Brittleness and fatigue effect of mono- and multi-layer PVD films on the cutting performance of coated cemented carbide inserts

The effect of brittleness and fatigue of mono- and multi-layer PVD films on coated tools cutting performance is introduced. Cemented carbide inserts were coated to the same overall film thickness with various numbers of layers. Nanoindentations were conducted to evaluate the hardness of the diverse coating structures. The film brittleness and fatigue were characterized by nano- and macro-impact tests respectively. The coated inserts’ wear behaviour was investigated in milling hardened steel. The attained results revealed the coatings’ brittleness and fatigue endurance enhancement by increasing the number of film's layers. This increase leads simultaneously to the coated tool life improvement.     

Influence of Ar ion etching on the surface topography of cemented carbide cutting inserts

In situ substrate cleaning by ion etching prior to physical vapor deposition of hard coatings alters topography and composition of the surface to be coated. Within this work, the influence of Ar ion etching on the surface topography of cemented carbide cutting inserts with different geometries was investigated. The surface of cutting inserts before and after ion etching was evaluated by different scanning electron microscopy techniques to illuminate the effect of ion etching on both, the cutting edges and the flat surface. Additionally, profilometric measurements were carried out to determine changes of the surface roughness and to quantify the removed material by measuring the step height between the etched and un-etched surface. Surface roughness and thickness of the removed layer increased with etching time at constant bias voltage, while the applied voltage had only a minor influence. In addition, energy-dispersive X-ray spectroscopy mappings indicated changes of the surface composition by ion etching due to preferential sputtering of the cobalt binder phase.     

The connection between cutting and clamping forces in turning

The chuck has, for a long time, been considered the weakest link of a lathe. This is mainly due to its two-fold connection, to the machine spindle on the one hand and to the workpiece on the other. An additional limitation of the chuck lies in the incomplete knowledge one has of the load it is exposed to during operation, which usually leads to a less than optimal machining process. Unless our understanding of the properties of clamping devices and of the effects of external loads is improved, the risk is great that this deficiency in our knowledge will be a limiting factor in the continuing development of machine tools [1]. The aim of this work has been to isolate and to investigate the factors that influence the necessary clamping forces when using jaw chucks. An extensive model development has been carried out towards a better understanding of the problem. The models thus developed have been analyzed as to their validity using the FEM and also through experimental studies. The present study has been limited to the processing of ring shaped, weak workpieces.     

Evaluation of wear of turning carbide inserts using neural networks

Recent trends, being towards mostly unmanned automated machining systems and consistent system operations, need reliable on-line monitoring processes. A proper on-line cutting tool condition monitoring system is essential for deciding when to change the tool. Many methods have been attempted in this connection.Recently, artificial neural networks have been tried for this purpose because of its inherent simplicity and reasonably quick data-processing capability. The present work uses the back propagation algorithm for training the neural network of 5-3-1 structure. The technique shows close matching of estimation of average flank wear and directly measured wear value. Thus the system developed demonstrates the possibility of successful tool wear monitoring on-line.     

A cBN-TiN composite coating for carbide inserts: Coating characterization and its applications for finish hard turning

Cubic boron nitride (cBN)-titanium nitride (TiN) composite coating combines the thermal stability and super abrasiveness of cubic boron nitride (cBN) and the good lubricity of TiN, offering the opportunity for designing cutting tools with application specific new geometries (flat, chip breaker, and round shape) and cost effectiveness. In particular, the cBN based coating on carbide inserts is complementary to widely used polycrystalline cubic boron nitride (PCBN) compact tools for finish hard turning applications. This paper reports the results of a study addressing the surface morphology, surface roughness, coating cross section, chemical composition, crystal structure, microhardness, adhesion, and the wear life of this cBN-based coating deposited on carbide inserts (SNMG432) for finish turning of hardened AISI 4340 steel bars. The surface quality of machined workpieces in terms of their surface roughness and white layer formation are also analyzed and the results are presented.     

