Available online at www.sciencedirect.com

ScienceDirect

Additive Manufacturing 14 (2014) 110118

Light curing strategies for lithography-basecustomized ceram

Gerald Mitteramskogler a,, Robert Gmeiner a, RutChristop lfg

a Christian D na Ulogy, F4 Schr 201

Abstract

Lithograp chnoAt the TU Vienna a digital light processing (DLP) system was developed for the fabrication of complex technical ceramics, requiring high levelsof detail and accuracy. The DLP-system used in this study creates a ceramic green part by stacking up layers of a photo-curable resin with a solidloading of around 45 vol.% zirconia. After a thermal debinding and sintering step the part turns into a dense ceramic and gains its final properties.The native resolution of the DLP process depends on the light engines DMD (digital mirror device) chip and the optics employed. Currently itis possible to print 3D-structures with a spatial resolution down to 40 m. A modification of the light source allows for the customization of thelight curing properties odimensionaloccurs due strategies (Lwas evaluatewithin the 3 2014 Pub

Keywords: A

1. Introdu

Additiveresource-efa layer-by-ing applicaparts madeceramics. Fticular, the

CorresponE-mail ad

(G. Mitterams

http://dx.doi.o2214-8604/strategy for each pixel of the exposed layers. This work presents methods to improve the geometrical accuracy as well as the structuralf the final 3D-printed ceramic part by using the full capabilities of the light source. On the one hand, the feasibility to control the

overgrowth to gain resolution below the native resolution of the light enginea sub-pixel resolutionwas evaluated. Overgrowthto light scattering and was found to be sensitive to both exposure time and exposed area. On the other hand, different light curingCSs) and depths of cure (Cd) were used for the 3D-printing of ceramic green parts and their influence on cracks in the final ceramicd. It was concluded that softstart LCSs, as well as higher values for Cd, reduce cracks in the final ceramic. Applying these findings

D-printing process may be another step toward flawless and highly accurate ceramic parts.lished by Elsevier B.V.

dditive manufacturing; Ceramic; Zirconia; Photopolymerization; Digital light processing

ction

manufacturing (AM) technologies allow for theficient fabrication of highly complex structures onlayer basis directly from 3D data [1]. For engineer-tions, AMTs are used to produce near net-shaped

of materials including unfilled polymers, metals oror the shaping of high strength oxide ceramics in par-

most commonly used AM technologies are: fused

ding author. +43 15880130857.dress: gerald.mitteramskogler@tuwien.ac.atkogler).

deposition modeling (FDM), selective laser sintering/melting(SLS/SLM), laser engineered net shaping (LENSTM), 3Dprinting (3DP), direct ink writing (DIP), laminated object man-ufacturing (LOM), stereolithography (SLA), and digital lightprocessing (DLP) [2,3]. Table 1 briefly describes the mentionedAM technologies and lists process-inherent assets and draw-backs. This review is based on recent literature and reflects theauthors opinions.

Using photochemical reactions triggered by light for theshaping of a part, instead of thermal energy (SLS, SLM) or abinder system (3DP), the photopolymerization-based technolo-gies (SLA, DLP) offer several benefits in cases where a higherfeature resolution and surface quality are required. A solid partis created on a layer-by-layer basis by photopolymerization of asuspension of ceramic particles in a photosensitive resin. SLA

rg/10.1016/j.addma.2014.08.003 2014 Published by Elsevier B.V.h Hofstetter a, Jrgen Stampfl a, Jrg Ebert c, Wooppler Laboratory for Photopolymers in Digital and Restorative Dentistry, Vien

b Institute of Materials Science and Technology, Vienna University of Technoc Ivoclar Vivadent AG, Bendererstrasse 2, 949

Available online 8 Septembe

hy-based additive manufacturing (AM) is increasingly becoming the ted additive manufacturing oficsh Felzmann a, Simon Gruber b,ang Wachter c, Jrgen Laubersheimer cniversity of Technology, Favoritenstrasse 9, 1040 Vienna, Austriaavoritenstrasse 9-11/E308, 1040 Vienna, Austriaaan, Liechtenstein4

logy of choice for the small series or single unit production.

G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118 111

Table 1Survey of AM technologies for the manufacturing of structural ceramics; legend to symbols: + good, o average, poor.

