US2716792A - Method of cast-forging metals - Google Patents

Description

Sept. 6, 1955 K. K. K. KRQYER METHOD 0F CAST-FORGING METALS Filed Oct. 5, 195C f/QZ.

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United States Patent O METHOD 0F CAST-FORGNG METALS Karl Kristian Kobs Kryer, Aarhus, Denmark Application October 5, 1950, Serial No. 188,578

5 Claims. (Cl. 22-209) This invention relates to a method of cast-forging metals.

One of the objects of the present invention is to provide an improved method of castforging whereby articles of a high and uniform quality may be produced on a commercial scale and at competitive prices.

The invention is based on certain recognitions regarding the manner in which the die closing operation should be conducted in the process of cast-forging in order to secure good and uniform results. It has been found that if the dies are closed together too slowly or with excessive delay, e. g. in order to await a state of semisolidiiication of the metal, the free surface of the metal has a tendency to oxidze, and besides, it is practically impossible to time the operation accurately enough for the metal to be engaged between the dies exactly in the state most favourable for the forging operation. If on the other hand the dies are closed together too quickly so that the metal is brusquely engaged between the dies, the metal will have a tendency to be violently displaced or even splashed up whereby it may solidify prematurely in places and on the whole assume a non-homogeneous character, and besides, the metal may be subjected to practically the full pressure available between the dies already before a substantial solidiiication of the bulk of the material has occurred whereby the forging effect becomes poor.

To overcome these difficulties, according to one feature of the invention, a method of cast-forging comprises the step of closing dies upon molten metal in a pressing operation at a suiiiciently low speed during the final period of distributing the metal over the entire space between said dies to allow for smooth displacement of the metal and/ or substantial progress of the solidification thereof during such period.

According to another feature of the invention, in a method as aforesaid, the die closing motion comprises a iirst stage at relatively high speed to trap the molten metal between the dies, and a second stage at substan tially reduced speed to shape and compress the metal between said dies.

As will readily be understood, the method according to the invention as set forth above is conducted in such a manner as to allow for smooth displacement of the metal and an efficient forging treatment thereof in a final die closing stage without necessitating a too accurate timing or a delay in the initial closing movement such as to unduly expose the molten metal to atmospheric inuences over an excessive period of time.

Preferably, according to the invention, the changeover from the first to the second stage of the die closing motion is performed by external means at a point of the die closing stroke where no substantial inner pressure has as yet come up in the metal, whereby full security is obtained against a too rapid or premature full closing of the mould.

It has been found that the die closing movement may advantageously be performed by means of a hydraulic Cil Patented Sept. 6, 1955 press capable of low pressure operation at relatively high speed and high pressure operation at relatively low speed. Such hydraulic presses are frequently constructedin such a manner that the changeover from one pressing stage to the other is performed automatically in dependence on the resistance encountered, but according to the invention, the changeover from high speed operation to low speed operation is effected by an artificial resistance which is operative at the desired point in the operating stroke of the press.

Such means may be constructed in the form of resilient means offering a resistance high enough to cause the changeover from high speed operation to low speed operation, but not so high as to unduly reduce the final pressure of the press.

Alternatively, the said means may be constructed in the form of a hydraulic buffer offering a resistance de* pending on speed, whereby it is obtained that nothing is detracted from the final pressure of the press, and, besides, the resistance of the hydraulic buffer may bef controlled at will during the stroke, e. g. so as to be reduced gradually as the forging operation proceeds.

lf a hydraulic press is used, which is operated by both a high pressure pump and a low pressure pump, the

' changeover from the high speed stage to the low speed stage may also be performed by setting the low pressurel pump out of operation in response to the movement for the press at a suitable point of the stroke thereof.

In tests carried out in connection with the present invention, it has also been found that one important difficulty in carrying out the process of cast-forging results from the fact that the molten metal under pressure has a tendency to adhere to the dies when the temperatures of die and metal necessary for the process are employed.

In order .to remedy this drawback, it is proposed, ac-

cording to the invention, to use dies having their active surfaces blue tempered in oil.

A further diiculty arises from the fact that the dies, and particularly the lower die, into which the-metal is poured or introduced in other suitablemanner, has a strongly cooling effect on the molten metal so that the latter may solidify prematurely at the places of contact with dies, and particularly the lower die, so that no further displacement or treatment of the metal is possible in these places.

This difficulty is overcome, according to the invention by applying a fine powder having heat insulating and lubricating properties, such as certain clays in combination with metal oxides, such as pipe clay, feldspar and graphite, to the active surfaces of at least one of the dies, preferably the lower die.

ln an advantageous mode of carrying into effect this powdering feature, the powder is supplied in the form of a suspension in a suitable liquid.

In the drawings:

Figures l and 2 show two different examples of moulds that may be employed in carrying out the method according to the invention, and

Figures 3 and 6 show diagrammatically various examples of means for changing-over the operating speed of a press used for carrying out the new process.

