EFFECT OF CUTTING SPEED AND SURFACE CHEMISTRY OF CUTTING TOOLS ON THE FORMATION OF BUL OR BUE AND SURFACE QUALITY OF THE GENERATED SURFACE IN DRY TURNING OF AA6005 ALUMINIUM ALLOY

In the present investigation, AA6005 (ISO: AlSiMg) alloy was machined in turning operation with different cutting tools, such as uncoated cemented carbide insert, PVD TiN coated, CVD diamond coated and PCD insert, under dry environment. Effect of cutting speed was studied for each of the cutting tools with regard to the formation of built-up layer (BUL) or built-up edge (BUE). The rake surface of the tools was characterized by optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopic microanalysis. Particular emphasis was given on wear mechanism of PVD TiN coated insert, conventionally used in machining ferrous alloys, during dry turning of AA6005 alloy. It has been observed that increase of cutting speed from 200 m/min to as high as 1000 m/min could not substantially reduce formation of BUL over tool rake surface during dry machining of AA6005 alloy with uncoated or PVD TiN coated cemented carbide inserts. The potential of diamond-based tools in dry machining of aluminium alloy was also studied. Finally, the effect of cutting speed on surface finish of the workpiece machined with different cutting tools was studied during dry turning of AA6005 alloy.     

Effect of cutting speed on cutting forces and wear mechanisms in high-speed face milling of Inconel 718 with Sialon ceramic tools

In this paper, a series of milling tests were carried out in order to identify the effects of cutting speed on cutting forces and tool wear when high-speed face milling Inconel 718 with Sialon ceramic tools. Both down-milling and up-milling operations were conducted. The cutting forces, tool wear morphologies, and the tool failure mechanisms in a wide range of cutting speeds (600–3,000 m/min) were discussed. Results showed that the resultant cutting forces firstly decrease and then increase with the increase of cutting speed. Under relatively lower cutting speeds (600 and 1,000 m/min), the dominant wear patterns is notching. Further increasing the speed to more than 1,400 m/min, the notching decreases a lot and flank wear becomes the dominant wear pattern. In general, at the same cutting speed, flaking on the rake face and notching on the flank face are more serious in down-milling operation than that in up-milling operation with the same metal removal volume. However, the surface roughness values for down-milling are lower than that for up-milling.     

The effect of oil mist supply on cutting point temperature and tool wear in driven rotary cutting

We examined cutting point temperature and tool wear in driven rotary cutting. Cutting tests under dry and minimum-quantity-lubrication (MQL) conditions of stainless steel (SUS304) were carried out. Cutting point temperature was measured using a tool-work-thermocouple method at various cutting speeds. Cutting point temperature tends to increase with increased cutting speed. In driven rotary cutting, cutting point temperature was lower than that of non-rotation cutting. At high-speed cutting of 500 m/min, cutting point temperature was over 1200 °C in the non-rotation tool, but 1000 °C with driven rotary cutting. In addition, when driven rotary cutting was used with MQL, cutting point temperature was decreased to 900 °C. The magnitude of tool wear corresponded almost precisely to cutting point temperature. Severe adhesion on the rake face was observed and resulted in progressive wear on the rake face in rotary cutting at a cutting speed of 100 m/min. The appropriate cutting speed range passively shifts higher from the viewpoint of cutting temperature with rotary cutting.     

涂层刀具前后刀面摩擦下界面应力分析

基于任意拉格朗日欧拉方法(ALE)建立金属正交切削加工的热力耦合的有限元模型,获得不同速度下切削稳定时涂层刀具前后刀面的接触应力、剪应力以及温度场。通过对涂层刀具施加已获得的刀具表面的应力场和温度场,分析了不同速度下摩擦分界点变化的规律以及对涂层基体界面应力的影响。结果表明,随着速度的增大,摩擦分界点逐渐有向前刀面移动的趋势,表明磨损的方式开始从后刀面磨损向前刀面月牙湾磨损转变,这与切削试验结果一致。同时随着速度的增大,涂层界面应力突变更加显著,表明高速条件下涂层更容易破坏,且速度越高,前刀面涂层破坏的几率越大。     

