Reversible square-shaped cutting insert and rotary cutting tool

In a cutting tool rotatable about a tool axis, a reversible cutting insert is removably secured in a tool body. The cutting insert has opposing top and bottom end surfaces interconnected by a peripheral surface, and a median plane located therebetween. The peripheral surface includes four side surfaces alternating with four corner surfaces, the side and corner surfaces intersecting the top surface to form top major cutting edges and top corner cutting edges, respectively. Each side surface has a median surface and a top major relief surface. Each top major relief surface forms an acute internal top major relief angle with the median plane, and the median plane intersects the four median surfaces to define an imaginary median square. In a top end view of the cutting insert, the four top major cutting edges define an imaginary top major square rotationally offset from the imaginary median square.

FIELD OF THE INVENTION

The present invention relates to cutting inserts and cutting tools for use in metal cutting processes, in general, and to rotatable cutting tools having reversible cutting inserts for milling operations, in particular.

BACKGROUND OF THE INVENTION

Within the field of rotatable cutting tools used in milling operations, there are many examples of reversible cutting inserts being removably secured in a cutting body. In some instances, the cutting inserts are square-shaped inserts.

U.S. Pat. No. 7,604,441 discloses a fully indexable square cutting insert having four side surfaces connecting to two end surfaces. At the intersection of each side surface with an end surface is a primary cutting edge which extends from an insert corner and along a first side surface, in a downward direction towards a median plane. A wiper extends from the same insert corner and along an adjacent side surface, in an upward direction away from the median plane, to rise above an abutment surface of an associated end surface. The geometry of the cutting insert and of the insert pocket in which the insert is seated are such that the primary cutting edge has a positive axial angle (helix), while the insert has an overall negative axial angle for providing axial clearance and an overall negative radial angle for providing radial clearance.

U.S. Pat. No. 8,491,234 discloses a double-sided cutting insert with a plurality of indexable convex cutting edges. The cutting insert has a top face and a bottom face, at least three convex cutting edges on each face connected by at least three nose corners, at least three peripheral side surfaces extending from each face toward a virtual middle plane; and a common lateral seating surface on each peripheral side surface. Each convex cutting edge has at least a curved cutting edge region, and further has a primary substantially straight cutting edge region intermediate the curved cutting edge region and the nose corner. Each peripheral side surface further has a primary planar facet associated with the primary substantially straight cutting edge, and each face is single-handed in same direction. Additionally, in various embodiments, the top and bottom faces of the cutting insert may be formed such that they are twisted or rotated with respect to each other.

U.S. Pat. No. 8,641,331 discloses a milling cutting insert having a square or triangular shaped cutting face delimited in the plan view by a peripheral cutting edge having linear cutting edges and curved cutting corners. Each of the cutting edges comprises an inclined region sloping toward a cutting corner, extending beyond the tangential point determined by the point at which the linear cutting edge transitions into a curved cutting corner, wherein adjacent thereto the cutting edge rises prior to the point determined by a cutting corner angle bisector, wherein said rising region extends to a cutting edge maximum on the other side of the cutting corner on the adjacent cutting edge, which is linear in plan view, from where the cutting edge continues, again inclined and sloping downward, resulting in a rotationally symmetric form having identically shaped cutting edges.

U.S. Pat. No. 9,724,770 discloses a double-sided cutting insert for milling which having eight main cutting edges and eight wiper edges. The cutting insert includes top and bottom faces and four side faces. Each side face includes first and second sub-faces inclined with respect to each other. The first sub-face has a main cutting edge adjacent to the top face and a wiper edge adjacent to the bottom face. The second sub-face has a wiper edge adjacent to the top face and a main cutting edge adjacent to the bottom face. The wiper edge of the second sub-face is inclined inwardly relative to the cutting insert with respect to the main cutting edge of the first sub-face. The wiper edge of the first sub-face is inclined inwardly relative to the cutting insert with respect to the main cutting edge of the second sub-face.

It is an object of the present invention to provide an improved reversible cutting insert having four major cutting edges per end surface.

It is also an object of the present invention to provide an improved reversible cutting insert having robust cutting edges.

It is a further object of the present invention to provide an improved rotatable cutting tool in which the cutting insert is removably secured in a tool body with a high level of stability.

It is still a further object of the present invention to provide an improved rotatable cutting tool in which an increased number of cutting inserts are circumferentially spaced around the tool body.

