US3137926A

US3137926A - Formation of fins on metal bar or tube stock

Info

Publication number: US3137926A
Application number: US725198A
Authority: US
Inventors: Barlow John Alfred; Martin Frank Edward; Maugham George Thomas; Champman Thomas Edwin; Dalby Edgar William
Original assignee: Fairey Engineering Ltd
Current assignee: WFEL Ltd
Priority date: 1957-04-02
Filing date: 1958-03-31
Publication date: 1964-06-23
Anticipated expiration: 1981-06-23

Description

June 23, 1964 J ow ETAL 3,137,926

FORMATION OF FINS ON METAL BAR OR TUBE STOCK Filed March 51, 1958 4 Sheets-Sheet l INVENTORS Jean 8- Bnkmw FRRNK E. Mari-IN Gemzaa T- MAWMN 'm mng E. CHAPMAN Enema w. DRLBY BY M Mia av June 23, 1 4 J. A. BARLOW ETAL FORMATION OF FINS 0N METAL BAR OR TUBE STOCK 4 Sheeis-Sheet 2 Filed March 31, 1958 He. 5 p.

INVENTORS Joe-m A. Baku-ow FRnNK E. MAR-rm. Game; 1'- Mus-MN. Thomas E. CMRPMAN. Emma N. put BY .1

' A'r'romeY FIG. 5B.

June 23, 1964 4 J. A. BARLOW ETAL 3,137,926

FORMATION OF FINS ON METAL BAR OR TUBE STOCK Filed March a1, 1958 4 Sheets-Sheet 5 INV TORS JOHN BRRl-OW FRANK E. MARTI GEORGE T. A BH N mas 5.cum maan: H. DALBY.

ATTORNEY June 23, 1964 J. A. BARLOW ETAL 3,137,926

FORMATION OF FINS ON METAL BAR OR TUBE STOCK Filed March 31, 1958 4 Sheets-Sheet 4 INVENTORS Jmm A. Bmusw Fmmx E. manna 6:025; T. mauaum TpqgmAS 'Eu MPMRN Eur-Ag w. Din.

ATTORN EY United States Patent 3,137,926 FORMATION OF FKLJS ON METAL BAR QR TUBE STUCK John Alfred Barlow, Frank Edward Martin, George Thomas Maugham, Thomas Edwin (Ihapman, and

Edgar William Dalby, all of Hayes, England, assignors,

by mesne assignments, to Fairey Engineering Limited,

Heston, Engiand, a company of Great Britain Filed Mar. 31, 1958, Ser. No. 725,198 Claims priority, application Great Britain Apr. 2, 1957 2 Claims. (Cl. 29-1575) This invention relates to the forming of an integral protruding fin on a workpiece and is particularly although not exclusively applicable to the formation of an integral external fin on metal stock of cylindrical bar or tubular form.

It is known to roll a thread on a metal bar using a number of small-diameter, rotatable discs freely mounted on a spindle by means of which the edges of the discs are pressed against the side of the slowly rotating bar. A similar method, using freely mounted discs of correspondingly larger radius, has been tried by the applicants for rolling thin, deep fins on bar or tube stock but was found unsuccessful.

According to the present invention a process of forming an integral fin on the surface of a workpiece made of a material which when heated becomes softened and capable of being extruded, includes pushing into contact with the workpiece surface a tool whose workpiece-engaging parts include a pair of spaced, generally parallel edges which are moving at high speed relatively to the workpiece in the direction of their lengths and substantially tangentially to the workpiece surface, the edges being separated by an elongated gap, so as to cause local heating and softening of the material of the workpiece and to displace the softened material outwardly into the gap to form a fin protruding beyond the original surface of the workpiece. The tool may be traversed slowly relatively to the workpiece surface whilst being pressed against it, in a direction generally parallel to the direction of movement of the edges at their region of contact with the workpiece.

In one form of the invention the tool is rotatably mounted and is rotated at high speed, and the workpieceengaging edges respectively include portions lying along or at a small angle of inclination to a circle coaxial with the axis of rotation of the tool.

Thus in one arrangement the tool may include two or more coaxial discs or annular flanges or'rings whose outer peripheral margins are spaced apart and afford the workpiece-engaging edges of the tool.