Resolution Surfacequality

Buildspeed

Post-processing

Productioncosts

Mp

FDM O O +

SLM SLS + O + O

LENSTM O O O

3DP O O O + O

DIP +

LOM

SL DLP +

uses a lasersection of layer at onby a digitaltems are coallow the othe exposuteristics of of slurry isgreen part cles are shaSL require(debinding(Figs. 1 and

Debindiof the greeBesides a tparametersstructure. Bfabricationthe final cein the light

Fig. 1. Parts technology pr

ucturing ram

lculasitiohe ped b

ramete thess othe

use

tionimiz+ + O O O

O O + O +

+ + O O

scanner to cure thin lines of slurry and draw the cross-the part, whereas the DLP-system cures the wholece using a light mask, which is dynamically created

micromirror device. The state of the art for DLP sys-nstant parameter light curing strategies (LCS), thatperator to choose the light intensity (mW/cm2) andre time (s) depending on the polymerization charac-the slurry. After one layer is completed, a fresh layer

coated and the process is repeated until the so-calledis built. Different to SLS, where the ceramic parti-ped and sintered in one step, a green part built with

s a thermal treatmentincluding a binder burnout) and sintering stepto achieve a dense ceramic part

2).

the strdebindwith ceand cacompo

In tdescribing paevaluathickn

On (LCS)merizato minng rates need to be carefully adjusted to the volumen part in order to avoid cracks in the final structure.emperature treatment that is too fast, the fabrication

of the green part could influence cracks in the finalae and Halloran [4] showed in a study the influence of

parameters of a green part made by SLA on cracks inramic. They conclude that residual monomer in gaps-curing pattern of the laser beam leads to cracks in

made of Al2O3 fabricated by using the DLP-based 3D printingesented in this paper.

are knownilar polymShrinkage bonds, wheis replacedLiterature oone limitin[1012]. Osoftstart LCkinetics ofcreates fewtle polymerintensity cudate viscoulowering sh

The utiling of a lawe show tlution of threducing thech.roperties

Process description References

Extruder and nozzle baseddeposition system with athermoplasticceramicpolymer material

[18,19]

High power laser fuses apolymerceramic compositeor directly sinters a ceramicpowder

[20,21]

Ceramic powder directlyinjected into molten poolcreated by high power laser

[22]

3D-jetting of organic blinderon a ceramic powder bed

[19]

Direct ink-jet printing of aceramic containing ink

[23,24]

Placing of layers of a laser cutceramic green tape

[25,26]

Photocuring of ceramiccontaining resin by a laserlight source or a LED

[6,27]

e during thermal debinding. Rather than on flawlessand sintering of green parts, most literature dealingic SLA or DLP-systems focuses on the measurementtion of the photopolymerization properties of slurryns [57].resent work, we are the first to use a DLP-processy Rohner et al. [8] to test the influence of light cur-ters on cracks after debinding. On the one hand wee influence of depth of cure (Cd)the polymerizedf the slurry when light curing of a layeron cracks.other hand, we test different light curing strategiesd to minimize shrinkage strains from photopoly-

on their influence of cracks after debinding. LCSe shrinkage strains caused by photopolymerization in the field of dental composites, exhibiting sim-erization kinetics as ceramic slurries used for SL.strains originate from the conversion of C C doublere the larger van der Waals inter-molecular spacing

by the smaller intramolecular covalent bonds [9].n dental composites explains shrinkage strains to beg factor for the performance of dental restorationsne way to reduce the inherent shrinkage is by usingS [1315]. Dewaele et al. [16] explain the reaction

a softstart polymerization. A lower initial intensityer polymerization centers and a more linear, less brit-

network. By delaying the gel-point before final highring, the material is given the ability to accommo-s flow before the rigid network is created and thusrinkage strains.

ized DLP-system projects images used for light cur-yer at a native resolution of 40 m. In this workhat it is possible to improve the geometrical reso-e green part without changing the projection optics,e overall building size of the 3D printer. In turbid

