An investigation on surface grinding using graphite as lubricant

Grinding requires high specific energy and the consequent development of high temperature impairs workpiece quality by inducing tensile residual stress, burn, micro cracks etc. Control of grinding temperature is achieved by providing effective cooling and lubrication. Conventional flood cooling is often ineffective due to the relative inaccessibility of the fluid to the actual grinding zone, film boiling etc. Further these fluids are also a source of health hazards. Minimization and possibly the elimination of fluid coolants by substituting their functions by some other means is of current research interest. This paper deals with an investigation on using graphite as a lubricating medium to reduce the heat generated at the grinding zone. An experimental set-up has been developed for this and a detailed comparison has been done with dry and coolant flooded grinding in terms of forces, specific energy, temperature and surface finish. Results show that grinding force, energy and temperature are reduced and resultant surface finish depends on workpiece material.     

Influence of the type of coolant lubricant in grinding with CBN tools

Oil and emulsion are two main grinding coolant lubricants (CLs) used in grinding processes with CBN tools. A comparison of these two CLs was performed as part of the long systematic research made by KSF. The comparison criteria presented in this paper are grinding forces and G-ratio. The results show that oil presents better function almost in every case for the selected grinding parameters and workpiece. However, it should be noted that the results could probably be different with other types of oil and emulsion.     

An investigation of graphite nanoplatelets as lubricant in grinding

Cooling and lubrication are very critical to ensure workpiece quality in grinding due to the high friction and intense heat generation involved in the process. Liquid lubricants have traditionally been used in flood form or minimum quantity lubrication (MQL), raising however, major environmental and economic concerns. The focus of this study is to evaluate the performance of graphite nanoplatelets as a lubricant in surface grinding. The role of graphite's characteristics such as form, size and concentration; and the effect of the carrying medium and the graphite's application method are determined based on an experimental study. The results indicate that graphite nanoplatelets significantly reduce the grinding forces, specific energy, and improve surface finish during surface grinding of hardened D-2 tool steel. A comparison with results obtained in conventional MQL grinding is also provided. The proper selection of graphite, carrying medium and application method can lead to a low cost, nontoxic and simple alternative to solid lubrication or MQL grinding.     

An experimental evaluation of graphite nanoplatelet based lubricant in micro-milling

Micro-milling is characterized by significant frictional interaction between the tool and workpiece, leading to relatively short tool life. This paper evaluates a graphite nanoplatelet based cutting fluid specifically developed to reduce friction and associated heat generation at the tool-workpiece interfaces in micro-milling. The results of micro-slot milling experiments on H13 tool steel (50 HRc) with and without graphite lubrication are presented. In particular, cutting forces, slot depth, and surface finish obtained under different lubrication conditions are compared and discussed. Possible explanations for the experimental observations are given.     

The effects of cutting fluid application methods on the grinding process

It is well known that a boundary layer of air is entrained around a rotating grinding wheel. The effects of the boundary layer have been under some scrutiny in recent years with most research being based on trying to overcome the boundary layer. The current investigation aims to show through experiment and modelling, the effects of the boundary layer on cutting fluid application and how it can be used to aid delivery by increasing flow rate beneath the wheel. Results from three experiments with different quantities of cutting fluid passing through the grinding zone are presented.     

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.     

Performance evaluation of solid lubricants in terms of machining parameters in turning

High speed machining of steel inherently generates large cutting temperatures, which not only reduce tool life but also impair the product quality. Application of cutting fluids influences the performance of machining because of its lubrication and cooling actions. Due to the hazards posed by conventional cutting fluids to ecology and health of the workers, there is a greater need to identify eco-friendly and user-friendly alternatives. Modern tribology has facilitated the use of effective unconventional methods like dry cutting, cryogenic cooling, minimum quantity lubrication and the use of solid lubricants. The present work features a specific study on the application of a solid lubricant mixture like Graphite in SAE 40 oil and boric acid in SAE 40 oil in turning of EN8 steel. Experimental results are encouraging with reduction in tool wear and surface roughness as compared to dry and wet machining.     

