Workpiece Surface Integrity Research Articles

Effect of direct LN2 single jet supply during turning of AISI D3 steel alloy using an optimization technique

The emerging demand for present and future research work to environment conscious machining is high surface integrity of machined workpiece. Researchers are continuously working to meet intrinsic and strict international standards with close tolerance limits for the fabrication of hard engineering materials. Cryogenic cooling with liquid nitrogen at the interface of tool and workpiece may provide a better alternative than conventional cutting fluids during turning operation. Design of experiments using Taguchi based L18 in dry and LN2 machining conditions has been used to carry the experiments with TiN coated tungsten carbide cutting inserts on the workpiece of AISI D3 steel alloy. The separate probability plot of surface roughness, cutting force, flank wear length and temperature at 95% of confidence level have been analysed for optimization and investigation of the experiment. ANOVA has been used to determine the effect of the contribution of control factors. The machining condition has the highest effect on the percentage contribution for surface roughness, cutting force, flank wear length and temperature as 62.42%, 59.77%, 70.03% and 49.69% respectively. The other contributing factors in order of decreasing effect have been observed as cutting speed, feed and depth of cut for machining characteristics. The predicted values at the optimized level have been confirmed by the actual performance of the experimental run. Regression models have been developed. R-Sq values for surface roughness, cutting force, flank wear length and temperature have been found as 83.02%, 84.58%, 77.85% and 81.09%. SEM images of cutting inserts depict the crater wear, built up edge and adhesive wear during dry where as negligible wear in cryogenic atmospheric turning operations. The EDS images of machined workpiece depict the Fe has major composition.

Influence of different grades of CuW electrodes when die sinking ED-machining of cemented carbide

This work investigates the influences of two different grades of copper–tungsten (CuW) electrodes with 65% and 85% of tungsten when sinking ED-machining cemented carbide (WC-Co) with 10% Co. In EDM, literature research works evaluating the influence of different grades of CuW electrodes when ED-machining the same WC-Co workpiece material were not found. In this work, rough, semi-finish, and finish EDM regimes were applied to evaluate process performance aspects as material removal rate (Vw) and volumetric relative wear (ϑ). Workpiece surface integrity was evaluated in terms of surface roughness, hardness, and chemical composition. From the results, the CuW85 electrode presented lower volumetric relative wear (ϑ) and higher material removal rate (Vw) than that of CuW65 electrode. Micro-cracks, from recast layer in direction to heat affected zone, were observed for both grades of CuW electrodes for rough ED-machining. Nanoindentation showed a hardness reduction of about 10% in heat-affected zone in relation to the base material for finishing regime with both CuW electrode grades. EDS revealed that the presence of Co and WC was not altered in recast layer and heat-affected zone.

Characterization of Zirconia-Based Ceramics After Microgrinding

Despite the recent developments of ductile mode machining, microgrinding of bioceramics can cause an insufficient surface and subsurface integrity due to the inherent hardness and brittleness of such materials. This work aims to determine the influence of a two-step grinding operation on zirconia-based ceramics. In this regard, zirconia (ZrO2) and zirconia toughened alumina (ZTA) specimens are ground with ultrasonic vibration assistance within a variation of the machining parameters using two grinding steps and different diamond grain sizes of the tools in each of the machining procedure. White light interferometry, scanning electron microscope, X-ray diffraction (XRD), and four-point bending tests are performed to evaluate surface roughness, microstructure, residual stresses, and flexural strength, respectively. The strategy applied suggests that the finished parts are suitable for certain biomedical uses like dental implants due to their optimum surface roughness. Moreover, concerning the mechanical properties, an increase of the flexural strength and compressive residual stresses of ground ZrO2 and ZTA workpieces were observed in comparison to the as-received specimens. These results, as well as the methodology proposed to investigate the surface integrity of the ground workpieces, are helpful to understand the bioceramic materials response under microgrinding conditions and to set further machining investigations.

Structuring of Bioceramics by Micro-Grinding for Dental Implant Applications.

