Manufacturing Chapter 11 questions
with 100% complete solutions already
passed
By the student. There are a large number of acceptable answers depending on the interpre-
tation of the problem by the student. Students may approach this as processes have been
application driven, material driven, or economics driven. For example, while investment cast-
ing is more expensive than sand casting, closer dimensional tolerances are possible and thus
for certain parts, e.g., barrels for handguns, investment casting is preferable. Consider also the
di
erences between the hot- and cold-chamber permanent-mold casting operations. While the
hot-chamber process is more automated, thus reducing cost, there are certain disadvantages. -
correct answer ✔✔What are the reasons for the large variety of casting processes that have
been
developed over the years? Explain with specifi
,c examples.
There are a number of reasons that risers are not as useful in die casting as they are in sand
casting. Recall that in sand casting, a riser is sized and located so that it provides molten
metal to the die cavity to compensate for metal shrinkage. In sand casting, the cooling rate
is relatively low, so that the cooling rate can be e
ectively manipulated by placement and
size of a riser. In die casting, it is essential that the cooling rate be high, or else the economic
justi
,cation for tooling and equipment cannot be made. Using risers would of course slow
the cooling time, and therefore they are economically undesirable. Further, the metals that
are used in die casting will therefore be ones that develop internal shrinkage porosity, but do
not separate from the mold wall, so that risers are not as necessary. - correct answer ✔✔Why
are risers not as useful in die casting as they are in sand casting?
The main drawbacks to having a riser too large are: the material in the riser is eventually
scrapped and has to be recycled; the riser hass to be cut o
, and a larger riser will cost
more to machine; an excessively large riser slows solidi
, cation; the riser may interfere with solidi
with 100% complete solutions already
passed
By the student. There are a large number of acceptable answers depending on the interpre-
tation of the problem by the student. Students may approach this as processes have been
application driven, material driven, or economics driven. For example, while investment cast-
ing is more expensive than sand casting, closer dimensional tolerances are possible and thus
for certain parts, e.g., barrels for handguns, investment casting is preferable. Consider also the
di
erences between the hot- and cold-chamber permanent-mold casting operations. While the
hot-chamber process is more automated, thus reducing cost, there are certain disadvantages. -
correct answer ✔✔What are the reasons for the large variety of casting processes that have
been
developed over the years? Explain with specifi
,c examples.
There are a number of reasons that risers are not as useful in die casting as they are in sand
casting. Recall that in sand casting, a riser is sized and located so that it provides molten
metal to the die cavity to compensate for metal shrinkage. In sand casting, the cooling rate
is relatively low, so that the cooling rate can be e
ectively manipulated by placement and
size of a riser. In die casting, it is essential that the cooling rate be high, or else the economic
justi
,cation for tooling and equipment cannot be made. Using risers would of course slow
the cooling time, and therefore they are economically undesirable. Further, the metals that
are used in die casting will therefore be ones that develop internal shrinkage porosity, but do
not separate from the mold wall, so that risers are not as necessary. - correct answer ✔✔Why
are risers not as useful in die casting as they are in sand casting?
The main drawbacks to having a riser too large are: the material in the riser is eventually
scrapped and has to be recycled; the riser hass to be cut o
, and a larger riser will cost
more to machine; an excessively large riser slows solidi
, cation; the riser may interfere with solidi
