rtm processes 1-8-08

rtm processes 1-8-08 - Resin Transfer Molding and Related...

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1 Resin Transfer Molding and Related Processes Douglas J. Gardner Professor Wood-Polymer Hybrid Composites Overview • Liquid Molding – Injection molding – Compression molding – Resin Transfer Molding • Pultrusion •E x
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2 Comparison of the three main types of Liquid Molding Choosing a Processing Strategy • When choosing a processing method for making a specific part, many design factors influence process selection: – Geometric issues - Part shape – Roughness - Tolerance – Part size - Material factors – Production factors - Production rate – Production Volume - Time to market • While all these issues influence process selection, the situation is not as simple as it appears. The factors are interrelated, and have a direct relationship to costs and the characteristics of the final part.
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3 Resin Transfer Molding • Originally introduced in the mid 1940s but met with little commercial success until the 1960s and 1970s • RTM appears uniquely capable of satisfying the low- cost/high-volume 500-50,000 parts per year of the automotive industry. • Variations of the RTM process make it well suited for the production of large, complex, thick-sectioned structures for infrastructure and military applications. For example, the glass-fiber / vinyl-ester bridge deck. • The automotive industry has used resin transfer molding (RTM) for decades. RTM Process-Step 1 • In the RTM process, dry (i.e., unimpregnated ) reinforcement is pre- shaped and oriented into a skeleton of the actual part known as the preform, which is inserted into a matched die mold.
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4 RTM Process-Step 2 • The mold is then closed, and a low-viscosity reactive fluid is injected into the tool. The air is displaced and escapes from vent ports placed at the high points. During this time, known as the injection or infiltration stage, the resin "wets out” the fibers. Heat applied to the mold activates polymerization mechanisms that solidify the resin in the step known as cure. RTM Process-Step 3 • The resin cure begins during filling and continues after the filling process. Once the part develops sufficient green strength, it is moved or demolded. Green strength refers to the strength of a part before it has completely cured. The green strength is an indication of how well it holds its shape until it is completely crosslinked.
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5 RTM Schematic • On first inspection, RTM appears to be a simple three-step process: preforming followed by injection and cure, as shown in this schematic. In reality, however, as shown by this schematic, it is much more complicated because processing is integrally coupled to performance. Benefits of RTM
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rtm processes 1-8-08 - Resin Transfer Molding and Related...

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