1 / 66

Metal Casting

Metal Casting. Process in which molten metal is poured into a mold (shaped after the part to be manufactured), then allowed to cool and solidify. Metal Casting (cont.). After solidification occurs the part is removed from the mold to cool further.

eringarrett
Download Presentation

Metal Casting

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Metal Casting • Process in which molten metal is poured into a mold (shaped after the part to be manufactured), then allowed to cool and solidify. Engr 241

  2. Engr 241

  3. Metal Casting (cont.) • After solidification occurs the part is removed from the mold to cool further. • The main objective is to produce parts free of defects and with the desired properties. Engr 241

  4. Process Characteristics • Complex shapes that may have internal cavities • Large or small parts. • Can use materials which are otherwise hard to shape. • Economical. • Near net shape manufacturing. Engr 241

  5. Considerations • Solidification – mold design and material effect cooling rate (Heat transfer). • Metal flow into mold cavity – Flow. Engr 241

  6. Fluid Flow • Basic Casting System • Pouring basin (cup). • Sprue, runners- channels • Gate- entry point for mold • Riser- reservoir Engr 241

  7. Engr 241

  8. Defects • Metallic projections. • flash, fins, swells. • Cavities. • blow holes, pinholes, shrinkage. • Discontinuities. • cracks, • cold or hot tearing – constrained from shrinking freely • cold shuts.- interface from two streams of liquid meeting Engr 241

  9. Defects (Continued) • Defective surface. • folds, laps, scars, adhering sand, oxide. • Incomplete casting. • misruns, insufficient metal, runout. • Incorrect dimensions or shape. • Inclusions. • non-metallic - slag Engr 241

  10. Molds Engr 241

  11. Expendable molds. • made of sand, plaster, or ceramics (mixed with bonding agents/binders). • broken up to remove casting. Engr 241

  12. Permanent molds • used repeatedly. • made from metals which maintain strength at high temperatures. Engr 241

  13. Composite molds. • two or more types of materials. • used to improve mold strength, cooling rates, cost of process. Engr 241

  14. Sand Casting • Consists in placing a pattern in sand to make an imprint, incorporating a gating system, filling the cavity with molten metal, letting it cool, breaking the mold to remove the casting. Engr 241

  15. Characteristics • Traditional casting method. • Loose tolerances. • “poor” surface finish. • low cost. Engr 241

  16. Examples of products • Engine blocks • Pump housings • Cylinder heads Engr 241

  17. Engr 241

  18. Sands • Silica based (SiO2), inexpensive, resistance to high temperature. Engr 241

  19. Sands (Cont.) • Mulling- mixing sand with additives - conditioning • Clay used as cohesive agent to aid in bonding sand particles Engr 241

  20. 3 Types of Sand Molds • 1. Green Sand: • sand, clay, and water. • least expensive. • Can dry mold surfaces – called “skin dried” Engr 241

  21. 2 Cold-box: • organic and inorganic binders added. • greater dimensional accuracy. • greater cost. Engr 241

  22. 3 No-bake: • synthetic liquid resin mixed with sand. • Cold-setting process- bonding of mold takes place without heat • Petrobond Engr 241

  23. Mold Components • Flask. • Cope (top) • Drag (bottom) • Parting line - seam • Pouring basin or pouring cup. • Sprue – molten metal flows downward. Engr 241

  24. Mold components (cont.) • Runner and gates. • Risers (blind and open). • Cores – form hollow regions • Vents – vent gasses Engr 241

  25. Engr 241

  26. Patterns • Used to create sand molds • Made of wood, aluminum, steel, plastic, cast iron. Engr 241

  27. Types of mold patterns • One piece (loose pattern). • simple shapes, low quantity production. • Split pattern • Two piece patterns, complex shapes. • Match plate • Split patterns secured to plate Engr 241

  28. Engr 241

  29. Engr 241

  30. Mold Components • Cores- provide internal cavities • Chaplets- anchors, supports for cores • Chill- insert for preferential cooling • Core prints – recesses to support core Engr 241

  31. Shell Mold Casting • Pattern coated with sand and binder • Cured in oven • Shell removed • Left with hollow shell for filling • Close tolerance good surface finish, low cost. Engr 241

  32. Engr 241

  33. Shell molding: • Close tolerances • Good surface finish • Low cost Engr 241

  34. Plaster-Mold Casting • Plaster of paris with talc and silica flour. • Mixed with water • Poured over pattern • Plaster sets – pattern removed Engr 241

  35. Plaster–mold casting(cont.) • Mold dried in oven • Poured in vacuum or under pressure due to low permeability • Low permeability (gas cannot escape) Engr 241

  36. Plaster mold casting characteristics: • Plaster can only withstand about 2200 deg F. • Good surface and details. • “Lower” temperature alloys (Mg, Al, Zn) Engr 241

  37. Ceramic-Mold Casting Similar to plaster mold casting but utilizes refractory mold materials of zircon, aluminum oxide and fused silica • Good dimensional accuracy and surface finish, but expensive. Engr 241

  38. Expendable-Pattern Casting • Also known as Lost Foam, Evaporative-pattern, or Lost Pattern Casting Engr 241

  39. Process: • Polystyrene pattern coated with refractory slurry • Polystyrene pattern buried in silica sand within flask • Sprue extending out of sand Engr 241

  40. Process (cont.) • Flask vibrated to settle sand around pattern • Molten metal poured over sprue • Polystyrene vaporizes as metal fills cavity Engr 241

  41. Engr 241

  42. Expendable Foam Advantages • simple process, no parting lines, or risers • inexpensive flasks, minimum finishing • polystyrene is cheap and gives good detail. • economical for long production runs (pattern mold cost). • can be automated. Engr 241

  43. Investment Casting Process • Inject wax (plastic) in to metal die (pattern shape) • Wax pattern dipped to coat in refractory slurry – dries to form hard shell Engr 241

  44. Investment casting (cont.) • Wax melted out of hardened shell • Molds connected to tree with central sprue • Molten metal poured in • Mold destroyed to expose solidified parts Engr 241

  45. Engr 241

  46. Characteristics • High quality • Good surface finish • Good detail • Expensive process Engr 241

  47. Vacuum Casting • Counter-gravity low pressure process. • Sand and urethane molded over metal die. • Gate is on the bottom. Engr 241

  48. Vacuum Casting (cont.) • Immersed into molten metal, which is drawn into mold cavity. • Thin wall, complex shapes, uniform properties, high volume, low cost. Engr 241

  49. Engr 241

  50. Die Casting • Type of permanent die casting • Molten metal is forced into a permanent mold (die) at high pressure. • Dies are steel or graphite • Two types of die casting Engr 241

More Related