Hole Quality Research Articles

Effect of cutting tool geometry on hole quality in orbital drilling

Effect of cutting tool geometry on hole quality in orbital drilling

Tracking of horizontal alignment of the long and large diameter uncharged hole in NATM tunnel

The long and large diameter uncharged hole boring (LLB) method is a cut blasting method that minimizes blast-induced vibrations by creating long and large diameter uncharged holes at the excavation face of tunnels prior to tunnel excavation. Drilling in this method typically uses a 50 m long with a 382 mm diameter hammer bit in the horizontal direction at the tunnel face. However, the significant weight and uni-directional rotation of the rod head, as well as variables such as geological characteristics, machine conditions, and inexperienced operators result in significant deviation from the target borehole alignment that hinders the vibration-dampening effect of the uncharged holes. Furthermore, since there is no method to verify the alignment of the boreholes until main tunnel construction, borehole misalignment is often not discovered until weeks after construction, which requires tunnel construction to cease until the equipment can be remobilized and an additional borehole be created, causing significant delays and increased costs for the entire tunnel project. In this study, the borehole alignment tracking and ground exploration system (BGS) is developed to predict and monitor the quality and alignment of boreholes for cut blasting methods such as the LLB methods immediately after boring. The BGS was subsequently tested at a subway construction site to evaluate its performance in the field. The measurements yielded by the BGS were compared with manually measured boring positions at every 5 m along the borehole. Although the BGS showed a maximum deviation of approximately 12% at a local point where the hole surface was relatively rough, the accuracy for the final boring position was approximately 97%, demonstrating excellent precision of the alignment tracking system. The BGS demonstrates excellent performance in predicting ground conditions and the boring quality of a cut hole immediately after drilling, and shows promise in various other applications for monitoring borehole alignment.

Investigation of the drilling behavior of the Ti6Al4V alloy and developing prediction model using artificial neural network

This study investigates the influence of cutting parameters on drilling performance for Ti6Al4V alloy using TiN-coated carbide drill bits in a dry drilling environment. The surface roughness, feed force, cutting moment, cutting temperature, tool performance, hole diameter, circularity, and cylindricity values of the hole were studied. The optimal drilling parameters were determined using ANOVA to achieve the desired hole sizes, and prediction models were developed using artificial neural networks (ANN). The experimental results revealed that the feed rate was the most influential parameter for feed forces (92%), whereas the cutting speed had the greatest effect on tool performance (98%). It was determined as a result of the analyses that the optimal feed rate for tool performance, cutting moment, surface roughness, cutting temperature, and feed forces was 0.05 mm/rev. The diameter of the hole was positively affected at high cutting speeds and feed rates. The circularity and cylindricity of the hole were adversely affected by these cutting conditions. Adhesive wear was seen on the drill bits in all cutting conditions, and surface roughness was negatively affected by this adhesive wear. Artificial neural networks (ANN) were used to predict operating cost outputs (feed force, tool performance) and hole quality outputs (surface roughness, deviation of hole diameter). The compatibility of the experimental results and the ANN model was examined in the control experiment. ANN was able to predict the surface roughness and hole diameter with deviation values of 3% and 7%, respectively. Similarly, the deviation values for feed force and tool performance were determined at 3% and 10%, respectively.

Hole quality improvement in CFRP/Ti6Al4V stacks using optimised flow rates for LCO2 and MQL sustainable cooling/lubrication

Carbon fibre reinforced polymer/titanium stacks (CFRP/Ti6Al4V) are employed in aeronautics due to their excellent weight-to-strength ratio and corrosion properties. However, these same material properties present challenges for hole making which cannot be solved using conventional water-based metalworking fluids (MWFs), as they cause degradation of the composite. Moreover, environmental and health concerns require exploration of alternative cooling/lubrication solutions. In this study, a controlled mixture of liquid carbon dioxide (LCO2) and minimum quantity lubrication (MQL) was supplied through the drilling tool. The effect of varying LCO2 and MQL flow rates was evaluated on cutting forces, temperatures, and several hole quality outputs. The optimal flow rates were then determined through multi-objective optimisation. The results show that the cooling/lubrication flow rate greatly affects the measured outputs, and that supplying LCO2 + MQL with optimised flow rates helps achieve superior quality holes in CFRP, Ti6Al4V and CFRP/Ti6Al4V stacks.

