1. Introduction Rapid prototyping fabricated by UV resin ...
Transcript of 1. Introduction Rapid prototyping fabricated by UV resin ...
Rapid prototypingfabricated by UV resinspray nozzles
C.C. Chang
The author
C.C. Chang is Associate Professor at the Department of
Mechanical Engineering, Kun-Shan University of Technology,
Tainan, Taiwan.
Keywords
Rapid prototypes, Resins, Spraying
Abstract
Rapid prototyping (RP) processes produce parts layer by layer
directly from 3D CAD models. Different kinds of rapid
prototyping machine (RPM) have been developed with
different mechanisms or materials. In this paper, a novel and
economic way to build the RP by means of injection nozzles
with ultra violet (UV) resins is proposed. The in-house made
RPM is constructed with two nozzles. The acrylic series is for
body material and the PU series is for the supporting
material. There are obvious boundaries since material
properties are different. Therefore, supports can be easily
removed from the main body after formation. The different
diameter of nozzles can be chosen in the system, and the
nozzles are also disposable. Besides, an interface system
generating the direct slicing from 3D CAD models and nozzle
paths for all layers is developed through PowerSOLUTION
(Delcam International, Birmingham, UK) macro commands.
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1. Introduction
In rapid prototyping (RP) technology, the
material addition methods may be divided by
the state of the prototype material before part
formation. There are liquid base, discrete
particles and solid sheets in classification.
The liquid-based technologies may entail the
solidification of a resin on contact with a laser,
the solidification of an electrosetting fluid, or
the melting and subsequent solidification of the
prototype material. The discrete-particle
processes compound powders either with a laser
or binding agents. The solid-sheet processes
maybe classified according to whether the sheets
are bonded with a laser or with an adhesive.
The most popular RP technology in the
current market may be sterolithography (SL).
This relies on a photosensitive monomer resin,
which forms a polymer when the resin exposes
to ultra violet (UV) light.
Besides, most SL systems basically use a
moving laser bean to cure resins in the
mechanism. There is another new technique
using multi-nozzles to spray resins before UV
light curing. The commercial system, Objet
(Objet Geometries, Rehovot, Israel) that uses
1536-nozzle raster jetting and two UV lamps
came to the market in 1998. InVision 3D printer
system (3D system, CA, USA) is also
announced recently. It combines 3D System’s
patented multi-jet modeling (MJM) printing
technology with an acrylic photopolymer
material.
There are still some limitations on producing
parts in SL process, such as non-linear
shrinkages, high-price equipments,
maintenances and material contaminations, etc.
In this paper, another novel and economic
way to build RP is proposed by means of
injection nozzles with UV resins. Two nozzles
are utilized to spray two different types of UV
resins, the acrylic type is for body material and
the PU type is for supporting material. Since the
material properties between body and support
are different, it is easy to seperate support from
body without impairing its surface. The UV
lamp is positioned on top of the platform and is
controlled by a shutter. After the contour and
Rapid Prototyping Journal
Volume 10 · Number 2 · 2004 · pp. 136–145
q Emerald Group Publishing Limited · ISSN 1355-2546
DOI 10.1108/13552540410527006
Received: 6 January 2003
Revised: 15 October 2003
Accepted: 10 November 2003
136
interior of the layer are sprayed with UV resin,
UV resin is instantly cured in a 2D cross-section
that can reduce distortion compared to point-
to-point curing process. Different diameter of
nozzles can be chosen in the system, and the
nozzles are disposable. Besides, an interface is
written to produce the direct slicing from 3D
CAD models and the nozzle paths for all layers
in PowerSOLUTION environments.
2. System structure
An in-house made UVRS-RP (UV resin spray-
RP) machine is financially supported by
National Science Council (NSC, NSC89-2218-
E-168-006, 1998-2000) in Taiwan. In the
UVRS-RP machine, there are six units,
including motion control unit, UV lamp unit,
air pump unit, power supply unit, material
supply unit and nozzle mechanism unit. The
mechanism of UVRS-RP machine is shown in
Figure 1(a). The relative positions of all units
are indicated in Figure 1(b). The real
appearance of UVRS-RP machine can be found
in Figure 1(c). The detailed design of all units is
stated in the following sections.
2.1 Motion control unit
The four-axial motion card (DMC 1700, Galil
Company) is selected to drive XY-directional
platform and Z-directional elevator. The fourth
axis is reserved for rotating platform in the
future. The XY-directional platform is
controlled by two linear-stepping motors (Lp-
460 £ 460, Powerly Enterprise). The movement
of the platform is controlled by the magnetic
force and air float so that the speed of the
platform can be increased greatly (maximum,
100 mm/s). The precision is 1mm and
repeatability is 3mm in XY-directional platform
(Dimension, 460 £ 460 mm). A servomotor
(precision, 1mm) is used to control the
Z-directional movement. The mechanism of
the three directional movements in motion
control unit is shown in Figure 2.
