Effects of Coating Materials on the Machinability of a Nickel Base,C-263, Alloy

PVD coated (TiN/TiCN/TiN, TiAIN and TiZrN) and uncoated carbide tools were used to machine a nickel base, C-263, alloy at high-speed conditions. The test results show that the multiple TiN/TiCN/TiN coated inserts gave the best overall performance in terms of tool life when machining at cutting speeds up to 68 m min and at depths of cut of 0.635 mm, 1.25 mm and 2.54 mm. All the tool grades tested gave fairly uniform surface roughness (Ra) values, below the rejection criterion, at lower speed conditions. The TiZrN coated inserts gave the lowest component forces when machining at lower cutting speed conditions while the TiA/N coated inserts gave the lowest component forces when machining at a higher speed of 68 m min^?1 and depth of cut of 1.25 mm. This tool performance can generally be attributed to the difference in their ability to provide effective lubrication at the cutting zone, thermal conductivity of the coating materials as well as the cutting conditions employed. The uncoated carbide tools generally encountered more severe crater wear, chipping/fracture of the cutting edges as well as pronounced notching during machining. This is due to their inability to provide effective lubrication at the cutting zone, thus impeding the gliding motion of the chips along the rake and flank faces respectively, thus accelerating flank wear. Analysis of the worn tool edges revealed adhesion of a compact “fin-shaped” structure of hardened burrs with saw-tooth like edges. This generally alters the initial geometry of the cutting edge, consequently resulting to poor surface finish with prolonged machining.     

Effect of High-Pressure Coolant Supplies when Machining Nickel-Base,Inconel 718, Alloy with Ceramic Tools

Chip breakability is significantly improved with the use of high pressure coolant supply. This is a result of the reduction in the tool-chip contact length during machining as the coolant under high pressure lifts the chip up after passing the deformation zone. Increasing the coolant pressure results in shorter ceramic tool life when machining Inconel 718 suggesting that the high pressure coolant supply reduces temperature at the cutting zone below a critical level where ceramic tools can perform satisfactorily. The inadequate fracture toughness of ceramic tools makes them more susceptible to failure by mechanical action such as notching at the depth of cut line and premature fracture. The notch wear rate increases with higher coolant supply pressure due to significant erosion of the tool material by the high pressure coolant jet. This mechanically related failure mode occurs on a random basis leading to inconsistency in tool performance, accelerated by fluctuations in thermal and mechanical properties when machining under high pressure coolant supplies.     

The Effect of Argon-Enriched Environment in High-Speed Machining of Titanium Alloy

A major factor hindering the machinability of titanium alloys is their tendency to react with most cutting tool materials, thereby encouraging solution wear during machining. Machining in an inert environment is envisaged to minimize chemical reaction at the tool-chip and tool-workpiece interfaces when machining commercially available titanium alloys at higher cutting conditions. This article presents the results of machining trials carried out with uncoated carbide (ISO K10 grade) tools in an argon-enriched environment at cutting conditions typical of finish turning operations. Comparative trials were carried out at the same cutting conditions under conventional coolant supply. Results of the machining trials show that machining in an argon-enriched environment gave lower tool life relative to conventional coolant supply. Nose wear was the dominant tool-failure mode in all the cutting conditions investigated. Argon is a poor conductor of heat; thus, heat generated during machining tends to concentrate in the cutting region and accelerate tool wear. Argon also has poor lubrication characteristics, leading to increasing friction at the cutting interfaces during machining and an increase in cutting forces required for efficient shearing of the workpiece.     

Wear behaviour of alumina based ceramic cutting tools on machining steels

The advanced ceramic cutting tools have very good wear resistance, high refractoriness, good mechanical strength and hot hardness. Alumina based ceramic cutting tools have very high abrasion resistance and hot hardness. Chemically they are more stable than high-speed steels and carbides, thus having less tendency to adhere to metals during machining and less tendency to form built-up edge. This results in good surface finish and dimensional accuracy in machining steels. In this paper wear behaviour of alumina based ceramic cutting tools is investigated. The machining tests were conducted using SiC whisker reinforced alumina ceramic cutting tool and Ti[C,N] mixed alumina ceramic cutting tool on martensitic stainless steel-grade 410 and EN 24 steel work pieces. Flank wear in Ti[C,N] mixed alumina ceramic cutting tool is lower than that of the SiC whisker reinforced alumina cutting tool. SiC whisker reinforced alumina cutting tool exhibits poor crater wear resistance while machining. Notch wear in SiC whisker reinforced alumina cutting tool is lower than that of the Ti[C,N] mixed alumina ceramic cutting tool. The flank wear, crater wear and notch wear are higher on machining martensitic stainless steel than on machining hardened steel. In summary Ti[C,N] mixed alumina cutting tool performs better than SiC whisker reinforced alumina cutting tool on machining martensitic stainless steel.     

