Simulation of textured surface topography during a low wear process

Wear experiments were conducted on a block-on ring tester. The stationary block made from cast iron of 50 HRC hardness was ground. The rotated ground ring was made from 42CrMo4 steel of 32 HRC hardness. The rings were modified by a burnishing technique in order to obtain surfaces with oil pockets. Oil pockets of spherical and of drop shape were tested. The correlation and regression analysis of parameters of textured surface topography was carried out. Two sets of surfaces were analysed: after machining and after “zero-wear”. As the result of analysis, minimum number of parameters describing this surface kind was obtained. A simple truncation model of the ring surface change was used. Worn surface topographies, after a low wear, were also modeled in a different way. An idea of the proposed method of surface topography modeling is imposition of random surface of Gaussian ordinate distribution on the base surface (after burnishing). The modeled surfaces were correctly matched to the measured surfaces in 90% of all analysed cases. Basing on the simulation, the local wear values during a low wear process were calculated and compared with experimental ones.     

The significance of near surface microstructure in the wear process

The wear process in which flake-like debris is developed and removed from the surface of metals in sliding contact is the direct result of heavy plastic deformation of a thin surface layer. The repeated ploughing of asperity contacts over a mating surface can produce high dislocation densities and eventual change in the microstructure to a cell-type structure found in heavily deformed metals. Cell sizes depend on material characteristics such as stacking fault energy, the applied stress and the temperature. It is shown that a cell structure can present many suitable pathways for subsurface crack generation and the release of thin wear flakes without the benefit of asperity cold welding and shear. Depth of crack formation and severity of wear can be associated with stacking fault energy. Changes in the microstructure caused by frictional heating or change in strain rate can cause abrupt changes in wear mode.     

Simulating cam and follower wear in valve train

ABSTRACT

The paper aims to predict the cam and follower wear in direct acting valve train considering the effects of operating conditions. A numerical approach has been developed using frictional and lubrication analysis which is applied in the cam/follower wear study. Loading and motion parameters have been determined from dynamic and kinematic analysis whereas the wear profiles are obtained by linear wear relation. The wear of cam/follower is largely dependent on the lubrication film thickness, normal loading/contact pressure and sliding velocity. At low camshaft speeds, the wear depth of cam/follower pair is higher whereas it decreases at higher speeds due to relatively thicker oil film. It is an original research work and is strongly believed that it would help to further improve the performance of engine valve train and would also provide an opportunity to control the operating conditions promoting wear.     

The delamination theory of wear and the wear of a composite surface

The delamination theory of wear postulates that there is a “nonworkhardening” soft surface layer which deforms continuously due to the instability of dislocations, and that the low speed sliding wear of metals is caused by the subsurface crack nucleation and propagation nearly parallel to the surface. A corollary of the theory is that when hard metal surfaces are plated with a soft metal to reduce the coefficient of friction and the wear rate, the soft metal layer must be thinner than a critical thickness so as to prevent the accumulation of dislocations in the plated layer and the formation of the delaminated layer. This corollary was investigated by plating annealed AISI 1018 steel with cadmium. The wear rate of the steel specimen plated with 0.1 μm cadmium on both of the contacting surfaces was three orders of magnitude smaller than the unplated specimen when they were tested in argon. In the case of thicker coatings, the cadmium layer wears by the delamination process which occurs within the plated layer. The very thin cadmium plate is also effective in reducing wear in inert oil, but not effective in an oxidizing atmosphere. The coefficient of friction of the 0.1 μm Cd plated steel was less than the unplated steel under all test conditions.     

Modeling and predicting for surface topography considering tool wear in milling process

This paper presents a model for the prediction of surface topography considering tool wear during the milling process. First, the cutting edge path equation, which can be transformed into equivalent polynomial equations and solved for discrete positions along the feed direction, is established including the effect of tool wear. Then, cutting edge is divided into a series of cutting points and an algorithm is proposed to determine the range of divided position angle. Finally, surface topography model is established based on the established cutting path equation, the range of position angle, the calculated cutting time, and spiral lag angle. By using this model, surface topography generation is simplified with respect to other models in literature and the modeling method of surface topography does not need to mesh the workpiece and the model can easily be extended to include other factors on surface generation. Based on the established surface topography model, an algorithm is proposed to simulate generation of surface profile in milling operation. Experimental work and validation of the established model is performed on a five-axis milling center by using stainless steel 1Cr18Ni9Ti and cemented carbides milling cutter. Cutting test results about the topography generation of the plane and cylindrical surface show good agreement with model predictions.     

