US3534802A - Pressure die casting method - Google Patents

Description

United States Patent 1 1 3,534,802

[72] Inventor Irving A. Carr [56] References Cited 60 9 Massachusets UNITED STATES PATENTS [2'1] App] No gig? 1,961,941 6/1934 Pack 164/113 2,786,234 3/1957 Beyer..... l64/154(X) [221 Wed (la-21,1968 3,038,220 6/1962 Saives 164/313 [451 Patented (M201 1970 3 270 383 9/1966 Hall et al 164/120 Au .31 1966 sen 1 W g 1 3,369,591 2/1968 wBlCh et a1 164/1 13 No. 576,288, now Patent No. 3,443,628, dated May 13, 1969. Divided and this FOREIGN PATENTS application Oct. 21, 1968, Ser. No. 769,016 953,647 1 H1956 Germany 164/314 475,544 11/1937 Great Britain... 164/313 924,494 4/1963 GreatBritain .1 164/312 981,654 1/1965 Great Britain 164/312 Primary Examiner.1. Spencer Overholser 54 PRESSURE DIE ST METHOD Assistant Examiner-John E. Roethel 0 Claims 4 Drawing F Attorneys-Richard P. Crowley and Richard L. Stevens 164/ 154 ABSTRACT: A method of die casting wherein the circum- [51] hit. CI 822d 27/ l ferential walls of an injection piston are wiped upwardly and [50] Field ofSearch 164/1 13, dow wardly by the chamber walls of an upper mold element v after each casting is formed, The wiping of the piston allows 318: 18/30(CV). 30(QP). Ring Digest for a continuous casting operation,

PRESSURE m j 33 33 24 I l l l l I l lllfillllll 26 Patented Oct. 26," 1970 3,534,802

Sheet 2 0f 2 I VENTOR IRVIN CARR W W ATTORNEY PRESSURE DIE CASTING METHOD This application is a division of copending application Ser, No. 576,288, filed Aug. 3l, 1966, now US. Pat. No. 3,443,628.

This invention relates to diecasting of moldable materials. More precisely the invention concerns an improved pressure diecasting apparatus and method especially useful for producing high quality metallic castings in a continuous and surprisingly economical fashion particularly of aluminum castings not generally subject to pressure diecasting techniques.

Pressure diecasting techniques and apparatus for accomplishing such techniques are well-known to the art. In present commercial practice. the apparatus most commonly employed is characterized by a horizontally disposed injection chamber, usually cylindrical in form, communicating with a vertically disposed mold cavity. In practice, the moldable or castablc material is introduced into the chamber and forced into the mold cavity by means of an injection piston reciprocating through said horizontal chamber.

Despite the widespread use of such diecasting techniques and apparatus, those well-skilled in the art are acutely aware of many disadvantages therein. For example, the horizontal configuration of such diecasting apparatus permits excessive gases, e.g., air to become entrapped or occluded in the moldable material during the injection thereof into the mold cavity. Accordingly, such apparatus must employ extremely high injection pressures, e.g., over l0.000 p.s,i.g. to insure the production of castings which are free of excessive porosity or other defects occasioned by entrapped gases. However, the use of such high pressure can lead to the problem of excessive flashing which oftentimes is encountered in present diecasting apparatus, and turbulent flow of material, which occludes or entraps air. In turn, excessive flashing generally implies premature sealing of the parting line between the mold halves thereby preventing the escape of air or gases from the mold cavity. Accordingly, higher injection pressures can oftentimes be a factor because of back pressure in the mold which also contributes to an undesirable degree of porosity in the ultimate casting.

Also, the horizontal configuration of present diecasting apparatus is generally regarded as highly inefficient by those well-skilled in the art. For example, the configuration requires that the mold cavity, or at least the major portion thereof, be disposed above the central axis of the reciprocating injection piston. Moreover, in present diecasting apparatus considerable down time is too often required because of unwanted sticking of the injection piston in the injection chamber or to the biscuit", 2.3., that portion of the casting which is formed in the injection chamber. In view of the above, an improved pressure diecasting apparatus which by reason of its structural features and functions can inherently overcome all or some of the disadvantages implicit in present apparatus would be a notable contribution to the art.

A principal object of the present invention is to provide improved pressure diecasting apparatus and method.

Another object of the present invention is to provide pressure diecasting apparatus which is inherently capable of producing castings of improved integrity and quality.

Still another object of the present invention is to provide pressure diecasting apparatus which can produce castings in a continuous, uninterrupted fashion.

