VCN AQUEOUS UNITS FOR POWDER REMOVAL FROM ADDITIVE MANUFACTURING PARTS
Surfactant solutions are perfect fluids for use in the VCN process. Vapor formation is instantaneous in surfactant solutions due to the low surface tension. The instantaneous explosion of vapor on a part’s internal surfaces forces liquid rapidly from the part carrying residual powder out to the bulk fluid. The rapid formation is intense, however the vapor bubbles formed are gentle on the internal surfaces preventing damage even to the most delicate part. Air is used to collapse the vapor and force fluid into the part for the next cycle. Repeating the cycles every few seconds results in a fast removal of powder from the part.
Surfactants can also assist with the removal of the powder from a surface. The polar nature of surfactants can neutralize surface charges that can resist the removal of small powder particles. Mild acid solutions can slightly etch surfaces to break solid bonds at the surface. Particles act as nucleation sites and as the solution evaporates near a particle, acid concentration can increase to be more effective.
Particles in aqueous systems are periodically removed and filtered to maintain a fresh solution. Repeating washes with particle free solutions or rinses removes residual particles. The process is fast so that many washes or rinses can be repeated without extending the total removal time significantly. Generally, a one- or two-minute VCN time removes most of the powder. The surfactant concentration does not need to be high so that operating costs and waste disposal volumes are low.
The above video shows an aqueous unit removing powder from a basket of small printed parts. The fluid level can be preset on a PLC to levels up to 2 feet. A typical VCN cycle is 1 minute, and the chamber can be drained to remove and filter the powder. The wash cycle can be repeated with clean heated solution as many times as required. Multiple VCN rinses can be run to remove residual powder and surfactant. The parts are then dried with heated air under vacuum.