Autodesk® Moldflow® as a Teaching Tool to Explain
Injection Molding and Detect Defects
Stephen Johnston, Ph.D. – The University of Massachusetts Lowell Plastics Engineering Department
ED5613-L
Autodesk Moldflow Insight is a powerful tool that can be used to explain the fundamental behavior of
injection molding. In addition to using Moldflow Insight to identify part defects and validate designs, it is also an
exceptional teaching tool for explaining polymer behavior, such as how polymers flow during filling and subsequently
cool, shrink, and warp. This hands-on lab will focus on how Moldflow Insight can be incorporated into the classroom or
the office to explain the injection molding process. Attendees will gain hands-on experience with Moldflow Insight
while working through case studies that have been developed as part of an undergraduate Mold Design Engineering
course. Moldflow Insight is used in the course as part of a rigorous art-to-part design project. Students design new
parts, validate their designs with Moldflow Insight, and ultimately machine prototype tooling and mold parts, thereby
validating the Moldflow predictions. We will also discuss the benefits and implications of incorporating Moldflow Insight
into the classroom in this manner.
Learning Objectives
At the end of this class, you will be able to:

Become familiar with the Autodesk Moldflow Insight interface, functionality, and capabilities

Describe how Moldflow Insight can explain the fundamental behavior of injection molding

Utilize Moldflow Insight to predict part defects and influence design decisions

Identify how Moldflow Insight can be incorporated into the academic environment in an engineering or technology
program
About the Speaker
Professor Stephen Johnston has his BS in plastics engineering tech from Penn State Behrend, and his
MS and PhD in plastics engineering from UMass Lowell. His industrial experience includes work at
Moldflow Corp. (prior to acquisition by Autodesk), where he provided technical support and quality
assurance testing. He also worked at Bausch & Lomb Inc. doing process validation and testing. Dr.
Johnston’s research interests include part design and mold design utilizing computer-aided engineering
and manufacturing technology. He also works in the areas of process monitoring, process control, and
process development for injection molding. His recent focus has been on the design and development of
medical devices in collaboration with smaller medical device companies and innovators. In addition to
his research, Professor Johnston teaches graduate and undergraduate courses in the areas of plastics
product design and mold design at UMass Lowell.
Stephen_Johnston@uml.edu
Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
I.
Tray Example: Investigate Filling Related Defects
A.
Set-up Autodesk Moldflow Insight Filling Analysis
1.
Open Autodesk Moldflow Insight
Select Start Menu (Windows Icon) > All Programs > Autodesk > Autodesk Moldflow
Insight 2012 > Autodesk Moldflow Synergy 2012.
Autodesk Moldflow Insight will open. At the top left select the Open icon and navigate to the
following location to Tray.mpi file for the class.
Open > C:\Datasets\Thursday\ED5613-L\ED5613-L_Johnston\
Tray_Filling_Defects\Tray_Project.mpi.
Double click on the Tray_Blank study in the Tasks pane at the left side of your screen. Your
screen should now look like the image below.
Project
View Pane
Ribbon Menu
Study
Tasks Pane
Layers
Pane
The Ribbon Menu at the top of the screen is very versatile. From the home tab you can access
new Ribbon Menu tabs by selecting the various icons. There are additional ribbons available by
selecting the icons for Geometry, Mesh, Boundary Conditions, Results, and Reports. For
example, if you select on the Results icon your ribbon will look like this. This ribbon can be
hidden again by selecting Finish Results.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
At the top of the Project View Pane you will see the Project we are working on and the
individual studies. The project file is at the top “Project ‘Tray_Filling_Defects’’. The individual
studies are seen below. Each study is an analysis with its own unique model, mesh, settings,
and results.
Study tasks and results are seen in the middle of the Study Tasks Pane. For each study you
work from the top to the bottom setting up the study before selecting “Start Analysis” at the
bottom of the window. The required actions can be initiated by double clicking on the individual
icons in the Study Tasks, or by going to the corresponding icon in the Home Ribbon.
Layer Selection is controlled for each study using the Layers Pane. This will allow you to
isolate portions of your model and turn on/off details.
2.
Import Model of Tray
Double click on Import Part from the Study Tasks. Browse up one level to ED5613L_Johnston and select the file “Tray_STL_Import.stl” Accept the default values for model
import. An STL file is a surface model that will come in as a Duel Domain® model. It was saved
in millimeters.
Caution: If you change the unit system in this window you change the size of your model
typically making it very large or very small. The active unit system is changes by selecting the
“M” icon at the top left of the screen then selecting Options > Active Units.
The model can be rotated using your middle mouse button or the view cube at the top right of
the modeling window. You can zoom in or out by rolling the middle mouse wheel.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
3.
