Wet Drilling Research Articles

Feasibility of respirable crystalline silica exposure reduction in small-scale tanzanite mining in Tanzania.

Respirable crystalline silica (RCS) exposures in tanzanite gem mining have been linked to tuberculosis and silicosis among miners. We conducted a plot study to assess RCS exposures and to introduce safer mining practices in one small-scale underground tanzanite mine. Personal and area air samples for RCS were collected during tanzanite mining operations before and after improved work practices employed to reduce exposures and analyzed using X-ray diffraction. Area samples were collected at the rest area, located approximately 300 m underground and 100 m from other work activities. Improved practices included the use of wet drilling methods and drilling with new bits. A total of 33 personal and 4 area air samples were collected. Pre-intervention, mean exposures for all operations, drilling operations, non-drilling activities, and area samples were 122 mg/m3, 247 mg/m3, 34.3 mg/m3, and 1.95 mg/m3, respectively which exceeded the U.S. OSHA Permissible Exposure Limit (PEL) by 2,440 times for all operations, by 4,946 times for drilling operations, by 686 times for non-drilling activities and 39 times for area samples collected at an underground rest area. The post-intervention results showed a 99% reduction of RCS exposures for wet drilling operations, 98.5% reduction for non-drilling activities, and 36% reduction for area samples. Despite improvements, post-intervention RCS exposures during drilling had a mean of 2.08 mg/m3 or more than 41 times the OSHA PEL. We successfully piloted a program to work with small-scale tanzanite miners to reduce RCS exposures and raise awareness about the occupational health risks of RCS, though additional measures are recommended to further reduce RCS exposures. Similar programs should be taken to scale throughout underground mining sites in Tanzania and other countries.

Porównanie geologii prezentowanej na przekroju poprzecznym i obserwowanej w terenie - lekcja z odkrywki węgla brunatnego Tomisławice, Zagłębie Konińskie w Polsce Centralnej

This article briefly focuses on comparing geological information shown in a cross-section with field data. An example from the Tomisławice opencast mine, where the first Mid-Polish lignite seam (MPLS-1) is currently exploited for electricity production, is used where two sites present large and even surprising differences. In the first case, they are due to technical reasons, i.e., wet drilling. The second case is most likely caused by the compaction of peat during its transformation into lignite. The obtained results clearly indicate that the actual geological structure observed in the field may differ significantly from that which is interpreted on the geological cross-sections based on borehole data.

Review on Dust Control Technologies in Coal Mines of China

China faces a challenge in the sustainable development of the coal industry due to pneumoconiosis problems. Dust control technologies are crucial for safe production and miners’ health, ensuring the industry’s longevity. This article reviews the development process of dust prevention and control in underground coal mines in China, summarizes various technologies, and divides them into dust suppression, open-space dust reduction, and mine dust collectors according to different stages and environments of use. In dust suppression technologies, coal-seam water injection can reduce total dust generation by 60%, wet rock drilling can reduce drilling dust in the presence of stable water sources and high-pressure bearing equipment, and water-seal blasting can reduce blasting dust by 50–70%. In open-space dust reduction technologies, spray dust suppression can remove total dust by 50–95% and the removal efficiencies of foam dedusting for total and respirable dust are reported to reach 95% and 85% under the right conditions, respectively. In dust collector technologies, dry collectors can remove 80–95% of total dust. Wet collectors achieve up to 90% efficiency, dependent on water supply and waste processing. This article also discusses vapor heterogeneous condensation technology as a promising method for improving respirable dust removal in humid mine environments.

Stone mining work and dust pollution in Birbhum district, West Bengal, India.

Dust pollution is common in Indian roads and several industrial settings (including mines) that affects human health. Identification and characterization of the dust particles in the mining area is essential for knowing the properties of the dust that effectively causes ailments to humans, particularly among workers those who are working in unorganized industrial settings. The present study aimed to determine the level of dust pollution and to know the size and characterize the dust particles in the Pachami-Hatgacha stone mine areas of Birbhum district, West Bengal, India. Dust samples were collected and analysed for Dynamic Light Scattering (DLS) to determine the size and shape of the particles, Fourier Transform Infrared Spectroscopy (FT-IR) to determine the free silica content, and X-ray Florence (XRF) analysis for quantitative estimation of components in the sample. All the analyses were done following standard instrumentation and techniques. The size of the dust particles was much less (ranges 101-298nm) than the size of respirable particles (2500nm). Those were mostly generated as well as precipitated during peak working hours of the day. Presence of considerable amounts of silica was confirmed by the FT-IR (strong and broad band at 1000cm-1) and XRF analysis (76.85% SiO2). Exposure to these dust particles may cause severe health impairments. Therefore, interventions like wet drilling and blasting, sprinkling of water during peak working hours, and awareness of use of personal protective devices among workers are required to reduce the risk and hazards associated with dust pollution to the health of miners and inhabitants around the mines.