Cutting performance and wear mechanisms of Sialon–Si3N4 graded nano-composite ceramic cutting tools

Sialon–Si₃N₄ graded nano-composite ceramic tool materials were fabricated by using hot-pressing technique. The residual stresses in the surface layer of the graded ceramic tool materials were calculated by the indentation method. The cutting performance and wear mechanisms of the graded tools were investigated via turning of Inconel 718 alloy in comparison with common reference tools. The surface roughness of the finish hard turning of Inconel 718 and the microstructures of the chips were also examined. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that graded structure in Sialon–Si₃N₄ graded ceramic tool materials can induce residual compressive stresses in the surface layer during fabrication process. Tool lifetime of graded ceramic tool was higher than that of the common reference tool. The longer tool life of the graded nano-composite ceramic tool was attributed to its synergistic strengthening and toughening mechanisms induced by the optimum graded compositional structure of the tool and the addition of nano-sized particles. Wear mechanisms identified in the machining tests involved adhesive wear and abrasive wear. The mechanisms responsible for the higher tool life were determined to be the formation of compressive residual stress in the surface layer of the graded tools, which led to an increase in the resistance to fracture.     

铁基粉末冶金材料的高速干切削试验研究

用陶瓷刀具、涂层刀具和硬质合金刀具进行了铁基粉末冶金零件的干切削对比试验,研究了切削速度、切削深度以及进给速度与刀具耐用度和加工表面粗糙度的关系,分析了陶瓷刀具的磨损机理。结果表明所选用陶瓷刀具的切削性能明显优于涂层刀具和硬质合金刀具;陶瓷刀具前刀面主要磨损形式为月牙洼磨损与剥落,后刀面的主要磨损原因为磨粒磨损;认为陶瓷刀具更适合用于粉末冶金零件的切削加工。     

Finish Machining of Nickel-Base Inconel 718 Alloy with Coated Carbide Tool under Conventional and High-Pressure Coolant Supplies

Single-point turning of Inconel 718 alloy with commercially available Physical Vapour Deposition (PVD)-coated carbide tools under conventional and high-pressure coolant supplies up to 20.3 MPa was carried out. Tool life, surface roughness (Ra), tool wear, and component forces were recorded and analyzed. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. The highest improvement in tool life (349%) was achieved when machining with 11 MPa coolant supply pressure at higher speed conditions of 60 m · min^?1. Machining with coolant pressures in excess of 11 MPa at cutting speeds up to 40 m · min^?1 lowered tool life more than when machining under conventional coolant flow at a feed rate of 0.1 mm · rev^?1. This suggests that there is a critical coolant pressure under which the cutting tools performed better under high-pressure coolant supplies.

Cutting forces increased with increasing cutting speed due probably to reactive forces introduced by the high-pressure coolant jet. Tool wear/wear rate increased gradually with prolonged machining with high coolant pressures due to improved coolant access to the cutting interface, hence lowering cutting temperature. Nose wear was the dominant tool failure mode when machining with coated carbide tools due probably to a reduction in the chip-tool and tool-workpiece contact length/area.     

Optimum design of cam-roller follower mechanism using a new evolutionary algorithm