It is yet still a further object of the present invention to provide an improved rotatable cutting tool capable of performing square shoulder milling operations.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there is provided a reversible cutting insert, comprising:

opposing top and bottom end surfaces interconnected by a continuous peripheral surface, with a median plane located between the top and bottom end surfaces and intersecting the peripheral surface to form an insert boundary line, and an insert axis perpendicular to the median plane about which the cutting insert is indexable,the peripheral surface including four side surfaces circumferentially alternating with four corner surfaces,the side and corner surfaces intersecting the top end surface at top side and top corner edges, respectively, with each top side edge having a top major cutting edge, and each top corner edge having a top corner cutting edge, andeach side surface including a median surface, and a top major relief surface adjacent the respective top major cutting edge,

in a cross-sectional view taken along one of the top major cutting edges, the respective top major relief surface forms an acute internal top major relief angle with the median plane, and

the median plane intersects the four median surfaces to define an imaginary median square having an imaginary inscribed median circle with a median diameter and a center coincident with the insert axis,

and wherein, in a top end view of the cutting insert:

the four top major cutting edges define an imaginary top major square having an imaginary inscribed top major circle with a top major diameter and a center coincident with the insert axis, and

the imaginary top major square is rotationally offset from the imaginary median square about the insert axis.

In accordance with another aspect of the invention, there is provided a cutting tool rotatable about a tool axis in a direction of rotation, comprising:

a tool body extending in a forward-to-rearward direction along the tool axis; and

at least one reversible cutting insert of the sort described above removably secured in an insert receiving pocket of the tool body,

one of the top corner cutting edges of each cutting insert is operative, and

one of the top major cutting edges of each cutting insert, adjacent the operative top corner cutting edge, is an operative top major cutting edge.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention relates to a reversible cutting insert20, as shown inFIGS.1to3, having opposing top and bottom end surfaces22,122interconnected by a continuous peripheral surface24, the peripheral surface24including four side surfaces26circumferentially alternating with four corner surfaces28.

In some embodiments of the present invention, the cutting insert20may preferably be manufactured by form pressing and sintering a cemented carbide, such as tungsten carbide, and may be coated or uncoated.

As shown inFIG.3, the cutting insert20has a median plane M located between the top and bottom end surfaces22,122and intersecting the peripheral surface24to form an insert boundary line LB.

In some embodiments of the present invention, the median plane M may be located halfway between the top and bottom end surfaces22,122.

Also, in some embodiments of the present invention, the cutting insert20may be configured such that in an end view, as shown inFIG.2, no portion of the cutting insert20extends outside the insert boundary line LB.

As shown inFIGS.1to3, the cutting insert20has an insert axis AI perpendicular to the median plane M, about which the cutting insert20is indexable.

In some embodiments of the present invention, a through bore30coaxial with the insert axis AI may intersect the top and bottom end surfaces22,122.

Also, in some embodiments of the present invention, the cutting insert20may be manufactured by direct pressing along the direction of the insert axis AI.

Further, in some embodiments of the present invention, the cutting insert20may be pressed into its final shape, and the peripheral surface24may be unground.

As shown inFIGS.1to3, the side and corner surfaces26,28intersect the top end surface22at top side and top corner edges32,34, respectively, with each top side edge32having a top major cutting edge36, and each top corner edge34having a top corner cutting edge38.

In some embodiments of the present invention, each top corner cutting edge38may be curved.

Also, in some embodiments of the present invention, each top major cutting edge36may tangentially adjoin one of the top corner cutting edges38.

As shown inFIG.3, the four top major cutting edges36may be entirely contained in a top horizontal plane PH perpendicular to the insert axis AI.

In some embodiments of the present invention, the four top corner cutting edges38may be entirely contained in the top horizontal plane PH.

As shown inFIGS.1to4, the top end surface22may have a top central surface40, and the top central surface40may be located between the median plane M and the top horizontal plane PH.

In some embodiments of the present invention, the top central surface40may be perpendicular to the insert axis AI.

Also, in some embodiments of the present invention, the through bore30may intersect the top central surface40.

As shown inFIGS.1and2, the top end surface22may include a top rake surface42extending adjacent the top side and top corner edges32,34.

In some embodiments of the present invention, the top rake surface42may surround the top central surface40.

As shown inFIGS.1to3, each top side edge32may include a top minor cutting edge44.

In some embodiments of the present invention, the four top minor cutting edges44may be entirely contained in the top horizontal plane PH.

Also, in some embodiments of the present invention, the top side and top corner edges32,34may be entirely contained in the top horizontal plane PH.

