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    Moldflow Design

    Analysis Solutions

    GLOSSARY

    Version 1.0

    November 2005

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    Copyright Moldflow Corporation and its subsidiaries worldwide 2005.

    All rights reserved. No part of this document may be reproduced in any form or by any means,

    electronic, mechanical photocopying or otherwise, without prior written permission of the copyright

    owner.

    Published by Moldflow Corporation.

    Whilst every effort has been made to avoid errors in the text, the author and publisher shall not be under

    any legal liability of any kind in respect of or arising out of the information contained herein.

    Moldflow, iMPA, MPA, Moldflow Plastics Advisers, the MPA logo, MPI, Moldflow Plastics Insight, the MPI

    logo, Dual Domain, MPX, Moldflow Plastics Xpert, the MPX logo, plasticszone, Shotscope, EZ-Track, MMS/

    Production Monitoring, Moldflow Manufacturing Solutions, Altanium, Celltrack and MMS are trademarks

    or registered trademarks of Moldflow Corporation and/or its subsidiaries and affiliates worldwide.

    All other trademarks are properties of their respective owners.

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    Contents

    A ..................................................................................................................... 11

    Air Shot ...................................................................................................... 11

    Air Trap ...................................................................................................... 11

    Amorphous Polymers................................................................................. 11

    Anisotropic Shrinkage................................................................................ 12

    Aspect Ratio ............................................................................................... 12

    Automation................................................................................................. 12

    B ..................................................................................................................... 13

    B-Splines .................................................................................................... 13

    Back Pressure ............................................................................................. 13

    Baffle .......................................................................................................... 13

    Balanced Flow............................................................................................ 14

    Barrel .......................................................................................................... 14

    Barrel Capacity........................................................................................... 14

    Barrel Effect ............................................................................................... 14

    Batch........................................................................................................... 15

    Bending Moment........................................................................................ 15

    Boss ............................................................................................................ 15Boundary Representation Solid.................................................................. 15

    Bubble ........................................................................................................ 15

    Bubbler ....................................................................................................... 16

    Buckling ..................................................................................................... 16

    Burn Mark .................................................................................................. 16

    C ..................................................................................................................... 17

    CAD............................................................................................................ 17

    CAM........................................................................................................... 17Cavity ......................................................................................................... 17

    Center Gate................................................................................................. 17

    Centroid...................................................................................................... 18

    Charge Stroke ............................................................................................. 18

    Check Ring ................................................................................................. 18

    Chiller......................................................................................................... 18

    Chord Height .............................................................................................. 19

    Clamp Capacity .......................................................................................... 19

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    Clamp Force ............................................................................................... 19

    Closed Loop Controller.............................................................................. 19

    Closed Volume ........................................................................................... 19

    Compensating Phase................................................................................... 20

    Composite Curve........................................................................................ 20

    Compressibility Model ............................................................................... 20

    Conic Arc ................................................................................................... 20

    Control Limits ............................................................................................ 20

    Cooling Channel......................................................................................... 21

    Cooling Time.............................................................................................. 21

    Core ............................................................................................................ 21

    Cracking ..................................................................................................... 21

    Crystalline Polymers .................................................................................. 22

    Crystallinity ................................................................................................ 22

    Crystallization ............................................................................................ 22

    Cure ............................................................................................................ 22

    Curve .......................................................................................................... 23

    Cushion....................................................................................................... 23

    Cycle Time ................................................................................................. 23

    D ..................................................................................................................... 25

    Decompression ........................................................................................... 25

    Delamination .............................................................................................. 25

    Density........................................................................................................ 25

    Design of Experiments (DOE) ................................................................... 25

    Disc Gate .................................................................................................... 26

    Dominant Flow Path................................................................................... 26

    Draft Angle................................................................................................. 26

    Drooling...................................................................................................... 26

    Dwell .......................................................................................................... 27

    Dynamic Flow ............................................................................................ 27

    E ..................................................................................................................... 29

    Ejection....................................................................................................... 29

    Ejection Temperature ................................................................................. 29

    Ejection Time ............................................................................................. 29

    Ejector Pins................................................................................................. 29

    Element....................................................................................................... 30

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    End of Fill................................................................................................... 30

    Extensional Viscosity ..................................................................................30

    F ..................................................................................................................... 31

    Family abbreviation.................................................................................... 31Family name............................................................................................... 31

    Fan Gate ..................................................................................................... 31

    Feasible Molding Window ......................................................................... 31

    Fiber Orientation ........................................................................................ 32

    Filler ........................................................................................................... 32

    Fillet............................................................................................................ 32

    Filling Phase............................................................................................... 32

    Filling Time................................................................................................ 32

    Finger Gate................................................................................................. 33

    Flash ........................................................................................................... 33

    Flow Leaders and Deflectors...................................................................... 33

    Flow Path.................................................................................................... 34

    Free Edge.................................................................................................... 34

    Free-form Curves and Surfaces.................................................................. 34

    Friction ....................................................................................................... 34

    G..................................................................................................................... 35

    Gate ............................................................................................................35

    Gate Freeze................................................................................................. 35

    Gloss Mark ................................................................................................. 35

    H ..................................................................................................................... 37

    Hesitation.....................................................................................................37

    High Cushion.............................................................................................. 37

    Hopper ........................................................................................................ 37

    Hydraulic Pressure ..................................................................................... 37

    I ....................................................................................................................... 39

    Injection Location....................................................................................... 39

    Injection Pressure ....................................................................................... 39

    Injection Time ............................................................................................ 39

    Injection Velocity ....................................................................................... 39

    Injection Volume ........................................................................................39

    Insert........................................................................................................... 40

    Intersecting Mesh Elements ....................................................................... 40

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    Isotropic Material ....................................................................................... 40

    J...................................................................................................................... 41

    Jetting ......................................................................................................... 41

    L ..................................................................................................................... 43

    Laminar Flow ............................................................................................. 43

    Loop............................................................................................................ 43

    M..................................................................................................................... 45

    Manifold Edge............................................................................................ 45

    Masterbatch ................................................................................................ 45

    Meld Line ................................................................................................... 45

    Melt Density ............................................................................................... 46

    Melt Temperature ....................................................................................... 46Mesh ........................................................................................................... 46

    Mesh - Midplane ........................................................................................ 46

    Mesh - Surface (Fusion) ............................................................................. 47

    Mesh - Volume (3D) ....................................................................................47

    Mesh Intersection ....................................................................................... 47

    Model.......................................................................................................... 48

    Mold ........................................................................................................... 48

    Mold Open Time ........................................................................................ 48

    Mold Temperature...................................................................................... 48

    Molding Window........................................................................................ 49

    N ..................................................................................................................... 51

    No-flow Temperature ................................................................................. 51

    Node ............................................................................................................51

    Nominal Part Thickness ............................................................................. 51

    Non-manifold Edge.................................................................................... 52

    Non-return Valve ........................................................................................ 52

    Normalized Thickness................................................................................ 52

    Nozzle Pressure .......................................................................................... 52

