A three-dimensional model of chip flow, chip curl and chip breaking under the concept of equivalent parameters

Chip control is a major problem in machining processes, especially in finishing operations. Previously, some research in chip control has been done using orthogonal cutting models, however the assumptions made in the models hardly satisfy most practical machining conditions in which the influences of tool corner radius cannot be ignored. The analytical and experimental research presented here deals with a three-dimensional model of chip flow, chip curl and chip breaking. Three features are considered: the geometrical feature, the kinetic feature and the mechanical feature. A set of equivalent characteristic parameters are defined and the relationship between the equivalent parameters and the machining parameters is developed. In addition to theoretical analysis for the equivalent parameters, some of the equivalent parameters are determined by experiment. Finally, a new criterion of chip breakage is given by using the developed model. It is shown that the predicted results agree reasonably well with experimental results.     

Reducibility of ceria–lanthana mixed oxides under temperature programmed hydrogen and inert gas flow conditions

The present paper deals with the preparation and characterization of La/Ce mixed oxides, with La molar contents of 20, 36 and 57%. We carry out the study of the structural, textural and redox properties of the mixed oxides, comparing our results with those for pure ceria. For this aim we use temperature programmed reduction (TPR), temperature programmed desorption (TPD), nitrogen physisorption at 77 K, X-ray diffraction and high resolution electron microscopy. The mixed oxides are more easy to reduce in a flow of hydrogen than ceria. Moreover, in an inert gas flow they release oxygen in higher amounts and at lower temperatures than pure CeO₂. The textural stability of the mixed oxides is also improved by incorporation of lanthana. All these properties make the ceria–lanthana mixed oxides interesting alternative candidates to substitute ceria in three-way catalyst formulations.     

Cutting composites: A discussion on mechanics modelling

Using the cutting of long fibre reinforced polymer and ceramic particle reinforced aluminium as the examples, this paper tends to understand some common features in the mechanics modelling of machining composites. It demonstrates that an accurate characterisation of matrix deformation, matrix–reinforcement interaction, and reinforcement deformation are key factors for the establishment of a model to reflect the principal material removal mechanisms. A precise understanding of these factors can be achieved through a logic process of mechanism exploration, model derivation and verification.     

Microstructure analysis and mechanical characteristics of tungsten inert gas and metal inert gas welded AA6082-T6 tubular joint: A comparative study

The present study is aimed to compare the microstructure characteristics and mechanical properties of AA6082 in T6 condition of tubular joints fabricated by tungsten inert gas welding (TIG) and metal inert gas welding (MIG) processes. The effect of welding processes was analysed based on optical microscopy image, tensile testing, and Vickers micro-hardness measurements. The results showed that the tensile strengths of the TIG-welded joints were better than those of the MIG-welded joints, due to the contribution of fine equiaxed grains formation with narrower spacing arms. In terms of joint efficiency, the TIG process produced more reliable strength, which was about 25% higher compared to the MIG-joint. A significant decay of hardness was recorded in the adjacent of the weld bead zone, shown in both joints, related to phase transformation, induced by high temperatures experienced by material. A very low hardness, which was about 1.08 GPa, was recorded in the MIG-welded specimens. The extent of the heat-affected-zone (HAZ) in the MIG-welded joints was slightly wider than those of the TIG-welded specimens, which corresponded with a higher heat input per unit length.     

A three-dimensional model of clip flow, chip curl and chip breaking for oblique cutting

In recent years, many publications have appeared dealing with chip breaking in orthogonal cutting of metals. However, in industry, oblique cutting and not orthogonal cutting is encountered in almost all actual machining operations. This paper deals with a model of chip flow, chip curl and chip breaking for oblique cutting. To simplify the analysis, a set of equivalent parameters are introduced. The relationship between the machining parameters and their corresponding equivalent parameters is developed theoretically and experimentally. To assess the level of chip breaking, a criterion of chiplbreaking is suggested under the concept of these equivalent parameters. The agreement of the experimental results with the predictive data of the model verifies that the definition of these equivalent parameters is reasonable. The influences of various machining parameters are discussed, in relation to their corresponding parameters. One significant finding is that the effect of each of the machining parameters on chip breaking is not totally inpdependent of one another. This implies that careful attention must be paid to the relationship between various machining parameters in three-dimensional parameters.     

