Residual stresses in turned AISI 4340 steel

The residual-stress distribution in the surface region of workpieces of annealed AISI 4340 steel that is turned under unlubricated conditions is determined using a deflection etching technique. The absolute value of the residual stresses at the machined surface are low and increase with an increase in depth beneath the machined surface to a maximum. They then decrease with a further increase in depth eventually becoming vanishingly small. Peak residual stresses are tensile at cutting speeds of 0.5 and 1.0 ms⁻¹ and are compressive at a cutting speed of 1.5 ms⁻¹ for all feed rates and depths of cut. Peak residual stresses and depth of the stressed region increase with an increase in feed rate and depth of cut, but decrease with an increase in cutting speed. The results of this investigation can be interpreted in terms of the variation of tool forces with cutting conditions.     

Application of artificial intelligent to predict surface roughness

Experimental Techniques - This article proposes for predicting the surface roughness of AISI 1040 steel material using the artificial intelligent. Cutting speed, feed rate, depth of cut, and nose...     

微织构刀具正交切削Ti6Al4V的试验研究

仿生摩擦学的出现,为刀具减摩技术提出了新的研究方向,通过钛合金的正交切削试验研究了表面微织构刀具在微量润滑和无润滑剂条件下的减摩性能.结果表明：表面微沟槽在润滑剂条件下可以有效地改善刀屑之间的摩擦,降低切削力与切削温度,同时表面微沟槽还可以改善钛合金的粘结现象;在无润滑剂条件下,微沟槽依然具有一定的＂润滑＂作用.     

Surface integrity of inconel-718 nickel-base superalloy using controlled and natural contact length tools. part I: Lubricated

The surface integrity of inconel-718 nickel-base superalloy was investigated using orthogonal cutting at various cutting speeds, depths of cut and chip-tool contact lengths under lubricated conditions. The experimental work involved the determination of residual stress, plastic strain and microhardness distribution in the surface region and the examination of the surface and subsurface using scanning electron and optical microscopy. Both residual stresses and plastic strains decreased and the quality of the mechined surface improved with an increase in cutting speed, a decrease in depth of cut and with tools having controlled chip-tool contact lengths. The results were interpreted in terms of the variation in shear plane length and consequently the variation in tool forces with cutting conditions.     

Surface integrity of inconel-718 nickel-base superalloy using controlled and natural contact length tools. Part II: Unlubricated

The surface integrity of inconel-718 nickel-base superalloy was investigated using orthogonal cutting at various cutting speeds, depths of cut and chip-tool contact lengths under unlubricated conditions. The experimental work involved the determination of residual stress, plastic strain and microhardness distribution in the surface region and the examination of the surface and subsurface using scanning electron and optical microscope. The results are interpreted in terms of the variation in shear-plane length and consequently the variation in tool forces with the cutting conditions. The results are compared with similar results obtained under lubricated conditions. It is found that the lubricant is effective at low cutting speeds in reducing the tool forces that led to lower hardness and plastic strain in the surface region. In general, the severity of surface damage in terms of intensity and total area affected was decreased with the application of a lubricant. Both residual stresses and plastic strains decreased and the quality of the machined surface improved with an increase in cutting speed, a decrease in depth of cut and with tools having controlled chip-tool contact lengths.     

金刚石切削Soda-lime玻璃中的刀具磨损及其对工件表面粗糙度的影响

金刚石切削加工光学玻璃时,工件表面粗糙度与刀具磨损直接相关,为研究切削距离递增下的金刚石刀具磨损及其对工件加工表面粗糙度的影响,进行了Soda-lime玻璃金刚石切削的刀具磨损试验,并对刀具磨损形貌、后刀面磨损带的材料成份、工件的表面形貌及粗糙度进行了检测.结果表明:切削距离递增下的金刚石刀具前刀面磨损表现为平滑且均匀的月牙洼磨损,后刀面磨损表现为磨损带逐渐增大,且磨损带内有沿切削方向的微沟槽产生;切削距离未达到150 m时,工件表面粗糙度Rq、Ra及Rmax值始终低于32、25及300 nm,切削距离超过150 m后,工件表面粗糙度显著增大.机械摩擦作用、热化学作用及磨料磨损作用为导致金刚石刀具磨损的主要原因.     

