B-SIM V2.5 Reference - Blow molding simulation | ||||||||

Parison extrusion optimization
From B-SIM point of view, an extrusion optimization means searching for such parameters of the extrusion process control (AWT, PWT, SFDR) so that the final thickness distribution is close to uniform.
B-SIM 2.45 comes with an optimization routine (option) which enables to automatically optimize AWT, PWT and SFDR. At the start of the optimization, the users can select what type of the extrusion control / what combination of controls should be optimized.
As the extrusion in B-SIM is simulated step by step and the parison continuum is approximated by a finite number of triangles, there are some problems arising, which can lead to a failure of the extrusion optimization. Basically, three things must be fulfilled in order to get reasonable optimization results. It is necessary to have a suitable number of: 1) elements (FE representation of parison) In general, the simulation results are poor when having low number of elements of FE grid. It is hard to give a "reasonable" value for the number of elements working in all cases. A suitable number of elements is also connected with the number of extrusion control points. By the "number of extrusion control points" we mean the number of points in time scale available on the extrusion equipment. Typically, 64 points can be used during one extrusion cycle. However, B-SIM does not put any limitations on the number of the extrusion control points, so it is user's responsibility to enter proper data. On the following figures, there is an explanation why the number of elements and the number of extrusion control points play a big role in the simulation of extrusion and consequently also in the extrusion optimization.
The last thing is number of the extrusion checkpoints. The extrusion checkpoint is the point where the thickness obtained by a modification of the extrusion setting is evaluated. A theoretical minimum of the checkpoints along the parison length is equal to the number of the extrusion control points in AWT(PWT) settings. A theoretical minimum of the checkpoints along the parison perimeter is not so easy to estimate as there is a linear interpolation used between SFDR settings. Anyway, B-SIM 2.45 requires the number of the checkpoints to be at least two times higher than the number of the extrusion control points (in both directions - longitudinal and circumferential). Obviously, the higher the number of the extrusion checkpoints, the better evaluation of the final thickness uniformity. However, an excessive number of control points can cause the optimization algorithm to be very slow. And, if the checkpoints fall into the same element, there is no difference in results and the whole optimization process is just slower, nothing else. To conclude, the whole concept is simple and easy to understand and use on a daily basis. However, the B-SIM optimization algorithm cannot be used as a simple, one-click tool. It requires the user to understand what is behind the algorithm and what has to be done in order to get reasonable optimization results. Please follow this link to see some practical optimization examples.
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