Millisecond Pulsed Laser Micro-drilling of Stainless Steel – Optimizing Hole Quality Using Response Surface Methodology

Millisecond Pulsed Laser Micro-drilling of Stainless Steel – Optimizing Hole Quality Using Response Surface Methodology

Reservoir Drilling and Openhole Gravel Packing with High-Density Cesium Formate Fluids in a High-Pressure, Marginal Mud Window Environment at Martin Linge

Summary High-density cesium/potassium (Cs/K) formate fluids were successfully utilized from reservoir drilling to upper completion installation in five productive Martin Linge high-rate gas wells. Four wells were completed with openhole gravel pack (OHGP) and one with standalone sand screens. The gravel packing operation marks what is considered to be the highest density carrier fluid OHGP successfully completed worldwide, with a specific gravity (SG) of 2.06. A complex operation under pressure and temperature conditions (745–780 bar and 135–140°C) that almost qualify as high pressure/high temperature (HP/HT), including managed pressure drilling (MPD), overbalanced screen running, and openhole gravel packing, was simplified by using the same base brine throughout the operation. Cs/K formate reservoir drilling fluid (RDF) and screen-running fluid were designed with biopolymeric additives and minimal calcium carbonate bridging particles. Clear Cs/K formate brine was chosen as gravel pack (GP) carrier fluid. The use of Cs/K formate fluids for all stages of the operation reduced the complexity of transitioning between the operational stages. In addition, the reservoir was only exposed to one filtrate without application of damaging weighting solids. The drilling fluid contributed to successful MPD and delivered wells with very good hole quality in the reservoir, which consisted of interbedded sandstone, coal stringers, and shale. The shale-stabilizing properties of concentrated formate brine–based fluids provided acceptable conditions for extended openhole time and allowed additional logging runs, including pore pressure measurements, under near-HP/HT conditions, before running the screens. One bottom-up cleanout was conducted before the screen-running fluid was circulated in and the screens installed. The spurt and seepage losses were low throughout the drilling and screen-running phases. No breaker treatment was required in any of the wells. All wells have proved to have good initial productivity and high well productivity index. The successful OHGP operations performed with the high fluid densities required in Equinor’s Martin Linge field have set a new standard for well completions in challenging high-pressure environments.

Improving hole quality of thick CFRP laminates through a laser-mechanical compound drilling process

Conventional mechanical drilling of thick carbon fiber reinforced plastic (CFRP) composite laminates is prone to machining-induced defects such as burrs, delamination, and severe tool wear. However, pulsed laser drilling as an improved strategy results in hole taper and the formation of a heat-affected zone (HAZ). Herein, a new laser-mechanical composite drilling process is proposed, which combines the advantages of pulsed laser drilling for avoiding tool wear and twist drilling for achieving high dimensional accuracy, significantly improving the drilling quality of thick CFRP laminates. The evolution mechanism of the hole taper and HAZ with processing conditions in pulsed laser drilling is investigated. Furthermore, a theoretical model is established to reveal the material removal mechanism during the reaming process. The thrust force variation, drilling quality and tool wear are analyzed and verified by comparative experiments. The results show that due to the shielding effect from the surface materials, the maximum hole taper and HAZ at the hole exit reach up to 37.5° and 650 μm, respectively, which can be removed effectively by subsequent reaming operations. Due to its small amount of material removal, the peak thrust force and the average thrust force in laser-mechanical drilling are only 53.8 % and 37.6 % of the critical thrust force of delamination, respectively, which can effectively inhibit delamination. Compared with direct twist drilling, the average wear of the main cutting edge in laser-mechanical drilling is decreased by 60.87 %, which greatly reduces the size of the delamination by 55 %.

