Workpiece Interface Research Articles

Influence of minimal quantity lubrication (MQL) technique in achining evolution: A review and applications

Metal working fluids (MWFs) are one of the types of lubricants, which are extensively used in machining operations. Most of the MWFs are mineral oil based fluids. Due to their advantages, the consumption of MWFs is increasing in machining industry. Mineral, synthetic and semi-synthetic MWFs involve in the ecological cycle with air, soil and water and their toxicity effects damages the ecosystem. Vegetable oil lubricants are potential substitutes for mineral oil not only because they are renewable raw materials but also because they are biodegradable and non-toxic. Currently, there is a wide-scale evaluation of the use of metal working fluids (MWFs) in machining. Industries are looking for ways to reduce the amount of lubricants in metal removing operations due to the ecological and economical aspects. By implementing near-dry machining or a minimal quantity of lubrication (MQL), MWFs consumption can be reduced. The MQL technique involves the application of a small quantity of lubricant dispensed to the tool–work piece interface by compressed air flow. This paper gives a review on the mechanical performance of minimum quantity lubrication compared to completely dry and flood lubrication for various machining operations.

A study on the performance of environmentally benign lubricants at elevated temperatures in bulk metal forming

The application of environmentally benign tribological systems becomes more and more important in cold forging operations. However, questions regarding the performance of these systems still oppose a widespread use in industry. Due to severe loads in cold forging, high tool temperatures of up to 200°C may occur as a result of forming energy and friction in combination with a high output in a short range of time. The temperature at the tool–workpiece interface is even higher, though an exact identification proves to be difficult. Former investigations regarding the influence of the relative velocity indicated that the occurring temperatures are primarily responsible for the decrease of the friction. The paper at hand presents the results of a systematic investigation of the influence of the temperature at the tool–workpiece interface on the performance of environmentally benign tribological systems.

Heat transfer analyses in friction stir welding of aluminium alloy

This work is aimed to develop a heat transfer model of friction stir welding process and subsequently to utilize the same for transient thermal analysis under differential influence of process parameters. The heat generation is assumed due to friction and plastic deformation at the tool–workpiece interface. A contact state variable is defined to estimate the amount of heat generation due to plastic deformation. The symmetric heat flux at the interfaces of flat tool shoulder surface, tool pin side, and bottom surfaces acts as heat input to the system by neglecting the effect of transverse tool speed. The heat generation from both the side and bottom surfaces of pin plays a significant role for the development of the temperature. Thermal history of friction stir welded AA1100 and AA6061 is estimated by developed numerical model and is compared with experimental results under similar welding conditions, thus validating the developed model. The experiments reveal that the temperature distributions are not symmetric with respect to welding line and maximum temperature occurs behind the tool pin. With the addition of heat generation due to plastic deformation, the heat transfer model precisely predicts the maximum temperature and time–temperature profiles at different welding conditions.

Comparative Performance In Hard Turning Of AISI 1015 Steel With Carbide Insert Using Orthogonal Array Design And Grey Relational Analysis Under Spray Impingement Cooling And Dry Environment

This study investigates the effects of cutting parameters on surface roughness (Ra), cutting temperature (T0C) at the chip tool interface and the material removal rate (MRR mm3/min) during hard machining of AISI 1015 (43 HRC) steel using carbide insert under dry and spray impingement cooling environment. A combined technique using orthogonal array and analysis of variance (ANOVA) was employed to investigate the contribution of spindle speed, feed rate, depth of cut and air pressure on responses. Utilization of IR camera is been effective to calculate the temperature at the interface of workpiece and the tool. It is observed that with spray impingement cooling, cutting performance improves compared to dry cutting. The predicted multi response optimization setting (N3-f1-d1-P2) ensures minimization of surface roughness, cutting temperature and maximization of material removal rate. Finally optimal result was validated by confirmatory test and the improvement in grey relational grade was found to be 0.288.

