Patent Publication Number: US-2023133391-A1

Title: Rotary cutting tool with high ramp angle capability

Description:
FIELD OF THE DISCLOSURE 
     In general, the disclosure relates to cutting tools for performing machining operations on a workpiece. In particular, the disclosure relates to a rotary cutting tool, such as a solid end mill, and the like, having an end face cutting edge with a radially outer curved rake face with a negative radial angle and a radially inner curved rake face with a highly positive radial angle for providing to maximize ramping feed rate, while extending tool life. 
     BACKGROUND OF THE DISCLOSURE 
     Conventional solid end mills having cutting edges disposed on both end surfaces and peripheral surfaces are frequently used in operation where it is desired that the tool remove material in both the axial and radial directions, as in the case of slotting operations. 
     Unfortunately, solid end mills experience performance difficulties, especially when ramping on an inclined tool path (i.e., ramping angle) while entering the workpiece. It has been observed that the steeper the ramping angle gets, the higher the risk of failure of the end mill. It has also been observed that the higher the number of blades and flutes of the end mill, lower ramping angles become practically impossible, digressing at an exponential fashion. 
     Managing chip formation and evacuation during ramping operations requires deep and sufficiently wide gashes at the end face, which lead to concerns about the structural strength of the end mill. In addition, a large number of flutes leads to even more design and performance concessions. Thus, it would be desirable to provide a rotary cutting tool, such as a solid end mill, and the like, that overcomes the problems mentioned above. 
     SUMMARY OF THE DISCLOSURE 
     The problem of providing a rotary cutting tool capable of very large ramping angles, while managing chip formation and evacuation, is solved by providing a rotary cutting tool, such as a solid end mill, and the like, having an end cutting edge with an end face configuration comprising at least two end face cutting edge portions, wherein each end face cutting edge portion is responsible for different fragments and/or ramping angles of a working tool path, while maintaining the overall structural stability of the rotary cutting tool. 
     In one embodiment, each end cutting edge comprises a first end face cutting edge portion and a second end face cutting edge portion. The first end face cutting edge portion is adjacent (i.e., adjoins) a cutting corner, which is proximate the outer diameter of the cutting tool. The first end face cutting edge portion is designed for moderate ramp angles of between about 3 degrees and about 5 degrees. In addition, the first end face cutting edge portion can have a curved and complex profile, or a straight and complex profile, or any combination thereof. Further, the first end face cutting edge portion can have either a positive radial angle or negative radial angle, depending on the material to be machined. For example, the radial angle can be between about +2 degrees and about −2 degrees for machining high temperature alloys, and the like. Still further, the first end face cutting edge portion can have a negative axial rake angle, depending on the material to be machined. For example, the axial rake angle can be between about −1 degrees and about −5 degrees for machining high temperature alloys, and the like. 
     The second end face cutting edge portion is radially inward and adjacent to (i.e., adjoins) the first end face cutting edge portion and generally faces the center of rotation. The second end face cutting edge portion is designed for large ramp angles of between about 15 degrees and about 45 degrees. The second end face cutting edge portion can have a curved and complex profile, or a straight and complex profile, or any combination thereof, but must follow an inward (i.e., center) pointing curved or radii profile. In addition, the second end face cutting edge portion has a highly positive radial angle, depending on the material to be machined. For example, the radial angle can be between about +11 degrees and about +15 degrees for machining high temperature alloys, and the like. Further, the second end face cutting edge portion can have a negative axial rake angle, depending on the material to be machined. For example, the axial rake angle can be between about −1 degrees and about −5 degrees for machining high temperature alloys, and the like. 
     Testing of the rotary cutting tool of the disclosure with five flutes achieved ramp angles of +45 degrees in titanium 6-4 without slowing down federates, while cutting smooth and outperforming conventional “center-cut” and “non-center-cut” solid end mills. 
     In one aspect, a rotary cutting tool comprises a shank portion and a cutting portion adjoining the shank portion and having a cutting end. The cutting portion has a plurality of blades separated by flutes. Each blade includes a leading face, a trailing face, and a land surface extending between the leading face and the trailing face. Each blade includes an end cutting edge extending from an outer diameter of the cutting portion towards the central, longitudinal axis, and a peripheral cutting edge at an intersection between the leading face and the land surface. The end cutting edge includes a first end face cutting edge portion proximate an outer diameter of the rotary cutting tool, and a second end face cutting edge portion adjoining the first end face cutting edge portion. The first end face cutting edge portion defines a first axial rake angle between about −1 degrees and about −15 degrees and a first radial angle between about −2 degrees and about 2 degrees, and the second end face cutting edge portion defines a second axial rake angle between about −1 degrees and about −15 degrees and a second radial angle between about 11 degrees and about 15degrees, thereby enabling the rotary cutting tool to perform a ramp operation with a ramp angle between about 15 degrees and about 45 degrees. 
