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Metal Casting Technologies : March 2007
EXAMPLE 2 -- CLUSTER OF GOLF CLUB HEADS When multiple castings are arranged on a tree, there may be less flexibility in part arrangement, but with careful study, the results can be even more spectacular, since improvements can be multiplied by the number of casting in the tree. Our second example shows two different cast golf club heads, each cast in a cluster of 6 castings. Both used a centered pouring cup, with a double width runner bar to distribute the metal. The main difference was that the first part was cast with each club head in a vertical orientation and the second part was cast horizontally. Results of the vertical orientation are shown in Figures 3A and B. Figure 3A shows a snapshot of the filling sequence, and Figure 3B is an x-ray view of macroporosity, or shrinkage. Several things are apparent from these views: 1) Filling is not equal. The center casting is filled very quickly by the metal dumping out of the runner into the casting. 2) There is quite a bit of splashing, in the pouring cup, in the feeder bars and in the castings themselves. 3) Poor temperature gradients have been set up, resulting in isolated shrinkage in each of the castings. When excessive mixing occurs, as would happen when the metal drops like this, it is very difficult to promote directional solidification. Contrast this vertical arrangement with the 6 club heads cast horizontally, as shown in Figures 4A and 4B. Note that the pouring cup and feeder bars are basically the same in both arrangements. The two main differences are that in the horizontally-cast heads, the metal drop distance from the feeder bars into the castings is much lower, and that the central two castings are not directly below the pouring cup, but offset to the side. While the castings do not all fill simultaneously, they fill much more similarly than do those in the vertical arrangement. There is almost no evidence of splashing, and since the gating goes directly into the heavy sections of the club heads the metal does not have a large drop. This promotes directional solidification. Shrinkage indications shown in Figure 4B show a virtually perfect set of castings. There is one very borderline indication in the casting shown at the top right, but as it is buried deep within the casting, it would not create a scrap casting. SUMMARY Both examples show how fluid flow analysis can clearly show the implications of the filling process on overall casting quality. You are able, through simulation, to actually see what is happening during filling, and can achieve a much better understanding of the metalcasting process. This leads to higher quality castings, produced more quickly and for less money. ● Figure 3B. Shrinkage prediction in the vertically-cast club heads. Figure 4A. The horizontally-cast club heads fill much more evenly and quietly, without splashing. Figure 4B. Shrinkage indications for the horizontally-cast club heads occur in the gating system only. Figure 3A. Filling of golf club heads in a vertical orientation. Note unequal filling rates and the splashing in the feeder bar METAL Casting Technologies March 2007 39