ME 323
Instructor: Ramesh Singh
HW#1
PHD QUALIFYING EXAM – SeptemberDate
2021assigned: 16.08.2025
MANUFACTURING PROCESSES -Date
I due: 24.08.2025
1. You areMaximum
designingmarks:
cylindrical
100 risers for a gear housing that will be sand cast from Time:aluminum
3 hours
alloy (This is an insulating mold). The risers are coated with an insulating sleeve so that
Only handwritten notes are allowed
their heat transfer rate is 2.5 times lower than the sand mold. If the characteristic dimension
Make suitable assumptions, if required and clearly mention them.
for heat transfer for the casting is 25 mm (V/A), determine the diameter of the risers. Assume
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there is no heat loss from the top surface of the risers.
2. You 1. are You
designing a sprue/runner/gate system to sand cast a component. The top of the sprue
are designing cylindrical risers for an engine block that will be sand cast from cast
is 6 cm above the gate (hₜ), and has a pouring basin 1.5 cm deep (hb). The diameter of the top
iron is(this
of the sprue is anThe
2.5 cm. insulating
molten mould).
metal hasThe characteristic
viscosity 2.0×10⁻³ dimension
N·s/m² and for density
heat transfer
2700 for the
kg/m³.
The mold is top-gated.
casting is 30 mm (V/A). Assume that the riser is placed on the top of the casting and the
• Use appropriate Reynolds number for gating design and comment on whether the flow is
top or
laminar surface of the and
turbulent, riserthe
is fully insulated.
possible implications for the casting quality.
• Determine a. Determine
a plausiblethediameter
diameter ofof the
the runner
riser to avoid aspiration. [5]
b. If we improve the insulation of the riser so that the rate of heat transfer in the riser is
3. Determine the solidification time of the following two iron castings when both are poured
one-third
with no superheats intoofsand
the sand mould,
molds determine
at initial the diameter
temperature of the riser. Physically explain
of 280C.
your findings. [10]
• A slab shaped casting 10 cm thick (h =10 cm) (Hint: Assume l, b >> h)
• A sphere 10 cm in diameter
2. While casting an L section, a shrinkage cavity is formed as shown in (a) of Figure 1.Q2.
4. While casting
Explain an L section,
physically whyathe
shrinkage
shrinkagecavity
cavityisis formed
avoided as shown
in (b) in of
and (c) Figure 1. Explain
the Figure 1.Q2.
physically why the shrinkage cavity is avoided in (b) and (c) in Figure 1.
[5]
Figure 1.Q2
Fig. 1. Casting of L-section
3. We need to fill a hemispherical mould cavity having a diameter of 100 mm using a middle
gate arrangement shown in the Figure 2.Q3. The sprue height is 120 mm and the gate cross-
section are 5 mm2. In order to fill the 3/4th volume of this mould, how much time would be
required. Assume g = 10 m/s2. 1 [15]
5.
• Find the cycle time for casting one part in a sand mold shown in Figure 1. The initial setup
time to prepare the mold and melt (molten metal) and transport the melt to the pouring
basin is 30 minutes. The post casting time for cooling, breaking and finishing is another 20
minutes. Assume liquid metal level at X-X is constant and the time to fill the runner and
vent is negligible. The cross-section of the mold is shown in Figure 1 and the depth (into
the page) of the mold is 1.0 m. Assume that the iron is poured at melting temperature and
ambient temperature is 250C. [15]
• If the top of the riser is insulated and there is 10% liquid volume shrinkage over the total
volume, design a cylindrical riser for this casting. [10]
Properties:
For Iron,
Tm = 15400C, Hf = 272 KJ/kg, rcasting = 7850 kg/m3, kcasting = 83 W/mK
For sand mold,
cm = 1.17 KJ/kg.K, km = 0.8655 W/mK, rm = 1600 kg/m3
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Figure 2: Cross-section of the mold
