This invention relates generally to the manufacture of tooling and
prototype parts and, more particularly, to the use of three-dimensional printing
techniques using computer models therefor.
Background of the Invention
Two needs in providing effective industrial productivity and competitiveness
lie in the reduction in time required to bring new products to the marketplace
and the need for providing for flexible manufacture of products in small quantities.
Thus, it is desirable to provide rapid part turnaround with a minimal investment
in tooling. Techniques for doing so should have the ability to tailor designs to
specfic tasks, to shorten the cycle time from design to manufacturing, and/or
to manufacture in very small lot sizes, as low as a single component, all at reasonable
cost. A major contributor to the time required to bring new products to market
is the time required to fabricate functioning prototypes. Rapid prototyping can
shorten the product development cycle and improve the design process by providing
rapid and effective feedback to the designer. Moreover, some applications require
rapid prototyping of non-functional parts for use in assessing the aesthetic aspects
of a design or the fit and assembly thereof.
Another major contributor to the time to bring a product to market
is the time required to develop tooling, such as molds and dies. For some types
of tooling, such as injection molding dies, the turnaround time for the design
and fabrication of a tool routinely extends to several months. The long lead times
are due to the fact that tooling is often one of a kind and can be extremely complex,
requiring a great deal of human attention to detail. Thus, tooling not only affects
lead time, but also manufacturing costs as well. In fact, tooling costs often
determine the minimum economic batch size for a given process. Prototyping requirements,
tooling lead time, and tooling cost are related in that it is the combination of
long lead times and high cost which make it impractical to fabricate preproduction
prototypes by the same process that will be used in production.
In the past several years, there has been considerable interest in
developing computerized, three-dimensional printing techniques, sometimes referred
to as "desktop manufacturing" techniques where no tooling is required. One such
system is known, the SLA 1 System, made and sold by 3D Systems, Inc. of Valencia,
California. This system operates on a principle called stereolithography wherein
a focused ultra-violet (UV) laser is vector scanned over the top of a bath of a
photopolymerizable liquid polymer plastic material. The UV laser causes the bath
to polymerize where the laser beam strikes the surface of the bath, resulting in
the creation of a first solid plastic layer at and just below the surface. The
solid layer is then lowered into the bath and the laser generated polymerization
process is repeated for the generation of the next layer, and so on, until a plurality
of superimposed layers forming the desired part is obtained. The most recently
created layer in each case is always lowered to a position for the creation of
the next layer slightly below the surface of the liquid bath.
An alternative approach, sometimes called Selective Laser Sintering
(SLS) has also been proposed by DTM Corporation of Austin, Texas. In such system,
a laser beam is used to sinter areas of a layer of loosely compacted plastic powder,
the powder being applied layer by layer. The term "sintering" refers to the process
by which particulates, such as powdered plastics, are caused to adhere into a solid
mass by means of externally applied energy. A SLS system uses the optical energy
supplied by a laser for such purpose.
Thus, a thin layer of powder is spread evenly onto a flat surface
with a roller mechanism. The thin powder surface is then raster-scanned with a
high-power laser beam from above. The powder material that is struck by the laser
beam is fused together. The areas not hit by the laser beam remain loose and fall
from the part when it is removed from the system. Successive layers of powder are
deposited and raster-scanned, one on top of another, until an entire part is complete.
Each layer is sintered deeply enough to bond it to the preceding layer. A similar
laser sintering approach has been proposed by Hydronetics, Inc. of Chicago, Illinois.
Another process suggested by the same company is designated as a Laminated Object
Manufacturing (LOM) technique wherein thin metallic foil layers are cut out to
appropriate shapes to form a part and the shaped layered pieces are laid one on
top of the other and suitably bonded to form the part involved.
Another process suggested for creating 3D models and prototypes,
sometimes called Ballistic Particle Manufacturing (BPM), has been proposed by Automated
Dynamic Corporation of Troy, NY. This process uses an ink-jet printing technique
wherein an ink-jet stream of liquid molten metal or a metal composite material
is used to create three-dimensional objects under computer control, similar to
the way an ink-jet printer produces two-dimensional graphic printing. A metal or
metal composite part is produced by ink-jet printing of successive cross sections,
one layer after another, to a target using a cold welding (i.e., rapid solidification)
technique, which causes bonding between the particles and the successive layers.
