The drilling mechanism of a novel laser produced micro-core drill from a solid PCD structure incorporating defined edge cutting teeth-and has been compared against a conventional micro-core drill utilising diamond abrasives in an electrolytically applied Nickel matrix. Evidence has been presented to show that the drilling mechanisms of the two drills are significantly different:
- The PCD core drill predominantly exhibits a shearing action of the carbon fibres during drilling. The defined edges of the cutting teeth produce well-defined hole surfaces, exit edges and fibre fractures showing clean cleaved ends.
- A more complex mechanism takes place during micro-core drilling using the electroplated diamond tool. Abrasive traces on the hole surface and reduced exit edge definitions are shown, with exposed fibre ends exhibiting irregular fractures caused by progressive/multiple contact with abrasives.
- The cutting forces of the electroplated micro-core drill was ca. 36% higher than for the PCD core drill when the tool was new and ca. 190% higher after 216 holes due to the pronounced abrasive fracture and surface clogging of the electroplated tool causing catastrophic delamination of the composite.
- The electroplated diamond micro-core drill produced 11% higher drilling temperatures than the PCD drill when new, which increased to 25% after 216 holes. The electroplated drill also produced a greater thermal spread (1.8 times greater along the 0° direction of fibre lay at 40° C for the 216th hole) than the PCD core drill.
These results have not only enhanced the understanding of the different mechanisms of diamond micro-core drilling, but have highlighted the benefits that can be realised in the drilling of abrasive composite structures with laser generated tools. This will provide enabling manufacturing capabilities in current and emerging applications of these high strength to weight materials.