US3349472A

US3349472A - Process for pressure-forming metallic bodies

Info

Publication number: US3349472A
Application number: US621718A
Authority: US
Inventors: Schlegel Werner
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-02-27
Filing date: 1966-09-15
Publication date: 1967-10-31
Anticipated expiration: 1984-10-31
Also published as: SE319504B; DE1227044B

Description

3,349,4- 72 PROCESS FOR PRESSURE-FORMING METALLIC BODIES Filed Sept. 15, 1956 Oct. 31, 1967 w. SCHLEGEL 5 Sheets-Sheet 1 /NI/EN70P WERNER SCHLEGEL AGENT 3,349,472 PROCESS FOR PRESSURE-FORMING METALLIC BODIES Filed SEPT. 15, 1966 Oct. 31, 1967 w. SCHLEGEL 3 Sheets-Sheet 2 m I I. v/////// a? .ll A

/N VEN70,Q WERNER SCHLEGEL B1 A? Al I 1967 w. SCHLEGEL 3,349,472

, Filed Sept. 15, 1966 PROCESS FOR' PRESSURE-FORMING METALLIC BODIES v .5 Sheets-Sheet 3 /NVN729/P WERNER SCHLEGEL -,p3' BY 3 AGENT United States Patent ()fifice 3,349,472 PROCESS FOR PRESSURE-FORMING METALLIC BODIES Werner Schlegel, Camphausenstrasse 2, Dusseldorf, Germany Filed Sept. 15, 1966, Ser. No. 621,718 Claims priority, application Germany, Feb. 27, 1962,

Sch 31,051; Oct. 9, 1965, Sch 37,851

7 Claims. (Cl. 29-528) This application is a continuation-in-part of my copending application Ser. No. 574,467, filed Aug. 23, 1966, and originally entitled, Process for Forging and Pressure- Finishing Cast-Metal Alloys,

In the aforementioned copending application, I describe a process and an apparatus for forging and pressurefinishing cast-metal bodies having a crystal transformation or recrystallization point at an elevated temperature below the melting or solidification point of the metal and ambient or room temperature. This process and system was particularly applicable to cast-metal alloys such as steels and cast irons which, after being cast in molds, were cooled to the forging temperature and then shaped under pressure to their final configuration.

In accordance with the improved method of my earlier application, the molten metal is cooled from the liquid or casting state in a casting mold to the transition temperature or range of temperatures at which a transformation of the crystal lattice takes place from the hightemperature form to the low-temperature form, the pressure finishing being carried out without passing below this temperature. The improved system derives in part from the fact that cast iron and most common metal alloys have a very high compressive strength but only limited tensile strength; hence these metals are comparatively brittle. With cast iron, it is the graphite or free-carbon content which is apparently responsible in large measure for the brittleness. In fact, the high compressive strength is a consequence of crystal strain developed in the solidified structure; this strain arises because the secondary graphite, which precipitates out within the transition or transformation temperature range of 906 to 721 C. (for cast iron), occupies from three to four times more volume than an iron crystal or grain. By carrying the pressure forming the body in the manner indicated above, the crystal structure is permitted to homogenize and equilibrate in thermodynamic respects so that the grains, crystals or atoms of the body are able to reorient themselves without leaving behind significant stress. In particular, the lamella separation of secondary graphite (in cast iron) is minimized so that a uniform stress distribution, which contributes significantly to raising the tensile strength, can result. In that application I point out further that the molds filled with molten metal should be conveyed to a soaking furnace or pit or to a homogenization oven whose temperature corresponds to the transition range of the alloy and thence to the forging press at the rate at which the latter can process the bodies. In this manner, a highly eflicient plant operation is obtainable.

