Introduo aos Fundamentos de Simulao da moldagem por injeo utilizando MPI Plastics Insight Injection Molding moldagem por injeoFlow Behavior comportamento do escoamentoDesign Principles princpios de Design

Disciplina Projeto Simulado em ComputadorProf. Antonio Flavio Aires Rodrigues

Injection Molding MachineHopper Depsito AlimentadorScrew (Ram) - RoscaBarrel - CilindroHydraulic UnitUnidade HidrulicaTool Ferramenta ou Molde

Injection Molding CycleCooling TimeTempo de ResfriamentoMold Open TimeTempo de Molde AbertoFill TimeTempo de PreenchimentoHold TimeTempo de Recalque

Injection Molding CycleCiclo de Moldagem por InjeoCycle Time:Tempo de CicloFill Time:Tempo de PreenchimentoHold Time:Tempo de RecalqueCooling Time:Tempo de ResfriamentoMold Open Time:Tempo de Molde Aberto22Sec.19102

Injection Molding ProcessProcesso de Moldagem por InjeoFillingMold closes, screw rapidly moves forward, frozen polymer skin forms at mold walls

PreenchimentoFechamento do molde, movimento rpido da rosca para frente, formao de pelcula fina solidificada na parede do molde

HopperBarrelScrewMoldCilindroMoldeUnidade de alimentaoRosca

Injection Molding ProcessProcesso de Moldagem por InjeoPacking Time (Holding)Cavity filled, packing begins, cooling occurring

Tempo de compactao (Recalque)Cavidade preenchida, incio do recalque, ocorrncia de resfriamento

Na Rosca aplicada uma especificada presso para o polmero plastificado a fim de compactar mais o plstico dentro da cavidade. Tambm chamado estgio de compensao.Screw is applying a specifiedpressure to the polymer meltin order to pack more plasticinto the cavity. Also calledcompensation stage.

Injection Molding ProcessProcesso de Moldagem por Injeo

Injection Molding ProcessProcesso de Moldagem por InjeoCoolingPacking complete, gate freezes off, cooling continuesScrew moves back and begins plasticating resin for next shot ResfriamentoCompactao completa, fim do congelamento da entrada, continuao do resfriamentoMovimento da rosca para trs e incio da plastificao da resina para prxima injeo

Injection Molding ProcessProcesso de Moldagem por InjeoMold OpenCooling completes, mold opens Molde abertoResfriamento completo, abertura do molde

The Injection MoldMolde de Injeoa.k.a. Stationary HalfPlaca Estacionriaa.k.a. Moving HalfPlaca Mvel(a)(b)Nozzle - BicoNozzle - Bico

Flow Behavior Comportamento do EscoamentoWhat Does a Plastic Molecule Do in an Injection Mold?O que faz uma molcula de plstico em um molde de injeo?

Phases of MoldingFases da MoldagemFilling - preenchimentoVolumetrically fill the cavity - Preenchimento volumtrico da cavidadePressurization - PressurizaoBuild up pressure in the cavity Criao da presso na cavidadeCompensation - CompensaoAdd extra material to reduce shrinkage Adio extra de material parareduzir a contraoFilling PhasePressurization PhaseCompensation PhaseFase de compensao

Fountain FlowFonte em fluxoDescribes the phenomena of how plastic flows in a mold Descreve os fenmenos de como plstico flui em um molde Material that first enters shows up at the surface near the gate - Material que primeiro entra em contato na superfcie perto da entrada Material that enters the cavity last, shows up in the center downstream - Material que entra na cavidade por ltimo, espetculos para cima no centro a jusante Has direct influence on molecular and fiber orientation at the part surface - Tem a influncia direta na orientao molecular e da fibra na superfcie da pea.Melt

Cross-Sectional Flow Molecular OrientationOrientao Molecular do escoamento na seo transversalMolecular Orientation is caused by shear flow. A orientao molecular causada pelo fluxo cisalhante The high amount of shear is inside the frozen layer, therefore the highest orientation A quantidade mais elevada de cisalhamento dentro da camada solidificada, portanto a orientao mais elevada.Shear rate - min max

