Rapid prototyping and tooling techniques allow for the quick fabrication of prototypes and tools with minimal lead time based on CAD models. Stereolithography is one of the earliest techniques and works by curing liquid photopolymer resin layer-by-layer with a laser. Multijet modeling is similar but uses inkjet print heads to deposit photopolymer layers. Selective laser sintering works by using a laser to sinter powder materials layer-by-layer. Fused deposition modeling extrudes thermoplastic filaments layer-by-layer. Together these additive techniques provide fast and flexible options for prototyping and manufacturing.

1. By
V. THULASIKANTH
Assistant Professor
Mechanical Engineering Department
vtkvsk@gmail.com
1
Rapid Prototyping and Tooling

2. Rapid Prototyping and Tooling
In the development of a new product, there is a need to produce a single
prototype, of a designed part or system before allocating large amounts of capital
to new production facilities or assembly lines.
Consequently, a working prototype is needed for design evaluation and
troubleshooting before a complex product or system is ready to be produced and
marketed.
The traditional method of fabricating a prototype part is machining, which can
require significant lead times.
A virtual prototype, which is a computer model of the part design on a CAD
system, may not be adequate for the designer to visualize the part.
It certainly is not sufficient to conduct real physical tests on the part, although it
is possible to perform simulated tests by finite element analysis or other methods.

3. Rapid Prototyping (RP) is a family of fabrication methods to make engineering
prototypes in minimum possible lead times based on a computer-aided design (CAD)
model of the item.
RP technologies, a solid physical part can be created in a relatively short time
The designer can therefore visually examine and physically feel the part and begin to
perform tests and experiments to assess its merits and shortcomings.
Rapid prototyping serves as an important tool for visualization and for concept
verification.
With suitable materials, the prototype can be used in subsequent manufacturing
operations to produce the final parts. Sometimes called direct prototyping, this approach
can serve as an important manufacturing technology.
Rapid-prototyping operations can be used in some applications to produce actual
tooling for manufacturing operations. Thus, one can obtain tooling in a matter of a few
days.
Advantages of RPT

4. Rapid-prototyping processes can be classified into three major groups:
Subtractive: As the names imply, subtractive processes involve material
removal from a workpiece that is larger than the final part.
Virtual processes: Use advanced computer-based visualization
technologies.
Additive processes: build up a part by adding material incrementally to
produce the part.
Classification of RPT

5. Subtractive Processes
The traditional method of fabricating a prototype part is machining, which can
require significant lead times.
This approach requires skilled operators using material removal by machining
and finishing operations one by one-until the prototype is completed.
To speed the process, subtractive processes increasingly use computer-based
technologies such as the following:
Computer-based drafting packages, which can produce three-dimensional
representations of parts.
Interpretation software, which can translate the CAD file into a format usable
by manufacturing software.
Manufacturing software, which is capable of planning the operations required
to produce the desired shape.
Computer-numerical-control (CNC) machinery with the capabilities necessary
to produce the parts.

6. If a prototype is required only for the purpose of shape verification, a soft material
(usually a polymer or a wax) is used as the workpiece in order to reduce or avoid any
machining difficulties.
The material intended for use in the actual application also can be machined, but
this operation may be more time consuming, depending on the machinability of the
material.
Depending on part complexity and machining capabilities, prototypes can be
produced in a few days to a few weeks.
Other starting materials can also be used, such as wood, plastics, or metals (e.g., a
machinable grade of aluminum or brass).
The CNC machines used for rapid prototyping are often small, and the terms desktop
milling or desktop machining are sometimes used for this technology.
Maximum starting block sizes in desktop machining are typically 180 mm (7 in) in the
x-direction, 150 mm (6 in) in the y-direction, and 150 mm (6 in) in the z-direction

7. VIRTUAL PROCESSES
Virtual prototyping is a software-based method that uses advanced graphics
and virtual-reality environments to allow designers to view and examine a part
in detail.
This technology, also known as simulation-based design, uses CAD packages
to render a part such that, in a 3-D interactive virtual environment, designers
can observe and evaluate the part as it is being drawn and developed.
Virtual prototyping has been gaining importance, especially because of the
availability of low-cost computers and simulation and analysis tools.

