WO1993000192A1

WO1993000192A1 - Plunge and feed milling cutter

Info

Publication number: WO1993000192A1
Application number: PCT/US1992/004646
Authority: WO
Inventors: Robert N. Mitchell
Original assignee: Kennametal, Inc.
Priority date: 1991-06-27
Filing date: 1992-05-28
Publication date: 1993-01-07
Also published as: IT1255188B; ITMI921582A1; ITMI921582A0; ZA924579B; FR2678186A1; AU2187592A

Abstract

A milling cutter (10) comprises a cutter body (12) with a plurality of insert seats (26) circumferentially spaced about an outer periphery of the cutter body (12). A cutting insert (36) is received in each of the insert seats (26). The miling cutter (10) of the present invention provides improved lateral and rotational support for the cutting insert (36) by providing a slot (32) in the bottom (28) of the insert seat (26) for receiving a corresponding rail (50) integrally formed on the cutting insert (36). The shape of the cutting insert (36) is such that a smooth sidewall can be machined.

Description

PLUNGE AND FEED MILLING CUTTER FIELD OF THE INVENTION The present invention relates generally to milling cutters and more particularly to a plunge and feed type milling cutter for removing a large amount of material rapidly from a workpiece.

BACKGROUND OF THE INVENTION Titanium, due to its relatively light weight and great strength, is often used in structural components for aircraft. Structural parts of aircraft are usually thin in cross-section and have deep pockets. Such parts are generally machined from a large, solid block of titanium which requires more material be removed from the block than will remain in the finished workpiece.

The primary method used for machining structural parts for aircraft has been using a drill to form access holes of a predetermined depth equal to the depth of the pocket being formed. A milling cutter is then lowered into the access hole and travels back and forth over the workpiece in the x and y dimensions until the entire area of the pocket is traversed. The cutter is then lowered further into the access hole and the process is repeated as many times as necessary to form a pocket of the desired depth.

One of the problems with the above described procedure is that it is extremely time consuming. The depth of cut which conventional cutters are capable of making is usually small in relation to the depth of the pocket being formed so that many passes over the workpiece are required. Further, the old procedure requires two different machining operations. Another drawback with the old procedure is that the cutter often leaves a rough finish on the side wall of the pocket being formed. Thus, an additional milling operation is required to smoothly finish the sidewall. SUMMARY AND OBJECTS OF THE INVENTION

The present invention is a plunge and feed type milling cutter which may be advantageously used to rapidly remove material from a workpiece in a single operation. The milling cutter is used by first feeding the cutter axially into the workpiece to a predetermined depth and then moving the cutter over the workpiece in the x and y directions to form a pocket of the desired length and width. Once the area of the pocket has been traversed, the cutter is again fed axially into the workpiece and the process is repeated until a pocket of the desired depth is obtained.

The sequential axial and lateral feeding of the milling cutter creates a situation in which the cutting inserts attached to the cutter body cut on an outside edge for 180 degrees of travel and on an inside edge for 180 degrees of travel. During cutting, there is a tendency for the cutting insert to be dislodged or rotated about the axis of its locking screw. The milling cutter of the present invention is designed to provide improved lateral and rotational support. Such improved support is accomplished by providing integrally formed rails on the back side of the cutting inserts which are received in corresponding grooves formed in the insert seat. The insertion of the rail on the insert into the slot on the insert seat provides greater lateral support and rotational stability. In a preferred embodiment of the invention, the cutting inserts are elongated along a longitudinal axis and include straight cutting edges extending parallel to the longitudinal axis. The insert may be oblong, rectangular, or any other shape having straight side edges. The straight side edges make it possible to smoothly finish a side wall of a groove formed in a

^Λ_ - workpiece by the milling cutter. Further, the oblong shape, in^co bination with the improved lateral and rotational stability of the insert allows greater depths of cuts to be made with the milling cutter as compared to conventional designs. Thus, fewer passes over the workpiece are required to reach the required depth. Accordingly, it is an object of the present invention to provide an improved milling cutter with lateral and rotational support for the cutting insert to prevent the cutting insert from slipping during milling operations. Another object of the present invention is to provide an improved milling cutter designed specifically for plunge and feed type milling operations.