Metallic implants were the only option for both medical and dental applications for decades. However, it has been reported that patients with metal implants can show allergic reactions. Consequently, technical ceramics have become an accessible material alternative due to their combination of biocompatibility and mechanical properties. Despite the recent developments in ductile mode machining, the micro-grinding of bioceramics can cause insufficient surface and subsurface integrity due to the inherent hardness and brittleness of these materials. This work aims to determine the influence on the surface and subsurface damage (SSD) of zirconia-based ceramics ground with diamond wheels of 10 mm diameter with a diamond grain size (dg) of 75 μm within eight grinding operations using a variation of the machining parameters, i.e., peripheral speed (vc), feed speed (vf), and depth of cut (ae). In this regard, dental thread structures were machined on fully sintered zirconia (ZrO2), alumina toughened zirconia (ATZ), and zirconia toughened alumina (ZTA) bioceramics. The ground workpieces were analysed through a scanning electron microscope (SEM), X-ray diffraction (XRD), and white light interferometry (WLI) to evaluate the microstructure, residual stresses, and surface roughness, respectively. Moreover, the grinding processes were monitored through forces measurement. Based on the machining parameters tested, the results showed that low peripheral speed (vc) and low depth of cut (ae) were the main conditions investigated to achieve the optimum surface integrity and the desired low grinding forces. Finally, the methodology proposed to investigate the surface integrity of the ground workpieces was helpful to understand the zirconia-based ceramics response under micro-grinding processes, as well as to set further machining parameters for dental implant threads.

Analytical modeling of temperature distribution in lead-screw whirling milling considering the transient un-deformed chip geometry

High temperature often occurs at the local cutting area during lead-screw whirling milling, which significantly affects workpiece surface integrity as well as tool life. The cutting process of lead-screw whirling milling comprises several recurrent characteristics, such as the un-deformed chip thickness and un-deformed chip width. The combined effects of un-deformed chip thickness and width cause time-varying variation in the size of the heat source, thus further affect the temperature distribution in the cutting area. This paper proposes a transient thermal analytical model to analyze the temperature distribution in the cutting area for lead-screw whirling milling. According to the complex trajectory of the tool relative to the rotation workpiece, the un-deformed chip geometry has been studied in detail at the two cutting stages. The time-varying tool-chip contact area and boundary equations of frictional heat source are firstly formulated to describe the size of the time-varying heat source. Secondly, the transient thermal analytical model is constructed taking into account the heat liberation intensity of the time-varying heat source. A series of experiments of whirling milling for lead-screw shaft are carried out, and the theoretical results evaluated by the proposed analytical model agree well with the experimental results. Furthermore, the effects of cutting conditions and un-deformed chip geometry on the temperature distribution have been analyzed, which can be used for process designers to make decisions in choosing the cutting parameters with optimized surface integrity and tool life.

New observations on built-up edge structures for improving machining performance during the cutting of superduplex stainless steel

Abstract This work features a comprehensive investigation of built-up edge (BUE) formation during machining of superduplex stainless steel (SDSS), grade UNS S32750. To visually investigate BUE formation during the machining test, a detailed examination of BUE structures obtained at different cutting speeds was performed. The BUE geometries were determined by scanning electron microscope (SEM) and 3D white light interferometry. In addition, various BUE adhesion patterns were analyzed through electron backscatter diffraction (EBSD) and nano-indentation methods. The examined BUE revealed a high level of grain refinement and elongation for both ferrite and austenite structures, as well as a tool protection effect at specific cutting speeds. Finally, the influence of BUE on the machining process in terms of chip formation and surface integrity was studied in detail. Considerable improvements could be made to the frictional conditions and workpiece surface integrity at low cutting speeds.

