Surface Integrity Parameters Research Articles

Prediction of residual stress in precision milling of AISI H13 steel

Surface integrity describes the attributes of a surface and it influences the functional performance of a work piece significantly. Residual stress is one of the major characterization parameters of surface integrity. Non-favorable residual stresses on a machined surface can reduce the fatigue life and performance of the machined part. It therefore requires a prediction model for residual stress in order to establish machining strategy to obtain favorable residual stress for prolonged fatigue life. Hardened tool steels have been widely used to make molds and dies by precision milling in aerospace and automotive industries. Knowledge of the relationship between residual stress on the machined molds and machining conditions is very important for process control. In this work, a prediction model for residual stress was developed by using a model-based approach on an Artificial Neural Network. This model is expected to predict the residual stress based on cutting parameters such as cutting speed, feed rate, depth of cut and tool lead angle. Several precision milling trials were carried out using a central composite design method. The networks have been trained and validated by experimental results. The performance of a feed forward neural network model with backpropagation was assessed and compared with a radial basis function network model by criterion of least mean squared error. Furthermore, the neural network prediction model was supported by the finite element simulation of the milling process to understand the formation mechanism of the residual stress in the machined surface. It was found, that the predicted values by the neural network model matched well with the experimental results. The radial basis function network showed better results than the feed forward network and was therefore chosen to take forward in the analysis. The feed rate was in this case the most influential factor, because it contributes significantly to heat and deformation on the work piece. The model could be used to optimize machining processes to obtain machining strategy for generating favorable residual stress and increasing fatigue life performance of the machined parts.

Influence of residual stress profile and surface microstructure on fatigue life of a 15-5PH

This works aims at identifying the influence of surface integrity parameters on fatigue life of a 15-5PH. The effect of residual stress profile, surface roughness and microstructure are investigated. Various cutting and superfinishing processes (turning, ball burnishing and belt finishing) are used so as to reach various engineered surface integrities and as a consequence to highlight the influence of each surface integrity parameter. Rotary-bending tests have been carried out on samples to determine the average fatigue strength at 2 million cycles. It is shown that the influence of a deep compressive sublayer is by far more important than the ones of surface roughness or microstructure. The so-called ‘white-layer’ brings also a slight improvement of fatigue resistance.

COMPARISON OF PARAMETERS OF SURFACE INTEGRITY OF MACHINED DUPLEX AND AUSTENITE STAINLESS STEELS IN RELATION TO TOOL GEOMETRY

The goal of this contribution was to describe parameters of surface integrity of two machined materials; austenite and duplex stainless steel. Residual stresses and presence of straininduced martensite were studied as a function of the side rake angle. Residual stresses of surface and sub-surface layers were determined using X-ray diffraction techniques and hole-drilling method. By using X-ray diffraction, it is possible to determine residual stresses in each phase separately, in comparison with hole-drilling method. The presence of strain-induced martensite was investigated using Barkhausen noise and optical microscope.

Solution to Inverse Problem of Manufacturing by Surface Modification With Controllable Surface Integrity Correlated to Performance: A Case Study of Thermally Sprayed Coatings for Wear Performance

Inverse problem of manufacturing is studied under a framework of high performance manufacturing of components with functional surface layer, where controllable generation of surface integrity is emphasized due to its pivotal role determining final performance. Surface modification techniques capable of controlling surface integrity are utilized to verify such a framework of manufacturing, by which the surface integrity desired for a high performance can be more effectively achieved as reducing the material and geometry constraints of manufacturing otherwise unobtainable during conventional machining processes. Here, thermal spraying of WC–Ni coatings is employed to coat stainless steel components for water-lubricated wear applications, on which a strategy for direct problem from process to performance is implemented with surface integrity adjustable through spray angle and inert N2 shielding. Subsequently, multiple surface integrity parameters can be evaluated to identify the major ones responsible for wear performance by elucidating the wear mechanism, involving surface features (coating porosity and WC phase retention) and surface characteristics (microhardness, elastic modulus, and toughness). The surface features predominantly determine tribological behaviors of coatings in combination with the surface characteristics that are intrinsically associated with the surface features. Consequently, the spray process with improved N2 shielding is designed according to the desired surface integrity parameters for higher wear resistance. It is demonstrated that the correlations from processes to performance could be fully understood and established via controllable surface integrity, facilitating solution to inverse problem of manufacturing, i.e., realization of a material and geometry integrated manufacturing.

