US3319321A - Method of making engine valve - Google Patents

Description

May 16, 1967 I l.. J. DAMS 3,319,321

METHOD OF MAKING ENGINE VALVE Filed Jan. 10, 1964 x INVENTOR. a auf J'Jd was United States Patent O 3,319,321 METHGD F MAKING ENGINE VALVE Louis J. Danis, Battle Creek, Mich., assigner to Eaton Manufacturing Company, Cleveland, Ohio, a corporation of Ghia Filed lan. 10, 1964, Ser. No. 337,064 7 Claims. (Cl. 29-156.7)

The present invention relates to an improved method of making an engine valve and more particularly to an improved process for forming poppet-type valves of the type used in internal combustion engines employing a ductile low-carbon steel which facilitates the formation by cold forging and/ or extrusion relatively intricate valve configurations followed by a subsequent preliminary machining and case hardening treatment and thereafter a final machining operation resulting in a valve having excellent performance characteristics and which is substantially simpler and more economical to manufacture.

Poppet-type valves for use in internal combustion engines, and particularly intake poppet valves of the type employed in automobile engines have heretofore been made employing medium and high-carbon alloy steels by either cold or hot forging techniques. While this manufacturing technique hasbeen satisfactory for most purposes, a continuing problem associated with these processes has been the difiiculty and lack of versatility in forming intricate valve shapes under cold-forming conditions. In addition, medium and high carbon alloy steels of the types conventionally employed necessitate more complex tooling and produce a greater toolor die wear rate resulting in increased tooling costs and in frequent down time for tool replacement. A further problem associated with the processes heretofore known has been the limitation imposed by medium and high-carbon alloy steels on the rate of production of valves due to the difliculty of forming and machining the material. In addition to the problems associated with the manufacture of such valves by the processes heretofore known, the valves themselves havek been found to be of less than optimum fatigue life and Wear resistance particularly in view of thev increased design performance of modern internal combustion engines.

lt is accordingly a principal object of the present invention to provide an improved method of making poppettype engine valves and to an improved valve made by the process which overcomes the problems and disadvantages associated with techniques heretofore employed.

Another object of the present invention is to provide an improved process for the manufacture of poppet-type engine valves employing a low-carbon steel which provides for substantially increased versatility and flexibility in obtaining intricate configurations and forms at room temperature while additionally providing for substantially increased production rates.

Still another object of the present inventionis to provide an improved process for forming poppet-type engine valves employing a low-carbon steel Which enables the use of simplier tooling and further reduces wear on the tools providing greater die life with corresponding reductions in production down time and improved manufacturing efiiciency.

A further object of the present invention is to provide an improved process and an improved poppet-type engine valve manufactured thereby which is more economical and simpler to manufacture, and which possess superior fatigue life and improved wear resistance over similar type valves made of medium and high-carbon alloy steels.

The foregoing and other objects and advantages of the present invention are achieved by a process employing a low-carbon steel which can be rapidly cold forged into any one of a variety of suitable shapes followed theren vmerci-al automobile engines.

3,3 l 9,321 Patented May 16, 1967 after by a preliminary machining and a case-hardening operation after whichthe case-hardened rough machined valve is subjected to a final finishing operation providing the requisite dimensional accuracy of the valve. It is also contemplated within the scope of the present invention that the original bar stock employed for cold forging may be annealed to increase its ductility and may also be annealed subsequent to the cold forging operation if desired to remove any undesirable residual stresses therein. It is further contemplated that the case-hardened valve blank can be drawn after the case-hardening operation and can be further subjected to a flame-hardening operation of the valve stem tip to provide a hard tip surface resistant to wear by an operating push rod, cam follower, or rocker arm disposed in contact therewith.

Other objects, features and advantages of the present invention will become apparent from the subsequent description, taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic flow diagram illustrating the necessary operating steps as well as optional steps which are employed in accordance with the practice of the improved process comprising the present invention;

FIGURE 2 is a side elevational view of a bar stock blank employed in subsequent cold-forming operations to form a finished valve;

FIGURE 3 is a side elevational view of the blank after an initial cold-extrusion operation; and

FIGURE 4 is a side elevational view of the resultant cold-forged valve blank prior to machining and case hardening.

