been t being Research DARPA tive making The the Gamer7l], process plications. quality suitable way tooling days, rected For [Prinz88, number method. is Abs are shell A demonstration an that cussed nent for 1 This Rapid quickly new aluminum pattern the adequate several can method work contract world define molds material, extant and in application commercially and Center, to Tooling by the manufacture toward for of be has made this Weiss9O]. the We yet pours, spraying has lifetime limited patterns quickly have for years, for the where been of F. and paper. point to permanent believe the Shaping for shows by prevented aluminum B. structure, making tooling quickly withstand, supported by time the spraying adequate of Prinz, production, our for years of the made, Tooling time quickly; The metal steel of by we the demands also exciting. many Edison and work Permanent Deposition, prototype shell zinc prototype by will L. the mold. The manufacturing promise is on sprayed making [MOGUL63, casting onto cost and onto the Schultz, made for prototype in Materials has dimensional Alcoa process improve the paramount, Aluminum tooling Engineering as Pittsburgh, shape. Aluminum a of Carnegie An substrates P. placed a geometry patterns We well. by been competi order A The making limited perma S. in tooling Center, tooling tooling is of initial the Mold Alcoa Sprayed D. Technology Fussell, from this Robotics dis has this The are ap the Engineering di on G. Company of Company Mellon Pennsylvania Design Laboratories Thuel, Pennsylvania Casting and for E. Steel Institute Center. between by of spray materials. permit Metal three We was manufacture directly goal first geometry variety The and [SchooplO]. carded. [Gursoz90], example, The with spraying pattern, and creased quickly of University P. Research Stereolithography L. Design of America, wires 3D Patrick Tool model of devised patterns build E. America tool attempted was backing. the days. Systems, device, spraying 15213 of Alijminumt Weiss, mechanical of 15069 the Research made from two of and addition operation. stereo1ithography face in solid to by Center up the We the attractiveness at and Using Carnegie a build is are consumable is where solid H. solid geometry part Inc., the these The free typically are patterns Center, in metal for formed manufacture manufactured 0. has beginning of 1924 up bodies of the form testing the geometry spraying modeling pattern Kirchner Mellon The an appropriate geometries; Valencia, been an enough being process purpose arc [Turner24] a (5FF) during NSF is tool has electrodes of University matter was commercialized of defined (SLA). Engineering is the of sprayed. is is environment with and the the systems, material California. greatly established the apparently by to then completed the approach. of of supports the one sprayed pattern pattern century deposit under coating an by — one metal made dis The tool of the arc the for in to to a a Page P. mold lease surface Conventional with coated the to The or materials 2 a With the aluminum. a ture perature exclusively shells, composite eas in commercial The rial steel. strated shell spray melting using from Our ing sure K) nation low zinc tice The moving carried metal material Fussell, Tooling form Casting permanent refractory the and 2 application of surfaces permanent melting in application onto for most process; alloys. graphite; metals agent applications. casting higher from our steel [Fussell9O]. low with we makes is the the life. are injection prototype making et gas. to point and include melted, recent patterns, layup for at, became pressure with cavity initial been process and also the the These (Tm work The a points sprayed metal Permanent temperature we is low wisdom Permanent of them refractory mold alloys, this area a area mold substrate pattern, relatively a tools not dies; coating —1800 efforts in chose the of has thermal molding pressure cast materials measure and interested tools Using success (pure of the alloys. suitable the promotes injection but economical for to suitable mold casting these in been are suggests making as Mold iron, the then K), relatively are mold. a our made also slurry commercial also we zinc a Mold the higher zinc soft. barrier. by or During manufacture domains. domain. and done directed transfer of processes are steel, for making have work atomized have acts in process Typical higher molding material a melts limits permanence a the for and of This Aluminum permanent or easy other long extending generally column for in tempera relatively low stainless has graphite as sprayed casting, sprayed casting demon various the toward combi at mate small Other spray a pres them prac mold steel tool- uses have high tem been and re and 693 ar we of of mold The make prototyping metallurgy from rectly than permanent The metal tooling priate sign proach the If as The utility internal curred manufacture duction manufactured pleted chining, industrial the ing create making six production tooling well mold heat withstand adequate and IC; pressure transient the low a months cost the demands mold high mold prototype is a include: prototype the cools properly for ability both of the the pressure sand meets as mold for tested from mold tools. the and of as surfaces, quality cost limited sprayed make preheat drawings actual experience mold making mold mold manufacturing runs; process might of for the elapse heat temperatures and mold. cast mold the the is to placed handling. two is of about to Our prototype parts. flows by mold withstand the part; — must delivered. too tooling molten needs part is EDM transfer part; production determine process surface the useful to, be cooling metal time The a from electro-discharge tools more goal generally prototype 5 great. to on maximum perhaps, and the in be kPa is and suggests cost electrodes. can sand the machining is this manufacture metal typically robust was needs: the permanent should tooling tools generally case rate systems; if to (0.7 also mold prototype are condition prototype be of The If time permanent the casting roughly runs if completion tools to manufactur met, long; into to the 670 psi) and for made. the required that enough cost a surface static be mold prove remove to the different mold as complex K; mold the this quickly. for time used molten typical reduce appro two is comes well. 1300 parts tools, is mold com of pro cor The ma the the to ap de in to to to to is of a Tools made of sprayed steel are able to meet these demands, at least for a limited num ber of cycles of the tool.
