Title of Invention

A MACHINE FOR THE MANUFACTURE OF GLOBOIDAL CAMS

Abstract

A machine for the manufacture of globoidal cams which comprises a compound slide mounted movable oscillating cutter head being fixed to a spindle being provided with a rotating cutter, the said cutter being connected to a drive motor, the said spindle being provided with a central axis pinion with a rack , the slide arm of the said rack being provided with a roller follower in such a manner so as to engage on to the groove of a rotatable master cam , the said master cam being connected by means such as a timing belt-pulley to a gear box and a prime mover and work piece being held in between headstock and tailstock and machine being characterized in the provision of a simple rotating master cam , a slide arm mounted on roller follower attached with a rack, a pinion co-axially mounted on the cutter.

Full Text

The present invention relates to a machine for the manufacture of globoidal cams. Globoidal cam is a specially shaped cylindrical cam (A) in which the follower is in the form of a turret (B) with a number of rollers equally spaced on a pitch circle as shown in fig. 1 of the drawings accompanying this specification. Such a mechanism is a special case of a swinging follower mechanism. Each full input rotation of the globoidal cam (A) produces one index motion and one dwell (stop) of the turret wheel (B). The shape of the globoidal cam and the number of rollers on the turret may change depending on specific application. These mechanisms are widely used to achieve rotary or linear indexing motions for packaging machines, confectionery wrapping and packing machines, index filling machines, machine tools and transfer lines eic. The novel machine of the present invention will be useful in the manufacture of globoidal cams in milling and grinding of complicated earn profile, which is done at present on costly 5-axis CNC machine tools only. This is entirely a new machine and so far non-existent. The prior art search covering literature, patents and industrial survey reveals that no existing cam milling and grinding machines working on mechanical and hydraulic copying principle can be used for machining of globoidal cams. In all machine tools used for cam profile machining, the cutter and the cam blank or job are moved relative to each other in a prescribed pattern. This pattern can be produced by a master cam or by CNC or more rarely by a linkage or similar mechanism. A detailed description of the kinematics of the present machine tools used for machining cylinder cams is given in the following paragraphs. (Table Removed) The modes of cutter motion for machining cylinder cams are, therefore, either of the following a) Stationery b) Moves in x- or y-direction only c) Moves in x- and y- directions simultaneously Any of the above modes of operation of the existing machine tools used for cylindrical cam profile machining is not suitable for machining a globoidal cam because exact simulation of the path and orientation of the swinging follower roller of a globoidal cam is not achievable just by the coordinated x and y movements of the cutter spindle. The machining of globoidal cam profile essentially requires an angular or swinging movement of the cutter spindle about a fixed axis in addition to rotary movement of the work piece. In a 5-axis CNC milling machine the cutter spindle is continuously provided with required coordinates of movement x, y and 0 for correct positions and orientations at every instant of time with respect to the rotating work piece. However, this machine is costly and requires trained manpower for programming, operation and maintenance. From the above noted prior art details, it is found that there is no cam milling/grinding machine, other than 5-axis CNC milling machine existing anywhere in the world which can be used for profile machining of a globoidal cam. The main object of the present invention is to provide a dedicated machine for manufacture of globoidal cams. Another object of the present invention is to provide a simple and low cost manufacturing facility of globoidal cams. Yet another object of the present invention is to provide a substitute for a 5-axis CNC milling machine for the manufacture of globoidal cams. In the drawings accompanying this specification, fig. 2 shows the schematic view of the kinematic scheme of the machine of the present invention wherein the rotating cutter (28) is linked to the rotating workpiece (globoidal cam) (15) through a 1:1 timer belt pulley (13) drive, master cam (6), roller follower (7), slide arm (8), rack-pinion (5), spindle (4), work spindle (14) and carrier (16) in a manner so as to have an exact simulation of the dwell and indexing motion of the turret of an indexing head in the cutter movement with respect to workpiece rotation during machining. The centre distance between the central axis of spindle (4) to which the cutter head is fixed and the axis of the workpiece (15) is set equal to the specified centre distance of the indexing assembly wherein the machined globoidal cam is going to be used