Burr Formation in milling with minimum quantity lubrication

In milling, burrs are formed on entry and exit edges of the workpiece to be machined like in all material removal processes. In the subsequent production these burrs have to be removed. Understanding the influencing factors and burr formation mechanisms can help to avoid or reduce burrs. Another possibility for saving costs is to reduce the process materials, for example, cutting fluids. This can be realised by using minimum quantity lubrication or dry machining. The investigations show which influence both methods have on burr formation.     

Feasibility study of the minimum quantity lubrication in high-speed end milling of NAK80 hardened steel by coated carbide tool

High-speed milling of hardened steels generates high cutting temperature and leads to detrimental effects on tool life and workpiece surface finish. In this paper, feasibility study of the minimum quantity lubrication (MQL) in high-speed end milling of NAK80 hardened steel by coated carbide tool was undertaken. Flood cooling and dry cutting experiments were conducted also for comparison. It is found that cutting under flood cooling condition results in the shortest tool life due to severe thermal cracks while the use of MQL leads to the best performance. MQL is beneficial to tool life both in the lower speed cutting and the higher speed cutting conditions. A less viscous oil of MQL is essential in high cutting speed so that cooling effect can be effective. SEM micrograph of the insert shows that the use of MQL in high-speed cutting can delay welding of chips on the tool and hence prolongs tool life as compared with dry cutting condition. The application of MQL also improves machined surface finish in high-speed milling of die steels.     

Burr formation in short hole drilling with minimum quantity lubrication

Machining with minimum quantity lubrication (MQL) is state of the art. Previous investigations were, however, concerned with tool optimisation and the surface quality of workpieces as well as coating technology. By now the same or partly better machining results than in conventional cutting with flood lubrication can be achieved due to adjusted tool geometries, workpiece materials and coatings. Tests about burr formation in short hole drilling exist for dry cutting or the machining with emulsion. This paper expands these results to the burr formation in machining with MQL.     

Improving minimum quantity lubrication in CBN grinding using compressed air wheel cleaning

The application of minimum quantity lubrication (MQL) in grinding has emerged as an alternative for reducing the abundant flow of cutting fluids, thus achieving cleaner production. Although considered an innovative technique in grinding operations, its widespread application is hindered due primarily to the high heat generation and wheel pore clogging caused by machined chips, harming the final product quality and increasing tool wear on the machine. This study sought to improve MQL use in grinding. In addition to the conventional MQL injected at the wheel/workpiece interface, a compressed air jet was used to clean the mixture of MQL oil and machined chips from clogged wheel pores. Experiments were conducted using external cylindrical plunge grinding on AISI 4340 quenched and tempered steel, and a vitrified cubic boron nitrite (CBN) wheel. The cooling-lubrication methods employed were the conventional flood coolant application, MQL (without cleaning), and MQL with a cleaning jet directed at the wheel surface at different angles of incidence. The main goal of these experiments was to verify the viability of replacing the traditional abundant flow of cutting fluid with MQL and wheel cleaning. The analyses were conducted by measuring the following output variables of the process: workpiece surface roughness and roundness errors, diametrical wheel wear, acoustic emission generated by the process, and metallographic images of the ground surface and subsurface. Results show the positive effects of implementing the cleaning jet technique as a technological improvement of minimum quantity lubrication in grinding in order to reduce the usage of cutting fluids. The MQL technique with cleaning compressed air jet, for a specific angle of incidence (30°), proved to be extremely efficient in the improvement of the surface quality and accurate workpiece shape; it also reduced wheel wear when compared to the other cooling-lubrication methods that were tested (without a cleaning jet).     

