Drill Geometry Research Articles

Improving Coolant Effectiveness through Drill Design Optimization in Gundrilling

Effective coolant application is essential to prevent thermo-mechanical failures of gun drills. This paper presents a novel study that enhances coolant effectiveness in evacuating chips from the cutting zone using a computational fluid dynamic (CFD) method. Drag coefficients and transport behaviour over a wide range of Reynold numbers were first established through a series of vertical drop tests. With these, a CFD model was then developed and calibrated with a set of horizontal drilling tests. Using this CFD model, critical drill geometries that lead to poor chip evacuation including the nose grind contour, coolant hole configuration and shoulder dub-off angle in commercial gun drills are identified. From this study, a new design that consists a 20° inner edge, 15° outer edge, 0° shoulder dub-off and kidney-shaped coolant channel is proposed and experimentally proven to be more superior than all other commercial designs.

Influence of machining parameters and tool structure on cutting force and hole wall damage in drilling CFRP with stepped drills

Carbon fiber-reinforced plastics (CFRPs) have many excellent properties, such as lightless, high specific strength, and high corrosion resistance, and they have been extensively used in the aeronautics and astronautics. It is a challenge for studies on the defect-free drilling technology and the causes of drilling defects to the CFRP materials. The purpose of this study is to research the machining parameters and the stepped drill geometry effect on cutting force and hole wall damage with the test methods. Both a twist drill and three stepped drills were employed in drilling CFRP plates under the experimental conditions. The effects of both the processing parameters and the stepped drill structure (the ratio of the pilot section diameter to the sizing diameter section diameter (D1/D)) on thrust force and hole wall damage were investigated, and the damage mechanism of hole walls was revealed by analyzing the cross-section features of the hole wall. The results show that the maximum thrust force of T3 (D1/D = 0.5) is minimal, so T3 should be selected to reduce the risk of delamination. D1/D, feed rate, and spindle speed are the main factors that affect the size of the hole wall damage. In addition, a special cutting force Fspec is defined to explain the influence of tool structure and feed rate on hole wall damage.

Surface characteristics and machining performance of TiAlN-, TiN- and AlCrN-coated tungsten carbide drills

This article presents a comprehensive analysis of surface characteristics and drilling performance of uncoated and coated tungsten carbide drills. The single- and double-layer coatings of TiN, TiAlN and AlCrN were examined in terms of surface roughness, microhardness and crack resistance. In addition, drilling torque and thrust force were experimentally measured and compared to the developed models based on the drilling mechanics and drill geometries. Tool wear and hole surface roughness were also considered to assess the machining performance of different coated tools. The results revealed that all coated drills can offer better cut surface quality, 28% lower cutting loads and longer tool life than the uncoated drills. Although AlCrN was found to be the hardest coating material among the others, it caused large wear on the cutting edges and poor surface roughness of produced holes. The lowest torque and thrust force were achievable using TiN-coated drill, while the use of TiAlN coating resulted in the lowest surface roughness and smallest tool wear. Furthermore, the drilling torque and thrust force model developed in this study were found to correspond to the experimental measures with the average error of 8.4%. The findings of this work could facilitate the selection of coating materials to advance the machining performance.

Investigations on drilling of hemp/glass hybrid composites

ABSTRACTThe present study aimed to examine the influence of tool geometry, spindle speed and feed on thrust force (TF) and delamination in hybrid hemp-glass composites. The pure glass polyester, pure hemp polyester and hybrid hemp/glass polyester composite specimens were prepared using hand layup technique. The drilling experiments were performed according to the full factorial design. Analysis of variance (ANOVA) was used to determine the impact of layering arrangement of fibers, feed (0.06, 0.18, 0.3 mm/rev), speed (1000, 3000, 5000 rpm), tool geometry (Plexi Point, Brad, Parabolic) and their interactions on TF and delamination. It was observed that drill geometry is major determinant for TF and delamination. Empirical models were developed using regression analysis and grey relational analysis was performed for optimizing the input parameters for TF and delamination at entry and exit.

