Cutting insert with helical geometry and holder therefor

A cutting tool insert and holder therefore, the drill insert having a helical geometry corresponding to helical flutes in a drill body holder which enable the drill tool assembly to more efficiently remove chips from a hole during operation, the drill insert comprising a drill insert body having a first end opposite a second end, a plurality of helical flutes formed in the drill insert body, a plurality of cutting edges formed at the interfaces of the plurality of helical flutes and the first end of the drill insert body, and an aperture formed in each helical flute.

TECHNICAL FIELD

The invention relates generally to a cutting insert to be placed into a tool holder for boring holes into metals. More specifically, the invention relates to a cutting tool insert having a helical geometry corresponding to helical flutes in a drill body holder which enables the drill tool assembly to more efficiently remove chips from a hole during operation.

BACKGROUND OF THE INVENTION

Drilling systems are frequently used to provide cylindrical holes in metallic workpieces. The cutting or boring action of the drill system may be carried out by an elongated, substantially cylindrical drilling tool, such as a combination of a tool holder and a drill insert, which is selectively attached thereto such as the type commonly referred to as a spade-type drill. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus, which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder, the cutting insert engages the material to be cut. Alternatively, the workpiece may be made to rotate relative to the holder and cutting insert, such as in positioning the holder in the tail stock of a lathe or the like. Further, the tool and workpiece may be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool, and allows for one tool to be used for a variety of different boring applications by simply changing the insert and not the entire drill assembly.

One problem with prior art spade-type cutting tools is that insert is typically configured as a flat blade and the holder is configured with a straight flute. Even when used with flush channels through the holder, these types of drill assemblies are best suited for drilling shallow holes at relatively slower speeds due to their poor chip removal. Helical flutes are provided in typical twist drills to help in chip removal. Large helix angled flutes (often 20 degrees or above) are used for effective chip removal at high drilling speeds.

Attempts have been made in the prior art to combine the versatility and cost-effectiveness of the spade-type insert and holder with the benefits of helical flutes, however, these efforts have resulted in complex or inadequate blade retaining systems as well as complex shaped blades which negate the cost benefits of the replaceable blade insert. Other prior art attempts have combined a helical flute with a portion of a straight flute at the drill insert connection end in order to accommodate a flat drill insert. However in terms of chip removal, improved performance can be obtained if the helical flute is adjacent the cutting edges. In this prior art configuration, the chips are first transported by a straight portion resulting in loss of efficiency in removing chips and forcing a slower cutting speed for the tool. In addition, the straight cutting edge of the flat cutting blade does not typically dissipate heat as well as a curved cutting edge. If the point does not adequately conduct heat away from its cutting edges, the temperature buildup will “burn” the point and diminish the life of the drill bit. The heat generated at the lip of the drill point is directly related to the load and stresses the lip is subjected to. The more efficiently load stresses are dissipated, the less heat is built up at the cutting edge of the drill point.

Some prior art inserts have been developed with radially curved cutting edges. However, these prior art inserts are apt to direct chips directly into the clamp arms of the holder during operation of the tool. The clamp arms and the holder are made of a steel material that is significantly softer than the hard carbide material typically used to manufacture the drill insert. The chips impacting against the clamp arms erode and wear the clamp arms. This chip erosion of the clamp arms significantly reduces the life of the holder.

Therefore, there remains a need in the art for a drill insert tool that overcomes one or more or the disadvantages identified in the prior art.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved spade drill. These and other advantages are provided by a drill insert comprising a drill insert body having a first end opposite a second end, a plurality of helical flutes formed in the drill insert body and extending axially from the first end to the second end, a plurality of curved cutting edges formed at the interfaces of the plurality of helical flutes and the first end of the drill insert body, and wherein the drill insert body includes at least two apertures, each aperture positioned through each helical flute and extending through the drill insert body to a generally planar attachment surface on an opposite side of the drill insert body.

