Additive fabrication apparatus and method

An additive fabrication apparatus using a fluid construction material which can be solidified, and including a fluid material extrusion assembly including trowels defining first and second surfaces, a first nozzle for delivering fluid material to a predetermined location, a first control for moving the extrusion assembly along a predetermined path defining an enclosed area, a first supply for delivering fluid material to the extrusion assembly to extrude the material from the first nozzle in a layer as the first nozzle is moved along the path, with the first and second surfaces moving with the first nozzle to produce a wall of the extruded material forming the enclosed area with a shaped outer surface and a shaped top surface, a second nozzle for delivering fluid material to the enclosed area, a second control for moving the second nozzle to position the second nozzle at the enclosed area, and a second supply for delivering fluid material to the second nozzle to fill in the enclosed area. A method of additive fabrication, which can be automated.

BACKGROUND OF THE INVENTION 
This invention relates to additive fabrication apparatus and methods, 
generally known as rapid prototyping techniques. Such techniques have 
found applications in: small batch actual production of parts or 
assemblies; prototyping of products to test functionality, fit for 
assembly, marketability, and other factors; mold, die and other tool 
making for other manufacturing processes such as casting, extrusion, EDM, 
etc.; and solid imaging of 3D data in domains such as mathematics, 
chemistry, medicine, etc., and sculpturing and other forms of art work. 
The major advantages of additive fabrication over the subtractive 
techniques such as metal cutting are: the ability to produce parts with 
unlimited geometrical complexity; the radically new possibility of 
designing the internal structure of parts; the possibility of unattended 
and automated operation; and the possibility of wasteless and 
environmentally sound fabrication. 
Due to the current global interest in shortening the product design and 
manufacturing cycle which is essential in the current competitive world 
market and due to the recent environmental concerns, additive processes 
are receiving a great deal of attention. The present invention is related 
to a new additive fabrication apparatus and method that has several 
superior features as compared with the existing techniques. 
Currently available additive automated fabrication techniques are briefly 
described below. 
Selective photocuring: The original SteroLithography and its variations 
fall in the category of selective photocuring. In these processes 
selective portions of successive layers (corresponding to cross sections 
of the object being built) of a special type of polymer resin are 
solidified by exposure to light. 
Selective sintering: In this process desired sections of thin successive 
layers of thermoplastic or metal powder are melted such that the powder 
particles are melted and fused together to form cross sections of the 
object. 
Robotically guided extrusion: This process forces thermoplastic paste 
through an extrusion nozzle which is moved about by a robotic arm to lay 
down the molten material in desired locations of each successive layer of 
the object. 
Droplet deposition on powder: In this process an adhesive liquid is 
ejected, usually by techniques similar to that used in the ink jet 
printers, to a thin powder layer to selectively join the powder particles 
to form solid cross sections of the object. The composite object may be 
later cured by heat for improved strength. This process is usually called 
3D Printing. 
Adhesion of cut sheets: This process separately cuts (usually by laser) the 
contour of each cross section of the object on sheets of a laminating 
material (usually butchery paper). The cut layers are successively 
laminated by heat to create the final object. 
Other techniques under development: Three dimensional welding in which a 
welding head is robotically guided to progressively melt and fuse (usually 
nickel-based steel) to build the desired object; controlled deposition of 
liquid droplets of various materials (recently metal) to progressively 
build the object layer-by-layer; and selective curing of photopolymer by 
two laser beams that meet at the curing points in a vat of liquid resin 
(the only method that does not use the successive layering technique) are 
some of the rapid prototyping processes that are currently under 
development. Most of these methods, especially the latter one, are far 
from being commercially feasible due to several major difficulties in 
creating acceptable part surface qualities and dimensional tolerances. 
All of the current additive processes, with the exception of the two-laser 
method, use the layering approach which builds up the object in horizontal 
layers each about 0.1 to 0.25 mm thick. Consequently, 40 to 100 layers for 
each vertical centimeter (100 to 250 layers per vertical inch) are built 
by these processes. 
The most popular processes are currently based on polymer selective 
photocuring. Although photocuring machines are the most expensive type of 
rapid prototyping equipment and photopolymers are the most expensive 
materials used in rapid prototyping, due to the accuracy of selective 
photocuring, this process is most widely used today. Photopolymer is an 
organic resin that solidifies (cures) under light in a particular range of 
wavelength (usually in the ultraviolet range). One of the reasons for the 
attractiveness of photopolymers is that they can be stored as liquid for a 
long time and then be solidified during manufacturing. The required light 
for photopolymer curing is provided either by a scanning laser beam or by 
a flood lamp which shines light through a masked sheet which lets the 
light through where the layer is to solidify. 