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 the transformations in grinding affected layer of ZTC

A complex transformation may be induced in the grinding affected layer of zirconia-toughened ceramics (ZTC). To explore the characteristics of transformation such as direction, magnitude and depth-dependent distribution under the ground surface of ZTC, Mg-PSZ, Y-PSZ and Si₃N₄+ZrO₂ etc., four kinds of ceramics have been ground using an orthogonal design test. By means of grinding forces, XRD analysis and SEM observation the main causes and mechanism of transformation are discussed for the conventional grinding processes. It is shown that: the ZTC phase would change either from t to m or from m to t, depending on the composition and heat-treatment of the ceramic materials: Transformation due to grinding is noticeable and influenced by the grinding parameters (V_s, a_p, V_w) strongly; The thickness of transformation layer is larger than the depth of wheel cut.     

Study on the grinding of advanced ceramics with slotted diamond wheels

Slotted diamond wheel grinding is a new machining technology. In this paper, an experimental study on the cutting force and the grinding temperature for ceramic face grinding using slotted diamond wheels is presented. Moreover, the empirical relationships related with the material removal rate, the surface roughness, the depth of cut, the wheel speed and the grain size are discussed. With these relationships, a temperature field for face grinding has been built. The work contributes to the fundamental theories for optimal design of slotted diamond wheels.     

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.     

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.     

Research on experiments and action mechanism with water vapor as coolant and lubricant in Green cutting

Green cutting has become focus of attention in ecological and environmental protection. Water vapor is cheap, pollution-free and eco-friendly. Therefore water vapor is a good and economical coolant and lubricant. Water vapor generator and vapor feeding system were developed to generate and feed water vapor. Comparative experiments were carried out in witch YT15 (P type in ISO) tool was used in cutting C45 steel under the conditions of compress air, oil water emulsion, water vapor as coolant and lubricant and dry cutting, respectively. The experimental results showed that with water vapor as coolant and lubricant the cutting force is further reduced, the friction coefficient, the chip deformation coefficient and the surface roughness value decreased and the cutting temperature lowered. Kinetic model of penetration capillary in tool–chip interface of cutting fluid revealed that the lubricity effect is much better with water vapor as coolant and lubricant because of its excellent penetration performance and forming of low shearing strength lubrication layer. Therefore, the use of water steam as coolant and lubricant proves to be a green cutting technique.     

An assessment of the applicability of cold air and oil mist in surface grinding

This paper discusses the application of an eco-grinding system using a mixture of compressed cold air and vegetable oil. The feasibility of the system was assessed using the surface grinding of plain carbon steel 1045 with a BWA60MVA1 wheel. The investigation showed that cold air can be used to suppress surface burning under certain material removal rates and has an advantage of reduced grinding forces. With the addition of very small amount of vegetable oil, a larger depth of cut can be performed without burning while keeping a good grinding quality. Grinding chips were of lamellar and leafy shapes, indicating a shearing mechanism of chip formation. There was no significant difference in subsurface hardness of the components ground with coolant or with cold air and oil mist (CAOM), although the latter showed a stronger dependence of surface residual stresses on the depth of cut due to the limited cooling capacity of CAOM.     

An experimental investigation into soft-pad grinding of wire-sawn silicon wafers

Silicon is the primary semiconductor material used to fabricate microchips. A series of processes are required to manufacture high-quality silicon wafers. Surface grinding is one of the processes used to flatten wire-sawn wafers. A major issue in grinding of wire-sawn wafers is reduction and elimination of wire-sawing induced waviness. Results of finite element analysis have shown that soft-pad grinding is very effective in reducing the waviness. This paper presents an experimental investigation into soft-pad grinding of wire-sawn silicon wafers. Wire-sawn wafers from a same silicon ingot were used for the study to ensure that these wafers have similar waviness. These wafers were ground using two different soft pads. As a comparison, some wafers were also ground on a rigid chuck. Effectiveness of soft-pad grinding in removing waviness has been clearly demonstrated.     

