US2985956A

US2985956A - Method for straightening and for relieving stresses in workpieces

Info

Publication number: US2985956A
Application number: US627446A
Authority: US
Inventors: Gerhard H Appel
Original assignee: Appel Process Ltd
Current assignee: Appel Process Ltd
Priority date: 1956-01-12
Filing date: 1956-12-10
Publication date: 1961-05-30
Anticipated expiration: 1978-05-30

Description

May 30, 1961 G. H. APPEL 2,935,956

METHOD FOR STRAIGHTENING AND FOR RELIEVING STRESSES IN WORKPIECES Original Filed Jan. 12, 1956 Ger/lard if aqp vel Wm W dtarngy:

United States Patent O METHOD FOR STRAIGHTENING AND FOR RELIEVING STRESSES IN WORKPIECES Gerhard H. Appel, Windsor, Ontario, Canada, assignor to Appel Process, Ltd., Windsor, Ontario, Canada, a company of Canada Original application Jan. 12, 1956, Ser. No. 558,750,

now Patent No. 2,894,421, dated July 14, 1959. Divided and this application Dec. '10, 1956, Ser. No. 627,446

6 Claims. (Cl. 29-544) This application is a division of a prior application, Ser., No. 558,750 of January 12, 1956, now Patent No. 2,894,421 of July 14, 1959, directed to apparatus.

The invention relates to a new method for relieving longitudinal stresses in elongated workpieces by cold forging.

An elongated workpiece is fed axially and intermittently in small increments through an annular set of hammers or forging dies with the workpiece being held at its trailing and leading ends in axial alinement with the throat of the dies. These impart, in off-beat relation to the feeding of the workpiece, a series of sharp, rapidly delivered hammer blows which reduce the increments to a plastic condition and thus relieve them of longitudinal stresses.

With the leading end held and guided to travel axially of the travel through the throat, the leading end, already plasticized and thus relieved of longitudinal stress, is not again subject to such stress.

With the line connecting the held and guided leading end, and the dies throat being a straight line, the work piece will also be straightened.

Other objects and advantages of the invention will become apparent from the following detailed description of the method and a preferred form of the apparatus for carrying it out as illustrated in the accompanying single figure of drawings.

The drawing is a partly sectioned, fragmentary plan view of a cold forging machine equipped with apparatus embodying the features of the invention and particularly adapted for carrying out the new straightening and stress relieving method.

For purposes of illustration the apparatus for carrying out the invention has been shown in a form adapted for application to a particular type of cold forging machine. It is to be understood, however, that this is merely exemplary and that the method may be carried out by other means or apparatus or in conjunction with cold forging or swaging machines other than the specific machine illustrated.

Referring to the drawing, the apparatus shown is adapted to carry out the new straightening and stress relieving method in cooperation with a cold forging machine of the type disclosed in the co-pending Appel application, Serial No. 450,500, filed August 17, 1954. It will be appreciated, however, that the method can be carried out in cooperation with other types of forging or swaging machines. Insofar as it conerns the present invention, the machine comprises a metal working tool unit or rotary die set 1 supported on a frame member 2 connected to other elements of the machine structure by spaced parallel tie rods 3. The tie rods support and guide a head 4 for linear translation toward and from the tool unit. Any suitable drive means may be utilized for translating the head. As shown in the drawing, the head 4 carries a chuck 5 adapted to grip and support one end of a workpiece such as the metal tube W. The chuck ice is rotated relatively slowly as the head advances to feed the workpiece axially through the tool unit 1.

The tool unit or die set 1 comprises a plurality of hammers of a die element 6 arranged in an annular series and supported for radial movement toward and from the workpiece which is fed coaxially through the set. It will be understood that the inner or work-engaging ends of the die elements are shaped to form the work to the desired external contour which may be round, or any other desired shape. In the case of the tubular workpieces, the internal shapes and dimensions are determined by a suitable mandrel 7' disposed within the workpiece within the area engaged by the die elements. In the exemplary machine the mandrel is carried at the end of the mandrel supported rod 8 extending back through the chuck 5 to the interior of the machine.

