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Understanding


Limitations and the Power of Knowledge


The power of advanced casting technology coupled with efficient and effective design gives the metalcasting industry a bright future. RICHARD B. GUNDLACH, ELEMENT MATERIALS TECHNOLOGY, WIXOM, MICHIGAN


W


hat matters most to management is the ability to stay in business and stay cost competitive. A good knowledge


of casting technology can be a powerful asset to produce better, more robust products. It is imperative that foundries educate their customers on the design of castings, and pos- sibly provide design services to customers. Alternately, they should offer design improvements to customers to take advantage of the properties of quality metal and the advan- tages of design only afforded in the casting process. Tey also need to learn how to reduce defect sizes and quantities in their castings by using the many new technologies avail- able today.


By using the power of advanced casting technology coupled with efficient and effective design the metalcasting industry will have a bright future. Te kinetics of the solidification process produces


microshrinkage porosity, coarse solidification structures and oftentimes, undesirable inclusions and second phases that develop as a result of alloy segregation during solidification. Te decrease in the solubility of gases during solidification also can produce internal porosity. Te casting process also can introduce inclusions due to reoxidation of the molten metal during pouring, as well as cause the entrainment of foreign debris that further adds discontinuities to castings. Te various voids, inclusions and microstructural features reduce strength and ductility and cause castings to suf- fer reduced monotonic and cyclic properties compared to wrought and forged metals. Te microstructures in castings are also much coarser than the grain size and second phase particles in wrought metals, further separating the properties of castings from wrought and forged parts. Heat treatments can be applied to castings to refine the grain structure and improve the


Fig. 1. Graph shows the stress concentration factor as a function of the notch geometry. (a) Plate with hole in tension, (b) Notched bar in tension.


November 2016 MODERN CASTING | 33


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