Precise Holes Research Articles

Study on chip fragmentation and hole quality in drilling of aluminium 6061 alloy with high pressure internal cooling

The drilling process is one of the most common processes on many manufacturing areas. It is used for high-quality hole drilling of Aluminium 6061 alloy. In this experimental study precise holes were drilled, using drills with high pressure internal cooling (50 Bar). The influence of the process parameters on holes quality is analysed. Another aspect studied is chip shape and evacuation.

Investigation of high performance drilling dynamics

Abstract The article deals with investigation of precision holes drilling in aluminum alloys by solid-carbide drills. With the help of developed mathematical model of the drilling process, the problem of increasing performance, improving the surface quality and holes precision by selecting the optimal cutting modes has been solved. The created mathematical model makes it possible to predict the holes precision. In the course of experiments, the influence of the cutting speed and tool feed on the holes precision and the processed surface roughness is determined. As a result of experimental studies, the possibility of holes drilling with IT7-IT8 accuracy was revealed.

Analysis of the Power Load when Finishing Very Precise Holes by Reaming Head MT3

Design and technological development of cutting tools represents a fluent process that combines new knowledge from all usable technical branches with actual needs and development results of component base, production technology and machine tools. The main factors which nowadays accelerate the development of cutting tools are constantly increasing demands to improve efficiency and productivity while reducing operation costs, the application of hard machinable materials, environmental protection issues, health and growing demands for greater safety. The article deals with methodology of measurement and evaluation of cutting forces and cutting torque at a special reaming head MT3 from FINAL Tools Inc. Solution of force loading during reaming by these modern tools enable to analyse the causes of cutting tool deficiencies starting from coating suitability up to weaknesses in their design. The article also analyses the significance of the reaming process from the reaming view point using a process liquid, including a tool life analysis combined with the tool wear.

Experimental study of Hole Taper in Laser Trepan Drilling of Nickel Based Super alloy Sheet

This research article reports the optimum laser drilling input parameter for getting minimum hole taper and experimentally investigates the behaviour of hole taper in selected laser drilling input parameters on Inconel -718 sheet. Inconel -718 is nickel based super alloy, has diverse application in the field of manufacturing industries, including aerospace, aircraft, automotive, medical equipments, food service equipments and many others. The material is well suited for applications requiring high strength in temperature ranges from cryogenic up to 1400°F. Inconel-718also exhibits excellent tensile and impact strength. The conventional drilling process faces difficulties to drill quality and precise holes in advanced materials due to its better mechanical properties. Making geometrical better hole is major concerned with conventional drilling process. With the help of Laser drilling process, a geometrically and dimensionally improved hole may be produced. The geometry of hole can be made further better if operating the Laser system at optimum parameters level. In this paper the effects of laser input parameters on hole taper have been investigated and optimal value of input parameters for reduced hole taper has been suggested. The experiments have been conducted by varying one parameter at a time. The experimental data are used to develop the multi regression model for hole taper. A reliable multi regression model is developed for hole taper and modern optimization tool, Genetic algorithm (GA) is used for optimization of the kerf taper. The optimal value of studied laser input parameters such as assist gas pressure, laser Current, stand-off distance, and cutting speed (Trepanning speed) have been suggested for getting lower value of hole taper. Finally, the effects of each laser input parameter of the kerf taper has been discussed

Influence of Drilling Parameters on Torque during Drilling of GFRP Composites Using Response Surface Methodology

Polymer based composites have marked their valuable presence in the area of aerospace, defense and automotive industry. Components made of composite, are assembled to main structure by fastener, which require accurate, precise high quality holes to be drilled. Drilling the hole in composite with accuracy require control over various processes parameters viz., speed, feed, drill bit size and thickens of specimen. TRIAC VMC machining center is used to drill the hole and to relate the cutting and machining parameters on the torque. MINITAB 14 software is used to analyze the collected data. As a function of cutting and specimen parameters this method could be useful for predicting torque parameters. The purpose of this work is to investigate the effect of drilling parameters to get low torque value. Results show that thickness of specimen and drill bit size are significant parameters influencing the torque and spindle speed and feed rate have least influence and overlaid plot indicates a feasible and low region of torque is observed for medium to large sized drill bits for the range of spindle speed selected. Response surface contour plots indicate the sensitivity of the drill size and specimen thickness to the torque.