3D modeling of recrystallized layer depth and residual stress in dry machining of nickel-based alloy

Surface integrity is one of the important requirements of engineers, and it should be controlled for manufacturing of different components. Among different indications of surface integrity, metallurgical aspects including microstructure changes and residual stresses are remarkably effective on performance and service life of the products. Machining process of Inconel 718 alloy is widely used in advanced industries, and therefore, surface integrity of machined workpieces is essential task. Since experimental investigation in this subject is really difficult and time-consuming, finite element modeling of machining processes is used as beneficial method. In this paper, 3D analysis of machining process of Inconel 718 alloy was carried out to evaluate surface integrity in terms of depth of the recrystallized layer and residual stress. At first section, experimental tests were conducted at different machining process to use them as the benchmark for evaluation of recrystallized layer depth in machining simulation. Using the critical strain criterion, the numerical results of recrystallized layer depth was calculated and successfully verified with corresponding experiments. To improve precision of the numerical results, the user subroutine was implemented in FE code to employ hardness-based flow stress and also cutting tool geometry was precisely measured. At the second section, residual stress distribution in the machined surface was firstly predicted using the elastic–plastic analysis and verified with experimental test. After that, the effect of testing conditions was evaluated and discussed on different indications of residual stress profile. Finally, there is reasonable hope that utilized strategy can be extended efficiently for other manufacturing processes.

Influence of cutting ratio and tool macro geometry on process characteristics and workpiece conditions in face milling

This paper presents the influences of the inverse cutting ratio (width-to-thickness b/h<1) and the macro cutting geometry on the chip formation, milling forces, tool deflection, as well as on the workpiece surface integrity in face milling. The investigations are based on the DoE method using finite element simulation and practical experiments. A significant decrease of the cutting force by up to 65%, was achieved using inverse cutting ratio. Accordingly, the mechanical tool deflection from its axis was reduced. At the same time, the residual tensile stresses of the workpiece surface increase applying the inverse cutting ratio.

Experimental Investigation of Oil Mist Assisted Cooling on Orthogonal Cutting of Ti6Al4V

Abstract In this study, a thermo-mechanical model of machining of Ti6Al4V using different oil-mist combination is developed to predict the tool and workpiece temperature at different cutting speed. Machining of chemically reactive materials like Ti6Al4V causes high localization of heat, which contribute to the high tool wear or even premature failure of the tool. The thermal gradient effect is dominating in machining under dry conditions because of its low thermal conductivity. This induces thermal stresses and microstructural changes in the workpiece, thus damaging the workpiece surface integrity. The objective of present work is to understand the effect of different oil mist cooling mixtures at the tool-chip interface and to evaluate the tool and workpiece temperature. Experiments were performed using various mist conditions for different cutting parameters and its effect on the temperature has been studied. Temperature measurement was carried out using a thermal imaging camera. A 2-D finite element thermo-mechanical model is developed using ABAQUS TM to predict the tool and workpiece temperature. Provision of mist cooling has shown a large reduction in the tool and workpiece temperature. It was observed that at low cutting speeds, lubrication characteristics of mist is predominant while at higher cutting speed lubrication suffers.

Material removal mechanism of laser-assisted grinding of RB-SiC ceramics and process optimization

Laser-assisted grinding (LAG) is a promising method for cost-effective machining of hard and brittle materials. Knowledge of material removal mechanism and attainable surface integrity are crucial to the development of this new technique. This paper focusing on the application of LAG to Reaction Bonded (RB)-SiC ceramics investigate the material removal mechanism, grinding force ratio and specific grinding energy as well as workpiece surface temperature and surface integrity, together with those of the conventional grinding for comparison. Response surface method and genetic algorithm were used to optimize the machining parameters, achieving minimum surface roughness and subsurface damage, maximum material removal rate. The experiments results revealed that the structural changes and hardness decrease enhanced the probability of plastic removal in LAG, therefore obtained better surface integrity. The error of 3-D finite element simulation model that developed to predict the temperature gradient produced by the laser radiation is found to be within 2.7%–15.8%.

