Diagnosis of injection-molded weld line in thermoplastic polymer by terahertz reflective imaging and scanning acoustic microscopy

Terahertz (THz) reflective imaging and scanning acoustic microscopy (SAM) were utilized for material characterization as well as quality control of an injection-molded thermoplastic electrical receptacle plate. V-notched weld lines that degrade the mechanical strength of injection-molded products significantly, are observed in both SAM and THz results. The dimension of V-shaped morphological feature of the weld line is ~ 400 μm in width and ~ 10 μm in depth. Position resolved THz birefringence also locates the weld line.