The current photocuring systems build the object in a vat of liquid 
polymer. As each layer is cured, a new resin layer covers the cured layer 
by either vertically moving the object to a lower depth in the vat, or by 
pouring more resin into the vat. When the last layer is cured either the 
object is raised or the vat is drained to remove the fabricated object 
from the vat. Another approach for layer creation builds the object as it 
is suspended from an ascending platform. For each new layer the liquid 
resin is poured in a thin layer on a plate of glass just below the last 
layer of the object. The bottom surface of the glass platform is exposed 
to either laser or flood lamp light for curing. 
When a laser beam is used for photocuring certain sections of each resin 
layer are scanned by the beam according to the 2D geometry of the related 
cross section of the object. The scanned sections solidify and the rest of 
the layer remain in liquid form. The laser method is potentially more 
energy efficient since it emits light only on specific surfaces and the 
monochromic nature of the laser beam results in more uniform curing for 
thicker layers. 
In the flood lamp approach a mask sheet is created, usually using ordinary 
laser printers and and transparent sheets. For each layer a mask sheet 
must be created. Excessive mask sheet consumption and complication in 
accurately feeding each sheet to the desired position may be considered as 
serious disadvantages of this technique. Certain methods use a single 
glass sheet which is electrostatically charged in desired sections. Black 
toner particles are then attracted by the charged sections. After light 
exposure the sheet is discharged, the toner is collected, the liquid 
polymer in sections of the layer which are not exposed to light are 
vacuumed and the process is repeated for the new layer on the same glass 
sheet. 
The flood lamp approach has two important advantages: first, the curing 
process for each layer may be much faster since the entire desired section 
of the layer is exposed instantly and simultaneously to light, and second, 
the broad spectrum of lamp light make the process less sensitive to 
variations in the polymer material, whereas a laser requires the polymer 
to be tuned to its specific frequency. 
Major drawbacks of the current rapid prototyping equipment, and methods 
include the following: 
a) The processes are slow (typically between 5 to 70 hours for relatively 
small objects). 
b) The parts fabricated by the current processes generally have poor 
surface quality. 
c) Parts created with most of the current methods have weak structures. 
d) There is a limited choice of materials that may be used. Some of these 
materials are relatively expensive (e.g. approximately $250 per pound for 
photopolymers). 
e) Current methods are limited to fabrication of part dimensions that are 
generally less than one meter is each dimension. 
f) The commercial machines using the current approaches are expensive 
(between $50K and $3M, with an average of $300K). Cost is especially high 
if laser or photo masking is used or if the processing machine has a large 
work envelope. Precision is also a big factor in the cost of the new 
methods. 
It is an object of the present invention to provide a new and improved 
apparatus and method for additive fabrication of products, including 
apparatus and method which can be automated. 
SUMMARY OF THE INVENTION 
The additive fabrication apparatus of the invention uses a fluid 
construction material which can be solidified, and includes trowel means 
defining a side surface, first nozzle means for delivering fluid material 
to a predetermined location, first control means for moving the first 
nozzle means along a predetermined path defining an enclosed area and for 
moving the trowel means along the predetermined path, first supply means 
for delivering fluid material to the first nozzle means to extrude the 
material from the first nozzle means in a layer as the first nozzle means 
is moved along the path, with the trowel means side surface producing a 
wall of the extruded material forming the enclosed area with a shaped 
outer surface and a top surface, second nozzle means for delivering fluid 
material to the enclosed area, second control means for moving the second 
nozzle means to position the second nozzle means at the enclosed area, and 
second supply means for delivering fluid material to the second nozzle 
means to fill in the enclosed area. 
The apparatus preferably includes means for solidifying the material in the 
area, and also preferably includes first and second trowels for shaping 
the side and top surfaces. Various mechanisms may be used for moving the 
trowels to define various shaped surfaces. 
