Thermo–fluid mechanisms controlling droplet based materials processes

Recently, the successful application of thermal spray deposition techniques to the manufacture of bulk materials and thin film coatings with improved structural properties has illuminated the need for a fundamental understanding of the physical phenomena that control the deposition process. However, the spray parameters have a complex statistical interdependence that renders their analysis difficult. Discrete droplet deposition processes provide phenomenologically simpler systems than thermal spray deposition processes while still retaining their salient features. Furthermore, discrete droplet deposition processes have found important manufacturing applications from soldering to rapid prototyping. Consequently, this review focuses on recent research in the area of droplet based materials processes. The emphasis is on fluid dynamics and thermal aspects as they relate to materials science issues. The design and operation of a number of representative droplet deposition approaches is also discussed in detail, paying special attention to applications in near net shape manufacturing and digital microfabrication. Finally, outstanding questions are identified.