6xxx系铝合金弧焊与高功率激光焊组织性能对比

为解决6061-T6铝合金焊后热影响区软化导致力学性能下降的问题,基于焊接接头余高大变形强化过时效软化区的思想,采用双轧辊系统对6061-T6薄板铝合金直流双脉冲熔化极气体保护焊(DC double pulse metal inert gas welding,DP-MIG焊)接头进行同步双面轧制,并分析了焊轧复合成形接头组织与力学性能. 结果表明,焊缝晶粒受到竖直方向的轧制力发生大塑性变形,内部气孔消失,焊缝区域变宽,邻近焊缝的热影响区受到来自焊缝的挤压力发生协同宏观变形,远离焊缝的过时效软化区组织受到来自焊缝处的压应力,从沿垂直焊缝方向产生部分协同形变强化;接头的硬度明显提升,过时效软化区的硬度由60 ~ 70 HV提升至80 ~ 90 HV,过时效软化区的拉伸性能也有所提升,当焊接速度为800 mm/min时,抗拉强度最佳可达到母材的83.6%,相较于焊接接头提升19.4%,进而实现了对过时效软化区的强化效果.     

Control of chip flow with guide grooves for continuous chip disposal and chip-pulling turning

This paper presents a new chip control method with guide grooves formed on the rake face to realize continuous chip disposal and chip-pulling turning. Chips are conventionally broken using chip breakers during turning operations for disposal. However, chips of highly ductile materials or thin chips generated in finishing can not be broken easily. In order to prevent the chips from jamming up, the authors propose to continuously guide the chips away from the cutting point. Special tool tips were developed and tested for guiding the chip. Chip controllability and mechanics of the chip-guided cutting are discussed in the present research.     

Experimental characterisation of the weld pool expansion in a tungsten inert gas configuration

In this study, we focus on the expansion of the weld pool in a welding process by tungsten inert gas (TIG). Use of high-speed imaging and metallographic investigations combined with electrical measurements allow us to determine the weld pool shape and dimensions evolution and the energy involved in the process for six durations of interaction (from 1 to 20?s) in a spot TIG configuration. Results show a fast increase of the weld dimensions on the first second. Otherwise, time does not seem to be an influent parameter on the weld shape. The comparison between experimental work and numerical model available in our team highlights differences between the predicted shapes and the observed ones.     

镍基合金/不锈钢钨极惰性气体钎焊接头的特性

选用CuSi3焊丝对镍基合金／不锈钢进行钨极惰性气体（TIG）钎焊实验,运用OM、SEM和EDS分析接头微观组织,通过拉伸实验和硬度实验评定接头的力学性能。结果表明：TIG钎焊接头具有熔焊和钎焊的双重性质,不锈钢母材局部熔化,生成Fe基熔合区;在接头搭接区及镍基合金母材与焊缝金属之间存在界面反应层,反应层可分为熔化未混合区、Ni基树枝晶和晶间Cu基区;焊缝区为Cu基体上分布着颗粒状Fe基固溶体;CuSi3接头剪切强度达到195MPa,接头断裂于焊缝与不锈钢界面处,断口为微孔聚合机制引起的塑性断裂：在界面处硬度值发生突变,Ni基树枝晶硬度值达到HV433.3,不锈钢熔合区中的Fe基体硬度值达到HV453．4,近界面处焊缝区Cu基体硬度值为HV150。     

