US2151776A - Method and apparatus for forming metal screw blanks - Google Patents

Description

March 28, 1939.

H. KOESTER 2,151,776

METHOD AND APPARATUS FCR FORMING METAL SCREW BLANKS r--- 58 1 5 7 l I 32* l 31 5:;- .96

| E 24 I v I Filed Jan. 31, 1938 J= 3 w J 1 l .97 l 35 23 36 I t 36 2.9. l I 34 1 30. I l A INVENTOR. HERMAN K055 TERI ATTORNEY.

Patented-Mar. 23, 1939 METHOD AND APPARATUS FOR FORMING, METAL SCREW BLANKS Herman Koester, Waterbury, Conn., assignor to The Bristol Company, Waterbury, Conn., a corporation of Connecticut Application January 31, 1938, Serial No. 187,784

9 Claims.

a solid cylindrical blank of metal with an enlargement at one end, forming a socket in the enlargedend, and forcing the blank by an angular or noncircular punch through a die opening that is smaller in diameter than the enlarged end of the blank, thereby drawing the metal of that portion onto the punch and causing the interior contour of the socket to conform to the exterior contour of the punch. Such a method is set forth in U. S. Letters Patent No. 960,244, issued to W. G. Allen, June 7, 1910. From a study of the principles-involved, it will be apparent that in this method the operation by which the socket is caused to assume its final form is in the nature of a drawing action, whereby, during the forming process, the fibres of tne metal are in a state of tension, with a resultant tendency to inherent weakness of the finished product at a point where, under conditions of use, it is likely to be submitted to relatively great stresses.

Another process involves theuse of a noncircular punch which enters the original socket in the blank, the tip of the punch engaging the bottom of the socket and forcing the metal into a cylindrical mold with a generally radial flow,

7 the walls of the mold serving to restrict the flow until it closes in upon the punch. In this process,

as in the former, the final conformation of the blank is effected by force applied to the metal by the tip of the punch, from which action is inseparable a certain splitting, shearing, or drawing tendency, by which the fibres of the metal are placed in a state of tension.

It is an object of this invention to provide a method and apparatus for forming screw blanks of the nature set forth, in which the final forming operation, including the conformation of the interior of the socket to the desired contour,

from blanks formed according to this process,

when tested under controlled conditions, show a resistance to breaking as much as fifteen percent higher than similar screws made from blanks of the same material formed by different methods.

It is proposed to accomplish the desired result by providing for use on a heading machine of the conventional type a forming member embodying two distinct sections-a longitudinally yielding mandrel adapted to enter a previously formed recess in a blank, and having its contour formed to the desired cross-section of the socket, and an annular portion surrounding said mandrel and having a substantially fiat face smaller in diameter than the previously enlarged portion of the blank, and adapted to engage the same, extruding it solely by compression through a die aperture of substantially the same diameter as that of the annular portion of the forming member.

The nature of the invention, however, will best be understood when described in connection with the accompanying drawing, in which:

Fig. 1 is a side elevation of a blank of uniform diameter, as cut from suitable bar or wire stock.

Fig. 2 is a side elevation, partially in section, showing the first step in the upsetting or heading process.

Fig. 3 is a similar view, showing the second step in the heading process.

Fig. 4 is a similar view showing the initial step in forming the socket.

Fig. 5 is a side elevation, partially in section, of the combined extrusion member and mandrel, and of the die through which the blank is finally extruded, showing said. parts of the mechanism in the position of initial engagement with the blank.

Fig. 6 is a similar view showing the flat-faced extrusion member and enclosed mandrel in engagement with the blank and having forced it part way through the die.

Fig. '7 is a similar view of the engaging parts of the punch, mandrel and die, showing said parts in the position of final engagement with the blank after extrusion through the die.

Referring to the drawing, a blank l0, Fig. 1, of suitable length and uniform cylindrical crosssection is first cut off from rod or wire stock. This blank is next upset to form a head thereon, which action is effected in two upsetting operations, bringing the blank successively into the forms shown in Fig. 2 and Fig. 3. While this part of the process presents no particular novelty, and for it no invention is claimed, yet, in order that there may be had a clear understanding of the whole process of forming the screw blank, it is outlined briefly as follows:

The blank I0 is inserted in a lower die ll above a conventional knock-out pin l2 closely fitting an axial aperture l3 of the same diameter as that of the blank [0. (It will be understood that in this description the terms upper, lower, etc., are purely relative, and that the process may be carried out as effectively in a machine having horizontally disposed die parts as in one wherein those elements are vertically disposed.) The upper end of the-blank in this position projects through a die cavity l4 formed in the upper face of the die ll coaxial with the aperture l3 and having its outer surface I5 conformed to a truncated cone and its bottom surface 16 departing slightly from a true fiat into a. conical conformation rising toward the center, and forming in the contour line of the section of the die an acute angle with the cylindrical surface of the aperture [3.