Prevalence and determinants of evidence of silicosis and impaired lung function among small scale tanzanite miners and the peri-mining community in northern Tanzania.

Limited data among miners in Tanzania suggests prevalence of silicosis, obstructive lung disease and restrictive lung disease to be around 1.6%, 1.9% and 8.8% respectively. Our study aimed to determine the prevalence and factors associated with silicosis and impaired lung function among tanzanite mining community in northern Tanzania. We conducted a cross-sectional study, involving 330 miners and 330 peri-mining community members in Mererani mines. Silicosis was defined based on study participants' history of exposure to mining dust and digital chest radiological findings with reference to the 2011 ILO classification of pneumoconiosis. Impaired lung function was determined by spirometry using American Thoracic Society/European Respiratory Society recommended system 3. Association between evidence of silicosis/impaired lung function and presumed risk factors were determined using binary logistic regression analyses. The study found that 99/330 (30.0%) of miners had silicosis. Total of 65 (9.8%) participants had impaired lung function, of whom 29 (4.4%) had Chronic Obstructive Pulmonary Disease, 32 (4.8%) had restrictive lung disease and 4 (0.6%) had both obstructive and restrictive lung diseases. Unexpectedly, miners who have worked for more than 10years and those worked for 6 to 10 years had 64% (aOR 0.34, CI = 0.17-0.67, p = 0.002) and 48% (aOR 0.52, CI = 0.30-0.89, p = 0.018) lower odds of having silicosis respectively compared those worked for up to 5 years. Participants with more than 10 years of work duration had more than 3-times higher odds of impaired lung function compared to those who had worked for up to 5 years (aOR 3.11, CI = 1.53-6.34, p<0.002). We found a concerningly high prevalence of silicosis despite short durations of exposure to occupational silica dust. Immediate dust control measures including deployment of wet drilling, wearing of personal protective equipment and regular monitoring of dust exposure need to be enforced by the Occupational Safety and Health Authority-Tanzania.

Concentrations of respirable crystalline silica and radon among tanzanite mining communities in Mererani, Tanzania.

Globally, the number of small-scale miners (SSM) is estimated to be more than 25 million, but it supports the livelihoods of around 100 million individuals. In Tanzania, the number of SSM has increased from an estimated 150,000 in 1987 to ~1.5 million in 2017. The miners are at a high risk of occupational-related health challenges. The study aimed to assess the concentrations of respirable crystalline silica (RCS) and radon among the tanzanite mining communities in Simanjiro District, Tanzania. We carried out a cross-sectional study involving the Mererani mines in Tanzania. These are underground mines comprised of informally employed miners, i.e. SSM. Concentrations of RCS and radon gas were measured in 44 study units, i.e. 22 mining pits and within 22 houses in the general community, e.g. shops in the peri-mining community. A total of 132 respirable personal dust exposure samples (PDS), 3 from each of the study units were taken, but only 66 PDS from the mining pits were analysed, as this was the main interest of this study. Radon concentration was measured by continuous monitoring throughout the working shift (and overnight for residences) using AlphaGuard monitor. The medians and comparison to the reference values, OSHA USA PEL and WHO/IARC references, were done for RCS and radon, respectively, using SPSS Ver. 27.0.0). The median time-weighted average (TWA) concentration of the RCS in the mining pits was 1.23 mg/m3. Of all 66 personal dust samples from the mining pits, 65 (98.5%) had concentrations of RCS above the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 0.05 mg/m3. Mining pits had a median radon concentration of 169.50 bq/m3, which is above the World Health Organization (WHO)/International Commission on Radiation Protection (ICRP) recommended reference of 100.00 bq/m3 but not above the upper reference of 300.00 bq/m3, while the community buildings had a median radon concentration of 88.00 bq/m3. Overall, 9 (20.5%) and 17 (38.6%) radon measurements were above 300.00 bq/m3 and between 100.00 and 300.00 bq/m3 references, respectively. Specifically, in the mining pits, 9 (40.9%) test results were above 300.00 bq/m3, while none of the test results in the community was above 300.00 bq/m3. The tanzanite SSM in Mererani we highly exposed to RCS, which increases the risk of pulmonary diseases, including silicosis, tuberculosis, and pulmonary malignancies. Immediate action by OSHA Tanzania should be enforcement of wearing respirators by all miners throughout the working hours. Health education programmes to the SSM must be strengthened and OSHA Tanzania should adopt the 0.05 mg/m3 PEL, and enforce other occupational health and safety measures, including regular use of dust suppression mechanisms (water spray and wet drilling) and monitoring of RCS exposures among SSM. Monitoring of radon exposure both in the mining pits and community buildings should be conducted, and mitigation measures should be implemented in areas that exceed the reference level of 100.00 bq/m3.

