Prior Art Tools of the type generally described above may be in the form of milling cutters, in particular face mills. Development in modern milling technology is directed towards higher and higher cutting speeds. This development is especially marked in the milling of easily workable materials, such as aluminium. Thus cutting speeds of up to the range of approx. 8,000-10,000 m/min are already used today in the machining of aluminium, speeds which for a face mill with a diameter of 100 mm require rotational speeds in the range of 25,000-32,000 rpm. For different reasons, some sort of fluid is supplied to the individual cutting inserts during the machining operation. In some cases, cooling liquid is supplied for the purpose of cooling the cutting inserts as well as the workpiece and in other cases air with a mist of oil may be supplied for the purpose of providing lubrication and a certain cooling. Also cooling gases may be supplied. Fundamental for the cooling or lubrication fluid is the purpose of giving the machined surfaces on the workpiece optimal properties, to cool the cutting inserts and the workpiece, as well as to counteract smearing of the machined material, e. g. aluminium, on the tool. Another

purpose of the fluid is to remove the chips that the cutting inserts removes from the workpiece.

Commercially available milling tools, which were known previously, utilise different solutions to lead the cooling and/or lubricating fluid to different cutting inserts on the tool. A commonly occurring solution is based on using branch ducts in the form of holes, which are drilled from points in the immediate vicinity of the individual cutting inserts to a central main duct inside the cutter head. This manufacturing method is, however, complicated and expensive as well as giving mediocre results with regard to the ability of the fluid to cool the cutting inserts and the workpiece and to remove the chips liberated.

Aims and Features of the Invention The present invention aims at obviating the shortcomings of previously known milling tools and at providing an improved milling tool. Therefore, a primary aim of the inven- tion is to provide a tool which is able to lead the requisite fluid to the different cutting inserts in an effective and powerful manner so as to, in this way, optimise the cooling and/or lubricating effect of the fluid. Furthermore, the invention aims at providing a tool which may guide and make effective the flow of chips from the cutter head in such a way that erosion of the surfaces of the chip spaces is counteracted. Another aim of the invention is to create a tool, which may be manufactured in a simple and inexpensive way. Another aim of the invention is to create a tool having minimum weight, which facilitates operations at high rotational, speeds, in particular in respect to the starting and stopping of the tool.

Further Elucidation of Prior Art Rotatable tools of the type initially mentioned in general terms are previously known from, e. g., US 960 526, DE 3 104 752 and DE 3 105 933. Common for these known tools is, however, that the branch ducts from the main duct for the fluid consist of drilled holes and not of grooves in the end surface of the cutter head.

A rotatable tool holder is previously known from US 5 941 664, which, per se, includes a number of individual fluid branch ducts. However, said branch ducts are defined by blades, which together form an impeller so as to feed cooling liquid from outside into a central main duct. This tool holder lacks every type of cutting insert, and in furthermore the branch ducts are not in the form of grooves outwardly open.

DE 19725100 describes a milling tool which in connection with the cutting insert- equipped end surface thereof has a central distributor body having a plurality of radially directed nozzles through which cooling liquid may be supplied out to the peripherally situated cutting inserts. However, not even here are any open grooves to be found in said end surface.

Brief Description of the Appended Drawings In the drawings: Fig 1 is a perspective view of a milling tool according to the invention, Fig 2 is a planar view from above of the tool according to fig 1 in an upside- down position, Fig 3 is a perspective view of an alternative embodiment of a tool as seen obliquely from below, Fig 4 is an analogous perspective exploded view showing the same tool having a fluid distributing device shown separated from the tool, Fig 5 is a planar view from above of the distributor device according to fig 4, Fig 6 is a section A-A in fig 5,

Fig 7 is a perspective view showing a third alternative embodiment of the tool according to the invention, Fig 8 is a perspective view of a second type of distributor device included in the tool according to fig 7, Fig 9 is a planar view from below of an additional alternative embodiment of the invention, Figs 10-12 are schematic planar views from below illustrating another three different, alternative embodiments of the invention, and Fig 13 is a schematic side view illustrating an alternative embodiment of the grooves included in the tool head of the tool.