Monitoring of Surface Damage in Rails After Long Term Cyclic Loading

This paper reports about possible concept in which surface damage of the rail after long tem cyclic loading can be executed. This study employs non destructive magnetic Barkhausen noise as a promising technique which exhibits very good sensitivity against extent of surface damage. Magnetic Barkhausen noise is correlated with the conventional parameters of surface integrity expressed in term of the thickness of damaged layer, its micro hardness as well as stress state. Furthermore, phase analysis of the real surface indicates that extensive phase transformations are produced by the repeated severe plastic deformation. Phase composition of the damaged layer indicates that structure transformation in the rail surface is thermally induced rather than deformation induced process

Influence of surface integrity on the fatigue behaviour of a hot-forged and shot-peened C70 steel component

Hot-forging is a process commonly used in the manufacturing of automobile parts such as connecting rods. Most hot-forged components are shot-blasted after forging in order to clean off the forging scale. The shot-blasting process is akin to shot-peening and greatly affects the surface integrity of the components by introducing hardening and residual stresses. This study focuses on the influence of the surface integrity on the fatigue behaviour of a hot-forged C70 steel connecting rod. Specimens were machined out of the connecting rods in order to perform fatigue testing on the forged surface. Several surfaces states, including shot-peened surfaces, were studied in order to quantify the influence of the surface integrity.A thorough characterisation of the surface integrity of the specimens was first performed. The hardness, residual stresses and microstructure gradients were analysed, and the surface of each specimen was scanned using a profilometer. The specimens show complex networks of surface defects introduced during forging, and the shot-blasting process introduces important surface residual stress and microstructure gradients. High cycle fatigue tests in plane bending were then performed on the specimens, with the surface scans helping to identify the critical defect on which crack initiation occurred. The fatigue results, presented in the form of a Kitagawa diagram, are analysed in order to determine which surface integrity parameters are the most influential on fatigue behaviour. The forging defects have an important negative effect on fatigue strength. After shot-blasting, the fatigue strength increases considerably because of the large compressive residual stresses introduced by the shot-blasting process.

Experimental Study of Strain Field Evolution During Milling Process

Strain field of the machined surface acts as one of the most critical surface integrity parameters and it has a great impact on the functional performance of high-end products. In this paper, the strain field evolutions during plain milling process are experimentally studied by digital image correlation technique. The deformations of the workpiece during the plain milling process are filmed by a high-speed camera. The time-varying strain fields of the workpiece including the transition and machined surfaces are determined by correlating the obtained images. Effects of two consecutive teeth with runout on the final strain fields are studied. Strain fluctuations due to the milling tooth approaching and leaving have been successfully captured. Besides, the instantaneous milling forces are measured and synchronized with the strain fields.

Analysis and optimization of cutter geometric parameters for surface integrity in milling titanium alloy using a modified grey–Taguchi method

