Simple Solutions That Work! Issue 14

ADVANCED MANUFACTURING SOLUTIONS 28 DAVID C. SCHMIDT Vice President Finite Solutions, Inc. ARTICLE TAKEAWAYS: • Permanent Mold Casting is the most complex of the gravity filling processes • Mold coatings and forced cooling improve simulation realism • Several speed-up techniques can be used to minimize simulation time, yet provide accurate results ADVANCED SIMULATION OF THE PERMANENT MOLD PROCESS Figure 1: Ingate Filling Model 9 Continued on next page W hen simulating gravity filling processes, permanent mold is the clear winner for complexity. Some of the reasons for this complexity are: • The mold is re-used, so you need to get the die up to operating temperatures before you evaluate results. With sand and investment casting, you only need to consider a single filling/cooling cycle. • The mold is conductive, like the metal poured into it, so interactions at die/metal interfaces are extremely important. Mold coating techniques and air gap formations significantly affect process outcomes. This requires additional data and calculation. • Complex forced heating and/ or cooling schemes can be used on the shop floor and need to be accounted for in simulation. This involves a more detailed model, as well as specifying how the heating or cooling scheme operates. In spite of these complexities, simulation of the permanent mold process can be straightforward and not too time consuming. Let’s see how we can set up a permanent mold simulation that provides realistic result with a minimum amount of calculation time. MODEL BUILDING CONSIDERATIONS Ingate filling vs fixed volume filling – The simplest way to model metal entry into the die is by creating an ingate made of “fill material”. This creates an interface where hot metal enters the system at a constant filling rate, based on the overall pouring time. For the greatest simulation accuracy in the permanent mold tilt pour process, however, a fixed volume method is used. Here a pouring cup is filled with hot metal, and the metal transfers from the pouring cup to the die as the die is rotated. The filling rate varies during the process, based on the rotation speed and the pull of gravity. Figures 1 and 2 show two variations of a brake caliper casting model, using ingate filling and fixed volume filling. The die has been removed for clarity. Figure 2: Fixed Volume Fill Model