Detailed Description of Preferred Embodiments of the Invention The tool illustrated in figs 1 and 2 is in the form of a cutter head 1 which is rotatable around a central, geometrical axis of rotation C. An arched envelope surface 2 extends rotationally symmetrically around the axis C, which transforms into a cylinder surface 3 on a shaft-like portion 4 of the cutter head. A first, plane end surface 5 which is opposite a second plane end surface 6 on the shaft portion 4 extends in a plane, perpendicularly to the axis of rotation C. Between these end surfaces 5,6, a central main duct 7 extends, in the form of a hole, e. g. a bore hole, through which cooling liquid or another fluid may pass. In the edge portion 8 forming the transition between the arched envelope surface 2 and the plane end surface 5, a plurality of tangentially spaced chip spaces 9 are recessed. In connection with said chip spaces, seats 10 are formed in which cutting inserts 11 are mounted. It is to advantage if said cutting inserts are of an indexable type, whereby the cutting inserts are fixed by means of screws.

Characteristic for the tool according to the invention is that a number of outwardly open grooves or recesses 12 are formed in the end surface 5. More precisely, the number of

grooves 12 corresponds to the number of cutting inserts 11 and chip spaces 9, respectively. The grooves 12 form branch ducts the purpose of which is to lead out the fluid taken in from outside in the main duct to the different cutting inserts 11. In the preferred embodiment, each individual duct is curved and extends from an inner end 13 near the outer port of the main duct 7 to an outer end 14 situated in front of the individual cutting insert 11 as seen in the direction of rotation of the tool (see the arrows in figs 1 and 2). More precisely, the individual groove is formed in such a way that the convex side of the groove is turned forwards towards the direction of rotation.

Land portions 15 having a wedge-like, inwardly tapering basic shape are defined between the different grooves 11. The surfaces of these land portions are plane and situated in a common plane (= the end surface 5) which is axially separated from the common plane in which horizontal, lower portions of the cutting inserts 11 are situated.

In this connection, it should also be pointed out that radially outer cutting edges of the cutting inserts protrude somewhat from the rear portions of the envelope surface 2.

Each individual groove 12 is delimited by two spaced-apart side surfaces 16,16 and an intermediate, suitably concavely rounded bottom surface 17 (of the two side surfaces 16, only one is visible in figs 1 and 2, respectively). In the embodiment illustrated in figs 1 and 2, the individual groove 12 is equally thin along the entire longitudinal extension thereof from the inner end 13 to the outer end or the opening 14. Furthermore, the side surfaces 16 of the individual groove are mutually parallel and oblique in relation to the axis of rotation C of the tool. More precisely, the side surfaces of the grooves are oblique in such a way that they lean upwards/rearwards from the end surface 5 as seen in the direction of rotation of the tool. However, it is also possible to form the groove in such a way that the two parallel side surfaces extend substantially parallel to the axis of rotation of the tool. In this connection, it should also be mentioned that it is feasible to form the groove with, on the one hand, one side surface which is parallel to the axis of rotation, and, on the other hand, one side surface which is oblique relative to the axis of rotation.

Although different arch-shapes of the grooves 12 are feasible, generally a cycloidal basic shape is preferred, whereby the cycloidal curve has a diameter that increases in the direction of the outer end of the groove.

The tool illustrated in figs 1 and 2 operates in the following way.

From a suitable, outer source (not shown), pressurized fluid (e. g. cooling liquid or air with a mist of oil) is fed into the main duct 7 via the end which ports in the end surface 6 of the shaft portion 4. When the tool is rotated at high speed, e. g. at a rotational speed of 25,000 rpm or more, a suction effect arises in each of the grooves 12 which attempts to suck the fluid arriving to the outer or lower end of the main duct in the direction outwards, towards the cutting inserts 11. This suction effect can be established thanks to the grooves, which means that the end portion of the cutter head during the rotation of the mill acts as an impeller in which the land portions 15 between nearby grooves constitute fan blades. In the same way as in a conventional fan, a negative pressure which acts radially in the direction outwards from the centre of the fan is provided along "the rear surface of each wing", i. e. along the side surface 16 behind each leading land portion. More precisely, the particles included in the fluid are pressed rearwards towards the opposite side surface 16 and are at the same time slung radially outwards by the centrifugal force.

