US 3680262 A
A novel grinder for provided for notching and gashing end mills in order to grind novel and improved shapes of the cutting edges and land or tooth faces of the end mill. This grinding action is especially valuable on ball end mills because the improved shape of the cutting edges provides more efficient cutting action, a longer life, and a better chip flow away from the cutting edges of the cutter.
Description (OCR text may contain errors)
United States Patent Aydelott et a1.
 END MILL GRINDER  Inventors: Max M. Aydelott, West Covina; Richard W. Beilfuss, Glendora; Ernst Borchert, III, Pomona, all of Calif.
 Assignee: Omark-Winslow Aerospace Tool Co., Portland, Oreg.
 Filed: Nov. 3, 1969 ] Appl. No.: 873,270
 US. Cl. ..51/96, 51/225, 51/288  Int. Cl. ..B24b 9/00  Field of Search ..51/96, 97, 219 R, 225, 288
 Reterences Cited UNITED STATES PATENTS 183,798 10/1876 Champlin ..-.51/219 [151 3,680,262 [451 Aug. 1,1972
253,890 2/1882 Rogers ..51/97 R 2,332,510 10/1943 Franzen ..51/225 2,870,579 1/1959 Siemsen et a1 ..51/219 R X 3,040,480 6/1962 Winslow et al. ..51/219 R X Primary Examiner-Lester M. Swingle Attorney-Forrest J. Lilly [5 7] ABSTRACT A novel grinder is provided for notching and gashing end mills in order to grind novel and improved shapes of the cutting edges and land or tooth faces of the end mill. This grinding action is especially valuable on ball end mills because the improved shape of the cutting edges provides more efficient cutting action, a longer life, and a better chip flow away from the cutting edges of the cutter.
15 Claims, 35 Drawing Figures END MILL GRINDER CROSS-REFERENCE TO RELATED APPLICATIONS only a portion.
BACKGROUND OF THE INVENTION The present invention relates generally to grinders for shaping or sharpening cutters for machine tools, and more especially to equipment of this type for grinding end mills, either to sharpen old ones or to grind new ones from blanks.
Heretofore, grinding end mills has been done largely by hand operations, with the aid of jigs and fixtures to steady the tool in the hand of the operator. While some grinders have been developed to partially mechanize the operation, these are relatively simple tools and do not satisfy the requirement for producing a highly sophisticated shape on the cutting edges of the mills. When grinding is basically a manually controlled operation, the product of such known procedures suffers from unpredictable and variable inaccuracies; and this in turn leads to a lack of uniformity in the final product. Also close control of the shape of the ground surfaces'is impossible to obtain. In operations involving a considerable amount of hand labor in moving or guiding the tool during a grinding operation, the relative cost of sharpening a mill is much greater than when it is done entirely by machine-controlled operation.
As a consequence of these conditions, mechanization of grinding end mills, as well as other cutting tools, is desired for reasons of economy and also for accuracy of grind which enables production of cutters which are precise duplicates of one another. This latter requirement is especially important when multiple-spindle machine tools are being used as it then becomes essential that all of the cutting tools cut in exactly the same manner and have the same useful production life.
Another advantage of mechanization of the grinding operation is that it is possible to produce novel shapes on the cutting edges because of the greater degree of control, not previously possible, over the relative movement of the cutter being sharpened and the grinding wheel.
It has been found for maximum efficiency in the case of ball end mills that, among other characteristics, the cutter should have a smooth tangential blend of the rake angle on the nose of the cutting elements with the rake angle on the full diameter.
Hence it becomes a general object of the present invention to produce a grinding machine for end mills which is able to exert greater control over the shape produced of the cutting edges to thereby produce on the cutting edges and adjacent ground surfaces of the end mill novel and more efficient shapes that could not previously be secured.
More particularly, it is an object to produce a grinder for end mills which obtains a better blend than has been heretofore possible between the rake angle on the cutting surfaces at the nose of the mill with the rake angle and helix angle at the full diameter of the mill.
It is especially an object to achieve a more efficient shape to the cutting edges on a ball end mill than has been possible with known grinding apparatus and procedures.
It is also an object of the present invention to provide novel shape to the ground surface on the end mill that improves the chip flow away from the cutting edges of the cutter.
SUMMARY OF THE INVENTION The above and other objects and advantages of the present invention have been achieved in a grinder comprising a grinding wheel, a tool holder, and mounting means of novel construction for supporting and moving the tool holder and a cutter therein over a predetermined path with respect to the grindwheel in order to perform certain gashing operations.