112 G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118

Fig. 2. Green parts (a), sintered parts (b), and a cellular structure [28] made of ZrO2 (c) fabricated

slurries, theexposed imresinpartiindexes [17allows for athe DLP-sy

2. Materia

2.1. Ceram

The ceracoating deving bladeslurries. Ththe DLP-sywavelengthsystem addthicknessesror device

Fig. 3. P

uringal valightn of ildinrs th

and the iimagre frr intently

ithayscated.erfor

sta con

gnal light-cured geometry grows beyond the intentionallyage by scatter light (overgrowth) that originates at thecle interface due to the materials different refractive]. We show that an exact control of the overgrowth

green part resolution below the native resolution ofstem, defined as the sub-pixel resolution.

ls and methods

ic DLP-system and customized LCS

mic DLP-system (Fig. 3) is equipped with a specialiceconsisting of a rotating mechanism and a coat-enabling the processing of highly viscous ceramice coating device provides a fresh layer of slurry andstem selectively exposes the slurry to light at 460 nm

to initiate a radical photopolymerization. The DLP-s the layers to fabricate the green part and typical layer

range from 15 m to 100 m. A digital micromir-

light cmatericreate ricatiothe butransfesystemwhichof the on mo

(highefrequesity). Wfile, grbe crewas pMA). Aused tooff) si(DMD) dynamically generates the images used for

rinciple of the ceramic DLP-system by Gruber et al. (2011).

ranged fromLCS.

2.2. Ceram

A photoon comme

lates. The photoinitiaof a non-re(TZ-3YS-Egeneous m150 FVZ (based on tmetric cenwere added3500 rpm. of 15 Pa s. by using the DLP-based technology presented in this paper.

. The micromirrors reflect the light either toward thet (on) or away from it onto a light absorber (off) to

or dark pixels. The DLP-system allows for the fab-green parts at an x/y resolution of 40 m. The size ofg platform is 76.8 mm 43.2 mm. A binary bitmape geometrical information of a layer to the DLP-

a sequence file determines the order and timing inmage is to be displayed and hence enables grayscalese. When the micromirrors of the DMD are switchedequently than off, the image appears to be brighternsity). When the micromirrors are switched off morethan on, the image appears to be darker (lower inten-

a combination of multiple images and a sequenceales for every single pixel of the exposed layer could

The creation of the images and the sequence filemed in MATLAB (R2011b, The Mathworks Inc.,ndard pulse width modulation (PWM) algorithm wasvert an analog light intensity curve to a digital (on,for the light engine. Sampling rates for the PWM 20 Hz to 100 Hz, depending on the length of the

ic lled photocurable slurry

-reactive suspension (slurry) was prepared basedrcially available di- and monofunctional methacry-slurry was a blend of 0.05 wt% of a highly reactivetor, 2 wt% of a dispersant, an absorber, and 10 wt%active diluent. A solid loading of zirconia powder, Tosoh, Japan) up to 45 vol% was achieved. A homo-

ixture was prepared by using a SpeedMixerTM DACHauschild, Hamn, Germany). The SpeedMixerTM ishe double rotation of the mixing cup (dual asym-trifuge). Both the organic and the ceramic powder

in the cup and the mixing parameters were 2 min atThe viscosity of the ceramic slurry was in the range

G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118 113

Fig. 4. Overlays of the exposed test patterns (marked pixels) and the light curedsamples for the outside case (a) and the inside case (b).

2.3. Measuring geometrical overgrowth

Light scattering effects cause the curing of a larger area thanoriginally defined as actually mnally exposoutside casthe light in13 mW/cmtotally expoof overgrowside lengthslurry the csions were evaluated uInstitutes o

2.4. Measu

We meato 13 mW/The slurrya filling he10 mm in dremoving t

gauge. To further investigate the influence of oxygen inhibi-tion on Cd, the slurry was degassed under vacuum prior to theinvestigation.

