US3293988A

US3293988A - Method and apparatus for broaching gears

Info

Publication number: US3293988A
Application number: US456697A
Authority: US
Inventors: Alfred B Strempel
Original assignee: GIANUINI CONTROLS CORP
Current assignee: GIANUINI CONTROLS Corp
Priority date: 1965-05-18
Filing date: 1965-05-18
Publication date: 1966-12-27
Anticipated expiration: 1983-12-27

Description

1966 A. B. STREMPEL 3,

METHOD AND APPARATUS FOR BROACHING GEARS Filed iylay 18, 1965 United States Patent O 3,293,983 METHQD AND APPARATUS EUR BRQAQHHNG GEAltEe Alfred B. Strernpel, Deep River, Conn., assignor to Giannini Controls Corporation, Duarte, Calif, a corporation of New York Filed May 18, 1965, Ser. No. 456,697 7 Claims. (Cl. 90-10) This invention has to do with improvements in conventional systems for producing gears wherein a gear blank is forcibly advanced through a series of distinct axially alined dies which progressively form gear teeth on the periphery of the blank.

The invention is particularly although not exclusively useful in connection with such broaching systems in which the gear blank is advanced by a pushing punch which accurately fits the final finishing or polishing die, thereby producing accurately formed teeth substantially free of burrs. The fundamentals of that method of operation and mechanism for carrying it out are fully described in the United States Patent 3,162,089, issued December 22, 1964, to Frank L. Riggio and me, as joint inventors, under the title Gear Broaching Apparatus.

One aspect of the present invention provides improved structure for the final die, and procedure for obtaining the desired very close fit of the pushing punch in the final die in systems of the type just described. In accordance with this aspect of the invention, the final die comprises a thin wall annular die insert with a conically tapered outer surface pressed into a die holder or die block with a matching tapered hole. During final fitting of the die to the pushing punch, the die can be pressed further into the die holder, thereby effectively shrinking the aperture in the die and reducing the dimensions of the die teeth in the circumferential direction. Also, as the die wears during use, it can be resized by forcing it further into the die holder, followed by relapping if needed.

We have found that such tapered form of a die assembly is effective only if the included angle of taper is within the critical range between about 3 and about the range between 4 and 8 being preferred.

A further aspect of the present invention is concerned more particularly with improved mechanism for broaching or shaving gears accurately and rapidly with minimum diificulty in clearing the chips from the working dies. A common difiiculty in forming parts by breaching or shaving results when one die cuts all the way around the blank, thus forming a ring of cut material. Such rings tend to plug up the chip space between the dies, and occupy an abnormal amount of space in the chip strainer.

The present invention avoids such difiiculties from ring formation without requiring any increase in the number of dies or otherwise reducing the efficiency and convenience with which the desired gear form is produced.

In the production of gears of high quality it is desirable that the initial blank have a diameter greater than the outside diameter of the finished gear, so that material is removed all around the blank during the breaching or shaving process. Only in that way can the concentricity of the finished gear be defined entirely during the broaching process and thus be independent of possible eccentricity of the blank.

In forming the channels between the gear teeth, the greatest depth of material that must be removed is at the roots of the teeth. It is desirable that all the cutting dies share significantly and preferably approximately uniformly in attaining that total depth of cut, so that both the number of dies and the maximum depth of cut by any one die may be as small as possible.

The present invention provides such substantial uni- 3293,93 Fatented Dec. 27, 1966 formly of cut by the several successive dies as well as accurate formation of the tops of the teeth, while avoiding any tendency toward the formation of chips of ring form.

That is accomplished by designing the first die and a subsequent cutting die to produce coordinated cutting action of specialized type. The first cutting die, which initiates formation of the channels between the gear teeth, is designed to clear the periphery of the blank at the points where the tops of the teeth will later be formed. A subsequent die then forms the tops of the teeth and also deepens the channels between the teeth. However, that die, which is preferably the second one and will be so denoted for clarity of description, clears the work at the sides of the previously cut channel. The dead spots produced by that clearance separate the two areas of cut at the tops of the gear teeth and at the bottoms of the channels, positively preventing the formation of rings.