The additive method of the invention for fabricating a product using a 
fluid construction material which can be solidified, trowel means defining 
a side surface, and first nozzle means for delivering the fluid material 
to a predetermined location, includes the steps of moving the first nozzle 
means along a predetermined path defining an enclosed area, moving the 
trowel means along the predetermined path, delivering fluid material to 
the first nozzle means to extrude the material from the first nozzle means 
in a layer as the first nozzle means is moved along the path, with the 
trowel means side surface producing a wall of the extruded material 
forming the enclosed area with a shaped outer surface and a top surface, 
and delivering fluid material to the enclosed area, filling in the area 
enclosed by the wall. 
The method preferably includes moving the trowel means to form a shaped 
side surface and a shaped top surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The presently preferred embodiment of the additive fabrication apparatus of 
the present invention is shown in FIG. 1, with an object 21 being created 
by the method of the invention utilizing the apparatus of FIG. 1. A fluid 
material extrusion assembly 22 is supported on an arm 23 of a conventional 
three axis servo controlled positioning system. The arm 23 is moved in the 
X direction by a drive 24 carried on another arm 25 which in turn is moved 
in the Y direction by a drive 26, which also drives the arm 25 in the Z 
direction on a post 27. The drives 24, 26 will be controlled by a 
conventional computer such as is used in present day numerically 
controlled machine tools and the like, to move the extrusion assembly 22 
along a predetermined path defining an enclosed area. In the embodiment 
illustrated in FIG. 1, the predetermined path is the rim 29 of the object 
21, which encloses the area 30. 
A nozzle 31 is driven by another servo controlled positioning system 32 to 
position the nozzle 31 at the area 30 for delivering a fluid construction 
material from a container 33 through a line 34 and a control valve 35 to 
the nozzle 31. The nozzle 31 and its associated control mechanism is 
utilized to fill in the area 30 formed by the rim 29. 
A simple form of the extrusion assembly is shown in FIG. 2, with a supply 
container 38 and a helical or auger feeder 39 driven by a motor 40 through 
a tube 41 to a nozzle 42. If desired, a heater 43 may be positioned around 
the tube 41. A top trowel 45 and a side trowel 46 are positioned adjacent 
the nozzle 42. 
A fluid construction material is placed in the container 38 and is extruded 
through the nozzle 42 onto the object being created, to form the rim 29. 
In the embodiment illustrated in FIG. 2, the trowel 45 defines the top 
surface of the rim and the trowel 46 defines the side surface of the rim. 
Both trowels are planar. 
The fluid construction material must be able to be softened to a fluid 
state for extrusion and/or pouring, and must be able to be solidified. 
Conventional casting and polymer photocuring materials may be utilized. 
Thermoplastics, photopolymers, plaster, epoxy, cement, metals and the like 
are suitable. The same material may be utilized with the extrusion 
assembly 22 and the nozzle 31, or different materials may be utilized, as 
desired. The extruded material from nozzle 42 preferably is a paste, while 
the material from nozzle 31 preferably is a liquid. 
Preferably a means 44 for solidifying the extruded material and the poured 
or injected material is included in the apparatus. The materials may be 
solidified by ultraviolet radiation, heat, cool or dry air, and the like, 
depending on the nature of the material. 
The operation of the additive fabrication apparatus is illustrated in FIG. 
3 in the formation of an object. In this illustration, the top trowel 45 
is horizontal and the side trowel 46 is vertical so as to form a square 
corner at the upper outer edge of the rim 29. A succession of rims 29 have 
been extruded one on top of the other, with the area 30 within each rim 
filled in from the nozzle 31, prior to forming the next rim. 
A more complex construction for the extrusion assembly 22 is shown in FIGS. 
1 and 12. The construction material is fed from a container 47 into an 
extrusion unit 48 with the auger driven by a motor 49. The material is 
forced out and downward through a sleeve 50 and nozzle 51, with the sleeve 
and nozzle being rotated by another motor 52. In this embodiment, the top 
trowel 45 is maintained in a horizontal position, while the side trowel 46 
may be pivoted from the vertical position to provide any desired angle for 
the side of the rim. The side trowel 46 is mounted on an arm 53 
edge-to-edge with the top trowel 45, and is pivoted by a motor 54, worm 
gear drive 55, and parallelogram linkage 56, with the arm 57 raised and 
lowered by rotation of the gear 58. The motor 54, the gear 58, and one of 
the arms of the parallelogram linkage are supported by mounting brackets 
59. 
The various positions obtainable for the side trowel with the mechanism of 
FIG. 12 are illustrated in FIGS. 13A, 13B and 13C. 
