June 2018

Setting up an Autodesk Moldflow Insight Analysis To Match an Actual Molding Process

Chapter 1 – 3

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Contents i

ContentsMatching a Molding Process - - - - - - - - - - - - - 1

Introduction - - - - - - - - - - - - - - - - - - - - - - - - 1Why match an actual molding process in Autodesk Moldflow Insight - 1What is usually compared - - - - - - - - - - - - - - - - - - - - - 1

Basic matching procedure - - - - - - - - - - - - - - - - - - 1Steps - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2

Model verification- - - - - - - - - - - - - - - - - - - - - - 2Thickness verification - - - - - - - - - - - - - - - - - - - - - - - 3

Autodesk Moldflow Insight to CAD - - - - - - - - - - - - - - - - - - - - - 3Autodesk Moldflow Insight to molded part - - - - - - - - - - - - - - - - - 3Core deflection - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4

Other geometry validation - - - - - - - - - - - - - - - - - - - - - 4

Runner system validation - - - - - - - - - - - - - - - - - - 5Model the runner system- - - - - - - - - - - - - - - - - - - - - - 5

Modeling the nozzle - - - - - - - - - - - - - - - - - - - - - - - - - - - -8

Runner and gate sizes - - - - - - - - - - - - - - - - - - - - - - - 8

Cooling system validation - - - - - - - - - - - - - - - - - 10Circuits - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 10Mold material - - - - - - - - - - - - - - - - - - - - - - - - - - 11Inserts - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11Mold boundaries- - - - - - - - - - - - - - - - - - - - - - - - - 12

Boundary element method (BEM) mold boundaries - - - - - - - - - - - - 12Finite element method (FEM) mold blocks - - - - - - - - - - - - - - - - - 13

Cooling parameter validation - - - - - - - - - - - - - - - 14Analysis sequence - - - - - - - - - - - - - - - - - - - - - - - - 14

ii Contents

Coolant temperature - - - - - - - - - - - - - - - - - - - - - - - 14Coolant flow rate - - - - - - - - - - - - - - - - - - - - - - - - - 15Coolant line fouling- - - - - - - - - - - - - - - - - - - - - - - - 15

Thermoplastic material data - - - - - - - - - - - - - - - - 16Viscosity data - - - - - - - - - - - - - - - - - - - - - - - - - - 17Juncture loss coefficients- - - - - - - - - - - - - - - - - - - - - 18PvT data - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 18Mechanical data - - - - - - - - - - - - - - - - - - - - - - - - - 18Shrinkage data - - - - - - - - - - - - - - - - - - - - - - - - - - 19

Process settings validation - - - - - - - - - - - - - - - - 20Cooling settings - - - - - - - - - - - - - - - - - - - - - - - - - 21

Mold surface temperature - - - - - - - - - - - - - - - - - - - - - - - - - 21Melt temperature - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 21Mold-open time - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -22Specify injection + pack + cool time - - - - - - - - - - - - - - - - - - - -22Cooling solver parameters - - - - - - - - - - - - - - - - - - - - - - - - -22

Flow settings- - - - - - - - - - - - - - - - - - - - - - - - - - - 23Molding machine definitions - - - - - - - - - - - - - - - - - - - - - - - -23Filling control - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -26Velocity/pressure switch-over - - - - - - - - - - - - - - - - - - - - - - -28Packing control - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -29Fiber orientation analysis check box - - - - - - - - - - - - - - - - - - - - 31

Warp settings - - - - - - - - - - - - - - - - - - - - - - - - - - 32Midplane meshes - - - - - - - - - - - - - - - - - - - - - - - - - - - - -32Dual Domain meshes - - - - - - - - - - - - - - - - - - - - - - - - - - -343D meshes - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -35

Viewing warpage results - - - - - - - - - - - - - - - - - - - - - 35

Molding verification - - - - - - - - - - - - - - - - - - - - 36Ram speed profiles - - - - - - - - - - - - - - - - - - - - - - - - 36

Contents iii

Ram pressure profiles - - - - - - - - - - - - - - - - - - - - - - 38Material preparation - - - - - - - - - - - - - - - - - - - - - - - 38Pressure measurement- - - - - - - - - - - - - - - - - - - - - - 38

Nozzle vs. Hydraulic pressure - - - - - - - - - - - - - - - - - - - - - - - 39Accounting for nozzle pressure drop- - - - - - - - - - - - - - - - - - - - 39Pressure sensors - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 40

Worn check ring - - - - - - - - - - - - - - - - - - - - - - - - - 40Shot to shot variation - - - - - - - - - - - - - - - - - - - - - - 42Venting - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 42Jetting - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 43

Conclusions - - - - - - - - - - - - - - - - - - - - - - - - 44Warp Troubleshooting Checklist - - - - - - - - - - - - - - 45

Acquire basic information- - - - - - - - - - - - - - - - - - - - - - - - - 45Preliminary checks - - - - - - - - - - - - - - - - - - - - - - - - - - - - 45Verify the part thicknesses - - - - - - - - - - - - - - - - - - - - - - - - 45Verify the feed system - - - - - - - - - - - - - - - - - - - - - - - - - - 45Verify the cooling system - - - - - - - - - - - - - - - - - - - - - - - - - 46Verify molded material - - - - - - - - - - - - - - - - - - - - - - - - - - 46Verify filling and packing - - - - - - - - - - - - - - - - - - - - - - - - - 46Verify warp- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 47

Still having problems - - - - - - - - - - - - - - - - - - - - - - 47

iv Contents

1

Matching a Molding Process

Introduction

Why match an actual molding process in Autodesk Moldflow InsightAn Autodesk Moldflow Insight analysis is set up to match an actual molding process so you can compare results between the simulation and the moldings. By making the comparison, you gain confidence and experience with:

Modeling geometry. Material data. Simulation capability.

With future work, design decisions are made confidently knowing that you can use Autodesk Moldflow Insight to solve problems encountered in the design of new parts and tools.

What is usually comparedComparing simulations to actual moldings is done in many ways: from comparing short shots to measuring warpage. Common methods of comparison include:

Filling pattern. Location of weld lines. Location of hesitation. Injection pressure. Packing pressure decay. Warpage. Deflections out of plane. Shrinkage. In plane change in size.

Basic matching procedureMatching an Autodesk Moldflow Insight analysis to an actual molding process requires ensuring many details are considered. This document will step through the procedure of ensuring that the model and process settings in Autodesk Moldflow Insight are as close as possible to the processing conditions used in production. In a perfect world, an analysis of the

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part including; filling, packing, cooling and warp is done in the design stage before the tool is built. Practically, this does not always happen, and even if it does, the tool and process settings used in production are not the same as what was analyzed. You need to validate all the parameters, as much as possible, are the same between the analysis model and production part.

StepsThe basic steps include:

1. Verify the model in Autodesk Moldflow Insight is the same as the mold steel, or shrinkage compensated CAD Data.

2. Verify the runner system is modeled and the same as used in production.3. Verify the cooling system is properly modeled.4. Verify the cooling parameters used in production and Autodesk Moldflow Insight are the

same.5. Verify the correct thermoplastic material data is used.6. Verify the filling, packing and parameters are the correct.7. Verify the there are no problems with the injection molding machine and the process was

stable when the parts are molded.

Model verificationOne thing you can count on, the model you analyzed is not exactly the same as what is being molded. There are many reasons for this including:

Engineering changes between the time you analyzed the part originally and the time the mold was made.

There may be a deviation between the CAD model of the tool and what is actually cut. The meshed model may represent part size not the tool size. The difference between the

two models is the shrinkage compensation. The mesh must have shrinkage compensation to evaluate linear dimensions. Warp shape and most of the time magnitude can be done with a model with a mesh representing the part size, however, there will be some error.