For forming a continuous helical fin extending coaxially around a workpiece of cylindrical form the latter may be slowly rotated Whilst the tool is traversed along the length of the workpiece. In this case the axis of rotation of the tool should preferably be inclined to the axis of the workpiece at an angle corresponding to the angle of lead of the helix.

The tool may include a milling cutter mounted behind the rotating edges in a position in which it will enter the groove between the adjacent convolutions of the helical fin to trim the base of the groove.

Similarly, circumferential or longitudinal fins may be formed by appropriately traversing the tool relatively to the workpiece surface.

In the one arrangement of the invention the tool may include a number n of workpiece-engaging rotary edges, where n is greater than 2, so that n1 fins are formed simultaneously.

According to a further feature of the invention two or more of the spaced workpiece-engaging edges of the tool are each comprised of one or more blunt leading hce edge portions each inclined to its own path of travel at a small angle in a direction rearwardly and away from the tool, so that the rotating tool delivers a series of impacts to the workpiece. Thus where the members comprise spaced coaxial discs, at least one pair of the discs may be formed with radial undulations extending around with the workpiece.

their peripheries. Alternatively the discs may each be formed with one or more outwardly protruding peripheral lugs, each lug affording a rearwardly inclined leading edge oblique to the direction of travel for engagement Again, the edge of each disc may be generally circular but formed with one or more flats for impact engagement with the workpiece.

In another form of the invention the members instead of being discs may take the form of thin spaced coaxial rings or flanges which surround the workpiece and are rotated at high speed about their common axis, the generally circular inner edges of the rings or flanges being pressed into engagement with the side of the workpiece to form circumferential or helical fins by outward displacement of the metal between the narrow annular spaces between the rings. The edges of the rings may be formed with undulations projections, discontinuities or other variations in their radial heights to afford impact portions as mentioned above. The rings may all be mounted within a common drum which is rotated about its axis and is moved transversely relatively to the workpiece to effect engagement of the rings with the workpiece.

The invention according to another of its aspects comprises apparatus for forming an integral fin by the method referred to on a material which when heated softens and is capable of being extruded, which comprises means for supporting the workpiece, a tool-holder carrying a tool having at least two spaced, generally parallel blunt edges separated by an elongated gap, means for moving the edges longitudinally at high speed relatively to the workpiece and means for advancing the tool to press the mov-: ing edges generally tangentially against the surface of the workpiece.

For example the apparatus may comprise a lathe, a tool-holder mounted on the cross-slide of the lathe, a tool mounted in the tool-holder and comprising a number of close-spaced coaxial rotary members having generally circular edges defining between them one or more narrow gaps driving means for rotating the members about their common axis at a high speed, means for moving the tool-holder in such a manner as to press the edges of the rotating members into the surface of the workpiece, and means for traversing the tool-holder to move the edges relatively to the workpiece surface in a direction generally transverse to the axis of rotation of the members whilst they are pressed against the workpiece.

The invention according to another aspect comprises a length of bar or tube formed with at least one integral external fin by the method referred to.

The invention may be carried into practice in various ways, but certain specific embodiments will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of apparatus for forming a continuous helical fin on a tubular metal workpiece,

FIGURE 2 is a diagram illustrating how the workpiece is set up in the apparatus, and how the fin is formed to. project beyond the original workpiece surface,

FIGURE 3 is a view showing diagrammatically the profile of a typical disc used in the apparatus of FIG- URE 1,

FIGURE 4 is a sectional diagrammatic view of a train of two discs and a cutter used for forming a single helical fin,

FIGURES 5A and 5D illustrate various modified forms of disc having different profiles,

FIGURE 6 is a perspective view similar to FIGURE 1 of a modified embodiment for forming a longitudinal fin,

FIGURE 7 is a perspective view of part of another modified embodiment employing rotating rings instead of discs,

FIGURE 8 is an end view of the cage and rings of the embodiment of FIGURE 7, and

FIGURE 9 is a section on line IXIX of FIGURE 8,

In the embodiment of FIGURES 1 to 5, the invention is applied to the formation of a continuous helical fin on a workpiece consisting of a length of cylindrical bar or tubular stock of light alloy, for example of magnesiumberyllium alloy.

