Initial Wear Stage Research Articles

The wear detection of mill-grinding tool based on acoustic emission sensor

The monitoring of tool wear plays an important role in improving the processing efficiency and reducing the production cost of enterprises. This paper is focused on the detection of electroplated diamond mill-grinding tools by using the acoustic emission sensor. The wear stages of mill-grinding tools are divided into three parts, namely initial wear stage, normal wear stage, and severe wear stage. The characteristic parameter method and the waveform analysis method are applied to analyze the acoustic emission signals. The wear characteristics of the tool and workpiece in different wear stages are observed and analyzed. The results indicate that the acoustic emission waveform is relatively stable in the initial wear stage, and the continuous acoustic emission signal is dominated. Moreover, the diamond abrasive grains are mainly worn and slightly broken in the normal wear stage, and there are some pits on the machined workpiece surface after the initial wear stage. In the severe wear stage, most of the abrasive grains are broken or broken in a large area, and there are burst acoustic emission signals in the waveform.

Tool wear prediction method based on symmetrized dot pattern and multi-covariance Gaussian process regression

Cutting tool plays a critical role in modern manufacturing system and tool wear prediction has a great effect on product cost and quality. Many efforts have been devoted to developing tool wear prediction models. The previous studies mainly focus on utilizing a single model during the whole prediction process named global model and thus ignore the local characteristics of different wear stages. However, paying no attention to the impact of wear stage division may lead to mismatch the distribution characteristics of datasets and overlapping of feature information, failing to get the desired accuracy. To achieve more accurate prediction results, this paper proposes a wear stage division-based tool wear prediction method (WSDTWP) based on the improved symmetrized dot pattern (ISDP) and multi-covariance Gaussian process regression (MCGPR). Firstly, according to the varying trend of tool wear value, tool wear process is divided into three stages, including initial wear stage, moderate wear stage and severe wear stage. Then, SDP technique reconstructs the original signals visually and the main SDP parameters are adaptively selected by developing an evaluation model. Further, to deal with the issue of high-dimension and small-size datasets in initial and severe wear stages, MCGPR is developed and hyperparameters are optimized by particle swarm optimization for accurately predicting tool wear. According to the varying prediction requirements, different approaches are assigned into different wear stages to achieve better performance. Finally, three cutting tests are conducted to validate the effectiveness of the proposed approach. The experimental results indicate that WSDTWP is more accurate than existing methods, which provides new theoretical and practical support for identifying tool working condition and predicting tool wear.

Investigations of the effects of combination treatments on the fretting fatigue resistance of GH4169 superalloy at an elevated temperature

In this work, a novel combination treatment was investigated as a means to improve the rotating bending fretting fatigue resistance of GH4169 superalloy at 650 °C. The properties, morphologies and composition were studied for magnetron-sputtered WS2/Ti films on substrates with and without a shot peening pre-treatment. The surface integrity and fretting fatigue performances at 650 °C were tested and compared for untreated, shot peened and combinedly treated specimens. The experimental results evidenced the significant role of shot peening pre-treatment in the adhesion behavior of oxidized films at elevated temperature. Furthermore, shot peening and magnetron sputtering were expected to have a synergistic effect to improve fretting fatigue resistance at elevated temperature. According to the surface integrity characterization and fretting fatigue tests, the surface hardened layer and the compressive residual stress fields induced by shot peening improved the fretting fatigue limit by 29%, and the average life was 12.4 times as that of the untreated specimens when the fatigue load was 600 MPa. The positive effect was attributed to the resistance properties during the initial adhesive wear stage, reduction of crack initiation and propagation and probable formation of a third body layer. Moreover, the films further increased the fretting fatigue life by 1.6 times compared with that of the shot peened specimens. The effectiveness of shot peening was retained, and the additional lubrication effect facilitated a more stable third body layer, which resulted in a longer fretting fatigue life.

