Integration of CFD Analysis into Die-Cast Process Design

This article was contributed by Alex Reikher, Ph.D., of Shiloh Industries

In today’s marketplace, organizations face increasing pressure from both old, well-established, and new, rapidly-growing economies. Globalization of the marketplace forces companies to be on the lookout for avenues to sustain their competitive advantage. Rapid developments in internet technology and free exchange of information, are some of the factors that reduce the period when companies can hold on to their competitive advantage. One of the ways organizations can maintain a leading position in the industry is to reduce time required to bring innovations to the marketplace. With the goal of compressing die-cast process development time, modeling with FLOW-3D has become an integral part of Shiloh Industries’ engineering department.

At Shiloh Industries, new projects start with conceptual development of the gate and runner system, approximate slow shot profile calculations, shot cylinder diameter, minimum ventilation area, and process pressure requirements. Flow analyses are performed in order to develop the best possible flow pattern and minimize air entrainment. After runner design is finalized, thermal analyses are run to help make the best decision on waterline placement.

Original geometry of the metal casting part

Figure 1: The casting part

An attractive feature of FLOW-3D is the ability to run separate analyses for every stage of the development process. It allows for a short development time in choosing the right shot profile, gate design, and waterlines location. A fully coupled flow and thermal analysis need to be carried out only once to verify that all components work well together without adverse interactions. An introduction of a general moving object (GMO) model allows the setting of the best plunger velocity in the shot sleeve during the slow shot stage. In the project described here, the part design has drastically changed from its current production version.

The part geometry is shown in Figure 1. It poses challenges during filling and solidification to ensure the required casting quality. For example, high internal stresses may develop in the tall rib section during solidification and subsequent cooling, resulting in undesirable buckling forces.

In the initial stages of the design process, twenty-one runner configurations were suggested for evaluation. FLOW-3D was used to evaluate all variants. Figure 2 shows some of the runner designs considered.
Examples of different runner systems

Figure 2: Three of the twenty-one runner systems modeled in FLOW-3D

Runner systems evaluated for flow pattern

Figure 3: Runners selected for further evaluation based on the flow pattern

The initial evaluation criterion of the runner systems was the flow pattern. After the first stage of the design process was completed, two conceptually different runner designs, shown in Figure 3, were accepted for further evaluation.

Solidification analyses were ran during the second stage of evaluation. Temperature distributions in the casting as well as in the die were analyzed. Figure 4 shows temperature distribution in the part at the end of solidification, using the final runner system design.

Temperature distribution at the end of solidification

Figure 4: Different views of the final runner system chosen based on temperature distribution in the part at the end of solidification

Conclusion

For over seven years, we have been able to prove to our group the accuracy and reliability of the predicted results using FLOW-3D as a die casting process modeling tool. These results have had good correlations with the actual casting defects, temperature distribution and flow patterns.

We are using FLOW-3D not only as a die casting process simulation tool, but also as a general CFD modeling tool. If during process development, design changes need to be recommended to a customer, FLOW-3D allows us to quickly and reliably evaluate these changes and present to the customer not only the proposed changes, but also the effects these changes will have on the part performance.