Title: Summary Part Casting

Choose the correct statement.

- Casting is a (near)-net-shape process: the cast shape is very close to the final (net) shape, reducing the need for surface finishing. (correct)
- Casting is a (near)-net-shape process: the cast shape is the final (net) shape – no post-cast processing is necessary.
- Casting is a (near)-net-shape process: extensive post-cast machining and surface finnishing is required.

- Advantages of casting over other manufacturing processes are: complex shapes with internal cavities can be cast, very large parts can be manufactured in one piece, metals that are difficult to form or machine (hard metals) can be cast. (correct)
- Advantages of casting over other manufacturing processes are: casting is a very inexpensive process, the tolerances of produced parts are high, very large parts can be manufactured.
- Advantages of casting over other manufacturing processes are: casting is a very inexpensive process, casting is a high-throughput production process, metals that are difficult to form or machine (hard metals) can be cast.

- Casting processes either use single-use molds (expendable molds) or permanent molds. (correct)
- Casting processes are only compatible with single-use molds (expendable molds).

- Expendable molds are generally made from sand, plaster, and ceramics. These materials can withstand the high temperatures of almost all molten metals. Often, the granular materials are mixed with binders. The mold is destroyed after each casting. (correct)
- Expendable molds are generally made from ceramic parts, as ceramics can withstand the high temperatures of almost all molten metals. The mold is destroyed after each casting.
- Expendable molds are generally made from material that automatically disintegrates at the high temperatures of molten metal: wax or styrofoam.

- Expendable molds are produced from patterns, which mimic the shape of the final metal part. These patterns are either permanent (as often in sand casting) or single-use (as in investment casting or lost-foam casting). (correct)
- Expendable molds are produced from patterns, which mimic the shape of the final metal part. These patterns are always single-use.

- Permanent molds are made of temperature-resistant metal. Hence, the process is not suitable for high-melting-point metals. The high thermal conductivity of the mold causes higher cooling rates and hence affect the resulting microstructure. Also, it guarantees a high production rate. (correct)
- Permanent molds are made of temperature-resistant ceramics. The process is thus suited for all metals. The high thermal conductivity of the mold causes higher cooling rates and hence affect the resulting microstructure. Also, it guarantees a high production rate.

- Traditional sand casting involves the following processing steps: 1) fabrication of a pattern, 2) imprint of the pattern in sand, 3) incorporation of a gating system (sprue and risers), 4) removal of the pattern, 5) filling of the mold cavity with molten metal, 6) cooling and solidification of the metal, 7), removal of the sand mold to recover the cast part. (correct)
- Traditional sand casting involves the following processing steps: 1) carving a mold cavity of desired shape into the sand, 2) incorporation of a gating system (sprue and risers), 3) filling of the mold cavity with molten metal, 4) cooling and solidification of the metal, 5), removal of the sand mold to recover the cast part.

- A sprue is the channel that supplies the molten metal to the mold. A riser may look like a sprue, but it has a different function. Molten metal rises through the risers from the mold cavity as the sprue is filled. A riser provides molten metal to thick parts of the mold to prevent shrink cavities as the metal cools. (correct)
- A sprue is the channel that supplies the molten metal to the mold. At the same time, it provides additional molten metal to thick parts of the mold to prevent shrink cavities as the metal cools. The risers allow gases which evolve upon casting to vent.

- A mold core is an insert made from sand. It is placed in the mold to form hollow regions in the cast part. (correct)
- A mold core is an insert made from sand. It is placed in the mold to provide further mechanical stability to the mold.

- Sand molds can be fabricated manually, by automated molding processes, or by additive manufacturing. (correct)
- Sand molds are usually manufactured and assembled manually.

- Investment casting is an expendable-mold process. In contrast to sand casting, it relies on single-use patterns (expendable patterns) for manufacturing of the mold. (correct)
- Investment casting is an expendable-mold process. Analogous to sand casting, it relies on the use of permanent patterns for formation of the mold.
- Investmend casting is a permanent-mold process.

