Additive Manufacturing

Additive Manufacturing (AM) creates three-dimensional (3D) objects by stepwise layer-by-layer building approaches which are controlled by a digital model. As a novel production technology for the design and manufacturing of high-performance components, the use of AM is increasing at a fast rate in wide ranging industries, such aerospace, medical technology and energy. Amongst several manufacturing methods, the use of powders is very attractive in AM, as it provides flexibility for a wide range of materials to be used.  Fine dry powder in the micrometre size range is spread thinly by a blade or roller.  The spread layer is locally heated by a radiative energy beam to melt or sinter the layer or bound otherwise.  For this purpose, the spread layer should be very thin, therefore requiring a narrow gap between the spreader and layering base, typically a few multiple of particle diameter.  This could cause non-uniformity in the spread layer, making flaws and defects in the structure.  Lack of sufficient understanding of this kind of near-boundary flow, such as the shear band within the heap and the transient jamming events occurring in the gap, hinders further advancement of this technology and introduction of new materials for high quality structures.  Hence, in Ghadiri Research Group, our focus is on understanding the flow of powders passing through narrow gaps and analysing the behaviour of micrometre sized particles during AM spreading process.

Cold Spraying is a solid-state coating technique during which powder particles are accelerated to high velocities by a supersonic gas jet in order to impact them onto a substrate to build up a thin functional wafer.  The impact velocity exceeds a material and process dependent critical velocity so that the particles plastically deform and adhere to the substrate.  The technique can be used to deposit different materials such as metals, ceramics, polymers and composites. Since cold spraying is a solid-state process, it offers unique advantages over traditional thermal spray techniques, e.g. stability for the deposition of oxygen/temperature-sensitive materials.  However, the efficiency of impingement is low and the conditions for attaining desirable wafer properties are not well-understood.  In this project a combined modelling and experimental work on the impact dynamics of micrometre-size particles is planned to enable a sensitivity analysis to be carried out on the influence of process condition and material properties on the wafer formation.

• Impact Deposition of Particles for The Manufacture of Electroceramics

• Ahmed, M., Pasha, M., Nan, W. and Ghadiri, M., 2020. A simple method for assessing powder spreadability for additive manufacturing. Powder Technology.
• Nan, W., Pasha, M. and Ghadiri, M., 2020. Numerical simulation of particle flow and segregation during roller spreading process in additive manufacturing. Powder Technology, 364, pp.811-821.
• Ghadiri, M., Pasha, M., Nan, W., Hare, C., Vivacqua, V., Zafar, U., Nezamabadi, S., Lopez, A., Pasha, M. and Nadimi, S., 2020. Cohesive powder flow: Trends and challenges in characterisation and analysis. KONA Powder and Particle Journal, p.2020018.
• Ghadiri, M., Matsusaka, S., Pasha, M., Nan, W., Hare, C., Vivacqua, V., Zafar, U., Nezamabadi, S., Lopez, A. and Nadimi, S., 2020. Rheometry of Cohesive Powder Flow. The Micromeritics.
• Nan, W., Pasha, M., Bonakdar, T., Lopez, A., Zafar, U., Nadimi, S. and Ghadiri, M., 2018. Jamming during particle spreading in additive manufacturing. Powder Technology, 338, pp.253-262.