Increasing tool life is a significant objective in production. Achieving this objective in a machining process poses a significant challenge, especially during cutting hard-to-cut materials such as superalloys, due to the severe tool chipping/failure at the beginning of the cut. Although numerous attempts have been carried out to improve tool performance and prolong tool life during the machining of difficult-to-cut materials over the past several years, researchers have not obtained sufficient control over sudden tool failure/chipping. The focus of this study is to prolong tool life and control tool chipping by developing an ultra-soft deposited layer on the cutting tool that can protect it during the machining of difficult-to-cut materials such as Inconel 718. In the current study, an ultra-soft layer of material is deposited on the tool through two different techniques; a typical physical vapor deposition (PVD) technique and a novel developed method called “pre-machining”. In the PVD method, the soft layer is deposited under a high vacuum environment using a PVD coater. In the novel pre-machining method, the soft layer is deposited through a very short machining process involving Al-Si. It should be mentioned that soft coatings have never been used before for machining applications of difficult-to-cut materials including Inconel 718. This study shows that in contrast to what is expected, depositing an ultra-soft layer on the cutting tool significantly improves tool performance, by reducing chipping, and improving the machined surface integrity during cutting of Inconel 718. The obtained results show up to a 500% ± 10% improvement in tool life and around a 150% ± 10% reduction in cutting forces. Significant reductions in work hardening, residual stress, and surface roughness on the machined surface were other main achievements of the current study. / Thesis / Doctor of Philosophy (PhD) / Inconel 718 is considered to be a difficult-to-cut material due to its poor machinability. Significant tool failure at the early stage of cutting is the main challenge of machining this material and is the most significant contributing factor to its high manufacturing costs. Studies show that the common methods used to tackle this issue have not been completely successful. The goal of the present study is to tackle the machining challenges of Inconel 718 by developing tool coatings that meet the specific needs of the material to eliminate tool failure and thereby improve overall machining performance. For this purpose, a new tool coating material and a novel deposition technique that can be used as an alternative for commonly used coatings were developed in this study to improve the tool performance during the machining of Inconel 718. In addition, thorough studies have been carried out to gain a better understanding of the dominant wear phenomena and tool surface treatments that result in an improvement in the machinability of Inconel 718.

Hard turning of difficult-to-cut materials is an economical method of machining components with high surface quality and mechanical performance. Conventionally in the machining industry, generating a component from raw goods includes a casting or forging process, rough machining, heat treatment to a desired hardness, and then finished-machining through a grinding process. Given the relative disadvantages of grinding, which include high specific energy consumption and low material removal rates, a newer technology has been introduced; hard turning. After the heat treatment of a cast part (generally in a range of 50-65 HRC), hard turning allows for immediate finished-machining. Hard turning reduces the production time, sequence, cost, and energy consumed. In addition, dry machining offsets environmental concerns associated with the use of coolant in grinding operations as well as other common turning operations. Higher specific forces and temperatures in the contact area between the tool and workpiece lead to excessive tool wear. Generated tool wear affects the quality of the machined surface. Therefore, minimizing tool wear and consequently the generated surface quality become the status quo. Adverse effects associated with generated heat at the tool tip can be reduced by using cutting fluid or by continuously providing a fresh cutting edge. The latter method will be applied in this thesis. Rotary tool cutting involves a tool in the form of a disk that rotates about its axis. Different types of rotary tools have been developed, all with similar functional characteristics, however few are commercially available. Rotary tools can be classified as either driven or self-propelled. The former is provided rotational motion by an external source while the latter is rotated by the chip flow over the rake face of the tool. A prototype self-propelled rotary tool (SPRT) for hard turning was developed which provides economical benefits and affordability for the user. It was tested on a turret-type CNC lathe by machining AISI 4140 Steel that was heat treated to 54-56HRC and Grade 5 Titanium (Ti-6Al-4V). Carbide inserts with ISO designation RCMT 09 T3 00 (9.5mm diameter) were used during machining. Both the SPRT rotational speed and the workpiece surface roughness were measured. Also, chips were collected and analyzed for each of the cutting conditions. The same procedure was followed during machining with the same tool which was denied the ability to rotate, therefore simulating a fixed tool with identical cutting conditions. Comparisons were made between tool life, surface roughness, and chip formation for the fixed tool and SPRT. Tool rotational speed was also analyzed for the SPRT. In general, the designed and prototyped SPRT showed very good performance and validated the advantages of self-propelled rotary tools. A typical automotive component that is hard turned from difficult-to-cut materials is a transmission input shaft. These components demand high strength and wear resistance as they couple the vehicle‟s engine power to the transmission and remaining driveline. / UOIT