Selection of tooling to perform specific operations like drilling and milling on ceramic materials using rotary ultrasonic machining process is an important aspect to meet stringent dimensions on workpiece as well as intended performance of tool. This phenomenon is more critical for micro rotary ultrasonic machining. In the present study, an effort was made to do micro drilling operation of Ø0.3 mm tool with varying geometry, having different wall thicknesses and abrasive grain sizes using design of experiments. The effect of tool-based parameters like grain size and wall thickness has been studied on axial cutting force, radial cutting force, tool wear, edge chipping area and taper. After examining axial and radial cutting forces, it has been concluded that lower wall thickness (80 μm) tool is good for drilling operation; and higher wall thickness (100 μm) tool is good for milling operation under same material removal rate conditions. It has been also investigated that lower wall thickness (80 μm) tool has less edge chipping area and less taper and can impart high drilling depth as compared to higher wall thickness (100 and 150 μm) tool. It is also concluded that lesser grain size (15 μm) tools are advantageous in terms of edge chipping area and cutting force for drilling and milling operations as compared to higher grain size (30, 35 and 45 μm) tool at constant material removal rate. Higher grain size tools have been broken at 1.13 mm³/h material removal rate conditions due to bad profile accuracy. But higher grain size tools have worked fairly well at less material removal rate condition. Higher grain size tools produced less wear. Tool wear was found minimum in higher wall thickness (100 μm) tool having higher abrasive grain size (30 μm). Using inferred results, Ø0.3 mm drilling experiments have been carried out on six aerospace ceramic materials. Also, groove of 0.5 mm size using Ø0.3 mm optimised tool has been successfully carried out in sintered SiC.     

Development of a novel cubic boron nitride cutting tool with a textured flank face for high-speed machining of Inconel 718

Nickel-based superalloys such as Inconel 718 offer several advantages, including high-temperature strength and high corrosion resistance; this has led to a rapid increase in the demand for such materials, particularly in the aircraft industry. In contrast, these alloys are known to be among the most difficult-to-cut materials because of their mechanical and chemical properties, and tools used for this purpose have extremely short lifetimes. Recently, cubic boron nitride (CBN), which is the second hardest of all known materials, has received significant attention as a material for cutting tools and has already established itself in many fields of application. However, the performance of CBN tools is still insufficient for practical use, especially in the high-speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 and performed cross-sectional observations of the CBN cutting tool in order to identify its wear mechanisms in continuous cutting operations under high-speed machining conditions (300 m/min). As a result, it was found that fatal tool failure occurs through crater and flank wear because of diffusion led by high cutting temperatures and subsequent chip adhesion to the tool flank face, accompanied by cutting edge chipping. Based on these results, a CBN cutting tool with a textured flank face was newly developed to improve the cutting tool life. Experimental: results showed that micro grooves generated on the flank face significantly suppressed the cutting edge chipping and remarkably extended the lifetime of the CBN tool during high-speed machining of Inconel 718.     

A metallurgical evaluation of tool wear and chip formation when machining pearlitic grey cast irons with dissimilar graphite morphologies

The need for superior in-service strength has meant that an increasing number of engineering components are now being made from pearlitic cast irons containing spheroidal graphite, rather than the more traditional cast irons containing flake graphite. Such changes of workpiece material have resulted in a rapid decline in tool life in many machining operations, particularly turning and facing.An investigation into the factors involved during chip formation which result in the observed patterns of tool wear is described in the work presented here. A series of turning tests were made on pearlitic grey cast irons containing flake (GA iron) and spheroidal (SG iron) graphite morphologies with cemented carbide (coated and uncoated) and ceramic tool materials. Built-up edge persisted to higher cutting speeds when cutting SG iron than GA iron, its periodic detachment causing attrition or fracture of the cutting edge. Smooth wear processes, probably caused by dissolution-diffusion and small strain discrete plastic deformation, were predominant on the rake and flank faces of the coated and ceramic tools when cutting both cast irons at high speed. Smooth wear was less rapid when cutting GA iron than SG iron because tool temperatures were reduced and “protective” nonmetallic layers, deposited from the chip-workpiece, interrupted dissolution-diffusion. When cutting SG iron, rapid wear of the uncoated cemented carbides was caused by attrition, while the relatively slower smooth wear, when cutting GA iron, was caused by dissolution-diffusion.     

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.     

