|Title of Invention||
A DRILL WITH AT LEAST TWO CUTTING EDGES
|Abstract||The invention relates to a drill with at least two cutting edges (7, 8) and each with an at least partially spiraled flow-channel (9, 10) extending fro them a shaft end (6) comprises a coolant channel (13, 14) extending from a shaft end (6) and running parallel to the tool axis (A), whose outlet openings (15, 16) are arranged in the flow- channel (9, 10) and oriented toward the cutting edge (7, 8).|
This invention relates to a drilling tool, in particular for metal materials, with at least two cutting edges and an at least partly helical chip flute that extends from each of the cutting edges toward the shank of the tool. A drill of this type is described in EP 0 750 960 B1, for example.
Cutting tools, in particular drills, are frequently operated with the use of coolant lubricants which are fed to the cutting edge or cutting edges of the tool through cooling channels in the tool. On the tool disclosed in EP 0 750 960 B1, a central cooling channel that begins at the end of the shank splits into a plurality of subchannels, to which groove-shaped tap channels are connected at a right angle to the cutting-side end of the drill. The coolant feed is therefore very complex.
US 3,436,990 describes a drill with a central cooling channel which toward the forward drill tip divides into subchannels which are oriented diagonally outward with respect to the longitudinal axis of the drill. DE 101 57 450 A1 is concerned with the problem of feeding the coolant into the rear-side end of the drill shank and provides an insert via which the coolant is fed into the drill shank without large-angle deflections.
The object of the invention is to describe a drill with a design that is constructively particularly simple and with an effective coolant feed.
The invention teaches a drill that has the characteristics disclosed in Claim 1. This drill has at least two cutting edges and two at least partly helical chip flutes that extend from the cutting-side end of the drill toward the end of the shank. Associated with each cutting edge is a cooling channel which extends from an inlet opening on the shank end to an outlet opening in the chip flute, so that the coolant or coolant lubricant
is conducted in the longitudinal direction of the tool directly to the cutting edge. The cooling channel runs in a straight line over its entire length or approximately its entire length, and is at least essentially parallel to and at some distance from the tool axis.
The completely straight configuration of the at least two cooling channels, corresponding to the number of the cutting edges, on one hand facilitates the efficient fabrication of the drill. On the other hand, the altogether straight cooling channels also have
The completely straight construction of the number of coolant channels corresponding to the number of cutting edges, but no less than two, favors efficient manufacturing of the drill bit. In addition, the continuously straight coolant channels also have flow-related advantages, especially when using minimal lubrication that operates using an air-oil mixture. Besides the low-resistance flow, not requiring the cooling lubricant to be rerouted within the drill bit is particularly relevant. Separation of the oil-air mixture, as may occur particularly with angular routing, is avoided. The tool can thus be used with small quantities of oil even at high machining speeds.
Additional advantages of this tool result from the fact that the cooling lubricant is supplied to the cutting edge from the coolant channel's opening that is recessed axially from the tool tip.
Any weakening of the tool in especially mechanically stressed areas of the tool tip is excluded by the coolant channel's outlet openings being recessed in the direction of the tool shaft. Preferentially, the axial distance between the center of the coolant channel's outlet opening and a cutting edge corner adjoining the cutting edge at the tool's circumference amounts to a minimum of 75% of the tool diameter and a maximum of double the tool diameter.
Compared to a coolant discharge on the tool's exterior, the discharge of the coolant at least generally in the tool's longitudinal direction has the advantage that cooling and/or lubrication is effective when applying the drill bit to the piece to be machined. In contrast, for outlet openings arranged on the tool's exterior through which the cooling lubricant is discharged radially outward with a movement component, the desired effectiveness of the cooling lubricant is not achieved before the drill bit along with the outlet opening penetrates into the workpiece.
