detailset DESIGN
Casting Cuts Lead Time, Cost JITEN SHAH, PRODUCT DEVELOPMENT & ANALYSIS, NAPERVILLE, ILLINOIS
CASTING PROFILE
Cast Component: Right extension arm.
Process: Nobake sand casting.
Material: Cast steel A148 135-125 grade. Weight: 450 lbs. Dimensions: 51 x 20 x 12 in.
C
ompanies making the investment in time and tooling to change a manufacturing process to metalcasting are doing so to fi nd a return through better lead times, improved quality and/or improved effi cien- cy. Such was the case for an extension arm for the military produced by May Foundry & Machine Co., Salt Lake City. Originally produced
as a casting welded to plate stock, the arm was redesigned as a single component cast in A148 135-125 grade steel. By casting in one piece, the customer realized quicker lead times and increased quality, plus it gained simplicity by purchasing the arm, which serves as a boom extension on a bomb loader, as a complete machined part. T e new single-piece cast component saved the customer an estimated $500 per part, which amounted to about $80,000 on the production run.
Mounting holes were machined instead of cast-in due to their small size.
• Cores are required to produce unaccessible interior features in the sand casting process and typically are placed manually into the mold.
• T e optimum core size (diameter or thickness) depends upon adjacent casting section thick- ness. T e location with reference to the parting plane and the ease of the placement into the mold also are considered when deciding be- tween as-cast and machined cored holes.
Smooth transitions lead to better fatigue life.
• Smooth transitions at the in- tersection, as shown here, help avoid localized stress concen- tration for better fatigue life.
• In properly designed steel cast- ings, features are placed where they will benefi t from direc- tional solidifi cation.
18 | METAL CASTING DESIGN & PURCHASING | May/Jun 2015
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