The third and subsequent cutting dies then further deepen the channels between the teeth until the full desired depth to the roots of the rough-cut teeth is attained. The number ofcutting dies will depend upon the size and form of the gear and-to some extent upon the material to be used. For relatively small and fine gears, such as are used in gear trains in timing mechanisms and the like, a total of four cutting dies ahead of the finishing die is generally suitable. For larger gears, as many as eight or ten cutting dies may be used.

In preferred form of the invention, each of the cutting dies except the first conforms accurately to the final tooth forms at the tops of the gear teeth. Hence, when the pushing punch is designed, as described in the above in the above identified patent, to fit accurately in the finishing die, it will be also fit all of the cutting dies except the first at the roots of the cutting teeth, and will therefore be accurately centered throughout its stroke and guided cleanly ino the finishing die.

It is preferred, further, that the sides of the teeth of each cutting die except the second conform essentially to the final tooth form except for a small uniform clearance which is removed by the final or finishing die. All of the cutting dies can then be broached with the same tools and can be finished with the same lap or laps, as will be more fully described.

It may be noted that the problem of ring formation does not arise when the tops of the gear teeth are not formed during the breaching or shaving process but coincide with the periphery of the initial blank, as shown, for example, in FIG. 8 of Patent 2,461,320 to Lee B. Green. As already indicated, optimum concentricity of the finished gear requires that all parts of the teeth be machined with reference to the same centering operation. Nor does the problem of ring formation arise in its present form when the initial blank is preformed with a scalloped edge approximating the desired gear teeth, as shown, for example, in Patent 2,237,959 to William L. Hansen et al. The latter system entails unacceptable expense, since it requires in addition to preforming the scalloped blank, that the blank be correctly positioned for shaving both as to rotation and as to centering.

In accordance with a further aspect of the invention, the described clearance between the second (or later) die and the sides of the previously cut channels in the blank is produced in a particularly convenient and accurate manner during the lapping of that die. Great economy is obtained by initially breaching all the cutting dies to the same tooth form, with the die teeth initially extending the full distance to the roots of the gear teeth to be formed. The sides and roots of the cutting teeth of the third and subsequent dies are then lapped to the same tooth form in a manner that may be essentially conventional. After such lapping to the desired common tooth form, the tops of the die teeth are ground off to give the desired progressive variation in their respective inner diameters to determine the relative depth of cut for each of the dies. In lapping the second die the width of the cutting teeth reduced by applying a yielding torsion, first in one direction and then in the other, to the lap. The described clearance between the sides of the cutting teeth and the work is thereby obtained without requiring a special lap.

The same procedure of applying torsion to the lap may also be utilized for finishing other working parts of the present gear shaving apparatus, particularly for lapping the final die to fit the pushing punch as precisely as possible.

A full understanding of the invention and of its further objects and advantages will be had from the following description of certain illustrative manners in which it may be carried out. The particulars of that description, and of the accompanying drawings which form a part of it, are intended only as illustration and not as a limitation upon the scope of the invention, which is defined in the appended claims.

In the drawings:

FIG. 1 is a vertical axial section representing the primary working parts of an illustrative gear shaving machine in accordance with the invention;

FIG. 2 is a side elevation, partly cut away, representing a final die insert in accordance with the invention;

FIG. 3 is a section on the line 33 of FIG. 1 at greatly enlarged scale;

FIG. 4 is a schematic side elevation representing a lapping machine in accordance with the invention; and

FIG. 5 is a fragmentary plan corresponding to FIG. 4.

FIG. 1 shows the primary working elements of an illustrative apparatus for shaving gears in accordance with the present invention. The pushing punch and the shedder punch 30 are mounted for movement in a coordinated manner along the axis 18, as by hydraulic cylinders, not explicitly shown, which are coupled to the outer ends of the punches in any suitably manner. Pushing punch 20 typically comprises a smooth cylindrical shank section 21, guided in the bearing block 22 which may be provided with a bushing 23, and a hobbed working section 24 which conforms accurately to the shape of the finished gear and is guided in the fitting punch guide 25 and also in the dies to be described. Shedder punch is typically of generally similar form, with the cylindrical shank section 31, working in the bearing block 32 with bushing 33, and the hobbed working section 34 conforming at least approximately to the finished gear and guided by punch guide 35. The bearing blocks and punch guides, as well as the dies and other members to be described, are fixedly mounted in coaxial alinement in any suitable manner, for example within a rigid rectangular frame or box, not explicitly shown, within which they fit closely. Such parts may be axially spaced from each other by spacing blocks such as 26 and 36. Further details of typical mounting and operating mechanism will be found in our prior patent, identified above.

