Automatic layout design of plastic injection mould cooling system

doi:10.1016/j.cad.2004.08.003

Computer-Aided Design

Volume 37, Issue 7, June 2005, Pages 645-662

https://doi.org/10.1016/j.cad.2004.08.003 Get rights and content

Abstract

This research extends our previous investigation of the automation of the preliminary design stage to the layout design stage of the cooling system design process. While the functional aspects of the cooling system are considered during the preliminary design stage, the layout design stage addresses both the functionality and manufacturability of the design. A graph structure is devised to capture a given preliminary design and a graph traversal algorithm is developed to generate candidate cooling circuits from the graph structure. Heuristic search is employed to develop the cooling circuits into the layout designs by generation of tentative manufacturing plans. A framework for fuzzy evaluation of the layout designs is developed to rate the various design alternatives generated. An experimental system is implemented to verify the feasibility of the approach, and examples generated from the system are presented to illustrate the major steps of the automatic design process.

Introduction

The function of the cooling system of a plastic injection mould is to provide thermal regulation in the injection moulding process. When the hot plastic melt enters into the mould impression, it cools down and solidifies by dissipating heat through the cooling system. As the cooling phase generally accounts for about two-thirds of the total cycle time of the injection moulding process, efficient cooling is very important to the productivity of the process. The cooling system also plays an important role in the product quality. A cooling system that provides uniform cooling across the entire part ensures product quality by preventing differential shrinkage, internal stresses, and mould release problems. In addition to the functional aspects, the design of a cooling system should also consider the manufacturability of the system to control the cost of mould construction.

The process of cooling system design is a complicated process and can be distinguished into three phases: preliminary design, layout design, and detail design. Although, CAD/CAM systems are widely used in the design of injection moulds, they are mainly limited to providing geometric modeling tools in the detail design phase. Specialized stand-alone or add-on software packages that provide interactive geometric modeling tools for designing various components or sub-systems of the mould structure are also commercially available. However, limited research works on automation tools that can play a more active role in the preliminary and layout design phases have been reported. In a previous research project, we developed a feature-based method which creates the preliminary design automatically [1], [2]. Given a plastic part with a complex shape, the feature-based method decomposes the part into simpler shape features, called cooling features. Cooling sub-circuits are then generated automatically to provide the required cooling function for each recognized feature. In the present research, automation in the design process is extended to the layout design phase. Techniques are developed which generate the layout design automatically from the preliminary design by considering both the functional and manufacturing aspects of the cooling system.

Section snippets

Related work

There are four major areas of research related to plastic injection mould cooling system, namely, computer-aided engineering (CAE) analysis, design optimization, new fabrication technology, and automatic design synthesis. Most of the early research work [[3], [4], [5], [6], [7]] focused on CAE analysis. After more than two decades of extensive research, commercial CAE packages such as MOLDFLOW and Moldex3D are now widely used in practice to analyze a given design. These CAE methods predict the

Overview of the method

In the preliminary design stage, the major issue to be addressed is the functional requirement, that is, the cooling requirement, of a given plastic part. The preliminary design specifies the type (e.g. U-circuit, parallel channels, bubblers, cooling towers, etc.), size (e.g. channel length and diameter), and the approximate locations of the cooling elements that form the cooling sub-circuits. Each sub-circuit provides the cooling function that carries away the heat from a region of the part.

Graph representation and operation on the preliminary design

Given a preliminary cooling system design in the form of a set of sub-circuits consisting of various type of cooling elements, a basic problem in generating the layout design is to identity appropriate connections within the sub-circuits (e.g. the interconnections between a set of parallel channels) and between adjacent sub-circuits (e.g. the connection between two U-circuits in two adjacent layers) so that they can be connected to form a complete cooling circuit. A graph-based technique is

Generation of candidate cooling circuits

To find the candidate cooling circuits from the connected graph G obtained from the previous step, an inlet is first selected among the nodes in G. Heuristics can be devised for this selection according to the specific requirement of a particular moulding condition. A simple heuristic that corresponds to a common practice in cooling system design is to select the node that is closest to the gate position. Starting from the selected inlet node, a set of simple paths is obtained from G by

Generation of layout designs

Given a candidate cooling circuit, the next task is to generate the layout design by developing a tentative manufacturing plan that (i) produces the cooling circuit in the mould insert, and (ii) connects the inlet and outlet of the circuit through the mould base to the side walls of the mould base. Fig. 5(a) shows a simple circuit and the mould insert. Fig. 5(b) shows the holes drilled in the mould insert that realize the circuit. Each channel in the circuit is formed by drilling a hole from a

Fuzzy evaluation of layout designs

A candidate layout design is evaluated from three major aspects, namely, cooling performance, manufacturability, and the structural strength of the mould insert. The rating I_R of a layout design is given by $I_{R} = (w_{c} \otimes I_{c}) \oplus (w_{m} \otimes I_{m}) \oplus (w_{s} \otimes I_{s})$

