Ultrasonic online nondestructive measurement method for melt density during molding

An ultrasonic online nondestructive measurement method for a melt density in injection molding, comprising the following steps:

• (1) mounting an ultrasonic probe on an outer side wall of a mold cavity, and emitting an ultrasonic wave toward a polymer melt in the mold cavity;
• (2) collecting reflection echoes of two surfaces of the melt in contact with a mold, wherein the reflection echo of the surface close to the probe is denoted as U1, and the other reflection echo is denoted as U2;
• (3) calculating an ultrasonic propagation velocity in the polymer melt based on time domain signals of the reflection echoes U1 and U2;
• calculating an acoustic impedance of the polymer melt based on frequency domain signal amplitude spectra of the reflection echo U1 and U2;
• and
• (4) calculating the melt density based on ρ=Z/c and the calculated ultrasonic propagation velocity and acoustic impedance, wherein Z is the acoustic impedance of the polymer melt, and c is the ultrasonic propagation velocity in the polymer melt.