Surface integrity determines the performance and quality of the end product. It often needs to change the input parameters, such as cutting parameter, cutting tool geometry and material, and tool coating, to obtain the best machining surface integrity. This article presents and demonstrates the effectiveness for the multi-objective optimization of cutter geometric parameters for surface integrity of milling Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy via grey relational analysis coupled with the Taguchi method, entropy weight method, and analytic hierarchy process. The main influence factors are chosen as radial rake angle, primary radial relief angle, and helix angle, while surface roughness and residual stress are taken as performance characteristics. Based on the Taguchi method, an L16 (43) orthogonal array is chosen for the experiments. The effect of cutter geometric parameters on surface roughness and residual stress is analysed by signal-to-noise ratio. Then, the multiple objectives optimization problem is successfully converted to a single-objective optimization of grey relational grade with the grey relational analysis. The weight coefficient for grey relational grade is determined by entropy weight method integrated with analytic hierarchy process. The results show that the order of importance for controllable factor to the milling surface integrity, in sequence, is radial rake angle, primary radial relief angle, and helix angle. The validation experiment verifies that the proposed optimization method has the ability to find out the optimal geometric parameters in terms of milling surface integrity.

Metallurgical Approach Towards Explaining Optimized EDM Process Parameters for Better Surface Integrity of AISI D2 Tool Steel

Many attempts have been made to model and optimize performance parameters of Electrical Discharge Machining (EDM) process. In this investigation, the experimental design includes L9 orthogonal array based on the Taguchi methodology. The corresponding effect of input current, duty cycle and spark on time, on surface integrity, has been studied on AISI D2 tool steel. The residual stress measurement is done using X-ray diffraction method. The obtained output results regarding material removal rate, surface roughness, crack density, and residual stress have been modeled and optimized by regression equation and Genetic algorithm respectively. In this investigation, a metallurgical approach has been introduced towards the explanation of the resulted optimized response parameters.

Hole Making of Inconel 718 Aerospace Alloy

Different surface integrity parameters have become one of the major interest within aero engine components production in the aerospace industry. Hole making process of nickel based super alloy Inconel 718 consists of two machining operations, where drilling is applied to remove stock material and is followed by reaming to meet required quality as well as tolerances of the component prescribed by drawing. In the present work, surface roughness parameters Ra and Rz in terms of machined surface integrity were investigated. Their evaluation was performed with respect to number of machined holes and type of employed cutting tool. The results indicate that use of face-cutting finishers produced holes with lower surface roughness when compared to twist drills. Special attention was paid to ensure that the cutting conditions correspond to the industrial practice. Both cutting tools used in experiments were ground from tungsten carbide.

Inverse surface integrity problem in ultrasonic impact-treated AISI 304 stainless steel components

The inverse problem for surface integrity is still not solved in practice during high-performance component manufacturing, i.e., it is not possible selecting an appropriate process as well as process parameters in advance according to the given surface integrity required for the high performance. The desired surface integrity is usually created by trial and error based on an iterative approach due to lack of quantitative correlations between the loads of a process and the surface integrity variations during manufacturing. The inverse surface integrity problem is studied for manufacturing AISI 304 stainless steel components by employing an ultrasonic impact treatment (UIT) to achieve an enhanced fatigue performance. The correlations are explored between the process loads of mechanical impact, corresponding material loading within the treated component and surface integrity change in the surface layer due to surface modification. Based on experimental and numerical studies, such correlations of UIT process are identified primarily as the quantitative correlation between external mechanical load and material loading of strain and stress, and that between material loading and changes in surface integrity parameters such as residual stress and microhardness due to surface modification. It is demonstrated that a knowledge-based solution of the inverse surface integrity problem is possibly achieved by establishing the correlations to derive process parameters from a given surface integrity for manufacturing of high-performance components.

Grinding of Inconel 713 Superalloy for Gas Turbines

From the viewpoint of residual stresses and microstructure of ground surface, Inconel 713 superalloy is an attractive material since it is frequently used in high temperature gas turbine applications where residual stresses are relevant for service life. The goal of this contribution is to find whether there exists a relation between grinding parameters and final surface integrity parameters such as residual stresses, roughness, crystalitte size, and generally, microstructure. Highly productive creep feed grinding has been applied to produce both simple flat areas and complex fir three blade root. It has been found that the used grinding method lead to very thin deformed layer on the surface with compressive residual stresses and fine crystallites. Moreover, the detailed analyses have been carried out in order to pinpoint plausible reasons behind crack origination.

