Moldflow Design Analysis Solutions

GLOSSARY

Version 1.0November 2005

2Copyright Moldflow Corporation and its subsidiaries worldwide 2005.

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ContentsA..................................................................................................................... 11

Air Shot ...................................................................................................... 11Air Trap ...................................................................................................... 11Amorphous Polymers ................................................................................. 11Anisotropic Shrinkage................................................................................ 12Aspect Ratio ............................................................................................... 12Automation................................................................................................. 12

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

B-Splines .................................................................................................... 13Back Pressure ............................................................................................. 13Baffle .......................................................................................................... 13Balanced Flow............................................................................................ 14Barrel .......................................................................................................... 14Barrel Capacity........................................................................................... 14Barrel Effect ............................................................................................... 14Batch........................................................................................................... 15Bending Moment........................................................................................ 15Boss ............................................................................................................ 15Boundary Representation Solid.................................................................. 15Bubble ........................................................................................................ 15Bubbler ....................................................................................................... 16Buckling ..................................................................................................... 16Burn Mark .................................................................................................. 16

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

CAD............................................................................................................ 17CAM........................................................................................................... 17Cavity ......................................................................................................... 17Center Gate................................................................................................. 17Centroid ...................................................................................................... 18Charge Stroke ............................................................................................. 18Check Ring ................................................................................................. 18

Chiller......................................................................................................... 18Chord Height .............................................................................................. 19Clamp Capacity .......................................................................................... 19 3

Clamp Force ............................................................................................... 19Closed Loop Controller .............................................................................. 19Closed Volume ........................................................................................... 19Compensating Phase................................................................................... 20Composite Curve........................................................................................ 20

Compressibility Model ............................................................................... 20Conic Arc ................................................................................................... 20Control Limits ............................................................................................ 20Cooling Channel......................................................................................... 21Cooling Time.............................................................................................. 21Core ............................................................................................................ 21Cracking ..................................................................................................... 21Crystalline Polymers .................................................................................. 22Crystallinity ................................................................................................ 22Crystallization ............................................................................................ 22Cure ............................................................................................................ 22Curve .......................................................................................................... 23Cushion....................................................................................................... 23Cycle Time ................................................................................................. 23

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

Decompression ........................................................................................... 25Delamination .............................................................................................. 25Density........................................................................................................ 25Design of Experiments (DOE) ................................................................... 25Disc Gate .................................................................................................... 26Dominant Flow Path................................................................................... 26Draft Angle................................................................................................. 26Drooling...................................................................................................... 26Dwell .......................................................................................................... 27Dynamic Flow ............................................................................................ 27

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

Ejection....................................................................................................... 29Ejection Temperature ................................................................................. 29Ejection Time ............................................................................................. 29Ejector Pins................................................................................................. 29Element....................................................................................................... 30 4

End of Fill................................................................................................... 30Extensional Viscosity ..................................................................................30

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

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

Fan Gate ..................................................................................................... 31Feasible Molding Window ......................................................................... 31Fiber Orientation ........................................................................................ 32Filler ........................................................................................................... 32Fillet............................................................................................................ 32Filling Phase ............................................................................................... 32Filling Time ................................................................................................ 32Finger Gate ................................................................................................. 33Flash ........................................................................................................... 33Flow Leaders and Deflectors...................................................................... 33Flow Path.................................................................................................... 34Free Edge.................................................................................................... 34Free-form Curves and Surfaces.................................................................. 34Friction ....................................................................................................... 34

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

Gate ............................................................................................................35Gate Freeze................................................................................................. 35Gloss Mark ................................................................................................. 35

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

Hesitation.....................................................................................................37High Cushion.............................................................................................. 37Hopper ........................................................................................................ 37Hydraulic Pressure ..................................................................................... 37

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

Injection Location....................................................................................... 39Injection Pressure ....................................................................................... 39Injection Time ............................................................................................ 39Injection Velocity ....................................................................................... 39Injection Volume ........................................................................................39Insert ........................................................................................................... 40Intersecting Mesh Elements ....................................................................... 40 5

