Design and fabrication of conformal cooling channels in molds:Review and progress updates

Conformal cooling (CC) channels are a series of cooling channels that are equidistant from the mold cavity surfaces. CC systems show great promise to substitute conventional straight-drilled cooling systems as the former can provide more uniform and efficient cooling effects and thus improve the production quality and efficiency significantly. Although the design and manufacturing of CC systems are getting increasing attention, a comprehensive and systematic classification, comparison, and evaluation are still missing. The design, manufacturing, and applications of CC channels are reviewed and evaluated systematically and comprehensively in this review paper. To achieve a uniform and rapid cooling, some key design parameters of CC channels related to shape, size, and location of the channel have to be calculated and chosen carefully taking into account the cooling performance, mechanical strength, and coolant pressure drop. CC layouts are classified into eight types. The basic type, more complex types, and hybrid straight-drilled-CC molds are suitable for simply-shaped parts, complex-shaped parts, and locally complex parts, respectively. By using CC channels, the cycle time can be reduced up to 70%, and the shape deviations can be improved significantly. Epoxy casting and L-PBF show the best applicability to Al-epoxy molds and metal molds, respectively, because of the high forming flexibility and fidelity. Meanwhile, LPD has an exclusive advantage to fabricate multi-materials molds although it cannot print overhang regions directly. Hybrid L-PBF/CNC milling pointed out the future direction for the fabrication of high dimensional-accuracy CC molds, although there is still a long way to reduce the cost and raise efficiency. CC molds are expected to substitute straight-drilled cooling molds in the future, as it can significantly improve part quality, raise production rate and reduce production cost. In addition to this, the use of CC channels can be expanded to some advanced products that require high-performance self-cooling, such as gas turbine engines, photoinjectors and gears, improving working conditions and extending lifetime

Thermo-mechanical Design Optimization of Conformal Cooling Channels using Design of Experiments Approach

Plastic injection molding is a versatile process and a major part of the present plastic manufacturing industry. Traditional die design is limited to straight (drilled) cooling channels, which don’t impart optimal thermal (or thermo-mechanical) performance. With the advent of additive manufacturing technology, design of injection molding tools with conformal cooling channels is now possible. The incorporation of conformal cooling channels can improve the thermal performance of an injection mold, though it may compromise the structural or mechanical stability of the mold. However, optimum conformal channels based on thermo-mechanical performance are not found in the literature. This paper proposes a design methodology to generate optimized design configurations of such channels in plastic injection molds. Design of experiments (DOEs) technique is used to study the effect of critical design parameters of conformal channels. In addition, a trade-off technique is utilized to obtain optimum design configurations of conformal cooling channels for “best” thermo-mechanical performance of a mold

A Thermomechanical Analysis of Conformal Cooling Channels in 3D Printed Plastic Injection Molds

Plastic injection molding is a versatile process, and a major part of the present plastic manufacturing industry. The traditional die design is limited to straight (drilled) cooling channels, which don't impart optimal thermal (or thermomechanical) performance. With the advent of additive manufacturing technology, injection molding tools with conformal cooling channels are now possible. However, optimum conformal channels based on thermomechanical performance are not found in the literature. This paper proposes a design methodology to generate optimized design configurations of such channels in plastic injection molds. The design of experiments (DOEs) technique is used to study the effect of the critical design parameters of conformal channels, as well as their cross-section geometries. In addition, designs for the "best" thermomechanical performance are identified. Finally, guidelines for selecting optimum design solutions given the plastic part thickness are provided

Design of additively manufacturable injection molds with conformal cooling

Additive manufacturing enables the production of intricate geometries including internal structures. This design freedom can be used advantageously to enhance heat transfer in injection molds by means of conformal cooling. The main goal is to reduce cycle times and to improve part quality through uniform cooling of the plastic products. This paper presents cooling design concepts for mold inserts. Their underlying approaches differ with respect to the shape and the cross-sectional geometries of cooling channels. Distinct inserts are additively manufactured by laser-based powder bed fusion (PBF-LB) of AISI 420 stainless steel. Experiments are carried out on a custom thermal test bench. Infrared thermography is used to examine the surface temperature, showing a reduction in cooling time by up to 41 % compared to conventional concepts. Additionally, the coolant flow is measured. The evaluation of the cooling characteristics reveal a critical trade-off between cycle time and uniformity of the surface temperature

The Deflection and Heat Transfer Analysis of Injection Mold Cavity with SLA Cooling Channel Insert