     In another aspect, a rotary cutting tool comprises a shank portion and a cutting portion adjoining the shank portion and having a cutting end. The cutting portion has a plurality of blades separated by flutes. Each blade includes a leading face, a trailing face, and a land surface extending between the leading face and the trailing face. Each blade includes an end cutting edge extending from an outer diameter of the cutting portion towards the central, longitudinal axis, and a peripheral cutting edge at an intersection between the leading face and the land surface. The end cutting edge includes a first end face cutting edge portion proximate an outer diameter of the rotary cutting tool, and a second end face cutting edge portion adjoining the first end face cutting edge portion. The first end face cutting edge portion defines a first axial rake angle between about −1 degrees and about −15 degrees, a first dish angle between about 1 degree and about 8 degrees and a first radial angle of between about −2 degrees and about 2 degrees, and the second end face cutting edge portion defines a second axial rake angle between about −1 degrees and about −15 degrees, a second dish angle between about 21 degrees and about 45 degrees and a second radial angle between about 11 degrees and about 15 degrees, thereby enabling the rotary cutting tool to perform a ramp operation with a ramp angle between about 15 degrees and about 45 degrees. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While various embodiments of the disclosure are illustrated, the particular embodiments shown should not be construed to limit the claims. It is anticipated that various changes and modifications may be made without departing from the scope of this disclosure. 
         FIG.  1    is a side view of a rotary cutting tool, such as an end mill, according to an embodiment of the disclosure; 
         FIG.  2    is an isometric view of the rotary cutting tool of  FIG.  1   ; 
         FIG.  3    is an end view of the rotary cutting tool of  FIG.  1   ; 
         FIG.  4    is an enlarged, partial side view of the cutting portion of the rotary cutting tool of  FIG.  1   ; 
         FIG.  5    is an enlarged isometric view of the cutting portion of the rotary cutting tool of  FIG.  1   ; and 
         FIG.  6    is a schematic diagram of the rotary cutting tool of the invention during a ramp operation. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     As used herein, directional phrases, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. Identical parts are provided with the same reference number in all drawings. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     Throughout the text and the claims, use of the word “about” in relation to a range of values (e.g., “about 22 to 35 wt %”) is intended to modify both the high and low values recited, and reflects the penumbra of variation associated with measurement, significant figures, and interchangeability, all as understood by a person having ordinary skill in the art to which this disclosure pertains. 
     For purposes of this specification (other than in the operating examples), unless otherwise indicated, all numbers expressing quantities and ranges of ingredients, process conditions, etc., are to be understood as modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired results sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Further, as used in this specification and the appended claims, the singular forms “a”, “an” and “the” are intended to include plural referents, unless expressly and unequivocally limited to one referent. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements including that found in the measuring instrument. Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, i.e., a range having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations. 
     In the following specification and the claims, a number of terms are referenced that have the following meanings. 
     The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Referring now to  FIGS.  1 - 5   , a rotary cutting tool  10  is shown according to an embodiment of the disclosure. In general, the rotary cutting tool  10 , such as an end mill, is elongate and has a central, longitudinal axis, A-A, which can also be considered as the rotational axis. As used herein, the term “elongate” or “elongated” is defined as something that is longer than it is wide. In other words, the width is smaller than its length. 
     The rotary cutting tool  10  comprises a shank portion  12  and a cutting portion  14  adjoining the shank portion  12 . The cutting portion  14  defines a cutting diameter, D, and includes a plurality of blades  18  separated by flutes  20  extending the length of the cutting portion  14 . In the illustrated embodiment, the end mill  10  has a total of five (5) blades  18  and flutes  20 . However, it will be appreciated that the invention is not limited by the number of blades and flutes, and that the invention can be practiced with a fewer or a greater number of blades and flutes. For example, the invention can be practiced with two blades and flutes, three blades and flutes, four blades and flutes, six blades and flutes, seven blades and flutes, eight blades and flutes, nine blades and flutes, ten blades and flutes, and the like. The end mill  10  rotates in a direction of the arrow, R ( FIG.  3   ). Each blade  18  has a leading face  22 , a trailing face  24 , and a land surface  26  bridging the leading face  22  and trailing face  24 . In addition, each blade  18  has an end face cutting edge  28  and a peripheral cutting edge  30  at the intersection between the leading face  22  and the land surface  26 . It should be appreciated that the land surface  26  acts as a relief surface for the peripheral cutting edge  30 . 