Initial deflection of the axial main flow in the duct 7 to radial partial flows in each one of the grooves 12 may take place in various ways depending on different factors, such as the rotational speed of the tool, the nature of the fluid as well as the pressure and volume of the incoming fluid. In the embodiment according to figs 1 and 2, deflection is assumed to take place without the help of particular means of deflection. This may for instance take place by first causing the tool to rotate at maximum speed and then starting and successively increasing the supply of fluid to the main duct 7. It is also feasible to load the grooves with fluid in a suitable way in connection with the commencement of rotation of the tool.

The result of the fanning effect achieved by means of the grooves is dependent on the mass flow of the fluid. If the mass flow through the main duct 7 for different reasons would become unsatisfactory, the effect is deteriorated (the fan has its own pump characteristics). In order to counteract the risk of insufficient mass flow through the main duct, particular air inlet channels 19 may be drilled in the cutter head. More pre- cisely, for each groove a channel hole 19 is drilled from an outer point near the shaft portion 4 of the cutter head to an inner point in the area of the inner end 13 of the individual groove 12. Such holes, which may be of comparatively small diameter, are in practice simple to produce in connection with the manufacture of the tool. Through the holes, air is sucked in from outside and added to the partial mass flows of fluid to the different grooves.

The fluid radially sucked-out through each individual groove will sweep along the appurtenant cutting insert 11 and cool or lubricate this as well as the portion of the workpiece with which the cutting insert is in instantaneous contact. Thereby, the fluid will see to it that chips are washed away not only from the cutting insert and the workpiece but also from the surfaces which define each individual chip space 9. In this connection, it should be emphasized that the partial flows of fluid through the grooves form jets, which throw out the chips in the radial direction in a common plane, directed perpendicularly to the axis of rotation of the tool. In this way, the flows of chips are directed out from the tool in an optimal way.

Reference is now made to figs 3-6, which illustrate an embodiment according to which the cutter head has been provided with particular means in order to deflect the axial main flow of the fluid to become radial partial flows. More precisely, the tool includes a screw 20 by means of which the same may be fixed in the usual way in a tool holder (not shown). The screw 20 consists of a tubular screw for allowing axial passage of fluid, and has a head 21 having a male screw 22. The cavity in the interior of the tubular screw ports into a hexagonal socket 23 in which a key may be applied to tighten the screw. A distributor device designated in its entirety 24 co-operates with the screw head 21, which device is composed of a circular plate 25 and a cylindrical bushing 26, which has an internal thread 27 (see fig 6). In the example shown, the plate 25 has a larger

diameter than the bushing 26, whereby the plate flares out a distance from the bushing.

In the immediate vicinity of the plate, the bushing has a number of radial holes 28 through which fluid may pass in the direction radially outwards. On the inside thereof, the plate 25 has a conical body 29 which when it is hit by the axial fluid flow directs the fluid in the direction of the holes 28. In the conical body 29, a hexagonal socket 30 is also formed for a key, by means of which the cap may be tightened on the screw head 21.

The function of the cap described should be obvious. When fluid is fed axially through the tubular screw 20, the conical body 29 and the plate 25 force the fluid to deflect in radially directed partial flows which pass out through the holes 28 and further to the different grooves 12 in the cutter head.

In figs 7 and 8, an alternative distributor device is illustrated which also in this case includes a circular plate 25 having an internal conical body 29. In this embodiment, the plate 25 has, however, a number of holes 31 for screws (not illustrated) by means of which the plate may be fixed in a circular countersink in the outer or lower end surface 5 of the cutter head. Said holes 31 are placed comparatively near the periphery of the plate so that in turn threaded holes for the fastening screws may be located outside the main duct in the cutter head. When the axial fluid flow through the main duct meets the plate 25, the same will be forced to reform as radial partial flows by means of the plate and the associated conical body.