Fast cooling in injection molding is the critical in the process economy. Among many different cooling channel designs available, conformal cooling offers the best and the most efficient cooling. However, limited awareness, accessibility, complexity, cost, knowledge, and experience limit the use of conformal cooling channels to be used into the mold in a molding process. Typically, SLM(Selective Laser Melting) method is used to create cavity inserts with conformal cooling channels, however, due to the difficulties listed above, applications of conformal cooling channels are very limited. For an inexpensive alternative SLA (Stereolithography Apparatus) can print cavity inserts with conformal cooling channels. However, due to the material properties, use of SLA printing is very limited. To overcome this limitation, hybrid design of metal cavity inserts with SLA cooling channels has proposed. In order to validate proposed design can withstand harsh injection molding conditions, the Deflection and Heat Transfer Analysis of Injection Mold Cavity with Stereolithography (SLA) Cooling Channel are studied. A cup-like cavity geometry was created using SOLIDWORKS and Autodesk Adviser was used for a flow analysis. The cavity insert design was modified to accommodate an SLA conformal cooling channels inserts made from Formlabs SLA 3D printer. P20 tool steel and a FormLabs resin type Grey Pro V1 were selected for this experiment for the metal and plastic respectively. Simple calculation was used to estimate compressive and deflection at different injection pressures were calculated to determine workable injection pressure ranges for the selected core thickness that is structurally viable for injection molding conditions. The deflection and stress of core thickness of three selected samples, 5, 7.5, and 10mm, were calculated and compared to 456MPa of the P20 tool steel fatigue strength. 5mm core thickness failed and is not viable, 7.5mm and 10mm were able to accommodate a wide range of injection pressures of 27MPa and 45MPa estimated using Autodesk Advisor. Finally, the temperature differences of coolant were measured by a simple heat gain and heat loss experiment. The hot water was passed to the mold inlet, placed in ice-laden water, and routed back to the hot water reservoir. The temperature difference between the mold inlet and outlet was measured using an infrared temperature reader. Taguchi L12 orthogonal array was used for design of experiment (DOE). Two levels of diameter, the pitch of the cooling channels, and the core thickness were used. At the same time, the flow rates (laminar, transitional, and turbulent flow) and temperatures are varied (60, 70, and 80℃) to carry out the thermal analysis in the experiment setup. It showed that the higher the flow rate, the lower the cooling diameter, and the lower pitch, the better and the higher the thermal efficiency of the mold because it accounted for the largest heat removal rate about 1.59KJ. It confirmed the higher the flow rate, the higher the heat removal. The higher the core thickness, the lesser the heat removal. The maximum heat removal of 1.59KJ is recorded with 7.5mm core thickness, 8mm cooling diameter and 12mm pitch. The Deflection and Heat Transfer Analysis of Injection Mold Cavity with Stereolithography (SLA) Cooling Channel Insert justified a simple use of easily available SLA to generate conformal cooling for molding conditions and specify workable conditions adoptable for further usage. The cost is relatively cheap compared to a SLM produced part. There is a significant cost reduction up to four times when a hybrid design is adopted

Design, simulation and optimization of conformal cooling channels in injection molds: a review

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 do so. Some of the parameters that can be significantly improved by the use of CCC are cooling time, total injection time, uniform temperature distribution, thermal stress, warpage thickness. 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 review article focuses the main aspects related to the use of CCC’s in injection molding, as follows: Sect. 1 presents an introduction, which focuses on the most important facts about the topic of this paper. Section 2 presents a comparison between straight cooling channels and conformal cooling channels. In Sect. 3, the theoretical background of injection molding is presented. In Sects. 3 to 7, the manufacturing, design, simulation and optimization of CCC’s are presented, respectively. Section 7 is about coupled approaches, in which several systems, methods or techniques are used together for better efficiency.This research was supported by the Research Grant number POCI-01-0247-FEDER-024516, co-funded by the European Regional Development Fund,by the Operational Program "Competitiveness and Internationalization”, inthe scope of “Portugal 2020

