Mechanisms involved in the improvement of Inconel 718 machinability by laser assisted machining (LAM)

The aim of the present research work has been to gain a broader understanding of how or why laser assisted machining (LAM) improves machinability of Inconel 718, a hard-to-machine material of interest in the aeronautic industry. This has been accomplished by, first, running short run tests to determine the laser parameters and configuration for which highest force reductions are obtained and also to determine the effect of cutting parameters (feed, cutting speed and depth of cut) on force reduction. Secondly, long run tests have been performed in order to analyze process variables such as cutting forces, tool wear and surface roughness. Temperatures and hardness have been also measured in order to gain a broader perspective of the process.Experimental results have demonstrated that LAM improves machinability of Inconel 718 since machining forces and final surface roughness are reduced. The novelty reached with the present research work is the identification of three mechanisms associated to the laser heating as the responsible of this machinability improvement: material yield strength reduction, material base hardness reduction (only in precipitation hardened Inconel 718) and elimination of the work hardening generated in previous machining passes. The reduction of the work hardening leads also to a lower notch wear that limits the risk of sudden failure of the cutting tool and thus the wear mode is changed to flank wear, which leads to a controllable tool life and better surface roughness.     

等温淬火球铁(ADI)的机械加工性能

等温淬火球铁(ADI)对工程界来说是一种相对较新的材料。其独特的金属基体显微组织奥铁体,即针状铁素体和充分反应的、热力学稳定的、力学上也稳定的,高碳奥氏体的混和组织,使其具有比普通球铁高得多的强度和韧性。然而,高强度、高硬度和高韧性使等淬球铁在机加工时切削刃口受到更高的应力,造成一定困难。考虑了等淬球铁特有的金属基体组织和力学性能,选择了合适的刀具,调整和优化了刀具及加工参数,等淬球铁完全可以成功地进行机加工,从而可以扩大等淬球铁的应用和进一步开拓等淬球铁的潜力。笔者论述了等淬球铁的组织特点,机加工特点,给出了机加工参考参数,并讨论了改善等淬球铁机械加工性能的方法。     

Direct laser assisted machining with a sapphire tool for bulk metallic glass

Bulk metallic glasses (BMGs) are amorphous metallic alloys with high strength and hardness. This paper discusses the machining process of Zr-BMG using a transparent sapphire tool with direct laser assistance. The laser beam passes through the tool and directly heats the workpiece material to improve its machinability. Micro textures were generated on the tool rake face to facilitate chip formation. Reduced cutting forces and improved surface finish were observed with direct laser assistance. The effects of machining speed and laser power on the material deformation mechanism were investigated. A finite element model was developed to investigate the cutting forces.     

Fundamental Wear Mechanisms when Machining Austempered Ductile Iron (ADI)

Austempered Ductile Iron (ADI) is characterised by improved mechanical properties but low machinability compared to conventional ductile iron materials and steels of similar strengths. The mechanical properties of ADI are achieved by a very fine austenitic-ferritic microstructure. However this unusual microstructure significantly affects mechanical and thermal machining properties. A keen understanding for the interactions of microstructure, chip formation, machining properties, cutting material and wear mechanisms is essential for the optimisation of the cutting process. This paper describes material and machining investigations as well as cutting simulations to reveal the wear mechanisms being responsible for the low machinability of ADI.     

Drilling of X2CrNi 19 11 stainless steel with hiped NiTi coating

This study investigated suitability of TiN and TiCN-coated cemented carbide tools in the machining of conventionally produced stainless steel with HIPed (Hot Isostatic Pressed) NiTi coating. Near-equiatomic nickel–titanium alloy (NiTi) has many attractive material properties, such as pseudo-elasticity and shape memory effects, which result into beneficial engineering properties, e.g. as cavitation resistant coatings in addition to its well-known shape memory properties. Stainless steels are often considered to be poorly machinable materials; materials with high elasticity are also difficult to machine. In drilling stainless steel with a pseudo-elastic coating material, machinability difficulties are caused by the high strength and work hardening rate of steel and the pseudo-elastic properties of the coating material. The machinability was studied by analyzing cemented carbide drills and chips. The interface between stainless steel and NiTi coating was examined with SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy) analysis. The effect of feed rate on chip formation and tool wear was analyzed. The cutting tests indicated that cutting speeds of 50 m/min, a feed rate of 0.1–0.2 mm/rev, and solid carbide drills can be applied, from a machinability standpoint. A HIPed pseudo-elastic coating decreases machinability. When effective cutting speeds and feed rates were utilized, optimal tool life was achieved without a decrease in coating properties.     