These and other objects of the invention are also provided by a drilling tool assembly comprising a holder having a first end, a second end, and a cylindrical drill portion between the first end and the second end, wherein the second end comprises a shank portion adapted to be fixedly attached in a drilling machine, wherein the first end comprises a holder slot having a bottom seating surface over at least a portion of the holder slot and at least one attachment arm positioned on each side of the holder slot, wherein each attachment arm has at least one aperture formed therein, and wherein the cylindrical drill portion has a first plurality of helical flutes formed therein, a drill insert comprising a drill insert body having a first drill insert end opposite a second drill insert end, a second plurality of helical flutes formed in the drill insert body and extending axially from the first drill insert end to the second drill insert end; a plurality of curved cutting edges formed at the interfaces of the second plurality of helical flutes and the first drill insert end of the drill insert body; and wherein the drill insert body includes at least two apertures, each aperture positioned through each helical flute and extending through the drill insert body to a generally planar attachment surface on an opposite side of the drill insert body, wherein the drill insert is removably secured to the holder by at least two fasteners, each fastener positioned through each helical flute of the second plurality of flutes and extending through the drill insert body into the aperture formed in each attachment arm of the holder.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to an embodiment of the invention,FIG. 1illustrates a drill tool assembly10generally indicated in an exploded view. Drill tool assembly10comprises a holder12, which has a drill body14and shank16associated therewith. The body14comprises a pair of helical flutes18formed therein. Holder12has, in general, a cylindrical shape with a holder end20opposite the shank16which is configured to securely support a drill insert35. As shown inFIG. 2, the holder end20has a clamping or holder slot30, which may extend across the entire diameter of the holder end20or, at least, over a center portion thereof at the general location of the rotational axis19of holder12. The holder slot30has a bottom wall32positioned in substantially perpendicular orientation relative to the rotational axis19of the holder12. In one embodiment, the assembly10may further include a locating boss or dowel pin24(seeFIG. 1), which is positioned precisely with respect to the axis19and extends from the bottom wall32of the holder slot30. The pin24may be positioned within a hole26extending downwardly from the bottom wall32of slot30along the axis19of the holder body in a press fit relationship to position pin24. Alternatively, the locating boss or pin24, may be configured in another manner to achieve the corresponding functionality of pin24, such as an integral member extending from bottom wall32. Referring again toFIG. 1, within the holder slot30, a drill insert35is precisely positioned with respect to the holder12to perform the desired drilling function in conjunction therewith. As will be hereinafter described in more detail, the insert35has a point geometry comprising a plurality of cutting surfaces, which are precisely positioned with respect to the axis19of the holder12to result in more efficient drilling operations using assembly10.

More particularly, an embodiment of holder12is shown inFIG. 2, and may be configured to include at its holder end20a pair of attachment arms or clamping arms34, which extend about holder slot30. The clamping arms34preferably include apertures36, which accommodate screws38(seeFIG. 1) to secure the drill insert35in its position within the holder slot30. In one embodiment, the holes36are threaded to engage screws38, and mate with screw holes formed in the drill insert35in a predetermined manner to precisely locate the drill insert in a predetermined location within holder slot30, as will be described in more detail. Each of the clamp arms34may also include a lubrication vent28or flush channels, which allows the application and flow of lubrication adjacent the cutting surfaces of the drill insert to facilitate the drilling operation. The clamp arms34may also include angled or curved surfaces forming part of the flutes18which facilitate chip removal on each side of the holder12. The seating surface32is also shown generally as a planar surface. In the configuration shown, hole26is formed in the seating surface32of slot30along the axis19which will accommodate a locator pin24as discussed above.

