Patent Application
20220324037
The present invention relates to a milling tool body being rotatable around a central rotation axis. The milling tool body has a front end surface and a rear end surface, wherein an envelope surface surrounds the central rotation axis and extends between the rear end surface and the front end surface. A plurality of insert pockets are formed in a transition between the envelope surface and the front end surface. The insert pockets are arranged for mounting cutting inserts for chip-removing machining, wherein the milling tool body in particular is arranged for a face and/or shoulder milling operation.
The present invention also relates to an assembly comprising the milling tool body and an adaptor for connecting the milling tool body to a milling machine.
The invention is related to problems that may arise in known milling tool bodies mounted to adaptors, which are used for connecting the milling tool bodies to milling machines.
U.S. Pat. No. 9,238,273 discloses such a known milling tool body, which is mounted to an adaptor (holder) by means of a screw. The milling tool body has a central through-hole forming a cylindrical seat for the adaptor comprising a relatively smaller diameter and a cylindrical coolant chamber comprising relatively larger diameter. An internal shoulder is formed inside the central through-hole between the cylindrical seat and the cylindrical coolant chamber, wherein the milling tool body is mounted to the adaptor by the screw head pressing against the internal shoulder of the central through-hole via a washer.
U.S. Pat. No. 9,623,497 discloses a similar milling tool body with a screw that is used for mounting the milling tool body to an adaptor inserted into a central through-hole of the milling tool body. A recessed surface is formed in a front face of the milling tool body. The recessed surface includes a cylindrical surface extending axially into the front face of the milling tool body, wherein an internal shoulder surface (seating surface) for the screw is extending radially inside of a bottom surface of the recessed surface. A coolant cap is furthermore secured by a retaining ring mounted in the cylindrical surface of the recessed surface, whereby the coolant cap is spaced from the retaining screw to form a coolant chamber with the recessed surface.
JP4349824 discloses another known milling tool body with a central through-hole having two different diameters. The milling tool body is attached to an adaptor (arbor) inserted into the central through-hole by means of a screw (fastening bolt), which is screwed into the adaptor and abuts an internal shoulder formed by the different diameters of the central through-hole.
The known milling tool bodies described above may suffer from vibrations caused by an unbalanced milling tool body, wherein the milling tool body wobbles when rotated around the central rotation axis (during milling). Furthermore, the milling tool bodies may suffer from axial/radial run-out, wherein the cutting inserts mounted in the insert pockets exhibit deviations in the positions between their respective cutting edges.
More precisely, the vibrations caused by the unbalanced rotating milling tool body may arise when the central through-hole comprises parts of different diameters, which are manufactured by separate drilling and/or milling operations performed from the rear end surface and the front end surface respectively on the milling tool body. Insufficient manufacturing tolerances during these drilling/milling operations may lead to non-concentric parts of different diameters. In other words, the milling tool body may thereby exhibit an uneven distribution of mass around the central rotation axis, which leads to vibrations during the milling operation. Additionally, the coupling force/load applied on the milling tool body, when mounting it to the adaptor, is concentrated centrally on the milling tool body as the screw head presses directly (or via a washer) on an internal shoulder surface, whereas the rear end surface is abutting the adaptor at a relatively larger diameter. The centrally applied coupling force from the screw head acting on the internal shoulder surface may induce an elastic deformation or bending of the milling tool body that causes axial/radial run-out on the mounted cutting inserts in the insert pockets.
The object of the present invention is that of providing a milling tool body exhibiting a reduced tendency to vibrate during use and a reduced axial/radial run-out when mounting the milling tool body to an adaptor. This in turn improves the machining precision or surface finish of the milled workpiece surface and decreases the wear of the cutting inserts mounted in the insert pockets of the milling tool body.