Effects of microstructure and strength on wear performance in rough milling of austempered ductile iron

The machinability of various grades of austempered ductile iron (ADI) has been investigated for rough milling operations. ADI 900, ADI 1050 and ADI 1200 grades were commercially produced, commercially heat treated and machined under controlled conditions using coated carbide inserts with coolant in the laboratory. The milling performance of the various grades was compared to that of AISI/SAE 4340 with similar hardness. In this study, machinability characteristics relative to wear rate (ISO 8688-2) and machining forces were measured and related to initial microstructure and properties. These preliminary results have been used to establish initial rough milling machining guidelines for machining ADI with coated carbide milling inserts.     

Experimental investigation on hard milling of high strength steel using PVD-AlTiN coated cemented carbide tool

High strength steel 30Cr3SiNiMoVA (30Cr3) is usually used to manufacture the key parts in aviation industry owing to its outstanding mechanical properties. However, 30Cr3 has poor machinability due to its high strength and high hardness. Hard milling is an efficient way in machining high strength steels. This paper investigated hard milling of 30Cr3 using a PVD-AlTiN coated cemented carbide tool with regard to cutting forces, surface roughness, chip formation and tool wear, respectively. The experimental results indicated that the increase of cutting speed from 70 to 110 m/min leads to direct reduction of cutting forces and improvement of surface finish, while both feed rate and depth of cut have negative effect on surface finish. The occurrence of oxidation on chip surfaces under high cutting temperature makes the chips show different colors which are strongly influenced by cutting speed. Saw-toothed chips were observed with the occurrence of the thermo-plastic instability within the primary shear zone. Micro-chipping and coating peeling were confirmed to be the primary tool failure modes. Serious abrasion wear and adhesive wear with some oxidative wear were confimed to be the main wear mode in hard milling of 30Cr3.     

Material-related aspects of the machinability of Austempered Ductile Iron

The exceptional properties of Austempered Ductile Iron (ADI) are widely known and can be ascribed to its austenitic-ferritic microstructure. Strain hardening of this material is exceptional and an advantage for many applications where high wear resistance is required, as well as the extraordinary combination of ductility and tensile strength. One reason which restricts the introduction of this material in practical applications is its poor machinability. This paper describes the material-sided influences on machinability, especially on the acting wear mechanism. The heat treatment factor austempering time, ADI grade and the alloying elements nickel and molybdenum are varied and investigated in external longitudinal turning operations.     

Evaluation of machinability in turning of microalloyed and quenched-tempered steels: Tool wear,statistical analysis,chip morphology

The machinability of microalloyed steel (30MnVS6) and quenched-tempered (QT) steels (AISI 1045 and AISI 5140), at different cutting condition, is presented in the paper. An experimental investigation was conducted to determine the effects of cutting speed, feed rate, hardness, and workpiece material on the flank wear land and tool life of coated cemented carbide inserts in the hard turning process. It was tried that for any test condition the hardness of these steels became almost identical by using appropriate heat-treatment processes. The statistical analysis was used for evaluation of different factors on cutting forces. Chips characteristics and chip/tool contact length were also investigated. The different sections (shear plane, microcrack, thickness and edge) of the chip were examined by scanning electron microscope (SEM). Shear planes and microcracks of the chips in microalloyed steel show that the chips of microalloyed steel are regular and discontinuous. Crater wear of the tools was studied by using video microscope in turning process. The results showed that the tool life and machinability of the microalloyed steel is better than the QT steels at identical cutting condition.     

Machinability of BN free-machining steel in turning

In the past few years, extensive researches have been done to improve the machinability of work materials in order to increase productivity and reduce the effect on the environment. To satisfy these demands, various free-machining steels have been researched and developed. One of them is BN free-machining steel that contains hexagonal boron nitride (h-BN). However, the machinability was not stable. In this study, machining tests were carried out to clarify the machinability of steels and appropriate chemical composition of work material and tool material to achieve high efficient machining. Tested work materials were plane carbon steel JIS S45C and BN free-machining steels. The JIS S45C was used as the standard. The tool wear in turning BN free-machining steel was smaller than that in turning standard steel. In case of turning BN1 with P30 at 200, 300 m/min, the wear progress rate of flank wear and crater depth were about half as much as that in turning standard steel. BN free-machining steel showed slightly lower cutting temperature and smaller cutting force in comparison with standard steel at the tested cutting speeds. Al and N were detected as a layer at the tool wear region of P grade carbide tools after turning BN free-machining steel at high cutting speed. It is thought that one of the main reasons of outstanding machinability of BN free-machining steel is that the deposited layer containing Al and N acts as diffusion barrier at the tool–chip interface. In turning larger Al content BN-added steel with higher Ti content cutting tools, a larger wear reduction was observed. Therefore, it is said that not only added BN but also appropriate Al is necessary in work material.     

