Castings- 2: Types and Properties
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
All castings are made by filling a mold with molten metal, and then allowing the metal to cool and solidify. The mold has a hollow cavity in the shape of the part. The type of mold and method of filling the mold determines the type of casting. All castings have three characteristics in common, which distinguishes them from most machined parts:

1. They have draft angles on some of the surfaces, as shown (image 1).
2. They have fillets and rounds instead of sharp corners, as shown (image 2).
3. Each casting has a sprue (or a sprue mark, if it has been removed by the time it reaches the machine shop) as shown (image 3).

In addition, most types of castings will have a parting line mark (image 4), which may be accompanied by a flash or a mismatch (image 5). The amount of draft, fillet radii, sprue, flash/mismatch depends on the type of casting. There are five types of castings (see chart left) which will be discussed individually on the following pages.

Image 1

Castings have draft angles so that the sand pattern can be extracted

Image 2

Castings have fillets and rounds instead of sharp corners, as shown

Image 3

Each casting has a sprue as shown (or a sprue mark, if it has been removed by the time it reaches the machine shop)

Image 4

most types of castings will have a parting line mark

Image 5

Sand Castings may be accompanied by flash or a mismatch

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label: casting, castings, sand casting, die casting, investment casting, bosses, lugs