Cooperating -with the lower die H is an upper movable die l1 having in its workingface a tapered aperture l8 adapted to receive the projecting end of the blank before and during the initial upsetting step. Thus, when the die I1 is brought down upon the die H with sufficient force, there will be formed upon the blank a relatively wide-bottomed upset portion l9, projecting slightly over the conical surface l6, but not completely filling the cavity Hi, the whole blank now having the form shown at Ina.

After the blank has been shaped as described, it is next shaped into the form shown at lllb, Fig. 3, this being effected by the die ll, carrying the partially upset blank, being brought into operative relationship with a die 20 having in its working face a recess 2| in the form of a shallow truncated cone of maximum diameter substantially the same as that of the recess I4 in the die ll. When the dies 20 and II are brought together, the upset portion I9 on the blank Illa will be caused to fill completely the recesses l4 and 2|, resulting in the formation on the blank of a head having a contour as indicated in Fig. 3, and adapted for the initial step in forming the socket.

After having been shaped to the conformation shown at lllb in Fig. 3, the blank may, if desired, be annealed, it then being transferred to a die 22 as shown in Fig. 4. The die 22 is similar to the die H, but the cavity therein is made slightly deeper than the cavity M by the addition of a short cylindrical portion asat 23, to accommodate the axial flow of metal attending the punching of the recess later to be developed into a socket. A punch member 24, having a cylindrical tip portion, preferably with a rounded end, is then brought into engagement with the fiattened top of the blank, and forced thereinto to a distance predetermined by adjustment, thus forming a recess 25 of a depth less than the desired ultimate depth of the socket, and of a diameter substantially equal to the maximum desired diameter of the finished socket. In this step of the process, the fiow of metal in the direction of punching being prevented by the presence of a knock-out pin 26, and lateral flow by the walls of the die cavity, the metal has no alternative but to flow backwards along the punch in a generally axial sense, filling the short cylindrical space 23, resulting in a recessed blank as shown at 100, having a head portion of axial length slightly greater than that of the head before recessing. The flow of the metal solely in a direction longitudinal of, and in opposition to, the movement of the punch has been found to produce a molecular condition which results in a blank better suited to formation by, and producing a stronger ultimate product after, the extrusion process now to be set forth, than is obtainable in blanks having a recess punched with restriction as to the outward radial flow of the metal.

The final forming of the blank is effected by a combination of forming tools shown in detail in Fig. 5. These comprise a die member 21 having formed therein an aperture with a smoothly tapered entrance portion 28 of maximum diameter somewhat greater than the minimum diameter of the lower part of the conical head on the blank I00, and a cylindrical portion 29 of diameter equal to the desired final diameter of the head portion of the completed blank. Beneath the cylindrical portion 29 is a cylindrical portion 30 of slightly greater diameter than that of portion 29, relieved to permit free passage of the completed blank.

A forming tool 3!, adapted to coact with the die 21 in finally forming the blank, is made up of two main portions, both adapted to engage the material of the blank during the forming process, but in such a manner as to segregate the nature of stresses exerted between these members and the blank, the stress in the one member being wholly axial, and in the other wholly radial. To

' this end, the tool comprises a housing portion 32 which terminates in an extended annular extruding member 33 having an outside diameter substantially the same as that desired for the head of the finished blank, and adapted to pass through the aperture portion 29 in the die 21.

Its inside diameter is substantially equal to the maximum desired diameter of the final form of the socket to be formed in the blank.

Within the housing portion 32, extending through the annular member 33 and free for limitedlongitudinal movement therein, is an extended mandrel member 34 having a tip portion 35 which is provided with grooves or flutes 35, or is otherwise conformed to the contour and dimensions of the non-circular socket which it is desired to form in the blank. This mandrel terminates in a head portion 36 positioned inwardly of the housing portion 32, and is movable in a cylindrical chamber 31 formed in the body thereof. A compression spring 38, contained within the chamber 31, tends to maintain the mandrel member 34 in a position where tip portion 35 projects its maximum distance out of the annular extruding member 33, and to an extent not less than the maximum depth required for the finished socket.

In the forming process, the blank I00, after again annealing if desired, is first positioned by a releasing grip (not shown in the drawing) in the path of the tool 3|, which is then brought a into engagement with the blank, carrying it into the die 21, as shown in Fig. 5. The strength of the spring 38 is sufficient to assure positive seating of the tip of the mandrel 34 in the recess previously formed in the blank, but not to exert appreciable extruding force upon the blank as the latter enters the tapered aperture portion 28 of the die 21. Consequently, as the headed portion of the blank is definitely engaged by the tapered walls of the aperture portion 28, both the blank and the mandrel member are momentarily brought to rest, the spring 38 yielding as the housing portion 32 and the extruding member 33 continue to advance toward the die 21.