Key improvements in the machining of difficult-to-cut aerospace superalloys

Significant advances have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions from practical and theoretical standpoints. This approach has enabled the aerospace industry to cope with constant introduction of new materials that allow the engine temperature to increase at a rate of 10 °C per annum since the 1950s. Improvements achieved from research and development activities in this area have particularly enhanced the machining of difficult-to-cut nickel base and titanium alloys that have traditionally exhibited low machinability due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation, etc. A good understanding of the cutting tool materials, cutting conditions, processing time and functionality of the machined component will lead to efficient and economic machining of nickel and titanium base superalloys. This paper presents an overview of major advances in machining techniques that have resulted to step increase in productivity, hence lower manufacturing cost, without adverse effect on the surface finish, surface integrity, circularity and hardness variation of the machined component.     

不同孕育剂处理的高强度灰铸铁加工性能研究

为研究不同孕育剂对灰铸铁切削加工性能的影响,制备了高强度HT350材质的试样.对比研究了孕育剂75SiFe、SrSi、BaSi、SiSr(80％)+75FeSi(20％)处理的高强度灰铸铁的力学性能和切削加工性能.结果表明,SiSr(80％)+75FeSi(20％)复合孕育处理的灰铸铁较单一孕育处理的灰铸铁石墨细小弯曲,基体组织均匀性好,具有较高的硬度以及较小的切削抗力,但其断面敏感性较大.单一孕育剂中75SiFe孕育处理的灰铸铁具有较高的抗拉强度、较小的硬度以及较低的断面敏感性.灰铸铁中A型石墨越细小,基体组织越均匀,灰铸铁的加工性能越好,说明显微组织的均匀性对灰铸铁的加工性能具有较大影响.     

Machinability improvement of titanium alloy (Ti–6Al–4V) via LAM and hybrid machining

Titanium alloy (Ti–6Al–4V) is one of the materials extensively used in the aerospace industry due to its excellent properties of high specific strength and corrosion resistance, but it also presents problems wherein it is an extremely difficult material to machine. The cost associated with titanium machining is also high due to lower cutting speeds (<60 m/min) and shorter tool life. Laser-assisted machining (LAM) and consequently hybrid machining is utilized to improve the tool life and the material removal rate. The effectiveness of the two processes is studied by varying the tool material and material removal temperature while measuring the cutting forces, specific cutting energy, surface roughness, microstructure and tool wear. Laser-assisted machining improved the machinability of titanium from low (60 m/min) to medium-high (107 m/min) cutting speeds; while hybrid machining improved the machinability from low to high (150–200 m/min) cutting speeds. The optimum material removal temperature was established as 250 °C. Two to three fold tool life improvement over conventional machining is achieved for hybrid machining up to cutting speeds of 200 m/min with a TiAlN coated carbide cutting tool. Tool wear predictions based on 3-D FEM simulation show good agreement with experimental tool wear measurements. Post-machining microstructure and microhardness profiles showed no change from pre-machining conditions. An economic analysis, based on estimated tooling and labor costs, shows that LAM and the hybrid machining process with a TiAlN coated tool can yield an overall cost savings of ～30% and ～40%, respectively.     

工件材料可切削性对可转位硬质合金刀具加工经济性影响规律研究

用2种不同牌号和不同槽型的硬质合金刀具分别对优质中碳钢45#和GCr15轴承套进行切削实验,通过应用金属切削原理结合加工经济学分析方法,对零部件的可切削性对生产效率、生产成本的作用机制进行研究,从而揭示其对后两者的影响规律性;通过切削实验,探究刀具使用寿命、工件可切削性系数和整体硬度的内在联系。研究表明:当工件可切削性系数提高、刀具使用寿命延长以及工件硬度降低时,其加工成本将呈指数化降低,同时生产效率也会成倍提高。研究获得刀具使用寿命与加工经济性的量化关系曲线,从而实现切削过程最优化的可量化目标。研究数据和研究方法可为切削过程优化、刀具设计与优选提供方法和数据支撑。      

Sintered,iron-based material with improved machinability

Conclusions With alloying of ZhGr1D3 material with molybdenum and sulfur by the addition to the charge of 1.5% molybdenum disulfide in place of zinc stearate lamellar sulfides and oxysulfides are formed in the structure in place of hard oxides, which provides an improvement in the machinability of the sintered material as a result of a decrease in impact loads on the cutting tool. The ZhGr1D3M1K0.5 material obtained as a result of such alloying presses better and has higher strength properties than ZhGr1D3 material obtained as a result of such alloying presses better and a higher strength properties than ZhGr1D3 material with the same level of plasticity, hardness, and corrosion resistance.Institute of Metallurgy, Ural Scientific Center, Academy of Sciences of the USSR. Vysokogorsk Machine Plant. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 30–32, March, 1984.     