Process monitoring on drilling fiber-reinforced plastics and aluminum stacks using acoustic emissions

In order to meet the lightweight demands in aviation industry, more and more multi-material composites are processed in aircrafts’ structural parts. A common connection to join these stack materials to other parts of the components is to use rivets. For that type of connection it is necessary to drill precise holes in the stack material. Due to the fact of the multi-layer design with different material properties and therefore a different machinability of the components, high demands on tool performance and process stability are set. When drilling carbon fiber reinforced plastics (CFRP), flaws, such as delamination and fringes as well as a poor bore hole quality, have to be avoided regarding the demands of the manufactured workpiece. In contrast, when processing the metal layer, there is a demand of burr-free holes after the machining process. This leads to high challenges in optimizing the drilling process and the tool geometry in order to accomplish long and reliable tool service times when processing generally expensive aircraft components.In order to monitor the drilling process of CFRP-aluminum stacks, this work shows the application of acoustic emission (AE) measurement technology to investigate the cutting mechanisms and enable a prediction for bore hole quality. For this purpose, the spectrum of the acoustic emission of the cutting process is examined for the various stages when cutting the different layers of the stack. Here, varying cutting mechanisms in regard to chip, burr formation and jamming of chips are observed and discussed. In wear-out tests the tool service times, the development of tool wear and the generated workpiece quality are recorded and the applicability of AE for process control is shown. Afterwards, suitable approaches are introduced in order to relate the tool wear state to the burr height by tracking the acoustic emission.

Drilling High Precision Holes in Ti6Al4V Using Rotary Ultrasonic Machining and Uncertainties Underlying Cutting Force, Tool Wear, and Production Inaccuracies.

Ti6Al4V alloys are difficult-to-cut materials that have extensive applications in the automotive and aerospace industry. A great deal of effort has been made to develop and improve the machining operations of Ti6Al4V alloys. This paper presents an experimental study that systematically analyzes the effects of the machining conditions (ultrasonic power, feed rate, spindle speed, and tool diameter) on the performance parameters (cutting force, tool wear, overcut error, and cylindricity error), while drilling high precision holes on the workpiece made of Ti6Al4V alloys using rotary ultrasonic machining (RUM). Numerical results were obtained by conducting experiments following the design of an experiment procedure. The effects of the machining conditions on each performance parameter have been determined by constructing a set of possibility distributions (i.e., trapezoidal fuzzy numbers) from the experimental data. A possibility distribution is a probability-distribution-neural representation of uncertainty, and is effective in quantifying the uncertainty underlying physical quantities when there is a limited number of data points which is the case here. Lastly, the optimal machining conditions have been identified using these possibility distributions.

The Effects of Different Electrode Types for Obtaining Surface Machining Shape on Shape Memory Alloy Using Electrochemical Machining

Shape memory alloy (SMA) is important material used for the medicine and aerospace industry due to its characteristics called the shape memory effect, which involves the recovery of deformed alloy to its original state through the application of temperature or stress. Consumers in modern society demand stability in parts. Electrochemical machining is one of the methods for obtained these stabilities in parts requirements. These parts of shape memory alloy require fine patterns in some applications. In order to machine a fine pattern, the electrochemical machining method is suitable. For precision electrochemical machining using different shape electrodes, the current density should be controlled precisely. And electrode shape is required for precise electrochemical machining. It is possible to obtain precise square holes on the SMA if the insulation layer controlled the unnecessary current between electrode and workpiece. If it is adjusting the unnecessary current to obtain the desired shape, it will be a great contribution to the medical industry and the aerospace industry. It is possible to process a desired shape to the shape memory alloy by micro controlling the unnecessary current. In case of the square electrode without insulation layer, it derives inexact square holes due to the unnecessary current. The results using the insulated electrode in only side show precise square holes. The removal rate improved in case of insulated electrode than others because insulation layer concentrate the applied current to the machining zone.

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.

Study on Application of Squeeze Film Damper in Precision Hole Grinding

Study on Application of Squeeze Film Damper in Precision Hole Grinding

Precision Drilling of Carbon Fiber Reinforced Plastics with Ball Nose End Mills

Carbon Fiber Reinforced Plastics (CFRP) is well known as a Carbon Fiber Reinforced Plastics (CFRP) is well known as a difficult-to-cut material that has very strong physical and mechanical characteristics. Drilling technique of CFRP that is one of the most important cutting operations is currently carried out in the aviation and automotive industries, among others. Parts manufactured from CFRP have many precision holes used as rivet holes and for various purposes. There are typicaly many problems involved in the precision drilling processes of CFRP plate such as burrs, chippings and delaminations of composite materials, and the rapid wear of the drilling tools. In this research study, various twist drill bits, square end mills and ball noses end mills made of materials including cemented-carbide, TiAlN PVD-coated cemented carbide, Diamond-Like Carbon (DLC) coated cemented carbide and high-speed steel, are tested. CFRP drilling tests without coolant are carried out on vertical machining centers. It is found that the ball nose end mill is the most suitable for drilling CFRP composite materials.

