Dry Drilling Research Articles

Delamination and hole wall roughness evaluation in air-cooled drilling of carbon fiber-reinforced polymer

Drilling of carbon fiber-reinforced polymer (CFRP) is widely employed in manufacturing processes in the aeronautical, automobile, and energy industries. The evaluation of the hole region focusing on wall roughness and delamination phenomena is extremely important to predict bolted joints' performance, where at least one of the adherent is a composite material. Thus, this work performed a statistical analysis on the delamination (entrance and exit of the plate) and wall roughness of drilling holes in an 8.6 mm thick CFRP plate carried out by an uncoated carbide drill under compressed air-cooling, varying the cutting speeds and feed rates. Since air-cooling usage combines positive aspects, such as low-cost implementation and shorter process time compared to ultrasonic-assisted drilling, it turns out to be an excellent alternative for aeronautical industry. Thus, the main contribution of the present work consists on analyzing the variation of the delamination in the entrance and exit of the first and tenth holes of a CFRP plate after dry and air-cooled drilling. This variation of the delamination between the cold drill (first hole) and the heated drill due to the drilling holes' sequence (after ten holes) is investigated for 18 different combinations of parameters (runs). For instance, it is shown that if the combination of parameters values is suitable, then it is possible to reduce the mean value of adjusted delamination factor for the entrance of the tenth hole around 11% when comparing cooled-air with dry cutting.

CFRP drilling under throttle and evaporative cryogenic cooling and micro-lubrication

Hole-making in CFRP plates has been unsustainable due to poor hole quality, high specific energy consumption, a trade-off between shortened drill life and low productivity, and high processing cost. This experimental study investigates the effects of using throttle and evaporative cryogenic fluids, actualized by applying compressed carbon dioxide and liquid nitrogen, respectively, and micro-lubrication on hole quality (roughness, coaxiality, and circularity), production economy (tool damage and process cost), structural intactness (delamination and uncut fibers), energy consumption, and machining forces. Additionally, the effects of applying drill pecking and cutting speed are also quantified. Based on the experimental results, micro-lubrication is found to have outperformed dry drilling and the two cryogenic coolants regarding the measures associated with process viability, such as tool wear, process cost, energy consumption, and machining forces. Throttle cryogenic cooling, on the other hand, yielded the best results in respect of the work quality measures, which includes hole quality and structural intactness. Pecking yielded disappointing results regarding most of the measures, whereas the high level of cutting speed yielded favorable results in respect of specific cutting energy and process cost.

Friction drilling of AA7075-T6 and AZ31B alloys under dry and oil containing ceramic particulates

This study investigates the friction drilling behaviors of AA7075-T6 aluminum and AZ31B magnesium alloys containing ceramic powders of B4C, SiC, and Al2O3 under dry and minimum quantity lubrication (MQL). The aim is to create a composite structure while applying the pressure of a drilling tool on the hole surface when adding ceramic powders into the cutting oil during frictional drilling. Friction drilling tests are performed at a constant spindle speed and feed speed, and the effects of dry and cutting oil mixtures containing ceramic particulates on the thrust force, temperature, hole surface quality, bushing profile, and thread stripping strength of the specimens are investigated. The results revealed that ceramic particles penetrated through the hole and created a composite structure on the surface. The dry friction drilling of AA7075-T6 and AZ31B yielded acceptable surface quality. However, the surface quality worsened considerably during the friction drilling of AA7075-T6 using the oil mixture, whereas the surface roughness and hole bushing of AZ31B magnesium alloys are not negatively affected by the ceramic containing oil mixtures. Petal formation and cracks appeared in the hole profiles of the AA7075-T6 aluminum alloy. Thread stripping tests indicate that the ceramic-particle- containing oil mixtures enhanced the thread shear strength of AA7075-T6 by 19.2 %, and the highest shear strength of 56.78 kN is achieved using the Al2O3 containing an oil mixture. The oil mixture-containing B4C ceramic particles improved the thread shear strength of AZ31B by 7.7 %.

