Abstract
Material extrusion (ME) is one of the most widely used additive manufacturing technologies, which can directly produce parts with complex geometries. However, since the working environment is increasingly complex, the built parts inevitably have to be subjected to dynamic loads, and it is urgent to study their dynamic performances so as to determine their reliability. In addition, the layer-by-layer forming process makes the ME parts inferior to those fabricated by traditional methods in terms of mechanical properties. It is important to find an effective method to improve the parts’ dynamic characteristics so that the reliability can be enhanced. To achieve these goals, the method of ultrasonic-vibration aided machining (UVAM) was proposed to improve the dynamic characteristics of polylactic acid ME parts in this paper, and the corresponding theoretical and experimental study was performed. Ordinary ME equipment was modified to an ultrasonic-vibrating one, by which the samples processed with and without UVAM utilized were prepared. With the modal test system, the dynamic characteristics of the samples were determined. Taking into account the influence of the porosity defects and ultrasonic vibration, the ME sample’s dynamic model was then established based on the finite element method. Through the comparison between the predicted and measured results, the proposed model was validated, and it can accurately predict the ME plates’ dynamic characteristics no matter processed with or without UVAM utilized. The results also showed that UVAM could significantly improve the ME plate’s dynamic characteristics. With the increasing vibration amplitude or frequency, the samples’ natural frequency and damping ratio would be increased, and the vibration response would be decreased. Compared to the three waveforms of ultrasonic vibration (sinusoidal, square, and triangle), the sinusoidal one has the best improvement effect.
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