8. Additive operations require elaborate software.
The first step is to obtain a CAD file description of the part.
The computer then constructs slices of the three-dimensional part.
Each slice is analyzed separately, and a set of instructions is compiled in order to
provide the rapid-prototyping machine with detailed information regarding the
manufacture of the part.
Starting Materials in Material Addition RP
1. Liquid monomers that are cured layer by layer into solid polymers
2. Powders that are aggregated and bonded layer by layer
3. Solid sheets that are laminated to create the solid part
Additive rapid-prototyping operations all build parts in layers, which are
typically 0.1 to 0.5 mm thick and can be thicker for some systems.
Additive Processes

10. The common approach to prepare the control instructions (part program) in all of the
current material addition RP techniques involves the following steps
1.Geometric modeling. This consists of modeling the component on a CAD system to
define its enclosed volume.
Solid modeling is the preferred technique because it provides a complete and
unambiguous mathematical representation of the geometry.
For rapid prototyping, the important issue is to distinguish the interior (mass) of the part
from its exterior, and solid modeling provides for this distinction.
2. Tessellation of the geometric model. In this step, the CAD model is converted into a
format that approximates its surfaces by triangles or polygons, with their vertices arranged
to distinguish the object’s interior from its exterior.
The common tessellation format used in rapid prototyping is STL, which has become the de
facto standard input format for nearly all RP systems.

11. 3. Slicing of the model into layers
In this step, the model in STL file format is sliced into closely spaced parallel
horizontal layers. Conversion of a solid model into layers is illustrated.
These layers are subsequently used by the RP system to construct the
physical model.
By convention, the layers are formed in the x-y plane orientation, and the
layering procedure occurs in the z-axis direction.
For each layer, a curing path is generated, called the STI file, which is the path
that will be followed by the RP system to cure (or otherwise solidify) the
layer.

12. There are many different ways to 3D print an object. But nearly all of them utilize
computer aided design (CAD) files.
CAD files are digitalized representations of an object. They're used by engineers
and manufacturers to turn ideas into computerized models that can be digitally
tested, improved and most recently, 3D printed.
In 3D printing or additive manufacturing CAD files must be translated into a
"language," or file type, that 3D printing machines can understand.
Standard Tessellation Language (STL) is one such file type and is the language
most commonly used for stereolithography, as well as other additive
manufacturing processes.
Since additive manufacturing works by adding one layer of material on top of
another, CAD models must be broken up into layers before being printed in three
dimensions.
STL files "cut up" CAD models, giving the 3D printing machine the information it
needs to print each layer of an object.
Production of STL file from 3d cad model

13. What is a STL File?
A STL file is a format used by Stereolithography software to
generate information needed to produce 3D models on
Stereolithography machines. In fact, the extension "stl" is said to be
derived from the word "Stereolithography."
A slightly more specific definition of a stl
file is a triangular representation of a 3D
object. The surface of an object is broken
into a logical series of triangles (see
illustration at right). Each triangle is
uniquely defined by its normal and three
points representing its vertices.
The stl file is a complete listing of the xyz coordinates of the vertices and normals
for the triangles that describe the 3D object.

14. Often a stl file can be termed "bad"
because of translation issues.
In many CAD systems, the number of
triangles that represent the model can be
defined by the user. If too many triangles
are created, the stl file size can become
unmanageable.
If too few triangles are created, curved
areas are not properly defined and a
cylinder begins to look like a hexagon (see
example below).
When creating a stl file, the goal is to achieve a balance between unmanageable file size
and a well-defined model with smooth curved geometries.

15. How to create a STL file?
Most CAD software packages offer stl conversion add-ins.
If we have access to conversion software, stl translation is relatively simple as
long as you have a clean-surfaced 3D model and a high-end computer.
Traditionally when converting to a stl file, the user is given several options for
resolution (sometimes called chord height, triangle tolerance, etc.). Depending
upon the size of the model, the geometry of small details, and the overall
curvature of the part, the tolerance can typically be set to .001 inch for average
models.
Small parts or models with fine details may require a tighter tolerance.

16. Additive Process techniques include;
Stereolitliograpliy,
MultiJet/ PolyJet modeling,
Fused deposition modeling,
Ballistic-particle manufacturing,
3D printing,
Selective laser sintering,
Electron-beam and
Laminated-object manufacturing.

