Single-lip Deep Hole Drilling Research Articles

In-process approach for editing the subsurface properties during single-lip deep hole drilling using a sensor-integrated tool

Single-lip deep-hole drilling (SLD) is characterized by high surface quality and compressive residual stress in the subsurface of the drill hole. These properties depend significantly on the thermomechanical conditions in the machining process. The desired subsurface properties can be adjusted in-process via process monitoring near the cutting zone with a sensor-integrated tool and closed loop control when the thermomechanical conditions are maintained in the optimum range. In this paper, a method is presented to control the thermomechanical conditions to adjust the properties in the subsurface. The process model integrated in the controller is implemented as a soft sensor and takes into account the residual stresses, the roughness, the hardness and the grain size in the surface as well as in the subsurface depending on the process control variables, such as the feed rate and cutting speed. The correlation between the process variables, the thermomechanical conditions of the cutting process and the subsurface properties are investigated both experimentally and by finite element (FE) simulations. Within a justified process parameter range, characteristic fields for the soft sensor were established for each property. In addition, the procedure of controller design and the employed hardware and interfaces are presented.

Development of a Multi-Sensor Concept for Real-Time Temperature Measurement at the Cutting Insert of a Single-Lip Deep Hole Drilling Tool

The mechanical energy resulting from cutting processes is turned almost completely in thermal energy, which encourages thermal procedures, such as diffusion, leading to higher wear in the cutting tool and thus to higher temperatures. Furthermore, high temperatures influence the properties of the marginal zones in the workpiece. In this presented work, the in-process temperature of a cutting insert during single-lip deep hole drilling (SLD) is investigated. Therefore, a sensor-integrated tool with resistance temperature detectors (RTD) placed beneath the cutting insert is developed. First, the thermal properties of the cutting insert are adjusted to fit the assembled tool. Afterwards, a CEL-Simulation is obtained to examine the temperature distribution at the cutting edge of the SLD-tool. The temperatures calculated by simulation can be compared to the in-process temperatures of the sensor integrated tool. Because of the usage of a cooling lubricant, simulated temperatures can be varied with a factor to fit the experimentally measured temperature curves. The highest temperature during the process appears at the outer edge of the cutting insert. By knowing the thermal properties, the maximum process temperatures for the deep hole drilling operation are to be calculated. The results represent a contribution to an interdisciplinary research project “Surface Conditioning in Machining Processes” (SPP 2086) of the German Research Foundation (DFG).

Sensor-Integrated Tool for Self-Optimizing Single-Lip Deep Hole Drilling

Single-lip deep-hole drilling (SLD) is characterized by high surface quality and compressive residual stress in the subsurface of the drill hole. These properties depend significantly on the thermo-mechanical conditions in the machining process. The required subsurface properties can be adjusted in-process via process monitoring and control when the thermo-mechanical conditions are maintained in the optimum range. Herein, a sensor-integrated SLD tool is introduced, which allows the temperatures near the cutting zone to be measured and the vibrations occurring directly at the drill head to be recorded. A microcontroller-based wireless measurement data transmission method is presented.

Cutting fluid behavior under consideration of chip formation during micro single-lip deep hole drilling of Inconel 718

ABSTRACT When micro-single-lip deep hole drilling the efficiency of the cutting fluid supply cannot be investigated experimentally due to the inaccessibility of the cutting zone. For this reason, this paper examines the cutting fluid behavior, taking into account the chip formation and the transient chip position, with the help of various combined simulation methods. Therefore, experimentally obtained chips are digitalized and converted into a Computer-Aided Design model for the following simulations. Furthermore, for a comparison of the simulations with the experiments, the velocity of the cutting fluid in the chip flute of the tool is measured by a similar Particle Image Velocimetry method. Then, a transient coupled particle simulation of Smoothed Particle Hydrodynamics and the Discrete Element Method is performed to obtain the transient chip positions along the chip flute under the influence of the cutting fluid. Based on these chip positions, a Computational Fluid Dynamics simulation follows to derive insights about the flow field and pressure field at certain points in time. This multi-physics simulation chain allows to deal with experimental results in a simulation context to gain further insights about the deep hole drilling process, which are experimentally inaccessible and allows further connections between experiment and simulation.

