NASA Tech Briefs, February 2005 27

An automated system of manufactur-ing equipment produces three-dimen-sional (3D) ceramic parts specified bycomputational models of the parts. Thesystem implements an advanced, auto-mated version of a generic rapid-proto-typing process in which the fabricationof an object having a possibly complex3D shape includes stacking of thinsheets, the outlines of which closely ap-proximate the horizontal cross sectionsof the object at their respective heights.In this process, the thin sheets are madeof a ceramic precursor material, and thestack is subsequently heated to trans-form it into a unitary ceramic object.

In addition to the computer used togenerate the computational model of

the part to be fabricated, the equip-ment used in this process includes:• A commercially available laminated-ob-

ject-manufacturing machine that wasoriginally designed for building woodlike3D objects from paper and was modifiedto accept sheets of ceramic precursor ma-terial, and

• A machine designed specifically to feedsingle sheets of ceramic precursor ma-terial to the laminated-object-manufac-turing machine.Like other rapid-prototyping

processes that utilize stacking of thinsheets, this process begins with genera-tion of the computational model of thepart to be fabricated, followed by com-putational sectioning of the part into lay-

ers of predetermined thickness that col-lectively define the shape of the part. In-formation about each layer is transmit-ted to rapid-prototyping equipment,where the part is built layer by layer.

What distinguishes this process fromother rapid-prototyping processes thatutilize stacking of thin sheets are the de-tails of the machines and the actions thatthey perform. In this process, flexiblesheets of ceramic precursor material(called “green” ceramic sheets) suitablefor lamination are produced by tape cast-ing. The binder used in the tape castingis specially formulated to enable lamina-tion of layers with little or no appliedheat or pressure. The tape is cut into in-dividual sheets, which are stacked in the

Manufacturing

Automated Rapid Prototyping of 3D Ceramic PartsUnlike in prior rapid-prototyping processes, there is no manual stacking of sheets.Marshall Space Flight Center, Alabama

Fabrication of Spherical Reflectors in Outer SpaceProcess takes advantage of vacuum.NASA’s Jet Propulsion Laboratory, Pasadena, California

A process is proposed for fabrication oflightweight spherical reflectors in outerspace for telescopes, radio antennas, andlight collectors that would be operatedthere. The process would obviate the rel-atively massive substrates and frames

needed to support such reflectors in nor-mal Earth gravitation. According to theproposal, fabrication of a reflector wouldbegin with blowing of a bubble to thespecified reflector radius. Taking advan-tage of the outer-space vacuum as a suit-

able environment for evaporative deposi-tion of metal, a metal-evaporation sourcewould be turned on and moved aroundthe bubble to deposit a reflective metalfilm over the specified reflector area to athickness of several microns. Then thesource would be moved and aimed to de-posit more metal around the edge of thereflector area, increasing the thicknessthere to ≈100 µm to form a frame. Thenthe bubble would be deflated and peeledoff the metal, leaving a thin-film sphericalmirror having an integral frame. The mir-ror would then be mounted for use.

The feasibility of this technology hasbeen proved by fabricating a prototypeat JPL. As shown in the figure, a 2-in.(≈5-cm) diameter hemispherical proto-type reflector was made from a polymerbubble coated with silver, forming a verysmooth surface.

This work was done by Yu Wang, JenniferDooley, and Mark Dragovan of Caltech andWally Serivens of the University of South Car-olina for NASA’s Jet Propulsion Labora-tory. Further information is contained in aTSP (see page 1). NPO-30649A Prototype Reflector was successfully produced, showing that the proposed fabrication is practicable.

https://ntrs.nasa.gov/search.jsp?R=20110014732 2020-07-31T00:57:45+00:00Z

28 NASA Tech Briefs, February 2005

sheet-feeding machine until used. Thesheet-feeding machine can hold enoughsheets for about 8 hours of continuousoperation.

A vacuum chuck in the sheet-feedingmachine picks up a single green ceramicsheet. The sheet is then coated with alamination-aiding material. The coatedsheet is wrapped around a roller, onwhich it is transported into the lami-nated-object-manufacturing machine.There, the roller is actuated in such amanner as to laminate the coated sheetonto the stack of previously laminatedand cut sheets.

Once the sheet has been thus incor-porated as the top layer of the stack, con-trol of the operation is passed back tothe laminated-object-manufacturing ma-chine. A carbon dioxide laser that is partof the laminated-object-manufacturingmachine cuts the desired cross-sectionaloutline out of the top layer. (To makethis possible, the laser operating para-meters are adjusted, in accordance with

the composition and thickness of the lay-ers, so that only the top layer is cut.) Themotion of the laser and thus the cuttingpath are determined by the computa-tional specification of the cross-sectionrepresented by the just-added top layer.

The excess layer material lying outsidethe cross section is temporarily left inplace to provide support as the 3D objectis built. In addition to cutting the outlineof the cross section, the laser cuts the ex-cess layer material into tiles to facilitateremoval of supporting material fromaround the 3D object after completion ofthe stack. After the cutting is finished,control is passed back to the sheet-feed-ing machine, which then laminates thenext sheet onto the stack. The laminatingand cutting steps are repeated until thestack is complete. The supporting mater-ial is then removed. Finally, the green ce-ramic stack is heat-treated in a furnace toremove the binder and sinter the ceramicto high density. This process has beenused to make objects from diverse engi-

neered ceramics, including alumina, zir-conia, silicon carbide, aluminum nitride,silicon nitride, aluminum silicates, hy-droxyapatite, and various titanates.

This work was done by Scott G. McMillin,Eugene A. Griffin, and Curtis W. Griffin ofLone Peak Engineering, Inc.; and Peter W.H. Coles and James D. Engle, Jr., of Automa-tion Engineering, LLC for Marshall SpaceFlight Center. For further information, con-tact the company at www.javelin3d.com.

In accordance with Public Law 96-517,the contractor has elected to retain title to thisinvention. Inquiries concerning rights for itscommercial use should be addressed to:

Curtis GriffinLone Peak Engineering, Inc.470 W Lawndale Dr., Suite GSalt Lake City, UT 84115Telephone No.: (801) 466-5518; Fax No.: (801) 466-5817Refer to MFS-31306, volume and number

of this NASA Tech Briefs issue, and thepage number.