In operation, the chuck 5 and the workpiece W are rotated while the head 4 advances intermittently and in olfbeat relation to the strokes of the dies to feed the workpiece axially through the die set. During such feed the hammers or die elements 6 are actuated intermittently and in ofi-beat relation to the feed to impart sharp, rapidly delivered hammer blows to the limited section or increment of the workpiece between the dies. The actuating mechanism may be of any preferred character and is usually arranged so that oppositely disposed hammers act simultaneously in delivering their hammer blows to opposite sides of the workpiece.

In straightening and relieving longitudinal stresses in accordance with the improved method, the leading end of the workpiece W as it emerges from the die set 1 is firmly engaged and rigidly held in coaxial alinement with the throat of the die set. It is also desirable although not essential to the attainment of the desired result, that the end of the workpiece supported by the chuck 5 be precisely alined with the die set. Any tendency of the workpiece to elongate more at one side than the other and thus to bend or twist transaxially is counteracted by the action of the die elements which plasticize and force the material and force it into precise axial alinement with the support at the reduced end of the workpiece. This, of course, develops longitudinal stresses along the entire length of the workpiece but those stresses are completely relieved when the material becomes plastic under the dies. Thus, the compensation for the conditions which produce the tendency to bend is elfected within the area where the metal is temporarilyin a plastic condition and therefore the redistribution of metal required for the production of a straight workpiece is effected without the development of any stresses in the workpiece. In the case of tubular workpieces, this redistribution of metal results in substantial equalization of the wall thickness throughout the entire length of the workpiece. Accordingly, by use of the new method, a straight, stress-free workpiece and therefore a better product is produced in a single operation and with material saving in production costs.

Any suitable means may be utilized for supporting the workpiece W upon its emergence from the die set. Thus, the support may comprise a series of stationarily supported members engageable with the workpiece at circumferentially spaced points to provide lateral support while permitting axial movement of the workpiece which finally is pushed through the metal working tool set and emerges as a finished product from the rear of the machine. Alternatively, the support may be arranged to grip the leading end of the workpiece and to move with it in a path pre 3 ward end by a plug 13. A socket 14, shaped and dimensioned to receive the end of the workpiece W with a tight gripping fit, is provided centrally of the plug.

In the particular machine illustrated a cylinder 11 is rotatably supported within a tubular liner 15 as by bearings 16. The liner is fitted into a rigid sleeve member 17 suitably secured to the frame structure of the machine. As herein shown, the sleeve is seated in an aperture 18 in the frame member 2 and is formed with a flange 19 adapted to abut the inner wall of the frame member and hold the sleeve against the axial movement. In this instance the sleeve also provides support for the die set 1 which is mounted on and secured to the forward end of the sleeve in any suitable manner.

The cylinder 11 is secured against the endwise move ment relative to the liner 15 by a collar element 20 which permits rotation of the cylinder with the piston and the workpiece supportcd'thereby. A port 21 in the sleeve and liner provides for admission of fluid coolant to the space between the cylinder and the liner, the coolant being discharged through a port 21' in the collar 20. Pressure fluid such as compressed air is admitted to the aft end of the cylinder by way of a port 22 in the end wall of the cylinder. Thus, by directing compressed air through the port 22, the piston 10 may be driven toward the forward end of the cylinder to impose a yieldable resistance to the advancing workpiece through the die set.

At the beginning of a forging operation, compressed air admitted to the cylinder 10 through the port 22 holds the piston 10 at the forward end of the cylinder closely adjacent the die set 1. The workpiece W therefore enters the socket 14- irnmediately on emerging from the forging dies. A substantial pressure as, for example, 50 p.s.i., is maintained in the cylinder as the forging operation proceeds, thus applying a yielding force to the piston counter to the feed of the workpiece. This effectually keeps the workpiece firmly seated in the socket and therefore coaxially alined with the die set through its entire length. The piston is forced back into the cylinder as the workpiece advances through the die set.