Multi-attribute optimization of drilling CFRP/Ti-6Al-4V alloy hybrid stacks using VIKOR

Drilling carbon reinforced polymer composites (carbon fiber-reinforced polymers, CFRP) and the hole quality produced are highly critical and significantly influence the performance and reliability of structures used in aircraft components. When CFRP composites are stacked together with titanium alloy, the damage caused by the machining operation is incalculable due to the burr and chip evacuation of metallic phases. In this article, efforts were made toward the identification of optimal machining conditions in drilling CFRP/titanium hybrid stacks. Experimental investigations on dry drilling of CFRP/titanium stacks were conducted with the aid of tungsten carbide drills. This research article discusses an improved compromise ranking method named VIKOR (VIseKriterijumska Optimizacija I Kompromisno Resenje) to determine the optimal machining parameters in drilling of CFRP/titanium stacks to produce high-quality holes. Attributes measured from experimental trials are: delamination factor of CFRP, burr height of titanium alloy, thrust force, torque, surface roughness, roundness and hole diameter of CFRP and titanium alloy. Experimental trial 13 with a combination of speed of 30 m/min, feed of 0.025 mm/rev was chosen as an ideal machining parameter in drilling CFRP/Ti-6Al-4V stacks without any trade-off. Confirmation tests convey that the results agree well with optimal parameters and the decision making in drilling such multimaterial stacks is highly consistent and judicious. In regard to the optimal parameters determined, investigations on tool life were performed and a tool life of 20 min for 0.10 mm flank wear land was observed.

Influence of cryogenic treatment duration of drills on drilling performance and hole quality of metal matrix composite materials

Influence of cryogenic treatment duration of drills on drilling performance and hole quality of metal matrix composite materials

A vision-based hole quality assessment technique for robotic drilling of composite materials using a hybrid classification model

A vision-based hole quality assessment technique for robotic drilling of composite materials using a hybrid classification model

Effect of drilling parameters on hole quality in drilling of pultruded GFRP composite material: Surface roughness, thrust force and delamination factor

Fiber reinforced polymer (FRP) composites are being used in a variety of areas. These materials need to be processed with some machining methods according to their usage areas, but their machinability is difficult. In this study, drilling is performed on glass fiber reinforced polymer (GFRP) composite produced by pultrusion with coated and uncoated drill. Then, surface roughness (SR), delamination factor (Fd) and thrust forces were investigated. Microstructures of chips formed during drilling were investigated and their effects on surface roughness were determined. Three distinct feed rates and cutting speeds were selected as machining parameters. Investigations showed that feed rate had a more significant effect on surface roughness, delamination factor and thrust force. It was understood that when the cutting speed increased, the surface roughness, thrust force and delamination factor decreased. Better results were obtained with TiN coated drills compared to uncoated drills.

Comparative Study of Percussion Drilling in Glasses with a Femtosecond Laser in Single Pulse, MHz-Burst, and GHz-Burst Regimes and Optimization of the Hole Aspect Ratio.

In this contribution, we present a comparative study on top-down drilling in sodalime glass, with a femtosecond laser operating in single-pulse, MHz-burst and GHz-burst modes, respectively. We investigate the hole depth, drilling rate, and hole morphology for these three regimes while keeping the same experimental conditions. We demonstrate that, for both burst regimes, the burst length has to be adapted for optimizing the hole depth. In the GHz-burst regime, the lower the ablation rate the longer the holes. The three drilling regimes lead to different hole morphologies, where the GHz-burst mode results in the best hole quality featuring glossy inner walls and an almost cylindrical morphology. Furthermore, we obtain crack-free holes, the deepest measuring 3.7 mm in length and 25 µm in entrance diameter corresponding to an aspect ratio of 150, which is the highest aspect ratio reported thus far with femtosecond GHz-burst drilling to the best of our knowledge.

ИССЛЕДОВАНИЕ РАССЕЯНИЯ ТВЕРДОСТИ КРУПНОГАБАРИТНЫХ КУЗНЕЧНО-ПРЕССОВЫХ ЗАГОТОВОК И ВЛИЯНИЯ НА ОБРАБАТЫВАЕМОСТЬ РЕЗАНИЕМ

The paper establishes the problem of lack of scientifically based solutions to ensure stability and quality of deep holes machining in conditions of hardness dispersion in large-sized blanks material. It was shown, that the solution to the problem could be the development of scientifically based recommendations for taking into account the inconstancy of machinability of large-sized forged blanks during stage of technological preparation of production, as well as for adaptive control of the deep drilling process.