3D numerical simulation of heat transfer during dry drilling of Inconel 718

Abstract The aim of this paper is to compute heat transfer as a function of drilling parameters with a relatively short computing time. Assuming that the geometry of the chips close to the cutting edges of the drill tool is almost the same throughout the drilling operation, a numerical strategy is developed in the second section in order to create analytically the geometry of the chips by means of the process parameters and the geometry of the drill tool. An efficient identification procedure is then presented to model the material flow. In the third section, an experimental device is detailed as well as its tomography geometrical analysis after drilling. A simple calibration strategy is developed in order to estimate the Taylor-Quinney coefficient and the thermal impact of the removal material on the hole surface. Then, an application is detailed to show the capability of the modeling proposed to simulate the temperature variation in the case of a large depth hole.

The effects of through tool cryogenic machining on the hole quality in GLARE® fibre metal laminates

GLARE® is a composite-metal laminate currently used in the Airbus A380 fuselage due to its excellent impact and fatigue performance. GLARE® undergo extensive drilling for riveting purposes making it prone to thermal effects and increased tool wear. Therefore, using coolants becomes necessary, however, conventional coolants can lead to moisture absorption. An alternative is to use cryogenic coolants due to their positive impact on machining aerospace materials in the past. In this study, through tool cryogenic machining technology is used for machining GLARE® laminates by delivering liquid nitrogen at −196 °C through the spindle allowing the coolant to be in direct and continuous contact with the cutting zone. The aim is to investigate the impact of drilling parameters and cryogenic cooling on surface roughness, hole size, circularity and hardness at hole entry and exit sides. In addition, microstructural evaluation using scanning electron microscopy. The results indicate that the cryogenic cooling improved hole surface finish and gave better hole size at the top, while it had no impact on hole circularity. The hardness was increased at the entry and exit sides of the hole compared to that observed in dry drilling tests while scanning electron microscopy revealed that burr formation was minimised.

Fuzzy Logic-Based Prediction of Drilling-Induced Temperatures at Varying Cutting Conditions along with Analysis of Chips Morphology and Burrs Formation

Friction and plastic deformation at the tool–chips interaction during a dry drilling process results in temperature rise and promotes tool wear and surface roughness. In most of the components produced in industries, a drilling process is used to make a hole for final assembly. Therefore, knowledge of temperatures produced during drilling operation at various machining input parameters is required for the best quality product. A fuzzy logic-based algorithm is developed to predict the temperature generated in the drilling process of AISI 1018 mild steel. The algorithm used speed and feed rate of the drill bit as input parameters to the fuzzy domain. A set of rules was used in the fuzzy domain to predict maximum temperature produced in the drilling process. The developed algorithm is simulated for various input speed and feed rate parameters and was verified through the maximum temperature measured during drilling of the studied material at selected speed–feed combinations. Experiments were conducted to validate the results of developed fuzzy logic-based algorithm by using non-contact infrared pyrometer for drilling of AISI 1018 steel. A good agreement between the predicted and experimentally measured maximum temperature was observed with an error less than 6%. It is found that temperature increases with increase in cutting speed and feed rate. Size of roll back burr formation at the hole perimeter significantly increases with increase in drill speed and feed rate. Segmental continuity in spiral or helix chips morphology is more at low feed and high cutting speed. Chip radius increases with increase in feed rate and results in damaging of the machined surface and causes burr formation while the radius decreases with cutting speed along with improved hole surface finish.