- Investment casting includes: 1) molding of wax or polymer pattern, 2) coating of pattern with a refractory material, 3), increase of the coating thickness, 4), melting or decomposition of the expendable pattern, 5) firing of the mold, 6) pouring of the liquid metal into the refractory mold, 7) cooling and solidification of metal, 8) braking of the mold and removal of cast parts. (correct)
- Investment casting includes: 1) molding of wax or polymer pattern, 2) coating of pattern with a thin layer of refractory material, 3) firing of the mold, 4) pouring of the liquid metal into the refractory mold, 5) cooling and solidification of metal, 6) braking of the mold and removal of cast parts.

- The investment casting process offerst the following advantages: suitable for high-melting-point alloys, good surface finish and high geometrical accuracy, intricate part geometries. (correct)
- The investment casting process offerst the following advantages: suitable for high-melting-point alloys, low cost, high throughput.

- Permanent-mold casting produces parts with a good surface finish, close dimensional tolerances, and uniform properties at high production rates. However, it is only suitable for comparably simple shapes made from low-melting point alloys (because of the limiting temperature-stability of the permanent molds). Also, it is only economical for large part numbers. (correct)
- Permanent-mold casting produces highly intricate parts with a good surface finish, close dimensional tolerances, and uniform properties at high production rates. However, it is only suitable for low-melting point alloys. Also, it is only economical for large part numbers.

- In the die-casting process, molten metal is forced into the die cavity under pressure. The cycle-time of the casting is decreased by active cooling of the die. The rapid cooling also results in a fine-grained, strong microstructure. (correct)
- In the die-casting process, molten metal is poured into the die cavity (similar to the sand-casting process). The cycle-time of the casting is decreased by active cooling of the die. The rapid cooling also results in a fine-grained, strong microstructure.
- In the die-casting process, molten metal is forced into the die cavity under pressure. The cycle-time of the casting is decreased by active cooling of the die. The rapid cooling also results in a large-grained, strong microstructure.

- Typical furnaces used in foundries are electric-arc furnaces (high melting rate), induction furnaces (in smaller foundries), and cupolas (major investment but melt large amounts of metals). (correct)
- Typical furnaces used in foundries are electric-arc furnaces (in smaller foundries), induction furnaces (for melting large amounts of metals), and cupolas (high melting rate).

- Flux and slag-forming consituents are added to the metal melt to purify the metal from oxides and other impurities such as dissolved gases. (correct)
- Flux and slag-forming consituents are added to the metal melt to introduce alloying elements and control the alloy composition.
- Flux and slag-forming consituents are added to the metal melt to speed up the melting process.

- A properly designed gating system is curcial for avoiding many defects in casting processes. (correct)
- A properly designed casting mold is crucial for defect-free casting. In contrast, the design of the gating system is relatively unimportant – it mainly influences the speed of casting.

- Solidification of pure metals takes place at a constant temperature (there is an arrest point in temperature), whereas solidification of alloys occurs over a range of temperatures. (correct)
- Solidification of pure metals and alloys takes place at a constant temperature (there is an arrest point in temperature).
- Solidification of pure metals and alloys takes place over a range of decreasing temperature (there is no arrest point in temperature), with the driving force for nucleation increasing with decreasing temperature.

- The composition and cooling rates of the molten metal both affect the size and shape of the grains and the dedrites in the solidifying alloy; in turn, these influence properties of the cast part. (correct)
- The composition of the molten metal mainly affects the size and shape of the grains and the dedrites in the solidifying alloy; in turn, these influence properties of the cast part. In contrast, the cooling rate mainly affects the production rate and hence the economic parameters of the process.

- Because most metals contract during solidification and cooling, various defects can arise in cast parts, for example cavities and cracks. Additionally, porosity can be caused by gases evolved during solidification (their solubility in the melt is higher than in the solid metal). (correct)
- Because most metals contract during solidification and cooling, various defects can arise in cast parts, for example cavities, cracks and porosity.
- Because most metals expand during solidification and cooling, various defects can arise in cast parts, for example cavities and cracks. Additionally, porosity can be caused by gases evolved during solidification (their solubility in the melt is higher than in the solid metal).