Using a grant from the Walmart Foundation to boost competitiveness of U.S. manufacturing, an Indiana academic research team has developed a new technology to aid in the design of plastic injection molds that can increase productivity, reduce costs, and improve product quality.
The technology uses applied mathematics and software development to optimally design 3D-printed injection molds with functionally graded internal lattice structure (Figure 1). The novel injection mold designs increase cooling efficiency and uniformity around the injected plastic part. The result is faster cooling and reduced stresses in the part, says Dr. Andres Tovar, who is heading up the project at Indiana University-Purdue University Indianapolis (IUPUI).
“The idea of using water flowing through a metal grid to improve cooling is well known, as in a radiator,” says Dr. Tovar. “What we have contributed are the design optimization algorithms that specify the geometry of lattice within the injection mold so that the cooling properties are optimized and the cost of the 3D-printed tool is reduced without compromising strength.”
IUPUI was awarded a $291,202 grant from the Walmart U.S. Manufacturing Innovation Fund in 2014 with the collaboration of the U.S. Conference of Mayors. The project’s goal is to reduce the cost and increase the performance and versatility of U.S.-manufactured plastic injection tooling through experimentally supported, multi-scale, thermo-mechanical topology optimization methods and metal additive manufacturing (3D printing).
The IUPUI research team is comprised of five faculty from the Purdue School of Engineering and Technology: Andres Tovar (principal investigator), Hazim El-Mounayri, Jing Zhang, Doug Acheson, and Razi Nalim. The team currently partners with the additive manufacturing company 3D Parts Manufacturing (Indianapolis, IN). The team has also collaborated with the injection molding company Hewitt Molding Co. (Kokomo, IN).
IUPUI is using a test part provided by Hewitt, a Walmart supplier. The part is a complex cap made from polypropylene. Metal injection molds are now being 3D-printed for an industrial test study that will be conducted this summer to verify the concept. Results will be reported to Walmart and the U.S. injection molding community, in part through the Manufacturers’ Association for Plastics Processors (MAPP).
Dr. Tovar believes the lattice concept of conformal cooling could reduce costs 25 to 30 percent compared to current approaches to conformal cooling using channels through solid structures (Figure 2). Cooling cycle time improvements could be as much as 50 percent above the benefits already provided by traditional conformal cooling. There would also be savings in energy and reduced part waste. He feels the approach would be most useful to applications requiring repeatable tight tolerances.
The IUPUI team is still looking for additional financial partners.