More particularly, the invention is concerned with an end mill provided with a new arrangement of coolant conduits to improve cutter performance and to produce workpieces having a finer surface finish.

In the machining of metals, cooling of the cutting tool is essential to avoid overheating thereof. The coolant is usually a liquid, (although it is possible to use a gas jet, which has advantages for the machining of cast iron) such liquid commonly comprising an aqueous solution of a soluble cutting oil. Water alone is an excellent coolant but is not used mainly to avoid rusting of the machine tool. Petroleum-based fluids are used where friction reduction and protection from welding action are of prime importance. The coolant also helps to avoid overheating of the work piece, washes away the generated chips to improve surface finish and provides some lubrication for surfaces of the cutting tool which rub against the workpiece, thereby reducing tool forces.

In short simple operations the coolant is often applied manually by the operator using a brush or spouted can. In production work a jet of coolant is pumped through piping from a reservoir and directed at the cutter, the used coolant being filtered and reused.

This method often requires splash guards. A more serious problem is that, as has been reported by various researchers, the coolant does not reach the cutting edges.

Particularly in slotting operations using an end mill, the abundant supply of coolant does not ensure that the cutting teeth most in need thereof are directly cooled and lubricated adequately; cooling is effected by conduction of heat from the cutting edges through the exposed body of the cutter which is easy to cool, provided it is not revolving so fast that centrifugal forces remove the coolant before it can do its work.

Referring again to one of the functions of the coolant being to wash away chips from the cutting area, in most machining operations the coolant only removes chips which have already been moved away from the cutting zone. Some improvement in applying coolant nearer the site where it is required has been achieved by the development of cutting tools wherein a central coolant conduit has several outlets branching at an angle from the central conduit and disposed along the sides of the tool for the distribution of coolant to the cutting edges at the sides of the tool, as seen in FIG. 1. A typical example of this arrangement is seen in US Patent no. 5,174, 692 wherein Martin discloses a drilling tool and apparatus with improved swarf removal.

In milling operations, particularly in deep slotting using an end mill, the use of an arrangement similar to that described by Martin will clear chips from the outer or upper portion of the slot being machined but not from the area where chip clearance is most critical-the bottom of the slot.

A further disadvantage of prior art end mills of the type having a central coolant conduit is that the long bore, aside from being difficult to manufacture, causes some loss of hydraulic pressure. Further pressure is lost as the coolant is forced to traverse a sharp angle on leaving the central bore. The resultant coolant flow is then too low to achieve effective chip evacuation, and too little heat is removed from the tool.

Yet a further disadvantage of this type of prior-art end-mill cutters is that the secondary conduit channels extend close to the outer diameter of the cutter. The resulting stress concentration in the vicinity of the cross-holes causes disastrous weakness in small diameter cutters, although in large diameter cutters the problem is of little consequence.

OBJECTS OF THE INVENTION: It is therefore one of the objects of the present invention to obviate the disadvantages of prior art end mills and to provide a cutter which receives coolant very near its end cutting edge.

It is a further object of the present invention to improve swarf removal from deep milled slots by arranging an end mill to release coolant from its end cutting faces and thereby to remove swarf from the bottom of the slot being milled as well as from the sides thereof.

SUMMARY OF THE INVENTION: The present invention achieves the above objects by providing an end mill cutter provided with a shank end, and a cutting end composed of a plurality of teeth each having a cutting edge and a back face, the cutter being provided with internal coolant conduits. The conduits comprise a center conduit extending along the central axis from the shank end to near the cutting end, and a plurality of secondary conduits substantially parallel to and spaced apart from the central axis and to/from each other, the secondary conduits extending from the back face of the teeth at the cutting end into the center conduit to provide fluid communication therewith. hi a preferred embodiment of the present invention there is provided an end mill cutter wherein the center conduit has a larger diameter at the shank end and a smaller diameter near the cutting end.

In a most preferred embodiment of the present invention there is provided an end mill cutter wherein in a cross-section taken along the central axis the center conduit has a parabolic form.