离子束增强沉积氮化钛膜改善硬质合金刀具抗切削损伤性能的研究

通过切削对比试验，考察了分别用离子束增强沉积法和离子镀法镀覆ＴｉＮ膜的硬质合金刀具和无镀层的同种硬质合金刀具的抗切削损伤性能．结果表明，在给定的试验条件下，有离子束增强沉积ＴｉＮ膜硬质合金刀具的切削距离远比无镀层刀具的长，也比有离子镀ＴｉＮ膜刀具的长，其前面和后面的损伤都很小．这是离子束增强沉积过程中各种参数可以分别调节，膜层质量易于控制，能够形成致密度高且与基体结合力强的硬质薄膜的结果．刀具切削损伤的原因主要有磨损和脆性损伤，这都与刀具材料同被切削金属产生的粘着有关     

Experimental study of the temperature field generated during orthogonal machining of an aluminum alloy

During the machining of metals, plastic deformation and friction lead to the generation of heat in the workpiece, which results in thermomechanically coupled deformation. Recently, several numerical models of this highly coupled process have been produced in response to increased interest in high speed machining. It is important to characterize the thermal field in the cutting zone in order to completely verify these models of high speed machining and to direct further advancement in this area. In this work, HgCdTe infrared detectors are used to experimentally measure the temperature distribution at the surface of a workpiece during orthogonal cutting. From these temperature measurements, the heat generated in the primary shear zone and the friction zone can be examined and characterized. A modified Hopkinson bar technique has been developed to perform orthogonal machining at speeds ranging from 10 to 100 m/s. In the present work, a cutting velocity of 15 m/s is employed in all the tests in order to demonstrate the capability of the apparatus and characterize thermal fields during low speed machining. Temperature fields are obtained during the orthogonal cutting of aluminum as a function of depth of cut. It is seen that depth of cut can vary both the maximum temperature as well as the distribution of the temperature field in the aluminum workpiece. the maximum temperature increased with depth of cut (238°C for 1.5 mm cut, 207°C for 1.0 mm cut and 138°C for 0.5 mm cut) and the temperature field extended further beneath the cut surface with decreasing depth of cut.     

The non-linear phenomena in vibration cutting system: The establishment of dynamic model

It is well-known that vibration cutting is an effective method to cut materials with accuracy. However, it often suffers from unevenness of surface roughness caused by the non-linear vibration phenomena in tool-work vibration system. To solve this problem, we propose a vibration cutting model described by two-dimensional differential equations to analyze the non-linear phenomena. This non-linear model reproduces the basic features of the real vibration cutting systems, that is, the reduction of the cutting force and the displacement of work by pulsing of the cutting force. In this report, our experiment shows that various non-linear phenomena exist in the vibration cutting system. Our non-linear model for the vibration cutting produce behaviors which qualitatively agree with these various non-linear phenomena. These behaviors can be classified by the Lyapunov exponents.     

桁架拓扑优化的多点逼近遗传算法

提出一种基于多点逼近函数和遗传算法的桁架拓扑优化方法。该方法建立了包含连续尺寸和离散拓扑两类变量的优化模型，并通过构造多点逼近函数建立了结构优化问题的第一级序列显式近似，然后采用分层优化方法：在外层对拓扑变量采用遗传算法进行优化；在内层对尺寸变量通过可由对偶法求解的第二级序列近似问题进行优化。几个经典的桁架拓扑优化算例表明该方法能以较少的结构分析次数获得比较理想的概率意义上的最优解。     

Controlling the Cut in Contour Residual Stress Measurements of Electron Beam Welded Ti-6Al-4V Alloy Plates

The multiple cut contour method is applied to map longitudinal and transverse components of residual stress in two nominally identical 50 mm thick electron beam welded Ti-6Al-4V alloy plates, one in the as-welded condition and a second welded plate in a post weld heat treated (PWHT) condition. The accuracy and resolution of the contour method results are directly linked to the quality of the electro-discharge machining cut made. Two symmetric surface contour artefacts associated with cutting titanium, surface bowing and a flared edge, are identified and their influence on residual stresses calculated by the contour method is quantified. The former artefact is controlled by undertaking a series of cutting trials with reduced power settings to find optimal cutting conditions. The latter is mitigated by attaching 5 mm thick sacrificial plates to the wire exit side of the test specimen. The low level of noise in the measured stress profiles for both the as-welded and PWHT plates demonstrates the importance of controlling the quality of a contour cut and the added value of undertaking cutting trials.     