    O..................................................................................................................... 53

    Open Loop Controller ................................................................................ 53

    Optimization................................................................................................53

    Orientation.................................................................................................. 53

    Orthotropic Material ....................................................................................53

    Overlapping Mesh Elements ...................................................................... 54

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    P ..................................................................................................................... 55

    Part.............................................................................................................. 55

    Parting Plane............................................................................................... 55

    Pinpoint Gate .............................................................................................. 55

    Plastication ................................................................................................. 56

    Point............................................................................................................ 56

    Poisson's Ratio............................................................................................ 56

    Polymer ...................................................................................................... 56

    Preferred Molding Window........................................................................ 57

    Pressure Gradient ....................................................................................... 57

    Pressure Profile........................................................................................... 57

    Pressure Stroke ........................................................................................... 57

    Pressurization Phase ................................................................................... 57

    Process Control........................................................................................... 58

    Process Parameters ..................................................................................... 58

    Process Window......................................................................................... 58

    Processing Conditions ................................................................................ 58

    Production Run........................................................................................... 59

    Purging ....................................................................................................... 59

    PVT ............................................................................................................ 59

    R ..................................................................................................................... 61

    Racetrack Effect ......................................................................................... 61

    Ram ............................................................................................................ 61

    Record Groove ........................................................................................... 61

    Region ........................................................................................................ 62

    Restricted Gate ........................................................................................... 62

    Reynold's Number ...................................................................................... 62

    Rib .............................................................................................................. 62

    Run ............................................................................................................. 62

    Runner / Runner System............................................................................. 63

    S ..................................................................................................................... 65

    Screw.......................................................................................................... 65

    Screw Back Position................................................................................... 65

    Screw Displacement ................................................................................... 65

    Screw Forward Position ............................................................................. 65

    Screw Velocity............................................................................................ 65

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    Semi-Crystalline......................................................................................... 66

    Set Points .................................................................................................... 66

    Shear........................................................................................................... 66

    Shear Rate................................................................................................... 66

    Shear Strain ................................................................................................ 66

    Shear Stress ................................................................................................ 66

    Shell............................................................................................................ 67

    Short Shot ................................................................................................... 67

    Shot Size ..................................................................................................... 67

    Shot Weight ................................................................................................ 67

    Shrinkage.................................................................................................... 68

    Sink Mark ................................................................................................... 68

    Solid............................................................................................................ 68

    Specific Heat .............................................................................................. 69

    Sprue........................................................................................................... 69

    Start of Fill.................................................................................................. 69

    STL File...................................................................................................... 69

    Streak Mark - Color.................................................................................... 69

    Streak Mark - Dark ..................................................................................... 70

    Streak Mark - Glass Fiber........................................................................... 70

    Streak Mark - White ................................................................................... 70

    Stroke.......................................................................................................... 70

    Suck Back................................................................................................... 71

    Surface.........................................................................................................71

    Switch-Over................................................................................................ 71

    T ..................................................................................................................... 73

    Tensile Strength .......................................................................................... 73

    Thermal Conductivity................................................................................. 73

    Thermal Degradation.................................................................................. 73

    Tooling Noise ..............................................................................................73

    Transducer .................................................................................................. 74

    Transition Temperature............................................................................... 74

    Translator.................................................................................................... 74

    Trimmed Surface........................................................................................ 74

    Turbulent Flow........................................................................................... 74

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    U ..................................................................................................................... 75

    Unbalanced Flow........................................................................................ 75

    Undercut ..................................................................................................... 75

    Underflow....................................................................................................75

    Uni-directional Flow .................................................................................. 76

    V ..................................................................................................................... 77

    Valve Gate .................................................................................................. 77

    Velocity Profile........................................................................................... 77

    Velocity Routines ....................................................................................... 77

    Velocity Stroke ........................................................................................... 77

    Velocity to Pressure Change-Over ............................................................. 78

    Vent............................................................................................................. 78

    Venting........................................................................................................ 78

    Viscosity ..................................................................................................... 78

    Viscosity Index........................................................................................... 78

    Viscosity Model.......................................................................................... 79

    Voids ........................................................................................................... 79

    VRML image.............................................................................................. 79

    W .................................................................................................................... 81

    Warpage...................................................................................................... 81

    Weld Line ................................................................................................... 81

    Wire-Sweep Index...................................................................................... 81

    Z ..................................................................................................................... 83

    Zero Screw Position ................................................................................... 83

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    A

    Air Shot

    An air shot is the injection of polymer melt into the air, instead of into the mold. The main purpose of anair shot is to act as a "test run," to make sure that the machine is operating properly.

    The cylinder is pulled back from contact with the sprue bushing and the injection piston is movedforward, forcing melted plastic from the nozzle. If the melt is caught in a metal cup, a pyrometer probecan be used to check the temperature of the melt as it exits from the nozzle. This is one of the moreaccurate measurements of the melt temperature.

    Air Trap

    An air trap is an air or gas bubble that has been trapped by converging flow fronts or trapped against thecavity wall. This causes a surface blemish on the part. Air traps can be prevented by changing the gatelocation or part thickness. Good practice is to place vents in the mold at the air trap location.

    Amorphous Polymers

    Amorphous polymers are a family of polymers that are characterized by entangled polymer chains that areloosely bound. The term amorphous indicates that there is no preferred orientation of the molecules,relative to each other, without external force. During injection molding amorphous polymers haveorientation.

    Amorphous polymers are in a super-cooled liquid state and generally shrink less than semi-crystallinepolymers. Amorphous polymers exhibit no x-ray diffraction pattern, because they are not crystalline innature.

    See also Crystalline Polymers on page 22, Semi-Crystalline on page 66.

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    B

    B-Splines

    A b-spline is a mathematical function that defines free-form curves and surfaces. IGES files that use b-splines instead of parametric splines are generally smaller in size.

    Back Pressure

    Back pressure is pressure that opposes the screw as it returns.

    The purpose of increasing back pressure is to make it harder for the screw to return. This increases theshear heating and the mixing of the material, which results in improved polymer melt quality.

    BaffleA baffle is a cooling system component which is constructed by inserting a metal plate in the cooling lineswhich forces the coolant to flow up one side of the plate and down the other. It is used to regulate anddirect the passage of coolant fluid so that the coolant can travel into difficult areas for more efficientcooling. By interrupting the flow in the cooling lines the baffles create turbulence around bends andimprove the heat transfer capability of the coolant.

    See also Bubbler on page 16

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    Balanced Flow

    Flow is balanced when the extremities of the mold fill at the same time and pressure, as shown in theillustration below. Balanced flow leads to uniform orientation, uniform shrinkage and less internal stress

    and warpage of the part. It also leads to cost savings with reduced material usage.Gate location, runner system design and part thickness affect flow balance.

    BarrelThe barrel is the cylinder of the plasticating chamber of an extruder or injection molding machine. Thecylinder forms the chamber within which the plastic resin is converted from a solid form to a viscousmelt.