The steel raw material used for forming the valve body may comprise any cold formable grade of low-carbon or low-alloy steel which is susceptible to case hardening such as by carbonitriding or carburizing including steel having a carbon content ranging from about 0.03% to about 0.6%. Carbon contents in a range of from about 0.08%

to about 0.25% are prepared for maximum workability of the material yas may be required in the most complex forming operations. 'Inaddition to the carbon constituents in the steel, the steel may further contain in addition to conventional quantities of impurities, up to about 5% of intentional alloying elements employed in standard SAE steel grades including alloying constituents such as nickel, manganese, chromium, molybdenum, boron, silicon, vanadium, etc.

The specific composition of the steel or low-alloy steel can be varied within the aforementioned definitionto provide a resultant steel having a degree of ductility sutiicient to enable cold-formation of the steel blanks into a valve of the desired configuration. Accordingly, where relatively complex conligurations of the valve are required necessitating a correspondingly greater degree of deformation of the blanks, the composition of the steel is controlled so as to provide the requisite ductility. Similarly, where a valve coniiguration necessitates less drastic reduction of the blank, then combinations of the aforementioned constituents can be employed providing a slightly lower degree of ductility while nevertheless providing for satisfactory deformation of the blank to the final configuration.

A steel which has been found eminently as satisfactory in accordance with the practice of the present invention comprises a fully annealed SAE 1018 steel which has a sufficient degree of ductility to enable cold deformation of the blank into poppet-type valve configurations of the most complex configuration presently employed in com- The composition of an SAE 1018 steel typically includes 0.15-0.20% carbon, 0.60-0.90% manganese, 0.4% maximum phosphorous,

3 0.5% maximum sulfur, and the balance iron. Typical properties of a fully annealed SAE 1018 steel are as follows:

Physical properties Yield strength, p.s.i 30,000 Tensile strength, p.s.i 55,000 iElongation (percent to inches) 45 Reduction of area, percent 70 B'rinell hardness 100 In order to employ a steel blank having the requisite degree of ductility, it is frequently desirable to subject the `raw bar stock material from which sheared blanks are cut to a complete, or partial spheroidization, or a simple subcritical annealing treatment prior to the cold-forming operation consistent with the composition of the steel, the degree of work hardness to which it has been subjected in the rolling mill, and the degree of deformation to which it is to be subjected consistent with the conguration of the valve to be manufactured. Maximum ductility of a steel blank requires complete spheroidization. A partial spheroidization or -a simple subcritical annealing treatment is frequently satisfactory while in many instances no annealing treatment at all can be employed to provide a steel blank of the requisite ductility.

With `reference to FIGURE 1, a schematic iiow sheet of the several process steps a-re diagrammatically indicated wherein the bar stock as received ean be sheared to the appropriate length forming blanks that can be directly cold forged or alternatively the bar stock either prior -to or after shearing can be subjected to an intervening annealing treatment as indicated by the dotted lines. In either event the steel blanks having a requisite degree of ductility is subjected to a cold forming operation which may comprise a single or multiple extrusion and/ or cold forging operation to produce a valve blank of la configuration corresponding closely to that of the nal machined valve. A typical sheared cylindrical blank indicated in FIG. 2 may for example be subjected to a cold extrusion operation wherein the stem portion of the valve is formed providing an extruded blank indicated at 12 in FIG. 3. The extruded blank 12 may thereafter be subjected to a second cold-forging operation such as a coinupsetting operation forming a valve blank indicated at 14 in FIG. 4 of a configuration corresponding substantially to that of the finished valve. The extrusion and cold forging of the steel blank 10 can be facilitated by subjecting the steel blank to a preliminary phosphating treatment forming a porous phosphate coating on the surfaces thereof which is thereafter coated or impregnated with a suitable drawing lubricant to increase the ease by which the blank is extruded and cold forged to the iinal shape. The use of such a phosphate coated surface is not critical to the practice of the present invention but constitutes a preferred practice particularly when the blank is to be subjected to a relatively drastic deformation.