In cutting operations, the cooling lubricant fed through the coolant channels preferentially does not strike the cutting edge, but rather strikes the chip formed by it or between the chip and the face. From a cross-sectional view of the tool, the twist angle between the outlet opening of the coolant channel and the cutting edge is at least -20° but no more than +45°, in particular at least -5° and no more than +15°. The angle of twist is thus defined as positive if the coolant channel's outlet opening precedes the tool's rotation. On the cutting edge not directly cooled by the cooling lubricant flowing out from the coolant channel's outlet openings, high temperatures may develop during cutting. This is particularly favorable for machining hard materials since thereby their typically highly temperature-dependent mechanical properties are intentionally utilized. The coolant jet striking the chip directly quenches it and thus tends to result in small fragmenting properties depending on the machined material. Thereby, one achieves the transfer of a large portion of the cutting heat to the chip and easy chip removal. The percentage of cutting heat transferred to the drill bit is kept comparatively low so that the drill bit expands only slightly during machining. This enables an especially high degree of manufacturing precision to be achieved during drilling.
The eccentric path of the coolant channels prevents weakening of the tool in the area of its axis. The mechanical stability of the entire tool is substantially influenced by the geometry of the flute. Preferentially, the flute's overall angle of twist, i.e., the angle between the cutting-side and shaft-side ends of the flute, is at least 90° and no more than 160°, especially at least 120° and no more than 160°. This results in a cross-sectional geometry of the drill bit on the shaft-side end of the flute that is especially well suited to absorb the forces incurred during cutting. The aforementioned angles
refer to a dual-cutting edge drilling tool. For triple- and multiple-cutting edge drill bits, lesser overall angles of twist are advantageous.
The drill bit's flutes preferentially have a larger angle of twist in the area of the drill bit tip than in the area facing the shaft. The angle of twist increasing toward the tool tip, also referred to as side-rake angle, promotes simple chip removal, while the comparatively low angle of twist in the area facing away from the tool tip allows for a completely straight design of the coolant channels even for longer drill bit embodiments, for example for drilling depths of more than triple the drill bit diameter. Preferentially, the drill bit is fluted linearly in the area adjoining the shaft.
The drill bit is constructed as a one-piece or multiple-piece unit, for example using screwed-on or soldered cutting inserts. According to a preferred design, the drill bit comprises a body and a tool tip that can be attached to it. The coolant channels thus run preferentially solely through the body. Thus, the coolant channels do not adversely impact the mechanical stability of the particularly stressed tool tip. The drill bit is therefore also suited for smaller diameters of less than 16 mm. Preferentially, the tool tip is held to the body without a screw connection and thus without any corresponding cross-sectional weakening of the body or tool tip.
The particular advantage of this invention is that in a drill bit with a partially linear and partially spiraled flute, an eccentric coolant channel runs completely straight and is aimed directly at the chip created during machining.
Several embodiments of the invention are explained in greater detail hereafter using drawings.
Fig. 1 depicts a side view of a drill bit.
Fig. 2 depicts the drill bit according to Fig. 1 from a foreshortened perspective.
Figs. 3a-d depict various embodiments of drill bits from a foreshortened perspective.
Fig. 4 depicts a tool tip as well as a section of a multi-part drill bit's body.
Fig. 5 depicts a top view of a drill bit's tip.
Fig. 6 depicts a foreshortened view of a section of the body according to Fig. 4.
Fig. 7 depicts a top view of the sectionally depicted body according to Fig. 6.
Fig. 8 schematically depicts various drill bit cross-sections.
Fig. 9 depicts a rear view of the body according to Fig. 4.
Fig. 10 depicts a foreshortened detailed view of a body with tool tip attached.
Fig. 11 schematically depicts, as in Fig. 10, the coolant supply to the tool tip.
Fig. 12 depicts a full view of the tool according to Fig. 11.
The same parts are labeled identically in all drawings.
Figs. 1 and 2 depict an initial embodiment of drill bit 1, also referred to as tool, which is comprised of body 2 and tool tip 3. Body 2 is preferentially made of steel, while tool tip 3 is preferentially made of carbide metal. Differing from the embodiment depicted, drill bit 1 may also be made out of a single piece of carbide metal. Drill bit 1 may also have several exchangeable cutting elements, for example indexable inserts. All materials or parts thereof, including ceramics, conventionally used in cutting technology can be used as materials for drill bit 1.
For cutting elements or coatings, polycrystalline diamonds (PCD) or cubic boronitride (CBN) are suitable.
Drill bit 1 comprises shaft 4 to which is attached a cutting part 5, which in turn comprises tool tip 3. Shaft 4, whose shaft ends are labeled with reference symbol 6, is drawn as a cylindrical shaft in the embodiment. Shaft shapes that differ from this can also be implemented.