Moreover, it was also demonstrated that the cast shapes of the workpieces (i.e. the preforms) should have essentially the same volume as the final shapes but with a difference in surface area. It was thus emphasized that, in accordance with the improved process, the expenditure of work and energy in pressure finishing the bodies, could be considerably reduced if the hot-working of the cast piece takes place at high press temperatures without going below the transition temperature range; the forging is advantageously combined with a pressure finishing or polishing. Accordingly, the cast shapes or preforms constituting the workpieces to be subjected to pressure finishing have a smaller surface area than the final shapes 3,349,472 Patented Oct. 31, 1967 emerging from the presses. The smaller surface area of the cast preform is determined by planimetric analysis for each cross-section of the finished workpiece, thereby establishing the smallest surface area or circumference applicable to each cross-section of the final workpiece. This method is simple to carry out and permits of designing the molds accurately to the corresponding requirements.

I have now found that essentially similar methods can solve a problem characteristic of nonalloyed relatively pure metals and especially the so-called light metals such as aluminum. Pure metals, especially aluminum, which are to be cast from the liquid state, are characterized by a unique physical property which renders them diflicult to handle. These pure metals (pure here referring to the lack of alloying ingredients) are found often to be highly viscous in the liquid state so that they tend to fill the casting molds rather poorly and leave voids or unfilled portions, especially when complex shapes are involved. For this reason, the metallurgical field has generally avoided casting techniques when using such metals or has resorted to alloying to modify the physical properties of the metal. Indeed, aluminum alloys tend to be more fiowable and less viscous than pure molten aluminum and such alloys frequently have an increased strength. However, alloying involves numerous disadvantages which are also significant. Thus, alloying ingredients increase the resistance of a cast body to forging and pressure deformation, give rise to internal or intercrystalline corrosion as a consequence of potential differences Within the crystal lattice, alter the characteristic electrode potential of the ,body, and modify deleteriously the creep resistance and "aging characteristics thereof.

It is, therefore, the principal object of the present invention to provide an improved process for the shaping of pure metals as well as of metal alloys, which are to be initially cast, and thereby to extend the principles originally set forth in my copending application mentioned above.

A more specific object of the present invention is to provide a method of and an apparatus for the shaping of metals while eliminating the aforementioned disadvantages.

In accordance with the present invention, the pure metal is cast in a mold from a melt and cooled below the critical recrystallization temperature and pressure formed in a shaping press, the mold cavity and the cast preform having the same volume as the pressed finished body but a smaller surface area than the latter. With respect to the surface-area relationship of the preform and the finished body, at identical volumes, the method for cast-metal alloys is the same as that for pure metals or nonalloyed castings.

The invention is based in part upon the recognition that pure metals almost invariably pass through a recrystallization phase. Thus, in accordance with this aspect of the invention, it may be stated that recrystallization phenomena are observed in metals or alloys which are brought to elevated temperatures. Upon such an increase in temperature, structural changes take place in the metallic body which significantly and disadvantageously effect the strength characteristics thereof. These recrystallization phenomena occur only above a critical temperature which is dependent upon the material, ie the pure metal. In accordance with the invention, this metal-dependent parameter is ascertained for each metal to be shaped and the casting thereof is cooled below the critical recrystallization temperature prior to mechanical shapening under pressure. The pressure shaping of the preform or casting is carried out without altering the volume of the workpiece, while increasing its surface area whereby the surface area of the preform is less than that of the finished body. This characteristic of the present invention may be summarized succinctly as the increasing of the specific surface area of the body by mechanical working; for the present purposes, the specific surface area will be defined as the ratio of external surface area to volume of the workpiece. In this manner, only the surface zones of the crystal structure are subjected to a deformation under pressure. It has been found to be important substantially uniformly to deform the body over its entire periphery or circumference so that uniform stresses are applied to the lattice and undesirable structural changes are avoided. By maintaining the relationship of surface areas of the preform and the finished body (and therefore the casting cavity and the forging space) in the manner previously indicated, I have found that the deformation of the body occurs substantially only along surface zones thereof with greater ease than has been possible heretofore. It appears that these surface zones of the preform are forced into the free spaces of the forging cavity with a creeping deformation of the metal grains or crystal structure only in these surface regions with a flow of metal which does not require the considerable stresses and forces hitherto necessary for forging metallic bodies. It can be established, therefore, that this improved deformation and mechanical working of the body yields an increase in the specific gravity thereof.

