US2344358A

US2344358A - Method of making forged pistons

Info

Publication number: US2344358A
Application number: US318721A
Authority: US
Inventors: Alexander H King
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1940-02-13
Filing date: 1940-02-13
Publication date: 1944-03-14
Anticipated expiration: 1961-03-14

Description

arch 14,1944. A. H. KlNG 9 9 METHOD OF MAKINGFORGED PISTONS Filed Feb. 13, 1940 v 2 Sheets-Sheet 1 INVENTOR ATTORNEY,

March M, 1944. A. H. KING METHOD OF MAKING'FORGED PISTONS 2 Sheets-Sheet 2 Filed Feb. 13, 1940 I 4m *3 ATTORNEY v INVE NTOR parent to those skilled in Patented Mar. 14, 1944 Alexander E. King, West Hartford, Conn.,

Aircraft Corporation, a corporation of Delaware or to United i'ord, Conn,

a m- Eest Hart- Application February 13, 1940, Serial No. 318,721

El Claims.

This invention relates to improvements in methods of making engine pistons and has particular reference to improvements in the construction and manufacture of forged pistons such as are ordinarily used in internal combustion engines.

An object of the invention resides in the production of an improved piston of the character indicated in which-there are present no sharp folds onbends such as might initiate a failure of the piston material.

A further. object resides in the production of forged pistons oi thecharacter indicated in which the shape of the major portion .of the interior of the piston is formed by the forging dies thus eliminating diificult and expensive machining operations on the interior of the piston.

A still further object resides in the provision of a simple and eficient methodof menufeciniring pistons of the character indicated without folding or bending the material thereof enough to unduly strain the piston material.

Other objects and advantages will be more particularly minted out hereinafter or will become apparent as the description proceeds.

In the accompanying drawings, in whichlike reference numerals are used to designate similar parts throughout, there is illustrated several different steps in the method of producing an immoved piston of the character indicated, and a finished piston embodying the improvements of this invention. The drawings, however, are for the p pose of illustration only and are not to be taken as limiting the invention as it will be 8.1

the art that variations in the method illustrated and additional steps as may be necessary or desired may be utilized and modifications in the piston construction may be resorted to without in any way exceeding the scope of the invention.

in the drawings,

Fig. 1 is a bottom plan view or a. piston blank in. an early stage of the production method.

Fig. 2 is a longitudinal sectional view taken on the line 22 01 Fig. 1. V

Fig. 3 is a longitudinal sectional view. taken on the line 3-3 of Fig. 1.

Fig. 41s a bottom plan view of the piston blank at ulster stage in the forging process.

Fig. 5 is a longitudinal sectional view taken on the line 55 of Fig. 4.

Fig. 6 is a longitudinal sectional view taken on the line 8-8 of Fig. 4.

Fig. 8 is a longitudinal sectional view on the line 38 of Fig. 7.

Fig. 9 is s longitudinal sectional view on the line 9-9 of Fig. 7.

Fig. 10 is a bottom plan view of the finished piston.

Fig. 11 is a longitudinal sectional view on the line H-Jiof Fig. 10, and

Fig. 12 is a longitudinal sectional view on the line E2i2 of Fig. 10.

As is well known to the art, an internal com- I bustion engine piston is a generally cup-shaped member having a. cylindrical wall or skirt portion open at one end and closed at the other end by the piston head. Internally this wall or shirt is provided with diametrically opposed thickened portions, ordinarily referred to as bosses. through which the spenfiures for theend por tions of the wrist pins for connecting the piston to its respective connecting rod extend. Good practice requires that the piston be made as light as possible consistent with adequate strength and sealing ability and an adequate bearing surface opposed to the wall of the cylinder within which it operates. In order to obtain a condition of minimum weight such pistons are conveniently made of a. relatively light material, such as an aluminum alloy, and are made as short as possible, keeping in view the above mentioned requirements of strength, sealing ability and suflicient hearing area. This condition frequently necessitates extending the wrist pin bosses to near the open end of the piston. In