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

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

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

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

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

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

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

Manifold Edge............................................................................................ 45Masterbatch ................................................................................................ 45Meld Line ................................................................................................... 45Melt Density ............................................................................................... 46Melt Temperature ....................................................................................... 46Mesh ........................................................................................................... 46Mesh - Midplane ........................................................................................ 46Mesh - Surface (Fusion) ............................................................................. 47Mesh - Volume (3D)....................................................................................47Mesh Intersection ....................................................................................... 47Model.......................................................................................................... 48Mold ........................................................................................................... 48Mold Open Time ........................................................................................ 48Mold Temperature ...................................................................................... 48Molding Window........................................................................................ 49

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

No-flow Temperature ................................................................................. 51Node ............................................................................................................51Nominal Part Thickness ............................................................................. 51Non-manifold Edge .................................................................................... 52Non-return Valve ........................................................................................ 52Normalized Thickness................................................................................ 52Nozzle Pressure .......................................................................................... 52

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

Open Loop Controller ................................................................................ 53Optimization................................................................................................53Orientation.................................................................................................. 53Orthotropic Material....................................................................................53Overlapping Mesh Elements ...................................................................... 54 6

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

Part.............................................................................................................. 55Parting Plane............................................................................................... 55Pinpoint Gate.............................................................................................. 55Plastication ................................................................................................. 56Point............................................................................................................ 56Poisson's Ratio............................................................................................ 56Polymer ...................................................................................................... 56Preferred Molding Window........................................................................ 57Pressure Gradient ....................................................................................... 57Pressure Profile........................................................................................... 57Pressure Stroke ........................................................................................... 57Pressurization Phase ................................................................................... 57Process Control........................................................................................... 58Process Parameters ..................................................................................... 58Process Window ......................................................................................... 58Processing Conditions ................................................................................ 58Production Run........................................................................................... 59Purging ....................................................................................................... 59PVT ............................................................................................................ 59

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

Racetrack Effect ......................................................................................... 61Ram ............................................................................................................ 61Record Groove ........................................................................................... 61Region ........................................................................................................ 62Restricted Gate ........................................................................................... 62Reynold's Number ...................................................................................... 62Rib .............................................................................................................. 62Run ............................................................................................................. 62Runner / Runner System............................................................................. 63

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

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

Screw Displacement ................................................................................... 65Screw Forward Position ............................................................................. 65Screw Velocity............................................................................................ 65 7

Semi-Crystalline......................................................................................... 66Set Points.................................................................................................... 66Shear........................................................................................................... 66Shear Rate................................................................................................... 66Shear Strain ................................................................................................ 66

Shear Stress ................................................................................................ 66Shell............................................................................................................ 67Short Shot ................................................................................................... 67Shot Size..................................................................................................... 67Shot Weight ................................................................................................ 67Shrinkage.................................................................................................... 68Sink Mark ................................................................................................... 68Solid............................................................................................................ 68Specific Heat .............................................................................................. 69Sprue........................................................................................................... 69Start of Fill.................................................................................................. 69STL File...................................................................................................... 69Streak Mark - Color.................................................................................... 69Streak Mark - Dark..................................................................................... 70Streak Mark - Glass Fiber........................................................................... 70Streak Mark - White ................................................................................... 70Stroke.......................................................................................................... 70Suck Back................................................................................................... 71Surface.........................................................................................................71Switch-Over................................................................................................ 71

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

Tensile Strength .......................................................................................... 73Thermal Conductivity................................................................................. 73Thermal Degradation.................................................................................. 73Tooling Noise ..............................................................................................73Transducer .................................................................................................. 74Transition Temperature............................................................................... 74Translator.................................................................................................... 74Trimmed Surface ........................................................................................ 74Turbulent Flow ........................................................................................... 74 8

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

Unbalanced Flow........................................................................................ 75Undercut ..................................................................................................... 75Underflow....................................................................................................75Uni-directional Flow .................................................................................. 76

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

Valve Gate .................................................................................................. 77Velocity Profile........................................................................................... 77Velocity Routines ....................................................................................... 77Velocity Stroke ........................................................................................... 77Velocity to Pressure Change-Over ............................................................. 78Vent............................................................................................................. 78Venting........................................................................................................ 78Viscosity ..................................................................................................... 78Viscosity Index ........................................................................................... 78Viscosity Model.......................................................................................... 79Voids ........................................................................................................... 79VRML image.............................................................................................. 79