In the case of relatively pure metals, which are cooled in accordance with the present invention below the crystal transformation point prior to mechanical working, the metal body possesses a fine-grain or small-crystal structure characteristic of high strength.

Furthermore, the rapid reduction of the temperature of the body to a level beneath the recrystallization temperature, is usually carried out as rapidly as possible so that the recrystallization characteristic of stabilization at this level cannot result. Crystal growth is thereby prevented and only a negligible reduction in strength, by virtue of the cooling action, can be observed. Another advantage of the present invention is that the finished nonalloyed body has a completely smooth surface and indeed, in the case of aluminum, a silver-like mirror finish. By comparison, aluminum alloys of the type used commonly heretofore have grayish-blue coloration and are not significantly corrosion-resistant.

In both cases (ie for metal alloys such as steels and cast iron and for pure metals such as aluminum) the final deformation is carried out in a hot-forming press or forge with a predetermined capacity in terms of numbers of articles to be processed per unit time. Cast-iron bodies (e.g. those having a carbon content generally ranging between 2 and 4%) are treated after casting in a soaking furnace advantageously held at a temperature in the recrystallization zone (say 910 C. to 720 C. for the ironbearing material). This soaking furnace or homogenizing oven can, in general terms, be considered to have a temperature of slightly above the critical recrystallization temperature and at least the lower limit thereof. The preforms are thus fed to the mold from the soaking furnace at a rate determined by the press capacity. In the case of pure aluminum bodies, the homogenization furnace is maintained at a temperature slightly below the critical recrystallization temperature and the bodies are supplied to the hot-forming press in accordance with its capacity. A homogenization furnace has the important advantage that the workpieces can be deformed at elevated temperatures (which correspond to or are below the recrystallization temperature as the case may be) without requiring reheating of the bodies. It is also possible, however, to cool pure-aluminum workpieces, after casting, to room temperature and then to deform them in the cold state in so-called cold-forging apparatus. Also in this case it is possible to obtain a fine-grained crystal structure having high strength.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1a is an elevational view of a plant for the casting, finishing and forging of metal objects in accordance with the present invention;

FIG. lb is a plan view thereof;

FIG. 2 is a side-elevational view, partly in section, of the casting mold, showing means for severing extraneous material from the casting body;

FIG. 3a shows plan and side-elevational views of a preformed workpiece to be forged, in accordance with the invention, with the cross-sections AK thereof taken along the lines A-A through K-K.

FIG. 3b shows plan and side elevational views of the metal body after forging wit-h corresponding cross-sections AK taken along the lines AA' through K'--K, respectively; and

FIG. 4 is a cross-sectional view through the forging device diagrammatically showing the forging plunger or ram.

The device shown in FIGS. 1 and 2 consists principally of a graphite-rod (e.g. are or resistance-heating) furnace 1, in which smelting occurs. A bucket 1', shiftable along the arm 1" of a crane 1a, serves to supply the raw material to the furnace. The melt 2 is transferred in batches to a crucible 2, from which it is dipped by a workman and poured into closed bipartite molds 4 disposed on a tumtable 3. At a discharge station D, diametrically opposite the pouring station P, the molds 4 are opened and the preformed workpieces or blanks of solid metal are fed into a soaking furnace 5, the temperature of which corresponds to the aforementioned transition range of the alloy or a temperature well below the transition range for pure metals; this range generally can be determined from the phase diagram of the alloy and lies between the A and A oc/'y transformation temperatures (for iron). A workman removes the preformed workpieces from the soaking furnace 5 and conveys them to the forging press 6.