17. Stereolithography This was the first material addition RP technology,
dating from about 1988 and introduced by3DSystems, Inc. based on the work of
inventor CharlesHull.
(STL) is a process for fabricating a solid plastic part out of a photosensitive
liquid polymer using a directed laser beam to solidify the polymer
Part fabrication is accomplished as a series of layers, in which one layer is added
onto the previous layer to gradually build the desired three dimensional
geometry.
The stereolithography apparatus consists of
(1) a platform that can be moved vertically inside a vessel containing the
photosensitive polymer
(2) a laser whose beam can be controlled in the x-y direction.
At the start of the process, the platform is positioned vertically near the surface
of the liquid photopolymer, and a laser beam is directed through a curing path
that comprises an area corresponding to the base (bottom layer) of the part.

18. STL (STereoLithography) is a file format native to the stereolithography CAD software
created by 3D Systems. STL is also known as Standard Tessellation Language.
This file format is supported by many other software packages; it is widely used for rapid
prototyping and computer-aided manufacturing.

20. This and subsequent curing paths are defined by the STL file (step 3 in
preparing the control instructions described in the preceding).
The action of the laser is to harden (cure) the photosensitive polymer where
the beam strikes the liquid, forming a solid layer of plastic that adheres to the
platform.
When the initial layer is completed, the platform is lowered by a distance
equal to the layer thickness, and a second layer is formed on top of the first by
the laser, and so on.
Before each new layer is cured, a wiper blade is passed over the viscous
liquid resin to ensure that its level is the same throughout the surface.
Each layer consists of its own area shape, so that the succession of layers,
one on top of the previous, creates the solid part shape.
Each layer is 0.076 to 0.50mm thick. Thinner layers provide better resolution
and allow more intricate part shapes; but processing time is greater.

21. After all of the layers have been formed, the photopolymer is about 95% cured.
The piece is therefore ‘‘baked’’ in a fluorescent oven to completely solidify the
polymer.
Excess polymer is removed with alcohol, and light sanding is sometimes used to
improve smoothness and appearance.

22. Photopolymers are typically acrylic [13], although use of epoxy for STL has
also been reported.
The starting materials are liquid monomers. Polymerization occurs upon
exposure to ultraviolet light produced by helium-cadmium or argon ion lasers.
 Scan speeds of STL lasers typically range between 500 and 2500 mm/s.
The time required to build the part by this layering process ranges from 1
hour for small parts of simple geometry up to several dozen hours for complex
parts.
Other factors that affect cycle time are scan speed and layer thickness.
The part build time in stereolithography can be estimated by determining the
time to complete each layer and then summing the times for all layers.

24. A common rapid-prototyping process-one that actually was developed prior to fused-
deposition modeling-is stereolit/aography (STL). This process (Fig. 20.6) is based on the
principle of curing (hardening) a liquid photopolymer into a specific shape. A vat containing
a mechanism whereby a platform can be lowered and raised is filled with a photocurable
liquid-acrylate polymer. The liquid is a mixture of acrylic monomers, oligomers (polymer
intermediates), and a photoinitiator (a compound that undergoes a reaction upon
absorbing light).

27. Multijet/Polyjet Modeling
Multijet Modeling (MJM) or Polyjet process is similar to inkjet printing, where
print heads deposit the photopolymer on the build tray.
Ultraviolet bulbs, alongside the jets, immediately cure and harden each layer,
thus eliminating the need for any postmodeling curing that is needed in
stereolithography.
The result is a smooth surface of thin layers as small as 16µm that can be
handled immediately after the process is completed.
Two different materials are used: One material is used for the actual model,
while a second, gel-like resin is used for support Each material is simultaneously
jetted and cured, layer by layer.
When the model is completed, the support material is removed with an
aqueous solution.

28. Build sizes are fairly large, with an envelope of up to 500 X400X200 mm.
These processes have capabilities similar to those of stereolithography and use similar
resins .
The main advantages are the capabilities of avoiding part cleanup and lengthy
postprocess curing operations, and the much thinner layers produced, thus allowing for
better resolution.

29. Selective Laser Sintering
Selective laser sintering (SLS) is a process based on the sintering of nonmetallic
or (less commonly) metallic powders selectively into an individual object.
The bottom of the processing chamber is equipped with two cylinders:
I.A powder-feed cylinder, which is raised incrementally to supply powder to the
part-build cylinder through a roller mechanism.
2. A part-build cylinder, which is lowered incrementally as the part is being
formed.
First, a thin layer of powder is deposited in the part-build cylinder.
Then a laser beam guided by a process-control computer using instructions
generated by the three-dimensional CAD program of the desired part is focused
on that layer, tracing and sintering a particular cross section into a solid mass.
The powder in other areas remains loose, yet it supports the sintered portion.
Another layer of powder is then deposited; this cycle is repeated again and
again until the entire three-dimensional part has been produced.

