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.     

A study of high-performance plane rake faced twist drills. Part II: Predictive force models

Predictive cutting models for the thrust, torque and power in drilling operations using modified plane rake faced twist drills are presented and discussed. The models are based on the mechanics of cutting approach incorporating the many tool and cutting process variables and have been assessed by numerically analysing the predicted trends and by comparing with the experimental data. It is shown that the model predictions are in excellent agreement with the experimental results with an average deviation of about 5%. Simpler “empirical-type” thrust, torque and power equations are also established for use as an accurate alternative to the complex predictive models to facilitate practical applications.     

Magneto-abrasive machining for the mechanical preparation of high-speed steel twist drills

In this paper investigations of the influence of magneto-abrasive machining (MAM) on the micro-geometry of the tool cutting edges and the surface quality of high-speed steel (HSS) twist drills are presented. It is shown that MAM makes it possible to reproduce defined radii of the cutting edges and corner edges of the drills and improves the tool surface quality. The optimally rounded cutting corner edge of the drill makes it possible to avoid the run-in period of the drill and increases the stability of the cutting edge substantially. This results in an improved wear behaviour and higher tool life of the drill.     

Effects of cutting angle,edge preparation,and nano-structured coating on milling performance of a gamma titanium aluminide

Gamma titanium aluminides are intermetallic alloys. Recently, they have been evaluated as important contenders for structural applications in the automotive and aerospace sectors. This is due to their excellent high-temperature performances and their significantly lower density compared to nickel-based superalloys. In this paper, an analysis of machinability of a gamma TiAl obtained via an electron beam melting (EBM) process is presented. The effects of tool geometry modifications, in terms of cutting tool angles and cutting edge preparation, were investigated. The reduction of radial rake angle and the drag finishing process for cutting edge preparation resulted in an increase of the tool life of the carbide end mills. Nanogradient tool coatings were also observed to affect tool wear during milling tests, and the results highlight that AlSiTiN coating performs better compared to CrAlSiN coating. A post-coating polishing treatment was also taken into account, and it allowed a further reduction of tool wear. The overall results indicate that the machinability of this difficult-to-cut material can be significantly improved by an adjustment of the cutting edge geometry, and by using an AlSiTiN coating system.     

Modeling of tool wear in drilling by statistical analysis and artificial neural network

The useful life of a cutting tool and its operating conditions largely control the economics of the machining operations. Hence, it is imperative that the condition of the cutting tool, particularly some indication as to when it requires changing, to be monitored. The drilling operation is frequently used as a preliminary step for many operations like boring, reaming and tapping, however, the operation itself is complex and demanding.

Back propagation neural networks were used for detection of drill wear. The neural network consisted of three layers input, hidden and output. Drill size, feed, spindle speed, torque, machining time and thrust force are given as inputs to the ANN and the flank wear was estimated. Drilling experiments with 8 mm drill size were performed by changing the cutting speed and feed at two different levels. The number of neurons in the hidden layer were selected from 1, 2, 3, …, 20. The learning rate was selected as 0.01 and no smoothing factor was used. The estimated values of tool wear were obtained by statistical analysis and by various neural network structures. Comparative analysis has been done between statistical analysis, neural network structures and the actual values of tool wear obtained by experimentation.     

High-speed machining of titanium alloys using the driven rotary tool

Machining of titanium at high cutting speeds such as from 4 m/s to 8 m/s is very challenging. In this paper, a new generation of driven rotary lathe tool was developed for high-speed machining of a titanium alloy, Ti–6Al–4V. The rotary tool was designed and fabricated based on the requirements of compact structure, sufficient stiffness and minimal edge runout. Cylindrical turning experiments were conducted using the driven rotary tool (DRT) and a stationary cutting tool with the same insert, for comparison in the high-speed machining of Ti–6Al–4V. The results showed that the DRT can significantly increase tool life. Increase in tool life of more than 60 times was achieved under certain conditions. The effects of the rotational speed of the insert were also investigated experimentally. Cutting forces were found to decline slightly with increase of the rotational speed. Tool wear appears to increase with the rotational speed in a certain speed range.     

Novel methods for rapid assessment of tool performance in milling

The paper examines the effectiveness of two innovative techniques designed to rapidly optimize a milling application. One of them relates to quantifying the relative wear of different insert grades concurrently in a single cutting test, by mounting the inserts in the same cutter, for a quick comparative performance evaluation. Experimental results that illustrate the validity and limitation of this concept, and a scheme for enhancing the reliability of the test method are presented. The other technique refers to rapid identification of the optimum feed/tooth that corresponds to maximum tool life. This entails a test wherein individual inserts in the cutter are subject to feed/tooth that are multiples of a base value, by selectively leaving appropriate number of consecutive insert pockets unoccupied. These novel techniques complement known accelerated tool life tests, and are expedient for industries that engage short production runs, in terms of selecting a suitable insert grade for an application, and determining optimal cutting conditions for the selected grade.     

