Fundicion centrifuga

Casting
2.810 Prof. Timothy Gutowski

Casting since about 4000 BC…

Ancient Greece; bronze statue casting circa 450BC

Iron works in early Europe, e.g. cast iron cannons from England circa 1543

Outline
• Sand Casting, Investment Casting, Die Casting • Basics and countermeasures • Phase Change, Shrinkage • Heat Transfer • Pattern Design • Variations & Developments • EnvironmentalIssues

Casting
Readings;
1. 2. 3. Kalpakjian, Chapters 10, 11, 12 Booothroyd, “Design for Die Casting” Flemings “Heat Flow in Solidification”

Note: a good heat transfer reference can be found by Prof John Lienhard online http://web.mit.edu/lienhard/www/ahtt.html

Casting Methods

• Sand Casting

High Temperature Alloy, Complex Geometry, Rough Surface Finish

• Investment CastingHigh Temperature Alloy, Complex Geometry, Moderately Smooth Surface Finish

• Die Casting

High Temperature Alloy, Moderate Geometry, Smooth Surface

Sand Casting

Sand Casting
Description: Tempered sand is packed into wood or metal pattern halves, removed form the pattern, and assembled with or without cores, and metal is poured into resultant cavities. Various core materials can be used.Molds are broken to remove castings. Specialized binders now in use can improve tolerances and surface finish. Metals: Most castable metals. Size Range: Limitation depends on foundry capabilities. Ounces to many tons. Tolerances: Non-Ferrous ± 1/32″ to 6″ Add ± .003″ to 3″, ± 3/64″ from 3″ to 6″. Across parting line add ± .020″ to ± .090″ depending on size. (Assumes metal patterns) SurfaceFinish: Non-Ferrous: 150-350 RMS Ferrous: 300-700RMS Minimum Draft Requirements: 1° to 5° Cores: 1° to 1 1/2° Normal Minimum Section Thickness: Non-Ferrous: 1/8″ - 1/4″ Ferrous: 1/4″ - 3/8″ Ordering Quantities: All quantities Normal Lead Time: Samples: 2-10 weeks Production 2-4 weeks A.S.A.

Sand Casting Mold Features

Vents, which are placed in

molds to carry off gases produced when the moltenmetal comes into contact with the sand in the molds and core. They also exhaust air from the mold cavity as the molten metal flows into the mold.

See Video from Mass Foundry

Production sand casting

Investment Casting
The investment-casting process, also called the lost-wax process, was first used during the period 4000-3500 B.C. The pattern is made of wax or a plastic such aspolystyrene. The sequences involved in investment casting are shown in Figure 11.18. The pattern is made by injecting molten wax or plastic into a metal die in the shape of the object.

Investment Casting
Description: Metal mold makes wax or plastic replica. There are sprued, then surrounded with investment material, baked out, and metal is poured in the resultant cavity. Molds are broken to removethe castings. Metals: Most castable metals. Size Range: fraction of an ounce to 150 lbs.. Tolerances: ± .003″ to 1/4″ ± .004″ to 1/2″, ± .005″ per inch to 3″ ± .003″ for each additional inch Surface Finish: 63-125RMS Minimum Draft Requirements: None Normal Minimum Section Thickness: .030″ (Small Areas) .060″ (Large Areas) Ordering Quantities: Aluminum: usually under 1,000 Other metals: allquantities Normal Lead Time: Samples: 5-16 weeks (depending on complexity) Production 4-12 weeks A.S.A. (depending on subsequent operations). Talbot Associates Inc.

Die Casting – Cold-Chamber Casting

Cycle in cold-chamber casting: (1) with die closed and ram withdrawn, molten metal is poured into the chamber; (2) ram forces metal to flow into die, maintaining pressure during the cooling andsolidification; and (3) ram is withdrawn, die is opened, and part is ejected. Used for higher temperature metals eg Aluminum, Copper and alloys

Die Casting – Hot-Chamber Casting
Cycle in hot-chamber casting: (1) with die closed and plunger withdrawn, molten metal flows into the chamber; (2) plunger forces metal in chamber to flow into die, maintaining pressure during cooling and solidification; and...