Comparative study of weld‐line strength for unfilled and glass‐filled thermoplastic polyamide‐6 materials

Abstract

The injection molding process is widely accepted for the processing of engineering thermoplastics due to the ease of manufacturing complex designs. Weld‐line is a defect occurring in injection molded parts when two flow fronts join each other. At weld‐line locations, parts exhibit lower mechanical strength mainly due to inadequate intermolecular diffusion and fiber orientation anisotropy. The present work is aimed at investigating and comparing weld‐line strength for unfilled and glass‐filled polyamide‐6 materials. To achieve this, polyamide‐6 unfilled, 30% glass‐filled, and 50% glass‐filled materials are used to manufacture plaques. The special‐purpose mold is designed to obtain plaques with and without weld‐lines with help of Moldflow simulations. The specimens for tensile tests are then cut from molded plaques and experimental testing is conducted to evaluate tensile properties. Fractured surfaces of specimens are examined using a scanning electron microscope. The results demonstrated a significant drop in tensile strength and modulus for glass‐filled material weld‐line specimens when compared to specimens of no weld‐line. However, for unfilled specimens, tensile strength and modulus are almost the same for samples with and without weld‐line. A reduction in tensile strength of 13%, 49%, and 57% is observed for unfilled, 30% glass‐filled, and 50% glass‐filled polyamide‐6 material respectively.

Weld‐lines and its strength evaluation in injection molded parts: A review

“…The changes in the area are calculated by taking the derivative of the area with respect to time as mentioned in Equation (13), where D is the interdiffusion coefficient, ΔG is the change in free enthalpy, k is Boltzmann constant and C diff is the calibration constant.…”

“…Software like Autodesk Moldflow and Moldex 3D are leading injection molding simulation tools. 13,27,41 The algorithms of these tools are robust and provide a good correlation with actual reality. The weld-line location prediction is well captured in these tools, however, to evaluate the strength of the weld-line for the plastic material non-linear algorithms are required and these flow simulation tools are mainly based on a linear algorithm, therefore prediction of weld-line strength still under development 15,42 and there are no standard results output available to get weld-line strength.…”

“…The ISO 527-2 and ASTM D638 have commonly followed procedures while conducting tensile tests. 6,13,53 Under these standards, different shapes and sizes of specimens are available with manufacturing method as injection molding and injection molding followed by machining. The selection of size, shape, and manufacturing process is as per the requirement from the test.…”

“…This can be because cooling and subsequent re‐solidification of the plastic has already taken place. Another possibility is that the molecules are not aligned with the flow channel at the molecular level 12–14 . A weld line is the end consequence in both scenarios.…”

“…Another possibility is that the molecules are not aligned with the flow channel at the molecular level. [12][13][14] A weld line is the end consequence in both scenarios.…”