As shown inFIGS.1and3, each side surface26includes a median surface46, and each side surface26also includes a top major relief surface48adjacent the respective top major cutting edge36.

In some embodiments of the present invention, each median surface46may be perpendicular to the median plane M.

Also, in some embodiments of the present invention, each top major relief surface48may intersect the top end surface22to form the respective top major cutting edge36.

Further, in some embodiments of the present invention, each top major relief surface48may not be intersected by the median plane M.

As shown inFIG.4, in a cross-sectional view taken along one of the top major cutting edges36, the respective top major relief surface48forms an acute internal top major relief angle131with the median plane M.

Also, as shown inFIG.4, the said cross-sectional view taken along one of the top major cutting edges36may contain the insert axis AI.

It should be appreciated that use of the terms “internal angle” and “external angle” throughout the description and claims refers to an angle between two linear features as measured internal and external to the member on which at least one of the linear features is formed, respectively.

It should also be appreciated that each top major relief surface48, also known as a ‘reversed’ relief surface, generally extends outwardly (i.e., in a direction away from the insert axis AI) from its respective top major cutting edge36towards the median plane M, so that each top major cutting edge36is beneficially supported and advantageously robust.

In some embodiments of the present invention, each top major relief surface48may be planar.

Also, in some embodiments of the present invention, the top major relief angle β1may have a minimum value of 75 degrees and a maximum value of 85 degrees, i.e. 75°≤β1≤85°.

For embodiments of the present invention in which the top major relief angle β1associated with each top major relief surface48has a minimum value of 75 degrees and a maximum value of 85 degrees, it should be appreciated that each top major cutting edge36is beneficially supported and advantageously robust.

As shown inFIG.4, in the cross-sectional view taken along one of the top major cutting edges36, the respective top major relief surface48may form an acute internal top major rake angle σ1with the top rake surface42.

In some embodiments of the present invention, the top major rake angle σ1may have a minimum value of 65 degrees and a maximum value of 75 degrees, i.e. 65°≤σ1≤75°.

As shown inFIG.3, in a side view of the cutting insert20, the top major relief surface48(visible in this view) may have a variable top major relief width WJ parallel to the insert axis AI, and the top major relief width WJ may increase in a sideways direction SD parallel to the median plane M

In some embodiments of the present invention, the top major relief width WJ may continuously increase in the sideways direction SD, along the entire length of the respective top major cutting edge36.

As shown inFIG.3, in the side view of the cutting insert20, the sideways direction SD may be from the top major cutting edge36to the top minor cutting edge44of the same top side edge32.

Also, as shown inFIG.3, each side surface26may include a top minor relief surface50adjacent the respective top minor cutting edge44.

In some embodiments of the present invention, each top minor relief surface50may intersect the top end surface22to form the respective top minor cutting edge44.

As shown inFIG.5, in a cross-sectional view taken along one of the top minor cutting edges44, the respective top minor relief surface50may be perpendicular to the median plane M.

In some embodiments of the present invention, each top minor relief surface50may be coplanar with its associated median surface46.

As shown inFIG.2, the median plane M intersects the four median surfaces46to define an imaginary median square SM having an imaginary inscribed median circle CM with a median diameter DM.

Also, as shown inFIG.2, it should be appreciated that the imaginary inscribed median circle CM has a center coincident with the insert axis AI.

Further, as shown inFIG.2, the imaginary median square SM may be divided into four identical quadrants Q1, Q2, Q3, Q4by mutually perpendicular first and second vertical planes PV1, PV2containing the insert axis AI and intersecting the four side surfaces26.

In some embodiments of the present invention, each top major cutting edge36may be located in, or span, two of the four quadrants Q1, Q2, Q3, Q4.

Also, in some embodiments of the present invention, each top major relief surface48may be located in, or span, two of the four quadrants Q1, Q2, Q3, Q4.

Further, in some embodiments of the present invention, each top corner cutting edge38may be located in only one of the four quadrants Q1, Q2, Q3, Q4.

Yet further, in some embodiments of the present invention, each top minor cutting edge44may be located in only one of the four quadrants Q1, Q2, Q3, Q4.

As shown inFIG.2, in a top end view of the cutting insert20, the four top major cutting edges36define an imaginary top major square SJ having an imaginary inscribed top major circle CJ with a top major diameter DJ.

Also, as shown inFIG.2, it should be appreciated that the imaginary inscribed top major circle CJ has a center coincident with the insert axis AI.