The tubular workpiece 10 is mounted between the headstock 11 and tailstock 12 of a screw-cutting capstan lathe 13 as shown in FIGURE 1. The two

end portions

14 and 15 of the workpiece 10 are turned down to a smaller diameter than that of the original workpiece which is indicated at 16 in FIGURE 2. At the headstock end the workpiece end 14 is slotted at 17 (FIGURE 2), and the spigot 18 of a centrepiece 19, is inserted in the end of the workpiece and is provided with a transverse driving pin 20 which engages in the slot 17 of the end 14 of the workpiece. The centrepiece 19 is mounted in the chuck 21 of the headstock 11 so that the workpiece will be rotated by the chuck.

At the other end 15 the workpiece is also provided with a centrepiece 22 which is journalled in a roller race 23 carried by the tailstock 12 so as to support the rotating end 15 of the workpiece.

Mounted on the cross-slide 24 of the lathe is a supporting structure 25 on top of which is mounted an electric motor 26. The structure 25 also carries a downwardly depending bearing tongue 27 and a bearing block 28 in which are journalled the ends of a spindle 29. A pair of coaxial discs 30 and a milling cutter 31 are rigidly mounted on the spindle 29 for rotation therewith and the spindle is driven at high speed by the motor 26 through a belt drive 32. The spindle axis is slightly above and to one side of the axis of the workpiece, so that by transverse movement of the cross-slide 24 the edges of the rotating discs can be advanced into contact with the edge of the workpiece. As illustrated in FIGURE 3, each of the discs 30 has its edge of smoothly undulating form, affording a series of radially projecting portions or radial projections 32 each of which has a smooth leading edge 33 backwardly inclined rearwardly and outwardly with respect to the direction of travel of the edge, the portions 32 thus constituting impact members whose leading blunt impact faces 33 will engage the metal of the workpiece with a hammer effect when the rapidly rotating discs 30 are pressed into the surface of the workpiece. The peripheral margins of the two discs 30 are spaced apart as shown in FIGURE 4 to define between them a deep annular recess 34 whose depth and cross-section correspond to those required in the fin to be formed.

It will be realised that in FIGURES 1 and 4 the width of the gap 34 between the margins of the two discs has been considerably exaggerated for the sake of clarity, since in general fins which are much thinner in relation to their height will be required and accordingly a much narrower recess 34 would be used. The milling cutter 31 which is arranged behind the rearmost disc 30 also de-. fines with that disc a second similar recess 35.

In operation the chuck 21 of the lathe, and with it a workpiece 10, is rotated slowly about its longitudinal axis at a speed of between 14 and 100 revolutions per minute, whilst the lathe saddle 36 is slowly traversed automatically along the length of the workpiece by means of a lead screw 37. At the same time the fin-forming tool constituted by the train of discs 30 and the milling cutter 31 is advanced into contact with the surface of the workpiece by transverse movement of the cross-slide 24, whilst the discs 30 are being rotated at high speed, for example 4500 revolutions per minute, the resultant repeated impacting and friction heating the metal of the workpiece in the region adjacent to the discs to a temperature sulficient to soften the metal, say 400 or 500 C. The traversing of the cross-slide 24 causes the spaced edges of the discs 30 to bite into the side of the rotating workpiece 10 the softened metal of the workpiece being displaced to either side of each disc and extruded radially outwardly into the annular recess 34 to form a fin which, due to the longitudinal traverse of the saddle 36, will be progressively formed as a continuous helical fin 38 of corresponding pitch and of section and height equal to the section and depth of the annular recess 34. Lubricant is continuously directed onto the contact faces of the discs 30 and of the workpiece 10 through nozzles one of which is visible at 39 in FIGURE 1. To aid in the formation of the helical fin 33, the axis of the spindle 29 on which the discs 39 are mounted is preferably inclined at a small angle, corresponding to the angle of lead of the helix, so that the planes of the faces of the discs 30 will approximately conform to the faces of the helical fin 38 with which they are in contact. The opposite faces of each disc 30 in the peripheral region are shown as parallel to one another in FIGURE 4, but in some cases, to facilitate the entry and exit of the discs 35) into the grooves between successive convolution of the fin 38, and also to relieve friction, the discs may be slightly thicker at their extreme peripheral portions. Alternately, if a fin of tapered crosssection is required, the marginal portion of the discs 30 may be themselves tapered in section in the outward direction to define between them a recess 34 which is wider at the top than at its bottom.