Precision Hole Making on Laminates Composite: Comparison between Drilling and Punching

Accurate and strong fastener assembly depends on precision of the hole. For structural material likes composites, these criteria is very important. Drilling is the most common method in producing hole on composites. But the main problem of drilling is excessive tool wear that may affect the quality of the holes. Punching is another alternative in making a hole. The main objective of this study is to compare between drilling and punching in terms of hole quality. The scanned images of the produced hole will be captured using commercial 3D optical surface measurement method namely Alicona IFM. The effect to the quality of the produced hole will be measured and compared between drilling and punching.

Modeling and optimization of geometrical characteristics in laser trepan drilling of titanium alloy

Laser drilling has become an alternative to drilling precise holes in advanced difficult-to-cut superalloys. Due to better hole quality and capability to generate macro-size holes, laser trepan drilling is becoming more popular as compared with laser percussion drilling. This paper presents a study of laser trepan drilling process performance in terms of geometrical quality characteristics, such as hole taper and circularity for drilling small diameter hole in difficult-to-cut Titanium alloy sheet. Due to involvement of different process parameters such as laser power, pulse width, pulse frequency, workpiece thickness, material composition, cutting speed, stand of distance and assist gas pressure, the laser cutting is a highly nonlinear and complex process. To handle this nonlinearity and complexity, genetic algorithm has been applied for the optimization. We used assist gas pressure, pulse width, pulse frequency and trepanning speed as input process parameters. The effect of significant process parameters on hole characteristics are discussed on the basis of data obtained through a well designed orthogonal array experimental matrix. Reliable empirical models have been developed for different quality characteristics. Improvements of 49% and 8% have been registered in hole taper and circularity, respectively, at optimum level of process parameters.

Comparative Analysis of Dry-EDM and Conventional EDM for the Manufacturing of Micro Holes in Si3N4-TiN

The importance of Electrical Discharge Machining (EDM) process is increasing, especially for the machining of electric conductive ceramic materials within the field of micro production technology. Due to its thermal working principle, EDM is particularly suitable because it allows almost force free machining independent of the material's mechanical properties [1]. High aspect ratios and precise micro holes with diameters D ≤ 0.3mm leads manufactures to more complex processes, which reduce the flushing in the working gap and therefore the stability of the process. Enabling the increase of flushing by gaseous dielectrics, dry-EDM technology represents an alternative solution.This paper presents a comparative analysis of dry-EDM with two different gases as dielectric (oxygen and argon) and conventional EDM (deionized water) to manufacture micro holes in Si3N4-TiN ceramic. The results show that the axis displacement y, voltage u0, and current iL differ for the processes. It can be observed that dry-EDM has higher effective pulse frequency fe and shorter relative motions between workpiece and tool electrode than the conventional EDM process [2].The differences observed in the discharge flow and relative motions between workpiece and tool electrode are related to the dielectric fluid properties. As for example, deionized water as a dielectric has a higher viscosity ηwa = 89·10-5 Pa·s than oxygen ηo2 = 2,1·10-5 Pa·s and argon ηar = 2,3·10-5 Pa·s. Thus, with the same flushing pressure of p = 80bar it is possible to achieve higher flow speed for faster removal of particles in dry-EDM. Furthermore, deionized water has a higher breakdown resistance ED_wa = 650 kV/cm than oxygen ED_o2 = 29 kV/cm and argon ED_ar = 6,5 kV/cm. The better flushing condition enables the increase of the effective pulse frequency fe for oxygen and a decrease of the electrode relative wear ϑ.

Precision hole making on laminate composite: a tool wear analysis and comparison between drilling and punching

Hole precision is highly critical for accurate and strong fastener assembly. This factor is considerably important for structural materials, such as composite materials. Drilling is the most commonly used process for producing holes on composites. However, drilling causes excessive tool wear, which may affect the quality of holes and result in damage, such as delamination. The main objective of this study is to compare the drilling and punching processes in terms of tool wear by using the focus variation technique. The scanned images of both the puncher and drill bits are obtained by using a 3D optical surface measurement device called Alicona IFM. Tool wear patterns from both drilling and punching are analysed and compared, and the effects of the processes on the quality of the produced holes are observed.

Micro-drilling and Threading of the Ti6Al4 V Titanium Alloy Produced through Additive Manufacturing

The paper presents the evaluation of the drillability characteristics of the Ti6Al4V titanium alloy produced through the Additive Manufacturing (AM) technology called Direct Metal Laser Sintering (DMLS). Holes of 1.6mm diameter were drilled on a 5-axis high-precision micro-milling machine under dry cutting conditions at varying cutting speed and feed rate. A specific measurement procedure was developed to quantify and compare the most representative geometrical features (diameter and perpendicularity) of the machined holes as well as the quantification of burrs. The influence of the AM material on the geometrical quality of high precision holes is discussed, taking into account the requirements of the following threading operations. Finally, thread milling experiments were carried out to prove the threading feasibility and performances based on the previous drilling experiments. From the results within the tested range of cutting conditions, the lowest values of the cutting speed and feed rate seem to be the best trade-off for achieving the required hole quality.