Further, as shown inFIG.2, in the top end view of the cutting insert20, the imaginary top major square SJ is rotationally offset from the imaginary median square SM about the insert axis AI. In the present application, “rotationally offset” means that both squares SJ and SM are centered about the index axis AI, but the sides of one of the squares are not parallel to the sides of the other square.

In some embodiments of the present invention, the median diameter DM may be greater than the top major diameter DJ.

Also, in some embodiments of the present invention, a maximum top major relief width WJMAXof each top major relief surface48may be greater than twenty percent of the top major diameter DJ, i.e. WJMAX>0.20*DJ.

Further, in some embodiments of the present invention, the maximum top major relief width WJMAXmay be greater than twenty percent of the median diameter DM, i.e. WJMAX>0.20*DM.

For embodiments of the present invention in which the maximum top major relief width WJMAXof each top major relief surface48is greater than twenty percent of the top major diameter DJ, it should be appreciated that each top major cutting edge36is advantageously robust.

As shown inFIGS.1,2and4, the through bore30has a bore axial extent EA from the top end surface22to the bottom end surface122.

In some embodiments of the present invention, the bore axial extent EA may be greater than forty percent of the top major diameter DJ, i.e. EA>0.40*DJ.

Also, in some embodiments of the present invention, the bore axial extent EA may be greater than forty percent of the median diameter DM, i.e. EA>0.40*DM.

As shown inFIG.2, the four top minor cutting edges44may define an imaginary top minor square SN having an imaginary inscribed top minor circle CN with a top minor diameter DN.

As shown inFIG.2, in the top end view of the cutting insert20, the imaginary top minor square SN may be coincident with the imaginary median square SM.

For embodiments of the present invention in which the imaginary top minor square SN is coincident with the imaginary median square SM, it should be appreciated that the median diameter DM may be equal to the top minor diameter DN.

As best seen in the top end view ofFIG.2, the imaginary top major square SJ is nested within the imaginary top minor square SN. Thus, in the end view of the insert20, the top major cutting edge36of a given top side edge32is recessed relative to the top minor cutting edge44of that same top side edge32. Furthermore, in some embodiments, in the top end view, the top major cutting edge36is longer than the top minor cutting edge44.

As shown inFIGS.1to3, each top corner cutting edge36has first and second corner end points NC1, NC2.

In some embodiments of the present invention, each first corner end point NC1may be coincident with a first minor end point NN1of one of the top minor cutting edges44, and each second corner end point NC2may be coincident with a first major end point NJ1of one of the top major cutting edges36.

As shown inFIG.2, in the top end view of the cutting insert20, the top major and top minor cutting edges36,44associated with each top corner cutting edge38may form an acute internal top corner angle α1.

In some embodiments of the present invention, the top corner angle α1may have a value greater than 80 degrees, i.e. α1>80°.

As shown inFIGS.1to3, each side surface26may have a top undercut52formed with respect to an undercut direction DU parallel to the associated side of the imaginary median square SM

It should be appreciated that use of the term “undercut” throughout the description and claims refers to a recess, where a straight line extending in a certain undercut direction from a given sub-surface of the recess intersects another sub-surface of the same recess.

In some embodiments of the present invention, each top undercut52may be recessed relative to an associated top minor relief surface50.

Also, in some embodiments of the present invention, each top major relief surface48may be disposed in the top undercut52of the respective side surface26.

As shown inFIGS.1to3, each top undercut52may include a top joining surface54. The top joining surface54may connect the top major relief surface48to the top minor relief surface50.

In some embodiments of the present invention, each top joining surface54may intersect the top end surface22at a top joining edge56.

Also, in some embodiments of the present invention, each top joining edge56may extend between the top major cutting edge36and the top minor cutting edge44associated with the same top side edge32.

Further, in some embodiments of the present invention, each top joining edge56may be a non-cutting edge.

As shown inFIGS.5and6, first and second imaginary straight lines L1, L2extend perpendicular to the median plane M and intersect one of the top corner cutting edge's first and second corner end points NC1, NC2, respectively.

In some embodiments of the present invention, the first imaginary straight line L1may intersect the insert boundary line LB.

Also, in some embodiments of the present invention, the second imaginary straight line L2may pass through the median plane M inside the insert boundary line LB.

As shown inFIGS.1to3, each corner surface28may include a top corner relief surface58adjacent the respective top corner cutting edge38.