This is a fuzzy weighted average [21], [22] of the cooling performance index I_c, the manufacturability index I_m, and the structural strength index I_s. The operators ⊕ and ⊗ represent fuzzy extended addition and multiplication. The weighting factors w's are fuzzy

Implementation and design example

To verify the feasibility of the proposed layout design process, an experimental system has been developed using C++ and is interfaced to the Unigraphics II CAD/CAM system. A design example is given in Fig. 13 to illustrate the major steps of the design process taken by the system. To simplify the illustration, only the cooling system in the core half is shown. Fig. 13(a) shows the input to the system, which is a preliminary design of the cooling system of an example part. Fig. 13(b) shows the

Conclusion and further work

Automation in the layout design of cooling systems for plastic injection moulds has been achieved in this research work. The automatic design process is formulated as a heuristic search process, whereby design alternatives are explored within a search space until a satisfactory design is obtained. A major issue in this research is the generation of candidate cooling circuits. This is achieved by devising a graph structure to capture a given preliminary design, and modification of the graph to

Acknowledgements

The work described in this paper was fully supported by a Strategic Research Grant from City University of Hong Kong (Project No. 7001348).

C.L. Li is an assistant professor in the Department of Manufacturing Engineering and Engineering Management, the City University of Hong Kong, Hong Kong. He received a BSc (Eng) in Mechanical Engineering from the University of Hong Kong in 1985, a MSc degree from Warwick University, UK, in 1987 and a PhD degree from the University of Hong Kong in 1998. He had five years of industrial experience in CAD/CAM applications and development before he joined the City University. His research interest

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Cited by (48)

