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In this story told in brief rhyming text, students in a class follow the proper procedures during a fire drill.

This article focuses on the problem of scaling on the inner wall of the drill pipe during the diamond rope coring drilling process, which affects the smooth salvage of the core. Based on the research results of predecessors at home and abroad, the main factors affecting the scaling on the inner wall of the drill pipe are sorted out systematically, and a calculation program that can calculate the scaling index I and critical diameter Dc conveniently and quickly is developed. The system can propose corresponding anti scaling and descaling measures based on the calculation results. It has been applied on site in engineering, providing useful scientific guidance for engineers to prevent scaling and ensure safe and efficient drilling.

In recent years, micro-hole drilling with a diameter of less than 1 mm has been widely applied in electronic information, semiconductor, metal processing, and other fields. Compared with conventional drilling, the engineer problems that micro drills are more prone to suffer failure in advance have restricted further development of mechanical micro drilling. In this paper, the main substrate materials of micro drills were introduced. And two important technical means to improve properties of tool material, namely, grain refinement and tool coating, were also introduced, which are current main research directions of micro drills from the perspective of materials. The failure mechanisms of micro drills were briefly analyzed, mainly tool wear and drill breakage. In the structure of micro drills, cutting edges and chip flutes are directly related to tool wear and drill breakage, respectively. So the structural optimization and design of micro drills, especially for key structures such as cutting edges and chip flutes, have to face great challenges. Based on the above, two pairs of requirements for micro drills were proposed, that is, the balance between chip evacuation and drill stiffness and the balance between cutting resistance and tool wear. So some innovative schemes and related researches of micro drills regarding cutting edges and chip flutes were reviewed. Finally, a summary of micro drill design and existing problems and challenges is proposed.

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.

Conical point drills are often used for making holes. In drill design, three drill point parameters, namely, drill point angle (or semi-point angle), chisel edge angle, and lip clearance angle, are specified. Geometrically, the conical point geometry is generated by two symmetric and oblique cones intersecting at the end of drill land. Thus, the drill point has to be designed in detail, which is to calculate the cone location and orientation parameters so that the drill point parameter values are equal to the specifications. Unfortunately, the previously proposed methods of drill point detailed design cannot be implemented in cutting tools companies, because one set of drill point parameter specifications can correspond to many sets of cone parameters which determine different drill point shapes. Moreover, the heel clearance flanks of some drills could rub stock material at the hole bottom while drilling, resulting in a large amount of force and heat, tool breakage, and severe wear. Drills with flank rubbing are invalid. However, the previous researches and applied industrial software cannot eliminate flank rubbing. To address the above problems, a practical and explicit mathematical model of conical drill point geometry without flank rubbing is established in this work. This work derives close-formed equations of the cone parameters and establishes a new criterion of flank rubbing detection. It can efficiently and consistently compute the cone parameters and detect flank rubbing for a valid drill point design. This explicit mathematical model is verified, and an approach to conical point detailed design is applied on two twist drills in the authors’ company. The differences between the drill point parameter values in the ground drill and the drill design parameter specifications are within an acceptable tolerance. Thus, the proposed method can be directly used in drill design and manufacturing in the tooling industry.

Various types of broken rock masses, such as those in fault-fracture zones and fracture zones, which form as a result of disturbance from tunnelling, are often encountered during underground engineering construction. These rock masses have low self-supporting capacity and poor stability, which can easily cause damage to surrounding rock, such as large deformation features, collapse and falling blocks, etc., posing a threat to construction safety. During a field project, reinforcement by grouting is a primary means for addressing the aforementioned problems. The effective measurement of rock mass characteristics (e.g., rock layer interfaces and the broken area of surrounding rock) provides a basis for the reasonable design of a grouting scheme. The quantitative evaluation of the effect of rock mass grouting is essential for optimizing the grouting scheme. In view of this, in this study, a multi-functional rock mass digital drilling test system and a special polycrystalline diamond compact drill bit for digital testing were developed and were applied to conduct digital drilling tests on intact, broken and grouted rock masses. In addition, a digital drilling test (DDT) technique-based method for measuring rock mass characteristics in real time and rapidly evaluating the grouting effect was proposed. The proposed method is capable of identifying rock layer interfaces, determining the broken area and obtaining the equivalent strength of grouted rock masses. This method is advantageous for obtaining quantitative and rapid test results, which can provide a theoretical basis and technical means for optimizing the grouting parameters and designing support schemes for underground engineering construction.

