Simple Solutions That Work! Issue 6

Introduction: Computer modeling is the process of simulating what happens when a casting is poured into a mold and the metal cools and solidifies. By simulating this process, we hope to predict potential defects in the casting and redesign the process to eliminate these defects, before making actual castings. The Design Process: Typically, the design process begins with receipt of part specifications from the customer. Traditionally this involved a paper drawing, however, nowadays most part geometries are contained in 3D CAD files, which facilitates the use of computer design and simulation. The first task of the foundry engineer is to decide on a basic process design for the casting, i.e., in what orientation the part will be cast, how it is to be gated, how it is to be risered and how many castings are to be produced in a single mold or tree. Computer simulation can be helpful even at this early stage of design. Many foundry engineers have adopted the practice of running a “naked” simulation of the part as received from the customer, completely surrounded by mold material without gates or risers. This can often be accomplished in just a few minutes with the right software, and allows the part to be viewed from a thermal standpoint; showing the progression of “natural” solidification and the location of thermal centers in the casting, Figure 1. In many cases this analysis will determine the orientation of the casting in the mold; contact points for risers become obvious, and the best orientation of the casting in order to accommodate those contact points can be decided immediately. It is helpful if the simulation software has built-in design rules for feeding and gating the casting (such as a Gating Design Wizard and a Riser Design Wizard) so that location, number and size of risers and suggested size and shape of gating components can be calculated more or less automatically to establish an initial rigging design for the casting, Figure 2. DAVID C. SCHMIDT Vice President FINITE SOLUTIONS, INC. ARTICLE TAKEAWAYS: • Simulation of unrigged castings drives gating/risering design • Flow simulation aids in process visualization • Computational Fluid Dynamics (CFD) enhances simulation accuracy SYSTEMS INTEGRATION Figure 1 “Naked” simulation of casting plotting solidification time. Figure 2 Model of casting with initial rigging design. Once the initial design is developed, it can be verified and fine-tuned by running complete flow and solidification analysis. This is required, due to the fact that design rules are general in nature and cannot take into account all of the dynamics that will occur within a complex casting/gating system. This means that it is necessary for the foundry to construct a 3D model of the casting with the complete proposed rigging system for computer modeling. 48 COMPUTERMODELINGOF THE CASTING PROCESS TOPREVENT DEFECTS