Tool life and workpiece surface integrity when turning an RR1000 nickel-based superalloy

Following a brief review on the turning of nickel-based superalloys, the paper evaluates the machinability and workpiece surface integrity of a powder metallurgy HIP-ed (PHIP) RR1000 alloy, involving two phases of turning experiments using TiN/Al2O3/Ti(C,N) coated carbide inserts. Based on a maximum flank wear criteria of 200 μm, tool life exceeded 40 min when operating at or below 100 m/min; however, Taylor tool life curves were extremely steep. At a feed rate of 0.08 mm/rev, workpiece surface roughness was ~ 0.5 μm Ra. Tests at cutting speeds of 80 m/min or less with new tools showed the ‘best/acceptable’ surface integrity with no visible white layer or plucking and a maximum distorted layer of ~ 6 μm deep. In contrast, the surfaces produced using worn tools at a cutting speed of 100 m/min showed a distorted layer of ~ 20 μm deep with evidence of surface laps and plucking to a depth of ~ 15 μm.

Influence of different input parameters on the contact conditions determing the surface integrity of workpieces in an unguided vibratory finishing process

The contact force and the relativevelocitybetween workpiece and abrasive media in a vibratory finishing have a strong effect on the material removal rate and the surface roughness of the machined workpieces. Both, the contact force as well as the relative velocity, are mainly influenced by the characteristics of the abrasive media type used as well as the geometry and the density of the workpieces. Furthermore, major influence factors on the contact conditions between the workpiece and abrasive media are the input parameters of the vibratory finishing machine, e.g. the mass distribution between the upper and the lower imbalance weights, the offset angle between the imbalance weights and the rotational speed. In order to determine the influence of the abrasive media and the workpiece characteristics as well as the different input parameters of the machine on the contact conditions, two measurement systems in the form of a camera-integrated workpiece and a workpiece with an integrated piezoelectric sensor have been used. The completely wireless construction of the measurement systems enabled the measurement of the contact force as well as the relative velocity without the influence of wires for data transfers and electrical power supply. The results have shown that the contact force as well as the relative velocityand therefore the surface integrity of the machined workpieces are mainly effected by the adjustments of the rotational speed and the size of the abrasive media.

Study on tool wear and workpiece surface integrity following drilling of CFRP laminates with variable feed rate strategy

Drilling carbon fibre reinforced plastic (CFRP) composites is often accompanied by workpiece delamination particularly at hole exit, which is dependent to a large extent on the applied feed rate/thrust force. In this paper, a variable feed rate strategy was investigated where drill feed was decreased from a maximum of 0.3 mm/rev to 0.01 mm/rev for the final 2 mm of hole depth, in order to reduce thrust force and minimise hole exit damage but without severely impacting process productivity. A full factorial experiment involving two variable factors (CFRP lay-up configuration at two levels and primary feed rate at three levels) was performed using diamond coated carbide tools. All tests achieved the 384 drilled hole criterion with tool flank wear ranging from 114 to 193 μm, chipping/delamination of the coating and abrasion were the principal tool wear modes. Delamination factor values at hole entry generally increased with primary feed rate and number of holes drilled by up to ~23%, with limited difference in exit delamination factor between the first and last holes drilled (maximum of 0.04). The reduced feed rate regime immediately prior to hole exit led to lower surface roughness by up to ~6.46 μm Ra compared with the entry location together with reduced fibre pull out and cavities compared to the rest of the hole when drilling with a new tool. Surface quality was however less apparent with increased numbers of holes drilled and tool wear.

Some insights on Combined Turning-Burnishing (CoTuB) process on workpiece surface integrity

This paper deals with a combined manufacturing process called Combined Turning-Burnishing (CoTuB) that performs turning and ball-burnishing simultaneously on the same machine tool. This innovative process aimed to enhance surface quality and integrity by exploiting rough turning conditions. Consequently, this implies an increase in productivity when compared to conventional surface treatment processes. For this reason, a device was manufactured in order to hold both commercial cutting and burnishing tools to carry out the removal material and the surface mechanical treatment processes simultaneously and under the same operation. As the design of CoTuB device sets the cutting tool ahead of the ball, turning is followed by burnishing operation along the manufactured surface. It has been depicted experimentally that a considerable improvement in surface quality could be achieved using the new combined process under suitable process parameters. Burnishing force, Ball burnishing diameter and depth of cut are independent parameters. In order to carry out a parametric process study, several experiments based on Taguchi method were performed. The aim is to identify the optimal turning/burnishing parameters when treating AISI 4140 steel. This helps to get a compromise between the optimal arithmetic surface roughness (Ra), the compressive residual stress state and the micro-hardness (μH).