The cold deformation of the blank either in a single or in a multiple forming operation can be achieved by any one of a variety of extrusion and/ or cold 4upset forging operations of the types well known in the art. By virtue of the relatively high degree of ductility of the blank, the forming operation can be achieved at rates substantially greater than those heretofore possible employing medium and high carbon alloy steels which additionally require in many instances a heating of the blank to an elevated temperature to facilitate physical deformation thereof. In accordance with the practice of the present invention the `deformation of the steel blank is -achieved in the cold or at a temperature below the recrystallization temperature in press equipment of the same type conventionally employed for hot forging operations.

The resultant valve blank 14 -as illustrated in FIG. 4 may thereafter be directly subjected to a straightening and machining operation to provide a valve slightly oversized from its finished dimensions or alternatively can be subjected to an intervening optional annealing treatment Ias indicated by the dotted lines in FIG. 1. The annealing treatment is desirable for the purposes of relieving some of the residual stresses inherent in the valve blank as a result of the cold-forming operation. While very high levels of residual s-tresses are permissible in the forged valve blank it is important that such stresses are symmetrically distributed so Vas to avoid warpage and dimensional distortion of the valve blank during subsequent case-hardening operations. Under situations where Ithe valve blank has substantially symmetrical -residual stresses therein and intervening annealing treatment between the cold forging and machining operation is not required. Since distor-tion of the valve blank during the case-hardening operation necessitates an increased degree of nal machining of the case-hardened valve, it is desirable in many instances to subject the cold-forged valve blank to an annealing operation. The annealing treatment is performed for the purpose of assuring dimensional stability and freedom from warpage of the machined valve when subjected to the heat in the case-hardening such as carburizing or carbonitridin-g, for example.

The valve blank whether or not subjected to -an `intervening annealing treatment is thereafter subjected to a straightening operation so as to position the valve head substantially perpendicular to the axis of the stern followed by a machining operation in which the stem, tip, head, and face of the valve a-re machined to within several thousands above the iinal finish dimension of the valve. At the completion of the straightening and machining operation the valve is thereafter subjected to -a case-hardening treatment to provide a hard surface layer on the surfaces thereof to increase its wea-r resistance. The depth of the hardened case can be varied consistent with the intended end use of the valve and the amount of metal that must be removed during the final machining operation to provide a valve of the `desired finish dimensions. Conventionally for intake valves employed in automobile internal combustion engines, a case-hardening depth in the finished valve of -about 0.010 inch provides for satisfactory operation where-as a medium depth case hardening of about 0.030 inch is preferred. Case hardening of the valve to a depth greater than about 0.30 inch does not detrimentally effect the performance land operating life of the valve and generally is not necess-ary due to the added cost of providing such an increase depth. The presence of a controlled case-hardened surface of a depth of at least 0.010 inch around the ductile core comprising a low carbon or low alloy steel of the type hereinbefore set forth provides for valve performance characteristics superior to `those heretofore obtained from valves of medium and high carbon alloy steels.

The type of case 'hardening and the degree of case hardening achieved will also vary consistent with the intended end use of the valves. In many cases it is necessary that only the valve tip indicated at 16 in FIG. 4 be fully hardened to a martensitic structure while unhardened pearlitic structures may be suitable to provide suitable stem and seat abrasion resistance in conventional automobile internal combustion engine use. For most engine applications, a valve made in accordance with the present process having a Rockwell hardness on the C-scale (Rc) on the valve tip of -about 50 or more land on the other surfaces of valve of about 20 Rc or more provides for satisfactory operation and high resistance to wear. Since a full martensitic struct-ure has a hardness in the range of about 50 to .about 60 Rc units, -a hardness in the valve tip of at least about 50 Rc can be achieved either during the primary case 'hardening operation or during a secondary localized case hardening of the tip itself such as for example by subjecting it to a flame-hardening treatment step as schematically illustrated in FIG. l. Intake valves made from a type 1018 steel in accordance with the present invention having Ia case depth ranging from about 0.015 to 0.020 inch of a hardness of about'Rc 30 on the face and stem thereof and a hardness of about Rc 60 on the valve tip achieved by a subsequent flamehardening treatment have been found to provide excellent operating characteristics.

