Optimizing Mechanical Performance of Injection Molded Multiple Gated Rotating Thermoplastic Components: Part 1 - Consideration of Structural Analysis and Knit Line
Engineering thermoplastics were successfully utilized in the design of injection molded rotating parts such as the impellers, wheels, and cooling fans of commercial air-cooled chillers, and gas and diesel engines.
Complex aerodynamic and mechanical performance of impellers and cooling fans are very important for the efficiency of integrated air-movement, climate control and cooling systems of various types of engines of vehicles, cars, heavy-duty tractors and trucks. The transportation and automotive industries have developed a culture of reliability and cost effectiveness, in which high risks and adventures are not encouraged.
Due to the wide and ever increasing application of thermoplastics for the transportation and automotive industries, the performance of the under-the-hood parts depend upon optimized design and processing technology and properties of polymer based materials.
The mechanical properties of the injection-molded thermoplastic components depend on the part and the molding tool design. For injection molding of the multi-blade 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 the industrial and automotive cooling fans), and the molding tool design are very important to get optimum flow patterns and to predict the locations of stress-bearing areas and knit lines (planes)1.
For non-reinforced or non-filled nylon, the mechanical performance in the knit lines (planes) areas are approximately equal to the mechanical performance of the resin (polyamide) used. Fiber-glass reinforced and fiber-glass/mineral nylons have mechanical properties of plastic in the knit (weld) line (plane) and is different from 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 weld planes (lines) become likely areas of crack initiation and propagation and possible molded part failure or damage.
In this investigation, we are presenting the results of analytical structural analysis and design optimization of various multiple gated rotating thermoplastic parts such as wheels, impellers, and multi-blade fans with an external ring under the influence of mechanical parameters of fiber-glass reinforced plastic in local knit (weld) plane areas. For determination of these mechanical properties in local (weld plane) and bulk (molded part) areas, the influence of molding (melt and mold temperatures, shear rate, etc.), and end-use (strain rate, temperature, moisture, etc.) conditions should be taken in to account.
The results from this study should help designers to accurately interpret the results of structural analysis and complex tensile (as basic) properties, such as strength, deformation and fatigue of nylon based plastics and to utilize these important material parameters at end-use conditions for a part life assessment.