a casting to improve its fatigue strength,” he said (see Fig. 2). “With certain castings, it makes more sense to do a repair than to make a new casting. You have to consider complexity along with what you’re trying to do with the casting, and whether it’s worth it.” With aluminum,


filtering often is required to meet high specifica- tion standards, and additions such as cores and metal inserts make casting a part a more complex process, adding to the cost. Design considerations such as wall thick- ness determine the number of chills and risers required to achieve the necessary mechanical properties, also affecting cost. “People like to reduce wall thickness for lightweighting or add thickness for


Figure 2. In recent work through AFS research, Eck reviewed how welding affects tensile strength and fatigue strength for aluminum alloys. Shown are room temperature tensile fatigue results for a 1 in. thick E357 aluminum sand casting.


structural stability,” said Weiss. “Te optimal range is between 4mm and 6mm for aluminum castings. When you’re above or below that, the cost factor goes up because of misruns on thin sections and chills or risers on heavy sections.” Te choice of aluminum alloy most often


does not have as great an impact on cost as the engineering choices and quality requirements beyond visual inspection (see Fig. 3). “When you are specifying very high mechanical properties or those higher than what is normally accepted in the industry or specifications such


Mar/Apr 2014 | METAL CASTING DESIGN & PURCHASING | 23


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