Orthogonal cutting mechanisms of CFRP/Ti6Al4V stacks

Abstract

The enhanced mechanical/physical properties and improved functionalities have made the carbon fiber-reinforced polymer/ titanium alloy (CFRP/Ti6Al4V) stacks very attractive to the modern aerospace industry. However, the current knowledge of machining CFRP/Ti6Al4V stacks remains insufficient to guide their industrial applications. The main contribution of the present paper lies in the scientific understanding of the coupling effects and underlying mechanisms dominating the stack chip formation and cutting response transfer via the orthogonal cutting method. A particular focus was placed on the identification of the impact of different cutting sequence strategies (i.e., cutting from CFRP to Ti6Al4V and from Ti6Al4V to CFRP) on the stack machinability. The orthogonal cutting tests were carefully performed on a shaper machine tool using the polycrystalline diamond (PCD)-tipped inserts. The present study covers a variety of aspects in the CFRP/Ti6Al4V machining including the chip removal process, cutting forces, chip features, bouncing-back phenomenon and machined surface quality. The results discussed in this work allow for a better cutting understanding of CFRP/Ti6Al4V stacks and could advance the state of knowledge of the subject area.

A Review on the Machinability of Aerospace-Grade CFRP/Titanium Stacks

“…This means that the machining mechanisms of the stacks cannot be simply considered as the combination of the chip removal modes for the individual composite and titanium phases, particularly for the drilling operation. To understand the operating cutting mechanisms of CFRP/Ti stacks, Xu and his co-authors [15,29,46,[49][50][51][52][53] have sought to utilize the orthogonal cutting method to inspect the chip separation modes governing the machining of these composite-metallic stacks. In their work, both the experimental observations and the numerical simulations were adopted to reveal the underlying mechanisms of the stack chip formation process.…”

“…Fig. 1 shows the dynamic chip separation process of the CFRP/Ti stacks under the orthogonal cutting configuration [15]. It is clear that the entire cutting process for the CFRP/Ti stacks can be divided into three stages involving the composite cutting, the interface machining and the titanium cutting.…”

“…When the tool cuts across the interface region, a rapid transition of the chip separation mode from brittle fracture to elastoplastic deformation takes place, which leads to the change of the chip type during the cutting process. This phenomenon may initiate severe cutting vibrations as well as tool chatters during the stack cutting process, thus increasing the risk of catastrophic failure of tools like micro chipping or edge fracture [15]. Finally, when the tool attacks the titanium alloy, serrated and continuous chips are produced flowing along the tool rake face because of the elastoplastic behavior of the metallic phase.…”

“…Multilayer sandwiches made of CFRP composites and titanium alloys are advanced structural materials combining the merits of both the material phases while their individual weaknesses are significantly avoided [10][11][12]. Although the introduction of titanium alloys can alleviate the weakness of the composite phase, the machinability of the stacked composite/titanium material system is further degraded [13][14][15]. The reason lies in the different properties and machining characteristics of the CFRP and titanium alloy.…”

“…However, the inherent poor machinability of the composite/titanium stacks has greatly restricted their industrial applications, and the drilling operation becomes rather challenging particularly when high surface quality and dimensional accuracy are demanded. Even though great endeavors have been made to investigate the fundamental mechanisms of cutting CFRP/Ti stacks covering a variety of machinability inputs [9][10][11]13,15,, the knowledge obtained is still very limited and cannot be fully transplanted to the precision machining of the hybrid composite materials.…”