# The Additive Manufacturing of Glass: A Critical Review
## 5 Summary and Future Needs
### Challenges and Future Needs  
Some of the key questions or future directions regarding glass AM that have become evident from the review herein include the following:  
* There is a need for research to develop the scalability and reproducibility of glass AM methods (and associated feedstock material processing) to produce models/components at a larger length scale (i.e., the exploration of glass AM which incorporates one (or more) dimensions that are >300 mm);
* Depending on the method of glass AM employed, achieving (and maintaining) the optical clarity of printed glass objects is a concern for applications that require clarity or complete transparency. This limitation is one that is not, however, specific to glass AM, but an existing limitation of all AM methods (including polymeric EAM, and metal and ceramic AM), with the possible exception of resin-based stereolithography methods;
* Further research in and analysis of postprocessing methods used upon glass AM-produced objects are required. The available information is insufficient in this area, with only incidental exploration of polishing and annealing or artistic techniques documented in the literature. Further exploration of more technical postprocessing presents an opportunity to improve aesthetic, optical, and mechanical properties in parallel with direct process improvements in glass AM;
* Studies should demonstrate the ability to exploit design limits specific to glass printing, such as the overhang angle, resolution of intricacy, capacity for complex topology, and integration of complex features. These have not been demonstrated to date, and have not been correlated with computational models;* There is a need for a better understanding (and modelling) of the strength of glass in the context of glass AM. Presently, there is a paucity of data in the domain of glass AM with respect to mechanical properties. There is also additional subtlety in mechanical properties across length scales. The performance of full, large-scale elements and objects is essential for art and architecture but is yet to be tested. Whilst component strength is critical, there is also a need to better understand the possibility of interlayer delamination in glass AM, which will require targeted testing;
* Further investigation into the detailed thermal behaviours of deposited glass during printing needs to be performed. Detailed knowledge of thermal behaviour does not exist for the specific area of glass 3D printing, limiting progress with the poor scalability of current implemented methods. The simulation of thermal behaviours and in situ thermal monitoring will provide vital insight, forming a basis for advanced process parameter optimisation;
* Commercial products prepared by glass AM remain in their infancy, and the ongoing (and broader) use of glass AM technology will illuminate further opportunities and prospects. Aspects similar to those in the existing glass industry must be investigated, such as the quality control procedures used for mass-produced glass items, including the reproducibility and consistency of properties;
* There are prospects for machine learning to contribute towards the rapid optimisation of glass AM processing parameters, allowing the accelerated insertion of glass AM technology in commercial products.  
[PERSON] and [PERSON]. Writing--Original Draft, Data Curation, Writing--Review and Editing, Formal analysis. C.U.-M., R.S., J.S. and T.K.: Writing--Review and Editing, Resources. N.B.: Writing--Original Draft, Data Curation, Writing--Review and Editing, Formal Analysis, Supervision, Project Administration. All authors have read and agreed to the published version of the manuscript.  
This research was supported in part by the CSIRO Next-generation Graduates Program, and Deakin University.  
Not applicable.  
[PERSON] and D.V. acknowledge the support of the CSIRO Next-generation Graduates Program.  
The authors declare no conflict of interest.