Grinding of aluminium silicon carbide metal matrix composite materials by electrolytic in-process dressing grinding

The grinding cost of metal matrix composite materials is more due to low removal rates and high rates of wear of super abrasive wheels. This electrolytic in-process dressing (ELID) technique uses a metal-bonded grinding wheel that is electrolytically dressed during the grinding process for abrasives that protrude continuously from super abrasive wheels. This research carries out ELID grinding using various current duty ratios and conventional grinding of 10% SiC_p reinforced 2,124 aluminium composite materials. Normal forces and tangential forces are monitored. Surface roughness of the ground surface, Vickers hardness numbers and metal removal rate (MRR) are measured. The results show that the cutting forces in the ELID grinding are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of grinding wheel and are less than conventional grinding forces. A smoother surface can be obtained at high current duty ratio in ELID grinding. The micro-hardness is reduced at high current duty ratio. In ELID, the MRR increases at high current duty ratio. The results of this investigation are presented in this paper.     

Metal transfer and wear in fine grinding

The transfer and wear characteristics of two widely used abrasive materials (A1₂O₃ and SiC) are studied when grinding two difficult materials (AISI T15 tool steel and Ti-6Al-4V titanium alloy). A newly developed accelerated wear technique (cluster overcut flygrinding) is employed together with Auger electron spectroscopy, X-ray diffraction and scanning transmission electron microscopy. Experimental results suggest that when grinding steel the wear of SiC is primarily due to oxidation, while the wear of Al₂O₃ is primarily due to metal build-up, resulting in microchipping. When a titanium alloy is being ground, both types of abrasive result in a microchipping type of wear, the rate of which decreases when the wheel speed is reduced.     

Experimental study of grinding fluids for abrasive-belt grinding of stainless steel

A number of ferritic stainless steels with high corrosion resistance have recently been developed, but these steels are known to be difficult to grind in coated abrasive-belt grinding operations. In order to formulate or select an optimum oil-based grinding fluid with which such stainless steels can be successfully ground, an optimum base oil was first experimentally selected, and then additives were evaluated for their effect in improving abrasive-belt grinding performance. A paraffinic mineral oil having a certain viscosity was found to be suitable for the base oil. Chemical grinding oil additives were found markedly effective in improving the abrasive-belt grinding performance for both 19Cr-2Mo ferritic stainless steel and SUS 304 austenitic steel, with those containing sulphur or chlorine being superior to those containing phosphorus, fatty acid or alcohol. Among all the additives tested, chemically active oils, such as sulphurized mineral oil, exhibited the best performance. Effects of chlorinated paraffins on the grinding performance could be perceived but were not so great as those of sulphur-series additives. The addition of TCP (tricresyl phosphate) to the grinding oil containing sulphur reduced metal removal in the case of 18Cr-2Mo ferritic stainless steel (SUS 444). In the case of SUS 430 ferritic stainless steel, however, TCP increased metal removal for a comparatively low sulphur concentration, but, above an optimum concentration of 0.4 wt% S, metal removal was reduced by TCP addition. A comparison of sulphur-series additives added to a sulphurized paraffinic mineral oil showed that nonyl polysulphide was superior to any other additives for improving the grinding performance in 19Cr-2Mo steel (SUS 444) and SUS 430. Excess addition of sulphurized fatty oil to a grinding fluid lowered the cutting ability of abrasive grains.     

In-process endpoint detection of weld seam removal in robotic abrasive belt grinding process

This paper proposes a novel approach for in-process endpoint detection of weld seam removal during robotic abrasive belt grinding process using discrete wavelet transform (DWT) and support vector machine (SVM). A virtual sensing system is developed consisting of a force sensor, accelerometer sensor and machine learning algorithm. This work also presents the trend of the sensor signature at each stage of weld seam evolution during its removal process. The wavelet decomposition coefficient is used to represent all possible types of transients in vibration and force signals generated during grinding over weld seam. “Daubechies-4” wavelet function was used to extract features from the sensors. An experimental investigation using three different weld profile conditions resulting from the weld seam removal process using abrasive belt grinding was identified. The SVM-based classifier was employed to predict the weld state. The results demonstrate that the developed diagnostic methodology can reliably predict endpoint at which weld seam is removed in real time during compliant abrasive belt grinding.     

