Multi-objective optimization of gate location and processing conditions in injection molding using MOEAs: experimental assessment

The definition of the gate location in injection molding is one of the most important factors in achieving dimensionally accuracy of the parts. This paper presents an optimization methodology for addressing this problem based on a Multi-objective Evolutionary Algorithm (MOEA). The algorithm adopted here is named Reduced Pareto Set Genetic Algorithm (RPSGA) and was used to create a balanced filling pattern using weld line characterization. The optimization approach proposed in this paper is an integration of evolutionary algorithms with Computer-Aided Engineering (CAE) software (Autodesk Moldflow Plastics software). The performance of the proposed optimization methodology was illustrated with an example consisting in the injection of a rectangular part with a non-symmetrical hole. The numerical results were experimentally assessed. Physical meaning was obtained which guaranteed a successful process optimization.This work was supported by the Portuguese Fundação para a Ciência e Tecnologia under grant SFRH/BD/28479/2006 and IPC/I3N – Institute for Polymers and Composites, University of Minho.info:eu-repo/semantics/publishedVersio

Design with Concurrent Approach: Development and Flow Analysis of Injection Mould Tool for Computer Monitor Lamp Holder

The plastic product manufacturing industry has been growing rapidly in recent years. One of the most popular processes for making plastic parts is injection moluding. The design of injection mould is critically important to product quality and efficient product processing. Mould-making companies, who wish to maintain the competitive edge, desire to shorten both design and manufacturing leading times by applying a systematic mould design process. The mould industry is an important support industry during the product development process, serving as an important link between the product designer and manufacturer. Product development has changed from the traditional serial process of design, followed by manufacture, to a more organized concurrent process where design and manufacture are considered at a very early stage of design. The research presents the basic structure of two plate injection mould design, injection moulding machine selection, process analysis of the injection mould design using mould flow analysis to optimize the mould cost in the design stage. This injection mould design system covers both the mould design process and mould knowledge management. In this work, CAE tools have been used in the design stage to reduce the losses to obtain the shortened lead time, high quality and achieving low cost of the mould. The design of an injection process involves the simultaneous consideration of plastic part design, mould design and injection moulding machine selection, production  scheduling and cost as early as possible in the design stage. The result indicated that conventional method will consume more time and also increases the cost of machining and delay in dispatching the product. If change in design happens before pre-production and after production by trial and error method then there will be a drastic increase in design change cost which effects on cycle time, waste of raw material, increase in process time and wastage of labour cost. These entire draw backs are eliminated by using computer aided design and computer aided engineering  technology for mould design and manufactured in very short period of time with minimum cost. The future scope of work is to include cooling, warpage and fatigue analysis to optimize tool design and tool life

In-Mold Assembly of Multi-Functional Structures

Combining the recent advances in injection moldable polymer composites with the multi-material molding techniques enable fabrication of multi-functional structures to serve multiple functions (e.g., carry load, support motion, dissipate heat, store energy). Current in-mold assembly methods, however, cannot be simply scaled to create structures with miniature features, as the process conditions and the assembly failure modes change with the feature size. This dissertation identifies and addresses the issues associated with the in-mold assembly of multi-functional structures with miniature components. First, the functional capability of embedding actuators is developed. As a part of this effort, computational modeling methods are developed to assess the functionality of the structure with respect to the material properties, process parameters and the heat source. Using these models, the effective material thermal conductivity required to dissipate the heat generated by the embedded small scale actuator is identified. Also, the influence of the fiber orientation on the heat dissipation performance is characterized. Finally, models for integrated product and process design are presented to ensure the miniature actuator survivability during embedding process. The second functional capability developed as a part of this dissertation is the in-mold assembly of multi-material structures capable of motion and load transfer, such as mechanisms with compliant hinges. The necessary hinge and link design features are identified. The shapes and orientations of these features are analyzed with respect to their functionality, mutual dependencies, and the process cost. The parametric model of the interface design is developed. This model is used to minimize both the final assembly weight and the mold complexity as the process cost measure. Also, to minimize the manufacturing waste and the risk of assembly failure due to unbalanced mold filling, the design optimization of runner systems used in multi-cavity molds for in-mold assembly is developed. The complete optimization model is characterized and formulated. The best method to solve the runner optimization problem is identified. To demonstrate the applicability of the tools developed in this dissertation towards the miniaturization of robotic devices, a case study of a novel miniature air vehicle drive mechanism is presented