    Barrel Capacity

    The barrel capacity is the maximum weight of material that a machine can produce from one forwardmotion of the ram or screw.

    See also Shot Size on page 67.

    Barrel EffectThe barrel effect is the effect of material compressibility while the material is in the barrel of the injectionmolding machine. This compressibility can be significant. A simulation that calculates and uses the barreleffect will produce more accurate results.

    See also Compressibility Model on page 20.

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    Batch

    A batch is the quantity of polymer that is made in one operation. A batch is also referred to as a lot.

    In CAE products, batch refers to the execution of consecutive analyses in one operation.

    Bending Moment

    A bending moment is the force or load applied to an entity that produces bending of that entity around anaxis.

    Boss

    A boss is a raised projection in a molded part that usually has a hole in it to provide additional material forsupporting a mechanical fastener, such as a screw.

    Boundary Representation Solid

    A boundary representation solid is a model format produced from a surface modeling CAD system. Thesolid is defined as a list of surfaces that enclose a volume.

    Bubble

    A bubble is a spherical, internal void caused by air or other gas trapped within a molded plastic product. Abubble differs from a blister in that the bubble is contained within the part, whereas a blister is on or nearthe surface of the part and generally causes deformation of the surface. A bubble also differs from a void,

    which is developed as a vacuum during cooling.

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    Bubbler

    A bubbler is cooling system component. It is a central circular channel that can be introduced into themold and is used to regulate and direct the passage of coolant fluid, so that the coolant can travel into

    difficult areas for more efficient cooling. The coolant flows through the central channel and then out andaround the outside of the channel to the outlet point.

    Both baffles and bubblers have the effect of increasing flow turbulence and thus increasing heat transferdue to the inclusion of additional bends in the coolant flow system. Their geometrical shape also enablesthe application of cooling to restricted areas.

    See also Baffle on page 13.

    Buckling

    Buckling is the conversion of in-plane membrane energy to bending energy and usually involves largedeformations of the part. It is the principle mode of failure of a planar thin structure under excessive in-plane loading.

    Burn Mark

    A burn mark is a defect that appears as a brown or black mark on the part surface. A burn mark can becaused by an un-vented air trap. This occurs when the trapped air is heated very quickly as it iscompressed, burning the surrounding plastic. Velocity profiling is often used to prevent this problem, bygiving air more time to escape from the mold.

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    C

    CAD

    Computer-Aided Design (CAD) is the process of using computer software programs to design parts,tools, molds, and assemblies.

    CAM

    Computer Aided Manufacturing (CAM), is the use of computers and computer technology to control,manage, operate, and monitor manufacturing processes.

    Cavity

    The cavity is the region within the mold that fills with plastic to form the part.

    Center Gate

    A center gate is a gate which is located in the center of the part. It can be a sprue (direct) gate or pinpointgate.

    See also Gate on page 35.

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    Centroid

    A point whose coordinates are the average of the coordinates of a given set of points and which for agiven planar or three-dimensional figure (as a triangle or sphere) corresponds to the center of mass.

    Charge Stroke

    See also Shot Size on page 67.

    Check Ring

    A check ring is the sliding ring of the non-return valve on the front of the screw. The check ring allowsmelted plastic to flow forward to the front of the screw during plastication, and prevents flow back intothe screw during injection. The check ring is a high wear item that can leak during injection, effectivelyreducing the pressure that is applied to the melted plastic.

    See also Non-return Valve on page 52.

    Chiller

    A chiller is a self-contained system comprised of a refrigeration unit and a coolant circulation mechanismconsisting of a reservoir and a pump. Chillers maintain optimal heat balance by constantly recirculatingchilled cooling fluids to injection molds.

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    Chord Height

    Chord height is the distance between the vertex of an arc and a straight line connecting two points on thearc (the distance c on the figure below).

    When generating a mesh, enabling chord height control increases the chance of creating a mesh thatclosely corresponds to curved surfaces. Without chord height control, some surface curves, such as fillets,degrade when meshed. Chord height control is effective only with parts that have curved surfaces.

    Clamp Capacity

    Clamp capacity is a measure of the largest projected area of cavities and runners that an injection moldingmachine can safely hold closed at full molding pressure.

    Clamp Force

    Clamp force is the force required to hold the mold closed while an opposing pressure is exerted by theplastic injected into the cavity.

    Closed Loop Controller

    A closed loop controller is one that responds to feedback from transducers that measure the value beingcontrolled. For example, cavity pressure can be controlled by placing a transducer in the cavity and usingthat measurement to adjust the pressure on the plastic in the injection molding cylinder.

    Closed Volume

    A closed volume is a group of surfaces connected together to form a polyhedron. A closed volume hasno free edges. The structure is used to form inserts and the mold boundary.

    See also Free Edge on page 34.

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    Compensating Phase

    The period during the injection molding process when plastic is injected to compensate for the plastic inthe cavity shrinking as it cools.

    Composite Curve

    A group of curves that are joined end to end to form a single curve. Composite curves are discontinuousif the start point of one curve is not the same as the end point of the previous curve.

    IGES composite curves are:

    Composite Curve (IGES Type 102)

    Boundary Entity (IGES Type 141) Curve on a Parametric Surface (IGES Type 142)

    Compressibility Model

    Heated plastics are compressible. The compressibility of a material affects the volume of plastic requiredto produce a finished part.A compressibility model describes the relationships between pressure,temperature, and the volume (PVT) of the plastic material. The compressibility model that the software

    uses is the 2-Domain Modified Tait PVT model with 13 coefficients.See also Barrel Effect on page 14.

    Conic Arc

    A mathematical form for representing ellipses, hyperbola and parabolas.

    Control Limits

    Control limits are statistically determined values between which a control variable is allowed to rangewithout adjusting the process. Control limits provide an indication of the variation in the injectionmolding process.

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    Cooling Channel

    A cooling channel is a passageway in a mold for circulating water or another cooling medium, in order tocontrol the temperature of the metal surfaces in contact with the plastic being molded.

    Cooling channels are typically connected to form a circuit. Cooling channel configurations can be serial orparallel.

    Cooling Time

    Gross cooling time is the time after the velocity phase until the part is sufficiently cooled to be ejectedfrom the mold. Therefore, gross cooling time is the sum of the pressure phase (packing and holding) andthe net cooling time.

    The net cooling time is the time after the pressure phase and before the part is ejected from the mold.

    Core

    The core is the part of the mold which shapes the inside of a molded part.

    Cracking

    Cracking is the formation of a narrow separation in a plastic component, usually by the rupture ofchemical bonds due to internal and external stress.

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    Crystalline Polymers

    Crystalline polymers are a family of polymers that are characterized by an ordered arrangement of themolecules which fit closely together. Typically, crystalline polymers are more dense than amorphous

    polymers. A polymer in a crystalline state is a solid, due to its solid crystals, which have definite geometricform.

    Crystalline polymers display an X-ray diffraction pattern. The degree of crystallinity determines theintensity of the pattern. The pattern can be used to identify the polymer.

    See also Amorphous Polymers on page 11.