Various sizes for the side trowel 46 may be utilized, with four different 
sizes substitutable for each other shown in FIG. 14. A boss 60 on the 
trowel 46 preferably is a snap fit into a mating opening in the arm 53. 
In operation, material is delivered to the nozzle 51 to extrude the 
material in a layer forming the rim 29 as the nozzle is moved along the 
path determined by the X, Y, Z positioning drive. The top and side trowels 
form the rim for enclosing the area, with a shaped outer surface and a 
shaped top surface corresponding to the shape of the trowels, planar in 
the embodiment illustrated. The fabrication apparatus may be produced with 
only one trowel, a side trowel which provides the desired shape, 
smoothness and accuracy for the side surface of the rim, with the shape of 
the top surface depending on the extrusion nozzle. The side trowel could 
be changed in position to also provide a shape for the top surface. 
However, the preferred embodiment utilizes both a top trowel and a side 
trowel. 
After the rim has been formed utilizing the extrusion assembly 22, the area 
enclosed by the rim is filled using the nozzle 31 to complete the layer. 
Then the process is repeated to produce the next layer. 
An important feature of the apparatus and process of the invention is the 
ability to create smooth and accurate surfaces at relatively high speed. 
The utilization of the trowels enables rapid creation of smooth object 
surfaces with great accuracy. Utilization of the now conventional computer 
control for positioning the nozzle provides creation of smooth and 
accurate surfaces which may be planar or which may have complicated free 
form shapes. The layering method permits creation of various surface 
shapes using only the two trowels, instead of a variety of tools needed in 
more traditional sculpturing and plastering. 
Internal walls 57 can be extruded within each layer to create square or 
other shapes of hatches 58, as shown in FIG. 4. The hatching process may 
be useful for large objects since with some materials curing may start 
before the liquid filler material spreads over the entire area. With the 
hatching step, each hatch is separately filled with the construction 
material, allowing more control of the spread and solidification of the 
material. Also, the hatching method can be utilized for concurrent 
extrusion of rims and pouring of filler. 
The area pouring nozzle 31 may be moved by the positioning system to 
various locations within the area. A control system for controlling the 
position and pouring from the nozzle 31 is illustrated in FIG. 5. 
A filling sensor system 61 is carried on the Y axis on arm 62 of the 
positioning system for the nozzle 31, with a probe tip 63 positioned 
beside the nozzle 31. The system includes a chamber 64 with an air inlet 
65 and adjustment valve 66, and an air outlet 67 with a fan 68 driven by a 
motor 69. The probe tip 63 is also connected to the chamber 64 by a line 
69. A pressure sensor 70 is connected to the chamber 64 and provides a 
pressure reading for a control unit 71 which functions to shut off the 
valve 35 feeding material to the nozzle 31, when the sensed pressure drops 
below a predetermined value. 
In operation, air is fanned out of the chamber 64 while the sensor 70 
registers the air pressure in the chamber. As the area enclosed by the rim 
fills, the top layer of the surface of the poured liquid approaches the 
probe tip 63 and the flow of air into the chamber reduces, with a 
corresponding drop in sensed chamber pressure. 
Pouring of liquid into the area to be filled through the nozzle 31 is 
stopped when the sensed pressure corresponds to the desired liquid surface 
level. The filling of the enclosed area may be performed after each rim is 
produced, or may be performed after several layers of rim are completed. 
If desired, the filling nozzle 31 may be positioned adjacent the extrusion 
nozzle 51 for movement by a single X, Y, Z motion control mechanism, 
alternatively extruding a rim and filling the enclosed area. Of course, 
the probe tip 63 could be supported by a separate position control system 
rather than being carried by the same system which supports the nozzle 31. 
Ordinarily, this would merely complicate the mechanism without achieving 
any particular advantage. 
One important characteristic of the extrusion process of the present 
invention is that the wall surface of the rim that faces the internal part 
of the object does not need to have a controlled shape, since it will be 
covered and bonded with the poured liquid. Therefore, regardless of the 
variations in the rate of extrusion, the outer and top sides of the 
extruded wall will be accurately controlled by the trowels. This allows 
for a less accurate and less elaborate extrusion mechanism which may be 
much less expensive than the mechanisms used in the current robotically 
guided extrusion machines. Note that in the current robotically guided 
extrusion system the width of each section created by one pass of 
extrusion has to be accurately controlled, since the entire surface of the 
layer is created using zigzagged extrusion passes that have to be 
perfectly adjacent with no gap between them. 