Still another technique, sometimes called Photochemical Machining,
proposed by Formigraphic Engine Co. of Berkeley, California, uses intersecting
laser beams to selectively harden or soften a polymer plastic block. The underlying
mechanism used is the photochemical cross-linking or degradation of the material.
It is desirable to devise a technique for providing such layered
parts which will work satisfactorily with ceramic or metal materials, or combinations
of such materials with each other or with other materials, but which will also
work satisfactorily with plastic particles or with other inorganic materials.
Such a technique could be more universally employed for the manufacture of components
from a larger variety of materials than the currently proposed techniques
Brief Summary of the Invention
In accordance with a preferred embodiment of the invention, powdered
material, e.g., a powdered ceramic, a powdered metal, or a powdered plastic, is
deposited in sequential layers one on top of the other. Following the deposit
of each layer of powdered material, a liquid binder material is selectively supplied
to the layer of powdered material using an ink-jet printing technique in accordance
with a computer model of the three-dimensional part being formed. Following the
sequential application of all of the required powder layers and binder material
to form the part in question, the unbound powder is appropriately removed, resulting
in the formation of the desired three-dimensional part. It is found that such
technique permits complex metal, ceramic, or metal-ceramic composite parts to be
effectively formed with a very high degree of resolution in a reasonably short
Such technique should be particularly useful, for example, in providing
for the rapid production of molds for metal casting and the rapid formation of
pre-forms for metal matrix composites. Such technique can also be used with plastic
materials to form plastic components or parts for various purposes.
Description of the Invention
The invention can be described in more detail with the help of the
accompanying drawings wherein
- FIG. 1 shows an isometric view of one particular embodiment of the invention;
- FIG. 2 shows diagrammatic views of different stages in forming a part in accordance
with the invention;
- FIG. 3, 4 and 5 show various exemplary techniques for setting the powder particles
by applying mechanical vibrations and acoustic energy thereto;
- FIG. 6 shows exemplary stages in the use of a drop-piston device for depositing
powder particles in accordance with the invention;
- FIGS. 7 and 8 show diagramatic views of the formation of a part having reentrant
- FIG. 9 shows a block diagram of an exemplary system which can be used in practicing
- FIG. 10 shows an exemplary flow chart of the steps used in the system of FIG.
8 to practice the invention.
- FIGS. 11 and 12 show isometric views of an exemplary 3-D model and the 2-D
slices thereof, respectively, of a part to be formed in accordance with the invention;
- FIG. 13 shows a plan view of the 1-D line segments of a 2-D slice of the model
shown in FIGS. 11 and 12.
One particular embodiment of the invention is shown in FIG. 1 which
depicts an apparatus 10 for forming a ceramic mold having six cavities 12A-12F
which can be used for casting six substantially identical parts. A powder dispersion
head 13 is driven reciprocally in a shuttle motion along the length of the mold
being formed. A suitable linear stepping motor assembly 18 can be used for moving
the powder distribution head 13 and the binder deposition head 15 (discussed below).
The powdered material, e.g., a ceramic powder, is dispensed in a confined region,
e.g., defined by a form 14, the powder being dispensed in a line as the dispensing
head 13 is moved in discrete steps along the mold length to form a relatively loose
layer thereof having a typical thickness of about 100-200 microns, for example.
While the material is described here as a powdered material, in some applications
it can be distributed in the form of fibers, for example. For convenience in describing
the invention, the term powder material will be construed to include fiber material.
The stepping motor can be moved at such high speeds that the motion of the head
13 will effectively be continuous in nature. Alternatively, the motor may be one
which inherently provides a continuous motion, such as a servo-controlled motor.
An initial layer is dispersed at the bottom of the form 14 and each subsequent
layer is dispersed sequentially on the preceding layer.
An ink-jet print head 15 having a plurality of ink-jet dispensers
is also driven by the stepping motor assembly in the same reciprocal manner so
as to follow the motion of the powder head and to selectively produce jets of a
liquid binder material at selected regions 16 which represent the walls of each
cavity, thereby causing the powdered material at such regions to become bonded.
