Inconel 718 (IN718) is a nickel-based superalloy extensively used within the aerospace sector as its properties mean jet engines can run at higher temperatures and, therefore, more efficiently. Additive Manufacturing (AM) of IN718 is now possible with near-net shape parts being manufactured through several different methods. AM parts, however, still need to be post-processed using machining to ensure that they have the precise dimensions and surface quality required by the aerospace industry. The properties of IN718 that make it desirable in engineering applications provide significant challenges during the machining process, with high heat generated in the cutting zone leading to rapid tool failure and high manufacturing costs. Flood coolant is a commonly used lubrication method to manage the heat generated during machining. However, environmental and health concerns associated with its use, as well as limitations when machining advanced alloys, mean alternative methods are being researched. A modified version of Minimum Quantity Lubrication (MQL) using nano lubricants (NMQL)is a method seeing an increasing amount of research for the machining of difficult-to-machine materials as the addition of nanoparticles can provide increased heat transfer and reduced friction leading to extended tool life.This research investigates the use of Tungsten Disulphide (WS2) NMQL for end milling both wrought and AM-IN718 using solid tungsten carbide end milling tools with it being compared to flood and dry machining environments. This thesis is split into five main sections: (i) review of state of the art in machining IN718 and identifying the research gaps, (ii) development of a systematic research methodology, (iii) investigating the impacts of WS2 particles on a base oil when used in an NMQL system, iv) investigating the impacts of WS2 NMQL on the machining of wrought IN178 (W-IN718), and (v) comparing the machining performance of AM-IN 718and W-IN718 with WS2 NMQL. This research showed a 22.5% increase in convective heat transfer and a 38.2% reduction in friction coefficient when using WS2 NMQL over MQL, leading to a maximum increase in tool life of 28.5%. Machining the heat-treated AM-IN718 (HT-AM-IN718) provided a significantly longer tool life than the machining of wrought, with the tool life being extended by 348.9%. The outer layer of the AM part generated a slightly lower cutting force than machining the bulk material. A correlation between the AM build angle and cutting forces was also identified during dry machining. When machining with NMQL, however, these differences became less apparent, indicating that when advanced coolant lubrication systems are used, the AM material can be treated as one material despite anisotropy in its microstructure
Machining of AM Inconel 718 Using Nano Lubricant MQL
Betts, J. (Author). 26 Jun 2024
Student thesis: Doctoral Thesis › PhD