Milling cutter with tangentially mounted inserts

A milling cutter with tangentially mounted cutting inserts includes cutter pockets that are arranged at one end of the cutter body such that the screws for retaining the inserts generally radiate from the cutter's center. The cutter pockets are designed to secure a generally rectangular insert with eight or less cutting edges. The number of inserts and corresponding flutes vary as a function of the diameter of the cutter body. For example, four inserts with corresponding flutes are mounted on a 1.25″ diameter cutter body, and three inserts with corresponding flutes are mounted on a 1.00″ diameter cutter body. The increased number of flutes provide for increased metal removal rates and higher feed rates, as compared to an inserted ball nose mill or end mill. The cutter pockets are angled such that there is sufficient clearance under the insert cutting edges and present a “reverse lead” so the cutter assembly can produce a slightly undercut profile on the workpiece, or fixturing of almost five degrees so the radius generated on the workpiece can be nearly the same as that generated by a ball nose mill. The cutting inserts include facets for generating very good surface finishes on the workpiece.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an indexable inserted milling tool. More particularly, this invention relates to a milling cutter with tangentially mounted indexable cutting inserts.

2. Description of the Related Art

In the process of milling turbine blades or “buckets”, one generally finds in use solid carbide end mills (SCEM), inserted carbide end mills (ICEM), and insert face mills for roughing only. Ball nose end mills (solid and inserted) are used for semi-finishing and in some case, finishing. The cutter paths programmed are typically radial or axial with regard to the blade form. In either case, there are axes of rotation on both the blade and the cutter, with additional axes used to produce large concave and convex surfaces. The paths are followed for as long as it takes to reduce either a block of material or a near-net shaped forging to its intended size and shape. The type of cutting tool used is generally dictated by the condition of the workpiece at the start of the process, and the capabilities of the machine. In both cases, the semi-finishing and finishing cuts are addressed by smaller diameter tools due to the radii of the turbine blade surfaces.

Axial cutter paths have been used on several types of single and multi-spindle NC and CNC machines. The path is basically one that travels across the front and back sides of the blade with cutting taking place across an edge of the blade between the cutting of two sides. The path includes the convex and concave surfaces, which change rather quickly as the progression of the tool makes its way around the blade, and slowly progresses from one end of the blade to the other.

Basically, radial paths travel from root or base to tenon or blade tip until the front or back of the blade is cut to depth. The path then moves along the leading or trailing edge to cut to the desired depth, and continues to the uncut front or back of the blade to finish removing material in the same manner as the opposite. This process has traditionally been accomplished with what is called a “Hydrotel” machine, which uses a dovetail-shaped cutter with round inserts. These multi-spindle machines are quickly becoming antiquated, spending on maintenance and refurbishing is drastically reduced, and the owners are opting for new CNC machines. Lately, machinists have found that the radial cutting path is more cost effective, and the ability to reduce or eliminate secondary finishing operations is obtainable with creative programming and tooling. This includes, but is not limited to, the tilting of the milling machine's spindle, or the workpiece such that a ball-nosed tool will not cut with the surfaces of the tool that have minimal effective speeds and feeds.

SUMMARY OF THE INVENTION

Briefly, according to this invention, there is provided a milling cutter tool comprising a milling cutter body having a plurality of insert receiving pockets, in combination with an indexable cutting insert tangentially mounted in the insert pocket. Each cutting insert comprises a body defined by first and second face surfaces, first and second long edge surfaces, and first and second radiused shorter edge surfaces, wherein each indexable cutting insert is tangentially mounted with a reverse lead angle. Each long edge surface defines a cutting face that includes a profile defined by a substantially flat central plateau, a first facet face, a second facet face and a third facet face.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, wherein like reference characters represent like elements, a cutting insert, shown generally at10, is shown according to the present invention inFIGS. 1–4. The cutting insert10is indexable about an axis of rotational symmetry, A, so that the cutting insert10has eight edges capable of functioning as effective cutting edges. The cutting insert10is capable of being used in a wide range of different cutting operations.

As seen inFIG. 1, the cutting insert10includes a body formed of a suitable cutting material and is defined by first and second planar face surfaces12,14disposed in substantially parallel planes. For purposes of convenience, the first and second face surfaces12,14will be referred to as upper and lower face surfaces12,14, respectively. The cutting insert10includes a clamping screw bore16having a longitudinal axis coinciding with the axis of symmetry, A, and extending between the first and second planar face surfaces12,14. The clamping screw bore16may include a pair of counter sinks18shaped as a part of a torus or a cone to receive a countersunk head screw20or any other fastening means, such as a pinlock or the like, to enable the screw20to lie slightly below the face surfaces12,14.

