Table 2. Design for Manufacturability Rules
Reduce the number of elements meeting at the junction
Make thickness uniform for elements
Reduce inner fi llet radius and inner chamfers
Increase interior angles (from acute to 90 degrees or more)
Provide outer fi llet radius or outer chamfer
Reduce the length of elements
Place a core at the middle of the junction
junctions can be established (Fig. 4). First, the designer should classify and identify the type of junction. Then, VEM-based solidifi cation simulation will produce temperature contours. The hot spot area is measured and compared against a pre- defi ned limit. If the hot spot area is more than the set limit, the junction design for manufacturing rules in Table 2 should be
applied to modify the junction design, subject to functional requirements. As an example, consider the original
design for an aluminum box corner junc- tion consisting of three plate elements meeting at a junction with thicknesses of 2.36 in. (50 mm), 1.18 in. (30 mm) and 0.59 in. (15 mm). The length of all the plates is 9.45 in. (240 mm).
Fig. 4. Casting de- signers can use this framework for junction redesign.
The fi rst revised design of the box
corner junction consisted of uniform walls of 1.18 in. thickness, leading to 90% reduction in hot spot area with a volumetric change of 14.21%. To seek further improvement, three more designs were considered: 1. uniform thickness along with a corner chamfer equal to the thickness of the plate, 2. uniform thickness along with a fi llet ra- dius equal to 50% thickness of the plate and 3. uniform thickness along with a fi llet radius equal to 75% thickness of the plate (Fig. 5). The most effective revision was uniform thickness with a corner chamfer. A benchmark part illustrates the knowledge gained from parametric analysis of an L junction and evolu- tion of design for manufacturability rules (Fig. 6). The original design had elements of non-uniform thickness meeting at a three-dimensional junc- tion. In the revised design, the ele- ments were made nearly uniform by reducing the thickness of the bottom plate and increasing the diameter of the hole. Solidifi cation analysis of the original design revealed the presence of a major hot spot region,
36 Metal Casting Design anD PurChasing
January/February 2010
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