Drilling of CFRP-Ti6Al4V stacks using CO2-cryogenic cooling

• Dry-drilling process for CFRP-Ti6Al4V aeronautical stacks was analyzed. • CO 2 cryogenic coolant was proposed and evaluated as an eco-friendly alternative. • The use of cryogenics cooling improves dry drilling results. In the work here presented, liquefied CO 2 is used as cutting fluid for drilling CFRP-Ti6Al4V stacks as alternative to dry-drilling. Several tests were performed using dry-drilling technique, to compare this with the performance of CO 2 cryogenic cooling. This work shows the feasibility of the proposed alternative, not only regarding technical issues but also environmental concerns. Results show that when CO 2 is used in drilling, hole diameter values diverge below 0.5 % from nominal values, tool tip temperature is drastically reduced, and surface integrity of CFRP layers are preserved. Drilling tool edges damage is reduced and so tool life extended. In short, dry-drilling process was notably improved by CO 2 assistance in comparison with dry drilling.

Cutting forces and chip morphology in LCO2 + MQL assisted robotic drilling of Ti6Al4V

Robotic drilling is receiving increasing attention in aerospace industry, where Ti6Al4V is used for multilayer composite/metal stacks. Being a difficult-to-machine material, dry drilling of Ti6Al4V results in excessive tool heating and premature tool wear. Through-tool flood lubrication in robotic drilling is difficult due to open and large working area. In addition, flood lubrication is not recommended for drilling of composite stacks. In this study, through-tool delivery of LCO2 + MQL is used on robotic drilling of Ti6Al4V with carbide tools. The flow rate of both LCO2 and MQL are individually varied to study the effect of coolant and lubricant flow rates on thrust force and torque values in comparison to dry drilling. Chip morphology is studied to observe the influence of LCO2 pressure on chip breakability. The results indicate a strong relation between LCO2 flow rate and thrust force due to material hardening and a strong relation between torque and MQL flow rate due to combined effects of lubrication in cutting zone and chip evacuation process. In dry drilling, strong chip adhesion to tool is observed, while LCO2 + MQL assisted drilling improves chip breakability and reduces the workpiece-material adhesion through combination of lower temperatures and lubrication barrier.

Tribological and dry drilling performance of WS<sub>2</sub>/Cr-AlCrN coatings

Tribological and dry drilling performance of WS<sub>2</sub>/Cr-AlCrN coatings

Microstructural assessment of drilled cross-sections on titanium generated under different cooling strategies

High heat generation during machining of titanium alloy causes microstructural damage on machined surfaces. Different cooling strategies in machining of titanium alloy have been studied to understand their effectiveness in improving heat dissipation and machined surface microstructure. In this work, heat-sink based cooling has been used to channelize an ice water for effecting positive heat dissipation. Before drilling experiments, solution annealing was performed on all Ti-6Al-4V samples to achieve an equiaxed microstructure. Extensive drilling experiments under dry, flood cooling and heat-sink based cooling environments were performed under different cutting parameters. Electron Backscatter Diffraction (EBSD) technique was utilized to characterize microstructure of titanium drilled entry and exit hole surfaces. Dry drilling showed the highest average of 40 μm of machining affected zone (MAZ), whereas the least MAZ average 3 μm which was evident in the heat-sink based cooling. Image quality (Kikuchi pattern intensity) quantification revealed the highest normalized IQ value, indicating the lowest deformation in heat-sink based cooling over dry and flood cooling at the entry and exit surfaces of the drilled samples. Misorientation maps show that low angle grain boundaries misorientation is reduced in heat-sink based cooling by maximum 75 % over dry drilling, and by 57 % over flood cooling, at the exit hole surfaces. Kernel average misorientation (KAM) analysis at the exit drilled hole surfaces shows that the local misorientation in heat-sink based cooling is reduced by 90 % as compared to dry drilling and by 60 % over flood cooling.