The effect of the severity of the grinding mode on the wear characteristics of grade 36 Al2O3- and Al2O3-ZeO2-coated abrasive belts

With the trend toward increased production rates, demands on coated abrasive belts are becoming increasingly severe. A study was made of the wear and performance characteristics of two abrasive minerals used in two very different modes of grinding, a low pressure constant-load grinding test (to represent relatively mild grinding and finishing applications) and a high pressure constant-rate test (to represent severe machining applications). Al₂O₃ and Al₂O₃-ZrO₂ minerals in a resin-bonded cloth-backed construction generally used for most metal-working applications were studied.A variety of techniques were used to analyze and to define wear and grinding performance. These included the measurement of the caliper, energy consumption, mineral utilization and surface profiles of the belts, together with scanning electron microscopy (SEM) observations of belts at various stages of wear. Substantial differences were found in many areas, both for the two mineral types used in the same grinding mode and for the same mineral used in different grinding modes. Interesting data showing mineral consumption during the grinding process and SEM visual identification of key differences in coated abrasive wear are presented. The study indicates that, although a coated abrasive belt can function effectively over a wide range of applications, its wear characteristics will vary with the severity of the application.     

钢轨砂带打磨与砂轮打磨综合性能对比实验研究

基于自主研发的锂电驱动钢轨砂带打磨机和砂轮打磨机,以60N型钢轨廓形作为实验对象,全面对比了新型钢轨砂带打磨技术和传统砂轮打磨技术的性能。结果表明：当打磨压力在45～75 N范围内时,砂带打磨的材料去除率约为砂轮打磨的15～30倍,而当压力增大到90 N时,砂带打磨的材料去除率高达砂轮打磨的102倍;砂带打磨的振动加速度、噪声和能耗均小于砂轮打磨;砂带打磨切屑为带状,而砂轮打磨则表现为高温熔融状,同时当打磨压力增大到105 N时,砂轮打磨后钢轨表面会出现发蓝现象,而砂带打磨不会;此外,砂带打磨的横向表面粗糙度大于砂轮打磨,最高可达8μm,但满足中国铁路钢轨养护要求的最大值10μm。综上,钢轨砂带打磨技术在材料去除率、振动、噪声、能耗和温度等方面显著优于传统砂轮打磨技术,预期将成为工程实际中解决钢轨严重病害问题的有效方法之一。     

Feature extraction method of abrasive belt wear state for rail grinding

Abstract

Abrasive belt has the advantages of high removal efficiency and high waste collection; furthermore, it does not easily damage the rail when applied in rail grinding. However, the poor wear consistency and short service life restrict its development in this field. It is important to explore the theory and technology of monitoring the abrasive belt wear condition to evaluate the means of improving the grinding performance of the belt. This article discusses the contact stress state between the belt and the rail surface. In addition, the study establishes the belt rail grinding force model during operation using the abrasive grain distribution function. The analysis of the force model proposes that the belt abrasion condition be monitored by using the force ratio parameter of the abrasive belt in the grinding process. The extraction method of the force ratio information is proposed in accordance with the grinding environment. The results of experiments successfully verified the validity of the method.     

Cu-3镍铜合金砂带磨削试验研究

分析了Cu-3镍铜合金砂带磨削加工过程中,砂带粒度和磨削用量的不同对磨削加工效率、工件表面质量和砂带磨损的影响。采用氧化铝磨料砂带在不同的砂带线速度或磨削压力下对镍铜合金进行了工艺试验,对材料去除量、工件表面粗糙度和砂带磨损量进行了测量。研究表明:增加砂带线速度和磨削压力可在一定程度上提高材料去除率和磨削比;随着磨削压力的增大,工件表面粗糙度呈增大趋势;随着砂带粒度的增大,工件表面粗糙度呈减小趋势;砂带线速度为25m/s,磨削压力为43N,砂带粒度为P240时,镍铜合金综合磨削效果最好。     

