A faster, simpler, and less-costly method
to produce complex ceramic molds for
casting metal parts has been developed. It
can help foundries to deliver a first article
within days of receiving a purchase order.
YEHORAM UZIEL
Chief Executive Officer
Soligen, Inc.
Successfully launching a new product into today's competitive market depends
on fast, efficient product development, coupled with quick and flexible
manufacturing processes. Timing is essential--a delay of a few months can
result in lost market share and may cause a potentially successful product
to fail. Companies introducing new products must achieve a combination of
efficient design, concurrent engineering, and just-in-time (JIT) production.
Once a prototype of a new product has been market tested, the race is on to
deliver it to the market before the competition shows up.
Computers have played a major role in expediting time-to-market for new
products. Today's designers use sophisticated computer aided design (CAD)
software to create designs on-screen, updating them easily when changes are
required. Meanwhile, assembly has become increasingly automated through
the use of computerized inventory control systems and assembly robots that
can work around the clock and without human error.
The first step--design--and the last step--assembly--have been largely
automated. The fabrication of parts remains the bottleneck in getting
products to market quickly.
Casting is the most effective method for producing metal parts, in
terms of both material use and labor cost. In comparison to other fabrication
methods, casting allows fewer geometrical constraints, a wider variety of
alloys, thin walls, and more. However, these advantages can be offset by
the long lead time between purchasing and acceptance, which is a result of
the need for a pattern to create the mold. The pattern design process often
requires iterative trial and error prototyping since gating design, usually
described as an art, is often based on empirical, mostly undocumented,
experience.
The role of computers in foundries.
Computers could assist the foundryman in both designing gating and analyzing
a design by simulating solidification. In some foundries, the pattern design
is made on CAD and then converted to a drawing, which instructs the pattern
or die maker. In these foundries, the same CAD data created to describe the
pattern or mold can be used for simulating the solidification of the molten
metal in the ceramic mold. However, the analysis can be costly in time and
money. Except for extremely intricate parts--which require sophisticated gating
design--such analysis may not justify the effort involved.
Functional prototyping
Competitive pressure induced by alternative fabrication methods attracted
the foundry community to a newly-developed technology--rapid prototyping.
In rapid prototyping, pioneered by 3D Systems, Inc. of Valencia, CA, a
physical object is created directly from a CAD file. The actual process,
called stereolithography, involves a laser solidifying liquid resin into
solid plastic and forming, in successive layers, a three dimensional "print"
of the part. Pattern makers view this technique as a method to create
patterns, or sections of patterns, directly from a CAD file. If draft angles
and parting lines are included in the pattern's CAD, plastic sections can be
made and then incorporated into a pattern. Rapid prototyping can make either
wax or plastic patterns that can be treated as a wax pattern substitute
and then destroyed or melted out for each build.
The main roadblock in foundries for using rapid prototyping more extensively
is the incompatibility of rapid prototyping to casting technology. Plastic
patterns are not durable enough and have long-term dimensional instability
(they may warp or distort as time goes by and internal stresses are
relieved). For investment casting, plastic patterns do not dissolve easily
and may crack the shells, and wax patterns made by laser sintering--which
involves joining wax powder particles into a wax object using a laser
beam--do not have the required accuracy and surface finish.
Direct Shell Production Casting
Direct shell production casting (DSPC) is a metalcasting process in which
the ceramic shell--complete with integral cores--is manufactured automatically and directly from the designer's CAD file, and without
tooling or patterns of any kind. It is a turn-key process that allows parts
designed on a computer screen to be fabricated by simply pouring molten
metal. It provides a complete solution, from customer's design data
acceptance, through mold design and production.
DSPC creates the equivalent of ceramic shells made for investment casting
by dipping a wax assembly into a ceramic slurry. Because DSPC eliminates
the need for a wax pattern, and since there is no need for tooling or setup
for creating the ceramic molds, DSPC truly combines the advantages of
casting and computerized numerical control (CNC) machining in a unique
process for fabricating metal parts.
The DSPC machine
The DSPC system consists of two pieces of equipment: a shell design unit
(SDU) and a shell production unit (SPU). The SDU is a graphics workstation
running specialized software that allows the geometry of a casting shell
to be generated from a CAD file. The SPU then automatically fabricates the
shell from raw materials.
Each turnkey DSPC machine, Expected to sell in the U.S. for about $300,000,
will feature a 16 x 16 x 16 in. workspace volume, layers of 0.002 in. thick
and 0.002 in. resolution. The DSPC molding shells can include several
cavities, allowing more than one copy of a pan to be made at a time. The
shells may also contain integral ceramic cores, allowing hollow parts to be
made. The projected build rate will be 350 in3/hr, and the total build time
for the entire workspace volume will vary from 9 to 20 hr, depending on the
geometry of the shell design. The cost per molding shell is estimated to be
between $250 and $2,500.
Internal mold surface finish is still a concern for developers. As the DSPC
machine's resolution improves, the final part finish will improve. Methods by
which the inside mold surfaces may be smoothed or coated to achieve improved
part surface quality are currently being tested.
