The influence of solid lubricant particle size on machining parameters in turning

Turning is one of the most fundamental and indispensable processes of metal removal in industry. The heat generated in the cutting zone during turning is critical in deciding the workpiece quality and tool life. Though cutting fluids are widely employed to carry away the heat in metal cutting, their usage poses threat to ecology and the health of workers. Hence, there arises a need to identify eco-friendly and user-friendly alternatives to conventional cutting fluids. Modern tribology has facilitated the use of solid lubricants. The present work features a specific study of the application of solid lubricant in turning. The process performance is judged in terms of cutting force, tool temperature, tool wear and the surface finish of workpiece, keeping the cutting conditions constant. The results obtained from the experiment show the effectiveness of the use of the solid lubricant as a viable alternative to dry and wet machining. The unique utility of solid lubricant is highlighted.     

Experimental investigation to study the effect of solid lubricants on cutting forces and surface quality in end milling

Milling is a widely employed material removal process for different materials. It is characterized by high material removal rate. Machining leads to high friction between tool and workpiece, and can result in high temperatures, impairing the dimensional accuracy and the surface quality of products. Application of conventional cutting fluid may not effectively control the heat generation in milling. Besides, cutting fluids are a major source of pollution. Solid lubricant assisted machining is an environmental friendly clean technology for desirable control of cutting temperature. The present work investigates the role of solid lubricant assisted machining with graphite and molybdenum disulphide lubricants on surface quality, cutting forces and specific energy while machining AISI 1045 steel using cutting tools of different tool geometry (radial rake angle and nose radius). The performance of solid lubricant assisted machining has been studied in comparison with that of wet machining. The results indicate that there is a considerable improvement in the process performance with solid lubricant assisted machining as compared to that of machining with cutting fluids.     

An investigation on solid lubricant moulded grinding wheels

The conventional flood coolants employed in grinding suffer many limitations in performing their functions. They cannot be recommended in the light of ecological and economic manufacture. Application of solid lubricant in grinding has proved to be a feasible alternative to the fluid coolants, if it could be applied in a proper way. Towards finding out an improved method of application of solid lubricant, attempts on development of solid lubricant moulded grinding wheels with various bonding and lubricants have been reported here. Such wheels with resin bonding were successfully made and improved process results were obtained. But the wheel wear depended on the type of the lubricant used.     

Performance of carbide tools with textured rake-face filled with solid lubricants in dry cutting processes

Surface texturing with different geometrical characteristics was made on the rake face of the WC/Co carbide tools, molybdenum disulfide (MoS₂) solid lubricants were filled into the textured rake-face. Dry cutting tests were carried out with these rake-face textured tools and a conventional tool. The effect of the texture shape on the cutting performance of these rake-face textured tools was investigated. Results show that the cutting forces, cutting temperature, and the friction coefficient at the tool-chip interface of the rake-face textured tools were significantly reduced compared with that of the conventional one. The rake-face textured tool with elliptical grooves on its rake face had the most improved cutting performance. Two mechanisms responsible were found, the first one is explained as the formation of a lubricating film with low shear strength at the tool-chip interface, which was released from the texturing and smeared on the rake face, and served as lubricating additive during dry cutting processes; the other one was explained by the reduced contact length at the tool-chip interface of the rake-face textured tools, which contributes to the decrease of the direct contact area between the chip and rake face.     

Influence of turning parameters on distortion of bearing rings

The turning of bearing rings often leads to undesired form and dimensional changes after heat treatment which are referred to as distortion. In order to investigate the influence of cutting parameters on distortion, external longitudinal turning experiments were conducted. After machining the ring geometry and the residual stresses around the rings’ circumference were measured. The residual stresses were then released by a subsequent heat treatment. After the heat treatment the ring geometry was measured again. The results show that the residual stresses induced by the machining process correlate well with the dimensional changes after heat treatment. The cutting parameters that have the highest influence on the dimensional changes are the feed rate and the depth of cut. Residual stresses induced by soft-machining lead to an increase of the ring diameter, depending on the machining parameters.     

Calculation of optimum cutting conditions for turning operations using a machining theory

A method is described for calculating the optimum cutting conditions in turning for objective criteria such as minimum cost or maximum production rate. The method uses a variable flow stress machining theory to predict cutting forces, stresses, etc. which are then used to check process constraints such as machine power, tool plastic deformation and built-up edge formation. A modified form of Taylor tool life equation where the constants are determined using the machining theory has been employed in predicting tool life for the optimisation procedure. The obtained results indicate that the described method is capable of selecting the appropriate cutting conditions.     