Novel highly-efficient and dress-free polishing technique with plasma-assisted surface modification and dressing

Slurry is widely used in polishing difficult-to-machine materials. However, it is accompanied with some issues, such as the agglomeration of abrasives and high disposal cost. Although using fixed abrasive grains instead of slurry can solve these issues, the problems of wear and of loading fixed abrasive grinding stones, which result in decrease of material removal rate (MRR), also need to be solved. Many researches have been conducted on the self-sharpening of fixed abrasive grinding stones. However, the self-sharpening of grinding stones is not efficient with ultra-low polishing pressure, which is not large enough to break bonds so as to expose new abrasives. In this study, a novel dress-free dry polishing process was proposed, where it combines plasma-assisted polishing and plasma-assisted dressing using Ar-based CF₄ plasma and a vitrified-bonded grinding stone. Polishing experiments were conducted on sintered AlN wafer. Also, as the main component of vitrified bond materials, silica was etched using CF₄ plasma, which is equivalent to the continuous dressing of grinding stone surfaces. Since new abrasives could be constantly exposed, a high MRR was maintained. Thus, a dress-free high integrity polishing process was realized. Moreover, the CF₄ plasma irradiation increased the MRR twice, as CF₄ plasma can not only dress a grinding stone in real time but can also modify AlN to AlF₃, which can easily be removed.     

Material removal mechanism of precision grinding of soft-brittle CdZnTe wafers

Cd_0.96Zn_0.04Te (111) wafers were precisely ground by #800, #1500, #3000, and #5000 diamond grinding wheel. For comparison, Cd_0.96Zn_0.04Te (110) wafers were machined by lapping, mechanical polishing, and chemical mechanical polishing. High-resolution environmental scanning electron microscopy equipped with energy dispersive spectroscopy and optical interference surface profiler both were employed to investigate the surface quality and material removal mechanism. The results show that the material removal mechanism of #800 grinding wheel is abrasive wear, fatigue wear, and adhesive wear, and that of #1500 is abrasive wear and fatigue wear. Both the material removal mechanism of #3000 and #5000 grinding wheel are abrasive wear, leading to the excellent ductile removal precision grinding. While the material removal mechanism of CMP on CdZnTe wafers is firstly chemical resolving reaction and secondly mechanical carrying action. Moreover, precision grinding exhibits high-efficiency character and eliminates the imbedding of free abrasives of Al₂O₃ and SiO₂.     

An investigation on surface grinding of hardened stainless steel S34700 and aluminum alloy AA6061 using minimum quantity of lubrication (MQL) technique

In grinding process, the abrasives plunge and slide against the workpiece during material removal with high specific energy consumption and high grinding zone temperature. To improve process efficiency, lubrication becomes an important requirement of the grinding fluids, along with chip removal and cooling the grinding zone. Grinding fluids have negative influences on the working environment and machining cost in terms of the health of the machine operator, pollution, the possibility of explosion (for oil), filtering, and waste disposal. The use of minimum quantity of lubrication (MQL) with an extremely low consumption of lubricant has been reported as a technologically and environmentally feasible alternative to flood cooling. This paper deals with an investigation of the grindability of hardened stainless steel (UNS S34700) and aluminum alloy AA6061 using dry, MQL, and conventional fluid techniques. One type of SiC and five types of Al₂O₃ wheels (corundum) as well as vegetable and synthetic ester MQL oils have been tested. The influences of wheel and coolant–lubricant types have been studied on the basis of the grinding forces, surface topography, and surface temperature. Synthetic ester MQL oil was found to give better grinding performance than the vegetable MQL oils. It was argued that the improved performance of the ester oil is caused by the formation of tribo-films on the abrasives and the workpiece, which enhances lubrication by inhibiting metal–abrasive interaction. Also, the grindability of the machined specimens was found to increase substantially by using the MQL grinding process with soft and coarse wheels. In MQL grinding of AA6061 alloy, the use of vegetable oil resulted in the lowest surface roughness, whereas using synthetic ester additives lead to highest surface roughness because of higher chip loading on the grinding wheel and consequently more redeposited material on the workpiece surface.     