The binder jets are dispensed along a line of the printhead 15 which is moved in
substantially the same manner as the dispensing head 13 of the powder material,
i.e., by a high speed stepping operation or by a continuous servo motor operation,
in each case providing effectively continuous movement of head 15 as discussed
above with reference to head 13. Typical binder droplet sizes are about 15-50 microns,
for example. The powder/binder layer forming process is repeated so as to build
up the mold parts layer by layer.
A diagram showing a part being fabricated in accordance with the
invention is depicted in FIG. 2 which diagrammatically depicts the flow thereof.
For a part 40 in question a layer of powder is deposited from a powder dispensing
head 41 into a form 42 over a previously formed layer which has already had binder
material deposited therein (A). A layer of binder material is then printed onto
the powder layer from binding jet head 43 to form the next layer 44 of bonded powder
articles (B). Such operation is repeated for each subsequent layer. An exemplary
intermediate stage of the formation of part 40 is shown at (C). When the final
bonded layer is printed as shown at (D), excess, unbonded powder is removed, the
finally formed part itself being depicted at (E).
While the layers become hardened or at least partially hardened as
each of the layers is laid down, once the desired final part configuration is achieved
and the layering process is completed, in some applications it may be desirable
that the form and its contents be heated or cured at a suitably selected temperature
to futher promote binding of the powder particles. In either case, whether a further
curing is or is not required, the loose, unbonded powder particles, e.g., at regions
17 (FIG. 1), are removed using a suitable technique, such as ultrasonic cleaning,
for example, so as to leave a finished part for use.
For effective use, the powder particles should be uniformly deposited
at a relatively high rate, the rate being selected in accordance with the application
for which the technique is used. For many useful applications the powder particles
can preferably be packed at relatively high densities, while in other applications
the density may be considerably lower where parts having greater porosity are desired.
Known techniques used in the fields of colloidal science and powder dispersion
chemistry can be used to provide the desired uniform depositions of such powders
at the required rates and densities. Thus, such powders can be dispensed either
as dry powders or in a liquid vehicle, such as in a colloidal dispersant or in
an aqueous suspension. In the dry state, the desired compaction of particles can
be achieved using mechanical vibrating compaction techniques or by applying acoustic
energy, i.e., either sonic or ultrasonic vibrations, to the deposited powder or
by applying a piezoelectric scraper to the deposited powder.
Such techniques are illustrated, for example, in FIGS. 3, 4 and 5,
respectively. FIG. 3 shows form 14 which is mechanically vibrated as shown by arrow
60 using a vibrating transducer system 61 for settling the powder particles 62
therein. In FIG. 4 a acoustic transducer system 63 is used to supply acoustic
energy 64 to the surface layer of powder 62 for such purpose. In FIG. 5 a vibrating
tranducer system 65 is used to vibrate a piezoelectric scraper 66 as shown by arrow
67 as it moves in the exemplary direction of arrow 68 to settle the powder 62.
The powder may also be deposited in a dry or in a wet form using
a drop piston approach wherein a dry or moist powder is deposited on the top of
a vertically movable piston and the piston is moved downwardly into a chamber,
excess powder being scraped off with a suitable scraper device.
As shown in FIG. 6, a piston 70 holds the part 71 shown as partially
formed within a chamber 72 at diagram (A). In order to deposit a layer of powder,
the piston is moved downwardly in the chamber, leaving a region in chamber 73 at
the top thereof for deposition of powder particles at diagram (B). Powder particles
74 are deposited in such region and a doctor blade 75, for example, is used to
scrape off excess powder at diagram (C). The part 71 having the newly deposited
layer 76 of powder thereon is then ready for the application of binder material
thereto at diagram (D).
In general, it is found that larger particles, for example, of about
20 microns or greater in size, are preferably deposited in a dry state, while smaller
particles, for example, of about 5 microns or smaller in size, can be deposited
either in a dry state or in a wet state in a liquid vehicle.
Colloidal dispersions of particles can be obtained in a liquid vehicle
by the addition of chemical dispersants. The liquid used in a wet powder dispersion
technique is removed, or partially removed, before the next layer is deposited.