PCBN刀具高速切削抗氢钢HR-2的性能研究

采用不同CBN含量和晶粒结构的PCBN刀具,在不同切削速度下进行了HR-2抗氢钢的高速精密切削试验。通过对PCBN刀具前、后刀面的显微形貌特征进行观测,分析了刀具的失效磨损机理,研究了不同CBN含量及不同切削速度对刀具使用寿命的影响。对刀具磨损的测量结果表明,PCBN刀具高速切削HR-2时,CBN含量高的刀具显示出更长的使用寿命,且在130-200m/min区间为最佳切削速度区域。SEM和EDS分析结果表明,高速精密切削HR-2的磨损机理为氧化磨损、扩散磨损、粘结磨损,同时存在磨粒磨损以及引起的微崩刃现象。     

Dry machining of aluminum for proper selection of cutting tool: tool performance and tool wear

Machining of aluminum and its alloy is very difficult due to the adhesion and diffusion of aluminum, thus the formation of built-up edge (BUE) on the surface. The BUE, which affects the surface integrity and tool life significantly, affects the service and performance of the workpiece. The minimization of BUE was carried out by selection of proper cutting speed, feed, depth of cut, and cutting tool material. This paper presents machining of rolled aluminum at cutting speeds of 336, 426, and 540 m/min, the feeds of 0.045, 0.06, and 0.09 mm/rev, and a constant depth of cut of 0.2 mm in dry condition. Five cutting tools WC SPUN grade, WC SPGN grade, WC + PVD (physical vapor deposition) TiN coating, WC + Ti (C, N) + Al₂O₃ PVD multilayer coatings, and PCD (polycrystalline diamond) were utilized for the experiments. The surface roughness produced, total flank wear, and cut chip thicknesses were measured. The characterization of the tool was carried out by a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) pattern. The chip underface was analyzed for the study of chip deformation produced after machining. The results indicated that the PCD tool provides better results in terms of roughness, tool wear, and smoother chip underface. It provides promising results in all aspects.     

Fundamental analysis of the mechanism of built-up edge formation based on direct scanning electron microscope observation

Direct scanning electron microscope (SEM) observation of the dynamic behaviour of the built-up edge (BUE) and local strain analysis around the BUE were carried out to investigate fundamentally the mechanism of BUE formation for low carbon steel. There are two types of crack which play significant roles in the mechanism of BUE formation: one forms below the flank face of the tool and the other forms subsequently ahead of the rake face of the tool. The former starts at the machined surface, a few tens of micrometres from the cutting edge of the tool, and grows in the primary shear zone accompanied by severe strain concentration. The latter occurs along the secondary shear zone and is caused by extensive shearing a certain distance away from the cutting edge of the tool. The morphology of the BUE is determined by the formation of both cracks, its growth depending on the strain concentration and the growth of the cracks.     

Slip-line modeling of built-up edge formation in machining

Extensive investigations on built-up edge (BUE) formation in machining have been conducted in the past. However, very little effort has been made to quantitatively predict the size of the BUE and its effect on chip flow and cutting forces under different machining conditions. This prediction is important because it is the key to predicting the fluctuation of cutting forces and provides better rationale for explaining various machining phenomena associated with BUE formation. A new slip-line model for machining with BUE formation and its associated hodograph are proposed in this paper. Consisting of four slip-line sub-regions, the new slip-line model meets both the stress equilibrium and velocity requirements of material flow. The new model simultaneously predicts the length and height of the BUE, cutting and thrust forces, chip up-curl radius, chip thickness, and tool–chip contact length. Dewhurst and Collins's matrix technique for numerically solving the slip-line problem is employed in the mathematical formulation of the model, with non-unique solutions being obtained. It is demonstrated that one of the four slip-line angles included in the new model directly governs the size and surface shape of the BUE. Compared with the well-known Lee and Shaffer's model, the new model predicts a much longer BUE covering a larger portion of the tool rake face. A small tool rake angle tends to generate a large BUE. The predicted trends of the variation of relevant machining parameters are consistent with experimental observations.     