Numerical Investigation of Conformal Cooling Channels in Injection Molds

To accommodate the increasing demand for consumer plastic products with higher quality and the industry’s desire for injection molding processes with higher production rate, metal 3D printing technologies have been introduced into the injection molding industry to fabricate cooling channels which can be placed more conformal to the working surface of the injection mold. These channels are referred to as conformal cooling channels. Since the manufacturing cost of mold-inserts with conformal cooling channels are higher than those with conventional cooling channels, it is necessary to confirm the advantage of using conformal cooling channels rather than conventional cooling channels. In this thesis, CFD simulations are used to compare the performances of a conventional cooling system and a conformal cooling system. The conformal cooling system is shown to have better cooling performance while not consuming more pumping power. Since the injection mold cooling system design is highly dependent on the geometry of the molded plastic part, it is difficult to construct general design guidelines for all conformal cooling channels. Therefore, commonly used conformal cooling systems that consist of U-shape bends are studied in this thesis. The influences of three geometrical design parameters, namely configuration of the U-shape bends, cooling channel depth from the heating surface and number of cooling channels, on the cooling performance are examined in a parametric study

Production of Injection Molding Tooling with Conformal Cooling Channels using The Three Dimensional Printing Process

Three Dimensional Printing is a desktop manufacturing process in which powdered materials are deposited in layers and selectively joined with binder from an ink-jet style printhead. Unbound powder is removed upon process completion, leaving a three dimensional part. Stainless steel injection molding inserts have been created from metal powder with the 3DP process. The freedom to create internal geometry by the use of the 3D-Printing process allows for the fabrication of molds with complex internal cooling passages. Tooling was developed with cooling channels designed to be conformal to the molding cavity. A finite difference simulation was constructed to study conformal channel design. A direct comparison of the mold surface temperature during the injection cycle of a 3D Printed mold with conformal channels and a mold machined with conventional straight channels was completed. The conformal passages produced with the 3DP process provide the ability to accurately control the temperature of the molding cavity throughout the process cycle. Surface temperature measurements demonstrated that the inserts with conformal cooling channels exhibited a more uniform surface temperature than the inserts machined with straight channels. Issues such as powder removal and post processing of green parts with small cooling channels were investigated.Mechanical Engineerin

Enhancing Thermal Simulations for Prototype Molds

Our goal was the thermal analysis of epoxy acrylate-based prototype molds with numerical simulations, and to compare and analyze the measured values and calculated results. The difference between the thermal calculations and the measured values is significant; the actual temperature of the mold is higher than the calculated values. Based on the numerical simulations, we found that in the case of epoxy acrylate-based mold inserts, temperature results can be made significantly more accurate by changing the heat transfer coefficient between the surface of the mold insert and the melt. We proved that in the case of small-series epoxy acrylate-based molds, the temperature dependence of the thermal properties of the mold material, and the temperature and pressure dependence of the heat transfer coefficient need to be taken into account for accurate temperature results. We proved that the heat transfer coefficient between the mold surface and the melt is considerably lower than in the case of metal molds, due to lower cavity pressure and a lower temperature difference between the mold surface and the melt

Development of Novel Low-Cost Rapid Tooling Solution by Incorporating Fused Deposition Modeling Sacrificial Patterns

Injection molding and additive manufacturing (3D-printing) are two manufacturing solutions that are suitable to produce plastic components. The material extrusion-based additive manufacturing (AM) process deposits beads side by side through an extrusion to build prototypes. This process is capable of manufacturing complex geometries, but it is very expensive and slow. As a result, it is not the best solution for manufacturing low to medium (10-5000) production volumes. Additionally, there are limited materials for AM as compared to injection molding. Injection molding process is very fast, reliable, and low-cost to produce thousands of a single product in a short time. However, the initial investment for building the mold is very high and it may take up to several weeks to manufacture a good quality mold. To cover the gap between these two processes, a low-cost tooling solution with a reduced build time has been developed that is suitable for low to medium production. Internal features are integrated within the tooling to investigate the possibility of building internal channels that can later be optimized to improve the cooling efficiency of the tool. The developed tooling solution was designed for a hands-free door handle. Design for manufacturing (DfM) strategies were applied to the initial CAD design to make it suitable for an injection molding process. Finite element analysis (FEA) and injection molding simulations were used to conduct virtual studies on this low-cost tooling solution. To create the internal features, soluble material (SR-30 developed by Stratasys) was used and Aremco 805 epoxy was cast to create the mold cavities. After curing the epoxy, the soluble patterns were dissolved to create the final mold. The developed tooling was able to manufacture the J-hook with a dimensional precision of approximately 1% - 3% of the desired geometries. Additionally, no sink mark or shrinkage was observed on the surfaces of the final product. Most importantly, the cost of the solution was kept under 500 CAD dollars and complex internal features were built without any additional support structure on the inside. Build time of the J-hook was reduced from 3 hours to less than 2 minutes and most importantly, the piece price of each J-hook was lowered by more than 44 CAD dollars per piece