Process Simulation Makes Casting Transparent
Casting process simulation pursues different goals: it ensures the quality of a cast part, sets up robust processes or identifies and eliminates sources of defects. The main strength of simulations is their ability to create transparency by providing insight into the casting process.
The quality of cast parts is pre-determined by both the component design and the casting technology. The more accurately critical areas in the casting component can be identified, the better are the chances for casting designers and foundrymen to influence the feasibility of the design during the planning phase.
Optimal design of complex castings often fails due to poor communication between the development department and the foundry. This applies to both component requirements and process conditions. The resulting iterative optimization process requires the time-consuming and cost-intensive production of prototypes and casting tests to secure the start of series production. Late design changes are usually not accepted by the end customer because the result in higher costs and increase time-to-market.
Using Casting Process Simulation at a Early Stage
The early use of casting process simulation is therefore widely accepted in order to avoid design errors. At the same time, it provides a communication platform for casting users and foundrymen to ensure the required quality of the component in production and to detect typical defects such as porosity.
Porosity caused by vibrations are usually caused by local thermal hotspots within the component. The picture above shows the local solidification periods in a steel cast part without the application of casting technology. Due to the extended solidification times, the thermal hotspot is located exclusively in the outer area of the casting part. Therefore, designers and foundrymen could conclude that only the outer ring of the casting and not the hub would be prone to porosity. Casting technology and possibly constructive measures would therefore only concentrate on this area.
A closer examination of the solidification sequence, however, shows that the remaining melt to be supplied in the hub area is cut off from the outer ring at an early stage. This is shown by the result of the local filling times.
Therefore, it is not only local solidification times that determine the possible formation of porosity, but above all by the material-dependent local "filling times". Therefore, it is advisable to evaluate different calculated quality criteria when using simulation results, depending on the problem. In principle, it is similar to a jigsaw puzzle: The more parts are used, the more accurate does the picture become. The following case of the Turkish company Hema Endüstri A. Ş. illustrates how crucial the exchange of this information is for the success of the process.
Dialogue Leads to Optimal Design
At Hema Endüstri A. Ş., a leading Turkish producer of automotive and mechanical engineering components, the development department and foundry work closely together from the very beginning. Magmasoft is the most important tool for the early analysis of the castability of a component design used by Hema Metal, the foundry of Hema Endüstri. By consistently using the simulation for the design of new casting products, the company was able to drastically reduce the number of trials and samples (on average 1.6 casting trials per new part). The intensive cooperation between the designer and the foundryman had obvious advantages.
Due to the maximum operating loads and strength simulations, the original geometry of a component had to be adapted to the selected gray cast iron. However, the prediction of the local strengths by means of Magmasoft showed that the component cross-sections had to be significantly reinforced, if cast iron was used. The associated weight increase, a more complex assembly process and, above all, cost increases were anything but ideal.
In close collaboration with the customer, a solution based on GJS as a casting material was examined. However, nodular graphite iron has a higher volume demand grey cast iron. Therefore, the casting technique had to be adapted with regard to geometry as well as runner and feeding systems.
The Best Possible Compromise Achieved Though Simulation
In consultation with the development department, the mechanical properties of the component had to be improved by reducing the thickness of the component wall. At the same time, it was possible to reduce the filling volume and optimize output. The virtual optimization provided the best compromise between all aspired objectives with minimal porosity in the critical area and a high cooling rate. This results in good mechanical properties and a very low casting volume. By reducing the thickness of the component walls, it was also possible to achieve the customer’s quality and cost objectives.
*Dr. -Ing. J. C. Sturm is Managing Director of Magma GmbH, Aachen.
This article was first published by konstruktionspraxis.
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