MXPA97006884A - Insert for strawberry with tip of b - Google Patents

Abstract

The present invention relates to a ball end milling cutter having a rotary cutter body on an axis A to make a rounded cut in a workpiece, removing chips therefrom having an insert mounted on one end of said workpiece. Strawberry body including an upper wall, a lower wall, an arched side wall and an arcuate cut edge defined at the intersection between said upper and lower walls, said arched cut edge having a profile that follows the contour of a sphere for preventing the generation of tool marks, characterized in that: said arcuate cut edge having an end portion crossing over said axis of rotation, said edge includes a plurality of sinousidal corrugations to reduce shear cutting forces and reduce vibration between a workpiece and said portion of said insert, and to improve the breaking and removal of chips from a workpiece

Description

INSERT FOR STRAWBERRY WITH BALL PUNTA BACKGROUND OF THE INVENTION This invention relates generally to a ball end mill insert, and specifically concerns such an insert, having sinusoidal corrugations along its cutting edge to reduce cutting and vibrating forces, and to facilitate the breaking and removal of shavings.

Inserts for ball-tipped cutters are well known in the prior art. Such inserts typically comprise an integral body formed from a hard material, resistant to use, having at least one arcuate cutting surface which may be formed in quadrants. The cutter itself includes an elongated cylindrical body having a spigot portion for adjustment to a rotary tool, and a semi-spherical shaped end formed by having a seat formed in quadrants for receiving and mounting the insert. The portion of the cutting edge closest to the tip of the semi-spherical end crosses a short distance over the rotation axis of the cutter to ensure that the cutting edge of the insert engages the workpiece along the axis of rotation of the cutter. body of the strawberry, thereby allowing the strawberry to perform an immersion operation on a workpiece.

Such ball-tipped cutters have proven to be highly versatile machine tools that are capable of performing immersion cuts much like a drill bit, offered face type like a conventional milling cutter, or even ramping operations that combine both cutting movements of insertion and face. However, applicants have noted a number of limitations in the performance of the insert used with such cutters in which the performance can be substantially improved. For example, applicants have noted that the region of the cutting edge intersecting the axis of rotation is subject to large amounts of heat generating shearing forces since the rotational speed of the cutting edge is zero on the axis, and very slow in the portion of the edge adjacent to the axis. Some insert designers have tried to solve this problem by forming the cutting edge so that it is close to traversing the axis of rotation. Unfortunately, such a design necessarily creates a small projection of material from the uncut workpiece at the point where the axis of rotation of the cutter body intersects the workpiece. As long as the unwanted protrusion of uncut material breaks periodically due to the forces applied thereto by the cutting operation, a small roughness may be created along the axis of rotation on the cutting surface.

Still other limitations include the relatively high cutting forces and vibrations associated with the use of a prior art ball nose cutter against the use of a more conventional (but unfortunately less versatile) end mill. Applicants have observed that one of the causes of such high cutting forces and vibrations is that all points of the cutting edge of the inserts used in such cutters are orthogonally adjusted to the workpiece at all times during the cutting operation. While it is possible to reduce the cutting forces and vibrations by mounting the insert at an angle with respect to the axis of rotation of the cutting body (thereby imparting an axial raking angle to the insert), such a technique requires the provision of relatively deep insert seats, which in turn weakens the cutter's body. Additionally, such an inclined assembly of the insert can cause an undesired concavity in the side walls of the cut made by the milling cutter, thereby creating a distortion in the shape of the cut when a true hemispherical profile is desired.

Finally, applicants have noted that some inserts for such ball point cutters do not effectively brittle the metal chips that result from certain cutting operations. Hence, if such a cutter is used to implement a thin cutting operation immersed in a highly ductile material, the insert used in the cutter may not effectively breach the resulting lamellas like chips, which may interfere with its ejection from the ejector groove. of chips from the cutter body and therefore interfere with the cutting operation.

Clearly an insert is required for use in a ball end mill that is capable of producing round cuts in a work piece, without the generation of great stresses and frictional heat where the cutting edge instersects the center line of the cutter. Ideally, one such cutter should be able to cut a workpiece with lower cutting forces and with less vibration than the prior art inserts without the need to tilt the insert at a substantial axial rake angle, thereby reducing the requirements of power while increasing the longevity of the tool. Finally, it would be desirable if such an insert were capable of imparting substantial breaking forces to the chips resulting from the cutting operation such that even very thin chips formed from highly ductile materials could curl and break into small pieces during the cutting operation. .

