Extension rate result (3D)

The Extension rate (3D) result is generated from Fill, Microchip Encapsulation and compression-type molding process analyses using 3D analysis technology, and shows the rate of extension in the mold-cavity at the time the result was written.

Note: For compression-type molding processes, this result is plotted displayed on the deformed mesh as the default setting. With this default setting, if you click through the time steps you can watch the polymer as it is compressed into the part shape. To turn it off, so that all you see is the result on the part, right-click the result, select Properties and uncheck Display on deformed mesh.

Using this result

The extension rate represents the amount of elongation the polymer undergoes as it passes through a change in thickness. Typically this is strongest at gate regions where the flow rate is high and the thickness changes can be large. A contraction is a reduction in thickness along the flow direction, and results in a positive extension (elongation) of the melt. Such extension occurs at the entrance to a gate. Inversely, a negative extension (compression in the flow direction) is experienced by the melt as it passes through an expansion (increase in thickness) such expansion occurs where a narrow gate connects to a thick part of the cavity. Fiber filled materials undergo significant orientation in regions of strong extension flow.

The Extension rate result can be used to see where the flow is undergoing a significant elongation deformation. This will have implications for understanding the additional pressure drop which occurs at gates (sometimes called the entrance pressure loss). The extension rate result is only available on tetrahedral elements. It is not available on beam elements.

The extension rate is equal to zero in a part with uniform thicknesses. When material flows through a contraction in the part, extension rate is positive, and when material flows through an expansion, extension rate is negative.

Tip: Use cutting planes to view the extension rate.

Things to look for

• An extension rate of 200 or less is acceptable. If the extension rate is higher than 200, the effects of extensional viscosity need to be considered, as the extensional viscosity may significantly increase the injection pressure required to fill the part. If the material you have selected has juncture loss coefficients data, the effect of extensional viscosity has been incorporated in the result.
• Local thickening at the end of flow or in thin sections can be used to reduce extension rate.
• Extension rate is related to flow kinematics and geometry. In injection molding sense, extension rate is more dependent on flow rate and geometry. The material property may influence the extension rate, but not dependent upon it. It is more like that the viscosity is influenced by extension rate.

Note: Changes to the model and materials can only be made using a licensed Autodesk Simulation Moldflow Adviser or Autodesk Simulation Moldflow Insight product.