Interactions between Surface Integrity Parameters on AISI 304 Austenitic Stainless Steel Components by Ultrasonic Impact Treatment

Surface modification processes are enabling a high performance manufacturing by improving surface integrity with controllable surface integrity parameters, particularly for high performance components demanding a combination of functional properties, such as wear, corrosion and/or anti-fatigue properties etc. Ultrasonic impact treatment (UIT) is known as a promising surface modification process for industrial practice to manufacture components with high anti-fatigue performance, on which a compressive residual stress layer can be introduced up to a typical depth of hundreds micrometers. In this study, combined properties of wear and corrosion resistance for AISI 304 austenitic stainless steel components is primarily concerned and achieved by employing an ultrasonic impact treatment process. Surface integrity of UIT processed AISI 304 austenitic stainless steel components can be effectively improved by controlling the surface integrity parameters including surface features and surface characteristics achievable with respect to the desired functional performance. The wear resistance of UIT processed stainless steel components is notably improved, with a corrosion resistance comparable to that of original ones even though austenite-to-martensite phase transformation is observed. The multiple surface integrity parameters of both surface features and surface characteristics simultaneously achieved by the surface modification, exhibiting strong interactions between them, are responsible for the high performance of components with combined properties.

Orthogonal Cutting Simulation of OFHC Copper Using a New Constitutive Model Considering the State of Stress and the Microstructure Effects

This work aims to develop an orthogonal cutting model for surface integrity prediction, which incorporates a new constitutive model of Oxygen Free High Conductivity (OFHC) copper. It accounts for the effects of the state of stress on the flow stress evolution up to fracture. Moreover, since surface integrity parameters are sensitive to the microstructure of the work material, this constitutive model highlights also the recrystallization effects on the flow stress. Orthogonal cutting model is validated using experimental designed cutting tests. More accurate predictions were obtained using this new constitutive model comparing to the classical Johnson-Cook model.

Material Loading in Inverse Surface Integrity Problem Solution of Cemented Carbide Component Manufacturing by Surface Modification

The inverse surface integrity problem could be effectively solved if the generation of a desired surface integrity be quantitatively correlated to process parameters or process loads. Possibility of establishing such a correlation is studied by employing a surface modification technique of high-intensity pulsed ion beam with well controlled thermo-mechanical load to manufacture WC-Ni cemented carbide component with enhanced wear resistance. The multiple surface integrity parameters including phase, microstructure and composition in addition to surface microhardness should be taken into account for establishing the correlation between process loads and surface integrity, since the interactions between the surface integrity parameters determine the wear performance of surface modified cemented carbides. The different process parameters can be quantitatively distinguished by material loading, i.e. the temperature and/or stress field evolution in the surface layer of cemented carbide under the different thermo-mechanical loads, while the material loading can be further correlated to the resultant changes in surface integrity. In this way, identification of material loading enables establishing a process-independent correlation between process loads and surface integrity for solving the inverse surface integrity problem.

Significance of surface integrity on high-performance manufacturing by surface modification