Analysis of the Effect of Sequential Injection Molding on Weld Lines Properties

This study analyzes a sequential injection molding process to improve weld lines properties and morphology using in-flow phenomena. varioterm technology has been applied and the combination of these techniques led to significant improvements on mechanical properties and weld line appearance. Fiber orientation has been improved and the interfacial bonding at weld line surface has been promoted, resulting in better local properties. weld line skin marks could possibly be eliminated

Optimization of the injection moulding process: from polymer plasticating to final part properties

Tese de doutoramento em Science and Polymer Engineering and CompositesRecently several scientific studies on the injection moulding process have addressed the establishment of relationships between the thermomechanical, the material morphology and the resultant moulding’s mechanical behavior. However, the absence of a link between the plasticating and filling phases of the process is evident in several studies. But the final conditions (e.g., thermal, homogenization) gathered in the plasticating phase are the initial conditions for the following ones, which can determine the moulded product properties and quality. The main objective of this work is to integrate the plasticating and filling and postfilling phases in order to develop computational tools able to optimize automatically the injection moulding process. Therefore, will be possible the optimization of the injection moulding process through the application of multi-objective evolutionary algorithms based methodology. Simultaneously, the establishment of relationships between the processing conditions, the thermomechanical environment, the induced morphology and the mechanical properties allow the optimization of the performance of injection moulded parts.Recentemente vários trabalhos científicos sobre o processo de injeção têm estabelecido relações entre a termomecânica do material, a sua morfologia e o comportamento mecânico da moldação. No entanto, é evidente em diversos estudos a ausência de uma ligação entre as fases de plasticização e enchimento da moldação. No entanto, as condições finais (por exemplo, térmicas, uniformização do material) obtidas na fase de plasticização são as condições iniciais das fases seguintes, determinando assim as propriedades e a qualidade do produto final. O objectivo principal deste trabalho é a integração das fases de plasticização, enchimento e pós-enchimento do processo de moldação por injeção com vista ao desenvolvimento de ferramentas computacionais capazes de otimizar o processo automaticamente. Assim, será possível a otimização das condições operatórias através do desenvolvimento de uma metodologia baseada em algoritmos evolutivos multi-objetivo. Simultâneamente, será possível estabelecer relações entre as condições de processamento, o ambiente termomecânico, a morfologia induzida no material e as propriedades mecânicas de forma a otimizar as caraterísticas finais das peças

Mechanical design of hybrid moulds: mechanical and thermal performance implications