Still another object of the present invention is to provide an improved milling cutter which is capable of rapidly removing material from a workpiece. Yet another object of the present invention is to provide an improved milling cutter which is capable of being axially fed into a workpiece to greater depths than conventional milling cutters.

Other objects and advantages of the present invention will be become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevation view of the milling cutter of the present invention.

Figure 2 is a view of the face of the milling cutter.

Figure 3 is an elevation view of the milling cutter with a portion shown in section.

Figure 4 is a fragmented perspective view of the milling cutter illustrating the insert seat. Figure 5A is a plan view of a cutting insert used in the milling cutter.

Figure 5B is a side elevation thereof. Figure 5C is a bottom view of the cutting insert shown from the back side. Figure 6A is a plan view of an alternate design of a cutting insert for use in the milling cutter.

Figure 6B is a side elevation thereof. Figure 6C is a bottom view thereof. Figure 7A is a plan view of a second alternate design of a cutting insert.

Figure 7B is an elevation view thereof. Figure 7C is a bottom view thereof. Figures 8A-8D are section views of a workpiece at various stages being milled using the present invention.

Figures 9A-9D are top plan views of the same workpiece at various states being milled using the present invention. DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, a milling cutter according to the present invention is shown therein and indicated generally by the numeral 10. The face milling cutter comprises a cutter body 12 which is mounted on an adapter 14. The adapter 14 has a tapered shank 16 which inserts into the spindle of a milling machine (not shown) . The cutter body 12 is generally cylindrical in shape and includes a forward end 18 formed with a central cavity 20. In the embodiment shown, six tool mounting lugs 22 are formed on the outer periphery of the cutter body 12. The tool mounting lugs 22 are equally spaced about the axis of the cutter body 12 and have recesses 23 therebetween as best shown in Figure 2. Each tool mounting lug 22 includes a tool mounting surface 24 which face in the direction of rotation of the cutter body 12. An insert seat 26 is formed in the tool mounting surface 24 of each lug 22. Each insert seat 26 includes a bottom 28 and a side wall 30 as best seen in Figure 4.

A plurality of cutting inserts 36 are received in respective insert seats 26. One example of a suitable insert is illustrated in Figures 5A-5C. Each insert 36 includes two parallel faces 38 and 40, and a side wall 42. The cutting inserts 36 have a positive rake angle. Thus, the side wall 42 forms an acute angle with the front face 38 and an obtuse angle with the back face 40. A cutting edge 44 is defined where the side wall 42 meets the front face 38. The cutting inserts 36 have a generally oblong configuration. For example, the cutting insert shown in Figures 5A and 5B has an elongated oval shape including two curved end portions 44a and 44b, and two straight portions 44c and 44d.

Figures 6A-6C show an alternate design for a cutting insert 36. This embodiment of the cutting insert 36 is generally rectangular in shape and includes straight end portions 44a and 44b, and straight side portions 44c and 44d, with the side portions 44c and 44d being longer than the end portions 44a and 44b. A small radius is formed at each corner where the end portions 44a and 44b meet the side portions 44c and 44d. A third design for the cutting insert 36 is illustrated in Figures 7A-7C and is indicated generally by the numeral 36. In this embodiment, the cutting insert 36 is generally rectangular in form and includes straight end portions 44a and 44b and straight side portions 44c and 4 d. As with the previous embodiment, all four corners are radiused. Unlike the previous embodiment, however, the radiuses at the four corners are not equal. Instead, two diagonally opposed corners include a large radius indicated generally at 44e, while the other two diagonally opposed corners include a smaller radius indicated generally at 44f.

The cutting insert 36 is mounted in the insert seat 26 in such a manner that one of the straight side edges 44c or 44d is presented in a radially outward direction making it possible to smoothly finish a sidewall surface of a cavity formed in a workpiece. The cutting insert 36 is secured in the insert seat by means of a locking screw 52^' as best seen in Figure 3. More particularly, a threaded hole 34 is formed in the bottom 28 of the insert seat 26 to threadable engage the shank 54 of the locking screw 52. The shank 54 of the locking screw 52 passes through a clearance hole 46 formed in the center of the cutting insert 36. The clearance hole 46 includes a tapered counterbore 48 which is engaged by a corresponding tapered surface on the head 56 of the locking screw 52. Upon tightening of the locking screw 52, -the engagement of the head 56 of the locking screw 52 with the tapered counterbore 48 presses the cutting insert 36 downwardly and inwardly against the bottom 28 and the side wall 30 of the insert seat respectively.