陶瓷刀具和PCBN刀具磨损形态的研究

对陶瓷刀具(CC650)和PCBN刀具(CB20)精车淬硬GCr15轴承钢时的刀具磨损形态及性能进行了对比试验；结合扫描电镜对刀具的磨损形态作观察；分析了刀具磨损特征及磨损机理。结果表明：刀具损坏的形态主要为前刀面磨损、后刀面磨损、微崩刃及破损等；陶瓷刀具和PCBN刀具的前后刀面磨损形态不同于典型的磨损形态，陶瓷刀具主后刀面的磨损量要比PCBN刀具的磨损量小。但两种刀具均适合于淬硬钢的精加工工序。     

Comparative evaluation of machinability characteristics of Nimonic C-263 using CVD and PVD coated tools

Machining of Nimonic C-263 has always been a challenging task owing to its hot strength, low thermal conductivity, tendency to work harden and affinity towards tool materials. Although coated tools have been used to overcome some of these challenges, selection of coated tool with appropriate deposition technique is of immense significance. The current study attempts to comparatively evaluate various performance measures in machining of Nimonic C-263 such as surface roughness, cutting force, cutting temperature, chip characteristics, and tool wear with particular emphasis on different modes of tool failure for commercially available inserts with multi-component coating deposited using chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques. Influence of cutting speed (V_c) and machining duration (t) has also been investigated using both coated tools. The study demonstrated remarkable decrease in surface roughness (74.3%), cutting force (6.3%), temperature (13.4%) and chip reduction coefficient (22%) with PVD coated tool consisting of alternate layers of TiN and TiAlN over its CVD coated counterpart with TiCN/Al₂O₃ coating in bilayer configuration. Severe plastic deformation and chipping of cutting edge and nose, abrasive nose and flank wear along with formation of built-up-layer (BUL) were identified as possible mechanisms of tool failure. PVD coated tool successfully restricted different modes of tool wear for the entire range of cutting speed. Superior performance can be attributed to the hardness and wear resistance properties, thermal stability due to presence of TiAlN phase and excellent toughness owing to PVD technique and multilayer architecture.     

Performance of ceramic tools in high-speed cutting iron-based superalloys

A series of turning tests were conducted to investigate the cutting performance of ceramic tools in high-speed turning iron-based superalloys GH2132 (A286). Three kinds of ceramic tools, KY1540, CC650, and CC670 were used and their materials are Sialon, Al₂O₃–Ti(C,N), and Al₂O₃–SiC_w, respectively. The cutting forces, cutting temperatures, tool wear morphologies, and tool failure mechanisms are discussed. The experimental results show that with the increase in cutting speed, the resultant cutting forces with KY1540 and CC670 tools show a tendency to increase first and then decrease while those for CC650 increase gradually. The cutting temperature increases monotonically with the increase in cutting speed. The optimum cutting speeds for KY1540 and CC650 when turning GH2132 are less than 100 m/min, while those for CC670 are between 100 and 200 m/min. Flank wear is the main reason that leads to tool failure of KY1540 and CC670 while notch wear is the main factor that leads to tool failure of CC650. Tool failure mechanisms of ceramic tools when machining GH2132 include adhesion, chipping, abrasion, and notching. Better surface roughness can be got using CC670 ceramic tools.     

微细铣削氧化锆陶瓷铣削力特征分析

针对硬态氧化锆陶瓷的微细精密加工问题,采用金刚石涂层微铣刀进行了微细铣削试验。介绍了微细铣削陶瓷材料时加工区的几何特征,分析了可能产生单齿铣削的原因。通过测力仪记录了铣削力信号,对特征力信号进行了描述和分析,研究了铣削参数以及刀具磨损对铣削力大小的影响。结果表明,微细铣削陶瓷材料时,由于每齿进给量非常小,故铣削过程易产生单齿铣削现象;铣削力轴向分量Fz的值最大,随着每齿进给量的增大,Fz呈明显上升趋势;随铣削路程的增加,刀具磨损加剧,铣削力也随之增大,受刀具磨损影响产生一定波动,特别是Fz,其增加幅度明显大于Fx和Fy的增加幅度。     

一种陶瓷材料磨削加工性的综合评判方法

磨削是目前工程陶瓷的主要加工方法 ,本文以陶瓷材料的物理、力学性能为依据 ,应用模糊数学中的模糊综合评判原理 ,建立了工程陶瓷材料磨削加工性的二级模糊综合评判模型 ,提出了一种对工程陶瓷材料磨削加工性进行综合评判的新方法。选择陶瓷材料的 3个力学性能参数构成因素集合 ,根据提出的评判方法 ,对 4种典型工程陶瓷材料的磨削加工性进行评价 ,并根据综合评价指标进行排序。结果表明 ,该方法的评判结果合理 ,评价方法易于运用计算机来处理 ,简单实用。此方法将工程陶瓷材料的可加工性的评价建立在材料性能参数分析的基础上 ,在磨削加工之前确定材料的磨削加工性。评价结果对工程陶瓷材料的加工过程中工具和工艺参数的确定具有重要指导作用。     