For embodiments of the present invention in which the second imaginary straight line L2passes through the median plane M inside the insert boundary line LB, it should be appreciated that each top corner relief surface58may be partially conical and taper in a direction away from the median plane M, so that each top minor cutting edge44is beneficially supported and advantageously robust.

In some embodiments of the present invention, a third imaginary straight line L3extending perpendicular to the median plane M and intersecting one of the top major cutting edge36at any point along its length, may pass through the median plane M inside the insert boundary line LB.

In some embodiments of the present invention, the top and bottom end surfaces22,122may be identical.

For embodiments of the present invention in which the top and bottom end surfaces22,122are identical, it should be appreciated throughout the figures, description and claims that all the features associated with the bottom end surface122have been allocated the same reference numeral as the corresponding features associated with the top end surface22, except they will be preceded by an extra one ‘hundreds’ digit.

In some embodiments of the present invention, the cutting insert20may exhibit two-fold rotational symmetry about a first axis A1formed at the intersection of the first vertical plane PV1and the median plane M.

Also, in some embodiments of the present invention, the cutting insert20may exhibit two-fold rotational symmetry about a second axis A2formed at the intersection of the second vertical plane PV2and the median plane M.

Further, in some embodiments of the present invention, the cutting insert20may exhibit four-fold rotational symmetry about the insert axis AI.

Another aspect of the present invention relates to a cutting tool60rotatable about a tool axis AT in a direction of rotation RD, as shown inFIGS.7to12. The cutting tool60has a tool body62extending in a forward-to-rearward direction DF, DR along the tool axis AT, and at least one reversible cutting insert20removably secured in an insert receiving pocket64of the tool body62.

In some embodiments of the present invention, the cutting tool60may have N cutting inserts20removably secured in N insert receiving pockets64circumferentially spaced around the tool body62, N being a positive integer greater than one.

It should be appreciated throughout the description and claims, that since N is a specific integer number greater than one, the plurality of cutting inserts20are equal in number to the plurality of insert receiving pockets64.

As shown inFIGS.7and8, the tool body62may have axially opposing front and rear body ends66,68.

In some embodiments of the present invention, each insert receiving pocket64may open out to the front body end66.

Also, in some embodiments of the present invention, the cutting tool60may exhibit N-fold rotational symmetry about the tool axis AT.

As shown inFIGS.13and14, each insert receiving pocket64may have a seat surface70with axial and radial support walls72,74transverse thereto.

In some embodiments of the present invention, the seat surface70may face in the direction of rotation RD.

Also, in some embodiments of the present invention, the seat surface70may be planar.

Further, in some embodiments of the present invention, the axial support wall72may face axially forwardly, and the radial support wall74may face radially outwardly.

In a secured state of the at least one reversible cutting insert20in its respective insert receiving pocket64:

the bottom end surface122may be in clamping contact with the seat surface70, a first one of the four side surfaces26amay be in clamping contact with the axial support wall72, and a second one of the four side surfaces26bmay be in clamping contact with the radial support wall74.

For embodiments of the present invention in which the top and bottom end surfaces22,122are identical, the bottom end surface122may have a bottom central surface140, and the bottom central surface140may be in clamping contact with the seat surface70.

As shown inFIGS.7and13, a clamping screw76may extend through the through bore30and threadingly engage a screw bore78having a bore axis AB in the seat surface70.

In some embodiments of the present invention, the insert axis AI may be offset from the bore axis AB.

For embodiments of the present invention in which the insert axis AI is offset from the bore axis AB, it should be appreciated that clamping contact is ensured, between the cutting insert's first and second side surfaces26a,26band the insert receiving pocket's axial and radial support walls72,74, respectively, upon tightening of the clamping screw76.

As shown inFIGS.15and16, in a cross-sectional view taken in a first tool plane PT1perpendicular to the tool axis AT and intersecting the at least one seat surface70, a second tool plane PT2contains the tool axis AT and a radially outermost seat point NO of one of the seat surfaces70.

In some embodiments of the present invention, the said seat surface70may form an acute internal radial pocket angle T1with the second tool plane PT2.

Also, in some embodiments of the present invention, it should be appreciated that the radially outermost seat point NO may not only be the radially outermost point of the seat surface70in the cross-sectional view taken in the first tool plane PT1, but the absolute radially outermost point of the seat surface70, relative to the tool axis AT.

For embodiments of the present invention in which each seat surface70faces in the direction of rotation RD and the radial pocket angle T1is an internal angle, as opposed to an external angle, it should be appreciated that reduced circumferential spacing between adjacent insert receiving pockets64may be achieved whilst successfully orienting and threadingly engaging each clamping screw76into the respective insert receiving pocket's screw bore78via the respective cutting insert's through bore30without obstruction from an adjacent rotationally leading portion of the tool body62.

