In 2D as well as in 3D simulations of blow molding and pressing, you can compute the thickness of the final object (as well as during shaping). In industrial processing, the thickness has to be understood as the distance between two arbitrary surfaces; it is therefore subjected to an appropriate definition. Also, from the point of view of modeling, it would require the identification of preferably distinct topological entities; however this cannot always be achieved. A technique has been implemented, which matches a reasonable industrial definition as much as possible: at a given point, it basically consists of evaluating the distance with respect to the closest opposite surface. A topological object has to be constructed for the thickness evaluation, and a few parameters for geometric tolerances have to be given. In 3D, the thickness is evaluated on the selected boundary; planes of symmetry can be discarded from the domain of evaluation. Note that in 2D, a similar scenario applies; however, since the display of a quantity along a line is not easy, the evaluation is expanded onto the domain via a Laplace equation.
Typically, the thickness at the end of the process is of interest. Hence, it is not necessary to perform a thickness evaluation at each time step. Also, since the thickness at a point is evaluated as a distance measured along a line perpendicular to the surface at this point, it is preferable to bound its value.
The procedure for setting up the evaluation of thickness is as follows.
Specify the domain of the evaluation.
Domain of evaluation
Specify the domain where you want the thickness to be evaluated; it coincides with the fluid domain in blow molding and pressing simulations, and with the solid domain when evaluating residual stresses and deformations.
Specify the boundary of the evaluation.
Boundary of the evaluation
Specify the border that is used as the basis for the evaluation of the thickness; it may consist of one or several entities, but typically symmetry planes and lines are not considered.
Update the current coordinates with displacements.
Take displacement into account
When the simulation involves the prediction of residual stresses and deformations (along with the Narayanaswamy model), it is possible to specify that the thickness has to be evaluated on the basis of coordinates updated with residual displacements. Note that the actual coordinates update is only performed internally.
Specify the activation time.
Modify the activation time
Typically, the thickness at the end of the process is of interest. Hence, it is not necessary to perform a thickness evaluation at each time step, and you may select the activation time for thickness evaluation. The thickness evaluation will be performed only when the simulation time is greater than or equal to the activation time.
Specify the thickness limit.
Modify the thickness limit
The thickness at a point is evaluated as a distance between the point and the opposite surface, measured along a line perpendicular to the surface at this point. It is preferable to bound its value in order to prevent geometrically irrelevant values.
Specify the geometric tolerance.
Modify the geometric tolerance
The thickness at a point is evaluated as a distance between the point and the opposite surface, measured along a line perpendicular to the surface at this point. The algorithm involves a search of geometric intersection (between the perpendicular line and boundary elements). A geometric tolerance is needed in order to compensate for round-off errors.