Vol. 11 No.1，Feb. 2013

New development on additive manufacturingtechnology and its applications

Tian Xiaoyong，Li Dichen，Zhang Anfeng，Lu Zhongliang，Lu Bingheng

(State Key Laboratory for Manufacturing Systems Engineering，Xi’an Jiaotong University，Xi’an 710049，China)

Abstract：Additive manufacturing technology has been developed in Xi’an Jiaotong University for almost twentyyears. Up to now，it is still attracting the attentions of the researchers or manufacturers all over the world. Some in-novative processes and frontier application research are all being conducted here to catch up with the new develop-ment of this technology. In the present paper，newly developed processes，such as UV- LED (Ultraviolet- LightEmitting Diode) stereolithography，ceramic stereolithography，and direct metal forming，will be described. Someresults of the frontier application researches，such as indirect fabrication of ceramic casting mould，wind-tunnel-testing models，and photonic crystals and metamaterials，will be also briefly reviewed.Key words：additive manufacturing; rapid prototyping; stereolithography

1 IntroductionAdditive manufacturing technologies，previous-

ly called rapid prototyping， are being researchedfrom 1995 in the Institute of Advanced Manufactur-ing Technology (IAMT)，School of Mechanical Engi-neering， Xi’an Jiaotong University. And then，IAMT became a division of State Key Laboratory forManufacturing Systems Engineering especially forrapid prototyping & manufacturing. In the year of2000，MOE (Ministry of Education) Engineering Re-search Center of Rapid Prototyping & Manufacturingwas founded. After 5 years’development，it was up-graded to the National Engineering Research Centerof Rapid Manufacturing. At the very beginning，UV-laser curing process with photo sensitive resin was in-vestigated，and the stereolithography machine was de-veloped in 1997. At the mean time，Shaanxi Heng-tong Intelligent Co.，Ltd was established to commer-cialize the SL machine. The platform for the R&D ofadditive manufacturing technologies is shown inFig.1. Frontier research was conducted in the StateKey Lab for Manufacturing Systems Engineering.The research results will be transferred to products inthe National Engineering Research Center of RapidManufacturing. Finally，the developed products will

be commercialized and industrialized by the ShaanxiHengtong Intelligent Machines Co.，Ltd. In this pa-per，we would like to briefly review our new R&D re-sults of the processes innovation and frontier researchactivities about the additive manufacturing technolo-gies.

Fig.1R&D platforms for the of additive manufacturingtechnologies in School of Mechanical

Engineering，Xi’an Jiaotong University

2 Processes innovation2.1 UV-LED stereolithography

A LED- SL system with high power UV- LEDlight source has been developed，which consists of aLED chip，a focusing lens set，a controllable LEDpower supply，a X- Y workbench，a Z- axis elevatorand the manipulation software as shown in Fig.2 [1].The divergent UV light emitted from the LED is fo-cused on the resin surface by the focusing lens set.

Received 30 October 2012

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The workbench drives the lens set to scan along X-Yplane controlled by the software system. In compari-son with UV laser，the price and energy consumptionof LED are much lower，which conforms to the con-ception of green manufacturing. With the growing de-mands for inexpensive SL apparatus，a broad applica-tion prospect can be anticipated. There is，however，

a technical problem to be solved yet. The focusinglens set is a little heavy. With the increasing of thescanning speed，the vibration of the lens set has anobvious effect on the scanning accuracy. To raise thescanning speed and reduce the vibration，a light opti-cal device is required to substitute the spherical lens.

Fig.2 The scheme of the LED-SL process (a)，and the machine developed byShaanxi Hengtong Intelligent Machine Co.，Ltd (b)

2.2 Ceramic stereolithography (CSL)The influence of silica suspensions ingredients

and laser exposure on curing behavior of the highlyconcentrated aqueous silica suspensions has been in-vestigated [2，3]. The curing behavior of aqueous ceram-ic suspensions was studied by analyzing the profilesof the single cured lines in comparison with that ofthe photosensitive resin，as shown in Fig.3a. Thecured depth and width of single cured lines increasedwith the ceramic mean diameter and monomer con-centrations. The cured width of single cured lines de-creased with the solid content，but the cured depth in-creased with the solid content of silica suspensions.

The cured depth and width of the single cured line alldecreased with the laser scanning speed. The experi-mental results show that the ingredients of ceramicsuspensions and laser exposure all have great influ-ence on curing behavior of the highly concentrated sil-ica suspensions，which indicates that the formula isan intrinsic factor on the curing behavior of ceramicsuspensions，and laser exposure is an exterior factor.A ceramic stereolithography machine was developedon the base of the SPS 450B UV- laser stereolithgro-phy machine. Ceramic parts，such as ceramic castingmoulds，were fabricated by using this CSL process，as shown in Fig.4.