The case hardening of the valve surfaces may be achieved by any one of the conventional case hardening techniques including carbonitriding, carburizing, cyaniding, nitriting, induction hardening, fi-ame hardening, and the like. In either event, the resultant valve is case hardened under conditions sufiicient to provide a case hardened depth of at least about 0.010 inch of a hardness of at least about Rc 20 on the general surfaces of the valve and a hardness of at least about Rc 50 on the valve tip.

In carburizing, carbon is introduced into the surface portion of the machined valve blank by holding the valve above the temperature at which austenite begins to form while in conta-ct with -a suitable carbonacious material which may either be in a solid, liquid or gaseous form. Alternatively, the machined valve blank can be subjected to a cyaniding treatment whereby carbon and nitrogen are introduced into the peripheral portions of the valve by maintaining it above the temperature at which austenite begins to form in contact with a molten cyanide of suitable composition. In carbonitriding, both carbon and nitrogen are introduced into the peripheral portions of the machined valve blank by heating it above the temperature at which austenite forms in an atmosphere that contains suitable gases such as hydrocarbon gases, carbon monoxide, and ammonia. In both flame hardening and induction hardening, the material is hardened by heating it above a preselected temperature and thereafter quenching it, forming a molecular structure of substantially increased hardness. In either event, the particular conditions and the duration of the case hardening operation are controlled so as to produce a hardened valve surface of a hardness and of a depth as heretofore set forth.

The heated valve blank removed from the case hardening operation is thereafter cooled in a manner so as to minimize warpage of the case-hardened blank. The specific cooling process employed such as air cooling, or quenching in a liquid such as oil, for example followed thereafter by air cooling will vary depending on the intensity .and nonuniformity of the stresses in the valve body which establish its` tendency to warp during the cooling step.

At the completion of the case-hardening treatment, the case-hardened valve blank may be subjected to a drawing or tempering operation if desired to further modify the ha-rdness characteristics of the case to within the limits hereinbefore set forth. The case-hardened valve blank, whether or not subjected to an intervening drawing oper-ation, may also be subjected to a localized hardening treatment such as a flame hardening of the tip if the type and position of the principal case-hardening treatment produced a tip hardness below about Rc 50. Under such conditions a localized heat treatment of the valve tip and also of the face of the valve as indicated at 18 in FIGURE 4 if desired, may be accomplished so as to provide the requisite hardness characteristics consistent with its intended end use. The resultant valve is thereafter subjected to a final machining operation in which the stem, tip, head, and valve face are ground or otherwise machined to the final dimensional configuration and degree of surface finish.

In order to further illustrate the process comprising the present invention the following example is provided. It will be understood that the specific steps and the conditions as set forth in the example are provided for illustrative purposes and are not intended to be limiting of the invention as set forth in the subjoined claims.

EXAMPLE I A raw cylindrical bar stock having a nominal diameter of 7/8 inch consisting of SAE 1018 merchant quality steel was sheared into blanks as illustrated in FIGURE 2.

These blanks were thereafter subjected to a spheroidizing annealing treatment at 1400 F. for a period of one hour and at 1250 F. for a period of 16 hours after which the blanks were furnace cooled to 1,000 F. and thereafter air cooled. The annealed blanks were thereafter descaled `and provided with a phosphate coating on the surfaces thereof which was impregnated with a lubricant and subjected to a two-blow cold forging operation. A resultant Valve blank of the general configuration shown in FIGURE 4 was produced which therafter was roll straightened to orient the head substantially perpendicular to the stem.