31. The loose particles are shaken off, and the part is recovered.
The part does not require further curing-unless it is a ceramic, which has to be fired to
develop strength.
A variety of materials can be used in this process, including polymers (such as ABS, PVC,
nylon, polyester, polystyrene, and epoxy), wax, metals, and ceramics with appropriate
binders.
It is most common to use polymers because of the smaller, less expensive, and less
complicated lasers required for sintering.
With ceramics and metals, it is common to sinter only a polymer binder that has been
blended with the ceramic or metal powders.
The resultant part can be carefully sintered in a furnace and infiltrated with another
metal if desired.
Thickness 0.075 to 0.50mm

32. Fused deposition modeling

33. In the fused-deposition-modeling process a gantry robot controlled extruder
head moves in two principal directions over a table, which can be raised and
lowered as needed.
A thermoplastic filament is extruded through the small orifice of a heated
die.
The initial layer is placed on a foam foundation by extruding the filament at a
constant rate while the extruder head follows a predetermined path.
When the first layer is completed, the table is lowered so that subsequent
layers can be superimposed.
Some parts are difficult to manufacture directly, because once the part has
been constructed up to height a, the next slice would require the filament to be
placed in a location where no material exists beneath to support it.
The solution is to extrude a support material separately from the modeling
material.
The use of such support structures allows all of the layers to be supported by

35. The support material is produced with a less dense filament spacing on a layer, so it is
weaker than the model material and can be broken off easily after the part is completed.
The layers in an FDM model are determined by the extrusion-die diameter, which
typically ranges from 0.050 to 0.12 mm.
This thickness represents the best achievable tolerance in the vertical direction. In the
x-y plane, dimensional accuracy can be as fine as 0.025 mm-as long as a filament can be
extruded into the feature.
A variety of polymers are available for different applications. Flat wire metal deposition
uses a metal Wire instead of a polymer filament, but also needs a laser to heat and bond
the deposited Wire to build parts.
Close examination of an FDM-produced part will indicate that a stepped surface exists
on oblique exterior planes.
If this surface roughness is objectionable, a heated tool can be used to smooth the
surface, the surface can be hand sanded, or a coating can be applied (often in the form of
a polishing Wax ).
The overall tolerances are then compromise d unless care is taken in these finishing
operations.

36. Electron-beam Melting
A process similar to selective laser sintering and electron-beam welding
electron-beam melting uses the energy source associated with an electron
beam to melt titanium or cobalt-chrome powder to make metal prototypes.
The workpiece is produced in a vacuum; the part build size is limited to
around 200 x200 x180 mm. Electron-beam melting (EBM) is up to 95% efficient
from an energy standpoint (compared with 10-20% efficiency for selective laser
Sintering)
The titanium powder is actually melted and fully dense parts can be
produced. A volume build rate of up to 60 cm3
/hr can be obtained, with
individual layer thicknesses of 0.05 0-0.200 mm.
Hot isostatic pressing also can be performed on parts to improve their fatigue
strength.
Although applied mainly to titanium and cobalt-chrome to date, the process is
being developed for stainless steels, aluminum, and copper alloys.

38. In the three-dimensional-printing (3DP) process, a print head deposits an
inorganic binder material onto a layer of polymer, ceramic, or metallic powder.
This RP technology was developed at Massachusetts Institute of Technology.
Three-dimensional printing (3DP) builds the part in the usual layer-by-layer
fashion using an ink-jet printer to eject an adhesive bonding material onto
successive layers of powders.
The binder is deposited in areas corresponding to the cross sections of the solid
part, as determined by slicing the CAD geometric model into layers.
The binder holds the powders together to form the solid part, while the
unbonded powders remain loose to be removed later.
While the loose powders are in place during the build process, they provide
support for overhanging and fragile features of the part.
When the build process is completed, the part is heat treated to strengthen the
bonding, followed by removal of the loose powders.

39. To further strengthen the part, a sintering step can be applied to bond the
individual powders.
The part is built on a platform whose level is controlled by a piston.
Process will be as follows
(1)A layer of powder is spread on the existing part-in-process.
(2)An ink-jet printing head moves across the surface, ejecting droplets of binder
on those regions that are to become the solid part.
(3)When the printing of the current layer is completed, the piston lowers the
platform for the next layer.
Starting materials in 3DP are powders of ceramic, metal, or cermet, and binders
that are polymeric or colloidal silica or silicon carbide.
Typical layer thickness ranges from 0.10 to 0.18 mm. The ink-jet printing head
moves across the layer at a speed of about 1.5 m/s, with ejection of liquid
binder determined during the sweep by raster scanning.