Comparison of Conventional and Dry Electrical Discharge Machining

For manufacturing of micro holes ElectricalDischarge Machining (EDM) can be used, which is well-established due toits thermal working principle that allows almost force free machining independent of the material’s mechanical properties. The importance of this production technology is increasing, especially for the machining of ceramic materials, which are required in many applications within the field of microtechnology. However, the production of precise micro holes with complex geometries and high aspect ratios is associated with a many challenges. Hightool electrode wear, low material removal rate and small gap widths are observed in the process. This paper presents an optimized dry EDM technology for the manufacturing of micro holes in Si3N4-TiNceramic. The experiments were carried out with different energy influencing process parameters for the spark discharge and flushing pressure, which were systematically evaluated by methods of statistical Design of Experiments. Subsequently dry EDM and conventional EDM micro drilling processes were compared and the differences between both processes were evaluated. The influences of liquid and gaseous dielectric are analyzed in terms of process stability and axis movements.

Temperature Prediction Model for Bone Drilling Based on Density Distribution and In Vivo Experiments for Minimally Invasive Robotic Cochlear Implantation.

Surgical robots have been proposed ex vivo to drill precise holes in the temporal bone for minimally invasive cochlear implantation. The main risk of the procedure is damage of the facial nerve due to mechanical interaction or due to temperature elevation during the drilling process. To evaluate the thermal risk of the drilling process, a simplified model is proposed which aims to enable an assessment of risk posed to the facial nerve for a given set of constant process parameters for different mastoid bone densities. The model uses the bone density distribution along the drilling trajectory in the mastoid bone to calculate a time dependent heat production function at the tip of the drill bit. Using a time dependent moving point source Green's function, the heat equation can be solved at a certain point in space so that the resulting temperatures can be calculated over time. The model was calibrated and initially verified with in vivo temperature data. The data was collected in minimally invasive robotic drilling of 12 holes in four different sheep. The sheep were anesthetized and the temperature elevations were measured with a thermocouple which was inserted in a previously drilled hole next to the planned drilling trajectory. Bone density distributions were extracted from pre-operative CT data by averaging Hounsfield values over the drill bit diameter. Post-operative [Formula: see text]CT data was used to verify the drilling accuracy of the trajectories. The comparison of measured and calculated temperatures shows a very good match for both heating and cooling phases. The average prediction error of the maximum temperature was less than 0.7 °C and the average root mean square error was approximately 0.5 °C. To analyze potential thermal damage, the model was used to calculate temperature profiles and cumulative equivalent minutes at 43 °C at a minimal distance to the facial nerve. For the selected drilling parameters, temperature elevation profiles and cumulative equivalent minutes suggest that thermal elevation of this minimally invasive cochlear implantation surgery may pose a risk to the facial nerve, especially in sclerotic or high density mastoid bones. Optimized drilling parameters need to be evaluated and the model could be used for future risk evaluation.

Experimental and parametric studies of Nd:YAG laser drilling on austenitic stainless steel

Laser drilling has swiftly become an economical and well-regulated substitute to conventional hole drilling methods such as wire EDM, punching, broaching, or other prevalent destructive processes, because of cleanliness, accurate results, precise holes, fast material removal rate, and possibility to make holes. Prompt expansion of laser technology in current years gave us facility to regulate laser input factors such as lamp current, pulse frequency, air pressure, and pulse width. The dimensional accuracy and quality of holes are very important for some specific applications of holes. Circularity of drilled hole at entry and exit, and taper are very important attributes which influence the quality of a drilled hole in laser drilling. For this reason, the experimentation based on central composite design is carried out on austenitic stainless steel for examining the effect of laser parameters, i.e., lamp current, pulse frequency, gas pressure, and pulse width, on the quality of drilled holes. A total of 31 experiments were carried out. Later, the models were predicted for output responses using response surface methodology and then tested for adequacy. It is found that the response surface methodology (RSM) predicted models are in close agreement with the experimental values. Hence, the models may be further used for optimization of process parameters using evolutionary algorithms.

Reaming of Very Precise Holes in Hydrostatic Component

Nowadays, one of the motive trend in engineering industry is transportation and manipulating technology. The hydrostatic mechanisms belong to the most important components and are created by hydraulic engines, pumps, switchgears etc. Inseparable part of hydraulic engine is a servo-valve which coordinates the fluid flow by a microscopic movement of piston. The servo-valve is a casting, usually made of ductile cast-iron that is necessary to machine. The functionality of hydrostatic circuits is influenced significantly by the precise movement of pistons.Therefore it is necessary to provide the dimension accuracy, machining quality and also the geometric shape of holes. This article describes the issue of holes reaming in hydrostatic components with a use of reamers made of sintered carbide and cermet.