Ultrasonic method and device for indirectly measuring cavity pressure of injection molding machine

An ultrasonic method for indirectly measuring a pressure of a cavity of an injection molding machine, comprising:

• emitting ultrasonic wave to each pull rod along an axial direction of the pull rod respectively at the same time, detecting a time difference between an ultrasonic wave echo on each pull rod in an injection molding process and an ultrasonic wave echo when the pull rod is under minimal strain, and obtaining an average pressure P inside the cavity of the injection molding machine according to the following formula:
• P
• ⁢
• =
• π
• ⁢
• R
• 2
• ·
• W
• ·
• Δ
• ⁢
• t
• total
• /
• A
• wherein R is the section radius of the pull rod;
• Δttotal is the sum of echo time differences of all the pull rods;
• W is a constant at least partially determined based on one or more Murnaghan constants and one or more Lamé constants of the material of the pull rod;
• and A is the projection area of the cavity on a plane perpendicular to the axial direction of the pull rod;
• wherein there are four pull rods;
• wherein an ultrasonic probe is arranged at the tail end of each pull rod;
• wherein the W is acquired by the following method:
• before detection, for the pull rod with the same material, conducting detection by a mold locking force sensor under different mold locking forces to acquire multiple groups of σ−Δt data, and fitting a straight line passing through the origin of σ−Δt data, and evaluating the slope of the straight line to acquire the W, where the σ is a stress on the pull rod as a y-coordinate and the Δt is a time difference of ultrasonic wave echoes, as an x-coordinate.