Fabrication of three-dimensional functionally graded materials using controlled polycaprolactone powder characteristics and laser material processing

Abstract

The functionally graded material is characterized by its gradual change in material compositions and properties over the volume of a component to optimize its functional value. To fabricate functionally graded material parts by additive laser material processing, appropriate powders are critical in term of their size, shape, and mechanical properties. This paper presents new methods to mass produce polycaprolactone powders, a type of biodegradable polymer, with deliberately modified properties as well as to fabricate functionally graded material parts using the modified powders by laser material processing. To modify the properties of the biodegradable polymer powder, this research used two different approaches: recrystallization and spraying. The two different modification methods enabled the significant change of the polycaprolactone powders' molecular weight that strongly affects mechanical properties. This controlled molecular weight change enabled the gradual variation of the mechanical properties in functionally graded material. By the two different modification methods, the raw materials with irregular shape and size were changed into powders with a round shape and similar sizes, so that they became more suitable for the laser material processing. We verified the modified powder properties such as the size distribution, shape, crystallinity degree, thermophysical properties, and molecular weight by using a variety of methods. The modified polycaprolactone powders with varying mixture ratios were sintered by Nd:YLF laser irradiation with 349-nm wavelength, and the different mechanical properties were verified by micro-tensile tests. As an application of functionally graded material, a biomedical trigger capsule was fabricated and its performance evaluation demonstrated the desired results according to three-dimensional functionally graded material design.