Die Casting Basics
Die is closed. Metal
is drawn in to tool
(plunger).
Metal solidifies
under pressure.
Tool injects metal
into cavity.
Die is opened.
Casting removed.
Cavity continues
to fill. (fractions
of a second)
Machine recovers to
initial orientation
(cycle starts over)
Properties: Pb-Sb vs. Zn-Al
L35
Pb-Sb Alloy
Zamak 3
Zn-Al Alloy
11.04
6.6
3.36
1.17
252-299
381 - 387
133.1
418.7
Thermal expansion
( um/m per ºC at 20-100 ºC)
27.8
27.4
Thermal conductivity
( cal/cm2/cm/ ºC/sec at 70-140ºC )
.073
.27
Viscosity (poise)
.032
.01
Density
( g/cm^3) at 21ºC
Solidification
shrinkage ( % )
Freezing
range ( ºC )
Specific heat capacity
( J/kg/ºC ) at 20 - 100 ºC
Stage III:
Temperature Monitoring Overview

Nozzle temperature


Die temperature


Nozzle freezing
Thermal expansions
Holding pot temperature


Temperature gradients
Excess superheat
Results:
Injection Pressure


Monitor weight as a
function of pressure
Decreasing Pressure:



Pressure Dependency Analysis
Reduces flashing
Decreases machine
errors
Weight variation for
each setting < 1%
*Tolerance
(41.24 – 43.80g)
Molten metal
leaking
through the
gap is called
‘flashing’.
Assume the upper and lower mold pieces have opposing faces which are perfectly smooth, but
3
with a gap of thickness 10
5
 m.. Consider if a Zn melt is pressurized to 3 10  Pa while
5
atmospheric pressure is 1 10  Pa. The viscosity of the Zn is 0.003 Pa s. Determine the steady
state volume flow rate through the mold gap if the circumference of the cylindrical mold is 6 m
and the distance from the inside of the mold to the outside of the mold is 0.2 m. Assume laminar
flow. Hint: think about flow between parallel plates.
VolumeFlowRate
2 P 3

 W
3 L 
Upper Mold
Atmospheric
Pressure
Lower Mold
Mold gap
Pressurized
Molten
Metal
Solution : The volume flow rate is given by the average velocity multiplied by the cross section of
flow, which is the same as the velocity profile integrated over the gap thickness multiplied by the
width of the gap, W
VolumeFlowRate
2 P 3

 W
3 L 
where  is the half thickness of the gap and W is the width (circumference in this case)
3
5
VolumeFlowRate 
2 P 3

 W
3 L 
  0.5 10
 m P  2 10  Pa
  0.003 Pa s
W  6 m
3
VolumeFlowRate  0.167
m
s
L  0.2 m
Upper Mold
Atmospheric
Pressure
Pressurized
Molten Metal
L(t1) L(t2) L(t3)
L(t4)
Lower Mold
Mold gap
The above problem is concerned with steady state flow of molten metal through the mold gap.
Of greater interest is the time required for the molten alloy to reach the outside of the mold
after it is first injected into the mold. We can estimate that time by letting L be the distance
between the melt and the tip of the flow through the mold gap and assuming that the rate of
change of the of L is the average rate of flow between parallel plates. Note that this is an
approximate solution to this problem.
AverageFlowRate
  

P
2
2
d
  y dy
L( t )

2  
2 L( t)  
dt
  




1

After integration with respect to y
P
d
L( t)
dt
3 L( t )  
2

Solving the differential equation by integration
L

 L( t( t) ) d L

0
1 2
L
2
2
P
t
    1 d

3 
0
P
3 
2
 t
The approximation that the
liquid:air interface velocity is
equal to the average velocity
of the steady stae profile was
introduced by E. W.
Washburn, Physical Review,
vol. 17, pp. 213-283, 1921.
P
1 2
L
2
3 
2
 t
The solutions for L from the Mathcad symbolic solver ('symbolics' on
the tool bar, then variable and then solve) are
1 
1

 1 2
2 
 6     P t   

 3 


1 
1
 1 2
2 
 6     P t   

 3 

Picking the positive one
1
L
1
3 
1
 6     P t  
2
2
t  0  0.001  0.01
1
1
L( t) 
1
 6     P t  
2
2
3 
0.4
L( t )
0.2
m
0
0
0.005
t
0.01
s
Looks like it will take about 0.005 seconds for the molten metal to begin flashing through
the mold wall gap given the parameters defined above.
Further discussion of the planar interface
approximation.
Flow profile is disturbed at the fluid air interface
Fluid
Air
Average velocity must be equal for incompressible fluid
Complications regarding the shape of the moving solid vapor interface.
Meniscus Formation
Represent the surface tensions of a multi-phase junction as vectors drawn parallel to the respective surfaces
The surface energies for the for the solid/liquid, the solid/vapor and the liquid/vapor interfaces are γsl, γsv, γlv
γlv
γsv
θ
γsl
The contact angle θ is a measure
of the magnitude of the solid
liquid interface energy compared
to the solid vapor and liquid
vapor energies.
Youngs’ Equation
Represent the surface tensions of a multi-phase junction as vectors drawn parallel to the respective surfaces
The surface energies for the for the solid/liquid, the solid/vapor and the liquid/vapor interfaces are γsl, γsv, γlv.
The vectors representing these surface energies must balance at the three phase triple junction. This equation
representing this balance is known as ‘Youngs’ equation”
γlv
γsv
θ
γsl
sv  sl  cos( )lv
γlv
γsv
γsl
Large γsl, non-wetting
θ Large
γlv
γsv
θ
γsl
Large γsv, wetting
θ small
θ
Interface shapes for ‘wetting’ and non-wetting contact angles
Liquid
Liquid
Vapor
Vapor