SUMMARY OF THE INVENTION The invention is an insert for use in ball nose cutters that overcomes or ameliorates all of the above-mentioned limitations associated with inserts of the prior art.

The insert of the invention generally comprises an insert body having a top surface, a bottom surface, and at least one arcuate side surface, and at least one arcuate cutting edge defined at the intersection between the top and side surfaces that it includes a plurality of sinusoidal undulations. The undulations advantageously reduce both the cutting forces and the vibration associated with the operation of the insert without the need to tilt the insert at an axial rake angle that could weaken the tool holder, and further improve crimping, breakage, and removal of metal chips produced by cutting.

The insert is particularly adapted for use in a milling body rotatable about an axis having a spigot portion at one end, for its adaptation of the cutter body to a rotary tool, and an insert seat at its other end for mounting the insert such that an end portion of the arcuate cutting edge rotates about the axis of rotation. The profile of the cutting edge is arched, and designed to make a hemispherical cut when rotated by a cutter body. A portion of the arched cutting edge crosses over the axis of rotation of the cutter body. The corrugations further serve to advantageously reduce the substantial shear stresses that are generated in the portion of the cutting edge that traverses the axis of rotation.

The lateral surface of the insert includes a lower portion of relief that terminates along the bottom surface of the body of the insert, and an upper portion of relief that terminates at the corrugated cutting edge. The upper relief portion is combined between the corrugated cutting edge and the lower relief portion to provide at least a minimum relief angle with the workpiece. Such combination allows the corrugated cutting edge to make suitable round cuts, whose walls are substantially free of unwanted flutes or other undesirable tool marking patterns.

The upper surface of the body of the insert includes a portion between grooves arranged behind the cutting edge to consolidate the edge. In the preferred embodiment, the portion between flutes is inclined between 5"and 10" with respect to the plane of the upper surface to impart a positive rake angle to the cutting edge, which also helps to reduce the cutting forces.

The upper surface of the body of the insert also includes a splinter chip slit disposed behind the spline portion having rounded bottom, front and back walls, the end portions of the front and rear walls being inclined between about 15 ° and 30 °. "with respect to the plane of the upper surface." The width of the splinter-chipping groove is about 5 times the height between the lowest point, the depression and the highest point of the crest of each one of the undulations. Such dimensioning, in conjunction with the positive rake angle imparted to the cutting edge by the portion between grooves, applies substantial curling forces to the chips produced by the cutting edge, which in turn tends to harden them. Additionally, the crest and depression portions of each of the corrugations apply tensional and compression forces alternately to such chips, which tend to harden them even further when they are folded. The combination of curling and bending forces results in a substantial cracking of the chips, which in turn causes the chips to break rapidly into small pieces that are easily expelled from the vicinity of the cutting operation by removal slots in the Strawberry.

BRIEF DESCRIPTION OF THE DIFFERENT FIGURES.

Figure 1 is a perspective view of the insert of the invention, mounted on a ball end mill; Figure 2 is an enlarged perspective view of the insert of Figure 1 shown without the surrounding mill body; Figure 3 is a side cross-sectional view of the insert of Figure 2 taken along line 3-3; Figures 4A to 4C are side cross-sectional views of the insert of Figure 2 taken along lines 3-3, 4B-4B, and $ c-4C, respectively; Figure 5 is a perspective view of the insert of Figure 1 illustrating how forces applied to a workpiece by the cutting edge of the insert generate a folded chip similar to that shown in Figure 6, and Figure 6 is a side cut-away view of the insert and cutter illustrated in Figure 1, performing a cutting operation on a work piece.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY With reference to Figure 1, in which the same numbers represent the same components through the various figures, the invention is particularly adapted for use in a ball tip cutter 1 having a long body 3 which rotates around a axis A when performing a cutting operation. The cutter body 3 includes a spigot portion 5 having a plane 7 which is removably connectable to a rotary tool (not shown). The cutter body 3 further includes an end portion generally hemispherical in shape 9 having a seat 11 in the shape of a recess which is complementary in shape to the cutting insert 15 of the invention. The insert 15 is secured in the seat 11 by means of a mounting screw 17. An interlocking shoulder 18 interengaging with an end hole present in the insert 15 to prevent the insert from rotating with respect to the mounting screw 17.