Fig.3 Comparison in the profiles with photosensitive resin and ceramic suspension (a)，and the developed CSL machine (b)

2.3 Direct metal formingScheme of the direct metal forming system is

show in Fig.5a [4，5]. It primarily includes a 1 000 WNd：YAG laser，a powder feeder，and a coaxial pow-der feeding nozzle. In the laser cladding process，the

depositing metal powder layer was simultaneously ir-radiated by a laser beam with focused diameter of 0.5mm. The stream field of powders was defocused be-low the depositing layer about 1 mm. The N2 feedingrate was 8 L/min. AISI316L powders with a diameter

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of 50~100 nm were used in the experiments，and thesubstrate used the same material. The experimental re-sults showed that the metal powder stream and laserspecific energy are both important factors which con-trol the high temperature behavior of molten pool anddetermine the microstructure of laser scanning track.

Based on the optimized processing conditions，highdefinition steam turbine blade of 316 L was fabricat-ed. The surface quality of the fabricated blade wasmeasured，and surface roughness (Ra) was in therange of 10.08 micrometer to 26.51 micrometer，asshown in Fig.5c.

Fig.4 Ceramic casting moulds were fabricated by using the CSL process

Fig.5 Scheme of direct metal forming process (a)，the laser cladding process (b)，and the fabricated turbine blade (c)

3 Application researches3.1 Indirect fabrication of ceramic casting mould

A new manufacturing process of integral ceram-ic mould was put forward by combining the gel-cast-ing process with SL technology [6，7]. The basic steps inthe fabrication process of integral ceramic mould areshown in Fig.6. First，a process system was designedand its corresponding prototype was rapidly fabricat-

ed by SL. Then ceramic slurry was poured into theprototype mould by gelcasting. The slurry was polym-erized in situ to form a green gel ceramic body，ofwhich all the parts were connected to form an integralcomponent. Finally，the integral ceramic mould wasobtained by vacuum drying，pyrolyzing and sinter-ing. Fig.7 shows the prototype of a hollow blade andthe metal parts fabricated by casting metal into the ce-ramic mould prepared by using above process.

Fig.6 Basic principles of the integral ceramic mould manufacturing process

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Fig.7 The SL prototype of a hollow blade (a)，metal blade cast by using the ceramic mould，front view photo(b) and side view photo(c)

3.2 Wind-tunnel-testing (WWT) modelBasedonrapidprototyping，a rapid fabrication tech-

nique for wind- tunnel models of flight vehicles has beenput forward.An integral tap-passagepressuremodelwasdeveloped，deriving from the study of dimensional com-pensation，taps and passages design and passage configu-rationdesign [8].Focusingon thedesignandfabricationofstructure-similar aeroelastic model，a new method is pre-sented in this paper and validate by the modal test. Anewmetal-resincompositestructureforthewind-tunnelmod-el was fabricated by the combination of SL and electro-chemicaldeposition.Thenewtechnologysavedtimeandcost. The developed speed of new design for the vehiclescanbeimproveddramatically.

The fabrication process includes the followingsteps. First，the plastic prototypes were fabricated bythe stereolithography process with photosensitive res-in，as shown in Fig.8a. Chemical treatment was em-ployed to roughen the surface in order to achieve asufficient adhesion of deposited metal on SL resin.Prior to the electro deposition process，SL part sur-face must be made conductive. For this work，electro-less deposition is chosen and fabricated in electrolessnickel deposition bath because it provides a betterbond than carbon painting，wherein a 1~2 µm thicklayer of nickel can be deposited. After nickel electrodeposition (Fig.8b) and assembly，the parts were test-ed in the wind tunnel.

Fig.8 Surface pressure SL model of main airfoil (a)，components of pressure model with three pairs of deflecting control surfaces (b)

3.3 Photonic crystal and metamaterials3.3.1 Photonic crystal (PC)

Two different fabrication processes，direct ce-ramic stereolithography described in section 2.2 andindirect process (discussed in section 3.1)，were uti-lized to prepare ceramic photonic crystals. CeramicPC structures fabricated using CSL process is shownin Fig.9a. For the indirect process，SL process wascombined with gel casting to fabricate 3D PCs (GHz)with diamond structures. Epoxy resin mold of inversediamond PC structure was produced by SL processwith a lattice constant of 12 mm. Then，gel casting

method was used to cast the alumina slurry contain-ing 55 % Al2O3 powder into the resin mold to obtainthe whole PC structure. The high refractive index con-trast between lattice and matrix was required in orderto get a larger PC band- gap. So the sample was putthrough the sintering process to increase the dielectricconstant of the ceramic part. The fabricated ceramicphotonic crystal is shown in Fig.9. The band- gap ofsuch a 3D PC structure was measured，as shown inFig.9b. Due to the complete band gap in three direc-tions，3D PC structures can be used in waveguidesand substrates for the microwave antenna [9].

