Drill Flute Research Articles

Autologous bone harvested during implant bed preparation: A randomized clinical trial comparing high-speed drilling with irrigation versus low-speed drilling without irrigation.

To compare collected bone weight and the frequency of autologous bone harvesting from the flutes of surgical drills used for implant bed preparation using two different drilling techniques. A comparative evaluation of radiographic bone density and bone quality was also made. A randomized clinical trial was made of 66 dental implants in patients with a single posterior edentulous site. The compared drilling techniques were high-speed drilling with irrigation (control group) and low-speed drilling without irrigation (test group). The bone collected in both groups was dried and weighed with a precise electronic balance. The frequency of harvesting was calculated. The median radiographic bone density of each implant site was measured using cone-beam computed tomography (CBCT) pixel values. Patient sex, age, implant position and dimensions, as well as the last drill diameter were analyzed as independent variables. The level of significance was 5%. The harvesting of bone chips from drill flutes proved possible in 51.5% of the procedures in the control group and in 100% in the test group (p < 0.001). There were also statistically significant differences in bone weight between the control group (6.7 ± 10.6 mg) and the test group (41.9 ± 30.3 mg) (p < 0.001). The CBCT pixel values were directly correlated with the collected bone weight in both groups. The median radiographic bone density, arch and last drill diameter were significantly associated with harvesting bone frequency and collected bone weight (p < 0.05). Our findings suggest that the frequency and weight of autologous bone harvested from drills are greater with low-speed drilling without irrigation than with high-speed drilling with irrigation. Radiographic bone density, arch and last drill diameter also significantly influenced the harvesting outcomes.

Drilling performance of micro-textured twist drill bit for TI-6AL-4V alloy: Validated FEM and statistical approaches

The titanium alloy, particularly Ti-6Al-4V, is an extensively demanded material in diverse sectors because of its superior physical and chemical properties. Nevertheless, the inherent hardness of the material causes challenges during machining operations. The alloy's heat-resistance characteristic induces increased friction and heat generation on cutting tools, ultimately causing a decrease in the tool life. In an attempt to overcome this issue, numerous forms of surface texturing have been investigated with the aim of improving the tribological characteristics of the material. The aim of the present investigation was to enhance the cutting performance of drill bits by implementing micro-textured patterns, hence minimizing thrust force, torque, and tool temperature. The combined effect of three distinct micro-textured geometries on a drill bit's flank, flute, and margin surfaces, with the influence of coating conditions, on the performance of drilling operations was investigated. The Finite Element Method (FEM) was used to perform a range of varied drilling operations. The Grey Relation Analysis (GRA) and General Linear Model (GLM) were employed to assess and compare the drilling performances with respect to thrust force, torque, and drill bit temperature. It was found that the square-sectioned textures on the side face exhibited the most obvious influence on the drilling performance. In the meantime, the textures found on the flute face were identified as having a comparatively smaller influence. The ideal configuration for the drill bit entailed a flank face with a square sectioned texture, a flute face without any texture, a margin face with a square sectioned texture, and a hard coating. As a result, the current situation substantially reduced cutting forces, tool wear, and tool temperature by 51 %, 20.5 %, and 23.4 % compared to the drilling condition without textured drill bits.

Performance analysis of drills with structured surfaces when drilling CFRP/AA7075 stack under MQL condition

When drilling multi-stack materials, the dissimilar material response, severe tool wear, and long hot metal chips pose serious challenges in achieving the requisite hole quality. There is difficulty in effectively lubricating the cutting zone as the drill penetrates deep into the drilled hole. Structuring the surfaces of cutting tools is an approach to improve their tribological performance. Micro-textures are created on the drill flute and margin surfaces using laser micro-machining to improve the micro-pool lubrication effect and reduce the friction during machining CFRP/aluminum alloy stacks. The performance of four different textured drills - dimple on flute, groove on flute, perpendicular and parallel grooves on margin – is compared with that of the non-textured drill. The thrust force, hole quality (roughness, roundness and delamination), tool wear (BUE and cutting edge rounding), and chip morphology are analyzed. Among the four textured drills, the dimple textured drill results in the best performance due to the improved micro-pool lubrication effect of micro-dimples in the flute region, thereby producing short metal chips and best hole quality. It also retains the texture depth for a longer duration as compared to the other textured drills.