The valve blanks thereafter were subjected to a preliminary machining operation wherein the stems were ground to -about 0.006 to about 0.007 inch over finish diameter and the heads and seats were turned to about 0.008 to about 0.009 inch over finish dimensions. The length of the valve blanks were ground 0.002 inch over the finish dimension. The machined valve blanks were thereafter racked and subjected to carbonitriding at a temperature of 1580 F. for one hour and forty-five minutes having an ammonia atmosphere of from 5 to 6% .and a dew point of 30 F. The carbonitrided valve blanks were thereafter further cooled to 800 F. and oil quenched to room temperature. The lresultant carbonitrided valve blanks had a case hardness of about 25 Rc and were thereafter subjected to a second machining operation wherein the stem was semi-finish ground and the tip was arne hardened with acetylene to a hardness in the range of about 55 to 60 Rc. At the completion of the fiame hardening treatment, the stem end, the seat and the stem of the valve were finish ground to the final finish dimensions.

Valves made in accordance with the process as described in the specification and as illustrated in the example have been found to provide very satisfactory operating conditions in conventional commercial automobile internal combustion engines and have been found moreover to provide for a substantial improvement in the simplicity and in the economy of valve manufacture over techniques heretofore known in the art.

While it will be apparent that the preferred embodiments herein illustrated are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation -and change without departing from the proper scope or fair meaning of the snbjoined claims.

What is claimed is:

1. A process for making a poppet-type engine valve which comprises the steps of providing a blank of a metal selected from the group consisting of carbon steel and low-alloy steel containing from about 0.03% to about 0.60% carbon and up to about 5% of intention-al alloying constituents, said steel further characterized as being susceptible to case hardening and having a degree of ductility enabling cold forming thereof, cold forming said blanks into a valve blank comprising a head portion and a stem portion, machining said valve blank to a configuration and size slightly greater than the final finish dimension, case hardening said valve blank to a depth to provide a finish valve surface hardness of at least about 20 Rc on the surfaces of the finished valve .and a hardness of at least about 50 Rc on the tip of Said stem, and thereafter finish machining said valve blank to the final dimension.

2. A process for making a poppet-type engine valve which comprises the steps of providing a blank of a metal selected from the group consisting of carbon steel and low-alloy steel containing from about 0.08% to about 0.25% carbon and up to about 5% of intentional alloying constituents, said steel further characterized as being susceptible to case hardening and having a degree of ductility enabling cold forming thereof, cold forming said blanks into a valve blank comprising a head portion and a stem portion, machining said valve blank to a configuration and size slightly greater than the final finish dimension, case hardening said valve blank to a depth to provide a finish Valve surface hardness of at least about 20 Rc on the surfaces of the finished valve and a hardness of at least about 50 Rc on the tip of said stem, and thereafter finish machining said valve blank to the final dimension.

3. A process for making a poppet-type engine valve which comprises the steps of providing a blank of a metal selected from the group consisting of carbon steel and low-alloy steel containing from about 0.03% to about 0.60% carbon `and up to about of intentional alloying constituents and further characterized as being sus* ceptible to case hardening, annealing said blank to provide a degree of ductility enabling cold forming thereof, cold forming said blank into a valve blank comprising a head portion and a stem portion, machining said valve blank to a configuration and size slightly greater than the final finish dimension, case hardening said valve blank to a depth to provide -a finish valve surface hardness of at least about 20 Rc on the surfaces of the valve and a hardness of at least about 50 Rc on the tip of said stern, and thereafter finish machining the said valve blank to the final dimensions.

4. A process for making a poppet-type engine valve which comprises the steps of providing a blank of a metal selected from the group consisting of carbon steel and low-alloy steel containing from about 0.03% to about 0.60% carbon and up to about 5% of intentional alloying constituents, said steel further characterized as being susceptible to case hardening and having a degree of ductility enabling cold forming thereof, cold forming said -blanks into a valve blank comprising a head portion and a stern portion, annealing said valve blank to relieve the residual stresses therein, machining said valve blank to a configuration and size slightly greater than the final finish dimension, case hardening said valve blank to a depth to provide -a finish valve surface hardness of at least about 20 Rc on the surfaces of the finished valve and a hardness of at least about 50 Rc on the tip of said stern, and thereafter finish machining said valve blank to the final dimension.