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Fig.9 Photonic crystals fabricated by ceramic stereolithography (a)，indirectceramic components fabrication process (b)

3.3.2 MetamaterialsA free-space broadband carpet-cloak，designed by

transformations optics and quasi- conformal mapping，was realized with all-dielectric gradient index rod-con-nected diamond- structured photonic crystals (PCs) inmetamaterial regime [10]. Complex three- dimensionalsample with smooth continuous changing unit cells wasfabricated precisely by stereolithography (SL) usingphoto- curable resin. Thus，by gradually varying theunit cell constitutive parameters of the diamond-basedPCs with nearly isotropic properties，the required com-plex spatial distribution of the refractive index profilewas ideally achieved to reduce the scattering of the elec-

tromagnetic wave. The non- resonant property of thesub- wavelength PCs unit cell resulted in broad band-width and relatively low loss. The component producedby SL is shown in Fig.10a. The comparison of the carpetcloak performance was simulated，as shown in Fig.10b.The irregular perturbation caused by the bump resultedin two main lobes in scattering field，while the cloakedbump and the conducting plane generated a similar sin-gle main lobe. The main lobe produced by the cloakedbump was a bit wider，due to slight impedance mis-match caused by the removal of the background medi-um. The simulation result proved that the designed car-pet cloak achieved a good performance.

Fig.10 The fabricated carpet cloak with smooth transition between adjacent unit cells (a)，and simulations of theelectric field distributions of a bump(b)，a bump concealed by the proposed carpet cloak(c)，and conducting

plane (d)，the far-field patterns of the scattered electromagnetic waves for above three cases (e)

4 Development trendAdditive manufacturing technologies will further

develop in the following three aspects [11].1) Additive manufacturing technologies will pro-

vide more daily consumer goods for the customers.3D printings developed quickly in the last decade.The equipment with this technique is called 3D print-er. It can be used as a peripheral to the computer athome or in the office，and directly output the 3D ge-ometries in the computers to a real plastic parts. It has

a wide application with its huge commercial value infields of industrial design，creative design of prod-ucts，artworks.

2) Functional components will be produced bythe additive manufacturing process，such as deposit-ing and melting metal powder layer by layer by usinglaser or e- beam as the energy source. This kind oftechnologies can directly fabricate functional metalparts，the mechanical properties of which are similarto those of the forged pieces. New materials，such asceramics，composites will be used in these technolo-

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gies.3) Integral fabrication of the texture and struc-

ture will be realized to achieve the controllable fabri-cation of the parts from the microstructure texture tothe macroscopic structures. For example，in the de-sign and fabrication process of the parts with compos-ite materials，inside texture and outside structure canbe finished synchronously. This is called an integralfabrication technology of“design- materials- fabrica-tion”.

5 ConclusionsDuring the last twenty years，additive manufac-

turing technologies have been studied and developedin School of Mechanical Engineering，Xi’an Jiao-tong University. Novel fabrication processes and typi-cal applications have been established. Some of theseresearch results have been transferred into productsand commercialized in the Chinese market and over-seas. In the future，we will focus on the followingtwo topics. First，products for the daily life will be de-veloped，such as 3D printer etc. By using the prod-ucts，the common people will be more familiar withthe additive manufacturing technologies and help fur-ther develop this kind of new manufacturing pattern.Second，customized and functional parts used in theindustrial products is to be developed. New materialsor composite will be utilized in the additive manufac-turing technologies to meet the requirements for themechanical，physical and chemical properties of theproducts.

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lithography technology with high power UV-LED light [J]. Rapid Pro-

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[2] Zhou Weizhao，Li Dichen，Chen Zhangwei. The influence of in-

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[9] Hu Yawen，Li Dichen，Dai Wei，et al. Fabrication of three- di-

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[10] Yin Ming，Tian Xiaoyong，Han Haoxue，et al. Free-space car-

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AuthorTian Xiaoyong，male，born in 1981，graduated from Clausthal University of Technology，Germany. And

now he is an assistant professor in State Key Laboratory for Manufacturing Systems Engineering，Xi’an Jiao-tong University，Xi’an，China. Dr. Tian has published over 15 papers. His current research is additive manufac-turing technologies，photonic crystals and metamaterials etc. He can be reached by E-mail：leoxyt@mail.xjtu.edu.cn

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