External sensor kit for injection molding apparatus and methods of use
Embodiments within the scope of the present disclosure are directed to external sensor kits that may be included in new injection molds or retrofitted into existing injection molds in order to approximate conditions within a mold, such as pressure or the location of a melt flow front. Such kits are designed to amplify meaningful measurements obtained by the external sensor kit so that noise measurements do not prevent the approximation of conditions within a mold. In some embodiments within the scope of the present disclosure, an external sensor kit includes a strain gauge sensor, a coupon, a support bracket, and a hammer. The strain gauge sensor is placed on a surface of the coupon and measures the strain in the coupon.
1. A method of injection molding, comprising:
amplifying a change in strain in a coupon secured to a mold side of a mold cavity by transmitting a force to the coupon using a portion of a hammer;
measuring, using a strain gauge sensor on the coupon secured against the mold cavity, the change in strain in the coupon;
approximating at least one of a pressure or a melt flow front location within the mold cavity based on the change in strain;
comparing the approximated pressure or melt flow front location to a trigger point; and,
if the approximated pressure or melt flow front location equals or exceeds the trigger point, activating a virtual cavity sensor, wherein upon activation, the virtual cavity sensor causes a controller to adjust an operation of a ram arranged to form a shot of molten thermoplastic material in view of the approximated pressure or melt flow front location, a nozzle arranged to inject the shot of molten thermoplastic material into the mold cavity.
2. The method of injection molding of claim 1 , wherein the portion of the hammer is located some distance away from a fixed point.
3. The method of injection molding of claim 2 , wherein amplifying a change in strain in a coupon includes one of configuring the coupon to have a geometry in which the cross-sectional area in a direction perpendicular to a direction the hammer acts upon the coupon decreases toward a center of the coupon and configuring the coupon to have a center portion made from a first material and outer portions made from a second material having a higher flexural modulus than the center portion.