Meaning
Mathematical technique used in finite element analysis enforces boundary constraints by adding artificial stiffness terms to the governing equations. The application of penalty formulation in injection moulding simulation allows engineers to model the contact between the molten plastic and the mould wall or the deflection of mould plates. This method allows small penetrations across the boundary to avoid the numerical instabilities associated with exact Lagrange multiplier methods.
It is a fundamental component of software used to optimize runner designs and gate locations.
Numerical Constraint
Enforcing the contact conditions prevents the flowing polymer from numerically penetrating the steel boundaries of the cavity. The simulation adjusts the penalty parameter to strike a balance between constraint enforcement and numerical stability. If the parameter is set too low, excessive penetration occurs, which leads to inaccurate part thickness predictions.
Simulation Efficiency
Fast convergence of the iterative solvers reduces the computational time required to analyze complex three-dimensional part geometries. Unlike exact constraint methods, this approach does not increase the number of degrees of freedom in the system of equations. This efficiency allows mould designers to quickly evaluate multiple gate configurations and cooling channel layouts during the design phase.
Process Prediction
Accurate modeling of the melt front progression helps in identifying potential weld lines and air traps before the tool is built. By simulating the contact pressure and friction at the cavity wall, the software can predict the injection pressure required to fill the part. Moulders rely on these predictions to select the appropriate injection moulding machine size and to prevent part defects like short shots or sink marks.