as a part. The workpiece (15) is held on a mandrel (26) between headstock (17) and tailstock (18). In the drawings accompanying this specification, figs 3a,3b,3c and 3d represent the front view, left side view, right side view and top view respectively of an embodiment of the novel machine. Fig. 3e represents a sectional view wherein the master cam (6), roller follower (7), slide (8) and the rack-pinion (5) are shown. The milling cutter (28) or the grinding wheel is mounted on a spindle head (1). The spindle is driven by an AC variable speed motor (2). The cutter-spindle-motor assembly fixed on a compound slide (3) is movable in two orthogonal directions in the vertical plane by means of graduated hand wheels (22,23) in order to set the cutter to required depth of cut for milling and grinding. The compound slide mounted cutter spindle assembly screwed onto the front end of spindle (4) can be swiveled about central axis of spindle (4) by rack pinion mechanism (5). The rack (5) and roller follower (7) are fixed on the slide arm (8). The swiveling motion of the cutter is achieved by rotating the master cam (6) which produces linear displacement of the roller follower, thereby of the slide arm (8) and the rack (5). The master cam (6) and the workpiece (15) are both driven from an AC variable speed motor (9) through gear box (10), helical gear (11), worm & worm gear (12) and timer belt-pulley (13). The workpiece (15) is held on a rotating mandrel (26) between head stock (17) and tailstock (18). The rotation of the work head spindle (14) is transferred to the workpiece (15) through a carrier (16). The clutch lever (29) is used to engage or disengage the rotation of master cam (6) with the that of the workpiece (15). The hand wheel (27) is provided in the headstock for manually tilling the cutter head to the required angle. The headstock and tailstock arc mounted on a table (19) which is again fixed to the knee (20). The knee can move up and down on the column guide way to adjust the centre distance between the axis of oscillating cutter head and the axis of the rotating workpiece. The knee is clamped in position by screws (21). All the electrical connections are conveniently located in pendent type control box (24) for the ease of operation. The cutter speed varies through a frequency changer and the speed is indicated on digital RPM meters (25). Accordingly, the present invention provides a machine for the manufacture of globoidal cams which comprises a compound slide (3,22,23) mounted movable oscillating cutter head (1), the said head fixed to swiveling spindle (4) being provided with a rotating cutter (28), the said cutter being connected to a drive motor (2), the said spindle (4) being provided with a central axis pinion (5) capable of meshing with a rack (5), the slide arm (8) of the said rack being provided with a roller follower (7) in such a manner so as to engage on to the groove of a rotatable master cam (6), the said master cam being connected by means such as a timing belt-pulley (13) to a gear box (10,11,12) and a prime mover (9), the said gear box and prime mover being also connected through a carrier (16) to workpiece (15) held on a rotatable mandrel (26) in between headstock (14,17,27,29)and tailstock (18), the said mandrel mounted workpiece being positioned in such a manner so as to enable the oscillating cutter to duplicate master cam profile, the said cutter master cam mechanism, job holding arrangement, gear box and prime movers being fixed on to a column and vertically movable knee (20,21) mounted table (19), the said prime movers/motors being connected to a control box (24) having rpm meter (25) and the said machine being characterized in the provision of a simple rotating master cam (6) , a slide arm (8) mounted on roller follower and attached with a rack, a pinion co-axially mounted with the axis of rotation of cutter head (28). The Special Purpose Machine (SPM) for the manufacture of Globoidal Cam operates usually in the following manner to manufacture a globoidal cam, through the process of milling and grinding. The master cam (6) may have any type of cam profile, such as, sine, modified sine, modified trapezoid, parabolic, simple harmonic, cycloidal, as per the requirement of the end product (15). The master cam profile has a simple shape which can be machined easily by any conventional cam machining method. With the help of the co-ordinated movements of the oscillating cutter and the rotating workpiece, it is possible to achieve the machining of the complicated shape of the globoidal cam. Initially, the milling head (1) is tilted to the extreme left position (with respect to the machine man) with the help of the hand wheel (27), the milling cutter (28) is kept clear from the work piece (15) which is held between headstock (17) and tailstock (18). The motor (2) is started and with the help of the graduated hand wheel (22), depth of cut is offered to the milling cutter (28). At this stage, motor (9) is started and the clutch lever (29) is applied to effect the master cam (6) to rotate. The same motor (9) also moves the work