A Thermomechanical Analysis of Conformal Cooling Channels in 3D Printed Plastic Injection Molds
01 Dec 2018-
TL;DR: In this article, the authors proposed a design methodology to generate optimized design configurations of conformal cooling channels in plastic injection molds, and the design of experiments (DOEs) technique was used to study the effect of the critical design parameters of conformally channels, as well as their cross-section geometries.
Abstract: 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.
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TL;DR: Conformal cooling (CC) channels as discussed by the authors are a series of cooling channels that are equidistant from the mold cavity surfaces, they can provide more uniform and efficient cooling effects and thus improve the production quality and efficiency significantly.
68 citations
TL;DR: In this article, a finite element analysis is combined with a gradient-based algorithm and robust genetic algorithm to determine the optimum layout of cooling channels to reduce the surface temperature difference of the melt, ejection, and warpage.
Abstract: Plastic lenses are light and can be mass-produced. Large-diameter aspheric plastic lenses play a substantial role in the optical industry. Injection molding is a popular technology for plastic optical manufacturing because it can achieve a high production rate. Highly efficient cooling channels are required for obtaining a uniform temperature distribution in mold cavities. With the recent advent of laser additive manufacturing, highly efficient three-dimensional spiral channels can be realized for conformal cooling technique. However, the design of conformal cooling channels is very complex and requires optimization analyses. In this study, finite element analysis is combined with a gradient-based algorithm and robust genetic algorithm to determine the optimum layout of cooling channels. According to the simulation results, the use of conformal cooling channels can reduce the surface temperature difference of the melt, ejection time, and warpage. Moreover, the optimal process parameters (such as melt temperature, mold temperature, filling time, and packing time) obtained from the design of experiments improved the fringe pattern and eliminated the local variation of birefringence. Thus, this study indicates how the optical properties of plastic lenses can be improved. The major contribution of present proposed methods can be applied to a mold core containing the conformal cooling channels by metal additive manufacturing.
23 citations
TL;DR: The algorithm surpassed the current state of the art since it uses as input variables firstly the discrete map of temperatures of the melt plastic flow at the end of the filling phase, and secondly a set of geometrical parameters extracted from the discrete mesh together with technological and functional requirements of cooling in injection molds.
Abstract: This paper presents a new method for the automated design of the conformal cooling system for injection molding technology based on a discrete multidimensional model of the plastic part. The algorithm surpasses the current state of the art since it uses as input variables firstly the discrete map of temperatures of the melt plastic flow at the end of the filling phase, and secondly a set of geometrical parameters extracted from the discrete mesh together with technological and functional requirements of cooling in injection molds. In the first phase, the algorithm groups and classifies the discrete temperature of the nodes at the end of the filling phase in geometrical areas called temperature clusters. The topological and rheological information of the clusters along with the geometrical and manufacturing information of the surface mesh remains stored in a multidimensional discrete model of the plastic part. Taking advantage of using genetic evolutionary algorithms and by applying a physical model linked to the cluster specifications the proposed algorithm automatically designs and dimensions all the parameters required for the conformal cooling system. The method presented improves on any conventional cooling system design model since the cooling times obtained are analogous to the cooling times of analytical models, including boundary conditions and ideal solutions not exceeding 5% of relative error in the cases analyzed. The final quality of the plastic parts after the cooling phase meets the minimum criteria and requirements established by the injection industry. As an additional advantage the proposed algorithm allows the validation and dimensioning of the injection mold cooling system automatically, without requiring experienced mold designers with extensive skills in manual computing.
23 citations
TL;DR: Here, the cooling inserts of high production steel moulds utilized to manufacture ribs for swimming pool sinks’ plastic cages are redesigned, simulated and manufactured, taking advantage of Selective Laser Melting possibilities and without modifying the geometry of the obtained parts, thus leading to important savings of time and some global costs in the production outcomes.
Abstract: Moulding technologies are remarkably effective for parts requiring high production volumes. Yet cooling the moulds after each injection can cause a significant loss of time. A possibility for reducing the cooling times is to use cooling inserts and conformal cooling strategies. In the present case, the original inserts of a mould must be substituted because the original material cannot be utilized anymore (toxicity). Will it be technically feasible to achieve a proper cooling only by modifying the inserts? Here, the cooling inserts of high production steel moulds utilized to manufacture ribs for swimming pool sinks' plastic cages are redesigned, simulated and manufactured, taking advantage of Selective Laser Melting possibilities and without modifying the geometry of the obtained parts, nor the rest of the moulds. The results reveal a reduction in the mould cooling times of up to 8%, while maintaining the same conformation properties, thus leading to important savings of time and some global costs in the production outcomes. The study also benchmarks the production economic limits of this approach compared to other possible strategies, such as the development of full new conformal cooling moulds or the industrial production of the parts with plastic additive manufacturing (multi jet fusion) technology.
13 citations
24 Oct 2020
TL;DR: In this paper, an additively manufactured mold insert with conformal cooling channels by means of selective laser melting (SLM) with the aim to reduce process cycles is presented. But, the results of the numerical analyses are compared with experimental 3D geometrical data of the additively constructed mold insert.