5A12铝合金有限宽薄板钨极惰性气体焊接的数值模拟

针对铝合金5A12有限薄板钨极惰性气体（TIG）焊接过程存在非准稳态的特点,提出了考虑热源预热作用及移动效应的二维高斯热源修正模型,并采用修正的二维高斯热源模型对其焊接热过程、焊接残余角变形和纵向残余应力进行数值模拟及研究,同时比较数值模拟及实验结果。实验结果表明：利用修正的二维高斯模型能较好地反映有限薄板的焊接特点,所计算的接头熔合区形状、热循环曲线与实验结果吻合良好。焊接残余角变形及焊接纵向残余应力也得到了与实验值较接近的模拟结果。利用此修正的二维高斯模型可提高焊接温度场、焊接纵向残余应力与变形数值模拟的准确性。     

Microstructures and properties of tungsten inert gas welding joint of super-eutectic ZA alloy

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Microstructure and tribological behavior of tungsten inert gas welding arc brazing tin-based babbit

The microstructure of the tin-based babbit obtained by the method of tungsten inert gas welding(TIG)arc brazing was studied by optical microscopy(OM) and X-ray diffraction(XRD).Tribological behavior was investigated by high-temperature friction and wear testing machine(HTFWT),laser scanning confocal microscopy(LSCM),scanning electron microscopy(SEM) and energydispersive spectrometer(EDS).It can be found that the higher welding current of the melting tin-based babbit makes it possible to form iso...     

Modeling, optimization and classification of weld quality in tungsten inert gas welding

In this paper, a neural network is used to construct the relationships between welding process parameters and weld pool geometry in tungsten inert gas (TIG) welding. An optimization algorithm called simulated annealing (SA) is then applied to the network for searching the process parameters with an optimal weld pool geometry. Finally, the quality of aluminum welds based on the weld pool geometry is classified and verified by a fuzzy clustering technique. Experimental results are presented to explain the proposed approach.     

低速干车削条件下车刀温度的红外测试研究

利用数控车床和手持式红外测温仪,研究了干车削铝棒过程中车削参数对车刀刀尖温度的影响规律,通过试验得到了不同车削参数下车削温度的时间曲线以及温度均方根值随车削参数的变化曲线。研究结果表明:同一走刀的车削过程中,刀尖温度具有时变特性。随着车削的进行,刀尖温度逐渐升高,至走刀结束时,温度达到最高值;刀具温度与车床主轴转速、进给速度、车削深度成正相关关系,车削参数越大,车削温度越高;刀尖温度均方根值随主轴转速按双线性规律变化,主轴转速超过一定值后,温度均方根值急剧升高;刀尖温度均方根值随进给速度、车削深度近似按线性规律变化,进给速度对刀尖温度的影响较大,车削深度对温度的影响最小。     

Comparative evaluation of tungsten inert gas and laser welding of AZ31 magnesium alloy

Abstract

Welding of AZ31 Mg alloy was conducted using various welding techniques, namely, tungsten inert gas (TIG) welding with Ar shielding gas, TIG welding with He shielding gas, CO₂ laser welding, and YAG laser welding. The results were comparatively evaluated in terms of weld bead formation and microstructural characterisation. It was found that TIG welding with both Ar and He gas shielding produced good welds without major defects. The penetration capacity can be improved using He gas shielding. Owing to their high energy density, CO₂ and YAG lasers can produce weld beads having high aspect ratio. Among the four techniques used, the YAG laser produced the finest weld microstructure, whereas TIG with Ar gas shielding produced the coarsest microstructure. Shielding is a key factor controlling the O contents in the welds. The more effective the shielding provided the lower the O content in the weld. Hardness reduction in the weld metals and heat affected zones was observed for all the techniques owing to the elimination of strengthening effects by the welding operation. In summary, the present study demonstrated advantages and limitations of the various welding techniques and provided an in depth understanding of the weldability of AZ31 Mg alloy.     