    Crystallinity

    Crystallinity is a solid, molecular state of some polymers which denotes compactness of the molecularchains. This characteristic is attributable to the existence of solid crystals with definite geometric form.

    Crystallization

    During cooling some polymers form an ordered molecular structure which are called crystals. The rate ofcrystallization is a function of both temperature and time. The level of crystallinity achieved is determinedby cooling rates. Rapid cooling rates are associated with lower levels of crystalline content and vice versa.

    The level of volumetric contraction (shrinkage) is also affected by degrees of crystallinity, with highercrystallinity resulting in greater shrinkage.

    In injected molded parts, thick regions tend to cool slowly relative to thinner sections, and so have highercrystalline content and hence higher volumetric contraction.

    Cure

    Cure is a stage reached by a thermosetting material that is sufficiently cross-linked to form a solid; thecross linking is the result of a chemical reaction.

    Sometimes this term is used to describe the solidification of thermoplastics; this is a physical process ofremoving heat from the thermoplastic.

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    Curve

    A line in three-dimensional space. A curve can be straight or contain bends.

    This includes:

    Line - a straight curve defined by two end points.

    Arc- a section of a circular curve defined by one of two methods:

    A center point and arc and angle

    Three points on a plane

    Spline- a cubic spline interpolation. on a supplied set of points.

    CushionThe cushion is the distance between the forward screw position and the zero screw position, and containspolymer left in the barrel after the cavity is filled. Most of the melt in the cushion is then used forcompensation flow during the packing stage.

    Cycle Time

    Cycle time is the time from the ejection of one part to the ejection of the next part. Cycle time is the sumof:

    Filling time.

    Packing time.

    Cooling time.

    Mold open time.

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    D

    Decompression

    Decompression is the movement of the screw away from the nozzle (without rotation) and is used toprevent drooling. Decompression may be used for low viscosity materials (for example, PA-66), where thenozzle does not have a valve gate to prevent drooling.

    Delamination

    Delamination is a localized separation of the surface of the part. The most common cause ofdelamination is excessive injection velocity.

    Density

    The density of a plastic part is measured by dividing its mass by its volume. A denser part has more plasticmolecules and more weight per volume. A part can have some regions with higher density than others.

    Design of Experiments (DOE)

    Design of Experiments (DOE) is an engineering method which determines which variables in yourdesign have the most, and least, effect on final part quality. DOE also analyzes how part quality changes asinput variables change. Engineers use DOE early in the design stage to improve designs.

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    Disc Gate

    A disc gate is a mold gate used in an identification of a molded part, generally having the same cross-section as the mold runner.

    Dominant Flow Path

    The dominant flow path is the flow path of least resistance (the smallest pressure drop) from the polymer

    injection location to the last place to fill. In the graphic below, the cone indicates the injection location andthe X indicates the last place to fill.

    The dominant flow path is normally, but not always, the longest flow path.

    Draft Angle

    The angle included in the part design to allow the part to be easily ejected from the mold.

    Drooling

    Drooling is leakage of polymer from the nozzle, sprue, or gate. This creates thin strands of plastic that canget caught in the mold.

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    Dwell

    Dwell is a pause in the mold closing cycle of a compression molding operation to permit gas to escapefrom the molding material.

    Dynamic Flow

    Dynamic flow is the flow before the cavity is actually full, when a flow front still exists towards the end ofthe cavity. This results in an area within the mold without plastic.

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    E

    Ejection

    Ejection is the removal of molded parts from the mold by mechanical means, or with compressed air.

    Ejection Temperature

    Ejection temperature is the averaged temperature of the part at the time it is ejected from the mold.

    A molded part should be ejected only when it has enough strength to undergo the force of ejection,without excessive warpage or marks from ejector pins. The ejection temperature depends on the resin,part thickness, application, and shop floor practice. A part ejected at a higher temperature can reduce thecooling time, but may increase warpage.

    Ejection Time

    Ejection time is the moment when the mold opens to eject the part. For example, an ejection time of 42

    seconds indicates that 42 seconds elapsed from the moment the mold closes for injection until themoment the mold opens for ejection.

    See also Mold Open Time on page 48.

    Ejector Pins

    Ejector pins are located on the mold and push the part out of the mold when the clamp is open.

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    Element

    A single sub-domain of a finite element mesh. Elements typically used in molding simulation are:

    Two-node linear elements, used to represent runners, cooling channels and connectors.

    Three-node triangular elements, used to represent surfaces.

    Four-node tetrahedral elements, used to represent solids.

    The properties of the element are assumed to be homogeneous.

    End of Fill

    The end of fill occurs when the polymer has reached the extremities of the mold cavity and the mold is

    volumetrically filled.

    Extensional Viscosity

    When a polymer flows through a large cross-section to a smaller one, it will extend longitudinally. This willresult in a pressure drop that will be dependent upon the extensional viscosity of the particular material.

    In practical injection molding situations, this pressure drop due to extensional effects is often seen when amaterial flows from a large runner into a very small gate. The change in cross-section is sudden and

    severe, resulting in a large pressure drop across the gate.

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    F

    Family abbreviation

    This is the shortened version of a material family name. For example, PC is the family abbreviation for thefamily name Polycarbonate.

    Some families contain subsets, and there is an abbreviation for each subset. For example, TPE, TPO,TPU, and TPR are family abbreviations within the Thermoplastic Elastomer family.

    Family name

    This is the name of a family of materials, for example, Polycarbonate. Each material is a member of afamily of materials.

    The shortened version of a family name is the family abbreviation. For example, PC is the familyabbreviation for Polycarbonate.

    Some families contain subsets, and there is an abbreviation for each subset. For example, TPE, TPO,TPU, and TPR are family abbreviations within the Thermoplastic Elastomer family.

    Fan Gate

    The fan gate is the opening between the mold runner and the mold cavity which has the shape of a fan.This shape helps reduce stress concentrations in the gate area by spreading the opening over a wider area.

    Feasible Molding Window

    A feasible molding window is represented by a set of boundaries that define a window-like shape. For theprocess setting ranges inside the window boundaries, the molding process is feasible; outside the windowboundaries, the molding process is not feasible.

    See also Preferred Molding Window on page 57.

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    Fiber Orientation

    Fiber orientation is the direction of the fibers' major axis, relative to the flow direction.

    In the illustration below:

    1 Random fibersare found at the entrance.

    2 Flow-aligned fibersare found in the converging flow area.

    3 Transversely aligned fibersare found in the diverging flow area.

    4 Fibers parallel to the flow directionare found in the restricted flow area.

    Filler

    Fillers are materials that can be added to a polymer for injection molding. Adding a filler to a polymer canincrease the strength of the polymer and ensure that good quality parts are produced.

    FilletA fillet is a rounded interior corner of a part that makes the part stronger.

    Filling Phase

    The period during the injection molding process when plastic is injected to fill the cavity.

    Filling Time

    The time required for the injection molding machine to fill the part.