Core deflection. Maintenance on the tool such as insert replacement may not be to the same tolerances as

the original components.

The most critical attribute to look at is the wall thickness. This can be done in two stages.

1. Verify the Autodesk Moldflow Insight model and the CAD model are the same.2. Verify that the Autodesk Moldflow Insight model and molded parts have the same

thickness.

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Thickness verification

Autodesk Moldflow Insight to CAD

Midplane meshes

For midplane models, the thickness assignment is normally verified by the user in the initial construction, so there is less chance of an error with midplane models. However, the thickness diagnostic should be used to verify that thicknesses are correct. All features should be checked. In addition to the nominal wall being correct, look for areas that you know are thick or thin. If the midplane model is not correct in these areas, the analysis will not pick up race-tracking or hesitation. Also ensure that the mesh density is appropriate. There should be at least 3 elements across a significant thickness change. A thickness change will start to become significant if the wall thickness change is about 25% or more. Smaller nominal walls increase the significance of the thickness changes.

Dual Domain meshes

For Dual Domain meshes, it is more important that the thickness be checked carefully, since Dual Domain automatically determines the thickness of the part. The user can manually set the thickness, but the change between the automatic calculation and the manual adjustment should only be done to correct for mistakes in the automatic calculation.

If the thickness assignments are not correct in Dual Domain in all locations, also look at the mesh match ratio. This should also be very high, (above 90%) to be considered a good model for the Cool + Flow + Warp analysis sequence. Like midplane, there should be 3 rows of elements across a significant thickness change.

3D

Since 3D does not have a thickness property, the thickness of the 3D model will be the same as the CAD model unless there is a meshing error when the initial surface mesh was created. Verify the mesh matches the imported CAD geometry to ensure a correct representation. Mesh density on thickness transitions are important for a 3D model as well. Make sure there is again at least 3 rows of elements across a significant change in thickness.

Autodesk Moldflow Insight to molded part

Assuming that the model is good between Autodesk Moldflow Insight and CAD, any problems found are likely due to tooling or engineering change issues. Look for variations in wall thickness on the molded part. If possible, cut the part into pieces to be able to measure the wall thickness in many places. In Figure 1, the part design was changed after the original design and flow analysis was done, significantly changing the fill pattern. When the filling pattern between the simulation and the molded part are not correct, carefully compare the

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molded part thickness to the model, and determine if there is any thickness variations. If there are, make adjustments to the Moldflow model and run the analysis again.

Figure 1: Change in thickness

Core deflection

Core deflection may be a problem. Check the wall thickness at several locations around cores to determine if the core has shifted. If you see a problem, it would be a good idea to check several parts to see if the thickness changes are consistent. If you see the core deflection, consider running a core deflection analysis. The predicted thicknesses of the part due to the deflecting core will be used in the warpage analysis.

Other geometry validationIt is a good idea to make sure not only thickness but other dimensions of the part are properly modeled between the Autodesk Moldflow Insight model and molded part such as over all dimensions, location of critical features, etc.

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Runner system validationThe feed system must be created for analysis in the Autodesk Moldflow Insight. The runner influences:

Pressure required to fill the tool, pressure ratio between the part and feed system. Shear heat of the polymer, i.e. the temperature entering the part. Flow rate in the part. Material compressibility. Volume ratio of the part to the runner.

Model the runner systemThe runner can have a very significant impact on the part. The pressure required to fill the runner system is one aspect. If you are comparing the simulation to the pressure required to fill the part on the machine, the runner system must be modeled. For some tools, the pressure drop through the runner system is a small fraction of the total pressure drop, but in other cases, the pressure drop in the runner may be much higher than the pressure drop of the part. Sometimes, many times the pressure drop of the part.

The runner’s influence on the compressibility of the material is another consideration. In the example shown in Figure 2 on page 6, the part has a volume of one cubic centimeter (1 cm3). It is a 16 cavity tool. The material is semi-crystalline and highly compressible. Analyzing the part by itself, the chosen injection time is 0.5 seconds, which requires a flow rate of 2 cm3/s. The actual time to switch-over for the part is 0.55 seconds. The tool is a 16 cavity mold with a geometrically balanced hot runner system. Therefore, the flow rate for the tool should be 32 cm3/s. However, the runner system has a significant influence on the compressibility of the material, which in turn influences the flow rate into the part.

When the flow rate is 32 cm3/s used with the runners, the time to switch-over for the part is 0.72 seconds, a 31% increase in fill time, due to compressibility of the material in the hot runner system. Assuming the processing engineer knew that the time at switch-over should be about 0.55 seconds, the flow rate must be adjusted to 38 cm3/sec, on the machine, to make the switch over time about 0.55 seconds.

If you needed to simulate the molding process, you know that the time to switch-over is 0.55 seconds and the flow rate is. If you did not have the runner system modeled and had a single cavity, the flow rate of 38 cm3/sec divided by 16 to get a flow rate of 2.375 cm3/s for a single tool. Running a fill analysis, for the single cavity tool, the time to switch-over is 0.46 seconds, not the target 0.55 seconds.

The pressure required to fill the part is also dependent on the flow rate. In Figure 3 on page 7, five studies are shown with various combinations of runners and flow rates. The key indicates the number of parts, (1part, or 16parts), then the flow rate (2ccs), and the time at switch-over

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(t=0.55). One example is 1 part with a runner using occurrence numbers. The specific path is highlighted in cyan in Figure 2.

Figure 3 on page 7 shows the pressure at the injection location for several studies. The red curve is the single part at the chosen injection time, and flow rate of 2 cm3/s. The green line shows the pressure of the 16 cavity tool with runners. The flow rate was adjusted to 32 cm3/s to be equal to the single part. However, the pressure to fill nearly doubles. Part of the increase is the pressure through the runner. The second reason for the increase is poor molding conditions. With the compressibility in the runner making the time to switch-over 0.73 seconds, the material’s temperature is dropping significantly causing the viscosity and pressure to spike. In this case, the pressure to switch-over drops when the flow rate is increased to 38 cm3/s to make the time to switch-over 0.57 s.

To simulate the molding process, you know the flow rate is 38 cm3/s. If you did not have a runner system, divide the flow rate by 16 to get a flow rate of 2.375 cm3/s. This is different than the original flow rate of 2 cm3/s, because of the flow rate required to account for the compressibility in the runner. The pressure required to fill the part is, in this case, is less than the pressure for the original part. In many cases, a faster flow rate would result in a higher pressure. The reason for the pressure dropping is that our benchmark flow rate of 2 cm3/s is a bit too slow for the part. If the processing conditions were more optimum, the changes in flow rate may not have as big an impact.

Figure 2: 16-cavity tool with one path highlighted

The volume of the runner system has a significant effect on the predicted pressure and cavity flow rate, as shown in Figure 4 on page 7. The diameter of the manifold is changed in Figure 4. The large manifold has a volume of 177 cm3, the nominal 53 cm3, and a small manifold sized at 31 cm3. All three manifolds have volumes greater than that of the part which is 16cm3. The volume of the hot runner system should be less than the volume of the parts to ensure the volume of the hot runner gets emptied at each shot. Even with the small manifold, it takes two shots to empty the manifold. The longer the residence time, the higher the likelihood of the material degrading in the manifold.

The large manifold is of particular interest because as a flow rate of 32 cm3/s, the part short shots because the flow rate in the part is too low. When the flow rate for the large manifold is increased, so the part’s switch-over time is about 0.57s, the pressure is quiet low and the parts fill. As you would expect, the pressure to fill with the small manifold is the highest.

