Patent Application
20150266107
The subject matter of the present application relates to drill margins, in particular drill margins of drills and drill heads configured for drilling ductile materials such as low carbon steel and alloy steel.
One measurement of drilling quality is the finish provided to workpiece. Providing a high-quality finish on ductile materials, such as low carbon steel or alloy steel, can be particularly challenging, and improved finish is often a desired result.
U.S. Pat. No. 8,419,322 discloses tool for use in a preformed round hole. More precisely it discloses a cutting insert with a minor edge cutting flank adjoining a minor cutting edge against a direction of rotation, and comprising a support element arranged at a distance from the major cutting edge against a feed direction. The support element has a radius of revolution larger than a pitch circle radius of the cutting insert, during a drilling operation. The support element is mentioned as being able to provide both a supporting function and a smoothing function.
The subject matter of the present application is applicable to drills and drill heads configured for creating and/or deepening preformed holes. Notably, drills of the present application are configured for only axially machining (i.e. drilling) and are not configured for machining in a non-axial direction (e.g. shouldering, ramping). More specifically, drills according to the present application are configured only for drilling holes of diameter corresponding to a cutting diameter of the tool. Nonetheless, the term “drill” is inclusive of drills configured to rotate and static drills configured to be static while a work piece is rotated.
In accordance with a first aspect of the subject matter of the present application, there is provided a drill or drill head having a central axis AC defining a front-to-rear direction and comprising:
The margin, and more particularly the margin extremity, has been found to provide a burnishing function, and test results received thus far have surprisingly found that longevity of a drill or drill head with such margin extremity is apparently increased over comparative tools.
It will be understood that a drill or drill head with the above geometry, prior to the present discovery, was expected to shatter upon compression in a hole being drilled. It was theorized and testing has surprisingly confirmed that at least when drilling low carbon steel or alloy steel (believed to be due to the ductility thereof) such geometry is not adversely affected.
In accordance with another aspect of the subject matter of the present application, there is provided a drill or drill head comprising a cutting portion; the cutting portion comprising a drill margin; the drill margin comprising a margin extremity adjacent to a relief surface and located outside of a cutting diameter.
It will be understood that the above is a summary, and that any of the aspects above may further comprise any of the features described hereinbelow. Specifically, the following features, either alone or in combination, may be applicable to any of the above aspects:
A. A drill or drill head can have a central axis AC defining a front-to-rear direction. A drill or drill head can by rotationally symmetric about the central axis AC. Cutting edge extremities of a drill or drill head can be equally circumferentially spaced about the central axis AC. Margins of a drill or drill head can be equally circumferentially spaced about the central axis AC.
B. A drill or drill head can comprise a plurality of cutting portions.
C. A cutting portion can comprise a rake surface, a relief surface, and a cutting edge formed at an intersection of the rake and relief surfaces.
D. A cutting edge can extend rearwardly to a cutting edge extremity defining a cutting diameter of the drill or drill head. A cutting edge can be configured for drilling ductile materials such as low carbon steel and alloy steel. A cutting edge can have a rake angle Θ, at a cutting edge extremity, of twenty to thirty degrees (20°≦Θ≦30°).
E. A cutting portion can comprise a margin extending rearwardly from a relief surface and also extending from a rake surface.
F. A margin can comprise a margin extremity adjacent to a relief surface and located outside of the cutting diameter. Stated differently, a margin extremity is located further from a central axis AC than a cutting edge extremity. Stated differently yet, a margin extremity constitutes a furthermost point from the central axis AC.
G. A margin can extend outside of a cutting diameter beginning from a cutting edge extremity. A margin can extend outside of the cutting diameter beginning from the cutting edge extremity, and continuously increase distance from the cutting diameter until a margin extremity. The continuous increase in distance can be at a decreasing rate (i.e. having a convexly-curved shape in a top view thereof).
H. A cutting portion can comprise a margin edge extending along an intersection of a margin and a rake surface. A margin, at each axial location along the margin edge, can comprise an extremity extending outside of a cutting diameter. A margin, at each axial location along the margin edge, can extend outside of the cutting diameter beginning from the margin edge. A margin, at each axial location along the margin edge, can continuously increase distance from the cutting diameter until an extremity. The continuous increase in distance can be at a decreasing rate (i.e. having a convexly-curved shape in a top view thereof).
I. A margin extremity can extend outside of a cutting diameter by a protrusion distance DP of at least one micron (0.001 mm). Thus far, successful results have been achieved with protrusion distances DP less than 5 microns (0.005 mm). A margin extremity can preferably extend outside of a cutting diameter by a protrusion distance DP of one to five microns (0.001 mm≦DP≦0.005 mm). A margin, at each axial location, can comprise an extremity extending outside of the cutting diameter by a protrusion distance DP corresponding to the values above mentioned in connection with the margin extremity.