In U. S. Patent no. 5,820, 313 Weber describes and claims a rotating shaft tool in which a main coolant channel extends longitudinally. A cutter head connected to the shaft has chip grooves and a groove discharge region, which is covered by a sleeve. The sleeve covers feed channels formed between the main channel and the groove discharge. At least one feed channel is parallel to the main channel and is curved to reach the groove discharge area. The coolant is thus discharged from the bottom of the open sleeve into the teeth grooves, there being no guarantee that the fluid will reach the lowest cutting edges. A glance at FIG. 1 in the Weber patent shows the sleeve end to be far away from the cutter end, and it cannot be brought into closer proximity thereto because the sleeve covers required cutting edges at the sides of the cutter.

In contradistinction thereto, the cutter of the present invention discharges coolant at the cutter extremity very near to the bottom cutting edges. Thus cooling and lubrication are more effective, and swarf is washed out not only from the bottom of the slot being machined but also from the sides thereof. The improved swarf removal is an important factor in improving the surface finish of the worlcpiece.

It will thus be realized that the novel cutter of the present invention serves to apply coolant during a slot milling operation in very close proximity to where it is required. Improved machinability and extended tool life result not only from better cooling and lubrication of the cutting zone but also from removing swarf in a more effective manner than. has been done previously.

It will also be observed that sharp angled bends between the cooling conduits have been eliminated, so that pressure loss during coolant flow is minimized.

It could be supposed that the cooling channels described in the present specification would weaken the cutter and cause early breakage in use. To test the strength of the end mill, prototypes of the cutter according to the present invention were manufactured and tested, and it was found that they withstood high cutting forces without breakage. This result, although somewhat surprising, can be explained by considering the disposition of the secondary conduits in the present invention relative to the outer cutter diameter and its central axis. When an external twisting moment is applied to a shaft of circular cross-section, the shear stress increases directly as the distance of the strained element from the center. Of course, the teeth of an end mill are far from representing a circular form, but the greatest strain, and therefor greatest stress, is experienced at the outer face furthest from the central axis also for forms other than circular.

End mill cutters are also subjected to a reversing bending torque. What has been explained regarding twisting applies also with regard to bending.

In the present invention the secondary conduits are in proximity to the central axis, i. e. in an area where strain, and therefor stress, are close to the minimum, and for this reason do not weaken the cutter to any noticeable extent.

It has been found that generally two outlet conduits are suitable for most purposes, whether the end mill has 2,3 or 4 teeth, as will be seen in the figures. For large end mills three or 4 outlet conduits can be provided if needed.

SHORT DESCRIPTION OF THE DRAWINGS: The invention will now be described further with reference to the accompanying drawings, which represent by example preferred embodiments of the invention.

Structural details are shown only as far as necessary for a fundamental understanding thereof. The described examples, together with the drawings, will make apparent to those skilled in the art how further forms of the invention may be realized.

In the drawings: FIG. 1 is a partially sectioned elevational view of a prior art end mill in use, showing a dense accumulation of chips near the cutting end; FIG. 2 is a partially sectioned elevational view of a preferred embodiment of the end mill according to the invention showing the coolant washing out chips from the cutting end; FIG. 3 is an end view of a two-tooth end mill cutter; FIG. 4 is a sectioned elevational view of an embodiment provided with an enlarged central conduit; FIG. 5 is a sectioned elevational view of an embodiment having a shaped central conduit; FIG. 6 is an end view of a three-tooth end mill cutter; and FIG. 7 is an end view of a four-tooth end mill cutter.

FIG. 8 is an elevational view of an embodiment having additional side conduits; FIG. 9 is a cross-section taken at AA in FIG. 8 ; FIG. 10 is an elevational cross-section taken at CC in FIG. 9; FIG. 11 is an elevational partly cross-sectional view taken at CC in FIG. 9; and FIG. 12 is a cross-section taken at BB in FIG. 8.