2.5. Inuence of LCS and Cd on cracks after thermaltreatment

As a testing geometry, cylindrical green parts of 10 mm indiameter and height were fabricated using a layer thicknesses of25 m. The reference parts were fabricated using a constant LCSat 13 mW/cm2 light intensity and 1.5 s exposure time, yieldinga measured Cd of around 100 m. To evaluate the influence ofLCS on cracks after thermal treatment, we used constant (ref-erence), exponential (exp 1, exp 2), and a softstart (softstart 1,softstart 2) LCS to fabricate green parts (Fig. 5). To evaluatethe influence of Cd on cracks after thermal treatment, we fabri-cated green parts with the mentioned LCS at a Cd of 75 m and

. To achieve different values for Cd the high-intensityre ti

abriceren

herm

er faspecmecmple

heat for

for parts

herm

. 6 s, debTMA

to th

Fig. 5. Exponexposed by the DLP-system. The overgrowth wasthe originally exposed length subtracted from the

easured length. Fig. 4 shows overlays of the origi-ed images and the cured and cleaned samples for thee (a) and the inside case (b). For the experiments,tensity of the exposed pixels was kept constant at2 and the influence of exposure time (0.83.2 s) andsed area (0.163.96 mm side length) on the amountth was evaluated. For the inside case, the opening

was kept constant at 0.36 mm. After exposure of theured samples were cleaned and the respective dimen-measured under a light microscope. The images weresing an image analysis software (ImageJ, Nationalf Health, USA).

ring depth of cure (Cd)

sured Cd for the given slurry at light intensities upcm2 and exposure times ranging from 0.5 s to 12 s.

was placed in a tray on top of the material vat atight of 1 mm and leveled with a blade. Circles ofiameter were exposed and subsequently cleaned by

he excess slurry. Cd was measured with a micrometer

150 mexposuwere fthe ref

2.6. T

Aftwith rethermoThe sawith achangevaluesgreen

2.7. T

Figdryingstudy, profileential (exp(x) 1, exp(x) 2) and soft start (softstart 1, softstart 2) LCS compared to conmes were varied accordingly. At least two cylindersated for each group and qualitatively compared withce.

al analysis

brication, the dimensional change of the green partst to an increase in temperature was analyzed usinghanical analysis (TMA), 2940 Fa. TA-Instruments.s were heated up from room temperature to 400 C

ing rate of 0.1 K/min. We evaluated the dimensional the LCS (softstart and constant) and the differentCd (75 m and 150 m) we used to fabricate the.

al treatment

hows the thermal treatment used in this study forinding and the final sintering of the parts. Prior to this

measurements were used to adjust the temperaturee geometry of the green part.

stant curing (reference). 100% light intensity equals 13 mW/cm2.

114 G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118

Fig. 6. Thermal treatment (drying, debinding, and sintering).

3. Results and discussion

3.1. Geometrical overgrowth

Figs. 7 side and thexposed lelight intensexposure titering causlength. Forsmaller thaclosure of outside andtively. The be explaineinner open

3.2. Depth

For the increase in ing on the li

parameters of 13 mW/cm2 light intensity and 1.5 s exposuretime, a Cd of around 100 m could be measured. The iso-energylines show that Cd is not linear with respect to the overall energy

d bute thegasbe ob

ue

to a withth vred ent

crac

erefo-priise

of thsionaicroith and 8 show the measured overgrowth for the out-e inside case calculated by subtracting the originallyngth by the actually measured length. At a givenity of 13 mW/cm2 the overgrowth increases with bothme and exposed area. For the outside case, light scat-es the actual length to be higher than the original

the inside case, it causes the actual length to ben the original length or even leads to a complete

the opening. A peak could be observed for both the inside cases at 2 mm and at 4 mm side length, respec-higher amount of overgrowth for the inside case couldd by the larger amount of surface surrounding the

ing.

of cure (Cd)

given slurry, an increase in exposure time causes anCd, which is converging to a maximum value depend-ght intensity applied (Fig. 9). For the reference curing

applieevaluafor a dcould

3.3. In

Duecracksing wia sinteprominzontaland thing 3Da stepwtering dimenlight mcated wFig. 7. Overgrowth of the outside length as a function of rectangle t higher intensities are favored for increased Cd. Toe influence of oxygen inhibition, Cd was measuredsed slurry and about three times greater values for Cdserved (Fig. 10).

nce of LCS and Cd on cracks after debinding

certain level of translucency of the dense zirconia,in the sintered ceramic can be visualized by ray-

isible light. The side view (a) and top view (b) ofreference specimen in front of a light source showhorizontal and vertical cracks (Fig. 11). The hori-ks do not entirely follow the layerwise orientationre might not originate from delamination issues dur-nting. The horizontal crack patterns instead show

crack propagation between the layers. Due to sin-e loosely packed powder to a compact ceramic, al shrinkage of around 20% occurred. Fig. 12 showsscopy images of the rayed ceramic cylinders fabri-the LCS presented aboveyielding a Cd of 100 m.side length and exposure duration.

