Analysis of a novel additively manufactured die reinforced by a shear-thickening fluid for vaporizing foil actuator forming

A new idea for forming geometrically intricate, low-production-volume parts, e.g., for patient-specific biomedical implants, without the time and cost of dedicated solid tooling used in conventional sheet metal forming is described. The forming is accomplished by the impulse process known as vaporizing foil actuator forming (VFAF). The novel die concept consists of a thin, additively-manufactured (AM) polymer shell, which gives the sheet its intended form, and a shear-thickening fluid (STF), which supports the AM-die during impulse forming. The advantage of the novel die concept lies in the use of a refillable, low-cost STF and an exchangeable, low-cost AM polymer shell, which offers greater flexibility, reduced lead time, and lower costs compared to conventional tools. The experiments are performed on 0.5 mm Titanium Grade 2 sheets, using Acrylonitrile Butadiene Styrene (ABS) plastic for the AM-die and a cornstarch-water mixture as the STF. The sheets are successfully formed into a truncated cone with a base diameter of 120 mm and a height of 20 mm, achieving nearly complete die-filling. For the first time, a working range depending on impulse pressure, STF viscosity (i.e., cornstarch concentration), and impact toughness of the AM-die for the used materials and geometries is found for VFAF. Furthermore, the forming result is independent of the STF height. The flexible liquid-solid tool is simulated in ABAQUS/Explicit, enabling a first predictive process design for impulse processes. The numerical results reveal that the STF contributes approximately 50% to the energy absorption after sheet impact.