. addition to being made as short as convenient Fig. '2 is a. bottom plan view of the piston blank it is a further requirement that the pistons contain no excess material over that required to provide the necessary strength and the necessary bearing areas and grooves for the piston rings. In thus reducing thetotal amount of material in the piston the head portion is frequently made relatively or fins which also serveas heat transfer elements and the walls of the skirt portions between the wrist pin bosses are in general, the thinnest portions of the piston since these portions of the piston are subjected tovery little stress. Practically all pistons o! the character -indicated are provided about the head end with a seriesof circumferential grooves for carrying sealing rings to seal the space between the D1 ton and the cylinder within which it operates. Good practice has indicated the necessity of also providing an oil control ring near the open end of the piston. Since the skirt porflon of the piston may be made much thinner than the thickthin and reinforced by spaced ridges operations and ness necessary to receive the groove for such a 1 ring, this necessitates an internal flange around the open end of the piston to reinforce the piston end to provide sufficient material for the rin carrying groove. According to one well known method of forged piston production, the piston skirt between the wrist pin bosses is made of a uniform thickness from the head to the open end of the piston and some material between the bosses is machined away below the bottom ring groove .to lighten the piston. This machining operation, however. is diflicultand expensive and does not remove all of the material in excess of that required for necessary piston strength. It is. therefore. .Wparent that it would be of great advantage to shape the interior of the piston to the correct contour during the forging operation. Heretofore, considerable difliculty has been experienced in forging pistons so that they will havethe correct interior shape without machining, the difllculty arising mainly from the necessity of providing the internal flange for the bottom ring groove which flange renders it difficult to remove the forming dies from the interior of the piston. It has also been known to reduce this difllculty by forming the material for this internal flange on the outside of the piston during earlier steps of the forging method and to turn this material in to form the internal flange when the forging is nearly complete. While this method has certain advantages and may be used successfully with pistons of certain favorable shapes and dimensions, for pistons of the general character indicated above, it tends to result in sharp bends and folds in the material of the bottom flange with consequent local highly stressed portions which tend to initiate fatigue cracks and ultimate failure of the piston.

It is among theobiects of the present invention to provide a piston with an interior shaped entirely by the forging operation and which at the same time is free of localized high stresses, cold-shuts, and other irregularities in the piston material which might be inducive to piston failure.

Referring now to the drawings in detail, Figs. 1, 2 and 3 show a piston blank at an early stage in the forging operation. Figs. 4, 5 and 6 show the same blank after additional forging operations have been performed upon it, Figs. '7, 8 and 9 show the same blank after still further forging Figs. 10, 11 and 12 show the finished piston after the forging and machining operations have been completed. These groups of figures are intended to show merely certain stages inthe forming ,of the piston and do not necessarily include all of the forging and machining steps or operations as there may be several steps between the initial billet and the blank shown in Figs. 1, 2 and 3. a number of steps between the form of the blank shown in Figs. 1, 2 and 8 and the form shown in Figs. 4, 5 and 6 and several steps between the form shown in Figs. '4, 5 and 6 and the form which the billet has taken at the stage illustrated in Figs. 7, 8 and 9 and additional forging and machining operations may be performed on the blank between the stage illustrated in Figs. 7, 8 and 9 and the finished piston illustrated in Figs. 10, 11 and 12. These illustrations, however, show certain important stages in the forming of the finished piston from the original billet.

At the stage shown in Figs. 1, 2 and 3 the blank has been given a generally cup-shaped form rathep sharply tapered from the closed end to bosses themselves and a ridge rial has been formed on the outside of the skirt I angles to the surface the open end to facilitate the removal of the forming dies and has been provided with a head portion l0, skirt portions i2 and wrist pin bosses II. The bosses are provided with extensions at the open end of the piston, as indicated at It. which extensions are thicker than the skirt portions between the bosses but not as thick as the is, of excess mateat the open end in each space between the thickened portions l8.-. As particularly shown in Fig. 1, these extensions or ridges of excess material it! are of a generally crescent shape having.

their greatest thickness at the point midway between the bosses l4 and tapering in each direction toward the bosses the shape being particularly indicated by the space between the outer line 20 and the dotted line 22 in Fig. 1 which lines indicate respectively the outer edge of the excess material and the line at which this material joins the main portion of the piston. skirt. These bodies of excess material disposed on diametrically opposite sides of the piston between the bosses i4 are given a definite cross sectional shape so that they will conform to the piston shape when folded in by later forging operations. The surface between the

lines

22 and 20 is flared outwardly with respect to the skirt i2, the surface between the line 20 and the top line 24 is disposed substantially at right portion between the

lines

22 and 20 so that when the excess material is folded in until the portion between the