Thus, such liquid is caused to evaporate rapidly before the ink-jet binder printing
occurs. Such evaporation can be achieved, for example, by using infra-red heating,
hot air heating or microwave heating techniques.
The ink-jet printing of the binder material should utilize droplets
of materials the shrink characteristics of which are selected so that the dimensional
tolerances of the part being made are maintained upon hardening thereof. While
the binder solution must have a relatively high binder content, the viscosity
thereof should be low enough so as to be able to flow through the printing head
for deposit into the powder material. The binder material should be selected to
penetrate the layer and to perform its binding action relatively rapidly in each
layer so that the next layer of powder particles can be subsequently applied thereto.
When using certain ink-jet technology the binder material may require at least
a minimum electrical conductivity, particularly when using currently available
continuous jet printing heads, for example, which require enough conductivity to
establish charge on the binder solution droplets as they are emitted from the head.
Where conductivity cannot be established in the binder, as with certain organic
solvents, for example, the binder can be applied using drop-on-demand print heads.
The binder material may be such that the bonded particles have a
high binding strength as each layer is deposited so that, when all the layers have
been bonded, the component formed thereby is ready for use without further processing.
In other cases, it may be desirable, or necessary, to perform further processing
of the part. For example, while the process may be such as to impart a reasonable
strength to the component which is formed, once the part is formed it can be further
heated or cured to further enhance the binding strength of the particles. The binder
in some cases can be removed during such heating or firing process, while in others
it can remain in the material after firing. Which operation occurs depends on
the particular binder material which has been selected for use and on the conditions,
e.g., temperature, under which the heating or firing process is performed. Other
post-processing operations may also be performed following the part formation.
The ink-jet printing mechanisms that can be used are known to the
art and normally are of two types, one being a continous jet stream print head
and the other a drop-on-demand stream print head. A high speed printer of the continous
type, for example, is the Dijit printer made and sold by Diconix, Inc. of Dayton,
Ohio, which has a line printing bar containing approximately 1500 jets which can
deliver up to 60 million droplets per second in a continous fashion and can print
at speeds up to 900 feet per minute. In such a system, the liquid material emerges
continuously from each jet nozzle under high pressure, the jet stream then disintegrating
into a train of droplets, the direction of which is controlled by electric control
Drop-on-demand systems, as now known to the art, generally use two
droplet generation mechanisms. One approach uses a piezoelectric element which
in one exemplary embodiment has the piezoelectric element attached to one wall
of a liquid reservoir. A pulse applied to the piezoelectric element slightly changes
the volume of the reservoir cavity and simultaneously induces a pressure wave in
the liquid. Such operation causes a droplet of the liquid to be ejected from a
nozzle attached to the cavity. The cavity refills by capillary action. Another
approach uses an evaporative bubble wherein a small resistive heater when actuated
causes some of the liquid to evaporate so as to form a vapor bubble which in turn
causes a small droplet of liquid to be ejected from the cavity. The cavity is
then refilled through capillary action. In general, continuous jet technology provides
higher droplet deposit rates than drop-on-demand technology.
The continuous or drop-on-demand ink-jet heads may use, for example,
a single jet, or an array of jets which are arranged to deposit the material in
an effectively linear manner, or a combination of two or more relatively short,
parallel arrays of jets arranged for parallel and effectively linear depositions
The rate at which a ceramic, metal, plastic, or composite component
can be made depends on the rates used to deposit the powder and to supply the binder
liquid, and on the rate at which each bonded layer hardens as the layers are deposited
one on the other.
If a dry powder dispersion is utilized, the powder application step
is less significant as a limiting factor in determing the overall printing rate.
If powder dispersion in a liquid vehicle is used, however, the layer must be at
least partially dry prior to the ink-jet application of the binder material. The
drying time will depend on the specific nature of the powder, binder, and solvent
The dimensions of the individual portions of the component being
formed, sometimes referred to as the "feature" size thereof, is primarily dependent
on the size of the binder droplets used, while the tolerance on such dimensions
primarily depends on the degree of the reproducibility of the droplet spread characteristics
of the binder material which is utilized.