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Figure 3: Pressure at injection location for several studies

Figure 4: Pressure at the injection location comparing runner volume and flow rate

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Modeling the nozzle

When replicating the pressure of the molding machine in the simulation is critical, consider where pressure on the machine is being measured, see Figure 5. If you have pressure data, preferably a curve throughout the cycle, you should model the machine nozzle to the point of the pressure transducer. If you have “injection pressure” from the machine controller, often the pressure transducer is behind the screw or in the hydraulic cylinder. In this case, model the entire machine nozzle starting at the barrel end cap, to account for pressure losses in the machine nozzle. In some cases, the pressure drop through the nozzle can be 20% or more of the total pressure required. The nozzle, in addition to other parts of the feed system, have changes in cross-sectional size. These changes in size influences the pressure drop. Material properties called Juncture loss coefficients help model the change in pressure drop. Not all materials have Juncture loss coefficients. See “Juncture loss coefficients” on page 18. for information on juncture losses and accounting for the pressure in the nozzle. See “Pressure measurement” on page 38. for more information on comparing the pressure from the molding machine to the simulation. The solver calculates the compressibility in the barrel.

Figure 5: Machine Nozzle

Runner and gate sizesEnsure that the runners in the tool are correctly cut. The runners in the simulation model must be the same as the tool. If the runners are different, modify the simulation model and run an analysis with the actual sizes used in the tool. In some cases, the tolerances held on runner systems are not very good.

To see the influence of changes in runner and gate size, a two cavity model with geometrically balanced runners was created. The part is 2.5 mm thick, 40 mm wide, and 100 mm long with a triangular projection at the end of fill so the last place to fill is consistent for all parts. The model used is shown in Figure 6 on page 9. The nominal secondary runner is 5 mm in diameter, and the nominal tertiary runner is 4 mm in diameter. About 70% of the total pressure drop with these nominal runner sizes is in the feed system, the remaining 30% is in the part. The Velocity/Pressure switch-over is at 99%. The runner size changes were 0.05 mm (0.002”) and 0.25 mm (0.010”).

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Figure 6: Runner sizes inconsistent

Figure 7 on page 10 summarizes the imbalance in volume and time. To calculate the volume, all the Fill time results were scaled from 0.95 to 1.12 seconds. The difference in the flow front location at 0.95 seconds was determined. The length difference between the flow front locations and the part cross-section (1 sq.cm) was used to calculate the volume imbalance. The time imbalance was determined be the fill time difference at the last point to fill. The imbalance with the 0.05 mm runner variation, is probably acceptable in most cases. However, the imbalance for the 0.25 mm runner variation is probably not acceptable.

The gate size nominally is 1 mm thick by 3 mm wide. The shear rate at the nominal size is about 22,000 1/sec. Changes in runner size influence the gate shear rate because once one cavity fills, the entire flow rate is directed to the other cavity. The shear rate imbalance at the gate is negligeable for the 0.05mm runner variation, but the shear rate spikes to 43,000 1/sec., nearly doubling because of the imbalance in the runners.

For full round runners, make sure that the runner mismatch does not exist or is very low. Figure 8 on page 10 shows an example of mismatched runners. If the runners are mismatched, the runners should be re-cut to eliminate the mismatch. To model the mismatch, model the runner in 3D and use tetrahedral elements. Determining the correct diameter to use to represent the mismatch will be difficult. For trapezoidal runners, make sure you have correct dimensions in all directions. The same would be true for all non-round runner cross sections.

The variation in balance will change widely depending on the specific mold design. It is best to ensure the size of the feed system in the simulation matches the sizes actually cut in the tool.

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Figure 7: Imbalance due to runner sizes incorrect, Fill time result scaled from 0.9 - 1.12s

Figure 8: Runner mismatch

Cooling system validation

CircuitsAll the cooling lines must be modeled in the tool. Be sure to verify the actual placement of the waterlines in the tool. All the diameters should be verified.

Ensure that all the circuits in the tool are modeled with hoses as necessary to replicate how the tool is plumbed in production. This may be an issue as many tools are not plumbed the same way each time the tool is set.

If you think the coolant source is pressure limited and not flow rate limited, consider modeling the quick disconnects used on the tool. In general, they are highly restrictive and will have a higher pressure drop for the quick disconnect as there is in the tool itself.

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Mold materialThe mold material should be considered. Most tools have several different tool materials in them. P20 is very common for the mold base. Other materials such as H-13, S-7, Stainless steels and others are used for various tooling components. The thermal conductivity of all these materials is close enough so the mold temperature distribution is statistically insignificant; however there is a statistical significance in the mold temperature. P20 is the default mold material. If the mold base is stainless steel or if most of the material, between the water lines and part, is a material other than P20, consider changing the mold material. Figure 9 compares the thermal conductivities of nearly 100 grades of materials used to make injection molds. For each grouping of materials, the median, minimum and maximum values for the grouping is indicated.

InsertsFigure 9 shows the range of thermal conductivities for many materials used to construct injection molds including non-ferris alloys such as beryllium copper alloys. Copper alloys have conductivities that are 2.5 to 10 times that of P20. If the tool has a copper alloy or some other high thermal conductivity alloy, make sure this area is modeled with an insert for the cooling analysis using the correct grade of material.

Figure 9: Thermal conductivities of various mold materials

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Mold boundariesBoundary element method (BEM) mold boundaries

When running a BEM cooling analysis, with an analysis sequence including Cool, the mold boundary should be created. The mold boundary is not mandatory, but will help the BEM cooling analysis converge better. If you have run a cooling analysis without a boundary, look carefully at the log file and Temperature, mold results. The log file may have warnings related to the convergence of the temperature solution. Adding a mold boundary may improve the results.

The mold boundary does not have to be the exact size of the tool. It defines the boundary of space for the explicit heat transfer analysis. It is best to create it so it encompasses all other geometry, including:

The water lines & hoses do not need to penetrate the mold boundary. It is best if they don’t. A cooling channel that passes through a triangular element, in this case on the mold boundary, may cause errors in the analysis making the temperature solution not correct in that local area. Figure 10 shows an example of a BEM cooling analysis model. The mold block does not encompass all of the cooling lines. When a cooling line passes through a mold block wall, the beam should not pass through or close to the centroid of an element on the mold block, so elements were deleted. By creating a mold block larger so it encompass’ the cooling channels, there will not be an analysis error caused by beams passing through triangular elements.

Figure 10: BEM cooling analysis model

Part. Feed system.

Water lines. Inserts.

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To create the mold boundary1. Determine the size to make the boundary.

The boundary should be about 50 mm to 100 mm (2 in to 4 in) larger in each of the X, Y, and Z directions.

2. Click Home > Geometry > Create > Mold Surface.

3. Enter the dimensions in the X, Y, and Z fields.

4. Modify the layer assignments and attributes if desired, to reduce the number of layers.

4.1 Move the Mold surface (default) (Regions) to the Mold surface (default) (Elements) layer.

4.2 Set the Mold surface (default) (Elements) layer display properties to:

Uncheck Visible for Node.

Uncheck Visible for Region.

Set Show as to Transparent for elements.

Finite element method (FEM) mold blocks

An FEM cooling analysis uses the analysis sequence that includes Cool (FEM). FEM models require the mold to have a tetrahedral mesh. Figure 11 on page 14 shows an example of an FEM study showing the mesh through the various components. FEM models can be used with Dual Domain or 3D part models. Water lines can be beams or tetrahedral elements. Beams are most common. Inserts are modeled to represent features of different mold materials such as a copper alloy. The model shown in Figure 11 was imported as an assembly so there is a distinct parting line. However, a mold block can be created in Synergy with the same tool as described above.

To create the mold block, the analysis sequence must contain Cool (FEM). When the Mold Surface tool is executed, it will create either regions, or a CAD body. Then the mold block must be meshed with the tool Mesh tab > Mesh panel > Mold Mesh. A triangular surface mesh is created first, then the tetras are created. Before creating the tetra mesh, the surface mesh should be checked for: intersections, overlaps, and free edges. The surface mesh must be watertight before converting to a tetra mesh.