5. A process for making a poppet-type engine valve which comprises the steps of providing a 4blank of a metal selected from the group consisting of carbon steel and low-alloy steel containing from about 0.03% to about 0.60% carbon and up to about 5% of intentional alloying constituents, said steel further characterized as being susceptible to case hardening and having a degree of ductility enabling cold forming thereof, cold forming said blanks into a valve blank comprising a head portion and a stem portion, machining said valve blank to a configuration and size slightly greater than the final finish dimension, case hardening said valve blank to a depth to provide a finish valve surface hardness of at least about 20 Rc on the surfaces of the finished valve, case hardening the tip of said stem to provide a hardness of at least about Rc on the finish surface of said tip, and thereafter finish machining said valve blank to the final dimension.

6. A process for making a poppet-type engine valve which comprises the steps of providing a blank of a metal selected from the group consisting of carbon steel and low-alloy steel containing from about 0.03% to `about 0.60% carbon and up to about 5% of intentional alloying constituents, said steel further characterized as being susceptible to case hardening and having a degree of ductility enabling cold forming thereof, cold forming said blanks into a valve blank comprising a head portion and a stern portion, machining said valve blank to a configuration and size slightly greater than the final finish dimension, case hardening said valve blank to a depth to provide a finish valve surface hardness of at least about 20 Rc on the surfaces of the finished valve, flame hardenng the tip of said stem to provide a hardness of at least about 50 Rc on the finish surface of said tip, and thereafter finish machining said valve blank to the final dimension,

7. A process for making a poppet-type engine valve which comprises the steps of providing a blank of a type 1018 steel, said steel further characterized as being susceptible to case hardening and having a degree of ductility enabling cold forming thereof, cold forming said blanks into a valve blank comprising a head portion and a stern portion, machining said valve blank to a configuration and size slightly greater than the final finish dimension, case hardening said valve blank to a depth to provide a finish valve surface hardness of at least about 20 Rc on the surfaces of the finished valve and a hardness of at least about 50 Rc on the tip of said stem, and thereafter finish machining said valve blank to the final dimension.

References Cited by the Examiner UNITED STATES PATENTS 1,100,779 6/1914 Rich 29-146.7 1,533,782 4/1925 Armstrong. 1,948,793 2/1934 Lewis 29-156.7 1,987,234 1/1935 Hill 29146.7 2,138,528 11/1938 Phillipps 29-156.7 XR 2,294,803 9/1942 Rich 123--188 2,323,971 7/1943 Blackmore et al.

29-156.7 XR 2,436,928 3/1948 Kempe 123-188 OTHER REFERENCES C. A. McGroder: Poppet Valves Made in One Piece in Iron Age, June 21, 1928, pages 1753 and 1754.

JOHN F. CAMPBELL, Primary Examiner.

WHITMORE A. WILTZ, Examiner.

I. C. HOLMAN, P. M. COHEN, Assistant Examiners.

Claims (1)

1. A PROCESS FOR MAKING A POPPET-TYPE ENGINE VALVE WHICH COMPRISES THE STEPS OF PROVIDING A BLANK OF METAL SELECTED FROM THE GROUP CONSISTING OF CARBON STEEL AND LOW-ALLOY STEEL CONTAINING FROM ABOUT 0.03% TO ABOUT 0.60% CARBON AND UP TO ABOUT 5% OF INTENTIONAL ALLOYING CONSTITUENTS, SAID STEEL FURTHER CHARACTERIZED AS BEING SUSCEPTIBLE TO CASE HARDENING AND HAVING A DEGREE OF DUCTILITY ENABLING COLD FORMING THEREOF, COLD FORMING SAID BLANKS INTO A VALVE BLANK COMPRISING A HEAD PORTION AND A STEM PORTION, MACHINING SAID VALVE BLANK TO A CONFIGURATION AND SIZE SLIGHTLY GREATER THAN THE FINAL FINISH DIMENSION, CASE HARDENING SAID VALVE BLANK TO A DEPTH TO PROVIDE A FINISH VALVE SURFACE HARDNESS OF AT LEAST

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