Effect of Cutting parameters, Point angle and reinforcement percentage on surface finish, in drilling of AL6061/Al2O3p MMC

The subject of this paper is concerned with the experimental study and the influence of cutting parameters, reinforcement percentage and drill geometry on surface finish, in drilling of Al6061/ Al2O3 Aluminum Metal Matrix Composite. The experimentation is conducted based on Taguchi method, The design have four factors, mixed level design of L-18 array with one column of two level and three columns of three levels had been selected for design. The effects of reinforcement percentage of Al2O3p, point angles of drill bits, Cutting Speed and Feed Rate on Surface Roughness, Mean Force, Torque and Cylindricity had been analyzed here. Moreover the causes of results based on analysis have been discussed.Metal Matrix Composites (MMC) offer numerous thermo-mechanical advantages over standard materials and alloys which make them better candidates in different applications. Their light weight, high stiffness and strength have attracted several industries such as automotive, aerospace, and defense for their wide range of products. However, the wide spread application of Meal Matrix Composites is still a challenge for industry. The hard and abrasive nature of the reinforcement particles is responsible for rapid tool wear and high machining costs. An effort has been made to analyze the machining parameters and surface finish for cost effective solution. The important effects have been discussed and percentage contribution of various process parameters speed, feed, point angle on surface finish, force, torque and Cylindricity have been determined.

Research on the influence of a new tap drill geometry on C45, 42CrMo4 and X5CrNi8 steel processing

The shearing of the chips in a blind hole thread presents a particular problem in machining industry. The tap geometry plays an important role in the tool's durability, influencing the forces during the tapping process and also the way in which the chips are evacuated. This paper analyzes the influence of the tap geometry on the cutting of materials such as C45, 42CrMo4 and X5CrNi8. An adequate geometry will extend the tap durability by controlling the chip when the tap reverses while still engaged in the tapping process. It relates to the improvement of a spiral tap drill, which discharges chips towards the shank via a helical flute. The article contains details about the tap geometries and the results obtained in this research. Based on the results obtained in this research, the purpose of this paper was achieved. The tap durability was improved, the chip deposition on the rake surface was reduced and the torsion torque has a smaller value compared to the standard tap geometry.

Fragment Size Distribution of Blasted Rock Mass

Rock mass is a heterogeneous material, and the heterogeneity of rock causes sizes distribution of fragmented rocks in blasting. Prediction of blasted rock mass fragmentation has a significant role in the overall economics of opencast mines. Blasting as primary fragmentation can significantly decrease the cost of loading, transport, crushing and milling operations. Blast fragmentation chiefly depends on the specific blast design (geometry of blast holes drilling, the quantity and class of explosive, the blasting form, the timing and partition, etc.) and on the properties of the rock mass (including the uniaxial compressive strength, the rock mass elastic Young modulus, the rock discontinuity characteristics and the rock density). Prediction and processing of blasting results researchers can accomplish by a variety of existing software’s and models, one of them is the Kuz-Ram model, which is possibly the most widely used approach to estimating fragmentation from blasting. This paper shows the estimation of fragmentation using the "SB" program, which was created by the authors. Mentioned program includes the Kuz-Ram model. Models of fragmentation are confirmed and calibrated by comparing the estimated fragmentation with actual post-blast fragmentation from image processing techniques. In this study, the Kuz-Ram fragmentation model has been used for an open-pit limestone quarry in Dalmatia, southern Croatia. The resulting calibrated value of the rock factor enables the quality prognosis of fragmentation in further blasting works, with changed drilling geometry and blast design parameters. It also facilitates simulation in the program to optimize blasting works and get the desired fragmentations of the blasted rock mass.

Drilling performance of functionally graded composite: Comparison with glass and carbon/epoxy composites

Functionally graded composite (FGC) materials are categorized as advanced materials that display different thermal and mechanical responses compared with well-known composites, such as carbon fiber or glass fiber-reinforced composites. This paper presents the experimental results for the drilling of three materials, namely glass/epoxy, carbon/epoxy, and FGC material. FGC was compared with carbon and glass/epoxy composites in terms of thrust force, delamination factor, diameter of hole, and roundness during drilling. This study illustrated that the drilling performance of FGC is considerably more complicated than that of more common composite materials, such as glass/epoxy and carbon/epoxy. Delamination factor at the exit of hole during drilling of FGC was mainly affected by the material placed at the exit of the hole. The proposed cutting parameters and drill geometries to minimize the occurrence of delamination during drilling of carbon/epoxy and glass/epoxy apparently does not meet the expectation in drilling FGC.