Correlation between subsurface properties, the thermo-mechanical process conditions and machining parameters using the CEL simulation method

In the present work, the applicability of the coupled Eulerian-Langragian method (CEL) was proved to model a drilling process. The CEL method enables complex three dimensional simulations with large deformations very time efficient with a sufficient accuracy. In this study, different process parameters were applied and the resulting feed force, maximum temperature and residual stress in the subsurface region were evaluated and validated by comparison with experimental data. With the resulting simulation data regression models were developed, which can be used in a process framework to control the thermo-mechanical state during single lip deep hole drilling.

Microstructure analysis of single-lip deep hole drilled bores by electron backscatter diffraction and magnetic Barkhausen noise

The surface integrity is crucial for the capability of machined parts; therefore, a detailed characterization of the obtained microstructure is very important for the assessment of machining processes. In this paper, the microstructure of single-lip deep drilled specimen, especially the formation of white etching layers (WEL), is considered by microscopic and micromagnetic investigations. Due to its asymmetrical nature, the single-lip deep hole drilling process induces severe plastic deformations in the bores surface. These severe deformations lead to a desirable fine-grained microstructure and the induction of beneficial compressive residual stresses. When too hard drilling parameters are chosen, the formation of a WEL can occur. These layers tend to be brittle and have tensile compressive stresses. The microstructures resulting from varied process parameters are characterized by light and electron microscopy as well with electron backscatter diffraction. These findings were correlated to the non-destructive magnetic Barkhausen noise measurement with a tailored bore sensor. This correlation enables an efficient and reliable evaluation of the process-induced microstructure and associated surface integrity.

Investigation of the thermomechanical loads on the bore surface during single-lip deep hole drilling of steel components

The surface integrity of components is decisive for their fatigue strength and is significantly influenced by applied machining processes. Particularly in drilling, the used coolant strategy affects the process stability and the surface quality produced due to its contribution to chip evacuation and the cooling and lubricating effect of the cutting zone. In this article, different cooling lubrication strategies are investigated in single-lip deep hole drilling of quenched and tempered AISI 4140 steel with respect to their effects on occurring thermomechanical loads and the resulting surface integrity parameters. The results for drilling with cutting oil, water-based emulsion and minimum quantity lubrication (MQL) under varying cutting parameters are analyzed with a focus on their impact on the bores’ subsurface microstructure and resulting hardening generated in the bores’ subsurface.

IN-PROCESS MEASUREMENT AND NUMERICAL DETERMINATION OF THE TEMPERATURE IN THE CONTACT ZONE DURING SINGLE LIP DEEP HOLE DRILLING

In this presented work, the main objective is the in-process measurement of the thermal as-is state near the drilling contact zone by means of a sensor-integrated tool for single lip deep hole drilling (SLD). Additionally, the mechanical quantities feed force and drilling torque are evaluated. The process monitoring is essential to optimize the surface quality as well as the subsurface properties such as hardness and residual stresses. These quantities are strongly dependent on the thermo-mechanical as-is state in the cutting zone and in the contact zone between the guide pads and the drill hole surface. This contribution gives a project overview including the development of a sensor-integrated single lip deep hole driller for the in-process temperature measurement, the integration of sensor systems in the tool as well as the experimental investigations on the temperature, the feed force and the drilling torque during drilling of a 42CrMo4 steel. The temperature measurement at eleven positions in the driller head provides data to observe the heat generation, distribution, and flow independently from the workpiece characteristics. However, one of the greatest benefits is the non-destructive fashion of the measurement system with their sensor integrated in the tool and thus the reusability. A simulation method, which uses the experimental results as a reference, is used to predict the thermo-mechanical conditions in the contact zone of the drill head and the workpiece. The results of these thermo-mechanical process simulations and the validation of this applied FE approach using the measured quantities are presented, too. The results of this work are part of an interdisciplinary research project in the framework of the priority program "Surface Conditioning in Machining Processes" (SPP 2086) of the German Research Foundation (DFG).

