Turning and drilling of parts made from sinter hardenable steel powders

Abstract

The constant demand for improved mechanical properties and lower production costs of PM parts has lead to the development of sinter hardenable steel powders. These powders produce fully martensitic microstructures by appropriately controlling the cooling rate during the sintering operation. Thus, the heat treatment operation (oil quenching) that would generally be required to obtain hardened parts can be eliminated. However, machining of the relatively hard sinter hardened parts is difficult.It then becomes critical to optimise the tool selection and the machining conditions, such as surface speed and feed. This paper presents guidelines for the turning and drilling of parts made with sinter hardenable powders, as well as a discussion on the effect of manganese sulphide particles and chip formation during turning.     

38—THE EFFECT OF SPINNING CONDITIONS ON THE TENSILE PROPERTIES OF CORE-SPUN YARNS

A critical assessment of the merits of core-spinning by means of comparisons of the strength and extension of core-spun yarns with all-staple-fibre yarns forms the basis of this paper. Core-spinning was done by introducing the filament under tension into the drafted strand as the latter entered the front rollers of the ring-frame. A 20-den (2.2-tex) nylon monofilament was used as core, and three types of staple-fibre covering were investigated. The effects of twist, pre-tension, and feeding arrangements on the geometrical disposition and tensile properties of the yarns were examined. Improvements in strength are, in general, realized at low twists by the incorporation of the filament and by further constraining it to occupy the core. The contribution of the components to the yarn strength and the process of breaking were also subjected to a detailed study. The studies reported provide an interesting insight into the extent of cohesion developed between the fibres during the straining of the yarn and its influence on the process of breaking and ultimately on yarn extension.     

Comparison of simulated pulse plating processes to practical experiments

Abstract

The development of any pulse sequence is a highly knowledge based process. Beside the knowledge of electrochemical electrolyte properties, the tailoring of the actual field line distribution and the local surface potentials via the applied pulse sequence is the main focus of the scientific development. The combination of pulse plating and numerical simulation offers a very high success rate for definition of pulse plating processes. Simulation tools are the only option to study current distribution and potential fields and are applicable for any possible electrolyte system and cell geometry. For developing a pulse plating sequence it is of major importance that the effect of single pulses within a pulse sequence can be calculated stepwise in high precision, taking into account the change of the substrate surface and geometry after each pulse step. Only in this way can the exact influence of cathodic and anodic pulse steps be retrieved. Additionally, the consideration of shieldings and cell geometry can be performed in parallel. Within this work a detailed study of the correlation between experimental data and the results of numerical simulation was performed focusing on the system Watts Nickel on steel. The conformity revealed by this study is excellent. The numerical simulation tool can be used for development and optimisation of pulse plating processes, if a stepwise, shape alteration including mathematical algorithm is used.     

Effect of VC addition on microstructural evolution of WC–Co alloy: mechanism of grain growth inhibition

Abstract

Specimens of WC–30Co and WC–1VC–30Co (wt-%) were heat treated at 1500°C for up to 64 h. During the early stage of heat treatment, it was observed that the addition of VC has effectively retarded the coarsening of WC grains. After the prolonged heat treatment, however, the abnormally grown, very large WC grains appeared in the WC–1VC–30Co specimen. The role of VC has been interpreted in terms of grain coarsening which is suggested to occur by a two-dimensional nucleation mechanism.     

Study of grain size and microhardness of submerged arc welded joint of AISI 1060 steel

Abstract

Change in microstructure, grain growth, hardness and residual stress in a weldment are very much dependent on the temperature distribution, peak temperature and cooling rate. In the present work, three-dimensional transient finite element analysis has been used to predict the cooling rate and peak temperature at different points of the submerged arc welded joint. Grain size and microhardness of the submerged arc welded joint of AISI 1060 steel were experimentally measured and explained on the basis of estimated peak temperatures and cooling rates.     