piece (15) through the carrier (16). The master-cam motion effects the oscillation of the milling head (1) to travel through the required depth of cut on the work piece to complete one cycle of operation when the milling head (1) reaches the extreme right position and stops, electrically, with the stoppage of the motor (9). Clutch lever (29) is disengaged and the milling head (1) is brought at the initial position (extreme left) through the hand wheel (27). Depth of cut is increased through the hand wheel (22) and the operation of cutting is repeated. After completing the cutting operation, grinding operation is taken up, exactly in the same manner as the cutting operation, only replacing the milling head with a grinding head provided with suitable grinding tool and offering the depth of cut with the graduated hand wheel (23). The machine of the present invention is novel as there is no cam milling/grinding machine as described and claimed in the present invention, existing anywhere in the world, which can be used for manufacture of globoidal cam by profile machining. The novelty of the machine of the present invention resides in the fact that a 5-axis CNC milling machine operation has been carried out by a two axis operation in the novel machine of the present invention. The non-obvious inventive step in the machine of the present invention is the use of a simple cam mechanism consisting of a conventional cylindrical cam and a translating roller follower to achieve the machining of most complicated three dimensionally variable cam geometry of a globoidal cam. The following example is given by way of illustration of the present invention and should not be construed to limit the scope of the present invention. Example 1 After developing the invented machine, few globoidal cams were manufactured on the same machine. One example goes like this. Material of the workpiece : 40Cr7A110Mo2, IS: 5517-1992 Length of the product: 85 mm Diameter of the product : 181 mm Nature of cam profile : Modified sine The milling cut was taken in twenty eight passes using HSS slot milling cutters of 16, 25, and 31.3 mm successively. It was possible to take maximum 4 mm depth of cut without any appreciable vibration of the machine. Total machining time for milling was about 6 hours and 30 minutes. Spindle rpm used for milling was 1200, 765 and 620 for cutter 16, 25 and 31 respectively. The cam surface was subsequently ground using a CBN grinding wheel of 30 mm. The spindle rpm used for grinding was 30,000 using a separate grinding head. Total machining time for grinding was 3 hours and 30 minutes approximately. The finished cam was used in the prototype of an indexing head tested for indexing accuracy. The performance was found satisfactory and within acceptable limits. The main advantages of the present invention are: 1. Dedicated machine for the special job of manufacturing globoidal cam. 2. Cost of manufacturing is less than that of CNC Machine 3. Simplicity of mechanism 4. Computer programming is not necessary. 5. Less skilled operator required than in a CNC Machine 6. Better maintainability and less downtime due to high reliability of mechanical components. We claim, 1 . A machine for the manufacture of globoidal cams which comprises a compound slide (3,22,23) mounted movable oscillating cutter head (1), the said head fixed to swivel ing spindle (4) being provided with a rotating cutter (28), the said cutter being connected to a drive motor (2), the said spindle (4) being provided with a central axis pinion (5) capable of meshing with a rack (5), the slide arm (8) of the said rack being provided with a roller follower (7) in such a manner so as to engage on to the groove of a rotatable master cam (6), the said master cam being connected by means such as a timing belt-pulley (13) to a gear box (10,11,12) and a prime mover (9), the said gear box and prime mover being also connected through a carrier (16) to workpiece (15) held on a rotatable mandrel (26) in between headstock (14,17,27,29)and tailstock (18), the said mandrel mounted workpiece being positioned in such a manner so as to enable the oscillating cutter to duplicate master cam profile, the said cutter master cam mechanism, job holding arrangement, gear box and prime movers being fixed on to a column and vertically movable knee (20,21) mounted table (19), the said prime movers/motors being connected to a control box (24) having rpm meter (25) and the said machine being characterized in the provision of a simple rotating master can slide arm (8) mounted on roller follower and attached with a rack, a pinion co-axially mounted with the axis of rotation of cutter head (28). 2. A machine for the manufacture of globoidal cams substantially as herein described with reference to figure 2,3a,3b,3c,3d & 3e of the drawings .

Documents:

1081-del-2000-abstract.pdf

1081-del-2000-claims.pdf

1081-del-2000-correspondence-others.pdf

1081-del-2000-correspondence-po.pdf

1081-del-2000-description (complete).pdf

1081-del-2000-drawings.pdf

1081-del-2000-form-1.pdf

1081-del-2000-form-19.pdf

1081-del-2000-form-2.pdf