涂层硬质合金刀片车削典型CFRP的工程技术研究

用相同几何结构、不同材质的2种涂层硬质合金刀片车削碳纤维增强复合材料T800H棒料,通过多分量力学传感器、压力传感器和高速摄影机监测车削过程中的切削载荷和刀具工作状态,通过光学扫描系统和数码显微系统观测分析工件已加工表面和切屑的形貌特征。结果表明:车削T800H棒料时,每种刀具都存在一个临界切削速度v_cr,在相同进给量f和恒定切削深度a_p的情况下,切削速度v_c对工件已加工表面质量影响小。实验还表明:采用硬度更高的刀具车削碳纤维,能获得更好的表面质量。      

The effect of substrate pretreatments and HPPMS-deposited adhesive interlayers’ materials on the cutting performance of coated cemented carbide inserts

High power pulsed magnetron sputtering (HPPMS), substrate pretreatments and adhesive interlayers can enhance tool life significantly. In the conducted research, TiAlN PVD-films and W-, Ti- or Cr-adhesive nanointerlayers were deposited by HPPMS on different superficially treated hardmetal inserts. The mechanical properties of the coatings were determined via nanoindentations and mathematical analysis. Additionally, inclined impact tests and milling investigations were performed to examine the substrate pretreatment and interlayer effects on film adhesion and wear behaviour. The results reveal that HPPMS jointly with an appropriate substrate pretreatment and a Cr-nanointerlayer lead to significant adhesion and cutting performance improvement.     

Investigation on wear behaviour of cryogenically treated TiAlN coated tungsten carbide inserts in turning

Cryogenic treatment has been ascribed as a way of improving the cutting life of tungsten carbide turning inserts. Most of the research conducted till date has not reported any effort to excavate the effect of cryogenic treatment on the performance of coated tungsten carbide inserts in terms of adhesion strength of coatings deposited on tungsten carbide substrate. In order to understand the effect of cryogenic treatment on the adhesion strength of coatings, a comparative investigation of the wear behaviour and machining performance of cryogenically treated coated tungsten carbide inserts in orthogonal turning has been carried out in this study. The commercially available TiAlN coated square shaped tungsten carbide inserts (P25) were procured and subjected to cryogenic treatment at two levels −110 °C (shallow treatment) and −196 °C (deep treatment) of temperature independently. The criterion selected for determining the turning performance was based on the maximum flank wear (0.6 mm) as recommended in ISO 3685-1993. The results showed that shallow cryogenically treated coated tungsten carbide inserts performed significantly better as compared with deep cryogenically treated and untreated inserts. Major outcome of the present study includes a substantial decrease in tool life of deep cryogenically treated inserts as compared to untreated inserts indicating the destructive effect of deep cryogenic temperature (−196 °C) on TiAlN coated inserts which is further supported by VDI-3198 indentation test.     

Experimental investigation of the cutting temperature when turning with coated indexable inserts

This paper deals with an experimental investigation into the different factors which influence the temperature which occur at the coating/substrate–chip interface when machining a medium carbon steel and an austenitic stainless steel. Both flat-faced and grooved inserts coated with TiC, TiC/TiN and TiC/Al₂O₃/TiN were used. A standard K-type thermocouple embedded in the workpiece was used to convert measured efms to the interfacial temperature. Some optimal coating structures for high speed machining of these steels corresponding to the minimum interface temperature were selected. In particular, it was observed that by the proper selection of the thermal properties of the coating and the workpiece materials, which result in a substantial increase in the interface temperature, the effect of a thermal barrier in the top layer of the coating can occur.     

Optimizing the use of dry cutting in rough turning steel operations

The main objective of using cutting fluids in machining operations is the reduction of temperature in the cutting region to increase tool life. However, the advantages offered by cutting fluids have been strongly debated because of their negative effects on the economic aspect, the environment and the health of workers using them. A trend to solve these problems is cutting without fluid, a method named dry cutting, which has been made possible due to technological innovations. This work aims to seek conditions in which dry cutting is satisfactory compared with the flood of fluid (called here wet cutting) usually used. Aiming at this goal, several experiments were carried out varying parameters such as cutting speed, feed, depth of cut and tool material in rough turning of ABNT 1045 steel in dry and wet cutting. The analysis of the results showed that wet turning is, as expected, better for tool life. The second conclusion is that dry cutting cannot be used with large depth of cut. But the main conclusion is that, if the tool material is changed to a more wear resistant one, dry cutting can be used with results very similar to those obtained with a flood of fluid.     