G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118 115

Fig. 8. Overgrowth of the inside length as a function of side length and exposure duration.

Fig. 9. Measulevel of energ

Using the reduction o(Fig. 12(a)(exp(x) 2) red Cd for different light curing parameters. The solid lines represent the results for y dose (iso-energy).

shorter exponential LCS exp(x) 1 showed no clearf cracks compared with the reference constant LCS). Longer times for the initial intensity increaseprevented vertical cracks and led to only minor

horizontal cstart LCS scracks. The(Fig. 12(d)

Fig. 10. Cd for degassed (dashed lines) and regular the same intensity (iso-intensity); the dashed lines show the same

racks (Fig. 12(b)). Cylinders fabricated with the soft-howed no vertical cracks and only smaller horizontal

fewest cracks were observed for the LCS softstart 2).

(solid lines) slurry.

116 G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118

Fig. 11. Side view (a) and top view (b) of a sintered reference cylinder built with a constant light intensity curing protocol at 13 mW/cm2 light intensity and 1.5 sexposure duration; lines mark the cracks visible within the ceramic.

To evaluate the influence of Cd on cracks after debinding, wevaried the high intensity curing time from originally 1.5 s to 0.8 sand 2.5 s, yielding values for Cd of 75 m and 150 m respec-tively. At the same layer thickness of 25 m, cylinders fabricatedat a Cd of 75 m again showed structural cracks similar to thereference part shown above. Using a Cd of 150 m and the con-stant LCS it was not possible to achieve flawless ceramics. Thecombination of the softstart LCS and a Cd of 150 m resultedin flawless specimens as seen in Fig. 13.

The curing of layer with the presented LCS softstart 2 can beregarded as a double light exposure approach. The initial softerpolymerization at 1.3 mW/cm2 for 10 s allows for a certain levelof viscous flow of the slurry before the gel-point is reached.A further reduction of shrinkage stresses might be achieved byusing even lower softstart intensities. As a drawback, the curingof the layers turns into a time consuming process, since lowerlight intensities require longer light exposure times for similarcuring results. The high-intensity light exposure at 13 mW/cm2

Fig. 12. Sintepropagation ared specimens fabricated with exponential LCS exp(x) 1 (a) and exp(x) 2 (b) andre highlighted. softstart LCS softstart 1 (c) and softstart 2 (d). Lines of crack

G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118 117

Fig. 13. Flawless cylindrical part fabricated with the LCS softstart 2 and a Cdof 150 m.

for 2.5 s completes the curing of the slurry and ensures the bond-ing to the previous layer. We have concluded that a higher depthof cure increases the bonding of the layers and improves thestructural properties of the final ceramic part.

3.4. Inuence LCS and Cd on structural and thermalproperties

We analyzed the fracture surface of green parts fabricated ata Cd of 75 m and 150 m using scanning electron microscopy(SEM) imaging. At a Cd of 75 m the fracture surface showssigns of the layered manufacturing route (Fig. 14(a)). At a Cdof 150 m the green structure seems homogeneous (Fig. 14(b)),which might indicate improved interlaminar bonding of the sin-gle layers.

Thermomechanical analysis (TMA) of green parts with 4 mmin diameter and height revealed a difference in dimensionalchange over temperature. The dimensional shrinkage of thegreen part is associated with evaporation of the diluent and pyrol-ysis of the organic. The escaping gaseous products pass throughthe mesh of ceramic particles and the remaining polymer net-work. At higher temperature rates, trapped debinding gasses leadto an increase in internal pressure of the green part visible as anexpansion in the TMA measurement. Using TMA, cracks dur-ing debinding of the green part can be seen as a peak in the rateof shrinkage. Specimens fabricated with a softstart LCS showedincreased shrinkage compared with the specimens fabricatedwith the constant LCS, see Fig. 15. The temperature at which amajor mass loss begins shifted to a higher temperature for the

icatedFig. 14. SEM micrographs of fracture surfaces of green parts fabrFig. 15. Result of TMA measurements. The samples were heated up to at a Cd of 75 m (a) and 150 m (b).

