**2. Contributions**

These topics were addressed in several high-quality scientific papers within this Special Issue. In what follows, the contents of the published manuscripts are briefly summarized.

Some of these contributions focused on material plastic behavior, as is the case in the work by Fang et al. [5], focusing on the direct assessment of the R-value in sheet metal based on the use of multicamera DIC systems, or the analysis of strain-hardening viscoplastic wide sheets submitted to bending under tension by Alexandrov and Lyamina [6]. Additionally, in this regard, the paper by Shahzamanian et al. [7] presented a numerical study of the influence of superimposed hydrostatic pressure on the damage mechanism by shear in sheet metal forming through the use of the shear modified GTN model to understand the effect of pressure on the shear damage mechanism.

Incremental sheet forming (ISF) was another topic of relevance in this Special Issue, dealt with in the work by Bautista-Monsalve et al. [8] through a novel machine-learningbased procedure for determining the surface finish quality of parts obtained by heat-assisted

**Citation:** Centeno, G.; Silva, M.B. Tube and Sheet Metal Forming Processes and Applications. *Metals* **2022**, *12*, 553. https://doi.org/ 10.3390/met12040553

Received: 21 March 2022 Accepted: 23 March 2022 Published: 25 March 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

SPIF. Additionally, the work by Suntaxi et al. [9] dealt with ISF, although in this case, concerning the multistage SPIF of thin-walled tubes from a numerical perspective. Other papers analyzing tube forming were carried out by Standley and Knezevic [10] dealing with the manufacturing of ultrafine metallic tubular structures by accumulative extrusion bonding, or the paper by Kishimoto et al. [11] which analyzed the deformation behavior causing the excessive thinning of micro metal tubes in hollow sinking.

Other contributions were dedicated to technological applications, such as the medical field in the case of Palumbo et al. [12], proposing an approach for the manufacture of cranial prostheses in sheet metal forming, the use of additive manufacturing by Tondini et al. [13] for the manufacturing of polymer tools for use in sheet metal forming, or the work by Hoffmann et al. [14] studying the reduction in warping in kinematic L-profile bending using local heating.

This compilation of research works has generously contributed to the success of this very interesting and high-quality Special Issue of *Metals*, devoted to "Tube and Sheet Metal Forming Processes and Applications".

**Funding:** The authors would like to express their gratitude for the funding received through grant numbers US-1263138 US/JUNTA/FEDER\_UE within "Proyectos I + D + i FEDER Andalucía 2014– 2020" and P18-RT-3866 US/JUNTA/FEDER\_UE funded under "PAIDI 2020: Proyectos I + D + i", as well as the Fundação para a Ciência e da Tecnologia of Portugal, through IDMEC under LAETA, project UIDB/50022/2020.

**Acknowledgments:** The guest editors would like to especially acknowledge all of the authors who contributed their excellent work to this Special Issue. Furthermore, we would also like to thank all the reviewers for their outstanding reviews of the manuscripts submitted and for providing help-ful and constructive comments. The guest editors would like to thank the Editorial Office involved in the preparation, editing, and management of this Special Issue. We would not have been able to reach the final collection of high-quality papers without the joint efforts.

**Conflicts of Interest:** The authors declare no conflict of interest.