lines

22 and 20 constitutes a continuation of the skirt the portion between the

lines

20 and 24 will constitute the end surface of the piston and the surface portion between the line 24 and the line 28, indicating the upper end of the inner surface of the skirt, is disposed substantially at right angles to the surface between. the

lines

20 and 24 and substantially parallel to the sur-- face between the

lines

22 and 20 so that, when tween the

lines

24 and 26 will constitute the inner surface of the end flange as will later appear. An inspection of Fig. 1 indicates that the

lines

20 and 24 constitute substantially concentric ellipses and that beveled areas between the

lines

20 and 24 and between the

lines

24 and 2 fair at their ends into the piston end surface portion adjacent the bosses i4.

At the stage illustrated in Figs. 4, 5 and 6 the taper of thepiston skirt portion has been somewhat redu'ced but the bodies of excess material II are still present on the exterior of the open end portions of the skirt and up to this stage the forging operations may be performed by solid die members since there is no return bend either interiorly or exteriorly of the piston blank which would necessitate a separation of either the ex-.

ternal or internal die.

At the stage illustrated in Figs. 7, 8 and 9 the bodies of excess material ll have been turned in to constitute parts of an upsetin'ternal flange of a sharp return bend or fold immediately over the ends of the wrist pinbosses such as would be present if excess material were applied to the exterior of the skirt all around and then forced inwardly over the ends of the bosses. Between the bosses there is little danger of setting up excessive strains or producing flaws in the material since there is suflicient space in this area for the material to flow and even out so that no strain will be present which will not be subtion, it. is to be understood that the invention is not limited to the particular construction and stantially eliminated in subsequent annealing operations. The blank may be changed from the form shown in Figs. 4, 5 and 6 to the form shown in Figs. 7, 8 and 9 by forcing it inwardly upon a multi-part internal die. Such a die is well known to the prior art and may have a central portion and detachableside portions which may be removed from under the flange 28 after the central portion has been removed. In this operation the former elliptical contour of the open end of the blank is changed to a circular contour, the skirt, as mentioned above, is straightened and the blank is put into shape for machining after such annealing or heat treating steps, as may be necessary or desired, have been performed. i

it is to be particularly noted that in applicants improved method the skirt material at the ends of the wrist pin bosses is not moved after the hosses are formed and there are therefore no re turn bends between this material and the end portions of the bosses and that the material that is moved decreases uniformly in thickness from a point midway between the bosses towards the ends of the bosses so that when this material is turned in very little material is moved in those portions of the skirt which are stiffened by the presence of the integral wrist pin bosses, the main movement occurring midway between the bosses where the skirt is relatively thin and flexible and where there is ample room to provide an easy return bend between the thickened portion and the interior surface or the skirt wall. By this improved method applicant is able to forges piston having a thinwalled skirt between the bosses and one which has forged therein the optimum internal contour for strength over weight characteristics and in which no excessive stresses or strains are set up in any part of the material.

After the stage illustrated in Figs. 7, 8 and 9 the piston blank, after suitable annealing and/or heat treating steps, may be machlned to produce the finished piston illustrated in Figs. l0, l1 and 12. This finished piston may be provided with a flat or dome shaped head iii and a series of circumferential grooves, as indicated at M, adjacent the head for the piston sealing rings. Over the portion including the ring grooves 30 the piston wall is thickened as indicated at 31 to provide sumcient material for the grooves but between this thickened portion 32 and the bottom flange dd and between the bosses M the piston skirtm quite thin, as indicated at 3|, and this thin section runs up substantially to the bosses M where it is iaired into the bosses by suitable fillets, vs

