US2997570A - Fusing method - Google Patents

Description

Aug. 22, 1961 E. A. THOMPSON FUSING METHOD Original Filed Dec. 30, 1957 I /56 IF K P" I 206 T v /4a H r we I l 1 l 1 EARL ,4. THOMPSON A TORNEY States Patent-O and this application July 13, 1959, Ser. No. 826,739 14 Claims. (Cl. 219- 107) This invention relates to a method for the electric fusion of metal parts. The invention is more particularly con cerned with a method for producing fused cast iron and steel tappets for automotive engines in which a cast iron base is directly joined to a tubular steel sleeve or body in a single short application of heat and pressure.

This application is a division of co-pending application Serial No. 706,116, filed December30, 1957, now Patent 2,935,596 of May 3, 1960, which is, in turn, a continuation-in-part of abandoned application Serial No. 637,589, filed January 31, 1957, and which in turn is a continuation-in-part of abandoned application Serial No. 407,005, filed January 29, 1954.

It has long been recognized that the wearing properties of cast iron are well suited for service as a follower member in direct contact with an automotive camshaft and that the body portion of a tappet is most desirably formed of steel. Such two-piece tappets have heretofore been difficult to manufacture because of the problems of forming a reliable joint between the cast iron and the steel which will stand the impact forces involved and which canbe produced in quantity at reasonable cost. Various proposals have been made for joining the cast iron and steel directly by an electric heating process without, however, achieving a commercially satisfactory machine or method for producing a thoroughly reliable junction economically. One diificulty involved resides in the difference in melting points between cast iron and steel. When a heating current high enough to melt'the iron is applied, the steel does not melt but the molten iron will flow as a liquid which instantaneously leaves the zone of juncture, preventing adherence of the two pieces. 7 It is an object of the present invention to provide an improved method for directly joining a cast iron piece to a steel piece having a higher melting point.

A further object is to provide such a method in which a pulse of electric heating current, together with the application of a strong compressive force will serve to both fuse the cast iron to the steel at one place and upset the steel into mechanical contact with solidcast iron at another place. i

A further object is to provide such a method in which the flow of the molten iron is confined and in which the upsetting of the steel takes place in a manner to eliminate the formation of irregularly projecting nodules of metal so that the finished joint presents a comparatively smooth and regular surface which needs no snagging and may be finished by conventional grinding methods.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of the present invention is illustrated.

In the drawings:

FIG. 1 is a fragmentary sectional view illustrating the parts of a two-piece tappet in position in a fusing machine and ready for fusing.

FIG. 2 is a view corresponding to FIG. 1 showing the starting stage in the fusing operation. a

FIG. 3 is a View corresponding to FIG. 1 showing the 'complete fused tappet at the completion of the fusing operation.

FIG. 4 is a view of the fused tappet ready for removal from the machine.

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FIG. 5 is a view of a finished tappet made according to a preferred form of the present invention.

There is shown diagrammatically and fragmentarily in FIGS. 1 through 4 the work engaging parts of a fusing machine which is fully disclosed in the parent application above identified. A work piece abutment 172 forms a stationary support against which the work may be pressed by a downwardly moving upper electrode 276 under the control of suitable motivating means. Mounted for horizontal relative movement are a pair of clamping electrodes 148 which are of semi-circular form to provide for tightly clamping a tubular steel work piece 414 between the opposed cavities of the electrodes 148. At their top portions, the electrodes 148 each carry aninsulated die 156 of stainless steel or other high melting point material. Mounted on top of the tube 414, and temporarily centered by the retractible plunger 206, is a cast iron button 446 having a shoulder resting on the tube and a smaller extension telescoping into the tube with a fairly large radial clearance.

Operation of the machine by motivating electrode 276 applies a high pressing force, pushing the button into the end of the tube. The application of the heating current between electrodes, 276 and 148, along with the pressure causes the upper end of the steel tube to soften; but not melt, and results in a swaging, or upsetting, of the tube Wall, both inwardly and outwardly in a radial direction. Thus, the steel is swaged into mechanical contact with the side wall of the telescoping portion of the button and is also swaged outwardly into contact with the insulated die 156.

At the same time, the cast iron is heated above its melting point locally adjacent the contacting faces of the two parts. The molten cast iron tends to fiow away from the joint face at first, but is prevented from flowing inwardly by the mechanical seal established by the inwardly upset end of the tube. Thus, the molten cast iron may only flow outwardly into contact with the die 156. Here it is blocked against downward flow by the outward upset of the steel tube and can only flow upwardly. That flow is stopped almost as soon as it starts by the chilling effect of the die 156 leaving a random edge formation as shown at 415.

It will be understood that the characteristics of the joint obtained may be varied depending upon a number of factors. Thus, for example, if the buttons are preheated to 400 F. or 500 F., the iron melts sufficiently soon during the swaging that the iron flows out to contact the die and solidify in the manner described. On the other hand, if the buttons are utilized at room temperature, or with considerably less pre-heating, the swaging of the steel may continue before the iron melts so as to extrude a portion of the steel upwardly past the boundary of the cast iron and into the clearance space between the button and the die before the cast iron can reach that space. In either event, a fusion of the iron to the red-hot, but unmolten, steel is obtained at the junction plane of the two pieces. This is supplemented by a mechanical bond through swaging or upsetting along the lower telescoping protuberance of the cast iron button.