A power spectrum analysis of effect of rolling texture on cutting forces in single-point diamond turning

In most of the existing metal cutting theories, the workpiece is assumed to be homogeneous and most continuum theories do not take into account the effect of crystallographic anisotropy that causes variations in the shear plane at the grain level and hence of the cutting force. As the depth of cut in single-point diamond turning (SPDT) is usually less than the average grain size of a polycrystalline aggregate, cutting is generally performed within a grain. At this scale, the difference in the individual grain properties cannot be integrated out and a continuum solution would be insufficient. As a result, this paper presents a power spectrum analysis of the periodic fluctuation of micro-cutting forces in SPDT of polycrystalline materials. The experimental results show that the features of the power spectra of the cutting forces can be well correlated with the change of rolling texture of the materials being cut. These findings help to explain quantitatively the fluctuation of micro-cutting forces and hence the effect of rolling texture in SPDT, which are not encountered in conventional machining.     

Modeling of turning process cutting forces for grooved tools

A mechanistic modeling approach to predicting cutting forces for grooved tools in turning has been developed. The model assumes the existence of an equivalent orthogonal cutting operation for any oblique operation. The effects of tool nose radius and chip flow have been incorporated by defining a set of equivalent groove parameters. Two calibration methods have been presented for the model. A variety of commercial grooved inserts were chosen to validate the model. The workpiece material used was AISI 1018 steel. The force predictions from the model were found in good agreement with the measured forces. The effects of cutting conditions and groove parameters on the cutting forces and their implication in designing grooved tools were also determined.     

Effect of the crystallinity of diamond coatings on cemented carbide inserts on their cutting performance in milling

Micro-crystalline diamond (MCD) coatings were deposited on cemented carbide inserts at different temperatures using hot filament chemical vapor deposition technique. For investigating the effect of the developed diamond crystallinity on the fatigue strength and wear behaviour of the prepared MCD coated inserts, inclined impact tests and milling investigations were conducted correspondingly. Raman spectra were recorded for capturing the crystalline phases after the film deposition and their potential changes after the impact and milling experiments induced by the mechanical and thermal loads. Thus, the explanation of the cutting performance of the employed diamond coated inserts with various crystalline phases was enabled.     

A method for measuring cutting forces in boring operations

In boring operations, two methods of measuring cutting forces are possible: measurement of forces exerted on the tool, by means of a dynamometric boring bar, or measurement of forces exerted on the workpiece, by means of a dynamometric table.In the second method, it is difficult to read the three components of the cutting force (tangential, radial and axial force), because the tool is rotating with respect to the workpiece. A three-component dynamometer on which the workpiece is clamped gives the axial (feed) force directly. The other two outputs, instead, are projections on two fixed axes of a force that is the sum of the radial and tangential components, and that rotates at spindle speed.This paper describes a simple, reliable method for solving the problem of obtaining the single components of the rotating force. Tangential and radial forces are measured continuously by means of an electrical resolver and lowcost electronic equipment.     

Optimal process parameters for parallel turning operations on shared cutting surfaces

To enhance productivity in industrial settings, turning machines are increasingly being used with multiple turrets. This machine configuration enables parallel machining at different or at the same cutting surface using independent tools. However, there is a dynamic interaction between the cutting processes due to the waviness induced on the shared cutting surface as well as due to the dynamic coupling through the machine structure. This dynamic interaction can lead to a significant reduction of the chip removal rate compared to two conventional processes. To utilize the productivity advantage of parallel turning processes, an examination of the process-machine-interaction considering the dynamic coupling of the cutting processes is required. Hence, this paper discusses parametrization for stable processing of parallel turning operations. Therefore, time and frequency domain-based simulation models are developed and matched with experimental cutting tests. Additionally, the influence of the radial angle between the tools is investigated. This angle influences the dead time between two successive cuts for parallel turning processes on the same cutting surface. The dead time in turn directly affects the process stability limit. Thus, with the help of the developed simulation models, an optimal process parametrization for parallel turning operations can be determined.     