T o facilitate disengagement of the workpiece from the socket 14- the piston is provided with a pressure actuated plunger 23 adapted to be projected into the socket 14 from its inner end. The plunger 23 as shown is formed with a cylindrical head 24 extending through an opening at the end wall of the piston. A flange 25 adjacent the forward end of the head limits rearward movement of the plunger.

Upon completion of the forging operation the head 4 and the chuck are retracted in the" usual manner with the dies preferably opened up to atford clearance for withdrawal of the work. The support piston '10, being subjected to the pressure in the cylinder, moves along with the work until it reaches the end of the cylinder. The pressure on the head 24 acts to advance the plunger 23 and push the workpiece from the socket. Upon its withdrawal from the die set, the workpiece may be released from the chuck and removed from the machine.

It will be apparent from the foregoing-that the novel straightening and stress relieving method provided by the invention materially. improves the product produced by cold forging and swaging operations. The finished workpiece produced by this method is precisely straight and completely free of bending stresses. In the case of tubular workpieces, the walls are more nearly of uniform thickness. Furthermore, production costs are reduced since a number of supplementary operations heretofore required are eliminated. While the new method can be carried out in various ways and with different types of equipment, the invention provides simple and efficient apparatus for that purpose which is easy to operate and which is readily applicable to conventional cold forging or swaging machines.

I claim as my invention:

1. In a method for cold forming an elongated, rodlike, metal work-piece, whether hollow or solid, comprising simultaneously applying to the surface of a minute increment of the metal workpiece at leastthree, radially arranged, inwardly directed, equally spaced, equal and opposed pressures engaging and substantially completely girdling the workpiece; in such method, that improvement which comprises applying the pressures to the workpiece by at least three radially arranged pressure applying dies providing a die throat, with each die subjected to two opposing, equal, transverse forces, each of which transverse forces has a transverse component and a radial component, the transverse components being directed so that they are equal and opposite and thus balance themselves out, leaving only a net radial resultant directed along an extension of the radius of the workpiece and towards the central axis of the workpiece so that each force on a die which applies pressure to the workpiece is truly radial to the workpiece and has no unbalanced transverse components; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece immediately as it emerges from the throat of the dies and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed.

2. In a method for cold forming an elongated rod-like metal workpiece, whether hollow or solid, which method comprises applying to each of many longitudinal adjacent minute increments of a metal workpiece, in successive steps, so as to extend over substantially its entire exterior surface, at least three, radially arranged. inwardly directed, equally spaced, equal and opposed and simultaneously applied pressures engaging and substantially completely girdling the workpiece; in such method that improvement which comprises applying the pressures to the workpiece by at least three radially arranged pressure applying dies providing a die throat with each die subjected to two opposing transverse forces, the two up posing transverse forces being so directed that their transverse components are equal and opposite and thus balance themselves out, leaving only a net radial resultant of the two forces, so that each force on a die which applies pressure to the workpiece becomes truly radial and has no unbalanced transverse components, and so that the pressures on the workpiece applied by each pressure applying die are balanced out by equal and opposite pressures applied by the remaining pressure applying dies; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece immediately as it emerges from the throat of the dies and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed.

3. A method for cold forming an elongated metal workpiece, hollow or solid, having a central axis, comprising the steps of surrounding substantially the entire outer peripheral surface of a single axial increment of the workpiece with at least three opposed dies providing a die throat, each die arranged radial relative to the workpiece central axis; simultaneously loading all of the dies by subjecting each of them to two equal and opposing forces which are transverse relative to the die axis and which are so arranged as to balance out all transverse components of said two opposing forces and leave only a radial resultant which radial resultant is directed towards the workpiece central axis along the die axis; whereby the resultant load on each die is radial and has no unbalanced transverse components, and with the said radial resultant on each die being equal to the radial resultant of every other die; moving the dies under the influence of their respective radial resultant loads into engagement with the workpiece increment for transmitting the respective resultant loads to the workpiece and thereby applying pressure to the workpiece for forming it; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed.