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Figure 11: FEM mold components

Cooling parameter validation

Analysis sequenceThe analysis sequence should be either Cool + Fill + Pack + Warp or Cool (FEM) + Fill + Pack + Warp. Preliminary analysis work can be done with different sequences, but the final sequence must be, one of the two above.

Coolant temperatureBoth coolant flow rate and temperature are important to verify for the analysis. The coolant temperature is normally not difficult to verify, as the coolant source usually has some sort of temperature readout. If the coolant source is not a heater or chiller at the press, some sort of temperature validation should be done. If there is day to day or season to season variation in the water temperature, this will be a source for error in the results between Autodesk Moldflow Insight and the molding process.

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Coolant flow rateThe flow rate of the coolant is normally much more difficult to verify. Depending on the cooling line layout, this can be a significant factor. Preferably, every circuit into the tool should have a controlled flow rate. This rarely happens. In this case, the total flow rate to the tool should be verified, even if this is as simple as timing the filling of a 5 gallon bucket with water. A better idea is a portable flow rate gauge that can be connected to a circuit using the quick disconnects.

If only the flow rate to the entire tool can be determined, the analysis should be set up using total flow rate rather than the flow rate per circuit.

:

To set the coolant properties1. Select the Inlet Boundary Condition at the end of a coolant circuit.

2. Right-click and select Properties from the context menu.

3. Ensure the Coolant type is correct.

If it is not water, select the correct coolant from the database.

3.1.Edit the coolant properties as necessary.4. Set the correct Coolant Control.

The default is 10,000 Reynolds number.

Total flow-rate (All Circuits) allows you to specify the total flow rate going to the tool.

If total flow-rate is used, all coolant inlets must be set to this value.

Flow rate or pressure for each circuit can also be set.

5. Set the correct Coolant inlet temperature.

Coolant line foulingWith steel tools, minerals can build up the on the inside diameter of the coolant lines. The thermal conductivity of this mineral deposit is only about 2% of the steel. The thermal resistance of 1 mm of a mineral deposit is equal to about 50 mm of steel. Autodesk Moldflow Insight can’t account for this buildup. If the tool has this buildup, the mold surface temperature will be hotter than is predicted in Autodesk Moldflow Insight. This may have an influence on the warpage, packing and possibly filling of the tool. There are solutions that can be pumped through cooling lines to clean them out. Clean out the cooling channels for a better running tool.

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Thermoplastic material dataMaterial data is one of the most important inputs for the analysis. The simulation should use the exact material that is being molded and the testing should be verified. Moldflow has implemented a material data quality assurance program. This has improved the data quality in the material database. However, when working on critical problems, in particular warpage, it is critical that the best possible material data is used. In addition to using the exact grade of material, the material should have a known testing source. Figure 12 shows examples of material data sources. The source has three components, rheological, pvT and mechanical properties. For the rheological data, the source is listed as:

Autodesk Moldflow Plastics Labs. Beaumont Advanced Processing. Manufacturer. Other.

Figure 12: Material Data source description

In the Autodesk Moldflow Insight 2019 release, about 42% of the materials were tested by Autodesk, 43% were tested by the manufacturer, and 15% by other sources. The other source is one of many different third party testing facilities. It is important that all data in particular rheological data is tested with methods suitable for injection molding simulation. In most cases, the testing methods are not known for data sources of Other and Manufacturer. Although the testing methods used for materials that are listed as unknown may be appropriate for injection molding, the material data should be considered a potential source of error in the simulation when the testing methods are not known. The data needed is also dependant on the type of analysis work being done, what is being compared between the actual molding and the simulation and the mesh type used in the simulation.

A material quality rating indicator has been implemented for thermoplastic materials. There are three levels including Filling, Packing, and Warpage. Each level has three ratings Bronze Silver and Gold, with Gold being the highest. The Filling level is the lowest, then Packing and Warpage is the highest. A higher level indicator such as warpage cannot have a higher rating than a lower level indicator. When duplicating an actual process, the material rating should be Gold for all levels. If a material is not Gold rated for all levels, investigate why. The material data may be acceptable, but it may not meet some quality standard, such as the date of the test. The lower the material rating, the more likely the material data is suspect.

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When doing a warpage analysis, you should have Gold rated data. However, still check the actual data. For midplane and Dual Domain, the material should have shrinkage testing and have CRIMS data. For 3D models, CRIMS data is not used, but mechanical data is. Be sure the material you are using has either CRIMS for midplane and Dual Domain, or mechanical data for 3D warpage analyses.

Viscosity dataWhen the exact grade of material that is being molded is not in the material database and a substitute is being used, care should be taken when choosing a substitute. Contact your materials supplier. They may have up to date material data for your material, or can help you pick a substitute material. You can also contact Autodesk Moldflow Plastics Labs at mplMoldflow@autodesk.com for assistance at picking a substitute.

A material must be found with a similar viscosity, in the same polymer family, with the same type and amount of fillers, and the same manufacturer when possible. Expect about a 10% difference in pressure prediction for about a 10% change in filler by weight. When you select a grade from a different manufacturer, a 40% difference in pressure is common.

With some materials, their viscosity is highly dependent on the pressure at which they are molded. In the example of Figure 13, the pressure at the end of fill is nearly 20MPa below the experimental pressure. By adding pressure dependence, the simulation was nearly identical to the experiment at the end of fill. Also notice that the pressures in the cavity are nearly identical between the experimental and simulations with and without pressure dependence.

Most materials in the database do not have pressure dependence in the viscosity model. If you are concerned about pressure dependence, consult Autodesk Moldflow Plastics Labs to obtain this data if it is needed.

Figure 13: Pressure dependence effect on viscosity

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Juncture loss coefficientsWhen the polymer passes through a change in diameter in a beam element such as the machine nozzle, runners or gates, there is a hydraulic pressure loss. This can be calculated using Bagley correction constants, C1 and C2. Some materials have these constants. For those materials that do not have the coefficients Autodesk Moldflow Plastics Labs can test this data. Figure 14 shows an example of how the juncture loss better predicts the pressure loss through a machine nozzle.

Figure 14: Juncture loss through a nozzle

PvT dataFigure 12 on page 16 shows an example list of material data sources, with PvT data, as both Measured, and Supplemental. Measured data means the specific grade of polymer has PvT data; while Supplemental means the PvT data is from a material of the same chemical type and filler level. Supplemental data is adequate for filling issues, but should not be used when comparing attributes that rely on packing such as, linear dimensions, warpage, and pressure traces during packing. Measured PvT data should be used when doing a warpage analysis.

Mechanical dataMechanical data should be measured when doing a 3D warpage analysis. However, most materials do not have measured mechanical properties. For midplane and Dual Domain meshes using CRIMS or residual strain shrinkage models, the measured mechanical data is not as critical as it is for 3D warpage.

For 3D warpage analysis, the warpage solution is sensitive to the coefficient of thermal expansion (CTE). For most materials this information is supplemental. Preferably, this information should be specific to the grade. The 3D meshed part shown in Figure 15 on

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page 19 was analyzed with different CTE values. The deflections are graphed in Figure 16. The CTE values were changed by +/- 25% and 50%.

Figure 15: Path plot used to compare CTE values

Figure 16: Comparison of CTE’s on a 3D warpage analysis

Shrinkage dataWhen using midplane and Dual Domain meshes, shrinkage data should be used when comparing warpage results. Figure 17 on page 20 shows an example of the warpage correlation for the part shown in Figure 18 on page 20. When shrinkage data is not used, the shrinkage model is called the Uncorrected residual stress model. The magnitude of the warpage is good in trend, but the magnitude is improved when shrinkage data is used by using the CRIMS shrinkage model. When comparing linear dimensions, or warpage on the part, the CRIMS or residual strain shrinkage models must be used to get a good correlation. Both of these shrinkage models require shrinkage testing.