A further object of the present invention is to provide pressure diecasting apparatus which can produce castings which are substantially free of porosityfrom a moldable material consisting essentially of metal. In accordance with this aspect of my invention I can, for example, produce high purity aluminum castings which can be subsequently anodized.

Other objects and advantages of the present invention will in part appear hereinafter or will in part be apparent to those well-skilled in the art.

The above objects and advantages are realized in accordance with the practice of the present invention by a pressure diecasting apparatus characterized by an unique combination of structural elements all of which cooperate in an integrated fashion to provide pressure diecasting apparatus and a method which can inherently produce high quality castings essentially free of porosity in an efficient continuous fashion.

One preferred method of operating my apparatus comprises a two-stage. pressure injection cycle wherein the molding material is first subjected to a relatively low pressure, generally less than 500 p.s.i.g., and thereafter to a high pressure, generally greater than 500 p.s.i.g., but usually much less than the pressure ordinarily required in conventional prior art processes employing the same material for a casting of similar" quality. For example, in the preparation of metal castings l have found that the use of a single, high pressure injection cycle often and typically creates a turbulent flow of the liquid metal into the cavity and against the parting line of the mold, which flow occludes air or other gases within the casting. Further, the high pressure used tends to throw the liquid metal against the internal walls of the cavity where it cools and inhibits the escape of gases or air entrapped within the inner portions of the cavity and material. Accordingly. the low pressure should be selected to effect the essentially nonturbulent flow of the molding material into the cavity, and in any event to permit the escape of all or a substantial part of the entrapped gases in the cavity. The injecting of molten metal into the die cavity may be carried out at the low temperature of not more than about 50F. above the arrest point. The pressure and rate of injection may, of course, vary depending upon the .metal, the temperature, and other factors known to those 'due to entrapped air or gases and flow resistance of the material is considerably less in my two or multiple cycle pressure injection process. The time and rate at which the high pressure cycle should be commenced may be determined by observing, detecting, measuring or otherwise determining the back pressure within the cavity. The high pressure application should be started in sufficient time so that there is a gradual and smooth transition from the low to the high pressure for the best results.

One embodiment of apparatus of the present invention comprises a vertical injection chamber which is preferably open at both ends. In turn, the injection chamber consists of two elementary chambers, an upper and lower chamber, separated by a horizontal joint connecting the chamber to a horizontally disposed mold cavity which comprises upper and lower mold halves separated by a horizontal parting line. In the apparatus of the present invention, the upper mold half is operationally connected with means to retract the upper mold half from the lower mold half through a predetermined distance.

The lower chamber is fixed to the lower mold half and closure means are provided in said lower chamber. The closure means comprise a reciprocal shaft or piston of approximately the same cross-sectional shape and area as the internal cross section of the chamber. The upper chamber is fixed to the upper retractable mold half and is provided with a reciprocal injection shaft. A portion of the length of the leading edge of said shaft is of approximately the same cross-sectional shape and area as the internal cross section of the upper chamber. The overall length of the injection shaft which is of approximately the same cross-sectional area and shape is especially critical in the apparatus of the present invention and the length thereof is at least as great, but preferably greater than the predetermined distance through which the upper mold is retracted from the lower mold half. The injection piston, therefore, always remains within the upper sleeve during the molding cycle except it is removed above the closed mold for the charging of the material to the upper chamber. This ensures continuous, uninterrupted, automatic operation of my apparatus and avoids the difficulties connected with continual reposition of pistons using snap-on devices.

The vertical configuration of the apparatus of the present invention has many outstanding advantages over the horizontal configuration of prior art pressure casting apparatus. For example, in charging moldable material to a vertical injection chamber, very little, if any, air can be entrapped or occluded in the charge. Instead, air is displaced from the chamber as the material is charged thereto, thereby significantly reducing the possibilities of excessive porosity in the final casting. Also. quite surprisingly, l have found that castings produced in apparatus employing a vertical configuration can have significantly less residual metal or scrap associated therewith than castings produced in apparatus employing a horizontal configuration by virtue of the short distance of material travel to fill the mold. For example, the casting produced in my apparatus in contrast to horizontal casting devices can represent a significantly greater percentage of the original charge of moldable material to the injection chamber. Occluded gases typically require substantial overflow wells which increases the percentage of scrap in conventional devices. while my apparatus permits significantly reduced or no overflow welds.

Another outstanding advantage of my vertical configuration is that alloys of high purity can be employed to produce anodizable castings. For example, anodizable castings of aluminum and aluminum alloys can be produced in the apparatus of the present invention as well as castings of iron, brass, magnesium, and the like.