The purpose of the circular milling cutter 31 which is also mounted on the spindle 29 behind the two discs 30 is to enter into the helical groove formed between successive convolutions of the helical fin 38 and to trim the base of the groove accurately to the required square or other section, as determined by the shape of the edges of the cutter teeth. For this purpose the milling cutter is of approximately the same radius and thickness as each of the discs 30 and is mounted just behind the rearmost disc 30 at corresponding axial spacing from it.

There is thus formed on a tubular or bar workpiece a continuous helical fin of extremely accurate dimensions the fin being formed extremely rapidly by a process similar to extrusion which produces no scrap metal at all except for the trivial quantity due to the trimming action of the milling cutter 31. It will also be observed from FIGURE 2 that the peripheral radius of the formed fin is greater than the original radius of the workpiece 10 itself whilst the thickness of the fin may be very small. Thus on a bar or tube of magnesium-beryllium alloy originally 1% inches in diameter a fin /2 inch deep and only a few thousandths of an inch in thickness can readily be formed.

It is preferred that the discs 30 and the workpiece 10 should be rotated in opposite directions, although since the speed of rotation of the workpiece is very small in comparison with that of the discs it would be almost equally satisfactory for the two to be rotated in the same direction, since the relative angular velocity between them will not be greatly different in the two cases. A suitable speed of rotation of the workpiece is 72 revolutions per minute, which can be produced conveniently on a screw-cutting 1athe To start the fin formation the rotating discs are merely advanced into contact with the cylindrical surface of the workpiece at one end and are pressed inwardly as the metal heats and softens. It is not necessary to provide a tapered end portion on the workpiece for leading the discs into the workpiece.

The arrangement described, using the train of two discs 30 as illustrated in FIGURE 4, produces a single helical fin. If a circumferential fin is required this can of course be produced by removing the milling cutter 31 and advancing the discs into the flank of the rotating workpiece without rotating the lead screw 37, so that there is no axial movement of the discs relatively to the workpiece. The axis of the spindle 29 should preferably be made parallel to the axis of the workpiece for this operation. By employing a larger number than two of the discs 30, all arranged side by side on the common spindle 29, a correspondingly increased number of circumferential fins can be formed simultaneously. Thus if n discs are provided, n1 fins will be formed simultaneously.

As already mentioned, the fin formation effected by the rapidly rotating discs constitutes a process of displacement or extrusion of the metal of the workpiece into the annular recesses between the discs, the metal having become heated and softened by the engagement of the discs with the workpiece. The discs themselves may have many diflerent profiles besides that illustrated in FIGURE 3, and with workpieces of certain metals it is even possible to form small fins by this process using circular discs Whose edges are perfectly smooth, the friction between the smooth edges of the discs and the workpiece sufiicing to heat and soften the metal suificiently for displacement radially outwardly between the discs. However the radial height of fins which can be formed with smooth discs is very limited and the process is slow.

Much higher fins can be formed, and at greater speed, if the edges of the discs are formed with suitable undulations, projections, or other suitable variations in height affording blunt leading edge portions which are inclined rearwardly and outwardly to their circular path of travel, to provide a succession of impact on the workpiece, the hammer effect of which greatly assists in the local heating and softening of the metal and in its displacement into fin form. Thus in FIGURE 3, each disc is formed with a smooth symmetrical peripheral undulation Certain other suitable forms of disc profile are illustrated in FIGURES 5A to 5D.

In FIGURE 5A, each disc is formed with a series of discontinuous lugs 50 protruding from the otherwise circular periphery 51. The lugs 50 are symmetrical and have smoothly curved rearwardly inclined leading edges 52, flattened tops 53, and rear edges 54 which are the mirror images of the leading edges. Like those of FIG- URE 3, the discs shown in FIGURE 5A being symmetrical in profile are reversible in operation, so that their useful life is correspondingly increased.