Tese de doutoramento em Ciência e Engenharia de PolímerosThe design and manufacture of injection moulds are the most time-consuming phases in the development of new plastics products. In the last two decades the advances in rapid prototyping and manufacturing technologies made possible the use of materials alternative to steel in some mould components. The integration of these components with conventional mould structures originated to the concept of hybrid mould. This alternative design solution aimed at satisfying the need for deployment of short series of new products more quickly and at competitive prices. This research work investigates the influence of materials used in moulding blocks of hybrid moulds in the mould performance, namely, reproducibility, operation regimes, thermal and mechanical issues. Furthermore it was analysed the effect on the definition of the more adequate processing conditions and the moulding properties. The study was based on tri-dimensional objects: a tubular cylindrical part and a more geometrically complex support box. The tube was produced in an existing simple instrumented hybrid mould and the support box was produced in a reusable and flexible hybrid mould. The latter was designed and manufactured in the context of this research work. The performance of the hybrid moulds was evaluated by comparing various combinations of moulding blocks (cavity and core) produced in alternative materials with the standard steel solution when injection moulding polypropylene. The comparison was based on the observation of the morphology structure of the mouldings, the thermal performance, the moulding shrinkage and the structural performance of the mould. The moulds were instrumented with pressure and temperature sensors and a load cell for monitoring the ejection force needed on a moulding pin incorporated in the lateral movement of the support box. The prediction of the moulding performance of the moulds was done using the injection moulding software Moldex3D. The mechanical performance of the components in alternative materials was done with the structural analysis software ANSYS Workbench. The results show the importance of predicting the mould regime temperature when establishing the appropriate processing conditions when softer materials are used in the moulding blocks. It was concluded that in the design of hybrid moulds it is necessary to consider the deformation of the moulding blocks that are caused by the pressure field during injection. This is critical to predict the shrinkage and the final dimensions of the mouldings.O projecto e o fabrico de moldes de injecção para plásticos ocupam um longo período de tempo no desenvolvimento de novos produtos. Nas duas últimas décadas os avanços das tecnologias de prototipagem e de fabrico rápido tornaram possível o uso de materiais metálicos alternativos e de resinas sintéticas em alguns componentes do molde. A inserção destes em estruturas convencionais deu origem ao conceito de molde híbrido. Esta solução alternativa procurou satisfazer a necessidade de colocar pequenas séries de novos produtos no mercado mais rapidamente e com preços competitivos. Este trabalho de investigação explora, essencialmente, a influência dos materiais usados nos blocos moldantes de moldes híbridos no desempenho do molde (ex. reprodutibilidade, regimes de funcionamento, aspectos térmicos e mecânicos). Também se estudou a sua influência no estabelecimento das condições processamento mais adequadas e nas propriedades das peças moldadas. Estudaram-se duas peças de geometria tridimensional: uma peça tubular e uma caixa-suporte com detalhes complexos. O tubo circular foi produzido num molde híbrido simples e já existente e a caixa-suporte num molde híbrido flexível e reutilizável. O segundo molde foi especificamente projectado e fabricado no âmbito deste trabalho de investigação. O desempenho dos moldes híbridos foi avaliado comparando o efeito de várias combinações de materiais alternativos nos blocos moldantes (bucha e cavidade) com a sua versão convencional em aço, na moldação de polipropileno. A comparação contemplou a observação da estrutura morfológica, o desempenho térmico, a contracção das moldações e o desempenho estrutural do molde. Os moldes foram instrumentados com sensores de pressão e temperatura e com uma célula de carga para medir a força de extracção de um pino moldante incorporado num movimento lateral da caixa-suporte. Utilizaram-se softwares de simulação do processo de moldação por injecção (Moldex3D) e estrutural (ANSYS Workbench) na previsão do desempenho dos componentes moldantes dos moldes híbridos. Os resultados mostram a importância da previsão do regime de temperatura de funcionamento do molde híbrido no estabelecimento das condições apropriadas ao processamento quando são utilizados materiais menos rígidos nos elementos moldantes. Foi constatado, ainda, que no projecto de moldes híbridos se devem considerar as deformações dos blocos moldantes causadas pelas pressões durante o ciclo para prever a contracção e as dimensões finais das peças moldadas.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/28113/200