Tool tip 3 has two cutting edges 7, 8 from which flutes 9, 10 each extend in the direction of shaft end 6. The cutting edge corners formed at the transition between cutting edges 7, 8 and the tool circumference of drill bit 1 are labeled 11, 12. Coolant channels 13, 14 are provided for coolant supply to cutting edges 7, 8; their outlet openings 15, 16 are arranged in flutes 9, 10. In Fig. 1, one can only see outlet opening 15. The axial distance a, in relation to tool axis A, between the center of outlet opening 15 and the cutting edge corners 11, 12 is approximately 10 to 25% greater than the tool diameter D of drill bit 1.
Figs. 3a to 3d depict four additional embodiments of drill bit 1, which each differ in the length of cutting part 5. In each embodiment, body 2 comprises a front, spiraled area of flutes 9, 10 in which they transition into tool tip 3. The angle of twist y (Fig. 1) in the area of tool tip 3 is greater than 15°. This ensures low cutting forces, good chip forming, and simple chip evacuation. A straight-fluted area is attached in the direction of shaft 4 on the twisted or spiraled area of flutes 9, 10, whereby in the depicted embodiments, the spiraled section that has a constant twist angle y within a length of less than double the tool diameter D transitions continuously into the straight-fluted area. While the straight-fluted area can be done away with in relatively short embodiments of tool 1 (Fig. 3a),
it may comprise the greater part of the cutting part 5 in longer embodiments. In embodiments according to Figs. 3a to 3d, the maximum drilling depth is three, five, seven or 10 times the tool diameter D. In each case, coolant channels 13, 14, of which only outlet opening 15 of coolant channel 13 is visible in the drawings, running parallel to tool axis A are formed completely straight.
Fig. 4 depicts a section of body 2 corresponding roughly to embodiments according to Figs. 3a to 3d as well as tool tip 3 inserted in body 2. Possible shapes of tool tip 3 are described, for example, in still unpublished German patent application 102 07 257.4-14 as well as the corresponding international application PCT/EP03/01526. With the possibility of screw-less attachment of tool tip 3 to body 2, drill bit 1 is especially suited for smaller drilling diameters, for example starting at 12 mm. Tool tip 3 does not comprise any coolant channels.
Fig. 5 depicts a top-view of tool tip 3 of drill bit 1 according to Figs. 1 and 2. Tool tip 3 depicted as a one-piece cutting element comprises two lobes 17, corresponding to the number of cutting edges 7, 8, which each rest against shank 18 of body 2. Tool tip 3 can thus be inserted in body 2 in the manner of a slide lock. Twisting of tool tip 3 relative to body 2 is possible by means of a tool not depicted, which engages with two grooves 19 of tool tip 3.
As can be seen in Fig. 5, each cutting edge 7, 8 cuts across the cross-section of coolant channels 13, 14. The angle between cutting edge corner 11,12 and the center of coolant channels 13, 14 is designated as twist angle a and preferentially amounts to between -5° and +15°. Coolant channels 13, 14 run perpendicular to the depicted plane.
In Fig. 6, one can see coolant channels 13, 14 in the sectionally depicted body 2. Coolant channels 13, 14 are set apart from tool axis A and thus from the weakest cross-sectional area of body 2 in such a way that even with relatively large coolant channels 13, 14, the mechanical stability of body 2 is basically not affected. The coolant channel diameter d (Fig. 7) is approx. 10 to 15% of the tool diameter D of tool tip 3.
Fig. 8 schematically depicts the course of flute 9 along tool axis A. The contour of flute 9 is depicted in the straight-fluted area adjoining shaft 4; broken lines depict the contour of flute 9 in the area of cutting edge corner 11. The total angle around which flute 9 is spiraled is labeled as total twist angle p. The second flute 10 is not depicted in Fig. 8. The total twist angle p is measured from 90 to 160° in such a manner that essentially a cross-sectional profile of body 2 having a double-T shape absorbs the forces of cutting edges 7, 8 transferred to body 2 in the straight-fluted area facing shaft 4.
Fig. 9 depicts a rear-view of body 2 with coolant channels 13,14 whose inlet openings 20, 21 are arranged on shaft end 6 in transverse slot 22. A centering cone 23 is located symmetrically to tool axis A. Coolant supply to this area is not provided.