J. An entire margin can be located outside of the cutting diameter.
K. A margin can extend an axial distance no greater than 0.1 mm from a relief surface, preferably no greater than 0.01 mm from the relief surface.
L. A margin can comprise a margin portion. The margin portion can be the only portion of the margin comprising an extremity located outside of the cutting diameter. The margin portion can extend an axial distance no greater than 0.1 mm from a relief surface, preferably no greater than 0.01 mm from the relief surface.
M. Each cutting portion or margin of a drill or drill head (i.e. all cutting portions or all margins) can have one or more of the features detailed above.
N. A margin width WM measured from the cutting edge extremity 24 to the flank surface 42 can be between 5% to 10% of the cutting diameter DC (0.05 DC≦WM≦0.10 DC). With a range of 6%±1% having been successfully tested.
For a better understanding of the subject matter of the present application, and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which:
Reference is made to
The drill 10 can comprise a drill body 12 and a drill head 14 configured to be mounted to the drill body 12.
The drill 10 is for metal cutting operations and the drill head 14 is typically made of extremely hard and wear-resistant material such as cemented carbide, either by form-pressing and then sintering carbide powders in a binder or by powder injection molding methods.
A central axis AC, about which the drill 10 is configured to rotate in a rotation direction DR, extends through the center of the drill body 12 and drill head 14 and can define a front-to-rear direction DFR.
Referring now to
Each cutting portion 16 comprises a rake surface 18, a relief surface 20 and a cutting edge 22 formed at an intersection of the rake and relief surfaces 18, 20.
Referring also to
The rake surface 16 is configured for chips (not shown) from a workpiece (not shown) to flow thereover.
In
The relief surface 18 can form an internal acute angle β, shown schematically, with the rake surface 16 to provide relief during drilling.
In this non-limiting example, the cutting edge 22 can comprise two cutting edge portions. For example the cutting edge 22 can comprise a minor cutting edge portion 22A extending rearwardly from the chisel 17, and a major cutting edge portion 22B extending from the minor cutting edge portion 22A to the cutting edge extremity 24. The minor cutting edge portion 22A is also shown to extend radially, whereas the major cutting edge portion 22B can form an internal obtuse angle a therewith. In any case, the minor cutting edge portions 22A are preferably one third to one quarter of the length of the major cutting edges 22B.
The drill head 14 comprises a plurality of margins 26. The margins 26 are identical (as are the cutting portions 16) and therefore further reference will only be made to one of the margins 26.
Regarding rotational symmetry, with specific reference to
Referring also to
Drawing attention to
Referring only to
The margin 26, particularly the margin extremity 28, can extend a protrusion distance DP of one to five microns (0.001 mm≦DP≦0.005 mm) outside of the cutting diameter DC.
The margin 26 can have a convexly-curved shape (i.e. it continuously extends outside of the cutting diameter DC at a decreasing rate).
The margin extremity 28 can be located in a margin portion 32 of the margin 26.
Referring now to
Accordingly, it will be understood that while the example shown has a preferred geometry, the entire margin 26 could be constituted entirely by the area shown as the margin portion 32. In such case, the cutting portion 16 could extend radially inwardly at axial positions lower than the margin portion 32 (not shown).
In any case, the margin 26 comprises a margin edge 36 extending along an intersection of the margin 26 and the rake surface 18. The margin 26, as shown in
At each cross section taken at axial positions which are not adjacent to the relief surface 20 (i.e. axially spaced from the relief surface 20; random axial positions are taken at the positions designated as 38 and 40 for exemplary purposes only) the margin 26 has a similar shape to the shape the margin portion 32, and as shown in
The margin 26 extends from the margin edge 36 to the margin extremity 28. The margin extremity 28 can be located at an intersection of a flank surface 42 and the margin 26.
A margin width WM measured from the cutting edge extremity 24 to the flank surface 42 can be between 5% to 10% of the cutting diameter DC (0.05 DC≦WM≦0.10 DC).
The flank surface 42 can extend inward to the drill head 14. In any case, as shown in
An outer diameter relief surface 44 can peripherally extend from the flank surface 42, in a direction away from the cutting edge extremity 24. The outer diameter relief surface 44 can be entirely located within the cutting diameter DC.
The description above includes an exemplary embodiment and details, and does not exclude non-exemplified embodiments and details from the claim scope of the present application.