Fuzzy adaptive networks in machining process modeling: surface roughness prediction for turning operations

Due to the complexity of the machine tool structure and the cutting process, the dynamics of machining processes are still not completely understood. This is especially true due to the demand of high-speed machining to increase productivity. In order to model and control these complex processes, new approaches, which can represent complex phenomenon combined with learning ability, are needed. The combined neural–fuzzy approach appears to be ideally suited for this purpose. In this paper, the recently developed fuzzy adaptive network (FAN) is used to model surface roughness in turning operations. The FAN network has both the learning ability of neural network and linguistic representation of complex, not well-understood, vague phenomenon. Furthermore, it can continuously improve the initially obtained rough model based on the daily operating data. To illustrate this approach, a model representing the influences of machining parameters on surface roughness is established and then the model is verified by the use of the results of pilot experiments. Finally, a comparison with the results based on statistical regression is provided.     

Improved wear performance by the incorporation of solid lubricants during thermal spraying

For components that are required to function in sliding or rubbing contact with other parts, degradation often occurs through wear due to friction between the two contacting surfaces. Depending on the nature of the materials being used, the addition of water as a lubricant may introduce corrosion and accelerate the degradation process. To improve the performance and increase the life of these components, coatings may be applied to the regions subject to the greatest wear. These coatings may be engineered to provide internal pockets of solid lubricant in order to improve the tribological performance. In the present study, coatings containing a solid lubricant were produced by thermal spraying feedstock powders consisting of a blend of tungsten carbide-metal and a fluorinated ethylene-propylene (FEP) copolymer-based material. The volume content of this teflon-based material in the feedstock ranged from 3.5 to 36%. These feedstocks were deposited using a high velocity oxy-fuel (HVOF) system to produce coatings having a level of porosity below 2%. Sliding wear tests in which coated rotors were tested in contact with stationary carbon-graphite disks identified an optimum level of teflon-based material in the feedstock formulation required to produce coatings exhibiting minimum wear. This optimum level was in the range of 7 to 17% by volume and depended on the composition of the cermet constituent. Reductions in mass loss for the couples on the order of 50% (an improvement in performance by a factor of approximately 2) were obtained for the best performing compositions, as compared to couples in which the coating contained no solid lubricant.     

Performance of supercritical carbon dioxide sprays as coolants and lubricants in representative metalworking operations

This paper investigates the cooling and lubrication properties of supercritical carbon dioxide (scCO₂) sprays as potential substitutes for aqueous emulsions and straight oils used in the metalworking industry today. Sprays of rapidly expanding scCO₂ act to cool and lubricate machining and forming processes by delivering a mixture of dry ice and lubricant deep into the cutting/forming zone. In this work, experiments with turning, milling, drilling, thread cutting, and thread forming were performed with scCO₂ and other metalworking fluids (MWFs) to evaluate their relative performance with respect to tool wear and machining torque. Observations reveal that scCO₂–MWFs are more effective in removing heat from the tool-workpiece interface than conventionally delivered (flood) aqueous MWFs as well as other gas-based MWF sprays. In addition, scCO₂–MWFs delivered in lubricant-expanded phase, where scCO₂ is used to increase volume of lubricant in the spray field, are shown to provide better lubricity than straight oils and oil-in-air minimum quantity lubrication (MQL) sprays. As a result, scCO₂–MWFs can reduce tool wear and improve machining productivity in a wide range of manufacturing operations leading to appreciable improvements in the economics of manufacturing. Also given that CO₂ is a recovered waste gas that is non-toxic, scCO₂–MWFs can improve the environmental and worker health performance of manufacturing operations.     

Improvement of Drill Performance in Metal Cutting Using MoST Solid Lubricant Coatings

METAL CUTTING or MACHINING plays a crucialrole in most manufacturing industries.New alloys andengineered materials that have to be machined are hard,tough,and abrasive and can also cause chemical wearof cutting tool materials.Depositing hard coatings on cutting tools is animportant development,which has enhanced cuttingtool performance as a result of providing higher wearresistance,lower friction,lower cutting forces,bettersurface finish of the workpieces,and longer tool life,which ena…     

Reliable tool life measurements in turning — an application to cutting fluid efficiency evaluation

The paper proposes a method to obtain reliable measurements of tool life in turning, discussing some aspects related to experimental procedure and measurement accuracy. The method (i) allows an experimental determination of the extended Taylor's equation, with a limited set of experiments and (ii) provides a basis for the quantification of tool life measurement uncertainty. The procedure was applied to cutting fluid efficiency evaluation. Six cutting oils, five of which formulated from vegetable basestock, were evaluated in turning. Experiments were run in a range of cutting parameters, according to a 2^3–1 factorial design, machining AISI 316L stainless steel with coated carbide tools. Tool life measurements were associated to an estimation of their uncertainty, and it was found that by taking three repetitions the uncertainty calculated with a coverage factor of two was on average three times bigger than the experimental standard deviation.     