In some embodiments of the present invention, the radial pocket angle τ1may have a value greater than 3 degrees, i.e. τt>3°.

As shown inFIG.15, the N radially outermost seat points NO of the N seat surfaces70define an imaginary seat circle CS having a maximum seat diameter DSMAX.

In some embodiments of the present invention, it should be appreciated that the imaginary seat circle CS may have a center coincident with the tool axis AT.

In some embodiments of the present invention, in the secured state of the at least one reversible cutting insert20, the bottom end surface122of each cutting insert20may be in contact with the respective radially outermost seat point NO.

Also, in some embodiments of the present invention, in the secured state of the at least one reversible cutting insert20, the bottom central surface140of each cutting insert20may be in contact with the respective radially outermost seat point NO.

As shown inFIGS.9and16, the top major relief surface48of the first side surface26amay make clamping contact with the axial support wall72, and the median surface46of the second side surface26bmay make clamping contact with the axial support wall74.

As shown inFIG.14, the axial support wall72may form an acute external axial support angle ϕ1with the seat surface70.

For embodiments of the present invention in which the axial support wall72forms an acute external axial support angle ϕ1with the seat surface70, it should be appreciated that that the axial support wall72is configured to provide ‘dove-tail’ clamping.

In some embodiments of the present invention, the acute axial support angle ϕ1may have a value less than or equal to 85 degrees, i.e. ϕ1≤85°.

Also, in some embodiments of the present invention, the acute axial support angle ϕ1may correspond with the top major relief angle β1.

For embodiments of the present invention in which the acute external axial support angle ϕ1corresponds with the top major relief angle β1, it should be appreciated that that dove-tail clamping contact may occur between the axial support wall72and the top major relief surface48of the first side surface26a.

Also, for embodiments of the present invention in which dove-tail clamping contact occurs between the axial support wall72and the top major relief surface48of the first side surface26a, it should be appreciated that the cutting insert20may be removably secured in its respective insert receiving pocket64with a high level of stability.

As shown inFIG.16, the radial support wall74may be perpendicular to the seat surface70.

In some embodiments of the present invention, the radial support wall74may include two axially spaced apart radial support sub-walls74a,74b, with respect to the tool axis AT.

As shown inFIGS.7to12, one of the top corner cutting edges38of each cutting insert20is operative, and one of the top major cutting edges36of each cutting insert20, adjacent the operative top corner cutting edge38, is operative.

It should be appreciated throughout the description and claims, that the cutting insert20may have four index positions on the top end surface22, and in each index position, a different one of the top corner cutting edges38is operative, and a different one of the top major cutting edges36is operative.

It should also be appreciated that the cutting insert20is reversible and may also be described as being ‘double-sided’ or ‘double-ended’, such that in the secured state in its respective insert receiving pocket64, the top end surface22may be in contact with the seat surface70, and for embodiments in which the top and bottom end surfaces22,122are identical, the bottom end surface122may have four bottom major cutting edges136, one of which is operative, and four bottom corner cutting edges138, one of which is operative.

As shown inFIGS.9and10, the top major relief width WJ of the top major relief surface48associated with the operative top major cutting edge36may increase in the sideways direction SD away from the operative top corner cutting edge38.

As shown inFIG.9, the operative top major cutting edge36of each cutting insert20may have a negative axial rake angle λ1.

In some embodiments of the present invention, the negative axial rake angle λ1 may have a magnitude greater than 3 degrees.

Also, in some embodiments of the present invention, one of the top minor cutting edges44of each cutting insert20, adjacent the operative top corner cutting edge38, may be operative. As shown inFIGS.11and12, the operative top minor cutting edge44of each cutting insert20may have a negative radial rake angle M.

In some embodiments of the present invention, the negative radial rake angle δ1may be greater than the radial pocket angle τ1, and it should be appreciated that increasing the radial pocket angle τ1results in an increased negative radial rake angle M.

Also, in some embodiments of the present invention, the negative radial rake angle δ1may have a magnitude greater than 10 degrees.

For embodiments of the present invention in which the radial rake angle δ1is a negative value, and particularly for embodiments in which the negative radial rake angle δ1has a magnitude greater than 10 degrees, it should be appreciated that the cutting load on the top minor cutting edges44may be evenly distributed therealong, thus reducing the risk of edge fracture.

