Understanding of plasticity size-effect governed mechanical response and incomplete die filling in a microscale double-punch molding configuration

Direct replication of microscale patterns onto metal surfaces by compression molding with patterned dies is used to fabricate metal-based structures for microsystem applications. Micron scale plasticity governs both the mechanical molding response and the geometric fidelity of replicated patterns. Microscale molding replication offers a technologically relevant example in which various plasticity size effects manifest themselves and control the effectiveness of the fabrication process. Microscale compression molding of a single-crystal Al specimen was studied by combining experimentation with conventional and strain gradient plasticity finite element simulations. In the single-punch molding configuration, single rectangular punches with different widths and lengths were used. In the double-punch configuration, two identically-dimensioned rectangular punches with a spacing in between were used. Under single-punch molding at the micron scale, both the absolute punch width as well as the length-to-width ratio affected the characteristic molding pressure. Under double-punch molding, both the measured characteristic molding pressure and the material flow to fill the gap between the two rectangular punches exhibited a significant dependence on the spacing to punch-width ratio and-when this ratio was fixed-on the absolute spacing between punches. The present study elucidates the impact of plasticity size effects on the efficacy of pattern replication by molding at the micron scale.