The milling cutter 10 of the present invention is particularly designed for plunge and feed type milling operations where the milling cutter is first fed axially into the workpiece to a predetermined depth and then fed alternately in a direction perpendicular to the axis of rotation of the milling cutter 10. When the lateral feeding of the milling cutter begins, the cutting inserts 36 will cut on their radially outward edges during 180 degrees of travel and on their radially inward edges during the next 180 degrees of travel. The cutting forces acting on the insert 36 tend to push the inset inwardly or outwardly in the radial direction. Additionally, there is a tendency for the cutting insert 36 to rotate about the axis of the locking screw 52 which can cause brinelling where the insert rubs against the side wall 30 of the insert seat 26.

The milling cutter 10 of the present invention is designed to provide improved lateral and rotational support for the cutting insert 36. The improved lateral and rotational support is provided by an integrally formed rail 50 formed on the back face 40 of the cutting insert 36 which is received in a similarly shaped slot 32 formed in the bottom 28 of the insert seat 26. The rail 50 extends along the longitudinal axis of the cutting insert 36. Alternately, the rail 50 could be formed on the bottom 28 of the insert seat 26 with the slot 32 being formed in the back face 40 of the cutting insert 36. In the embodiment shown, the rail 50 has a generally rectangular cross-section. It will be appreciated, however, that other configurations, such a v-shaped rails, may be used.

Referring now to Figures 8A-8D and Figures 9A-9D, a method for using the milling cutter 10 of the present invention is illustrated. More particularly, these figures illustrate how the milling cutter 10 of the present invention can be used to mill a cavity (shown in dotted lines) in a workpiece. The milling cutter 10 is first fed axially into the workpiece A to a predetermined depth Dl as shown in Figure 8A. During axial feeding of the milling cutter 10, an annular groove B is formed in workpiece A as shown in Figure 9A. A core C of material is left inside the annular groove B. After feeding the milling cutter 10 to the predetermined depth Dl, the milling cutter 10 is fed laterally as shown in Figure 8B. As the milling cutter 10 is moved laterally, the inserts 36 will cut on the radially outward directed edges of the insert 36 for 180 degrees of travel and will cut on the radially inward directed edges of the insert 36 for the next 180 degrees of travel. After traveling laterally a distance equal to the diameter of the milling 10, the entire core C will be removed. The milling cutter 10 will continue to move laterally until a groove of the desired length is made, as shown in Figures 8C and 9C. The milling cutter 10 is then fed axially into the workpiece A to a predetermined depth D2 as shown in

Figures 8D and 9D. The milling cutter 10 is then moved back towards its original starting point in a direction

_- perpendicular to the axis of the milling cutter. The sequence can be repeated as many times as necessary to mill a cavity of any predetermined depth. The cutter 10 can also be moved back and forth in both the x and y dimensions to form a cavity wider than the diameter of the cutter 10. Also, the cutter 10 can be simultaneously moved axially and laterally for form an incline or ramp in the workpiece.

During the axial feeding of the milling cutter 10, there is a potential problem with the formation of long continuous chips. This situation is undesirable since a continuous chip tends to wrap around the spindle of the milling machine. It is far more desirable to break the chip into small segments so that the chips can be carried away by the coolant. In order to break the chip into small segments, the milling cutter 10 is fed intermittently into the workpiece. In other words, the milling cutter 10 is instantaneously paused at a predetermined interval during axial feeding of the cutter into the workpiece. Such intermittent axial feeding may not be required when the chip formed is discontinuous.