The Influence of Gaps and Misalignment on Friction Stir Welded Butt Joints of Medium-Sized Parts

In order to industrialize friction stir welding (FSW) processes, not only the machine concept itself needs to be evaluated, but also the robustness of the process application being carried out on the machine. Especially for FSW of medium-sized and larger parts, a small degree of misalignment can have an increasing influence on the weld quality. Therefore an exemplary tolerance study for friction stir welded butt joints was conducted. The intentional introduction of gaps between the sheets to be welded can limit the welding process and thus the weld quality. However, for the considered experimental set-up it can be shown that the introduction of a well-defined gap can support the welding process and weld quality. The experimental procedure was carried out on a parallel kinematic machine - a so-called Pentapod. This machine is suitable for large and complex three-dimensional structures. Although the machine is able to record the process forces (Fx, Fy and Fz) acting on the tool–work piece interface, the forces acting perpendicular to the clamping system are still unknown. Therefore additional load cells were integrated into the clamping system to measure the in-process reaction forces. The combined results of the force measurements give a nearly complete overview of the internal loads during the process. In conjunction with knowledge about gaps and misalignment, the data gained in this study can help to understand and predict the clamping behaviour, and thus design rules for future clamping systems can be derived.

A fundamental investigation on rotating tool cold expansion: numerical and experimental perspectives

In this study, we present the development of a novel technique for cold expansion using a rotating tapered mandrel that friction processes the cylindrical wall of the fastener hole and simultaneously cold expands it. The developed technique, named as rotating tool cold expansion (RTCE), is experimentally and numerically investigated. A 3D thermomechanical finite element model for predicting the compressive residual stress, responsible for delaying crack propagation from the edges of the holes, is introduced. The efficacy is that RTCE is assessed for varying degrees of cold expansion under different lubricating conditions at the tool–workpiece interface, such as dry, metal working fluid, and nanopowder. The plastic deformation combined with friction stirring at the tool–workpiece interface helps the RTCE in controlling the surface damage at entry and exit of the hole that is most often observed with the conventional cold expansion technique. Enhanced friction due to the nanopowder at the tool–workpiece interface helps in sustaining efficacy of the RTCE even at a higher degree of cold expansion which otherwise leads to surface damage with other mediums.

An explicit finite element model to study the influence of rake angle and friction during orthogonal metal cutting

A fundamental understanding of the tribology aspects of machining processes is essential for increasing the dimensional accuracy and surface integrity of finished products. To this end, the present investigation simulates an orthogonal metal cutting using an explicit finite element code, LS-DYNA. In the simulations, a rigid cutting tool of variable rake angle was moved at different velocities against an aluminum workpiece. A damage material model was utilized for the workpiece to capture the chip separation behavior and the simultaneous breakage of the chip into multiple fragments. The friction factor at the cutting tool–workpiece interface was varied through a contact model to predict cutting forces and dynamic chip formation. Overall, the results showed that the explicit finite element is a powerful tool for simulating metal cutting and discontinuous chip formation. The separation of the chip from the workpiece was accurately predicted. Numerical results found that rake angle and friction factor have a significantly influence on the discontinuous chip formation process, chip morphology, chip size, and cutting forces when compared to the cutting velocity during metal cutting. The model was validated against the experimental and numerical results obtained in the literature, and a good agreement with the current numerical results was found.

A new abrasive wear law for the sticking and sliding contacts when machining metallic alloys

Abrasive wear was usually identified as the main wear mode occurring at the tool–chip and the tool–workpiece interfaces during machining operations such as turning, milling, and drilling. From an experimental point of view, the mechanisms governing the abrasion process are still not fully understood. This is due on one hand to the contact confinement between tool and workpiece and on the other hand to the high thermomechanical loading applied to the cutting tool during a machining process. Abrasion is often assumed to be closely linked to the microstructure of materials and caused by hard particles trapped at the tool–workpiece interface. The objective of this research work is to develop a predictive wear modeling taking into account the sliding and sticking nature of the contact. The proposed model is based on an analytical approach including a statistical description of the distribution of particles. The latter are assumed with a conical shape and embedded in the contact area. The volume of the removed material per unit time is chosen in this study as the main parameter to describe the abrasive wear mode. The sliding and sticking zones at the tool–chip and tool–workpiece interfaces depend on the evolution of the local conditions of stress, the sliding velocity and the friction coefficient. A new abrasive wear law is then proposed to estimate the tool life which is often considered in industrial applications. Finally, a parametric study was performed to highlight the influence of cutting conditions and the contact nature on the productivity rate for a given tool-material combination.