The working dies are coaxially mounted between

punch guides

25 and 35, together With spacing plates which may perform additional functions. In the present embodiment, four successive cutting dies are shown at 40, distinguished by the numerals A, B, C and D. The single finishing die is shown at 50. Adjacent dies are mutually spaced by the spacing plates 42 of inverted U-form. Vertical channels 44 in the upper portions of the spacing plates form coolant nozzles for directing oil downward to cool the dies and carry off chips through the passages formed between the vertical legs of the spacing plates. Oil under pressure is supplied to passages 44 during the working stroke of the machine via the conduit 52 and distributing chamber 54.

Work blanks 60 are fed to the machine through a vertical feed track 64, the lower part of which is formed by a channel 65 in punch guide 25 and front face of the transfer hole plate 66. The latter plate also serves to space the first die 40A from the feed track and from punch guide 25, and is channeled on its rearward face to form a chip clearing passage 67 and oil nozzle 68 for clearing chips from the front face of the first die. Detailed construction and operation of the mechanism for feeding and positioning the blanks may be conventional and need not be described here. A channel 63 in punch guide 25 permits visual checking of the blank positions, especially during set-up.

For clarity of illustration, both

punches

20 and 30 are shown in FIG. 1 in their fully retracted positions. In typical operation of the machine, shedder punch 30 moves to the right, as seen in FIG. 1, and the tapered pilot pin 38 projecting coaxially from its working face 39 picks up the central aperture 61 of a blank 60 in track 64. Pusher punch 20 advances to the left until its working face 29 engages the blank, pressing it firmly onto the pilot pin 38, which is received in the fitting bore 29 in the pusher punch. The blank is thereby held essentially rigidly between the two mutually alined punches in accurately centered position with respect to the blank aperture.

The work stroke is effected by essentially positive forward movement of pusher punch 20, to the left as seen in FIG. 1, against a yielding force maintained by shedder punch 30. The blank is thereby moved smoothly through the successive die apertures. Cutting edges at the peripheries of those apertures progressively form gear teeth on the blank periphery. The cutting dies 40 shave the gear to within a few thousandths of an inch of the desired form, and the remainder is shaved off as the gear passes through the final or finish die 50. About one to two thousandths is typically left on the sides of the gear teeth to be removed by the final die, about two to four thousandths at the roots of the teeth, and essentially zero at the tops of the teeth.

After passing through the finish die, the forward movement of the gear is checked by two depending arms 72 of the stripper plate 70, which also serves as spacer between the final die and shedder punch guide 35. The stripper arms are laterally spaced by less than the diameter of the gear, and clearance for them is provided by flatted side areas of the shedder punch, indicated at 73. The shedder punch is then retracted to the position shown, withdrawing pin 38 from the gear aperture, and the pusher punch is withdrawn to the position shown, ready for another cycle of operation. The finished gear is thereby released, and may be swept downward to a storage bin by a blast of oil from the conduit 74 and the nozzle 75. That method of delivering the finished gear is merely illustrative, and may be considered an alternative to the delivery system described in my above identified patent.

In accordance with one aspect of the present invention, finishing die comprises the die element 76 of relatively thin annular or sleeve form, mounted in the die holder or block 78, which has the same outside dimensions as cutting dies 4-9. Die insert 76 is provided with die teeth 77 on its inner face, and its outer surface 79 is conically tapered and is received in a matching tapered hole in the die block. That die structure facilitates production of finishing die teeth 77 that fit the external flutes on pusher punch 25 with maximum practicable precision, not only along the sides of the respective teeth but also at the tops and roots of the teeth. Such fit insures clean gear surfaces, smooth and accurate over the entire thickness of the stock.