Turning toFIGS. 3A–3D, an embodiment of the drill insert35is shown. The drill insert35may form a modified spade drill blade, with peripheral cylindrical side surfaces60of the blade being generally arcuate and having a center at the rotational axis19of the holder12once the insert35is positioned and secured with holder12. When secured with holder12, drill insert35will also have a rotational axis, which desirably is coaxial with axis19of holder12. Drill insert35comprises a drill insert body37having a first end, or cutting end82opposite a second end, or support end84, and a first face side86opposite a second face side88. The support end84of the drill insert body37is a generally planar surface and the cutting end82has at least two curved cutting edges64. Each face side86,88, comprises an attachment surface92and a helical flute98. The attachment surfaces92are generally planar and parallel to each other, although not limited as such. The peripheral cylindrical side surfaces60may also include a helical margin61adjacent the helical flute98. The drill insert body37includes at least two apertures70, each aperture positioned through each helical flute98and extending through the drill insert body37to the attachment surface92of the opposite face side. The helical flutes98are formed at the same helix angle as that of flutes18of the holder and positioned to form a continuous flute when the drill insert is assembled on the holder12. The fact that the flute98is adjacent the cutting edge64results in efficient and quick removal of chips. Accordingly, the helical flutes98,18enable the drill tool assembly10to remove chips from a drilled hole efficiently and quickly, even at high drilling speeds. The cutting edges64are formed by the interface of the cutting end82and the helical flutes98of the insert35resulting in the advantage of a curved cutting edge which generally dissipates heat more effectively than a straight cutting edge as in typical spade-type blade inserts.

As previously mentioned, the drill insert35includes curved cutting edges64on its upper surface82on each side of the axial center62, also known as the dead center. The cutting edges64may include a plurality of cutting components, which cooperate together to provide the desired cutting surface64for the material and/or drilling application. In general, the insert35is designed to cut when rotationally driven in conjunction with holder12in a predetermined direction, and is not reversible, although such drilling blade configurations are known to those skilled in the art and could be used in conjunction with the present invention if desired.

The drill insert apertures70are formed in helical flutes98and cooperate with the apertures36in clamp arms34to secure insert35within holder slot30and seated against seating surface32. Additionally, apertures70are preferably formed with countersunk portions formed as a bearing surface adapted to be engaged by a corresponding tapered or like surface on the screws or other fastening mechanism38. The enlarged clamping head of the screws38may be of any convenient shape, such as conical, ball-shaped, or in another form to correspond with the similar surfaces in the tool holder12and insert35. In a typical fashion, by offsetting the axes of the apertures36and70, upon securing insert35within slot30by means of screws38, the insert35will be forced downwardly against the seating surface32. Insert35may include a locating slot65, which allows positioning of the locating pin24therein. This connection is further described in co-owned U.S. Pat. No. 5,957,635, which is herein incorporated by reference.

Insert35may also include a notch feature66as best shown inFIGS. 3A,3C, and3D. A notch66is located on either side of the chisel68, which is formed across the insert web and extends through axial center62. A negative feature of drill inserts and twist drills, in general, is that the chisel must act as a cutting edge. The chisel68has a negative rake angle, which does not cut efficiently but rather deforms the metal. This results in high thrust forces being required and excessive heat being developed at the point62. The notch66forms a type of flute on either side of insert35, which reduces the web and length of chisel68. Prior art notches typically were formed as a full radius. The prior art notches provide a neutral cutting edge, which still does not efficiently cut but rather extrudes or deforms the metal. In the embodiment shown, the notch66is shaped like a “V” having a radiused trough42at the bottom of the notch66and a first generally planar side44on a leading side of trough42and a second generally planar side46on the opposite side, or trailing side of the trough42, forming an angle φ. Like the prior art web-thinning techniques, the notch66also reduces the length of the cutting edges64as the leading side44of the notch66is cut into a portion of the cutting edge64. However, the notch66of the present invention is formed such that the trough42of the notch66is at a skewed angle with respect to axis19such that the leading edge44of the notch66forms a positive rake angle cutting edge48. Such a notch is disclosed in co-owned, co-pending U.S. patent application Ser. No. 09/975,221, filed Oct. 11, 2001, and hereby incorporated by reference. Therefore, the notch66actually extends the effective positive rake angle cutting edge length of drill tool assembly10. The multiple cutting edges64,48, aggressively bite into the material to be drilled as the drill tool assembly10rotates. Additionally, the positive rake angle cutting edge48results in enhanced self-centering of the drill tool assembly10by providing an aggressive geometry which bites into the material near the chisel68. The negative or neutral prior art web thinning techniques allowed the drill point to “walk” along the surface of the material to be cut, thus moving the drill away from the desired location, or resulted in bell-mouthing of the drill hole entrance.