As the annular flat faced extruding member 33 engages the flattened top portion of the blank, the latter is forced more deeply into the tapered aperture portion 28, the first wedging action on the sides of the head causing. its metal to flow in such a manner that the walls of the recess grip the tip portion 35 of the mandrel 34, and, as the blank continues to be forced into the tapered portion of the die, to conform to the shape of the mandrel. The metal of the upper portion of the head will flow in upon the mandrel; and, as the diameter of the head becomes lessened withits passage through the narrow aperture portion 29, not only will the flutes or other characteristic conformations of the mandrel be completely filled with extruded metal, but the surplus metal attendant upon the reduction in cross-section of the head portion of the blank will be caused to flow in a generally longitudinal sense relative to the mandrel, causing the head portion of 'the blank to be lengthened. The gripping action of the metal upon the tip of the mandrel, coupled with the force of the spring 38, will prevent the mandrel being forced back into the housing; and, as the metal of the blank is compressed or extruded toward the mandrel, the latter will ad- Vance at a higher rate than the extruding member, so that as the head is built up and elongated by the flowing metal, the socket will assume a depth greater than that of the originally punched recess. This action, which is shown in Fig. 6. will continue until the blank has been forced all the way through the cylindrical portion of the lurgical characteristics of the original blank, the

finished blank Ind may be caused to assume such dimensions that the base of the head, originally containing a slightly conical recess, formed by the part l6 of the blanking die, will assume a substantially flat conformation, as shown in Fig. 6, while the depth'of the finished socket, while greater than that of the original recess,w ill be slightly less than the possible distance which the mandrel 34 may project from theannular ex truding member 33. The latter condition being fulfilled, the blank, immediately upon the head portion passing through the cylindrical-aperture portion 29, will be forced away from the extruding member 33 by action of the compression spring 38 forcing the mandrel 34 to its extreme projected position, thus .leavinga slight space. as at 39, between the annular face of the extruding member and the head of the completed blank, thus facilitating removal of the finished blank by means of automatic stripping mechanism (notshown in the drawing). Thus there has been provided a method of and means for forming a screw blank by a process in which the metal is subjected only to an action in the nature of extrusion under. compression, rather than drawing under tension, and therefore is not at any time made subject to the weakening strains attendant upon forming the metal under conditions of tension or' outwardly exerted radial stress.

I claim:

1. Means for forming a socketed screw blank or the like from a cylindrical blank with recessed head, comprising a die having therein an aperture with cylindrical section of diameter less than the diameter of said blank and with a tapered section forming an approach thereto and-adapted to receive the blank, together with an annular extrusion member adapted to engage said blank for forcing it through said cylindrical section, and a coaxially disposed mandrel permanently mounted in the extrusion member, movable axially thereto and adapted to project beyond the same to enter the recess in said blank to an extent limited by the bottom of the recess, the protruding terminal portion of the mandrel bearing peripheral conformations to impart a predetermined contour to the walls of said recess as the material of the blank is laterally compressed upon the said terminal portion under the action of the extrusion member.

2. Means for forming a socketed screw blank or the like from a cylindrical blank with recessed head, comprising a die having therein an aperture with cylindrical section of diameter less than the diameter'of said blank and with a tapered section forming an approach thereto and adapted to receive the blank,'together with an annu- .to project beyond the same to enter the recess in said blank to the full extent of its depth, the

protruding terminal portion of the mandrel bearing peripheral conformations to impart a predetermined contour to the walls of said recess as the material of, the blank is laterally compressed upon the said terminal portion under the action of the extrusion member.

3. Means for forming a socketed screw blank or the like from a cylindrical blank with recessed head, comprising a die having therein an aperture with cylindrical section of diameter less than the diameter of said blank and with a tapered section forming an approach thereto and adapted to receive the-blank, together with an annular extrusion member having an annular fiat pressure face of an outside diameter equal substantially to that of the finished head of the blank and an innner diameter equal substantially to that of the final form of the finished socket. said face being adapted to engage said blank for forcing it through 'said cylindrical section, and a coaxially disposed mandrel permanently mounted in the extrusion member, movable axially thereto and. adapted to project beyond the same to enter the recess in said blank to an extent limited bythe bottom of the recess, the protruded to receive the blank, together with an annular extrusion member adapted to engage said blank for forcing it through said cylindrical section, and a. coaxially disposed mandrel portion mounted in the extrusion member and adapted to project beyond the same to enter the recess in said blank to the full extent of its depth, longitudinally yieldable relatively to the extrusion member, and having a protruding terminal portion' bearing peripheral conformations to impart a predetermined contour to the walls of said recess as the material of the blank is laterally coming terminal portion of the mandrel bearing pepressed upon the said terminal portion under the action of the extrusion member.