Mechanism of minimum quantity lubrication in high-speed milling of hardened steel

The rapid wear rate of cutting tools due to high cutting temperature is a critical problem to be solved in high-speed machining (HSM) of hardened steels. Near-dry machining such as minimum quantity lubrication (MQL) is regarded as one of the solutions to this difficulty. However, the function of MQL in HSM is still uncertain so far which prevents MQL from widely being utilized in the machining of hardened steels. In this paper, the mechanism of MQL in HSM of hardened steel is investigated more comprehensively. Comparing with dry cutting, the tool performance can be enhanced by MQL under all cutting speeds in this study. It is found that MQL can provide extra oxygen to promote the formation of a protective oxide layer in between the chip–tool interface. This layer is basically quaternary compound oxides of Fe, Mn, Si, and Al, and is proved to act as diffusion barriers effectively. Hence, the strength and wear resistance of a cutting tool can be retained which leads to a significant improvement of tool life. It is found that there exists an optimal cutting speed at which a stable protective oxide layer can be formed. When cutting speed is lower than this speed, there is less oxide layer and the improvement of tool life is less apparent. As the cutting speed is far beyond the optimal value, the protective layer is absent and the thermal cracks are apt to occur at the cutting edge due to large fluctuation of temperature. Resultantly, application of MQL is inappropriate in the extreme high-speed cutting condition irrespective of its little increase in tool life. Based on this study, it is concluded that the tool life can be effectively improved by MQL in HSM of NAK80 hardened steels when cutting parameters are chosen properly.     

Cutting performance of different coatings during minimum quantity lubrication drilling of aluminum silicon B319 cast alloy

Cutting performance of cemented carbide drills with various coatings was investigated in detail under minimum quantity lubrication (MQL) conditions. An advanced dual-channel Bielomatik MQL system was installed in an Okuma machining center. A specially designed Mapal drill was selected for the studies to eliminate voids between the tool and the MQL tool holder that can interfere with mist delivery. Using this design, a mist flow rate of 25 mL/min was achieved through the drills.Progressive frictional/wear studies were performed. Coated drills were tested in three stages (50, 500, and 7000 holes). During short term drilling tests (50-hole level), cutting performance was comprehensively evaluated for a range of coatings by measuring several in-situ frictional characteristics of the cutting process, such as cutting forces, and related characteristics including, chip type and undersurface morphology. Wear patterns of the cutting tools were indentified as well. Selected coatings were tested further. The best cutting performance based on the 500-hole testing was found with the diamond coating. However, excessive brittleness of the entire coating/substrate system led to premature failure of the drill after 4300 holes. The low-hydrogen DLC coating that also showed promising cutting performance based on the 500-hole test was selected as the next candidate for further testing. Drills with low-hydrogen DLC coating achieved 7200 drilled holes with a flank wear of only 110 μm and moderate intensity of workpiece material pickup. This results in a better surface finish of drilled holes.Based on this study, the Mapal drills with the low-hydrogen DLC coating provided comparable machining performance to that possible with traditional wet machining, but with the environmental and cost advantages possible with MQL.     

Influence of refrigeration/lubrication condition on SAE 52100 hardened steel turning at several cutting speeds

Nowadays, the use of cutting fluids on machining operations has been questioned, due to problems they may cause to the environment, due to damage to human health and also more due to the severe laws regarding industrial waste that have been passed. Therefore, industries are being forced to review the production processes aiming either, at elimination or, when it is not possible, a sharp reduction in the use of these fluids. The technique of minimum volume of oil (MVO) has been studied in machining processes as one alternative to the use of abundant cutting fluid. Research has shown that this technique, which is the pulverisation of a minimum volume of oil in a flow of compressed air, in several cases, reduces tool wear when compared to complete dry cutting, causing the improvement of the workpiece surface quality and an increase in tool life. In this work, the influence of MVO (oil flow of 10 ml/h) in the wear of a cubic boron nitride (CBN) tool, when turning 52100 hardened steel, was studied. Aiming at a comparison of the results, the experiments were also carried out under two other conditions: dry cutting and cutting with abundant soluble oil (wet cutting). During the experiments, the influence of cutting speed on CBN tool wear for the three refrigeration conditions was also checked. Besides this, tool wear and workpiece surface roughness was also measured as cutting time elapsed.     