Effect of cooling method on small diameter blind-hole drilling of new β-type dental Ti-Zr-Nb alloy

Abstract A β-type titanium-zirconium-niobium alloy (Ti-Zr-Nb alloy) is an ideal substitute for the currently used dental implants with the advantages of high specific strength, low elastic modulus, good biocompatibility, non-toxicity and corrosion resistance. However, its low elastic modulus and sticking characteristics results in poor heat dissipation and severe wear and tear making it difficult to drill. In this paper, a 2 mm diameter solid carbide twist drill was used to conduct small hole drilling experiments on a new, self-smelted, low-modulus β-type Ti-Zr-Nb alloy. The effects of the drilling parameters and five cooling methods (dry, flooded, cryogenic, minimum quantity lubrication (MQL) and cryogenic-minimum quantity lubrication (CMQL)) on thrust force, surface quality, microhardness and tool wear were studied. Results showed the minimum thrust force was obtained during the drilling process with the MQL cooling method and the β-type Ti-Zr-Nb alloy which did not exhibit low temperature brittleness was not suitable for processing at cryogenic cooling because the low temperature changed the yield strength and the stress for plastic deformation of the material's surface. The main wear mechanism of the β-type Ti-Zr-Nr alloy was adhesion, and the material properties and crystal structure of Ti-Zr-Nb alloy were the physical foundations that produced the adhesion phenomenon. However, cooling conditions also had an important effect on wear. Oxidative wear tended to occur when there was little or no coolant, and fatigue wear was observed with the signal of cracking, pitting and layer delamination using the cooling method of CMQL. The sawtooth angle ϕ of chips was larger under the dry drilling and cryogenic cooling methods, than that of the other three cooling methods. The MQL cooling method is recommended to effectively improve the tool durability.

Chronic Manganese Toxicity in Indian Mines-An Historical Account of the Contributions of Dr. T.P. Niyogi.

The mining of manganese ore in India started in the year 1899, in Nagpur district of the Central Provinces. Almost six decades later, in 1957, Dr. T. P. Niyogi examined several young men involved in dry drilling of Manganese ore, who had symptoms of muscular pain, weakness, clumsy movements, asthenia, anorexia, insomnia, and gait difficulties. These patients were also emotionally disturbed and prone to falls and accidents. He concluded that these symptoms were due to chronic manganese toxicity with parkinsonian features and psychiatric manifestations which he published in 1958.[1] This lead to the formation of an Enquiry Committee by the Ministry of Labour and Employment, Government of India which instituted corrective measures in mining of manganese in India. Very few reports of chronic toxicity due to inhalation of manganese have been reported subsequently. This paper highlights the contributions of Dr. T.P. Niyogi who was the Civil Surgeon in Chhindwara, MP during that period.

Theoretical and Experimental Studies of Internal Cuttings Removal Bit

Abstract The oil and gas exploration without rig (also known as badger exploration) is a novel exploration technology that removes the need for fixed rig drilling, bringing with it the promise of huge savings in terms of time and money and its low impact on the environment. The implementation of this technology is an autonomous exploration tool, which can drill into rock using an electrically powered bit to loosen and crush the formation ahead of it, and crushed cuttings is moved through the device and deposited in the space behind it. Because there is no drilling fluid in badger drilling, a new way of transporting cuttings is urgently needed. In this paper, a new kind of bit named internal cuttings removal (ICR) bit is developed for badger exploration, and it can not only drill rock but also collect and transport cuttings to the bit behind through the inner cavity of the bit. Compared with the common polycrystalline diamond compact (PDC) bit, the junk slots are removed, but the helical blades and screw conveyor are added on the ICR bit. Theoretically, the two effects of rotating helical blades on cuttings moving are studied, based on the conditions of low and high rotating speed, respectively. Moreover, the rate of cuttings removal of the ICR bit is given in formulas, and in order to ensure the cuttings is removed from bottomhole timely, and the maximum permissible rate of penetration (ROP) of the ICR bit is proposed. Finally, two samples of the ICR bit with different structural parameters were built and tested in dry and wet rock drilling experiments, and experimental results show that the ICR bit can achieve the expected goal of ICR, but wet cuttings has a significant influence on the performance of the ICR bit. By comparing the drilling results of two bits, it can be found that the concave blade surface, a small number of blades, and small inner cone angle have the positive effects on the cuttings removal of the ICR bit. The above work is helpful for the development and implementation of badger exploration technology.

