  Citation: Kanbur, B.B.; Zhou, Y.; Shen, S.; Wong, K.H.; Chen, C.; Shocket, A.; Duan, F. Metal Additive Manufacturing of Plastic Injection Molds with Conformal Cooling Channels. Polymers 2022, 14, 424. https://doi.org/10.3390/ polym14030424 Academic Editors: Ming-Shyan Huang and Jian-Yu Chen Received: 17 December 2021 Accepted: 20 January 2022 Published: 21 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Metal Additive Manufacturing of Plastic Injection Molds with Conformal Cooling Channels Baris Burak Kanbur 1,2,† , Yi Zhou 1,2,† , Suping Shen 1,2,† , Kim Hai Wong 3 , Charles Chen 3 , Abe Shocket 3 and Fei Duan 2, * 1 Singapore Centre for 3D Printing (SC3DP), Nanyang Technological University (NTU), Singapore 639798, Singapore; bbkanbur@ntu.edu.sg (B.B.K.); yi.zhou@ntu.edu.sg (Y.Z.); spshen@ntu.edu.sg (S.S.) 2 School of Mechanical and Aerospace Engineering, Nanyang Technological University (NTU), Singapore 639798, Singapore 3 Tyco Electronics Singapore Pte Ltd., TE Connectivity, Singapore 239920, Singapore; kimhai.wong@te.com (K.H.W.); chen.charles@te.com (C.C.); ashocket@te.com (A.S.) * Correspondence: feiduan@ntu.edu.sg † These authors contributed equally to this work. Abstract: Conformal cooling channels (CCCs) are widely used in the plastic injection molding process to improve the product quality and operational performance. Tooling that incorporates CCCs can be fabricated through metal additive manufacturing (MAM). The present work focuses on the MAM of a plastic injection mold insert with different CCC types that are circular, serpentine, and tapered channels with/without body-centered cubic (BCC) lattices. The entire manufacturing process of the mold insert is explained from the design step to the final printing step including the computational thermal & mechanical simulations, performance assessments, and multiobjective optimization. Compared to the traditional channels, conformal cooling channels achieved up to 62.9% better cooling performance with a better thermal uniformity on the mold surface. The optimum mold geometry is decided using the multiobjective optimization procedure according to the multiple objectives of cooling time, temperature non-uniformity, and pressure drop in the channel. Direct Metal Laser Sintering (DMLS) method is used for manufacturing the molds and the quality of the printed molds are analyzed with the X-ray Computed Tomography (X-ray CT) technique. The errors between the design and the printed parameters are less than 5% for the circular and tapered channels while the maximum deviation of the strut diameters of the BCC is 0.06 mm. Keywords: metal additive manufacturing; 3D printing; computer-aided engineering; computer- aided design; conformal cooling; heat transfer; conjugate heat transfer; Direct Metal Laser Sintering; multiobjective optimization; plastic injection 1. Introduction Plastic injection is one of the most affordable and broad thermoplastic polymer-related processes for mass production purposes in the industry [1,2]. It has four main steps that are (in a sequence) (i) melt plastic injection, (ii) packing in the mold, (iii) cooling process and (iv) ejection from the mold [3]. The total consumed time during these steps is called total cyclic time whilst the cooling step shares 70% to 80% of the total cyclic time [4]. Notwithstanding that all these steps have crucial importance on the plastic injection molding process, insufficient or low-quality cooling can result in negative impacts on the product quality like unwanted warpage and shrinkage. In general, there are two critical parameters to manage the cooling process well: cooling time and temperature uniformity on the mold surface. The decrease of cooling time is the desired point for performance improvements of the cooling step of the plastic injection molds since it can decrease the risks of warpage and shrinkage while it also achieves shorter cyclic time, Polymers 2022, 14, 424. https://doi.org/10.3390/polym14030424 https://www.mdpi.com/journal/polymers