It should also be noted that when a hatching configuration of FIG. 4 is 
used, the shapes of both sides of the internal walls are unimportant, as 
they are later covered and bonded with liquid material. Therefore, when 
extruding internal walls the side trowel is not required. Also a plurality 
of the pouring nozzles 31 may be used to fill a plurality of areas 
simultaneously. 
When a filling material is used in the paste state, the area may be filled 
by injection. FIG. 6 shows an injection assembly 74 whereby each hatch or 
area 58 is individually filled by injection with the paste material. 
Preferably the assembly 74 includes a plate 74A which is larger than the 
enclosed area and rests on the rim. After each injection the injection 
nozzle makes a horizontal move (in any direction) to disconnect the 
injected material from the material inside the injection nozzle. 
An alternative and simpler configuration for the extrusion nozzle 31 and 
top and side trowels 45, 46 is shown in FIG. 7. The nozzle 31 and the top 
trowel 45 are carried on a mounting block 75. The side trowel 46 is 
carried on guide rods 76 moving through the mounting block, with 
retraction springs 77 normally holding the lower edge of the side trowel 
above the bottom surface of the top trowel. A solenoid 78 or other drive 
mechanism such as a stepper motor, is carried on the mounting block 75 and 
when desired, pushes the side trowel downward to the position shown in 
FIG. 7. In this configuration, the side trowel is pushed downward when 
needed for forming a side wall, and is retracted upward when the nozzle is 
forming a wall of a hatch. Movement of the nozzle in the direction A is 
utilized for extruding an external wall and movement in direction B is 
utilized for extruding an internal wall of a structure such as is shown in 
FIG. 4. This operation is shown in FIGS. 8A and 8B. In FIG. 8A, the side 
trowel 46 is extended downward and the nozzle is moving into the paper, 
extruding a rim with a shaped side wall and a shaped top. In FIG. 8B, the 
side trowel 46 is retracted upward and the nozzle is moved sideways 
forming an internal wall with a shaped top, with no concern for side 
shaping. 
FIGS. 9A and 9B are a side perspective view and a top view, respectively, 
illustrating the forming of a straight wall or rim 29. The nozzle assembly 
can be rotated about the vertical nozzle access to provide other contours 
such as the concave shape shown in FIGS. 10A and 10B, and the convex shape 
shown in FIGS. 11A and 11B. Where adhesion of the construction material to 
a trowel is a problem, a coating of a non-stick synthetic resin polymer 
material, such as Teflon, may be utilized on the trowel surface. 
A side trowel assembly with a curving trowel surface is illustrated in FIG. 
15 and FIGS. 16A, 16B and 16C. This configuration provides a doubly curved 
convex or concave surface, such as exists as the outside and inside walls 
of a sphere. A side trowel 81 is formed of a sheet of flexible material, 
such as a thin steel sheet, and has an edge 82 and an opposite edge 83. A 
non-flexible section 84 is joined to the trowel 81 at the edge 83, with a 
spring 85 connected to the section 84. The spring 85 is positioned between 
the section 84 and a support plate 86. In the embodiment illustrated, the 
spring is normally in the expanded position of FIG. 16C and is pulled to 
the partially compressed position of FIG. 16A and the compressed position 
of FIG. 16B by a cable 87 in a sheath 88, for controlling the shape of the 
trowel 81. Alternatively, the spring 85 may be normal in the position of 
FIG. 16B and is extended to the positions of FIGS. 16A and 16C by a push 
rod which replaces the cable 87. 
The support plate 86 positions the trowel edge 82 at an edge of the top 
trowel 45, as seen in FIG. 16A. The support plate 86 is carried on arms 89 
attached to the extrusion assembly 22 for movement with the X arm 23. 
The major advantages of the present invention include: 
Surface Quality: Current additive processes generally generate objects in 
which all surfaces lack smoothness and the thickness of the fabrication 
layers is evident on them. Surface quality in the current methods is 
especially poor in oblique surfaces since they exhibit an obvious 
staircasing. Since the surface geometry in the new method is controlled by 
smooth trowels the positions of which are accurately controlled by 
computer, the object surfaces in the new method have a quality which is 
unprecedented in the rapid prototyping field. 