3 Manufacture of Permanent Mold Tool The geometry of this tool was designed from the geometry of a simple connecting rod. The connecting rod was modeled in NOODLES, a non-manifold geometric modeller being programmed at Carnegie Mellon University. This geometry is shown in Figure 1. We elected to manufacture, for this exper iment, only one of the two mold halves. We simulated the second half with a 3 cm (1.2 inch) steel plate.
Working from the connecting rod geome Figure 2. Solid Model Representation of the try, the part which would form the mold Connecting Rod Pattern cavity was also modeled in NOODLES. Casting process expertise was used here to The connecting rod mold pattern was then add appropriate casting features (sprue, made in a stereolithography apparatus. runner, gates, well, vent, and overflow), Figure 3 shows a plastic pattern from that and also to modify the original geometry to process. make it manufacturable; draft was added, and some holes were removed from the connecting rod to permit a proper flow of metal and subsequent solidification in the mold cavity. The modified geometry is shown in Figure 2.
Figure 3. Stereolithography Made Connecting Rod Pattern Figure 4 schematically shows the devel opment of a sprayed tool. The starting point Figure 1. Solid Model Representation of a is the stereolithography made pattern with Connecting Rod the same face geometry as the desired tool face geometry. The sequence then follows this scheme:
P. Fussell, et at, Permanent Mold Page 3 Fusible Pattern Remove Shell
Sprayed Back form Spray Pattern Alloy Face Make
Desired
Page P. up
Transfer Tool Fusible Steel
Alloy Fussell, the Tool the
Steel
backing
heat material
the The
application,
to
the
0.75 less
tool.
transfer
tool
the The
4 pattern,
steel a creating
some The
contain A
to
Figure
transfer
the
frame
Manufacture
temperatures
Manufadured
as-sprayed
fusible
steel
steel
frame
fusible
This
SLA
from
et
mm
sprayed
mass
fusible
at,
the
4.
material
that
and
is
pattern.
sprayed
a
(0.03
Permanent
sprayed
tool
pattern
the
step
Schematic
is
placed
alloy
ahoy
negative
castable
fusible
it
the
alloy.
placed
supports
tool. was
Tool
is
mold
surface
inches).
from
of
is
form to
LI
to
important
Steel
of
on
that
shell made
is
Sprayed
added
ahoy.
Mold
form
______
a on
‘Spraycd
epoxy.
the
SLA
face,
the
removed, impression
Sequence
thickness
is
the
as
the
is
Figure
will
is
backed
with
process,
the
SLA
it to
pattern
sprayed
shell.
and
backed
fusible
Tool
was
This
the
to
withstand
face
410 pattern
Steel
reason
5
for
and
of
have
pattern,
up
applied
In
step
shows
of
carry
of to
stain
about
with
alloy
onto
with
this
the
the
the the
a
to
is
400
about
the
The
inches);
shell process. intended
ually
A
ceptably
In
Figure
portion
this
mold.
mold’s
tern Finally,
perature mold
mold
will Alternatively,
compression
match
efficient
expansion
ably
clamping
iñnch).
surface
was
left
3
5.
to experiment,
support
this
is
This
matched
match
fiat
face
face,
Figure
Connecting
of
Back
in
working
10
removed,
uniform,
the
the
is
the
was
excursions.
surface
microns forces
the
curvature
appearance
during
of
acceptable
but
mold
of
the
fusible
and
the
tool
the
6
shell
the
Sprayed the
a
face
is
which
not
material
co-efficient
clamping
leaving
weak
the
with
about
face
result
Rod
face’s
intended
RMS
a
mold
the
from
alloy
before
was
photograph
add
sprayed
warped
Casting
if
Shell
closed in
a
of
processes’
average
+0.6
of
expansion
it face
the
eliminated
roughness
shear;
stress
that
the
transfer
the
loads
stress
casting.
is
dimensions.