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

Warpage...................................................................................................... 81Weld Line ................................................................................................... 81Wire-Sweep Index ...................................................................................... 81

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

Zero Screw Position ................................................................................... 83 9

10

AAir ShotAn air shot is the injection of polymer melt into the air, instead of into the mold. The main purpose of an air 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 moved forward, forcing melted plastic from the nozzle. If the melt is caught in a metal cup, a pyrometer probe can be used to check the temperature of the melt as it exits from the nozzle. This is one of the more accurate measurements of the melt temperature.

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

Amorphous PolymersAmorphous polymers are a family of polymers that are characterized by entangled polymer chains that are loosely 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 have orientation.

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

See also Crystalline Polymers on page 22, Semi-Crystalline on page 66.11

Anisotropic ShrinkageAnisotropic shrinkage is shrinkage that has different magnitudes in different directions. Anisotropic shrinkage occurs in filled materials due to the restriction of shrinkage along the fiber length, which tends to be in the flow direction. It also occurs in un-filled materials when the molecules have insufficient time to relax from the viscous elongation due to shear during flow.

Aspect RatioAspect ratio normally refers to the relation between width and height of a mesh element. These are important because they affect analysis accuracy. Aspect ratios are especially important in sensitive areas such as gates, or gas channels in a gas-injection simulation.

The term aspect ratio is also used when describing fibers. In this context, aspect ratio is the ratio of the length of the fiber to the diameter.

AutomationAutomation is the science of machinery or mechanisms which are so self-controlled and automatic that manual input is not required during operation. Automation is the technique of making a process automatic. 12

BB-SplinesA 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 PressureBack 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 the shear 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 lines which forces the coolant to flow up one side of the plate and down the other. It is used to regulate and direct the passage of coolant fluid so that the coolant can travel into difficult areas for more efficient cooling. By interrupting the flow in the cooling lines the baffles create turbulence around bends and improve the heat transfer capability of the coolant.

See also Bubbler on page 16 13

Balanced FlowFlow is balanced when the extremities of the mold fill at the same time and pressure, as shown in the illustration 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. The cylinder forms the chamber within which the plastic resin is converted from a solid form to a viscous melt.

Barrel CapacityThe barrel capacity is the maximum weight of material that a machine can produce from one forward motion 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 injection molding machine. This compressibility can be significant. A simulation that calculates and uses the barrel effect will produce more accurate results.

See also Compressibility Model on page 20. 14

BatchA 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 MomentA bending moment is the force or load applied to an entity that produces bending of that entity around an axis.

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

Boundary Representation SolidA boundary representation solid is a model format produced from a surface modeling CAD system. The solid is defined as a list of surfaces that enclose a volume.

BubbleA bubble is a spherical, internal void caused by air or other gas trapped within a molded plastic product. A bubble differs from a blister in that the bubble is contained within the part, whereas a blister is on or near the 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. 15

BubblerA bubbler is cooling system component. It is a central circular channel that can be introduced into the mold 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 and around the outside of the channel to the outlet point.

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

See also Baffle on page 13.

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

Burn MarkA burn mark is a defect that appears as a brown or black mark on the part surface. A burn mark can be caused by an un-vented air trap. This occurs when the trapped air is heated very quickly as it is compressed, burning the surrounding plastic. Velocity profiling is often used to prevent this problem, by giving air more time to escape from the mold. 16

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

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

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

Center GateA center gate is a gate which is located in the center of the part. It can be a sprue (direct) gate or pinpoint gate.

See also Gate on page 35. 17

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

Charge StrokeSee also Shot Size on page 67.

Check RingA check ring is the sliding ring of the non-return valve on the front of the screw. The check ring allows melted plastic to flow forward to the front of the screw during plastication, and prevents flow back into the screw during injection. The check ring is a high wear item that can leak during injection, effectively reducing the pressure that is applied to the melted plastic.

See also Non-return Valve on page 52.

