Metering and dispensing of powder; the quest for new solid freeforming techniques

The need to meter and dispense dry powders or mixtures of powders occurs in a wide range of processes and industries. These include the preparation of pharmaceutical products, the mixing of pigments for paints, inks and glazes, the incorporation of processing additives and pigments into polymer processing lines such as extrusion and in solid freeforming processes. This short review identifies the common features of powder handling in these widely different areas and seeks to distinguish and classify the various principles. Examples are given of designs that span a range of industries. This review is stimulated by current developments in the selective laser sintering of powder assemblies; a solid freeforming pathway for polymer, ceramic and metal prototyping and manufacturing. The goal is to find metering and dispensing systems that are effective in providing the spatial arrangement of composition. Dispensing methods that can produce patterns of different powders are sought. Selective laser sintering of powder assemblies can then be extended from a method of rendering shape to one in which both shape and composition are delivered directly into the external world from a computer file.