A contribution to the rare earth intermetallic chemistry: Praseodymium-magnesium alloy system

Pr-Mg alloys were studied in the range 0–100 at. % Mg. By using X-ray powder diffraction, optical and scanning electron microscopy, electron probe micro-analysis and differential thermal analysis, the different intermediate phases were identified and their crystal structures confirmed or determined. The following phase equilibria have been also determined: PrMg (cubic, cP2, CsCl type, melting point 765°C), PrMg₂ (cubic, cF24, MgCu₂ type, peritectic formation 740°C), PrMg₃ (cubic, CF16-BiF₃ type, melting point 790°C), Pr₅Mg₄₁ (tetragonal, tI92 Ce₅Mg₄₁-type, peritectic formation 575°C) and PrMg₁₂ (tetragonal, tI26 ThMn₁₂-type, peritectic formation 565°C) PrMg₂ undergoes a eutectoidal decomposition at 670°C. Three eutectic reactions were observed to occur at 735°C and 40·0 at. % Mg, at 725°C and 59·5 at. % Mg and at 560°C and 95·0 at. % Mg, respectively. The (β-Pr) terminal solid solution was observed to decompose eutectoidally at 510°C and 19·5 at. % Mg. The data obtained in this study are compared with those relating to other previously studied R-Mg systems.The crystallochemical characteristics of the binary phases formed by Mg with the rare earths and with the alkaline earths are briefly discussed.     

Corrosion behaviour of 304LN activated tungsten inert gas and flux-cored arc weld metals

Activated tungsten inert gas (A-TIG) and flux-cored arc (FCA) weld metals were prepared using 304LN stainless steel plate. The weld metals were thermally aged at 923, 973 and 1023?K for 100?h to study the decomposition of initial δ-ferrite in A-TIG (～10 ferrite number (FN)) and FCA (～5 FN) weld metals into secondary phases like M₂₃C₆ carbides, χ and σ. Ferrite number is the measurement of δ-ferrite based on the principle of magnetic property using ferritescope. Preliminary microstructural studies revealed the formation of carbides in FCA weld metals aged at 923?K for 100?h, which was correlated with higher carbon content (0.04?wt-%), and also ageing at higher temperature transformed δ-ferrite into χ/σ phases. However, A-TIG weld metals showed the transformation of δ-ferrite mainly into χ/σ phases. The δ-ferrite transformation kinetics was found to be sluggish in A-TIG weld metals compared to FCA weld metals. This difference was attributed to the difference in the carbon contents of A-TIG and FCA welds. Activated tungsten inert gas weld metals showed better uniform and pitting corrosion resistance compared to FCA weld metals in as-deposited and thermally aged conditions. Presence of higher amount of initial δ-ferrite content in A-TIG weld metal helped diffusion of minor alloying elements like sulphur and phosphorous into it, thereby reducing their microsegregation at the δ/γ interface boundaries and subsequent pitting corrosion attack. Thus, A-TIG welding process was found to be superior compared to FCA welding process.     

A contribution to the kinetic theory of pitting corrosion

In this paper, irreversible thermodynamic considerations have been applied to the pitting corrosion phenomenon. From the standpoint that pitting corrosion is a macroscopically localized heterogeneous process, a capillary model has been used for the purpose of the explanation. A discriminatory equation for pit growth was obtained by consideration of the stationary state which the pit system will reach in a given environment. The present method was useful in defining the pitting potential exactly, and to explain various experimental facts concerning pitting corrosion.     

Residual welding stresses in laser beam and tungsten inert gas weldments of titanium alloy

Abstract

The residual welding stresses in laser beam (LB) and tungsten inert gas (TIG) weldments of a titanium alloy in thin plate form were investigated experimentally in the present work. A hole drilling technique was used to measure the residual stresses in the weldments. The effects of the welding method and post-weld heat treatment (PWHT) on the residual stresses were analysed. The results show that (i) the residual stress distribution in the LB welded joints is similar to that obtained for traditional fusion welding processes, although the distribution zone is much narrower in LB welding, (ii) the residual stress in the heat affected zone for LB welding is about 100 MPa lower than that for TIG welding, and (iii) PWHT in vacuum greatly relieves the welding residual stress.