Speed: In the current robotically guided extrusion approach the entire 
volume of the object must be scanned by the extrusion nozzle at the slow 
extrusion speed. As a result, it may take several hours to build even a 
small object, e.g., 5 hours for a 10 cubic centimeter object. The new 
method, on the other hand, creates only the periphery of each 
two-dimensional cross section and possibly a few walls for internal 
hatches using extrusion. Therefore, the time for the slow process of 
extrusion is dramatically reduced in the new method. 
Another factor that impacts the speed of the new method is the layer 
thickness which may be variable and, in average, much larger than the 
usual layer thickness in other layering methods. The current photocuring 
techniques do not permit thick layers due to the curing penetration depth 
of the laser beam and ultraviolet flood lamp. The robotically guided 
extrusion cannot make thick layers since the external surfaces of the 
object will be very rough and inaccurate when thick volumes of material 
are extruded. The trowel system used in the new method allows for accurate 
and smooth layer edges regardless of the layer thickness. 
Materials Used: The new method can use thermoplastics, and photopolymers as 
well as many other materials that are currently not used in rapid 
prototyping, e.g., plaster, cement, clay, concrete, etc. Another property 
in the new method is the possibility of feeding the extrusion nozzle or 
the pouring outlet from various input ports to eject a variety of 
materials or mixtures of materials, e.g., resins, to create various colors 
and other physical properties. 
If some of the new system components, i.e., extrusion nozzle, trowels, and 
pouring mechanism, are made out of strong and high temperature resistant 
materials such as tungsten, then a variety of metals and alloys may be 
used to create metallic parts with accuracies comparable to those of parts 
produced by metal cutting or die casting processes. 
Structural Properties: The structural properties of the current additive 
methods are generally not very good. This is mainly due to the bonding 
problems related to the geometry of solidified elements. For example, in 
laser photocuring the parabolic profile of a laser beam results in 
microscopic dispersal of cured regions in an uncured matrix. Likewise, in 
the robotically guided extrusion method, the cylindrical profile of 
extruded material may leave air gaps between various extruded depositions. 
In the new method each rectangular, honeycomb, or free form section of 
each layer is cured in its entirety. This results in better material 
properties. In addition, this process allows for mixing the resin with 
short fibers or other filler materials to reduce curing distortion and 
create strong composites. Another advantage of the new method is that 
better bonding between successive layers results as each layer is poured 
or injected on the top of the previous layer which is freshly solidified 
and is prone to near-perfect bonding. 
Large Object Fabrication: Current layering methods of automated fabrication 
generally apply to small parts due to limitations in one or more 
components of the system used. For example, in selective photocuring the 
size of the area that can be effectively scanned by a laser beam is 
limited, and in flood lamp photomasking there is a practical limitation on 
the size of the mask. In the new method large objects such as furniture 
pieces, car bodies, boats, and building construction components, e.g., 
doors, windows, etc, may be built by controlling the large versions of the 
extrusion and pouring mechanisms by large gantry type robots. Conventional 
extrusion machines, such as those used in plastic extrusion, may be used 
in the new process for extruding various types of materials such as 
fiberglass. 
Photocuring Without Laser or Masks: When using photopolymers in the 
conventional photocuring techniques, expensive laser generators or mask 
making processes, and a process of vacuuming uncured polymer lakes in 
various parts of each cured polymer layer are needed. The new technique 
allows the use of photocuring using one or more flood lamps without the 
need for mask making, since each layer of photopolymer liquid is contained 
by the extruded layer edges or rim in the new method. 
Overhang Structures Fabrication: The pivoting side trowel design in the new 
method allows for fabrication of overhang sections that are not directly 
possible by other rapid prototyping methods. 
Mold Making for Casting: The new method may be effectively used to create 
the internal surfaces of casting molds. For example, plaster paste may be 
used for extrusion of layer walls. The side trowel can be used for forming 
the inner, instead of the outer, surface of the external layers walls. 
Various types of materials may be poured within the layer walls. For 
example, if photopolymer resin is poured within the wall of each layer, 
then at the end of the process a complete polymer part with smooth 
surfaces will be created within a thin plaster shell which can be easily 
separated. 
Lower Machine Cost: Compared to the current commercial machines that can 
match the precision (none will be able to match the surface quality) of 
the new process, it is expected that the commercial machines based on the 
new process will be significantly less expensive. The current processes 
that may be able to match the precision of the new process are selective 
photocuring processes that require either expensive laser generators, or 
expensive mask making modules. The most expensive part of the machines 
designed for the new process will be the conventional motion control 
mechanisms that are commonly used in the numerical control machines and 
industrial robots.