Drilling plays an important role in the production processes of the manufacturing industry, and in the course of history several improvements have been made in tool material and geometry. Frequently the use of solid drills is a necessary step in the final production stage. Nowadays the industry is being challenged not only by the lower prices offered by foreign competitors, but also by higher energy costs in the UK and environmental standards. A promising opportunity is the use of surface modified tools in cutting processes with a positive impact in reducing cutting forces and improving machining performance. This study therefore researches the use of structured surfaces on cutting tools as a novel way of improving manufacturing performance.Prior to this research, surfaces of different deterministic patterns have been studied to give a specific function in the conventional cutting process. However, less than a handful of studies have focused on drilling. Moreover the existing studies have been limited to evaluating the effects of structured surfaces in the rake face of the tools. The rake face is directly relevant for chip flow, but does not dominate tool life and surface integrity in machining. Therefore, the aim of the research was to focus on surface structuring on drilling tools, an area which is rarely focussed on; and more significantly, to research structuring the flank face, which is adjacent or in contact with the newly machined surface, and hence has impact on the quality of the machined component.The sinking electro discharge machining (SEDM) process was researched and used for the creation of structures on HSS drilling tools. Parameters of SEDM were optimised and it was found that working with a low current of 8A and voltage of 150V, it was possible to effectively structure parallel sunken slots. The location of the structures on the flank face was informed by research on contact area and phenomenon evaluation. By evaluating the contact length in the flank face between the tool and the workpiece while drilling, the structured surface was limited to 1mm from the edge and across the flank face. In addition, this study proposed a contact length model of flank face contact, with AISI 1045 steel, dependent on the actual chip thickness. The rule of thumb developed is that in drilling, the contact length on the flank face extends to four times the chip thickness. Yet, for aluminium alloy 2050, it was only double the chip thickness. This indicated the importance of considering the work material in the design and location of structures. The evaluation of cutting forces while drilling indicated not only a decrease of around 30% in fluctuations of force, but also a reduction in both torque and thrust force of about 14% and 2% respectively. This research has developed fundamental basis for the design and the location of flank face structures, as informed by the contact phenomenon in machining. This is important for developing tailored structures on tools for drilling different workpiece materials, through achieving successful reduction in power consumption by using structured tools. This thesis proved that modification of drill tool surfaces can bring specific function improvements.
|Date of Award||31 Dec 2015|
- The University of Manchester
|Supervisor||Paul Mativenga (Supervisor) & Carl Diver (Supervisor)|
- Structured Surface
- Surface Engineering