Optimisation of friction stir welding process parameters to weld cast aluminium alloy A413 – an experimental approach

Abstract

A413 is a high strength eutectic aluminium silicon cast alloy used in the food, chemical, marine, electrical and automotive industries. Fusion welding of these cast alloys can lead to problems such as porosity, microfissuring and hot cracking, etc. However, friction stir welding can be used to weld these cast alloys effectively, without defects. In this investigation, an attempt was made to optimise the friction stir welding process parameters for joining the cast aluminium alloy A413. Joints were made using four levels each of tool rotation speed, welding speed and axial force. The quality of the weld zone was analysed using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a tool rotation speed of 900 rev min^?1, a welding speed of 75 mm min^?1 and an axial force of 3 kN showed the best tensile strength.     

Influence of Prior Deformation on The Sensitisation of AISI Type 304 Stainless Steel and Applicability of EPR Technique

Abstract

The influence of prior plastic deformation on the degree of sensitisation (DOS) of AISI 304 stainless steel has been studied for various levels of cold work ranging from 0 to 25% using the ASTM standard A262 practices A and E, and the electrochemical potentiokinetic reactivation (EPR) technique. Peak current density and reactivation charge density were determined from single loop EPR experiments and the ratio of the peak current during reactivation to that during activation was determined from double loop EPR experiments. The feasibility of using these techniques for determining the DOS in cold worked samples was examined. The reproducibility of the EPR results is rather poor. There appears to be no well defined systematic trend between the degree of cold work and the DOS as estimated from the EPR parameters. EPR parameters were found to be dependent on the temperature of aging and the degree of prior cold work. Threshold values above which a sample can be treated as sensitised cannot therefore be determined from EPR tests without being confirmed independently by conventional ASTM standard methods.     

Classic contributions: cryogenic treatment Effects of cryogenic treatments on mechanical properties and wear behaviour of high-speed steel M2

Abstract

In this contribution, originally published in 2000, the levels of hardness, impact toughness and wear resistance of M2 high-speed steel after conventional heat treatment are compared with those imparted by additional subzero and deep cryogenic processing.     

Classic contributions: cryogenic treatment Influence of deep cryogenic treatment on microstructure,mechanical properties and dimensional changes of vacuum heat-treated high-speed steel

Abstract

In this contribution, originally published in 2002, it is shown that the microstructure of AISI M2 high-speed steel can be modified substantially by a vacuum heat treatment combined with a deep cryogenic treatment to optimise the ratio between hardness and fracture toughness. This ratio is affected significantly by the volume fractions of retained austenite and undissolved eutectic carbides, as well as by the mean distance between these carbides. Values calculated using a newly developed semiempirical equation prove that, for given vacuum heat treatment conditions, the volume fraction of retained austenite and the hardness have a significant effect on the fracture toughness. Analysis of vacuum heat-treated modified 'Navy C' ring specimens confirms that the dimensional changes can be controlled. The main factors that influence the dimensional changes are the volume fraction of retained austenite and the steel's hardness.     

A multi-link system control strategy based on biological reaching movement

In the multi-link arm control process, the problems of trajectory planning and trajectory realization have been recognized as being of key importance. We developed a technique by which to realize a reaching movement control of the multi-link arm system, which was inspired by experimental results for reaching movements of macaques or human beings. The proposed method can treat the effect of the dynamics of the multi-link system and the trajectory planning of the end-effector, which has a bell-shaped speed profile, as well as the difficulties of redundancies of multi-link systems. Two-link arm reaching movement experiments revealed the same features, as demonstrated by the results of biological experiments on humans and macaques. In addition, the results obtained using a two-dimensional four-link model in a standing-up movement control experiment agreed well with 'standing-up from a chair' movement of human beings. Since the proposed method has a simple structure and its implementation process is simple, the proposed method will be effective for use in a multi-link system control strategy.     

MOTION VELOCITY SMOOTH LINK IN HIGH SPEED MACHINING

To deal with over-shooting and gouging in high speed machining,a novel approach for velocity smooth link is proposed. Considering discrete tool path,cubic spline curve fitting is used to find dangerous points,and according to spatial geometric properties of tool path and the kinematics theory,maximum optimal velocities at dangerous points are obtained. Based on method of velocity control characteristics stored in control system,a fast algorithm for velocity smooth link is analyzed and formulated. On-line implementation results show that the proposed approach makes velocity changing more smoothly compared with traditional velocity control methods and improves producti-vity greatly.     

HIGH SPEED MILLING OF GRAPHITE ELECTRODE WITH ENDMILL OF SMALL DIAMETER

Graphite becomes the prevailing electrode material in electrical discharging machining (EDM)currently.Orthogonal cutting experiments are carried out to study the characteristics of graph- ite chip formation process.High speed milling experiments are conducted to study tool wear and cutting forces.The results show that depth of cut has great influence on graphite chip formation.The removal process of graphite in high speed milling is the mutual result of cutting and grinding process. Graphite is prone to cause severe abrasion wear to coated carbide endmills due to its high abrasive- ness nature.The major patterns of tool wear are flank wear,rake wear,micro-chipping and breakage. Cutting forces can be reduced by adoption of higher cutting speed,moderate feed per tooth,smaller radial and axial depths of cut,and up cutting.     

Modelling of steel shrinkage and optimisation of mould taper for high speed continuous casting

Abstract

In high speed continuous casting, optimisation of mould taper is key for intensifying heat transfer and for improving the quality of the cast products. Mathematical modelling has been carried out by combining heat transfer, steel shrinkage and parabolic continuous taper model in order to optimise the mould taper profile. These models have been assembled to a set of software, the inputs of which include the steel grade, casting speed, casting temperature, length and the cross-section of mould tube, while the outputs consist of surface temperature of the strand, thickness of solidified shell, thermal linear expansion coefficient, steel shrinkage, distortion of the mould tube wall, the actual air gap, total taper and the continuous taper profile. Optimum mould taper has a parabolic profile which is tapered inwards that changes continuously along the length of the strand in order to achieve reduction in air gap while avoiding distortion of the mould tube.     

一种节能意识的多路径QoS保证路由协议

综合SPEED与SEEM协议,提出了一种混合型协议QoSDM。它针对多数QoS保证的路由协议没有特别考虑到无线传感器节点的能量约束的问题,在sink和多个源节点之间找到多条路径,减少碰撞的发生,利用多个节点代表源节点来接收和转发数据包。多径搜索使用的是全球网络知识,具有先进性。仿真结果表明,既保留了与SPEED相近的可靠性和时延性能,又具有SEEM多路径路由协议的节能QoS保证效率,展现了此协议的潜力和效益。这特别适合于高QoS要求情况下又需要节省能源消耗的情形,符合当前的研究趋势。     

Tool design and stir zone grain size in AZ31 friction stir spot welds

Abstract

The influence of tool design and tool rotational speed variations on the torque, energy output, stir zone temperature and average grain size in the stir zones of AZ31 friction stir spot welds was investigated. The average stir zone grain size decreased by ～1 μm in AZ31 friction stir spot welds made using a three-flat/threaded tool design and tool rotational speeds of 2250 and 3000 rev min^?1. However, there was no statistically significant influence of tool design on the average grain sizes in friction stir spot welds made using tool rotational speeds of 1500 and 1000 rev min^?1. There was no evidence of grain growth in the stir zones of AZ31 friction stir spot welds. Similar torque, calculated energy output and stir zone temperature values were found in AZ31 friction stir spot welds made using threaded and three-flat threaded tool designs and tool rotational speeds from 1000 to 3000 rev min^?1.