40207_20 - RESIN TRANSFER MOLDING Lihwa Fong and S.G....

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RESIN TRANSFER MOLDING 20 Lihwa Fong and S.G. Advani 20.1 INTRODUCTION ready for its removal from the mold when suf- Resin Transfer Molding (RTM) is a closed mold process in which matched male and female molds, preplaced with fiber preform, are clamped to form composite components. Resin mix is transferred into the cavity through injection ports at a relatively low pres- sure. Injection pressure is normally less than 690 kPa (or 1OOpsi). The displaced air is allowed to escape through vents to avoid dry spots. Cure cycle is dependent on part thick- ness, type of resin system and the temperature of the mold and resin system. The part cures in the mold, normally heated by controller, and is ficient green strength is attained. Processes that are based on similar principles include Structural Reaction Injection Molding (SRIM) and different versions of vacuum assisted RTM (Figs. 20.1 and 20.2). RTM offers the promise of producing low cost composite parts with complex structures and large near net shapes. Relatively fast cycle times with good surface definition and appearance are easily achievable. The ability to consolidate parts allows the saving of con- siderable amount of time over conventional lay-up processes. Since RTM is not limited by the size of the autoclave or by pressure, new Mixing Head 1 Vent Port r ---- --- - I I 1 I - I I I I I I I I I I Pumpunit --------- Fig. 20.1 Schematic of the RTM process. Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7
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434 Resin transfer molding ISOCYANATE POLYOL HYDRAULICS MACHME MODE HEAD Fig. 20.2 Basic construction of a SRIM machine. tooling approaches can be utilized to fabricate large, complicated structures. However, the development of the RTM process has not ful- filled its full potential. For example, the RTM process is yet to be automated in operations such as preforming, reinforcement loading, demolding, and trimming. Therefore, RTM can be considered an intermediate volume molding process (Krolewski, 1990). Several unresolved issues in RTM encoun- tered by composite engineers are in the areas of process automation, preforming, tooling, mold flow analysis and resin chemistry. During the last decade, rapid advances in RTM technology development have demon- strated the potential of the RTM process for producing advanced composite parts. The advantages and associated disadvantages of the RTM process are summarized. As the development of this process is rapid, some of the disadvantages may be overcome by the advances made in this technology. Advantages are: 0 Class A surface: Surface definition is supe- rior to lay-up. In addition, using matched tools for the mold, one can improve the fin- ish of all the surfaces. 0 Close tolerance: Parts can be made with bet- ter reproducibility than with layup.
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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40207_20 - RESIN TRANSFER MOLDING Lihwa Fong and S.G....

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