Ink-jet printing of a liquid binder using currently known ink-jet
devices can provide jet droplet sizes of as low as 15 microns, for example. It
is possible that even smaller droplet sizes will be practical, with the lower limit
on droplet size arising from surface energy considerations in the creation of
new surface area and in the increased likelihood of the clogging of small jets.
Overall part tolerance will depend not only on drop spreading, but
also on material shrinkage and the reproducibility of shrinkage characteristics
as well. As an example, if the binder/powder combination shrinks by 1% and the
shrinkage is reproducible to within 5% of its nominal value of 1%, an overall
variation due to shrinkage can be approximately 0.0005 inches/inch. The actual
shrinkage that occurs during binder curing or deposition is a relatively strong
function of particle rearrangement. Dimensional tolerance and particle packing
can be empirically determined for the best results in each case.
Alumina, zirconia, zircon (i.e., zirconium silicate), and silicon
carbide are representative ceramic materials which can be bonded using the techniques
of the invention. Both natural and synthetic dispersants are available for these
materials in organic vehicles. For example, alumina is very effectively dispersed
by glyceride surfactants in toluene/MEK solvents, as is used for casting thin sheets
of particles in the production of dielectric substrates in the electronic packaging
industry. Silicon carbide, for example, can be easily dispersed in hexane if small
amounts of OLOA 1200 (as obtained, for example, from Chevron Chemical Co. Oronite
Additives Div. of San Francisco, CaLifornia) are present. OLOA is primarily used
as an additive in crank case oil where it acts as a dispersant for metal particles
produced by engine wear.
Organic binders have been used in the ceramics industry and are typically
polymeric resins obtained from a variety of sources. They can be either water soluble,
such as celluosic binders, as used in extrusion technology, or they can be soluble
in only volatile organic solvents, such as the butyral resins, as used in tape
casting technology. The latter water soluble systems can be removed relatively
quickly and seem particularly useful in the technique of the invention. Another
type of organic binder would be a ceramic precursor material such as polycarbosilazane.
Inorganic binders are useful in cases where the binder is to be incorporated
into the final component. Such binders are generally silicate based and are typically
formed from the polymerization of silicic acid or its salts in aqueous solution.
Another exemplary inorganic binder which can be used is TEOS (tetraethylorthosilicate).
During drying, the colloidal silica aggregates at the necks of the matrix particles
to form a cement-like bond. During firing, the silica flows and acts to rearrange
the matrix particles through the action of surface tension forces and remains after
firing. Soluble silicate materials have been used as binders in refractory castable
materials, for example, and have the advantage, when used in the technique of
the invention, of producing substantially the same type of molded refractory body
that is used in the casting industry.
In some applications, it may be preferable that the binder harden
relatively rapidly upon being deposited so that the next layer of particles placed
on a surface of the previous layer is not subject to particle rearrangement due
to capillary forces. Moreover, a hardened binder is not subject to contamination
from solvents which may be used in powder deposition. In other cases, it may not
be necessary that the binder be fully hardened between layers and a subsequent
layer of powder particles may be deposited on a previous layer which is not yet
Where hardening occurs at the time the binder is deposited, thermal
curing, i.e., evaporation of the binder carrier liquid, for such purpose would
generally require that the component being formed be warmed as the printing of
the binder material is performed, while the printhead itself is cooled so that
unprinted binder material in the reservoir of the ink-jet head retains its desired
properties. Such hardening can be achieved by heating the binder material indirectly,
as by heating the overall apparatus in which the part is being formed using an
appropriate external heat source, for example, or by heating the binder material
directly as by applying hot air to the binder material or by applying infra-red
energy or microwave energy thereto. Alternatively, a variety of thermally activated
chemical reactions could also be used to harden the binder. For example, gelation
of alkali silicate solutions can be made to occur by a change in pH accompanying
the decomposition of organic reagents. Thus, a mixture of alkali silicate and
formamide could be printed on to a hot component being formed. The rapid increase
in temperature would greatly increase the formamide decomposition rate and, therefore,
rapidly change the pH of the binder. Other thermally or chemically initiated techniques
for hardening of the binder upon deposit thereof could be devised within the skill
of those in the art.
While liquid and colloidal binder materials have been discussed above,
in some applications binder material may be deposited in the form of binder particles
entrained in a liquid. Such binder materials can be supplied via specially designed
compound ink-jet structures capable of providing such entrained binder materials.
