Low-pressure powder injection molding using an innovative injection press concept

Abstract

In low-pressure powder injection molding, the injection presses are equipped with an interconnecting pipe in which the segregation of feedstocks may occur during the dead time of the process. This segregation phenomenon limits the use of low-viscosity feedstocks leading to a decrease in the capacity to produce more complex-shaped components. The full moldability potential of the process is still limited by the injection method proposed in the commercial machines. A new injection concept was developed to increase the moldability of powder-binder mixtures, while avoiding segregation within the injection press. This innovative injection system consists of eliminating the interconnecting pipe and injection valve by using a sliding platform concept which was adapted for the transportation of the feedstock from the container to the mold cavity. Validation of the injection system was performed using three wax-based feedstocks. Injection profiles obtained with two different molds were correlated with the rheological behavior of the feedstocks, and thermogravimetric analyses were used to quantify the segregation within the system. An experimental simulation of the segregation within the machine confirmed that the injection method avoids segregation for a feedstock exhibiting a viscosity as low as 0.1 Pa·s. The best moldability properties were obtained with the feedstock containing paraffin wax and stearic acid.