Figure 2(a)                                                                                      Figure 2(b)


The dimensionnal limiting aspect of this process is more linked to the polymerization of the ceramic system rather than the resolution mechanical resolution of the machine or the optical system of control of the laser beam position. In a stereolithography printing machine, a laser beam with a specified power and wavelength is sent through a beam expander to be deflected by a pair of X and Y mirors. These form the optical scanning system of the printing machine(figure 3).



Figure 3

The optical scanning system can be replaced by a DMD (Digital Mircromirrors Device) like in figure 4. In this case all the surface of each layer is irradiated in one time and the fabrication time of the part is decreased. The principal limitation is the dimensionnal accuracy wanted for the final part related to the size of the object. As the micromirros have a defined size, the resolution of the printed part is directly linked to the number of mirrors and the objective lense associated to the DMD. This process is generally called microstereolithography.  However it is possible to built large parts by moving the part or the DMD matrix during the scanning of each layer. This type of machine requires a good synchronization between the XY positionning system and the DMD sytem in order to have a good dimensionnal accuracy of the green printed part.


Figure 4

The photopolymerisation process occurs by the interaction of the laser beam with the curable ceramic system, curing a predetermined depth of the past after a controlled time of exposure (inversely proportional to the laser scanning speed) [5].The solidification of the ceramic past depends on the energy per unit area (or exposure) transmitted during the motion of the focused spot on the working surface. There is a threshold critical exposure energy that must be exceeded for the photopolymer to solidify. To maintain accuracy and cohesion during part building using a stereoliyhography printing machine, the polymerized thickness (Ep) and the cured line width (Lp) must be controlled [6][7][8]. Parameters which influence characteristics of the green parts are the physical and chemical properties of the resin, the speed and resolution of the optical scanning system, the power, the wavelength, the spot size of the laser and the recoating system.

Ceramic pastes arecomposed of a reactive system consisting of a dispersion of ceramic particles in a curable resin. This resin consists essentially in one or more monomer(s)/ oligomer(s) and a photoinitiator, controlling the polymerization reaction. There are many types of liquid photopolymers that can be solidified by exposure to electro-magnetic radiation, including wavelengths in the gamma rays, X-rays, UV and visible range, or electron-beam. The majority of photopolymers used in the commercial stereolithography systems, including 3D Systems are low viscosity acrylate oligomers and monomers. Stereolihtography machines generally use UV-curable resins. They are therefore called reactive suspensions [9]. The schematic illustration of a reactive suspension is presented in the figure 5.


Figure 5


References

[1] P. JACOBS. “Rapid prototyping and manufacturing: fundamentals of stereolithography”. Society of Manufacturing engineers, 1st edition, 1992, ISBN: 0872634256

[2] CW. HULL. “Method for production of three-dimensional bodies by stereolithography”.Patent number : 5174943, Filing date: Aug 23, 1991, Issue date: Dec 29, 1992

[3] JW . HALLORAN, V TOMECKOVA. “Predictive models for the photopolymerization of ceramic suspensions " Journal of the European Ceramic Society, Volume 30, Issue 14, October 2010, Pages 2833-2840

[4] T. CHARTIER, S. CORBEL ET AL. " Ceramic suspensions suitable for stereolithography », journal of the europ. Ceram. Soc., vol.18, issue 6, 1998, pages 583-590

[5] P. BARTOLO. “Stereolithography: materials, processes and applications”, Springer, 2011, page 81

[6] V. TOMECKOVA, JW. HALLORAN. "Predictive models for the photopolymerization of ceramic suspensions", J Eur Ceram Soc 2010;30:2833–40. doi:10.1016/j.jeurceramsoc.2010.01.027

[7] T. CHARTIER, A. BADEV, Y. ABOULIATIM, P. LEBAUDY, L. LECAMP. "Stereolithography process: Influence of the rheology of silica suspensions and of the medium on polymerization kinetics – Cured depth and width". J Eur Ceram Soc 2012;32:1625–34. doi:10.1016/j.jeurceramsoc.2012.01.010

[8] SP. GENTRY, JW. HALLORAN. "Depth and width of cured lines in photopolymerizable ceramic suspensions". J Eur Ceram Soc 2013;33:1981–8. doi:10.1016/j.jeurceramsoc.2013.02.033

[9] A. BADEV, T. CHARTIER ET AL. "Photopolymerization kinetics of a polyether acrylate in the presence of ceramic fillers used in stereolithography", journal of Photochemistry and Photobiology A: Chemistry, Volume 222, Issue 1, 5 July 2011, Pages 117-122


Examples of printed parts

Made by: 3DCeram
Material: Alumina
Postprocessing: as sintered

 


Made by: 3DCeram
Material: Zirconia
Postprocessing: as sintered


Made by: 3DCeram
Material: Hydroxy-apatyte
Postprocessing: as sintered