Hybrid stacks made of carbon reinforced plastic (CFRP) and Ti-6Al-4V alloy (Ti) are often drilled together to reduce positional errors, enhance tight tolerances and minimize machining time. However, this is a complex task due to the dissimilar properties of each material. Tool geometry has a significant impact on the machinability of CFRP/Ti stacks. In this study, the influence of flute number and stepped bit design was experimentally investigated. Confocal and SEM microscopy were used to analyse the evolution of the cutting-edge micro-geometry and the dominant wear modes. The results have shown that a stepped design with three flutes leads to a slower wear progression, lower cutting forces and less hole damage. Furthermore, this paper also highlights the influence of the geometrical characteristics of the stepped tool design on the drilling stage number and on the shape of the thrust force signal. The information gathered can be used for the improvement of the process competitiveness in terms of the reduction of production time and cost.
Materials undergo various loading conditions during different manufacturing processes, including varying strain rates and temperatures. Research has shown that the deformation of metals and alloys during manufacturing processes such as metal forming, machining, and friction stir welding (FSW), can reach a strain rate ranging from 10−1 to 106 s−1. Hence, studying the flow behavior of materials at different strain rates is important to understanding the material response during manufacturing processes. Experimental data for a low strain rate of <101 s−1 and a high strain rate of >103 s−1 are readily available by using traditional testing devices such as a servo-hydraulic testing machine and the split Hopkinson pressure bar method, respectively. However, for the intermediate strain rate (101 to 103 s−1), very few testing devices are available. Testing the intermediate strain rate requires a demanding test regime, in which researchers have expanded the use of special instruments. This review paper describes the development and evolution of the existing intermediate strain rate testing devices. They are divided based on the loading mechanism; it includes the high-speed servo-hydraulic testing machines, hybrid testing apparatus, the drop tower, and the flywheel machine. A general description of the testing device is systematically reviewed; which includes the working principles, some critical theories, technological innovation in load measurement techniques, components of the device, basic technical assumption, and measuring techniques. In addition, some research direction on future implementation and development of an intermediate strain rate apparatus is also discussed in detail.
The present work focuses on the manufacturing of Ti-6Al-4V parts using hot single point incremental forming (SPIF), a non-conventional forming technology mainly oriented toward the fabrication of prototypes, spare parts, or very low volume series. In the used procedure, the entire sheet is heated and kept at uniform temperature while the tool incrementally forms the part, with the limited accuracy of the obtained parts being the major drawback of the process. Thus, this work proposes two approaches to improve the geometric accuracy of Ti-6Al-4V SPIF parts: (i) correct the tool path by applying an intelligent process model (IPM) that counteracts deviations associated with the springback, and (ii) skip overforming deviations associated with the deflection of the sheet along the perimeter of the part based on a design improvement. For this purpose, a generic asymmetric design that incorporates features of a typical aerospace Ti-6Al-4V part is used. The results point out the potential of both solutions to significantly improve the accuracy of the parts. The application of the IPM model leads to an accuracy improvement up to 49%, whereas a 25.4% improvement can be attributed to the addendum introduction. The geometric accuracy study includes the two finishing operations needed to obtain the part, namely decontamination and trimming.
Two relevant references of the IJPEM journal have been included in the final version (ref. 2 and ref. 24). Regarding the JPGT, a relevant paper related to the topic of the present manuscript had already been included (ref. 11).•The box frame of several figures has been removed.Yours Sincerely,
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