Effects of reinforcements and cutting parameters on machinability of polypropylene-based biocomposite reinforced with biocarbon particles and chopped miscanthus fibers

New biocomposites are increasingly being developed and applied in engineering and manufacturing. The reinforcement type used in biocomposite is one of the major factors that greatly affect the machinability of biocomposite. This study investigated the drilling of two biocomposites (polypropylene-based biocomposite reinforced with biocarbon M1 (30 wt% biocarbon + PP/POE/MAPP) and chopped miscanthus fibers M2 (30 wt% miscanthus + PP/POE/MAPP)). A full factorial design was used for this study. The effects of drilling parameters and reinforcement types on surface roughness, thrust force, specific cutting energy, fine particles, and ultrafine particle generation were measured and analyzed. The results show that the thrust force and specific cutting energy during drilling of biocomposite M1 is bigger than that of biocomposite M2 under the same cutting conditions. However, the surface roughness and fine dust emitted when drilling biocomposite M1 are smaller than those from biocomposite M2, respectively. The reinforcement types of biocomposite, cutting parameters and drill diameter greatly affected fine particles emission. Meanwhile, the cutting conditions are not statistically significant for ultrafine particle generation during dry drilling of both biocomposites.

Machinability and surface integrity of adhesively bonded Ti/CFRP/Ti hybrid composite laminates under dry and cryogenic conditions

The current work compares the machinability of conventional drilling of hybrid titanium/carbon fiber reinforced plastics/titanium ( Ti/CFRP/Ti ) stack laminates in a single shot under dry and cryogenic conditions. Damage at metal-composite interface (MCI), thrust force, torque, burr height, surface roughness, average hole size, circularity error, and perpendicularity error are considered as experimental outcomes to investigate the influence of cryogenic cooling on the machinability of Ti/CFRP/Ti stacks. The experimental outcomes indicate that the hole quality significantly improved under cryogenic condition compared to dry drilling for the range of drilling parameters chosen. However, cryogenic cutting yields an increased thrust force due to increase in the hardness of Ti sheet at low temperatures. Scanning acoustic microscopy (SAM) was capable of capturing damage at MCI. Scanning electron microscope (SEM) and micro-computed tomography (μ-CT) are also used to assess the drilling induced damages on hole wall surface under both (dry and cryogenic) conditions.

Artificial neural networks applied to prediction of surface roughness in dry drilling of some polymers

Polymers become more and more attractive for automotive and aerospace industries due to their remarkable mechanical, thermal and electrical properties that make these materials suitable for many industrial applications. Machining of polymers is of a great interest among researchers and engineers due to the possibility of replacing expensive materials with plastics that have similar mechanical characteristics, but of a lower cost. Drilling is the most common mechanical machining operation in manufacturing of parts. Within this context, it is essential to analyze this cutting process and find the best solution for controlling the output parameters of the process, such as surface roughness and cutting forces. The present work concerns the developing of an artificial neural model for the prediction of surface roughness in dry drilling of some polymeric materials: high density polyethylene (grade HDPE 1000), polyamide (grade PA6) and polyacetale (grade POM-C). The neural model was built based on trial-and-error method, by modifying the number of hidden layers and the number of hidden neurons on each layer. The experimental plan was designed to be suitable for artificial neural network prediction. The aim of experimental work was to study the effect of cutting parameters (spindle speed, feed rate and drill diameter) on the quality of machined surface (surface roughness). This paper proposes a neural model that is able to predict the surface roughness considering not only the cutting parameters, but the type of material. Moreover, a study concerning the accuracy of the neural model depending on the number of hidden layers and the number of hidden neurons on each hidden layer was carried out. The predicted values of roughness were compared with experimental data in order to determine the precision of the neural model.