40. The sweep time, together with the spreading of the powders, permits a cycle time per
layer of about 2 seconds

41. Laminated-Object Manufacturing
Laminated-object manufacturing produces a solid physical model by stacking layers of
sheet stock that are each cut to an outline corresponding to the cross-sectional shape of a
CAD model that has been sliced into layers.
The layers are bonded one on top of the previous one before cutting. After cutting, the
excess material in the layer remains in place to support the part during building.
Starting material in LOM can be virtually any material in sheet stock form, such as paper,
plastic, cellulose, metals, or fiber-reinforced materials.
Stock thickness is 0.05 to 0.50 mm .In LOM, the sheet material is usually supplied with
adhesive backing as rolls that are spooled between two reels.
Otherwise, the LOM process must include an adhesive coating step for each layer.
The data preparation phase in LOM consists of slicing the geometric model using the STL
file for the given part.
The slicing function is accomplished by LOMSliceTM
, the special software used in
laminated-object manufacturing. Slicing the STL model in LOM is performed after each
layer has been physically completed and the vertical height of the part has been
measured.

44. (1) LOMSliceTM computes the cross-sectional perimeter of the STL model based on the
measured height of the physical part at the current layer of completion.
(2)A laser beam is used to cut along the perimeter, as well as to crosshatch the exterior
portions of the sheet for subsequent removal.
The laser is typically a 25 or 50 W CO2 laser. The cutting trajectory is controlled by means
of an x-y positioning system. The cutting depth is controlled so that only the top layer is
cut.
(3) The platform holding the stack is lowered, and the sheet stock is advanced between
supply roll and take-up spool for the next layer.
The platform is then raised to a height consistent with the stock thickness and a heated
roller moves across the new layer to bond it to the previous layer.
The height of the physical stack is measured in preparation for the next slicing
computation by LOMSliceTM
.
When all of the layers are completed, the new part is separated from the excess external
material using a hammer, putty knife, and wood carving tools.
LOM part sizes can be relatively large among RP processes, with work volumes up to 800
mm 500 mm by 550 mm (32 in 20 in 22 in). More common work volumes are 380 mm 250
mm 350 mm

45. Solid-ground Curing or solid based curing
This process is unique in that entire slices of a part are manufactured at one time. As a result,
a large throughput is achieved, compared with that from other rapidprototyping processes.
However, solid-ground curing (SGC) is among the most expensive processes; hence, its
adoption has been much less common than that of other types of rapid prototyping, and new
machines are not available. Basic all , the method consists of the following steps:
I. Once a slice is created by the computer software, a mask of the slice is printed on a glass
sheet by an electrostatic printing process similar to that used in laser printers. A mask is
required because the area of the slice where the solid material is desired remains transparent.
2. While the mask is being prepared, a thin layer of photoreactive polymer is deposited on the
work surface and is spread evenly.
3. The photo mask is placed over the work surface, and an ultraviolet floodlight is projected
through the mask. Wherever the mask is clear, the light shines through to cure the polymer
and causes the desired slice to be hardened.
4. The unaffected resin (still liquid) is vacuumed off the surface.
5. Water-soluble liquid wax is spread across the work area, filling the cavities previously
occupied by the unexposed liquid polymer. Since the workpiece is on a chilling plate and the
workspace remains cool, the wax hardens quickly. 6. The layer is then milled to achieve the
correct thickness and flatness.
7. This process is repeated-layer by layer-until the part is completed. Solid-ground curing has
the advantage of a high production rate, because entire slices are produced at once and two
glass screens are used concurrently. That is, while one mask is being used to expose the
polymer, the next mask already is being prepared, and it is ready as soon as the milling
operation is completed.

46. Rapid Tooling
Rapid-prototyping techniques have made possible much faster product
development times, and they are having a major effect on other manufacturing
processes.
When appropriate materials are used, rapid-prototyping machinery can produce
blanks for investment casting or similar processes, so that metallic parts can now
be obtained quickly and inexpensively, even for lot sizes as small as one part.
Such technologies also can be applied to producing molds for operations (such as
injection molding, sand and shell mold casting, and even forging), thereby
significantly reducing the lead time between design and manufacture.