ChillerA chiller is a self-contained system comprised of a refrigeration unit and a coolant circulation mechanism consisting of a reservoir and a pump. Chillers maintain optimal heat balance by constantly recirculating chilled cooling fluids to injection molds. 18

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

When generating a mesh, enabling chord height control increases the chance of creating a mesh that closely 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 CapacityClamp capacity is a measure of the largest projected area of cavities and runners that an injection molding machine can safely hold closed at full molding pressure.

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

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

Closed VolumeA closed volume is a group of surfaces connected together to form a polyhedron. A closed volume has no free edges. The structure is used to form inserts and the mold boundary.

See also Free Edge on page 34. 19

Compensating PhaseThe period during the injection molding process when plastic is injected to compensate for the plastic in the cavity shrinking as it cools.

Composite CurveA group of curves that are joined end to end to form a single curve. Composite curves are discontinuous if 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 ModelHeated plastics are compressible. The compressibility of a material affects the volume of plastic required to 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 ArcA mathematical form for representing ellipses, hyperbola and parabolas.

Control LimitsControl limits are statistically determined values between which a control variable is allowed to range without adjusting the process. Control limits provide an indication of the variation in the injection molding process. 20

Cooling ChannelA cooling channel is a passageway in a mold for circulating water or another cooling medium, in order to control 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 or parallel.

Cooling TimeGross cooling time is the time after the velocity phase until the part is sufficiently cooled to be ejected from the mold. Therefore, gross cooling time is the sum of the pressure phase (packing and holding) and the net cooling time.

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

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

CrackingCracking is the formation of a narrow separation in a plastic component, usually by the rupture of chemical bonds due to internal and external stress. 21

Crystalline PolymersCrystalline polymers are a family of polymers that are characterized by an ordered arrangement of the molecules 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 geometric form.

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

See also Amorphous Polymers on page 11.

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

CrystallizationDuring cooling some polymers form an ordered molecular structure which are called crystals. The rate of crystallization is a function of both temperature and time. The level of crystallinity achieved is determined by 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 higher crystallinity resulting in greater shrinkage.

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

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

Sometimes this term is used to describe the solidification of thermoplastics; this is a physical process of removing heat from the thermoplastic. 22

CurveA 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:h A center point and arc and angleh 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 contains polymer left in the barrel after the cavity is filled. Most of the melt in the cushion is then used for compensation flow during the packing stage.

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

Filling time. Packing time. Cooling time. Mold open time. 23

24

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

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

DensityThe density of a plastic part is measured by dividing its mass by its volume. A denser part has more plastic molecules 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 your design have the most, and least, effect on final part quality. DOE also analyzes how part quality changes as input variables change. Engineers use DOE early in the design stage to improve designs. 25

Disc GateA 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 PathThe 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 and the X indicates the last place to fill.

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

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

DroolingDrooling is leakage of polymer from the nozzle, sprue, or gate. This creates thin strands of plastic that can get caught in the mold. 26

DwellDwell is a pause in the mold closing cycle of a compression molding operation to permit gas to escape from the molding material.

Dynamic FlowDynamic flow is the flow before the cavity is actually full, when a flow front still exists towards the end of the cavity. This results in an area within the mold without plastic. 27

28

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

Ejection TemperatureEjection 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 the cooling time, but may increase warpage.

Ejection TimeEjection 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 the moment the mold opens for ejection.

See also Mold Open Time on page 48.

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

29

ElementA 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 FillThe end of fill occurs when the polymer has reached the extremities of the mold cavity and the mold is volumetrically filled.

Extensional ViscosityWhen a polymer flows through a large cross-section to a smaller one, it will extend longitudinally. This will result 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 a material 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. 30

FFamily abbreviationThis is the shortened version of a material family name. For example, PC is the family abbreviation for the family 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 nameThis is the name of a family of materials, for example, Polycarbonate. Each material is a member of a family of materials.

The shortened version of a family name is the family abbreviation. For example, PC is the family abbreviation 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 GateThe 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 WindowA feasible molding window is represented by a set of boundaries that define a window-like shape. For the process setting ranges inside the window boundaries, the molding process is feasible; outside the window boundaries, the molding process is not feasible.

