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Journal of Materials Processing Technology 175 (2006) 1519An example of simulation tools use for large injection moulds design:The CONTENURTM2400l solid waste containerJ. Aisaa, C. Javierrea, J.A. De la SernabaT.I.I.P., C.S.I.C. Associated Unit, Department of Mechanical Engineering, University of Zaragoza, SpainbCONTENUR ESPANA, S.L., Pol gono Industrial Los Angeles, Getafe, Madrid, SpainAbstractLarge containers with volumes above 1100l are usually produced using procedures such as rotomoulding process. These techniques haveno part weight or dimensional limits. T.I.I.P., injection moulding plastic group of the Department of Mechanical Engineering of the ZaragozaUniversity, developed with CONTENURTMa new product under European norms for solid waste containers up to 2000l volume; the resultwas a new main body up to 60kg weight in one part. The design process combined several CAE tools (aesthetical design, mechanical designand rheological simulation) and, in last June, showed final result and passed different tests. Nowadays, more than 5000 samples are on thestreets without basic modifications in the mould (more than 100tonnes weight). The paper focuses on the methodology used to integrate tooland process design with product definition (i.e. injection pressure and clamp force versus thickness and part shape). Some parameters aboutprocess control in this particular mould (injection rate, temperature, viscosity, gate location, .) are detailed. 2005 Elsevier B.V. All rights reserved.Keywords: CAE design; Container; Injection moulding1. IntroductionCAE tools have constituted an authentic revolution in thelast years within injection of thermoplastics. The sequentialprocess until the final solution (including several setups suchas development, test of prototypes, modification of figures,new test, .) has been replaced by a faster one consistingof a procedure with the designer, transformer and final clientworking together on the same computer files (“concurrentengineering”). Therefore, the timing for mould manufac-ture and completion has been reduced enormously; however,some interesting advices about CAE use are described in 1.The Workshop of Injection of the Plastics Industry of theUniversity of Zaragoza (T.I.I.P.), C.S.I.C. Associated Unit,has been working with CAE tools on injection of thermo-plasticsformorethan15years,withenormousadvantageforhundreds of projects made in different sectors (automotive,household-electric, packaging, toys, etc.). T.I.I.P. activitiesCorresponding author.E-mail address: tiipunizar.es (J. Aisa).URL: .included several research projects (rheological characteriza-tion,semiautomaticmoulddesign,.)workingtogetherwithdifferent European companies.Nevertheless, this group has always been conscious ofthe necessity to arrange simulation with procedure of man-ufacture next to the machine, of such a form that has beencollaborated and directed by the constitution of the ResearchAssociationoftheWorkshopofInjectionofthePlasticIndus-try (a.i.T.I.I.P.) foundation, which provides services to theinjection companies without a profit spirit (Fig. 1). Thistechnological center has been supported by various nationalorganizations such as the Aragons Government and Span-ish Department of Industry through different programs andresearch lines (new processes like gas-assisted techniques orcascadeinjectionmoulding,newdesigns,process-measuringtechniques using pressure and temperature devices .).2. The CONTENUR ProjectWhen, in 1999, the first Spanish company involved inthe manufacture of containers for the collection of urban0924-0136/$ see front matter 2005 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2005.04.00616J. Aisa et al. / Journal of Materials Processing Technology 175 (2006) 1519Fig. 1. a.i.T.I.I.P. injection moulding area, general view.solid remainders (CONTENUR SPAIN, S.L.) went to theT.I.I.P.a.i.T.I.I.P. Group to work jointly on the design ofpieces of great size in injection, then arrived the moment fortesting the real possibilities of these programs in this field.Themainobjectiveoftheprojectwasthefastmanufactureof containers of great capacity (2400l and more) to competewith market products with welded metallic plate solutions orplastic ones made by rotational moulding with the inclusionof expensive reinforcement structures. Obviously, betweenall the pieces that constituted the set, the main challenge wasthe manufacture of a single part bucket.The literature shows several part and mould design exam-ples and failure advices 2,3, but it is not possible to findbig plastic parts up to 40kg weight and a mistake in thismouldsizewillhavenoeasysolution(tooltransporttomouldmakers manufacturing plant will be too expensive, and trialand error method is not available).For the design of this element, the following aspects hadto be considered: basic dimensions agreed with the European Norm EN12574 4; unloading resistance (discharge sides) (Fig. 2); high impact resistance for functional conditions and loca-tion (parking areas, for example); easily cleaning surfaces; friendly aspect, aesthetical design; minimum cost (not only for processing and assembly butalso for on-street maintenance); restriction of the clamping force imposed by the installedpressmachine(bigspecialmachineswithlimitedclampingrange between 5000 and 10,000tonnes); prepared for labelling, that is to say, with visible free andflat spaces; material restrictions: same materials used for other CON-TENUR designs.Special mention requires two limitations: minimum costand maximum clamping force under mentioned limits. For aminimum cost, thickness is fundamental (by the cost of rawmaterial), inasmuch as the time of manufacture; therefore,Fig. 2. Boundary conditions for unloading operation, nonlinear materialmodel, finite element model.the cost of the machine derived approximately depends onthe square of the thickness 5.On the other hand, to reduce the closing force, the pro-jected area of the piece and the distribution of pressures arestrongly related with part thickness (narrow sections causeda high injection pressure, which could as well suppose a highforce of closing).The methodology applied, developed by Castany et al.,not only for injection moulding but also for other similartechniques 68, is as given below:(a) Determination of the feasibility of the product: clampingforce evaluation and thickness part on an agreed basicgeometry to adjust dimensions with the European norm.Only general design lines, and not functional details,were included in this step. Some basic results are shownin Table 1. These analyses were made with basic param-eters for generic material family, high-density polyethy-lene (Table 2). For advanced steps, calculations weremade using several temperature conditions.