Generally, the grinder is constructed with reference to X, Y, and Z principal geometric axes that lie respectively in one of three mutually perpendicular planes. From the standpoint of the geometry of design, these axes may be considered as being mutually perpendicular and to intersect at a common point P,, and they may do so in the machine. From the standpoint of design, these three axes are fixed as reference axes. In the machine, the corresponding axes are designated X,, Y,, and Z,, respectively, and the physical elements that are the counterparts of the design or geometric axes can assume these same reference positions or they may be moved away from the reference positions laterally or angularly. Especially is this so of adjustments or displacements of the machine elements corresponding to or representing the X and Z axes that are necessary to produce particular grinds or to accommodate particular sizes and shapes of cutters. For this reason, flexibility in the location of the machine counterparts of the geometric axes is built into the machine so that while these axes in the machine may be offset or rotated with respect to their initial position as may be required during grinding operations.
The vertical Z, axis and the horizontal X, axis established by major machine elements are each independently movable in relation to the other axes to obtain the necessary flexibility of three-dimensional movement required for grinding the cutters. Means are provided for feeding the cutter toward and away from the grindwheel by swinging the Z, axis in a short horizontal are about a second vertical axis identified as 2,. The grindwheel revolves about a third vertical axis Z intersected by the geometric reference axis Y. The X, axis may be perpendicular to the Y, axis, which is parallel to but offset from the Y axis, but means are provided to enable the X, axis to be swung in a horizontal are about the Z, axis to a position other than perpendicular to the Y, axis during the actual grind operation. Also the X, axis can be shifted laterally toward and. away from the grindwheel. The Y axis is not represented by a tangible machine element.
The cutter is mounted in a tool holder which, in turn, is mounted in a workhead adapted to position the tool holder initially with the longitudinal axis of the cutter horizontal and in the Y-Z plane, or in a plane parallel thereto coinciding at this time with the Y, axis. Means are provided for swinging the tool holder and cutter about the X, axis and also about the Z axis as is necessary for various grinds. A cam and follower arrangement is provided for controlling rotation of the workhead about X axis as a function of cutter movement about the Z axis so that by simultaneous rotation about two' axes, the desired shapes can be ground on the cutter.
The nose of a ball end mill has the rake angle provided by grinding the side face of the land in an operation referred to as gashing. Controlled movements of the cutter simultaneously about the two mutually perpendicular axesX and Z produces a smooth tangential blend between'the rake angle on the nose of the cutter and the side face of the land at the full diameter of the cutter. There is also produced a radius at the base of this side face which is greatest near the center of the cutter and which diminishes towards the periphery of the cutter that provides improved control or flow of the chips away from the cutting edges of the cutter during a milling operation. The exact shapes ground on the ball end mill have not been obtainable heretofore as no grinder had the capability of doing so.
BRIEF DESCRIPTION OF THE DRAWINGS with the upper portion of the housing broken away and e the workhead elevated into grinding position.
F [GA is a diagram showing the locator and cutter positioned thereby, and also the direction of the X axis shift relative to the X axis for A rotation.
FIG.4A is a combined section and elevation of FIG.4 viewed from the right thereof.
F IG.5 is a side elevation, viewed as in FIG.3, of a part of the mechanism for imparting motion to the workhead and the support column therefor.
FIG.6 is a fragmentary side elevation, similar to a portion of FIGS, showing the workhead tilted forward to the initial or loading position.
FlG.7 is a vertical section through the column supporting the workhead taken on line 7-7 of FIGS.
FIG.8 is a fragmentary vertical section showing the upper portion of the column supporting the workhead as on line 8-8 of FIG. 3 the workhead being rotated upwardly 90 from the loading position for purposes of illustration.
FIG.9 is a fragmentary vertical section and elevation on line 9-9 of FIGS of the cam and follower mechanism for controlling the workhead rotation about the X axis. v
FIG.10 is a side elevation of FIG.9 viewed from the right thereof.
FIG.ll is a fragmentary side elevation, similar to a portion of FIG.-l0 showing the relative movement of the cam and follower mechanism therein.
FIG.12 is a combined elevation and median section through the tool holder with a cutter in place in the tool holder.
FIG.13 is a section through'the workhead and the tool holder taken on broken line l3l3 of FIG. 14.
FIG.14 is a front elevation of the workhead when tilted to the initial or loading position.