High-Speed Machining of Malleable Cast Iron by Various Cutting Tools Coated by Physical Vapor Deposition

The coating material of a tool directly affects the efficiency and cost of machining malleable cast iron.However,the machining adaptability of various coating materials to malleable cast iron has been insufficiently researched.In this paper,turning tests were conducted on cemented carbide tools with different coatings(a thick TiN/TiAlN coating,a thin TiN/TiAlN coating,and a nanocomposite(nc)TiAlSiN coating).All coatings were applied by physical vapor deposi-tion.In a comparative study of chip morphology,cutting force,cutting temperature,specific cutting energy,tool wear,and surface roughness,this study analyzed the cutting characteristics of the tools coated with various materials,and established the relationship between the cutting parameters and machining objectives.The results showed that in malleable cast iron machining,the coating material significantly affects the cutting performance of the tool.Among the three tools,the nc-TiAlSiN-coated carbide tool achieved the minimum cutting force,the lowest cutting tempera-ture,least tool wear,longest tool life,and best surface quality.Moreover,in comparisons between cemented-carbide and compacted-graphite cast iron machined under the same conditions,the wear mechanism of the coated tools was found to depend on the cast iron being machined.Therefore,the performance requirements of a tool depend on multiple factors,and selecting an appropriately coated tool for a particular cast iron material is essential.     

WEAR PERFORMANCE OF MULTILAYER-COATED CARBIDE TOOLS

Three multilayer-coated carbides [two trigon-shaped inserts: Ti(C,N)/TiC/Al₂O₃ (T1), Ti(C,N)/ Al₂O₃/TiN (T2) and one 80°-rhomboid shaped insert: TiC/Al₂O₃/TiN (T3)] were used to machine a martensitic stainless steel at various combinations of cutting speed and feed rate without coolant to assess their wear performance. Significant nose wear and chipping/fracture of the cutting edge were the predominant failure modes affecting tool performance at higher speed conditions. Plucking of tool materials was the main rake face wear phenomenon observed on T1 grade insert with alumina as the top-layer coating when machining at the lower speed conditions. Attrition and plastic flow were the main wear mechanisms observed on the ceramic coating layers, with dissolution-diffusion being the probable wear mechanism of the tool grades where tungsten carbide substrate had direct contact with the flowing chip. The fitted statistical wear models revealed T3 grade insert with 80°-rhomboid shape as having the highest speed-feed capability, resulting in the highest material removal rate relative to T1 and T2 grade inserts with trigon shapes.     

Performance of coated, cemented carbide, mixed-ceramic and PCBN-H tools when turning W320 steel

TiN-coated cemented carbide, mixed ceramic and PCBN with a high percentage of CBN (PCBN-H) tools were used for reconditioned turning of hardened and tempered W320 steel hot working dies. The dies are usually scraped after their useful life because they are difficult to be reconditioned by machining. One alternative to scraping these dies is to convert them, increasing their internal diameters by internal turning. The machining experiments showed that coated carbide tools performed better at cutting speeds up to 120 m/min, while PCBN tools were superior at higher speeds up to 200 m/min. Mixed ceramic tools did not perform well under the conditions investigated. The tribological system showed abrasion, adhesion and plastic deformation as the dominant wear mechanisms. Chipping on the tool rake and flank faces, as well as catastrophic failure, was also observed in some experiments.     

陶瓷刀具的磨损寿命可靠性

在连续切削的条件下，Ａｌ２Ｏ３基陶瓷刀具的失效形式是以磨粒磨损为主的磨损失效，其磨损寿命服从对数正态分布。提出了利用 Ｍｏｎｔｅ Ｃａｒｌｏ方法同切削试验相结合的方法计算Ａｌ２Ｏ３基陶瓷刀具磨损寿命的经典可靠度与模糊可靠度。结果表明刀具材料的断裂韧度对两种可靠度的影响都较为明显，因而可以利用断裂韧度来估算磨损寿命可靠度。模糊可靠度的计算结果更为合理。