Characterization of Composite Dust Generated During Milling of Uni-Directional and Random Fiber Composites

Abstract

As every manufacturer of carbon-fiber composite structures knows, one of the most nettlesome aspects of the production process is that machining, drilling and sanding of carbon fiber composites produces fine dust. These composite materials typically consist of epoxy matrix material reinforced with carbon, graphite, glass, and/or para-aramid fibers. Matrix materials are usually epoxy, polyester, phenolic, fluorocarbon, polyether-sulfone, and silicon. The most commonly used are epoxies and polyesters, which are less expensive than epoxies. It can build up on and short out computers, control panels and servomotors. In the air, it can be inhaled and threaten human health. Further, the accumulation of any dust in a manufacturing facility can be problematic from the regulatory perspective. In fact, dust has been blamed for several explosions in manufacturing facilities, leading the U.S. Occupational Safety and Health Admin. (OSHA) and many local governments to more closely monitor and regulate dust accumulation in all manufacturing environments. An increase in human exposure to potentially toxic airborne fibers has accompanied the increased use of composite materials. The dust emitted during the machining of composite materials is potentially damaging to the human lung. Several studies have attempted to characterize the damage to the lung caused by airborne particles from composites, while other studies have characterized the size and concentration of the dust emitted. Some studies have shown that the chip formation process affects the size distribution of the particles emitted during the machining of composites. Health hazard evaluation of composite matrix material is usually conducted by examining the individual materials that are in the resin system and using sound scientific judgment. The main objective of this research is to quantify the amount of dust generated during machining (predominantly milling) of composites and to calculate what percentage of this dust is harmful to the workers in such composite dust laden environments. This criteria is based on PM (Particulate matter) aerosol standards defined by OSHA in regard to safety and well-being. In addition this research will also highlight the effect of stacking sequence of laminates on the concentration of dust generated and the characterization of these particle sizes. This research also further aims to develop optimized cutting conditions that will help in reducing the amount of dust that would be generated by using an experimental study. During this study different tests were carried out to characterize the different effects that are observed during the machining of Uni-Directional and random fiber composites. The machining dust results showed a very good correlation between the different real time measuring instruments and validated the design of the iso-kinetic sampling tower. Mean aerodynamic diameters of particles found during the machining of Uni-Directional composites was 0.19 um and that of random fiber composites was found to be 0.28 um. Tests to find out the optimal cutting conditions for the lowest amount of dust generated was found to be that of using a low cutting speed, high feed and lower depth of cuts. These conditions however might not aid the best surface finish. Hence a compromise or a trade-off is required.