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Figure 17: CRIMS vs. uncorrected residual stress (Courtesy of Rhodia Engineering Plastics)

Figure 18: Part used to measure warpage (Courtesy of Rhodia Engineering Plastics)

Process settings validationCollect all the information necessary about the processing conditions used for production. When possible, get printouts from the machine controller to see the actual settings and machine response rather than a machine setup sheet which may not reflect the currently running process. Once all the machine parameters are collected, determine how the data must be converted so it can be used as input using the Process Settings Wizard.

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Cooling settings

Mold surface temperature

Since you are trying to duplicate an existing process, the cycle time is defined. The mold surface temperature is not used for this type of analysis except for an initial starting point.

However, this number should represent the “Target” mold temperature you would like to achieve. The cooling analysis will be driven by the cycle time and the coolant temperature entered. The difference between Mold surface temperature and coolant inlet temperature is at a minimum 5ºC (9ºF) to 70ºC (125ºF) at a maximum.

Once the analysis is done, the actual mold surface temperature should be compared to the cooling analysis result. To do this, measure the cavity and core surface temperatures using an IR camera or hand held pyrometer. Like the melt temperature, it should be done several times. The press should cycle 3 to 5 times between measurements. A minimum of 5 measurements should be done for each location.

Melt temperature

On the molding machine, there is a wide variety of controls that influence the “melt temperature”. For the purposes of a flow analysis, the melt temperature is uniform, and is equal to the temperature of an air shot.

Measuring the melt temperature on the molding machine

The best way to measure and verify the melt temperature is with an air shot.

To measure the melt temperature1. During a stable production run, interrupt the process.

2. Purge a full shot at the flow rate of injection.

Depending on the size of the shot, the purging can be done:

Directly on the machine base.

On a piece of cardboard or some other type of insolated material.

In a Teflon cup.

3. Immediately measure the temperature with a hand held Pyrometer.

You want a pyrometer with a very quick response time as the melt is constantly cooling.

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Mold-open time

The mold-open time specifies the time taken from the completion of one molding cycle, to the beginning of the next. This information can be calculated from the process information for the press.

Specify injection + pack + cool time

The injection + packing + cooling time is equivalent to the total cycle time minus the mold-open time. The times for required here can be calculated from the machine setting printout.

Cooling solver parameters

BEM solver parameters

For BEM cooling analyses, typically the default solver parameters are used. If there are areas in the results with high temperature gradients that you don’t expect, turn off the aggregated mesh solver, shown in Figure 19. The analysis time will be much longer but will represent the temperature gradients better.

Figure 19: BEM cool solver parameters

There is significant debate into the exact procedure used to measure the melt temperature when taking an air shot. Some parties say that stirring the molten plastic achieves the most accurate temperature. Others would say that the pyrometer should not be stirred. In either case, preheating the pyrometer to the expected melt temperature or above is generally considered a good idea.

The melt temperature should be measured several times to ensure a consistent answer, no matter what method of purge collection and stirring philosophy you adopt. Between each measurement, the molding press should be allowed to cycle to get the plastication stable again.

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FEM solver parameters

With an FEM analysis, you have more options for how to set it up. The Mold Temperature options, shown in Figure 20, include:

Averaged within cycle, which is equivalent to BEM solver output. Transient within cycle. Transient from production startup.

In most cases Averaged within cycle will give you excellent results and will work well as input to filling, packing and warpage. The averaged within cycle also runs faster than BEM models in most cases. If however, there are hot spots in the tool that are well above the mold temperature guidelines or differential cooling is the primary cause of warpage, then setting the mold temperature option to Transient within cycle is a good idea.

Figure 20: FEM cooling - mold temperature options

Flow settings

Molding machine definitions

Most flow analysis work can be done with the Default molding machine. However, if you need to match the production process, you will need to either select the exact machine used from the machine database or create/modify an existing one. Typically the parameters that need to be set include:

Injection unit - Machine screw diameter. Hydraulic unit - Machine pressure limit, either by injection pressure or hydraulic pressure. Clamping unit - Maximum machine clamp force.

The screw diameter must be set if an absolute ram speed profile is to be used. The barrel diameter is needed to calculate the proper volumetric flow rate. The injection pressure and clamp force are not critical but good to have. If the machine is pressure limited or the maximum clamp force is reached, the solvers will modify the injection or packing phases to

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maintain the limit. If however, the injection settings are kept will above the machine’s actual limit, then you just interpret the results and make changes to lower the pressure or clamp force.

For matching an actual process, setting the machine’s pressure limit is only critical if the machine is pressure limited. It is not likely that machine is clamp tonnage limited to the point the clamp force is exceeded in the process you are trying to duplicate. If it is clamp force limited the part would flash.

To select a molding machine in a specific study1. Double click on the Process Settings in the Study Tasks List.

2. Navigate to the Flow Setting page.

3. Click on Advanced Options.

4. Click Select in the Injection molding machine frame.

5. Pick the specific molding machine you are using.

Use the Search tool to help narrow down the search.

Click the Select button when the machine is found.

Edit machine definitions

If the machine being used in production is not found, the parameters of the machine can be edited.

To edit a machine1. Double click on the Process Settings in the Study Tasks List.

2. Navigate to the Flow Setting page.

3. Click on Advanced Options.

4. Click Edit in the Injection molding machine frame.

This will allow you to edit the currently selected machine, probably the default machine.

5. Click the Injection Unit Tab.

6. Ensure you set the following:

Maximum machine injection stroke.

Maximum machine injection rate.

Machine screw diameter.

Filling control.

Make sure you select the method your molding machine sets the filling or velocity control.

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Ram Speed control steps.

Pressure control steps.

7. Click on the Hydraulic Unit tab.

Ensure the following is correct:

Maximum machine injection pressure.

Maximum machine hydraulic pressure.

Intensification ratio.

Make sure that the hydraulic pressure * intensification ratio = injection pressure.

8. Click on the Hydraulic Unit tab.

Ensure the following is correct:

Maximum machine clamp force.

Check, Do not exceed maximum clamp force.

Pressure limited simulation

Figure 21 on page 26 shows an example of a simulation that is pressure limited. The Pressure at the Injection Location shows a flat line at the pressure limit. The pressure limit for the machine was low at 120 MPa. The Default molding machine was edited in the study to match the machine capacity. Once the simulation reaches the limit, the solver will slow the flow rate to maintain the pressure. In severe cases, a short shot will result. If the fill pressure is close to the machine pressure limit, is it important to ensure the molding machine definition has the machine’s pressure limit defined.

If the machine information is not present or correct, you will not be able to properly set up the velocity profile that is used on the molding machine.

Setting the machine information as described above can only be used for study you have open when editing the data and any study you create by saving as or duplicating from this study.

If you plan on using these machine’s settings again, create a molding machine property manually and save it to a personal database using Tools > New Personal Database.

You may want review the online-help topic “To create a new personal database” for complete details.

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Figure 21: Pressure limited analysis

Filling control

The most difficult aspect to match between Autodesk Moldflow Insight and the molding floor is the filling control information. There are many different methods machine controllers use to input this information. Autodesk Moldflow Insight gives you many methods of inputting the filling control information. The molding machine should have one of the filling controls supported by Autodesk Moldflow Insight listed below:

The method of velocity input. Ram speed vs. ram position. Flow rate vs. ram position. %Maximum ram speed vs. ram position. Ram speed vs. time. Flow rate vs. time. %Maximum ram speed vs. time.

The screw diameter is needed to use the ram speed profiles listed above. Make sure you understand the units involved. The machine’s controller may not use the same units as required for input in the simulation. As an example, the shot size may be done in centimeters, and the simulation requires inches.