2.2 UV lamp unit
UV lamp unit includes electrical control box,
shutter control, cooling fan, vent and UV lamp
set (Figure 3). The UV lamp (UV-Light-
GY751, max. 3 kW, UV Light Enterprise) is
positioned on the top of the platform as shown
in Figure 2. The UV-resin is instantly cured in
Figure 1
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a 2D cross-section layer by layer in the
exposure of UV light. Three different powers,
100 per cent(3.6 kW), 75 per cent(2.7 kW),
and 50 per cent(1.8 kW) are adjustable.
The minimum exposure time of 0.1 s can
be reached. All input signals are controlled
through computer programming.
2.3 Air supply unit
Air pressure is supplied by air pump. Pressure
valves are used to adjust the flow rate of air to
support and move the XY-directional platform,
to control the switch and timing of lamp shutter,
to control the valve of nozzles and amount of
resins.
2.4 Power supply unit
In the UVRS-RP machine, there are three
different sets of power supply (AC 220 V, AC
110 V, and DC 24 V). The AC 220 V is supplied
for the lamp unit. The AC 220 V is transformed
into AC 110 V for computer unit, XY-
directional platform, and Z-directional
servomotor. The DC 24 V is supplied for all
sensors.
2.5 Material supply unit
Material supply unit includes vacuum mixer,
resin vat, and pipes as shown in Figure 4. A lot
of materials, such as PU, PE, ABS, acrylic, etc.,
can be selected as a UV photo curing. This relies
on a photosensitive monomer resin, which
forms a polymer and solidifies when exposed to
UV light. PU resin is chosen as the body
material and acrylic resin as supporting
material. The bubble of resin is obviously
eliminated after vacuum mixing as shown in
Figure 4(c).
Figure 2 The mechanism of three directional movement in the motion control unit
Figure 3 UV lamp unit included (a) shutter, (b) UV lamp set, (c) cooling fan and
vent, and (d) electrical control box
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2.6 Nozzle unit
The mechanism of nozzle unit is shown in
Figure 5(a). The switch of thimble controls the
flow-rate of resin. Two nozzles (TS 5420,
Techcon Systems) are used. One nozzle is to
spray the body material, and the other is to spray
the supporting material. Nozzle diameter ranges
from 0.06 to 4.5 mm. Nozzle pressure is in the
range of 0-10 kg/cm2 and the maximum flow-
rate is 1,680 ml/min. The diameter of nozzles
is changeable, and the nozzles are disposable
(Figure 5(b)). Here, it is easier to maintain
and arrange different diameter of nozzles for
different paths like Automatic Tool Changer
(ATC) mechanism of CNC machining center.
3. Processes of fabricating RP
The processes of RP fabricating are not only to
calculate nozzle paths but also to cure UV resin
through machine movement. The procedure of
calculating nozzle paths is shown in Figure 6(a).
The 3D CAD model has to be sliced first and
then contours of all layers are translated into
G-Codes of nozzle paths. The G-Codes format
can be accepted by most of motion control cards
in the current market.
Basically, the curing process comprises of the
following steps.
(1) At first, the nozzle sprays the cross-sectional
area of the body by the acrylic resin in a
layer.
(2) After hatching the area of the body, it is
instantly cured by UV light. The planer
deflection and the distortion can be reduced
since it is in the 2D contour curing.
(3) If supports must be built, another nozzle
sprays the PU resin to fill up the support
area. Then, the support is also cured by the
UV light.
The nozzles will be raised by one pitch distance
in the Z-direction and repeat steps (1)-(3) until
the model is fully built.
The procedure in curing steps is shown
in Figure 6(b). Since the properties of the
materials between the body and the support
are different, obvious boundaries existed
in two different materials. Therefore, the
support material can be easily separated by
light force.
Figure 4 Material supply unit included (a) vacuum mixer, (b) resin vat, and
(c) comparison of the resin after vacuum mixing
Figure 5
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4. Software interfaces
4.1 Direct slicing from 3D CAD models in
PowerSHAPE
The errors in STL format to approximate the
3D CAD model sometimes can not be
neglected. It also consumes too much
computing time in the slicing process.
Therefore, in this technology, a 3D CAD model
is directly sliced to avoid approximation errors.
PowerSHAPE is the CAD module of
PowerSOLUTION. The 3D CAD models can
be built through the PowerSHAPE. We develop
an interface by PowerSHAPE variables with VB
languages without changing the macro file, since
it is variable parameters in the interface. The
interface is to slice the model automatically and
directly in PowerSHAPE environment. The
flow chart is shown in Figure 7. The dialog box
of slicing interface is shown in Figure 8(a).
