Patent Publication Number: US-2005133187-A1

Title: Die casting method system and die cast product

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to die casting. More particularly, the present invention relates to the casting of components having internal passages.  
     BACKGROUND OF THE INVENTION  
      In many applications, die cast products involving internal passages are necessary. These passages are typically for fluids, such as for example, water, oils, and gases, and are generally introduced by machining the passages into the product after it has been cast.  
      However, where after-cast machining is currently used, such processing can add significant cost to the final product. In other cases, the complex fluid flow patterns that are most desired are often difficult, costly, or impossible to achieve using current machining methodology.  
      Accordingly, it is desirable to provide a method and system to introduce passages into a die cast product before or during the casting of the product itself.  
     SUMMARY OF THE INVENTION  
      The foregoing needs are met, to an extent, by the present invention, wherein in one embodiment of the present invention a method for production of a casting incorporating a passage is provided comprising disposing at least one tube in a mold and casting a metal around the tube. The metal may be molten or semi-solid metal and comprise aluminum and aluminum alloys. The tubes of the invention may also comprise any metal, including, but not limited to, steel, and be crimped or clamped in some embodiments.  
      The outer surface of the tubes can be treated prior to casting. Such treatments include spraying the surface with an aluminum composition, shot blasting, and/or metal plating. In some embodiments of the present invention, fluids may be passed through the cast-in tubes before, during, and after casting. Molds of the present invention may comprise passages that match the direction of the tube through the casting.  
      In accordance with another embodiment of the present invention a system for production of a casting incorporating a passage is provided comprising a disposing means that places at least one tube in a mold and a casting means that casts a metal around the tube. The metal may be molten or semi-solid metal and comprise aluminum and aluminum alloys. The tubes of the invention may also comprise any metal, including, but not limited to, steel, and be crimped or clamped in some embodiments.  
      The outer surface of the tubes can be treated prior to casting. Such treatments include spraying the surface with an aluminum composition, shot blasting, and/or metal plating. In some embodiments of the present invention, fluids may be passed through the cast-in tubes before, during, and after casting. Molds of the present invention may comprise passages that match the direction of the tube through the casting.  
      Another embodiment of the invention provides a cast product having at least one tube and metal cast around the tube.  
      There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.  
      In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.  
      As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagrammatic representation of a tube and mold, designed with passages to hold the tube.  
       FIG. 2  is a cross-sectional view taken along the  2 - 2  in  FIG. 1 .  
       FIG. 3  is a diagrammatic representation of an alternate tube design and mold, also designed with a passage to accommodate the tube.  
       FIG. 4  is a cross-sectional view taken from the  4 - 4  in  FIG. 3 .  
       FIG. 5  is a diagrammatic representation of a tube design that crosses over itself.  
       FIG. 6  is a diagrammatic representation of two tubes that comprise an intersection. 
    