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    Finger Gate

    The finger gate is used when presentation is important and you want to avoid disfiguring the top face of apart. It tunnels down from the parting plane and comes up on the underside of the part (see below).

    This gate is also known by the following names: banana, winkle, cow-horn, bent-tunnel gate and cashew.

    Flash

    A flash occurs when the polymer is not totally contained within the mold cavity. The most commoncauses of flash are an excessive velocity stroke, injection velocity, packing pressure, and a low clamp force.

    Remove flash by either reducing the injection velocity or increasing the clamp force.

    Flow Leaders and DeflectorsFlow leaders and deflectors are surfaces with thicknesses designed to direct the flow front, either byattracting it (leaders) or by deflecting it (deflectors). Flow leaders are thicker parts of the cavity (indicatedby the yellow arrow in the figure below) which attract the flow. Deflectors are thinner parts of the cavity(indicated by the red arrow) which constrict the flow and slow it down.

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    Flow Path

    A flow path is a route along which molten plastic moves within the cavity.

    Free Edge

    A free edge is an element edge that is not shared by other elements. A free edge has an element attached

    to only one side. An edge is a line segment that connects two mesh nodes.

    In Fusion and 3D meshes, free edges should be corrected because they indicate elements which have notbeen correctly attached.

    See also Manifold Edge on page 45and Non-manifold Edge on page 52.

    Free-form Curves and Surfaces

    These curves and the surfaces that are formed from them follow no mathematical relationship.

    FrictionFriction is a force which acts against motion. When a part is being ejected, if there is high friction betweenthe part and the mold walls, then the part may be impossible to eject, or it may be damaged duringejection.

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    G

    Gate

    The gate is the channel through which the molten polymer flows from the runner into the cavity.Generally, the gate is small and solidifies first.

    Gate Freeze

    Gate freeze is the moment during the packing phase when polymer at the gate has frozen solid and nomore polymer can be packed into the mold cavity.

    Gloss Mark

    Gloss is the shiny appearance of a molded part's surface. Differences in the gloss finish of a part arecaused by different projection behaviors of the plastic at the mold wall, due to different coolingconditions and shrinkage differences. You can remove dull surface patches by drying the material,decreasing the injection speed or increasing back pressure.

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    H

    Hesitation

    In a part with multiple flow paths, the flow can slow down or hesitate in thin regions. This allows the meltto cool in thin regions and in some cases freeze before filling is complete, causing short shots. Flowhesitation is most likely to occur in parts containing thin diaphragms, ribs and hinges.

    High Cushion

    High cushion occurs when the cushion is too large and the material is kept in the barrel for too long. Thiscan result in defects such as short shot.

    Hopper

    The hopper is the molding machine container that holds the polymer and feeds it to the injection moldingscrew.

    Hydraulic Pressure

    Hydraulic pressure is the pressure applied to the injection ram during the injection phase. Setting hydraulicpressure is one way of specifying the velocity phase for the molding cycle. The hydraulic line pressure isthe pressure in the main supply line from the pump; typically measured by means of a gauge in thehydraulic line. There is a direct relationship between the injection pressure and the hydraulic line pressurecalled the machine intensification ratio.

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    I

    Injection Location

    The injection location is the place where the molten plastic is forced into the mold cavity.

    Different injection locations can have different effects on the appearance and quality of the part.

    Injection Pressure

    The injection pressure is the pressure that is applied to the ram during the injection phase, causing thematerial to flow, and can be measured approximately by a transducer located in the nozzle. There is adirect relationship between the injection pressure and the hydraulic line pressure called the machineintensification ratio.

    Injection Time

    The injection time is the time it takes to fill the cavity.

    Injection Velocity

    The injection velocity is the speed at which polymer is injected into the mold cavity during the injectionphase. If the injection velocity is too high, it can cause part defects such as flash and delamination.

    Injection Volume

    The injection volume is the amount of polymer injected into the mold cavity during the velocity phase.

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    Insert

    An insert is a component that is placed into the mold before the injection phase and is anchored into theplastic part by being partially or wholly surrounded by the injected plastic. Typical inserts may have

    threads, may be electrically conductive, or may be a different plastic material.

    Intersecting Mesh Elements

    Intersecting mesh elements are mesh elements that lie on different planes and intersect each other.

    Illustration 1)shows the elements joined at their edges. This is common for ribs. These mesh elementsare acceptable.

    Illustration2)shows intersecting elements which cut through each other. This is not acceptable. Removeintersecting elements before you run an analysis.

    Isotropic Material

    An isotropic material has material properties that are the same in all directions. There are no directionaleffects of orientation or crystallinity.

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    J

    Jetting

    Jetting is the snake-like stream of polymer melt that occurs when the melt is pushed at a high velocitythrough restrictive areas (such as the nozzle, runner, or gate), into open, thicker areas, without formingcontact with the mold wall.

    In the jet, contact points form between the folds of melt, creating small welds. Jetting can lead to partweakness, surface blemishes, and internal defects.

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    L

    Laminar Flow

    Laminar flow occurs when a fluid (such as water) moves slowly, with fluid particles following straight-linepaths parallel to channel or walls. Laminar flow is defined as that with a Reynolds number of less thanapproximately 2300. Reynolds numbers greater than this indicate turbulent flow.

    Loop

    A group of connected curves that form a complete boundary of a surface.

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    M

    Manifold Edge

    A manifold edge is a mesh edge that has two entities attached to it. An edge is a line segment thatconnects two mesh nodes.

    In a Fusion mesh, manifold edges are the only type of edges which are correct. All other types should becorrected.

    A= Free Edges

    B = Manifold Edge

    C= Non-Manifold Edge

    See also Free Edge on page 34and Non-manifold Edge on page 52.

    Masterbatch

    A masterbatch is a concentration of filler or additives in a polymer. The mixture is added in small amountsto create the desired mix.

    Meld Line

    A meld line is a weakness or visible flaw created when two or more flows meet and converge while fillinga part. A meld line is typically formed by parallel flows, whereas weld lines are formed by flows meeting athigher angles, often head-on. Meld lines tend to be less weak than weld lines. The quality of the meld lineis dependent on the material type, the type and amount of fillers, and the pressure and temperature at themeld line.

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    Melt Density

    Melt density is a single point density value of a polymer at its average processing temperature, and at zero,or near zero, pressure.

    Melt Temperature

    The melt temperature is the temperature of the polymer as it starts to flow into die.

    Mesh

    Injection molding simulation involves solving the governing equations of mass, momentum, and energynumerically over the physical domain. The numerical implementation involves discretizing the physicaldomain into a number of sub-domains, or elements. The dependent variables (velocity, pressure,temperature) are approximated within each element. In short, the continuous domain is broken into manyconnected sub-domains and the dependent variables are approximated over the whole domain.

    Mesh density is the number of elements per unit area. In general, the more elements in the mesh, themore accurate the analysis results, at the expense of longer calculation times.

    See also Mesh - Midplane on page 46, Mesh - Surface (Fusion) on page 47and Mesh -Volume (3D) on page 47.