Ultrasonic-assisted drilling of nickel-based super alloy in conel 601: An experimental study

In this study, a comparison between ultrasonic-assisted drilling (UAD) and conventional drilling (CD) is presented under different feed rates using thrust force, torque, and hole geometrical errors as output responses. The experiments were done on plates of Inconel 601 (nickel-based superalloy), which is classified as a difficult-to-cut alloy due to its high Nickel content (60%), high hardness (43 HRC), and low thermal conductivity. The experiments were performed using DMG Mori Ultrasonic 20 linear, which is equipped with ultrasonic tool holderoscillating at 20 kHz with 7 μm amplitude. A coated carbide single margin twist drill had been used in the experiments. Full factorial design of experiments approach was employed, and the results had been statistically analyzed to find the most significant factor affecting the process responses. The results showed that the ultrasonic assistance had reduced the thrust force, and torque compared to conventional drilling (CD). Also, a reduction in holecylindricity error was detectedduring UAD, whichimprovesthe hole quality. In case of UAD, twist drills did not suffer from a physical wear, however notch wear was observed in CD drills. Chip morphology was also studied. Short segmented chips were obtained when using UAD which improved chip evacuation and reduced the chance of chip jamming in the drill flutes.

Investigations into solid lubricant filled textured tools on hole geometry and surface integrity during drilling of aluminium alloy

Generation of holes in aluminium alloy is difficult task for manufacturing industries due to chemical affinity with the drilling tool. This results in creation of build edge that leads to high power consumption and variation in form and surface profile of hole geometry. To overcome this, an attempt has been executed to design a textured pattern over the drill margin and flute surface by fiber laser micro machining process. This laser texture pattern on drill tool act as a source to accommodate more solid lubricant during deep drilling process. A detailed experiment has been conducted to study the influence of solid lubricant filled textured tools on hole geometry and surface integrity and finally compared with dry, blasocut, non-textured coated solid lubricant drill tools. It is inferred that accuracy of the hole is improved in solid lubricant filled textured drill tool over non-textured lubricant, blasocut and dry machining. The continuous, smooth and spiral shaped morphology of the chip with less friction is the indication of improvement in the hole accuracy. Cylindricity error, burr height and surface roughness are observed minimum in texture filled graphite and MoS2 assisted drilling. Good surface finish of 100 nm is achieved at higher cutting speed in graphite filled textured drill tool.

Effect of feed condition on thrust force and torque during continuous and step-by-step drilling of cortical bone

Abstract Chip evacuation is one of the fundamental difficulties during continuous drilling of the cortical bone. As the drilling process progresses, discontinuous chips tend to cluster together and clog the drill flutes, which can result in increased temperature, poor hole quality, elevated thrust force and torque, and can even cause the drill bit to break. In this study, continuous and step-by-step drilling processes of the cortical bone were conducted to investigate the thrust force and torque using experimental and numerical modeling methods. By using the finite element method, an elastic–plastic constitutive model was employed to predict the thrust force and torque experienced during bone drilling, and a series of drilling tests was conducted. The experimental results showed a significant increase in the thrust force and torque owing to the chip clogging during the continuous drilling process while this increase was not observed in the simulations. It was shown that the step-by-step drilling method can reduce the increased thrust force and torque during the drilling of cortical bone, and the numerical results of this drilling process were demonstrated to be consistent with the experimental ones. The reduced thrust force and torque indicated that the chip clogging may be reduced by using the step-by-step drilling method, and the numerical results suggested that the finite element model can be used to assist surgeons in selecting drilling conditions to control the process in step-by-step drilling of the cortical bone.