In Figure l, 1 is a lower die and 2 an upper die combining to form a mould in which the cast-forging takes place. The dies 1 and 2 are attached to a lower and upper press table or piston 3 and 4 respectively, that may be relatively moved towards one another in a manner not shown. To carry out the cast-forging, the upper die 2 is moved upwards, whereafter molten metal is poured into the lower die 1. The upper die 2 is then lowered to the position shown in Fig. l, and during this movement, as will be described in further i) detail in the following, is first moved at a relatively high speed and is thereafter suddenly changed over to a considerably lower speed `before a substantial inner pressure has as yet been developed in the metal trapped between the dies 1 anclZ.

In the construction of the mould shown in Fig. l, the dies 1 and 2 make a perfect or practically perfect sealing contact in the zone 5, while in the embodiment illustrated in Fig. 2 a small clearance is present in this zone, so that a moulding fin is formed. Since the metal can thus to a certain extent escape at the edge of the mould illustrated in Fig. 2, it is possible in this case to obtain a high degree of mechanical treatment of the nished product and thereby a favourable and advantageous breaking down of the crystalline structure. It is observed, however, that a satisfactory mechanical treatment is frequently obtainable also in the embodiment illustrated in Fig. l particularly when castforging aluminum.

Figs. 36 illustrate diierent ways in which the desited change-over of the press from high speed to low speed may be effected when a hydraulic press is used. In these figures, which are purely diagrammatical, the dies have been omitted, and the figures only show the press tables or pistons 3 and 4 and the means for chang,

ing-over the piston movement from one stage to another.

In Fig. 3, a threaded stud 6 is attached to the upper piston 4 and carries a screw-threaded cap 7 serving as an abutment. A bundle of leave springs 8 `is carried by the lower piston 3 in a position facing the cap 7, so as to be struck by the latter when the pistons 3 and 4 move towards one another. The cap 7 is adjusted so as to strike the bundle of springs 8 when the dies attached to the pistons have been closed together to such an extent that the metal has been trapped between the dies but has not yet been subjected to substantial pressure or distributed over the entire space between the dies. When the cap 7 strikes the springs 8, the changeover of the piston speed is effected in known manner as a consequence of the resistance to the piston movement thereby created. The counter pressure or resistance offered by the springs 8 remains undiminishcd or is even increased during `the whole linal stage of the operation and is consequently subtracted from the nal pressure, of the press, and it should therefore not be selected higher than absolutely necessary for effecting the changeover.

In the embodiment illustrated in Fig. 4, the lower piston 3 carries a stud 9 having a screw thread with which engages a cap 10 carrying a bundle of rubber' discs 11 so that o'n movement of the pistons towards one another the latter will strike the upper piston 4 and thereby create a counter pressure. The function is exactly the same as in the embodiment illustrated in Fig. 3.

In Fig. 5, the lower piston carries a hydraulic cylinder 12 with a plunger 13 carrying an adjustable screw cap 14 which forms an abutment striking the upper piston 4 at a suitable point of the piston stroke. A conduit 15 with an adjustable check valve 16 is connected to the oil space of the cylinder 12. When the upper piston 4 and the abutment 14 strike one another, the oil brake or hydraulic buffer lformed by the cylinder 12 and the plunger '13 otter a counter pressure that may be controlled by adjusting the check valve 16. In contradstinction to the embodiment illustrated in Figs. 3 and 4, the counter pressure oiered by the hydraulic buffer of Fig. 5 exists only as long as the `pistons are in movement so that there will lbe no reduction of the final pressure of the press. When the pistons are again withdrawn after completion of the operation, the braking plunger 13 is again moved to the position shown in the drawing in a manner not shown, e. g. by hydraulic or mechanical means.

In the embodiment illustrated in Fig. 6, the lower piston 3 is slidably mounted in a hydraulic cylinder 17 to which a hydraulic medium is fed from a reservoir 18 partly by means of a high pressure pump 19 and partly by means of a low pressure pump 20, the supply through the latter taking place by way of a non-return valve 21. 22 is a control valve which, when operated, short-circuits the high and low pressure pumps, and, when closed, permits both pumps to become effective to raise the piston 3. In this embodiment, the low pressure pump is set out of operation in response to the movement of the piston 3 when the latter has come to the desired level in which the change-over of the piston speed is to take place. For this purpose, the lower piston 3 may carry a nose, not shown, cooperating with a stationary abutment in such a f manner that when the latter is struck by the nose it sets the low pressure pump out of operation, e. g. by mechanical, electrical or hydraulic means, either by stopping the motor of the low pressure pump or by closing a valve in the supply conduit leading from the low pressure pump. The means by which these functions take place are well known in the art and do not form part of the invention and are therefore not illustrated in the drawing.