Generate Mesh
Double click on Create Mesh in the study tasks pane. Change the Global Edge Length to
2.5mm. Select Mesh Now to start meshing. Accept the defaults for the meshing dialog boxes
that appear. After meshing is complete you can minimize the mesh log by selecting the Logs
icon at the bottom right of the model window.
Select the Mesh icon from the home tab to activate the Mesh Ribbon.
Select Mesh Statistics > Show
This is not a good Duel Domain® mesh. The max aspect ratio of 54.4 is too high. Ideally it
would be below 6. It is good that there are no free edges, non-manifold edges, unoriented
elements, intersecting elements, or overlapping elements. However, the match ratios are
around 80%, which is lower than desired.
Typically small features such as rounds, drafts, and raised lettering will cause poor aspect
ratios. Select Aspect Ratio > Show to see the aspect ratio diagnostic. Notice that the poor
aspect ratio elements are on the curved surfaces that are difficult to represent with flat
elements.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
Round or thick features that are not thin-wall geometry will cause poor match ratios. Select
Mesh Match > Show. Notice that the thick regions around the rim have a poor match ratio.
The aspect ratio can be fixed manually using the Mesh Repair Tools in the Mesh Ribbon.
There is no good way to improve the mesh match for the areas with poor mesh match since this
is based on part geometry.
To streamline this lab, an improved Duel Domain® mesh has already been generated. Double
click on “Tray_Duel_Dom_Mesh” in the list of studies in the Tasks Pane. This will open a new
study with a completely new mesh. Check the Mesh Statistics and the Mesh Diagnostics to
see how it has been improved.
Since the match ratio is still not acceptable, we will run this analysis as a 3D analysis. This will
create 3D tetrahedral elements throughout the part. Mesh Match is no longer applicable.
Right click on Duel Domain Mesh in the study tasks pane. Select Set Mesh Type > 3D.
Double click on 3D Mesh in the study tasks pane. We are going to accept the default values for
meshing. Select Mesh Now. Accept the defaults for the dialog boxes that appear during and
after meshing.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
4.
Select Material
Right click on Generic PP: Generic Default in the study tasks pane. Select Select Material
In the Select Material window that appears select Search. In the Search Criteria window that
appears select Trade name: and enter “RJ470” for the substring. Select Search.
Select the Borealis RJ470MO material that appears and click on Select.
5.
Select Injection Location
Double click on Set Injection Locations in the study tasks pane. Select a node at the center of
round edge at the rim of the part to match the location on the actual part.
6.
Input Process Settings
We are going to accept the default processing conditions. This means that Moldflow will run at
the recommended mold and melt temperatures and automatically calculate the injection velocity
and switchover position.
To view these settings double click on Process Settings in the study tasks pane.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
7.
Run Analysis
We are ready to run the analysis. Select Start Analysis in the study tasks pane. Accept the
messages that appear. An analysis log will appear at the bottom of the model window showing
the progress of the analysis. You can open/close the analysis log without affecting the analysis.
Analysis results will also start appearing at the bottom of the study tasks pane.
B.
1.
Analyze Results
Fill Pattern
The first result to check is the fill time result. This shows how the polymer fills the mold during
the injection process. To view the fill time result click on the box next to Fill Time under the
results folder in the Study Tasks Pane.
To animate this result through time select Results from the Home Ribbon to bring up the
Results Ribbon. Next select the play button under the animation settings.
Question: How does this result compare to the short shot of the actual part?
2.
Weld Line Location
You can see from the fill time plot and from the short shots that the melt front travels around the
tall standing cores and will form a weld line behind the cores. Scroll to the bottom of the results
list in the study tasks pane, find the weld line result, and select it.
To more easy visualization how the weld lines form, right click on Fill Time result and select
Overlay. This will display both results at the same time. You can animate the fill time result
again and watch as the weld line forms.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
Question: Why is the weld line result predicting a jagged line when the actual part shows
a straight weld line?
Answer: ____________________________________________________________________
3.
Air Trap Location
Repeat the steps above to look at the air traps in the molding. When they are overlayed with
the fill time result you will notice that there are two very significant air traps, one at the center of
each core.
Question: On the actual part an ejector pin is located at the center of each core. What is
its significance and what defect would be expected if it was not located there?
Answer:
_____________________________________________________________________
4.
Temperature Through Thickness
To verify that fountain flow is being simulated we need to look at the flow profile within the
model. To do this we will turn on a section view.
Select the View Ribbon > Edit > Plane ZX > Close. Select the Temperature result from the
study tasks pane. Return to the Results Ribbon and animate this result through time. You can
clearly see the frozen layer develop as the melt is being injected.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
The Next Step: If you finish early or are interested in how these results will change, delete the
injection cone, add in one or more new injection cones, and rerun the analysis. How did the
results change?
