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Metal Casting Technologies : March 2006
Using the PQ²-diagram, it can be verified if the machine hydraulics is able to convert the defined parameters (Fig. 7). The PQ²- diagram is calculated from the following parameters; firstly, the machine parameters that can be stored in the data base of the simulation program, classified under the corresponding machine types; and secondly, the tool parameters that are calculated from the CAD-model of the die. With the verified parameters the simulation program is able to calculate (and if necessary to optimize) various process values like filling time, gate velocity, necessary closing force, etc. (Fig. 8). Identification of casting rors due to suboptimal filling The results of the mold filling simulation allow an evaluation of the chosen casting parameters and the runner in respect to the anticipated quality of the casting. The typical casting errors due to suboptimal filling are visible welding lines, cold runs, or pores as a result of entrapped air. With the help of mold filling simulation it is possible to verify the formation and development of those errors (Fig. 9 and 10). Errors like erosion of the mold are caused by the filling process, too. Generally, ero- sion is a result of high melt temperatures in connection with high melt velocities. Those conditions usually occur at the gate but also at positions where the melt is redirected (Fig. 11). Ideally, the die filling process is directed in a manner that the casting can direction- ally solidify towards the biscuit. At the same time, the volume of the gating system should be reduced as much as possible. It is often required to have a certain area of the casting with a minimal amount of en- trapped gas. For this purpose the location or the design of the runner and gating system is modified, where the simulation verifies this alteration. Simulation of the casting solidification The solidification of the melt is character- ized by a number of metallurgical-physical phenomena that eventually determine the local properties of the casting. Those need to be considered in the simulation with appropriate modeling approaches. The main aspects in high pressure die casting are the shrinkage during solidification and the microstructure formation. Shrinkage during solidification The volume contraction during the solidifi- cation of the metal melt leads to shrinkage cavities and dispersed porosity depending on the alloy and the wall thickness of the Figure 8 Figure 9 Figure 10 METAL Casting Technologies March 2006 ADVERTORIAL er