DSPC technology has the potential to create a structural change in the
foundry industry, and conceivably to consolidate the sand, investment, and
diecasting industries into one. Moreover, DSPC presents a breakthrough in
the way that metal parts are designed and manufactured. In the near future,
designs which have no geometrical constraints and do not require expensive
tooling will be feasible. In addition, design changes will
be easily incorporated.
Because DSPC is not subject to distortion, what you see on the computer
screen is what you get as a ceramic mold. Drawing will not be needed, since
the engineer will be able to send the CAD file via modem or network to the
foundry and, within days, receive as many functional parts, ready for
assembly, as he may need. The foundry, relieved from pattern or mold making
will import the CAD file, design gating on screen and pour metal into the
DSPC-made shell to form the near net shape part.
DSPC makes possible true just-in-time (JIT) production and concurrent
engineering. Since no tooling or setup are required, it is a technology
with the potential to produce parts at a cost that is almost independent of
the quantity ordered, and to eliminate the distinction between prototype
and production metal parts. DSPC will also help reduce inventories (since
there is no cost advantage to fabricate parts in large quantities) and
production turnaround time. Furthermore, when no machining is required, the
cost of pans produced with DSPC will be determined primarily by the cost of
the metal, rather than geometrical complexity. This new capability should
have a tremendous impact on new product development and greatly simplify
cost engineering and purchasing functions.
DSPC's initial applications are in low-volume manufacturing, such as
prototyping of complex metal parts (whether or not these parts are intended
to be produced with investment casting). In addition, DSPC is suitable for
producing one-of-a-kind parts, as well as tooling for plastics molding and
diecasting.
In only a few years, production rates and part quality will be high enough
that DSPC could become more economical than investment casting for all parts
and run sizes.
Later, DSPC is expected to achieve sufficient production rates and accuracy
that it could displace other casting processes and CNC machining to become
a dominant method for producing metal parts.
End of article
Sidebars
Why CAD is not more widely used
in the foundry industry
In recent years Computer Aided Design (CAD) has become an essential tool
for designing metal parts. CAD eliminates the manual drafting process, and
allows the engineer to design more sophisticated parts with greater
precision. However, the ultimate output of expensive software and computing
power is a two-dimensional paper drawing. Foundries must interpret the part's
design drawing into a pattern design, requiring shrinkage compensation,
filleting of sharp comers, and the incorporation of draft angles and parting
lines. Such modifications usually require tie foundry to regenerate the CAD
file, making the customer CAD file of no use to the foundry. It is easier
for the foundry engineer to mark the customer's drawing and forward it to
the pattern or mold maker than to redo the CAD.
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Background on Soligen
Soligen, Inc. was founded in 1991 to commercialize DSPC technology with the
goal of providing the foundry industry with a rapid, tool-less process for
creating metal parts. Last year, Soligen obtained the exclusive license to
develop Three Dimensional Printing (30P) invented at the Massachusetts
Institute of Technology, Cambridge, MA. The company's management team has
extensive experience in the rapid prototyping industry.
Soligen, a company
based in a new 10,000 square foot manufacturing facility in Northridge, CA,
is presently focusing on the first-generation DSPC Alpha machines. Soligen's
Alpha group consists of three members: Pratt & Whitney, Johnson & Johnson,
and Sandia National Laboratories. The Alpha group is helping Soligen in
commercializing DSPC technology by testing the concept in "real-life"
environments. Feedback from the Alpha group helps Soligen to prioritize DSPC
performance enhancements and test each software or hardware improvement.
Several primary applications for these machines will be examined.
Richard Aubin, project manager at Pratt & Whitney, East Karford, CT,
says: "We're excited about the direct shell production process because of
its potential to compress lead time for investment castings. This is one of
the few technologies that extends current manufacturing capabilities to
fabricate parts and tooling that are not possible with conventional
manufacturing methods. It is conceivable that with additional development
this technology will dramatically change the way production parts are
fabricated."
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Soligen Ships First DSPC System
In January, the first alpha DSPC system was installed at Sandia National
Laboratories in Albuquerque, NM. The installation of the first of three
alpha units comes only seven months after the start of the engineering effort
to commercialize the DSPC process.
DSPC has the potential for radically reshaping manufacturing. Using a
three-dimensional technique--pioneered by MIT and under exclusive worldwide
license to Soligen--to literally "print" the ceramic molds used to cast
metal parts, Soligen's process can potentially reduce the longest lead time
component of industrial manufacturing--fabrication of metal parts and
tooling.
Printing ceramic molds directly from a computer-aided design (CAD) file
allows manufacturers and design engineers to combine the benefits of
investment casting with the quick turnaround time found in computer-numerical
controlled (CNC) machining to create a new paradigm for metal parts production.
Recognizing this, alpha partners signed up in mid-1992 to purchase early
production versions of the DSPC system.
"We are very excited about Soligen's DSPC technology and are glad to be
a participant in the alpha program," said Leif Gonnsen, system operator at
Sandia. "DSPC could potentially have a very large impact on the way metal
parts are made, and Sandia, with its commitment to helping U.S. industry
develop leading-edge manufacturing technologies, will evaluate the
technology seriously."
Soligen also announced that the company poured aluminum into the first
ceramic mold generated by its DSPC system, producing a metal part.
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