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
II.
Do Don’t Plaque: Investigate Shrinkage & Warpage Defects
A.
Set-up Autodesk Moldflow Insight Fill/Pack/Warp Analysis
We are now going to set up a fill, pack, and warp analysis to investigate shrinkage related
defects. You can save your work and close the tray model that we have been working on.
1.
Open Analysis
Open > C:\Datasets\Thursday\ED5613-L\ED5613-L_Johnston\
Do_Dont_Sink_Warp_Defects\Do_Dont_Part.mpi.
Double click on the Do_Dont_Duel_Domain study in the Tasks pane
2.
Mesh Statistics and Diagnostics for Duel Domain® Mesh
Select the Mesh icon from the home tab to activate the Mesh Ribbon. Select Mesh Statistics
> Show
This is a relatively clean mesh. The max aspect ratio of 10.2 is acceptable although ideally it
would be below 6. There are no free edges, non-manifold edges, unoriented elements,
intersecting elements, or overlapping elements, which is critical. Finally, the match ratios are
around 95%, which is quite good.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
Select Mesh Match > Show
Notice that the round bosses, especially the large solid one, have a high degree of unmatched
elements. The thick flange also has a large number of unmatched elements. The Duel
Domain® mesh will have reduced accuracy in these areas. These thick areas are best meshed
as 3D elements since they are not thin wall geometry. Because we are looking at the effect of
these thick areas we are going to mesh the model as 3D.
3.
Mesh 3D
Right click on Duel Domain Mesh in the study tasks pane. Select Set Mesh Type > 3D.
Double click on 3D Mesh in the study tasks pane. We are going to accept the default values for
meshing. Select Mesh Now.
Accept the defaults for the dialog boxes that appear during and after meshing.
4.
Select Analysis Sequence
Right click on Fill in the study tasks pane. Select Set Analysis Sequence. Select
Fill+Pack+Warp > OK
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
5.
Select Material
Follow the same steps for selecting Borealis RJ470MO as were followed for the Tray example.
Refer to topic I-A-4 for detailed step by step info.
6.
Select Injection Location
Double click on Set Injection Locations in the study tasks pane. Select a node at the center of
the plaque that correlates to the injection location on the actual part. The injection location is on
the smooth side of the part and is located on the edge of the thick section.
7.
Input Process Settings
We will again choose the default process settings.
8.
Run Analysis
We are ready to run the analysis. Select Start Analysis in the study tasks pane. Accept the
messages that appear. Since the analysis will take some time to complete, we can go and look
at a previously solved analysis by opening the Do_Dont_3D_Solved.sdy file from the Project
Pane.
B.
1.
Analyze Results
Fill Time
Again we will check the fill time result first. Notice that the fill is not balanced. The thicker area
has less resistance to flow so it fills rapidly compared to the thin side. Once it has completed
filling all the flow is directed into the thin side, the flow accelerates and finishes filling the cavity.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
Question: How does this result compare to the short shot of the actual part?
2.
Pressure
The Pressure plot shows how much injection pressure is required to force the melt into the
cavity. To minimize differential shrinkage we would like the entire part to fill and pack with a
uniform pressure. Notice that the pressure rapidly increases in the thick section once it fills
since the melt goes hydrostatic. As you animate through the pressure plot notice that the
pressure decays very quickly in the thin side compared to the thick side. This is because the
melt is freezing off in this area and can no longer transmit pressure.
3.
Weld Lines and Air Traps
While not specifically the target of this analysis, look at the location of the weld lines and air
traps that form.
Question: How do the weld lines compare to the short shot of the actual part?
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
4.
Sink Mark Estimate
Select on the Sink Mark Estimate result to see the estimated depth of the resulting sink marks.
Notice that the thicker the rib or boss is compared to the nominal wall the larger the sink mark
will be. The largest sink mark is under the solid round boss. Its 11.5 mm thickness is 300% of
the 3.8 mm nominal wall thickness. The smallest sink mark is on the thin 1.3 mm rib that is on
the 1.9 mm nominal wall. The rib is therefore 67% of the nominal wall thickness and the sink
mark is minimal.
To further investigate the effect of wall thickness on sink marks you can either use the measure
tool located under View Ribbon > Navigate > Measure, or you can look at the thickness
diagnostic for our duel domain mesh. To do this select the Do_Dont_Duel_Dom.sdy file from
the Project Pane. Then select Home Ribbon > Mesh > Mesh Ribbon > Thickness > Show.
Finally, query the results by selecting Results Ribbon > Examine Result and select nodes of
interest. The results from this are shown below for your convenience.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
5.
