86400 Batu Pahat, Johor, Malaysia

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1 Applied Mechanics and Materials Vols (2014) pp (2014) Trans Tech Publications, Switzerland doi: / Study on Layer Fabrication for 3D Structure of Photoreactive Polymer Using DLP Projector Khairu K. 1,a, M. Ibrahim. 2,b, S. Hassan 3,c, H. Hehsan 4,d Ashari Kasmin 5,e, Fazial E. 6,f 1 6 Faculty of Mechanical & Manufacturing Eng., Universiti Tun Hussein Onn Malaysia, Batu Pahat, Johor, Malaysia a khairu.uthm@gmail.com, b mustaffa@uthm.edu.my, c suhaimihas@uthm.edu.my, d haffiz@uthm.edu.my, e asyari@uthm.edu.my, f Keywords: Rapid Prototyping, Microstereolithography Photoreactive polymer, Photoabsorber, Time, Layer Thickness, 3D microstructure. Abstract. This paper presents a research on 3D part fabrication from composition of photo initiator (Phenylbis(2,4,6-trimethylbenzoyl)), photo absorber (Sudan I) and 1, 6- Hexanediol polymer effect based on curing parameters. A DLP projector was used as energy light source which initiated the photo reactive polymer at three different light source distances with three different exposed to evaluate photoreactive polymer solidification phenomena. The experiment results obtained shows that Sudan I composition, light intensity value and exposure of the varied photo absorber give significant effect to layer thicknes, surface roughness and hardness value. These works also prove that photo absorber composition solution gave a different mechanical properties effect for 3D microstructure fabrication. Introduction Solid freeform fabrication (SFF) technologies also referred to as rapid prototyping or additive layered manufacturing and other names can produce detailed three-dimensional (3D) structures. 3D structures are produced by continiously stacking serial layers, which are sliced from a 3D computer model with desired slicing thickness. The first commercial stereo lithography (SL) machine was released by 3D systems in 1988 [1-2]. In 1993, Ikuta et al. introduced microstereo lithography technology and developed several types of micro-stereo lithography apparatus[3]. Then in 1997, Bertsch et al. developed a micro-stereo lithography apparatus employing a pattern generator in which a Uv laser and dynamic LCD pattern generator were used to generate the cross section of a 3D structure [4-7]. The principle in projection-based stereo lithography process is whereby the pattern of a sliced section is focused on the resin surface at one and the light source can be generated from a laser or a lamp.the light source of traditional image processing machines like projectors is commonly white light; therefore, it is completely reflected to the focusing and the thickness of structures built. A number of previous researchers have reported on using some form of light absorption or polymerization inhibition as means for reducing cure depths in MicroSL, resulting in more precise feature detail. The pioneering work of Zissi et al. [8], for example, theoretically derived the cure depth and width according to light absorption, and further shown both theoretically and experimentally that cure width and depth could be reduced using a photo absorber and these effects were shown as a function of the concentration of photo absorber in solution. This study intends to investigate the photo absorber composition at varied distance and exposed on layer thickness, hardness value and dimensional error to fabricated 3d structure using a DLP projector as energy light source. The successfull layer structure was measured and analysed with tool maker measuring microscope to get the layer thickness, durometer type D for shore hardness value and vertical profile projector to measure the dimensional error. The 3-D structure fabrication are closely related to layer curing All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: , Faculty of Mechanical & Manufacturing Eng., Universiti Tun Hussein Onn Malaysia, Batu Pahat, Johor, Malaysia, Batu Pahat, Malaysia-06/11/13,10:27:00)