Automated surface finishing of plastic injection mold steel with spherical grinding and ball burnishing processes

This study investigates the possibilities of automated spherical grinding and ball burnishing surface finishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding tool holder has been accomplished in this study. The optimal surface grinding parameters were determined using Taguchi’s orthogonal array method for plastic injection molding steel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the combination of an abrasive material of PA Al₂O₃, a grinding speed of 18000 rpm, a grinding depth of 20 μm, and a feed of 50 mm/min. The surface roughness R_a of the specimen can be improved from about 1.60 μm to 0.35 μm by using the optimal parameters for surface grinding. Surface roughness R_a can be further improved from about 0.343 μm to 0.06 μm by using the ball burnishing process with the optimal burnishing parameters. Applying the optimal surface grinding and burnishing parameters sequentially to a fine-milled freeform surface mold insert, the surface roughness R_a of freeform surface region on the tested part can be improved from about 2.15 μm to 0.07 μm.     

Edge burr development when using a cemented carbide micro-drill: Formation and control mechanisms

To explore the mechanism of formation and methods of control of edge burr in the grinding and forming of cemented carbide micro-drill, the morphology, material composition, and the edge structure of the generated area of the edge burrs are studied. Through indentation and scratch experiments, the critical grinding depth (h_c) of grinding machining is calculated to be 0.793–1.052 μm. The grinding experiments have verified the effects of the actual grinding depth h₀ of different single abrasive particles on the edge burr and the effectiveness of the method of controlling the burr by increasing the cutting angle of the abrasive particles. The experimental results show that edge burrs are mainly concentrated on the cutting edge close to the outer cylinder of the micro-drill. When the actual grinding depth h₀ of a single abrasive particle is less than the critical grinding depth h_c, workpiece material is mainly subjected to plastic deformation removal, the length L of the edge burr along the edge direction is 10–20 μm, the width W of the burr perpendicular to the edge direction is 1–3 μm. The formation of edge burrs is mainly related to the actual grinding depth and the abrasive grain cutting angle γ of abrasive grains. With the increase of h₀, the length L of the edge burr decreases, and the width W thereto first increases, then decreases. Increasing the cutting angle of abrasive particles can control the edge burr. By changing the grinding direction of the grinding wheel, the cutting angle of the abrasive particles can be changed from an acute angle to an obtuse angle, thereby eliminating the edge burr without affecting the performance of micro-drilling.     

超声振动精密砂带磨削0Cr17Ni4Cu4Nb不锈钢的试验研究

介绍了超声波振动精密砂带磨削机理,通过超声波振动精密砂带磨削与普通砂带磨削0Cr17Ni4Cu4Nb不锈钢的对比试验,弄清了超声波振动在砂带磨削过程中的作用,证明了超声波振动精密砂带磨削是加工不锈钢等难加工材料的一种有效方法。     

Tribocorrosion behaviour of Fe–17Cr stainless steel in acid and alkaline solutions

The effect of applied potential, load and frequency on the tribocorrosion behaviour of a ferritic stainless steel in aqueous solution is investigated under sliding wear conditions using a reciprocating motion tribometer including an alumina pin sliding on a metal plate. The tribometer is equipped with a reference electrode and a counter electrode for electrochemical experiments. The total metal removal rate of the stainless steel is determined from the rate of penetration of the pin and from an analysis of the wear track at the end of a wear experiment while the fraction of electrochemically removed metal is deduced from the current measured during the wear experiments. Two electrolytes are used, 0.5 M H₂SO₄ and 1 M NaOH. Applied potentials are in the passive potential region except for a few experiments performed under cathodic polarisation. The obtained results demonstrate the interdependence of electrochemical and mechanical mechanisms and the importance of the passivation behaviour of the metal in the electrolyte used. In sulphuric acid the electrochemical metal removal rate depends strongly on the value of the applied potential in the passive region, but not in NaOH because in the latter electrolyte the anodic charge serves only for film formation rather than dissolution. The effect of mechanical parameters on the rate of electrochemical metal removal is in qualitative agreement with a previously developed model. The presence of debris in the contact after test was found to depend on the prevailing electrochemical conditions.     

