Outcome: A new design of feeders to address the root cause of shrinkage porosity defects in an inlet manifold casting was worked out and later meticulously implemented on a customers die, and this resulted in excellent results.
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 substantially reduced in the locations tried. The squeeze pin concept was extended to include application as a mechanical squeeze/shear gate to reduce fettling requirement also. The mechanism implemented on a test is 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-rays [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.
Tailoring of CASTs new die coat for LPDC and GDC
Aim: To commercialise the die coat technology for low pressure and gravity die casting and further improve die coat properties.
CASTs 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.
Modeling of fluid flow inside a die cavity using smoothed particle hydrodynamics
Aim: To develop a simulation technique to assist industry in design and optimization of dies and products.
Outcome: This year has seen extensive developments in the Smoothed Particle Hydrodynamics (SPH) code along with testing undertaken to improve the robustness and speed of modeling. Enhancements were also made to the visualisation techniques used to display results from SPHs 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 castings filling pattern during production were consistent with the SPH modeling 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 soon. 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.
Automated fault detection in aluminium die casting
Aim: To develop and implement an automatic fault detection system for surface and sub-surface defects.
Outcome: 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 tested in a series of grueling trials this year. Through prototyping, the CAST team have designed and developed a working system, CASTvision. For Fords 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 Fords 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.
Cycle time reduction
Aim: To increase productivity of high pressure die casting by reducing casting machine cycle time by 30%.
Outcome: More than a 20% reduction in cycle time was achieved and implemented on selected parts at two plants of industry partners. The project involved identification of opportunities to reduce the process cycle time, performing focused research to prove the concept and then carrying out the actual trials to prove the theoretical findings. This necessitated the involvement of shop-floor staff in order to totally 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. Collaboration in every sense of the word…
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 modeling and simulation were implemented on the shop-floor with the help and support of staff from Ford and Nissan. The changes, once tried out during a production period, were later implemented as part of the process, hence providing on-going 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. These are impressive figures indeed. In future work CSIRO proposed to 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. For improved die filling, solidification patterns and maximum yield, CSIRO researchers apply thermal control techniques to reduce cycle time and rejection rates, manipulating advanced computer simulation tools as well as analogue modelling, and real-time X-ray flow visualisation of die filling.
Some More innovations :
- In Australia, an emerging market wherein pressure die casting has been straddling an ever-increasing popularity and importance in the manufacturing methodologies, rather significant benchmarks have been achieved recently in high-pressure casting for Fords continuously variable transmission housing exported to Europe.
- CSIRO researchers investigated the problem of the controlling die temperature at the start of a production run and were able to bring about a 40% reduction in warm-up reject castings. This is a vital lead to further research in optimising the energy consumption, a recurring sore point with automated industries employing powerful machinery.
- In yet another case, stress analysis of a gearbox endplate casting showed some weak points, which allowed the cover to flex and cause oil leaks. By modifying the design and using magnesium, it was possible to move the stress area away from the edge of the casting and use less metal. The magnesium component weighed 850 g compared with 1400 g used previously - a saving in mass of 40% for a product that was also much stronger.
- Also in light metals casting, CSIRO has designed a high-pressure die-cast for a PIN entry terminal or automatic transaction machine made from a cast-to-shape alloy steel tool.
- The Australian Die Casting Association is pleased with CSIROs record of research input to industry. It believes the success in having die-casting research implemented into industry practice is to be found in adopting an approach which is inclusive of the problems faced on the manufacturing shop floor.
- As a leading manufacturing research organisation since the 1930s, currently CSIRO can call on the expertise of about 3000 scientists/engineers across the gamut of scientific disciplines for specialist consultation on industry projects.
- Among past successes is the PQ2 Diagram, which matches high-pressure die-casting dies to die-casting machine performance. It is now considered a fundamental die design tool. As well, the design and use of tapered tangential runners for aluminium and zinc die-casting helps die-casters worldwide to produce high-quality, cost-effective pressure die-castings.
- CASTFLOW, a software package for runner design, and CASTHERM for thermal design of dies came out of the PQ2 Diagram and were commercialised by CASTEC (Australia) Pty Ltd.
The President of the Australian Die Casting Association, Graham Wilson, says Australian companies have benefited from CSIRO collaborative research which has assisted them in finding export markets. He also emphasises that what has occurred is the smooth application of high technology to the manufacturing industry, providing strong employment opportunities and tool making spin-offs. This implies that in producing technologically difficult components for niche markets, Australian die-casters have shown their strengths, using their in-house expertise to solve problems for manufacturers, rather than in designing simpler mass market products. This expertise has been recognised in local-global partnerships to manufacture components predominantly for the automotive industry, Wilson Nissan Casting Australia Pty Ltd, declares it has had a highly productive involvement in collaboration with CSIRO and expects this to continue.