高速球铣加工表面微沟槽形貌形成方法及其减摩性能研究

高速球铣加工表面通常具有一定的残留形貌,采用Matlab形貌仿真与切削加工试验研究了高速球铣加工表面微沟槽形貌的形成方法;并基于流体动压润滑理论,通过Fluent流体仿真与润滑工况下的滑动摩擦试验,研究了表面微沟槽形貌的承载能力关于滑动速度和径向切深的响应规律,并分析了减摩机理. 结果表明:当给定每齿进给量后,随着径向切深的增大,可以获得具有微沟槽特征的表面形貌. 微沟槽承载能力随着滑动速度的提高而逐渐增大;随着径向切深的提高,承载能力呈现先增后减的趋势,这是由于其与楔形效应和逆流现象交互作用影响相关,当径向切深较小时,楔形效应占主导地位,承载能力较强,随着径向切深的进一步增大,逆流现象会严重减弱楔形效应,导致微沟槽承载能力下降.      

Novel Experimental Method to Determine the Cutting Effectiveness of Grinding Grits

This work presents a novel experimental apparatus to determine the cutting effectiveness of grinding grits. The apparatus consists of a custom high-speed scratch tester, a force measurement system, and an offline 3D optical profilometer. Preliminary results based on a spherical tool are presented to demonstrate the usefulness of the system. Experiments were performed at depths of cut ranging from 0.3 μm to 7.5 μm at cutting speeds of 5 m/s to 30 m/s in 5 m/s increments. High resolution scans of the scratch profiles provided insight into the change in the cutting mechanics as the depth of cut and cutting speed were increased. In general, lower cutting speeds produced higher pile-up heights while higher cutting speeds produced lower pile-up heights. The force measurements indicated that the normal forces increased with cutting speed due to strain rate hardening of the workpiece material while the tangential forces decreased with cutting speed due to a reduction in the coefficient of friction and a change in the cutting mechanics. The force ratio data and the specific energy data both demonstrated high slopes at low depths of cut due to asperity contact between the tool and the workpiece. The modular nature of the developed system allows different grit geometries to be investigated.     

Experimental considerations for steady state edge excavation under a constant cutting depth for a mortar specimen using a disk cutter bit

This paper aims to investigate experimentally steady state excavation performance under a constant cutting depth, especially the specific cutting energy of a disk cutter bit in the free edge part of a mortar specimen. Here, the tangential, lateral and normal forces acting on a disk cutter bit having three tip angles and the amount of debris were measured for several cutting spaces and cutting depths. As a result, it was observed that the specific cutting energy, i.e. the ratio of the excavation power of the disk cutter bit to the amount of debris, showed a minimum value of the ratio of cutting space to cutting depth of five, at which ratio the most efficient excavation could be attained.     

珩磨缸套表面粗糙度预测及多目标优化研究

为了对粗珩阶段缸套内孔表面粗糙度Rk粗糙度集中的Rk、Rpk和Rvk进行预测,进而对粗珩加工参数进行优化,以珩磨压力(P)、珩磨头旋转速度(VR)和往复速度(VRe)为决定因素,Rk粗糙度集为目标响应,进行多目标优化.建立基于广义回归神经网络(Generalized regression neural network, GRNN)与响应曲面法(Response surface methodology,RSM)的粗糙度预测模型,并采用三因素三水平的全因子珩磨试验进行验证,结果表明所建立模型的预测结果与试验结果具有很好的一致性. GRNN预测模型决定系数R²的均值为0.959,RSM多元回归预测模型决定系数R²的均值为0.963,与RSM所建立的多元回归预测模型相比,GRNN预测模型在预测Rk和Rpk时,预测精度更高,预测误差更小,R²分别提高了0.025和0.020,在预测Rvk时RSM多元回归模型更优,R²提高了0.057.进一步结合响应曲面法分析了3个决定因素对粗糙度的影响显著性并进行了排序,对于...     

A Methodology for Temperature Correction When Using Two-Color Pyrometers - Compensation for Surface Topography and Material

In this investigation, the applicability of the two-color pyrometer technique for temperature measurements in dry hard turning of AISI 52100 steel was studied, where both machined surfaces as well as cutting tools were considered. The impacts of differing hard turned surface topography on the two-color pyrometer readings was studied by conducting temperature measurements on reference samples created using cutting tools with different degrees of tool flank wear. In order to conduct measurements in a controlled environment, a specially designed furnace was developed in which the samples were heated step-wise up to 1,000 °C in a protective atmosphere. At each testing temperature, the temperatures measured by the two-color pyrometer were compared with temperatures recorded by thermocouples. For all materials and surfaces as studied here, the two-color pyrometer generally recorded significantly lower temperatures than the thermocouples; for the hard turned surfaces, depending on the surface topography, the temperatures were as much as ~20 % lower and for the CBN cutting tools, ~13 % lower. To be able to use the two-color pyrometer technique for temperature measurements in hard turning of AISI 52100 steel, a linear approximation function was determined resulting in three unique equations, one for each of the studied materials and surfaces. By using the developed approximation function, the measured cutting temperatures can be adjusted to compensate for differing materials or surface topographies for comparable machining conditions. Even though the proposed equations are unique for the hard turning conditions as studied here, the proposed methodology can be applied to determine the temperature compensation required for other surface topographies, as well as other materials.     

