detailset DESIGN
Zero draft vertical mating faces allow for a better fi t to the clamp assembly.
• Features normal to the parting plane must have draft or reducing cross-sectional area go- ing away from the parting plane to allow the pattern to be stripped away from the mold. T e amount of draft required depends on the type and quality of the tooling, depth of the feature and, most importantly, the molding process used. For sand casting, draft is typi- cally around two degrees.
• When the draft interferes with how the com- ponent fi ts other parts, additional machining may be required. However, through careful design and placement of the casting features and tooling, including core confi gurations, it is possible to create zero draft features, as shown in this tube clamp.
Core consolidation allows design engineers to hold tighter true positioning tolerances, zero- draft vertical surfaces as well as optimized machining stocks on cored features.
• Cores are necessary to produce internal features as well as those not easily ac- cessible from the parting line. Howev- er, every cored feature adds variability to the dimensional tolerances due to clearance required between the core print on the core and the mating core print on the pattern.
• Core consolidation into an assembly allows better handling and placement of the core or cores into the mold cav- ity and prevents the cores from fl oat- ing due to the buoyancy of the liquid metal during fi lling and earlier stages of solidifi cation.
• Core assembly also improves the cycle time because only one core setup operation is required.
Generous draft and fi llets impact the overall casting surface fi nish and quality.
• T e casting process gives design engineers the fl ex- ibility for smoother transitions from thicker to thinner sections. Adequate radii and fi llets in varying cross- sectional areas eliminate or reduce the stress concen- tration eff ects, providing cleaner castings with better component fatigue life in service.
Original Weldment
• Certain fi llet and radii are not possible due to core and parting plane confi gurations and may require manual grinding.
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.
Jan/Feb 2016 | METAL CASTING DESIGN & PURCHASING | 17
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