Mechanical and thermal damage in cortical bone drilling in vivo

Recently, the failure rate of fracture fixation to fractured bone has increased. Mechanical and thermal damage to the bone, which influences the contact area and cell growth between the bone and the screw, is the primary reason for fixation failure. However, research has mainly focused on force and temperature in bone drilling. In this study, the characteristics of hole edges, microcracks, empty lacunae, and osteon necrosis were investigated as viewed in the transverse and longitudinal sections after drilling. Drilling force and temperature were also recorded for comparing the relationship with mechanical and thermal damage. Experiments were conducted in vivo using five different drill geometries under the same drilling parameters. Characteristics of the hole wall were detected using computed tomography. Microcracks and necrosis were analyzed using the pathological sectioning method. The maximum microcrack was approximately 3000 and 1400 μm in the transverse section and longitudinal section, respectively, which were much larger than those observed in previous studies. Empty lacuna and osteon necrosis, starting from the Haversian canal, were also found. The drill bit geometry, chisel edge, flute number, edges, and steps had a strong effect on bone damage, particularly the chisel edge. The standard and classic surgical drill caused the greatest surface damage and necrosis of the five drill bit geometries studied. The microstructural features including osteons and matrix played an important role in numbers and length of microcracks and necrosis. More microcracks were generated in the transverse direction, while a greater length of the empty lacuna was generated in the longitudinal direction under the same drilling parameters. Microcracks mainly propagated in a straight manner in and parallel to the interstitial bone matrix and cement line. Drilling forces were not directly correlated with bone damage; thus, hole performance should be considered to evaluate the superiority and inferiority of drill bits rather than the drill force alone.

Effects of the drill flute number on drilling of a casted AZ91 magnesium alloy

AbstractThis experimental study aims to reveal the effect of the drill flute number on the thrust force, tool wear, tool life, chip morphology, surface hardness and microstructure in the drilling of a cast AZ91 magnesium alloy. The results showed that the cutting flute number and cutting parameters have an important effect on thrust force, tool life, wear, chip morphology, microstructure, and drilled hole hardness. When the 2-flute drill was used, less thrust force was generated during the drilling. On the other hand, less tool wear occurred with the 3-flute drill. In scanning electron microscopy (SEM) microstructural analyses, grain refinement was observed in the microstructure of the borehole surface although grain growth was also observed due to a rise in temperature. In addition, the microhardness of the borehole surface decreased as the number of holes increased, and the 2-flute drill bit provided holes with higher stiffness than the 3-flute drill bit.

Effect of drill flute direction on delamination at the exit in drilling Carbon Fiber Reinforced Plastic

Drilling holes on Carbon Fiber Reinforced Plastic components is inevitable for mechanical assembly in the aerospace field. Delamination at the exit frequently occurs and substantially reduces the service life of components. Drill flute direction is one of the main factors affecting delamination at the exit. The article aims to study the effect of drill flute direction on delamination and further to guide the suitable choice of drill flute direction. Comparative experiments are performed in drilling Carbon Fiber Reinforced Plastic for the drills with different drill flute directions, when a small cutting edge radius is involved. Based on the experimental results, the effects of drill flute direction on the thrust force, force state of the uncut fibers at the exit, and delamination propagation at the exit are obtained. Meanwhile, the phenomenon that delamination at the exit varies with the drill flute direction significantly is explained from aspects of thrust force and force state of the uncut fibers at the exit. The drill with left hand helix owns the most serious delamination at the exit among the tested drills because of its high thrust force and serious tearing function for the uncut fibers at the exit. POLYM. COMPOS., 40:E1434–E1440, 2019. © 2018 Society of Plastics Engineers

Design of grinding wheel profile for new micro drill flute

Derived from our previous research, a new micro drill bit with higher accuracy and productivity was developed. Because the drill flute plays a significant role in its cutting performance, the design of grinding wheel profile for the new micro drill flute by an inverse problem method is examined in this research. First, the cross-section of the new micro drill flute is modeled by mathematical equations. Second, machine parameters and workpiece geometric parameters are set up. Third, the engagement equation between the grinding wheel and flute surfaces is developed. Fourth, that equation is solved to obtain the locus of contact points. Finally, the translation and rotation transformations of that locus are carried out to obtain the grinding wheel profile for the new micro drill flute. Numerical examples are demonstrated and validated by Vericut software.