See also Preferred Molding Window on page 57. 31

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

In the illustration below:

1 Random fibers are found at the entrance.

2 Flow-aligned fibers are found in the converging flow area.

3 Transversely aligned fibers are found in the diverging flow area.

4 Fibers parallel to the flow direction are found in the restricted flow area.

FillerFillers are materials that can be added to a polymer for injection molding. Adding a filler to a polymer can increase 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 PhaseThe period during the injection molding process when plastic is injected to fill the cavity.

Filling TimeThe time required for the injection molding machine to fill the part. 32

Finger GateThe finger gate is used when presentation is important and you want to avoid disfiguring the top face of a part. 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.

FlashA flash occurs when the polymer is not totally contained within the mold cavity. The most common causes 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 by attracting it (leaders) or by deflecting it (deflectors). Flow leaders are thicker parts of the cavity (indicated by 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. 33

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

Free EdgeA 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 not been correctly attached.

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

Free-form Curves and SurfacesThese 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 between the part and the mold walls, then the part may be impossible to eject, or it may be damaged during ejection. 34

GGateThe 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 FreezeGate freeze is the moment during the packing phase when polymer at the gate has frozen solid and no more polymer can be packed into the mold cavity.

Gloss MarkGloss is the shiny appearance of a molded part's surface. Differences in the gloss finish of a part are caused by different projection behaviors of the plastic at the mold wall, due to different cooling conditions and shrinkage differences. You can remove dull surface patches by drying the material, decreasing the injection speed or increasing back pressure. 35

36

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

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

HopperThe hopper is the molding machine container that holds the polymer and feeds it to the injection molding screw.

Hydraulic PressureHydraulic pressure is the pressure applied to the injection ram during the injection phase. Setting hydraulic pressure is one way of specifying the velocity phase for the molding cycle. The hydraulic line pressure is the pressure in the main supply line from the pump; typically measured by means of a gauge in the hydraulic line. There is a direct relationship between the injection pressure and the hydraulic line pressure called the machine intensification ratio. 37

38

IInjection LocationThe 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 PressureThe injection pressure is the pressure that is applied to the ram during the injection phase, causing the material to flow, and can be measured approximately by a transducer located in the nozzle. There is a direct relationship between the injection pressure and the hydraulic line pressure called the machine intensification ratio.

Injection TimeThe injection time is the time it takes to fill the cavity.

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

Injection VolumeThe injection volume is the amount of polymer injected into the mold cavity during the velocity phase. 39

InsertAn insert is a component that is placed into the mold before the injection phase and is anchored into the plastic 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 ElementsIntersecting 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 elements are acceptable.

Illustration 2) shows intersecting elements which cut through each other. This is not acceptable. Remove intersecting elements before you run an analysis.

Isotropic MaterialAn isotropic material has material properties that are the same in all directions. There are no directional effects of orientation or crystallinity. 40

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

In the jet, contact points form between the folds of melt, creating small welds. Jetting can lead to part weakness, surface blemishes, and internal defects. 41

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

LoopA group of connected curves that form a complete boundary of a surface. 43

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MManifold EdgeA manifold edge is a mesh edge that has two entities attached to it. An edge is a line segment that connects two mesh nodes.

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

A = Free Edges

B = Manifold Edge

C = Non-Manifold Edge

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

MasterbatchA masterbatch is a concentration of filler or additives in a polymer. The mixture is added in small amounts to create the desired mix.

Meld LineA meld line is a weakness or visible flaw created when two or more flows meet and converge while filling a part. A meld line is typically formed by parallel flows, whereas weld lines are formed by flows meeting at higher angles, often head-on. Meld lines tend to be less weak than weld lines. The quality of the meld line is dependent on the material type, the type and amount of fillers, and the pressure and temperature at the meld line. 45

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

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

MeshInjection molding simulation involves solving the governing equations of mass, momentum, and energy numerically over the physical domain. The numerical implementation involves discretizing the physical domain 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 many connected 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, the more accurate the analysis results, at the expense of longer calculation times.

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

Mesh - MidplaneConsists 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 thickness from the model. The two-dimensional Midplane mesh represent the solid model, using the thickness information, during a molding analysis.