PTFE in Wet and Dry Drilling: Two-Tier Modeling and Optimization through ANFIS

This research is done to determine the optimum parameters to drill polytetrafluoroethylene (PTFE) and to investigate the effect of two-tier modeling for enhanced response in optimization. RSM model was done with L27 experimental design, considering speed (N), feed (f), and tool point angle (Ɵ). RSM data were further trained and tested using the Adaptive Neuro-Fuzzy Inference System (ANFIS), and β coefficient values were restructured to form revised RSM model. Both nonrevised RSM model and revised RSM model were used in Genetic Algorithm to locate the minimum surface roughness. ANFIS revised RSM model deviates from the experimental results by 2.6% and 2.86% for dry and wet condition; meanwhile, nonrevised RSM model deviates by 4.76% and 4.94%, respectively. The research concludes that two-tier modeling using RSM and ANFIS is better. Spindle speed of 1656 rpm, feed rate of 0.05 mm/min, and point angle of 100° are the optimum conditions to drill PTFE material where the best surface quality of 0.68 μm at wet drilling can be achieved.

Influence of Drilling Methods on the Results of Standard Penetration Test in Loess–Paleosol Sequence

Standard penetration test (SPT) is an important in situ measurement for field investigation of geotechnical and geological engineering. The drilling approaches for implementation of SPT can be classified into dry, wet, and water circulation drillings according to the amount of water used during drilling process. However, the influences of these drilling methods on the SPT results remain unclear, especially when being used in loess–paleosol sequence that is water sensitive. In this study, SPT tests were conducted in a typical loess stratum in the Loess Plateau of China. The difference of SPT N values under the above three drilling methods was compared together with the analysis of characteristics of samples from SPT sampler. The results showed that the N value exhibits positive correlation with dry density of the soil and negative correlation with moisture content. In shallow soil, the average N value under water circulation drilling was slightly higher than that of dry and wet drilling. This is because that the residual soil at the bottom of the drillhole caused by water circulation drilling provides additional penetration resistance. In deep soil, the difference of average N values among all three drilling methods was minimal although the structure of the samples from the SPT sampler differs from one another, indicating the determination of soil density on the SPT result. Empirical equations were proposed for the estimation of unconfined compressive strength of loess–paleosol sequence on the basis of SPT N values under the three drilling methods. Considering the efficiency of drilling and stability of SPT results, it is suggested that wet drilling is the most applicable method for implementation of SPT in the field investigation of loess–paleosol sequence.

Comparison of surface integrity for dry and wet drilling of 49Fe-49Co-2V alloy

Working performances of the components made out of 49Fe-49Co-2V alloy are closely related to the surface integrity of the drilled holes, which are influenced remarkably by the cooling conditions. The present study focuses on the surface integrity differences between wet and dry drilled 49Fe-49Co-2V alloy holes. The drilled hole surface roughness and topographies, metallurgical and mechanical properties, and the exit characterizations were obtained using optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction microscopy (EBSD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Vickers hardness techniques, etc. The effects of cooling conditions on the surface integrity were concluded and the influence mechanisms were analyzed based on the force and temperature differences in drilling process with different cooling conditions. It is found that the surface roughness and the thickness of refined-grain region of the dry drilled holes are larger than those of wet drilled holes; work hardening induced by wet drilling is more serious than dry drilling; chippings occurred in the exits of the wet drilled holes due to the material brittleness, which could be avoided by dry drilling. The surface integrity differences of wet and dry drilled holes are closely related to the force and temperature differences in drilling process with different cooling conditions.

