Adaptive Conformal Cooling of Injection Molds Using Additively Manufactured TPMS Structures

In injection molding, cooling channels are usually manufactured with a straight shape, and thus have low cooling efficiency for a curved mold. Recently, additive manufacturing (AM) was used to fabricate conformal cooling channels that could maintain a consistent distance from the curved surface of the mold. Because this conformal cooling channel was designed to obtain a uniform temperature on the mold surface, it could not efficiently cool locally heated regions (hot spots). This study developed an adaptive conformal cooling method that supports localized-yet-uniform cooling for the heated region by employing micro-cellular cooling structures instead of the typical cooling channels. An injection molding simulation was conducted to predict the locally heated region, and a mold core was designed to include a triply periodic minimal surface (TPMS) structure near the heated region. Two biomimetic TPMS structures, Schwarz-diamond and gyroid structures, were designed and fabricated using a digital light processing (DLP)-type polymer AM process. Various design parameters of the TPMS structures, the TPMS shapes and base coordinates, were investigated in terms of the conformal cooling performance. The mold core with the best TPMS design was fabricated using a powder-bed fusion (PBF)-type metal AM process, and injection molding experiments were conducted using the additively manufactured mold core. The developed mold with TPMS cooling achieved a 15 s cooling time to satisfy the dimensional tolerance, which corresponds to a 40% reduction in comparison with that of the conventional cooling (25 s).

A Simple Method of Reducing Coolant Leakage for Direct Metal Printed Injection Mold with Conformal Cooling Channels Using General Process Parameters and Heat Treatment

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.

Structural Analysis of Molds with Conformal Cooling Channels: A Numerical Study

The manufacturing of Conformal cooling channels (CCC’s) is now easier and more affordable, owing to the recent developments in the field of additive manufacturing. The use of CCC’s allows better cooling performances than the conventional (straight-drilled) channels, in the injection molding process. The main reason is that CCC’s can follow the pathways of the molded geometry, while the conventional channels, manufactured by traditional machining techniques, are not able to. Using CCCs can significantly improve the cycle time, allow to obtain a more uniform temperature distribution, and reduce thermal stresses and warpage. However, the design process for CCC is more complex than for conventional channels. Computer-aided engineering (CAE) simulations are important for achieving effective and affordable design. This article presents important results regarding molds with new conformal cooling channels geometries. The aim is to assess the maximum pressure that the parts can be subjected to in a real injection molding application. Linear structural analyses are carried over in the Finite Element Method Software ANSYS Workbench 2020 R2, in order to analyze both the resistance and stiffness behavior of the studied geometries. The results are analyzed according to several metrics. The results were discussed and it could be concluded that some of the structures are suitable for the typical operating conditions of the injection molding process.

Design, Optimization and Validation of Conformal Cooling Technique for Additively Manufactured Mold Insert

Injection molding is a cyclic process comprising of cooling phase as the largest part of this cycle. Providing efficient cooling in lesser cycle times is of significant importance in the molding industry. Conformal cooling is a proven technique for reduction in cycle times for injection molding. In this study, we have replaced a conventional cooling circuit with an optimized conformal cooling circuit in an injection molding tool (mold). The required heat transfer rate, coolant flow rate and diameter of channel was analytically calculated. Hybrid Laser powder bed fusion technique was used to manufacture this mold tool with conformal channels. The material used for manufacturing mold was maraging steel (M300). Thermal efficiency of the conformal channels was experimentally calculated using thermal imaging. Autodesk MoldFlow software was used to simulate and predict the cooling time required using conformal cooling channels. The results showed a decrease in cooling time and increase in cooling efficiency with the help of conformal cooling in additively manufactured mold insert.

A Hybrid Cooling Model Based on the Use of Newly Designed Fluted Conformal Cooling Channels and Fastcool Inserts for Green Molds

The paper presents a hybrid cooling model based on the use of newly designed fluted conformal cooling channels in combination with inserts manufactured with Fastcool material. The hybrid cooling design was applied to an industrial part with complex geometry, high rates of thickness, and deep internal concavities. The geometry of the industrial part, besides the ejection system requirements of the mold, makes it impossible to cool it adequately using traditional or conformal standard methods. The addition of helical flutes in the circular conformal cooling channel surfaces generates a high number of vortexes and turbulences in the coolant flow, fostering the thermal exchange between the flow and the plastic part. The use of a Fastcool insert allows an optimal transfer of the heat flow in the slender core of the plastic part. An additional conformal cooling channel layout was required, not for the cooling of the plastic part, but for cooling the Fastcool insert, improving the thermal exchange between the Fastcool insert and the coolant flow. In this way, it is possible to maintain a constant heat exchange throughout the manufacturing cycle of the plastic part. A transient numerical analysis validated the improvements of the hybrid design presented, obtaining reductions in cycle time for the analyzed part by 27.442% in comparison with traditional cooling systems. The design of the 1 mm helical fluted conformal cooling channels and the use of the Fastcool insert cooled by a conformal cooling channel improves by 4334.9% the thermal exchange between the cooling elements and the plastic part. Additionally, it improves by 51.666% the uniformity and the gradient of the temperature map in comparison with the traditional cooling solution. The results obtained in this paper are in line with the sustainability criteria of green molds, centered on reducing the cycle time and improving the quality of the complex molded parts.

Evaluation of Cooling Performance of an Additive Manufactured Gravity Die Casting Mold with Conformal Cooling Channel

A cooling channel with an optimized design provides not only high throughput with gravity die casting, but also guarantees product quality. A conformal cooling channel (CC) whose structure follows the shapes or surfaces of the mold cavity has attracted great attention in the die casting industry, because it allows rapid and uniform cooling. However, implementing conformal cooling remains highly challenging, because the complicated geometries of CC are difficult to form using conventional fabrication methods such as drilling and milling. In recent years, advances in additive manufacturing (AM) technology have made it possible to fabricate products with complex and elaborate structures. In this paper, a gravity die casting mold with CC was designed and built using AM technology. The cooling channel performance was estimated and evaluated using an Al-Si-Cu alloy casting simulation and die casting experiments, respectively. The casting simulation results showed that the cooling performance of the CC was enhanced by ca. 10% compared with that of a conventional cooling channel. The experimental cooling performance of the CC improved by ca. 8% compared to that of a conventional cooling channel, and the increment in performance was consistent with the simulation results. In addition, microstructural evidence clarified that the effective cooling performance of CC could be attributed to the decrement (ca. 17%) of the secondary dendrite arm spacing (SDAS) of the Al-Si-Cu alloy. In this research, AM technology provides a novel way to fabricate functionally superior CC molds that are hardly producible with traditional methods.