Based on the foregoing, it is apparent that the milling cutter 10 of the present invention can be used to rapidly remove material from a large workpiece in a single operation. The milling cutter 10, due to the shape and increased stability of the insert, can make greafe&r depths of cut than conventional milling cutters requiring fewer passes to mill a cavity of a predetermined size and depth. Further, the improved stability of the insert prevents the insert from being dislodged or rotated when cutting on both the inner and outer edge of the insert. The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

WHAT IS CLAIMED IS: 1. A milling cutter comprising:

(a) a generally cylindrical cutter body having a plurality of recessed insert seats circumferentially spaced about an outer periphery of the cutter body, wherein each of said insert seats include a bottom and a side wall;

(b) a plurality of cutting inserts received in said insert seats, said cutting inserts having two parallel faces and side edges between said parallel faces;

(c) support means for providing rotational and lateral support for the cutting insert including a projecting element formed on either the cutting insert or the bottom of the insert seat, and a groove formed on the other of the two parts for receiving the projecting element; and

(d) means for retaining said cutting inserts in their respective insert seats.

2. The milling cutter according to Claim 1 wherein projecting element comprises an elongated rail.

3. The milling cutter according to Claim 2 wherein the rail is integrally formed with the cutting insert.

4. The milling cutter according to Claim 1 wherein the means for retaining the cutting insert in the insert seat includes a threaded hole formed in the bottom of the insert seat, a clearance hole formed in -li¬

the cutting insert and having a conical counterbore, and a screw comprising a head and a threaded shank, wherein the shank is threadably engaged in the threaded hole in the insert seat until the head of the screw engages the counterbore of the clearance hole.

5. The milling cutter according to Claim 1 wherein the cutting insert is elongated along a longitudinal axis of the insert and includes at least two, longitudinally extending straight edges disposed parallel to said longitudinal axis.

6. The milling cutter according to Claim 5 wherein the cutting insert is generally oval-shaped and includes two curved edges joining the straight edges at opposite ends of the insert.

7. The milling cutter according to Claim 5 wherein the cutting insert is generally rectangular in shape and includes two transversely extending edges joining the longitudinal edges.

8. The milling cutter according to Claim 5 wherein the cutting insert is indexable.

9. A milling cutter comprising:

(a) a generally cylindrical cutter body having a plurality of recessed insert seats circumferentially spaced about an outer periphery of the cutter body;

(b) a plurality of cutting inserts received in respective insert seats on the cutter body, each said insert being elongated along a longitudinal axis and having two longitudinally extending straight cutting edges disposed parallel to said longitudinal axis, wherein one of said straight cutting edges is disposed radially outward from the outer periphery of the cutter body for removing a chip from a workpiece during the milling operation; and (c) means for retaining the cutting inserts within the insert seats.

10. The milling cutter according to Claim 9 wherein the cutting insert is elongated along a longitudinal axis of the insert and includes at least two, longitudinally extending straight edges disposed parallel to said longitudinal axis.

11. The milling cutter according to Claim 9 wherein the cutting insert is generally oval-shaped and includes two curved edges joining the straight edges at opposite ends of the insert.

12. The milling cutter according to Claim 9 wherein the cutting insert is generally rectangular in shape and includes two transversely extending edges joining the longitudinal edges.

13. A milling cutter comprising: (a) a generally cylindrical cutter body having a forward end and formed with a plurality of recessed insert seats, wherein each insert seat includes a bottom and a side wall;

(b) a plurality of cutting inserts received in said insert seats for engaging a workpiece and removing a chip therefrom, each said insert being elongated along a longitudinal axis and having two ends and two longitudinally extending straight edges extending between the two ends, wherein one straight end is disposed radially outward of the cutter body and one end extends forward of the forward end of the cutter body;

(d) means for retaining the cutting inserts within the insert seats.

14. The milling cutter according to Claim 13 wherein projecting element comprises an elongated rail.

15. The milling cutter according to Claim 13 wherein the rail is integrally formed with the cutting insert.

16. The milling cutter according to Claim 13 wherein the means for retaining the cutting insert in the insert seat includes a threaded hole formed in the bottom of the insert seat, a clearance hole formed in the cutting insert and having a conical counterbore, and a screw comprising a head and a threaded shank, wherein the shank is threadably engaged in the threaded hole in the insert seat until the head of the screw engages the counterbore of the clearance hole.

17. The milling cutter according to Claim 13 wherein the cutting insert is elongated along a longitudinal axis of the insert and includes at least two, longitudinally extending straight edges disposed parallel to said longitudinal axis.

18. The milling cutter according to Claim 13 wherein the cutting insert is generally oval-shaped and includes two curved edges joining the straight edges at opposite ends of the insert.