Analyses of two manufacturing systems in drilling of CGI: drilling and reaming × drilling

In many applications in the metalworking industries, mass production of parts with holes possessing critical finish requirements for precision assembly operations demands tolerances in the working range of IT7 to IT5. However, this may not be achieved with regular twist drills, and further finishing processes such as reaming is normally required. To perform reaming, the workpiece needs to be previously drilled, so that two different cutting tools are needed and twice as much time is needed to machine compared with workpieces that need to be drilled, which in turn affects productivity and competitiveness. Therefore, any investment in the production of tools and techniques aiming to reduce the machining time of close tolerance holes, and lower tool wear rates and at a lower cost, will receive special attention from the machining sector. In this context, this paper presents technical and economic analyses of two manufacturing systems in drilling (drilling specially designed drill and regular drill with reamers) of compacted graphite iron (CGI) workpieces. The technical analysis was based on the tool wear mechanism, hole quality, and machining time, whereas the economic analysis was on total machining cost for use of specially designed drill and regular drills followed by reamers. Results showed lower wear on the specially designed drills compared with reamers. Also, the finish and dimensional deviations were similar to those obtained with reamers. Up to 40% of reduction in the machining time was achieved by using the specially designed drill, which resulted in a 57% reduction of the total cost.