**Eva María Rubio 1,\*, María Villeta 2, José Luis Valencia <sup>2</sup> and José Manuel Sáenz de Pipaón <sup>1</sup>**


Received: 7 July 2018; Accepted: 3 August 2018; Published: 7 August 2018

**Abstract:** Drilling is one of the most common machining operations in the aeronautic and aerospace industries. For assembling parts, a large number of holes are usually drilled into the parts so that they can be joined later by rivets. As these holes are subjected to fatigue cycles, they have to be checked regularly for maintenance or repair, since small cracks or damage in its contour can quickly cause breakage of the part, which can have dangerous consequences. This paper focuses on finding the best combinations of cutting parameters to perform repair and maintenance operations of holes in stacked hybrid magnesium–titanium–magnesium components in an efficient, timely, and sustainable (without lubricants or coolants) manner, under dry drilling conditions. For the machining trials, experiments were designed and completed. A product of a full factorial 23 and a block of two factors (3 × 2) was used with surface roughness as the response variable measured as the mean roughness average*.* Analysis of variance (ANOVA) was used to examine the results. A set of optimized tool and cutting conditions is presented for performing dry drilling repair operations.

**Keywords:** hybrid components stack; titanium; magnesium; repair and maintenance operations; drilling; dry machining; roughness average (*Ra*); ANOVA