The improvements so far include:
- Reduction in metal loss of more than 1.5%.
- Soldering downtime reduced by as much as 3%.
New projects have developed from the interchange of ideas across the membership of the Cooperative Research Centre for Cast Metals Manufacturing (CAST), which is supported by Australian governments, CSIRO, several universities, smelting companies, manufacturers and die-casting companies. A unique combination of participants, indeed. Laser cladding of die surfaces: This technique looks at the controlled generation of highly [thermally] stable alloys on the die surfaces, metal powder being carried to the point of melting through an advanced microprocessor controlled carrier gas system. A patent pending on a soldering-resistant material for laser cladding. Nissan Casting Australia, claims an early outcome of the collaboration was a die for a water-cooled, low-pressure cylinder head, which was made available to all car manufacturers taking part in the project.
Other successful projects included:
- a reduction in the incidence of soldering,
- an investigation into die-casting machine parameters and
- the development of a machine monitoring system using sensors.
A shot monitoring project incorporating linear transducers gave very accurate results, and also allowed for the clear identification of what was happening in the die-casting tool itself. These findings are very crucial in overall understanding of the operational problems in PDC. Ongoing research aims to improve productivity and reduce costs. CSIRO sees lucrative chances in expanding services to industry beyond national borders, with die-casting teams in Melbourne, looking towards filling a gap in agreed process- and die-design guidelines for gravity die-casting technology and low-pressure die-casting all over the world. Inconsistency, reduced reliability and reduced profit in the final products are often the result of dies designed using a trial-and-error method, they claim, and rightfully so indeed. They are also making extensive use of computer simulation for immediate needs in die design, while also addressing the lack of guidelines. This involves 3D simulation of metal flow during die-filling, heat flow and solidification, and, in some cases, residual stress which may cause distortion of casting and dies.
The CSIRO research team uses major software packages such as MAGMAsoft, ProCAST, FLOW-3D, as well as software it has developed. The team also holds extensive databases of thermo-physical properties, especially heat transfer data for a range of materials, in order to model fluid flow and heat flow processes. Pilot plant machines for low- and high-pressure, squeeze and gravity tilt die-casting are available for die trials and experimentation in aluminium and magnesium alloys. Australia is a growing exporter of aluminium castings, to the extent that automotive die-casting exports now exceed the domestic industry consumption. Cylinder heads are exported to Toyota, Mitsubishi and Nissan in Japan, and to Daewoo in Korea. Engine components are sent to both Japan and Korea, transmission cases are exported to the European and Japanese markets, and wheels are exported to the USA as well as being available on the global market. CSIRO has designed tooling for a number of aluminium automotive gravity die-castings. Examples are an inlet manifold for a four-cylinder car engine, with a complex and heavy sand core producing thin walls and an excellent surface finish. CSIROs research facilities are extensive, including the following:
o A 250 t Toshiba cold chamber machine,
o An IDRA 125 t magnesium hot chamber machine,
o A Rimatic low-pressure die-casting machine,
o A Rauch magnesium melter and dosing furnace,
o A UBE squeeze casting machine,
o A battery of gravity tilt casting machines,
o A horizontal continuous direct chill caster and
o A twin roll caster, both for magnesium casting. Associated support facilities cover the following:
o several aluminium and magnesium melting furnaces,
o mechanical testing equipment,
o a cabinet X-ray fluoroscope,
o a fluidised bed heat treatment furnace,
o an infra-red thermal imaging camera, spectrometers and electron microscopy. All together a formidable array of developmental arsenal indeed.
Conclusion
From the discussion above, it is obvious that a lot of applied research has been carried out in many places for fine-tuning some of the innovations in pressure die casting process and its variants. Many useful ideas have already been translated into actual and tangible benefits as shown above. It is therefore the authors sincerest wish to assist any pressure die casting industry in India where new ideas and technologies can find a fertile ground. The technological gap between us and the more technologically-advanced nations is narrowing down almost on a daily basis though of course there happen to be blind spots where the gap is as large as ever. It needs a concerted effort on part of the laboratories, academia and the industry. A beginning has to be made somewhere and PDC as a lively segment of our industry today, could provide that much-required springboard to take the first plunge
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