This object is achieved by the milling tool body of claim 1. Accordingly, the milling tool body of the present invention has a front end surface and a rear end surface, wherein an envelope surface surrounds a central rotation axis and extends between the rear end surface and the front end surface. The milling tool body includes a plurality of insert pockets formed in a transition between the envelope surface and the front end surface. The milling tool body is characterized in that a first central through-hole of constant diameter extends between the rear end surface and the front end surface, wherein the milling tool body includes a locking disc with a second central through-hole and a fastening device arranged to extend through the second central through-hole of the locking disc, wherein the locking disc is arranged to press against the front end surface of the milling tool body when mounting the milling tool body to an adaptor by the fastening device being mountable to an end of the adaptor which is insertable into the first central through-hole of the milling tool body.
The constant diameter of the first central through-hole excludes that the first central through-hole has any inner flanges or internal shoulder surfaces for mounting the milling tool body with the fastening device (screw). In this way, the first central through-hole can be manufactured in for instance a single drilling operation from only one side of the milling tool body, so that further drilling or milling from the opposite side for manufacturing of inner flanges/internal shoulder surfaces and coolant chambers being recessed in relation to the front end surface is no longer required. This reduces the risk of manufacturing an unbalanced milling tool body that gives rise to vibrations during milling.
Furthermore, the locking disc is a loaded component, coupled to the adaptor with the fastening device, wherein the locking disc is arranged to press against the front end surface at a more radially outer region of the milling tool body. The compressive forces/load on the milling tool body will thus be more evenly distributed compared to when the milling tool body is coupled to an adaptor by a screw pressing directly (or via a washer) against an inner shoulder surface of the milling tool body. This will result in less elastic deformation or bending of the mounted milling tool body, whereby the axial/radial run-out on the cutting edges on the cutting inserts mounted in the insert pockets of the milling tool body is reduced.
In an embodiment of the milling tool body, a diameter of the locking disc is at least 50% of a maximum diameter of the milling tool body. In this way, the coupling force provided by the locking disc is further improved by moving it more radially outwards to at least 50% of the maximum diameter of the milling tool body. The locking disc and the adaptor at the rear end surface can hereby provide opposite and more aligned compression forces, which will result in less elastic deformation or bending of the mounted milling tool body, whereby the axial/radial run-out of the milling tool body is further reduced. The locking disc may also provide a more distributed force/load on the front end surface of the milling tool body, which is beneficial in reducing the elastic deformation or bending of the mounted milling tool body.
In a further embodiment of the milling tool body, a diameter of the locking disc is substantially the same as a diameter of the rear end surface. Hence, the rear end surface is hereby provided with a planar mounting surface having an outer diameter that is essentially the same as an outer diameter of the locking disc. The substantially same diameters do not mean that they must exhibit the exact same diameter. Instead, a substantially same diameter should hereby be understood as also including deviations of ±10% between the diameters of the locking disc and rear end surface of the milling tool body. In this way, the locking disc and rear end surface exhibit the same diameters, so that the locking disc and the adaptor at the rear end surface provides opposite and aligned compression forces, which minimizes the risk for elastic deformation or bending of the mounted tool body, so that the axial/radial run-out of the milling tool body is further reduced.
In yet an embodiment of the milling tool body, the front end surface comprises a plurality of radial coolant grooves for conducting coolant from the first central through-hole toward the insert pockets, wherein the radial coolant grooves are at least partly covered by the locking disc when mounting the milling tool body to the adaptor. Such coolant grooves are simpler to manufacture than internal coolant channels. The manufacturing of a milling tool body providing coolant to the cutting inserts mounted in the insert pockets is hereby facilitated, since it is not necessary to drill internal coolant channels all the way through the milling tool body or machine a large coolant chamber, which is recessed in the front end surface. Instead, the radial coolant grooves can be formed in the front end surface, which is covered by the locking disc that presses against the front end surface of the milling tool body.
In a further embodiment of the milling tool body, the radial coolant grooves in the front end surface extend between the first central through-hole and the insert pockets. In other words, the radial coolant grooves extend all the way between the first central through-hole and the insert pockets. In this way, the coolant is directed to the insert pockets solely inside the coolant grooves. This simplifies manufacturing compared to having internal coolant channels in the milling tool body.