Modeling and optimization of the flute profile of micro-drill

The profile of drill flute has a great influence on the drilling performance of micro-drill. It is promising to obtain a desired flute profile with a standard wheel by adjusting the wheel position parameters during the grinding process. To investigate the flute profile characteristics under different wheel position parameters and its effect on the drilling performance, this paper presents a method for modeling and optimization of the micro-drill flute considering the wheel installation angle and the offset distance from the wheel origin to the drill blank origin. Based on this model, the flute profile of micro-drill is numerically simulated by MATLAB software firstly, and then, the 3D model of micro-drill with different flute profiles is established by UG software. Finally, the micro-drilling process on 304 austenitic stainless steel is simulated by DEFORM software, and the chip morphology and the drilling force are analyzed and discussed. The results show that the wheel installation angle has an obvious effect on the flute profile and its radial rake angle and flute width, and the wheel offset distance only influences the flute width evidently. The micro-drill with flute ground by smaller wheel installation angle owns straighter cutting lip shape and larger chip evacuation capacity, and its thrust force and torque are smaller than those of other micro-drills. Moreover, spiral chip is generated due to the intense side curl and up curl of the chip, resulting in the easiness of the chip removal. However, for the micro-drills with flute ground by larger wheel installation angle, the chip morphology is string and the drilling force is larger. At last, the mathematical model of the drill flute and its numerical simulation result are validated by experimentally fabricating the micro-drill flute. Then, the optimized micro-drill is manufactured by a six-axis computer numerical control (CNC) grinding machine, and its flute profile is fabricated using a standard conical grinding wheel with a smaller wheel installation angle.

DLCコーテッドドリルを用いたプリント配線板の小径穴あけ加工に関する研究

In recent years, needs for micro drilling are increasing, accompanying the development of higher wiring density of printed circuit board (PCB). When drilling PCB for the purpose of making the electric through holes, it has been said that the drill breakage is caused by being filled the chips of GFRP and copper of PCB in the drill flutes. The aim of this study is to clarify the effect of PCB drilling using DLC coated drill on tool wear, chip evacuation and cutting torque. Series of drilling tests of PCB have been carried out to investigate the amount of drill wear, the chips evacuation behavior out of drilled hole with the drill, the shape of chips produced and the cutting torque using DLC-coated drill and non-coated drill. The chips evacuation behavior out of drilled hole with the drill is filmed by a high-speed motion camera and the shape of chips produced is observed by a microscope. The cutting torque is measured by a dynamometer; Kistler 9329A. The amounts of drill flank wear and margin wear using DLC-coated drill and non-coated drill are almost the same. The chips of GFRP using DLC-coated drill are shorter and smaller than those using non-coated drill. The chips evacuation out of drilled hole with the drill using DLC-coated drill is better than those using non-coated drill, and cutting torque using DLC-coated drill is lower than those using non-coated drill.

Structured white light scanning of rabbit Achilles tendon

BackgroundThe cross-sectional area (CSA) of a material is used to calculate stress under load. The mechanical behaviour of soft tissue is of clinical interest in the management of injury; however, measuring CSA of soft tissue is challenging as samples are geometrically irregular and may deform during measurement. This study presents a simple method, using structured light scanning (SLS), to acquire a 3D model of rabbit Achilles tendon in vitro for measuring CSA of a tendon. MethodThe Artec Spider™ 3D scanner uses structured light and stereophotogrammetry technologies to acquire shape data and reconstruct a 3D model of an object. In this study, the 3D scanner was integrated with a custom mechanical rig, permitting 360-degree acquisition of the morphology of six New Zealand White rabbit Achilles tendons. The reconstructed 3D model was then used to measure CSA of the tendon. SLS, together with callipers and micro-CT, was used to measure CSA of objects with a regular or complex shape, such as a drill flute and human cervical vertebra, for validating the accuracy and repeatability of the technique. ResultsCSA of six tendons was measured with a coefficient of variation of less than 2%. The mean CSA was 9.9±1.0mm2, comparable with those reported by other researchers. Scanning of phantoms demonstrated similar results to μCT. ConclusionThe technique developed in this study offers a simple and accurate method for effectively measuring CSA of soft tissue such as tendons. This allows for localised calculation of stress along the length, assisting in the understanding of the function, injury mechanisms and rehabilitation of tissue.