The casting arrangement can naturally also be a sandcasting arrangement, known per se, although turntables with split permanent molds are preferred. As FIG. 2 shows, the molds 4 arranged on the turntable 3 each consist of two mold halves 7 and 8. Mold half 7 is movable by pneumatic or hydraulic means 9, so that it is closed against the other mold half and juxtaposed therewith in the casting zone P, but is opened upon approaching the soaking furnace 5, so that the casting can be extracted from the mold. For this purpose there are associated with the mold halves 7, 8 ejector pins 10, normally held out of the mold cavity by springs 10, which, on opening of the mold, strike with their rearward ends against an abutment 12; the latter arrests the pins 10, so that on further relative displacement of the mold halves away from each other they eject the castings, which then fall onto a conveyor belt or the like, schematically shown at 10", disposed beneath the mold, whence they can be conveyed automatically to the soaking furnaces. The furnace may likewise be provided with a conveyor for continuously carrying the bodies therethrough.

To cut off the pouring heads, vent risers and other excess, a device is provided which comprises a cut-off plunger 13. The plunger 13 has an aperture 16, normally registering with the pouring spout 16' of the mold, and is displaceable by pneumatic or hydraulic means 14 through aligned slots 15, 17, in the mold halves 7 and 8 so that the riser projecting through the opening 16 is sheared off upon actuation of cylinder 14. The means 9 for closing and opening the mold halves 7, 8 as well as the pneumatic or hydraulic means 14 for the cut-off plunger are controlled in accordance with the rotation of the mold turntable 3.

In FIG. 3, there is shown in comparison with one another the preferred workpiece 19 and the finished body 20 after forging of a door handle, with their associated cross-sections. In accordance with the corresponding finished article 20, the preformed workpiece or casting 19 receives a smaller surface area by approximate formation of the mold. This smaller surface area for the cast (i.e. preformed) shape of the workpiece 19 is fixed by planimetric determination of the smallest peripheral distance or circumference applicable to the corresponding crosssectional area of the finished article 20.

The plunger 18 of the forging press 6 shown diagrammatically in FIG. 4 illustrates clearly how a plunger can be stepped in such manner that the deforming forces are transmitted through the steps of the workpiece to be deformed. Thus there are no tapered pressing surfaces provided on the plunger, but step-like sections 18a-18d, which successively engage the workpiece 6 held by the anvil 6" of press 6, and exert a shearing action thereon while effecting a creeping displacement of material in the direction of

arrows

21, 22 while the main component of the press force (arrow 23) is transformed into a downwardly and inwardly acting force (arrow 24) against the reaction forces (arrows 25). Thus there is almost no material removal and only a reshaping of the body from its cast configuration into the desired one. The steps of plunger or ram 18 will of course be designed to suit the particular conditions.

It will be apparent that many modifications are possible within the spirit and scope of the invention claimed. Thus for example there exists the possibility or mechan-izing the transfer of the hot workpieces from the mold tumtable to the soaking furnace and from the latter to the forging press. Additionally, the turntable 3 may synchronize the operation of the power means 14, which activates the shearing member 13, and the drive means 9 for the mold members via a microswitch 28, the latter being tripped at the discharge station D to energize the

electromagnetic valves

29 and 30 associated with these means. Another switch 31 is energized at the casting station P to close the molds and restore the shearing member 13 to its original position.

While the apparatus has been described above in conjunction with the formation of a cast-iron body whose transition or transformation range of 906 C. to 721 C. is not passed during the cooling of the body and which is worked at this temperature, it will be understood that the identical considerations except for the temperature conditions will be involved in the formation of a purealu-minum body or any other so-called light metal of pure (nonalloy) state. Thus the recrystallization temperature of pure aluminum is approximately 470 C. and the castaluminum bodies are cooled rapidly therebelow. I have discovered that the bodies are best worked after they have been cooled to a level of 150 C. to 250 C. and then worked at this temperature. The soaking or homogenization furnace 5 of the apparatus would, in this case, be maintained at a temperature between 150 C. and 250 C. For other pure metals, transition temperatures are available from the literature and phase diagrams and the forging temperatures will be selected accordingly.

