In-situ ultrasonic characterization of microcellular injection molding

Abstract

Microcellular injection molding (MIM) has been extensively employed for manufacturing foamed polymeric products. It has the advantages of saving energy and material costs, along with attaining better dimensional stability. However, the in-situ characterization of MIM is still challenging. In this study, an ultrasonic method for the real-time detection of variations in the foam structure—i.e., cell size (D), surface roughness (Ra), and skin layer thickness (h)—during the MIM process is proposed. This is the first time that ultrasonic technology has been employed to characterize the MIM process. Experiments were carried out to confirm the feasibility of the proposed method. Experimental results showed that the ultrasonic signals exhibited great consistency, and the duration process times of the ultrasonic signals (tduration) and the change of the ultrasonic speed (vvariation) in the transducer path could be used to characterize the variations of cell size and skin layer thickness. The time delay of the first ultrasonic signal (tstart) and the largest ultrasonic amplitude of the ultrasonic signals (Amax) could be employed to characterize the variations of surface roughness. The developed ultrasonic characterization method has several advantages, such as being low-cost, on-line, and non-destructive, and it has promising applications in the characterization of the MIM process.