润滑剂在温挤压中的应用研究

对40Cr、1Cr18Ni9Ti钢温挤压润滑剂应用研究,发现不同成分的润滑剂其润滑效果具有很大的区别。挤压温度低于400℃时,各种润滑剂均具有较低的摩擦因数,石墨系润滑剂的摩擦因数最低,润滑效果相对最好;挤压温度高于400℃时,石墨系润滑剂仍保持较低的摩擦因数,PbO的摩擦因数增加最快。     

Mechanisms of self-lubrication in patterned TiN coatings containing solid lubricant microreservoirs

The tribological mechanisms of friction and lubrication have been investigated in TiN coatings patterned to contain microscopic reservoirs for solid lubricant entrapment. Photo-lithography was used to fabricate three sets of samples on silicon wafers, varying the reservoir size (4 and 9 μm) and spacing (11 and 25 μm), which resulted in samples with a nominal reservoir area of either 2 or 10%. Pin-on-disk tests were run using lubricants of graphite and indium and counterfaces of alumina and steel (440C). In most cases, the samples with the 9 μm holes spaced 25 μm apart gave the lowest friction coefficients and longest wear life. Analysis of the wear tracks by SEM/EDS methods showed carbon to be present in the holes of the graphite/steel counterface samples, but TiO₂ was found in the holes of the graphite/alumina counterface samples. For the indium/steel counterface samples indium was detected within the microreservoirs, but iron was also found, transferred from the ball. These experiments highlight a variety of tribological mechanisms that can operate in microreservoir-patterned coatings.     

灰度模糊算法优化Al-SiC-Gr混合金属基复合材料的加工参数

石墨颗粒增强金属基复合材料能够提供更好的切削加工性能和摩擦性能。用灰度模糊算法优化Al-SiC-Gr混合金属基复合材料的加工参数,以获得到具有优秀综合性能的材料。当混合金属基复合材料中SiC-Gr的质量分数分别为5%、7.5%和10%时,对应的拉伸强度分别为170、210和204 MPa。另外,与另外2种材料相比,Al-10%（SiC-Gr）复合材料具有更好的切削加工性能。与其他的灰度技术相比,灰度模糊逻辑算法在输出方面提高了推理的合理性,降低了不确定性。实验结果表明,在设置的相同加工参数下,与其他的灰度技术相比,灰度模糊逻辑算法的推理合理性从0.619提高到0.891,且同时保证材料具有更好的综合性能。     

Relationships between the fretting wear behavior and the ball cratering resistance of solid lubricant coatings

Employing solid lubricant coatings to reduce friction is one of the most effective methods to mitigate fretting damage. However, facing numerous available coatings, users often feel confounded, and the selection of the optimum coating for a specific application is still a tough task. Some simple methods are expected to help the selection. Ball cratering as a promising technique is becoming popular in the developing process of new coatings to assess their abrasion resistance. The objective of this paper is to identify the relationships between the fretting behavior and the ball cratering resistance of coatings, and attempt to use ball cratering to pre-select coatings for fretting conditions in order to cut down the number of candidate coatings and shorten the fretting tests. In this study, several bonded solid lubricant coatings, principally based on PTFE or MoS₂, were investigated by ball cratering and fretting tests. The results showed that the coatings in ball cratering presented similar tribological performance as in fretting tests in terms of endurance and wear resistance, i.e., the coatings with good ball cratering resistance also exhibited long lifetime in fretting tests, so ball cratering can be considered as a simple test to pre-select solid lubricant coatings for fretting applications.     

Evaluation of cutting force uncertainty components in turning

A procedure is proposed for the evaluation of those uncertainty components of a single cutting force measurement in turning that are related to the contributions of the dynamometer calibration and the cutting process itself. Based on an empirical model including errors from both sources, the uncertainty for a single measurement of cutting force is presented, and expressions for the expected uncertainty vs. cutting parameters are proposed. This approach gives the possibility of evaluating cutting force uncertainty components in turning, for a defined range of cutting parameters, based on few experiments.     

Lubricity of volatile lubricants in sheet metal rolling

A series of experiments is carried out by using a rolling type tribometer to investigate the lubricity of the volatile lubricants at high speed forming. The roll material is the die steel alloy SKD11, and the workpiece material is the mild steel SPCE with a rough surface and the aluminum alloy A3004 with a smooth surface. Experimental results show that the friction coefficient decreases with increasing working velocity for both SPCE and A3004, in any lubricant. With an increase of reduction in thickness, the friction coefficient decreases for SPCE, but increases for A3004. Some volatile lubricants have the same lubricity as the generally used mineral oil with low-viscosity by judging from the value of friction coefficient, the surface appearance of rolled workpiece and the roll surface damage.     

Suppression mechanism of tool wear by phosphorous addition in diamond turning of electroless nickel deposits

An appropriate phosphorous addition to electroless nickel deposits remarkably reduces tool wear in diamond turning. To understand the wear suppression mechanism of phosphorous addition, erosion tests simulating tool wear process and ab initio molecular dynamics calculations of interactions between diamond and Ni-P and Ni are carried out. The erosion tests show that carbon diffusion into the workpiece is reduced, and the ab initio calculations suggest that dissociation of carbon atoms on diamond surface due to the interaction with the workpiece is reduced. The results suggest that another possible additive to suppress tool wear can be found by the method proposed.