An example of such a composite structure is discussed, for example, in the article
"Ink-Jet Printing," J. Heinzle and C.H. Hertz, Advances In Electronics and Electron
Physics, Vol. 65.
Moreover, in some applications in the fabrication of a part, the
binder material which is used need not be a single binder material, but different
binder materials can be used for different regions of the part being formed, the
different materials being supplied by separate binder deposition heads. A dual
head system is shown in FIG. 2 wherein a second head 43A is depicted in phantom
therein at (B).
Many possible combinations of powder and binder materials can be
selected in accordance with the invention. For example, ceramic powders or ceramic
fibers can be used with either inorganic or organic binder materials or with a
metallic binder material; a metal powder can be used with a metallic binder or
a ceramic binder; and a plastic powder can be used with a solvent binder or a plastic
binder, e.g., a low viscosity epoxy plastic material. Other appropriate combinations
of powder and binder materials will occur to those in the art for various applications.
One useful application of the invention lies in the printing of molds
for metal casting, particularly when the mold has a relatively complex configuration.
Currently, complex, high precision castings are made by lost-wax casting, or investment
casting. The process begins with the fabrication of an aluminum die which is used
to mold wax positives of the part to be cast. The die is usually made by electric
discharge machining. Wax positives are then made and connected together by hand
with wax runner systems to form a tree. If the part is to have internal voids,
a ceramic core is included in the wax positives. The tree is then dipped repeatedly
into ceramic slurries with a drying cycle between each dipping operation. Following
a final dry, the wax is melted and burned out of the shell mold and the mold is
finally ready for casting. In its basic form, such lost-wax casting technique has
long been used in the art.
With the technique of the invention, a ceramic shell mold can be
fabricated directly to its final shape with no wax positives needed at all. The
internal cavities can be fabricated by leaving the binder material out of these
areas. The loose, unjointed powder will then wash out of the mold through the
same passageways that will later admit molten metal in the final mold. FIGS. 7
and 8 show diagrammatic views of the formation of a part having reentrant features.
Thus, in FIG. 7, the binder material is printed at three selected regions 20, 21
and 22 for an initial set of sequential layers, while, for a final set of sequential
layers, the selected region 23 encompasses all three previously formed regions
as shown in FIG. 8. For the printing of molds, typical powder materials, as discussed
above, might include alumina, silica, zirconia, and zircon, for example. A typical
binder would be colloidal silica. Moreover, the techniques of the invention can
be used to form the cores only.
When making molds with core regions, it may be advantageous to use
one particular binder material for the main body of the mold and a modified binder
material in the core regions thereof, the depositing of the binder at the core
regions requiring the use of a second printhead, for example. The technique of
the invention has at least two advantages over lost-wax techniques for the creation
of molds, one lying in the reduction in cost for small and moderate batches of
parts and the other in the ability to produce a large variety of different molds
and other parts with a relatively short turnaround time.
A relatively simple example of a system for performing the above
powder distribution control operation and the nozzle control operation for the
binder material is discussed with reference to the block diagram of FIG. 9 and
the flow chart of FIG. 10. As seen in FIG. 9, a microcomputer 30 of any type which
is usable for conventional computer-aided-design (CAD) operations, as would be
well-known to the art, can be suitably programmed for the purpose of the invention.
The microcomputer 30 is used to create a three-dimensional (3-D) model of the
component to be made using well-known CAD techniques. An exemplary computerized
3-D model 50 is depicted in FIG. 11. A slicing algorithm is used to identify selected
successive slices, i.e., to provide data with respect to selected 2-D layers,
of the 3-D model 50 beginning at a bottom layer or slice thereof, for example.
Exemplary layers 51 of the model 50 are depicted in the exploded view of FIG. 12.
The development of a specific slicing algorithm for such purpose is well within
the skill of those in the art.