Surface integrity and wear evolution of high strength aluminum alloy after high-speed oblique cutting

In this paper, we present an experimental study on the surface frictional wear mechanism of the high-strength aluminum alloy after high-speed milling. We use a surface profilometer and an X-ray stress tester to characterize the milled surface integrity of the material, and UMT-3 friction testing machine to obtain its surface roughness, oxygen content, hardness, and wear morphology during different wear stages. The results show that milling-induced residual tensile stress makes the cut surface more prone to fatigue cracking and consequently abrasive wear in the initial wear stage. The larger the angle between the friction pair movement direction, the greater the chance of adhesive wear and abrasive wear. A complete friction stage pattern can be obtained at a high load (15 N) and a low sliding speed (0.6 mm/s). The friction pair enters a stable wear stage after 20 sliding cycles. Work hardening constitutes the main driver of stable wear.

Sawing characteristics of diamond wire cutting sapphire crystal based on tool life cycle

Diamond wire saw cutting technology has been widely used in the slicing of sapphire crystal. The ultra-high hardness of sapphire makes the sawing characteristics of diamond saw wire constantly change. At present, there is a lack of in-depth understanding about the influence of sawing characteristics on the quality of sapphire as-sawn wafer, which leads to the unreasonable matching between the process parameters and the sawing characteristics of the saw wire, and reduces the as-sawn wafer quality and the saw wire life. In this paper, the slicing sapphire crystal experiment was carried out with constant process parameters and the variation of saw wire bow angle, nominal diameter and saw kerf loss, surface morphology and surface roughness of the as-sawn wafer during the whole life cycle of the saw wire from initial cutting to breakage was studied. The evolution mechanism of wear and sawing characteristics in the whole life cycle of saw wire was explored, and a reasonable processing scheme which can match the sawing characteristics was put forward. The research results show that in the whole life cycle of the saw wire, the abrasives emerge from the plating layer in turn, then the cutting edge are blunted, and finally the abrasives are greatly flattened and a small amount of falling off. Saw wire has experienced initial wear, stable wear and sever wear, and the proportion of three stages in the whole life cycle is about 0.3: 0.6: 0.1. Compared with the initial stage of wear and the late stage of rapid wear, the saw wire has higher sawing characteristics and better as-sawn wafer quality in the middle stable wear period. The sawing characteristics of new saw wire is relatively weak at the beginning of cutting, so the feed speed of workpiece should be increased gradually from low to high; When most of the abrasives finish sharpening edge, a relatively stable and high feed speed can be adopted; When the abrasives are obviously flattened or fall off, the feed speed should be decreased to accommodate the significantly reduced. cutting performance of diamond saw wire.

Modelling of floorpan wear in passenger vehicles using artificial neural networks

This paper analysed modelling damage to floorpan structures (a part of a passenger vehicle's body) using artificial neural networks (ANN). Critical obstacles in the process of elaborating a precise method of floorpan wear forecasting include the large number of measurement points required, the need to take into consideration the operating conditions and the measurement accuracy during data collection that is widely accepted by manufacturers. During the study, a preliminary analysis of the collected data was conducted for distances between floorpan reference points, using two-dimensional self-organising maps (SOM), which reduced the size of the analysed parameter space and usage for analysis of the Euclidean distance comparison between network nodes. Using a double-layer network, the characteristics of floorpan wear in mileage function were then obtained. Individual and generalised qualities were taken into consideration from the safety point of view. An analysis of the influence of network parameters on the emergence of regression dependence was also conducted. The obtained results confirmed the hypothesis that it is possible to highlight an initial stage of floorpan wear, a stabilised period of wear and a stage characterised by a rapid increase in the distances between reference points.