Influence of Wheel Position Parameters on Flute Profile of Micro-Drill

Drill flute has a great influence on the drilling performance of micro-drill, and its profile largely depends on the grinding parameters, wheel profile and position. It is promising to obtain a desired flute profile with a standard wheel by adjusting the wheel position parameters. To investigate the influence of wheel position parameters on the flute profile, the micro-drill flute is simulated by MATLAB software considering the wheel installation angle and the offset distance from wheel origin to the drill blank origin, and the radial rake angle, flute width and chip evacuation capacity are quantitatively calculated to evaluate the flute profile. The simulated results show that the wheel installation angle has an obvious effect on the three performance parameters of flute profile, and the wheel offset distance only influences a parameter, i.e., the flute width evidently. The radial rake angle of drill flute increases obviously with the increased wheel installation angle, and decreases slightly with the increased wheel offset distance. With the decreased wheel installation angle, the flute width of drill flute increases causing the reduction of micro-drill strength but improvement of the chip evacuation capacity. With the increased wheel offset distance, the flute width also increases resulting in the reduction of micro-drill strength but no obvious change on chip evacuation capacity. Thus the wheel installation angle can be used as a main factor among the wheel position parameters to obtain the desired flute profile.

Investigation of warping effect on coupled torsional-axial vibration of drilling tool

Coupled torsional-axial vibration of the drilling tool plays a significant role in the machining dynamics of the drilling process. This paper models the torsional-axial vibration of the drilling tool due to the warping deformation of the pretwisted flute. The warping-dependent cross-sectional properties of the drill flute are obtained from 2D finite element method. Natural frequency and mode shape corresponding to the torsional-axial vibration of the drill are predicted. The effects of helix angle, web thickness, and aspect ratio on the coupled torsional-axial dynamics are analyzed for conventional and micro drilling. The simulations are validated by experimental results using modal testing technique. The proposed model is able to provide guidance in selecting geometric configuration of the drilling tool for required torsional-axial dynamic behavior with high computational efficiency and guide the drilling process in order to reach desired hole quality.

Obstruction-type Chip Breakers for Controllable Chips and Improved Cooling/Lubrication During Drilling – A Feasibility Study

During drilling, long stringy chips resulting from ductile plastic deformation of engineering materials cause severe chip clogging within the narrow helical flutes and edge chipping, leading to premature tool wear and breakage, poor tool life, poor hole quality and the productivity. Cutting fluid cannot efficiently access to the cutting edge that plays a vital role for improving machining performance. To address the localized heat and chip control issues during drilling, research was previously performed using conventional flood cooling, modified tool geometry, tool coating materials, and internal coolant via through hole(s). This works focuses on design and insertion of some obstruction-type chip breakers such as ribs and pins on the drill flutes and their influence on chip formation behavior. For feasibility experiments, small round pins made of stainless steel at a diameter of about 0.8-0.85mm diameter are prepared and attached on the electro-discharge machined (EDM) blind holes on twisted drill flutes. By varying spindle speed and feed rate, drilling experiments are performed on two engineering materials including Al6061 and Inconel 625 superalloys at four cutting conditions. Most chips are found to be broken and some split into two fractions due to the pins. Force and power values with pin-inserted drill bits were found to be reduced from 5-9%. This finding indicates that there is a good potential to implement such obstruction-type chip-breakers on the drill flutes for obtaining controllable chip while also improving coolant flow at the cutting edge through the tiny tool-chip interface.