Effect of flame conditions on abrasive wear performance of HVOF sprayed nanostructured WC-12Co coatings

Nanostructured WC-12Co coatings were deposited by high velocity oxy-fuel (HVOF) spraying with an agglomerated powder. The effect of flame conditions on the microstructure of the nanostructured coatings was investigated. The wear properties of the coatings were characterized using a dry rubber-wheel wear test. The results show that the nanostructured WC-Co coatings consist of WC, W2C, W and an amorphous binder phase. The microstructure of the coating is significantly influenced by the ratio of oxygen flow to fuel flow. Under the lower ratio of oxygen/fuel flow, the nanostructured coating presents a relative dense microstructure and severe decarburization of WC phase occurs during spraying. With increasing ratio of oxygen/fuel flow, the bonding of WC particles in the coating becomes loose resulting from the original structure of feedstock and the decarburization of WC becomes less owing to limited heating to the powder. Both the decarburization of WC particles in spraying and the bonding among WC particles in the coatings affect the wear performance. The examination of the worn surfaces of the nanostructured coatings reveals that the dominant wear mechanisms would be spalling from the interface of WCCo splats when spray particles undergo a limited melting. While the melting state of the spray particles is improved,the dominant wear mechanisms become the plastic deformation and plowing of the matrix and spalling of WC particles from the matrix.     

Tool life determination based on the measurement of wear and tool force ratio variation

Non-linear regression analysis techniques are used to establish models for wear and tool life determination in terms of the variation of a ratio of force components acting at the tool tip. The ratio of the thrust component of force to the power, or vertical, force component has been used to develop models for (i) its initial value as a function of feed, (ii) wear, and (iii) tool lifetimes. Predictions of the latter model have been compared with the results of experiments, and with predictions of an extended Taylor model. In all cases, good predictive capability of the model has been demonstrated. It is argued that the models are suitable for use in adaptive control strategies for centre lathe turning.     

高硬度合金加工热力因素对刀具磨损影响研究进展

针对高硬度合金材料在切削加工中刀具磨损严重的问题,总结了切削力模型、切削温度模型和相关实验研究,阐述了切削力和切削温度与刀具磨损之间的具体联系。从热力耦合的角度出发,综述了刀具磨损机制的研究进展。对高硬度合金切削加工中刀具磨损研究的新方向进行了讨论。     

Analytical Models Based on Composite Layer for Computation of Tool-Chip Interface Temperatures in Machining Steels with Multilayer Coated Cutting Tools

In this study the method of elementary balances (MBE) is applied to predict the temperature fields in uncoated and coated carbide cutting tools. Numerical computations are supported by the experimentally/analytically obtained values of the contact length, the total heat flux and the heat partitioning. The changes in the tool temperature maps, resulting from variable thermal properties of tested materials are considered. In particular, the distribution of temperature across the thin film of 0.01 mm and corresponding temperature rise distribution curves along the rake and flank faces are completely displayed. The simulations have been validated against the measured average rake face temperatures.     

等离子重叠熔敷对Fe-Cr-C-Ti涂层性能的影响

由于材料的磨损性能与其组织关系密切,因此重叠熔敷涂层的制备方法对涂层磨损性能也有着重要影响. 在前期试验基础上制得等离子一层、二层和三层重叠熔敷涂层,采用SEM等观察了重叠熔敷涂层的显微组织和磨损形貌,用半自动显微硬度计进行硬度测试,用磨损试验机测试计算了涂层的摩擦系数,并通过比较3种重叠熔敷涂层的组织和磨损性能,探讨了重叠熔敷工艺对涂层磨损性能的影响,以指导涂层的制备工艺. 结果表明,随着重叠熔敷层数的增加,涂层摩擦系数降低,耐磨性能和载荷特性显著提高.     

Optimization of cutting parameters for maximizing tool life

Optimum use of the cutting tool is a growing need in modern industries since the cost of production is directly affected by this. This paper presents a new approach for improving the cutting tool life by using optimal values of velocity and feed throughout the cutting process. A tool life equation has been established from experimental data and the adhesion wear model. Optimization techniques have been used to maximize the tool life subject to practical constraints while maintaining a constant metal removal rate. The experimental results showed an improvement in tool life by 30%.     

The effects of process faults and misalignments on the cutting force system and hole quality in reaming

A chip thickness and cutting force model that considers the deflection of the tool and the regenerative effect resulting from the presence of process faults and misalignments has been developed for the reaming process. Through a series of experiments, the model has been calibrated and validated. The model predicts tool displacement, torque, thrust, X and Y forces, and the average radius of the reamed hole. The developed model is also shown to be capable of being used as a basis for the on-line detection of process faults present in the system.     