Simulating sliding wear with finite element method

Wear of components is often a critical factor influencing the product service life. Wear prediction is therefore an important part of engineering. The wear simulation approach with commercial finite element (FE) software ANSYS is presented in this paper. A modelling and simulation procedure is proposed and used with the linear wear law and the Euler integration scheme. Good care, however, must be taken to assure model validity and numerical solution convergence. A spherical pin-on-disc unlubricated steel contact was analysed both experimentally and with FEM, and the Lim and Ashby wear map was used to identify the wear mechanism. It was shown that the FEA wear simulation results of a given geometry and loading can be treated on the basis of wear coefficient−sliding distance change equivalence. The finite element software ANSYS is well suited for the solving of contact problems as well as the wear simulation. The actual scatter of the wear coefficient being within the limits of ±40–60% led to considerable deviation of wear simulation results. These results must therefore be evaluated on a relative scale to compare different design options.     

Development of a laser surface melting process for improvement of the wear resistance of gray cast iron

A new laser heat treatment, involving the heating of the metal surface above its melting point, was developed on gray cast iron. Microstructural analysis performed by transmission electron microscopy of remelted layers showed several types of structures depending on the cooling rate of the workpiece.Laboratory wear tests were carried out on a pin-on-ring machine simulating the cam-and-tappet system to evaluate the tribological properties of the laser-remelted layers. Results were similar to those obtained in an induction-hardened nodular cast iron conventionally used for automotive applications.Melted layers 0.5–0.7 mm thick with a hardness above 50 HRC were obtained on an automotive camshaft.     

The dependence of tool overhang on surface quality and tool wear in the turning process

In the turning process, the importance of machining parameter choice is increased, as it controls the surface quality required. Tool overhang is a cutting tool parameter that has not been investigated in as much detail as some of the better known ones. It is appropriate to keep the tool overhang as short as possible; however, a longer tool overhang may be required depending on the geometry of the workpiece and when using the hole-turning process in particular. In this study, we investigate the effects of changes in the tool overhang in the external turning process on both the surface quality of the workpiece and tool wear. For this purpose, we used workpieces of AISI 1050 material with diameters of 20, 30, and 40 mm; and the surface roughness of the workpiece and tool wear were determined through experiments using constant cutting speed and feed rates with different depth of cuts (DOCs) and tool overhangs. We observed that the effect of the DOC on the surface roughness is negligible, but tool overhang is more important. The deflection of the cutting tool increases with tool overhang. Two different analytical methods were compared to determine the dependence of tool deflection on the tool overhang. Also, the real tool deflection values were determined using a comparator. We observed that the tool deflection values were quite compatible with the tool deflection results obtained using the second analytical method.     

A study on wear and worn surfaces of grey cast iron affected by a novel silicate additive

A novel aluminium silicate hydroxide additive has shown excellent anti‐wear effect in practical applications and has been mainly studied on steels in laboratory conditions. In this paper, the pin‐on‐disk sliding wear tests were carried out to investigate the wear and worn surfaces of grey cast iron with additives in different concentration. It was found that the silicate additive showed an obvious anti‐wear effect and a reliable duration, reduced the number of pits and cracks on the worn surfaces and improved the nanohardness of the worn surfaces of grey cast iron disks by 72%. Furthermore, Raman spectroscopy displayed that the carbon structure of the worn surface of grey cast iron disks with the additive had an obvious transformation from nanocrystalline graphite to amorphous carbon. Copyright © 2015 John Wiley & Sons, Ltd.     

Fine friction cutting: a useful wear process

Friction cutting of metals was first reported almost 160 years ago. This review concentrates on its latest development, the slitting of nickel-chromium, titanium and ferrous alloys by toothless, water-cooled, mild steel discs spinning with a rim speed between 50 and 100 ms⁻¹. Slits an thin an 0.25 mm can be produced with little surface damage.Slitting occurs by adhesive wear. When oxidation leading to a mild wear state can be prevented, area slitting rates greater than 10 mm² s⁻¹ can be achieved: this is the case with nickel-chromium and titanium alloys and with soft or hardened stainless and tool steels. Oxidation cannot be prevented with carbon steels and most cast irons, so these metals cannot in general be slit usefully by fine friction cutting     

Effect of the worn status of wheel/rail profiles on wheel wear over curved tracks

Journal of Mechanical Science and Technology - The worn status of wheel/rail profiles could change the wheel-rail contact and influence the wear rates of the wheel and rail. Worn wheel profiles of...     