Experimental evaluation of the lubrication performance of MoS2/CNT nanofluid for minimal quantity lubrication in Ni-based alloy grinding

A nanofluid minimum quantity lubrication with addition of one kind of nanoparticle has several limitations, such as grinding of difficult-to-cutting materials. Hybrid nanoparticles integrate the properties of two or more kinds of nanoparticles, thus having better lubrication and heat transfer performances than single nanoparticle additives. However, the use of hybrid nanoparticles in nanofluid minimum quantity lubrication grinding has not been reported. This study aims to determine whether hybrid nanoparticles have better lubrication performance than pure nanoparticle. A hybrid nanofluid consisting of MoS₂ nanoparticles with good lubrication effect and CNTs with high heat conductivity coefficient is investigated. The effects of the hybrid nanofluid on grinding force, coefficient of friction, and workpiece surface quality for Ni-based alloy grinding are analyzed. Results show that the MoS₂/CNT hybrid nanoparticles achieve better lubrication effect than single nanoparticles. The optimal MoS₂/CNT mixing ratio and nanofluid concentration are 2:1 and 6 wt%, respectively.     

Effect of MQL on the tool life of small twist drills in deep-hole drilling

Drilling of deep and small boreholes using twist drills has to be considered as one of the most difficult metal cutting operations. There are many reasons for this, one of them being that the cutting fluid has to be supplied externally. This research work investigates in how far the manner of supplying and the type of minimum quantity lubricant have an effect on the tool life of coated and uncoated high-speed steel twist drills of 1.5 mm diameter. Deep-hole drilling is performed as the holes, drilled into plain carbon steel, had a depth of 10 times the diameter. The feasibility of dry machining as an appropriate alternative to MQL in deep-hole drilling has also been investigated. This work shows that, compared to a continuous supply of the minimum quantity lubricant, a discontinuous supply brings about a significant reduction in tool life, especially in the case of heat-sensitive drills. With respect to the type of minimum quantity lubricant, a low-viscous type with a high cooling-capability gave rise to a notably prolonged tool life. It is also shown that dry drilling is associated with strongly accelerated tool wear for most of the twist drills tested, resulting in a significant reduction in tool life.     

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.     

Study on the internal stress of nickel coating electrodeposited in an electrolyte mixed with supercritical carbon dioxide

This study focuses on the internal stress in the nickel deposit during electroplating through the additive-free Watts bath electrolyte mixed with and without supercritical carbon dioxide (Sc-CO₂). The results showed that the Ni films plated in Sc-CO₂ had brighter, smoother surface and higher hardness than plated in conventional electrolyte without Sc-CO₂. However, there existed more nano-sized pinholes via TEM and AFM measurements in the Sc-CO₂ specimens. It was found that during electroplating the Sc-CO₂ occluded into the coating through the nano-sized pinholes/voids influenced the internal stress of the deposit. On the other hand, the periodic plating characteristics of the Sc-CO₂ electroplating led to higher relative peak magnitude of Ni {111} over {200} in crystalline orientation revealed in X-ray diffraction patterns. As a result, the internal stress in the nickel film plated through the Sc-CO₂ method was significantly higher than that in the conventional one. Moreover, the more CO₂ volume fraction used in Sc-CO₂ electroplating resulted in even higher internal stress of nickel film.     

Modeling steel corrosion under supercritical CO2 conditions

Corrosion in the presence of CO₂ was studied under supercritical conditions (high pressure and moderate temperature) using different carbon steels and various corrosion resistant alloys (CRA's). An objective of this work was, among others, to put the results in perspective relative to various CO₂ corrosion models that have been developed and published over the years. In particular, the NORSOK, FREECORP, and OLI models were used for comparison, while others were discussed as well. The systems investigated were (a) supercritical CO₂ (SC CO₂) saturated with water (no separate water phase), (b) a water mist phase in equilibrium with SC CO₂, (c) a water/brine phase in equilibrium with SC CO₂. It was found that the OLI model best simulates the experimental corrosion rates observed in system (c) where coupons were corroded in the aqueous phase at high velocities in the rotating cage. The varying susceptibility of different carbon steels to corrosion under these conditions is highlighted. CRA steels are comparatively more resistant.     