indicated at 35 in Fig. 10. A bottom ring groove M is provided in the bottom flange 2B and suitablewrist pin apertures ll are provided through the bosses i l but no machining operations on the intcrior of the piston are required except the minor lathe operations for rounding the inner surface of the flange 2! and, if desired, providing the bevel 42 around the interior of this flange. While a particular piston construction and certain selected stages in the process of manufacturing such a piston have been hereinabove described and illustrated in the accompanying drawings tor the purpose oi disclosing the invenprocess stages so illustrated and described but that various changes in both the construction the interior or said annular portion extending to" near the open end thereof, said annular portion including skirt portions between said bosses, portions over the ends 01 said bosses thicker than said skirt portions and external radial extensions at the open end thereof between said thickened portions over the ends of said bosses, said blank havingin general an elliptical contour at its open end, and reforging said blank to reduce the flare of said annular p rtion, chang the elliptical contour of said open end to a substantially circular contour and move said external radial extensions into substantial circumferential alignment with the thickened portions of said annular portion over said bosses without materially disturbing the material of said thickened portions, to provide a blank having an open end portion thicker than said skirt portion the parts of which between said bosses are constituted by flange portions having a return bend and the parts of which over said bosses are constituted-by said thickened portions without a return bend. 2. The method of manufacturing an engine piston having an annular reinforcing portion around the open end thereof and wrist pin bosses which extend to a location spaced from the open end of said piston by a distance substantially the same as the width ofsaid annular portion, said method comprising, forging a metal billet into a cup shaped blank having a closed end section and a flared annular section including said wrist pin bosses, skirt portions between said bosses having a thicheas less than the thickness of said annular portion, extensions from the ends of said bosses to the open end of said blank ha ing. outer surfaces 1 in the plane of the external surface of said flared section and having a thickness greater than the thickness of said skirt portions, and external outwardly disposed ridges at the ends of said skirt portions also having a thickness greater than the thickness of said skirt portions, and reiorging said blank to reduce the external surface or said annular section to a substantially cylindrical shape and bend said skirt ridges inwardly to constitute with said boss extensions the said annular reinforcing mrtio'n around the interior of the open end of said piston.

3. The method or manufacturing an engine piston having an annular reintorcing portion around a thickness less than the thickness of said annular portion. extensionsirom the end of said bosses to the open end of said blank having a thickness greater than the thickness of said skirt portions and having outer surfaces lying in the plane of the outer surface of said flared section, and ridges on the ends of said skirt portions extending radially outward at their center portions beyond said skirt portion and having their end portions faired into said boss extensions, said ridges also having a thickness greater than the thickness of said skirt portions, and'reforging said blank to reduce the external surface of said flared section to a substantially cylindrical shape and bend said ridges inwardly to constitute with said boss extensions the said annular reinforcing portion around the interior of the open end of said piston.

' 4. The method of manufacturing an engine piston which comprises, forging a metal billet into a cup shaped blank having a closed end and a flared annular portion including a pair of internal diametrically opposed wrist pin bosses extending to near the open end of said blank, skirt portions between said bosses, extensions from the ends of said bosses to the open end of said blank of a thickness greater than the thickness of said skirt portions, and external ridges on said skirt portions between said boss extensions, the interior of said blank having no overhanging portions which would interfere with the removal of a solid die therefrom, reforging said blank to reduce the external surface of said annular portion to a subtions between said bosses thicker than said skirt I disposed outwardly at an angle to the plane of said skirt to form ridges overhanging the exterior surface of said skirt between said bosses, said ridges being adapted to be swaged inwardly to form with said sections over said bosses a continuous annular thickened portion which is machined to provide a circular reinforcing flange around the open end of said skirt.

stantially cylindrical shape and, without materially disturbing the metal in said extensions. -converting said ridges on said skirt portions into internal flange portions of a thickness greater than the thickness of said skirt portions suificient to receive a piston ring groove and forming with said wrist pin-boss extensions a smooth annular reinforcing portion at the open end of said blank.

5. A forged blank for an engine piston comprising, a cup-shaped member having a generally cylindrical skirt portion open at one end and closed at the opposite end by an integral head portion, integral wrist pin bosses on the interior of said skirt portion, the ends of said bosses being spaced 6. In a method of forging engine pistons, the steps of: forging a metal billet to form a cupshaped blank comprising an annular section having a head closing one end thereof, said annular section including internal bosses and skirt portions between said bosses, a reinforcing annulus of greater thickness than said skirt portions extending around said annular section at the open end thereof, said reinforcing annulus comprisin first sections over said bosses no part of which overhangs the interior surface of said annular section and the outer surface of which forms a continuation of the outer surface of said annular section, and second sections over said skirt portions no part of which overhangs the interior surface of said annular section and the outer surface of which overhangs the outer surface-of said annular section; and reforging said blank, without materially working the metal of said first sections, to bend said second sections inwardly to a position where they overhang the interior surface of said annular section and their outer surfaces form a continuation of the outer surface of said annular section to provide with said first sections a continuous circular flange of greater thickness than said skirt portions around the open end of said annular section. a ALEXANDER H. KING.