Modeling gates for 3D Fill+Pack analysis

When analyzing a 3D model, the implied gate size of the model is of critical significance when predicting injection pressure for a part.

Modeling gates for 3D analyses

The 3D flow solver has two ways to achieve accurate injection pressure results:

• Values derived from a modeled gate and a specific gate injection node.
• If no gate is modeled (direct injection to qualitatively test the effect of gate size on the results), a virtual gate diameter (gate contact diameter) is automatically assigned based on the part geometry, or in the case of small parts the average facet size of the tetrahedral elements on the surface around the injection location. The gate contact diameter can also be manually specified from the Solver Parameters dialog.

The gate contact diameter is used by the solver to set the appropriate viscosity of the tetrahedron nodes at/near the injection point. All nodes inside the gate diameter are treated as injection nodes and will have the same temperature, pressure, and shrinkage.

If you want to compare 3D and Dual Domain pressure results, a runner system is required.

Recommended gate modeling technique

In order to achieve accurate injection pressures for 3D Fill+Pack results from a modeled gate, model the gate as a tab connected to the cavity. Then you can define the whole face of the tab as the injection location, and regardless of the mesh size, you will have the same area for the injection gate. As an alternative, you can pick more of the surrounding nodes in the fine mesh, and so make a gate that has approximately the same size as the gate in the coarse model.

Note: The dependence on mesh size for determining a modeled gate size is different for 3D analyses. This is inherent in the nature of 3D analyses. In shell models, the thickness of the gate is assigned as an attribute. In 3D, the thickness is a concept that only comes from the surrounding geometry.

Comparing injection pressures

With the ability to use beam runner feed systems with a 3D cavity model, there is a second option available that allows you to compare pressures in 3D Fill+Pack against those in Dual Domain Fill+Pack. If you model a short beam runner system (even just the gate will do) for both 3D and Dual Domain, and then pick the end node as the injection node, then the gate size in the two analyses will match.