Patent Application
20070081872
This application claims priority under 35 U.S.C. § 119 to Swedish Patent Application No. 0502204-1, filed on Oct. 5, 2005, the disclosure of which is incorporated by reference herein in its entirety.
The present invention relates generally to a replaceable milling cutter head, which has, on one hand, an external envelope surface, which has a rotationally symmetrical basic shape in respect of a central axis, and includes a plurality of peripherally spaced-apart cutting edges and chip flutes, and, on the other hand, two axially spaced-apart, front and rear ends, an axial hole extending all the way through a frame of the same, the milling cutter head having a flat, pulley-like basic shape, such that the axial distance between the two ends is at most half as large as the greatest outer diameter thereof. The invention also relates to a milling cutter tool having such a milling cutter head.
Within the field of milling machining of, in particular, metallic workpieces, a plurality of proposals of milling cutter tools have recently been made, the milling cutter heads of which are made in a single piece of cemented carbide, the requisite cutting edges being formed in the proper cemented carbide body (contrary to such cutting edges that are included in separate cemented-carbide inserts, which individually are detachably mounted on a milling cutter head of steel). Such milling cutter heads of cemented carbide having integrated cutting edges are commonly denominated loose tops, in particular when they are included in small milling cutters, such as shank-end mills, contour mills and the like. Examples of milling cutter tools that make use of such loose tops are found in the following patent documents: WO 03/097281, WO 03/101650, EP 0911101, EP 1237670, EP 1342521, DE 3230688, U.S. Pat. No. 6,241,433, U.S. Pat. No. 6,276,879, U.S. Pat. No. 6,494,648 and U.S. Pat. No. 6,497,540.
The majority of previously known milling cutter heads of cemented carbide, which are assembled from a rotatable and frequently cylindrical basic body, have an elongate shape, such that the axial extension of the milling cutter head is larger than the diameter thereof, as well as a male-like fastening member that projects rearward from the rear end of the milling cutter head, in order to be possible to be inserted into a female-like seat in a free, front end of the basic body. This generally elongate shape of the milling cutter head has, among other things, the consequence of subjecting the tool to considerable bending loads in the interface between the rear end of the milling cutter head and the front end of the basic body, because the predominant radial cutting forces act on the free, front end of the milling cutter head. Furthermore, the generally elongate shape entails the disadvantage that the means for transferring torques from the basic body to the milling cutter head, for geometrical reasons, cannot be made with anything else but a very limited radial extension. In other words, the torque arm for the transfer of torque becomes limited, and the contact surfaces between the two components small. In this connection, it should be mentioned that such tools that solely rely on threaded joints for the transfer of torque are quite objectionable. Another disadvantage of previously known milling cutter heads is that the consumption of the expensive cemented carbide material in the manufacture becomes comparatively large in relation to the number of active cutting edges on the same. In addition, the cutting edges will frequently be formed along at least the major part of the axial length of the milling cutter head and at times the entire length, in spite of the cutting edges in many applications being utilized only along a smaller part of the length thereof. Thus, in fine milling, for instance, it occurs that only 1-10% of the entire edge length become worn, while 90-99% remain unutilized.
The present invention aims at obviating the above-mentioned disadvantages of previously known milling cutter tools and at providing an improved milling cutter tool having an improved milling cutter head. Therefore, an object of the invention, in a first aspect, is to provide a milling cutter head that, on one hand, can be fixed in a stable and exact way on the basic body of the tool, and on the other hand has an interface acting against the basic body via which interface considerable torques can be transferred from the basic body to the milling cutter head, without the same skidding or being dislodged from the desired position thereof.
Another object of the invention is to provide a milling cutter head having a geometry that allows the formation of a large number of cutting edges located close to each other as well as the appurtenant chip flutes. In an embodiment, the invention aims at providing a milling cutter head that is particularly suitable for milling at small cutting depths, such as in fine milling. In other words, the milling cutter head should be possible to be made without unnecessary long and costly cutting edges.
Yet another object of the invention is to provide a cemented carbide milling cutter head that is simple and inexpensive to manufacture by means of known manufacturing methods, e.g., compression-moulding and sintering, more precisely under the utilization of minimal amounts of expensive material. In this connection, the milling cutter head should also be possible to be finished in a simple way.
In another aspect, the invention also relates to a milling cutter tool, which in the assembled state includes a milling cutter head as well as a rotatable basic body. An object in this respect is to provide a milling cutter tool, the interface of which between the basic body and the milling cutter head is formed in such a way that the fixation of the milling cutter head in the desired position becomes reliable, stable and exact in a repeatable way. Another object of the invention is to provide a milling cutter tool, the milling cutter head of which does not run the risk of coming loose from the basic body as a consequence of failing holding functions.
In an embodiment, the invention provides a replaceable milling cutter head, which has an external envelope surface having a rotationally symmetrical basic shape in respect of a central axis. The cutter head includes a plurality of peripherally spaced-apart cutting edges and chip flutes, and two axially spaced-apart, front and rear ends. An axial hole extends all the way through a frame of the cutter head. The milling cutter head has a flat, pulley-like basic shape, such that the axial distance between the two ends thereof is at most half as large as the greatest outer diameter thereof. A hollow space for receiving a male element of a basic body is recessed in the rear end of the milling cutter head. The cross-section area of the hollow space, in a plane perpendicular to the center axis, amounts to at least 25% of the total cross-section area of the milling cutter head, as determined by the outer diameter.