Development of In-Mold Assembly Methods for Producing Mesoscale Revolute Joints

In-mold assembly is a promising process for producing articulated joints. It utilizes injection molding to automate assembly operations, which may otherwise require high labor times for production. Since injection molding is a high throughput process, in-mold assembly holds considerable promise in bulk production of assembled parts. However, current in-mold assembly methods cannot be used for manufacturing in-mold assembled products at the mesoscale. This is because the process changes considerably when the sizes of the molded parts are reduced. The premolded component in a mesoscale joint consists of miniature features. Hence, when a high temperature, high pressure polymer melt is injected on top of it, it is susceptible to plastic deformation. Due to presence of a mesoscale premolded component which is susceptible to deformation, traditional shrinkage models alone can not be used to characterize and control the clearances. This dissertation identifies and addresses issues pertaining to in-mold assembly of revolute joints at the mesoscale. First, this dissertation identifies defect modes which are unique to in-mold assembly at the mesoscale. Then it develops mold design templates which can be used for manufacturing in-mold assembled mesoscale revolute joints. Further, issues related to the deformation of the mesoscale premolded component are identified. Two novel mold design solutions to realize mesoscale in-mold assembled revolute joints are presented. The first involves use of mold inserts to constrain the premolded component to inhibit its deformation. The second involves use of a bi-directional flow of the polymer melt over the premolded component to balance the deforming forces experienced by it. Finally, methods to predict and control clearances that would be obtained in mesoscale in-mold assembled revolute joints are presented. To demonstrate the utility of the tools built as part of this research effort, a case study of a miniature robotic application built using mesoscale in-mold assembly methods is presented. This dissertation provides a new approach for manufacturing mesoscale assemblies which can lead to reduction in product cost and create several new product possibilities

Study of the behavior of a thermoplastic injection mold and prediction of fatigue failure with numerical simulation