Advancing electrochemical drilling process via coupling of flow field and electric field in pulsating state generated by a novel tube tool

This paper introduces an improvement to electrochemical drilling process by coupling flow field and electric field in pulsating state. A novel tube with half-wedged shape at the end (HW-tube) is prepared, with both sidewall and wedged part of the HW-tube insulated. Only the flat part is utilized to provide electric field for electrochemical drilling. By rotating the HW-tube, both flow field and electric field in pulsating state are generated, alternating in different positions within the inter-electrode gap (IEG). The pulsating flow field enhances the mass transfer process, while pulsating electric field disperses material dissolution process and distribution of electrolytic by-products. Both pulsating fields are coupled at the same frequency, further enhancing the electrochemical drilling process. Simulation results indicate that both flow field and electric field in pulsating state are generated. Compared to the traditional tube, the HW-tube significantly reduces the number of residual particles in IEG, and this number is further reduced by increasing the rotation speed. Experimental results reveal that the surface quality and dimensional uniformity of small hole are improved with HW-tube. With feed rate of 2.22 mm/min, a small hole with diameter of 1.52 ± 0.017 mm is drilled, resulting in a surface roughness of 0.331 μm.

Force-Position Hybrid Compensation Control for Path Deviation in Robot-Assisted Bone Drilling.

Bone drilling is a common procedure in orthopedic surgery and is frequently attempted using robot-assisted techniques. However, drilling on rigid, slippery, and steep cortical surfaces, which are frequently encountered in robot-assisted operations due to limited workspace, can lead to tool path deviation. Path deviation can have significant impacts on positioning accuracy, hole quality, and surgical safety. In this paper, we consider the deformation of the tool and the robot as the main factors contributing to path deviation. To address this issue, we establish a multi-stage mechanistic model of tool-bone interaction and develop a stiffness model of the robot. Additionally, a joint stiffness identification method is proposed. To compensate for path deviation in robot-assisted bone drilling, a force-position hybrid compensation control framework is proposed based on the derived models and a compensation strategy of path prediction. Our experimental results validate the effectiveness of the proposed compensation control method. Specifically, the path deviation is significantly reduced by 56.6%, the force of the tool is reduced by 38.5%, and the hole quality is substantially improved. The proposed compensation control method based on a multi-stage mechanistic model and joint stiffness identification method can significantly improve the accuracy and safety of robot-assisted bone drilling.

Investigation of CFRP damages induced by the interface high temperature and mixed tool wear mechanism in drilling of thin-walled CFRP /Ti stacks

Due to the poor thermal conductivity and machinability of CFRP and Ti6Al4V, significant heat accumulation at the interface and rapid tool wear are considered the main factors restricting the hole quality. This study conducted a thin-walled CFRP/Ti stack drilling experiment to investigate the evolution of the thrust force, temperature and tool wear versus different drilled hole numbers and spindle speeds, affected by which the novel material removal behavior was revealed. Results showed that the thrust force and interface temperature increased with the hole number and spindle speed, causing a significant increase in the cutting edge rounding and flank face wear dominated by the many fiber bundles and metal debris. In turn, the various tool wear led radial interface temperature to alternately transfer between Φ = 45° and 135°. Under the cyclic thermo-mechanical function, the fibers underwent significant bending deformation as they lost the support of the degenerated matrix resin, forming severe subsurface damage when the interface temperature exceeded the matrix glass transition temperature (Tg = 110 °C). Combined with the comprehensive evaluation of exit damages, a relatively higher spindle speed was preferred for selecting the initial drilling of thin-walled CFRP/Ti stack and gradually reducing the spindle speed with increasing tool wear extent.

Measurement and analysis of radial force, radial torque and surface integrity in micro-drilling of an Al7075-T6 alloy

