section attributes, section orientation (angular references), additional geomet- ric features and feedability properties (Fig. 2). Section attributes include: • L-length of element; • t-thickness of element; • h-height; • r-fi llet radius. Additional geometric features include:
• A-cross-section area; • h/t-extent of contact between adja- cent element;
• cross-section type: (R) rectangular, (C) circular, (O) oval and (FF) free- form;
• central hole (if present): shape, sur- face area;
• plane orthogonal to junction: num- ber of such planes and their section properties, offset of such planes from junction and their orientation. Junctions of two (V or L), three (Y or
T) and four (X or K) sections, as well as 3-D variations can be derived from the previous classifi cation (Fig. 3). By analyzing the infl uence of geo-
metrical parameters, such as inner ra- dius, outer radius, thickness, angle and length of junction, on hot spot areas, design for manufacturing guidelines for junctions of complex castings can be formulated. In recent tests, the inner radius was
varied between 0 and 2.36 in. (60 mm) for an L junction, and the solidifi cation simulation showed that the larger the inner radius, the larger the hot spot area. When the outer radius was varied between 0 and 2.36 in., it was deter- mined that the larger the outer radius, the smaller the hot spot area. Further, solidifi cation simulation showed that the thicker a section of a junction, the larger the hot spot area, and the larger the angle of the junction, the smaller the hot spot area. A longer side resulted in a larger hot spot area. The relative infl uence of the param-
eters can be compared using the ratio of percentage change in hot spot area to the percentage change in junction volume, which gives an effectiveness rating. The design change that gives a high reduction in hot spot area for a low change in volume is preferred (Table 1). Inner radius has the highest impact (up to 173 effectiveness) because even a small change in fi llet radius affects the
Online Resource
Visit
www.metalcastingdesign.com to read “Joining, Changing Sections,” which discusses how to plan arrangements of sections to avoid shrinkage defects.
January/February 2010 Fig. 3. Junctions are classifi ed in three-dimensional form.
thermal concentration considerably. The effectiveness of outer radius changes are somewhat similar to inner radius. Varia- tions in length are also highly effective, but it sharply reduces and becomes steady when section length exceeds
three times the thickness. Increasing the thickness increases the hot spot area, but this is associated with a large increase in volume, as well, so it is less effective in reducing the shrinkage defect. Variations in the angle also are less effective.
Rules of Thumb Using this analysis, a framework for
design for manufacturing guidelines of Metal Casting Design anD PurChasing 35 Fig. 2. The proper casting junction parameters are illustrated here.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60