In another embodiment of the milling tool body, the radial coolant grooves in the front end surface are connected to internal coolant channels in the milling tool body, the internal coolant channels extending between the radial coolant grooves and the insert pockets. Hence, each internal coolant channel is drilled in an outer portion of the milling tool body and is communicating with each radial coolant groove. In this way, the direction of the coolant can be optimized so the coolant reaches the insert pockets at a desired angle. Furthermore, the radial coolant groove is preferably connected to the internal coolant channel at a position situated radially inside a diameter of the locking disc. The locking disc will hereby completely cover the radial coolant grooves, wherein the radial coolant grooves transform into the internal coolant channels at the position situated inside the locking disc.
In an embodiment of the milling tool body, the front end surface is forming an annular relief surface, which surrounds the central rotation axis and is configured to provide an axial gap to the locking disc, wherein the front end surface is forming an abutment surface, which is surrounding the annular relief surface and is in contact with the locking disc when mounting the milling tool body to the adaptor. The annular relief surface ensures that the contact between the locking disc and the front end surface is provided radially outwards in the area of the abutment surface surrounding the annular relief surface. Preferably, the abutment surface is provided at an outer annular region of the locking disc (slightly inside the maximum diameter of the locking disc). A more defined/controlled contact between the locking disc and the front end surface is thereby achieved. Furthermore, the locking disc may bend somewhat when mounting the milling tool body to the adaptor, wherein the annular relief surface ensures that a bending locking disc does not block a supply of coolant from outlets at an end of the adaptor.
In the previous embodiment, the annular relief surface may form a conical relief surface extending at an acute angle θ with the central rotation axis as seen in longitudinal sections containing the central rotation axis of the milling tool body. In this way, the gap formed between the locking disc and the front end surface increases in the direction radially inwards, so that the gap is larger in an inner region where a bending of the locking disc exhibits the highest deflection (around the second central through-hole and the fastening device). The acute angle θ on the conical relief surface may be in the range 89.5°≤θ≤86°. In other words, the conical relief surface is forming a rather small slope (0.5°-4°) with a horizontal plane perpendicular with the rotational axis or the plane of the locking disc. The purpose of the relief surface is merely to provide a small axial gap to ensure on the one hand that the locking disc is contacting the abutment surface in a defined outer radial region, and on the other hand that any potential bending of the locking disc does not block the supply of coolant from the adaptor in an inner radial region of the front end surface of the milling tool body.
In yet a further embodiment, the abutment surface, as seen in longitudinal sections containing the central rotation axis of the milling tool body, is forming a convex abutment surface for contacting the locking disc when mounting the milling tool body to the adaptor. The convex abutment surface ensures a defined (circle/line) contact between the locking disc and the abutment surface surrounding the annular relief surface. The convex abutment surface provides a higher pressure in the circular/line contact between the locking disc and the convex abutment surface to prevent leakage of coolant at the periphery of the locking disc, so that the coolant instead passes through the coolant grooves (and the internal coolant channels) of the milling tool body.
In another embodiment, the locking disc comprises a ring-shaped contact surface at an outer portion of the locking disc, wherein the ring-shaped contact surface, as seen in longitudinal sections containing the central rotation axis of the milling tool body, is forming a convex contact surface for contacting the front end surface when mounting the milling tool body to the adaptor. This is an alternative solution to having the convex abutment surface in the front end surface of the milling tool body.
In an embodiment the milling tool body is disc-shaped by the rear end surface comprising a planar mounting surface directly connected to the envelope surface, which extends at a continuously increasing diameter from the planar mounting surface toward the front end surface. Hence, the milling tool body is disc-shaped in the meaning that it does not have a cylindrical rear end portion as conventional milling tool bodies (as shown in for instance the prior art mentioned above). In this way the disc-shaped milling tool body reduces the distance that the milling tool body extends from the adaptor (also known as tool overhang). The reduced distance or tool overhang of the milling tool body will further reduce vibrations during the milling operation. Moreover, the disc-shaped tool body also reduces production and shipping cost of the milling tool body due to less material and lower weight on the milling tool body. The relatively lower weight of the milling tool body is also beneficial in reducing vibrations during milling.