Failure mechanisms of a PCD tool in high-speed face milling of Ti–6Al–4V alloy

High-speed milling tests were carried out on Ti–6Al–4V titanium alloy with a polycrystalline diamond (PCD) tool. Tool wear morphologies were observed and examined with a digital microscope. The main tool failure mechanisms were discussed and analyzed utilizing scanning electron microscope, and the element distribution of the failed tool surface was detected using energy dispersive spectroscopy. Results showed that tool flank wear rate increased with the increase in cutting speed. The PCD tool is suitable for machining of Ti–6Al–4V titanium alloy with a cutting speed around 250 m/min. The PCD tool exhibited relatively serious chipping and spalling at cutting speed higher than 375 m/min, within further increasing of the cutting speed the flank wear and breakage increased greatly as a result of the enhanced thermal–mechanical impacts. In addition, the PCD tool could hardly work at cutting speed of 1,000 m/min due to the catastrophic fracture of the cutting edge and intense flank wear. There was evidence of workpiece material adhesion on the tool rake face and flank face in very close proximity to the cutting edge rather than on the chipped or flaked surface, which thereby leads to the accelerating flank wear. The failure mechanisms of PCD tool in high-speed wet milling of Ti–6Al–4V titanium alloy were mainly premature breakage and synergistic interaction among adhesive wear and abrasive wear.     

Cutting performance of coated carbide tools in high-speed face milling of AISI H13 hardened steel

In the present study, high-speed face milling of AISI H13 hardened steel was conducted to investigate the cutting performance of coated carbide tools. The characteristics of chip morphology, tool life, tool wear mechanisms, and surface roughness were analyzed and compared for different cutting conditions. It was found that as the cutting speed increased, the chip morphology evolved in different ways under different milling conditions (up, down, and symmetric milling). Individual saw-tooth segments and sphere-like chip formed at the cutting speed of 2,500 m/min. Owing to the relatively low mechanical load, longest tool life can be obtained in up milling when the cutting speed was no more than 1,000 m/min. As the cutting speed increased over 1,500 m/min, highest tool life existed in symmetric milling. When the cutting speed was 500 m/min, owing to the higher mechanical load, the flaked region on the tool rake face in symmetric milling was much larger than that in up and down milling. There was no obvious wear on the tool rake face at the cutting speed of 2,500 m/min due to the short tool-chip contact length. In symmetric milling, the delamination of tool material, which did not occur in up and down milling, was caused by the relatively large cutting force. Abrasion had great effect on the tool flank wear in symmetric milling. With the increment of cutting speed, surface roughness decreased first and then increased rapidly. Lowest surface roughness can be obtained at the cutting speed of about 1,500 m/min.     

Machinability issues in turning of Al-SiC (10p) metal matrix composites

The paper presents the results of an experimental investigation on the machinability of fabricated aluminum metal matrix composite (A356/SiC/10p) during continuous turning of composite rods using medium grade polycrystalline diamond (PCD 1500) inserts. MMC’s are very difficult to machine and PCD tools are considered by far, the best choice for the machining of these materials. Experiments were conducted at LMW-CNC-LAL-2 production lathe using PCD 1500 grade insert at various cutting conditions and parameters such as surface roughness, specific power consumed, and tool wear were measured. Machining was continued till the flank wear land on the tool crossed 0.4 mm. The influences of cutting speed on the insert wear and built-up edges (BUEs) formation were studied. The present results reaffirm the suitability of PCD for machining MMCs. Though BUE formation was observed at low cutting speeds, at high cutting speeds very good surface finish and low specific power consumption could be achieved.     

