In recent years, the use of CFRP with titanium and/or aluminum to form materials for stacking has gained popularity for aircraft construction. In practice, single-shot drilling is used to create perfectly aligned holes for the composite-metal stack. Usually, standard twist drills, which are commonly available from tool suppliers, are used for practical reasons. However, existing twist drill bits exhibit rapid wear upon the drilling of composite-metal stack layers in single shot, due to the widely contrasting properties of the composite-metal stack, which causes poor surface quality. The stringent quality requirements for aircraft component manufacturing demands frequent drill bit replacement and thus incurs additional costs, a concern still unresolved for aircraft component manufacturers. Owing to highly contrasting properties of a composite-metal stack, it is obvious that standard twist drill cannot fulfil the rigorous drilling requirements, as it is pushed to the limit for the fabrication of high-quality, defect-free holes. In this work, customised twist drills of a tungsten carbide (WC) material with different geometric features were specially fabricated and tested. Twenty drill bits with customised geometries of varying chisel edge angle (30–45°), primary clearance angle (6–8°), and point angle (130–140°) were fabricated. The stacked-up materials used in this study was CFRP and aluminum alloy 7075-T6 (Al7075-T6) with a total thickness of 3.587 mm. This study aims to investigate the effect of twist drill geometry on hole quality using drilling thrust force signature as indicator. All drilling experiments were performed at spindle speed of 2600 rev/min and feed rate of 0.05 mm/rev. Design of experiments utilising response surface methodology (RSM) method was used to construct the experimental array. Analysis of variance (ANOVA) was used to study the effect of parameters and their significance to the thrust force and thus the hole quality. The study shows that the most significant parameter affecting the drilling thrust force and hole surface roughness is primary clearance angle, followed by chisel edge angle. Correlation models of CFRP thrust force (Y₁), Al7075-T6 thrust force (Y₂), CFRP hole surface roughness (Y₃), Al7075-T6 hole surface roughness (Y₄) as a function of the tool geometry were established. The results indicated that the proposed correlation models could be used to predict the performance indicators within the limit of factors investigated. The optimum twist drill geometry was established at 45° of chisel edge angle, 7° of primary clearance angle, and 130° of point angle for the drilling of CFRP/Al7075-T6 stack material in a single-shot process. The error between the predicted and actual experiment values was between 6.64% and 8.17% for the optimum drill geometry. The results from this work contribute new knowledge to drilling thrust force signature and hole quality in the single-shot drilling of composite-metal stacks and, specifically, could be used as a practical guideline for the single-shot drilling of CFRP/Al7075-T6 stack for aircraft manufacturing.

User experience and many machine breakdown records of FDM rapid prototyping indicated that moisture effects on Acrylonitrile Butadiene Styrene (ABS) which consequently causes physical, morphological and thermal stability changes to the polymer, is the major cause of problem. These reports claim that these changes may have caused nozzle blockage on the liquefier of the Fused Deposition Modeling (FDM) machine although no thorough investigation were done. Experiments are therefore conducted to verify these assumptions. It has been observed that physical changes do not cause nozzle clogging. The clogging is due to the morphological and thermal stability changes of ABS when the material is exposed to moisture.

Drilling two different materials in a layer, or stack-up, is being practiced widely in the aerospace industry to minimize critical dimension mismatch and error in the subsequent assembly process, but the compatibility of the drill to compensate the widely differing properties of composite is still a major challenge to the industry. In this paper, the effect of customized twist drill geometry and drilling parameters are being investigated based on the thrust force signature generated during the drilling of CFRP/Al7075-T6. Based on ANOVA, it is found that the maximum thrust force for both CFRP and Al7075-T6 are highly dependent on the feed rate. Through the analysis of maximum thrust force, supported by hole diameter error, hole surface roughness, and chip formation, it is found that the optimum tool parameters selection includes a helix angle of 30°, primary clearance angle of 6°, point angle of 130°, chisel edge angle of 30°, speed of 2600 rev/min and feed rate of 0.05 mm/rev. The optimum parameters obtained in this study are benchmarked against existing industry practice of the capability to produce higher hole quality and efficiency, which is set at 2600 rev/min for speed and 0.1 mm/rev for feed rate.

Recently, there has been rising interest in 4D printing (4DP) technology. It is a new technology that emerged from 3D printing technology but can produce a dynamic product that can change its shape and properties when subjected to external stimuli. 4DP is an additive manufacturing process that uses materials receptive to stimuli, such as shape memory polymer (SMP), that can alter its shape once exposed to applied stimuli like heat, water, light, electricity, pressure, etc. Two frequently used SMPs are polylactic acid (PLA) and thermoplastic polyurethane (TPU), owing to their excellent shape memory properties, biodegradability, and biocompatibility. The shape memory performance of the 4D printed SMP is quantified by shape recovery ratio (R_r) and shape fixity ratio (R_f), which is highly dependent on the printing parameters. Some of the important printing parameters that influence shape memory performance are printing speed, raster angle, layer thickness, and nozzle temperature. Due to 4DP’s ability to produce a dynamic product, it is widely used to revolutionize several fields such as biomedical, textile, aerospace, soft robotic, and electronic fields. This review paper discusses and provides a better understanding of the 4DP technology, the shape recovery mechanism, the effect of 4DP parameters on shape recovery performance, applications of 4DP technology, challenges faced, and future perspectives regarding the 4DP technology.