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Design Considerations for 3-D-Printed Cores and Molds


Developments in additive manufacturing mean engineers have a new set of considerations when designing molds and cores. KIP WOODS AND SAIRAM RAVI, UNIVERSITY OF NORTHERN IOWA, CEDAR FALLS, IOWA


T


he growth of 3-D printing capabilities has become a hot topic in manufacturing. For metalcasters in particu-


lar, what was a way of producing pro- totypes and niche tooling has grown into a process capable of producing large numbers of molds and cores with excellent dimensional accuracy and mechanical and physical properties. Trials with a 3-D sand printer


were conducted at the Univ. of Northern Iowa to explore different design aspects that have to be con- sidered before printing sand molds or cores. Although the research was con- ducted on a particular 3-D printer, the design considerations discussed in this paper can be used effectively for


sand additive manufacturing technol- ogy on the whole. Te production of molds and cores with 3-D printers offers advantages compared to conventional molding methods. A design engineer has more freedom in designing parts and does not have to consider limitations such as drafts or undercuts. Also, multiple-piece parts in nobake or coldbox systems can be printed in a single piece with a 3-D printer to reduce stacking tolerances. Te finished parts also have excellent dimensional accuracy and mechanical properties, due to the bonding of sand at every thin layer.


Design Considerations Once solidification modeling is


complete, the initial positioning or orientation of the part can be deter- mined. In the trials, solidification design was run using a commercially available simulation software pack- age for the metalcasting industry. A solidification simulation was first run on the casting to determine possible porosity. Risers were placed at appro- priate spots and the solidification process was repeated until a sound casting was obtained. Te rest of the casting system was designed and a fill- ing simulation was run to determine metal velocity and air entrapment. After the initial casting system design was completed, different design considerations were taken into account for 3-D-printed cores and molds.


Fig. 1. The original coldbox core for the airbrake included eight differ- ent sections.


24 | MODERN CASTING May 2015


Fig. 2. The core was reduced to a single piece after conversion to the 3-D-printing method.


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