Simulation Study on Single-Lip Deep Hole Drilling Using Design of Experiments

Single-lip deep hole drilling (SLD) is characterized by a high surface quality and compressive residual stress in the subsurface of the drill hole. These properties are strongly dependent on the cutting parameters of the SLD process and the actual geometry of the insert and the guide pads. In the present work, full 3D FE simulations of the SLD process were carried out to analyze the thermo-mechanical as-is state in the drilling contact zone by evaluating the feed force, the temperature, as well as the residual stress in the drill hole subsurface. An extensive simulation study was conducted on the effect of the process parameters on the properties using design of experiments (DoE). For the simulations, the Johnson–Cook (JC) constitutive law and the element elimination technique (EET) were applied to represent the material behavior of the workpiece, including chip formation. In-process measurements as well as results from the hole-drilling method to determine residual stresses were conducted to verify the numerical results. By means of DoE and analysis of variance (ANOVA), regression models were developed to describe the effect of the feed rate, cutting speed, and guide pad height on the temperature, feed force, and residual stress in the subsurface.

Chip formation simulation and analysis of the mechanical loads during micro single-lip deep hole drilling of Inconel 718 with varying cooling lubricant pressure

The micro single-lip deep hole drilling process is subjected to many difficulties. Especially the machining of difficult-to-cut materials like the nickel-based alloy Inconel 718 results in high thermal and mechanical loads. Irregularities in the drilling process, which lead to early tool failures must be avoided. A major challenge for micro single-lip deep hole drilling is to generate favorable chips and guarantee good chip removal. Since the chip flute of single-lip deep hole drilling tools is straight, the only mechanism to transport the chips and remove them from the bore hole is the coolant flow. In this paper the mechanical loads and the resulting chip formation for various cooling lubricant pressures are analyzed using tools with a diameter of d = 2 mm. In the experiments feed force, drilling torque, tool wear, bore hole quality as well as diameter and roundness deviations were evaluated. Individual chips are digitized and prepared as CAD models for the future consideration of the chip removal in flow simulations of the cooling lubricant. Additional FEM computational analyses of the three-dimensional chip formation with a geometric representation of the chip shape were carried out. This way not only provides valuable validated information about the process and the chip formation but also creates a basis for further investigations, which will allow an innovative simulation of the coolant flow and considers the chip formation and the chip shape.

Numerical Investigations on Single Lip Deep Hole Drilling

The surface quality and the subsurface properties such as hardness and residual stress of a drill hole are dependent on the cutting parameters of the single lip deep hole drilling process and therefore on the thermo-mechanical as-is state in the cutting zone and in the contact zone between the guide pads and the drill hole surface. In the present work, this highly dynamic and unsteady-state process including large deformation and heat generation FE simulations were carried out to analyze the mechanical as-is state in the drilling contact zone by evaluating the temperature, the feed force as well as the residual stress in the drill hole subsurface. Besides, in-process measurements as well as results from the hole drilling method to determine residual stresses are presented to verify the numerical results. For the simulations, the Johnson-Cook (JC) constitutive law was applied to represent the material behavior of the workpiece to cover strain rate as well as temperature dependent plasticity. The chip formation in the simulations was realized by means of the element elimination technique (EET).This contribution introduces the research project and the performed measurements with respect to the influence of the thermal and mechanical boundary conditions in this machining process focusing on the temperature and the feed force while drilling a 42CrMo4 steel and the residual stress in the drill hole subsurface. With this simulation approach, the chip formation as well as the residual stress distribution in thickness direction were reproduced successfully. The comparison of the process data, such as temperature, feed force or residual stress shows a qualitative agreement of the simulation and the experimental results, too.

Investigation of Laser Drilled Pilot Holes and Additively Generated Pilot Holes as Drilling Guides for Single-lip Deep Hole Drilling

Investigation of Laser Drilled Pilot Holes and Additively Generated Pilot Holes as Drilling Guides for Single-lip Deep Hole Drilling

Temperature monitoring in the subsurface during single lip deep hole drilling

Abstract The surface quality and the subsurface properties such as hardness, residual stresses and grain size of a drill hole are dependent on the cutting parameters of the single lip deep hole drilling process and therefore on the thermomechanical as-is state in the cutting zone and in the contact zone between the guide pads and the drill hole surface. In this contribution, the main objectives are the in-process measurement of the thermal as-is state in the subsurface of a drilling hole by means of thermocouples as well as the feed force and drilling torque evaluation. FE simulation results to verify the investigations and to predict the thermomechanical conditions in the cutting zone are presented as well. The work is part of an interdisciplinary research project in the framework of the priority program “Surface Conditioning in Machining Processes” (SPP 2086) of the German Research Foundation (DFG). This contribution provides an overview of the effects of cutting parameters, cooling lubrication and including wear on the thermal conditions in the subsurface and mechanical loads during this machining process. At first, a test set up for the in-process temperature measurement will be presented with the execution as well as the analysis of the resulting temperature, feed force and drilling torque during drilling a 42CrMo4 steel. Furthermore, the results of process simulations and the validation of this applied FE approach with measured quantities are presented.