PCD刀具连续切削花岗岩的性能研究

用三种不同晶粒尺寸的自制PCD刀具,在三种切削速度下进行了花岗岩的湿式连续切削试验。对刀具前、后刀面的显微形貌特征进行了观测,分析了刀具失效机理,比较了不同晶粒尺寸及不同切削条件下刀具的切削寿命。对刀具后刀面磨损的测量结果表明,在三种切削速度下,粗颗粒PCD刀具显示出更长的刀具寿命;随着切削速度的增加,三种刀具的寿命都有所下降。SEM二次电子图像显示,PCD010和PCD005刀具的磨损机制为硬质点的机械磨损,而晶粒较粗的PCD030刀具的主要磨损机制为机械磨损,同时伴有穿晶磨损。     

Effect of coating layer loss on the wear rate change of coated carbide tools in turning process

This paper reports an experimental study of flank wear on TiN- and TiAlN-coated carbide tools in the turning of AISI 1045, AISI 4135, ductile cast iron, and Inconel 718, and it was conducted with the purpose of showing the relationship between the change in wear rate and the loss of coating layer on the cutting edge. It was found that the relation between cutting distance and flank wear in log-log scale clearly shows the change in wear rate, thus providing a straightforward way to determine the relation between worn out coating layer and increase in wear rate. This relation was confirmed by analyzing the presence of coating layer before and after the inflection point appears by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) photographs. It was observed that the coating layer on the flank face is worn away and finally is worn out. However, even if the layer on the flank face is worn out, tool wear is suppressed as long as the coating layer on the cutting edge exists. On the other hand, when the coating layer on the cutting edge is worn out, the wear resistance of the tool depends on the substrate; thus, the wear rate increases. According to the results, as the cutting speed increases, the change in wear rate appears in a shorter cutting distance, making flank wear to be high. High pressure and high temperature act on the rake face; thus, thermal stability of the coating layer in the cutting edge is important. A low cutting speed decreases cutting efficiency, but a high cutting speed causes flank wear to be high; therefore, in order to optimize machining cost, an acceptable cutting speed, from the standpoint of tool wear, should be selected.     

A comparative study of multilayer and functionally graded coated tools in high-speed machining

Multilayer-coated tool systems have been effective in controlling mechanical and thermal loads, especially in high-speed cutting regime. In this study, cutting performance of tungsten carbide tools with restricted contact length and multilayer chemical vapour deposition deposited coatings, TiCN/Al₂O₃/TiN (in series) and TiCN/Al₂O₃–TiN (functionally graded), was investigated in dry turning. Cutting tests were conducted on low carbon alloy steel AISI/SAE 4140 over a wide range of cutting speeds between 200 and 879?m/min. Results including cutting forces, chip compression ratio, shear angle, contact area inclusive of sticking and sliding phenomena and tool flank wear are presented. In particular, prediction of heat partition into the cutting tool inserts was carried out using a combination of experimental tests and the finite element method. The results show that coating layouts and cutting tool edge geometry can significantly affect heat distribution into the cutting tool. The paper clearly shows the role and potential benefits of applying different top coats on the rake and flank faces with regards contact phenomenon, impact on thermal shielding and tool wear. An appropriate coating layout selection is crucial in controlling tool wear, especially in high-speed machining.     

Suppression of notch wear of a whisker reinforced ceramic tool in air-jet-assisted high-speed machining of Inconel 718

This paper describes the notch and flank wear specific to a SiC whisker reinforced alumina tool in air jet assisted (AJA) turning of nickel-base superalloy Inconel 718 at high cutting speeds. An AJA machining experiment has revealed that the air jet applied to the tool tip in addition to coolant dramatically reduces the depth-of-cut notch wear. As a result, the width of flank wear, but not the size of notch wear, determined the life of a ceramic tool in AJA machining of Inconel 718. This is a reason for the large extension and small variation of the tool life when high speed AJA machining is adopted. The maximum tool life length reached 2160 m at a cutting speed of 660 m/min under the given cutting conditions. Finally, the mechanisms of the notch and flank wear of a SiC whisker reinforced alumina tool in AJA machining are discussed from the viewpoints of tribochemical reactions and tool wear anisotropy.     

Ultraprecision turning of electroless nickel: effects of crystal orientation and origin of diamond tools

This paper deals with (i) the performance of natural and artificial diamond tools and (ii) the effects of crystal orientations at rake face of diamond tool for long distance (>200 km) ultraprecision machining of electroless nickel. The criteria for cutting performance of the diamond tool include flank wear, crater wear, workpiece surface finish, and cutting forces. Experimental results show that the natural diamond tool has superior performance compared to the artificial one as it experienced lower cutting forces and lower flank and crater wears. It was also found that the cutting tool with {110} crystal orientation at rake face performs better than the tool with {100} crystal orientation in terms of amount of wear, surface finish, and cutting forces.     