Performance evaluation of the minimum quantity lubrication with Al2O3- mixed vegetable-oil-based cutting fluid in drilling of AISI 321 stainless steel

Abstract Due to increased awareness of ecological and health related problems, the researchers are actively searching for renewable and biodegradable cutting lubricants. Vegetable oils with solid lubricants are being explored as a potential source of environmentally helpful lubricants due to good combination of biodegradability, renewability and fabulous lubrication performance. Although sunflower oil poses good cooling capability, yet its application has not been explored extensively in drilling. Therefore, in this research work minimum quantity lubrication (MQL) technique with Al2O3-mixed vegetable-oil-based cutting fluid was implemented. The main objective of this experiment is to analyze the performance of various coolant-lubricant environments (dry, flood, pure MQL and nanofluid MQL) with regard to drilling forces, surface roughness, drill tip temperature and tool wear mechanism in the drilling of AISI 321 stainless steel by using HSS drill tools. In the MQL conditions, coolant supply rate and air pressure are fixed at 120 mL/hr and 6 bar respectively. In addition to explore the cooling capabilities of sunflower oil, nano-Al2O3 were added to the sunflower oil to prepare different concentration (0.5 wt.%, 1.0 wt.% and 1.5 wt.%) nanofluids. Results indicated that MQL drilling with Al2O3-mixed vegetable-oil-based cutting fluid achieved much better performance as compared to the dry, wet and pure MQL drilling. Thrust force, torque, surface roughness and drill tip temperature approximately reduced 44 %, 67 %, 56 % and 26 % respectively at the 30th hole under nanofluid MQL drilling (with 1.5 wt.% of aluminium oxide nanoparticles) as compared to flood conditions. Moreover, tool wear rate reduced significantly while machining under NFMQL conditions. Better results of nanofluid MQL drilling may be attributed to the fact that NFMQL is capable for producing higher cooling effect due to the lubrication characteristics of nanoparticles.

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.

Investigation of the effects of drill geometry on drilling performance and hole quality

In this study, the effects of drill geometry on cutting performance and hole quality in the drilling process were investigated. Two newly developed drill geometries were compared with two commercially available drill geometries. In the drilling tests on GGG50 cast iron, 4 different drills, 4 different cutting speeds and 4 different feed rates were used for L16 experimental design. The drilling tests were performed with and without cutting fluid. The results were evaluated using the axiomatic design method, one of the multi-criteria decision making methods, in terms of thrust force, surface roughness, deviation on hole diameter and length of adhering workpiece material around the chisel edges. From the obtained results, it was seen that the best results were obtained from one of the newly developed drill geometries. In addition, wear test was carried out without cutting fluid using the drill which performed best. With this best performed drill, after 100 drilling operations in wet and dry conditions and after 1500 drilling operations in dry conditions, SEM images were taken from the used drills. After drilling 100 holes both in dry and wet drilling conditions, there was almost no wear on the drills. However, some adhered workpiece material was seen on the drills. In addition, the amount of adhered workpiece significantly increased in dry drilling condition.

Pulmonary tuberculosis among stone miners of India vis-à-vis silica exposure

Background:Tuberculosis is one of the biggest public health concerns in India with a prevalence of 195 cases per 100000. Silica is cytotoxic to macrophage which is primary defense mechanism to tubercular bacilli and, hence, exposure to silica dust increases risk for TB. Silica exposed persons are at 2.8 to 39 times greater risk of affected by pulmonary tuberculosis in comparison to healthy subjects.Methodology:A cross-sectional epidemiological study was conducted among 935 workers in sandstone mining. Full-size posteroanterior view (PA) chest X-ray in full inspiration was evaluated and evidence of tuberculosis was noted. Fourier transform infrared spectrophotometer was used for determining the free silica in 23 dust samples.Results:6.4% X-rays showed evidence of TB and silica dust concentration was 0.11 to 0.16 mg/m3. The TB cases significantly increased from 2% to 6% to 12.7% as the work exposure increased from <10 years to 11–20 years to >20 years respectively. 8.5% of the TB cases were seen among the workers having more than 10 years of work exposure. The odds ratio (95% CI) for work exposure more than 10 years to less than 10 years was 4.53 (1.92–10.65).Conclusion:Reduction of silica particles from work environment can significantly reduce the number of TB cases and hence wet drilling should be practiced and personal protective equipment should be regularly used.

