Method of injection molding using one or more external sensors as a virtual cavity sensor

A method of injection molding, comprising:

• measuring, using at least one strain gauge sensor, a change in strain in a mold side of a mold cavity;
• approximating, by a controller, at least one of a pressure or a melt flow front location within the mold cavity based on the change in strain;
• comparing, by the controller, the approximated pressure or melt flow front location to a trigger point;
• determining, by the controller, that the approximated pressure or melt flow front location equals or exceeds the trigger point;
• and
• activating, by the controller, a virtual cavity sensor,
• wherein upon activation, the virtual cavity sensor tracks approximated pressures calculated from the change in strain measurements measured by the at least one strain gauge sensor over time, and compares the results of the approximated pressure tracking to a pre-defined pressure-time curve, the pre-defined pressure-time curve being a parabolic curve that approaches an asymptote at a maximum pressure setting the mold cavity is set to achieve.