Field of the Invention

[0001] The present invention is directed to the manufacture of gears and in particular to cuting tools for the manufacture of gears such as bevel and hypoid gears.

Background of the Invention

[0002] Bevel and hypoid gears can be cut, by a generating or non-generating method, in a single or intermittent indexing process (face milling) or in a continuous indexing process (face hobbing). A basic cuting setup in the generating or cradle plane will put the center of the cutter head in a position which is away from the generating gear center (cradle axis) by an amount known as the radial distance. The silhouette of the cutter blades represents one tooth of the generating gear while the cutter rotates. Common face cutters for bevel gear cutting have several blade groups with each group having between one and four cutting blades commonly referred to as “stick” or “bar” blades. Most common are alternating (completing) cuters with one outside cutting blade and one inside cutting blade. In order to achieve an equal chip load of all inside blades and all outside blades during the cutting process, it is the goal to have the cutting edges of all outside blades and all inside blades follow each other with the same radial position.

[0003] In the case of the most common stick blade cutters, the cutter head 10 (Figure 1) is a disk with slots and a clamping provision for blade sticks. The cutter head blade receiving slots can have different cross-sections, such as square, rectangular, pentagon or round as is known in the art. The blade sticks for the different slot designs usually have the respective complementary cross-section of the blade receiving slot. The stick blade dimensions are defined by amounts slightly smaller than the cutter head receiving slots which allows the blades to be inserted into the slots and positioned within the slots.

[0004] The common rectangular blade systems hold the blades in position against the cutting forces by friction. The blades with a pentagon shaped cross section are held in position against the cutting forces by a positive seating. In case of a round blade cross section, the blades can be either held by friction or by a positive seating, depending on the clamping principle.

Summary of the Invention

[0005] The present invention is directed to a cutter head having a plurality of cutting blade receiving slots with at least one of the cutting blade receiving slots having a foursided, non-rectangular, cross-section.

[0006] Another embodiment of the invention comprises a cutting blade having a having a four-sided, non-rectangular cross-section wherein the cross-sectional shape of a cutting blade is complementary to the cross-sectional shape of a four-sided, non- rectangular cutting blade receiving slot such that the cutting blade can be positioned and clamped in the cutting blade receiving slot.

[0007] In a preferred embodiment, the cutter head comprises a plurality of cutting blade receiving slots wherein, with respect to the rotational direction of the cutter head about its axis of rotation during a cutting process, at least one blade receiving slot includes a leading side surface having a slot depth, W2, and a trailing side surface, which is a seating surface, having a slot depth, W1, wherein W2 is less than (<) W1. The blade receiving slot further includes an outer side surface and an inner side angular surface, which is also a seating surface, extending between the leading and trailing side surfaces.

Brief Description of the Drawings

[0008] Figure 1 shows a three-dimensional view of a face milling cutter head with rectangular blade slots.

[0009] Figure 2 shows a cutter head section with a rectangular slot cross section and a rectangular blade cross section. The clamping force uses friction to hold the blade in its position against the cutting force Fc.

[0010] Figure 3 shows a cutter head section 30 with a five-sided slot cross section and a five-sided blade cross section. The clamping force presses the blade via contacting surface 37 into the prismatic seat, consisting off the contacting surfaces 35 and 36 which results in a positive (form) seating.

[0011] Figure 4 shows a cutter head section with a circular (round) slot cross section and a blade which has a circular (round) cross section, where the circular shape is interrupted by a flat section. The diameter of the slot is larger than the diameter of the blade. The arrangement in Figure 4 provides friction seating.

[0012] Figure 5 shows a cutter head section with a four-sided, not rectangular, slot cross section.

[0013] Figure 6 shows a cutter head section with a four-sided, not rectangular, slot cross section including a machining groove or check. [0014] Figure 7 shows a cutter head section with a four-sided, not rectangular, slot cross section and a four-sided, not rectangular, cutting blade cross section.

[0015] Figure 8 shows a cutter head section with a four-sided, not rectangular, slot cross section and a four-sided, not rectangular, cutting blade cross section with a radial spacer block.

[0016] Figure 9 is an isometric view of a four-sided, not rectangular, cutting blade showing a back contact side and an inner angular contact side.

[0017] Figure 10 shows an opposite side view of the cutting blade of Figure 9 showing the front and outer sides as well as a cutting edge, clearance edge and a front face.

[0018] Figure 11 illustrates a partial view of a cutter head having a cutting blade positioned in each of two blade receiving slots.