Sliding wear behavior of cold-sprayed Ni-WC composite coatings: Influence OF WC content

Metal Matrix Composites reinforced with WC particles and Co or Ni as matrices are well-known for their unique combination of hardness, toughness, and thus superior wear performance. Previous studies showed that the structure of the coating including carbide size and content, and morphology as well as matrix/binder microstructure must be carefully tailored to achieve desirable wear properties. In this study, Ni–WCNi composite coatings were deposited using the cold spray. Agglomerated WCNi powders and spherical Ni powders were used as feedstock materials. It was found that Ni–WCNi coatings can be tailored to contain 13-54 vol% WC and display a varied hardness ranging between 225 and 550 HV1. A higher concentration of WC in initial feedstock led to more compaction of WCNi particles in coatings, the lower mean free path between WC particles, and harder coatings. The sliding wear behavior of coatings was studied with a sliding speed of 3 mm/s under normal loads of 5 and 12 N. Coatings with higher WC fill ratios were found to be more wear-resistant than coatings with less or no WC. This is related to the uniform distribution of WC particles with the lower mean free path that minimized adhesive wear at the initial stages of wear and helped to develop a higher coverage of protective mechanically mixed layers. However, the protective role of mechanically mixed layers was reduced at higher load, caused by subsurface crack propagation at WC particle interfaces, and was related to strain accumulation in highly compacted WC coatings. A qualitative comparison of coating cohesion strengths was performed using scratch tests on the polished cross-section of coatings and correlated to wear properties.

Grain wear evolution of cubic boron nitride abrasives during single grain grinding of powder metallurgy superalloy FGH96

The grain wear evolution during grinding powder metallurgy superalloy FGH96 using a single abrasive grain of cubic boron nitride (CBN) under different undeformed chip thickness and abrasive wheel speed was investigated. The wear behavior of single abrasive grain (SAG) was extracted based on the variation feature of grinding force, radial wear, grain topography and material remove characteristics. Meanwhile, acoustic emission (AE) testing is used to analyze the grain wear evolution. The results show that micro fracture firstly occurs at the original defects of SAG at the initial wear stage. Attrition wear and micro fracture are responsible for the steady wear stage, while micro and macro fracture are dominant at severe wear stage. Besides, the manner of the plastic adiabatic shear remove occurs in the process of grinding FGH96. Furthermore, sudden increase of root mean square (RMS) of AE signal can be applied to reflect the fracture of SAG, whereas the continuously gradual decrease can be considered the attrition wear or material adhesion, which can provide a technical support for monitoring the grain wear during grinding.

Addition of Si3N4 Strengthens SiC Coatings via Heat Treatment with Nitrogen Gas onto Carbon/Carbon Composites

We report the synthesis of SiC/Si3N4 coatings on carbon/carbon composites via pack cementation and heat treatment with nitrogen gas, the latter of which improves the coating wear resistance. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) are used to analyse the microstructure, surface morphology, chemical states and elemental distribution, respectively, of SiC and SiC/Si3N4 coatings. In addition, we analyse the tribological behaviour of the SiC and SiC/Si3N4 coatings and the related microstructure and wear mechanisms. The results show that SiC/Si3N4 coatings are compact and contain the three phases: Si3N4, SiC and C. Additionally, specimens with the SiC/Si3N4 coating have smaller, more stable friction coefficients and less weight loss than specimens with only the SiC coating. Adhesive wear and abrasive wear are the main wear mechanisms contributing to the higher friction coefficient of the SiC coating. Furthermore, with the SiC/Si3N4 coating, adhesive wear is the main wear mechanism causing a high friction coefficient at the initial stage of frictional wear. In the subsequent stages of frictional wear, the graphite in the SiC/Si3N4 coating generates a thin lubricating film that decreases the friction coefficient.

Cutting performance and wear mechanisms of TiAlN PVD-coated cemented carbide tool in high speed turning of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy

The high-speed finish turning tests of Ti-17 titanium alloy (Ti-5Al-2Sn-2Zr-4Mo-4Cr) were carried out by using PVD cemented carbide tools with TiAlN coating. The machinability behaviors in terms of cutting forces, cutting temperatures, surface roughness, and tool service life were measured and evaluated under different machining parameter conditions, and the empirical prediction model of these variables were established depending on the cutting parameters. Incorporating the measured results of scanning electron microscopy (SEM) as well as energy dispersive spectroscopy (EDS), the initial tool wear patterns and the eventual wear patterns when the tool wear states meet the failure criteria were comparably investigated and analyzed. It was found that during the initial wear stage, the sticking wear zone and the sliding wear zone can be distinguished on the tool wear interface. The main wear patterns of are peeling off of coating material, crater wear of rake face, edge breakage and edge wear of tool tip after reaching the tool failure rejection criterion. The cutting tool wear mechanisms were systematically studied, and the results show that the wear mechanisms of a TiAlN PVD-coated carbide cutting tool in turning Ti-17 titanium alloy were dominated by the interaction wear effect among the adhesion, oxidation and diffusion between cemented carbide substrate and workpiece material.

On the commensuration of plastic plowing at the microscale

Improving the wear properties requires an understanding of the mechanisms during the initial stages of wear. This paper focuses on the transition from static indentation to dynamic wear, i.e. the evolution from stationary to sliding contact. By using single micrometer-sized roughness peaks on copper, cementite and austenitic steel, we observe that the conservation of contact area, elastic recovery, and the front pile-up development are the dominant mechanisms. The elastic recovery leads to an additional contact area at the backside of the asperity. The influence of the crystallographic orientation was found to be negligible during the initial increase in wear depth but significant during the later stages. Moreover, the partial wear depth recovery is observed only in ductile materials.

Influences of coating thickness on cutting temperature for dry hard turning Inconel 718 with PVD TiAlN coated carbide tools in initial tool wear stage

Abstract High cutting temperatures are induced in the dry cutting process of Inconel 718 for its high hardness 439 HBW and low thermal conductivity 13.4 W/(m K). Due to its thermal barrier effect and antifriction effect, the TiAlN coatings have been deposited on carbide tools with various coating thicknesses for dry turning Inconel 718. However, the influences of TiAlN coating thickness on cutting temperature of dry turning Inconel 718 were not investigated in details. In this research, PVD TiAlN tools with coating thickness 1 μm and 2 μm were fabricated and characterized. The cutting temperatures and cutting forces of dry turning Inconel 718 were measured within cutting speed ranges 30−120 m/min. Average friction coefficient at coated tool-chip interface was calculated to analyze the coating antifriction effect. Thicker coating induced large temperature increment of 19−30 °C compared with thinner coating within cutting speed ranges of 30−120 m/min in initial tool wear stage. The results showed that PVD TiAlN coated tool with coating thickness 1 μm was more suitable for dry turning Inconel 718 within cutting speed ranges 90−120 m/min by obtaining better coating antifriction effect and lower cutting temperature.

The self-lubricating behavior and evolution mechanisms of the surface microporous friction interface of M50-(Sn-Ag-Cu) material

The friction interface structure has an important influence on the friction behavior of self-lubricating materials. In this paper, M50 material covered with surface micropores filled with Sn-Ag-Cu (MM-Salloy) was prepared by laser melt deposition. From 25–450 °C, the friction test results show that MM-Salloy exhibits distinguished tribological properties due to the existence of the microporous friction interface. Analysis indicates that Sn-Ag-Cu in surface micropores can dynamically precipitates to the worn surface of MM-Salloy to achieve a lubricating effect, and the increasing of temperature is beneficial to the dynamic precipitation of Sn-Ag-Cu. The whole friction process can be divided into the initial wear stage, fast wear stage and stable wear stage. At stable wear stage, the friction interface is mainly composed of a lubricant-rich surface lubrication layer and a subsurface load-bearing layer, which greatly improves the material's wear resistance. Especially at 350 °C, the surface lubrication layer and subsurface load-bearing layer are most easily formed.

