Research on the machining of titanium alloy with graphene based nanofluids
Creators: name: Yi, Shuang
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401406
subject: Machining
classificationCode: 401408
subject: Manufacturing processes and technologies (excl. textiles)

description: The excellent mechanical property and unrivalled corrosion resistance of titanium alloys lead to their wide application in the aerospace, defence industry and biomedical engineering. However, titanium alloys are difficult to machine due to their low thermal conductivity and high chemical reactivity, which in turn result in severe cutting conditions including high temperature at tool-chip interface and highly abrasive interactions at tool-workpiece interface. The harsh conditions of high temperature and large friction adversely affect tool life, cause premature tool failure and eventually lead to extremely low machining efficiency. <br><br>Recently, the advance in developing new nanoparticles opened new opportunities for manufacturing industry. Graphene oxide (GO) is two-dimension material and have the  outstanding thermal conductivity (5000 W/m-K.) and  excellent tribological properties of GO  make GO nanofluids an ideal cooling media for machining titanium alloys, in particular Ti-6Al-4V. Based on the properties of graphene oxide and relevant research carried out so far, it is reasonable to predict that the application of graphene oxide nanofluids in machining processes may result in substantial enhancement of cooling effects and consequently result in lower cutting temperature, smaller cutting force, less tool wear, better surface quality and improved machining efficiency. However, there is a lack of fundamental knowledge and in-depth understanding of the working mechanism of GO in the machining processes and it is unclear how their performances will be in machining titanium alloys. <br><br>This thesis investigated the working mechanism and performance of different types of GO nanofluids in different machining process including both turning and drilling. Two novel models of using GO nanofluids in turning processes which can accurately predict the change in cutting temperature and cutting forces were developed. The cutting temperature model was created by considering the thermal conductivity and specific heat of the GO nanofluids along with their heat transfer coefficient and friction coefficient, whereas the cutting force model was developed by taking into account friction, tool geometry and the friction coefficient associated with the thermal properties of nanofluids. In this research, the GO nanoparticles could increase the lubrication and reduce friction force. Reduction of friction of about 4.01%, 5.36% and 3.37% were achieved when 0.1 wt.%, 0.3 wt.% and 0.5 wt.% GO nanofluids were applied. With the increase in the concentration of  GO nanofluids, the cutting temperature and cutting force generally dropped. However, the reduction rate of cutting force when the concentration was 0.5wt.% was lower than that of 0.3 wt.%. For the cutting tools, While fractures, adhesion chips and BUE were found on the tool rake face under conventional cooling condition, less BUE and attrition wear were observed when GO coolant was applied. Flank wear and the wear of rake face were reduced by 77.78% and 41.21%. The GO concentration of 0.3 wt.% showed the best performance on tool wear. Surface topography showed that GO nanofluids resulted in less scratch and plastic deformations than those processed by conventional fluid. The average surface roughness was 27.51% less when using GO suspended fluid. Cutting temperature decreased by 30.87 ℃, 34.90 ℃ and 36.80 ℃, respectively when GO nanofluids of 0.1 wt.%, 0.3 wt.% and 0.5 wt.% were applied while the feed rate was 0.05 mm/rev and the pressure of coolant was 1 Bar. When feed rate was increased to 0.1 mm/rev, the cutting temperature increased as well. In the meantime, higher coolant pressure lead to lower cutting temperature under same cutting conditions.<br><br>By analysing cutting temperature, cutting force, chip morphology, workpiece microstructure, material diffusion and cutting vibration through a series of well-designed cutting experiments with different types of tools and coolants, the theories of tool wear and new machining mechanisms of applying GO nanofluids were found. This work will be able to to provide useful information to the industry and stimulate further research in this area.