[0019] Figure 12 shows a cutter head section with a four-sided, not rectangular, slot cross section and a five-sided cutting blade cross section with a radial spacer block.

Detailed Description of the Preferred Embodiment

[0020] The terms “invention,” “the invention,” and “the present invention” used in this specification are intended to refer broadly to all of the subject matter of this specification and any patent claims below. Statements containing these terms should not be understood to limit the subject matter described herein or to limit the meaning or scope of any patent claims below. Furthermore, this specification does not seek to describe or limit the subject matter covered by any claims in any particular part, paragraph, statement or drawing of the application. The subject matter should be understood by reference to the entire specification, all drawings and any claim below. The invention is capable of other constructions and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purposes of description and should not be regarded as limiting.

[0021] The use of “including”, “having” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise and the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0022] Although references may be made below to directions such as upper, lower, upward, downward, rearward, bottom, top, front, rear, etc., in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or limit the present invention in any form. In addition, terms such as “first”, “second”, “third”, etc., are used to herein for purposes of description and are not intended to indicate or imply importance or significance unless explicitly stated.

[0023] The details of the invention will now be discussed with reference to the accompanying drawings which illustrate the invention by way of example only. In the drawings, similar features or components will be referred to by like reference numbers. The size and relative sizes of certain aspects or elements may be exaggerated for clarity or detailed explanation purposes.

[0024] In the context of the present invention, the term "bevel" gears is understood to be of sufficient scope to include those types of gears known as bevel gears, "hypoid" gears, as well as those gears known as "crown" or "face" gears. [0025] Figure 1 shows a three-dimensional view of a known face milling cutter head 10 with rectangular outside blade slots 15 and rectangular inside blade slots 16. Slots 15 and 16 represent one blade group 11. Cutter head 10 rotates in the cutting process in direction 14.

[0026] Figure 2 shows a section 20 of a known cutter head with a rectangular slot 21 and a rectangular blade 22. Clamp screw 23 is in contact with clamp block 24 which allows the surfaces 25 and 26 to develop a friction forces FFI and FF2 in the same magnitude but opposite direction than the cutting force Fc (Fc = -FFI-FF2).

[0027] Figure 3 shows a cutter head section 30 with a five-sided (pentagon shaped) slot 31 and a five-sided blade 32 (see US 6,120,217 for example). Clamp screw 33 is in contact with the clamp block 34 and presses the blade 32 via surface 37 in the two prismatic seating surfaces 35 and 36. In case a cutting force Fc is applied, the reaction Forces FRI and FR2, which are perpendicular to the surfaces 37 and 35, will act against the cutting force Fc and balance it (equilibrium). The tight, positive blade seating will allow the reaction forces to adjust (theoretically) to any cutting force magnitude, because the reaction forces are independent from any surface friction.

[0028] Figure 4 shows a section 40 of a known cutter head with a round slot 41 and a round blade 42 having a flat section 47. The diameter of the blade 42 has to be smaller than the diameter of the cutter slot 41 in order to provide a clearance fit between slot and blade for quasi force free insertion of the blades. Clamp screw 43 is in contact with blade surface 47 and presses the blade 42 against point 45. Depending on the curvature differences, point 45 will spread to a contacting surface area. In case of the presence of a cutting force Fc, the reaction forces FFI (friction force on surface 47) and FF2 (friction force in point 45) will act against the cutting force with the same magnitude but opposite direction. In case of high cutting forces, the friction forces FFI +FF2 might be smaller than the magnitude of the cutting force Fc, which will result in a blade slippage. Another disadvantage of the arrangement in Figure 4 can be seen in the clamp screw 43 contacting blade flat section 47 as the only geometrical feature to provide a defined rotational seating orientation 56 which is insufficient for cutting blades.

[0029] Figure 5 shows a section of an inventive cutter head 50 comprising a foursided, not rectangular (i.e. non-rectangular), cutting blade receiving slot 51 (seen in axial cross-section defined by a plane perpendicular to the axis of rotation of cutter head 50) having sides 55, 56, 57 and 58. For discussion and illustration purposes, cutting blade receiving slot 51 (in all drawing Figures) extends parallel to the axis of rotation of cutter head 50 between the top surface (106 in Figure 11) and the bottom surface (not shown) of the cutter head. Sides 55 and 56 are mounting or seating surfaces against which a cutting blade will contact and seat upon being positioned and clamped in slot 51 . Side 55 is a trailing or back seating surface with reference to direction “R” of cutter head rotation during machining and is preferably parallel to leading side 57. The distance between the sides 55 and 57 is referred to as the width of the tooth slot. Side 56 is an angular seating surface extending between and intersecting leading or front side 57 (defined with respect to direction R) and trailing side 55.

