09Lecture-ch11 - Manufacturing and Production Processes...

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Manufacturing and Production Processes ENGR 3190U – Lecture 09 Chapter 11 - Metal Casting Processes Sections 11.1, 11.1.1, 11.1.3, 11.2.1 – 4, 11.3.1, 11.3.3, 11.3.4, 11.5, 11.7 1. Sand Casting 2. Other Expendable Mold Casting Processes 3. Permanent Mold Casting Processes 4. Casting Quality 5. Product Design Considerations 6. Metal Casting Calculations ( 09Lecture-Calc.doc ) 7. Video Clips : sand casting, evaporative foam casting, investment casting, die casting
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2 Categories of Casting Processes 1. Expendable mold processes - mold is sacrificed to remove part Advantage: more complex shapes possible Disadvantage: production rates often limited by time to make mold rather than casting itself 1. Permanent mold processes - mold is made of metal and can be used to make many castings Advantage: higher production rates Disadvantage: geometries limited by need to open mold
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Figure 11.1 A large sand casting weighing over 680 kg (1500 lb) for an air compressor frame (photo courtesy of Elkhart Foundry).
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Making the Sand Mold The cavity in the sand mold is formed by packing sand around a pattern, then separating the mold into two halves and removing the pattern If casting is to have internal surfaces, a core must be included in mold Buoyancy Calculations in Metal Casting 09Lecture-Calc.doc A new sand mold must be made for each part produced
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Sand Casting - Desirable Mold Properties Strength ‑ to maintain shape and resist erosion Permeability ‑ to allow hot air and gases to pass through voids in sand Thermal stability ‑ to resist cracking on contact with molten metal Collapsibility ‑ ability to give way and allow casting to shrink without cracking the casting Reusability ‑ can sand from broken mold be reused to make other molds?
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Sand Casting - Foundry Sands Silica (SiO 2 ) or silica mixed with other minerals Good refractory properties ‑ capacity to endure high temperatures Small grain size yields better surface finish on the cast part Large grain size is more permeable, allowing gases to escape during pouring Irregular grain shapes strengthen molds due to interlocking, compared to round grains Disadvantage: interlocking tends to reduce permeability
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Types of Sand Mold Green‑sand molds - mixture of sand, clay, and water; “Green" means mold contains moisture at time of pouring Dry‑sand mold - organic binders rather than clay And mold is baked to improve strength Skin‑dried mold - drying mold cavity surface of a green‑sand mold to a depth of 10 to 25 mm, using torches or heating lamps
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Other Expendable Mold Processes Play video clips Shell Molding Vacuum Molding Expanded Polystyrene Process Investment Casting Plaster Mold and Ceramic Mold Casting
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Shell Mold
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Shell Mold (1) a match‑plate or cope‑and‑drag metal pattern is heated and placed over a box containing sand mixed with thermosetting resin (2) box is inverted so that sand and resin fall onto the hot pattern, causing a
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  • Spring '10
  • yang
  • Sand casting, Die casting, Permanent mold casting, Die Casting Machines

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