One of the major differences in the operation between the apparatus of U.S. Pat. No. 3,038,220 and mine is that my apparatus is characterized by.nonsticking and continuous operation, that is to say, each casting cycle which includes the injection of the moldable material into the cavity and the extraction of the finished casting therefrom, can be continuously re peated without interruption. In contrast thereto. the apparatus of U.S. Pat. No. 3,038,220 is not continuous, but instead each cycle must be interrupted after extraction of the casting from the mold in order to detach the injection piston from the injection shaft oftentimes because the casting is stuck thereto, or to clean the piston of any moldable material which can adhere to the circumferential portion thereof. However. in my apparatus, such interruptions are unnecessary and my apparatus can be operated in a continuous fashion, since the novel features thereof not only provide means for repeated cleaning or wiping of the circumference portion of the injection shaft, but also said features assure that said shaft will not gall or solder in the injection chamber.

My invention will be better understood with reference to the attached drawings which illustrate especially preferred arrangements of apparatus suitable for accomplishing the purposes of the present invention.

FIG. 1 is a diagrammatic vertical axial section of my ap paratus where the parts are shown in their positions before the injection step, the moldable material being shown in the upper portion of the injection cylinder.

FIG. 2 is another section corresponding to FIG. 1, but showing the parts in their positions after the injection of the moldable material into the mold cavity.

FIG. 3 is a view similar to FIGS. 1 and 2 showing the parts in their first positions before extraction of the set casting.

FIG. 4 is a view similar to FIGS. 1, 2 and 3 showing the position of the parts on ejection of the set casting.

Referring now particularly to FIG. 1, there is shown upper and lower mold halves l0 and 12 respectively, separated by horizontal parting line 14. Mold halves I0 and 12 form a series of mold cavities 7 connected to and about the central vertical injection chamber 31 by feed passages 5. Generally, the openings of feed passages 5 are disposed radially about the inner cross section of chamber 31, so that residual moldable material remaining therein after the casting has set will form an integral part of the ultimate casting in the form of arms radiating from the biscuit formed in chamber 31. Vertical injection chamber 31 comprises upper chamber 16 fixed to upper mold half 10, so that the lower edges of chamber 16 are flush with the lower surface of upper half 10. Upper chamber 16 is characterized by an inner recessed annulus 17 about the upper portion of the chamber and a nipple 15 for the introduc tion of a lubricant to the annulus 17 for lubricating of the piston 20 during the cycling operation. Lower chamber 18 is fixed to lower mold half 12 and the upper edges of chamber 18 are flush with the upper surface of mold half 12. As shown, closure means comprises a valve 20 connected to reciprocating means 22 shown as a coiled spring. Reciprocating means 22 permits closure means 20 to move from a first position in chamber 31 wherein feed passages 5 are disconnected from chamber 31 to a second position in which feed passages 5 are connected to chamber 31. A pressure detecting or sensing element 8 is shown within cavity 7 to indicate the cavity pressure during operation. This detecting means communicates to and controls the pressure applied by reciprocating means 24.

Valve 20 is slidably mounted in a valve chamber containing a tapered or shaped valve seat 19 against which seat the valve 20 moves and snugly fits during the injecting or casting cycle. Valve shaft 21 is secured to reciprocating means 22, mounted on an ejector plate 27 containing ejector pins 28 and extending upwardly into ejector chambers in the lower mold half 12. The lower end of valve shaft 21 is positioned a set distance from the ejector plate 27 so that when the valve 20 is rested in the valve seat 19, the end of valve shaft 21 is against ejector plate 27. Thus. the distance from the one end of the valve shaft 21 and the ejector plate 27 should be the same as the distance valve 20 moves to become firmly rested in valve seat 19. This arrangement prevents bounce of the valve 20 during operation, permits the use of increased injection pressures, and reduces the projected molding area relative to the closing pressure needed to close the mold.

The ejection means comprises ejector pins 28 which are adapted for slidable movement through a support or base plate 29 securely mounted to the lower mold half 12 and to the ground (not shown). A ram means 26 is provided to move the ejector plate 27 and pins 28 upward for extraction of the set casting from the lower mold half 12. and to move the valve shaft 21 upward to aid in the ejection process.