There is seen in FIG. 1 a prior art end mill cutter 10. A central coolant conduit 12 receives high pressure fluid at the shank end 14 of the cutter. Fluid reaches the end of the central conduit 12, from where flow is split into a plurality of secondary conduits 16, which branch off the central conduit 12 at an angle and enter the channel being milled 18 at an intermediate depth. Little flow takes place below this depth, as pressures on both sides of the cutter are about equal. If fluid pressure is adequate chips 20 generated above this depth are washed out. There is no assurance that coolant reaches the cutting edges 22. Referring now to FIG. 2, there is seen an end mill cutter 30 according to the present invention. The cutter is provided with a shank end 32, and a cutting end 34 composed of a plurality of teeth 36 each having a cutting edge 38 and a back face 40 visible in FIG. 3. The cutter 30 has internal conduits for a high pressure coolant/lubricant. A center conduit 42 extends along the central axis from the shank end 32 to near the cutting end 34. The axes of the two secondary conduits 44 are disposed substantially parallel to and spaced apart by a short distance from the central axis. Consequently the secondary conduits 44 are also parallel to each other. The secondary conduits 44 extend into the center conduit 42 to provide fluid communication therewith, and extend through the back face 40 of the teeth 36 at the cutting end 34 to supply coolant very near to the cutting zone. Thus the coolant arrives in the zone where it is most effective to cool and lubricate the cutter, and thereafter exiting washes chips 20 away from the whole profile of the cutter.

With reference to the rest of the figures, similar reference numerals have been used to identify similar parts.

FIG. 3 illustrates an end mill cutter 48 wherein each tooth 50 is provided with a secondary coolant conduit 52. The cutter has two teeth 50 and the same number of secondary conduits 52.

Seen in FIG. 4 is an end mill cutter 54 similar to the cutter 30 seen in FIG. 2. The center conduit has a larger diameter 56 at the shank end and a smaller diameter 58 near the cutting end. Elimination of the long small diameter bore of the conduit 42 seen in FIG. 2, which may have a length/diameter ratio exceeding 25: 1, serves to ease manufacture of the cutter 54 and also reduces hydraulic pressure loss along the central conduit 56.

Referring now to FIG. 5, there is depicted an end mill cutter 60 similar to the cutter 54 seen in FIG. 4. In a cross-section taken along the central axis, the shank portion of the center conduit 62 has a parabolic form. This form further improves fluid flow through the center conduit. The present embodiment is particularly advantageous for carbide cutters produced by powder metallurgy, as the smaller volume of the present embodiment results in material savings during cutter manufacture.

FIG. 6 shows a three-tooth end mill cutter 64. The figure shows a suitable arrangement for positioning the two coolant outlets 66 relative to the three teeth 68.

FIG. 7 illustrates a four-tooth cutter 70 provided with two coolant outlets 72.

Turning now to FIGS. 8,9 and 10, and ignoring for the time being section BB, there is seen an end mill cutter 74 further provided with two transverse conduits 76 extending from the center conduit 12 to a side of the cutter and between the teeth 36 thereof.

This arrangement is useful where a stronger coolant flow is required in addition to flow originating from the two secondary conduits 16 parallel to and spaced apart from the central conduit 12.

Typically, although not in the present embodiment, the number of transverse conduits 76 is equal to the number of cutter teeth 36.

FIGS. 11. and 12 show a further four-tooth end mill cutter 78 provided with transverse conduits 80 extending from the secondary conduits 16 to a side of the cutter 78 and between the teeth 36 thereof.

Referring again to FIG. 8 and including section BB, it is seen that many different arrangements are possible when some of the traverse conduits 76 are connected to the central conduit 42 while others are connected to the secondary conduits 44 parallel to and spaced apart from the central conduit 42.

As is known in the prior art (see FIG. 1), traverse conduits 16 may be drilled at other than right angles to the cutter center axis. The chosen design is selected on the basis of the material to be machined, depth of cut required, cutter feed, required tool rigidity and other factors such as coolant viscosity and available coolant pump pressure.

The scope of the described invention is intended to include all embodiments coming within the meaning of the following claims. The foregoing examples illustrate useful forms of the invention, but are not to be considered as limiting its scope, as those skilled in the art will readily be aware that additional variants and modifications of the invention can be formulated without departing from the meaning of the following claims.