400 C at a heating rate of 0.1 K/min.

118 G. Mitteramskogler et al. / Additive Manufacturing 14 (2014) 110118

specimens at 150 m. This might be explained by a more rigidnetwork caused by longer exposure times, which increase theactivation energy needed for the evaporation of the diluent. Thehigher amosoftstart LCphotopolymduring the

4. Conclu

This woused for thimprove therties of thsintering. Wslurry causthe final gregarding ocluded thatfor the succSoftstart Ling from pimprove th

To implused for liga contour imwidth of thtrolled by a resolutiodefined as ssize. Besidthe core imsoftstart LCceramic pa

Acknowled

The resTechnical Ufinancial sPhotopolymVivadent A

Appendix

Supplemin the onlin

Reference

[1] Wohlersing and Associat

[2] Halloran1999;98

[3] Gebhard3D DrucGmbH C

[4] Bae C-J, Halloran JW. Influence of residual monomer on cracking inceramics fabricated by stereolithography. Int J Appl Ceram Technol2011;8:128995.

mbly K (Thesis) Characterization of curing kinetics and polymerizationinkagtopo

lloranotoporam Sartierphy pdiumc 2012hner G

procers. Utts Dworksga RRolym

nt Mamer elopm1;90verla

dental N, J

evant H, Sta

shrintts Detics waeleet al. ymerss traiffith Msions

llini Ag of

wis JAensio

es-Chh percedialkes J

of Zrtotyp

lla Vamics8;5:2la B,

ps forcess

ert J, jet pr6.

ang Yminat4.indleinatizmanka Ramic aned

ingiveunt of total shrinkage for parts fabricated with theS may be explained by a more rigid network aftererization, which causes higher levels of shrinkage

drying of the part.

sion

rk presents a modification of a special DLP-systeme 3D-printing of ceramic green parts in order to

e geometrical accuracy, as well as the structural prop-e final structural ceramic part after debinding ande found that light scattering within the ceramic filled

es a certain amount of widening of dimensions ineometry and that this overgrowth is both sensitiveverall exposure area and exposure time. We con-

softstart LCS and higher values for Cd are preferredessful thermal processing of a 3D-printed green part.CS are applied to reduce internal stresses originat-hotopolymerization, whereas higher values for Cde interlaminar bonding of the layers.ement these findings in the DLP-system, the imageht curing of a layer could be split into a core image and

age, which are light cured consecutively. At a certaine contour the amount of overgrowth could be con-

the light exposure duration. This approach achievesn below the spatial resolution of the DLP-system,ub-pixel resolution, without a loss in overall buildinges the time-controlled curing of the contour images,age of a layer could be light-cured with the presentedS to improve the structural properties of the final

rt.

gments

earch presented in this paper was conducted at theniversity of Vienna. We gratefully acknowledge the

upport from the Christian Doppler Laboratory forers in Digital and Restorative Dentistry and Ivoclar

G (Liechtenstein).

A. Supplementary data

entary data associated with this article can be found,e version, at doi:10.1016/j.addma.2014.08.003.

s

TT, Associates W. Wohlers report 2012: additive manufactur-three dimensional printing state of the industry annual. Wohlerses; 2012.

JW. Freeform fabrication of ceramics. Br Ceram Trans:299303.t A. Generative fertigungsverfahren: additive manufacturing undken fr prototyping tooling produktion. Carl Hanser Verlago KG; 2013.

[5] Kashrpho

[6] HaPhCe

[7] Chgrame

So[8] Ro

forlay

[9] Wanet

[10] Braof pDe

[11] Cradev201

[12] Kleof

[13] Ilierel

[14] Luand

[15] Wakin

[16] DeG, polgla

[17] Grpen

[18] Beelin

[19] Ledim

[20] YvhigPro

[21] WiingPro

[22] Bacer

200[23] Ute

stePro

[24] Ebink673

[25] Zh(la531

[26] Schlam

[27] FelLiscer

[28] CleThe in ceramic-loaded photocurable resins for large area masklesslymerization (LAMP). Georgia Institute of Technology; 2009.

