The Effect of Thickness on the Weld-Line Strength of Injection-Molded Thermoplastic Composites

Abstract

Weld lines are a major concern to designers since they result in poor mechanical properties. Designers may overdesign parts when considering anticipated failure modes and safety factors by locating weld lines in non-critical areas without taking into account material factors. This study focus on the effect of part thickness on the weldline strength of injection-molded short-fiber-reinforced thermoplastic composites. Comparisons were made with specimens without weld lines. The use of design data which takes into account fiber orientation and part thickness will enable designers to more accurately predict the performance of an injection-molded thermoplastic composites under applied load.

Investigation into fibre orientation and weldline reduction of injection moulded short glass-fibre/polyamide 6-6 automotive components

“…Several studies [9][10][11][12][13][14] have noted the presence of voids or pores in the regions near weldlines. This is due to gas entrapment at the time when the two flow fronts meet and recombine after flowing around an obstacle.…”

“…This was achieved using the depth measurement function of the Keyance VHX-1000 digital optical microscope, Figure 10 (middle). As stated by several studies [9][10][11][12][13][14] pores occur in the vicinity of weldlines due to gas entrapment. The locations of these pores correlate well with the locations of the weldlines in the simulation where the component was injected from both sides.…”

Effect of molding condition and pellets material on the weld property of injection molded jute/polylactic acid

“…It is especially used to produce a wide variety of complex geometry articles in one automated production step with low wear of the processing equipment. High production rate, short cycle times, and low percentage of scrap are accounting the advantages that make this process very attractive from engineering and economical point of view [9–12]. However, weld line is one of the typical problems seen in injection molding.…”

“…The presence of weld lines not only detracts from the surface quality but also significantly reduces the mechanical strength of injection‐molded parts. Although it is not always easy to completely eliminate weld lines, the weld line strength of injection‐molded parts could be improved through suitable adjustment of processing parameters, mold design, and so on [9–19]. In particular, Wu and Liang [10] discussed the effects of process parameters and cross‐sectional dimensions on weld line characteristics of polypropylene (PP) and high density polyethylene (HDPE).…”

“…Therefore, the mechanical strength obtained from a standard tensile test is not suitable for microinjection‐molding processes. Patcharaphun and Jariyatammanukul [11] investigated the influence of part thickness on the weld line strength of injection molding short‐glass‐fiber reinforced PP. It was found the tensile strength tended to decrease as the wall thickness increased from 2 to 6 mm and they thought the increment of the thickness of specimens did not produce any major changes in the weld line strength injection molded PP composites.…”