In some embodiments of the present invention, a radial clearance angle (not shown) between the operative top major relief surface48of each cutting insert20and a workpiece80may have a value between 5 and 10 degrees.

Whilst it should be generally appreciated fromFIGS.15and16, that increasing the radial pocket angle τ1results in an increased radial clearance angle, by virtue of the top major relief surfaces48being configured as ‘reversed’ relief surfaces, higher values of radial pocket angle τ1can be achieved whilst maintaining optimum values of the radial clearance angle, for example, between 5 and 10 degrees.

As shown inFIG.16, a cutting force FC acting upon the operative top major cutting edge36of each cutting insert36is directed in a tangential force direction FD, and an acute radial tipping angle τ1may be formed between the tangential force direction FD and the seat surface70.

In some embodiments of the present invention, the radial tipping angle ε1may have a value between 70 degrees and 80 degrees, i.e. 70°<ε1<80°.

It should be generally appreciated fromFIGS.15and16, that increasing the radial pocket angle τ1results in a decreased radial tipping angle ε1, which would normally be associated with reduced clamping stability. However, due to the dove-tail clamping contact between the axial support wall72and the top major relief surface48of the first side surface26aof the respective cutting insert20, higher values of radial pocket angle τ1can be achieved whilst maintaining high levels of clamping stability.

As shown inFIGS.11and15, the operative top major cutting edge36of each cutting insert20may define a tool cutting diameter DTC.

It is known in the art that the number N of cutting inserts20and the number N of insert receiving pockets64circumferentially spaced around the tool body62may be generally proportional to the tool cutting diameter DTC. In embodiments of the present invention configured with radial pocket angles τ1which are internal angles, as opposed to external angles, reduced circumferential spacing between adjacent insert receiving pockets64may be achieved whilst successfully orienting and threadingly engaging each clamping screw76into the respective insert receiving pocket's screw bore78via the respective cutting insert's through bore30without obstruction from an adjacent rotationally leading portion of the tool body62, such that the number N of insert receiving pockets64and the number N of cutting inserts20may be increased, for a given tool cutting diameter DTC.

In some embodiments of the present invention, N multiplied by a pocket spacing factor FP may equal the tool cutting diameter DTC, i.e. N*FP=DTC, and the pocket spacing factor FP may be equal to or less than 8.5, i.e. FP<8.5.

Also, in some embodiments of the present invention, the pocket spacing factor FP may be equal to or less than 8, i.e. FP<8.

It should be appreciated throughout the specification and claims, that the pocket spacing factor FP has units of millimeters, and the ratio of N to the tool cutting diameter DTC applies when the tool cutting diameter DTC is measured in millimeters.

For embodiments of the present invention in which N multiplied by a pocket spacing factor FP equals the tool cutting diameter DTC, i.e. N*FP=DTC, as shown inFIG.11, it should be appreciated that an angular spacing extent ES (in degrees) between circumferentially adjacent insert receiving pockets64equals 360°/(DTC/FP), i.e. ES=360°/(DTC/FP).

As shown inFIGS.15and16, half the difference between the tool cutting diameter DTC and the maximum seat diameter DSMAXdefines a first radial extent ER1.

In some embodiments of the present invention, the first radial extent ER1may be less than twenty-five percent of the top major diameter DJ, i.e. ER1<0.25*DJ.

For embodiments of the present invention in which the first radial extent ER1is less than twenty-five percent of the top major diameter DJ, it should be appreciated that a radial tipping moment (not shown) of the cutting force FC about the respective radially outermost seat point NO is advantageously reduced.

As shown inFIG.16, the imaginary seat circle CS intersects the top end surface22of each cutting insert20at a top intersection point NI.

In some embodiments of the present invention, the top intersection point NI and the operative top corner cutting edge38of the same cutting insert20may be located in the same one of the insert's four quadrants Q1, Q2, Q3, Q4, and thus the operative top corner cutting edge38may be well supported by the seat surface70.

As shown inFIGS.8and10, the cutting tool60has a cutting depth DC measured parallel to the tool axis AT.

In some embodiments of the present invention, a maximum cutting depth DCMAXof the cutting tool60in the forward direction DF along the tool axis AT may be greater than one-half of each insert's top major diameter DJ, i.e. DCMAX>DJ/2.

Also, in some embodiments of the present invention, the maximum cutting depth DCMAXmay be greater than one-half of each insert's median diameter DM, i.e. DCMAX>DM/2.