JW, Tomeckova V, Gentry S, Das S, Cilino P, Yuan D, et al.lymerization of powder suspensions for shaping ceramics. J Euroc 2011;31:26139.

T, Badev A, Abouliatim Y, Lebaudy P, Lecamp L. Stereolitho-rocess: influence of the rheology of silica suspensions and of the

on polymerization kinetics cured depth and width. J Eur Ceram;32:162534., Wachter W, Appert C, Patzer J, Stampfl J. Device and method

essing light-polymerizable material for building up an object inS8623264 B2 (2014).C. Reaction kinetics and mechanics in photo-polymerised. Dent Mater 2005;21:2735., Ballester RY, Ferracane JL. Factors involved in the development

erization shrinkage stress in resin-composites: a systematic review.ter 2005;21:96270.NB, Stansbury JW, Bowman CN. Recent advances andents in composite dental restorative materials. J Dent Res

:40216.an CJ, Feilzer AJ. Polymerization shrinkage and contraction stress

resin composites. Dent Mater 2005;21:11507.elen E, Hickel R. Is the soft-start polymerisation concept stillfor modern curing units? Clin Oral Investig 2011;15:219.nsbury JW, Bowman CN. Impact of curing protocol on conversionkage stress. J Dent Res 2005;84:8226.C, Hindi AA. Intrinsic soft-start polymerisation shrinkage-in an acrylate-based resin-composite. Dent Mater 1999;15:3945.

M, Asmussen E, Peutzfeldt A, Munksgaard EC, Benetti AR, FinnInfluence of curing protocol on selected properties of light-curings: degree of conversion, volume contraction, elastic modulus, andnsition temperature. Dent Mater 2009;25:157684.

L, Halloran JW. Scattering of ultraviolet radiation in turbid sus-. J Appl Phys 1997;81:253846., Shor L, Guceri SI. New developments in fused deposition mod-

ceramics. Rapid Prototyp J 2005;11:21420., Smay JE, Stuecker J, Cesarano J. Direct ink writing of three-nal ceramic structures. J Am Ceram Soc 2006;89:3599609.ristian H, Jan W, Wilhelm M, Konrad W, Reinhart P. Net shapedformance oxide ceramic parts by selective laser melting. Phys

2010;5(Part B):58794., Hagedorn Y-C, Meiners W, Wissenbach K. Additive manufactur-O2Al2O3 ceramic components by selective laser melting. Rapid

J 2013;19:517.K, Bose S, Bandyopadhyay A. Processing of bulk alumina

using laser engineered net shaping. Int J Appl Ceram Technol3442.Storti D, Anderson R, Ganter M. A review of process development

new material systems in three dimensional printing (3DP). J Manuf2008;10:96104.zkol E, Zeichner A, Uibel K, Weiss , Koops U, et al. Directinting of dental prostheses made of zirconia. J Dent Res 2009;88:

, He X, Du S, Zhang J. Al2O3 ceramics preparation by LOMed object manufacturing). Int J Adv Manuf Technol 2001;17:

r K, Roosen A. Manufacture of 3D structures by cold low pressureon of ceramic green tapes. J Eur Ceram Soc 2009;29:899904.n R, Gruber S, Mitteramskogler G, Tesavibul P, Boccaccini AR,, et al. Lithography-based additive manufacturing of cellularstructures. Adv Eng Mater 2012;14:10528.

and scaled cellular lamp for competition by NewPerfection rse; n.d.

Light curing strategies for lithography-based additive manufacturing of customized ceramics1 Introduction2 Materials and methods2.1 Ceramic DLP-system and customized LCS2.2 Ceramic filled photocurable slurry2.3 Measuring geometrical overgrowth2.4 Measuring depth of cure (Cd)2.5 Influence of LCS and Cd on cracks after thermal treatment2.6 Thermal analysis2.7 Thermal treatment

3 Results and discussion3.1 Geometrical overgrowth3.2 Depth of cure (Cd)3.3 Influence of LCS and Cd on cracks after debinding3.4 Influence LCS and Cd on structural and thermal properties

4 ConclusionAcknowledgmentsAppendix A Supplementary dataReferences