CAE DS – High Pressure Die Casting Design
An Example of a HPDC Simulation
Finite different method (FDM); Software: Novaflow&Solid
In the industry quality, shortening the time of construction and mass-production is
getting more and more important. Considering these three factors together computer
simulation has become a more and more applicated tool besides the technological
experiments in the past few years. The engineer planning programs can quicken and
make reliable the work with the part tasks (e.g. planning of gating and cooling systems) but couldn’t substitute the simulation programs which can check the results.
The purpose of simulating any industrial process is to model the underlying physics
so that important process variables can be identified and controlled, resulting in
significant benefits.
If the process of filling and solidifying a mold cavity is accurately modeled, shrinkage
cavities and other casting defects can be predicted; the effects on metal fluid flow and
solidification of changing the gating/risering method or many other process variable
can be simulated; and molten metal trial iterations can be significantly reduced and
used primarily for concept validation.
There are three basic types of computer simulation methods:
−
−
−
empirical programs based on experimental results and experience,
semi-empirical programs based on experimental results in addition to basic
physics.
physics-based first principles programs that require complex mathematics and
accurate material thermophysical data.
The aim of modeling the filling and solidification of a casting is to:
−
−
−
−
−
−
−
−
predict the influence of the gating/methoding/casting design on turbulence,
predict oxide entrapment and other flow-related defects,
provide temperature profiles during and at the end of filling for more accurate solidification analysis,
predict the pattern of solidification, indicating where shrinkage cavities and
associated defects may arise,
predict other solidification defects (such as hot tears),
predict solidification times,
predict microstructure of casting sections (such as segregation),
predict stress/strain.
High Pressure Die Casting Simulation Example - 1
CAE DS – High Pressure Die Casting Design
The simulated casting can be seen in figure 1.
Image 1. The simulated casting geometry
Pre-Processing
First we have to define the calculated geometry and the mould around. We have to
define the sizes in X, Y, Z directions, the minimal mould thickness and the casting
position (see figure 2). We also have to determine the element size.
Image 2. Defining the calculated box
In the next step we have to define the materials of the geometry. For the mould we
have chosen a die material called Orvar Supreme (1.2343). Initial temperature of the
mould is 200°C (pre-heated). We have to define the alloy of the casting, in this case
aluminum based alloy (AlSi9Cu3) the casting temperature is 710°C.
High Pressure Die Casting Simulation Example - 2
CAE DS – High Pressure Die Casting Design
Image 3. Boundary conditions on gating
Image 4. Shrinkage calculation model
Image 5. Tempering channels
Image 6. Heat and
cooling channels
High Pressure Die Casting Simulation Example - 3
CAE DS – High Pressure Die Casting Design
In the next step we have to define the gating point. This is the point where the melt
enter the cavity. We have to define one point in the plane and the program calculates a
circle around it. In case of HPDC it is a good solution because the biscuit has a circle
cross-section.
We have to define the feeding point also. In case of HPDC this point must be in the
biscuit, but e.g. in the case of gravity casting it must be in the risers.
We have to define the shrinkage calculation. In case of HPDC, because of the fast die
filling, the gravity does not really affect the shrinkage. So we can shrinkage without
gravity factor.
We have to define the boundary conditions on the gating. The piston is heated on a
constant temperature se we can define this temperature as boundary.
After these steps we must define cycle calculation. We have to do this only in the case
of HPDC or gravity die casting. In the firs calculation round the temperature of the
mould is homogeneous. But if we want to compare our results with real life experiments we have to have an inhomogeneous temperature field. So we have to define
cycle calculation. The data can be seen on figure 3.
Image 7. Cycle calculation
In case of cycle calculation we have to define all the steps during manufacturing:
−
−
−
−
−
casting time
closing time of the mould
opening of the mould
spraying the die (spraying element, time, temperature, amount)
standing the die on open air (temperature, amount) etc.
After defining the calculation stop criteria (e.g. time, solidified casting part, maximum
temperature) we define the save of the data and we can start main-processing (the
calculation).