See also Mesh on page 46. 46

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

A surface mesh analysis simulates the flow of the melt on both the top and bottom parts of the mold cavity. 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 locations determined 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 of four 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 IntersectionSee also Intersecting Mesh Elements on page 40.

See also Overlapping Mesh Elements on page 54. 47

ModelA mathematical description of the relationships of the physical entity being described. For example, a geometry model is a mathematical description of the physical shape and characteristics of the part. Other models include viscosity model, process model, etc.

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

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

See also Cycle Time on page 23.

Mold TemperatureThe 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. 48

Molding WindowA process window or molding window, defines the limits of molding conditions under which an acceptable 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 the process window. A poor quality part (marked "X"), is outside the process window. 49

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NNo-flow TemperatureThe no-flow temperature is the temperature at which a polymer ceases to flow inside the mold cavity after injection.

NodeIn 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 an injection 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 are generated. 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 beam element.

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. 51

Non-manifold EdgeA non-manifold edge is a mesh edge with more than two entities attached to it. An edge is a line segment that connects two mesh nodes.

On a Fusion mesh, non-manifold edges should be corrected because they indicate elements which have not been correctly attached.

A = Free Edges

B = Manifold Edge

C = Non-Manifold Edge

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

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

Normalized ThicknessNormalized thickness is a measurement of part thickness. The normalized thickness value ranges from -1 to 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 of specifying the injection pressure of the polymer. 52

OOpen Loop ControllerAn open loop controller does not respond to measurements of the value being controlled.

See also Closed Loop Controller on page 19.

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

OrientationDuring shear flow, polymer molecules align themselves in the direction of flow. The extent of this orientation 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, the molecular orientation is "frozen in".

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

Orthotropic MaterialAn orthotropic material consists of either oriented fibers or oriented polymer chains. Mechanical properties in the direction parallel to the orientation are different from those in the perpendicular direction. 53

Overlapping Mesh ElementsOverlapping mesh elements are mesh elements that overlap in the same plane. Remove overlapping elements 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 still filling. 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. 54

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

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

Pinpoint GateA pinpoint gate is a small gate, generally 0.75mm or less in diameter. In multi-cavity molds, the dimensions of pinpoint gates must be held within very tight tolerances in order to fill all cavities at the same 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 to small 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 be transferred from center of part. 55

PlasticationPlastication is the process in which raw material is changed to melt and pushed to the front of the screw through a rotational action.

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

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

PolymerA polymer is a natural or synthetic compound, usually of high molecular weight. Its long-chained structure consists of repeated linked molecular units called monomers (or mers). Monomers are relatively light 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 of polymeric compound. Plastics are generally formulated with plasticizers, stabilizers, fillers, and other additives 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 and solidification (for thermoplastics) or a chemical reaction (for thermosets). 56

Preferred Molding WindowA preferred molding window is a refinement of a feasible molding window. It is represented by a set of boundaries 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 process is not optimal, but it may be feasible.

See also Feasible Molding Window on page 31.

Pressure GradientThe 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 from higher elevations to lower elevations.

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

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

Pressure StrokeThe pressure stroke is the proportion of the total stroke performed under pressure control. This is the distance between the velocity to pressure change-over position and the screw forward position in an injection molding machine.

Pressurization PhaseThe pressurization phase is the period during the injection molding process when extra plastic is injected to ensure all corners and edges of the mold cavity are full of plastic. 57

Process ControlProcess control is the monitoring and correction of production.

Process ParametersProcess parameters are variables that typically correspond to molding machine settings. Commonly used process parameters include:

Maximum injection pressure. Screw cushion. Pressure stroke. Cycle time. Charge stroke. Mean injection pressure.

Process WindowA process window or molding window, defines the limits of molding conditions under which an acceptable 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 the process window. A poor quality part (marked "X"), is outside the process window.

Processing ConditionsProcessing 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. 58

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

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

PVTPressure-Volume-Temperature (PVT) data describes the specific volume (1/density) of a material as a function of temperature and pressure. It describes the temperature/pressure relationship for polymers over the entire processing range. 59

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RRacetrack EffectThe 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. The recombined 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.

RamIn the injection molding process the ram (or screw) is the part of the injection molding machine that pushes the polymer into the mold.

See also Screw on page 65.