Machinability of Al2024, Al6061, and Al5083 alloys using multi-hole simultaneous drilling approach

Aluminium alloys are extensively used in different industries due to their good mechanical properties, machinability, low cost and reliable inspection. Drilling is one of the most important machining processes for assembly operations. The number of holes required in an assembly may vary from several holes to millions depending on the application which increases the manufacturing time and costs. In this study, a multi-spindle drill head also known as the poly-drill head is used to perform multi-hole simultaneous drilling with the aim to increase productivity. Dry drilling tests are performed on Al2024, Al6061, and Al5083 aluminium alloys using uncoated carbide tools. Thrust force, hole quality in terms of surface roughness, burr and chip formation, as well as post-machining tool conditions, were investigated under different drilling parameters. Experimental results showed that Al2024 produced fewer burrs around the hole edges, less built-up edge on tools and formed short and broken chips. Holes machined in Al6061 alloy had a good surface roughness while lowest thrust force was recorded in holes drilled in Al5083 alloy.

Multiple Sensor Monitoring of CFRP Drilling to Define Cutting Parameters Sensitivity on Surface Roughness, Cylindricity and Diameter.

Machining parameters affects the final quality of components made in carbon fiber reinforced plastic (CFRP) composite materials. In this framework, the work here presented aims at studying the right combination of cutting speed (vc) and feed rate (vf), for dry drilling of carbon fiber reinforced plastic composite materials, which obtained better results regarding roughness, hole cylindricity, and diameter. A series of experimental tests were carried out under different drilling conditions (vc/vf), monitoring the thrust force (Fz), torque (T), and electric power (EP), to define which one can help more for industrial daily life production. Results validation was carried out using the analysis of variance, in order to relate main machining parameters cutting speed and linear feed, with thrust force, drilling torque, main spindle electric power and hole quality parameters (average roughness, cylindricity and diameter). The conclusions show that thrust force is not proportional to the cutting speed and the best combinations of cutting speed and feed were found out around the average values of tested parameters. Spindle electric power is an interesting element to take into account because it is easy to consider in real production.

Cryogenic drilling of carbon fibre reinforced thermoplastic and thermoset polymers

Carbon fibre reinforced polymers (CFRP) are suitable materials for high-end applications due to the high strength to weight ratio. This important advantage counteracts to their machinability because the inherent anisotropy and the heterogeneity lead a high difficulty to reach good quality in terms of surface integrity, dimensional and geometrical tolerances. Hereupon, this paper determines the effect of the cryogenic and dry drilling as well as tool feed rate on delamination, uncut fibres, hole diameter and roundness when applying thermoplastic and thermoset CFRP as workpiece material. Scanning electron microscopy (SEM), and specific cutting and thrust energies aided to explain the damages’ phenomena. The results showed that hole quality varies along hole depth and depends both on composite’s matrix and drilling strategy. Delamination and uncut fibres are distinct at the hole entrance and exit since they depend on surrounding matrix/fibre layers. Cryogenic drilling reduced both delamination at the hole exit and uncut fibres at the hole entry for the thermoset materials. Finally, the variation in hole diameter and roundness was minimized when drilling thermoplastic matrix by using cryogenic cooling.

RETRACTED: Evaluation of tool temperature distribution in MQL drilling of aluminum 2024-T351

Minimum quantity lubrication (MQL) as a green technology is widely employed in metal removal manufacturing, which can achieve lower cutting temperature and higher machining efficiency environmentally. However, how to evaluate the tool temperature distribution in drilling process with MQL is still significantly lacking. For this purpose, a tool-foil thermocouple system was developed and the influence of cooling conditions and cutting variations on tool temperature has been experimentally analyzed during high-throughput drilling of aluminum alloy AA2024 in current study. Results indicate that the maximum temperature along cutting edge is observed near drill center due to heat accumulation. Using MQL can decrease the temperature difference between drill center and outer corner compared with dry and air cooling conditions. Temperature distribution profiles are more sensitive to feed rate than cutting speed. Increasing feed rate can result in a great increasing of average temperature. Chipping is only observed on the peripheral corner under MQL condition, while adhesion and built up edge (BUE) almost extend across the whole cutting edge under dry drilling due to the absence of lubrication and coolant.