Referring now toFIGS. 4A–4C, another embodiment of a drill insert35′ is shown. Drill insert35′ differs from insert35of the previous embodiment in that drill insert35′ includes a boss102projecting radially outward from the central portion of each face side86′,88′. Each boss102may have a radially outermost surface104which may be parallel with the surface104on the opposite face side. The boss102comprises a first surface105extending transverse to the attachment surface92′ and may be formed either parallel or transverse to the rotational axis of the insert35′. The extension of the bosses102allows the formation of a second helical flute portion106on the drill insert35′. The second helical flute portion106is formed adjacent the drill insert helical flute98′ and separated therefrom by a ridge108. The second helical flute106in combination with helical flute98′ provides a wider flute and allows more curl in the chip formation during operation of the drill insert35′. Ridge108between the two flutes98′,106, acts as a chipbreaker. As the chip is formed along the leading helical flute98′, the ridge108causes the chip to break, resulting in smaller chips which are more easily removed from the hole during operation of the drill insert35′. Another benefit of the boss102is that it protects the clamp arms of the holder from chip erosion. The boss102shields a significant portion of the clamp arm. In addition, the second flute106directs the chip away from the clamp arms. Accordingly, the boss102feature of the drill insert35′ eliminates chip erosion and prolongs the life of the holder.

Still another embodiment of the drill insert of the present invention is shown inFIGS. 5A–5C. Insert35″ differs from insert35′ of the previous embodiment in that it does not have a locating slot in the planar surface of the second end84″ of the insert35″. In order to properly locate the drill insert35″ on the holder, the drill insert35″ comprises a locating boss110projecting radially outward from the central portion of each face side86″,88″. Similar to the previous embodiment, each boss110may have a radially outermost surface114which may be parallel with the surface114on the opposite face side. The boss110comprises a first locating surface125extending transverse to the attachment surface92″ and may be formed either parallel or transverse to the rotational axis of the insert35″. As with the previous embodiment, the extension of the bosses110allows the formation of a second helical flute portion116on the drill insert35″. The second helical flute portion116is formed adjacent the drill insert helical flute98″ and separated therefrom by a ridge118. The second helical flute116in combination with helical flute98″ provides a wider flute and allows more curl in the chip formation during operation of the drill insert35″. Ridge118between the two flutes98,116, acts as a chipbreaker. As the chip is formed along the leading helical flute98, the ridge118causes the chip to break, resulting in smaller chips which are more easily removed from the hole during operation of the drill insert35″. Another benefit of the boss110is that it protects the clamp arms34′ of the holder12′ from chip erosion.

Referring now toFIGS. 6A–6C, the holder12′ differs from holder12in the locating of the drill insert35″ on the holder12′. Holder12′ comprises at its holder end20′ a pair of attachment arms34′, which extend about holder slot30′. Each attachment arm34′ of the holder12′ includes a locating recess136formed therein corresponding to the locating boss110of the drill insert35″ in order to ensure that the drill insert35″ is properly located in the holder slot30′. The holder12′ also comprises helical flutes18′ and a second helical flute19adjacent helical flutes18′ and separated therefrom by a ridge17.

The drill tool assembly10′ is shown inFIGS. 7A–7Bin an assembled state. The drill tool assembly10′ shows that the helical flutes98″,116, of the insert35″ combines with the helical flutes18′,19of the holder12′ to form a continuous helical flute having generally the same helix angle and extending to the first end of the drill insert35″. The holder12′ also comprises a plurality of lands148, each land148formed between the helical flutes18′ of the holder12′. The peripheral cylindrical surface60″ of drill insert35″ forms a drill insert land portion generally corresponding to the lands148′ of the holder12′, such that the land60″ extends to the first end of the drill insert35″. The drill insert land portion60″ may comprise helical margin61″ formed on the leading end of the peripheral cylindrical surface adjacent an insert helical flute98″.

It is contemplated that the drill insert is made of a sintered metallic hard material such as carbide, cermet, ceramic, monocrystalline and polycrystalline diamond, or boron nitride. However, the drill insert may also be comprised of high speed steel.

Although the present invention has been described above in detail, the same is by way of illustration and example only and is not to be taken as a limitation on the present invention. Accordingly, the scope and content of the present invention are to be defined only by the terms of the appended claims.