Summary

While emerging nanotechnologies are creating promising opportunities in several sectors of activity, studies suggest that the nanoparticles (NPs) they generate could have negative effects, particularly on health and the environment. These may be generated during the manufacture, handling and assembly of ordinary metal components, as well as those made from nanomaterials. Other everyday activities, such as automobile braking, can also produce NPs. Consequently, it is vital to find ways of controlling these risks. However, conventional techniques and methods of risk assessment are not directly applicable to NPs. The objective of the present project is to establish an effective method for measuring, controlling and characterizing NPs applicable to industrial manufacturing processes.

The study required laboratory tests for the machining and friction; these were performed on machine tools of an industrial calibre, and coupled with simulations of the behaviour of airborne particles and airflows in the machine enclosures. It used equipment for particle sampling (SMPS, APS, MOUDI) and characterization (a scanning electron microscope, or SEM; a transmission electron microscope, or TEM; and an atomic force microscope, or MFA). Among other things, the present project, allows us to:

• Establish a sampling, collection and measurement procedure: develop sampling methods and substrate preparation adapted to the NPs and the various microscopes employed (SEM, TEM and AFM); improve measurement by developing correction factors for the form and density of the particles.
• Determine the conditions surrounding the generation of NPs during the friction and machining of aluminum alloy components, as well the concentrations and aerodynamic diameter distributions these particles. We have thus developed strategies for reduction at source of NP emissions during machining and friction processes, strategies based on the choice of operating conditions.
• Demonstrate that the machining of ordinary alloys, those not considered nanomaterials, emits more NPs than particles of micrometric dimensions, and that most of these NPs are smaller than 20 nanometres.
• Classify common machining operations (milling, turning and drilling) and dry friction operations according to their NP emission capacity. For the aluminum alloys tested, milling is the operation that emits the most NPs.

This study demonstrated the need to know the trajectory and form of the particles when they are emitted, with a view to improving their capture and the accuracy of their measurement. It also revealed the presence of ultrafine particles in machining operations for shaping ordinary materials not containing NPs. The emission of these particles depends on the processes employed and their parameters, as well as on the cutting materials and the materials cut, all of which determine the potential for controlling the emission of these particles. Typical cases of nanomaterials, as well as of composites containing or not containing nanoparticles, merit consideration.

In the present report, the term nanoparticles (NPs) refers to the ultrafine particles of nanometric dimensions that are emitted during the machining of metal components (or other processes for performing this function).