Process performance and life cycle assessment of friction drilling on dual-phase steel

The use of friction drilling technique for hole making in tube dual phase steels was presented in this paper as an alternative to conventional drilling techniques. Due to the higher environmental consciousness growing up in the last years in different industrial environments, the feasibility of the proposed alternative must be analyzed taking into account both, technical and environmental aspects. In order to perform a complete environmental approach for conventional drilling, different lubri-cooling technologies were tested: dry drilling, wet drilling and minimum quantity of lubrication (MQL) drilling using high-oleic sunflower oil. From the technical point of view, results show that using friction drilling, the surface quality obtained was more appropriate. The deformed material provides a perfect base for future threading or joining operations and, moreover, the thermal affected layer observed in micrographies provides a 20 μm hardened layer which reduce surface wear and damages, improving hole zone life. From the environmental point of view, a life cycle assessment (LCA) was carried out for both drilling techniques and different lubricooling environments. Results show that friction drilling presents an ecologic improvement, obtaining a notable reduction in all impact categories. Analyzing both points of view, friction drilling is presented as a solution that improves current drilling processes of metal sheets.

Wet vs dry CFRP drilling: Comparison of cutting fluid delivery methods

This work studied the impact of flood and through-tool cutting fluid delivery methods during the drilling of carbon fibre reinforced polymer (CFRP) composite panels against a dry baseline condition. The cutting fluid considered was a water-based, composite-specific fluid, and the cutting tool was a Ø6.35 mm diamond-coated drill bit. After an initial design of experiments (DOE) approach enabled the establishment of appropriate cutting parameters to minimise delamination, both delivery methods and dry baseline drilling were compared in terms of tool wear and hole quality. The increased heat removal efficiency of through-tool delivery method is theorized to have prevented the localised softening of the resin and consequently maintained high abrasiveness of the composite workpiece, ultimately developing the highest tool wear for the given parameters. After drilling 600 holes, dry drilling exhibited the best results and lowest variation of hole quality metrics, i.e. the most stable process. However, after drilling 300 holes, flood delivery produced a better performance for cylindricity and perpendicularity and similar exit delamination factor (Fd) than dry drilling. Interestingly, through-tool delivery exhibited a slightly better performance than dry drilling when the analysis and comparison is conducted after the first 100 holes drilled only. These results indicate that hole diameter is highly dependent on tool wear and demonstrates that heat evacuation helps to produce holes with better cylindricity and perpendicularity, since hole distortion is highly affected by heat up and cool down cycles and the different coefficient of thermal expansion (CTE) across the laminate.

The Construction of Economic Green Buildings in Sinai and Suez Canal Zone Using Compressed Stabilized Earth Technique

Currently, there are several technologies applied in many societies to improve the use of the environmental resources such as the use of soil with some binders in the construction of buildings, and the usage of the stabilized earth architecture technique by new urban communities. One of the advantages of these buildings is that they make good use of the environment and save energy and expenditure. This project deals with the use of the sandy soil which resulted from the excavation of the buildings. It also targets the design and building of whole low energy, ecological, and low-cost green building/villages in the future projects in Sinai and Suez Canal zone, using stabilized earth architecture. The sandy soil under study is that of the sand on the east side of the Suez Canal in Sinai which is a by-product of the dry excavation and wet drilling of the canal. This paper showed that passive and energy efficient techniques incorporated in building designs can reduce the electricity requirements. The most effective parameter is the thermal efficiency of building envelope and blocking sun rays. The available renewable energy systems can meet parts of building loads. Thermal bridges are not so common in the bearing wall construction method. Herein in this paper, several specimens were collected from different sites in Elferdan and Serapum in Sinai (Suez canal zone) along the east side of the Suez Canal to investigate the suitability of stabilizing this soil for the production of compressed earth blocks for low-cost ecologic building construction. Several tests, e.g., sieve analysis and the proctor test, were made of the specimens. The results showed that the ratio of salts, chlorides and sulfates were low. In addition, the specimens collected sieve analysis ranged from coarse to fine sand. Stabilizing the materials resulted from the by-production in the industry can be used for minimizing the coast of compressed stabilized earth buildings with high engineering properties. Experiments on the produced compressed stabilized earth bricks (CSEB) with different level of stabilizing agent (by-product materials) were made using one of the specimens collected from Elferdan zone. The results showed that the 35% CKD ratio of sand weight can be considered as the optimum CKD content; which provides the best properties for the admixture as long as the percentages of cement (OPC) and the fiber-reinforced polymer (FRP) are 5% and 0.07% of sand weight, respectively. The rest of this research will be completed in the next parts, which includes finding more mechanical, engineering, and thermal properties of the produced CSEB.

