Banh, L., Nguyen, P., Ngo, C. and Nguyen, T. 2016. Optimal surface roughness of die steels in powder mixed electrical discharge machining using titan powder. Science and Technology Development Journal. 19, 1 (Mar. 2016), 114-120. DOI:https://doi.org/https://doi.org/10.32508/stdj.v19i1.616.