FIG. 15 is a horizontal section through the indexing workhead on line 15-15 of FIG. 14.
FIG.16 is a plan view of the indexing lock disc in the workhead of FIG. 15 viewed on line 16-16 therein.
FIG.17 is a plan view of an overrunning clutch in the indexing workhead viewed on line 17-17 of FIG. 15.
FIG.18 is a combined plan view and section of the workhead support, taken partially on line l8l8 of FIG. 8.
FIG. 18A is a section taken on the broken section line 18A-18A of FIG. 8.
FIG.19 is a schematic view in perspective of the grindwheel, the workhead, and the column on which the workhead is mounted, together with a mechanism for producing the desired movements of the workhead relative to the grindwheel.
FIG.20 is a diagram showing a geometric relationship of the several design axes and the directions of offset and movements of the cutter relative to the axes.
FIG.21 is a side elevation of the cutting end of a ball end mill.
FIGS.21A, 21B, and 21C are fragmentary sections showing the changing radius or fillet ground at the base of the side face of the land on the nose of the ball end mill of FIG.22 as indicated by sections 21A-21A, 218-218, and 21C-21C, respectively, therein.
FIG.22 is a plan view of the cutting end of the ball end mill of FIG.21.
FIGS. 23A, 23B, 23C and 23D are a series of schematic views showing four successive positions of an end mill while undergoing gashing and notching grinds.
FIG.24 is a fragmentary median section of the periphery of the grindwheel showing a cutter in contact therewith for grinding.
FIG.25 is a schematic view of the basic electrical circuit.
FIG.26 (in two parts, A and B) is a diagram of the au' tomatic control system, including a logic circuit, show ing the 7 air and hydraulic elements controlling the sequence of operations of the grinder.
DESCRIPTION OF A PREFERRED EMBODIMENT General The detailed construction and operation of the cutter grinder can be more easily understood from a preliminary discussion of the concepts and general principles followed in its design and construction.
One of the first features apparent from inspection of FIG.1 is that an entire installation involves three separate stations. These stations use, as far as possible, common parts, and therefore the stations have an overall similarity in appearance, although they each perform separate and independent functions and consequently have different control systems.
Each station is based upon the same common design features or concept, but modified to the extent necessary to perform the particular grinding operations of that individual station.
The cutter grinder with which we are here concerned is the one normally at station No. 2 and it has certain features unique to this station and the functions performed there. Like the grinder at each of the other stations, it is designed and built with reference to three geometric axes that lie respectively in three mutually perpendicular and intersecting planes. IN accord with common practice these axes are designated as the X, Y,
and Z axes. The X and Y axes are horizontal and extend respectively from left to right of an observer standing at the front of the machine and toward and away from the observer at the same point. The Z axis is vertical, passing through the intersection of the X and Y axes. This geometric relationship of the three principal axes is shown in FIG.20, but this relationship is not unchanging, as embodied in the counterpart elements of the grinder. Other axes are designated by the same reference letter as the parallel principal axis with the addition of a subscript. Also in accord with common usage; rotation of machine elements about one of its principal axes, as indicated diagrammatically in FIG.20, is designated A, C, C or C rotation when about the X Z, Z or 2,, axes, respectively.
The machine X axis, established by a major machine element, is always horizontal but can be raised and lowered, rotated horizontally, or shifted laterally; and the Y axis can be considered to rise and fall with the X axis to maintain its intersection therewith. The machine has two major vertical axes for cutter movement; the Z axis is fixed and the Z axis is movable about the Z axis. The X-Z plane at all times at station 02 contains both vertical axes; but the X axis can swing about the Z axis so that the X-Z plane may not always include the Z axis.
Referring now to FIG.1, there is illustrated therein the three stations of a complete installation, it being realized that the stations may be installed and used separately and individually. Cutters are manually loaded and unloaded at each of the three stations and transferred from one station to another as required, so that no fixed spatial relationship between the stations is necessary.
Still referring to FIG.1, station No l is a radius and outside diameter grinder. This machine performs a nose or end rough grind followed by a continuous grind around the periphery of the cutter to establish the outside diameter, as is disclosed more fully in the above identified copending application.
Station No. 2 is designated as a gasher and performs the axial and rake angle grinds, a flute blend grind, and center notching at selected lands. These grinds are difficult to accomplish with precision and require a complexity of motion not present in the other stations.
Station No. 3 is termed a reliever and performs primary and secondary relief angle grinds, starting at the nose center line and progressing around the nose periphery to grind continuously the full length of the flutes.