An experimental investigation of the effects of workpiece and grinding parameters on minimum quantity lubrication—MQL grinding

Coolant is a term generally used to describe grinding fluids used for cooling and lubricating in grinding process. The main purposes of a grinding fluid can be categorized into lubrication, cooling, transportation of chips, cleaning of the grinding wheel and minimizing the corrosion. On the other hand, grinding fluids have negative influences on the working environment in terms of the health of the machine operator, pollution and the possibility of explosion (for oil). Furthermore, the cost of the grinding fluid, filtering and waste disposal of the metal working fluids is even higher than the tool cost and constitutes a great part of the total cost. Additionally, grinding fluids can not effectively penetrate into the contact zone, are health hazard and their consumption must be restricted. Generally, compared to other machining processes, grinding involves high specific energy. Major fraction of this energy is changed into heat, which makes harmful effect on the surface quality as well as the tool wear. Since there is no coolant lubricant to transfer the heat from the contact zone in dry grinding, surface damages are not preventable. Alternatives to current practices are getting more serious consideration in response to environmental and operational cost pressures. One attractive alternative is the minimum quantity lubrication (MQL) grinding or the near dry grinding (NDG). In near dry grinding an air–oil mixture called an aerosol is fed into the wheel-work contact zone. Compared to dry grinding, MQL grinding substantially enhances cutting performance in terms of increasing wheel life and improving the quality of the ground parts. In this research, the influences of workpiece hardness and grinding parameters including wheel speed, feed rate and depth of cut have been studied on the basis of the grinding forces and surface quality properties to develop optimum grinding performances such as cooling, lubrication, high ecological and environmental safety.     

An experimental investigation of system matching in ultrasonic vibration assisted grinding for titanium

This paper presents a fundamental investigation of the system matching mechanisms involved in ultrasonic vibration assisted grinding (UAG) of titanium processing. The effects of system matching on grinding force and surface roughness are studied experimentally. The design of experiments and experimental equipment are described in detail. In this investigation, a five-variable four-level fractional factorial design is used to conduct experiments. The experiments are employed to reveal the main effects as well as the interaction effects of the ultrasonic parameters on the process outputs such as material removal rate (MRR), grinding force, surface topography and surface roughness. Experimental results showing that the application of system matching in UAG can improve the work piece grinding quality.     

An experimental investigation of rotary diamond truing and dressing of vitreous bond wheels for ceramic grinding

Experiments of rotary diamond truing and dressing of vitreous bond grinding wheels were conducted to investigate the effects of feed, speed ratio, and overlap ratio on cylindrical grinding of zirconia. The applications of ceramic engine components with complex and precise form and the lack of technology for precision truing of diamond grinding wheels have driven the need to study the use of vitreous bond CBN and SiC wheels for form grinding of ceramics. Truing and grinding forces and the roundness and surface finish of ground zirconia parts were measured. By varying truing process parameters, a wide range of surface finish and roundness could be achieved. Experimental results showed that wheels trued at speed ratio below −1.0 could grind parts with fine surface finish and good roundness. The analysis of truing and grinding results showed the trend of increasing grinding force at higher specific truing energy and better surface finish at higher grinding force. The lack of speed control of the direct–drive, variable–speed truing spindle was observed and its effect on the reverse of direction of truing force at positive speed ratios was studied.     

Computer controlled detonation spraying of WC/Co coatings containing MoS2 solid lubricant

Composite WC/Co + MoS₂ coatings were deposited onto steel substrates by Computer Controlled Detonation Spraying using three spraying modes: very cold, cold and normal. Maximal content of MoS₂ in a sprayed powder was 10 wt.%. Characterization of coatings was made with chemical and phase analyses, microhardness measurement, morphology and microstructure investigation. X-ray diffraction study shows that residual MoS₂ exists only in coatings obtained at very cold and cold spraying modes. At normal spraying mode complete decomposition of the solid lubricant occurs during spraying. From the engineering point of view, the coating applied at the cold mode using a powder containing 10 wt.% MoS₂ is the most promising. Such a coating has microhardness of 650 HV_0.2 and a porosity of 10%.     

Influence of microstructures of binder and abrasive grain on selected operational properties of ceramic grinding wheels made of alumina

The operational properties of ceramic abrasive tools made of alundum and submicrocrystalline alumina with advanced binders have been investigated. The traditional glass binders were replaced with the glass–crystalline binders where augite (Ca(Mg,Fe)[Si₂O₆] and gahnite ZnAl₂O₄ constituted the basic crystalline phase. The occurrence of such crystalline phases causes such binders to wear in the course of grinding in a similar way to the mechanism of submicrocrystalline-grain wear. It exerts a beneficial influence on the radial wear of grinding wheels (ΔR), the metal removal rate (G) and the arithmetic mean roughness value (Ra). These parameters depend not only on the binder structure, amorphous or glass–crystalline, but also on the microstructure of abrasive grains and the grinding speed.