Effects on surface and peripheral zone during single lip deep hole drilling

To adjust the defined surface and peripheral zone properties, such as hardness, residual stresses and surface quality, machining processes are in many cases followed by forming or heat treatment processes. A focused management of the machining process can already adjust the desired properties. The here presented work is part of an interdisciplinary research project in the framework of the priority program "Surface Conditioning in Machining Processes" (SPP 2086) of the German Research Foundation (DFG). This research project has the main objectives to determine the thermo-mechanical as-is state of the drilling peripheral zone during the process by means of a sensor-integrated tool for single lip deep hole drilling as well as to control the process parameters to achieve the aimed peripheral zone properties.Preliminary test series are related to the determination of the thermo-mechanical boundary conditions. From the obtained results, the requirements concerning the sensor-integrated tool can be derived. Further steps include the development of a sensor-integrated tool for the in-process determination of temperature, forces, moments and vibrations, the selection and integration of sensor systems as well as the correlation of process factors with peripheral zone condition. Especially for the determination of the temperature at the affected zone, a multi-sensor approach was chosen. The formulation of a control strategy and its implementation in the deep hole drilling machine of the Institute for Machine Tools (IfW) will finalize the first project phase. Required surface and peripheral zone properties can then be controlled based on measurement and simulation data. Effects on the peripheral zone can then be investigated using process simulations.This contribution gives an overview of the objectives and the planned project steps. Experimental investigations on temperature, feed force and drilling torque during single lip deep hole drilling are described. Also first results of the process simulation and their validation with measured quantities are presented.

Determination of thermo-mechanical quantities with a sensor-integrated tool for single lip deep hole drilling

To adjust the subsurface workpiece properties, such as hardness and residual stresses as well as surface quality, machining processes are often followed by forming, peening or heat treatment processes. An appropriate setup of the machining process can adjust the desired properties. The work presented here is part of an interdisciplinary research project in the framework of the priority program "Surface Conditioning in Machining Processes" (SPP 2086) of the German Research Foundation (DFG). This research project has the main objectives to determine the actual thermo-mechanical state of the surface and subsurface in single lip deep hole drilling during the process by means of a sensor-integrated tool as well as to control the process parameters to achieve the desired workpiece properties.Preliminary test series are related to the determination of the thermo-mechanical boundary conditions with thermal, material and machining models. From the obtained results, the requirements concerning the sensor-integrated tool can be derived. Further steps include the development of a tool for the in-process determination of the real cutting conditions, the selection and integration of sensor systems as well as the correlation of process states with workpiece conditions. The single lip deep hole drilling tool will be equipped with sensor systems for the acquisition of temperatures, forces, torques and vibrations close to the affected zone. In particular, for the determination of the process temperature close to the cutting zone, a multi-sensor approach was chosen. Effects on the workpiece can then be investigated using material simulations. The elaboration of a control strategy and its implementation in a deep hole drilling machine will finalize the current project phase. The final goal is that the required workpiece surface and subsurface properties can be controlled based on measurement and simulation data.

Modeling the motion of the cooling lubricant in drilling processes using the finite volume and the smoothed particle hydrodynamics methods

The process of single-lip deep hole drilling is used in various industrial applications for the production of small bores with a high length to diameter ratio. Especially the cooling and the lubrication of the machining zone have a great influence on the tool life, on the transport of chips, as well as on the quality of the resulting bore. In this paper, two approaches for the modeling and simulation of drilling processes are presented. On the one hand, the Finite Volume Method is used for the stationary simulation of the flow field. Assuming the entire bore to be filled with coolant, the focus is laid on a precise description of important fluid mechanical quantities along the cutting edges. The results show that the mass exchange of the cooling lubricant close to the cutting edge is far too low in order to guarantee the required cooling effect. On the other hand, a coupled meshless approach for the transient simulation is presented. The cooling lubricant is there modeled by the Smoothed Particle Hydrodynamics method and the Discrete Element Method is used for the description of chips. In contrast to the Finite Volume simulation, the main focus is laid on the evolution of the free surfaces and the transport of particles. The results show that the transport of chips by the cooling lubricant can be described well. Furthermore, also the transient Smoothed Particle Hydrodynamics simulations show an insufficient mass exchange behind the cutting edges matching the steady-state results from the Finite Volume simulation with a bore completely filled with coolant.