In FIGURE SE a disc 55 is shown which has but a single protruding lug 56 of the same pattern as the lugs 50 of FIGURE 5A, the remainder of the circumferential edge of the disc 55 being circular and smooth.

In FIGURE 5C a disc 58 is shown which is formed with protrusions 59 of generally unsymmetrical form, each protruding lug or tooth 59 having a gently inclined leading edge 60 leading over a rounded tip 61 to a trailing edge 62 which is steeply cut away or may even be undercut. The disc 58 is therefore unidirectional. In practice the discs 58 may comprise conventional milling cutters the tips of the teeth of which have been ground down to smoothly rounded form, and these cutters will be rotated in the reverse direction to that employed for milling so that the backs of the teeth constitute the rearwardly inclined leading edges which first strike the metal of the workpiece.

Another possible form of disc is illustrated in FIGURE 7 5D in which the edge of a circular disc 63 is formed with four flats or chords 64 spaced uniformly around its periphery the corners afforded by the adjacent ends of adjacent flats 64 constitute the necessary impact portions whose leading edges strike the workpiece with a hammer effect.

Many other forms of disc profile suitable for producing an impact effect on the workpiece may be conceived, to provide one or more impact portions each affording rearwardly and outwardly inclined smooth leading edges to strike the work and heat and plasticise the metal, the leading edge being followed up by a trailing portion or lug of greater radial height which is dragged through the pasticised metal forming a groove and displacing the metal sideways. The displaced metal between two adjacent discs is then extruded between them into fin form, the side faces of the trailing portions of the adjacent impact portions of the discs serving to shape and steady the newly extruded fin until it has cooled sufficiently to be self-supporting. The process may thus be described as a form of rotary impact extrusion of a fin, and as mentioned above it enables fins of greater height to be formed than is possible using plain-edged discs.

In the second embodiment of the invention illustrated in FIGURE 6 the general arrangement of the capstan lathe 13 and of the supporting structure 25 mounted on the carriage as of the lathe is as before, and similar parts are given the same reference numerals. In this case, however, a longitudinal fin 76 is required to be formed on the workpiece Iii parellel to its axis, and accordingly the spindle 29 which carries the two discs 30 is arranged with its axis and that of the discs transverse to the axis of the workpiece, the spindle being driven as before by means of the motor 26 through the belt drive 32 but the motor axis being at right angles to that employed in the embodiment of FIGURE 1. Since the fin '76 is required to be longitudinal, the workpiece must not rotate during fin formation and accordingly it is supported by a block 72 mounted on the base of the ructure 25. Moreover, since the chuck 21 will usually rotate when the carriage 36 of the lathe is moved, a roller race 73 is interposed between a centerpiece 74 spigoted into the end of the workpiece It) and the chuck 21 of the lathe. At the tail stock end, the turned-down end 15 of the workpiece is supported directly by a tool holder 75 secured to the turret of the lathe, no ball race being required at that end.

The two discs 3t mounted on the spindle 29 may be of the undulating type illustrated in FIGURE 3 or of any the other types shown in FIGURES 5A to 5D. No milling cutter is provided however in association with the discs, which are disposed with their general planes symmetrically located on either side of the vertical plane through the axis of the workpiece. In operation, as previously, the discs are advanced into engagement with the upper part of the workpiece at one end, so as to heat and plasticise the metal locally by the friction and impacting of the undulating edges of the discs. The lathe carriage 36 is slowly traversed along the length of the workpiece, so that a single longitudinal fin 7% is extruded between the two rapidly rotating discs 39 as the carriage 36 advances along the workpiece. The fin may be formed completely from end to end of the workpiece, and it is not necessary to provide a tapered lead-in portion at either end of the workpiece, as the discs are simply advanced into engagement with the square edge of the end of the workpiece to start the fin formation.

If a number of longitudinal fins is requ red to be formed at spaced intervals around the circumference of the Workpiece, succession of passes along the length of the workpiece by the discs 39 can be made, the workpiece being rotated through a suitable angle about its axis between successive passes.