Design and fabrication of conformal cooling channels in molds: Review and progress updates
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Citation Excerpt :
Also, it is found that the proper topological design could result in a higher cooling efficiency even if molds with a lower heat conductivity are used [20]. In addition to a proper design to meet the requirement of cooling performance, there is an equally important concern pertaining to the CC channel system, namely its manufacturability [66]. Due to the complex 3D internal structures that are characteristic of optimal CC designs, it's impossible to machine CC channels using conventional mechanical cutting methods (subtractive manufacturing).
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 laser powder bed fusion (L-PBF) show the best applicability to aluminum (Al)-epoxy molds and metal molds, respectively, because of the high forming flexibility and fidelity. Meanwhile, laser powder deposition (LPD) has an exclusive advantage to fabricate multi-materials molds although it cannot print overhang regions directly. Hybrid L-PBF/computer-numerical-control (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.
A new method for the automated design of cooling systems in injection molds
2018, CAD Computer Aided Design
This paper presents a new method for the automatic design of the cooling system in injection molds, based on the discrete geometry of the plastic part. In a first phase the new algorithm recognizes the discrete topology of the part, obtaining its depth map and detecting flat, concave regions and slender details which are difficult to cool. The algorithm performs an automatic analysis of the heat transfer, taking into account functional parameters, in order to guarantee a uniform cooling of the part. Based firstly on the limit range distance from which the horizontal straight channels lose cooling effectiveness and secondly on the depth map data, the algorithm provides an optimal layout for the cooling system of the part by adapting it to its geometry. By means of adapting the precision of the algorithm to the molded geometry, both horizontal straight channels for low concavity areas and baffle matrices for concave regions are used. In a second phase, the parameters of the cooling system such as channel diameter, channel separation, etc., are dimensioned by means of genetic optimization algorithms. A second genetic optimization algorithm ensures uniformity and balance in the layout of the cooling system for the plastic part. The result is the design of the cooling system for the plastic part with the same performance as the conformal system. A constant distance between the cooling channels and the part surface is maintained, and at the same time the manufacturing of the mold using CNC techniques and traditional metal materials could be achieved. Complementarily, the algorithm performs an interference analysis with other parts of the mold such as the ejection system. The method does not need a subsequent CAE analysis since it takes into account functional and technical parameters related to heat transfer in its design, thus ensuring its functionality. The algorithm is independent of the CAD modeler used to create the part since it performs a recognition analysis of the part surfaces, being able to be implemented in any CAD system. The data obtained in the design can be used additionally in later applications including the automated design of the injection mold.
Thermo-mechanical Design Optimization of Conformal Cooling Channels using Design of Experiments Approach
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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.
Optimal design of longitudinal conformal cooling channels in hot stamping tools
2016, Applied Thermal Engineering
Citation Excerpt :
Agazzi et al. [18] developed a robust methodology based on morphological surfaces to design a high efficiency cooling system. Li et al. [19–23] continuously put forward different mathematical methods, to name just a few, feature-based approach, graph traversal algorithm, part segmentation by superquadric fitting, configuration space method and C-space method to automatically search for the optimal cooling layout of injection mold. Wang et al. [24] also developed a program for the automating conformal cooling design in the basis of centroidal Voronoi diagram and geometric modeling algorithm.
A new longitudinal CCC (conformal cooling channels) design in a B-pillar tool is proposed in this study. Three kinds of design parameters, the radius (Rad) of cooling channels, the distance (H) from channel center to tool work surface and the ratio (rat) of each channel center, are defined in a parameterized CAD model with the new design. For optimizing the layout of the longitudinal CCC which is determined by the above design parameters, an integrated process established by multiple software platforms based on the response surface methodology and multi-objective optimization is put forward. A design matrix with 17 factors and 50 levels is generated through OLH (optimal Latin hypercube) method. The average temperature and temperature deviation of work surface are used to evaluate the cooling performance. Quadratic response surface models are established to describe the relationship between design parameters and evaluation objectives. The accuracy of fitting models is checked by error analysis. The layout of the longitudinal CCC is optimized to find the Pareto-optimal frontier which consists of some optimal combinations of design parameters. Besides, the influence of initial design is discussed and a novel manufacture method of hot stamping tools with longitudinal CCC is briefly introduced.
Thermal simulations and measurements for rapid tool inserts in injection molding applications
2015, Applied Thermal Engineering
Citation Excerpt :
Lin [15] developed a neural network method to optimize the injection mold cooling systems. Li et al. developed [16] and improved [17] an automatic method to design conventional cooling systems. Wang et al. [18] presented an automatic process for designing conformal cooling circuits.
Rapid prototyping (RP) is a widely used process in the industry to shorten development time. Another advantage of this technology is the ability to create conformal cooling systems, thus not only cooling time and cycle time can be shortened, but also shrinkage, thus warpage can be decreased. The main disadvantage of Rapid prototyping materials is their low thermal conductivity, which strongly influences cooling properties and warpage.
The research based on a special developed injection mold for novel rapid prototyping based mold inserts with cooling systems. A method has been introduced to determine the most important thermal parameters for injection molding simulations using rapid tools. Those parameters, which can be measured such as the specific heat and thermal conductivity of the mold materials, are directly implemented into the software. The heat transfer coefficient between the polymer melt and the rapid tool insert surface cannot be measured in a reasonable way, thus simulation software was used to determine that based on indirect calculation derived from real measurements. In the paper, the method was proved with Fused Deposition Modeling (FDM) and Polyjet mold inserts.
Performance evaluation of a software engineering tool for automated design of cooling systems in injection moulding
2013, Procedia CIRP
This paper presents a software tool for automating the design of cooling systems for injection moulding and a validation of its performance. Cooling system designs were automatically generated by the proposed software tool and by applying a best practice tool engineering design approach. The two different design methods (i.e. automatic and manual) were applied to the mould design of two thin-walled products, namely a rectangular flat box and a cylindrical container with a flat base. Injection moulding process simulations based on the finite element method were performed to assess the quality of the moulded parts. Results indicate the tool is capable of generating feasible cooling solutions. Recommendations are provided for improving the performance of the tool.

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C.G. Li is a PhD student in the Department of Manufacturing Engineering and Engineering Management, the City University of Hong Kong. He received a BSc (Eng) in Mining Machinery from JiLin Industrial University in China in 1992, a MSc (Eng) in Machinery Manufacturing from Zhejiang University in China in 1995. He had eight years of industrial experience in CAD/CAM applications and communication equipment manufacturing before he studied in the City University of Hong Kong. His research interests include intelligent CAD/CAM systems and plastic injection mould design automation.

A.C.K. Mok received his BSc degree in Production Engineering from the University of Aston in Birmingham in England in 1979. He is now a Chartered Engineer and holding memberships in the Institution of Electric Engineers in UK and the Hong Kong Institution of Engineers. He started his job as a production engineer and worked up to the post of engineering manager in one of the largest manufacturers in Hong Kong from 1980 to 1988, specializing in new product development and tool design. He obtained his MPhil from the City University of Hong Kong in 1996. He is currently an assistant professor in the Department of Manufacturing Engineering and Engineering Management of the City University of Hong Kong.

View full text

Automatic layout design of plastic injection mould cooling system

Abstract

Introduction

Section snippets

Related work

Overview of the method

Graph representation and operation on the preliminary design

Generation of candidate cooling circuits

Generation of layout designs

Fuzzy evaluation of layout designs

Implementation and design example

Conclusion and further work

Acknowledgements

Comput Aided Des

Comput Aided Des

Eng Appl Artif Intell

Comput Aided Des

Fuzzy Sets Syst

Fuzzy Sets Syst

CAE of mold cooling in injection molding using a three-dimensional numerical simulation

Trans ASME J Eng Ind