06. Casting Processes

06. Casting Processes - 1 Casting Processes Casting...

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Unformatted text preview: 1 Casting Processes Casting Processes Egyptian foundrymen are casting bronze doors Casting Pits on the Athenian Agora Making a large bronze statue 2 Typical Cast Parts (a) (c) Sources : Courtesy of Central Foundry Division of General Motors Corporation, Courtesy of Polaroid Corporation and Chicago White Metal Casting, Inc. (b) (d) Topics today 1. Fundamentals 2 Sand Casting 2. Sand Casting 3. Investment Casting 4. Die Casting ¡ Injection Molding 5. Other casting methods 6. Design considerations 3 Casting Processes Material is melted Heated to proper temperature Molten material is poured into a mold Solidifies The part from the mold is removed Cleaning, finishing and inspection Advantages of Casting Processes • Complex shapes • Parts can have hollow sections or cavities • Very large parts • Intricate shaping of metals that are difficult to machine or uneconomical 4 Cross Section of a Mold Casting Terminology • Pattern – approximate duplicate of the part to be cast • Molding material – material that is packed around the pattern to provide the mold cavity • Gating system – network of channels that delivers the molten metal to the mold • Pouring cup – portion of the gating system that controls the delivery of the metal • Flask – rigid frame that holds the molding aggregate • Cope – top half of the pattern • Drag – bottom half of the pattern • Core the delivery of the metal • Sprue – vertical portion of the gating system • Runners – horizontal channels • Gates – controlled entrances • Parting line – separates the cope and drag – sand or metal shape that is inserted into the mold to create internal features • Mold cavity – combination of the mold material and cores • Riser – additional void in the mold that provides additional metal to compensate for shrinkage • Draft – angle or taper on a pattern that allows for easy removal of the casting from the mold • Casting – describes both the process and the product when molten metal is poured and solidified 5 Cooling Curves of a Pure Metal Prediction of Solidification Time: Chvorinov’s Rule • Chvorinov’s Rule: – t s =B(V/A) n where n=1.5 to 2.0 • t s is the time from pouring to solidification • B is the mold constant • V is the volume of the casting A is the surface area through which heat is rejected • A is the surface area through which heat is rejected 6 Considerations in Casting • Molten Metal Problems • Fluidity and Pouring Temperature • Gating Systems Gating Systems • Solidification Shrinkage • Risers and Riser Design • Pattern Design • Pattern Removal • Design Considerations Molten Metal Problems • Chemical reactions can occur between molten metal and its surroundings • Gas porosity – Gas that is not rejected from the liquid metal may be trapped upon solidification • Reactions can lead to defects in the final castings – Metal oxides may form when molten metal reacts with oxygen – Dross or slag is the material...
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This note was uploaded on 04/10/2008 for the course MFE 331 taught by Professor Moon during the Spring '08 term at Syracuse.

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06. Casting Processes - 1 Casting Processes Casting...

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