(b) Materialselection,combiningmeltflowindex(MFI)andmechanicalbehaviour,andinjectionpointlocationsweresimulated, without even knowing the final geometry ofthecomponent.Bestresultswerefoundforseveralinjec-tion points arranged around the bottom area in the mainTable 1Results for simple plastic model, first analysis using simulation toolsMain body thickness(mm)/weight (kg)Maximum injectionpressure (MPa)Required clampingforce (kN)6/5296166,0007/6071122,0008/685594,0009/764474,00010/843559,000J. Aisa et al. / Journal of Materials Processing Technology 175 (2006) 151917Table 2Computing parameters for basic simulationsMelt temperature (C)240Injection time at constant ram speedIn seconds20In percent50Mould temperature (C)40Fig. 3. Basic line, Pro-Engineer software, before final moulding arrange-ments.body of the container. This criteria was also imposed bymould structure and part shape.(c) Analysis of the body form and thickness of the partcomparing constructive alternatives: its sidewall shapes,metallic elements of reinforcement and, if necessary,inclusion of the tubes injected with gas-assisted tech-niques to increase inertia of the sections, etc., were con-sidered.(d) Obviously,moulddimensionsandthepresenceofunder-cuts supposed a problem added for the design of pieceand mould. In this way, semicircular shape of the borderTable 3Basic dimensions for 2400l main body (mm)Height1600Width1480Length1600of the upper container was a hard design problem; it wasrequiredforfunctionalusebutsupposedanundercutareainvolving slides in the mould.(e) Part volume was adapted and different aesthetic formsappearedfeasible conjunction of the possible thick-ness by manufacture with the thickness and forms bymechanical resistance. In this step, finite analysis, solid3D design and filling simulation were made simultane-ously(Figs.3and4).Thefinalpartdimensionsareshownin Table 3.Withthesebasicmagnitudescalculatedinthesefoursteps,the design team had an initial point for the final drawing ofgeometry and the inclusion of the elements of details likesettling down of output angles, radios, position of acces-soriesoftheset(cork,skid,etc.).Industrialflowanalysiswasset in definitive way, fixing optimum positions for manifoldworking together with the mould maker, Kyowa IndustrialCompany with mould plants in the USA, Japan and Mexico.The main aspects of the process and their simulations(other details cannot be presented in order to protect indus-trial know-how) are:1. Model of the figure with geometries type 2.5D.2. Location of the entry points to the cavity. The use of racetracks for a better control of the filling was considered,following rheological design rule for simultaneous end offilling at the end of the cavity (avoiding over-pack effect),especially considering the border shape with semicircularareas.3. Optimal conditions of process: the selection of temper-ature and its relation with thickness and cycle stronglyconditioned the permissible values for the design. Valuesbetween 210 and 250C were evaluated.Fig. 4. Software C-Mold: plastic temperature at ejection and cooling lines layout.18J. Aisa et al. / Journal of Materials Processing Technology 175 (2006) 1519Fig. 5. Real container model used for testing industrial conditions in 2400lmould.4. The adjustment of the filling form by means of the cor-rectprogrammingofspeedsbecameessential.Atconstantspeed profile, the increase of pressure-supposed values ofinadmissible force of closing by the limitation imposedto the dimensions of the machine. In the final arrange-ment for container mould, several ram speed stages wererecommended.This procedure was experimentally validated with realtests using already existing smaller dimension container(Fig. 5).TypicalramspeedprofilecalculatedwithCAEtechniquesis shown in Fig. 6, but this “function” cannot be trans-latedtotheinjectionmachinewithoutpracticalarrangements,because hydraulic systems are not able to follow all thosegradients exactly. Anyway, around 15% less clamping forcecould be achieved after this optimisation procedure.5. After the filling possibilities were fixed, this was verifiedwith a new numerical model by the mould maker fromthe initial ideas sent by the design equipment and withthe final hot runner system data necessary for the mould.Fig. 6. Theoretical ram speed profile from computer results.Fig. 7. Real sample in CONTENUR assembly plant.The sequential technology was considered as a possibil-ity with the purpose of reducing filling pressure, but thepracticalarrangement,themaintenanceandpossibleshut-downs underestimated their use.6. Finally,theanalysesofcoolingofthemould,packingandwarpage induced by the process were developed. In thisway, different constructive materials were used accordingtotheirthermalconductivity,adjustingcoolinglayoutpro-vided by Kyowa Industrial Company. Final mould weightwas higher than 150,000kg (up to 150metrictonnes).Actually, more than 6000 pieces were made withoutdetecting any problem in the injection, expulsion or the lifeof the component in good condition (Figs. 7 and 8), and pro-cessing rates are similar with other existing 1000l containers(2025 parts per hour). Other components were simultane-ously designed and, in fact, it was more complicated to getFig. 8. Complete 2400l waste container, including all components.J. Aisa et al. / Journal of Materials Processing Technology 175 (2006) 151919fine results, for example, in container lids, obviously smallerthan the body.Fortheauthors,thefinalconclusionisthatCAEtoolswerebasic in design process, and also