Microstructure and cutting performance of CrTiAlN coating for high-speed dry milling

Using a closed field unbalanced magnetron sputtering system, the cemented carbide end mills were coated with a CrTiAlN hard coating, which consisted of a Cr adhesive layer, a CrN interlayer and a CrTiAlN top layer. The microstructure and mechanical properties of the coating were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro indentation and scratch test. The cutting performance of the coated end mills were conducted by high-speed dry milling hardened steel (P20, HRC 45). The results indicates that the coating is composed of (Cr, Ti, Al)N columnar grains with nanolayers. The coating exhibits good adhesion to cemented carbide substrate and high microhardness of around 30 GPa. The coated end mills show significant improvement on tool life and much lower cutting force as compared to the uncoated ones. And the related mechanisms were discussed.     

SVET method for characterizing anti-corrosion performance of metal-rich coatings

The galvanic interaction between a metal-rich coating and the underlying metal substrate was characterized by a new analysis method based on the scanning vibrating electrode technique (SVET). The total anodic current at various immersion periods was evaluated by integrating the anodic current density on SVET maps. Zinc-rich paints (ZRPs) coated on a steel panel were used to demonstrate the experimental approach. The anti-corrosion performance of the ZRP was analyzed based on the integrated anodic current and the experimental E_OC-i_Int diagram. Closely correlative behaviour was found between the integrated anodic current and the open-circuit potential.     

Tool wear and machining performance of cBN–TiN coated carbide inserts and PCBN compact inserts in turning AISI 4340 hardened steel

PCBN is the dominant tool material for hard turning applications due to its high hardness, high wear resistance, and high thermal stability. However, the inflexibility of fabricating PCBN inserts with complex tool geometries and the prohibitive cost of PCBN inserts are some of the concerns in furthering the implementation of CBN based materials for hard turning. In this paper, we present the results of a thorough investigation of cBN plus TiN (cBN–TiN) composite-coated, commercial grade, carbide inserts (CNMA 432, WC–Co (6% Co)) for hard turning applications in an effort to address these concerns. The effect of cutting speed and feed rate on tool wear (tool life), surface roughness, and cutting forces of the cBN–TiN coated carbide inserts was experimented and analyzed using analysis of variance (ANOVA) technique, and the cutting conditions for their maximum tool life were evaluated. The tool wear, surface roughness, and cutting forces of the cBN–TiN coated and commercially available PCBN tipped inserts were compared under similar cutting conditions. Both flank wear and crater wear were observed. The flank wear is mainly due to abrasive actions of the martensite present in the hardened AISI 4340 alloy. The crater wear of the cBN–TiN coated inserts is less than that of the PCBN inserts because of the lubricity of TiN capping layer on the cBN–TiN coating. The coated CNMA 432 inserts produce a good surface finish (<1.6 μm) and yield a tool life of about 18 min per cutting edge. In addition, cost analysis based on total machining cost per part was performed for the comparison of the economic viability between the cBN–TiN coated and PCBN inserts.     

Residual stresses as a factor in the selection of tungsten carbide coatings for a jet engine application

Tungsten carbide thermal spray coatings are important to the aerospace industry for the mitigation of midspan damper wear on jet engine fan and compressor blades. However, in some cases the coating can fail due to spallation and cracking, and in other situations the fatigue life of a fan or compressor blade is reduced when a coating is applied. Coating failures can result in decreased engine performance and costly maintenance time. A comprehensive experimental research program was conducted to evaluate coating crack resistance in bending, low-cycle fatigue properties of the coating and substrate, coating performance in jet engine tests, and microstructures for a wide range of coating compositions and application processes. Coating residual stress distributions also were evaluated. Eleven coatings were ranked according to their performance relative to the other coatings in each evaluation category. Results from the bend and low-cycle fatigue evaluations were compared to the experimentally evaluated residual stresses. Comparisons of rankings indicate a strong correlation between performance and the residual stresses in the coatings. Results from the program were used to select a suitable coating system for final in-service use based on two important criteria: (1) the coating must not fail while in service, and (2) the coating must not induce crack propagation into the substrate of the midspan damper.     

Laser cladding of stainless steel with Ni–Cr3C2 and Ni–WC for improving erosive–corrosive wear performance

The microstructure and the erosive–corrosive wear (ECW) performance of laser-clad Ni–Cr₃C₂ and Ni–WC coatings with overlapping clad tracks (OCT) on a 0.2% C martensitic stainless steel were investigated by scanning electron microscopy (SEM), XRD, EDX techniques and ECW testing. The coating produced by completely dissolving Cr₃C₂ particles in laser melted pool is composed of austenite (γ) dendrites surrounded by a γ-M₇C₃ eutectic, whereas another one is of granular solidifying structure in which contains the incompletely dissolved WC particles. The microhardness of Ni–WC coating is higher than that of Ni–Cr₃C₂, about 300 HV average. The main reason of microhardness difference is that two coatings have different solidified structure. The comparison of ECW tests found that the reduction of ECW rate dose not occur with the increase of hardness. The Ni–Cr₃C₂ coating with lower hardness has a lower ECW rate with respect to the Ni–WC one. Both average ECW rate decreased by approximately 30% and 60% as compared to that of stainless steel substrate, and both coatings had different ECW mechanism. The increase of ECW resistance is closely related to structure state, kind and amount of carbides, microhardness and toughening ability of the clad layer.