It should be pointed out in advance that the exact motion required of the cutter for grinding at station No.
' 2 is determined by the type or style of cutter. As will become apparent from subsequent description, the station has sufficient flexibility in movement of the cutter to grind accurately a straight or flat end mill, a ball end mill, or one of the intervening intermediate shape generally referred to as a radiused end mill.
Grinder Structure The grinder comprises a frame which is indicated generally at 10 and which may be of any suitable design and construction. A protective enclosure or housing is mounted upon the frame as shown in FlG.2 to enclose the moving parts, both for safety and to confine splatter of coolant and debris produced in the grinding operation. The housing may be of any suitable shape and size. The grinder includes panels on which are mounted external controls.
One of the major elements of .the machine is the grindwheel assembly shown in side elevation in H63 and diagrammatically in FlG.19 in its relation to other elements of the grinder. This assembly comprises grindwheel 12 attached on the upper end of spindle 14 rotatably mounted in hydrostatic bearing 15. On the lower end of spindle 14 is carried a pulley 16 over which passes one or more belts 17. These belts also pass over a pulley on the output shaft of electric motor 18 (or 2MTR of FlG.25), of any suitable type. Spindle bearing 15 and motor 18 are mounted on slide 20. As shown in FIG.19, slide 20 is provided on one side with dovetail 21 which moves relative to frame 10 on and between a pair of rails 22 mounted on the frame. While means are also provided for moving the grindwheel automatically to a desired position, this arrangement also permits the grindwheel to be moved toward and away from the tool, by manually operated lead screw 24 passing through a fixed nut, not shown, on the slide. The lead screw extends forwardly of the grinder and is provided at one end outside of the housing with hand wheel 25 by means of which the lead screw may be rotated.
The axis of revolution of grindwheel 12 is a vertical axis designated asZ which is parallel to and spaced from principal axis 2,. This axis is normally stationary, but can be adjusted to compensate for wear. For this purpose, movement of the grindwheel assembly is produced by hand wheel 25 and lead screw 24 toward and away from Z axis along the Y axis.
Means are provided for holding a cutter to be ground and for moving the cutter over a predetermined path relative to grindwheel 12, such means being shown in detail in FlGS.3-9. The assembly of these parts is shown in a diagrammatic perspective in FIG. 19.
A cutter-26 to be ground is illustrated in FIGS. 12, 13, and 19 as being mounted in work holder 27 which in turn is mounted in work head 28. Work holder 27 is essentially a sleeve having at one end a central bore of a reduced diameter to receive the cutter shank. A plurality of such holders are provided at each station, each holder having a bore of selected size in order to receive the shank of a particular size of cutter 26. The outside diameters of all holders are the same to fit into workhead 28 as in FIG.13 so that the holders are in effect adapters which enable workhead 28 to receive cutters of different diameters and lengths and hold them for proper grinding engagement with grindwheel 12.
Details of workhead 28 are shown in FIG.13 wherein it will be seen that rotor 30 is mounted to turn within the fixed body of workhead 28. The rotor has a sleevelike configuration with an annular gear body 31 extending around the periphery of the rotor. Gear body 31 carries gear teeth 32 by which the rotor is driven. The opposed radial faces of gear 31 serve as axial thrust bearings and ride in contact with bearing blocks 33 at opposite sides of the gear. The cylindrical surface of sleeve at either side of gear 31 is a radial bearing and is in contact with a bearing block 33. Lubrication for these bearing surfaces is provided by hydraulic line 35 connected to the workhead and supplying lubricating fluid under pressure to a network of distribution passages 35a, as shown in FIG.13. A dynamic oil seal 34 is held in the workhead at each end of rotor 33, and rotor 30 is provided with a hydrostatic type of bearing. A fluid return line is shown at 350.
Inside rotor 30 is abutment ring 36 which is slidably received within the rotor and held in place by lock ring 37 which is externally threaded and screwed intothe end of rotor 30 to hold abutment ring 36 in place. At the inner end of the abutment ring is a contractable annular chuck 38 which is held between abutment ring 36 and annular piston 39. When operating fluid under pressure is introduced from line 35 through passages a to annular space 40 around the piston, piston 39 is forced upwardly in FIG.13 against chuck 38. The inclined surfaces on the opposite ends of chuck 38 engaging abutment 36 and piston 39 cause the chuck to contract and grip tool holder 27 as the piston moves up. When fluid pressure in annular passage 40 is released, the resilience of the parts causes the chuck to expand and release the tool holder.
