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Aluminium Die Casting
| To optimise casting technologies to ensure
reliable,low-cost production of high-integrity cast components. |
Aluminium is the established metal of choice for the
production of light weight components in the automotive, aerospace
and transport industries. Casting liquid aluminium alloys into metal
moulds using processes such as gravity, low pressure and high pressure
die casting is a cost effective means of producing complex shapes
that require minimal machining. Australia's automotive industry
supports a strong local aluminium die casting industry, producing
parts that include automotive transmission housings, cylinder heads,
inlet manifolds and engine sumps.
Growth in world automotive
markets for aluminium die cast components is creating significant
opportunities and challenges for the Australian industry, which
is positioning itself as a global player. Through partnerships between
our research organisations and key automotive participants such
as Nissan and Ford, CAST has developed innovative and novel technologies
that have benefited our partner's productivity. In turn, these technologies
have created IP that is poised on the verge of commercialisation.
An example featured is CASTcoat™
a project that began as postgraduate research at CSIRO and The University
of Queensland. It was developed further under CAST project funding
at CSIRO with industrial trials at Nissan, Ford, Merne Products,
Castalloy and others. Now it is a provisionally patented technology.
Projects
Cycle Time Reduction
To increase productivity of high pressure die
casting by reducing casting machine cycle time by 30%.
More than a 20% reduction in
cycle time has been achieved and implemented on selected parts at
two industry partner plants. The project has involved identification
of opportunities to reduce the process cycle time, performing research
to prove the concept and then carrying out the actual trial to prove
the theoretical findings. This necessitated the involvement of shopfloor
staff in order to implement changes to the process. Such trials
are often in conflict with the day to day production of parts and
only through true cooperation has it been possible to achieve the
project objectives.
The third year of this project
has shown the development of true cooperation between researchers
and industrial partners where the latest research findings obtained
through modelling and simulation have been implemented on the shopfloor
with the help and support of staff from Ford and Nissan. The changes,
once trialed during a production period, have been implemented as
part of the process, hence providing ongoing cost benefits through
a reduction in the time required to produce each component.
An example of implementation
is a reduction in cycle time at Nissan on a gearbox side cover produced
in a twin cavity die that has shown successful production results
over many months from an original cycle time of 75 seconds down
to 60 seconds. Whilst research at Ford on a converter housing casting
has shown successful implementation of cycle time reduction from
90 seconds to 74 seconds.
In future work we will look
for further opportunities with current stakeholders and the die
casting industry in general, to implement the horizontal deployment
of cycle time reduction across other machines and parts.
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Automated Fault Detection
in Aluminium Die Casting
To develop and implement an automatic fault detection
system for surface and sub-surface defects.
A fully automated fault detection
machine called CASTvision has been developed and a prototype system
is ready for extended in-plant on-line trials. This project is in
its third year and exciting results are now emerging. The results
from the algorithm, which was designed and developed during the
second year of the project, have been put to the test this year.
Through prototyping, the CAST team have designed and developed a
working system, CASTvision. For Ford's converter housing casting
the off-line system can detect and discriminate between defective
and good parts. The prototype system is capable of identifying blocked
holes on any of the holes on this complex casting. Off-line systems
have also been developed where hot tears and cold shuts can be detected
on Ford's structural sump casting.
Work at Nissan on their pump
cover casting has resulted in a CASTvision prototype system for
in-line fault detection. The system is able to capture images and
identify certain categories of defects on the surface of the part.
This project has demonstrated that advances in machine vision applied
to fault detection of aluminium castings can be taken from the concept
stage through to a working prototype very successfully. The next
step for this project is to take the concepts from single part to
multi part systems able to handle more complex shapes and surfaces.
This outcome will be a strong candidate for future commercialisation.
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Modelling of Fluid Flow
Inside a Die Cavity Using Smoothed Particle Hydrodynamics
To develop a simulation technique to assist industry
in design and optimisation of dies and products.
This year has seen extensive
developments in the Smoothed Particle Hydrodynamics (SPH) code along
with testing undertaken to improve the robustness and speed of modelling.