Comparison of creep behaviour of 2.25Cr–1Mo/9Cr–1Mo dissimilar weld joint with its base and weld metals

Abstract

Evaluation of the creep behaviour of 2.25Cr–1Mo and 9Cr–1Mo ferritic steel base metals, 9Cr–1Mo steel weld metal, and 2.25Cr–1Mo/9Cr–1Mo ferritic–ferritic dissimilar weld joints has been carried out at 823 K in the stress range 100–260 MPa. The weld joint was fabricated by shielded metal arc welding using basic coated 9Cr–1Mo electrodes. Investigations of the microstructure and hardness variations across the joint in the as welded, post-weld heat treated (973 K/1 h), and creep tested conditions were performed. The heat affected zone (HAZ) in both the steels consisted of a coarse prior austenitic grain region, a fine prior austenitic grain region, and an intercritical structure. In the post-weld heat treated condition, a white etched soft decarburised zone in 2.25Cr–1Mo steel base metal and a black etched hard carburised zone in 9Cr–1Mo steel weld metal around the weld fusion line developed. Hardness troughs also developed in the intercritical HAZ regions of both the steels. The width of the carburised and decarburised zones and hardness differences of these zones were found to increase with creep exposure. The 9Cr–1Mo steel weld metal showed higher creep strength compared to both the base metals. The 9Cr–1Mo steel base metal exhibited better creep resistance than the 2.25Cr–1Mo steel base metal at lower applied stresses. The dissimilar joint revealed lower creep rupture strength than both the base metals and weld metal. The creep strain was found to concentrate in the decarburised zone of 2.25Cr–1Mo steel and in the intercritical HAZ regions of both the steels. Creep failure in the stress range examined occurred in the intercritical HAZ of 2.25Cr–1Mo steel even though this region showed higher hardness than the decarburised zone. Extensive creep cavitation and cracks were observed in the decarburised zone.     

用逐步升压法和Weibull参数估计油纸绝缘寿命

为评估油纸绝缘老化寿命 ,采用逐步升压法加速电老化油纸绝缘模型 ,利用Weibull概率分布对同一电压等级下多次试验得到的击穿寿命统计分析 ,利用反幂函数和指数函数拟合试验数据 ,求得两个模型中的电压耐受系数 ,用以评估油纸绝缘的电老化寿命。同时用恒定电压法试验作对比分析 ,结果表明 ,两种加压方法计算结果吻合 ,而逐步升压法简单 ,数据分散性小     

40—THE EQUILIBRIUM DISTRIBUTION OF VEGETABLE PARTICLES IN THE BEARD OF A WORSTED RECTILINEAR COMB

A mathematical model is presented that accounts for the distribution of vegetable particles in the beard of a rectilinear comb. The average advancement of a particle in a particular cross-section is dependent on the proportion of moving fibres and the time for which they move in that section.     

脉冲变压器锥形绕组电压分布数值分析

采用数值计算方法 ,根据实际脉冲变压器锥形绕组的结构 ,建立了相应的匝间电容电感有限元计算模型及等效电网络分析数学模型 ,计算了脉冲电压激励下锥形绕组匝间的电压分布。结果表明 :高压端的振荡频率明显高于低压端 ;电压分布不均匀 ,绕组高压端承受了大部分压降     

Human-assistance robotic system based on distributed computing technology

Population aging is becoming an increasingly pressing problem for society. Thus, the timely development of supporting systems to improve care cost and the quality of life of the elderly is becoming particularly important. Because of the dispersal of the elderly and disabled, a standard software architecture that can implement network-distributed software sharing and improve the cost of writing and maintaining software is in high demand. This paper proposes using distributing computing technology CORBA to integrate network-distributed software and robotic systems for supporting the aged or disabled. Using CORBA as a communication architecture, we implemented a networkdistributed human-assistance robotic system. We developed a hardware base including a robot arm and an omnidirectional mobile robot, developed key technologies such as localization of a mobile robot, real-time recognition, real-time multimedia, and implemented several CORBA servers including a Web user management server, a task-level robot arm control server, a live image and video feedback server, a mobile robot control server, and an indoor Global Positioning System server. With the user controlling a robot arm with 5 d.o.f. to cooperate with an omnidirectional mobile robot, the developed system can provide basic services to support the aged and disabled.