Cross-Sectional Heat TransferTransferncia de calor na seo transversalThere should be a balance between heat input from shear and heat loss to the tool - Deve haver um balano entre a entrada de calor do cisalhamento e da perda de calor para o molde.Faster Injection Rate Taxa de injeo rpidaSlower Injection Rate lenta taxa de injeoVS.Heat Loss

into the ToolFrozen LayerHeatInputHighShearRatePlasticFlow

Injection Time / Frozen layer thicknessTempo de injeo / espessura da cmada solidificadaFaster injection times will produce a thinner frozen layer, and a thicker flow channel - Tempos de injeo rpidos produziro uma camada solidificada mais fina, e um canal de escoamento mais grosso.

Pressure-Volume-Temperature (PVT)Presso-Volume-Temperatura (PVT)Describes the temperature/pressure relationship for polymers over the entire processing range - Descreve a relao da temperatura / presso para polmeros sobre uma faixa processando inteira.

Shrinkage Contrao - EncolhimentoGate along edge -Entrada ao longo ladoFinal PartMoldShrinkage in the direction of flow is usually much greater than across the flow for un-filled materials - O encolhimento no sentido do fluxo geralmente muito maior do que transversal ao escoamento para materiais em preenchimento.

Design Principles Princpios de DesignUse Design Principles and Moldflow technology so you dont have to do this: O uso de princpios de Design e tecnologias MoldFlow assim voc no precisa fazer isto:

Moldflow Design PhilosophyMoldFlow Fisolofia de Design Number of gates - Nmeros de entradasThe number of gates used is based on the pressure to fill the cavity. In general, one selects the minimum number of gates to fill the cavity. - Nmero de entradas usadas baseadas na presso para preencher a cavidade. Em geral, uma seleo de um nmero mnimo de entradas para preencher a cavidade.Position of gates - Posio das entradasThe position of the gate is determined by the flow balancing principle. A posio da entrada determinada pelo princpios de balanceamento de fluxo.Flow pattern Escoamento padro The mold should fill with a straight fill pattern with no changes in direction during filling. O molde dever ser preenchido com um padro de preenchimento retilineo sem mudanas na direo durante o preenchimento.

Moldflow Design PhilosophyMoldFlow Filosofia de Design Runner Design - Projeto dos canaisThe runner system is designed to achieve the required filling pattern in the cavity. O sistema de canais desenhado para obter o padro de preenchimento requerido na cavidade.Sequence of Analysis - Seqncia de AnliseThe procedure of the mold design always starts with the cavity. - O procedimento para o projeto do molde sempre inicia com a cavidade.

Project Design Procedure Using Moldflow Procedimento Design de projeto usando o MoldFlowDetermine the design criteria for the project Determinar o critrio de design para o projetoUse previous experience of analyst Usar experincia prvias para analisarDiscuss the project with all disciplines involved in the project Discutir o projeto com todas grupos envolvidos no projetoUse Moldflow Design Principles Usar princpios de projeto com MoldFlowUse Moldflow Design Rules with the software Critrios de Design usando o MoldFlow Interpret results and make changes where necessary Interpretar os resultados e fazer as alteraes quando necessriasDiscuss changes with all disciplines involved in the project Discutir as alteraes com todas as reas envolvidas no projetoRepeat Moldflow analysis to ensure acceptable results - Repetir as anlises no MoldFlow para assegurar a aceitao dos resultados

Flow Concepts Conceito de FluxoUnidirectional and controlled flow pattern Padro de fluxo controlado e unidirecionalFlow balancing Fluxo balanceadoConstant pressure gradient Gradiente de presso constanteMaximum shear stress Mxima tenso de cisalhamentoUniform cooling Resfriamento uniformePositioning weld and meld lines Posicionamento das linhas de solda e agrupamento (mistura)Avoid hesitation effects - Impedir efeito de hesitaoAvoid underflow - Impedir Balancing with flow leaders and flow deflectors Balanceamento com guia de fluxo e defletores de fluxoAcceptable runner/cavity ratio Aceitar razo canais/cavidades

Uni-Directions and Controlled Flow Pattern Padro de fluxo controlado e unidirecionalThe uni-directional flow principle says that the plastic should flow in one direction with a straight flow front throughout filling. This gives a uni-directional orientation pattern O princpio do fluxo unidirecional diz que o plstico deveria escoar em uma direo com uma frente de fluxo retilnea preenchendo completamente. Isto dar uma padro de orientao unidirecional.Orientation is different Directions, flow marks, high stresses, & warping.Orientao esta em diferentes direes, marcas de fluxo, grande tenso, e empenamento.Orientation in one direction, Uniform, shrinkage, & stresses. Orientao em uma direo, uniforme, contrao e tenso.

