This project investigated the dimensional accuracy of parts produced using the rapid prototyping method of fused deposition modelling (FDM). Parts with six features common to products were created on a Stratasys FDM2000 out of acrylonitrile butadiene styrene and then measured with a coordinate measurement machine and digital micrometers. An analysis of 12 different dimensions on parts produced using FDM identified that part size, location in the work envelope, and envelope temperature had a significant effect on the dimensional accuracy of FDM.
The warp of a phenolic resin/fiberglass honeycomb composite panel is investigated using void and volatile analysis, and a solution to geometric warp is proposed and tested. The surface void content in semicured phenolic polymer composite facesheets was found to be an indicator for the average warp value of a fully cured composite laminate panel. Several potential sources in the resin formulation for producing voids in the phenolic resin/fiberglass composite sheets were investigated. Ultimately, high surface tension and polymer incompatible cosolvents are correlated to the population of voids. It is proposed that these voids act as sites for the relief of internal stresses that develop in the phenolic matrix during the final cure of the part. Void-inducing additives are added at the formulation stage which phase separate from the polymer matrix in partially cured fiberglass/phenolic composite sheets, and upon evaporation, lead to voids that prevent warping in honeycomb composite panels.
A lab scale continuous process solvent-based prepreg manufacturing machine (prepreg treater) is a useful tool for small-scale production runs carried out by research teams involved in various projects related to advanced composites. Such a machine can also be used in school laboratories for teaching purposes. However, industrial compact prepreg treaters available for purchase are prohibitively expensive.This document details the work done by undergraduate students at Western Washington University to design, develop, and qualify a modestly budgeted, solvent-based prepreg manufacturing machine to be used for investigation of new prepreg resin systems. The steps undertaken to manufacture the machine and qualify it are explained in detail and can be helpful to educational institutions that may have requirements of such a treater for research and/or teaching.
DefinitionsPrepreg is commonly defined as a reinforced fabric that has been impregnated with a resin matrix. It is frequently used in place of a traditional hand layup for a number of reasons, including increased control over resin content, decreased scrap and mess, and generally improved reproducibility during processing.[1] Following impregnation of the pre-polymeric resin system into fibers, the prepreg is considered B-staged. At this point in processing, the resin has undergone a partial cure and begun to crosslink. As such, storage in freezers is required, to prevent further crosslinking of the material into a fully cured C-stage product. [2] Prepreg is manufactured primarily using two processes: solvent coating and hot melt coating. In the solvent coating process, fabric is threaded between metal rollers and run through a resin bath, then fed through a series of ovens to partially cure the material. Following a short cooling period, the prepreg is ultimately wound up at the other end of the machine into a roll, for ease of storage [3]. The resin in the bath is dissolved in a solvent, typically an alcohol or acetone, to reduce its viscosity and increase its ability to penetrate the fibers. The solvents are released as volatiles in large in-line ovens as a part of the process during B-staging. In contrast, to produce prepreg using hot melt coating, fabric is run through a carrier paper containing a fixed quantity of resin, followed by the application of pressure with heated compaction rollers. This simultaneously impregnates the fabric and B-stages the resin. The fabric is then cooled and the paper removed.
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