The research presented in this paper investigated the effects of spindle speed and feed rate on the resultant cutting forces (thrust force and torque) and temperatures while drilling SawBones^® biomechanical test materials and cadaveric cortical bone (bovine and porcine femur) specimens. It also investigated cortical bone anisotropy on the cutting forces, when drilling in axial and radial directions. The cutting forces are only affected by the feed rate, whereas the cutting temperature in contrast is affected by both spindle speed and feed rate. The temperature distribution indicates friction as the primary heat source, which is caused by the rubbing of the tool margins and the already cut chips over the borehole wall. Cutting forces were considerably higher when drilling animal cortical bone, in comparison to cortical test material. Drilling direction, and therewith anisotropy, appears to have a negligible effect on the cutting forces. The results suggest that this can be attributed to the osteons being cut at an angle rather than in purely axial or radial direction, as a result of a twist drill's point angle.

This paper investigates the performance of small diameter high-speed steel twist drills drilling boreholes with a depth of ten times the diameter into carbon steel AISI 1045 using minimum quantity lubrication. The performance of small twist drills is determined, first, by their deep-hole drilling capability, i.e., in how far the cutting forces can be kept at a noncritical level by maintaining the chip disposal, and, second, by their tool life. This work shows that both the deep-hole drilling capability and tool life of small drills are strongly dependent on their geometry, in particular the size of the chip flutes, and the flute surface topography.

Composites from carbon fibre reinforced polymers (CFRPs) play a significant role in modern manufacturing. They are typically used in aerospace and other industries that require high strength-to-weight ratios. Composite machining, however, remains a challenging job and sometimes is hampered by poor efficiency. Despite considerable research being conducted over the past few years on the machining of composite materials, the material nevertheless suffers from delamination, fibre loss, and imperfect finishing of the fuselage. Laser technology is becoming increasingly popular as an alternative approach to cutting and drilling composites. Experiments have been conducted with a CFRP thickness of 25.4 mm using fibre laser to test the effect of the machining parameters on the primary performance measurements. In this study, different machining criteria are used to assess the fibre laser ability of thick CFRP composites for drilling operation. The experimental findings revealed that a fibre laser is capable of penetrating a thick CFRP to a depth of 22 mm by using a novel drilling procedure.

Carbon fibre reinforced polymer composites (CFRPs) can be costly to manufacture, but they are typically used anywhere a high strength-to-weight ratio and a high steadiness (rigidity) are needed in many industrial applications, particularly in aerospace. Drilling composites with a laser tends to be a feasible method since one of the composite phases is often in the form of a polymer, and polymers in general have a very high absorption coefficient for infrared radiation. The feasibility of sequential laser–mechanical drilling for a thick CFRP is discussed in this article. A 1 kW fibre laser was chosen as a pre-drilling instrument (or initial stage), and mechanical drilling was the final step. The sequential drilling method dropped the overall thrust and torque by an average of 61%, which greatly increased the productivity and reduced the mechanical stress on the cutting tool while also increasing the lifespan of the bit. The sequential drilling (i.e., laser 8 mm and mechanical 8 mm) for both drill bits (i.e., 2- and 3-flute uncoated tungsten carbide) and the laser pre-drilling techniques has demonstrated the highest delamination factor (S_FDSR) ratios. A new laser–mechanical sequence drilling technique is thus established, assessed, and tested when thick CFRP composites are drilled.

Although substantial research work has been conducted in order to understand and improve the drilling of multi-material aerospace stacks, some key aspects related to process and tool parameters and their impact on the interface quality still need to be addressed. This paper reports on the research conducted to investigate the impact of tool point angle and interlayer gap width on borehole quality, focussing on the interface region. A number of drilling tests were carried out using tools with different point angles and CFRP/titanium stacks with different interlayer gap widths. The results show that the damage on the CFRP interlayer surface is caused by the drilling of the titanium layer, as some of the upwards-travelling titanium chips penetrate into the stack interface. An increase in tool point angle results in larger entry burrs on the titanium interlayer surface, which is attributed to the correlation between tool point angle and thrust force and the capability of tools with low point angles to remove damage generated by surface skidding. The introduction of an interlayer gap promotes the ingress of titanium chips into the stack interface, thereby leading to more pronounced interface damage.