FIG. 2 shows an illustrative finishing die insert element 76. The included conical angle 6' of external mounting surface 79 is somewhat exaggerated for clarity of illustration. The wall thickness of insert 76 is selected, with regard to the material and conical angle, so that the insert can be pressed into the conical hole in the die holder to shrink the die without requiring excessive force and without expanding the die holder. For an insert of tool steel the wall thickness is typically about 0.025 inch at the smaller end of the die, measured from the root of the teeth in the die to the outside surface '79. The conical angle must be small enough to prevent the die insert from popping out of the die holder, and at the same time must be large enough to keep the insert from being pressed further into the die holder by the resistance of the shaving process while the tools are working. We have found that both of those conditions can be met effectively if the included angle 0 is within the range between about 3 and about The range between about 4 and about 8 is preferred, and the value of 6 is particularly convenient, since it produces a ratio of 10 to 1 between the axial distance the insert is pressed into the holder and the resulting reduction of the die diameter.

The outer dimensions of the die element are initially made large enough, as indicated at 100, to provide an effectively rigid unit during breaching or other rough forming of the internal die teeth 77. That excess material is then removed and the die element is pressed lightly into its mounting block 78, ready for lapping. Initial lapping is done from the back of the die with a lap having a slight taper, typically about 0.003 inch in the 4 inches of its length. The outer diameter of the die aperture is preferably first brought to a value that exceeds that of the pushing punch by one or two thousands of an inch, while the die teeth are still wide enough to prevent free entrance of the pushing punch. As soon as that punch will go in without producing a press fit, the punch and die are ready to be lapped together. The punch is worked in the die in as many places as there are teeth on the punch, using very fine diamond lapping compound. After the punch is free in all places, the die is removed from the lapping machine and the die insert is pressed one or two thousands of an inch farther into the die holder. This shrinks the diameter of the die, bringing the die teeth slightly closer together. The die and punch are then lapped again. This is repeated until the clearance on the top of the teeth is gone, preferably leading to a fit on the entire periphery of the teeth within 0.0001 or 0.0002. The surfaces of the final die assembly are then preferably ground to remove any part of the insert that protrudes beyond the surface on either side of the die holder and to aline the edge faces of the holder with the die aperture.

FIG. 3 shows preferred illustrative shapes of the respective cutting edges of the several cutting dies in accordance with a further aspect of the present invention. The figure may be considered a view looking in the direction of the working stroke of the machine from a point just ahead of the first cutting die 453A. The view is greatly enlarged and shows one tooth of each die in full and a portion of the adjacent tooth. Those die teeth are denoted by the numeral $0 followed by letters to indicate the respective dies. The sides of the respective die teeth are denoted by the numeral 82 and the roots of the teeth by the numeral 84, with similar letters to distinguish the different dies. The letter E refers to finishing die 50 with teeth 77. It will be noted that the sides 82 of some of the successive die teeth are partially superposed, and also the root surfaces 84, or the bottoms of the channels between the die teeth, are mainly superposed. The tops of the cutting die teeth are indicated at 86 with distinguishing letters, and are all spaced radially from each other by distances that are approximately, although not exactly, equal.

The actual removal of material from the blank is done primarily by the edges 86 at the tops of the cutting teeth. Those edges are typically circular about axis 13. For clarity of illustration, the areas of blank 60 that are removed by the respective cutting dies are shaded in dotdash lines, which are not to be confused with conventional shading to denote a section through an element. It will be seen that the primary cutting is shared approximately equally between all of the cutting dies. Thus, for any given number of dies, the depth of cut of each die can be held to a minimum.

The form of the final gear is determined by that of finishing die 50, shown in FIG. 3 with root edges at 84E corresponding to the tops of the gear teeth, side edges 82E corresponding to the sides of the gear teeth, and tops 85E corresponding to the gear teeth roots. The outer gear diameter, at MB, is spaced inside the initial periphery of the blanks d0 by a distance indicated at fit}. In accordance with one aspect of the present invention, that periphery is first cut back toward 84E by the second cutting die rather than by the first; and the root edges of the second and all subsequent dies, preferably including also the finishing die, have their root edges at the same diameter. The first cutitng die, on the other hand, has a root edge at 84A, spaced outside of the blank periphery by an appreciable clearance distance indicated at 92 in FIG. 2. That clearance 92 insures that the first cutting die cannot produce a chip of ring form. The areas 91 cut by its respective teeth 80A are positively separated circumferentially by the regions 93 that are left undisturbed.