There are two main parameters, the slicing
thickness and slicing number in the left hand
side of Figure 8(a). When the slicing pitch is
known, 2D contours of the model can be
Figure 6
Figure 7 The flow chart of automatic and direct slicing algorithm by VB
language
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automatically generated as shown in the right
hand side of Figure 8(a).
4.2 Motion path of the nozzle from
PowerMILL
The motion paths of nozzles are generated in
PowerMILL, which is the CAM module of
PowerSOLUTION. The main purpose of this
module is to produce the G-code of nozzle
paths. The main difference between the
cutting tool and nozzle is the movement in the
Z-direction. The nozzle is to inject materials on
each layer from bottom to top, while the cutting
tool is to mill materials from top to bottom.
Nozzle paths of each layer are generated and the
motion code is transmitted to the controller
(DMC 1700, Galil Company) to drive the
nozzles. Another interface is generated for
translating G-codes to special codes, which can
be accepted by DMC 1700.
All interfaces are successfully developed to
apply in the UVRS-RP machine. An example
for producing nozzle paths directly from 3D
CAD model for all slicing layers is shown in
Figure 8(b). The yellow lines are nozzle paths of
all layers in the right hand side. The different
diameter of nozzles can be chosen in the left
hand side. The red lines are the paths of nozzle
in the Z-direction from bottom to top in
Figure 8(b).
4.3 Support calculation
If the part has the overhanging or inner
structure, the supports must be built in
fabricating RP. The support structure has to
be considered in most sterolithography
systems. When a slicing cross-sectional area of
a 3D body is larger than the next one, the
supports have to be constructed. As shown in
Figure 9(a), the differences between the two
areas are in fact the supporting area. The
algorithm of calculating the supporting area is
indicated in Figure 9(b).
5. Results and discussion
As shown in Figure 10(a), the boundaries of
both body and support material are quite
smooth by using direct slicing scheme. The
support material (PU resin) is easy to be
separated from the body material (acrylic resin)
since the materials are different, as shown in
Figure 10(b). PU resin is soft and can be bent in
room temperature while acrylic resin is hard and
rigid, as shown in Figure 10(c).
An example of RP with Chinese character,
shown in Figure 11, is completely constructed
by the UVRS-RP machine in 10 min. The speed
is quicker than the traditional machining. In
Figure 12(a), the hatch spacing is 20 per cent
Figure 8
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overlap and half a phase is shifted in the second
layer, so these two ways ensure the accuracy in
height and width control. The cured lines of
photopolymer are shown in Figure 12(b) and
the cured layers in vertical direction are shown
in Figure 12(c). The model of a human body is
fabricated by UV-RP machine as shown in
Figure 13.
The advantages of UV-RP machine with direct
slicing scheme are as follows.
(1) For direct slicing from 3D CAD model, the
errors and mistakes can be reduced greatly,
and the speed of calculation can be
increased.
(2) The nozzles can be arranged like machining
tools (ATC). Therefore, it is possible to
Figure 9
Rapid prototyping fabricated by UV resin spray nozzles
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assign nozzles of different diameter on
different paths. For example, a smaller
nozzle can be applied on spraying the
boundary for each layer, while the larger
nozzle can be used to fill up the interior of
the boundary. In this way, both accuracy
and speed can be greatly increased for RP
process.
(3) The distortion and deflection can
be reduced in surface photo-curing
process, compared to point-to-point
curing process.
(4) For most printing type RP makers, such as
Sanders, Actua, 3D Printing, etc., the
nozzle is expensive and the life of the
nozzle is limited. The disposable nozzle
is easy to maintain and price is very
cheap here.
(5) Generally, it is difficult to write control
system and interface in developing the RP
system in a short time. It is an easy way to
develop the interface for different RP
machine through macro commands in
PowerSOLUTION.
Also, there are still a lot of limitations existed in
the scheme and RP machine such as the
following.
(1) The control system and translation
interfaces have to be mounted in
PowerSOLUTION environment.
(2) The amount of material sprayed is hard
to predict in the beginning and ending
periods of all paths. This will affect the
accuracy of the RP model. Therefore,
the right timing of on-and-off switch has
to be found.
(3) The support material in the inner structure
is difficult to be removed cleanly.
(4) The concentration in material depends on
many parameters and is hard to control.
Taguchi Methods is used to find optimal
conditions in the research.