Abstract: Injection moulding is one the most familiar processes for manufacturing of plastic parts by injecting molten thermoplastic polymers into a metallic mould. The cycle time of this process consists of the phases of injection, packing, cooling, and ejection of the final product. Shortening of cycle time is a key consideration to increase productivity. Therefore, in this manuscript the adoption of additively manufactured mould inserts with conformal cooling channels by means of selective laser melting (SLM) with the aim to reduce process cycles is presented. The design and manufacture of a mould insert with conformal cooling channels for producing pressure fitting thermoplastic parts is described. Numerical analysis of the injection process and simulation of shape distortions after SLM were conducted providing useful results for the design and manufacture of the mould insert. The results of the numerical analyses are compared with experimental 3D geometrical data of the additively manufactured mould insert. Temperature measurements during the real injection moulding process demonstrating promising findings. The adoption of the introduced method for the series production of injection moulded thermoplastics proves a shortening of cycle times of up to 32% and a final product shape quality improvement of up to 77% when using mould inserts with conformal cooling channels over the conventional mould inserts.
11 citations
References
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Book•
30 Nov 1985
TL;DR: Injection molding has been studied extensively in the literature as discussed by the authors, including the complete Injection Molding Process (IMP) and a detailed overview of the main steps of the process.
Abstract: Preface. 1. The Complete Injection Molding Process. 2. Injection Molding Machine. 3. Plasticizing. 4. Molds to Products. 5. Fundamentals of Designing Products. 6. Molding Materials. 7. Process Control. 8. Design Features that Influence Product Performances. 9. Computer Operations. 10. Auxiliary Equipment and Secondary Operations. 11. Troubleshooting and Maintenance. 12. Testing, Inspection, and Quality Control. 13. Statistical Process Control and Quality Control. 14. Costing, Economics, Management. 15. Specialized Injection Molding Processes. 16. Injection Molding Competitive. 17. Summary. Appendices. References.
693 citations
TL;DR: In this paper, a tooling set was created to mold a split ring shape and conformal cooling channels were placed in both the cavity and core sides of the tool, and a 2D finite difference model accurately captured the observed temperature histories of the mold.
Abstract: A Solid Freeform Fabrication Process called Three Dimensional Printing is applied to the fabrication of injection molding tooling with cooling channels which are conformal to the molding cavity. The tool is created by spreading layers of stainless steel powder and selectviely joining the powder in the layers by ink-jet printing of a binder material. Unbound powder is removed from without and within the green part thus defined. The green part is sintered and infiltrated with a copper alloy to produce a fully dense tool. The infiltrant is kept out of the cooling channels by elevating the tool above the free surface of the pool of infiltrant in the crucible, thus creating a controlled negative pressure within the infiltrant. An upper limit to the separation of tooling cavity and cooling channel was derived based on transient heat transfer considerations. A tooling set was created to mold a split ring shape and conformal cooling channels were placed in both the cavity and core sides of the tool. The performance of this tool was compared against the performance of a tooling set with straight cooling channels. Thermocouples buried in the core and cavity showed that the conformal tool had no period of transient behavior at the start of molding, while the tool with straight channels took 10–15 cycles to come to an equilibrium temperature some 40°C above the temperature of the coolant. The conformal tool was also found to maintain a more uniform temperature within the tool during an individual molding cycle. The gap in the molded split rings did not change from cycle to cycle with the conformal tool, while it did with the conventional tool. A 2-D finite difference model accurately captured the observed temperature histories of the mold with conformal cooling channels.
265 citations
TL;DR: In this article, an optimum and efficient design for conformal cooling/heating channels in the configuration of an injection molding tool using FEA and thermal heat transfer analysis is presented.
214 citations
TL;DR: In this article, a modular approach to the design of conformal cooling channels is presented, where the tool is divided into geometric regions and a channel system is designed for each region.
Abstract: Solid Freeform Fabrication technologies have demonstrated the potential to produce tooling with cooling channels, which are conformal to the molding cavity. 3D Printed tools with conformal cooling channels have demonstrated simultaneous improvements in production rate and part quality as compared with conventional production tools. Conformal cooling lines of high performance and high complexity can be created, thus presenting a challenge to the tooling designer. A systematic, modular approach to the design of conformal cooling channels is presented. Cooling is local to the surface of the tool, so the tool is divided into geometric regions and a channel system is designed for each region. Each channel system is itself modeled as composed of cooling elements, typically the region spanned by two channels. Six criteria are applied, including: a transient heat transfer condition, which dictates a maximum distance from mold surface to cooling channel; considerations of pressure and temperature drop along the flow channel; and considerations of the strength of the mold. These criteria are treated as constraints, and successful designs are sought that define windows bounded by these constraints. The methodology is demonstrated through application to a complex core and cavity for injection molding.
166 citations
TL;DR: An automatic method for designing conformal cooling circuits, which is an essential component that directly affects the quality and timing for products fabricated by rapid tooling, is presented.
Abstract: This paper presents an automatic method for designing conformal cooling circuits, which is an essential component that directly affects the quality and timing for products fabricated by rapid tooling. To reduce the time of cooling and to control the uniformity of temperature and volumetric shrinkage, industry expects to have cooling channels that are conformal to the shape of the products. We achieve the goal of automatically designing such conformal cooling circuits in a twofold manner. First, the relationship between the conformal cooling and the geometry shape of cooling circuit is formulated. Based on that, we investigate a geometric modeling algorithm to design a cooling circuit approaching conformal cooling. Simulations have been made to verify the advantage of the cooling circuit generated by our algorithm.
131 citations