Enhancements were also made to the visualisation techniques used
to display results from SPH's three dimensional (3D) simulation
results. 3D SPH isothermal simulations and animations of parts from
Nissan and Metaldyne showing complex filling patterns were completed.
Observations by staff at Nissan Casting of the casting's filling
pattern during production were consistent with the SPH modelling
predictions.
Water analogue images from
a clear perspex model of a servo piston die casting part and digitised
short shots of an aluminium casting were completed for validation
with flow predictions from SPH. The validation process and further
computational speed improvements will be completed next year. Further
developments of the SPH code particularly in the areas of heat transfer,
solidification, surface oxide prediction, robustness and speed are
planned in future work.
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Tailoring of CAST's New
Die Coat for LPDC and GDC
To commercialise the die coat technology for
low pressure and gravity die casting and further improve die coat
properties.
CAST's new die coat was given
the trade name of CASTcoat™. Industrial trials of CASTcoat™
were carried out successfully in several low pressure and gravity
die casting plants. Its performance was enhanced in low draft angle
areas of the die by application of a sealer. Two provisional patents
covering inventions related to CASTcoat™ have been lodged.
Information
Sheet - CASTcoatTM
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Integrated Gravity Die
Design Methodology
To develop an integrated die design methodology
for gravity die casting that can achieve optimal die filling, optimal
feeding and yield, and dimensional stability.
A new design of feeders to
address the root cause of shrinkage porosity defects in an inlet
manifold casting was implemented on a customer's die and resulted
in excellent outcomes. A study was completed on the use of "squeeze
pins" to reduce or eliminate shrinkage defects in a gravity
test die. The squeeze pin technique demonstrated that surface shrinkage
can be effectively eliminated and associated internal micro shrinkage
can be significantly reduced in the locations tried. The squeeze
pin concept was extended to include application as a mechanical
squeeze/shear gate to reduce fettling requirement. The mechanism
implemented on a test die allowed the shearing of the gate before
full solidification, with adjustment to produce variable gate widths.
The final part of the methodology
to be developed is optimal die filling through variable tilt pouring
from a ladle. To ensure smooth flow, the variable tilting motion
can be programmed to match the filling rate with changes in the
instantaneous flow area. Flow evaluation is done by real time X-ray
radiography on a test die. The effect of die geometry, especially
wall thickness, on die distortion will be investigated using computer
simulation that models thermal stresses in casting cycles.
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Improved Quality Aluminium
Automotive Castings
To improve the overall performance of low pressure
die casting operations by implementing improved tools in design
and process control to reduce casting defects.
Successful development of appropriate
tooling design and process control has been achieved for the low
pressure die casting (LPDC) process to cast small automotive components.
A multi-cavity die design was selected and optimised by solidification
simulation. Several dies of this design are being used to produce
high-volume, high-integrity parts. Casting parameters were also
investigated to improve the casting quality and reduce the cycle
time. Die trials were conducted on an LPDC research die to investigate
the effect of casting geometry and process parameters on shrinkage
defects in castings having several fundamental features of cylinder
heads. The die trial successfully produced castings with shrinkage
defects in one particular area sandwiched in the sand core, as predicted.
Analysis of castings made on the LPDC pseudo-cylinder head research
die will be completed to establish relationships between porosity
defects and process parameters.
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Reduction in Metal Pressure
in the HPDC Process
To investigate the role of metal pressure on
the production of quality parts in high pressure die casting.
In the final six months of
this project, effort was focused on innovative technologies. One
such technology was designed to absorb impact pressure spikes that
cause detrimental flashing and the other technology involved revamping
the hydraulics of ageing die casting machines to improve product
quality. A novel shock absorbing technology was developed that utilised
existing casting overflows. Die casting trials at CSIRO confirmed
the effectiveness of this technology in absorbing impact pressure
shocks upon cavity filling. Through in-plant trials at Nissan Casting
Plant the limits of hydraulic valve timing and circuit functioning
were confirmed. A proposal for a revamp to improve intensification
pressure response was put forward. The project concluded in December
2001. Ford Australia may adopt the reduced pressure operating parameters
for the production of their new Barra model engine sumps later in
2002.
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