[0030] Intersection angle ai located between sides 57 and 56 is greater than ninety degrees (i.e. > 90°) and intersection angle az located between sides 55 and 56 is less than ninety degrees (i.e. < 90°). Side 58 is an outer side of slot 51 and includes at least one opening, preferably a threaded opening, through which a clamp screw (e.g. 53 in Figure 7) or other clamping mechanism may extend. Outer side 58 is preferably perpendicular to sides 55 and 57. Angular side 56 may be considered to be an “inner” side with respect to the axis of rotation (see Figure 11) of cutter head 50 since angular side 56 is closer (radially) to the axis of rotation than side 58. Hence, side 58 is an “outer” side of slot 51 with respect to the same axis of rotation. Side 55 has a slot depth, Wi, and side 57 has a slot depth, Wz, that is less than Wi (i.e. Wz < Wi). [0031 ] Figure 6 is the same as Figure 5 except for the inclusion of a groove 59 known as a “check” which serves to provide machining clearance when finishing the clamping and seating surfaces 55 and 56 since many tools cannot adequately and repeatedly machine a sharp corner and besides, a sharp corner may cause stress concentrations.

[0032] Figure 7 shows the inventive cutter head 50 of Figure 5 including a stick-type or bar-type cutting blade 52 (shown in cross-section defined by a plane perpendicular to the axis of rotation of cutter head 50) mounted in slot 51 wherein the cutting blade 52 comprises four sides that are not rectangular (i.e. non-rectangular) and is defined by outer side 60, leading or front side 61 , trailing or back contact side 62 and inner angular contact side 64. The distance between sides 61 and 62 is referred to as the width of the cutting blade and the distance between side 60 and contact side 64 is referred to as the thickness of the cutting blade. The terms “leading” and “trailing” are defined in accordance with the operational orientation of the cutting blade 52 as mounted in slot 51 during machining. A cutting edge, not shown, is located on the front side 61 of blade 52 at the end of the portion of the blade that projects out from the front face of the cutter head 50. For discussion and illustration purposes, cutting blade 52 extends parallel to the axis of rotation of cutter head 50.

[0033] The clamping force Fciamp from clamp screw 53 and clamp block 54 is transferred into the blade 52 via contact with the surface of blade outer side 60. In order to achieve equilibrium between the clamping force and the surfaces of contact sides 62 and 64 of the blade, the clamping force Fciamp is separated into the normal forces FNI and FN2. Normal force FNI presses the blade onto slot seating surface 55 and normal force FNZ presses the blade onto slot seating surface 56. FRI is the reaction force of FNI and FR2 is the reaction force of FN2. The clamp force holds the blade tight and stiff in the correct position. The cutting force Fc will only have a reaction force FRS on surface 55. Surface 55 is perpendicular to the average cutting force Fc, which creates a reaction force FR3 of the same magnitude but opposite direction of the cutting force. This condition is optimal for a precise and stiff blade seating in a cutter head. As a result of clamping and cutting forces, a small gap 70 will exist between the front side 61 of cutting blade 52 and the leading side 57 of slot 51. If desired, the blade corner formed by the intersection of sides 55 and 56 may be slightly rounded so as to eliminate a sharp corner.

[0034] The four sided, not rectangular, blade slot 51 and cutting blade design result in one seating surface 55 of the slot 51 being perpendicular to the average cutting force Fc. The second seating surface 56 is oriented at an angle (Figure 5) and therefore achieves a sliding of the cutting blade 52 against seating surface 55 during the blade clamping with clamp force Fciamp. Compared to the state of the art, the inventive arrangement between cutting blade and cutter head mounting slot enables the clamping force to press the blade firmly against the seating surfaces while one of the seating surfaces is perpendicular to the average cutting force. The arrangement shown in Figure 7 presents a significant static and dynamic increase in seating stiffness and seating accuracy compared to the state-of-the-art solutions during the cutting process. An increased cutting force Fc will increase the contact pressure on seating surface 55 by the same factor.

