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

Abstract

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. POLYM. ENG. SCI., 45:1021-1030, 2005.

Practical Applications of Taguchi Method for Optimization of Processing Parameters for Plastic Injection Moulding: A Retrospective Review

“…Based on the experimental data at optimal level combination, the weld-line defect has significantly reduced through the optimization and it was found that the melt temperature was the most important parameter affecting the visibility of weld-line. In another study, [36] further improved the weldline strength of an injection-moulded part by utilizing the Taguchi optimization method. The study was carried out on a special-designed mould wherein the specimens which are having different cross-sections can be injection-moulded with and without weld-line.…”

Microinjection Molding of Enhanced Thermoplastics

“…In order to overcome those weaknesses, alternative solutions have to be considered. For example, if geometry of micro parts allows for a positive draft angle, the latter could assist the proper demolding of the microparts (Grave et al, 2007;Wu & Liang, 2005). A concept of more even distribution of ejection forces has been applied when ejection with pins was substituted with the micro ejection block used as striper plate to thrust the microparts (Wu & Liang, 2005).…”

“…Adhesion forces between polymer and mould tool may vary significantly for different polymer grades and should be accounted for successful demolding of the microparts. The latter may be achieved by fine surface finishing of the mould cavity, positive draft angles and by using release agents (Wu & Liang, 2005;Grave et al, 2007). The variety of factors involved into the transformation of the polymer melt within the microcavity makes the interpretation of the cause-effect relationship uneasy task even for neat (unfilled) thermoplastics.…”

“…For example, if geometry of micro parts allows for a positive draft angle, the latter could assist the proper demolding of the microparts (Grave et al, 2007;Wu & Liang, 2005). A concept of more even distribution of ejection forces has been applied when ejection with pins was substituted with the micro ejection block used as striper plate to thrust the microparts (Wu & Liang, 2005). Ejection of the high aspect ratio micro structures, molded within the insert of rough surface finishing, may be successfully accomplished with vacuum assisted demolding (Michaeli et al, 2000).…”

Welding lines formation in holes obtained by low pressure injection molding of ceramic parts

“…However, when dealing with holes produced by inserts (core), this becomes a main issue [8], mainly because of the cracks, voids and welding lines. Welding lines in injection molding usually occur because of the separation of the material flow, enforced by some obstruction and its posterior junction [18][19][20][21]. These welding lines are potentialized by the low part of organic vehicle in the feedstock.…”