It has been proved that surface integrity involving numerous surface integrity parameters has a profound influence on component performance. However, it is still difficult to achieve a high performance of combined functional properties since the surface integrity of the high-performance component is frequently limited by merely using material removal manufacturing. In this work, surface modification is alternatively employed to explore influence of various surface integrity parameters in a controllable way on achieving the high-performance manufacturing of components with combined properties including anti-fatigue performance and corrosion resistance, thermal insulating and oxidation resistance, temperature sensing and wear resistance, otherwise unattainable in conventional material removal manufacturing. Three typical surface modification techniques principally based on a series of processing loads, such as thermochemical load from plasma-based low-energy ion implantation, thermomechanical load from ion beam shock processing by high-intensity pulsed ion beam irradiation, and chemical load from non-aqueous sol-gel thin film deposition respectively, were selected for generating a new surface layer on base materials of components toward an improved surface integrity with desired multiple surface integrity parameters. In all cases, two categories of surface integrity parameters are identified in relation to the functional properties of components, i.e., surface features and surface characteristics, where the former include the features of topography and chemical composition, grain morphology, and phase structure, etc. on surface and subsurface directly created by the surface modification, and the latter include all the physical and chemical properties associated with the new surface layer, such as microhardness, residual stress, electrical potential, optical properties, etc. The surface features and surface characteristics in surface integrity present a synergetic effect on the high performance with combined properties as a result of coupled interactions between the surface integrity parameters. Therefore, the multiple surface integrity parameters controllable with active interactions achieved by surface modification processes effectively improve the surface integrity according to the desired high-performance component of combined properties, enabling a high-performance manufacturing.

Statistical characteristics of surface integrity by fiber laser cutting of Nitinol vascular stents

Nitinol alloys have been widely used in manufacturing of vascular stents due to the outstanding properties such as superelasticity, shape memory, and superior biocompatibility. Laser cutting is the dominant process for manufacturing Nitinol stents. Conventional laser cutting usually produces unsatisfactory surface integrity which has a significant detrimental impact on stent performance. Emerging as a competitive process, fiber laser with high beam quality is expected to produce much less thermal damage such as striation, dross, heat affected zone (HAZ), and recast layer. To understand the process capability of fiber laser cutting of Nitinol alloy, a design-of-experiment based laser cutting experiment was performed. The kerf geometry, roughness, topography, microstructure, and hardness were studied to better understand the nature of the HAZ and recast layer in fiber laser cutting. Moreover, effect size analysis was conducted to investigate the relationship between surface integrity and process parameters.

Surface Morphology of Duplex Stainless Steel (DSS) in Dry Turning Process

Sustainable manufacturing in most developed countries is one of principal goals in today manufacturing industry. The reduction in use of oil-based CLFs is most ecologically important task of machining processes. The paper presents the contribution in engineering of surfaces particularly in surface morphology of Stainless Steels. The objective of the investigation was to determine the surface texture of duplex stainless steel after turning with coated carbide tool point. The investigation included geometrical parameters of Surface Integrity for different cutting parameters in dry turning process of duplex stainless steel.

Influence of Technological Cutting Parameters on Surface Texture of Austenitic Stainless Steel

The paper presents the contribution in engineering of surfaces particularly in surface texture of Austenitic Stainless Steels. The objective of the investigation was to determine the surface texture of austenitic stainless steel after turning with coated carbide tool point. The investigation included geometrical parameters of Surface Integrity for different technological cutting parameters in dry turning process of austenitic stainless steel. The article presents the surface roughness parameters with the roughness profiles (irregular slopes). The percentage of isotropic surfaces and Bearing Area of ​​Primary Model. Analyses were performed for variable cutting parameters. An Infinite Focus Measurement Machine (IFM) was used for the surface texture analysis. The study was performed within a production facility during the machining of electric motor parts and deep-well pumps.

Analysis and Prediction of Surface Integrity in Machining: A Review

Surface integrity is widely used for evaluating the quality of machined components. It has a set of various parameters which can be grouped as: (a) topography parameters such as surface roughness, textures and waviness (b) mechanical parameters such as residual stresses and hardness, and (c) metallurgical state such as microstructure, phase transformation, grain size and shape, inclusions etc. Surface roughness and residual stresses are among the most significant parameters of surface integrity, so that it is worth investigating them particularly. Many factors affect the surface integrity of machined components, including cutting parameters, tool parameters, material properties and vibrations. We can make prediction and optimization for surface integrity by taking advantage of these factors. This paper reviews previous studies and gives a comprehensive summary of surface integrity in the following order: introduction of surface integrity, main parameters of surface integrity, factors affecting surface integrity, prediction and optimization for surface integrity.