[0035] Figure 8 shows a section of cutter head 50 with a four-sided, not rectangular, slot cross section 51 and a four-sided, not rectangular, cutting blade 52 shown in cross section as in Figure 7. In order to achieve a different radial location of the blade (with respect to the rotational axis of the cutter head 50), a radial shimming spacer block 67 is used to increase the radial blade position (i.e. distance of the blade 52 from the rotational axis of the cutter head 50) by an amount 63. The spacer block 67 is shaped in order to tightly contact slot seating surfaces 55 and 56 at respective contact surfaces 65 and 66 as well as the blade contacting surface 64 via spacer block seating surface 69. The connecting screw 68 connects the spacer block 67 to the body of cutter head 50. [0036] Radial blade shimming with a spacer block 67 enables a wider range of different gear geometries to be cut with the same cutter head. This flexibility is very desirable in order to reduce cutter head inventory which heretofore was only possible by accepting a reduction in stiffness and accuracy when the traditional parallel spacer was placed between the slot surface 25 and a cutting blade 22 (see Figure 2) of the friction blade clamping. The inventive spacer block 67 is shaped to accommodate and maintain the positive blade seating of blade 52 with surfaces towards the slot seating surfaces 55 and 56 of the cutter head body 50 and towards the blade surface 64. Spacer block 67 increases the radial position of blade 52 by an amount 63. The amount 63 may differ within a variety of available spacer blocks in order to provide a high flexibility for the usage of different blade sizes and for covering a wider range of gear geometries.

[0037] A cutting blade 52 shown in cross-section in Figures 7 and 8 is shown in isometric view in Figures 9 and 10. Figure 9 shows a four-sided, non-rectangular crosssection, cutting blade 52 having an overall length between the tip and bottom end of the cutting blade, as normally viewed in Figure 9, and comprising a lower shank portion and an upper cutting end portion. Cutting blade 52 comprises outer side 60, leading or front side 61 , trailing or back contact side 62 and inner angular contact side 64. The terms “leading” and “trailing” are defined in accordance with the operational orientation of the cutting blade 52 as mounted in a blade mounting slot (e.g. 51 in Figure 7) during machining. The thickness of cutting blade 52 is greater at back contact side 62 than at front side 61 . A cutting edge 90 is located on the front side 61 of blade 52 at the end of the portion of the blade (i.e. the cutting end portion) that projects out from the front face of a cutter head (e.g. 50 in Figure 11). Cutting blade 52 also includes a shoulder 91 , cutting side profile surface 92 and tip relief surface 98. A rectangular reference crosssection is shown at 100.

[0038] Figure 10 shows an opposite view of the cutting blade of Figure 9 wherein front face 94, clearance edge 95, clearance side profile surface 96 and shoulder 93 are visible. Front face 94 is shown oriented at a rake angle K which is shown illustrating a positive value rake angle but could be zero or negative in value.

[0039] Figure 11 shows a partial view of a cutter head 50 rotatable about a tool axis T in a clockwise direction R. The cutter head 50 comprises a plurality of cutting blade receiving slots 51. Inside cutting blade 102 and outside cutting blade 104 are shown positioned in respective receiving slots of the cutter head and projecting from the face 106 of the cutter head 50.

[0040] Figure 12 shows a section of cutter head 50 with a four-sided, not rectangular, slot cross section 51 and a five-sided blade 72 shown in cross-section. A cutting edge, not shown, is located on the front side of blade 72 (i.e. on the side adjacent to gap 70) at the end of the portion of the blade that projects out from the front face of the cutter head 50. In order to achieve a different radial location of the blade (with respect to the rotational axis of the cutter head 50), a radial shimming spacer block 77 is used to increase the radial blade position (i.e. distance of the blade 72 from the rotational axis of the cutter head 50) by an amount 73. The spacer block 77 is shaped in order to tightly contact slot seating surfaces 55 and 56 via respective contact surfaces 81 and 82 as well as the contacting surfaces 74 and 79 of cutting blade 72 via respective spacer block seating surfaces 83 and 84. The connecting screw 78 connects the spacer block 77 with the body of cutter head 50. As a result of clamping and cutting forces, small gaps 70, 71 will exist between the front side of cutting blade 52 and the leading side 57 of slot 51 , and between the back side of cutting blade 52 and the trailing side 55 of slot 51.

[0041] Spacer block 77 is shaped to accommodate the seating towards the slot surfaces 55 and 56 of the cutter head body 50 and towards the cutting blade 72 having contact surfaces 74 and 79. Spacer block 77 increases the radial position of blade 52 by an amount 73. The amount 73 can differ within a variety of available spacer blocks in order to provide a high flexibility for the usage of different blade sizes and for covering a wider range of gear geometries.

[0042] While the invention has been described with reference to preferred embodiments it is to be understood that the invention is not limited to the particulars thereof. The present invention is intended to include modifications which would be apparent to those skilled in the art to which the subject matter pertains without deviating from the spirit and scope of the appended claims.