47. Several methods have been devised for the rapid production of tooling (RT) by
means of rapid-prototyping processes. The advantages to rapid tooling include
the following:
1.The high cost of labor and short supply of skilled patternmakers can be
overcome.
2. There is a major reduction in lead time.
3. Hollow designs can be adopted easily so that lightweight castings can be
produced more easily.
4. The integral use of CAD technologies allows the use of modular dies with
base-mold tooling (match plates) and specially fabricated inserts. This modular
technique can further reduce tooling costs.
5. Chill- and cooling-channel placement in molds can be optimized more easily,
leading to reduced cycle times.

48. 6. Shrinkage due to solidification or thermal contraction can be compensated for
automatically through software to produce tooling of the proper size and, in
turn, to produce the desired parts.
The main shortcoming of rapid tooling is the potentially reduced tool or pattern
life (compared to those obtained from machined tool and die materials, such as
tool steels or tungsten carbides).
The simplest method of applying rapid-prototyping operations to other
manufacturing processes is in the direct production of patterns or molds.
Example : Investment casting
The individual patterns are made in a rapid-prototyping operation (in this case,
stereolithography) and then used as patterns in assembling a tree for
investment casting.
As drawn in CAD programs, the parts are usually software modified to account
for shrinkage, and it is then that the modified part is produced in the
rapidprototyping machinery.

50. Example: 3DP
3DP can easily produce a ceramic-mold casting shell or a sand mold in which
an aluminum-oxide or aluminum-silica powder is fused with a silica binder.
The molds have to be post processed in two steps: curing at around 150°C and
then firing at 1000°-1500°C.
Example: Injection Molding
Injection molding in which the mold or, more typically, a mold insert is
manufactured by rapid prototyping.
The advantage of rapid tooling is the capability to produce a mold or a mold
insert that can be used to manufacture components without the time lag
(typically several months) traditionally required for the procurement of
tooling.
Furthermore, the design is simplified, because the designer need only analyze
a CAD file of the desired part; software then produces the tool geometry and
automatically compensates for shrinkage.

51. Room-temperature vulcanizing (RTV) molding/urethane casting can be
performed by preparing a pattern of a part by any rapid-prototyping operation.
The pattern is coated with a parting agent and may or may not be modified to
define mold parting lines.
Liquid RTV rubber is poured over the pattern, and cures (usually within a few
hours) to produce mold halves. The mold is then used with liquid urethanes in
injection molding or reaction-injection molding operations
Epoxy or aluminum-filled epoxy molds also can be produced, but mold
design then requires special care.
With RTV rubber, the mold flexibility allows it to be peeled off the cured part.
With epoxy molds, the high stiffness precludes this method of part removal, and
mold design is more complicated.
Thus, drafts are needed, and undercuts and other design features that can be
produced by RTV molding must be avoided.
Other rapid-tooling approaches

52. Acetal clear epoxy solid (ACES) injection molding, also known as direct
AIM, refers to the use of rapid prototyping (usually stereolithography) to
directly produce molds suitable for injection molding.
The molds are shells with an open end to allow filling with a material such as
epoxy, aluminum-filled epoxy, or a low-melting-point metal.
Depending on the polymer used in injection molding, mold life may be as few
as 10 parts, although a few hundred parts per mold are possible.
Sprayed-metal tooling.
In this process a pattern is created through rapid prototyping.
A metal spray operation then coats the pattern surface with a zinc-aluminum
alloy. The metal coating is placed in a flask and potted with an epoxy or an
aluminum-filled epoxy material.
In some applications, cooling lines can be incorporated into the mold before
the epoxy is applied. The pattern is removed; two such mold halves are then
suitable for use in injection-molding operations.

53. Keltool process.
In the Keltool process, an RTV mold is produced based on a rapid-prototyped
pattern, as described earlier.
The mold is then filled with a mixture of powdered A6 tool steel tungsten
carbide, and polymer binder, and is allowed to cure.
The so-called green tool (green, as in ceramics and powdermetallurgy) is fired
to burn off the polymer and fuse the steel and the tungsten-carbide powders.
The tool is then infiltrated with copper in a furnace to produce the final mold.
The mold can subsequently be machined or polished to attain a superior
surface finish and good dimensional tolerances.
Keltool molds are limited in size to around 150 >< 150 >< 150 mm, so,
typically, a mold insert suitable for high-volume molding operations is
produced.
Depending on the material and processing conditions, mold life can range