Improved Surface Integrity Research Articles

Simulation Research on Micro-Milling Process Based on ABAQUS

With the more and more micro mechanical parts are coming into the use of many fields, the micro machining is becoming a new tendency in the future manufacture industry. As a kind of common machining method, milling is also favor in the micro-fabrication field since its good machining precision and forming ability. In this work, cutting process simulation of micro-milling was done to analyze the influence of machining data and tool geometry on the cutting process such as temperature and stress distribution during machining by using ABAQUS software. The results from this simulation can provide some useful information for choosing reasonable cutting edge and machining data to improve surface integrity and prolong cutting tool life in micro-milling operation.

Analysis of suspension stability for nanofluid applied in minimum quantity lubricant grinding

The nanofluid is usually applied in minimum quantity lubricant (MQL) grinding to decrease grinding temperature and to improve surface integrity of workpiece. However, a large challenge in the application process of nanofluid is the sedimentation of the nanoparticles due to their poor suspension stability in the base fluid. Then, the lubrication and heat conduction characteristics of nanofluid will be deteriorated, and the nanofluid cannot be atomized as expected during grinding. Therefore, the heat transfer performance of nanofluid during MQL grinding severely decreased. In this study, the force state of nanoparticle in base fluid was analyzed and the effect of dispersant on the force state of nanoparticle was researched. The suspension stability of Al2O3 (0.5 wt.%) nanofluid was investigated under different ultrasonic vibration times, pH values, and dispersant concentrations (sodium dodecyl benzene sulfonate, SDBS). It is found that the suspension stability of nanofluid is quite poor under short-time ultrasonic vibration condition, and the nanofluid with good suspension stability can be obtained when the ultrasonic vibration time exceeds 0.5 h. A higher concentration of SDBS will lead to a better suspension stability of nanofluid when the concentration of SDBS is quite low. However, if the concentration of SDBS exceeds 0.5 wt.%, there is oversaturated adsorption on the nanoparticles surface which results in the deterioration of suspension stability of nanofluid with the increase of the SDBS concentration. As pH value is below 7, the suspension stability of nanofluid is significantly improved with the increase of pH value. The sedimentation clearly appeared in the disperse system when pH value is higher than 7. The dispersion morphology of the Al2O3 nanoparticles in disperse system is analyzed by using a scanning electron microscope. It is found that some large aggregates appeared when no dispersant was applied in the disperse system, and the Al2O3 nanoparticles are uniformly dispersed in disperse system with the application of the dispersant.

Powder Metallurgical Components: Improvement of Surface Integrity by Deep Rolling and Case Hardening

In many cases, powder metallurgical components are heat treated in order to improve the component behavior. An established heat treatment technique for wrought materials is case-hardening. But up to now, this procedure is not applied for powder metallurgical components, since the existing porous microstructure avoids adjusting a defined carbon depth profile. As a consequence a carbonization of the core and a full hardening can occur, leading to a disadvantageous phase and residual stress distribution. However, a new approach for case hardening of powder metallurgical components is to perform a surface densification prior to the heat treatment. In this study this approach is realized by using a deep rolling process. In order to verify the functionality of the process chain, the surface integrity was analyzed after each processing step using X-ray diffraction measurements and materialographic methods. There is clear evidence that the open porous structure could be transferred into a surface densified graded porous layer. As a consequence the carburization is dominated by solid state diffusion enabling to adjust a defined carbon depth profile leading to a martensitic surface layer and compressive residual stresses in the near surface zone. Subsequent fatigue strength experiments for sintered samples as well as for additional densified or densified plus case-hardened specimens were performed in order to demonstrate the enhanced mechanical properties. A significant increase in fatigue strength can be measured.

High-quality machining of CFRP with high helix end mill

Side milling tests of CFRP (Carbon Fiber Reinforced Plastics) without coolant are carried out by DLC (Diamond-Like Carbon)-coated carbide end mills. Four types of DLC-coated end mills are chosen: UBMS (UnBalanced Magnetron Sputtered) and AIP (Arc Ion Plated) coatings having different helix angles, respectively. The surface integrity is evaluated in terms of 3D profiles of the machined surface, generation of fluffing, delamination and pull-out of the carbon fiber. The cutting force and tool wear with respect to the fiber orientation are also examined. The inclination milling with high helix angle end mill is proposed in which the end mill is tilted in such a way that the resultant cutting force acts parallel to the work surface. This unique approach enables to reduce tool wear and to improve surface integrity of machined surface of CFRP.