Drill tip wandering during the entrance in the workpiece is a significant issue in micro-drilling because it directly affects hole quality, drill bit and dynamic stability. Although radial force and radial torque significantly influence drill tip wandering, measuring these characteristics has always been challenging, particularly due to their extremely low values. Therefore, the current research work aimed at measuring and analysing radial force and radial torque and correlating them with hole quality characteristics for the first time. Micro-holes are drilled on Al7075-T6 workpiece material using the pilot hole drilling technique under a wide range of spindle speeds and feeds. Radial force and radial torque exhibit increasing and decreasing behaviour with spindle speed, indicating the ‘size effect’. The oversize error shows an increasing trend with spindle speed and is closely related to radial force and radial torque. The deformation layer displays an increasing and decreasing pattern with spindle speed, clearly separating size effect regions. Furthermore, under a field-emission scanning electron microscope (FESEM), the deformation layer shows a higher possibility of cracks in the shearing region. However, due to the size effect, material accumulation with lesser or no cracks are obtained in the ploughing and transition regions. Hence, this research work clearly shows evidence of the ‘size effect’ and correlates it with radial force and radial torque for the first time. In addition, the impact of radial force and radial torque on hole oversize error and deformation layer in micro-drilling is being reported for the first time.

Effectiveness of coolant on sustainable drilling and hole quality of titanium alloy

The present research investigated the effects of input parameters such as feed rate, cutting speed and coolant type on sustainability and hole quality during the drilling of Ti-6Al-4V alloy. Several output parameters such as surface roughness, burr height, chip thickness ratio, thrust force, torque and peak power consumption were measured and analysed. Higher cutting speeds (2000 r/min) and lower feed rates (0.04 mm/rev) are recommended to be used to reduce drilling torque (0.77 Nm), thrust force (695 N) and power consumption (0.07 kW). However, it should be noted that increasing cutting speed (2000 r/min) can increase tool tip temperature which is detrimental, particularly for low thermal conductivity materials such as titanium alloys. In addition to that, the effect of tool wear also cannot be negated, as increased tool wear generates more heat in the cutting zone which was not effectively removed due to the poor thermal conductivity of titanium. Liquid nitrogen and chilled air had the greatest influence on temperature reduction at the cutting zone, however, its poor penetration and lubrication properties diminished hole quality. Minimum quantity lubrication conditions proved to strike a balance between good hole quality and enhancing sustainable machining by lowering torque, force and power consumption.

Study on helical milling of SS 304 with small diameter tools under the influence of minimum quantity lubrication (MQL)

The objective of the present work is to study the effect of minimum quantity lubrication (MQL) on the performance of helical milling for machining high-quality holes with a small-diameter tool. Helical milling with small tools (diameter < 5 mm) has been a challenging domain due to the problem of tool deflection, which deteriorates the hole quality and adversely affects the process efficiency. In this study, helical milling of stainless steel (SS 304) is carried to machine holes using a 3 mm diameter coated carbide tool in minimum quantity lubrication (MQL), and the performance is compared with dry and conventional flood cooling based on the hole quality and tool wear. The findings of this study reveal that MQL results in high-quality holes with the least circularity and cylindricity errors compared to dry and flood lubrication. Surface morphology study of the machined holes shows that the holes generated in MQL have smoother surfaces with no evidence of severe surface defects. MQL can also significantly mitigate the problem of tool deflection encountered in small-diameter tools and reduce tool wear by 33.3% and 21.7% compared to dry and flood lubrication, respectively. As per ISO 286-2 standard, hole quality up to grade H8 is achieved with MQL, while dry condition and flood lubrication yield hole quality corresponding to H9 grade. This study concludes that MQL-assisted helical milling is one of the sustainable alternatives for the production of high-quality small-diameter holes in stainless steel.

Cumulative effect of Shearing parameters and Ramp angle on Hole surface quality in Ti6Al4V by Helical milling strategy

Hole creation is a common contour in drilling and milling. However, drilling big holes in Ti6Al4V is difficult. It is due to the thermally increased metallurgical behavior of Ti6Al4V, which mortifies drill bits and degrades hole quality. To solve this issue, the current research investigates Helical milling through Computer Aided Tool Path as a viable option for Hole production by functionally managing shearing parameters. This approach drives the process parameters helically at a certain Ramp angle to achieve improved surface quality in the Hole. The analysis of variance reveals that the Cutting Speed and Feed/tooth affect the Circularity of the Hole. Furthermore, Axial DOC and Ramp angle significantly impactHole surface texture. The cumulative impact of Cutting Speed at 60 m/min, Feed/tooth at 0.06 mm, and Axial Depth of Cut at 0.6 mm applied at a Ramp angle of 1.50 through theHelical milling tool path under Hybrid nano Flood lubrication catch the outstanding Hole Quality.