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Also important is the starting ram position, and cushion warning limit. This information is required for the Absolute ram speed profiles listed above. The method of V/P switch-over is also important. If position is used, the location must be known. If the molding machine uses a pressure transducer in the tool to control the V/P switch-over, this information must be known. The location of the transducer and the pressure to trigger the switch-over must be determined.

The best choice for a velocity profile when trying to match a production process is Absolute Ram Speed Profile. Fill time, or flow rate can be used, but the vast majority of molding processes have some sort of velocity profile. By using fill time or flow rate, you are introducing errors into your analysis because you are trying to replicate an existing process. Fill time and flow rate are most common when optimizing the process, before production has started. Figure 22 shows an example of the errors caused by using an injection time versus using the actual injection profile. The graph on the left shows the pressure trace of the simulation using an injection time compared to the molding. The injection time was used based on the time to switch-over. The graph on the right shows pressure traces when an actual ram speed profile was used. The simulation closely represents the time when the flow front reaches the pressure transducers and the pressure profile.

Figure 22: Injection time vs. injection velocity

To define the absolute profile, the values of the profile must be entered with the values in the first column listed in ascending order if the value is time, or descending order, if the value is ram position. Figure 23 on page 28 shows an example of a ram speed profile where there is a linear change in ram speed between the ram positions. Not all molding machines allow for this change. Figure 24 on page 28 shows a similar profile, but in this case, the ram speed is stepped. Make sure you understand how the machine controller works regarding profiles. There should be graphical outputs showing the set and actual profiles so you can see how the machine works. The Starting ram position value and the first ram position in the table are the same in the examples below. However, the values do not need to be the same. The ram speed between the starting ram position and the first ram position listed in the table is the ram speed listed for the first ram position.

Using injection time Using an injection profile

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Figure 23: Absolute profile, ram speed vs. ram position-profiled

Figure 24: Absolute profile, ram speed vs. ram position-block

Velocity/pressure switch-over

In most molding setups, switch-over is done by ram position. Ram position defines the switch-over by the location of the ram expressed in linear units of millimeters or inches. This switch-over method can only be used with an absolute ram speed profile. Getting the V/P switch-over correct can make a big difference in the maximum injection pressure and the maximum clamp force used.

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When comparing the pressures from the simulation to the actual molding, it is dangerous to consider just the maximum pressure. In Figure 25, the switch-over was set at 90% and 99%. The difference in pressures are very significant due to the small thin geometry at the end of fill. When switching at 90%, the flow front is just entering the thin area and at 99%, the thin area is nearly filled. If the simulation was compared to the actual part only by maximum pressure, the simulation may look like it is not predicting the pressure correctly, but the problem may be the switch-over in the simulation vs. the molding.

Figure 25: Pressure spike at end of fill

Switch-over by time

Switching over by time might be a useful tool for matching an actual process. Most machine controllers output the time at switch-over. If the ram speed is constant, you know the time at switch-over and you have short shots, you can iterate the input injection time, or flow rate to get the correct short shots at the time of switch-over. Run a fill analysis, setting the switch-over to the time you have from the machine. Set the filling control that you want to use. Compare the short shots to the filling pattern at the V/P switch-over. Using switch-over by time is a simple approach to match an actual process if the fill velocity is constant.

Packing control

The pack/hold control specifies the method by which the pressure phase of the molding process is controlled. The following options can be set to enter your profile:

%Fill Pressure vs. Time. Pack Pressure vs. Time. Hydraulic Pressure vs. Time. % Maximum machine pressure vs. Time.

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The vast majority of the time Pack Pressure vs. Time is used. many machine controllers output hydraulic pressure not plastic pressure. The packing control is generally much easier to get and understand than the filling control. The main thing to determine in addition to the pressure and times used in the profile is the shape of the profile. Some molding machines can only use a block profile; others can have a linear decay in the profile, shown in Figure 26. A block profile has the pressure change instantaneously from one pressure to another and the pressures are constant. A liner profile has programmable times for the change between one pressure and another.

Figure 26: Example profiles

With packing control, make sure you know the pressure definition. It most likely will be hydraulic pressure, but some controllers use plastic pressure. There are two ways to handle this:

Use the Hydraulic Pressure vs. Time control. You must make sure the intensification ratio in the machine database is correct. Manually convert between Hydraulic pressure and pack pressure (plastic pressure) and

use this pressure.

Machine hydraulic response time

The injection molding machine database includes a parameter for Machine hydraulic response time, as shown in Figure 27. The default machine has a very small value of 0.01 seconds. All of the specific machines in the database have a value of 0.2 seconds. This response time is used to interpret packing profiles with duration values less than the response time. When a packing profile has a 0 duration, the profile step uses the machine hydraulic response time value listed in the injection molding machine database. Figure 28 shows an example of how the profile is modified based on the response time in the machine database. One line represents the default response time, and the other represents a very long 1.0 second response time.

When entering a packing profile, the response can be handled in the following ways:

Enter a 0 (zero) for a duration and let the default machine response time be used. The default molding machine have a very low value, faster than molding machines can respond, resulting in a unrealistic profile.

Time

Pre

ssu

re

Block Profiled

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Enter a 0 (zero) for a duration and modify the Machine hydraulic response time in the machine database to a more realistic value.

Enter the duration with a realistic value to account for the machine response such as 0.2 seconds.

Figure 27: Machine hydraulic response time in machine database

Figure 28: Graph showing influence of machine response time on packing profile

Fiber orientation analysis check box

The “Fiber Orientation” check box is checked by default. If you are not running a fiber filled material the check box does nothing checked or unchecked.

The fiber analysis will run only if all the following conditions are met:

Fiber license or a performance license is available. The material is fiber filled with an aspect ratio is over 1. Most fiber aspect ratios on the database are 25. Fiber option is checked on.

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Warp settingsThe warp settings are different depending on the mesh type. Most warpage settings are not critical for duplicating a molding process, but many times you need to duplicate a molding process to solve warpage problems.

Midplane meshes

Warp analysis type

The default is automatic. However, by the time you are running this analysis to duplicate an existing process you should know if the part has buckled or not. This is the primary reason for the automatic. Therefore, the setting will probably need to be set to either:

Small deflection. Large deflection.

If the part does not buckle, the small deflection should be fine. Many people choose large deflection anyway. The large deflection analysis would capture any slight non-linear trend in the deflection even if it did not buckle.

Isolate cause of warpage

Turn this option on if you want the analysis that you are setting up to output information about the dominant cause of warpage. You will receive four sets of deflection results representing the deflection of the part considering all factors of warpage including:

Differential cooling. Differential shrinkage. Orientation effects. Corner effects.

Stress result(s) to output

The default is none, and generally is not changed. This setting will have no influence on the prediction of warpage. Stress results are used to view the residual stress on the part and as in input to the Shrink analysis.

For midplane meshes, this option is available for small deflection and buckling analyses. The buckling analysis results are in the Analysis Log of the analysis will include a sensitivity factor for each of the possible contributors. The small deflection analysis will be deflection plots.

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Consider gate surface and cold runners

By default, gates and runners are NOT considered. If you were to change this, it would assume the gate and runners are not removed from the parts until the part has completely cooled and shrunk. The assumption with the shrinkage models is at least one week.

Consider mold thermal expansion

Select this check box if you want the warpage or stress analysis to consider the effect of mold thermal expansion on the warpage and/or molded-in stress levels in the part. During injection molding, the mold expands as the temperature increases, causing the cavity to become larger than its initial dimensions. This cavity expansion helps to compensate for part shrinkage during cooling, resulting in actual shrinkage that is smaller than that predicted without accounting for thermal expansion of the mold. This is off by default. Consider using this option if the part is very large and the mold temperature is high. Then the dimensional change of the mold may have a minor impact on the warpage of the part.