5. Means for forming a socketed screw blank or the like from a cylindrical blank with recessed head, comprising a die having therein an aperture with cylindrical section of diameter less than the diameter of said blank and with a tapered section forming an approach thereto and adapted to receive the blank, together with an annular extrusion member having an annular fiat pressure face at one end adapted to engage said blank for forcing it through said cylindrical section and the other end of said member being enlarged to afford a housing, a mandrel mounted in the extrusion member coaxially therewith and longitudinally movable relatively thereto, and resilient means mounted in the housing of the extrusion member bearing upon an end of the mandrel to extend its opposite end beyond the flat pressure face, the protruding terminal portion being adapted to enter said recess and bearing longi tudinal flutes to impart a predetermined contour to the walls of said recess as the material of the blank is laterally compressed upon the said terminal portion under the action of the extrusion member.

6. Means for forming a socketed screw blank or the like from a cylindrical blank with recessed I head, comprising a die having therein an aperture with cylindrical section of diameter less than the diameter of said blank and with a tapered section forming an approach thereto and adapted to receive the blank, together with an annular extrusion member having an annular fiat pressure face at one end adapted to engage said blank for forcing it through said cylindrical section and the other end 'of said member being enlarged to afford a housing, a mandrel comprising a rod passing through the extrusion portion of the extrusion member, its protruding tip bearing longitudinal flutes and adapted to enter said recess, the other end of the rod terminating in a head portion within the housing, and a compression spring within the housing bearing upon said head to cause said tip to protrude beyond the said extrusion member.

7. In the manufacture of socketed screws or the like: the process of forming a socketed blank from a solid cylindrical blank with a recessed enlargement at one end, which comprises forcing the blank through a circular die openingsmaller than the enlarged end of the blank by apply pressure thereto solely by means of the annular fiat face of a hollow extrusion member with outside contour equal substantially to the diameter of said opening; and, prior to the engagement of the annular flat face with the blank, introducing from the said hollow member into the recess of said blank a mandrel portion of predetermined conformation, the mandrel being free for axial movement relatively to the extrusion member and exerting substantially no extrusion pressure upon the blank and the movement of said mandrel being temporarily interrupted with the extrusion member continuing through the die, whereby as the blank is forced through said die opening solely by the annular face of the extrusion member the metal of said enlarged portion of the blank is laterally compressed onto the introduced mandrel portion, and the recess in said enlargement is caused to assume a contour corresponding to the cross-section of the introduced mandrel portion and a depth independent of the axial dimension of saidmandrel. I

' 8. In the manufacture of socketed screws or the like: the process of forming a socketed blank from a solid cylindrical blank with a recessed enlargement at one end, which comprises forcing the blank through a circular die opening smaller than the enlarged end of the blank by applying pressure thereto solely by means of the annular fiat face of a hollow extrusion member with outside contour equal substantially to the diameter of said opening; and, prior to the engagement of the annular flat face with the blank, yieldingly introducing from the said hollow member into the recess of said blank a mandrel portion of predetermined conformation and to the full depth of said recess, the mandrel exerting substantially no extrusion pressure upon the blank, whereby as the latter is forced through said die opening solely by the annular face of the extrusion member the metal of said enlarged portion of the blank is laterally compressed onto the introduced mandrel portion, and the recess in said enlargement is caused to assume a contour corresponding to the cross-section of the introduced mandrel portion.

9. In the manufacture of socketed screws or the like: the process of forming a socketed blank from a solid cylindrical blank with an enlargement at one end, which comprises first punching a recess in the enlargement of the blank by punch and die means conformed to limit metal flow under the action of the punch to a direction substantially in opposition to the direction of the force applied to said. punch, forcing the blank through a circular die opening smaller than the enlarged end of the blank by applying pressure thereto solely by means of the annular flat face of a hollow extrusion member with outside contour equal substantially to the diameter of said opening; and, prior' to the engagement of the annular fiat face with the blank, introducing from the said hollow member into the recess of said blank a mandrel portion of predetermined conformation, the mandrel being free for axial movement relatively to the extrusion member and exerting substantially no extrusion pressure upon the blank and the movement of said mandrel being temporarily interrupted with the extrusion member continuing through the die, whereby asthe blank is forced through said die opening solely by-. the annular face of the extrusion member the metal of said enlarged portion of the blank is laterally compressed onto the introduced mandrel portion, and the recess in said enlargement is-caused to assume a contour corresponding to the cross-section of the introduced mandrel portion and a depth independent of the axial dimension of said mandrel.

IERMAN KOESTER.

Images