♦FDM is able to only melt polymer-type material at 200–550 oC. Nozzle blocking issue, high viscous glass, weak adhesion problem. Second built, outer ceramic heatable nozzle added problems solved, and an and an external torch was used for annealing (automated but harder for flat glasses). Nozzle set to 80mm above the print. The nozzle diameter is 4.5 mm, which is bigger than traditional polymer print nozzles, which leads to lower precision in design. Only soda-lime can be used due to its low working temperature; boronsilicate may be used in the future. Quartz glass is impossible to use with FDM.
♦Cracks are pores that occur in the SLM method due to the high thermal expansion and high elastic modulus combination of silica glass properties. The use of alumina substrates could reduce this occurrence, but not completely solve it. Defects decrease refractivity and cause an opaque appearance. Low contact angle is vital in DED; the angle must be lower than 90 degrees; otherwise, unmelted, discontinuous structures may present. With the DED approach and the use of wire and fibers instead of powder glass, refractivity could be increased. Angle feed rate, scan speed, and laser power are the most important parameters against the formation of defects.
♦Indirect AM requires RT, binders, and post-processes like drying, sintering, and debinding. DIW has a lower viscosity advantage, so it enables a wider production range among glass types. Silica fumes are used, and TiO2 and rare-earth oxide dopants would increase refractivity. The incidence of cracking is lower, but particles could cluster. A sol-gel approach for DIW can overcome the clustering problem. DIW is limited to simple and 2D-shaped production.
♦SiO2 particles are merged with resin monomers, which are curable with UV and make complex designs achievable.
♦Suspended nanoparticles are used with the resin mixture borosilicate and phosphateslicate glass, which can be produced without issute. Pore size is much lower compared to SLA.
♦TPP is allowing the production of micron-scaled products. Laser sources measuring 505nm or 1030nm are suitable. A smaller particle size requires better surface quality.