Consider corner effects

Select this option if you want the warpage analysis to calculate and account for deformations due to mold-restraint induced differential shrinkage. Use this option if your model has ribs or is box like geometry, see Figure 29. Many times a warpage analysis is run with this on and off so the user can judge what setting is best. Most parts are more box like then frame like, so corner effects should be used.

Figure 29: Corner Effects

If you use this option, ensure that a suitable mold material has been selected. This is where the key material property used by this option - the coefficient of thermal expansion of the mold - is defined.

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Dual Domain meshes

Dual Domain can only run a small deflection analysis. It can’t determine if the part buckles. Most parts will not buckle. The available warp options are discussed below.

Consider mold thermal expansion

This is the same as Midplane.

Isolate cause of warpage

Turn this option on if you want the analysis that you are setting up to output information about the dominant cause of warpage. You will receive four sets of deflection results representing the deflection of the part considering all factors of warpage including:

Differential cooling. Differential shrinkage. Orientation effects. Corner effects.

Matrix solver

This option relates to the selection of the equation solver to be used in the warpage analysis. If this option is set to Automatic, the analysis will automatically use a matrix solver appropriate to the size of the model, and for Midplane models, compatible with the selected Warpage analysis type option. For small models, the Direct option is used. For large models, using an iterative matrix solver can improve the performance of the solver by reducing analysis time and memory requirement. The AMG option is preferred unless memory requirement becomes the limiting factor. You can override the automatic selection.

The Direct solver is a simple matrix solver which is efficient for small to medium sized models. For large models, the direct solver becomes less efficient and requires a large amount of memory (disk swap space).

The AMG (Algebraic Multi-Grid) iterative solver is very efficient for large models. Choosing this option can significantly reduce analysis time but requires a larger amount of memory than the SSORCG option. For Midplane models, the AMG solver does not support Warpage analysis type set to Automatic or Buckling.

The SSORCG (Symmetric Successive Over-Relaxation Conjugate Gradient) iterative solver (previously known as Iterative Solver) is less efficient than the AMG option for large models but requires less memory. For Midplane models, the SSORCG solver does not support Warpage analysis type set to Automatic or Buckling.

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3D meshes

For 3D meshes, you can run a small deflection, large deflection or buckling analysis. The vast majority of parts, using a 3D mesh, will not buckle, therefore the small deflection analysis will give accurate results. However, if the small deflection analysis is under predicting the deflection, run a large deflection analysis.

Consider mold thermal expansion

This is the same as Midplane.

Use mesh aggregation

By default, this is checked. It is not likely the mesh aggregation is influencing the amount of warp. If the deflection is much different than the molded parts, try running without mesh aggregation.

Isolate cause of warpage

Isolating the cause of warpage will not improve the accuracy of the warpage results, in an effort to duplicate the molding process, but it will help you diagnose what the cause of the warpage is so corrective action can be made.

Number of threads for parallelization

The default is maximum. This uses as many processors on the computer as possible to reduce analysis time.

Viewing warpage results When viewing warpage results, it is critical the deflections from the simulation are viewed with the same reference as the molded parts. In Figure 30 on page 36, the front edge was compared using the default method of looking at the deflections called best fit, that does not use anchors and using anchors. The anchors define a reference plane. In the case of the dustpan, the edge of the pan is defined as the X-axis, and the bow of the front edge is in the Z-direction. The same reference must be used for looking at the deflection plots and the actual molded parts. With the Best fit, the zero deflection location is not known so you can’t directly compare deflections with best fit to the actual part.

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Figure 30:Use of anchors for viewing warpage

Molding verificationIn addition to ensuring the analysis is correctly set up, the molding process must also be carefully checked to ensure it is consistent with how the simulation is run. Areas to check include:

Ram speed profilesWhen setting the ram speed profile on the molding press, the profile must be achievable and stable. The achievable and stable profile can then be used in the simulation. In Figure 31 on page 37, the machine controller was set with a flow rate of 93 cm3/sec. However, the machine could not deliver that flow rate. The maximum flow rate achieved was only 68 cm3/sec. and the average flow rate was only 52 cm3/sec. The differences in flow rate will make a significant difference in how the part fills and packs out. The machine showed no indications of any problems when the 93 cm3/sec. flow rate was not being achieved. It was only after viewing the ram position trace that an issue detected. The simulation must be run with the velocity profile the machine actual achieved, not the one that was set.

Ram speed and pressure profiles. Material preparation. Pressure measurement Pressure measurement locations. Nozzle vs. Hydraulic pressure.

Accounting for nozzle pressure drop. Pressure sensors. Shot to shot variation. Venting.

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Figure 31: Injection speed capacity

Figure 32 shows an example of nozzle and cavity pressure traces both from unstable and stable cycles. On the left, the five cycles are not stable. The ram is moving about the same, but the pressures in the cavity are not stable. On the right, the press has stabilized. There is better shot to shot repeatability. It is only when the set velocity profile is achieved and is stable should the parameters be used in the simulation and the parts from these cycles be used to compare to the simulation.

Figure 32: Cycle stabilization

Averageflow rate52 cm3/sec.

Maximum flow rate 68 cm3/sec.

Not stable Stable

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Ram pressure profilesLike the ram speed profiles, the pressure profiles must be achievable and stable. Only a achievable and stable packing profile should be used as input to the simulation, and for comparison between the simulation and molding.

Material preparationMaterial tested by Moldflow is dried according to the specification of the material manufacturer. Therefore, the simulation assumes the material is properly dried. When molding parts to be compared to the simulation, the material must also be properly dried. Figure 33 shows when nylon was dried for 17 hours at different temperatures how the viscosity changes. Lower drying temperatures can cause a 2-5 times decrease in viscosity. This can change the pressure to fill by about 50%.

Figure 33: Viscosity changes due to drying (Y.P. Khanna, P.K. Han & E.D. Day, Allied Signal Inc., New Jersey. Polymer Engineering and Science 1996 Vol 36/13 pages 1745-1754.)

Pressure measurementWhen comparing the pressure between the molding machine and the simulation, peak pressure should not be used. A pressure trace of the entire molding cycle should be used. In a typical analysis, the maximum pressure occurs at the V/P switch-over unless there is a significant reduction in the volumetric flow rate at switch-over. On a molding machine, the peak pressure may be at the start of the cycle due to a cold slug of material. This is more likely to occur with hot runner systems. In the tip of the hot drop, there is a sensitive temperature balance. If the temperature is too high, the tip will drool, causing molding problems. If the tip is too cold, the pressure to start injection will be very high and create a flow defect caused by this cold slug. Currently, the flow simulation does not account for this cold slug. By comparing the pressure trace of the entire shot, any pressure spike caused by this cold slug can be ignored.

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Nozzle vs. Hydraulic pressure

When comparing the pressures between the molding machine and the simulation, the plastic pressure should be measured directly and not be calculated by the hydraulic pressure when ever possible. Figure 34 shows a difference between the injection pressure calculated from the hydraulic pressure and measured nozzle pressure. For the injection pressure calculated from the hydraulic pressure the hydraulic pressure was multiplied by the intensification ratio. During the filling phase, the “hydraulic” injection pressure is always higher than the nozzle pressure by over 10 MPa. The differences are due pressure losses in the hydraulic system due to compressibility and resistance.

Figure 34: Nozzle pressure versus hydraulic pressure

Accounting for nozzle pressure drop

The pressure drop in the nozzle of the machine can be a significant amount of the total pressure required to fill the part, 20% or more. Preferably, the nozzle, of the machine, should be modeled. Ensure there is a node at the pressure transducer location to so the pressure at this location can determined in the simulation. This will make it easy to correlate the pressure between the simulation and the molding.