Computational Fluid Dynamic Analysis of Eccentric Atomization Spray Cooling Nozzle Designs for Micromachining

A recent development in cooling and lubrication technology for micromachining processes is the use of atomized spray cooling systems. These systems have been shown to be more effective than traditional methods of cooling and lubrication for extending tool life in micromachining. Typical nozzle systems for atomization spray cooling incorporate the mixing of high-speed gas and an atomized fluid carried by a gas stream. In a two-phase atomization spray cooling system, the atomized fluid can easily access the tool–workpiece interface, removing heat through evaporation and lubricating the region by the spreading of oil micro-droplets. The success of the system is determined in a large part by the nozzle design, which determines the atomized droplet's behavior at the cutting zone. In this study, computational fluid dynamics are used to investigate the effect of nozzle design on droplet delivery to the tool. An eccentric-angle nozzle design is evaluated through droplet flow modeling. A design of simulations methodology is used to study the design parameters of initial droplet velocity, high-speed gas velocity, and the angle change between the two inlets. The system is modeled as a steady-state multiphase system without phase change, and droplet interaction with the continuous phase is dictated in the model by drag forces and fluid surface tension. The Lagrangian method, with a one-way coupling approach, is used to analyze droplet delivery at the cutting zone. Following a factorial experimental design, deionized water droplets and a semisynthetic cutting fluid are evaluated through model simulations. Statistical analysis of responses (droplet velocity at tool, spray thickness, and droplet density at tool) show that droplet velocity is crucial for the nozzle design and that modifying the studied parameters does not change droplet density in the cutting zone.

New stochastic wear law to predict the abrasive flank wear and tool life in machining process

Tool wear and tool failure are some of the main critical problems in industrial manufacturing fields since they affect the quality of the machined part and raise production costs. Improving our knowledge of wear mechanisms and capabilities of wear prediction are therefore of great importance in the machining process. Abrasion, adhesion and diffusion are usually identified as the three main wear modes at the tool–chip and the tool–workpiece interfaces. From an experimental point of view, the analysis of mechanisms that govern the wear process is still difficult to conduct. The objective of this research work is then to develop a wear modeling focusing on the abrasive wear mode at the tool–workpiece interface. This wear phenomenon is assumed to be closely linked to the microstructure’s material workpiece and caused by hard conical particles trapped into the contact between the cutting tool and the workpiece. The proposed model is based on an analytical approach including a statistical description governing the distribution of particles with conical shape embedded in the contact area. The volume of the removed material per unit time was chosen in this study as the main parameter to describe abrasive flank wear mode. A parameter [Formula: see text] was introduced as the sudden flank wear which occurs in the former few cutting instants. A parametric study has been conducted that highlights the slight effect of the adopted value. The effect of the cutting conditions (cutting speed, pressure) at the tool flank that has a major influence on the wear rate, was deduced from a numerical study on the 42CrMo4/WC-Co tool–workpiece combination. Finally, a wear criterion has been proposed to estimate the tool life in order to address the concerns of industries.

Minimum Quantity Lubrication (MQL) in Machining: Benefits and Drawbacks

 Abstract—Micro lubrication or also known as minimum quantity lubrication (MQL) serves as an alternative to flood cooling by reducing the volume of cutting fluid used in the machining process; but not without significant health concerns. Flood cooling is primarily used to cool and lubricate the cutting tool and work piece interface during machining process. The adverse health effects caused by the use of coolants and the potential economic advantages of greener machining methods are drawing manufacturer’s attention to adapt and develop new methods of using lubricants. The objective of this paper is to review the state of the art literature in machining using MQL, highlight the benefits, but also stress the adverse health effects of using minimum quantity lubrication. Finally we highlight areas of relevant future research.

