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|Title:||CONTROL OF TRIBOFILMS FORMATION IN MACHINING HARD MATERIALS|
|Keywords:||CONTROL OF TRIBOFILMS FORMATION IN MACHINING HARD MATERIALS|
|Abstract:||The study of factors governing cutting tool performance and life is driven by manufacturers’ need to increase economic efficiency in their production facilities. Tooling and process optimization represent an ongoing opportunity for realizing substantial improvements, thus manufacturers continue to focus on promoting design and development of cutting tools and surface treatment technology relevant to machining. The central goal of cutting tool technology is to increase productivity while simultaneously reducing cost and meeting the quality targets of the machined parts. This thesis considers a nano-tribological approach to explain some of the past performance improvements in cutting tools used in dry machining applications and to look for opportunities to make further improvements in this field. The approach considers tribofilms, which are often described as tribo-oxides composed of either the base cutting tool material or freshly cut workpiece material transferred to the tool that have formed on the friction surface through interaction with the environment (air or cutting fluids) and a tribo-oxidation process. In general, the formation of tribofilms plays an important role in friction and wear behaviour by offering thermal protection and/or in-situ lubrication, which is especially important during dry machining of hard workpiece materials. The formation of various tribofilms on cutting tools have been reported through: 1) cutting tools with surface modification and further tribo-oxidation during the cutting process; 2) mass transfer from freshly cut workpiece material due to tool/chip contact in machining; and 3) interaction between the cutting tool surface and the cutting environment. This dissertation presents a novel method to control the formation of tribofilms on the cutting tool surface during machining of hard materials such as Inconel DA 718 and hardened steels (AISI T1 and AISI D2), with coated and uncoated tools. In particular, the frictional conditions experienced by the cutting tool during the initial period of cutting (the running-in stage) are shown to strongly influence whether or not beneficial processes related to adaptability will trigger. Employing a more aggressive cutting speed during the running-in stage noticeably enhances the generation of protective/lubricious tribo-ceramic films on the friction surface. When the cutting speed is subsequently reduced, the accelerated formation of beneficial tribofilms previously initiated is not fully removed and therefore the rate of tool wear is considerably less than if the tool is run at the lower cutting speed for its entire life. In addition, preliminary results are presented regarding tribofilms formation under the influence of the cutting environment, specifically the nature of the cooling medium used, which demonstrates an entirely different avenue to explore in terms of fine-tuning of tribofilms generation. The overall objective of this dissertation is to highlight different approaches to control the tribofilms formed on the cutting tool surface in order to benefit the machining process and to improve cutting tool life, material remove rate and the machined surface quality. Additionally, little work has been found demonstrating the formation of tribofilms on the tool surface through mass transfer from the workpiece material or through interaction with the cooling medium. Thus a secondary objective of this work is to demonstrate the formation of tribofilms through these different means and to investigate the effect of cutting parameters on their formation.|
|Appears in Collections:||Open Access Dissertations and Theses|
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