Direct Forming of 3-D Sandwich Parts by Fused Deposition Method Using Double Nozzle

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By applying a characteristic solidification sequence of melting and solidification in the Fused Spinning Deposition method and the difference in melting point of materials, direct forming of sandwich parts consisting of different metallic materials is expected to be available without bonding heat-treatment. In the present work, as an application of the FSD method, the conditions for direct forming of duplex tube castings consisting of inner and outer metallic materials were examined using a double nozzle type FSD apparatus. Al-4mass%Cu alloy and Cu-20mass%Sn alloy were used as outer and inner materials of duplex tube castings. After piling up the Al-Cu alloy melt to form the outer tube, the Cu-Sn alloy melt was deposited inside the Al-Cu alloy tube in contact with the side surface of the outer tube. Changing the time interval t between the start of deposition of outer and inner tubes, the microstructures on the vertical section were observed using OM, SEM and TEM. For smaller Δt, melting-down of the outer tube with low melting point occurred and, for greater Δt, insufficient interface bonding between the outer and inner tubes was observed. In the case of an adequate time interval, Δt=196s, complete interface bonding and duplex tube shaping were achieved, where two interfaces were observed on the outer and inner tube sides. The microstructures near the interfaces consisted of complex phases appeared in the Al-Cu-Sn ternary phase diagram. It was demonstrated from the results obtained that direct forming is possible by setting a suitable time interval between the start of deposition of outer and inner tubes without bonding heat-treatment by the FSD method using double nozzles.