Drilling of pultruded and liquid composite moulded glass/epoxy thick composites: Experimental and statistical investigation

Composites are often one of the foremost difficult-to-machine materials. Out of many defects due to hole making process, the prime concern is delamination. This investigation aims to reveal the best drill geometry and corresponding optimal process parameter levels for making defect tolerance holes in thick pultruded and liquid composite moulded (LCM) composites. The novelty in this work are carrying out drilling operations with special geometry drills in thick composites, considering the entire depth of hole for assessing the damage and studying the influence of self-excited vibration of the work material. Minimization of drilling forces, drilling-induced damage and tri-axial self-excited vibration of the work material have been executed simultaneously to reveal the optimum process parameter levels for drilling the tested composite materials with each of the selected drill tools. It has been found that three flute and four-facet WC twist drills are more suitable for pultruded and LCM composites, respectively.

Experimental analysis of drilling induced damage in biocomposites

This paper focuses on the analysis of drilling induced damage on biocomposites (woven fibers of cotton, flax and jute combined with polylactic acid, PLA, as the matrix). The main contribution of this work is the analysis of the influence of cutting parameters and drill geometry on fully biodegradable composites based on two different types of PLA and different fibers types. The damaged area was studied both at the hole entry and exit. Contrary to the behavior commonly observed when drilling conventional composites, delamination was negligible. The hole entry and exit damage were analyzed and quantified in terms of the fraying extension being the dominant. The damage extension was found to be dependent on the matrix, fiber type and drill geometry. The combination between cotton fiber and the small drill point angle showed the lowest level of damage. On the other hand, composite reinforced with flax fibers (those that exhibited the highest tensile strength) presented the greatest damage extension, increasing with the number of layers of the composite. The matrix based on polymer 10361D PLA, recommended for natural fibers because of the better interface cohesion, resulted in reduced fraying. Concerning the influence of cutting parameters, damage decreased when increasing the cutting speed and feed rate.

An approach to evaluate delamination factor when drilling carbon fiber-reinforced plastics using different drill geometries: experiment and finite element study

Delamination is one of the major damages associated with drilling carbon fiber-reinforced plastics (CFRP), Peel-up and Push-out are two recognizable delamination mechanisms, while drilling without using a back-up plate under the workpiece complicates the delamination mechanism even more. Minimizing delamination is dependent on many factors such as cutting parameters, geometry and type of drill bits used. The objective of this study is to present a new approach to measure the equivalent adjusted delamination factor (F e d a ) when drilling unidirectional CFRP laminates without using a back-up plate and comparing it experimentally and numerically with conventional delamination factor (F d ) and adjusted delamination factor (F d a ). A polycrystalline diamond (PCD) twist drill and a special diamond coated double point angle drill was used for drilling in this study. The 3D finite element model was developed in ANSYS-Explicit to simulate the drilling process using the ply-based modeling method instead of a conventional zone-based concept. Experimental drilling validation process was implemented by utilizing a CNC machining center. Results show that the F e d a obtained is suitable to estimate the drilling induced damages, damage analysis shows that good agreements were obtained from the experiments and finite element method (FEM) simulation, while the special diamond coated double point angle drill seemed to provide a better hole quality, and drilling induced damage is highly affected by feed rate which is considered one of the important parameter.

