Finite element analysis of the residual stresses in T-joint fillet welds made of similar and dissimilar steels

In this paper, weld residual stress analyses are performed for T-joint fillet welds made of similar and dissimilar steels. Three-dimensional uncoupled thermo-mechanical finite element model which can accurately capture residual stresses in a weld piece is developed in order to predict the residual stress states in the fillet-welded T-joint. Results show that the maximum longitudinal residual stresses near the weld toes of the similar steel welds increase with increasing yield stress of the steel welded. For the dissimilar steel welds, the overall trend, shape and magnitude of the residual stress profiles in flange and web are similar to those of the corresponding similar steel welds despite the slight difference between the residual stresses in parts at which the flange and web come in contact with each other.     

Influence of process parameters on impact toughness and hardness of dissimilar AISI 4140 and AISI 304 continuous drive friction welds

Dissimilar joints between austenitic stainless steel and low alloy steel are extensively used in many high temperature applications in the energy conversion systems. In the present investigation, emphasis is made on the influence of process parameters on the impact toughness and hardness of the friction welded joints between these two materials. The important process parameters in friction welding such as friction force, forge force, and burn-off lengths are considered for optimization by Taguchi method using L₈ 2⁷ orthogonal array. It is found that under low friction force, forging force, and burn-off conditions, the impact toughness is high due to the observed acicular martensite. Low impact toughness is reported for the welds made at higher levels of the parameters. Carbon depletion is also observed close to interface in low alloy steel side. Microhardness at the weld center is less than the microhardness on either side at the interface of low alloy steel and austenitic stainless steel close to weld center. The contribution of each parameter and significance of interactions of these parameters is determined by Taguchi method. Among these parameters, friction force has significant influence and forging force has negligible influence on microhardness. The burn-off has maximum influence while forge force has minimum effect on toughness of the welds. Statistical analysis of variance is carried out, optimum process parameters are evaluated, and regression equations are obtained.     

Effect of process parameters on the macrostructure and defect formation in friction stir lap welding of AA5456 aluminum alloy

Friction stir welding could be considered as a suitable technique for joining of aluminum alloys due to the emerging of different problems in fusion welding of these alloys, especially in lap joint designs. For this purpose, it is necessary to optimize the process parameters while in this study, the combined effects of tool rotation and welding travel speed on the macrostructure and defect formation of friction stir lap welding of AA5456 was investigated. The rotating tool was plunged from the 5 mm-thick AA5456-H321 (top sheet) surface into the 2.5 mm-thick AA5456-O (bottom sheet) and lap joints were fabricated by rotational speeds of 300, 600, 800 and 1000 rpm and welding speeds of 15, 30, 60 and 100 mm min⁻¹. The effect of tool rotation and welding speed on the macrostructure, material flow and defect formation, i.e. hooking, kissing-bond and cavity, were studied by optical microscopy and scanning electron microscope. The results declared that hooking height decreased as the welding speed increased while kissing-bond was formed at higher welding speeds. Moreover, hooking region was extended as the tool rotational speed increased. However, at a high rotational speed, cavity was even created.     

A control system for uniform bead in fillet arc welding on tack welds

Positioning a workpiece accurately and preventing weld distortion, tack welding is often adopted before main welding in the construction of welded structures. However, this tack weld deteriorates the final weld bead profile, so that the grinding process is usually performed for a uniform weld bead profile. In this study, a control system for uniform weld bead is proposed for the fillet arc welding on tack welds. The system consists of GMA welding machine, torch manipulator, laser vision sensor for measuring the tack weld size and the database for optimal welding conditions. Experiments have been performed for constructing the database and for evaluating the control capability of the system. It has been shown that the system has the capability to smooth the bead at the high level of quality.     

Investigation on the effects of SiC particle addition in the weld zone during friction stir welding of Al 6351 alloy

The International Journal of Advanced Manufacturing Technology - This study attempts to incorporate SiC particles in the weld zone during friction stir welding of Al 6351 alloy. SiC particles of...     

Investigation on the effects of laser power and scanning speed on polypropylene diode transmission welds

For mechanical product, tolerance includes Dimensional Tolerance, Form, Profile, Orientation, Location, Runout, and Assembly Mating Tolerance. Generally, the error of part or product is restricted by a kind of tolerance or several kinds of tolerance. In order to analyze error and its stack-up of mechanical product effectively and absolutely, this paper presents an integrated modeling method of unified tolerance representation based on Key Features (KFs) and Graph Theory in order to deal with these types of tolerances simultaneously. The method includes three steps. The first is to build a tolerance-meta model covering KFs, the relationship set of KFs, the type of tolerance, attributes of tolerance, and variational direction of KF. The model of Dimensional Tolerance, Form, Profile, Orientation, Location, and Runout can be built by tolerance-meta model. The second is to build a model of part’s tolerance and Assembly Mating Tolerance based on sum arithmetic of Graph Theory. The third is to build the integrated tolerance model including Dimensional Tolerance, Form, Profile, Orientation, Location, Runout, and Assembly Mating Tolerance. The integrated model is propitious to represent tolerancing experience from engineers. The method is applied successfully to build the integrated tolerance model for a component of aircraft’s fuselage.     