Injection piston 30 is shown disposed outside upper chamber 16 so that moldable material 32 can be introduced to chamber 31. Moldable material 32 can be introduced to chamber 31 by ladling or by other techniques known to the art which need not necessarily require that piston 30 be completely removed from the confines of chamber 16. Piston 30 is connected to suitable reciprocating means 24 which is not illustrated in detail since features of such means are wellknown to the art. A length of the Ieading'portion of piston 30 represented by L2 is of approximately the same cross-sectional shape and area as the internal cross section of chamber 16, so that at least that portion of piston 30 represented by L2 can provide a close but slidable, fluid-tight fit in upper chamber 16. Rods 34 which are securely attached to upper mold half 12 are operationally connected with suitable reciprocating means 33 to retractupper mold 10 from lower half 12 through a predetermined distance such as to a position represented by parting line P-P. The parting line P-P of the moving upper half of the mold should not be above the maximum length of the injection piston 30 during the operating cycle. In operation the upper mold 10 moves first to the open P-P position and then the piston 30 can move to the distance desired.

In operation a moldable material .such as a molten aluminum alloy is ladled into the upper injection chamber 16 with the apparatus shown as in FIG. 1.

Referring now to FIG. 2, injection piston 30 has moved downwardly to inject the moldable material 32, which can be an anodizable alloy, into cavities 7. In my preferred apparatus reciprocating means 24 can apply two different pressures to piston 30 in the injection step. Initially, a low injection pressure is applied to piston 30, whereby cavities 7 are filled with moldable material 32 without turbulence and at a reduced velocity, so that any gases in the cavities can be freely vented through parting line 14. In such a fashion, a peripheral seal is formed in cavities 7 with a minimum of flashing. The pressure initially applied to piston 30 will vary depending primarily upon the particular moldable material involved However, for illustrative purposes, pressures between about 400 psi. to about 500 p.s.i., or somewhat higher can be employed, for example, with molten metal like an aluminum-magnesium anodizable high strength corrosion-resistant alloy such as Almag 35, When cavities 7 are filled with moldable material 32, a pressure detection device 8, such aspressure switch 8 shown, actuates means 24 to apply a higher injection or forging pressureon piston 30. Suitable high injection pressures can vary but generally pressures in the range of from 1,000 p.s.i. to 1,500 p.s.i., can be employed. Those well-skilled in the art will readily recognize that the aboverange of suitable injection pressures is considerably lower than injection pressures generally or presently employed in pressure diecasting apparatus for these metals. However, in accordance with this preferred method of operation, I am able to produce castings ofhigh density and extremely low porosity which are features especially required in castings of anodizable alloys in order to assure the application of a uniform anodized finish thereon. The low and high pressures are imparted as shown by a single piston 30. However, if desired a piston within a piston arrangement may be employed so that one piston isused for low pressure and the other or both used for the high pressure step.

On application of the low pressure by piston 30, valve 20'is depressed below the horizontal parting line 14 and against the valve seat 19, with one end of the valve shaft moved against ejector plate 27, whereby upon application of the high pres sure, valve 20 is secure, and increased pressure without bounce or movement of valve 20 can be accomplished. Of course, the operation of the reciprocating means for the piston 30, mold halves, and the valve can be controlled by limit switches set at the proper distances to actuate the means, thereby providing automatic and continuous operation.

FIGS. 3 and 4 illustrate the manner of extracting or ejecting the castings formed in the apparatus of the present invention. After the casting is set, the high injection pressure is maintained on injection piston 30 and retraction means 33 is actuated to retract upper mold half together with upper chamber-16 from'lower mold half 1.2 through a predetermined distance such as to the position represented by parting line P-P. It will be apparent that even in said retracted position, upper chamber 16 is in communication with at least a portion of the leading edge of the injection piston 30 which is of ap- 4 proximately the same cross-sectional shape and area as the internal cross section of chamber 16. In the preferred practice of my invention,injection piston 30 is next withdrawn from the injection position through the lower edge of upper chamber 16 Simultaneous with or after the withdrawal of shaft 30, ram means 26 is actuated and drives against ejector plate 27, which in turn causes ejector pins 28 and valve shaft 21 and valve 20 to move upwardly and eject the set casting from lower mold half 12. It will be readily apparent that if the biscuit should stick to injection piston 30, then the biscuit and casting will be dislodged therefrom as piston 30 is withdrawn through chamber 16. After the metal has been injected and a set casting formed, the upper piston 30 remains in place to hold the biscuit down, while the upper mold half 10 moves to the open position P-P or open position. Then the piston 30 moves upwardly through mold half 10 and upper injection chamber 16 where its piston walls are wiped by contact with the injection chamber walls. After this cycle the mold half 10 can be moved to any position. This operation permits positive holding of the biscuit by piston 30 when the mold is opened, while the ejector means (pins 28 and valve 20) provide positive ejection of the casting from the lower mold half 12. Moreover, any residual metal that may have flashed on or otherwise adhered to the outer circumferential portion of injection shaft 30 will be readily wiped therefrom as shaft 30 is withdrawn through upper chamber 16.