Numerical characterisation of the friction coefficient at the tool-chip-workpiece interface during friction tests of AISI 1045

The characterisation of frictional phenomena at the tool–chip–workpiece interface in metal cutting remains a challenge. This paper aims at identifying a workpiece surface temperature and an equivalent plastic strain at this interface during the dry cutting of an AISI 1045 with TiN–coated carbide tools. A 3D arbitrary Lagrangian Eulerian (ALE) numerical model simulating the frictional test has been developed to extract local parameters around the spherical pin, such as the plastic strain and the workpiece surface temperature, from experimental macroscopic measurements. A large range of sliding velocities (5–300/min) has been investigated. It has been shown that plastic strain and workpiece surface temperature are mainly dependent on sliding velocity. Two friction regimes have been identified. These numerical results provide a better understanding of the tribological phenomena along the tool–chip–workpiece interfaces in dry machining of an AISI 1045 steel with a TiN–coated carbide tool.

Bio-inspired self-sharpening cutting tool surface for finish hard turning of steel

This research presents the structural analysis and machining results of a 3-D nanostructured coating designed for finish turning of ferrous alloys. The coating design, inspired from sea urchin and shark teeth architectures, delivers serrated cutting edges and self-sharpening. The coating is realized using cubic boron nitride particles (<2μm in size) in soft titanium nitride matrix to produce superior tool life and consistent surface finish (<1.6μm), on-par or better than polished PCBN inserts, during finish hard-turning of 4340 alloy steel. This research also discusses mechanism based on coating materials and morphology for reducing surface contact and sliding friction at the tool–workpiece interface.

Weld temperature effects during friction stir welding of dissimilar aluminum alloys 6061-t6 and 7075-t6

The objective of this work is to establish nominal friction stir [butt] welding process parameters for joining 4.76-mm-thick aluminum alloys 6061-T6 and 7075-T6 and to improve the joint quality via programmed tool offsets. In addition, dynamic tool–workpiece interface temperatures are measured during welding and used to explain the effects of alloy placement and weld tool offset from the joint. Weld tool offsets into the retreating side AA7075 increase the measured tensile strength of the dissimilar joint. The increased joint strength is facilitated by lower average weld temperatures with increasing amount of AA7075 stirred into the nugget.

Effects of tool–workpiece interface temperature on weld quality and quality improvements through temperature control in friction stir welding

A real-time wireless temperature measurement system has been developed and successfully implemented for closed-loop control of tool shoulder–workpiece interface temperature. The system employs two thermocouples in through holes and measures the shoulder and pin interface temperatures with an angular resolution as small as 10°. Both temperatures correlate with weld quality (mechanical testing and weld cross sections), e.g., all welds in 4.76-mm-thick 6061-T6 with an average shoulder interface temperature below 520 °C and an average pin interface temperature below 460 °C fail in the weld zone instead of the heat-affected zone, have unacceptable tensile strengths and in some cases voids. Similarly, welds with shoulder temperatures above the solidus temperature result in a degradation of the weld quality. It was found that a shoulder interface temperature of 533 °C results in the highest weld quality; hence, this temperature should be used as the setpoint temperature in the control system with a constant travel speed of 400 mm/min. The temperature measurement strategy was shown to be able to indicate welds with insufficient shoulder–workpiece contact, thus potentially identifying and preventing welds with detrimental weld quality due to lack of penetration. It was shown that backing plates of different thermal diffusivity change the heat flow out of the weld zone, hence weld temperature, and caused a measurable impact on the weld strength. By changing other process parameters, e.g., through a temperature control system, weld quality can be maintained in the presence of such changing thermal boundary conditions.

Determining work-brush interface temperature in magnetic abrasive finishing process

Magnetic abrasive finishing (MAF) is a process in which the work surface is finished by removing the material in the form of micro chips by magnetic abrasive particles (MAPs) in the presence of magnetic field in the finishing zone. During the MAF process, the frictional heat is generated at the workpiece surface due to the rubbing action of magnetic abrasive particles with the work surface. The order of temperature rise is important to study, as finishing mechanism and surface integrity of work materials depend upon it. The measurement of temperature distribution during MAF operation at the interface of work piece and flexible magnetic abrasive brush (FMAB) interface is difficult. In the present analysis, finite element based ANSYS software has been used to model and simulate magnetic field distribution, magnetic pressure and temperature distribution at work-brush interface during the process. In this work the maximum magnetic flux density has been simulated of the order of 0.223T at 0.91A of current in electromagnet coil. Magnetic pressure on MAPs due to magnetic field of electromagnetic coil has been calculated to evaluate the frictional heat flux generated at the work-brush interface. Transient thermal analysis of workpiece domain has been performed to predict the temperature rise due to frictional heat flux. The predicted temperature on work-brush interface was found in the range of 34–51°C. The developed simulation results based on FEA have been validated with experimental findings.