For embodiments of the present invention in which the top major and top minor cutting edges36,44associated with each top corner cutting edge38form the acute internal top corner angle α1and/or each side surface26includes the top undercut52with respect to the undercut direction DU, it should be appreciated that a portion of the cutting insert20located axially rearward of the operative top major cutting edge36, with respect to the tool axis AT, may extend radially beyond the tool cutting diameter DTC, thus limiting the maximum cutting depth DCMAXto a value less than the insert's top major diameter DJ.

Although the maximum cutting depth DCMAXmay be limited to a value less than the insert's top major diameter DJ, as shown inFIGS.8and10, the cutting tool60may be used in milling operations, whereby each cutting insert20is oriented in its respective insert receiving pocket64to cut a true ninety-degree, or square, shoulder in the workpiece80.

As shown inFIGS.10to12, each cutting insert20has an axially forwardmost insert point NF, and the N axially forwardmost insert points NF of the N cutting inserts20define an imaginary face circle CF having a face cutting diameter DFC.

In some embodiments of the present invention, it should be appreciated that the imaginary face circle CF may have a center coincident with the tool axis AT.

As shown inFIG.12, half the difference between the tool cutting diameter DTC and the face cutting diameter DFC defines a second radial extent ER2.

In some embodiments of the present invention, the second radial extent ER2may be less than twenty percent of the top major diameter DJ, i.e. ER2<0.20*DJ.

For embodiments of the present invention in which the cutting tool60has a N cutting inserts20and N insert receiving pockets64, it should be appreciated that the plurality of axially forwardmost insert points NF may be contained in a third tool plane PT3(also referred to as a “face milling plane PT3”) perpendicular to the tool axis AT.

In some embodiments of the present invention, each axially forwardmost insert point NF may be contained in its associated operative top corner cutting edge38.

Also, in some embodiments of the present invention, each axially forwardmost insert point NF may be coincident with the first corner end point NC1of its associated operative top corner cutting edge38, and the operative top minor cutting edge44may be substantially parallel to the third tool plane PT3.

For embodiments of the present invention in which the face cutting diameter DFC is relatively large and the second radial extent ER2is less than twenty percent of the top major diameter DJ, it should be appreciated that the cutting tool60may be advantageously used in face milling operations to maximize the horizontal machined extent of the workpiece80.

Also, for embodiments of the present invention in which the cutting tool60is used in milling operations, for example, face milling operations, it should be appreciated that the cutting path length of each cutting insert20in the workpiece80, for each revolution of the cutting tool60, may be proportional to the tool cutting diameter DTC, and the heat load generated by the cutting action of each cutting insert20may increase with increased tool cutting diameter DTC.

Although it is known in the art that increasing the size and mass of a cutting insert can contribute to dissipating the heat load generated by its cutting action, and that the median diameter DM of each cutting insert20may be related to the tool cutting diameter DTC, for embodiments of the present invention in which the cutting insert20is robustly configured with ‘reversed’ relief surfaces adjacent the top major cutting edges36, the size of the cutting insert20relative to the tool cutting diameter DTC may be reduced.

In some embodiments of the present invention, the median diameter DM multiplied by an insert size factor FI may equal the tool cutting diameter DTC, i.e. DM*FI=DTC, and the insert size factor FI may be greater than 12, i.e. FI>12.

For embodiments of the present invention in which the insert size factor FI is greater than 12, it should be appreciated that that reducing the amount of cemented carbide required to produce smaller sized cutting inserts20results in less expensive manufacturing costs. Also, smaller sized cutting inserts20contribute to the reduced circumferential spacing between adjacent insert receiving pockets64.

The present invention contemplates rotary cutting tools having a tool cutting diameter DTC less than 100 mm and an insert size factor FI greater than 12. Although, the abovementioned insert size factor FI of greater than 12 may be theoretically applied to cutting tools60having a tool cutting diameter DTC of less than 100 mm, it is acknowledged that practical factors associated with using excessively small diameter clamping screws76to removably secure smaller sized cutting inserts20in corresponding sized insert receiving pockets64may present challenges in such configurations.

It should be appreciated throughout the specification and claims, that the insert size factor FI has no units, and the ratio of the median diameter DM to the tool cutting diameter DTC applies when both the median diameter DM and the tool cutting diameter DTC are measured in the same units, for examples, millimeters.

Although the present invention has been described to a certain degree of particularity, it should be understood that various alterations and modifications could be made without departing from the spirit or scope of the invention as hereinafter claimed.