With respect now to Figures 2 and 3, the insert 15 of the invention is formed of an insert body 22 which is entirely formed of a hard, wear-resistant material such as tungsten carbide, although any of a number of materials well known in the prior art can be employed for this purpose. The body of the insert 22 includes an upper wall 24 having a planar portion 26, and a planar bottom wall 28. The upper and bottom walls 24 and 28 are interconnected by means of a pair of opposite and arched side walls 30. The body of the insert 22 further includes a pair of opposite end recesses 32 that are complementary in shape to the retainer shoulder 18 of the cutter body 3 to secure the insert 15 in the seat 11 as previously described.

The body of the insert 22 includes a pair of opposite, indexable cutting edges 34, defined at the intersection between the arcuate side walls 30 and the top wall 24. Each cutting edge 34 includes at least two corrugations 36, and preferably between 3 and five corrugations , as best seen in Figure 23. Each ripple includes a ridge portion 38 and a depression portion 40, which together form a single, sinusoidal wave. In the preferred embodiment, each of the undulations 36 has the same period and amplitude. Preferably, the height h of each of the corrugations 36 is no greater than 40% of the maximum thickness T of the body of the insert 22. If the height h is much greater than 40% of the thickness T, the body of the insert 22 becomes excessively weak in the depressed portions 40 of the corrugations 36, which could lead to the breakage of the insert 15. On the other hand, if the height h is less than about 15% of the thickness of the insert T, the advantages of reducing the the shearing force and vibration of the invention decrease considerably. In the preferred embodiment, the height h is about 25% of the thickness of the insert T. 10 As shown in Figure 2, each cutting edge 34 is arcuate along its length with respect to the center point C of a circle having a radius R in which the central point C is coplanar with the flat portion 26 of the upper wall 24. As shown in Figure 3each cutting edge 34 is also arched along its width so that each edge 34 conforms to a wall of a sphere S having the same central point C. Such a contour advantageously allows the cutting edge 34 to make a cut hemispherical in a work piece while using the benefits provided by the undulations 36 on the edge 34.

Each of the side walls 30 includes a lower relief surface 42, and an upper relief surface 44. The lower relief surface 42 is preferably inclined at an angle "a" of between about 7"and 15" in relation to to a line orthogonally disposed with respect to the planar portion 26 of the upper wall 24. A smaller angle would not ensure that the cutting edge 34 could couple a workpiece without interference from the side wall 30, while a larger angle could unduly weaken to the cutting edge 34.

As shown in Figures 4A to 4C, the cutting edge 34 intersects the upper relief surface 44 when it rises from the depression portion 40 to the ridge portion 38 of the corrugations 36. The upper relief surface 44 is, in FIG. effect, combined between the cutting edge 34 and the lower relief surface 42 to provide a relief angle f? -I3 between the cutting edge 3 and the side wall of the insert 15 while preserving the spherical profile of the cutting edge 34. FIG. 4A illustrates the case where the cutting edge 34 intersects the depression portion 40 of the corrugations 36. In this case, there is almost no upper relief surface 44, and a relatively wide relief angle fi is provided by the lower relief surface. 42. However, in the case of Figure 4B where the cutting edge 34 intersects an intermediate portion between the ridge 38 and depression 40 portions, an upper relief surface 44 interconnects the bottom end of the ridge 38. cutting edge 34 with the upper end of the lower relief surface 42, and providing a relief angle f2. In this figure, hi illustrates the height of the spherical cutting edge 34, while h2 illustrates the height of the upper relief surface 44, where h? + H2 is equal to h. Figure 4C illustrates the case where the cutting edge 34 intersects the ridge portion 38 of a ripple 36. Here, the length 2 of the relief surface 44 is maximized, and equals the height h of the ripples 36. As is evident from the drawings, the upper relief surface 44 continues to provide a relief angle f3 to the cutting edge 34. In all cases, the relief angle is at least 3 °.