    Mesh - Midplane

    Consists of three-node triangular elements located at the half-thickness of the part surface.

    Creating a Midplane mesh from a solid model involves extracting the mesh and the element thicknessfrom the model. The two-dimensional Midplane mesh represent the solid model, using the thicknessinformation, during a molding analysis.

    See also Mesh on page 46.

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    Mesh - Surface (Fusion)

    A mesh consisting of surface (double-skin) shell elements. Surface mesh elements can be 3 or 6 nodedplanar, straight-edged triangles.

    A surface mesh analysis simulates the flow of the melt on both the top and bottom parts of the moldcavity. Consistency between the results on the opposite sides is maintained by using "connectors" -elements with zero flow and heat resistance. The connectors are inserted automatically at locationsdetermined by the geometric features of the model.

    A surface mesh can include Midplane areas.

    See also Mesh on page 46.

    Mesh - Volume (3D)

    A volume mesh consists of solid, tetrahedral shaped mesh elements. Each tetrahedral element consists offour Midplane mesh elements joined to create a solid tetrahedron. Tetrahedral elements have four nodes,

    four faces and six edges and allow an accurate 3D flow simulation to be calculated.

    See also Mesh on page 46.

    Mesh Intersection

    See also Intersecting Mesh Elements on page 40.

    See also Overlapping Mesh Elements on page 54.

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    Model

    A mathematical description of the relationships of the physical entity being described. For example, ageometry model is a mathematical description of the physical shape and characteristics of the part. Other

    models include viscosity model, process model, etc.

    Mold

    The mold is the steel tool used on the injection molding machine. The mold acts as a heat exchanger inwhich the molten thermoplastic solidifies to the shape defined by the cavity.

    Mold Open Time

    Mold open time is the duration of time during which the mold is open. Mold open time begins when themold opens for part ejection and ends when the mold closes so that the screw can begin moving forwardfor injection.

    See also Cycle Time on page 23.

    Mold Temperature

    The mold temperature is the temperature of the plastic-metal interface, or the mold surface temperature(inside the mold). In the image below, the arrow shows the plastic-metal interface.

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    Molding Window

    A process window or molding window, defines the limits of molding conditions under which anacceptable part can be produced. If molding conditions fall within this region, then a good part can be

    made.On the graph below, a good quality part (labeled with a checkmark), is encircled by the boundaries of theprocess window. A poor quality part (marked "X"), is outside the process window.

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    N

    No-flow Temperature

    The no-flow temperature is the temperature at which a polymer ceases to flow inside the mold cavity afterinjection.

    Node

    In the context of model geometry

    A node is a special coordinate position in space. Nodes are saved with a model.

    When modeling, you typically create nodes and then use nodes to create curves and regions.

    Nodes take on special significance when you assign attributes to them. For example, you might assign aninjection location, a coolant inlet, a constraint, or a load to a model node.

    In the context of mesh

    When you mesh a model, model nodes are converted to mesh nodes and additional mesh nodes aregenerated. Mesh nodes are the vertices of Midplane, Fusion, and 3D mesh elements and the ends of

    beam elements. The graphic below shows mesh nodes at the vertices of a triangular element and a beamelement.

    When you run an analysis, certain results are recorded at mesh nodes.

    Nominal Part ThicknessNominal part thickness is the thickness of the part at the thickest section.

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    Non-manifold Edge

    A non-manifold edge is a mesh edge with more than two entities attached to it. An edge is a line segmentthat connects two mesh nodes.

    On a Fusion mesh, non-manifold edges should be corrected because they indicate elements which havenot been correctly attached.

    A = Free Edges

    B = Manifold Edge

    C = Non-Manifold Edge

    See also Free Edge on page 34and Manifold Edge on page 45.

    Non-return Valve

    The non-return valve is located in front of the injection screw on an injection molding machine. It allowsmaterial to flow in one direction and closes to prevent back flow.

    Normalized Thickness

    Normalized thickness is a measurement of part thickness. The normalized thickness value ranges from -1to 1, where 0 is the center of the part and 1 and -1 are the plastic/metal interfaces, or mold walls.

    Nozzle PressureNozzle pressure is the pressure applied to the polymer at the nozzle. Setting nozzle pressure is one way ofspecifying the injection pressure of the polymer.

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    O

    Open Loop Controller

    An open loop controller does not respond to measurements of the value being controlled.

    See also Closed Loop Controller on page 19.

    Optimization

    Optimization is the process of finding the best conditions for molding a particular part. The partgeometry, the material selection, the injection location, and the processing conditions can all be optimized.

    Orientation

    During shear flow, polymer molecules align themselves in the direction of flow. The extent of thisorientation depends on the shear rate to which the material is subjected and the temperature of the melt.

    When the material stops flowing, the induced molecular orientation begins to relax at a rate dependent on

    the material's relaxation time and temperature. If the material freezes before relaxation is complete, themolecular orientation is "frozen in".

    Frozen-in orientation affects the mechanical properties of the material and also the shrinkage in thedirection of material orientation. For a given element, the mechanical properties and the amount ofshrinkage are different in directions parallel and perpendicular to the direction of material orientation.

    Orthotropic Material

    An orthotropic material consists of either oriented fibers or oriented polymer chains. Mechanicalproperties in the direction parallel to the orientation are different from those in the perpendiculardirection.

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    Overlapping Mesh Elements

    Overlapping mesh elements are mesh elements that overlap in the same plane. Remove overlappingelements from a mesh because they interfere with accurate analyses.

    Overlapping elements are shown in the illustration below.

    1) Mesh elements do not overlap.

    2) Partially overlapping mesh elements.

    3) Fully overlapping mesh elements.

    See also Intersecting Mesh Elements on page 40.Overpacking occurs when extra material is compressed into one flow path while other flow paths are stillfilling. The shortest and thickest flow paths fill first, resulting in overpacking.

    Overpacking can cause warpage, flashing and excessive cycle time and part weight.

    Overpacking generally occurs in sections with the shortest fill time.

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    P

    Part

    The part is the object that will be made. It is the finished product of the molding process.

    Parting Plane

    The parting plane is the surface of the two mold halves that separates when the mold opens.

    Pinpoint Gate

    A pinpoint gate is a small gate, generally 0.75mm or less in diameter. In multi-cavity molds, thedimensions of pinpoint gates must be held within very tight tolerances in order to fill all cavities at thesame time.

    The advantage of such a small gate is that it leaves a small, easily-removed mark on the part.

    Disadvantages include the following:

    The melt tends to freeze early in a pinpoint gate, as the flow slows. For this reason its use is limited tosmall parts and to resins with good fluidity.

    Pinpoint gates often require a third plate (for part removal), increasing mold expense.

    Pinpoints gates can lead to very high shear rate and high entrance pressure loss.

    An indirect gate is a variant of a pinpoint gate. Indirect gates are used when the injection location must betransferred from center of part.

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    Plastication

    Plastication is the process in which raw material is changed to melt and pushed to the front of the screwthrough a rotational action.