The regions 93 of the blank are removed by the second die, with root edge at 84B. Also, the teeth 80B of the second die deepen the channels between the gear teeth, which were started by the teeth 80A of the first die. In order to permit the second die to accomplish both of those cuts without formation of rings, die teeth 80B are narrower than the teeth of all the other dies, having side edges at 82B that are set back by a distance indicated at 94 from the common line of the tooth sides of the other cutting dies. That clearance 94 positively produces dead spots in the cutting action of the second die at both sides of every tooth, indicated at 95. Hence the chips are kept small. Those chips are of two types, corresponding to the areas 93 between the initial blank periphery and the tops of the gear teeth as finally formed; and the areas 95 which deepen the channels 91 already cut by the first die between the gear teeth. That deepening action extends almost the full width of the channels, and contributes significantly toward the total work of gear formation.

A further aspect of the invention provides a convenient and effective method of producing a set of dies and cooperating elements having the described characteristics. In making the dies and punch guides, a pilot hole is first formed and is then shaped approximately to the desired form and size, typically by broaching or by electrical discharge machining. After suitable heat treatment, which norm-ally precedes such machining or follows breaching, the dies are lapped to proper size and tooth form by a special lapping process. A brass lap of the order of four inches long is bobbed with about two to three thousandths of an inch taper, and with the pilot end of the lap just small enough to enter the die that is to 'be lapped. All dies are lapped from the back side, thereby creating a slight taper from the back. The punch guides are lapped alternately from both sides, producing a slight bell-mouthed condition.

An illustrative lapping machine is shown somewhat schematically in FIGS. 4 and 5. The spindle 104 carries the lap 106 by means of a chuck of any suitable type and is freely rotatably mounted in the quill 108 in axially defined position. Quill 108 is vertically movable in the machine frame 110 by means of a rack and pinion, as by the manual handle 109, much in the manner of a drill press quill. Automatic mechanism is preferably provided for reciprocating the quill, with such factors as speed of lap travel, power and length of stroke all adjustable. Such mechanism may employ, for example, a double-acting pneumatic cylinder with a four-way valve control and variable pressure air supply. Such a cylinder may be consideredto be incorporated in quill 103 of FIG. 4, moving the spindle up and down relative to the quill and thus supplementing the action obtainable with handle 109. The die 112 to be lapped in held down on the horizontal table 114 by a releasable clamp 116 which facilitates accurate placement of the die and permits its rotation to receive the lap in different positions.

A wet diamond compound of suitable grade is used for lapping. As the die material is worn away, the lap is fed down deeper into the die by the handle 109 until the part of the lap that is the right diameter has entered the die or punch guide. The lap is frequently withdrawn from the die, rotated a tooth or two and re-entered to insure uniformity of all teeth.

In accordance with the preferred procedure of the present invention, such lapping is carried out initially by a lap having teeth somewhat thinner than corresponds to the desired tooth form of the die or punch guide until the work has been brought to the proper outer or rootdiameter. The sides of the teeth are then further lapped without enlarging the outer diameter of the work. That is accomplished by applying a light yielding torque to the lap as it is reciprooated in the work. Such torque may conveniently be applied by mounting a torque arm 120 on the upper end of quill 108 above the machine frame, preferably by means of a friction clutch structure that permits convenient manual adjustment of the orientation of the arm but holds it effectively locked in the set orientation. A shorter spindle .arm 122 is fixedly mounted on the upper end of the spindle. A tension spring 124 is mounted between the end of spindle arm 122 and a suitable bracket at a larger radius on torque arm 120, thereby tending to rotate the spindle into position with thetwo arms alined. Since rotation of the lap is prevented by its engagement in the teeth of the work, a yielding torque may be applied between the lap and the work in either direction and of conveniently variable magnitude by rotating the torque arm to a sutaible angle with respect to the spindle arm. Such torque applies pressure to one side of the teeth all the way around the work. The direction of torque and the position of the lap in the work are altered frequently to obtain symmetry and uniformity of tooth form.