Contact of surface asperities in wear

Stresses have been examined under the elliptical Hertzian contact area, which appear during a real contact between two asperities in the process of sliding friction. The stresses are found according to the Mises-Hencky criterion and characterize the ability of the material to change its shape. Relationships have been found of such a maximum stress under the surface of the contact area depending on the geometric parameters of the contact area, on the friction coefficient and the maximum pressure in the centre of contact area. The processing of the calculation data was conducted according to a special program on a computer and yielded an approximate relationship to calculate the maximum reduced stress. The distribution of dangerous stresses under the contact surface has been shown. The most critical points may be both within the surface layer of the material and on the contact area itself.     

Shape of a worn slider

A slider can be expected to wear in due time to a shape that gives a uniform contact pressure and consequently uniform friction stress. Computation of the worn shape is discussed using the theory of elasticity. The results show that the trailing edge may be worn down more than the leading edge. The worn shape at a sharp corner may be either convex or concave depending on the elastic constants, the friction coefficient and the corner angle.     

High resolution observations of friction-induced oxide and its interaction with the worn surface

A detailed transmission electron microscopy study of oxide and oxygen-containing phase formation during the sliding wear of metals, composites and coatings is provided. A wide range of different materials types are reported in order to compare and contrast their oxidational wear behaviour: a low carbon stainless steel, a H21 tool steel containing 7%TiC particles, a 17%Cr white iron, an Al–Si/30%SiC composite, an Al–alloy (6092)–15%Ni₃Al composite and finally a 3rd generation TiAlN/CrN ‘superhard’ multilayer coating. For the ferrous alloys, nanoscale oxides and oxygen-containing phases were formed that exhibited excellent adhesion to the substrate. In all cases, an increase in oxide coverage of the surface was associated with a decrease in Lancaster wear coefficient. The oxide at the surface of the 316L and H21+7%TiC was found to deform with the substrate, forming a mechanically mixed layer that enhanced surface wear resistance. Evidence of oxidational wear is presented for the wear of the Al–Si–30%SiC composite, but this did not give a beneficial effect in wear, a result of the brittle nature of the oxide that resulted in detachment of fine (150nm) thick fragments. The worn surface of the Al–alloy (6092)–15%Ni₃Al and TiAlN/CrN coating was characterized by reaction with the counterface and subsequent oxidation, the product of which enhanced wear resistance. The observations are related to the classical theory of oxidational wear.     

Tool wear and surface quality in milling of a gamma-TiAl intermetallic

Advanced structural materials for high-temperature applications are often required in aerospace and automotive fields. Gamma titanium aluminides, intermetallic alloys that contain less than 60?wt.% of Ti, around 30–35 wt.% of aluminum, and other alloy elements, can be used as an alternative to more traditional materials for thermally and mechanically stressed components in aerospace and automotive engines, since they show an attractive combination of favorable strength-to-weight ratio, refractoriness, oxidation resistance, high elastic modulus, and strength retention at elevated temperatures, together with good creep resistance properties. Unfortunately such properties, along with high hardness and brittleness at room temperature, surface damage, and short and unpredictable tool life, undermine their machinability, so that gamma-TiAl are regarded as difficult to cut materials. A deeper knowledge of their machinability is therefore still required. In this context the paper presents the results of an experimental campaign aimed at investigating the machinability of a gamma titanium aluminide, of aeronautic interest, fabricated via electron beam melting and then thermally treated. Milling experiments have been conducted with varying cutting speed, feed, and lubrication conditions (dry, wet, and minimum quantity lubrication). The results are presented in terms of correlation between cutting parameters and lubrication condition with tool wear, surface hardness and roughness, and chip morphology. Tool life, surface roughness, and chirp morphology showed dependence on the cutting parameters. Lubrication conditions were observed to heavily affect tool wear, and minimum quantity lubrication was shown to be by far the method that allows to extend tool life.     

Surface roughness evolutions in sliding wear process

Wear debris analysis is a technique for machine condition monitoring and fault diagnosis. One key issue that affects the application of wear debris analysis for machine condition monitoring is whether the morphology of the wear particles accurately depicts their original states and the surface morphology of the components from which the particles separate. This study aimed to investigate the evolution of the surface morphology of wear debris in relation to change in the surface morphology of wear components in sliding wear process. Sliding wear tests were conducted using a ball-on-disc tester under proper lubrication and improper lubrication conditions. The study of the particle size distribution and the surfaces of both the wear debris and the tested samples in relation to the wear condition and the wear rates of the wear components were carried out in this study. The evolutions of the surface topographies of both the wear debris and the wear components as wear progressed were investigated. This study has provided insight to the progress of material degradation through the study of wear debris. The results of this research have clearly demonstrated that: (a) there is a good correlation of the surface morphology of wear debris and that of the wear components, and (b) the surface morphology of wear debris contains valuable information for machine condition monitoring.