Element Density (No. of node/dofs)
| • | Place an adequate number of elements in the flow path. This is essential to capture the flow and avoid choking. |
| • | In a typical cross-section of the profile or extruded part, place 4 to 5 elements (linear) across each section. |
Element Quality
| • | When the mesh contains higher order elements (HEX20/HEX27), make sure that the element Jacobian (in HyperMesh or your mesh generator) is greater than 0.4. |
| • | Even though it is not necessary for HEX8 (linear elements), the same guideline is still recommended. |
| • | Mid nodes on the sides/face of an higher order element should be preferably placed at the mid-point between (or closer to this) the corner node. If not, this will affect the Jacobian computations inside HyperXtrude. |
Checks for Errors
Before exporting the data from the HyperXtrude user profile, check for:
| • | Duplicate nodes/elements |
| • | If it is a 2D or axisymmetric problem, make sure the normal point to +ve Z axis |
| • | 95 percent of the errors made in HyperXtrude data decks are incorrect data in BCs and process parameters. Double-checking your values for consistency will save you time. |
Tips Specific to Metal Extrusion
| • | For steady state runs, you do not need to mesh the entire billet. The length of the billet meshed can be as small as two times the billet diameter. |
| • | In the billet region, use exponential/linear biasing to place more elements near the die opening and fewer elements at the inlet boundary. |
| • | The profile section must be at least 1.5 times the billet diameter. |
| • | For free surface prediction, use second order elements (p=2) in the elements that are located downstream of the die. |
| • | Orient the mesh such that the primary flow direction is along positive Z-axis. |
| • | When generating the mesh, place the origin (0,0,0) such that x=0 and y=0 is the center of the die and z=0 is the die face that is in contact with the billet. This is not essential but will help in setting up the unsteady moving mesh analysis. |
| • | For flat dies, use the automatic meshing feature in HXpre. Please note that this will work only for metal extrusion dies. |
| • | Have at least two elements in the land region (bearing) along the extrusion direction. |
| • | In hollow dies, make sure there are enough elements in the welding chamber region to allow for proper modeling of the merging of the fluid downstream from the bridges (use at least three or four elements in the flow direction). |
General Tips
| • | Renumber the nodes and elements, however, this step is not essential. |
| • | Orient the unit normals on boundary faces in a consistent manner inside HyperMesh. This is especially important for the boundary faces, which have Symmetry BC. In HyperMesh, element Jacobians greater than 0.4 (less for quadratic meshes). |
| • | For axisymmetric analyses, use second-order elements (Quad8 or Quad9). |
| • | Non-QUAD elements are NOT supported for 2D analysis. |
| • | For 3D geometry with curved boundaries, use HEX20. |
| • | Around die exit, element aspect ratios should be close to 1.0 (good transition) |
See Also:
Guidelines for Simulation