Record GrooveThe appearance of this surface defect is similar to the grooves on a record. Record grooves are formed when 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 injection time. 61

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

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

Reynold's NumberThe Reynolds Number is a ratio that defines the rate of fluid flow in pipes. The onset of turbulence in water is between 2300-4000. The Reynolds Number is assigned to cooling circuits when the flow rate is not known. A Reynolds Number of 4000 is considered fully turbulent but we recommend using a Reynolds Number of 10,000 to represent turbulent flow when running an analysis.

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

RunSee also Production Run on page 59. 62

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

A runner system includes the following:

Runners, shown in red. Sprue, shown in green. Gates, shown in yellow. 63

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SScrewThe screw is the part of the injection molding machine that pushes the polymer into the mold, that is, the shaft that rotates within the barrel of the injection molding machine to process and prepare the material for injection.

Screw Back PositionThe screw back position is the position that the screw is brought back to before the start of the next cycle.

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

Screw Forward PositionThe screw forward position is the furthest forward position of the screw during a cycle.

Screw VelocityScrew velocity is the speed with which the screw has moved during the injection phase. 65

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

See also Crystalline Polymers on page 22.

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

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

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

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

Shear StressShear stress is caused by friction between the moving plastic and the mold wall and between the layers of plastic moving at different rates. High shear stress can cause the plastic to degrade or to fail, due to stress cracks. 66

ShellA group of connected surfaces that form an open shell.

Short ShotA short shot is the incomplete filling of a mold cavity which results in the production of an incomplete part.

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

Shot size is also known as charge stroke.

Shot WeightIn 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. 67

ShrinkageShrinkage 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 materials tend 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 MarkA 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 occur on the opposite side from ribs or bosses because the additional thickness causes increased contraction.

SolidA set of connected surfaces that form a closed shell, enclosing a volume of material, assumed to be homogeneous in properties. 68

Specific HeatThe specific heat (Cp) of a material is the amount of heat required to raise the temperature of a unit mass of 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 averaged across the temperature range of 50C to the material's maximum processing temperature.The unit of measure for specific heat is J/kg-C, Joules per kilogram celsius.

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

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

STL FileSTL (stereolithography) is a tessellated representation of the surfaces of a solid, using triangles. STL was initially 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 - ColorUsually occurs because of different orientation of the pigments in the flow, or poor blending in the plastication stage. 69

Streak Mark - DarkDark colored brown or silver streaks can be caused by thermal damage to the material during filling, or inadequate tool venting. Rectify the venting system, or reduce the injection speed or pressure to avoid dark streaks.

Streak Mark - Glass FiberRough and mat streaks can be caused by differential shrinkage or premature freezing of glass-filled material against the mold wall. Using shorter glass fibers, increasing melt temperature, or increasing mold wall temperature may help solve the problem.

Streak Mark - WhiteAlso 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 and stretched in the direction of the flow causing streak marks.

StrokeThe stroke is the distance between the screw back position and the screw forward position of an injection molding screw. This provides a measure of the amount of polymer injected during a cycle. 70

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

SurfaceA 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 mathematical representation in the CAD industry.)

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

Surfaces provide important information for meshing operations, which allow much better meshes to be achieved 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 to the 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 a specified value, when a specified percentage of the volume is filled, or when other conditions are met. 71

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

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

Thermal DegradationThermal 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 the nozzle diameter is too small.

Tooling NoiseExcessive tooling noise may occur due to molding problems where the injection pressure is too high toward the end of the velocity phase. Excessive tooling noise may lead to tool damage after repeated usage.

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

Transition TemperatureThe transition temperature is the polymer freeze temperature. At this temperature, the melt-to-solid transition occurs.

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

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

Trimmed SurfaceA trimmed surface is a NURBS surface with a set of curves defined in the UV space of the surface. This provides 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 CAD industry.)

Turbulent Flow Turbulent Flow occurs when a fluid (such as water) flows with fluid particles experiencing erratic variations in direction and speed. Turbulent flow is defined as that with a Reynolds number greater than 4000. Low Reynolds numbers indicate laminar flow. 74

UUnbalanced FlowUnbalanced flow occurs when polymer melt completely fills some flow paths in the mold before other flow paths have filled.