Influence of melt treatments and turning inserts on cutting force and surface integrity in turning of Al-12Si and Al-12Si-3Cu cast alloys

The microstructures, machinability and surface characteristics of Al-12Si and Al-12Si-3Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al-12Si-3Cu alloys have microstructures consisting of uniformly distributed α-Al dendrites, eutectic Al-silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (un-coated, PVD and Polished CVD diamond coated) were evaluated in machining Al-12Si and Al-12Si-3Cu cast alloys under dry environment using a lathe. The Polished CVD diamond coated insert outperformed the un-coated or PVD-coated cutting inserts which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The Polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstrutural changes in the Al-12Si and Al-12Si-3Cu cast alloys and their machinability and surface finish when different turning inserts used.     

Wear behaviour of cryogenically treated tungsten carbide inserts under dry and wet turning conditions

Cryogenic treatment has been acknowledged as a means of extending the life of tungsten carbide inserts but no study has been reported in open literature regarding the effect of coolant on the performance of cryogenically treated tungsten carbide inserts in turning. In order to understand the effect of coolant, a comparative investigation of the wear behaviour of cryogenically treated tungsten carbide inserts in dry and wet orthogonal turning has been carried out in this study. The commercially available uncoated square-shaped tungsten carbide inserts with chip breakers were procured and cryogenically treated at ?196 °C and the cutting tests were executed in accordance to the International Standard Organisation, ISO 3685-1993 for continuous and interrupted machining mode. The criterion selected for determining the tool life was based on the maximum flank wear (0.6 mm) and the selection of cutting conditions was made to ensure the significant wear at a suitable time interval. The results showed that cryogenically treated tungsten carbide inserts performed significantly better in wet turning conditions under both continuous and interrupted machining modes especially at higher cutting speeds. A considerable increase in tool life was also recorded in interrupted machining mode as compared with continuous machining mode.     

Generalized modeling of chip geometry and cutting forces in multi-point thread turning

A generalized mechanics model of multi-point thread turning operations is presented. The cross section of the chip is determined from the thread profiles of the current and previous teeth as well as the infeed settings of the tool. The chip is discretized along the cutting edge, and the cutting force coefficients are evaluated for each element considering the varying effective oblique cutting angles and chip thickness. The nonlinear Kienzle force model is used to account for the effect of edge radius at low chip thickness values. Total cutting forces are obtained by resolving the elemental forces in the insert coordinate system, and integrating them along the engaged teeth. The experimentally validated generalized mechanics model can be used to predict the chip and cutting load distributions for multi-point inserts with custom thread profiles and infeed plans. The model can be used for both process planning and insert design.     

A new model for the prediction of cutting forces in micro-end-milling operations

In this work an analytical forces model for real micro-end-milling is developed by regarding the main factors which have influence on the process. The run-out or eccentric deviation of the tool path is taken into account as well as the tool deflection. A linear equation system has to be solved to obtain the forces, so it requires a low computational cost. Size effect is also considered since the chip thickness is comparable to the edge radius and therefore there is chip removal only when it is higher than a certain value. This phenomenon causes variation in the entry and exit angles of the tool in the workpiece. These factors have already been studied in conventional milling. However, since they have not been yet considered for micromilling, the validity of mechanistic models is limited. The model has been developed for two different types of side micromilling: up milling and down milling. Experimental results carried out on Steel and Aluminum show a good correlation with the model. The forces model proposed in this work can be used in a process monitoring in real time as well as in adaptive control of the process.     

PCBN刀具干车淬硬钢时倒棱前角对切削力和刀具磨损的影响

PCBN刀具磨出负倒棱是为了加强刀具的刃口强度，以减少刀具加工时可能出现的破损情况。本文通过对PCBN刀具加工淬硬轴承钢GCr15的一系列试验数据加以分析，得出倒棱前角和切削力、刀具磨损之间的关系，进而得出在实际加工情况下应该采用的最佳倒棱前角值。试验表明：当倒棱前角取15度且切削速度为125m／s时，刀具具有最好的加工效果，不但切削力可以达到最小值，刀具磨损最轻，而且刀具寿命也达到了最大值。