The role of casting porosity in fatigue properties of Al−Si 319 lost foam cast alloy

The tensile, fracture toughness and fatigue properties of Al−Si 319 lost-foam-cast alloy were determined at room temperature. The fatigue properties of this alloy were also determined at 150°C. Fatigue cracks were always initiated at the largest casting pore. Initial pore sizes were measured using a scanning electron microscope. Surface replication showed that majority of the fatigue life was spent in fatigue crack propagation and permitted the estimation of the constants in the Paris power law and the threshold stress intensity factor (ΔK _th ). The role of internal casting porosity was quantified using a linear elastic fracture mechanics (LEFM) model for fatigue crack growth. The predicted lives agreed with the measured values within a factor of two.     

Identification of bolted lap joints parameters in assembled structures

Bolted lap joints have significant influence on the dynamical behaviour of the assembled structures due to creation of strong local flexibility and damping. In modelling the dynamical behaviour of assembled structures the joint interface model must be represented accurately. A nonlinear model for bolted lap joints and interfaces is proposed capable of representing the dominant physics involved in the joint such as micro/macro-slip. The joint interface is modelled using a combination of linear and nonlinear springs and a damper to simulate the damping effects of the joint. An estimate of the response of the structure with a nonlinear model for the bolted joint under external excitations is obtained using the method of multiple scales. The parameters of the model, i.e. the spring constants and the damper coefficient, are functions of normal and tangential stresses at the joint interface and are identified by minimizing the difference between the model predictions and the experimentally measured data.     

Investigation of the effects of main roll-forming process parameters on quality for a V-section profile from AHSS

The cold-roll-forming process is one of the main processes for mass production of the profiles with constant cross-section in many industrial sectors. The introduction of advanced high-strength steels (AHSS), such as DP-series and TRIP-series, into the production of roll-formed profiles has brought new challenges. The current paper exploits the finite elements (FE) method and investigates the effects of the main roll-forming process parameters, namely the roll-forming line velocity, rolls inter-distance, rolls gap, and rolls diameter, on quality characteristics. These characteristics are the distribution of longitudinal and transversal strains on final profile, total, and elastic longitudinal strains and longitudinal residual strains at strips edge along the forming direction and dimensional accuracy of the profile after the final roll station.     

阀门电动装置导线搭接工艺改进

阐述了阀门电动装置运行现场导线搭接的常见问题与搭接工艺的改进。     

Built-up edge effects on process outputs of titanium alloy micro milling

Built-up edge (BUE) is generally known to cause surface finish problems in the micro milling process. The loose particles from the BUE may be deposited on the machined surface, causing surface roughness to increase. On the other hand, a stable BUE formation may protect the tool from rapid tool wear, which hinders the productivity of the micro milling process. Despite its common presence in practice, the influence of BUE on the process outputs of micro milling has not been studied in detail. This paper investigates the relationship between BUE formation and process outputs in micro milling of titanium alloy Ti6Al4V using an experimental approach. Micro end mills used in this study are fabricated to have a single straight edge using wire electrical discharge machining. An initial experimental effort was conducted to study the relationship between micro cutting tool geometry, surface roughness, and micro milling process forces and hence conditions to form stable BUE on the tool tip have been identified. The influence of micro milling process conditions on BUE size, and their combined effect on forces, surface roughness, and burr formation is investigated. Long-term micro milling experiment was performed to observe the protective effect of BUE on tool life. The results show that tailored micro cutting tools having stable BUE can be designed to machine titanium alloys with long tool life with acceptable surface quality.     

Integrated process design of Al6061 alloy bolts for fastening offshore platforms

In this study, we design an integrated manufacturing process for Al6061 alloy bolts to fasten offshore platforms. The proposed scheme includes the theoretical design and numerical study for the heading, trimming, and thread-rolling process. For the theoretical design, the initial rod diameter and the penetration depth (PD) in the thread-rolling process are calculated according to thread standards and geometric relation. The dimensions of the initial workpiece for the heading process are obtained using the volume constancy law. Considering process limitations to predict the defects, the number of stages is set, and the preform is then determined using the design rule in the heading process. Based on the theoretical design, finite-element (FE)-analysis is conducted. In order to predict the defects and fracture phenomena, the ductile fracture criterion was applied during the heading and trimming processes. The Taguchi method is used to optimize the trimming and thread-rolling process with the set of design parameters, such as the PD, transfer velocity, and revolutions per minute in the thread-rolling process, and the blade radius (BR), land width, and stop distance in the trimming process, respectively. Results show that the PD and BR have the most significant effect on the dimensional accuracy and forming load. To validate the proposed design, the aluminum alloy bolt-forming experiment is performed. We obtain the sound Al6061 alloy M12 hexagonal bolt shaped with highdimensional accuracy. Therefore, this research provides valuable guidelines for the design of the integrated forming process in actual bolt production.

     

Effect of process parameters on friction stir welding of aluminum alloy 2219-T87

In this work, successful friction stir welding of aluminum alloy 2219 using an adapted milling machine is reported. The downward or forging force was found to be dependent upon shoulder diameter and rotational speed whereas longitudinal or welding force on welding speed and pin diameter. Tensile strength of welds was significantly affected by welding speed and shoulder diameter whereas welding speed strongly affected percentage elongation. Metallographic studies revealed fine equiaxed grains in weld nugget and microstructural changes in thermo-mechanically affected zone were found to be the result of combined and interactive influences of frictional heat and deformation. A maximum joining efficiency of 75% was obtained for welds with reasonably good percentage elongation. TEM studies indicated coarsening and/or dissolving of precipitates in nugget. For the gas metal arc weld, SEM investigations revealed segregation of copper at grain boundaries in partially melted zone.