My invention also permits efficient lubrication of the upper injection chamber 16 and piston 30 during operation without contamination of the molding material or interruption of operation. In horizontal type pressure injection apparatus lubricant often tends to puddle at the bottom or lower portion of the injection piston rather than to form a thin film about the piston. This lubricant may come into contact with the molding material and particularly with a molten metal cause contamination. My apparatus permits uniform, thin film lubrication of the entire piston and prevents lubricant from contacting the molding material. In my apparatus andmethod a lubricant such as graphite may be introduced through nipple 15 into annulus 17 when the injection piston is in an injection position (FIG. 2) or during injection so that the lubricant is spread or wiped on movement onto the walls of the injection chamber 16 and on the piston walls.

It will be apparent that after the casting has been extracted, my apparatus is immediately ready for another casting cycle without any interruptions such as disengaging either the injection piston 30 or lower valve 20. Accordingly, my apparatus and method present a vertical pressure diecasting apparatus which obtains all the advantages of such a vertical configuration and which can be operated in a continuous fashion to produce castings of unexpectedly high quality. Although my apparatus has been described in conjunction with my preferred two-pressure method of operating, my apparatus may likewise be employed for simple or multiple pressure injection operations where desired.

Many modifications in the features offered above for the purposes of illustrating my invention can be employed therein without departing from the spirit and scope of the invention defined in the appended claims.

For example, my principles may be applied to various diecasting apparatus and can be used with inclined or biased pressure diecasting apparatus.

Iclaim: 1. A method for preparing metal castings wherein a reciprocating mold element includes an injection chamber which chamber communicates with a casting cavity, said chamber containing a close fitting injection piston adapted to inject molten metal into the casting cavity which comprises:

moving the injection piston from a first open to a second closed position to inject molten metal into the casting cavity;

wiping the circumferential side of the injection piston upwardly by withdrawing the mold element through a predetermined distance from a first to a second position; and

wiping the circumferential side of the piston downwardly with the chamber walls by withdrawing the injection piston from the second to its first position.

2. The method of claim 1 wherein the molten metal is injected into the mold cavity under a relatively low pressure of not greater than about 500 lbs. per square inch and at a controlled rate below which flash and turbulance is experienced to fill the casting cavity and thereafter subjecting the injected metal to a high forging pressure to produce a casting of the desired quality.

3. The method of claim 2 which includes controlling the relatively high forging pressure to provide for the gradual rise in pressure from the low to the high pressure thereby precluding turbulance resulting from irregular pressure.

4. The method of claim 2 which includes detecting the pressure induced in the mold cavity by injecting the metal and when substantial filling of the cavity is detected subjecting the metal in the die cavity to a relatively high forging pressure of greater than 500 lbs. per square inch.

5. The method of claim 1 wherein the injecting of the molten metal is at a temperature slightly over the arrest point of the metal.

6. The method of claim ll wherein the molten metal is aluminum or an aluminum alloy.

7. The method of claim 1 wherein a second mold element includes an ejection chamber said chamber contains a close fitting reciprocating injection piston which further comprises forming the mold elements to define a casting cavity and pouring' the molten metal into thfiijection chamber while the ejection piston is in the first position.

8. The method of claim 7 which comprises wiping the circumferential walls of the ejection piston with the ejection chamber walls when the ejection piston moves between a fi'rst position and a second position.

9. A casting formed by the method of claim 1.

10. A method for preparing metal castings wherein a reciprocating upper mold element includes an injection chamber which communicates with a casting cavity said chamber containing a close fitting injection piston adapted to inject molten metal into the casting cavity, a lower mold element which includes an ejection chamber said chamber containing a close fitting reciprocating ejection piston which comprises:

forming the upper and lower mold elements 'to define a casting cavity;

pouring molten metal into the upper chamber while the injection piston isin the'fi'rst position;

injecting the molten metal into the casting cavity by moving the ejection piston from its first to its second position;

wiping the circumferential sides of the injection piston by moving the upper mold element upwardly through a predetermined distance;

wiping a second time the circumferential walls of the injection piston by moving the injection piston from its second to its first position; I p v ejecting the casting so formed; and

repeating the above steps in sequence.

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