It will easily be understood that devices of many other kinds may be used for carrying out the method according to the invention. Thus, the hydraulic press may be replaced by a mechanical press provided with power transmitting means such as cams of a shape to secure a sudden reduction of the piston velocity at a suitable point of the stroke.

The new process is particularly applicable to non-ferrous metals such as aluminum and aluminum alloys and opens up the possibility of making, e. g. pistons for automobile and aircraft engines from alloys that hitherto could not be cast.

I claim:

l. A method of producing cast-forged metal objects between an upper and lower die comprising the steps of pouring into the lower die molten metal in a quantity predetermined to be that needed initially between the dies to form the desired article therebetween when the dies arc fully closed, relatively moving the dies toward one another at relatively high speed and low pressure to trap the molten metal between the dies, suddenly altering the closing movement of the dies to a lower speed and a higher pressure at the point in the closing movement of the dies where the volume of the space between the dies is substantially equal to the volume of the aforesaid quantity of molten metal, whereby the closing movement is altered before the dies exert a substantial pressure on the molten metal, and thereafter continuing the closing movement of the dies at lower speed and higher pressure until the closing movement is halted by the resistance offered by the then castforged metal between the then fully `closed dies.

2. A method according to claim l, in which the active surfaces of said dies are blue tempered in oil prior to said pouring step.

3. A method according to claim 2, in which the tempered surface of at least one of said dies has applied thereto a tine powder having heat insulating and lubricating properties.

4. `A method according to claim 3, in which the powder is applied in the form of a suspension in a suitable liquid.

5. A method of producing cast-forged metal objects between an upper and lower die comprising the steps of pouring into the lower die molten lmetal in a quantity predetermined to be that needed initially between the dies to form the desired article therebetween when the dies are fully closed, relatively moving the dies toward one another at relatively high speed and low pressure to trap the molten metal between the dies, suddenly opposing against the closing movement of the dies an external, constantly increasing resistance at the point in the closing movement where the volume of space between the dies is substantially equal to the volume of the aforesaid quantity `ot molten metal, whereby the closing movement is altered to proceed at a lower speed and higher pressure before the dies exert a substantial pressure on the molten metal, and thereafter continuing the closing movement of the dies at lower speed and higher pressure until the closing movement is halted by the resistance oiered by the then castforged metal between the then fully closed dies.

UNITED STATES PATENTS References Cited in the ile of this patent 1,222,786 Morris Apr. 17, 1917 1,347,728 Wills July 27, 1920 1,450,648 Schwartz Apr. 3, 1923 1,463,771 Claassen July 31, 1923 1,935,059 Pack Nov. 14, 1933 1,956,907 Miller et al May l, 1934 6 Morin May 8, 1934 Smith Nov. 28, 1939 Vontobel Dec. 12, 1939 Lester et al Dec. 19, 1944 Hopkins Nov. 13, 1945 Misfeldt Dec. 18, 1945 Lester Dec. 3, 1946 Doering et al June 3, 1947 Dean Sept. 9, 1947 Mallach Mar. 14, 1950 Holmes et al Nov. 28, 1950 Ring Nov. 18, 1952 Holder Apr. 14, 1953 FOREIGN PATENTS Great Britain June 30, 1948

Claims (1)

1. A METHOD OF PRODUCING CAST-FORGED METAL OBJECTS BETWEEN AN UPPER AND LOWER DIE COMPRISING THE STEPS OF PORING INTO THE LOWER DIE MOLTEN METAL IN A QUANTITY PREDETERMINED TO BE THAT NEEDED INITIALLY BETWEEN THE DIES TO FORM THE DESIRED ARTICLE THEREBETWEEN WHEN THE DIES ARE FULLY CLOSED, RELATIVELY MOVING THE DIES TOWARD ONE ANOTHER AT RELATIVELY HIGH SPEED AND LOW PRESSURE TO TRAP THE MOLTEN METAL BETWEEN THE DIES, SUDDENLY ALTERING THE CLOSING MOVEMENT OF THE DIES TO A LOWER SPEED AND A HIGHER PRESSURE AT THE POINT IN THE CLOSING MOVEMENT OF THE DIES WHERE THE VOLUME OF THE SPACE BETWEEN THE DIES IS SUBSTANTIALLY EQUAL TO THE VOLUME OF THE AFORESAID QUANTITY OF MOLTEN METAL, WHEREBY THE CLOSING MOVEMENT IS ALTERED BEFORE THE DIES EXERT A SUBSTANTIAL PRESSURE ON THE MOLTEN METAL, AND THEREAFTER CONTINUING THE CLOSING MOVEMENT OF THE DIES AT LOWER SPEED AND HIGHER PRESSURE UNTIL THE CLOSING MOVEMENT IS HALTED BY THE RESISTANCE OFFERED BY THE THEN CAST-FORGED METAL BETWEEN THE THEN FULLY CLOSED DIES.

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