プリント配線板の小径穴あけ加工における切りくず排出機構に関する研究

Series of drilling tests of PCB have been carried out to investigate the shape of chips produced and the chips evacuation behavior out of drilling hole at the drilling rotational speed of from 20×103min-1 to 160×103min-1. With an increase in the drilling rotational speed, the chips evacuation out of drilling hole is very well, the chips of GFRP are short and small pieces and both of maximum cutting torque and average cutting torque are decreasing. On the other hand, the chips evacuation behavior out of drilling hole is worse because of increasing coefficient of between surface of drill flute and chip with an increase in the drilling rotational speed, and both of maximum cutting torque and average cutting torque are increasing. The chips of GFRP grow long and large pieces after adhering one chip to another chip when the drill flutes are full with chips.

Modeling, simulation and manufacturing of drill flutes

The designing of twist drill flutes (as well as that of end mills and of some combined tools) cannot be separated from the way they are manufactured. The aim of this paper is to present an intuitive direct method for modelling, simulation and manufacturing of the drill flutes with different shapes using conical grinding wheels with standardized shapes. The mathematical approach is described, which enables us to determine the flute profile in a section perpendicular to its axis as well as the manufacturing parameters. The grinding wheel has an initial position with respect to the cylindrical work piece, which is described using four parameters (Denavit Hartenberg parameters). We have presented algorithms in pseudocode that produce the flute shape and that compute the optimum parameters of the wheel position in the manufacturing process. Subsequently, a software application based on the aforementioned model is able to create visualizations of the flute shape. The analysis of the flute shape has enabled us to understand the influence of the geometrical parameters and the position of the grinding wheel on the resulting product in the grinding process. The order in which these parameters are to be set is also specified. We have built atlases of maps presenting the influence of the geometrical parameters and the position of the grinding wheel in the grinding process upon the shape of the flute. The validity of the method is proven by the agreement of the computed values with the input and output data produced by experiment. The proposed method allows helical flutes to be generated solely by using cylindrical and conical grinding wheels of standard shapes.

On the properties of PVD coating based on nanodiamond and molybdenum disulfide nanolayers and its efficiency when drilling of aluminum alloy

PVD coatings, based on nano-diamond (ND) and molybdenum disulfide nano-layers are tested and the results are presented in this paper. The best coating is built of 40 repeated functional blocks, where each block contains four alternating 10nm thick layers consisting of Cr+5% ND, Cr, Cr+MoS2 and Cr. It was determined from friction tests that the optimal total thickness is 40 blocks. The AlSi9Cu3(Fe) aluminum alloy was used as the testing material. The HS6-5 steel twist drills of 6.0mm in diameter were used, with and without protective coatings, at the cutting speed of 75.3m/min and the feed rate of 0.06mm/rev.Large burrs were formed when uncoated drills were used. In the case of using coated drills the vast majority of holes did not show any burrs or the sizes of the burrs were considerably smaller. The number of holes with burrs increased slightly with the drilling time. The built-up edges were formed along the major cutting edges of the drill. The intensity of built-up formation varied and depended on the drills used: the uncoated drills have built-up edges to a significantly greater height than the drills with the coating. Pickups are formed at the area of the drill chisel edge and at drill flutes and pickup sizes are more significant for the uncoated drills. The VB value of the flank surface wear for the uncoated drill was significantly higher as compared to the coated drill. The tool life of coated drill was found to be approximately 2.5 times longer in comparison with the uncoated drill.

Computer Aided Design of Grinding Wheel for Drill Flute Production

Twist drill flute profile design is necessary in order to determine the required grinding wheel profile for a flute production. An accurate drill flute profile design is generated for two-flute conical twist drills using analytical equations to generate a drill flute profile design needed for the production of twist drills with straight lips. The required grinding wheel profile for a flute production was expressed in digitized form as well as in terms of two curve-fitted circular arcs. The drill flute profile geometry can never be precisely generated when required grinding wheel profile is represented by two circular arcs and the generated flute profile is just a very good approximation of the design flute profile. A CAD (computer aided design) software has been developed using MATLAB to determine the required grinding wheel profile for generating a given drill flute profile design.