In the embodiment illustrated in FIGURES 7 to 9, the general principle of fin formation by the application of a rapidly moving pair of spaced edges to the workpiece is employed as in the previous embodiments, but in this case the edges instead of being constituted by the outside edges of a number of coaxial discs are constituted by the inside edges of a number of coaxial rings 30 surrounding the workpiece.

Thus a pair of rings formed with internal, generally circular edge portions 81 of reduced axial thickness, is mounted, together with a milling cutter 82 of the ring type of the same general dimensions, in a stack bounded by a suitable number of packing rings 83 serving to increase the axial length of the stack to a convenient size. The stack is clamped together by means of bolts 84 between flanged end rings 85 having flanges 86 so as to form a drum into whose interior protrude the peripheral portions 81 of the rings 80, and the teeth of the milling cutter 82. The drum is mounted for rotation within roller races 93 which are supported by the sides of nonrotating pegs 87 protruding inwardly from the side walls 88 of a supporting bridge 89 secured to a base plate 99, which is mounted on the cross-slide of the lathe carriage 36 for movement transversely to the workpiece 10. The drum constituted by the stack of

rings

80, 82 and 83 and 85 is thus rotatably mounted within the bridge 89 and is driven at a high speed of rotation about the axis of the rings 80 by a belt drive 91 from an electric motor 92 mounted on the base plate 90 to one side of the bridge 89.

The workpiece 10, which is mounted as in the embodiment of FIGURE 1 between the head stock and tail stock of the lathe for rotation with the chuck, extends through the

rings

80, 82, 83, and 85 so that by suitable transverse movement of the cross slides of the lathes the inwardly projecting edge portions 81 of the rapidly rotating rings 80 can be pressed into contact with the side of the workpiece, whilst the latter is being rotated by the chuck and whilst the rings 80 are being traversed slowly along the length of the workpiece by the longitudinal movement of the carriage 36 affected by the lead screw 37. There is thus formed on the workpiece 10 an external helical screw thread 94 by a process which is precisely analogous with that employing the discs 38 as described in relation to FIGURE 1, save only that in the present case internal edges of the rings 80 which surround the workpiece are used to soften the metal and to displace it radially outwardly into helical fin form.

The internal diameters of the rings 80 and of the milling cutter 82 must clearly be considerably larger than the external diameter of the workpiece, and in practice the internal diameter of the ring edges will usually be at least twice the original external diameter of the workpiece 10. As before, the edges of the inwardly protruding marginal portions 81 of the rings 80 are all formed with a suitable pattern of radial undulations or protrusions, in this case constituting the converse of the unsymmetrical tooth arrangement of the disc 58 shown in FIGURE C. Thus as shown in FIGURE 8 the internal edge of each disc 80 is formed with a series of radial inwardly protruding lugs or teeth 95, each providing a rearwardly and inwardly inclined leading edge 96 and a more steeply inclined trailing edge 97, separated by a smoothly rounded tip 98.

The embodiment of FIGURES '7 to 9 using rotating rings which surround the workpiece for the purpose of forming an extruded external fin around the workpiece, can of course be used equally for the formation of circumferential fins as for the formation of a helical fin, and in both cases two or more fins may be formed simultaneously by the use of a suitable number of the rings 80. Moreover this embodiment has the advantage that the bearing arrangements for supporting the rapidly rotating rings 80 may be made very much larger and more substantial than is convenient in cases where rotating discs are used, so that these hearings will be able to stand up to much greater bearing pressures due to the reaction of the workpiece during fin formation. This in turn enables the apparatus to be used for fin formation on tougher metals or alloys or those having relatively high melting points, for example copper or steel or other ductile or malleable metals. For example it is envisaged that for fin formation on a steel workpiece it will probably be essential to use an arrangement of rings such as the rings 80 instead of discs for forming the fins, simply on account of the more robust bearing means which can thereby be provided.

In all the specific embodiments which have been described and illustrated, a tubular workpiece has been employed. It is found in certain instances that where discs or rings having undulating or irregular edges are used to provide an impact effect on the metal or the workpiece to assist the fin formation, small internal circumferential ridges may be formed thereby within the bore of the tubular workpiece. If such internal ridges cannot be tolerated and an accurate smooth-bored end product is required, the formation of such ridges may be prevented by the insertion of a solid close-fitting mandrel within the bore of the tubular workpiece. Moreover the various apparatus described can equally be used of course for fin formation on solid cylindrical bar stock instead of on tubular stock.