The intensity of the heating current and the time of application are subject to some variation depending upon the size of the parts to be joined and the composition of their metals. In a typical automotive tappet of A; diam.- eter tubular stock with about ,4 wall thickness, a heating time of about 30 cycles of 60 cycle current is suitable. The power usage may be of the order of magnitude of KVA.

If desired, the heating current may be applied in stages, first at a low value for pre-heating the pieces. During the pre-heating step the upper end of the tube 414 and the adjacent facial region of the button, which is in contact with the tube, may be brought to a temperature which is just below the melting temperature of cast iron, that is, around 2000 F. ,When the tube 414 is a steel tube, the top end Will be brought, during the preheating step,..to a forging temperature of about 1800 F. The current will take the shortest path between the electrode 148 and electrode 276, and therefore, only the upper end of the tube 414, as well as the button 446 will be heated any substantial amount. After the pre-heating stage the final fusing current of high value may be ap plied to raise the temperature of the cast iron button above its melting point locally adjacent the interfacial areas between the tube and button as previously described. With the use of a pro-heating stage, the steel tube may be brought to a higher forging temperature and thus a more extensive upset, or forging thereof, may be obtained.

While the parts are described as being directly joined, the use of that and like expressions is intended to include joining parts which may have thin coatings on them of a different metal or other material and which may become embedded or alloyed in the metal forming the zone of juncture.

It will thus be seen that the present invention provides an improved method performed through the use of a chilling die adjacent the faces of pieces to be joined and produces an improved joint in the final product which has a high mechanical strength and which is of a homogeneous nature in that there is no extraneous material separating the two metals. Due to the migration of carbon from the cast iron to the steel, the joint has a zone of significant width across which the carbon content varies from a high value in the cast iron to a low value in the steel. The joint is formed with such an intimate bond between the two metals that there is no line visible, except under a microscope, when the edge of the joint has been machined smooth, aud t-he fused piece looks, when finished, as though made from a single body of metal.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all connng within the scope of the claims which follow.

What is claimed is as follows:

1. The method of making a valve tappet which comprises clamping a tubular steel body between electrodes by diametral pressure at a short distance from the end thereof, pressing a cast iron end piece endwise toward the said end of the body, applying a heating current between the end piece and the body sufiicient to melt the iron adjacent the joint without melting the steel of the tubular body and confining the flow of molten iron and softened steel within die mold extensions of the electrodes surrounding but spaced from the unjoined parts whereby a combined upsetting of the steel and fusion of the cast iron to the body is produced.

2. The method of making a valve tappet which comprises clamping a tubular steel body between electrodes by diametral pressure at a short distance from the end thereof, pressing a cast iron end piece endwise toward the said end of the body, applying a heating current between the end piece and the body sufiicient to melt the iron adjacent the joint without melting the steel of the tubular body and confining the flow of molteniron and softened steel within electrically insulated die mold extensions of the electrodes surrounding but spaced from the unjoined parts whereby a combined upsetting of the steel and fusion of the cast iron to the body is produced.

3. The method of making a valve tappet which comprises clamping a tubular steel body between electrodes by diametral pressure at a short distance from the end thereof, pressing a cast iron end piece endwise toward the said end of the body, applying a heating current between the end piece and the body sufiicient to melt the iron adjacent the joint without melting the steel of the tubular body and confining the flow of molten iron 4 and softened steel within die mold extensions of the elec trodes surrounding but spaced from the unjoined parts whereby a combined upsetting of the steel and fusion of the cast iron to the body is produced and subjecting the die molds to a cooling period betweensuccessive fusing operations.

4. The method of making a valve tappet which compirses clamping a tubular steel body between electrodes by diametral pressure at a short distance from the end thereof, placing a cast iron end piece in surface contact with the end surface of the steel body, laterally centering the end piece with respect to the body, pressing the cast iron end piece endwise toward the said end of the body, applying a heating current between the end piece and the body sufiicient to melt the iron adjacent the joint without melting the steel of the tubular body and confining the flow of molteniron and softened steel within die mold extensions of the electrodes surrounding but spaced from the unjoined parts whereby a combined upsetting of the steeland fusion of the cast iron to the body is produced.

5. T he method of making a valve tappet which comprises, placing a steel tubular body and a cast ferrous base end piece together with surf-aces in interfacial relationship and with a part of the end piece projecting into the tubular body and then weld uniting the interfaces by heating the contacting surfaces of the body and end piece to the melting temperature of the ferrous base.

6. The method of making a valve tappet which comprises, placing a steel tubular body and a cast iron end piece together with surfaces in intefacial relationship and with a part of the end piece projecting into an end of the tubular body, and then locally heating to the melting temperature of the cast iron both the end of the tubular body and the region of the cast iron end piece adjacent to and contacting the said end of the tubular body and, while at said temperature, forcing the metal of the body to be displaced inwardly into tight mechanical contact with the projecting part of the end piece and, during the same heating operation, forming a fusion weld at said end of the body.