Flow Balancing Balanceamento de Fluxo

The flow balancing principle says all flow paths within a mold should be balanced, i.e. fill in equal time with equal pressure O princpio de balanceamento de fluxo diz que todos os caminhos de fluxo em um molde devem ser balanceados, isto , preenchimento em igual tempo com igual presso.Naturally balanced runner system Sistema de canais naturalmente balanceadoSame distance and conditions between the nozzle and all cavities Igual distncia e condies entre o bico e todas cavidadesAll cavities filling at the same time pressure and temperature Preenchimento de todas cavidades em igual tempo, presso e temperatura.

Flow Balancing Balanceamento de Fluxo

Artificially balanced runner system Sistema de canais artificialmente balanceadosSizes of the runners are different in order to deliver plastic melt to all cavities at the same pressure, so that all the cavities fill at the same time Tamanho para os canais diferente para distribuir o plstico plastificado para todas as cavidades igual presso, de modo que todas cavidades so preenchidas no mesmo tempo.

Flow BalancingArtificially balanced runnersLimitations:Very small partsParts which contain very thin sectionsParts where sink marks are importantWhere the ratio of runner lengths to be balanced is too greatBeforeAfter

Constant Pressure GradientThe constant pressure gradient principle says that the most efficient filling pattern is when the pressure gradient, i.e. pressure per unit length, is constant along the flow pathPressure spiking at end of fill before switchover lowers pressure

Maximum Shear StressThe shear stress during filling should be less than the critical level. The value of this critical level depends on the material and application

Material: ABSStress Limit: 0.3 Mpa

Stress plotted is above the material limit

Uniform CoolingWhen plastic is in contact with the mold, and one side is cold and the other is hot, differential cooling takes place. This causes a bowing to the hot side, as the hot side takes longer to cool and shrink

Uniform CoolingPart cross-section should cool evenly, cavity to core. If it does not in a corner, the corner will pull in to less than 90 degrees, producing the typical bowed box warpageHeat is concentrated in the corner of the coreCavityColdCoreHotHot Corner(shrinks relative to frozen sections, causing warpage)

Positioning Weld and Meld LinesPosition weld and meld lines in the least sensitive areas, if they cant be eliminatedWeld Lines are formed when two flow fronts meet head on Meld Lines are formed when two flow fronts meet and flow in the same direction

Avoid Hesitation EffectsGateRib did not fillPosition gates as far away as possible from where the flow divides into thick and thin flow paths to avoid hesitation effects

Gate

Avoid Hesitation EffectsGATES make poor flow control devicesLow pressure drop in runnersMiddle cavity hesitating more than right cavityHESITATION EFFECTMaterial freezes off in the gate closest to the sprueTRADITIONAL APPROACHFirst gate opened 0.010 in thickness and width, from 0.030 to 0.040Now first cavity filling much faster than other cavities

Avoid UnderflowGoodNotGood!A change in flow direction between the time an area fills and the end of fillThe blue velocity angle arrows should be perpendicular to the multi-color fill contour lines

Avoid UnderflowFLOI4Arrows show direction plastic moving at the instant of fillFlow frontWeld Line moves inside frozen layer

Balancing with Flow Leaders and Flow DeflectorsUniform ThicknessBalanced ThicknessBalanced FillingUnbalanced FillingSubtly increase (leader) or decrease (deflector) the wall thickness to influence the filling pattern to create a balanced fill within the part

Acceptable Runner/Cavity RatioVolume of parts: 192.0 ccVolume of feed system: 13.4 ccFeed system: 7.0% of part volumeDesign runner systems for high pressure drops, thus minimizing material in the runner, in order to give a low ratio of runner to cavity volume

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