detailset DESIGN
A proprietary thermal barrier coating aids directional solidifi cation in a conformable compressed natural gas tank. • In semi-permanent molds, where sand cores are inserted into the met- al mold to produce internal passages, it is important to control the heat transfer at the metal mold interface to achieve the desired directional solidifi cation, which predicates the overall internal soundness and local mechanical properties.
• Casting process simulation assists in validating and optimizing the process parameters to achieve the desired results. In this case, a propri- etary thermal barrier technology was used to help direct solidifi cation.
Top/Core
Casting confi guration, especially section thickness, determines directional solidifi cation. • T e casting supplier paid close attention to the risering and gat- ing system for this class 8 truck transmission housing, along with the permanent mold heating and cooling systems, to achieve the desired thermal balance to promote directional solidifi cation.
• Section thicknesses were varied so they are thicker near the risers, which remain liquid longer than the sections they are attached to, in order to feed liquid metal to the section during solidifi cation.
• Computer simulation predicted the isolated hot spots which, if not fed, would lead to shrinkage and porosity. External feeding aids, such as localized air chills, reduce hot spots when carefully designed.
Bottom/Drag Water jacket core
Nesting the water jacket and exhaust cores in this one-piece exhaust manifold yields better wall thick- ness control for improved thermal performance of the fi nished product, which was produced via the semi-permanent molding process. • T e wall thickness of the manifold is designed to be stable by incorporating a water jacket core nested/pre-assembled with the exhaust core, thereby eliminating the potential for the cores’ rela- tive movement. Consistent wall thickness also yields predictable solidifi cation, cooling rate and properties for aluminum castings.
• Along with computational fl uid dynamics, casting process simula- tion of fi lling, solidifi cation, microstructure and mechanical proper- ties is an important tool for the development of complex castings.
Exhaust core Water jacket core
Jiten Shah is president of Product Development & Analysis (PDA) LLC (
www.pda-llc.com), Naperville, Illinois, and a 25-year casting design and manufacturing veteran.
Sept/Oct 2016 | METAL CASTING DESIGN & PURCHASING | 19
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