7. The method of making a valve tappet which comprises, placing a metal body having a tubular end and a metal end piece having a lower melting point than the melting point of the tubular end together with their surfaces in interfacial engagement, heating the interfacial surfaces to substantially the melting temperature of the end piece and subjecting the parts to pressure axially of the body having the tubular end to force the tubular end of the body into the end piece and fuse the same together.

8. The method of making a valve tappet which comprises placing a metal tubular body and a metal end piece together with surfaces in interfacial relationship, the metal body being made of a metal having a higher melting temperature than the metal of the end piece, applying electric current to said body and said end piece sufficient to heat the surfaces in interfacial relationship to the melting temperature of the metal of the end piece and less than the melting temperature of the metal of the body, and subjecting the parts while at said temperature to pressure axially of the tubular body to fusion bond the body and end piece.

9. The method of joining a piece of cast iron to a piece of steel which comprises forming one piece with an end contact face adjacent to a perpendicularly extending surface and forming the other piece with a shoulder corresponding dimensionally with said face and also adjacent to a perpendicularly extending surface, placing said pieces together with the face abutting the shoulder and with said perpendicular surfaces parallel and in slightly spaced juxtaposition, applying electric current to heat the pieces adjacent their contact areas to a temperature above the melting point of the cast iron and below the melting point of the steel, and forcing the pieces together with suflicient pressure to upset the steel laterally into mechanical contact with the cast iron along the juxtaposed surfaces while restraining the softened steel and molten cast iron against flow away from the immediate situs of the joint.

10. The method of joining a piece of cast iron to a piece of steel which comprises forming the steel piece with an end contact face adjacent to a perpendicularly extending surface and forming the cast iron piece with a shoulder corresponding dimensionally with said face and also adjacent to a perpendicularly extending surface, placing said pieces together with the face abutting the shoulder and with said perpendicular surfaces parallel and in slightly spaced juxtaposition, applying electric current to heat the pieces adjacent their contact areas to a temperature above the melting point of the cast iron and below the melting point of the steel, and forcing the pieces together with suflicient pressure to upset the steel laterally into mechanical contact with the cast iron along the juxtaposed surfaces and chilling that portion of the steel and iron which tends to leave the immediate situs of the joint.

11. The method of joining a piece of cast iron to a piece of steel which comprises forming the steel piece with an end contact face adjacent to a perpendicularly extending surface and forming the cast iron piece with a shoulder corresponding dimensionally with said face and also adjacent to a perpendicularly extending surface, placing said pieces together with the face abutting the shoulder and with said perpendicular surfaces parallel and in slightly spaced juxtaposition, applying electric current to heat the pieces adjacent their contact areas to a temperature above the melting point of the cast iron and below the melting point of the steel, and forcing the pieces together with sufficient pressure to upset the steel laterally into mechanical contact with the cast iron along the juxtaposed surfaces and maintaining a relatively cold rigid molding surface adjacent one side of the joint.

12. The method of joining a piece of cast iron to a piece of steel which comprises forming the steel piece with an end contact face adjacent to a perpendicularly extending surface and forming the cast iron piece with a shoulder corresponding dimensionally with said face and also adjacent to a perpendicularly extending surface, placing said pieces together with the face abutting the shoulder and with said perpendicular surfaces parallel and in slightly spaced juxtaposition and establishing a conductin relationship of each piece to one of a pair of welding electrodes while applying current therethrough to heat the pieces adjacent their contact areas to a temperature above the melting point of the cast iron and below the melting point of the steel, forcing the pieces together with sufiicient pressure to upset the steel laterally into mechanical contact with the cast iron along the juxtaposed surfaces, and maintaining a relatively cold rigid molding surface in non-conducting relation to one side of the joint.

13. The method of joining a piece of cast iron to a piece of steel having a higher melting point than the cast iron which comprises placing the pieces with their surfaces to be joined in abutting contact, applying an electric current across the joint to heat the pieces to a temperature above the melting point of the cast iron but below the melting point of the steel, applying a welding and forging force to the pieces to upset the steel laterally and limiting the lateral flow of the softened steel and the molten iron by relatively cold barriers, one on each side of the joint surfaces and extending perpendicularly and in spaced relation thereto prior to upsetting.

14. The method of joining a piece of cast iron to a piece of steel having a higher melting point than the cast iron which comprises placing the pieces with their surfaces to be joined in abutting contact, applying an electric current across the joint to heat the pieces to a temperature above the melting point of the cast iron but below the melting point of the steel, applying a welding and forging force to the pieces to upset the steel laterally and limiting the lateral flow of the softened steel and the molten iron by relatively cold barriers, one on each side of the joint surfaces and extending perpendicularly and in spaced relation thereto prior to upsetting, one of said barriers comprising an offset extension of the cast iron piece.

References Cited in the file of this patent UNITED STATES PATENTS 1,503,315 Gail July 29, 1924 1,691,779 McDonald Nov. 13, 1923 2,352,754 Aderson July 4, 1944

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