Microstructure, Tribological Behavior, and Strengthening Mechanisms of the Friction Interface Layer with Nanocrystalline Structure of Ni3Al Matrix Self-lubricating Composites

This work investigated the microstructure, tribological behavior and strengthening mechanisms of friction interface layer with nanocrystalline structure of graphene-reinforced Ni3Al matrix composites (GNMCs) synthesized using laser melting deposition. A dislocation density-based model was selected to analyze the mechanisms of the improvement in the wear resistance of the friction interface layer from initial wear stage to stable wear stage. Results show that GNMCs exhibit excellent antifriction and wear resistance in the stable wear stage due to the formation of friction interface layer with nanocrystalline structure. Grain boundary strengthening is the predominant strengthening mechanism of friction interface layer of GNMCs. Dislocations are blocked at grain boundaries to form complex dislocation barriers, further contributing to the high strength and wear resistance. The dislocation density-based model can be successfully used to predict the mechanical response of the friction interface layer subjected to the grain refinement during sliding friction process.

Analysis of the initial stage of fatigue wear in heterostructure materials under contact cyclic loading

Introduction. The process of formation of fatigue defects in metal alloys with different structural morphology is considered. The work objective is to develop a computational tool for determining the moment of the defect nucleation under cyclic loading.Materials and Methods. A physical model is built, calculation expressions are presented. The physical model is based on the theory of dislocations. It is shown that a structure factor is particularly important in the process of fracture nucleus origination under dynamic cyclic loading. Depending on the structure and properties of the material, as well as on the nature of the loads, the critical fatigue defect develops in the form of cracks, pores or micro-crater wear.Research Results. A numerical experiment was performed to determine the moment of nucleation of the critical-size defect in iron-base alloys under the drop hypervelocity impacts. Comparative data of calculations and bench tests for droplet impingement erosion of steels and alloys with the structure of ferrite, austenite, sorbitol and martensite are presented. The efficiency of the nucleation stage during the incubation period of erosive wear of the materials studied was evaluated.Discussion and Conclusions. There are no strict instrumental methods for determining the duration of the nucleation stage; therefore, it is recommended to use the proposed analytical model. In addition, the work performed gave a significant application result, i.e. it showed that the focused design of the material structure can significantly increase the wear resistance.

Study on the cutting performance in machining assembled hardened steel workpiece with torus cutter

Torus cutters are increasingly used in machining high-hardness materials because of high processing efficiency. However, due to the large hardness variation in assembled hardened steel workpiece, the tool wear occurs easily in machining process. This severely affects the machined surface quality. Here, we conduct a research on the tool wear and the machined surface quality in milling assembled hardened steel mold with a torus cutter. The experimental results show the abrasive wear mechanism dominates the initial tool wear stage of the torus cutter. As the tool wear intensifies, the adhesive wear gradually occurs due to the effect of alternating stress and impact load. Thus, the mixing effect of the abrasive and adhesive wears further accelerates tool wear, resulting in occurrence of obvious crater wear band on the rake face and coating tearing area on the flank face. Finally, the cutter is damaged by the fatigue wear mechanism, reducing seriously the cutting performance. With increase of flank wear, moreover, there are increasingly obvious differences in both the surface morphology and the cutting force at the two sides of the joint seam of the assembled hardened steel parts, including larger height difference at the two sides of the joint seam and sudden change of cutting force, as a result, leading to decreasing cutting stability and deteriorating seriously machined surface quality.

Necessity of multidimensional evaluation of the high-speed ball-end milled surface of hardened AISI D2 steel from a wear resistance perspective

This paper focuses on revealing the anisotropy of surface integrity and wear resistance of high-speed ball-end milled surfaces of hardened cold work die steel AISI D2. Dry milling tests were performed on a five-axis high-speed machining center by using a two-edged coated solid carbide ball-end milling cutter. Then, wear resistance of a hard milled surface was evaluated through block-on-ring wear tests under unlubricated condition. Results showed that ball-end milled surfaces present anisotropic characteristics in terms of surface topography, subsurface microhardness, and yield strength. Moreover, the wear resistance for ball-end milled surfaces shows dependence on sliding direction because of the anisotropy of surface integrity. Benefiting from surface work hardening, wear loss for the hard milled surface was at least 62% less than that for polished ones in the initial wear stage (10 min). However, the subsurface softening zone induced by a high-speed hard milling process has poor wear resistance due to the decrease of microhardness and yield strength. This study indicates the necessity of multidimensional evaluation for high-speed ball-end milled surfaces and the possibility of improving wear behavior by selecting appropriate sliding direction.