of
mm
completed
the
strong
material.
spraying
shell
from
Tool
does
sprayed
thermal
(120
thus
on
(0.025 to
of
resid
mold.
tem pat
—
the
the
the
not
ac
the
co
by
to
of
in it surface. The more spherical droplets arrived at the substrate rel atively solid, and did not flatten. Regions of oxide; these are slightly darker regions in figure7. The ox ides are formed at the arc and in transit from the arc to the substrate. They appear both as lines between the lamella and as larger, mis- formed, oxide droplets themselves. Systems sprayed using air typically range from 30% to 50% volume ox ide. The sample shown in figure 7 was sprayed using Argon as an at omizing gas; this typically reduces the oxide levels to 10% to 15% vol ume. The casting tool shell was sprayed using inert gas to reduce oxide levels.
Figure 6. Connecting Rod Casting Tool — Face of Sprayed Shell The mold’s sprayed surface was not ro bust; a thickness of only 0.75 mm was not adequate for the mechanical handling we gave it. During final processing, a small portion of the shell was chipped. This par ticular failure would be unexpected in a mold made of wrought material; a similar load would have only scratched the wrought tool’s surface. 4 Microstructure of the SprayedMetal Shefi
Shells which have been built up from sprayed materials do not have the mi crostructure of shells made from wrought Figure 7. SEM Photomicrograph of Typical materials [Fussell9l]. Figure 7 shows a Sprayed Shell typical scanning electron microscope pho tomicrograph of sprayed material. There Voids; these are structural holes in are three types of regions in the photo the sprayed material. They appear graph: singly and also grouped together; the voids are artifacts of the rapidly Solidified droplets of metal; these solidified spray process where the are structurally either formed into droplets periodically arrive. Some of flattened lamella, or retain some the dark lines between metal spherical quality. The lamella ar lamella may also be micro-voids, rived at the substrate in either very small in scale compared to the molten or mushy condition, and resolution of this SEM. The shells flattened upon splatting onto the sprayed with this style of arc-spray P. Fussell, et at, Permanent Mold Page 5 I •
apparatus generally show a volume void content from 3% to 8%. Permanent molds are typically cycled sev eral times (1.e., several parts are made) be The surface in figure 7 is an as-sprayed fore the mold produces good parts. The surface, showing a typical surface mor first part made in this tool showed phology and surface roughness. promise; it was better than that typically made by a first cycle mold. The tool failed to The quality of the shell, and particularly an extent after this first part and we the void fraction of the material, is heavily elected to not continue using the tool. Yet influenced by the spraying parameters. even one part showed that the basic pattern For this shell, the single most important was adequately designed to make parts; variable is the angle of incidence of the one purpose of the experimental prototype particles as they arrive on the substrate; mold was met. arriving perpendicular to the surface is best, with even angles from 10 to 25 degrees away from perpendicular greatly degrad ing the material quality. Under these con ditions, void content increases, and the void morphology is altered: the voids tend to appear in clusters. This factor plays a strong role in sprayed tool manufacture. The vertical walls of the connecting rod mold (e. g., at the base of the connecting rod in figure 5) were difficult to spray; the sprayed material was not optimally de posited. The failure in the tool during preparation and the during the tool’s use occurred in these regions.
A gross structure composed of metal lamella which are generally separated by thin layers of oxide and shot through with voids can not be as strong or as robust as structures made from wrought materials. Figure 8. First Aluminum Part from the None-the-less, the sprayed structure is ad Sprayed Steel Permanent Mold equate for the needs of a prototype tool, and the sprayed system can be formed quickly. The part showed reasonable, but not excel In fact, the forming time is independent, lent, surface quality and dimensional within limits, of the complexity of the sub quality. The cooling of the connecting rod, strate pattern; this is not true for conven in this first pour, was not optimal for pro tionally manufactured tools. ducing the best part. This is due to both the mold’s internal design, and our lack of use Alternative spraying processes can pro of the tool. duce materials that are competitive with wrought materials [Lavemia88, Mathur89, We elected to not pour a second part in the Safai8l], at the loss of rapidly making the tool. The tool failed when a —4mm2 portion final tool shape. of the tool surface flaked away in the region of the connecting rod base. The failure was 5 Aluminum Casting using the Tool on a