Deran Turan - 514111013 - (1st Week Unanswered Terms)

Microstereolithography (Previous)

Anohter RP(rapid prototyping) approach, called microstereolithography, is based on stereolithography (STL), but the scale of the processing steps is reduced in size.Whereas the layer thickness in conventional stereolithography ranges between 75 qm and 500 qm,microstereolithography (MSTL) uses layer thicknesses between 10 to 20 qm typically , with even thinner layers possible.

(Mikell P.Groover ,Fundamentals of modern manufacturing second edition, page 867)

Microstereolithography (Modelling) (New) (Better) : Microstereolithography (MSL) is very similar to stereolithography. The manufacture of 3D micro-objects by using a SL technique first needs a strong correction in the process control, in order to have an accuracy of less than 10 µm in the three directions of space. This method differs from the SL method in that the focus point of the laser beam remains fixed on the surface of the resin, while an x–y positioning stage moves the resin reactor in which the object is made. However, the reactor must be translated very slowly to ensure that the surface of the liquid resin is stable during polymerization. As such, the outer size of the microstructure has to be limited unless a long manufacturing time is allowed. The fabrication of 20 µm thick ceramic micro-components has been achieved with this method. The apparatus consists of a He–Cd laser with acoustic-optic shutter controlled by the computer as shown in Figure 3.44. The laser beam is then deflected by two computer-controlled low inertia galva-nometric mirrors with the aid of focusing lens onto the open surface of the polymer containing photoinitiators. An XYZ  positioner moves the reactor containing the polymer and the laser beam is focused on the layer to be solidified. Multifunctional smart materials involve the integration of polymer sand nanoceramic particles by chemical bonding as side groups on a polymer backbone. The concept is to design a backbone with functional groups that will serve as anchor points for the metal oxides. The nanoparticles such as  PZT, PLZT, etc. must have active surfaces or functional groups that can bond with the polymer chain. The nanoparticles provide the piezoelectric function in the polymer and the backbone provides mechanical strength and structural integrity, electrical conductivity, etc. The multifunctionality of these polymers provides a large-scale strain under electric field and thus can be used as actuators for MEMS based devices such as micro pumps. Functional and structural ceramic materials possess unique properties such as high temperature/chemical resistance, low thermal conductivity, ferroelectricity and piezoelectricity, etc. 3D ceramic microstructures are of special interest in applications such as micro-engines and micro-fluidics. The fabrication of ceramic microstructures differs from that of polymeric MSL.

Figure 3.44. Schematic diagram of the Microstereolithography unit

In ceramic MSL, the homogeneous ceramic suspensionis prepared. Submicron ceramic powders are mixed with monomer,photoinitiator, dispersant, dilutents, etc. by ball milling for several hours. The prepared ceramic suspension is then put into the vat and ready for MSL based on the CAD design. After MSL, the green body ceramic micro-parts are then obtained. To obtain the dense microceramic parts, the green body is next put into a furnace to burn out the polymer binders and further sintered in a high temperature furnace. The binder burnout and the sintering temperature vary with different polymers and ceramics. After sintering, ceramic microstructures areready for assembly and application. MSL can be very useful for building microparts in micromechanics,microbiotics (microactuators) and microfluidics. Current litho-graphic processes previously mentioned have the limitation that complex structures cannot be made easily. Thus, MSL can be used for more complex geometries. 

(CHAU C. K., LEONG K. F. and LIM C.S., Rapid Prototyping Principles and Applications, p. 103-105)