With specific reference to Figure 3 again, the upper wall 24 includes a narrow grooved surface 46 disposed immediately behind the cutting edge 34. The surface between grooves 46 advantageously strengthens the cutting edge 34, thereby increasing the longevity of the insert 15. In the preferred embodiment, the surface between ribs 46 is arranged at a rake angle "b" of between about 5"and 10" with respect to the planar portion 26 of the upper surface 24. Such a positive rake angle helps reduce the cutting forces assuring that the cutting edge 34 cuts the workpiece 66 (shown in Figure 5) by a slicing action, as opposed to a scraping action.

Arranged immediately behind the surface between splines 46 is a chip curling slot 48. The slot 48 is arched essentially in cross section, having a rounded bottom wall 50, a rounded front wall 52, and a rounded rear wall 54. rounded rear wall 54 terminates in a right back wall 56 that is orthogonal with respect to planar portion 26 of upper wall 24. Front and rear walls 52, 54 of slot 48 are disposed at angles "d" and "e" with respect to the planar portion 25 of the upper wall 24, which encourages the chips produced by the cutting edge 34 to curl as they slide on the upper wall 24 of the insert 15. In the preferred embodiment, amboa angles d and e are preferably between about 20 * and 30 * from the plane of the upper surface 24. Since these walls are arched, those angles are determined from a tangential line with the extrusions outer walls of the front and rear walls 52, 54.

Arranged directly in the middle of the body of the insert 22 is a bore 58 for receiving the aforementioned mounting screw 17. The bore includes a tang portion 60 and a head portion 62 for receiving the pin and head of the mounting screw 17, respectively.

Figures 5 and 6 illustrate how the cutting insert 15 of the invention operates when mounted in the seat 11 in the semi-spherical end portion 9 of a cutter body 3 and rotates about a rotation axis A. A small segment 67 of the cutting edge extends over the axis of rotation A so that all portions of the rounded cut 64 are engaged by the cutting edge 34. While the amount of shear and heat generated in the vicinity of the end segment 67 they are larger than in other parts of the cutting edge 34 due to the fact that the rotational speed of the cutting edge is zero at this point, the corrugations 36 reduce the cutting forces and the heat by reducing the cutting forces along the cutting edge 34, and by reduction in addition to the vibration associated with the cutting operation. These advantageous reductions in cutting, heat and vibration forces result from the fact that the cutting edge 34 does not initially cut the workpiece 66 simultaneously along the same line. Instead, the crest portion 38 of the corrugations 36 forms conductive portions of the cutting edge that fits the workpiece 66 first, while the depression portions 40 provide drag portions of the cutting edge 34. Additionally, these corrugations 36 produce metal chips 68 advantageously, having crease folds 70 therein. As shown in Figure 5, such folding is caused by the fact that the ridge portion 38 of each ripple 36 tends to extend the splinter outward during the cutting operation, thereby creating a thinned portion 71, while the depression portion 40 of each ripple 36 tends to create a compressed portion 72 in the sliver 68. The generation of such folds 70 with alternately thinned and compressed portions 71 and 72, in combination with the crimping forces applied to the chips 68 as a result of the positive raking angle of the surface between grooves 46 and the provision of the splinter groove 48, effectively still break very thin chips, which in turn allows them to be broken and easily expelled out of the groove 19 present in the hemispherical portion end 9 of the cutter body 3.

While this invention has been described with respect to a specific embodiment, various additions, modifications, and variations of this invention will become apparent to persons skilled in the art. All such modifications, additions and variations are within the scope of this invention, which is limited only by the claims appended hereto.

Claims (19)

WHAT IS REVINDED IS:

1. An insert for use in a ball-tipped cutter to make a round cut in a workpiece by removal of chips therefrom when rotating around an axis, comprising: an insert body including an upper wall, a lower wall, an arcuate side wall, and an arched cutting edge, defined at an intersection between said top and side walls, said arcuate cutting edge including a plurality of sinusoidal corrugations to reduce shear forces , reduce vibration, and improve breakage and removal of chips from the workpiece.

2. The insert described in claim 1, wherein an end portion of the cutting edge of said insert crosses said axis of rotation, and said sinusoidal corrugations reduce the shear forces in said end portion of the insert during a cutting operation.