Referring now toFIGS. 2–4, the cutting insert10is defined by first and second edge surfaces22,24, which define cutting faces that extend between the long sides of the face surfaces12,14. For purposes of convenience, the first and second edge surfaces22,24will be referred to long edge surfaces22,24. Because the cutting insert10is symmetric about a longitudinal axis, L, some of the discussion for the long edge surface24may be omitted for brevity. Each long edge surface22,24defines a cutting face that includes a profile defined by a substantially flat central plateau26that is substantially parallel to a plane, P. Each long edge surface22,24also includes a first facet face28having a downward angle29in the range of approximately 5° to 45°, for example, approximately 30° with respect to the plane, P, a second facet face30that is substantially parallel to the plane, P, and a third facet face32having an upward angle31in the range of approximately 5° to 45°, for example, approximately 20° with respect to the plane, P. It should be noted that the plane, P, is substantially parallel to the longitudinal axis, L, of the cutting insert10.

As shown inFIG. 2, the central plateau26may have a slightly higher elevation than the face surfaces12,14and is generally hexagonal in shape (as viewed inFIG. 3) that includes a pair of opposite sides26aand two pair of angled sides26bto form a pair of radiused corners26c. The angled sides26bof the central plateau26form an acute angle33of approximately 80° with respect to each other. The facet faces28,30and32provide for effective chip control. However, it will be appreciated that the invention is not limited by the number of facet faces or the angles of the facet faces, and that the invention can be practiced with any desirable number of facet faces with angles that provide effective chip control.

The primary cutting edge for a given index of the cutting insert10extends from section line4—4(or apex of the radius) to the intersection of the shorter radiused edge surface34and the angled sides26b, as shown inFIG. 3. The cutting edge28awill cut, but is not intended for such cutting in the illustrated example of the invention. In order for the cutting edge28ato cut effectively, the cutting insert design would need the chip control to extend along that portion of the cutting insert10. Thus, the focus of cutting edges that can effectively cut should be constrained to the radius edges for cutting to somewhat shallow depths, as is the typical process for low power CNC milling machines in certain industries, for example, the turbine blade machining industry.

The cutting insert10is also defined by first and second radiused edge surfaces34,36that extend between the shorter sides of the face surfaces12,14. For purposes of convenience, the first and second edge surfaces34,36will be referred to as shorter radiused edge surfaces34,36. A first cutting edge38is defined along the intersection of the long edge surface22with the upper face surface12and along the intersection of the long edge surface22with the shorter radiused edge surface34. A second cutting edge40is defined along the intersection of the long edge surface22with the lower face surface14and along the intersection of the long edge surface22with the shorter radiused edge surface36. Because the insert10is symmetric about the longitudinal axis, L, a third cutting edge42is defined along the intersection of the long edge surface24with the upper face surface12and along the intersection of the long edge surface24with the shorter radiused edge surface34. A fourth cutting edge44(shown in phantom inFIG. 1) is defined along the intersection of the long edge surface24with the lower face surface14and along the intersection of the long edge surface24with the shorter radiused edge surface36. When one cutting edge becomes worn, the insert10may be indexed 180° about the axis, A, of the clamping screw bore16to bring the other cutting edge on the same face surface12,14into active cutting position. In addition, the insert10can be indexed 180° about a vertical axis, V, to bring the other cutting edge on the other face surface12,14into active cutting position. The insert10may include a locating dimple39for assisting in the positioning of the insert10in the cutting tool.

Referring now toFIGS. 5–9, an end milling cutter, shown generally at50, rotatable about a central axis52in the direction of the arrow54is adapted to receive three cutting inserts10. The milling cutter50includes a cylindrical metal body56having a shank58at its inner end and formed with three angularly spaced insert receiving pockets60. In one aspect of the invention, the inserts10are angled so as to present a negative axial rake angle61of approximately 5° to facilitate chip formation and removal from the workpiece, W, as shown inFIGS. 6 and 9. However, it will be appreciated that the invention is not limited by the magnitude of the negative axial rake angle, and that the invention can be practiced with any desirable negative axial or radial rake angle.