    Point

    A point is a position in space. The first stage of creating a model is usually the creation of points, whichare then joined together to create surfaces.

    Poisson's Ratio

    The Poisson's ratio (n12) pertains to a material under tensile stress, and is defined as the ratio of lateral (ortransverse) contraction strain (in the second principal direction) to the longitudinal strain (in the firstprincipal direction).

    Polymer

    A polymer is a natural or synthetic compound, usually of high molecular weight. Its long-chainedstructure consists of repeated linked molecular units called monomers (or mers). Monomers are relativelylight and simple. A chemical polyermization process builds polymers from monomers.

    Although the term plastics is often used as a synonym for polymer, plastics are actually one type ofpolymeric compound. Plastics are generally formulated with plasticizers, stabilizers, fillers, and otheradditives for the purpose of processing and performance.

    Non-plastic polymeric systems include rubbers, fibers, adhesives, and surface coatings.

    Processing polymers into end products mainly involves physical phase change such as melting andsolidification (for thermoplastics) or a chemical reaction (for thermosets).

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    Preferred Molding Window

    A preferred molding window is a refinement of a feasible molding window. It is represented by a set ofboundaries that define a window-like shape. For the process setting ranges inside the preferred molding

    window boundaries, the molding process is optimal; outside the window boundaries, the molding processis not optimal, but it may be feasible.

    See also Feasible Molding Window on page 31.

    Pressure Gradient

    The pressure gradient in the molten polymer is the pressure drop per unit of length along the flow path.The pressure drop from one location to another is the force that pushes the molten polymer to flow

    during filling. Polymer always moves from higher pressure to lower pressure, akin to water flowing fromhigher elevations to lower elevations.

    Filling with a more uniform pressure gradient is desirable. Non-uniform pressure gradients often indicateproblems such as flow hesitation, over-packing (resulting in flash) and under-packing (resulting inexcessive shrinkage).

    Pressure Profile

    A pressure profile is a graph made up of set points joined by lines. The set points determine the pressureto be applied at specific time intervals. The pressure profile controls how the part is packed out during thepressure stage of a cycle.

    Pressure Stroke

    The pressure stroke is the proportion of the total stroke performed under pressure control. This is thedistance between the velocity to pressure change-over position and the screw forward position in aninjection molding machine.

    Pressurization Phase

    The pressurization phase is the period during the injection molding process when extra plastic is injectedto ensure all corners and edges of the mold cavity are full of plastic.

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    Process Control

    Process control is the monitoring and correction of production.

    Process Parameters

    Process parameters are variables that typically correspond to molding machine settings. Commonly usedprocess parameters include:

    Maximum injection pressure.

    Screw cushion.

    Pressure stroke.

    Cycle time.

    Charge stroke.

    Mean injection pressure.

    Process Window

    A process window or molding window, defines the limits of molding conditions under which anacceptable part can be produced. If molding conditions fall within this region, then a good part can be

    made.

    On the graph below, a good quality part (labeled with a checkmark), is encircled by the boundaries of theprocess window. A poor quality part (marked "X"), is outside the process window.

    Processing Conditions

    Processing conditions are the variables that control the molding process. These include:

    The injection velocity.

    The pressure applied to the melt.

    The mold and melt temperatures.

    The material grade being used.

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    Production Run

    A production run is a series of parts made under a particular set a process conditions, for example, aparticular set velocity and pressure profiles.

    Purging

    Purging is the cleaning of one color or type of material from the injection molding machine. This can bedone by forcing the material out with a new color, a new material, or with another purging material.

    PVT

    Pressure-Volume-Temperature (PVT) data describes the specific volume (1/density) of a material as afunction of temperature and pressure. It describes the temperature/pressure relationship for polymersover the entire processing range.

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    R

    Racetrack Effect

    The racetrack effect occurs when molten plastic flows into thicker regions more easily than thin regions.The flow divides and then fills thicker sections before combining again to fill the thinner sections. Therecombined flow can reverse to meet the oncoming flow in the thinner section.

    The racetrack effect can cause air traps, weld lines and regions of high internal stress.

    Ram

    In the injection molding process the ram (or screw) is the part of the injection molding machine thatpushes the polymer into the mold.

    See also Screw on page 65.

    Record Groove

    The appearance of this surface defect is similar to the grooves on a record. Record grooves are formedwhen a high flow resistance exists in the mold, thus leading to a repeated temporary stagnation of the

    flow fronts.To prevent this defect, the mold and melt temperatures should be increased while decreasing the injectiontime.

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    Region

    A planar space defined by a consistent set of curves. The curves connect but must not intersect.

    Restricted Gate

    A restricted gate is a small opening between the cavity and runner in an injection mold. The gate breakscleanly after each part is made to assist part recovery.

    Reynold's Number

    The Reynolds Number is a ratio that defines the rate of fluid flow in pipes. The onset of turbulence inwater is between 2300-4000. The Reynolds Number is assigned to cooling circuits when the flow rate isnot known. A Reynolds Number of 4000 is considered fully turbulent but we recommend using aReynolds Number of 10,000 to represent turbulent flow when running an analysis.

    Rib

    A rib is a long, thin intersecting wall that is used to reinforce the outer walls of the plastic part.

    Run

    See also Production Run on page 59.

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    Runner / Runner System

    Runners are the channels that feed the polymer from the sprue to the gates of each cavity in the mold.

    A runner systemincludes the following:

    Runners, shown in red.

    Sprue, shown in green.

    Gates, shown in yellow.

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    S

    Screw

    The screw is the part of the injection molding machine that pushes the polymer into the mold, that is, theshaft that rotates within the barrel of the injection molding machine to process and prepare the materialfor injection.

    Screw Back Position

    The screw back position is the position that the screw is brought back to before the start of the next cycle.

    Screw Displacement

    Screw displacement is the distance the screw has moved during the injection phase.

    Screw Forward Position

    The screw forward position is the furthest forward position of the screw during a cycle.

    Screw Velocity

    Screw velocity is the speed with which the screw has moved during the injection phase.

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    Semi-Crystalline

    A plastic in a mixed state of crystalline and amorphous conditions. Most plastics are semi-crystalline. Thecrystalline content determines the physical properties or the part.

    See also Crystalline Polymers on page 22.

    Set Points

    Set points are the defining points on the velocity and pressure profiles. For the velocity profile, it is adiscrete injection velocity and time/displacement coordinate. For the pressure profile, it is a discreteinjection pressure and time/displacement coordinate.

    Shear

    Shear is a type of deformation caused by friction between the moving plastic and the mold wall.

    Shear Rate

    Shear rate is the rate of change of shear strain with time.

    Shear Strain

    The shear strain of the polymer is the ratio of the deformed state compared to the original state, when apolymer has been deformed due to an applied load.

    Shear Stress

    Shear stress is caused by friction between the moving plastic and the mold wall and between the layers ofplastic moving at different rates. High shear stress can cause the plastic to degrade or to fail, due to stresscracks.

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    Shell

    A group of connected surfaces that form an open shell.

