ME1331 Manufacturing lecture 2 - Module ME1331:...

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Module ME1331: Manufacturing Methods Lecture 2: Casting Processes (Part 1 of 2) Dr. Alasdair Cairns Cairns 2010/2011
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Contents • Introduction • Fundamentals of metal casting • Metal casting processes – Sand casting – Shell mould casting – Plaster mould casting – Lost foam casting Cairns 2010/2011
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What is Casting? The process of pouring molten metal into the cavity of a mould Cairns 2010/2011 Evidence of first use as early as 4000 B.C.
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History of Casting Cairns 2010/2011 One of the main processes used to make weapons, coins, jewellery and ornaments
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Solidification of Pure Metals Lead 327°C Aluminium 660°C Copper 1082°C Silicon 1423°C on 537 A pure metal has a well-defined melting/freezing point i.e. when cooled it solidifies at a constant temperature The thermal “arrest” is due to the latent heat of fusion (during molecular nucleation and growth the latent heat keeps the remaining liquid at this temperature) The energy associated with a solid is less than the energy of the liquid Iron 1537°C Titanium 1668°C Tungsten 3410°C
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Solidification of Alloys Aluminium alloys 476-654°C Copper alloys 885-1260°C Example Phase Diagram In case of alloys the solidification temperature changes with the percentage of the alloying element Steel 1371-1532°C Titanium alloys 1549-1649°C
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Types of Mould (1) Open mould: metal is simply poured into the open mould Closed mould: metal is poured into the more complex cavity using the “gating” system
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Types of Mould (2) To optimise the flow and the solidification processes, a typical, gravity casting system includes: sprue, runners, gates and risers (feeders).
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Three Categories of Mould • Expendable moulds – Refractory materials (capable of withstanding heat) – Sand, plaster, ceramics etc. – Usually mixed with bonding agents for improved properties – Pattern available for re-use • Permanent moulds – High temperature metal – Better conductivity hence finer structures • Composite moulds – Two or more materials (sand, ceramic, metals) – Combines the advantages
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Three Important Factors in Casting • Flow of the molten metal into the mould cavity – Viscosity, rate of pouring, inclusions, mould design etc. • Influence of the type of mould material Cairns 2010/2011 – Surface characteristics (roughness), conductivity, strength, permeability etc. • Solidification and cooling of the metal in the mould – Shrinkage, defects etc.
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Casting Defects To avoid defects of the casting: – During quick, turbulent flow gasses are entrained and entrapped in the casting. The casting becomes porous. – Other defects: cavities, discontinuities (cracks, cold or hot tearing), surface defects (folds, laps, adhering sand), incomplete casting, incorrect dimensional shape, inclusions (generally non-metallic) Hot tear due to constrained shrinking Example of porosity in an engine cylinder head (highlighted via dye impregnation) Example of a re-oxidation macro-inclusion in a casting
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This note was uploaded on 04/20/2011 for the course ME 1331 taught by Professor Zeshan during the Spring '11 term at American College of Computer & Information Sciences.

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ME1331 Manufacturing lecture 2 - Module ME1331:...

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