Each pocket60includes a platform62upon which the insert10is seated. The platform62is angled such that the insert10presents a “reverse lead” angle63in assembly, an (ANSI) lead angle65, or an (ISO) lead angle67on the workpiece, W (FIG. 9). In the illustrated embodiment using a progressive process, the machine's spindle or workpiece is tilted approximately 5° such that the cutting insert10presents a zero degree (ANSI) angle65, or ninety degree (ISO) lead angle67, as shown inFIGS. 7 and 9. The reverse lead angle63ensures that a tool, such as a ball-nosed tool, does not cut with the end of the tool where the cutting speed and feed rate is essentially zero. In the illustrated embodiment, the milling cutter50having about a 1.00 inch diameter produces an elliptical cut having an ellipse with a 0.442 inch semi major axis and a 0.043 inch semi minor axis. It will be appreciated that the dimensions of the cutting insert10can vary depending on design of the tool. For example, the radius of the cutting insert10can be used to determine the size of the insert, the size of the cutter, the axial depth of the cut, as well as the ellipse for metal cutting productivity.

In addition, the reverse lead angle63provides for the insert10to present additional cutting edges to the workpiece, W. For example, when the insert10is mounted such that the upper face surface12is facing outwardly, the reverse lead angle63causes the first cutting edge38to be further defined by two cutting edges38a,38bdefined by the intersection of the long edge surface22with the upper face surface12and the intersection of the long edge surface22with the short edge surfaces34,36that are adjacent the upper face surface12. Similarly, when the insert10is mounted such that the lower face surface14is facing outwardly, the reverse lead angle63causes the second cutting edge40to be further defined by two cutting edges40a,40bdefined by the intersection of the long edge surface22with the lower face surface14and the intersection of the long edge surface22with the short edge surfaces34,36that are adjacent the lower face surface14. Likewise, the third and fourth cutting edges42,44have additional cutting edges because the insert10is mounted with the reverse lead angle63of the invention. Thus, the insert10of the invention has a total of eight cutting edges, as compared to an insert with four cutting edges that is mounted with a lead angle of zero degrees. As a result, the insert10of the invention is more economical to use than a conventional insert that is mounted with a lead angle of zero degrees.

Each pocket60further includes two substantially flat and planar locating abutments64,66disposed adjacent the inner and trailing sides, respectively, of the pocket60. Each insert10is mounted in the pocket60by threading the clamping screw20into the clamping screw bore16and into a tapped bore (not shown) in the platform62.

In operation, a portion of the cutting edges38a,38b,40a,40bthat are defined by the intersection of the cuttting edge surfaces38,40and the upper and lower surfaces12,14, respectively, provide for a full radiused cutting edge which is relatively large at the cutting edge itself. By virtue of the full radiused cutting edge, the insert10with the two radiused ends may effectively span the gap between two spaced inserts of an adjacent row. The strength of the cutting edges38a,38b,40a,40b(and42a,42b,44a,44b) are increased by forming the radiused corners on these cutting edges.

The milling cutter50with three improved cutting inserts10of the present invention circumferentially mounted approximately 120° with respect to each other has a diameter of about 1.00 inches. However, the principles of the present invention can be implemented with any desirable milling cutter as is only limited by its diameter. For example, as shown inFIG. 10, the invention can be practiced with a milling cutter, shown generally at70, having a diameter of about 1.25 inches, rather than a diameter of about 1.00 inches. The larger diameter of the milling cutter70allows for four improved cutting inserts10to be circumferentially mounted at approximately 90° with respect to each other. The larger diameter milling cutter70with an approximately 5 degree “reverse lead” angle63and a negative axial rake angle61of approximately 5° provides an elliptical cut having an ellipse with a 0.545 semi major axis and a 0.054 semi minor axis. Thus, the elliptical cut produced by the cutting inserts10mounted on the milling cutter of the invention is a function of the radius of the cutting insert10. Thus, the milling cutter of the invention can produce any desired elliptical cut by varying the radius of the cutting insert10, and/or the axial and radial rakes.

In light of the foregoing, it will be apparent that the present invention bring to the art a new and improved on-edge indexable insert10in which a “reverse lead” angle63provides a milling cutter that can produce a slightly undercut profile on the workpiece if desired (i.e., at the root of a blade), while providing for twice the cutting edges when compared to conventionally mounted inserts. In addition, the indexable insert10of the present invention possesses cutting edges that have a greater effective length and greater strength when compared with inserts that are radiused in a conventional manner.

The documents, patents and patent applications referred to herein are hereby incorporated by reference.

While the invention has been specifically described in connection with various embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.