2 912 4th Mechanical and Manufacturing Engineering characteristic and therefore it is important to gain insight the relationship of photo absorber composition that affecting the mechanical properties of fabricated samples. Experimental Detail Experimental Set up Fig.1(a) shows the experimental apparatus for the photo reactive polymer solidification experiment consist of Digital Light Processing (DLP) projector imaging lens, resin vat and stepper motor as z axis stage. This setup are following the first setup by Bertsh in 2003 that consist of a Liquid Crystal Display (LCD) projector,converging lens, reflecting mirror, resin vat and z axis stage (Fig.1(b)). Fig.1(c) The BenQ DLP projector with light source 2700 ANSI Lumen was used and this data projectors emit enough UV light to initiated free radical reaction of polymerization. The structure pattern was drawn using Power Point software as the dynamical sliced section layer of the part with a black and white region images, and reflects the patterned light towards the projector tube lens. Red region images was used to calibrate sharp images on the top surface of the solution at Z axis stage, this red light text source will not polymerize the polymer solution. While the z axis was set to 5 µm for each step down. (a) (b) (c) Fig. 1 (a) Schematic drawing of the projection stereo lithography system apparatus (b) ) schematic drawing of the projection stereo lithography system apparatus from Bertsh (c) experimental apparatus setup. Photopolymer material preparation The material preparation done by mixed 24.5 ml of photoreactive polymers 1,6 - HexanediolDiacrylate (HDDA; CAS , Sigma Aldrich, USA), 1.00 grams of Phneylbis (Irgacure 819; CAS ,Sigma Aldrich,USA) as photoinitiator and Sudan I (Sudan 1; CAS , Sigma Aldrich,USA) was added in the solution with three different concentration. For this experiment, the concentration of Sudan I was mixed in three concentrations 0.001, and grams.the solution was allowed to mix in a sealed vial on a magnetic bar stir plate thoroughly at least 24 hours to become fully homogenous. Setup for Z Stage Distance For the elevator or Z stage mechanism, TDC 001 Cube Driver Motor was use as motor stage driver and MTS 50/M-Z8 Translation Stage as stage translation. Both of equipments are from Thorlab.The APT software is use for translation control while the platform for resin solidification are fabricated from aluminium by milling machine and attached onto the MTS 50/M-Z8 Translation Stage. The 3D structure was constructed layer by layer consisted of 100 layers. The stage then moved deeper into the liquid after solidification of each successive layer, leaving thin layer of liquid above the previously cured layer. The focusing varied from 5s, 10s and 15s, the z axis stage distance held constant 5µm for each layer to polymerize. The 3d structure was constructed using 100 layers for each focusing interval set-up. Optical setup The polymerized layers can be obtained and controlled by adjusting the focusing [9]. Means the exposed of UV light energy absorbed to initiate the solution to polymerize with single exposure for each layer. A DLP projector apparatus with a white projection images was formed on the resin surface. The focusing varied from 5second to 15second with 5 second

3 Applied Mechanics and Materials Vols intervals, the z axis stage distance held constant 5μm for each layer to polymerize. The 3D structure was constructed using 100 layers for each focusing interval set-up. There are three varied distance for the distance between DLP projector to the surface of elevator stage that start from 220 mm, 320mm and 420mm. The different distance will give the different effect to the mechanical properties effect for fabricated 3D structure. Material Composition Effect on Layer Thickness The amount of photo absorber limits the penetration depth of the light and therefore reduces the cure depth for a given constant photoinitiator concentration and light projection. The Sudan I will control the percentage of light penetration to the exposed resin surface and it will give different value for the layer thickness based on the different quantity of Sudan I. Each sample are exposed with three different of distance (420mm, 320mm and 220mm) and three different exposed (5s, 10s, 15s). Material Composition Effect on Surface Roughness Measurement The photo reactive polymer was solidified using varied photo absorber composition and exposed of Uv light energy absorbed. The solidified surface was measured with surface roughness tester machine (Mitutoyo SJ 400). The sample was placed horizontally on the work bench, and then stylus tip detectors are move down touched the surface of work piece. The indicator level was adjusted to the middle line set as zero datum.the stylus tip indicator move 4mm in distance scratching the material surface parallel to workbench, the surface roughness value was recorded and analyze. Material Composition Effect on Surface Hardness The Shore tests have been commonly referred as Durometers and the results frequently called Durometer hardness. The standards ASTM D-2240 was used for Shore test methods. By using durometer the needle for D type for polymer material was located onto the sample surface at 45 degree angle and then with constatnt pressure press tilt until 90 degree angle, the measured data was recorded. One sample each was selected and measured with varied z axis stage and focusing. Result and Discussion Composition effect on layer thickness. The amount of photo absorber limits the penetration depth of the light and reduces the cure depth for a given constant photoinitiator concentration and light projection. The fabricated layer thickness of structure for each composition gave varied values. As depecited in Fig.2 the graph pattern shown the layer thickness increased as the photo absorber composition reduced. Even the overall graph for layer thickness effect shown unstable trend, but the major trend shown that the layer thickness will reduced while the Sudan I composition increased. The distance shown unstable trend for the layer thickness value, but the highest value for layer thickness occur at 5 sec exposed with 440 mm distance with 0.001g Sudan I. The experiment result measured total layer thickness was dissimilar cause of the distorted structure formed due to rapid polymerization or nonuniform light. The top layer was highly crosslink, causes the insufficient for the below layer to diffuse and crosslink reaction. Table 1. Layer thickness with varied material composition Layer thickness (µm) Fig.2 Layer thickness with varied Sudan I,

