About AFS and Metalcasting

Joining, Changing Sections

The most important aims in designing aluminum castings are to plan components for ease of casting production and to improve casting soundness. Planning arrangements of sections so that progressive solidification is toward the heavier sections helps reach these objectives.

This principle should be adhered to when designing for joining and changing sections. Sharp corners should be filleted because fillets prevent cracks, tears and shrinkage at re-entry angles. Additionally, make corners more moldable, and reduce stress concentration in the casting when in service. Fillets should be large enough to meet engineering stress requirements and reduce stress concentration, but not so large that they cause shrinkage.

In a well-designed casting, all sections are no thicker than necessary to give it the desired structural strength. They should be as uniform in thickness as possible to facilitate directional solidification.
Here are some comparisons of good and poor designs for joining and changing sections.  METAL

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When joining equal walls, keep the radius of the corner equal to the width of the walls to avoid a hot spot.

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The preferred radius for joining unequal walls at a corner should equal half the sum of the widths of the two sections.

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Above are four improving variations for changing wall thickness.

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To join equal intersecting walls, keep the radius of the intersection equal to the wall thickness.

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Joining unequal intersecting walls relies on the same basic principle as joining unequal walls at a corner.

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Staggered ribs reduce distortion caused by thermal contraction, reduce metal mass in local areas and minimize the possibility of hot spots.