The mold used in an injection molding process consists of a top half and a bottom half. Each half is 60 mm × 60 × mm × 20 mm and is constructed of metal ( ρ = 7800 kg/m 3 , c = 450 J/kg ⋅ K ). The cold mold ( l 00 ° C ) s to be heated w 2 00 ° C with pressurized water (available at 275 ° C and a total flow rate of 0.0 2 kg / s ) prior to injecting the thermoplastic material. The injection takes only a fraction of a second, and the hot mold ( 2 00 ° C ) is subsequently cooled with cold water (available at 25 ° C and a total flow rate of 0.0 2 kg / s ) prior to ejecting the molded part. After part ejection, which also takes a fraction of a second, the process is repeated. (a) In conventional mold design, straight cooling (healing) passages are bored through the mold in a location where the passages will not interfere with the molded part. Determine the initial heating rate and the initial cooling rate of the mold when five 5 − mm -diameter, 6 0 − mm -1ong passages are bored in each half of the mold (10 passages total). The velocity distribution of the water is fully developed at the entrance of each passage in the hot (or cold) mold (b) New additive manufacturing processes, known as selective freeform fabrication, or SFF, are used to construct molds that are configured with conformal cooling passages. Consider the same mold as before, but now a 5 − mm -diameter, coiled, conformal cooling passage is designed within each half of the SFF-manufactured mold. Each of the two coiled passages has N = 2 turns. The coiled passage does not interfere with the molded part. The conformal channels have a coil diameter C = 5 0 mm . The total water flow remains the same as in part (a) ( 0.0 1 kg / s per coil). Determine the initial heating rate and the initial cooling rate of the mold. (c) Compare the surface areas of the conventional and conformal cooling passages. Compare the rate at which the mold temperature changes for molds configured with the conventional and conformal healing and cooling passages. Which cooling passage, conventional or conformal, will enable production of more parts per day? Neglect the presence of the thermoplastic material.
The mold used in an injection molding process consists of a top half and a bottom half. Each half is 60 mm × 60 × mm × 20 mm and is constructed of metal ( ρ = 7800 kg/m 3 , c = 450 J/kg ⋅ K ). The cold mold ( l 00 ° C ) s to be heated w 2 00 ° C with pressurized water (available at 275 ° C and a total flow rate of 0.0 2 kg / s ) prior to injecting the thermoplastic material. The injection takes only a fraction of a second, and the hot mold ( 2 00 ° C ) is subsequently cooled with cold water (available at 25 ° C and a total flow rate of 0.0 2 kg / s ) prior to ejecting the molded part. After part ejection, which also takes a fraction of a second, the process is repeated. (a) In conventional mold design, straight cooling (healing) passages are bored through the mold in a location where the passages will not interfere with the molded part. Determine the initial heating rate and the initial cooling rate of the mold when five 5 − mm -diameter, 6 0 − mm -1ong passages are bored in each half of the mold (10 passages total). The velocity distribution of the water is fully developed at the entrance of each passage in the hot (or cold) mold (b) New additive manufacturing processes, known as selective freeform fabrication, or SFF, are used to construct molds that are configured with conformal cooling passages. Consider the same mold as before, but now a 5 − mm -diameter, coiled, conformal cooling passage is designed within each half of the SFF-manufactured mold. Each of the two coiled passages has N = 2 turns. The coiled passage does not interfere with the molded part. The conformal channels have a coil diameter C = 5 0 mm . The total water flow remains the same as in part (a) ( 0.0 1 kg / s per coil). Determine the initial heating rate and the initial cooling rate of the mold. (c) Compare the surface areas of the conventional and conformal cooling passages. Compare the rate at which the mold temperature changes for molds configured with the conventional and conformal healing and cooling passages. Which cooling passage, conventional or conformal, will enable production of more parts per day? Neglect the presence of the thermoplastic material.
Solution Summary: The author explains the initial heating rate and cooling rate of the mold. The specific heat of metal is c=450 J/kgK.
The mold used in an injection molding process consists of a top half and a bottom half. Each half is
60
mm
×
60
×
mm
×
20
mm
and is constructed of metal (
ρ
=
7800
kg/m
3
,
c
=
450
J/kg
⋅
K
). The cold mold (
l
00
°
C
) s to be heated w
2
00
°
C
with pressurized water (available at
275
°
C
and a total flow rate of
0.0
2 kg
/
s
) prior to injecting the thermoplastic material. The injection takes only a fraction of a second, and the hot mold (
2
00
°
C
) is subsequently cooled with cold water (available at
25
°
C
and a total flow rate of
0.0
2 kg
/
s
) prior to ejecting the molded part. After part ejection, which also takes a fraction of a second, the process is repeated.
(a) In conventional mold design, straight cooling (healing) passages are bored through the mold in a location where the passages will not interfere with the molded part. Determine the initial heating rate and the initial cooling rate of the mold when five
5
−
mm
-diameter,
6
0
−
mm
-1ong passages are bored in each half of the mold (10 passages total). The velocity distribution of the water is fully developed at the entrance of each passage in the hot (or cold) mold
(b) New additive manufacturing processes, known as selective freeform fabrication, or SFF, are used to construct molds that are configured with conformal cooling passages. Consider the same mold as before, but now a
5
−
mm
-diameter, coiled, conformal cooling passage is designed within each half of the SFF-manufactured mold. Each of the two coiled passages has N = 2 turns. The coiled passage does not interfere with the molded part. The conformal channels have a coil diameter
C
=
5
0
mm
. The total water flow remains the same as in part (a) (
0.0
1 kg
/
s
per coil). Determine the initial heating rate and the initial cooling rate of the mold.
(c) Compare the surface areas of the conventional and conformal cooling passages. Compare the rate at which the mold temperature changes for molds configured with the conventional and conformal healing and cooling passages. Which cooling passage, conventional or conformal, will enable production of more parts per day? Neglect the presence of the thermoplastic material.
A component is sand casted in pure aluminum. The level of the metal inside a
pouring basin is 215 mm above the level of the metal in the mould. For a
viscosity value of 0.0017 Ns/m² and a circular runner with a diameter of 11 mm,
calculate:
2.1
The velocity and rate of flow of the metal into the mould.
2.2 What effect does turbulent flow in a gating system have on the casting?
2.3 Which measures can be implemented to reduce turbulent flow?
A horizontal true centrifugal casting process is used to make lead pipe for
chemical plants. The pipe has length = 0.5 m, outside diameter = 70 mm, and
wall thickness = 6.0 mm. Determine the rotational speed that will provide a
G-factor = 60.
%3D
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Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning