Part 1: Designing for Moldability - MTN KALIP

1 part 1: Designing for MoldabilityChapter 1 Injection pressure Equations Factors that influence injection pressure requirementsChapter 2 Filling pattern Melt front velocity influences filling patternChapter 3 MFA and MFV Varying MFV Equation How flow dynamics affect orientation Flow balanceChapter 4 Material properties for part design Stress-strain behavior Fatigue Impact strength Thermal mechanical behaviorDesign for strength Short-term loading Long-term loading Repeated loading High velocity and impact loading Loading at extreme temperaturesPart thickness Cycle time increases with thickness Thick parts tend to warp Thin, uniform parts improve surface quality Reducing part thicknessBoosting structural integrity with ribs Typical uses for ribs Designing ribsDesign for assembly Tolerances: fit between parts Annular snap-fit joints Torsion snap-fit joints Fasteners Inserts Welding processesChapter 5 Runner systems Runner size considerations Payoffs of good runner designDetermining the number of cavities FormulasPlanning the runner system layout Balanced vs.

2 Unbalanced layoutsDetermining sprue dimensionsDesigning runner cross sections Recommended cross-sectional designs Hydraulic diameter and flow resistanceDetermining runner dimensions Example: using empirical data to calculate runner dimensions Typical runner diametersHot runner systems Types of hot runner systemsRunner balancing Reducing runner diameter Using tighter process controlsDesign rules Runner size Raising melt temperature Branched runners Runner intersections Hot runners Easy ejectionChapter 6 Gate design overview Single vs. multiple gates Gate dimensions Gate locationGate types Manually trimmed gates Automatically trimmed gatesDesign rules Gate location Gate length Gate size Gate thickness Freeze-off time Fiber-filled materialsChapter 7 Design Example: Optimizing gates and ram speed profile C-MOLD Filling EZ analysis C-MOLD Filling and Post Filling analysisPart 2.

3 Designing for Productivity and PerformanceChapter 8 Mold cooling system overview Mold cooling system componentsCooling-channel configurationAlternative cooling devices Baffles Bubblers Thermal pins Cooling slender cores Cooling large cores Cooling cylinder coresCooling system equations Cooling time Reynolds number and coolant flowChapter 9 Residual stress Flow-induced residual stress Thermal-induced residual stress Process-induced vs. in-cavity residual stressChapter 10 Shrinkage and warpage Shrinkage Warpage Warpage due to differential shrinkageDesign rules for shrinkage and warpage Wall thickness Balanced filling Packing pressure Cooling system Residual stressChapter 11 Design Example: Reducing shrinkage and warpage DescriptionPart 3.

4 TroubleshootingChapter 12 Air traps Problems caused by air traps RemediesChapter 13 Black specks/black streaks Causes of black specks/black streaks RemediesChapter 14 Brittleness Causes of brittleness RemediesChapter 15 Burn marks Causes of burn marks RemediesChapter 16 Delamination Causes of delamination RemediesChapter 17 Dimensional variation Causes of dimensional variation RemediesChapter 18 Discoloration Causes of discoloration RemediesChapter 19 Fish eyes Causes of fish eyes RemediesChapter 20 Flash Causes of flash RemediesChapter 21 Flow marks Causes of flow marks RemediesChapter 22 Hesitation Problems caused by hesitation RemediesChapter 23 Jetting Effects of jetting RemediesChapter 24 Ripples Cause of ripples RemediesChapter 25 Short shot Causes of short shot RemediesChapter 26 Silver streaks Causes of silver streaks RemediesChapter 27 Sink marks and voids Causes of sink marks and voids RemediesChapter 28 Weld lines and meld lines Problems caused by weld lines Strength of weld lines RemediesPart 3.

5 ReferenceAppendix AInjection Molding Overview Development of the injection molding machine Development of the injection molding processCo-injection (sandwich) moldingFusible core injection moldingGas-assisted injection molding Benefits of the gas-assist process Typical applicationsInjection-compression moldingLamellar (microlayer) injection moldingLive-feed injection moldingLow-pressure injection moldingPush-pull injection moldingReactive molding Types of reactive materials Processing Design considerationsStructural foam injection moldingThin-wall moldingAppendix BInjection molding machine Machine specification Machine function Auxiliary equipmentMachine components Injection system Mold system Hydraulic system Clamping system Molded systemMachine operating sequenceScrew operation Back pressure Injection speed Screw rotation speed CushionSecondary operations Assembly Decoration Other secondary operationsAppendix CSetting process conditions Setting machine process conditionsAppendix DWhat are plastics?

6 Polymer alloys and blends Polymer compositesClassification of plastics Structures and properties of plasticsThermoplastics Market share distribution of thermoplastics Structures and properties of thermoplastics Amorphous polymers (Semi-)crystalline polymers Liquid crystal polymersThermosets Cross-linking (reaction) Processing thermosetsAdditives, fillers, and reinforcements Modifying polymer properties Low-aspect fillers High-aspect fillers: fibersResin data tableAppendix EHow does plastic flow? Deformation Viscoelastic behaviorMelt shear viscosity Newtonian fluid vs. non-Newtonian fluid Shear-thinning behavior Shear rate distributionPressure-driven flow Melt flow length Injection pressure vs.

7 Fill time Flow instabilityFountain flow Injection pressurePressure drives the meltPressure is the driving force that overcomes the resistance of polymer melt (seePressure-driven flow), pushing the polymer to fill and pack the mold cavity. If you place anumber of pressure sensors along the flow path of the polymer melt, the pressuredistribution in the polymer melt can be obtained, as schematically illustrated in Figure 1. Pressure decreases along the delivery system and the on a simplification of classic fluid mechanics theory, the injection pressure required to fill thedelivery system (the sprue, runner, and gate) and cavities can be correlated with several relevantmaterial, design, and processing parameters.

8 In the following equations, P is the injection pressureand n is a material constant (the power-law coefficient), which typically ranges from to (with being a good approximation) for a variety of polymer melts. Figure 2 shows injectionpressure as a function of several of these parameters. Circular channel flow The melt flow in the sprue, runner, and cylindrical gatesInjection Pressure Strip channel flow Such as melt flow in a thin cavityFIGURE 2. Injection pressure as a function of melt viscosity, flow length, volumetric flow rate, and partthicknessFactors that influence injection pressurerequirementsThe following diagrams illustrate the design and processing factors that influence injection pressure.

9 Variable Higher injection pressurerequired Lower injection pressurerequired part DESIGN Injection PressurePart thickness part surface area GATE DESIGN Gate size Flow length PROCESSING CONDITIONS Melttemperature Mold-wall(coolant)temperature Injection PressureRam speed MATERIAL SELECTION Melt flow index Injection Pressure Filling patternWhat is the filling pattern?The filling pattern is the transient progression of the melt front within the delivery systemand mold cavities. It plays an important role in determining the quality of the front velocity influences filling pattern Constant MFV The ideal filling pattern has melt reaching every extremity of the cavity simultaneously, with aconstant melt-front velocity (MFV) (see Chapter 3) throughout the process.

10 Otherwise, localizedover-packing at prematurely filled regions might arise within the part . Variable MFV A variable MFV during filling also leads to changes in the molecular or fiber orientation thatimmediately freeze at the part surface region when the molten plastic contacts the cold 1. Computer-simulated filling pattern in a color-shaded imageFilling Pattern MFA and MFVD efinitionHere we present two simple yet important design and process parameters: melt-frontvelocity (MFV) and melt-front area (MFA). As its name suggests, melt-front velocity is themelt-front advancement speed. Melt-front area is defined as the cross-sectional area ofthe advancing melt front: either the length of the melt front multiplied by the thickness ofthe part (see the diagram below), the cross-sectional area of the runner, or a sum of both,if the melt is flowing in both places.