Residual stresses and cutting forces in cryogenic milling of Inconel 718

Due to its excellent mechanical and corrosion resistance at high temperatures, the Inconel 718 alloy has several applications in the aerospace and nuclear industries. The microstructure of this material acquires rapid hardening during machining and its low thermal conductivity contributes to high temperatures in the cutting zone. As the temperature increases, the cutting tool wear accelerates, compromising the final quality of the machined part. These factors turn Inconel 718 a difficult-to-cut material and generate residual stresses due to thermal and mechanics loads during machining. The cutting fluids purpose is to cool and lubricate the process, as well as to remove the chip from the cutting zone. Liquid nitrogen (LN2) was used to meet the gap of research involving residual stresses analysis in cryogenic machining. This study presents an experimental analysis of the Inconel 718 end milling on the residual stresses generation, cutting forces, tool wear and surface integrity of the machined workpiece. The results were compared to a previous study concluding that the cutting fluids did not influenced the cutting forces levels, and the results with LN2 were increasing along the cutting length. The cryogenic method presented low residual stresses levels and improved workpiece surface roughness compared to flood method, although the flood method contributed for compressive residual stresses, which may be beneficial to the service life of the machined component.

Surface integrity after internal load oriented multistage contact deep rolling

Mechanical treatment by deep rolling generates an improvement of the surface integrity by inducing compressive residual stress, strain hardening as well as a reduction of the surface roughness. The resulting material modification is based on the plastic deformation of surface and subsurface layers caused by the movement of a deep rolling tool across the workpiece surface under defined conditions in terms of rolling force, ball diameter and number of contacts. A correlation between the process parameters and the surface integrity to predict the modification in the workpiece is of limited validity. It is more useful to consider the internal load during the mechanical treatment in form of stress fields occurring during the process. This paper shows an approach to describe the internal load based on the hertzian stress in combination with the elastic model considering the multiple contacts in a deep rolling process. A defined variation of process parameters regarding the internal loads and the number of contacts was performed. It is shown that the correlation between internal loads and material modification (process signature) offers a good approximation to describe the surface integrity of workpieces after multistage contact in deep rolling processes. The description of material modification based on equivalent stress depth profiles enables the prediction of maximum of compressive residual stress after multistage deep rolling.

Effects of cryogenic cooling on the surface integrity in hard turning of AISI D6 steel

Methods able to enhance surface integrity of machined components have been one of the emerging areas in manufacturing engineering, and a technique that has been providing satisfying results in the last years is cryogenic machining. Besides promoting surface integrity improvement, it is considered an alternative to the use of conventional cutting fluids, which is in accordance with the latest global trends for sustainable means of production. In this sense, replacing grinding operation, which uses large volumes of conventional cutting fluids, by hard turning assisted by liquid nitrogen, for example, could be a good choice. The aim of this work was to investigate the effects of cryogenic cooling on the surface integrity of quenched and tempered AISI D6 tool steel after turning operation. Dry and cryogenic turning trials with polycrystalline cubic boron nitride tools were performed and the results of surface integrity (surface roughness and topography, microhardness and residual stresses, as well as the modified microstructure of the deformed layer) were analyzed for comparison. The results showed that cryogenic cooling played an important role in modifying the workpiece surface integrity, providing low values of surface roughness (similar to those obtained in grinding operations), as well as higher values of surface microhardness and compressive residual stresses as compared to the dry condition.