Tese de doutoramento em Engenharia MecânicaO objetivo deste trabalho é a criação de uma metodologia de análise da resistência à fadiga de moldes de injeção de termoplásticos. Uma metodologia capaz de satisfazer o mercado atual que exige a diminuição do tempo de entrega e custos de moldes de injeção, sem comprometer a sua fiabilidade. Para o desenvolvimento desta metodologia, foram utilizados modelos digitais. Com estes modelos é possível executar-se várias iterações sem os custos de um modelo físico. Além do menor custo dos modelos digitais, também é possível compreender o comportamento de cada molde no decorrer da fase de projeto. Com o aumento da complexidade dos componentes injetados, o estudo da resistência à fadiga tende a ser cada vez mais importante. Neste trabalho serão apresentados cuidados a ter na preparação dos modelos digitais, de forma a obter-se resultados fiáveis. No desenvolvimento desta metodologia, usaram-se dois softwares de simulação numérica para gerar os modelos digitais. Um deles dedica-se ao estudo reológico de peças termoplásticas e outro ao comportamento estrutural dos moldes de injeção. A execução de simulações numéricas requer uma boa caracterização dos materiais usados. No caso dos termoplásticos, os fabricantes têm uma grande base de dados com a informação necessária para as simulações numéricas. No entanto, para as simulações estruturais, os fabricantes tendem apenas a fornecer os dados das curvas monotónicas, os quais não fornecem qualquer informação sobre o comportamento à fadiga. Portanto, neste trabalho foram estudados modelos empíricos que se adaptam aos aços usados em moldes de injeção, a partir dos quais é possível gerar as curvas S-N e e-N. De modo a avaliar qual o modelo empírico que se adaptaria melhor a esta área, foram realizados ensaios experimentais com provetes feitos em EN 1.2311. A partir destes ensaios, escolheu-se o modelo empírico mais conservador. Com base no modelo empírico escolhido, foi desenvolvida uma aplicação capaz de gerar as curvas S-N e e-N, a partir das informações fornecidas pela aciaria. Além da caracterização dos materiais, também é importante que as condições de carregamento do modelo numérico estrutural sejam o mais aproximadas possível do que irá ocorrer no modelo físico. Como as cargas deste modelo numérico podem ser previstas a partir do modelo numérico reológico, a criação de uma ponte entre estes dois modelos numéricos é imprescindível. Logo, neste trabalho foi construída uma aplicação capaz de converter os dados gerados pelo software comercial Moldflow em ficheiros capazes de serem lidos por softwares comerciais de simulação numérica estrutural. Usando esta aplicação para a conversão dos dados, foram realizadas simulações e comparadas com os respetivos modelos físicos. Verificou-se que é possível replicar o comportamento do molde em modelos digitais. No entanto, os modelos digitais dos moldes de injeção estudados tenderam a apresentar resultados conservadores quando comparados com os modelos físicos. Por fim, foi desenvolvida uma aplicação capaz de usar dados calculados a partir de softwares comerciais de cálculo numérico estrutural para a determinação da resistência dos moldes à fadiga. Aqui foi tido em conta o modelo para geração das curvas de fadiga dos materiais validado. Os modelos de cálculo à fadiga na aplicação baseiam-se na regra de Palmgren – Miner para a determinação dos ciclos até à nucleação da fissura. O cálculo das tensões alternadas foi realizado a partir de dois métodos, o critério da tensão de corte octaédrica e o método de Sines. Para testar a aplicação foram escolhidos cinco moldes que apresentaram falhas por fadiga. Em seguida, foi aplicada a metodologia proposta neste trabalho para a determinação da resistência dos mesmos à fadiga. A partir da aplicação desta metodologia e das ferramentas desenvolvidas para o seu emprego, foi possível verificar que esta é capaz de prever as zonas onde ocorreram as falhas, bem como outras com probabilidade de nucleação de fissuras. Portanto, no decorrer deste trabalho foi possível criar uma metodologia e ferramentas de apoio para o cálculo de moldes à fadiga. Assim, projetistas de moldes podem ter uma boa perspetiva da resistência à fadiga de moldes de injeção ainda em projeto, tendo por base métodos científicos.The objective of this work is to create a methodology to analyze the fatigue resistance of thermoplastic injection molds. A methodology capable of satisfying the current market that demands a decrease in the delivery time and costs of injection molds, without compromising their reliability. To develop this methodology, digital models were used. With these models it is possible to execute several iterations without the costs of a physical model. Besides the lower cost of digital models, it is also possible to understand the behavior of each mold during the design phase. With the increasing complexity of injected components, the study of fatigue resistance tends to be more and more important. In this work, care will be presented in the preparation of the digital models, in order to obtain reliable results. In the development of this methodology, two numerical simulation software’s were used to generate the digital models. One of them is dedicated to the rheological study of thermoplastic parts and the other to the structural behavior of injection molds. The execution of numerical simulations requires a good characterization of the materials used. In the case of thermoplastics, manufacturers have a large database with the information needed for numerical simulations. However, for structural simulations, manufacturers tend to provide only monotonic curve data, which do not provide any information about fatigue behavior. Therefore, in this work, empirical models that fit the steels used in injection molds were studied, from which it is possible to generate the S-N and e-N curves. In order to evaluate which empirical model would best fit this area, experimental tests were performed with specimens made in EN 1.2311. From these tests, the most conservative empirical model was chosen. Based on the chosen empirical model, an application capable of generating the S-N and e-N curves from the information provided by the steel mill was developed. Besides the characterization of the materials, it is also important that the loading conditions of the numerical structural model are as close as possible to what will occur in the physical model. Since the loads of this numerical model can be predicted from the rheological numerical model, the creation of a bridge between these two numerical models is essential. Therefore, in this work was built an application capable of converting the data generated by the commercial software Moldflow into files capable of being read by commercial structural numerical simulation software. Using this application for data conversion, simulations were performed and compared with the respective physical models. It was found that it is possible to replicate the mold behavior in digital models. However, the digital models of the injection molds studied tended to present conservative results when compared to the physical models. Finally, an application capable of using data calculated from commercial numerical structural calculation software was developed for determining the fatigue resistance of molds. Here the validated model for generating the fatigue curves of the materials was taken into account. The fatigue calculation models in the application are based on the Palmgren - Miner rule for the determination of the cycles until crack nucleation. The alternating stresses calculation was performed from two methods, the octahedral shear stress criterion and the Sines method. To test the application, five molds that presented fatigue failures were chosen. Then, the methodology proposed in this work was applied to determine their fatigue resistance. From the application of this methodology and the tools developed for its use, it was possible to verify that it is able to predict the areas where the failures occurred, as well as others with a probability of crack nucleation. Therefore, during this work it was possible to create a methodology and support tools for the calculation of fatigue molds. Thus, mold designers can have a good perspective of the fatigue resistance of injection molds still in project, based on scientific methods