Rotor 30 rotates about its longitudinal axis which is coincident with and establishes cutter axis T passing through successive positions T T and T in FIG. 20. The rotor is driven by hydraulic motor 42 mounted on workhead 28, hydraulic fluid under pressure being circulated to and through the motor by the hydraulic lines (not shown) connected to the motor at ports 43. The
output shaft 44 of motor 42 is connected by coupling.
45 to gear 46 on shaft 46a which is rotatably mounted in the workhead by suitable radial and thrust bearings, as shown in FIG.13. Gear 46 meshes with and drives gear 32 on rotor 30. V
Means are provided for supporting and moving workhead 28 in three dimensions in order to provide the necessary movement of tool 26 held in the workhead to attain the desired shaping by the grindwheel. As a part of this supporting and moving means, the workhead is provided on one .side with guide block 48 (see FIG.8) which has in one face a groove adapted to receive slidingly dovetail 50a on mating block 50. This structure permits relative sliding movement of the workhead and tool only in a straight line along the Y axis relative'to block 50, which may be considered as relatively stationary. This motion is designated as the X-axis offset in FIG.20, but is not used at station No. 2 except to zero in the machine and compensate for inaccuracies in manufacture, after which the slide may be pinned. Y Sliding movement of block 48 with respect to block fixed or non-functional during grinding operations and is provided 'essentially as a means for adjustment to zero in the machine to correct for manufacturing inaccuracies. Block 50 is normally pinned in place once the desired adjustment is made.
Workhead 28 is supported by leg 51 for angular movement about the horizontal X, axis, referred to as A rotation. For this purpose, the lower end of leg 51 is bored, as shown in FIG. 8, to receive pin 54. The pin has a tapered shoulder which in cooperation with an opposite taper on washer 55 adjoining clamp nut 55a connects the pin nonrotatably to leg 51. Pin 54 projects beyond leg 51 where it is received in bearings 57 which establish rotation of pivot pin 54 and the parts mounted thereon about the horizontal X, axis.
Bearings 57 are carried in the upwardly extending leg of an L-shaped bracket 58. The lower leg of bracket 58 extends horizontally and rests upon the top surface of base 59. Bracket 58 is provided on its under face with a depending rib 58a that fits snugly into a groove of corresponding size in base 59 to allow bracket 58, spindle 54, and the workhead to shift along the Y axis. This is referred to as the A rotation shift, and allows lateral shift of the X, machine axis for A rotation out of coincidence with the X axis to obtain a desired adjustment of the positionof the nose of the cutter with respect to the grindwheel. This shift is illustrated in FIG.4 and F IG.20 as a movement toward and away from the grindwheel.
Opposing set screws 59a are held in threaded holes in brackets 59b on base 59 to secure fine position adjustment and to lock bracket 58 and the X -axis pin or spindle 54 in the desired position. Added clamping is provided by machine screws 59c in threaded holes in base 59.
In the undersurface of base 59 is a recess with converging sidewalls that receives dovetail 600 which is a part of arm 60, in order to provide a sliding connection between the base 59 and arm 60. Movement of base 59 and parts supported thereby is rectilinear and horizontal, and is controlled by lead screw 61 having a threaded connection at lug 59d to bracket 58 and rotatably mounted in arm 60, the lead screw being manually rotated by thumb screw 63.
The sliding connection between base 59 and arm 60 provided by dovetail 60a primarily affords'controlled rectilinear movement of workhead. 28. Movement produced at this slide is along the X, axis whereby tool 26 can be transversed along the X, axis to accurately position the tool relative to the Y axis for grinding operations. This is the movement designated Y-axis offset in FIG.20..During any such traversing movement, workhead 28, blocks 48, 50, and leg 51, supporting it on angle bracket 58, move horizontally as a unit.
Angular movement of the workhead about the X axis relative to bracket 58 and arm 60 (rotation of leg 51- on spindle 54) is efiected by double-acting hydraulic cylinder 64 which is pivotally connected at 65 to leg 51 FIGS). A piston in cylinder 64 may be moved in either direction within the cylinder by admitting hydraulic fluid under pressure into a selected end of the cylinder. Attached to. the piston, not shown in the drawings, is piston rod 66, the outer end of which is pivotally connected at 67, as shown in FIG.3, to a fixed lug on the face of bracket 58. Since the lower end of