Statistical analysis of process parameters in drilling of AL/SICP metal matrix composite

Four micro-holes were made using micro-EDM on rake face of the cemented carbide (WC/TiC/Co) tools. MoS₂, CaF₂, and graphite solid lubricants were respectively embedded into the four micro-holes to form self-lubricated tools (SLT-1, SLT-2, and SLT-3). Dry machining tests on hardened steel were carried out with these self-lubricated tools and conventional tools (SLT-4). The cutting forces, average friction coefficient between tool and chip, and tool wear were measured and compared. It was shown that the cutting forces and tool wear of self-lubricated tools were clearly reduced compared with those of the SLT-4 conventional tool. The SLT-1 self-lubricated tool embedded with MoS₂ just exhibited lower friction coefficient between tool and chip in cutting speed of less than 100?m/min; the SLT-2 self-lubricated tool embedded with CaF₂ possessed lower friction coefficient in cutting speed of more than 100?m/min; and the SLT-3 self-lubricated tool embedded with graphite accomplished good lubricating behaviors steadily under the test conditions. It is indicated that cemented carbide inserts with four micro-holes on rake face embedded with appropriate solid lubricants on rake face is an effective way to reduce cutting forces and rake wear.     

Wear mechanism of coated tools in the turning of ductile cast iron having wide range of tensile strength

In this study different specimens of ductile cast iron with tensile strength ranking from 400 MPa to 675 MPa were turned with K15 carbide, TiN coated and TiAlN coated tool in order to investigate wear mechanism and performance. Cutting forces and cutting temperature were similar for both coated tools, however flank wear and BUE were the lowest on the TiAlN coated tool, for this reason the TiAlN coated tool is suitable in the machining of ductile cast iron. The proposed tool wear mechanism is based on like-intermittent cutting caused by the pass from hard matrix to the soft graphite occasioning wear by adhesion. The analysis of the flank wear on coated tools is proposed by means of the wear curves in logarithmic scale instead of the usual linear scale. In this way, the change in wear rate is easily observed. This phenomenon was related with the wear out of the coating layer. The partial loss of the coating layer on cutting edge was confirmed by the EDS mapping images and SEM photographs.     

Wear of Ceramic Cutting Tools in Ni-Based Superalloy Machining

The machining performance of monolithic and composite silicon nitride and Al₂O₃-based cutting tools in continuous turning of Inconel 718 was examined. The character of tool wear has been found to vary, depending on the feed rate and cutting speeds. At a lower cutting speed, of 120 m/min, tool life is restricted by depth-of-cut notching, while at high cutting speeds (300 m/min), tools fail due to nose wear and fracture. The sensitivity of monolithic Si₃N₄ and Al₂O₃ to depth-of-cut notching was found to he significantly reduced with the addition of SiC whiskers, and to a lesser extent with TiC particulates. The ceramic composites also exhibited resistance to nose and flank wear that was higher than that of the monoliths. The internal stress distribution for the cutting tool has been calculated using the finite element method and is the basis for explaining fracture beneath the rake face. Cutting tool wear results are discussed in terms of chemical and mechanical properties of the ceramic tool material, abrasive wear, thermal shock resistance, and metal cutting conditions.     

CN35硬质合金涂层刀具高速车削淬硬钢的磨损与破损形态

借助于扫描电镜照片和能谱分析,对高速车削淬硬45钢时CN35硬质合金涂层刀具的失效形态及其机理进行了观察和分析。结果显示,在高速切削条件下,涂层刀具的失效形态主要分为破损与磨损两种,刀具正常磨损失效过程仍然遵循常规切削条件下三个阶段的程序。刀具破损失效发生在低速切削阶段,且随着切削速度的提高,破损部位由后刀面转移到前刀面;高速切削时,刀具失效形式倾向于后刀面磨损、边界磨损和切削刃斜面磨损,因高热、粘结、疲劳、氧化、扩散和热裂等原因造成刀具切削功能丧失。