Fig. 10 depicts in detail another embodiment of drill bit 1 comprised of body 2 and tool tip 3. In this case, outlet openings 15, 16 are located on the edge of flutes 9, 10, i.e., near the transition area toward back side 24 of drill bit 1. Fig. 11 schematically depicts the course of coolant jet 25 in the vicinity of cutting edge 7, 8 on tool tip 3. The portion of coolant jet 25 penetrating tool tip 3 is only depicted to geometrically clarify jet direction
S of the coolant, which is essentially parallel to tool axis A. In fact, coolant jet 25 strikes the chip produced at cutting edges 7, 8 so that it is intensively cooled by direct coolant impact briefly after producing the chip. Heat transfer from chip to drill bit 1 is thus substantially prevented. At the same time, a high temperature that is preferential for cutting hard materials can be reached at cutting edges 7, 8. By orienting coolant jet 25 within the cross-section of drill bit 1 along tool axis A, cooling and lubrication is effective directly right upon applying drill bit 1 to the workpiece to be machined.
Similar to Fig. 11, Fig. 12 depicts drill bit 1 with schematically indicated coolant jet 25. The completely straight conduction of cooling lubricant through drill bit 1 provides for a very low-resistance flow, whereby no separation effects occur. Drill bit 1 is thus especially suited for minimum quantity lubrication.
1. Drill with at least two cutting edges (7, 8) and an at least partly helical chip flute (9, 10) extending from each of said cutting edges toward a shank end (6),
cooling channels (13,14) that begin from the shank end (6) and run continuously parallel to the tool axis (A), the outlet openings (15, 16) of which cooling channels are located in the chip flutes (9, 10) and are oriented toward the cutting edges (7, 8).
2. Drill bit in accordance with Claim 1 characterized by
a total twist angle ((3) of flute (9,10) of at least 90°.
3. Drill bit in accordance with Claims 1 or 2 characterized by
a total twist angle (J3) of flute (9, 10) of 160° maximum.
4. Drill bit in accordance with one of the Claims 1 to 3 characterized in that
the flute (9, 10) has an angle of twist (y) that increases to the cutting edge (7, 8).
5. Drill bit in accordance with one of the Claims 1 to 4 characterized in that
the flute (9, 10) does not have a spiraled area.
6. Drill bit in accordance with one of the Claims 1 to 5 characterized by
a twist angle (a) between outlet opening (15, 16) of the coolant channel (13, 14) and the cutting edge (7, 8) of at least -20°.
7. Drill bit in accordance with one of the Claims 1 to 6 characterized by
a twist angle (a) between outlet opening (15, 16) of the coolant channel (13, 14) and the cutting edge (7, 8) of 45° maximum.
8. Drill bit in accordance with one of the Claims 1 to 7 characterized by
an axial distance (a) between the outlet opening (15, 16) of the coolant channel (13, 14) and a cutting edge corner (11, 12) adjoining the cutting edge (7, 8) on the tool circumference of at least 75% of the tool diameter (D).
9. Drill bit in accordance with one of the Claims 1 to 8, characterized by
an axial distance (a) between the outlet opening (15, 16) of the coolant channel (13, 14) and a cutting edge corner (11, 12) adjoining the cutting edge (7, 8) on the tool circumference of twice the tool diameter (D) maximum.
10. Drill bit in accordance with one of the Claims 1 to 9 characterized by
a tool tip (3) that can be attached to a body (2).
11. Drill bit in accordance with Claim 10 characterized in that
the outlet opening (15, 16) of the coolant channel (13, 14) is arranged in the body (2).
A drill bit with at least two cutting edges (7, 8) and each with an at least partially spiraled flute (9, 10) extending from them to a shaft end (6) comprises a coolant channel (13, 14) extending from a shaft end (6) and running parallel to the tool axis (A), whose outlet openings (15, 16) are arranged in the flute (9, 10) and oriented toward the cutting edge
|Indian Patent Application Number||637/CHENP/2006|
|PG Journal Number||13/2009|
|Date of Filing||21-Feb-2006|
|Name of Patentee||KENNAMETAL INC.|
|Applicant Address||1600 Technology Way, Latrobe, PA 15650-0231,|
|PCT International Classification Number||B23B51/06|
|PCT International Application Number||PCT/EP04/005974|
|PCT International Filing date||2004-06-03|