Experimental investigations on single-lip deep hole drilling of superalloy Inconel 718 with small diameters

Recent trends in downsizing, as well as miniaturization of components, increase the importance of deep hole drilling with small diameters in various industrial applications. For the manufacturing of deep holes, many processes are used. In addition to mechanical cutting, processes based on thermal material removal mechanisms like electrical discharge machining (EDM), laser drilling and electron-beam drilling are established. Whereas non-mechanical processes can be used for the machining of extremely hard and high-strength materials, substantial disadvantages are the restrictions in the realizable hole diameter and depth dimensions, the long production times, the requirement for special-purpose machinery, as well as the limited bore hole quality. In the aerospace industry, where nickel-based superalloys are widespread, high requirements lie on the surface integrity due to high stress loads during operation. Hence, the major drawback of these non-mechanical processes is the alteration of the subsurface zone, which could affect the part safety. In contrast, the mechanical machining of nickel-based superalloys is extremely difficult due to material properties such as high strength, high tendency to work hardening and low thermal conductivity which results in increased mechanical tool loads and heavy abrasive and adhesive tool wear. An additional challenge is constituted by the chip removal and the unfavorable ratio of cutting edge rounding and undeformed chip thickness caused by the limitation in the feed rates, if deep hole drilling with small diameters and high-length-to-diameter ratios of difficult-to-cut materials like nickel-based superalloys is required. Up to now, the use of standard tool geometries in small diameter single-lip deep hole drilling of Inconel 718 has not been productive and leads to limited process stability and drilling lengths as well as insufficient bore hole quality. Concerning this matter, this paper presents a process adaption using a tailored cutting edge design to accomplish the predominant challenges. Substantial analysis on gun drilling in Inconel 718 regarding mechanical tool loads, chip formation, the tool wear, as well as bore hole quality will be presented.

Process Combination for the Manufacturing of Deep Holes with Small Diameters

The industrial relevance of bore holes with small diameters and high length-to-diameter ratios rises with the growing requirements on parts and the tendency of components toward downsizing. Examples are components for medical and biomedical products or fuel injection in the automotive industry. An adapted process design is necessary for the production of deep holes with very small diameters, especially when the conditions at the beginning of the deep hole drilling process are unfavorable. In these applications, a hybrid process consisting of a laser pre-drilling and a single-lip deep hole drilling can shorten the process chain in machining components with non-planar surfaces, or can reduce tool wear in machining case-hardened materials. In this research, the combination of laser and single-lip drilling processes was realized and investigated for the very first time. In addition, results for the machining of workpieces with non-planar surfaces are presented.

Thermal Aspects in Deep Hole Drilling of Aluminium Cast Alloy Using Twist Drills and MQL

The deep hole drilling process with solid carbide twist drills is an efficient alternative to the classic single-lip deep hole drilling, due to the generally higher feed rates possible and the consequently higher productivity. Furthermore the minimum quantity lubrication (MQL) can be applied, in order to reduce the production costs and implement an environmentally friendly process. Because of the significantly reduced cooling performance when using MQL, a higher heat loading results for the tool and the workpiece. This paper presents the investigations of the temperature distribution in the workpiece and the heat balance of the deep hole drilling process.

Deep hole drilling using tools with small diameters—Process analysis and process design

This paper is focused on the drilling of bore holes with high length-to-diameter ratios and diameters less than 2mm which are needed, for example, in medical and automotive applications. In the presented research, the influence of cutting data and tool design on tool wear and chip formation has been analysed. First the experimental set-up is described followed by an in-depth process analysis of the single-lip deep hole drilling process under investigation. The next section deals with a process combination, where laser and mechanical drilling are combined in order to improve process reliability and productivity.