Experimental Study on the Effect of Point Angle on Force and Temperature in Ultrasonically Assisted Bone Drilling

Drilling of bone is a common surgical procedure in orthopedics to produce holes for screw insertion. The force and temperature rise in bone drilling are two important factors affecting the outcome of the process. The present work attempts to investigate the effect of drill point angle on the level of force and temperature in bone in the presence of ultrasonic vibrations imposed on the drill along the drilling direction. The effect of drill speed on the drilling force and bone temperature was studied using two types of drills with different point angles. The influence of a range of ultrasonic frequencies and amplitudes of vibrations on drilling force, torque and surface temperature of bone was also investigated. The drilling force and bone temperature were found to be strongly influenced by the drill point angle in the presence of ultrasonic vibrations. The drill with larger point angle caused more force and temperature compared to the drill with smaller point angle. Ultrasonic frequency above 15 kHz was observed to produce more temperature in bone for both types of drill geometries. This study found drill with smaller point angle favorable for safe and efficient drilling in bone.

Burr Height as Quality Indicator in Single Shot Drilling of Stacked CFRP/Aluminium Composite

In drilling metallic parts, burr height is one of the quality indicators that is used for hole quality assessment, and burr height need to be minimized for best hole quality. This is important because the induced exit burr height usually causes serious problem for further assembly of the stack up during the riveting and fasteners installation. This paper aims to establish an appropriate choice of drill geometry and drilling parameters to achieve a minimum or eliminate the burr height formation when drilling stacked Carbon Fibre Reinforced Plastic (CFRP)/aluminium 7075 T-6 composite in a single shot drilling process. The two levels of fractional factorials method was used to determine the optimum setting that give minimum burr height and the percentage of significance for each parameter in drilling a stack up materials was further analysed. The results revealed that burr height formation for stack up materials can be minimized at 15° of helix angle, 8° of primary clearance angle, 130°of point angle, 30° of chisel edge angle at spindle speed 2600 RPM and 0.05 mm/rev. A minimum burr height of 133.62 µm was found at these optimized combinations of parameters.

Analysis of local cutting edge geometry on temperature distribution and surface integrity when dry drilling of aeronautical alloys

A suitable choice of tool geometry and tool material and the optimization of cutting conditions is the way towards dry machining, especially for difficult to machine materials. The current paper proposes an experimental work about dry drilling of AA 7075 aluminium and more particularly Ti-6Al-4V titanium alloys. Effects of complex drill geometry on thrust force and cutting temperature variations are explored. This study includes drill normal rake angle definition using a mathematical formulation based on tool CAD definition. Temperature distribution along the drill cutting edge is estimated with a specific device. Cutting forces are measured using a dynamometer table. Hole surface integrity is studied by observation of microstructures, on surface and sub-surface. Micro-hardness tests complete the measurements. Results show that temperature is much higher when drilling titanium Ti-6Al-4V than when drilling aluminium AA7075, with variations from 450 to 540 °C along the main cutting edge. Temperature variation along the cutting edge depends on cutting speed, work material and local geometry. Microstructural observations reveal that surface and subsurface are affected with grains elongation in cutting direction. Temperature and microstructural deformation increase with drilling depth.

Investigation on hole quality of cutting conditions in drilling of CFRP composite

Surface damages and delamination occurred in drilling of the carbon fiber reinforced polymer composite materials, which change depending on their physical and mechanical properties and cutting conditions, and so affect the hole quality. Therefore, it is requires to be selective with regards to drill geometry and drilling parameters during drilling of CFRP. This study investigated the effects of cutting parameters and drill geometry on the hole quality in terms of hole diameter and surface roughness during the drilling of CFRP composite laminate. Drilling experiments were performed with three different levels of drilling parameters that are point angle, cutting speed and feed rate. At the end of the drilling tests, it has determined that if the feed rate increases, the surface roughness value increases while the hole diameter decreases. The feed rate was determined as the most important parameter with a PCR of 78.02% according to analysis of variance. The better hole quality was obtained with 130° drill among the three drill geometry.