4. A method for cold forming a metal workpiece, hollow or solid, which is elongated and rod-like in shape and thus has an elongated central axis, said method employing at least three pressure applying dies which are equally spaced on workpiece radii circumferentially around the periphery of the workpiece in a plane normal to its axis and which dies girdle the workpiece and are movable towards and away from the axis, said dies providing a die throat, said method further comprising repeated identical cycles of steps with each cycle including the dies engaging and acting on a small axial increment of the workpiece and with each cycle comprising the steps of gradually and simultaneously moving all of the dies equal minute distances inwardly towards the workpiece axis inwardly of the workpiece surface and under equal loads whereby the dies gradually squeeze the workpiece increment then worked upon until the metal in that workpiece increment flows and the periphery of that workpiece increment assumes the shape of the die faces engaging the workpiece; then stopping the inward movement of the dies and holding the die loads for a short time; and then retracting the dies away from the workpiece axis; and then moving the workpiece axially through the dies to present a succeeeding increment of the workpiece to the dies; and repeating the cycles until all increments of the workpiece from one end to the other have been successively engaged and formed by the dies; in such method, that improvement which comprises applying the pressures to the workpiece by subjecting each of the dies to two opposing transverse forces each of which forces have transverse components and radial components and with their transverse components being so directed that they are equal and opposite and balance themselves out leaving only a net radial resultant so that each force on each of the dies, which applies pressure to the workpiece, is truly radial and has no net or unbalanced transverse components; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed.

5. A method for cold forming an elongated metal workpiece, hollow or solid, having a central axis comprising numerous identical cycles of steps, with each successive cycle acting upon a successive single axial increment of the workpiece, each cycle comprising essentially the steps of surrounding substantially the entire outer peripheral surface of a single axial increment of the workpiece with at least three opposed pressure applying dies which are arranged radially relative to the workpiece axis to provide a die throat; simultaneously loading all of the dies and moving them under the influence of their loads towards and into pressure applying engagement with the workpiece, with the movement of each of said dies being only in the direction of a single radius of the workpiece, with the load on each of the dies being formed of a radially directed resultant force directed only in the same direction as the respective single radius which defines the direction of movement of that die, and also being formed of pairs of non-radial force components with each non-radial force component of each pair being equal to and opposite to and counterbalancing and cancelling out the other non-radial force component of that pair and with the radially directed resultant forces of each of the dies being equal to one another; holding the dies in a pressure applying engagement with the workpiece for a pre-determined time for forming the workpiece increment; then releasing the loads simultaneously and retracting the dies from the workpiece along the same path in which they moved towards the work-piece; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed.

6. A method for cold forming a metal workpiece having a central axis comprising loading substantially the entire outer periphery of a single increment of the workpiece with forces that are inwardly directed and which resolve into force components which are either radial to the workpiece axis or are normal to radii of the workpiece and tangent to a hypothetical circle whose axis is the axis of the workpiece; and with all of the radial force components being in balance at the axis of the workpiece and with each of said normal force components being balanced by another equal and opposite normal force component; there being no forces at any time which do not resolve into truly radial components or normal-to-radii components; said loading being characterized by being rapidly applied and removed in a uniform time pattern; applying the loading to successive increments of the workpiece; and changing the increments upon which the loading is applied during the load removed time of the loading time pattern; the method further including axially push feeding the workpiece through a throat of dies which provide the forces and engaging the leading end of the workpiece immediately as it emerges from the throat of the dies and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed.

References Cited in the file of this patent UNITED STATES PATENTS 431,041 Fritzpatrick et al July 1, 1890 585,151 Kennedy June 22, 1897 589,694 Capewell Sept. 7, 1897 654,590 Baker July 31, 1900 1,963,942 Flynn June 19, 1934 1,986,426 De Bats Jan. 1, 1935 2,114,302 Harter Apr. 19, 1938 2,247,863 Tiedemann July 31, 1941 2,301,094 Tiedemann Nov. 3, 1942' 2,561,101 Dewey July 17, 1951 2,929,282 Retterath Mar. 22, 1960