Time to Reach Ejection Temperature
Select the Time to Reach Ejection Temperature from the Study Tasks Pane. To see how the
part cools we will use a cutting plane. Right Click on Time to Reach Ejection Temperature >
Properties > Scaling > Specified > enter 0-90 seconds > OK. This will scale the plot so it
corresponds to our default 90 second cycle.
Select the View Ribbon > Edit > Plane ZX > Close. You should now see the time distribution
across the inside of the part. Notice that the large solid boss is hollow. This indicates that it has
not completely frozen at 90 seconds when it is ejected from the mold. Also notice that it takes
approximately three times longer for the thick section to cool compared to the thin section (38
sec to 12 sec). Remember that we only have applied a pack pressure for 10 seconds;
therefore, we can expect a much higher shrinkage from the thick section than the thin section.
You can also animate the Temperature Plot through time as we did previously in section I-B-4
to see how the part cools. Please refer to that section if you need to review the instructions.
6.
Average Volumetric Shrinkage
Select the Average Volumetric Shrinkage result from the Study Tasks Pane. Notice how wall
thickness affects the average volumetric shrinkage: 15.5% for the 3.8 mm wall thickness and
6.5% for the 1.9 mm wall thickness. The differential shrinkage will cause warpage.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
7.
Deflection Results
Select Deflection. all effects: Deflection to see the deformed shape of the part. To get a feel
for the deformed shape, Right Click on Deflection. all effects: Deflection > Properties >
Deflection > enter a Scale Factor Value of 10 > OK. This will scale the deflection result so
that the deformed shape is more easily visualized.
Notice that the part has shrunk in the X and Y directions, but it is deflecting out-of-plane in the Z
direction. Linear shrinkage is commonly accounted for when building molds, but out-of-plane
deformation is very difficult to account for during tool design. Therefore, it is important that we
understand the root cause of this deformation.
Select Deflection. all effects: Z Component to see the out of plane warpage of the part.
Again increase the scale factor by 10 for visualization. Right Click on Deflection. all effects:
Deflection > Properties > Deflection > enter a Scale Factor Value of 10 > OK.
To clearly judge the magnitude of the warpage we will use an anchor plane that is essentially a
datum from which deflection values are measured from. Select Results Ribbon > Visualize >
Enter “N15357, N13902, N15736” for Anchor Nodes > select Apply to All Deflection Plots
in this Study > Apply > Close the Window. This has placed the warpage plane at the bottom
of the part and the scale now measures deflection from that plane.
Questions: How well does the deformed shape of the part match the deformed shape of
the actual parts? What is the maximum deflection predicted by the analysis and what is
the maximum deflection observed on the part?
Answer: ___________________________________________________________________
It is important to note that the magnitude of the warpage is very dependent on process
conditions that affect shrinkage such as pack pressure, pack time, melt temperature, etc. By
choosing default process conditions the magnitude will not reflect the actual magnitude, but the
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
deformed shape should be in good agreement. The analysis could also be improved by
modeling the mold cooling and feed system.
Select Deflection. all effects: X Component. Right Click on Deflection. all effects: X
Component > Properties > Methods > Contour > OK. This will display contours of equal
deformation on the part rather than a shaded model. This plot now shows how the part shrinks
in the X direction. Notice that there is a higher rate of shrinkage in the thick section compared
to the thin section, which is displayed by more closely spaced contours. The deflection in each
area is relatively uniform since the contours are approximately vertical. Therefore, the
deflection in the X direction is not the primary cause of the warpage.
Select Deflection. all effects: Y Component. Right Click on Deflection. all effects: Y
Component > Properties > Methods > Contour > OK. This plot now shows how the part
shrinks in the Y direction. Notice that there is still a higher rate of shrinkage in the thick section
compared to the thin section, which is displayed by more closely spaced contours. However,
these sections are connected together in the middle of the part. Notice how the contour lines
take a steep jog as they cross thickness change. This differential shrinkage is responsible for
the out-of-plane warpage we are seeing in the Z direction.
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Autodesk® Moldflow® as a Teaching Tool to Explain Injection Molding and Detect Defects
The thin section solidifies first at a lower shrinkage. As the thick section continues to shrink it is
being constrained by the dimension of the thin section and the only way to make these
dimensions similar is to twist the part out-of-plane. This will happen as the part cools in the
mold, but since the mold is constraining the part stress develops. Once the mold opens the
part will instantly warp based on the stress level and the modulus of the material in order to
minimize the molded in stresses.
The Next Step: If you finish early or are interested in how these results will change, open the
process settings and adjust the melt temperature, mold temperature, or pack pressure profile
and rerun the analysis. How did the deflection results change? Also experiment with different
gate locations to see how it affects the results.
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