The invention described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the appended claims.

I claim:

1. A method of producing bodies from a metal having a crystal transformation between a high-temperature form and a low-temperature form, comprising the steps of casting the metal in a liquid state in a mold; solidifying the metallic body thus produced and cooling it to a forging temperature in the temperature range at which said transformation takes place; and forging said body after said cooling thereof, the configuration of said body generally approaching the configuration of the object to be produced, said body having a volume substantially identical with said object but a surface area different therefrom, said body being reshaped upon forging to conform to the contours of said object, said method further comprising the steps of planimetrically determining the minimum circumferential distance associated with each cross-section of said object and forming said mold with a configuration in accordance with the planimet-rically determined minimum surface area of the volume of said object.

2. A method as defined in claim 1 wherein said body is brought to said forging temperature upon removal from said mold in a soaking furnace for uniformly heating said body and is forged immediately after removal from said soaking furnace.

3. A method as defined in claim 1 wherein said mold is formed with a cavity and a pouring spout communicating with said cavity, further comprising the step of shearing excessive metal from said body at a temperature within said range prior to forging.

4. A method as defined in claim 1 wherein the forging of said body is carried out by subjecting said body to contact with a stepped ram having portions successively engageable with said body for deforming it with a shearing action adapted to shape said body without substantial removal of material.

5. A method as defined in claim 1 wherein said metal is an iron-bearing metallic material and said temperature range is between substantially 910 C. and 720 C., said forging being carried out without cooling below said range.

6. A method as defined in claim 1 wherein said metal is nonalloyed and said forging is carried out at a temperature below said range.

7. A method defined in claim 6 wherein said metal is aluminum and the forging is carried out at a temperature of substantially to 250 C.

References Cited UNITED STATES PATENTS 356,974 2/ 1887 Bagaley 29-528 2,246,886 6/1941 Kroll 1482 2,310,703 2/1943 McGleney 148-2 2,871,557 2/ 1959 Tarmann et a1. 29528 2,995,816 8/ 1961 Ma 2.9--528 JOHN F. CAMPBELL, Primary Examiner.

-P. M. COHEN, Assistant Examiner.

Claims

1. A METHOD OF PRODUCING BODIES FROM A METAL HAVING A CRYSTAL TRANSFORMATION BETWEEN A HIGH-TEMPERATURE FORM AND A LOW-TEMPERATURE FORM, COMPRISING THE STEPS OF CASTING THE METAL IN A LIQUID STATE IN A MOLD; SOLIDIFYING THE METALLIC BODY THUS PRODUCED AND COOLING IT TO A FORGING TEMPERATURE IN THE TEMPERATURE RANGE AT WHICH SAID TRANSFORMATION TAKES PLACE; AND FORGING SAID BODY AFTER SAID COOLING THEREOF, THE CONFIGURATION OF SAID BODY GENERALLY APPROACHING THE CONFIGURATION OF THE OBJECT TO BE PRODUCED, SAID BODY HAVING A VOLUME SUBSTANTIALLY IDENTICAL WITH SAID OBJECT BUT A SURFACE AREA DIFFERENT THEREFROM, SAID BODY BEING RESHAPED UPON FORGING TO CONFORM TO THE CONTOURS OF SAID OBJECT, SAID METHOD FURTHER COMPRISING THE STEPS OF PLANIMETRICALLY DETERMINING THE MINIMUM CIRCUMFERENTIAL DISTANCE ASSOCIATED WITH EACH CROSS-SECTION OF SAID OBJECT AND FORMING SAID MOLD WITH A CONFIGURATION IN ACCORDANCE WITH THE PLANIMETRICALLY DETERMINED MINIMUM SURFACE AREA OF THE VOLUME OF SAID OBJECT.