On the Measurement of Friction Coefficient at the Curved Surface in Metal Forming

Friction at the interface of die and workpiece plays an important role in metal forming. This paper introduces measurement methods of friction coefficient at curved surface in recent years, and divides the friction coefficient measurement methods into direct measurement methods and indirect measurement methods. Furthermore, the working principles and technical characteristics of these methods are explained.

A study of the diamond tool wear suppression mechanism in vibration-assisted machining of steel

Inability of machining steel strongly inhibits the application of diamond machining in manufacturing industry, especially in the fields of ultra-precision and micro machining. In recent years, vibration-assisted machining (VAM) has been proved to be capable of efficiently suppressing the diamond tool wear in cutting steel. Currently, the prevailing speculation claimed by most researchers for such suppression is that the tool–workpiece flash temperature was reduced in VAM, which would slow the chemical reaction between iron on steel and carbon on diamond. However, the correctness of this speculation has not been proved by any experimental or theoretical research. In this paper, in order to understand the true wear suppression mechanism of diamond tools in VAM of steel, a study is conducted by measuring the workpiece temperatures and modeling the cutting energy consumption in both VAM and conventional cutting (CC). Based on the comparison results, it is concluded that the cutting temperature and energy consumption in VAM are not smaller than in CC, and hence the reduced diamond tool wear in VAM should not be caused by the claimed reduced temperature, especially when the material removal rate is very small. Finally, based on the EDS analysis and the comparison of experimental results under different air pressure, two probable reasons are proposed for the significantly reduced diamond tool wear in VAM of steel: (i) increase of gas pressure at the tool–workpiece interface and (ii) generation of an oxide layer on the freshly machined surface.

Microlubrication Effects During End Milling AISI 1018 Steel

Flood cooling is primarily used to cool and lubricate the cutting tool and workpiece interface during a machining process. But the adverse health effects caused by the use of flood coolants are drawing manufacturers' attention to develop methods for controlling occupational exposure to cutting fluids. Microlubrication serves as an alternative to flood cooling by reducing the volume of cutting fluid used in the machining process. In this study the effects of microlubrication during end milling of AISI 1018 steel was investigated using vegetable based cutting fluid aerosol. A solid carbide cutting tool was used with varying cutting speeds and feed rates having a constant depth of cut. A full factorial experiment was conducted and regression models were generated along with parameter optimization for the aerosol mass concentration and the aerosol particle size. The study shows that with a proper selection of the cutting parameters it is possible to reduce the aerosol mass concentration in end milling under microlubrication. But more scientific assessments are needed to lower the mass concentration of the aerosol particles, below the recommended value of 5 mg/m3 by Occupational Safety and Health Administration (OSHA). Limited studies have been reported to investigate the effectiveness and quality of mist produced under microlubrication. No study has been reported to date on end milling 1018 steel under microlubrication.

Turning modeling and simulation of an aerospace grade aluminum alloy using two-dimensional and three-dimensional finite element method

This article presents the development of two-dimensional and three-dimensional finite element–based turning models, for better prediction of chip morphology and machined surface topology. Capabilities of a commercial finite element code Abaqus®/Explicit have been exploited to perform coupled temperature–displacement simulations of an aerospace grade aluminum alloy A2024-T351 machining. The findings show that two-dimensional cutting models predict chip morphologies and machined surface textures on a plane section (with unit thickness) passing through the center of workpiece width, and not at the edges. The contribution highlights the importance of three-dimensional machining models for a close corroboration of experimental and numerical results. Three-dimensional cutting simulations show that a small percentage of material volume flows toward workpiece edges (out of plane deformation), augmenting the contact pressures at the edges of tool rake face–workpiece interface. This enhances the burr formation process. Computational results concerning chip morphologies and cutting forces were found in good correlation with experimental ones. In the final part of the article, numerical simulation results with a modified version of a particular turning tool have been discussed. It has been found that the proposed geometry of the tool is helpful in reducing burr formation as well as cutting force amplitude during initial contact of cutting tool with the workpiece material.