     As used herein, axial rake angle is defined as the angle between the cutter tooth face of a blade of a milling cutter or reamer and a line parallel to its axis of rotation. 
     Radial rake angle is defined as the angle between the cutter tooth face of a blade and a radial line passing through the cutting edge in a plane perpendicular to the cutter axis. 
     End rake angle is defined as the angle between the cutting tip at the end of a blade and a radial line passing through the cutting edge in a plane perpendicular to the cutter axis. 
     Positive axial rake angle is defined as a rake geometry indicating that the that the cutting edge is positioned on the axial centerline of the cutter with the top surface of the cutting edge sloping back and away from the axial centerline. 
     Positive radial rake angle is defined as a rake geometry indicating that the cutting edge is positioned on the radial centerline of the cutter with the top surface of the cutting edge sloping back and away from the radial centerline. 
     Positive end rake angle is defined as a rake geometry indicating that the cutting tip at the end of the blade is positioned on the radial centerline of the cutter with the cutting tip sloping back and away from the radial centerline. 
     Ramp milling is defined as a combination of Z-axis movement simultaneous with X, Y, or combined axis movement. 
     Dish angle is defined as the angle formed by the end cutting edge with respect to a plane perpendicular to the cutter axis. 
     Helix angle is defined as the angle made by the leading face of the land with a plane containing the cutter axis. 
     Ramp angle is defined as the angle made by the cutter when moving the cutter in both the Z-axis direction and an additional axis (X- or Y-axis) relative to the work, and is defined by the equation: 
       Ramp Angle=ARCTAN ((Z-axis feed)/(X_Y-axis feed))   (1)
 
     A high ramp angle is defined as a ramp angle of at least 10 degrees. 
     As shown in  FIGS.  1 - 5   , the end cutting edge  20  of each blade  18  extends from an outer diameter, OD, of the cutting portion  14  towards the central longitudinal axis, A-A. The end cutting edge  20  of each blade  18  defines a dish profile and a radial profile. As described herein, dish profile refers to the profile or shape of an end cutting portion of a blade when viewed from a side of the cutting tool, as shown in  FIG.  1   . As used herein, a radial profile refers to the profile of the end cutting portion of a blade when viewed from an end of the cutting tool, as shown in  FIG.  3   . In the illustrated embodiment, each blade  18  extends less than the full distance from the outer diameter, OD, to the central longitudinal axis, A-A. However, it should be appreciated that the principles of the invention can be practiced with a rotary cutting tool in which each blade  18  extends the full distance from the outer diameter, OD, to the central longitudinal axis, A-A. 
     The blades  18  and flutes  20  of the cutting portion  14  extend helically within the cutting portion  14  at a helix angle  32  of between about 30 degrees and about 45 degrees with respect to the central, longitudinal axis, A-A. In other embodiments, the blades  18  and flutes  20  are “straight flutes” that extend substantially parallel to the central, longitudinal axis, A-A. In the illustrated embodiment, the blades  18  and flutes  20  of the cutting portion  14  extend helically within the cutting portion  14  at a helix angle  32  of about 38 degrees. 
     Referring now to  FIG.  3   , the angular spacing  34  between adjacent blades  18  and flutes  20  is substantially unequal to minimize vibration during a machining operation. In the illustrated embodiment, for example, the angular spacing  34  may be between about 62 degrees to about 80 degrees. However, it will be appreciated that the invention is not limited by unequally spaced blades and flutes, and that the invention can be practiced with equally spaced blades and flutes (i.e., 360/5=72 degrees). 