In a further embodiment of the milling tool body, the rear end surface further comprises driving slots being recessed in relation to the planar mounting surface and the envelope surface connected thereto. In this way, a stable driving connection is achieved without the addition of material to the milling tool body in comparison with the known milling tool bodies having the cylindrical rear end portions including driving slots. This further reduces the weight of the milling tool body, which also reduces vibrations during milling as well as the production/shipping cost of the milling tool body.
In an embodiment of the milling tool body, the fastening device is a screw having a threaded shank and a screw head with a bearing surface that tapers toward the threaded shank, wherein the second central through-hole of the locking disc includes a chamfered surface for abutting the tapering bearing surface of the screw head, so that the screw head becomes at least partly countersunk in the second through-hole of the locking disc when mounting the milling tool body to the adaptor. This reduces the axial protrusion of the screw head from the locking disc, since the tapering bearing surface of the screw head is abutting the chamfered surface located inside the second through-hole. Hence, it reduces the axial protrusion of the screw head and ensures that the screw head is situated axially inside the axial foremost position of the cutting inserts mounted in the insert pockets. The screw head is preferably a flat head with the tapering bearing surface. Hence, the flat screw head provides a relatively short screw head for further reducing the axial protrusion of the screw head from the locking disc. The chamfered surface of the second central through-hole and the tapering bearing surface of the screw head preferably exhibit a conical extension. However, the tapering bearing surface and chamfered surface may also exhibit a concavely and convexly curved extension respectively. Hence, the bearing surface and the chamfered surface hereby exhibit a complementary shape for abutment each other.
The present invention further relates to an assembly comprising the milling tool body mentioned above and an adaptor including a cylindrical shaft portion, which is insertable into the first central through-hole of the milling tool body, wherein the fastening device is a screw and an end of the cylindrical shaft portion comprises a central screw hole. Accordingly, the assembly comprising the milling tool body with the locking disc and the adaptor is coupled by mounting the screw into the central screw hole at the end of the adaptor, whereby the mounted assembly or a rear end portion of the adaptor can be connected to a milling machine.
In an embodiment of the assembly, the adaptor comprises at least one internal coolant passageway extending in parallel with the central screw hole inside the cylindrical shaft portion, wherein the at least one internal coolant passageway has an outlet situated radially outside the central screw hole in the end of the cylindrical shaft portion. In other words, the coolant outlet and central screw hole are placed side by side in the end of the cylindrical shaft portion, which central screw hole connects the locking disc to the adaptor. In this way the coolant from the outlets is provided radially outside the central screw hole and can be conducted further radially outwards in coolant grooves provided between the front end surface and the locking disc of the milling tool body. Preferably, the adaptor comprises several internal coolant passageways extending in parallel with the central screw hole, the internal coolant passageways being evenly distributed around the central screw hole and having outlets being evenly distributed around the central screw hole. This ensures an even distribution of coolant around the entire circumference of the milling tool body.
Embodiments are described with references to the drawings, in which:
Additionally, as can be seen in
The milling tool body in the shown embodiment is disc-shaped by the rear end surface 3 comprising a planar mounting surface 3a directly connected to the envelope surface 4, which extends at a continuously increasing diameter from the planar mounting surface 3a toward the front end surface 2. The envelope surface 4 is not extending at the continuously increasing diameter all the way to the front end surface 2. Instead, the milling tool body 1 hereby exhibits a maximum diameter DMAX at an outer periphery of the pockets 5 (see
The rear end surface 3 of the milling tool body further comprises driving slots 3b or keyways being recessed in relation to the planar mounting surface 3a and the envelope surface 4. The adaptor 10 is provided with corresponding driving keys 10b that engage the driving slots/keyways 3b when mounting the adaptor to the milling tool body. In other words, the milling tool body and the adaptor is forming an arbor mounting for transferring torque between the adaptor and the milling tool body.