Whilst the workpiece-en gaging rotary edges of the tool in the various specific embodiments have been described and illustrated as being in the form of separate discs or rings, it will be clear that the tool might equally take the form of a cylindrical hub or drum formed with a series of spaced coaxial integral annular fianges protruding either outwardly or inwardly as the case may be.

Again, the tool might also take the form of a suitable chain or strip rotated around pulleys or sprockets and pressed into engagement with the workpiece. For example a bandsaw having suitable rounded teeth, driven in the reverse direction to that employed for cutting, might be employed.

What we claim as our invention and desire to secure by Letters Patent is:

1. The method of forming an integral fin on the surface of a workpiece made of a material which becomes softened and capable of extrusion when heated, compris ing the steps of: progressively and simultaneously applying to the surface of the workpiece along relatively spaced parallel paths, extending along the opposite sides of the intended location of the fin, and at locations maintained substantially abreast of each other along said paths, rapid successions of impacts directed generally normally to said surface, to locally heat and extrude material from the said parallel paths into the space between said paths to form said fins, and during the extrusion and thereafter for a predetermined period, continuously confining and supporting a portion of the extruded material between substantially parallel planes generally normal to said surface and coincident with the relatively adjacent edges of said paths.

2. The process of forming an integral fin on the cylindrical surface of a workpiece made of a material capable of extrusion, comprising the steps of: progressively and simultaneously applying to said cylindrical surface along relatively uniformly spaced paths extending helically around said surface, rapid successions of generally radial impacts, to indent said surface along said paths and extrude at least part of the displaced material into the space between said paths and during the extrusion and thereafter for a predetermined period, continuously confining and supporting a portion of the extruded material within a space having the cross-sectional configuration desired in the said fin.

References Cited in the file of this patent UNITED STATES PATENTS 80,022 Shefiield July 14, 1868 1,840,641 Short Jan. 12, 1932 1,909,005 Paugh May 16, 1933 2,170,513 Asbeck Aug. 22, 1939 2,188,456 Galber Jan. 30, 1940 2,306,827 Mohan Dec. 29, 1942 2,402,209 Ryder June 18, 1946 2,562,785 Hill July 31, 1951 2,586,011 Doelter Feb. 19, 1952 2,661,526 Bruegger Dec. 8, 1953 2,680,975 Goldsmith June 15, 1954 2,715,846 Grob Aug. 23, 1955 2,779,223 Schustcr Jan. 29, 1957 2,807,971 Garner et al Oct. 1, 1957

Claims

1. THE METHOD OF FORMING AN INTEGRAL FIN ON THE SURFACE OF A WORKPIECE MADE OF A MATERIAL WHICH BECOMES SOFTENED AND CAPABLE OF EXTRUSION WHEN HEATED, COMPRISING THE STEPS OF: PROGRESSIVELY AND SIMULTANEOUSLY APPLYING TO THE SURFACE OF THE WORKPIECE ALONG RELATIVELY SPACED PARALLEL PATHS, EXTENDING ALONG THE OPPOSITE SIDES OF THE INTENDED LOCATION OF THE FIN, AND AT LOCATIONS MAINTAINED SUBSTANTIALLY ABREAST OF EACH OTHER ALONG SAID PATHS, RAPID SUCCESSIONS OF IMPACTS DIRECTED GENERALLY NORMALLY TO SAID SURFACE, TO LOCALLY HEAT AND EXTRUDE MATERIAL FROM THE SAID PARALLEL PATHS INTO THE SPACE BETWEEN SAID PATHS TO FORM SAID FINS, AND DURING THE EXTRUSION AND THEREAFTER FOR A PREDETERMINED PERIOD, CONTINUOUSLY CONFINING AND SUPPORTING A PORTION OF THE EXTRUDED MATERIAL BETWEEN SUBSTANTIALLY PARALLEL PLANES GENERALLY NORMAL TO SAID SURFACE AND COINCIDENT WITH THE RELATIVELY ADJACENT EDGES OF SAID PATHS.