The embodiment illustrated in fig 9 differs from the embodiment according to figs 1 and 2 only in that the particular air inlet channels 19 are missing.

How the grooves 12 may widen in the direction from the inner ends thereof to the outer ends thereof is schematically illustrated in fig 10. In other words, said grooves have an increasing cross-sectional area with increasing radius. The effect of the grooves widening in the outward direction is that the fluid expands in the grooves and that the turbine fan achieved easily pumps out large partial flows of which, however, the speed of the fluid is moderate.

In fig 11, an embodiment is illustrated according to which each individual groove 12 widens in the direction from the outer end thereof to the inner end thereof. In this case, the fluid will be compressed in the grooves, whereby the turbine fan pumps out a limited flow of fluid in which, however, the speed and pressure, respectively, of the fluid has been increased.

Common for the two embodiments according to figs 10 and 11 is that the grooves 12 are narrow in comparison with the nearby, surrounding land portions 15. In other words, the total projection area of the grooves is smaller than the total projection area of the land portions.

In fig 12, an alternative embodiment is shown according to which the total projection area of the grooves or of the recesses 12 is larger than the total projection area of the land portions 15 between the grooves. In other words, here the land portions are comparatively narrow in relation to the grooves. In this embodiment, large quantities of fluid may be pumped out, although at low speed and low pressure.

In fig 13, an embodiment is illustrated according to which the two side surfaces 16 of the individual groove 12 diverge from the end surface 5 of the tool head towards the common bottom surface 17 for the side surfaces.

An important advantage of the invention is that the tool, thanks to the fan-forming grooves, provides exhaustion of powerful partial fluid flows from the main duct towards the individual cutting insert and the chip spaces thereof in an automatic way.

Furthermore, the partial fluid flows obtained are directed radially in a plane perpendicularly to the axis of rotation. Therefore, contrary to the obliquely drilled branch duct holes in previously known milling tools, the tool according to the invention guarantees an efficient disposal of chips from the cutting insert and surrounding chip spaces. Furthermore, the manufacture of the tool according to the invention is simple in comparison with previously applied manufacturing methods. Among other things, there is the advantage that the open grooves in the end surface of the tool head do not

interfere with the possibilities of the designer to form and locate the cutting insert and the appurtenant chip spaces, respectively, in an uninhibited way. Another advantage is that the grooves cause a reduction of the total weight of the tool; something which is especially important in connection with high rotary speeds. More precisely, a minimal weight of the tool facilitates the starting as well as the stopping torque of the tool.

Feasible Modifications of the Invention The invention is not solely restricted to the embodiments described above and shown in the drawings. Thus, it is feasible that instead of curved grooves substantially straight grooves may be used. If the grooves are given a curved shape, the arch-shape may furthermore be turned in the opposite direction in relation to the embodiments illustrated in the drawings, i. e. with the convexity directed rearwards instead of forwards in relation to the direction of rotation. In case the milling tool is equipped with a distributor device of the type described, the distributor plate may be given a larger diameter than the plates which have been exemplified, whereby the grooves will at least partially be covered by the distributor plate. Although the grooves initially in connection with the manufacture are entirely open outwards, the same may thus entirely or partly be covered by a distributor plate in the operative state thereof. Furthermore, the different grooves on one and the same cutter head may be given different widths. For instance, every second groove may be wider than the nearby grooves. Furthermore, different grooves in one and the same cutter head may have different inclinations, either at each one of the two sidewalls defining each groove or at both sidewalls in each pair.

Furthermore, the different grooves need not necessarily be equidistantly spaced-apart.

Thus, it is feasible to place the grooves irregularly in relation to each other also in the case where the cutting inserts are equidistantly spaced-apart from each other.