High Pressure Die Casting Simulation Example - 4
CAE DS – High Pressure Die Casting Design
Post-processing
In the following figures we can see the filling and the solidification of the casting. On
the right side we can see the temperature scale between 250-670°C, under it we can see
the time steps (h, m, and s).
Filled volume
3,74%
We can see that the melt does not start to fill the gating system consistently (because
of high speed).
Filled volume
24,04%
High Pressure Die Casting Simulation Example - 5
CAE DS – High Pressure Die Casting Design
The melt enters the cavity. The temperature of the air in the die changes (~100°C).
Filled volume
28,02%
Filled volume
30,07%
Filled volume
36,07%
The melt run around at the side of the casting geometry.
High Pressure Die Casting Simulation Example - 6
CAE DS – High Pressure Die Casting Design
Filled volume
46,12%
We can see two locked air part in both side of the gating point but the temperature of
them are different.
Filled volume
56,03%
The melt starts to solidify before the whole cavity is filled.
Filled volume
82,06%
High Pressure Die Casting Simulation Example - 7
CAE DS – High Pressure Die Casting Design
Filled volume
100,00%, liquid
phase 99,99%
End of filling, cavity filled 100%. The liquid volume is 99,99% which means that the
solidification has started. From this picture we can see the solidification of the casting.
Liquid phase
99,36%
The gating system starts to solidify down.
High Pressure Die Casting Simulation Example - 8
CAE DS – High Pressure Die Casting Design
Liquid phase
29,69%
Because of big surfaces and thin walls some casting parts solidify faster than others.
The biscuit is still around casting temperature because of the thick wall and the heating effect of the piston. It also aids feeding.
Liquid phase
9,82%
Liquid phase
4,99%
We are about the end of the cycle and the biscuit temperature is still very high.
High Pressure Die Casting Simulation Example - 9
CAE DS – High Pressure Die Casting Design
Liquid phase
In the following figures we can see the filling of the cavity. The scale on the right side
is liquid phase between 5-95%.
Filled volume
18,12%
Filled volume
28,02%
High Pressure Die Casting Simulation Example - 10
CAE DS – High Pressure Die Casting Design
Filled volume
32,04%
We can see a lot of air inclusions in the casting.
Filled volume
42,11%
The melt reaches the opposite wall and starts to fill around.
High Pressure Die Casting Simulation Example - 11
CAE DS – High Pressure Die Casting Design
Filled volume
46,12%
Filled volume
54,03%
Filled volume
68,04%
High Pressure Die Casting Simulation Example - 12
CAE DS – High Pressure Die Casting Design
Filled volume
82,06%
The closed air can cause porosity if the overflows are not connected.
Filled volume
92,06%
We can see the last filled part of the casting.
High Pressure Die Casting Simulation Example - 13
CAE DS – High Pressure Die Casting Design
Filled volume
100,00%
Velocity of the melt in the mould
In the following pictures we can see the velocity of the melt. The scale is -10-50m/s.
Filled volume
20,02%
High Pressure Die Casting Simulation Example - 14
CAE DS – High Pressure Die Casting Design
Filled volume
24,04%
Filled volume
30,07%
Filled volume
38,01%
High Pressure Die Casting Simulation Example - 15
CAE DS – High Pressure Die Casting Design
Filled volume
50,00%
Filled volume
62,12%
Filled volume
72,01%
High Pressure Die Casting Simulation Example - 16
CAE DS – High Pressure Die Casting Design
Filled volume
82,06%
Filled volume
96,06%
Conclusions
By the help of simulation we can analyze the flow characteristic, the effects of cores to
the metal flow, the last filled form parts and the air ingates. With the analysis of
solidification we can examine the hot spots, the efficiency of the gating system, the
efficiency of the cooling system and the solidification morphology.
The materials and the boundary conditions can change easily, so different experiments can be done in a short time.
High Pressure Die Casting Simulation Example - 17