UndercutAn undercut is a trapped area in a model, that cannot be ejected from the mold. These areas require a slide, which usually slides in a perpendicular direction to the core and cavity segments as these areas are separated. In the image below, the the section labeled a is the undercut, and the section labeled b is the parting plane.

UnderflowFlow 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. 75

Uni-directional FlowUni-directional flow is flow in one direction, with a straight flow front, during the filling phase. This is desirable because it improves the mechanical properties and quality of the part. Flow direction is determined by polymer injection location. 76

VValve GateA valve gate is a component of a hot runner system. The sprues from the hot runner drop through the cavity plate to the part(s). Each sprue has a rod that can be moved forward to cut off flow through the sprue. The opening of the sprue is timed to be just after the melt front has passed that location. The lower pressure drop through the hot runner system is passed on to the gate, allowing lower filling pressures and reduction in the number of weld lines in the part.

Velocity ProfileThe velocity profile is a graph made up of set points joined by lines. The set points determine the velocity to be used at specific displacement measurements. The velocity profile controls how the part is filled during the injection stage of a cycle.

Velocity RoutinesRoutines are complete processes within Setup Xpert that optimize one aspect of a profile. There are six velocity routines that are used to optimize the velocity phase of the cycle, including the velocity stroke and the velocity profile. While the velocity profile routines are being used, the pressure profile is set to zero.

Velocity StrokeThe velocity stroke is the distance between the screw back position and the velocity to pressure change-over position in an injection molding machine. This is the proportion of the total stroke performed under velocity control. 77

Velocity to Pressure Change-OverThis is the position of the screw when the machine switches the screw displacement control from velocity control (used in the filling stage), to pressure control (used in the packing stage).

VentA vent is a small channel at the end of a flow path that allows air to escape the cavity.

VentingWhen air is trapped within the cavity, for example, at the last point to fill in the mold or at weld lines, blackening or "dieseling" of the part can occur. Venting involves making a minor modification to the mold in the problem area so that entraped air can escape.

ViscosityThe viscosity of a material is a measure of its resistance to flow within a mold cavity.

Viscosity IndexThe viscosity of the material at 1000 1/s shear rate and at a specified temperature.

For example, VI(240)125 means that the material has a viscosity of 125 Pa.s at a shear rate of 1000 1/s and a temperature of 240C.

The viscosity index is used to compare the viscosity of one material to another. 78

Viscosity ModelThe viscosity of polymers is dependent on temperature, pressure and shear rate. The relationship of the variables can be described by one of several equations, called models. For this product you can use either the Cross-WLF or the Second Order model.

VoidsVoids are caused by the plastic pulling away from the middle of the part as the molten plastic cools. The problem is material shrinkage during the cooling phase. Voids are a cosmetic defect if the part is transparent and can be a structural defect if the void is large.

Eliminate voids by using proper cavity pressurization in the packing phase.

VRML imageA VRML image is a three-dimensional image of your model. You can embed a VRML results image in a report. If the person reading your report has a VRML plugin, they can rotate the image, to view the results from all sides of the model. 79

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WWarpageWarpage is a part defect caused by a non-uniform change of internal stresses.

Weld LineA weld line is a weakness or visible flaw created when two or more flow paths meet during the filling process. If the two flow fronts have cooled before meeting they don't interdiffuse well and can cause a weakness in the molded part. A line, notch and /or color change can appear.

Move weld lines to areas where strength is of less importance and visual appearance is less obvious. You can move weld lines by changing:

Polymer injection location. Wall thickness.

Wire-Sweep IndexA value that represents the force created by the flow of plastic past the wires of an integrated circuit. The wire sweep index (also known as sweep index) is the sum of viscosity times velocity at each grid point in the model, with the result averaged by the number of grid points.

If the wire sweep index is high in regions of the model containing wires, then it indicates a possible location for wire breakage. Since viscosity is dependent on temperature, shear rate, and the rate of cure, a sweep index may be reduced by changes to these variables. 81

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Z

Zero Screw PositionThe zero screw position is the furthest forward position possible for the screw. This is when the end of the screw is in contact with the barrel or hits machine 'stops'.