Machining of high-strength carbon fiber reinforced polymers (CFRPs) has faced great challenges in quality control and tool wear management due to their inherent heterogeneity and high abrasiveness leading to serious workpiece damage and rapid tool wear. The present paper contributes to an experimental investigation of evaluating the machinability of one type of high-strength T800/X850 CFRPs representative of aircraft components. The novelty of this work lies in identifying the effects of different specialized drills on the drilling process of the high-strength CFRPs by covering a variety of aspects involving the drilling forces, hole morphologies, workpiece damage, hole dimensional accuracy, and tool wear. Both the in-situ and post-process measuring results were correlated with the input process parameters and the used drill bits. A particular focus was placed on the inspections of the resulting tool morphologies and wear mechanisms governing the drilling of the high-strength CFRPs. The results highlight the importance of using functionally designed drills and optimum cutting conditions in realizing the damage-free drilling of T800/X850 composites.

Ultrasound vibration for hole-making can improve the hole-making quality of carbon fiber composite materials, but there are differences due to variations in the hole-making conditions and material properties. The handheld ultrasonic drilling tool is equipped with an ultrasonic vibration function, but the influence pattern of its drilling quality on the new composite materials is still unclear. Therefore, this paper conducts ultrasonic vibration experiments based on twist drills (hard alloy drills) and new composite materials, and discusses the influencing laws of ultrasonic vibration, dampers, and rotational speed on burrs and cracking. The results show that the drilling effect is better when using ultrasonic vibration and installing dampers. Moreover, a high rotational speed leads to significantly better drilling quality compared to a low rotational speed. The research findings of this paper provide references for the promotion and technical research of ultrasonic tools.

Unfavorable geological phenomena such as fault development and weak surrounding rocks are the common challenges encountered in tunnel excavation. However, the conventional rock mass classification method is complex, and the data obtained through disturbed rock samples cannot be used to dynamically and accurately class the surrounding rock in real time. In this study, discrete element method (DEM) is applied to simulate the rock-breaking process by pneumatic rock drill, and the drilling parameters of the surrounding rocks with different classes including drilling rate, vibration acceleration, and vibration frequency, are acquired during the excavation. The simulation results are verified through the data obtained by field tests in Luoping tunnel and Zilinshan tunnel of the Sandu Expressway in Guizhou province, China. Furthermore, a standard database for the dynamic classification of surrounding rocks is established. The numerical simulations reveal a good correlation between the average drilling rate, vibration acceleration, and vibration frequency of drill bit and the class of surrounding rock, and these factors can be used as dynamic evaluation indices for advanced geological prediction during tunnel construction. Overall, the results can serve as a useful reference for advanced geological prediction and dynamic classification of surrounding rocks during the construction of tunnels.

Bone drilling is an important process in orthopaedic and dental surgery, where excessive heat and poor surface integrity can lead to thermal osteonecrosis and loss of implant stability. Thermal response and post-drilling surface roughness are frequently examined independently, even though their interdependence remains poorly understood despite extensive analysis of their individual characteristics. This study combines an experimental investigation of maximum temperature ( T max ) and surface roughness ( Ra & Rz ) during drilling under the same conditions. A full factorial design was adopted with SS316L and ZrO 2 drill bits of 2.5, 3.0, and 3.5 mm diameter, a feed rate of 30–50 mm/min, and a spindle speed of 900–1300 rpm. The findings demonstrate that the spindle speed is the most important factor affecting T max and surface roughness. SS316L exercises produced increased temperatures ( T max of 61 °C) and roughness ( Ra of 17 μm), often higher than the 47 °C thermal limit. By comparison, ZrO 2 drills had lower T max (< 42.5 °C) and were more uniform in surface quality. The Pearson correlation analysis showed that T max and Ra had a moderate, diameter-dependent correlation with SS316L, whereas weaker correlations were observed with ZrO 2 . The results indicate that combined thermo-surface testing is important and suggest that ZrO2 drills perform better under controlled experimental conditions. Graphical Abstract