Effects of geometry and injection-molding parameters on weld-line strength

Polymeric flows in microchannels are found to differ significantly from those in macrogeometries. Increasing the mechanical properties of microstructures is one of the most important issues in injection-molding processes. Weld-line characteristics of structures with different cross-sections are investigated in this study. The effects of process parameters and cross-sectional dimensions on the tensile strength of a weld line are discussed. A mold was designed in such a way that specimens with and without weld lines can be developed separately. Five specimens, with different cross-sections, are injection-molded simultaneously. Both polypropylene (PP) and high density polyethylene (HDPE) are used in this study. With the Taguchi method, four process variables: melt temperature, mold temperature, injection speed, and packing pressure were found to be the most influential. Experimental results show that the weld-line strength from a standard test is not applicable in microinjection molding. The microstructure of weld lines is clearly observed from the micrographs. (c) 2005 Society of Plastics Engineers.