Improvement of surface integrity of cold forging tools by adaption of tool making process

Cold forging enables mass production of steel based components. High loads within cold forging presuppose high loadable tool materials. This is why apart from tool steels cemented carbides are mainly used as tool materials. Due to brittleness of these materials, fatigue is one of the major limits of tool life. Tool manufacturing requires a combination of hard machining and subsequent machining steps. For hard machining of complex tool geometries electrical discharge machining (EDM) represents the industrial standard. The thermal influenced surface layer has to be removed by post and fine machining steps. The resulting surface integrity has a major influence on the internal strength of a tool. Correlations between tool manufacturing, surface properties and tool behavior will gain knowledge for an optimized tool production. In this context, scope of the present paper are the investigation and description of the interactions between tool manufacturing and resulting surface properties for tools made of cemented carbide and tool steel. Within the article, the surface properties caused by a conventional process chain consisting of EDM and polishing are quantified. In addition, these results are compared to an adapted process chain with an integrated peening process. The results reveal that the conventional and the adapted process chain lead to similar surface topographies and roughness values. However, the integration of a peening process shifts the residual stress level towards higher compressive stresses.

Elliptic vibration-assisted cutting of fibre-reinforced polymer composites: Understanding the material removal mechanisms

This paper develops an elliptic vibration-assisted (EVA) technique to effectively cut fibre-reinforced polymer (FRP) composites using a simple tool. A novel vibrator was invented to work at the anti-resonant frequency to realize stable and high variational velocities. A three-dimensional microstructure-based finite element model was also established to explore the material removal mechanisms in the EVA cutting. It was found that the application of vibration can significantly decrease the cutting forces and reduce the subsurface damage in a workpiece. The vibration in the cutting direction is more effective in reducing the cutting force, but that normal to the cutting direction has the advantage of chip removal. When the vibration is applied to both the directions in the EVA cutting, an optimal cutting process can be reached, providing much smaller cutting forces, a much improved surface integrity, and an extended tool life. The study concluded that the ratio of the tool-feed-rate to the maximum vibration velocity in the cutting direction, and the ratio of the cutting distance in a single tool vibration cycle to the fibre diameter are the key parameters. To maximise the advantage of the EVA cutting, it is necessary that these two parameters are below their critical values.

Improving surface integrity in finish machining of Inconel 718 alloy using intelligent systems

In machining of hard materials, surface integrity is one of the major customer requirements which comprise the study of the changes induced to the workpiece. Surface roughness and residual stress are often considered as the most significant indications of surface integrity. Inducing tensile residual stress during the machining processes is a critical problem which should be avoided or minimized to obtain better service quality and component life. This problem becomes more evident in the presence of rough machined surface because fatigue life of manufactured components might be decreased significantly. Inconel 718 superalloy is one of the hard materials used extensively in the aerospace industries. It is prone to tensile residual stress in machined surface. Thus, controlling and optimizing residual stress and surface roughness in machining of Inconel 718 are so needed. Intelligent techniques based on the predictive and optimization models can be used efficiently for this purpose. In this study, the optimal machining parameters including cutting speed, depth of cut, and feed rate were accessed by intelligent systems to evaluate the state of residual stress and surface roughness in finish turning of Inconel 718. The results of experiments and analyses indicated that implemented techniques in this work provided a robust framework for improving surface integrity in machining of Inconel 718 alloy. It was shown that cutting speed has more effect on surface integrity than other investigated parameters. Also, depth of cut and feed rate were found in the moderate range to obtain satisfactory state of tensile residual stress and surface roughness.