If modeling the nozzle is not possible, estimate the pressure drop. To determine the pressure drop through the nozzle back off the nozzle so it is not touching the mold surface. Give yourself enough room like if you were purging the material. Make sure you are using the same process setup. Run through the process so it injects into the air. Take the pressure measurement and add this amount to the pressure given in Autodesk Moldflow Insight and this will be your total pressure drop. For example, an analyzed model includes the sprue, runner system, and parts. However, it does not include the nozzle geometry. Given this set-up, the V/P switch-over pressure is predicted to be 75 MPa. Since the nozzle geometry is not

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available, an air shot must be performed at the injection molding machine using the same injection velocity that the part is filled with. The resultant pressure read out is the pressure at the nozzle, this value should be added to the simulation's pressure drop for an appropriate simulation vs. reality comparison.

Figure 35: Nozzle air shot pressure

Pressure sensors

When using pressure transducers, care must be used to ensure their proper performance. When a transducer is mounted under a pin, fit between the pin and the hole is critical. To much friction between the pin and the hole will delay in the signal and possibly lower the magnitude of the pressure. Mercury filled sensors can be inaccurate at the very top and bottom of their range. They also exhibit a hystereses effect.

Worn check ringFigure 36 on page 41 shows an example where the velocity profile in the simulation was set to the same profile as the molding machine. For cavity pressure transducer 2, there was a large error in the flow rate because the simulation indicates a different time to reach the location compared to the transducer. The problem was determined to be a worn check ring. Figure 37 on page 41 shows the displacement of the ram and cavity pressure transducers in the cavity. The packing time was extended for a very long time. The ram continues to move even after the parts are frozen as indicated by a zero pressure at the transducer.

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Figure 36: Error in cavity pressure due to worn check-ring

Figure 37: Validate worn check ring

Flow rate error

Ram movement

during filling

Ram movement

during packing

Ram Position

Cavity Transducer

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Shot to shot variationWhen molding parts to be used to compare to the simulation, ensure that the process is stable before measuring the parts. Also, measure multiple parts. Ensure that you have repeatable measurements on the same part. Determine the average and 95% confidence intervals for the part. When comparing the simulation to the moldings, the simulation can be considered accurate when the simulation results are within the confidence limits of the experimental data. Figure 38 shows the deflection statistics for three molded samples of the same part, molded with nominally the same molding setup. There was a large variation in deflection between the three parts, so the confidence interval is very wide. Without knowing the shot to shot variation on the parts, if the simulation was compared to just one molded part, it may seem to be in error.

Figure 38:Shot to shot warpage variation

VentingThe typical simulation assumes perfect venting in the tool. if tools are not properly vented, the filling pattern may not be predicted correctly. Figure 39 shows a small sample part with 3 pressure transducers spaced evenly along the flow length. The third one is near the end of fill. With a constant flow rate, the flow front should get from one transducer to another at the same time, approximately one second. However, the third transducer shows an early reading.

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Figure 39: Short shot on part past pressure transducer

Figure 40 shows another short shot on the part, this time the flow front does not reach the transducer. However, this transducer still shows pressure. This is due to air pressure ahead of the flow front due to insufficient venting. In the graph of Figure 40, the solid red line is the original shot shown in Figure 39, and the dots represent the pressure with the short shot shown in Figure 40. The magnitude of the air pressure is less than 1 MPa.

The solution to the problem is to get the tool vented. However

Figure 40:Second short shot before pressure transducer

JettingA series of short shots should be molded to ensure the filling pattern is correct in the simulation and to ensure the filling will not impact the pressure comparisons. Figure 41 on page 44 shows an example where jetting prevented the pressure transducer from registering when it should. The pressure transducer was picking up pressure near the gate at over 1.4 seconds. The simulation started filling the same area at about 0.8 seconds.

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Figure 41: Part jetting over tool’s pressure transducers

ConclusionsA systematic approach for problem elimination is required when comparing simulation results to molded parts. Before the comparison is to begin, you must understand what is going to be used for the comparison, and ensure that both the moldings and the simulations are set up to provide the correct data necessary for the comparison. When problems occur with the comparison, a careful investigation of the factors that may cause the error must be done. These factors may be:

Machine capability. Machine response time. Material preparation. Material characterization. Material stability. Part measurement methods and repeatability of measurements. Part geometry representation in the model. Matching of processing conditions in the simulation with those of the molding process.

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Warp Troubleshooting ChecklistUse the following list to help ensure you have done everything possible to make sure the simulation is the same as the molded parts.

Acquire basic information

1. Obtain a copy of the study and screen shots that show a correlation problem between the simulation and molded parts.

2. Obtain a copy of the processing conditions used to create the molded part being compared.

Preliminary checks

1. Ensure there are no mesh defects.

High aspect ratios.

Intersecting elements.

Unoriented elements.

Etc.

2. Ensure the element orientation is correct.

3. Ensure the study has a runner system modeled.

4. Ensure the study has cooling lines modeled.

5. Ensure there fill parameters and cooling time are NOT set to automatic.

6. Check for warning or error messages in the Analysis Log.

Verify the part thicknesses

Verify the feed system

1. There must be at least three beam elements or three rows of triangular elements across the gate.

2. Ensure tetrahedral or triangular elements are used when the width to height ratio of the gate is greater than 4:1.

3. Ensure the gate and runner sizes in the study are the same as the molded part/tool.

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Verify the cooling system

1. Ensure the cooling channel placement and sizes in the study are the same as the tool.

2. Ensure the coolant media used in the study is the same as used when molding the parts.

Water, glycol, etc.

3. Ensure the coolant flow rates used in the study are the same as used to mold the parts.

4. Ensure the coolant temperatures used in the study are the same as used to mold the parts.

5. Ensure the mold material used in the study is the same material as the mold base.

6. Ensure any inserts used have the correct mold material defined.

6.1.Ensure cooling lines and runners within the inserts have the same mold material as the insert.

7. Ensure a mold boundary is created in the study.

7.1.Ensure the mold boundary mesh orientation is correct.

Verify molded material

1. Ensure the material being used in the analysis is the same material used to mold the parts.

Added colorant may affect the results, however most rheological and shrinkage testing is done without colorants added.

2. Ensure for fiber filled materials a fiber flow analysis was used. Verify there are fiber results.

3. Ensure for Fusion and midplane meshes the CRIMS or residual strain shrinkage models were used.

Verify filling and packing

1. Ensure the proper injection molding machine is selected if an absolute ram speed profile is being used.

2. Ensure the packing profile used in the analysis is the same as the one used to mold the parts being measured.

3. Ensure the melt temperature used in the analysis is the same as an air shot temperature and not heater band settings.

4. Ensure the mold surface temperature set in the analysis is the measured temperature of the mold surface (plastic/metal interface) and not just the thermometer temperature setting or coolant temperature.

This is only important if a cooling analysis is not run. If a cooling analysis is not run, this could be a bigger source of error than the wrong mold surface temperature.

5. Ensure the V/P switch-over position is correct.

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6. Ensure the cooling time is specified and not set to automatic.

This is only important if a cooling analysis is not run. If a cooling analysis is not run, this could be a bigger source of error than the wrong cooling time.

7. Ensure the Geometry influence in the cool solver parameters is set to Ideal.

This may not always be possible due to computer limitations.

8. Ensure the mesh aggregation is off for parts with tetrahedral meshes.

9. Assign the proper mold open time.

Verify warp

1. Ensure the consider corner effects box is checked on the warp process settings page, if the part is deemed suitable for corner effects.

2. Ensure the anchoring system used to measure the warpage in the simulation represents the same constraints used to measure warpage for the actual parts.

Still having problems1. Contact Autodesk Support.

2. Provide to support:

Studies

All information used above to validate the study to the molded part.

Molded part, full shot with runners.

Short shots, created at the same processing conditions used to make the full shot, just with a reduced barrel shot size.

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