Effects of Drill Geometry and Penetration Angle on Temperature and Holes Surfaces for Cortical Bovine Bone: An in Vitro Study

Drilling of bone is the most important part of the internal and external fixation processes in orthopaedic surgery. This surgical procedure usually is performed manually with a hand-held tool and is greatly dependent on the surgeon skill. Imprecise manipulation of the hand-held tool can cause the drill skidding across the bone surface and leads to a localized increase in temperature resulting a thermal necrosis on the soft tissue surrounding the hole surface. The magnitudes of the friction energy are greatly dependent with the drill geometry design and the penetration angle. For the sake of importance on studying this phenomenon, this paper aim to investigate the effects of drill geometry on temperatures rise and hole surface in bone drilling procedure. Totals of 17 drills were designed and tested with different geometry namely point angle, helix angle and web thickness on different penetration angle (00, 150, and 300) to mimic the manually control penetration by the surgeon. From the conducted investigation, the most significant parameter that affects the temperature rise and holes surface quality was the penetration angle followed by the point angle. In addition, the interaction between helix angle and web thickness also controlled the drilling temperature and the performance of the hole surface.

Low-frequency modulation-assisted drilling of carbon-epoxy composite laminates

Carbon fiber-reinforced plastics (CFRPs) have a wide spectrum of industrial applications because of their outstanding multifunctional properties. However, the machining performance of CFRPs is poor which has restricted further expansion of their application range. The damage that is induced during machining is considered as a major hindrance for the applicability of CFRP components for structural applications. In order to mitigate this perplexing challenge, an emerging machining method namely, modulation-assisted machining has been adopted which has not been investigated earlier in context of drilling of CFRP laminates. The drilling performance of the CFRP laminates has been analyzed using both conventional and modulation-assisted drilling techniques. The influence of the feed, frequency of rotation, drill geometry, frequency of modulation, and modulation amplitude on the force and subsequently damage has been experimentally investigated. The results indicate that modulation-assisted drilling technique produces better quality holes than conventional drilling under identical conditions.

A computational fluid dynamics (CFD) model for effective coolant application in deep hole gundrilling

Effective coolant application in deep hole gundrilling is crucial to prevent rapid degradation and failure of drills through high performance cooling, lubrication and chip evacuation. This paper presents a novel methodology to increase effectiveness of coolant application through strategic optimization of gun drill designs that leads to appreciable tool life improvement, based on computational fluid dynamics (CFD) analysis. Through the analyses of coolant flow characteristics and rheological properties, conventional designs of critical drill geometries like nose grind contour, coolant hole configuration and shoulder dub-off angle, which are detrimental to coolant application and hence tool life are determined. A new, optimized gun drill design for the drilling of deep holes on Ni-based alloys is proposed. All findings are experimentally substantiated.

A Review of Backup Mechanism for Reducing Delamination when Drilling Composite Laminates

Over the past decades, composite materials have been increasingly utilized in various industries because of their superior mechanical properties and resistance to corrosion. Drilling is essential to produce precise holes when load-carrying structures are produced using composites. Because of the non-homogeneous and anisotropic property of composite laminates, delamination often occurs at the point where the drill exits, which affects reliability and safety. Some studies present a suppressed mechanism to prevent delamination when drilling composite laminates. The experimental results demonstrate delamination is significantly reduced by various suppressed mechanisms and greater feed rates produce the same level of delamination. The use of special drill geometries and backup has been demonstrated to be more advantageous than the use of adapted feed controls. The basis for the future development of a suppression mechanism for drilling composite laminates is determined.

Thermo-mechanical modelling of FRP cross-ply composite laminates drilling: Delamination damage analysis

Abstract Among other factors, thrust force, feed rate, twist drill bit chisel edge and point angle are the principal factors responsible for delamination drilling-induced damage during thermo-mechanical deformation. Hence, in this paper, an analytical thermo-mechanical model is proposed to predict critical feed rate and critical thrust force at the onset of delamination crack on CFRP composite cross-ply laminates, using the principle of linear elastic fracture mechanics (LEFM), classical plate theory, cutting mechanics and energy conservation theory. The delamination zone (crack opening Mode I) is modelled as an elliptical plate. The advantages of this proposed model over the existing models in literature are that the influence of drill geometry (chisel edge and point angle) on push-out delamination are incorporated, and mix loads condition are considered. The forces on chisel edges and cutting lips are modelled as a concentrated (point) and uniformly distributed loads, resulting into a better prediction. The model is validated with models in the literature and the results obtained show the flexibility of the proposed model to imitate the results of existing models.