Optimizing Mechanical Performance of Injection Molded Multiple Gated Rotating Thermoplastic Components: Part 2 - Knit Line
/Weld Inter-Phase Integrity
Due to the wide and ever increasing application of thermoplastics for the transportation and automotive industries, the performance of the under-the-hood plastic parts depend upon optimized design and processing technology and properties of polymer based materials. Nylon (polyamide) based plastics are used widely for automotive cooling fans and various under-the-hood injection molded components.
For injection molding of multi-blade cooling fans and various rotating plastic parts the complex of multiple gating injection molding tools were used. Both the design of the various rotating parts (including industrial and automotive cooling fan, and the molding tool design are very important to get optimum flow patterns and to predict the locations and interaction of stress-bearing areas and knit lines (planes or inter-phases)1. The mechanical performance of the injection-molded thermoplastic components depends on the peculiarity of the part and the molding tool design.
In Part 1 of this paper2, we are presenting results of structural design analysis (comprehensive analytical and linear FEA) and design optimization of a multiple gated rotating components with a ring under the influence of the design parameters. In Part 2 of this paper, we are discussing the mechanical properties of fiber-glass reinforced thermoplastic in local (weld plane) and bulk (molded part) areas with the influence of molding and end-use conditions.
The analysis of this study shows, that for non-reinforced or non-filled nylon, the mechanical performance in the knit-line (weld plane) areas are approximately equal to the mechanical performance of used resin (polyamide).
For fiber-glass reinforced and fiber-glass/mineral nylons, the mechanical properties of plastic in the knit (weld) line (plane) are different from the basic mechanical properties of reinforced plastic due to flow patterns and local fiber-glass re-orientation in the weld plane areas. Due to the above changes, the knit (weld) lines become likely areas of crack initiation and propagation and possible molded part failure or damage.
The results from this complex study should help plastic part designers to accurately interpret the results of the structural analysis and complex tensile properties such as strength, deformation and fatigue of nylon based plastics and to utilize these important material parameters at end-use conditions for a plastic part life assessment.