In another embodiment, the invention provides a milling cutter tool including a rotatable basic body and a replaceable milling cutter head, which has an external envelope surface having a rotationally symmetrical basic shape in respect of a central axis. The cutter head includes a plurality of peripherally spaced-apart cutting edges and chip flutes, and two axially spaced-apart, front and rear ends. The cutter head has a flat, pulley-like basic shape, such that the axial distance between the two ends thereof is at most half as large as the greatest outer diameter thereof. The milling cutter head is connected to the basic body via a male element having means for the transfer of torque from the basic body to the milling cutter head. The milling cutter head is fixable on the basic body by means of a tightening device. A hollow space in which the male element engages is recessed in the rear end of the milling cutter head, an end surface thereof being urged against a bottom surface of the hollow space. The cross-section area of the hollow space and the male element respectively amounts to at least 25% of the total cross-section area of the milling cutter head, as determined by the outer diameter.
The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain features of the invention.
In
In the example, not only the milling cutter head 2, but also the basic body 1, has a rotationally symmetrical basic shape defined by a central axis C around which the tool is rotatable. Advantageously—though not necessarily—the basic body 1 has an elongate shape, and is, in this case, delimited along the major part of the length thereof by a cylindrical envelope surface 4. At the front, free end thereof, the basic body transforms into a thinner, male-like element or member 5, which is delimited by a rotationally symmetrical envelope surface 6, as well as a planar end surface 7. Most suitably, the envelope surface 6 is cylindrical.
The milling cutter head 2 has front and rear ends 8 and 9, respectively, between which a generally rotationally symmetrical envelope surface 10 extends. In the envelope surface, a plurality of peripherally spaced-apart cutting edges 11 are formed, between which there are chip flutes 12. Thus, although the envelope surface is not smooth, the same has, however, in respect of geometry, a rotationally symmetrical basic shape, which may be entirely or partly cylindrical, conical or arched. In the example shown, the edges extend 11 only along a part of the axial distance between the ends 8 and 9, a smooth, circumferential surface 13 being left between the set of cutting edges and the rear end 9 of the milling cutter head. Most suitably, the cutting edges are equidistantly spaced-apart along the circumference of the milling cutter head.
The screw 3 includes a head 14, as well as a shank 15 having a male thread 16. In is formed, through which the screw shank 15 can pass in order to be tightened in a female thread 18 in a central hole 19, which mouths in the front end of the basic body.
Reference is now made to
In the rear end 9 of the milling cutter head, a hollow space 20 opens, which is delimited by a bottom surface 21 and an endless circumferential limiting surface 22. Around the hollow space 20, a ring-shaped end surface 23 extends, which together with the limiting surfaces 13 and 22 delimits a ring- or rim-shaped part 24. In the preferred embodiment, the surface 22 is rotationally symmetrical, more precisely cylindrical, while the bottom surface 21 is planar and extends perpendicularly to the center axis C. Also the end surface 23 may advantageously be planar and smooth.
A second hollow space 25 opens in the front end 8 of the milling cutter head. In the same way as the first-mentioned hollow space, this hollow space 25 may be delimited by a planar bottom surface 26 and a rotationally symmetrical, suitably cylindrical limiting surface 27. Also surface 27 is formed on the inside of a ring-shaped part 28 of the milling cutter head. Ring part 28 is, however, directed forward and is axially delimited by a suitably planar front end surface 29.
In
Characteristic of the milling cutter head according to the invention is that the same has a flat, pulley-like basic shape, such that the axial distance L between the two ends is at most half as large as the greatest outer diameter D1, at the same time as the cross-section area of the rear hollow space 20, in a plane perpendicular to the center axis C, amounts to at least 25% of the total cross-section area of the body, such as this is determined by outer diameter D1. In the example shown, the length L amounts to ⅓ (i.e., 33%) of the diameter D1. Within the scope of the invention, this ratio L/D1 may vary most considerably within the range below 0.5. However, it should not be below 0.15. In practice, a ratio L/DI within the range of 0.2-0.4, suitably 0.3-0.35, is preferred.
The cross-section area of the rear hollow space 20, in relation to the total cross-section area of the milling cutter head, is determined by the ratio between the diameters D3 and D1. In accordance with the invention, the hollow space 20 shall have an inner diameter D3 that amounts to at least 50% of the outer diameter D1. On the other hand, the inner diameter D3 should not exceed 85% of the outer diameter D1. In the example shown, the diameter D3 amounts to about 70% of the diameter D1.