    Short Shot

    A short shot is the incomplete filling of a mold cavity which results in the production of an incompletepart.

    Shot Size

    The shot size is the distance between the screw back position and the zero screw position of an injectionmolding screw. This is a measure of the polymer available for injection for each part.

    Shot size is also known as charge stroke.

    Shot Weight

    In injection molding, the shot weight is the mass of plastic delivered in one complete filling of the mold,including the molded parts, sprue, runners, and flash.

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    Shrinkage

    Shrinkage is the reduction in the dimensions of a plastic part, compared with the mold dimensions.Shrinkage occurs as the polymer cools. Shrinkage can vary in different directions.

    Crystalline and semi-crystalline materials are particularly prone to thermal shrinkage; amorphous materialstend to shrink less. Excessive shrinkage can be caused by the following factors:

    Low injection pressure.

    Short pack-hold time or cooling time.

    High melt temperature.

    High mold temperature.

    Low holding pressure.

    Sink Mark

    A defect on the surface of a molded part. Sink marks are caused mainly by thermal contraction(shrinkage) during packing, if the temperature and pressure are not controlled correctly. They can occuron the opposite side from ribs or bosses because the additional thickness causes increased contraction.

    Solid

    A set of connected surfaces that form a closed shell, enclosing a volume of material, assumed to behomogeneous in properties.

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    Specific Heat

    The specific heat (Cp) of a material is the amount of heat required to raise the temperature of a unit massof material by one degree Centigrade. It is essentially a measure of a material's ability to convert heat input

    to an actual temperature increase. It is measured at zero pressure and a range of temperatures, or averagedacross the temperature range of 50C to the material's maximum processing temperature.The unit ofmeasure for specific heat is J/kg-C, Joules per kilogram celsius.

    Sprue

    The sprue is the main feed channel that connects the mold cavity with runners leading to each cavity gate.

    Start of Fill

    The start of fill is the time at which melted polymer starts to flow. This happens after the screw has startedto move and corresponds to the start of the pressure rise in the nozzle.

    STL File

    STL (stereolithography) is a tessellated representation of the surfaces of a solid, using triangles. STL wasinitially used in rapid prototyping. STL files can be in either ASCII or binary format. All major CAD/CAM systems can generate an STL file of a solid model.

    Streak Mark - Color

    Usually occurs because of different orientation of the pigments in the flow, or poor blending in theplastication stage.

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    Streak Mark - Dark

    Dark colored brown or silver streaks can be caused by thermal damage to the material during filling, orinadequate tool venting. Rectify the venting system, or reduce the injection speed or pressure to avoid

    dark streaks.

    Streak Mark - Glass Fiber

    Rough and mat streaks can be caused by differential shrinkage or premature freezing of glass-filledmaterial against the mold wall. Using shorter glass fibers, increasing melt temperature, or increasing mold

    wall temperature may help solve the problem.

    Streak Mark - White

    Also shown as silver streaks.

    There are a few different types:

    Moisture - Streaking occurs opposite the flow direction, due to a high residual moisture content.Drying the material properly will remove this defect.

    Air - Air is trapped and cannot escape while the mold is filling. The air is drawn to the surface andstretched in the direction of the flow causing streak marks.

    Stroke

    The stroke is the distance between the screw back position and the screw forward position of an injectionmolding screw. This provides a measure of the amount of polymer injected during a cycle.

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    Suck Back

    Also known as decompression or pull-back, suck back is a technique used to clear polymer from theinjection nozzle by moving the screw away from the nozzle.

    Surface

    A rectangular surface defined by a grid of points which represent the control points of a NURBS

    definition of a surface. (NURBS is a Non-Uniform Rational B Spline, a common mathematicalrepresentation in the CAD industry.)

    NURBS surfaces are not often used, because they are limited to a rectangular shape. Trimmed surfaces aremore useful and common. More?

    Surfaces provide important information for meshing operations, which allow much better meshes to beachieved than via facet-based mesh input.

    See also Trimmed Surface on page 74.

    Switch-OverDesignates the transition from one phase to another, for example, the transition from the filling phase tothe packing phase. Various switch-over methods can be used.

    For example, fill-to-pack switch-over can be initiated when the injection time or pressure reaches aspecified value, when a specified percentage of the volume is filled, or when other conditions are met.

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    T

    Tensile Strength

    Tensile strength is the maximum nominal stress sustained by a material being pulled from both ends, at aspecified temperature and at a specified rate of stretching.

    Thermal Conductivity

    The thermal conductivity of a material is the rate of heat transfer by conduction per unit length perdegrees Celsius. It is expressed in units of W/m.C. It is essentially a measure of the rate at which amaterial can dissipate heat, and is determined under pressure and averaged across the material's melttemperature range.

    Thermal Degradation

    Thermal degradation is a break down of material quality, resulting in poor parts. Thermal degradation

    may occur if the barrel temperatures are too high, the rotational speed of the screw is too fast, or thenozzle diameter is too small.

    Tooling Noise

    Excessive tooling noise may occur due to molding problems where the injection pressure is too hightoward the end of the velocity phase. Excessive tooling noise may lead to tool damage after repeatedusage.

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    Transducer

    A transducer is a mechanical or electrical device that is used to measure a value and transmit themeasurement to a recorder, or to a device that can compare the measurement with a desired value.

    Transition Temperature

    The transition temperature is the polymer freeze temperature. At this temperature, the melt-to-solidtransition occurs.

    The transition temperature corresponds to the glass-transition temperature (Tg) for amorphous materialsand to the crystallization temperature (Tc) for semi-crystalline polymers.

    Translator

    A utility that converts mesh or models from one CAD format to another.

    Trimmed Surface

    A trimmed surface is a NURBS surface with a set of curves defined in the UV space of the surface. Thisprovides an easy way to define non-rectangular representations (patches) of surfaces.

    (NURBS is a Non-Uniform Rational B Spline, a common mathematical representation in the CADindustry.)

    Turbulent Flow

    Turbulent Flow occurs when a fluid (such as water) flows with fluid particles experiencing erraticvariations in direction and speed. Turbulent flow is defined as that with a Reynolds number greater than4000. Low Reynolds numbers indicate laminar flow.

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    U

    Unbalanced Flow

    Unbalanced flow occurs when polymer melt completely fills some flow paths in the mold before otherflow paths have filled.

    Undercut

    An undercut is a trapped area in a model, that cannot be ejected from the mold. These areas require aslide, which usually slides in a perpendicular direction to the core and cavity segments as these areas areseparated. In the image below, the the section labeled ais the undercut, and the section labeled bis theparting plane.

    Underflow

    Flow fronts from 2 directions meet, then pause momentarily, long enough for a frozen layer to develop,then the polymer in one of the flows reverses direction and flows back between the outer frozen layers.

    When the flow reverses the frozen layer partly re-melts due to frictional heating. This flow reversal gives

    poor part quality, both from surface appearance and structural viewpoints.To avoid underflow balance all flows so that their flow fronts meet at the end of fill.

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    Uni-directional Flow

    Un