In Penalty Technique for Detecting Contact, we have seen how the contact force is applied on the fluid and how the formulation employed invokes the mold velocity. If the mold velocity is imposed, this data is directly used for calculating the force at the contact. When the mold motion is controlled via a force, you must solve the classical momentum equation for the solid mold given below:
 | (17–4) |
where,
| = | force applied on the mold of mass M |
| = | resistance from the fluid that undergoes the deformation |
| = | acceleration undergone by the mold |
| = | total mass of the moving part (that is, the mold and moving components attached to it) |
and 
are user data. The mold velocity results from the time integration
of the acceleration, and is subjected to an initial velocity condition. The
direction of displacement is along the direction of the force, so the force
must be nonzero.
is obtained from the integration of the forces given by Equation 17–1 and Equation 17–2. For the sake of stability, it is
recommended that you set the convergence test value to be
10-4 or smaller (see Convergence and Divergence).
When the mold motion is controlled via a force, only a translation is permitted. Moreover, it is recommended that you specify the maximum displacement of the mold. This will stop the motion of the mold when appropriate. This displacement is evaluated along the direction of the force. When the maximum displacement is reached, the simulation continues with a fixed mold at that final position. For non-shell models, it is expected that as the domain deformation increases, so too the shear forces increase inside the domain; this in turn increases the fluid forces that act on the mold and oppose its motion, which significantly slows down the motion of the mold. For such cases, you should specify whether the mold displacement is bounded and to what value it is bounded. For shell models, on the other hand, there are no shear forces building up in the domain to slow down the motion, and so the likelihood of unrealistic mold motion is higher. Therefore, you must specify the maximum mold displacement for shell models.