Additive manufacturing (AM) is going through an exponential growth, due to its enormous potential for rapid manufacturing of complex shapes. One of the manufacturing methods is based on powder processing, but its major bottleneck is associated with powder spreading, as mechanical arching adversely affects both product quality and speed of production. Here we analyse transient jamming of gas-atomised metal powders during spreading. These particles are highly frictional, as they have asperities and multiple spheres and are prone to jamming in narrow gaps. Therefore their detailed characterisations of mechanical properties are critical to be able to reliably predict the jamming frequency as influenced by powder properties and process conditions. Special methods have been used to determine the physical and mechanical properties of gas-atomised stainless steel powders. These properties are then used in numerical simulations of powder spreading by the Discrete Element Method. Particle shape is reconstructed for the simulations as a function of particle size. The characteristic size D 90 by number (i.e. the particle size, based on the projected-area diameter, for which 90% of particles by number are smaller than this value) is used as the particle dimension accountable for jamming. Jamming is manifested by empty patches over the work surface. Its frequency and period have been characterised as a function of the spreader gap height, expressed as multiple of D 90 . The probability of formation of empty patches and their mean length, the latter indicating jamming duration, increase sharply with the decrease of the gap height. The collapse of the mechanical arches leads to particle bursts after the blade. The frequency of jamming for a given survival time decreases exponentially as the survival time increases.
Additive manufacturing (AM) has attracted increasing attention in a wide range of applications, due to its ability for rapid manufacturing of complex shapes directly from a Computer-Aided Design (3D CAD) output. One of the manufacturing methods is based on powder processing, where a thin bed is formed to which an energy beam is applied to sinter and melt the powder. A major bottleneck in this method is associated with powder spreading, as its dynamics is sensitive to powder properties, machine design and operation conditions, such as speed of spreading. The effects of gap height and blade spreading speed on the evolving shear band and mass flow rate through the gap have been simulated by Discrete Element Method, using the most realistic physical and mechanical properties of the particles. It is shown that the particle velocity in the powder heap in front of the blade could well be described by a universal curve given by the Gauss error function. The mass flow rate through the gap increases linearly with the gap height. There exist two flow regimes with the increase of the blade spreading speed. Initially, the mass flow rate has a linear dependence on the blade speed, but eventually approaches an asymptotic value, implying a limit beyond which the mass flow rate cannot be further increased. This has an important implication on the speed of spreading.
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