    
     DETAILED DESCRIPTION  
      The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present invention provides a method for the production of castings with incorporated passages, where the castings are from cast metal and where tubes are cast-in with a superheated molten metal to form the passages.  
      The cast metal may be any metal including, but not limited to steel, zinc, magnesium, or combinations thereof. In some embodiments, aluminum and aluminum alloys are cast. Aluminum alloys include 357 alloy, 380 alloy, ADC12 alloy, 356.2 alloy, and other aluminum-silicon alloys.  
      A variety of presses and die cast methods may be used with the present invention. For example, squeeze casting, gravity casting, and high and low pressure die casting methods may all be used. In some embodiments, vertical die cast presses may also be used. Vertical die cast presses manufactured by THT Presses preferred in some applications are disclosed in U.S. Pat. Nos. 5,660,223 and 5,429,175, assigned to and commercially available from THT Presses, Inc., Dayton, Ohio. THT presses of this invention may be classified as “indexing-type” or “shuttle-type.” Though the indexing press will be detailed in an embodiment below, both types of presses may be used in the instant invention.  
      The THT presses, such as a 200 Ton Indexing Shot Machine, a 1000 Ton Shuttle Machine, or a 100 Ton Shuttle Machine, in particular, are capable of operating at a higher speed and with a shorter cycle time than previously known die casting presses and which, as a result, produce higher quality parts with reduced porosity. The die casting presses are also simpler and less expensive in construction, requiring less maintenance and therefore more convenient to service.  
      The casting methods of the present invention need not be limited to die casting methods of molten metal. In fact, in some embodiments, semi-solid metal (SSM) casting may be preferred. SSM casting is defined broadly herein to encompass any casting technique whereby the metal introduced into a die cavity is greater than 20% granular (i.e., solids). SSM casting techniques that are known in the art include, but are not limited to, rheocasting and thixocasting.  
      SSM casting may be preferred in some embodiments of the present invention because it is performed at lower temperatures where often 20% -70% of the metal is granular and thus in a slurry, rather than liquid state. The cooler temperatures can extend the useful life of the dies. Moreover, the slurry state of the metal reduces turbulence within the metal flow as it is introduced into the die, so as to reduce the incorporation of air and gas into the metal as it is being cast. Thus, porosity and quality control complications are reduced.  
      In one embodiment, vertical die cast presses are used with SSM casting techniques. In other words, SSM is cast using a vertical die casting apparatus. Specifically, the indexing time (i.e., the delay between indexing between the pour station  80  and transfer station  85 ) can be used to control the time the molten metal is cooled in the shot sleeve to reach the SSM range. That is, the amount of time the metal spends in the shot sleeve before it is injected into the molds can be regulated or optimized for a desirable microstructure. Alternatively, molten metal at a predetermined temperature may be poured into the shot sleeve of shuttle presses, i.e. presses that lack the indexing feature.  
      The shear forces present in SSM casting may be more suitable to the present invention in some embodiments over traditional molten metal casting methods. In such an event, larger tubes ranging from about 0.25 inches to about 0.37 inches in outer diameter may be incorporated into the cast-in tube castings than otherwise possible.  
      Many metals and alloys known in the art can be used for SSM casting and can be employed with the instant invention. In some embodiments aluminum-silicon alloys can be used. By definition, aluminum alloys with up to but less than about 11.7 weight percent Si are defined “hypoeutectic”, whereas those with greater than about 11.7 weight percent Si are defined “hypereutectic”. In all instances, the term “about” has been incorporated in this disclosure to account for the inherent inaccuracies associated with measuring chemical weights and measurements known and present in the art. In yet other embodiments, aluminum-silicon copper alloys and/or aluminum-copper alloys may be used with the present invention.  
      Tubes that may be cast-in in the present invention may comprise any metal, preferably steel or hydraulic tubing in some embodiments. The steel tubes can have a composition with less than about 0.17 weight percent carbon, less than about 0.35 weight percent silicon, less than about 0.04 weight percent sulfur, less than about 0.04 weight percent phosphorus and between about 0.40-0.80 weight percent manganese. Preferably, the tubes are free from surface defects, blow holes and cracks.  
      Tubes of the present invention can be of varying wall thickness. Where deformation of the tube is not desirable, the wall thickness and composition is preferably strong enough to withstand pressures of 6,000 psi to 20,000 psi and more preferably, pressures of 8,000 psi to 12,000 psi. For steel tubes, the corresponding wall thickness may range from about 0.02 inches to about 0.04 inches, but a wider range may also be acceptable.  
      Referring now to  FIGS. 1 and 2  there is shown a die  1  into which a guide  2  has been cut. The guide  2  can be cut to fit the path of a tube  3  which is to be embedded into the metal cast. The tube  3  may of any design or path. For example, the tube  3  may have one opening on one face of the mold or cast and then another opening on another face of the mold or cast as shown in  FIG. 1 . However, in some embodiments, tube  3  may have and opening on one face and then be tapered, crimped, or clamped at the other end such that fluids become trapped inside the cast as shown in  FIGS. 3 and 4 . Alternatively, tubes may have paths that cross over ( FIG. 5 ) or intersect ( FIG. 6 ). All such configurations and others are within the scope of the present invention.  
      In addition, more than one tube may be incorporated into a cast-in tube mold or product. All such tubes should be accounted for in the design of the mold such that guide  2  may be cut into each half of the mold to accommodate the tube or tubes.  
      The tubes  3  may optionally be machined at one or more openings  4 . For example, threading for screws or bolts may be inserted. In other embodiments, the outer surface of the tubes may be coated with a thin surface layer to reduce the likelihood of tube movement (such as slipping or rolling) within the cast product. Coatings may include, such as, for example, alumina and aluminum oxide, and may be sprayed on or plated. The thickness of such coating applications will be apparent to one of ordinary skill in the art. Other treatments to the outer surface of the tubes can include shot blasting or grating.  
      Referring back to  FIG. 1 , once a tube design and accompanying mold are selected, the tube  3  is generally located by gravity in the mold  1  by predetermined guide  2  in the lower half of the mold. The tubes are then secondarily located and secured using a reverse passages in the upper half of the mold such that the tube is secured and crimped or clamped in place.  
      Where SSM casting is desired, preferably, the metal is be cast is heated in a range from about 10° C. to about 15° C. above the liquidus temperature (i.e., the semi-solid temperature). For Al—Si alloys this generally ranges from about 585° C. to about 590° C. The melt temperature is then allowed to cool to form a semi-solid slurry before it is finally cast.  
      In some applications, the mold  1  and tube  3  design is such that, optionally, a cooling medium can be passed through the tubing before, during, and/or after the casting process is taking place. In such an embodiment, couplers may be added to the open end of the tube allow for entry of fluids for cooling. The couplers could then be removed, machined, or sheared from the final cast product. This procedure may enhance internal casting cooling rates and thus, cycle times. Also, internal cooling has the potential to improve the metallurgical properties and/or casting integrity of the final cast product. Alternatively, improved tube bonding with the cast is possible.  
      The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.