Figure 10 The part (acrylic resin) and support (PU resin) material cured by the UV lamp in one layer
Figure 11 The example of RP with Chinese character (nozzle
diameter: 0.36 mm, UV exposure time: 0.5 s, UV light power:
1.8 kW, and total finishing time: 10 min)
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6. Conclusion
In this paper, a novel and economic way is
proposed to fabricate RP through nozzle spray
with UV resins. It performs well by using direct-
slicing scheme and arranging nozzle paths
through PowerSOLUTION environment.
In commercial systems, such as Objet and
InVision, the technique of resin spraying by
multi-nozzle jetting is used. However, the tiny
nozzle orifices are easily blocked by solidified
resin and the maintenance is difficult.
By comparison, the nozzles with different
diameters in the present system are not only
changeable but also can be assigned for different
paths. Still there are some imperfections in both
software and hardware compared to current
commercial systems. The potential is obvious
and those limitations will be improved in the
future.
Further reading
Chang, C.C. (2000), Develop 4-axes Scanning Techniques andCombine UVRS-RP to Fabricate the Rapid Prototyping.National Science Council of Taiwan, NSC892218-E-168-006.
Chang, C.C. and Chiang, H.W. (2002a), “Reconstruction theCAD model of complex object by abrasive computedtomography”, 2002 IEEE/ASME InternationalConference on Advanced Manufacturing Technologiesand Education in the 21st Century, Taiwan.
Chang, C.C. and Chiang, H.W. (2002b), “Three-dimensionalimage reconstruction of complex objects by abrasivecomputed tomography apparatus”, InternationalJournal of Advanced Manufacturing Technology,Vol. 22 No. 9-10, pp. 708-14.
Chang, C.C. and Chiang, H.W. (2002c), “Direct slicing andG-code contour for rapid prototyping machine of UVresin spray by PowerSOLUTION macro commands”,International Journal of Advanced ManufacturingTechnology, (on line publication).
Chang, C.C., Chiang, H.W. and Sun, S.H. (2002), “Directslicing and G-code contour for rapid prototyping bypowerSOLUTION macro commands”, 2002 IEEE/ASMEInternational Conference on Advanced ManufacturingTechnologies and Education in the 21st Century,Taiwan.
Figure 12 (a) The arrangement of hatch-spacing is 20 per cent
overlap and a half phase shifted in the second layer,
(b) the cured lines of photopolymer, and (c) the cured layers
of photopolymer in the vertical direction
Figure 13 Rp made by UVRS-RP machine (slicing thickness:
1 mm, and nozzle diameter: 0.5 mm)
Rapid prototyping fabricated by UV resin spray nozzles
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Chen, X., Wang, C., Ye, X., Xialo, Y. and Huang, S. (2001),“Direct slicing from power SHAPE models for rapidprototyping”, The International Journal of AdvancedManufacturing Technology, pp. 543-7.
Jacob, G.G.K., Kai, C.C. and Mei, T. (1999), “Development ofa new rapid prototyping interface”, Computers inIndustry, Vol. 39, pp. 61-70.
Jamieson, R. and Hacker, H. (1995), “Direct slicing of CADmodels for rapid prototyping”, Rapid PrototypingJournal, Vol. 1, pp. 4-12.
Kai, C.C., Lim, C-S. and Fai, L.K. (2002), Rapid Prototyping:Principles & Applications in Manufacturing, WorldScientific Pub. Company, Singapore.
Kochan, D., Kai, C.C. and Zhaohui, D. (1999), “Rapidprototyping issues in the 21st century”, Computers inIndustry, Vol. 39, pp. 3-10.
Kruth, J.P. (1991), “Material incress manufacturing by rapidprototyping technologies”, CIRP Annals, Vol. 40 No. 2,pp. 603-14.
Lee, M.Y., Chang, C.C. and Lin, C-C. (2002), “3D imagereconstruction and rapid prototyping models improvedefect evaluation, treatment planning, implant design,and surgeon accuracy”, IEEE Engineering in Medicineand Biology, Vol. 21 No. 2, pp. 38-44.
Onuh, S.O. and Yusuf, Y.Y. (1999), “Rapid prototypingtechnology: applications and benefits for rapid productdevelopment”, Journal of Intelligent Manufacturing,Vol. 10, pp. 301-11.
Pham, D.T. and Gault, R.S. (1998), “A comparison of rapidprototyping technologies”, International Journal ofMachine Tools and Manufacture, Vol. 38, pp. 1257-87.
Susila, B., Gunasekaran, A., Arunachalam, S. andRadhakrishnan, P. (1999), “Interfacing geometricmodel data with rapid prototyping system”, Journal ofIntelligent Manufacturing, Vol. 10, pp. 323-30.
Wohlers, T. (1997), Rapid Prototyping State of the Industry:1997 Worldwide Progress Report, RPA of SME,Dearborn, MI.
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