A review of hybrid manufacturing processes – state of the art and future perspectives

Today, hybrid manufacturing technology has drawn significant interests from both academia and industry due to the capability to make products in a more efficient and productive way. Although there is no specific consensus on the definition of the term ‘hybrid processes’, researchers have explored a number of approaches to combine different manufacturing processes with the similar objectives of improving surface integrity, increasing material removal rate, reducing tool wear, reducing production time and extending application areas. Thus, hybrid processes open up new opportunities and applications for manufacturing various components which are not able to be produced economically by processes on their own. This review paper starts with the classification of current manufacturing processes based on processes being defined as additive, subtractive, transformative, joining and dividing. Definitions of hybrid processes from other researchers in the literature are then introduced. The major part of this paper reviews existing hybrid processes reported over the past two decades. Finally, this paper attempts to propose possible definitions of hybrid processes along with the authors’ classification, followed by discussion of their developments, limitations and future research needs.

Multi-objective Process Optimization to Improve Surface Integrity on Turned Surface of Al/SiCp Metal Matrix Composites Using Grey Relational Analysis

The utilization of Al/SiCp metal matrix composites in different engineering fields has undergone a tremendous increase due to its tailor-made properties that can be achieved by varying the size and volume fraction of reinforcement. However, the difficulty in machining of metal matrix composites (MMCs) arises not only from the excessive wear of the cutting tools but also from fracturing of the reinforcement particles which leaves pits and cavities. These characteristics in machining of MMCs affect the machined surface integrity. Hence, the objective of this study is to identify the optimum process parameters to improve the surface integrity on Al/SiCp composites. The machined surface integrity have been analysed as a function of processing parameters, such as feed rate, cutting speed, depth of cut and cutting tool geometry. Surface integrity is associated with surface roughness and sub surface damage. Both these response variables are governed by the cutting forces, surface finish, residual stresses generated on the machined surface and microhardness variation beneath the machined surfaces. Thus, to improve the surface integrity on Al/SiCp composites multi objective process parameter optimization is performed using grey relational analysis. Experiments on Al/SiCp composites of four different compositions are performed using L27 orthogonal array as per the Taguchi method. Analysis of experimental results indicates that the surface roughness is more sensitive to a change in size than a change in volume fraction of reinforcement. Investigations on sub-surface integrity involving micro-hardness variation have shown that depth of altered material zone (AMZ) changes with a change in size of abrasive reinforcement in MMCs. The grey relational analysis shown that wiper insert geometry with 0.8mm tool nose radius, 0.05mm rev-1 feed, 40 m min-1 cutting speed and 0.2mm depth of cut are optimized machining conditions that enhances the surface integrity on Al/SiCp composite within the scope of the experiments performed.

Characterization of Surfaces Obtained by Precision Hard Turning of AISI 52100 in Relation to RCF Life

Traditionally, components of hardened steels, such as bearings, gears, shafts and rails, are finished by grinding process. In this study, Precision Hard Turning (PHT) is proposed as an alternative finishing process to manufacture AISI 52100 bearing components (60-62 HRC), because PHT improves surface integrity and therefore increases the Rolling Contact Fatigue (RCF) life. An experimental design is used, under dry condition using cubic Boron Nitride (c-BN) cutting tools, to investigate the effect of cutting parameters on surface integrity characterised via surface roughness, microstructure analysis and residual stresses. Then, fatigue life tests are performed on a twin-disk machine. SEM observations of transversal cross-sections of all samples show the presence of a very fine and white layer (<1μm) on the top surface and a thermal affected zone of 40-50μm in the sub- surface. PHT does not affect quantitatively the percentage of the different microstructural phases and leads to decrease the number of dislocations in the transition zone compared to the bulk material, which is correlated to decrease of nanohardness in the transition zone. Compressive residual stresses are measured in surface and sub-surface and their level is more in compression in the circumferential direction than in tangential direction. Levels of roughness decrease as cutting speed increases. RCF life of bearing steel components machined by PHT reached 5.2 (at Ra=0.11μm) and 0.32 million cycles (at Ra=0.25μm). Therefore, RCF life increases as the roughness amplitude Ra decreases.