It should be pointed out that, in the example, the ring-shaped part 24, which surrounds the rear hollow space 20, is equally thick along the entire circumference thereof, more precisely by the fact that the inner, cylindrical surface 22 is concentric with the external, likewise generally cylindrical envelope surface 10 (or the surface 13). Between the two planar bottom surfaces 21, 26, a material portion designated 30 is delimited, which forms a central frame or partition wall between the hollow spaces 20, 25. The thickness of said partition wall is designated T1, while the axial depths of the hollow spaces 20, 25 are designated T2 and T3, respectively. As is clearly seen in
By the fact that the bottom surfaces 21, 26 are planar and mutually parallel, as well as extend perpendicularly to the center axis C, it follows that the partition wall 30 in its entirety extends in a plane perpendicular to the center axis.
Now reference is made again to
In the shown, preferred embodiment, the through hole 17 through the partition wall 30 is utilized as a female-like seat for the receipt of the driver 31. For this reason, in this case the hole 17 has been given a generally triangular shape corresponding to the triangular shape of the driver. The endless hole-edge surface that delimits the hole 17 includes therefore three concavely arched surfaces 36 located corner-wise, as well as three side surfaces 37 extending between the same and having an convexly arched shape. The fit between, on one hand, the surfaces 33, 34, and on the other hand the surfaces 36, 37, should be fine, e.g., within the range of 0.01-0.05 mm. For the sake of completeness, it should be pointed out that imaginary generatrices, which geometrically generate said surfaces, are parallel to the center axis C.
An emphasized feature of the described milling cutter head is that the driver 31 and the co-operating seat, i.e. the hole 17, has a considerable radial extension. In
It should be pointed out that the means for the transfer of torque to the milling cutter head may be made in other ways than in the form of an out of round driver of the basic body and an out of round seat in the milling cutter head, and that it is not necessary to utilize the hole 17 as a seat. On the contrary, an object of the hole 17 is to allow the shank 15 of the screw 3 serving as a tightening device to pass through the milling cutter head 2 and be drawn into the basic body 1 during clamping of the milling cutter head. Against this background, it is feasible to give the hole 17 a conventional cylindrical shape, at the same time as the transfer of torque is provided in another way. For instance, one or more projections retreated radially from the center axis may be inserted into a corresponding number of seats, which open in the bottom surface 21. Conversely, it is feasible to form such projections on the bottom surface 21 at the same time as the requisite seats mouth in the planar end surface 7 of the basic body 1.
It is important for the stability of the milling cutter head on the basic body that the male member 5 protrudes a distance into the rear hollow space 20 in the milling cutter head 2, wherein the envelope surface 6 of the male member should have a fine fit (0.01 to 0.05 mm) against the inner limiting surface 22 of the hollow space. This means that the shown driver 31 could be spared, if the transfer of torque is provided in another way. In this connection, it should be pointed out that the surfaces contacting each other in the composed state of the tool, viz. the surface pairs 7, 21 and 6, 22, both have a radial extension that is considerable in relation to the outer diameter of the milling cutter head. This ensures that the fixation of the milling cutter head on the basic body becomes stable and reliable, also in case the tool is subjected to most varying combinations of axial and radial cutting forces.
Two other factors, both of which relate to the tightening screw 3, also contribute significantly to the stable fixation of the milling cutter head. In the embodiment shown in
The second factor is illustrated in
Reference is now made to
In U.S. Pat. No. 6,497,540 (more precisely in
By the generally flat, pulley-like shape thereof in combination with the radially ample, hollow space for the receipt of the front end of the basic body, the milling cutter head according to the invention offers a number of advantages above previously known milling cutter heads. Thus, this basic shape offers the possibility of constructing the cutter head with a large number of cutting edges located close to each other, at the same time as the fixation of the cutter head on the rotatable basic body becomes very stable and exact, since, on one hand, the planar contact surfaces have a large radial extension, and on the other hand the rotationally symmetrical contact surfaces are situated at a large radial distance from the center axis. Furthermore, by the fact that the rear hollow space has a large radial extension, the possibility of constructing the tool with driver members is offered, which in turn are radially far retreated from the center axis; something which in turn ensures that large torques can be transferred from the basic body to the milling cutter head by means of moderate forces in the interfaces between the contact surfaces. In the indexable embodiment thereof according to
While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the invention, as defined in the appended claims and their equivalents thereof. For example, as has been indicated above, it is feasible to form one or more projections on the bottom surface in the rear hollow space of the milling cutter head, and allow the same projections to co-operate with holes or seats in the planar end surface of the basic body. Important for the stability of the milling cutter head is that the front portion of the basic body projects a distance into the rear hollow space of the milling cutter head, and not whether the means for the transfer of torque are one or more male-like members placed on the basic body and co-operating with seats in the milling cutter head. Furthermore, in this connection, it should be pointed out that the transfer of torque also may be provided by the fact that the circumferential contact surface 6 of the basic body, which co-operates with the inner, endless contact surface 22, is made with an out of round, e.g., polygonal shape, at the same time as the surface 22 is given a complementary shape. Furthermore, for the fixation of the milling cutter head on the basic body, it is feasible to use other tightening devices than a screw having a male thread. Thus, a drawbar without a thread may be used, which is drawn into the basic body by other suitable means, e.g., an eccentric mechanism or the like. Also such a drawbar may, however, advantageously be constructed with a resilient head of the type included in the shown tightening screw. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0502204-1 | Oct 2005 | SE | national |
