Method of injection molding using one or more strain gauges as a virtual sensor

A method of injection molding, comprising:

• providing a first strain gauge sensor on an exterior surface of a first mold side of a mold cavity near a parting line between the first mold side and a second mold side of the mold cavity;
• providing a second strain gauge sensor on an exterior surface of the second mold side;
• measuring, using the first strain gauge sensor and the second strain gauge sensor, a change in strain in the first mold side and the second mold side of a mold cavity under both a closing force exerted by a clamping unit and an opening force exerted by thermoplastic molten material as it is injected into the mold cavity;
• approximating, by a controller, a pressure within the mold cavity based on the change in strain in the first mold side and the second mold side;
• comparing, by the controller, the approximated pressure to a pre-set trigger point, wherein the pre-set trigger point occurs when the change in strain is a relaxing tensile strain;
• determining, by the controller that the approximated pressure equals or exceeds the pre-set trigger point;
• and
• in response to the determining, via the controller, that the approximated pressure equals or exceeds the pre-set trigger point, activating, by the controller, a virtual cavity sensor having an optimal pre-defined pressure-time curve, 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 the optimal pre-defined pressure-time curve.

An injection molding system comprising:

• at least one strain gage on an exterior of a mold surface configured to measure a change in strain in a mold side of a mold cavity under both a closing force exerted by a clamping unit and an opening force exerted by thermoplastic molten material as it is injected into the mold cavity;
• a controller operatively connected to the at least one strain gage, the controller configured to:
• approximate a pressure within the mold cavity based on the change in strain measured by the at least one strain gage,
• compare the approximated pressure to a pre-set trigger point, wherein the pre-set trigger point occurs when the change in strain is a relaxing tensile strain,
• determine that the approximated pressure equals or exceeds the pre-set trigger point, and
• in response to the determination, activate a virtual cavity sensor;
• and
• the virtual cavity sensor, wherein the virtual cavity sensor is operatively connected to the controller, has an optimal pre-defined pressure-time curve, and, upon activation, is configured to:
• track the approximated pressure based on the change in strain measurements measured by the at least one strain gauge sensor over time, and
• compare the results of the approximated pressure tracking to the optimal pre-defined pressure-time curve.