As can be seen in
The front end surface 2 is further forming an annular relief surface 2c surrounding the central rotation axis R, wherein the annular relief surface 2c is configured to provide an axial gap A to the locking disc 7. The axial gap A between the locking disc 7 and the annular relief surface 2c is hereby very small and barely visible in
The front end surface 2 is further forming an abutment surface 2d, which is surrounding the annular relief surface 2c, wherein the abutment surface 2d is arranged to be in contact with the locking disc 7 when mounting the milling tool body 1 to the adaptor 10. The abutment surface 2d in the shown embodiment is forming a convex abutment surface 2d, as seen in the longitudinal section of
The fastening device is a screw 9 having a threaded shank 9a and a screw head 9b with a bearing surface 9c that tapers toward the threaded shank 9a, wherein the second central through-hole 8 of the locking disc 7 includes a chamfered surface 8a for abutting the tapering bearing surface 9c of the screw head 9b, so that the screw head 9b becomes at least partly countersunk in the second through-hole 8 of the locking disc 7 when mounting the milling tool body 1 to the adaptor 10. As can be seen in
As can be seen in
The first central through-hole 6 of constant diameter can hereby be manufactured by a single drilling/milling operation from either the front end 2 or the rear end 3 of the milling tool body, which reduces the risk of manufacturing an unbalanced milling tool body that gives rise to vibrations during milling. In other words, the milling tool body does not require the manufacturing inner mounting flanges/internal shoulder surfaces (or large coolant chambers being recessed in relation to the front end surface). Instead, the locking disc 7 with the screw 9 extending through the second central through-hole 8 is mounted into the central screw hole 12 in the end of the adaptor 10, whereby the locking disc 7 presses against the convex abutment surface 2d, which is situated at an outer annular radial region that is substantially the same as the diameter DR of the planar mounting surface 3a at the rear end 3 of the milling tool body. The front and rear forces that act on the mounted milling tool body 1 are thereby oppositely directed and aligned to minimize elastic deformation or bending of the milling tool body so that the axial/radial run-out on the mounted milling tool body is minimized.
Additionally, the conical relief surface 2c along the front end surface 2 on the milling tool body 1 provides a small axial gap A to safeguard on the one hand that the locking disc 7 is contacting front end surface 2 in a defined outer annular radial region (the convex abutment surface 2d), and on the other hand that any potential bending of the locking disc 7 does not block the supply of coolant from the coolant outlets 13a of the adaptor 13. Although, the locking disc may be made rather thick/stiff, it may nevertheless become bent if the screw 9 is mounted with an excessive torque into the screw hole 12. The deflection caused by such bending of the locking disc 7 is greatest around the centre of the second screw hole 12, wherein the conical relief surface 2c is arranged to provide the largest axial gap A to the locking disc 7 to safeguard the outer contact and flow of coolant from the outlets 13a. The coolant that exits the coolant outlets 13a can thereby flow along the coolant grooves 2a provided in the front end surface 2 and into the internal coolant channels 2b that conduct the coolant further to the insert pockets 5, so that the coolant reaches the insert pockets 5 at a desired angle toward a cutting insert mounted therein. Furthermore, the radial coolant groove 2a is connected to the internal coolant channel 2b at a position situated radially inside a diameter Do of the locking disc 7, so that the locking disc 7 will cover the radial coolant grooves 2a to prevent leakage and provide effective transfer of coolant to the pockets 5. The convex abutment surface 2d further provides a defined line/circular contact with the locking disc 7 to minimize leakage of coolant at the periphery of the locking disc 7 and ensure that the coolant is transferred to the internal coolant channels 2b. The same effect can hereby be achieved by providing the locking disc 7 with a ring-shaped contact surface at an outer portion of the locking disc 7, wherein the ring-shaped contact surface, as seen in longitudinal sections containing the central rotation axis R of the milling tool body 1, is forming a convex contact surface for contacting the front end surface 2 when mounting the milling tool body 1 to the adaptor 10. Additionally, the front end surface 2 on the milling tool body could alternatively be provided with coolant grooves 2b all the way between the first through-hole 6 and the insert pockets 5. This would simplify production of the milling tool body 1 yet may reduce the efficiency in the supply of coolant to the insert pockets 5.
The invention is of course not limited to the embodiments described above, but may be varied and modified within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19194539.3 | Aug 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/073189 | 8/19/2020 | WO |