A new design method for adaptive IIR system identification using hybrid particle swarm optimization and gravitational search algorithm

Design of adaptive infinite impulse response (IIR) filter is the process of utilizing adaptive algorithm to iteratively determine the filter parameters to obtain an optimal model for the unknown plant based on minimizing the error cost function. However, the error cost surface of IIR filter is generally nonlinear, non-differentiable and multimodal. Hence, an efficient global optimization technique is required to minimize the error cost objective. A novel hybrid particle swarm optimization and gravitational search algorithm (HPSO–GSA) is proposed in this paper for IIR filter design. The proposed HPSO–GSA updates particle positions through obeying the influence of gravity acceleration in GSA and receiving direction of cognitive memory and social sharing information from PSO by means of coevolutionary strategy. The effect of key parameters on the performance of the proposed algorithm is firstly studied, and the proper parameters in HPSO–GSA are established using five benchmark plants along with the same-order model. The simulation studies have been performed for the performance comparison of eight algorithms such as PSO, GSA, QPSO, DPSO, FO-DPSO, GAPSO, PSOGSA and the proposed HPSO–GSA for unknown IIR system identification with the same-order and reduced-order filters. Simulation results show that the proposed algorithm has advantages over PSO, GSA and other PSO-based variants in terms of the convergence speed and the MSE levels.     

Experimental and numerical investigation of the uncut chip thickness reduction in Ti6Al4V orthogonal cutting

The downsizing of traditional cutting (“macro-cutting”) to micro-cutting introduces changes in the cutting process. The uncut chip thickness decreases and the cutting edge radius of the tool cannot be neglected anymore. The minimum chip thickness phenomenon takes importance, as well as ploughing. The size effect appears and the influence of the microstructure grows. Determining the value of the uncut chip thickness is a major concern to produce high quality parts. This paper focuses on the determination of that value experimentally with a setup providing strictly orthogonal cutting configuration and a one-time machining of the surface, as well as numerically with a finite element model by only changing the value of the uncut chip thickness. Specificities of micro-cutting are highlighted experimentally and numerically. The cutting refusal is observed in both cases and the minimum chip thickness is estimated (at minimum 25 % of the cutting edge radius) with a good correlation.     

A Mechanics Based Model for Study of Dynamics of Milling Operations

A unified mechanics based model with multiple degrees of freedom is developed and numerically simulated to study workpiece-tool interactions during milling of ductile workpieces with helical tools. A refined orthogonal cutting model is used at each section of the tool, and the milling forces are determined by using a spatial integration scheme along the axis of the tool. Both regenerative and loss of contact effects are considered in determining the cutting forces, which makes the model well suited for a wide range of milling operations. The model also allows for partial engagement of a tool with a workpiece, which is an important feature needed for milling operations with helical tools. Time domain simulations are carried out by using the developed model to predict the stability boundaries in the space of the tool spindle speed and the axial depth of cut. Poincaré sections are used to determine loss of stability from period-one motions to other motions such as two-period quasiperiodic motions, as a control parameter is varied.     

Machining unreinforced polymers with high-velocity water jets

Sapphire nozzles of 0.076-mm to 0.178-mm diameter have been used with a water intensifier, operating at pressures up to 4.2 kbar, to produce continuous jets with velocities around 6.6×10⁴ cm/s. These jets have been used to machine (slit) sheet specimens of polymethylmethacrylate (PMMA), polycarbonate and acetal at feed rates up to 4 cm/s. A previous paper describes the jet cutting system and analyzes data for PMMA and a phenolic laminate. This paper presents and analyzes data for polycarbonate and acetal; it also reanalyzes the PMMA data. A cutting theory described previously is modified and extended so that depth of cut can be directly related to nozzle pressure, jet flow rate, specimen feed rate and nozzle diameter. In its original form, this energy theory cannot account for the effect of changes in nozzle diameter. It is shown that there is excellent agreement between the predictions of the modified theory and the experimental data. The theory is also used to explain the surface appearance of a typical cut.