Finite difference simulation and experimental investigation: effects of physical synergetic properties of nanoparticles on temperature distribution and surface integrity of workpiece in nanofluid MQL grinding process

Application of nanofluids in minimum quantity lubrication (MQL) system in grinding has been proven as an effective approach to counter the negative effects of high temperature evolution in grinding process. However, the cooling and tribological properties of nanolubricants are physical synergetic as the morphology, atomic structure, and physical properties of nanoparticles are determining factors on their performance in MQL systems. Graphite and CuO nanoparticles are representatives of nanoparticles with different atomic structures and physical properties. In this study, a finite difference model based on exponential distribution of moving heat source in wheel-workpiece contact area has been developed to determine the energy partition and temperature distribution of workpiece in nanofluid MQL grinding process using graphite and CuO nanofluids as lubricants. In order to study the effects of atomic structures of nanoparticles on the tribological properties of nanofluids, surface roughness and SEM images of ground surfaces have been evaluated. The results showed that CuO nanofluids with rolling action of nanoparticles in the contact area provide lower energy partition and better surface quality of workpiece in comparison with that of graphite nanofluids with sliding mechanism of atomic planes of nanoparticles at the wheel-workpiece interface during grinding process.

Design for Manufacturing of Variable Microgeometry Cutting Tools

Cutting edge microgeometry has gained special attention of late in the machining research community. Machine tool vibration, tool life, and workpiece surface integrity are all influenced by cutting edge size/shape. To optimize the machining process, variable microgeometry (VMG) cutting tools, in which the edge microgeometry varies along the edgeline with respect to specific variables (such as machining parameters or expected tool wear), are manufactured. Despite the advantages of VMG tools, a major hindrance in their development is the manufacturing complexity that demands high precision multi-axis edge preparation processes following extensive machine setup, fixturing, and programming. This paper details the proof of concept of a design criterion, which leads to the manufacturing of VMG cutting tools by only traditional edge preparation processes. The present method relies on the existing relationship between the edge radius subsequent to the edge preparation process and the tool wedge angle. The validity of the proposed method is first examined by a numerical simulation of the edge preparation. Carbide cutting tool inserts are then designed based on the proposed idea. Robust VMG generation subsequent to edge preparation by microblasting is demonstrated through microgeometric measurements. VMG chemical vapor deposition-coated carbide tools manufactured by the proposed approach are evaluated for turning hardened steel, and optimal designs are identified with respect to tool life and workpiece surface roughness. To address the design consideration, finite element (FE) modeling provides valuable insight into the machining process. FE modeled stress and temperature distribution clarify the experimental observations and reveal the design constraints.

Effect of Built-Up Edge Formation during Stable State of Wear in AISI 304 Stainless Steel on Machining Performance and Surface Integrity of the Machined Part

During machining of stainless steels at low cutting -speeds, workpiece material tends to adhere to the cutting tool at the tool–chip interface, forming built-up edge (BUE). BUE has a great importance in machining processes; it can significantly modify the phenomenon in the cutting zone, directly affecting the workpiece surface integrity, cutting tool forces, and chip formation. The American Iron and Steel Institute (AISI) 304 stainless steel has a high tendency to form an unstable BUE, leading to deterioration of the surface quality. Therefore, it is necessary to understand the nature of the surface integrity induced during machining operations. Although many reports have been published on the effect of tool wear during machining of AISI 304 stainless steel on surface integrity, studies on the influence of the BUE phenomenon in the stable state of wear have not been investigated so far. The main goal of the present work is to investigate the close link between the BUE formation, surface integrity and cutting forces in the stable sate of wear for uncoated cutting tool during the cutting tests of AISI 304 stainless steel. The cutting parameters were chosen to induce BUE formation during machining. X-ray diffraction (XRD) method was used for measuring superficial residual stresses of the machined surface through the stable state of wear in the cutting and feed directions. In addition, surface roughness of the machined surface was investigated using the Alicona microscope and Scanning Electron Microscopy (SEM) was used to reveal the surface distortions created during the cutting process, combined with chip undersurface analyses. The investigated BUE formation during the stable state of wear showed that the BUE can cause a significant improvement in the surface integrity and cutting forces. Moreover, it can be used to compensate for tool wear through changing the tool geometry, leading to the protection of the cutting tool from wear.