Surface modification of the patterned Al6061/SUS304 metal plates using the large electron beam

Polishing is a finishing process used to improve surface integrity by reducing surface roughness and residual stress caused by other machining processes. The recently developed electron beam polishing method was used in this study to improve surface quality. In this process, an electron beam with a maximum diameter of 60mm was applied for a few microseconds to melt and evaporate a metal surface. Al6061 and SUS304 metal plates were prepared with different geometric patterns and subjected to electron beam polishing. The surface roughness of the patterned SUS304 metal plate was significantly improved. However, the surface roughness of the patterned Al6061 metal plate became worse. Although the surface hardness decreased by approximately 10% on the re-solidified layers on both types of plates, the contact angle increased due to changes in surface morphology. The microstructure variation after the electron beam irradiation was also examined and compared with the thickness prediction of the re-solidified layer for Al6061 and SUS304 metal plates.

Improvements in surface integrity and fatigue life of low plasticity burnished surfaces

Low plasticity burnishing (LPB) is a state–of–the–art method of surface enhancement. It improves surface integrity by providing deep and thermally stable surface compression. Some of the surface integrity characteristics which can be improved by LPB technology are: surface finish, surface hardness, low– and high–cycle fatigue strength and wear resistance. In the present study, full factorial experiments were conducted on AISI 1045 and AISI 316L work materials using a newly designed LPB tool to evaluate the effect of LPB parameters on the fatigue life of these materials. Effect of LPB parameters and their interactions on high cycle fatigue life of the above materials was assessed quantitatively. Optimum levels of parameters for maximum fatigue life have been determined. An expression correlating fatigue life and these LPB parameters has also been developed. Assessment of surface integrity has also has been done by evaluating the depth of compression and wear resistance.

プラズマ窒化処理がステンレス刃物鋼の表面性状に及ぼす影響

Plasma nitriding treatment is very effective for the hardening of precision metal parts. Especially, high density plasma nitriding can efficiently generate a high density ion with installed hollow cathode, which decreases the damage of the workpiece. As a result, the parts can be cleaned, etched, heated, and nitrided effectively. In this study, an improvement of surface integrity of stainless steel SUS440C is experimentally investigated by nitriding. The experimental analysis made it clear that the surface hardness of workpiece increased due to the generation of nitrided layer even under the low temperature condition like 513K. The nitrided layer was hardened with an increase of process temperature and process time, until a maximum surface hardness of 1700HV.

Enhanced surface integrity and dimensional accuracy by simultaneous micro-ED/EC milling

This paper presents the simultaneous micro-ED/EC milling that provides significantly improved surface integrity and dimensional accuracy when compared with micro-ED or micro-EC milling alone. The concurrent occurrence of electrochemical reaction and electrical discharge is attained by exploiting partially deionized water with appropriate process control. Machining speed is judiciously adjusted to promote electrochemical reaction for improving surface finish. Concurrently, short voltage pulses localize dissolution zone for greater precision while also remove micron-thick layer generated by discharge craters from the machined surface. Micro-shapes with enhanced surface finish and dimensional accuracy are produced to demonstrate the feasibility and capability of the aforementioned approach.

The effects of cryogenic cooling on surface integrity in hard machining: A comparison with dry machining

This paper presents results of an experimental study of cryogenic machining of hardened AISI 52100 steel, focusing on surface integrity. Experiments were performed under dry and cryogenic cooling conditions using CBN tools varying cutting speeds, workpiece hardness and tool geometry. Surface integrity parameters (surface roughness, white layer thickness, residual stresses, metallurgical conditions including grain size, phase transformation, etc.) were investigated to establish the effects of cryogenic cooling on the surface integrity of the machined component, and results were compared with those from dry hard machining. Overall, cryogenic cooling provides improved surface integrity leading to extended product life and performance.

Surface Integrity in Ultrahigh Speed Micromachining

A new ultrahigh speed micro-spindle was used for micro-milling and micro-grinding at speeds greater than 300,000rpm. Micro-milling was performed on an aluminium alloy with micro-end-mills ranging in diameter from 50 to 300μm. The dimensional accuracy of straight cuts made at different speeds, feed rates and depths of cut was measured. The edge quality improved and burr formation tendency decreased as surface speed and feed rate were increased. Micro-grinding was performed with diamond tools on ceramics used for preparation of dental restorations. The propensity for generation of machining-related damage, such as surface and subsurface microcracks, were greatly reduced by machining at ultrahigh speeds and high feed rates. Major advantage of ultrahigh speed machining is the improvement of surface integrity with respect to generation of burr-free and damage-free micro-machined parts.