3. The insert described in claim 1, wherein said side wall of said insert body includes a lower relief portion, and a top relief portion disposed between said lower relief portion and said cutting edge, and the profile of said cutting edge. follows the contour of a sphere to prevent the formation of tool marks.

4. The insert described in claim 3, wherein the profile of said upper relief portion provides a relief angle.

5. The inserts described in claim 4, wherein said relief angle is at least 3 °.

6. The insert described in claim 4, wherein said top wall includes a planar portion, and said bottom relief portion of said side wall is inclined at a relief angle of between about 5 * and 15 * with respect to a plane orthogonal to said planar portion.

7. The insert described in claim 1, wherein said top wall further includes a portion of grooved surface disposed behind said cutting edge to strengthen said cutting edge.

8. The insert described in claim 7, wherein said top wall includes a planar portion, and said surface portion between ridges is inclined between 5 ° and 10 * with respect to said planar portion of said top wall to impart a positive rake angle. to said edge.

9. The insert described in claim 7, wherein said top wall includes a splinter chip slit behind said surface portion between splines.

10. The insert described in claim 9, wherein said slot includes a bottom wall, and front and rear walls that are inclined between 15 * and 30 * with respect to the planar portion of said top wall.

11. The insert described in claim 10, wherein said slot further includes a back wall which intersects said back wall and which is orthogonal to said planar portion of said top wall.

12. An insert for use in a ball point cutter to make a round cut in a workpiece by removing chips from the mime when rotated about an axis, comprising: an insert body including an upper wall, a bottom wall, an arcuate side wall, and an arcuate cutting edge defined at an intersection between said top and side walls, said cutting edge including a plurality of sinusoidal ndulations to reduce the cutting forces and vibration and improving the breaking and removal of chips, each ripple including a ridge portion and a depression portion, said ridge having at least two ripples having the same period and amplitude.

13. The insert described in claim 12, wherein a height difference between the crest and depression portions of each of said corrugations is between about 20% and 35% of the maximum thickness of the insert.

14. The insert described in claim 12, wherein an end portion of the cutting edge of said insert crosses said axis of rotation, and said sinusoidal corrugations reduce the shear forces on said end portion of the insert during a cutting operation.

15. The insert described in claim 12, wherein said side wall of said insert body includes a lower relief portion, and a top relief portion disposed between said lower relief portion and said cutting edge, and said cutting edge follows the contour of a sphere to prevent the generation of unwanted tool marks.

16. The insert described in claim 15, wherein the profile of said upper relief portion provides a relief angle.

17. The insert described in claim 16, wherein said relief angle is at least 3 *.

18. An insert for use is a ball point cutter for making a round cut on a workpiece by removing chips from it when it is rotated about an axis, comprising: an insert body including an upper wall, a lower wall, an arcuate side wall having a lower relief portion and an upper relief portion, and an arcuate cutting edge, defined at an intersection between said upper wall and said upper relief portion of said side wall, said cutting edge including a plurality of sinusoidal corrugations to reduce the cutting and vibrating forces and improve the breaking and removal of chips, each ripple including a ridge portion and a depression portion, said ridge having at least two undulations having the same period and amplitude, where the profile of said cutting edge follows the contour of a sphere.

19. The insert described in claim 18, wherein said insert includes two opposing arcuate cutting edges, and is indexable. R E S U E N An insert is provided for use in a ball nose cutter (1), which includes an insert body (22) having an upper wall (24), a bottom wall (28), and at least one arcuate side wall ( 30). An arched cutting edge (34) is defined at the intersection between the top and side walls, which includes a plurality of sinusoidal corrugations (36) to reduce cutting forces, and vibration, and improve breakage and removal of shavings removed from a workpiece (66) during a cutting operation. A final portion of the insert (67) crosses the axis of rotation (A) when the insert is mounted on the seat of an end mill body (3), and the corrugations (36) reduce the considerable shear forces applied to the cutting edge ( 34) in this place. The cutting edge has a profile that follows the contour of a sphere to allow the machining of a round cut. The side wall (30) of the body of the insert includes an upper relieving portion (44) disposed directly under the cutting edge, with a relief angle to prevent corrugations from making unwanted flutes or marks on the walls of the rounded cut.