below;

wherein a portion of the die hole forms a filling cavity which is defined at least by a top surface (31) of the lower punch (3) and the inner wall (11) and into which a powdery material can be filled; and

wherein the upper and lower punches (2, 3) are configured to compress the powdery material filled in the filling cavity in a vertical direction which corresponds to the widthwise direction of the drill tip to be formed by the powdery material.
The compression mold of claim 1, wherein the upper punch (2) has a bottom surface (21) which comprises a transverse face (22) and an oblique face (23) , and the lower punch (3) has a top surface (31) which comprises a transverse face (32) and an oblique face (33) , the transverse faces (22 and 32) being configured to form a base portion (41) of the drill tip, while the oblique faces (23 and 33) being configured to form an edge portion (42) of the drill tip.
The compression mold of claim 2, wherein the filling cavity is defined by the top surface (31) of the lower punch (3) , the inner wall (11) , and an upper surface of the die (1) .
The compression mold of claim 3, wherein at least a portion of the upper surface of the die (1) is formed as an oblique upper surface portion (12) , at least a portion of the die hole being opened upwardly through the oblique upper surface portion (12) .
The compression mold of claim 4, wherein the oblique upper surface portion (12) is oblique with respect to a horizontal direction by an angle (γ) , the angle (γ) being equal to or not equal to the oblique angle (α) of the oblique face (23) of the upper punch (2) .
The compression mold of any one of claims 3 to 5, wherein the upper surface of the die (1) further comprises a horizontal upper surface portion (13) , a portion of the die hole being opened upwardly through the horizontal upper surface portion (13) .
The compression mold of any one of claims 3 to 5, wherein the upper surface of the die (1) comprises a combination of at least one oblique upper surface portion and at least one horizontal upper surface portion, the least one oblique upper surface portion and the least one horizontal upper surface portion being designed to achieve desired densities of various portions of the drill tip to be formed.
The compression mold of any one of claims 1 to 7, wherein at least one of the upper and lower punches (2, 3) is a split-type punch which comprises two or more punch parts that can be moved in the widthwise direction of the drill tip to be formed independently with respect to each other.
A compression method for forming a carbide drill tip of a drill bit by using the compression mold of any one of claims 1 to 8 comprising the steps of:

moving the lower punch (3) upwards into the die (1) to form a filling cavity inside the die (1) ; filling a powdery material into the filling cavity ; and

moving the upper punch (2) downwards into the die (1) to compress the powdery material filled in the filling cavity in a vertical direction which corresponds to the widthwise direction of the drill tip to be formed by the powdery material.
The compression method of claim 9, further comprising further moving the lower punch (3) upwards when the upper punch (2) is being moved downwards or after the upper punch (2) has finished its downward movement.
The compression method of claim 9 or 10, further comprising controlling the downward moving of the upper punch (2) and/or the further upward moving of the lower punch (3) to control the dimension of an head portion (46) of the drill tip in the widthwise direction.