A more versatile delivery system for fused deposition has recently been developed. This system uses a very stiff, precise, and compact actuator to drive a small piston/cylinder extruder that has a heated nozzle. Because feed rods are used as the feed material, this newly developed delivery system does not have the materials limitations of conventional delivery systems.

This innovative technology is a mechanical assembly that can achieve high extrusion pressure that can be constructed in a compact enough form to retrofit existing fused deposition systems. The heart of this mechanical system is the combination of a hollow cylindrical servo motor and a ball screw, which are used to directly drive the piston of a piston extruder. The end of the screw is secured on a plate, which slides on four posts to provide counter-rotation. This plate also prevents any axial misalignment of the screw and houses the load cell. The four posts provide a frame that attaches to a top plate to support the motor and a bottom plate to support the cylinder of the piston extruder. These elements form a very stiff mechanical linkage with very low lag or backlash and produce very precise volumetric displacement of material.

The cylindrical pancake motors for this invention were designed to eliminate gear reductions and avoid backlash in direct- drive equipment. Because the stator has been moved to the outside of the rotor, these motors produce very high torque at extremely low and controlled angular velocities. The increased radius and mass of the rotor translate to very high torque and rotor inertia. Also, the cylindrical motor is hollow, which allows the ball nut to fit inside the motor. This makes the actuator assembly very compact.

Two configurations of the high-pressure deposition were fabricated. One configuration was designed to retrofit into a Statasys Fused Deposition Modeler (FDM). The second configuration was designed for an Advanced Ceramics Research, Inc., (ACR) in-house fused deposition system. In the FDM, the head is moved in the horizontal plane and material is deposited onto a base that is moved vertically. In the ACR in-house system, the head is mounted on a stationary bridge and material is deposited onto a base which is moved in the horizontal plane and vertically beneath the head. The ACR system has more piston displacement, but the basic design of both units is the same.

This innovative technology has been used to free-form a number of important functional materials, such as polyaryletherketone, polycarbonate, thermoplastic polyurethane, and polylactic acid/polyglycolic acid block copolymer. This delivery system has also been used to fabricate green bodies that were subsequently fired to high density, including alumina, yttria stabilized zirconia, and silicon nitride.

Testing of these materials showed that the mechanical properties of the materials systems developed with this new invention greatly surpassed those of other free-formed polymer materials.

A completed ACR in-house High-Pressure Fused-Deposition System is depicted in this photo.

This work was done by Peter Creegan, Robert Hoffman, and Gabriel Chambers of Advanced Ceramics Research, Inc., and Kevin Stuffle of Materials and Machines, Inc., for Marshall Space Flight Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

the Patent Counsel
Marshall Space Flight Center; (205) 544-0021.


Motion Control Tech Briefs Magazine

This article first appeared in the June, 1998 issue of Motion Control Tech Briefs Magazine.

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