Article
A Simple Method of Reducing Coolant Leakage for Direct
Metal Printed Injection Mold with Conformal Cooling
Channels Using General Process Parameters and
Heat Treatment
Chil-Chyuan Kuo
1,2,
* and Shao-Xuan Qiu
1
Citation: Kuo, C.-C.; Qiu, S.-X. A
Simple Method of Reducing Coolant
Leakage for Direct Metal Printed
Injection Mold with Conformal
Cooling Channels Using General
Process Parameters and Heat
Treatment. Materials 2021, 14, 7258.
https://doi.org/10.3390/ma14237258
Academic Editor: Ludwig Cardon
Received: 31 October 2021
Accepted: 24 November 2021
Published: 27 November 2021
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1
Department of Mechanical Engineering, Ming Chi University of Technology, New Taipei City 243, Taiwan;
M05118021@mail.mcut.edu.tw
2
Research Center for Intelligent Medical Devices, Ming Chi University of Technology,
New Taipei City 243, Taiwan
* Correspondence: jacksonk@mail.mcut.edu.tw
Abstract:
Direct metal printing is a promising technique for manufacturing injection molds with
complex conformal cooling channels from maraging steel powder, which is widely applied in
automotive or aerospace industries. However, two major disadvantages of direct metal printing
are the narrow process window and length of time consumed. The fabrication of high-density
injection molds is frequently applied to prevent coolant leakage during the cooling stage. In this
study, we propose a simple method of reducing coolant leakage for a direct-metal-printed injection
mold with conformal cooling channels by combining injection mold fabrication with general process
parameters, as well as solution and aging treatment (SAT). This study comprehensively investigates
the microstructural evolution of the injection mold after SAT using field-emission scanning electron
microscopy and energy-dispersive X-ray spectroscopy. We found that the surface hardness of the
injection mold was enhanced from HV 189 to HV 546 as the Ni-Mo precipitates increased from 12.8
to 18.5%. The size of the pores was reduced significantly due to iron oxide precipitates because the
relative density of the injection mold increased from 99.18 to 99.72%. The total production time
of the wax injection mold without coolant leakage during the cooling stage was only 62% that of
the production time of the wax injection mold fabricated with high-density process parameters. A
significant savings of up to 46% of the production cost of the injection mold was obtained.
Keywords:
direct metal printing; maraging steel powder; coolant leakage; heat treatment; precipitate
1. Introduction
Additive manufacturing (AM) [
1
,
2
] technology has been widely used to produce
prototypes and physical models in industry because it has the capacity to manufacture
components with sophisticated geometries. Metal AM technology in particular has received
much attention, in techniques such as selective laser melting [
3
], direct metal laser sintering,
vacuum diffusion bonding, selective laser sintering, and selective electron beam melting.
Additionally, it can be used to manufacture injection molds [
4
] for the mass production of
new products. Mazzarisi et al. [
5
] studied three main process parameters of direct laser
metal deposition and suggested the best ranges of process parameters to establish the
most suitable parameters for predicting the geometric characteristics of clad. The results
showed that new formulations were in good agreement with the behaviors defined in
the literature. Contaldi et al. [
6
] investigated the effects of powder reuse for two kinds of
precipitation-hardening stainless steel. They found that reusing the excess metal powder in
powder bed fusion processes is possible and no significant variation was observed for the
martensitic phase. Alafaghani et al. [
7
] studied the effects of manufacturing procedures on
the mechanical properties of metal laser sintering parts. The results showed that IN718 and
Materials 2021, 14, 7258. https://doi.org/10.3390/ma14237258 https://www.mdpi.com/journal/materials