Progress of the lapping of a die or punch guide can be conveniently checked by using the completed pushing punch as a plug gage. Use of that punch as the final lap in fitting the insert of the final die has already been described. In finishing the cutting die, the desired tooth form, as already pointed out in connection with FIG. 3, is suchthat the roots 84 of the die teeth fit the tops of the teeth on the pusher punch accurately, and that the sides 82 of the die teeth and the tops 86D of the teeth of the last cutting die clear the corresponding surfaces of the pusher punch by a small amount, typically one or two thousandths of an inch, which will be removed by the final die. That clearance is checked during lapping of the cutting dies by inserting the punch in the die and measuring the rotary play in any suitable manner.

In preparing a set of cutting dies, they are preferably all rough cut to the same tooth form. The teeth of the first cutting die are first ground oil to produce the concentric cutting edges indicated at 86A in FIG. 3, and that die is then lapped to deepen the channels between the teeth to the outer diameter indicated at 84A, spaced outside the periphery of the gear blank 60, and to shape the sides of the teeth as at 82A.

All the cutting dies other than the first are preferably lapped before grinding. That lapping first brings the outer diameter to the common surface shown at 84B, C and D in FIG. 3 by use of a lap with suitably thin teeth. The sides of the teeth are then shaped to provide the desired clearance. The sides of the teeth of the second die are lapped back further than the others by one or two thousandths to provide the clearance 94 to avoid chips of ring form as already discussed. That latter lapping, and preferably also the shaping of the sides of the teeth of the other cutting dies, is accomplished by torsion lapping, which permits modification of the sides of the teeth without disturbing the root diameter that has already been established. Finally, after completion of the described lapping, the teeth of the cutting dies other than the first are ground back to the desired stepped radii, shown typically at 868, C and D in FIG. 3.

The described procedure is thus capable of producing a set of dies which work effectively together to shave a gear with maximum efficiency and precision. Each die shares significantly and approximately equally in the work of removing material from the gear blank, and with positive avoidance of ring chips. Moreover, the accurate uniformity of root diameter among all the cutting dies except the first insures precise centering of the pushing punch and the work as they move through the series of cutting dies and enter the final die.

I claim: 1. A machine for broaching a circular blank to form a gear, said machine comprising in combination a series of ordered, axially alined, apertured dies with cutting edges at the peripheries of the apertures,

means for axially moving a blank successively through the apertures of the respective dies to progressively form gear teeth at the blank periphery to produce a gear, the initial diameter of the blank exceeding the outer diameter of the formed gear, the first die having circumferentially spaced cutting teeth adapted to cut channels of predetermined width in the periphery of the blank between the gear teeth, and having an aperture diameter between said cutting teeth that exceeds said initial diameter of the blank, and the second die having an aperture that clears the sides of said channels in the blank and having first cutting edges adapted to deepen said blank channels and second cutting edges adapted to form the tops of the gear teeth to substantially their final shapes. 2. A machine for broaching a circular blank to form a gear, said machine comprising in combination a series of ordered, axially alined, apertured dies with cutting edges at the peripheries of the apertures,

means for axially moving a blank successively through the apertures of the respective dies to progressively form gear teeth at the blank periphery to produce a gear, the initial diameter of the blank exceeding the outer diameter of the formed gear,

the first die having circumferentially spaced cutting teeth adapted to cut channels of predetermined width in the periphery of the blank between the gear teeth, and having an aperture diameter between said cutting teeth that exceeds said initial diameter of the blank, and a subsequent die having cutting edges adapted to form the tops of the gear teeth and to clear at least a portion of the boundary of each said blank channel.

