**Author details**

Pavlina Kalcheva Toteva-Lyutova1\*, Stoyan Dimitrov Slavov1 and Krassimira Stoyanova Koleva2

\*Address all correspondence to: pavlina\_toteva@abv.bg

1 Department of Technology of Machine Tools and Manufacturing, Technical University of Varna, Bulgaria

2 Department of Technical Mechanics, Technical University of Varna, Bulgaria