A comparison between wet and cryogenic drilling of CFRP/Ti stacks

ABSTRACTThis paper compares conventional and cryogenic cooling in the deep hole drilling of carbon fiber reinforced polymer (CFRP)/Ti stacks. Various parameters are taken into account to find if the use of cryogenic coolant is justified by the improvement of the final results. Both the thrust and the torque were acquired continuously during the machining operations and compared both in average and distribution. The use of a cryogenic coolant brings a reduction in thrust force and torque without any sensible drawback. Overall the results prove that cryogenic drilling is a suitable technology for CFRP/Ti stack drill.

Finite element modelling study on small-hole peck drilling of SiCp/Al composites

In this paper, a 3D finite element model for simulating the 3-mm-diameter peck drilling behavior of SiCp/Al composites was developed by using commercial code ABAQUS/Explicit. In order to improve the calculation accuracy, the proposed model incorporates a real drill by reverse engineering, a Johnson-Cook model developed for SiCp/Al composites, the damage initiation for chip separation, and characteristic-length related damage evolution for representing strain-softening behavior after damage initiation. The FE model is verified with the corresponding small-hole wet peck drilling experiments in terms of thrust force and torque. Then, the model is used to study on the influence of edge radius on the chip formation. The predicted chip is divided into two segments due to the sharp intersection of two curved edges of lips, and this is in good consistency with the actual chips from the experiment. At last, the formation of edge defects is analyzed by a modified FE model. The actual edge defect formation is determined by the random distribution of SiC particles and complicated crack types and opening theory. This necessitates the establishment of microstructure-based model in the future.

Wet vs dry CFRP drilling: Influence of cutting fluid on tool performance

Carbon fibre reinforced polymer (CFRP) cutting operations have core features which include; i) chip types consisting of sub 50 micron particles and ii) aggressive abrasion-dominated tool wear. The workpieces used in this investigation were manufactured in a single batch from aerospace-grade, out-of-autoclave, quasi-isotropic, thermoset prepreg materials. Initially, a number of conventional tests were performed to assess the performance of isolated cutting fluid chemicals. The fluid-to-fluid variance was shown to be less significant in these tests when compared against dry conditions. A 6 percent basic micro-emulsion concentrate produced the best results with dry setup produced lower torque results than any cutting fluid tested. Production-style drilling trials were undertaken to investigate the tool life under varying fluid conditions from basic to commercially available. These trials indicated that dry, tip-extracted conditions enabled an extended tool life prior to coating failure against the best cutting fluid with identical parameters, machine tool, cutting tool and workpiece material manufacture conditions. The hypothesis for this reduction in tool performance under general wet conditions is that heat introduced by the drilling process changes the CFRP polymer’s visco-elastic properties thus reducing the abrasive interaction between tool and workpiece during material removal processes. The best cutting fluid, a 5 percent semi-synthetic, commercially available chemistry, produced approximately 60 holes more than the poorest performing chemistry.

Wet Core Drilling of CFRP with an Electrodeposited Diamond Core Drill - Effects of Cutting Conditions on Chip Evacuation and Core Jamming

This study investigated the cutting characteristics of electrodeposited diamond core drill when used to drill a CFRP under wet condition. The effects of different tool shapes, grain sizes and feed rates were examined. A normal core drill, an eccentric with slits core drill (E.S.), and an eccentric with slits and chamfers core drill (E.S.C.) were used. The normal core drill had the shape of a hollow cylinder. The E.S. core drill had the inner cylinder shifted from the center of this tool and slits in the bottom of this tool. The E.S.C. core drill had chamfers on the periphery of this tool. The normal core drill caused severe workpiece core jamming even at 1st hole drilling, and its electro-deposited area was covered entirely by adhered chips. In the case of the E.S. core drill and E.S.C. core drill, the workpiece core did not jam and the thrust force was smaller than that of the normal core drill. The effect of chamfers was little. The E.S.C. core drill with #200 caused smaller surface roughness than that with #100. However, the thrust force was two times larger, and the delamination was observed at the exit point of the hole. In the lower feed rate per revolution the better surface roughness and the lower thrust force were obtained irrespective of the tool shape while the cutting speed showed little effect.