near vertical wall and would have acted as a locking catch between part and The tool was tested by casting an alu tool, so the part would have been difficult to minum part at Alcoa Laboratories. This remove. tool was pre-heated to about 700 K and poured with an aluminum alloy. The part The shell also cracked; the crack in lightly from the first pour is shown in figure 8. be seen in figure 9 in the sprue. This is al P. Fussell, et at, Permanent Mold Page 6 most certainly from the thinness of the The dimensional quality of a tool is also of shell combined with the temperature cy concern, even in prototype tooling. The cling of the tool. The crack failure would prototype process in permanent mold tool not have prevented us from making more ing yields two valuable results: a tool de prototype parts. sign where molten metal properly flows, and prototype parts that come from the casting process. Dimensions are of partic ular concern for the latter result. The tol erance buildup starts with SFF technolo gies; the spray process replicates the sur face finish with high fidelity, yet the sprayed shell dimensions vary about ± 0.25 mm (± 0.010 inch) from the pattern di mensions. This tolerance buildup is a sub ject of keen attention. Our next step is the creation of a mold that meets both goals of a prototype tool. Our hope is to manufacture as many 10 to 20 parts from a prototype mold, excluding the parts used to pre-heat and understand the tool. In parallel with improving aluminum casting tooling, we also intend to extend the idea of sprayed metal tooling to other domains. One domain of interest is an am bient temperature, higher load application, such as a stamping die tool. Figure 9. Sprayed Steel Permanent Mold Acknowledgment after Pouring This work has been supported by the 6 Continuing Work Aluminum Company of America, by Carnegie Mellon University We are pleased under a that this initial experiment DARPAcontract for Shaping by Deposition, has shown limited success. The survival of by the Engineering Design Research the tool and the quality of the part both Center, an NSF Engineering Research show enough promise to continue with this Center, and by the Edison Materials effort. Technology Center. The principal continuing work must con We particularly thank Mr. Charles West centrate on making a better tool, i. e., the and his staff at Alcoa Laboratories, Molten internal structure of the tool must be Metal Processing stronger Division, for their assis and more robust to withstand both tance in specifying the modifications to the the preparation work, the thermal cycling mold pattern, and for pouring the mold. the mold experiences, and the mechanical handling of removing the cast part. This Refernc aim can probably best be achieved by more carefully spraying the steel shell to prevent [Fussell9O] P. S. Fussell, L. E. Weiss, “Steel-Based regions of poor quality shell, and also by Sprayed Metal Tooling,” Solid Freeform Fabrication making the shell thicker and thus more Symposium Proceedings, J. Beaman, H. Marcus, D. robust. The latter approach must be bal Bourell, J. Barlow, Editors, Center for Materials anced with a need to avoid warpage of the Science, University of Texas at Austin, 1990. mold face during and after spraying.
P. Fussell, et at, Permanent Mold Page 7 PageS P. Manufacturing Rapid S. pg. [Weiss90] Stereolithography Spraying,” pg. [Turner24] Metallzerstauber,” [Schoopl0l Materials,” 214. Technotog), [Safai8l] Technologies DARPA, [Prinz88J Metalliting [MOGUL63J metaltugic), and “Analysis [Mathur89J Engineering, (North-Holland), Deposition Boundaries,” “Vertex-based Preiss, [Lavemia88] [Gursoz90] Technique,” [Garner7lJ Engineering of Prinz, [Fussell9lJ Carnegie Fussell, Fussell, Arc 291-312 1391. Engineering, Tool 15 Sprayed L. Editors, March S. F. E. L. Mellon of et Journal M. S. Manufacturing T. of E. Vol. Paul Treatise P. P. Company Vol. Safai, SPE B. the E. at, Weiss, Metattizing Design for E. in Mahalingham, Metals: U. Levent H. M.J. Mathur, S. Representation Prinz, Review, Metal Weiss, 20, Permanent 1988 Elsevier J. Spray Geometric 37, Schoop, a J. Journat Fussell, Turner, University, 1990. Vol. and Chemical H. Teaching Laverma of Academic Wozny, Garner, No. on Research Controlling the Gursoz, Shells”, A Herman, “Shaping of 98, I. Thermal Deposition D. March, Materials 2, Review,” America “Dusen Institute Manual: Science Vol. L. H. W. 1988. Apelian, 1989. System Modeling J.U. Mold “New Gursoz, & Zeitung, Factory,” 0. and E. Press, 1991. in Y. 27, Center N. of “Plasma by 1990. Kirchner, Spraying,” Für preparation, Ballard, Choi, Turner the Publishers, Materials E. No. (MoGUL), Non-manifold of J. Process.” Mold Flame Science Deposition, Based & Metals, 1981, P. Grant, F. Microstructure for 1910, 5, A. Report Proposal & Patrick, B. May Making Sprayed and Lawley, Product F. “Metal Spraying, On F. pp. Prinz, and Vol. ASME’s 1963 B. Acts “Spray No. Science B. 1971. B. K Series, 183- Prinz, Vital 34, to 2, V. “A P.