20
MOLTEN METAL FLOW IN HIGH INTEGRITY DIE CASTING PROCESSES
Figure 2.9 Graphical illustration of die fill with atomized metal flow in con-
ventional die casting.
Example Calculation 2.4
Using the vacuum die casting process, a component is manufac- tured with a conventional aluminum alloy. Calculate the Reynolds
number for this process to determine if metal flow at the gate is laminar or turbulent given that the gate is 2 mm wide and 35 mm
in length. The velocity of metal at the gate is 50,000 cmsec. The density and viscosity of liquid aluminum are 2.7 gcm
3
and 1 ⫻ 10
⫺3
gcm 䡠 sec, respectively.
2
Solution For this case, the characteristic length is the width of the gate.
Using Equation 2.1, Dv
Re ⫽
3
0.2 cm 50,000 cmsec 2.7 gcm ⫽
⫺3
1 ⫻ 10 gcm 䡠 sec
⫽ 27,000,000 Due to the extremely high Reynolds number ⬎10,000, fluid flow
2.5 METAL FLOW IN SQUEEZE CASTING
21
a b
Figure 2.10 Short shots of identical castings illustrating the difference between
a planar filling and b nonplanar filling. Courtesy of Formcast, Inc.
at the gate in this vacuum die casting example is extremely tur- bulent.
2.5 METAL FLOW IN SQUEEZE CASTING
Due to larger gate cross sections and longer fill times in compar- ison to conventional die casting, atomization of the liquid metal
is avoided when squeeze casting. Both planar and nonplanar flows occur in squeeze casting. Achieving planar flow, however, is de-
pendent on the die design and optimization of the process para- meters. Figure 2.10 is a picture showing two short shots of
identical castings. In Figure 2.10a planar filling occurred within
22
MOLTEN METAL FLOW IN HIGH INTEGRITY DIE CASTING PROCESSES
the die, while nonplanar filling occurred in Figure 2.10b. These differences in metal flow were made possible by adjusting
machine-controlled process parameters. Be that as it may, for complex component geometries, nonplanar fill may be unavoida-
ble.
Example Calculation 2.5
Utilizing a common commercial aluminum alloy, a component is manufactured using squeeze casting technology. Parameters for
this process include a gate velocity of 500 cmsec and circular gate diameter of 10 mm. Determine if the liquid metal flow
through the gate is laminar. The density and viscosity of liquid aluminum are 2.7 gcm
3
and 1 ⫻ 10
⫺3
gcm 䡠 sec, respectively.
2
Solution Using Equation 2.1, the Reynolds number may be used to deter-
mine if the metal flow is laminar at the gate. Since the gate ge- ometry is circular, the characteristic length is the diameter of the
gate
3
: Dv
Re ⫽
3
1.0 cm 500 cmsec 2.7 gcm ⫽
⫺3
1 ⫻ 10 gcm 䡠 sec
⫽ 1,350,000 For fluid flow through a circular cross section, the transition from
laminar to turbulent flow is completed when the Reynolds number reaches 3000.
3
Fluid flow at the gate is not laminar. Flow is tur- bulent for this squeeze casting example.
2.6 METAL FLOW IN SEMI-SOLID METALWORKING
Semi-solid metalworking is often incorrectly sighted as exhibiting laminar flow when filling the die cavity.
4–6
This misconception has been proliferated in the sales and marketing of semi-solid