     As shown in  FIG.  3   , the end face cutting edge  28  of each blade  18  includes a corner cutting edge  36  proximate the outer diameter, OD, of the end mill  10 . In the illustrated embodiment, the corner cutting edge  36  is formed with a radius for providing strength to the corner cutting edge  36 . However, it will be appreciated that the invention is not limited by having a radiused corner cutting edge  36 , and that the invention can be practiced with a sharp corner cutting edge (i.e., without a radius), a chamfered corner cutting edge, and the like. The end face cutting edge  28  further includes a first end face cutting edge portion  38  adjoining the corner cutting edge  36 , and a second end face cutting edge portion  40  adjoining the first end face cutting edge portion  38 . In the illustrated embodiment, the first end face cutting edge portion  38  is disposed radially outward with respect to the second end face cutting edge portion  40 . In other words, the second end face cutting edge portion  40  is disposed radially inward with respect to the first end face cutting edge portion  38 . In the illustrated embodiment, the end face cutting edge  28  does not extend the entire distance from the outer diameter, OD, to the central, longitudinal axis, A-A. However, it will be appreciated that the invention is not limited by the length of the end face cutting edge  28 , and that the invention can be practiced with the end face cutting edge  28  extending the entire distance from the outer diameter, OD, to the central, longitudinal axis, A-A, of the cutting tool  10 . 
     As shown in  FIG.  5   , each end face cutting edge  28  has a primary clearance surface  42  adjoining both the first end face cutting edge portion  38  and the second end face cutting edge portion  40 , and a second clearance surface  44  adjoining the primary clearance surface  42 . As understood in the art, the primary and secondary clearance surfaces  42 ,  44  provide clearance for the end face cutting edge  28  during machining operations. Similarly, the corner cutting edge  36  has a corner primary relief surface  46  and a corner secondary relief surface  48  to provide clearance for the corner cutting edge  36 . In addition, the first end face cutting edge portion  38  has a first curved rake face  50  and the second end face cutting edge portion  40  has a second curved rake face  52 . In the illustrated embodiment, the first curved rake face  50  and the second curved rake face  52  have different axial and radial angles. As seen in  FIG.  5   , each flute  20  has a flute rake face  53  that adjoins the peripheral cutting edge  30  and the first curved rake face  50  for providing clearance for the peripheral cutting edge  30 . 
     As shown in  FIG.  3   , one aspect of the invention is that the first end face cutting edge portion  38  defines a first radial angle  54 , and the second end face cutting edge portion  40  defines a second radial angle  56  that is different than the first radial angle  54 . For example, the first radial angle  54  can be between about +2 degrees and about −2 degrees with respect to a plane, P Y -P Y , that is substantially perpendicular to the central, longitudinal axis, A-A, (i.e., parallel to the y-axis), which has been found to be desirable for machining high temperature alloys, and the like. 
     By contrast, the second radial angle  56  of the second end face cutting edge portion  40  is highly positive, depending on the material to be machined. For example, the second radial angle  56  can be between about +11 degrees and about +15 degrees, which has been found to be desirable for machining high temperature alloys, and the like. 
     As shown in  FIG.  4   , the first end face cutting edge portion  38  defines a first dish angle  58  with respect to the plane, P X -P X , that is substantially perpendicular to the central, longitudinal axis, A-A, (i.e., parallel to the x-axis) and the second end face cutting edge portion  40  defines a second dish angle  60  with respect to the plane, P X -P X . More specifically, the first dish angle  58  is smaller in magnitude than the second dish angle  60 . In other words, the second dish angle  60  is larger in magnitude than the first dish angle  58 . In addition, the first dish angle  58  varies in a radial direction along the first end face cutting edge portion  38 . Likewise, the second dish angle  60  varies in a radial direction along the second end face cutting edge portion  40 . For example, the first dish angle  58  can vary in a range between about 0.5 degrees and about 8 degrees, and the second dish angle  60  can vary in a range between about 4 degrees and about 80 degrees. In one embodiment, for example, the first dish angle  58  can vary from about 1 degree to about 4 degrees, and the second dish angle  60  can vary from about 4 degrees to about 75 degrees. It will be appreciated that the invention can be practiced with other dish angles, so long as the first dish angle  58  is smaller in magnitude than the second dish angle  60 . 
     The first end face cutting edge portion  38  defines a first axial rake angle  62  with respect to a plane, P Z -P Z , that is substantially parallel to the central, longitudinal axis, A-A, (i.e., parallel to the z-axis), depending on the material to be machined. In one embodiment, the first axial rake angle  58  is between about −1 degrees and about −15 degrees, which has been found to be desirable for machining high temperature alloys, and the like 
     Similar to the first cutting end edge portion  38 , the second end face cutting edge portion  40  defines a negative second axial rake angle  64  with respect to the plane, P Z -P Z , depending on the material to be machined. For example, the second axial rake angle  64  can be between about −1 degrees and about −15 degrees for machining high temperature alloys, and the like. 
       FIG.  6    shows a schematic diagram of the end mill  10  of the invention during a ramp operation (i.e., moving in the x-z plane) in the direction of the arrow  66  at a ramp angle  68  of greater than 15 degrees. In the illustrated embodiment, the ramp angle  68  is about 20 degrees. As shown in  FIG.  6   , the end mill  10  rotates in the clockwise direction and the leading face  22  is the right-hand side of the end mill  10 , while the trailing face  24  is the left-hand side of the end mill  10 . During the ramp operation, only the corner cutting edge  36  and the first cutting portion  38  of the cutting end  16  contact the work  100  at the leading face  22 . It may appear that the second end face cutting edge portion  40  of the cutting end  16  may be slightly contacting the work  100  in  FIG.  6   . In reality, the second cutting portion  40  of the cutting end  16  on the right-hand side of end mill  10  does not contact the work  100 . 
     On the other hand, both the first cutting portion  38  and the second cutting portion  40  of the cutting end  16  when the trailing face  24  contacts the work  100 . The corner cutting edge  36  may contact the work  100 , but not the entire corner cutting edge  36 , unlike the corner cutting edge  36  when the leading face  22  contacts the work  100 . 
     As mentioned above, the first end face cutting edge portion  38  is designed for moderate ramp angles  68  of between about 3 degrees and about 5 degrees. In addition, the first end face cutting edge portion  68  can have a curved and complex profile, or a straight and complex profile, or any combination thereof. Further, the first end face cutting edge portion  38  can have either a positive first radial angle  54  or negative first radial angle  54 , depending on the material to be machined. For example, the first radial angle  54  can be between about +2 degrees and about −2 degrees for machining high temperature alloys, and the like. Still further, the first end face cutting edge portion  38  can have a negative first axial rake angle  62 , depending on the material to be machined. For example, the first axial rake angle  62  can be between about −1 degrees and about −15 degrees for machining high temperature alloys, and the like. 
     By contrast, the second end face cutting edge portion  40  is designed for large ramp angles  68  of between about 15 degrees and about 45 degrees. The second end face cutting edge portion  40  can have a curved and complex profile, or a straight and complex profile, or any combination thereof, but must follow an inward (i.e., center) pointing curved or radii profile. In addition, the second end face cutting edge portion  40  has a highly positive second radial angle  56 , depending on the material to be machined. For example, the second radial angle  56  can be between about 11 degrees and about 15 degrees for machining high temperature alloys, and the like. Further, the second end face cutting edge portion  40  can have a negative second axial rake angle  64 , depending on the material to be machined. For example, the second axial rake angle  64  can be between about −1 degrees and about −5 degrees for machining high temperature alloys, and the like. 
     As described above, the highly positive second radial angle  56  the second end face cutting edge portion  40  of the cutting end  16  contacts the work  100  in such a way that the rotary cutting tool  10  is capable of performing a ramp operation with the ramp angle  68  of between about 15 degrees and about 45 degrees. As a result, the entire trailing face  24  of the end mill  10  aggressively cuts the work  100 . In addition, the end mill  10  of the invention, which is a non-center cutting tool, is able to perform a plunge operation at an extremely high ramp angle, unlike conventional non-center cutting tools. 
     In addition to the above-described embodiments, it is to be understood that additional configurations may also be possible. For example, in some embodiments, any one or more of the axial profiles (first, second, third, fourth, and subsequent) may be curved or straight. Such embodiments can include embodiments in which all of the axial profiles in a cutting tool are curved, all axial profiles are straight, and/or some axial profiles are curved, and others are straight. In certain embodiments, all axial profiles are the same or substantially the same. In some other embodiments, all axial profiles differ from one another, generating a “variable helix” effect among the blades. Moreover, in some embodiments, some axial profiles may be the same or substantially the same as at least one other axial profile but may differ from one at least one other axial profile. 
     It is to be understood that although individual blades are described separately herein that any individual properties of particular blades may be applicable to one or more other blades on the rotary cutting tool. Alternatively, in some embodiments, no two blades in a rotary cutting tool may have the same dish and/or axial profiles. Additionally, it is to be understood that although embodiments are described herein have five or fewer blades, that any number of blades may be used consistent with the principles of the invention. 
     Having described presently preferred embodiments the disclosure may be otherwise embodied within the scope of the appended claims.