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Both net present value (NPV) and equivalent annual cost (EAC) are appropriate methods for modifying an investment project. While Net Present Value may assist investors in evaluating the project's cash flows, EAC illustrates the cost of several projects over a year. The purpose of this research is to discover whether one of the two metrics, NPV or EAC, is superior. Net Present Value is the difference between the present value of cash flows and the present value of cash flows after a period. The annual cost of ownership, operation, and maintenance are equivalent. To establish whether NPV or EAC is the more appropriate technique for adjusting investment projects, this essay use them to estimate the optimal machine life. After evaluating the calculation procedure for this issue and using these two approaches, the findings indicate that EAC is more appropriate for investment projects with varying durations. These findings imply that net present value is more appropriate for estimating the cost of a project over a specified period; thus, when dealing with investments with varying life spans, equivalent annual cost is a better option than net present value.

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Gun drills have widely been in use in deep-hole drilling of manufacturing in automobiles and models. They could improve straightness and surface roughness of holes. However, with the improvement of material property and the increasing need for drilling holes that have big aspect ratio, problems like breaking and removing chips when drilling deep holes continue to appear, which would break the cutting tool when these problems are severe. All these problems would greatly lower the durability and the ability of machining of gun drills. Additionally, as for drilling holes on crankshaft that’s made of 42CrMo, for example, due to its high fatigue strength and great toughness, it’s not easy to break chips and cutting tools worn down in a fast rate. Aimed at prolonging the lifetime of gun drills when drilling materials that are relatively difficult to drill and improving the manufacturing productivity, this paper presents a kind of gun drill with groove-type chip breaker and describes the geometrical parameters of groove-type chip breaker.