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tips & techniques
Working with the New Moldflow Performance Adviser
By Murali Annareddy, Moldflow Corporation
With the release of Moldflow Plastics Advisers® (MPA®) 7.0, two optional, add-on modules to Moldflow Mold Adviser are available. These add-on modules allow users to simulate more phases of the injection molding process and evaluate molded part performance and cooling circuit design. The result is faster mold commissioning, minimal mold rework, a more robust manufacturing process and faster time to market.
The focus of this article is on the new Moldflow Performance Adviser module. The Moldflow Performance Adviser module extends the capabilities of Moldflow Mold Adviser to simulate the packing phase of the injection molding process to predict and minimize undesirable part shrinkage, as well as provide a warpage indicator tool that indicates if a part is likely to warp or deform beyond acceptable levels. Here, we provide guidelines for determining the reference plane which is used in generating the warpage indicator plots.
Warpage Indicator Plots
The warpage indicator plot is a three-color display based on the analogy of a traffic light. It is produced by comparing the part deflections perpendicular to a user-defined reference plane with a nominal maximum deflection (NMD) value. This NMD value is also user-specified. The definition of the colors is as follows:
- The green (low) color represents the regions where the deflections are less than 80 percent of the specified NMD value. The warpage in these areas is low.
- The yellow (medium) color represents regions where the deflections are between 80 percent and 120 percent of the specified NMD value. The warpage in these areas is significant enough to warrant consideration of corrective measures.
- The Red (high) color represents regions where the deflections exceed 120 percent of the specified NMD value. The warpage in these areas is substantial and corrective measure should be taken.
Four warpage indicator plots are generated for a given reference plane and NMD value. Understanding that warpage comes from three sources — non-uniform shrinkage, non-uniform cooling and material/fiber orientation — it is critical to know the cause of the warpage in the part design in order to take appropriate corrective measures. Therefore, the analysis calculates the individual components of the warpage. This information is then translated into four warpage indicator plots, one of each of the three individual sources of warpage as well as one of the overall warpage.
Evaluating Part Warpage
The first step in evaluating part warpage is to review the deflected shape of the part. There are a number of different aspects that you should consider when assessing the deflected shape of the part, including:
- Is the deflection across the entire width of the part or limited to a few specific regions?
- If a few specific regions are affected, which regions are they?
- If the part is required to mate with another part, will the deformations of the part prevent or hinder this mating?
Tip: A useful tool to leverage when viewing the deformed shape is the option to magnify the deflection by a scale factor. This option can be accessed from the animation toolbar. Using the animation toolbar, you can magnify the deflection by up to a factor of 20.
Once you have a fairly good idea of how the part warps, the next task is to evaluate whether the deflection is within tolerance or not. This is where the warpage indicator plots are useful.
As indicated earlier, there are two inputs to creating the warpage indicator plots. The first is the selection of a reference plane and the second is the specification of a nominal maximum deflection (NMD) value.
Warpage Reference Plane
The reference plane is defined by selecting three locations on the part. The reference plane is used to calculate the part deflections perpendicular to the reference plane (in other words, out-of-plane deflection). These deflections are then compared to the specified NMD value to produce the three-color warpage indicator plots.
Careful consideration should be given to the selection of the reference plane. Preferably, the reference plane should be located across a flat section of the part, where you can easily visualize the deflections, and where the implications of the deflections can be most clearly interpreted. Possible locations may include:
- The area of a part that is required to lie flat on a surface, or
- The joining plane to a mating component.
The three locations should be selected over a large area to define an easily visualized reference plane relative to which the deflections are to be measured.
Other important aspects to note about the reference plane are:
The order in which the points are selected is not important and does not influence the resultant warpage indicator plots. The example below shows two warpage indicator plots of the same geometry. The only difference in the two plots is the order (marked as 1-2-3) in which the reference plane points were selected. The two plots clearly illustrate that the resultant warpage indicator plots are not influenced by the order of the selection of the points.
If the surface on which the points are being selected is curved (non-planar), we recommend selecting the points closer to each other. The example shown below highlights this aspect. The plot on the left has the three reference plane points closer to each other while that on the right has the points spread apart. The resultant warpage indicator plots are different.
Depending on the shape of the warped part, several reference planes may be required to evaluate whether the different sections of your model are within tolerance. In the example model shown here, the first image shows the part deflection (scaled to 20 times for illustration). If we focus on side A, its deflection is primarily in the X and Z directions. To evaluate whether each of these deflections are within tolerance would require the creation of two separate reference planes.
The second image shows a reference plane created by picking three points along side A; the resultant warpage indicator plot can be used to evaluate warpage in the X direction.
The third image shows a parting plane created by picking three points on the edge of side A; here, the resultant warpage indicator plot can help in evaluating warpage in the Z direction.
Upon reviewing a warpage indicator plot, if the warpage exceeds the acceptable level (the user-specified NMD value), the next task is to ascertain the primary source of the warpage, whether it is from non-uniform shrinkage, non-uniform cooling or material/fiber orientation. This can be done by reviewing the three additional warpage indicator plots or by using the Results Adviser to query specific locations on the part. The on-line help provides comprehensive advice on how to resolve warpage due to each of the three sources.
For more information about Moldflow Plastics Advisers products, go to www.moldflow.com/products/MPA/.
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