Conformal cooling analysis for a complex piece in Moldflow

openIl raffreddamento conforme (Conformal cooling, CC) ha il potenziale per definire il futuro dello stampaggio a iniezione e della produzione di stampi. Creando canali CC che seguono la geometria del pezzo, gli ingegneri possono ottimizzare molto più facilmente le linee di raffreddamento. I risultati sono costi ridotti e maggiori profitti. Il seguente lavoro fa parte di un progetto più ampio (S4PLAST- "Sustainable Plastics Advanced solutions") dove, in collaborazione con l'azienda Erofio, si stanno studiando soluzioni alla necessità di simulazioni più accurate dello stampaggio ad iniezione di parti con sistemi CC complessi. Essendo CC una tecnologia relativamente nuova, i software di simulazione sono ancora in fase di sviluppo. Questo progetto di tesi è pensato per aiutare Erofio a simulare le fasi iniziali dello sviluppo di nuovi pezzi con geometria complessa. L'intento principale è quello di studiare le possibili modalità di importazione in Moldflow di geometrie e dati già esistenti, cercare di eseguire ed eventualmente correggere errori nell'analisi e, infine, ottenere risultati che possano essere utilizzati per lo sviluppo delle condizioni di produzione ottimali. Questo progetto ha quindi lo scopo di comprendere i limiti dell'analisi in Moldflow di sistemi che richiedono CC. Questa tesi approfondisce lo studio di fattibilità dell'analisi Moldflow su sistemi che richiedono CC, al fine tentare di simulare questi canali in modo più vicino possibile alla realtà. Questo progetto definisce che è possibile simulare il processo di stampaggio a iniezione per pezzi complessi che richiedono circuiti CC in Moldflow. Tuttavia, il software sembra essere ancora in fase di sviluppo per la simulazione di sistemi CC, con grossi problemi soprattutto nella procedura di importazione. Per quanto riguarda il pezzo fornito dall'azienda, i risultati dell'analisi Moldflow suggeriscono che non è possibile produrre il pezzo con le geometrie e l'insieme di parametri forniti.CC will define the future of injection molding and mold manufacturing. By creating CC channels that follow the unique geometry of an injection molded part, engineers can better optimize their cooling lines. The results are reduced costs and increased profits. The following work is part of a bigger project (S4PLAST- "Sustainable Plastics Advanced solutions) where, in collaboration with the Erofio company, the need for more accurate injection molding simulation of parts with complex CC systems is being assessed. Being CC a relatively new technology, software programs are still under development. This thesis project is intended to simulate the initial steps of the development of new complex pieces. The main goal is to study the possible ways to import already existing geometries and data into Moldflow, try to run and eventually correct errors and problems in the analysis, and in the end, obtain results that can be used for the development of the optimal production conditions. This project is intended to understand the limits of Moldflow analysis on systems that require CC. This thesis goes in-depth on the feasibility study of Moldflow analysis on systems that require CC in order to be able to simulate numerically the cooling system as close to reality as possible. This project determined that it is possible to simulate the injection molding process for complex pieces that require CC circuits in Moldflow. However, Moldflow seems to be in its infancy for the simulation of CC systems with major problems, especially when importing complex geometries. Regarding the company-provided piece, Moldflow analysis results suggest that it is not possible to produce the piece with the geometries and set of parameters given by the company