Metallization on polymer by catalyzation in supercritical CO2 and electroless plating in dense CO2 emulsion

In this study we propose a novel technique for electroless plating on polymer substrates using a dense CO₂ beyond the critical point. Ni–P thin films were fabricated by a novel, hybrid technique consisting of two processes: catalyzation in supercritical CO₂ with Pd bis-acetylacetonate and electroless plating in emulsion with dense carbon dioxide. These catalyzation processes were discussed by atomic force microscopic images and the roughness of the surface. Catalyzation in supercritical CO₂ enabled the nucleation of a large number of Pd nuclei on a polyimide substrate without chemical pretreatment, and the deposition of a uniform Ni–P metal film. Conventional catalyzation without chemical pretreatment led to the deposition of only a few nuclei in sparse, island-like formations. The deposition behavior of Pd nuclei in supercritical CO₂ was different from that in conventional catalyzation. When a polyimide was catalyzed in supercritical CO₂ and plated by conventional electroless plating in electrolyte solution, the plated film was pocked with small, peeled sections formed via the hydrogen bubbles of the sub-reaction and nodules formed via crystal growth of Ni–P. In contrast, the electroless plating in emulsion with dense CO₂ produced a uniformly plated film without peeling or nodules. The improved uniformity was attained by the solubility and diffusivity of the dense CO₂ beyond the critical point in the emulsion.     

梯度材料硬质合金辊环

采用专利技术，研制了具有良好的润滑耐磨性能的硫化物，氧化物梯度材料，并开发成功梯度材料LGM硬质合金辊环，介绍了其工业试验结果，得出梯度材料LGM辊环比普通硬质合金辊环寿命提高50％以上。     

CO2 welding with straight polarity

Powering the arc from a single-phase rectifier with a capacitor voltage multiplier and a choke coil inductance of 1.2 mH results in the formation of welded joints in welding with wires with a diameter of 0.8 and 1.2 mm with a current of 12 A or higher at straight polarity in CO₂. At a current lower than 50 A, the melting factor increases and the difference in the melting rates at straight polarity decreases in comparison with the melting rate at reversed polarity. According to films and oscillograms, the transfer of large droplets is accompanied by neither displacement of the droplets from the electrode axis nor by more intensive splashing.     

Corrosion behaviour of Cr13 steel in CO2 saturated brine with high chloride concentration

The corrosion behaviour of martensitic stainless injection‐pipeline steel X46Cr13 exposed to CO₂ saturated artificial saline brine with high chloride concentration similar to onshore CCS‐site at Ketzin, Germany has been investigated by means of electrochemical technique and microscopic observations at short exposure times (up to 24 h) and by mass loss and metallographic observations at exposure times up to 17520 h. Pitting corrosion kinetics has been characterised and the predictions about the corrosion mechanism are made.     

Long term corrosion of X70 steel and iron in humid supercritical CO2 with SO2 and O2 impurities

Abstract

The corrosion of X70 steel and iron in supercritical CO₂/SO₂/O₂/H₂O environment were investigated after a 454 h exposure. Optical microscopy was applied to observe the morphology of etch pits and synthesise the three-dimensional morphology. X-ray diffraction and X-ray photoelectron spectroscopy were employed to detect the composition of product scales. Experimental results verified that the localised corrosion occurred on the X70 steel sample under corrosion product deposits. Ferrous sulphate, sulphur and iron sulphide were detected as the corrosion products.     

P110钢在不同温度含饱和H_2S/CO_2腐蚀溶液中的腐蚀行为

利用腐蚀失重试验,电化学试验和扫描电子显微镜等方法研究了不同温度下P110钢在含饱和H_2S/CO_2气体的5%NaCl溶液中的腐蚀行为。研究表明:随着温度的升高,P110钢的腐蚀速率呈现出了先增大后减小的规律;在含饱和H_2S/CO_2气体的5%NaCl溶液中,由于温度升高促进了点蚀的发生,在较高温度时形成全面腐蚀,但温度的升高导致H_2S、CO_2气体的溶解度降低,抑制了点蚀的发生,形成厚而致密的腐蚀产物膜,使腐蚀速率随温度升高而降低。