Sikiru Oluwarotimi Ismail

Recent advances in twist drill design for composite machining: A critical review

In the field of composite technology, inefficient and poor designs of twist drills contribute immensely to the challenges facing drilling of composite materials. An attempt to report some of the drill design methods and their inherent challenges confronting composite machining necessitates the writing of this article. A critical review has been conducted to offer a clear understanding of the current advances in the field of mechanical drilling of composite materials, focusing on geometry, material and parametric tool designs. The inter-dependable effects of thrust force, cutting speed, feed rate, cutting force and torque on drill design are similarly reviewed. This article also reveals other associated issues facing composite drilling including delamination, surface roughness, rapid tool wear and drill breakage. Well-designed drill geometry and good knowledge of drilling parameters afford the producers of polycrystalline diamond, carbide and high-speed steel tooling materials better opportunity of developing a drill that will minimise delamination of the reinforced composites and tool wear and produce a high-quality surface. Twist drill manufacturers and users will benefit from this article as they seek to have well-designed and improved drills.

Philosophical study on composites and their drilling techniques

Due to the advancement in the properties, design and manufacturing of fibre-reinforced polymer composite materials, especially the natural or bio-based types, their wide applications have been significantly enhanced compared to the conventional materials (metals and alloys). With this trend, there is a strong interest and importance in understanding the machinability of these materials. Machinability of these materials depends, among other parameters, on properties of fibres and matrices, drilling conditions, parameters and techniques. Among the machining operations of these composites, drilling is the most crucial and common operation. Hence, this chapter focuses on better understanding of biocomposites and various composite conventional and non-conventional drilling techniques. The primary aim of this chapter, therefore, is to provide comparative analysis between conventional and non-conventional drilling of composite materials.

The post-impact response of flax/UP composite laminates under low velocity impact loading:

Flax fibre-reinforced unsaturated polyester composite laminates were fabricated by vacuum bagging process and their impact and post-impact responses were investigated through experimental testing and finite element simulations. Samples of 60 mm × 60 mm × 6.2 mm were cut from the composite laminates and were subjected to a low-velocity impact loading to near perforation using hemispherical steel impactor at three different energy levels, 25, 27 and 29 Joules. Post-impact was employed to obtain full penetration. The impacted composite plates were modelled with various lay-ups using finite element software LS-DYNA (LS-DYNA User’s Manual 1997) to provide a validated finite element model for the future investigation in the field. The effects of impact and post-impact on the failure mechanisms were evaluated using scanning electron microscopy. Parameters measured were load bearing capability, energy absorption and damage modes. The results indicate that both peak load and the energy absorption were reduced significantly after the post-impact events. Consequently, it was observed from the visual images of the damages sites that the extent of damage increased with increased incident energy and post-impact events.

Finite element analysis on conventional drilling of natural fibre-reinforced polymer bio-composites

Finite element analysis (FEA) on conventional drilling of two biocomposite materials, consist of hybrid woven flax-basalt and woven basalt fibre with vinyl ester matrix, designated as composite materials A and B respectively, has been conducted. The simulation results using LS-DYNA and ANSYS software depict that different reinforcements (flax and basalt fibres) of the composite materials significantly influenced the degree of resistance, strength, deformation and elasticity exhibited during the machining process. It was observed that drillinginduced damage were experienced in different degrees by the materials. The quality of the holes produced was affected by the characteristics of these materials, when experimentally validated. Also, significant differences in tensile strength and impact of the drilling operation on the plies of the two materials were observed. Material A experienced higher stress and lower tensile strength, resulting into a higher level of push-out delamination, uncut-fibre and fibre pull-out, among other rampant drilling-induced damage, than material B. Both materials possessed high stress and deformation, which were more at the edges (entry and exit) of the drilled holes rather than the centre point where the drill impacted the hole. The equivalent elastic strain further shows a high level of impact at the surface of material A, unlike material B. Comparatively, the composite material B (woven basalt fibre reinforced polymer) has a better machinability when compared with hybrid material A (woven flax-basalt). Hence, it implies that the FRP composite materials responded to damage differently under same machining (drilling) process and condition.

Analysis and impacts of chips formation on hole quality during fibre-reinforced plastic composites machining

This work presents the effect of chips formation types on the quality of drilled holes of natural and conventional hemp and carbon fibre-reinforced plastic (HFRP and CFRP) composites respectively. The results depict that variation in chips morphology depends on drilling parameters, drill geometry and composite compositions (matrix and fibre properties). HFRP samples produced continuous brown ribbon-like chips, which were short and melted at lower feed rate and cutting speed, implying that higher feed rate and cutting speed produced wider, longer and lighter chips. CFRP samples generated discontinuous black powder-like chips, with small and abrasive chips at the same applied drilling parameters. These formation and morphology affected quality of drilled holes: lower surface roughness in CFRP, but lower delamination and drill wear in HFRP samples. Evidently, an increased feed rate, cutting speed and drill diameter caused an increase in chips formation, validating the material removal rate (MRR) model results.