船用螺旋桨砂带磨削研究

为改善船用螺旋桨叶片的磨削效果,采用两种不同磨料砂带对螺旋桨叶片进行了磨削试验。讨论了砂带线速度、法向磨削压力、磨料种类对材料去除率的影响;分析了砂带粒度和接触轮硬度对表面粗糙度的影响。试验表明:使用砂带磨削螺旋桨不仅可行,并且具有较高的材料去除率,可获得较小的加工表面粗糙度。该研究为确定合理的螺旋桨砂带磨削工艺参数提供了依据。     

SEM observations of the sliding behavior of A12O3 and CBN against steel

Both aluminum oxide (A1₂O₃) and cubic boron nitride (CBN) are being used as the abrasive medium in grinding wheels. To compare the effectiveness of these abrasives, a study was made, using the scanning electron microscope (SEM), to observe the sliding behavior and surface damage resulting from single particles of polycrystalline A1₂O₃ and CBN sliding dry against hardened M-50 tool steel. These experiments were run in the chamber of the SEM, which permitted direct observation of the contact areas at high magnifications. Friction force was monitored and videotape recordings were made continuously during these tests. Significantly lower friction and smoother wear tracks were obtained with the CBN. The A1₂O₃ grit produced much sharper ridges and considerable microcracking on the ridges. These microcracks were formed perpendicular to the wear track. The wear tracks obtained in the SEM were compared with the surfaces produced by surface grinding hardened steel with both CBN and A1₂O₃ wheels. At high magnifications, marked similarities between the ground surfaces and the surfaces produced by the basic sliding tests were noted. It is suggested that because of the large number of microcracks formed during the grinding process with the A1₂O₃, the fatigue life of parts ground with an A1₂O₃ wheel would be shorter than those ground with CBN. Practical experience indicates that this is true.     

On the formation of a quick-stop chip during single grit grinding

An experimental method is described for the provision of quick-stop chips in an authentic grinding grit-workpiece situation. Metallographical and scanning electron microscopical examinations of the chips have provided information to aid the elucidation of the mechanism of metal removed during grinding with abrasive particles having large negative rake angles.     

Tribological behaviour of two imidazolium ionic liquids as lubricant additives for steel/steel contacts

In this paper two room-temperature ionic liquids (ILs), 1-hexyl-3-methylimidazolium tetrafluroborate [HMIM][BF₄] and 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF₆], have been studied as 1%wt. additives of a mineral hydrocracking oil for steel–steel contacts. Rheological properties of the mixtures and base oil were determined over shear rates and temperatures ranging 1–1000 s^?1 and 40–100 °C, respectively. Friction and wear testing was made using a block-on-ring tribometer set for pure sliding contact and XPS was used to analyze wear surfaces. [HMIM][PF₆] and [HMIM][BF₄] increased the viscosity of the base oil and decreased friction and wear. Friction and wear reduction are related to reactivity of the anion of the ionic liquids with surfaces forming FeF₃, B₂O₃, and species such as P₂O₅ or PO₄^3?.     

Ductility and the abrasive wear of an ultrahigh strength steel

Ploughing of material to either side of the grooves made by abrasive particles and single indenters was observed for both abrasive wear and single point cutting. The degree of ploughing decreases as the hardness of the material being tested increases. It is possible to incorporate ploughing into the usual equation for the volume abrasive wear rate by introducing a term 1 ? f, where f is the fraction of a wear groove ploughed to either side of the abrasive particle but not removed from the surface. The equation becomes volume wear rate $\text{≈}\text{L(1?f}\text{H}{}_{\mathrm{s}}$ where L is the applied load and H_s is the surface hardness. Although it is possible to relate 1 ? f to hardness through single point scratching experiments, there is evidence that 1 ? f could depend primarily on ductility and not on hardness. As an initial step in exploring the dependence of this ploughing term on the mechanical properties of the abraded material, a simple model of the abrasive wear process is proposed. This model is evaluated in terms of the abrasive wear and tensile properties of a low alloy steel heat treated to hardnesses ranging from 496 to 680 HV.