Once a particular 2-D slice has been selected, the slice is then
reduced to a series of one-dimensional (1-D) scan lines thereof as depicted in
the plan view of FIG. 13. The development of a suitable reducing algorithm for
such purpose would also be well within the skill of the art. Each of the scan
lines 52 can comprise a single line segment (e.g., segment 53A of scan line 52A)
or two or more shorter line segments, (e.g., segments 53B of scan line 52B), each
line segment having a defined starting point on a scan line and a defined line
segment length. For example, the line segments 53B have starting points at x&sub1;
and x&sub2;, respectively, as measured from a reference line 54, and lengths l&sub1;
and l&sub2;, respectively, as measured from their starting points x&sub1; and x&sub2;.
The microcomputer 30 actuates the powder distribution operation when
a particular 2-D slice of the 3-D model which has been created has been selected
by supplying a powder "START" signal to a powder distribution controller circuit
31 which is used to actuate a powder distribution system 32 to permit a layer
of powder for the selected slice to be deposited as by a powder head device in
a suitable manner as discussed above. For example, the powder is deposited over
the entire confined region within which the selected slice is located. Once the
powder is distributed, the operation of powder distribution controller is stopped
when the microcomputer 30 issues a powder "STOP" signal signifying that powder
distribution over such region has been completed.
Microcomputer 30 then selects a scan line, i.e., the first scan line
of the selected 2-D slice and then selects a line segment, e.g., the first 1-D
line segment of the selected scan line and supplies data defining the starting
point thereof and the length thereof to a binder jet nozzle control circuit 33.
For simplicity in describing the operation it is assumed that a single binder jet
nozzle is used and that such nozzle scans the line segments of a slice in a manner
such that the overall 2-D slice is scanned in a conventional raster scan (X-Y)
operation. When the real time position of the nozzle is at the starting point
of the selected line segment, the nozzle 35 is turned on at the start of the line
segment and is turned off at the end of the line segment in accordance with the
defined starting point and length data supplied from computer 30 for that line
segment. Each successive line segment is similarly scanned for the selected scan
line and for each successive scan line of the selected slice in the same manner.
For such purpose, the nozzle carrier system starts its motion with a scan "BEGIN"
signal from microcomputer 30 so that it is moved both in the X axis (the "fast"
axis) direction and in the Y axis (the "slow" axis) direction. Data as to the real
time position of the nozzle carrier (and, hence, the nozzle) is supplied to the
nozzle control circuit. When the complete slice has been scanned, a scan "STOP"
signal signifies an end of the slice scan condition.
As each line segment is scanned, a determination is made as to whether
nozzle operation has occurred for all line segments of a particular scan line of
the selected slice. If not, the next line segment is scanned and the nozzle control
operation for that line segment is performed. When nozzle operation for the final
line segment of a particular scan line has been completed, a determination is made
as to whether the scan line involved is the final scan line of the selected slice.
If not, the next scan line is selected and the scanning and nozzle control process
for each successive line segment of such scan line of the slice is performed. When
nozzle operation for the final scan line of a particular slice has been completed,
a determination is then made as to whether such slice is the final slice of the
overall 3-D model. If not, the next slice is selected and the overall process for
each line segment of such scan line thereof is rejected, including the powder
deposition and nozzle binder deposition required for all the scan lines thereof.
When the binder material has been supplied the final slice of the 3-D model, the
operation is completed.
The necessary programming required to implement the flow chart of
FIG. 10 using the components of FIG. 9 would be well within the skill of the art
and need not be discussed in further detail. Such an approach can be used for a
single nozzle as described above and can be readily adapted for use with a binder
head having multiple nozzles, e.g., an array of nozzles for providing an effective
linear deposition of binder material, or a plurality of relatively shorter, multiple
In addition to the above discussed embodiments of the invention,
further variations or modifications of the techniques disclosed above will occur
to those in the art. For example, the binder, rather than being applied in a wet
state, can be applied in a dry state using materials having a low melting point
so that, when applied and heated, the melted material penetrates the powder particles
and when hardened bonds them together. Further, two or more different types of
powder particles can be applied via two or more separate powder dispersion heads
so as to deposit the different powders at different regions of the part being formed.
The powder at such regions can then be bonded using the same or different binder
materials so that different physical characteristics can be obtained at such different
regions. Other modifications or extensions of the invention may occur to those
in the art within the spirit and scope thereof. Hence, the invention is not to
be construed as limited to the specific embodiments described above, except as
defined by the appended claims.