EFFECT OF EDM ASSISTED BY MAGNETIC FIELD ON SURFACE INTEGRITY OF ARMOURED STEEL

In the present study, EDM assisted by magnetic field process is proposed. The effect of EDM assisted by magnetic field process parameters on the surface integrity of armoured steel (HV500) has been studied. The response surface methodology (RSM) is employed to identify the effect of EDM machining parameters, i.e., peak current, magnetic flux density, duty factor and flushing pressure, on the surface integrity of machined component. The process performance criterion such as surface roughness (Ra) was evaluated. RSM was employed to develop the experimental model. Experiments performed on a newly designed experimental setup developed in the laboratory. The surface integrity was also explored by the scanning electron microscope (SEM) and micro-hardness testing to evaluate the effects of the EDM process assisted by magnetic field. This paper studies the topography of the ED-machined surface, the size and the amount of cracks on the surface layer. Hardness variation in the depth of the defective layer, when machining with and without magnetic field of the copper and graphite electrodes under different machining conditions has also been tested. SEM, micro-hardness testing results together with surface topography investigation showed that EDM assisted by magnetic field has the applicability to improve surface integrity.

Surface integrity of Inconel 718 when finish turning with PVD coated carbide tool under MQL

This paper reports the results of an experimental works to investigate the effect of cutting parameters and machining conditions on surface integrity when finish turning Inconel 718, a highly corrosive resistant, nickel-based super alloy, under three cutting conditions (DRY, MQL 50mL/h and MQL 100mL/h). The microstructure analysis using SEM on the machined surface suggests that severe deformation took place, leading to microstructure alteration at sub surface level measuring from a few to several micron in thickness. Work hardening under the machined surface was evident from the micro-hardness measurements where higher hardness reading was measured near the surface. The results of this study show that MQL may possibly improve surface integrity characteristics.

Surface Roughness Prediction in Precision Surface Grinding of Nano-Ceramic Coating Based on Improved ANFIS

For improving surface integrity and machining quality after precision grinding of the parts of nano-ceramic coating, and investigating its prediction technique of surface roughness, the prediction model of surface roughness in precision surface grinding of nano-ceramic coating based on adaptive network-based fuzzy inference system (ANFIS) was proposed in this paper. Then, the proposed prediction model was improved by hybrid Taguchi genetic algorithm (HTGA). At last, by comparative analysis of prediction results from traditional BP neural network model, simple ANFIS model and improved ANFIS model, the effectiveness of the proposed model was verified using grinding parameters and measured surface roughness in grinding tests as training and testing samples. It showed that the prediction accuracy of the improved ANFIS model proposed in this paper was higher, and it was an effective prediction method of surface roughness in precision grinding of nano-ceramic coating.

Research on the Fracture Phenomenon of Zirconia-Toughened Alumina Ceramics under Ultrasonic Vibration

A study of the fracture phenomenon of zirconia-toughened alumina (ZTA) ceramics was carried. It analyzes the mechanisms of crack propagation of ZTA ceramics, and constructs fracture experiments of ZTA ceramics, so the propagation behavior on fracture in ZTA ceramics was investigated according to the experiment. By contrast, intercrystalline fracture happed in V-shaped groove of ceramic specimen under normal load without ultrasonic vibration during ceramic fracture, and transcrystalline fracture happed in V-shaped groove of ceramic specimen under normal load with ultrasonic vibration during ceramic fracture. Furthermore, the loading force of ceramic specimen under normal load with ultrasonic vibration is smaller than that under normal load without ultrasonic vibration all other conditions being equal. The results of fracture experiment prove that ultrasonic vibration assisted is good for the fracture of ceramic specimen, and it also proves that ultrasonic vibration assisted grinding may raise the working efficiency and improve surface integrity of ceramics from the standpoint of the fracture.