Lost foam casting of dual alloy engine block

• US 5,000,244 A
• Filed: 12/04/1989
• Issued: 03/19/1991
• Est. Priority Date: 12/04/1989
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Osborne, Richard J.
• Primary Examiner(s): Seidel, Richard K.
• Assistant Examiner(s): BATTEN JR, J REED
• Application Number:
  US07/445,205
• Time in Patent Office: 470 Days
• Field of Search: 164/34, 164/93, 164/94, 164/95, 164/96, 164/91
• US Class Current: 164/34
• CPC Class Codes: B22C 9/046 Use of patterns which are eliminated by the liquid metal in the mould
• CPC Class Codes: B22D 19/16 for making compound objects cast of two or more different metals, e.g. for making rolls for rolling mills casting compound ingots B22D7/02
• CPC Class Codes: F02B 2075/1816 four
• CPC Class Codes: F02F 1/102 Attachment of cylinders to crankcase
• CPC Class Codes: F02F 1/108 Siamese-type cylinders, i.e. cylinders cast together
• CPC Class Codes: F02F 2007/009 Hypereutectic aluminum, e.g. aluminum alloys with high SI content
• CPC Class Codes: F02F 2200/08 using a lost model, e.g. foam casting
• CPC Class Codes: F05C 2201/021 Aluminium

Abstract

In a preferred embodiment, a compound aluminium alloy engine block casting comprises at least a piston-travel region of a cylinder wall section formed of a first alloy, preferably hypereutectic aluminum-silicon alloy, and a remainder including a crankcase section and a water jacket wall formed of a distinct second alloy, preferably hypoeutectic aluminum-silicon alloy. The engine block casting is made by a lost foam process that employs an expendable pattern formed of expanded polystyrene or the like. The pattern comprises a first runner system for casting the first alloy to decompose and replace a portion of the pattern corresponding to the piston-travel region of the casting, and a second runner system for casting the second alloy to decompose and replace the remainder of the pattern. The first alloy and the second alloy are independently but concurrently cast into a singular mold, such that the entire pattern is duplicated, whereupon the alloys merge and fuse to form an integral casting. The preferred product engine block casting advantageously combines the high wear resistance of the hypereutectic aluminum alloy in the cylinder wall section and the reduced porosity and improved machinability of the hypoeutectic alloy throughout the balance of the casting.

Claims

1. A lost foam casting process for producing a compound alloy engine block casting, said engine block casting comprising a crankcase section, a cylinder wall section extending from the crankcase section and a water jacket wall also extending from the crankcase section about the cylinder wall section but spaced apart therefrom, said cylinder wall section defining at least one cylinder bore and having a piston-travel region adjacent an outer end remote from the crankcase section, said engine block casting being formed of a plurality of metal alloys such that said cylinder wall piston-travel region is composed of a first alloy and said crankcase section and said water jacket wall are composed of a second alloy, said process comprising

embedding in an unbonded particulate mold an expendable pattern comprising a product form substantially sized and shaped to produce the engine block casting and having portions corresponding to the crankcase section, the cylinder wall section and the water jacket wall, said pattern further comprising a first runner system including a melt pour surface and connected to the cylinder wall portion for conveying molten metal from the melt pour surface to the cylinder wall portion, and a second runner system including a melt pour surface distinct from the first runner system melt pour surface and connected to the water jacket wall portion for conveying molten metal from the second runner system melt pour surface to the water jacket wall portion, said pattern being formed of a polymeric material thermally decomposable at metal casting temperatures and embedded in the mold such that the first runner system melt pour surface and the second runner system melt pour surface are exposed and spaced apart for independent contact with cast metal,

casting molten first alloy into contact with the first runner system melt pour surface to decompose and replace at least the piston-travel region,

concurrently casting molten second alloy into contact with the second runner system melt pour surface to decompose and replace the water jacket wall portion and the crankcase portion, said casting of said alloys continuing so as to decompose and replace the entire pattern, whereupon the alloys flow together,

solidifying the cast alloys to form the engine block casting, whereupon the alloys fuse to produce an integral engine block casting, and

removing the engine block casting from the mold, and separating runner replacement metal from the engine block casting.

2. A lost foam casting process for producing a compound alloy engine block casting, said engine block casting comprising a crankcase section, a cylinder wall section extending from the crankcase section and a water jacket wall extending from the crankcase section about the cylinder wall section but spaced apart therefrom, said cylinder wall section defining at least one cylinder bore and having a piston-travel region adjacent an outer end remote from the crankcase section, said engine block casting being formed of a plurality of aluminum alloys such that said cylinder wall piston-receiving region is composed of a first aluminum alloy and said crankcase section and said water jacket wall are composed of a second aluminum alloy, said process comprising

embedding in an unbonded particulate mold an expanded polystyrene pattern comprising a product form substantially sized and shaped to produce the engine block casting and having portions corresponding to the crankcase section, the cylinder wall section and the water jacket wall, said pattern further comprising a first runner portion including a melt pour surface and connected to the cylinder wall portion for conveying molten metal from the melt pour surface to the cylinder wall portion, and a second runner portion including a melt pour surface distinct from the first runner melt pour surface and connected to the water jacket wall portion for conveying molten metal from the second runner melt pour surface to the water jacket wall portion, said pattern being embedded in the mold such that the first runner melt pour surface and the second runner melt pour surface are exposed and spaced apart for independent contact with cast metal,

casting molten first aluminum alloy into contact with the first runner melt pour surface to decompose and replace at least the piston-travel region,

concurrently casting molten second aluminum alloy into contact with the second runner melt pour surface to decompose and replace the water jacket wall portion and the crankcase portion, said casting of said alloys continuing so as to decompose and replace the entire pattern, whereupon the alloys flow together,

solidifying the cast alloys to form the engine block casting, whereupon the alloys fuse to produce an integral engine block casting, and

removing the engine block casting from the mold.

3. The lost foam casting process in claim 2 wherein the first aluminum alloy is a hypereutectic aluminum-silicon alloy and the second aluminum alloy is hypoeutectic aluminum-silicon alloy.