4 914 4th Mechanical and Manufacturing Engineering Composition effect on Surface Roughness Measurement. The graph was plotted in Fig.3 was compared between Sudan I composition and exposed with different distance. The exposed allow the light energy absorbed initiate the radical s reaction polymerization from liquid to solid structure. The Fig.3 graphs shown the exposed increased as the surface roughness value decreased. The lower surface roughness values indicate a smooth and better quality surface formed. As compared to the three compositions mixed, exposed 15s was sufficient to photo reactive polymerized. The lowest surface roughness value can be view at gram Sudan I at 15 sec exposed and 220 mm height.. Although the roughness value was low, the thicker layer thickness was formed due to crosslink reaction of polymerization. Table 2. Surface roughness with varied material composition Surface Roughness (Ra) Fig.3 Surface roughness with varied Sudan I, The fabricated sample by experiment conducted to the surface roughness values depending on the percentage composition of the Sudan I and exposed used. Each structure provides the physical appearance of different quality. From research conducted, as in Fig. 5 shows some examples of various forms 3d structure which can be made in the size of micro level. Composition effect on Hardness Shore test. The hardness of specimen was measured to analyze the mechanical properties of fabricated 3d structure. Quantitative data was collected for the hardness shore test with varied of the z axis stage distance and focusing interval. As demonstrated plot graph in Fig. 4, the overall acquired data shown that the hardness value will increase due the incremental of Sudan I composition as well as longer exposed. This indicated longer will give more layer thickness formed due to crosslink reaction of polymerization. Table 3. Hardness value with varied material composition Hardness value Fig.4 Hardness value with varied Sudan I, Fig.5. Sample structure fabricated with different Sudan I composition,. Summary The photo absorber was effectively used to control light penetration for fabrication 3D microstructures in micro stereolithography. However, different concentrations of the Sudan I at different exposure and different light source distance shown significantly affected for

5 Applied Mechanics and Materials Vols mechanical property of success layer. For the layer thickness, the major trend shown that the layer thickness will reduced while the Sudan I composition increased. Layer thickness also increased when it exposed at longer to the light source. Whereas surface roughness results shown the exposed increased as the surface roughness value decreased. Lastly for the hardness shown that the hardness value will increase due the incremental of Sudan I composition as well as longer exposed. This indicated longer will give more layer thickness formed due to crosslink reaction of polymerization. References [1] D Chua, C.K., Leong, K.F. and Lim, C.S.). ed.rapid Prototyping: Principles and Applications. World Scientific Publishing Singapore, 2003 [2] Gebhardt, A., ed. Rapid Prototyping. Hanser Gardner Publications: Cincinnati, OH. (2003). [3] Ikuta K, H.K., Real three-dimensional microfabrication using stereolithography and metal mold. Proc IEEE, (International Workshop on Micro Electro Mechanical Systems(MEMS 93) (1993)p [4] Bertsch, A., Zissi, S., Jezequel, J.Y., Corbel,S. and Andre, J.C., Microstereophotolithography using a liquidcrystal display as dynamic mask-generator. Microsystem Technologies,. Vol. 3 (No.2): (1997)p [5] Bertsch A, L.H., Renaud P, 3D Microfabrication by Combining Microstereolithography and Thick resist Uv lithography. Sens Actuators, (1999): p [6] Bertsch A, B.P., Vogt C, Renaud P, Rapid Prototyping of Small Size Objects. Rapid Prototyping.. 6(4): (2000)p [7] Bertsch A, J.J., Andre JC Study of spatial resolution of a new 3D microfabrication process: the microstereolithography using a dynamic mask-generator technique. Jphotochem Photobiol A,1997(107): p [8] Zissi, S., Bertsch, A., Jezequel, J.Y., Corbel, S., Lougnot, D.J.and Andre, J.C., Stereolithography and microtechniques, Microsystem Technologies, Vol. 2 No. 2, (1996)p [9] Cox, A.X., C.-G; Fang, N., Microstereolitography: A Review In The Proceeding of ICOMM: International Conference on Micromanufacturing, Urbana, IL, Sept 13-15, [CD-ROM], 2006.