3. A machine for broaching a circular blank to form a gear, said machine comprising in combination a series of ordered, axially alined, apertured dies with cutting edges at the peripheries of the apertures, an axially alined punch having a transverse working face that accurately fits the aperture of the final die,

means for supporting in axial alinement upon the working face of the punch a circular blank having an initial diameter that exceeds the outer diameter of the aperture in the final die,

means for moving the punch in a forward working stroke to advance the working face and the blank successively through the dies other than the final die and at least into the final die to progressively form gear teeth at the blank periphery to form a gear, the first die having circumferentially spaced cutting teeth adapted to cut channels of predetermined width in the periphery of the blank between the gear teeth and having an aperture diameter between said cutting teeth that exceeds said initial diameter of the blank, the second die having first cutting edges adapted to deepen said blank channels and second cutting edges adapted to form the tops of the gear teeth to substantially their final shapes, said first and second cutting edges being mutually spaced by portions of the aperture periphery that clear the sides of said channels formed by the first die,

the dies after the second die having circumferentially spaced teeth separated by guide surfaces that positively guide the punch in its movement toward the final die.

4. A machine for broaching a circular blank to form a gear, said machine comprising in combination a series of ordered, axially alined, apertured dies with cutting edges at the peripheries of the apertures,

an axially alined punch having a transverse working face that accurately fits the aperture of the final die,

means for moving the punch in a forward working stroke to advance the working face and the blank successively through the dies other than the final dies and at least into the final die to progressively form gear teeth at the blank periphery to form a gear,

said final die comprising an annular die element having die teeth on its inner periphery and having a conically tapered outer periphery, and a conically apertured support in which the die element is mounted,

the included conical angle of the die element outer periphery and of the support aperture having a common value such that friction between the support and the mounted die element prevents relative forward movement of the die element during said working stroke of the punch and blank and also prevents relative rearward movement of the die element in absence of said working stroke.

5. A machine as defined in claim 4, and wherein said conical angles have values that are substantially equal and are between about four and about eight degrees.

6. A machine as defined in claim 4, and wherein the common value of said conical angles is approximately six degrees.

7. A die having an aperture in the shape of a desired gear periphery and accurately fitting a punch, said die comprising an annular die element having die teeth on its inner periphery and having a conically tapered outer periphery,

and a conically apertured support in which the die element is coaXially mounted,

References Cited by the Examiner UNITED STATES PATENTS 2,392,747 1/ 1946 La Pointe -63 3,022,710 2/1962 Kopec 2995 .1 3,057,264 10/ 1962 Musser 90-63 3,080,776 3/ 1963 Muenchinger 76107 3,111,865 11/1963 Wildhaber 76101 3,194,090 7/1965 Becker 76-107 WILLIAM W. DYER, JR., Primary Examiner.

G. A. DOST, Assistant Examiner,

Claims

1. A MACHINE FOR BROACHING A CIRCULAR BLANK TO FORM A GEAR, SAID MACHINE COMPRISING IN COMBINATION A SERIES OF ORDERED, AXIALLY ALINED, APERTURED DIES WITH CUTTING EDGES AT THE PERIPHERIES OF THE APERTURES, MEANS FOR AXIALLY MOVING A BLANK SUCCESSIVELY THROUGH THE APERTURES OF THE RESPECTIVE DIES TO PROGRESSIVELY FORM GEAR TEETH AT THE BLANK PERIPHERY TO PRODUCE A GEAR, THE INITIAL DIAMETER OF THE BLANK EXCEEDING THE OUTER DIAMETER OF THE FORMED GEAR, THE FIRST DIE HAVING CIRCUMFERENTIALLY SPACED CUTTING TEETH ADAPTED TO CUT CHANNELS OF PREDETERMINED WIDTH IN THE PERIPHERY OF THE BLANK BETWEEN THE GEAR TEETH, AND HAVING AN APERTURE DIAMETER BETWEEN SAID CUTTING TEETH THAT EXCEEDS SAID INITIAL DIAMETER OF THE BLANK, AND THE SECOND DIE HAVING AN APERTURE THAT CLEARS THE SIDES OF SAID CHANNELS IN THE BLANK AND HAVING FIRST CUTTING EDGES ADAPTED TO DEEPEN SAID BLANK CHANNELS AND SECOND CUTTING EDGES ADAPTED TO FORM THE TOPS OF THE GEAR TEETH TO SUBSTANTIALLY THEIR FINAL SHAPES.