合金铸铁轿车铸件切削加工性能探讨

对合金铸铁轿车铸件材料的切削加工性能进行探讨。从非铸件材料和铸件材料两个方面对实际生产中合金铸铁轿车铸件的切削性能问题进行了全面的分析。铸件清理质量差、尺寸精度超差和不稳定、存在夹杂物、加工机床、刀具和切削用量不合适等非铸件材料原因,以及铸件边角或薄壁处有碳化物、合金元素的不良影响、冶金质量差、铸件表层组织异常等铸件材料原因都会引起铸件切削问题。提出了解决这些问题的措施:防止铸件粘砂,消除夹杂物,严格控制尺寸精度和形位公差(如曲轴和凸轮轴的弯曲度分别控制在1.5 mm和1.0 mm范围内),提高基准面质量,严格控制形成硬质点和易偏析的合金元素加入量,控制炉料质量,提高铸件的冶金质量,尽量降低型砂水分,并使型砂有足够的煤粉含量等。     

Machinability analysis in turning tungsten–copper composite for application in EDM electrodes

Electro-discharge machining (EDM) is widely used in tooling industry, where it is applied on materials, which are too hard to be machined with conventional techniques. The tungsten–copper is broadly used as an EDM electrode for machining of die steel and tungsten carbide workpieces. As, tungsten–copper electrode is more costly than conventional electrodes, there is a need to understand the machinability aspects in turning of this material. Hence, an attempt has been made in this paper to study the effects of cutting conditions on machinability characteristics such as cutting force, feed force, depth force, machining force, power, specific cutting force, arithmetic average surface roughness and maximum peak to valley height during tungsten–copper turning with K10 carbide cutting tool. The response surface methodology (RSM) based second order mathematical models of machinability aspects are developed using the data obtained through full factorial design (FFD). The adequacy of the machinability models is tested through the analysis of variance (ANOVA). The response surface analysis reveals that a combination of higher cutting speed with low-to-medium feed rate is advantageous in reducing the forces, power and surface roughness, which in turn increases the specific cutting force.     

High Speed Turning of H-13 Tool Steel Using Ceramics and PCBN

H-13 is the toughest tool steel used in machined die casting and forging dies. Due to its extreme hardness and poor thermal conductivity high speed cutting results in high temperature and stresses. This gives rise to surface damage of the workpiece and accelerated tool wear. This study evaluates the performance of different tools including ceramics and PCBN using practical finite element simulations and high speed orthogonal cutting tests. The machinability of H-13 was evaluated by tool wear, surface roughness, and cutting force measurements. From the 2D finite element model for orthogonal cutting, stresses and temperature distributions were predicted and compared for the different tool materials.     

超细晶硬质合金刀具车削不锈钢的切削温度研究

超细晶硬质合金刀具由于具有更高的硬度和抗弯强度,可以满足现代制造业的更高要求,在难加工材料高速切削领域显示出明显优势。在不锈钢材料的加工过程中,切削温度对刀具的磨损有极大的影响,而多数实验方法很难测得刀具表面具体的温度分布。借助DEFORM仿真分析软件,模拟超细晶硬质合金刀具对304不锈钢的车削过程;依据正交试验方法,分析切削用量三要素切削速度、进给量和背吃刀量对刀具温度的影响规律;通过实际车削实验与仿真结果进行比较,并与普通晶粒硬质合金刀具进行对比。结果表明:与普通晶粒硬质合金刀具加工相似,切削速度对超细晶粒硬质合金刀具温度的影响程度最大,其次是进给量,最后是背吃刀量;超细晶粒硬质合金比普通晶粒硬质合金刀具具有更好的散热性,尤其在较高速度条件下切削,优势更加明显。     

Predictive machinability models for a selected hard material in turning operations

In this paper, empirical models for tool life, surface roughness and cutting force are developed for turning operations. Process parameters (cutting speed, feed rate, depth of cut and tool nose radius) are used as inputs to the developed machinability models. Two important data mining techniques are used; they are response surface methodology and neural networks. Data of 28 experiments when turning austenitic AISI 302 have been used to generate, compare and evaluate the proposed models of tool life, cutting force and surface roughness for the considered material.