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.

Electronic access

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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

http://www.emeraldinsight.com/researchregister

http://www.emeraldinsight.com/1355-2546.htm

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

Rapid prototyping fabricated by UV resin spray nozzles

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Volume 10 · Number 2 · 2004 · 136–145

137

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


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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)


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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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1. introduction rapid prototyping fabricated by uv resin

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