Research On Ulreasonic Vibration Assisted Micro-embossing With PMMA

In recent years, with the development of micro-forming process of polymer more technologies have been investigated in this field. Ultrasonic-assisted hot embossing is a new micro fabrication process. Compared with traditional micro-forming technology, it has a lot of strength like high-efficiency, environmentally friendly, easily conducted, short producing period etc. Many experiments are conducted on this technology by researchers around the world. Lots of advantages as it has, this technology is still in a state of experiment. The theory of how ultrasonic affects the process of hot embossing, the law of ultrasonic parameters and embossing results are still not clear.In this paper, PMMA was used as experimental material, and discussed the response of thermo plasticity materials when the temperature is around mollification point. I chose Viscoelastic material model to define PMMA in finite element simulation. The viscoelastic constitutive equation of PMMA was obtained. The relaxation modulus was fitted with Prony series, and the coefficients of the Prony series polynomial were determined. ABAQUS finite element simulation models of different temperatures, duty cycles, and ultrasonic boundary conditions were established. The influence of ultrasonic boundary condition in the process of hot embossing at different temperatures was studied. The result shows that the filling rate increases when ultrasonic was applied, and the filling rate increased greatly when the temperature is under glass transformation point. The influence of ultrasonic amplitude has on filling rate during the embossing process at different temperatures and duty ratios was studied. The result indicated that the filling rate increased in advance and then decreased when the amplitude gradually increased. The simulation result also showed that the ultrasonic arouses stress waves in the material duri ng the process which enhances the mobility of PMMA and lead to a higher filling rate. But when the amplitude reached a certain value, the stress waves in the material caused great element distortion and the filling rate decreased along with the surface quality.After figuring out the theory of how ultrasonic affects the filling rate of hot embossing, ultrasonic-assisted micro-embossing system was built and a series of experiments was conducted, and the influence that ultrasonic amplitude, structure dimension, duty cycle have on the filling rate in the process was studied. The result shows that when the dimension is small hot embossing has a higher filling rate but when the dimension went bigger, the filling rate of ultrasonic-assisted embossing became higher. This technology also reduced residual stress of the product.