Coupling transient mixed lubrication and wear for journal bearing modeling

Abstract A transient Mixed Lubrication-Wear coupling model (MLW coupling model) is developed to investigate the mixed lubrication and wear performances of journal bearings, and a wear experiment for journal bearing is performed to support the validity of the developed numerical model. In the coupling numerical model, the transient interaction between the behaviour of mixed lubrication and wear is considered by incorporating the wear depth distribution, which is determined by the developed friction fatigue wear model, into the film gap equation. The evolutions of the worn surface profile, wear rate, fluid pressure and asperity contact pressure over operating time are calculated by the developed numerical model. The simulated results demonstrate that the transient wear process affects the distribution trend of lubrication performances significantly, and a worn surface profile may exist that provides an optimal tribology performance of journal bearings. The simulated results also demonstrate that there are two wear stages, identified by initial and steady wear stage, of journal bearings under mixed lubrication condition. Furthermore, the effects of the input parameters, including the radius clearance(C), surface roughness (σ), asperity curvature radius (β) and boundary friction coefficient(μc), on the predicted mixed lubrication and wear performance are evaluated.

Analysis of tool wear performance and surface quality in post milling of additive manufactured 316L stainless steel

Laser additive manufacturing (LAM) technology applied to the 316L stainless steel is attracting interest in the machining industry since it can shorten the production cycle and reduce numbers of machining steps. It still needs to be machined because of the poor surface quality, so the tool wear of post milling process after LAM needs to be studied. However, there are a few studies about the tool wear in milling of laser additive manufacturing stainless steel alloy. The aim of the paper is to evaluate the tool wear performance and surface quality when post milling the 316L stainless steel under different post milling (PM) time. The tool wear behavior was investigated using different analysis techniques. 3-D surface contour profilometer was used to measure the surface roughness and observe the morphology of small area; digital optical ultra-depth microscope analysis was carried out to evaluate tool wear and broken; the wear width of the blade was an indicator of the degree of the tool wear; different post milling methods were also compared. The obtained results demonstrate that the height of the LAM parts were connected with the heat dissipation effect; there are three stages of tool wear: initial wear stage, normal processing stage, and severe broken stage; usually the down-milling is better than up-milling at the bottom surface roughness, quality and edge morphology.

Evaluation of tooth wear by estimating enamel thickness with quantitative light-induced fluorescence technology.

Various techniques have been suggested to quantitatively assess tooth wear; most have limited clinical application. The first aim of this in vitro study was to estimate the residual enamel thickness of teeth with various degrees of occlusal wear using quantitative light-induced fluorescence (QLF). The second aim was to identify relationships between the fluorescence parameters of QLF and the conventional tooth wear index (TWI) system. Sixty-nine extracted permanent premolars and molars with initial stages of tooth wear (TWI score 1a-2: enamel wear to dentin exposure) were used. Two blinded and trained examiners participated in evaluation procedures. Occlusal QLF-digital (QLF-D) images were acquired for selecting area of interest (AOI) and calculating fluorescence for occlusal tooth wear (ΔFwear) of the AOI by the first examiner. Each specimen was cross-sectioned in the buccal-lingual direction. Enamel thickness from images obtained by stereomicroscopy and TWI of each sample was determined by the second examiner. Spearman correlation was used to determine the relationship of ΔFwear with enamel thickness and TWI. ΔFwear values were compared between histological scores with the Mann-Whitney U test. Seventy-six AOIs were analyzed. As enamel thickness decreased, ΔFwear values significantly increased and strongly correlated with enamel thickness (Spearman rho = -0.825, P < 0.001). There were significant differences in ΔFwear values among TWI scores (P < 0.001); ΔFwear strongly correlated with TWI (Spearman rho = 0.753, P < 0.001). ΔFwear values, which denote fluorescence difference by using QLF, showed a strong correlation with residual enamel thickness and tooth wear severity.