Materials Science Forum Vols. 580-582

Abstract: Gas Metal Arc (GMA) welding process has widely been employed due to the wide range of applications, cheap consumables and easy handling. A suitable mathematical model to achieve a high level of welding performance and quality should be required to study the characteristics for the effects of process parameters on the bead geometry in the GMA welding process. The objective of this paper is to present development of three empirical models (linear, curvilinear and intelligent model) based on full factorial design with two replications to estimate process parameters on top-bead width in robotic GMA welding process. Regression analysis was employed for optimization of the coefficients of linear and curvilinear models, but Genetic Algorithm (GA) was utilized to estimate the coefficients of intelligent model. ANOVA analysis using experimental data were carried out representation of main and interaction effects between process parameters on top-bead width. Resulting solutions and graphical representation showed that the developed intelligent model can be used for prediction on top-bead width in robotic GMA welding process

Abstract: This paper proposes an image sensing system for the TIG (Tungsten Inert Gas) welding process of aluminum pipe. In automatic welding process, it is important to recognize the molten pool during the welding process. The use of CCD camera as vision sensor obtains the information of molten pool. The research was conducted for welding of aluminum alloy Al6063S-T5 with controlled welding speed and the AC welding polarity. Firstly, histogram analysis and range of brightness threshold was established. Secondly, by using the differential value of brightness of molten pool, the edge of molten pool can be detected. Finally, to overcome the unsteady detected edge, the ellipse approximation was used to obtain the image parameters, which are width, length and area. From the experiments it is shown that the recognition of molten pool using vision sensor is an effective method.

Abstract: Increased efficiency and emission reduction in modern power plants lead to the use of new advanced materials with enhanced creep strength, with the objective to increase the steam parameters of power plants. With over ten years on market and wide experience related to its use, ASTM Grade 92 is becoming one of the most required materials when high service temperatures are reached (max. 610°C). Its composition, with 9%Cr and 1.5%W, gives rise to martensitic microstructures which offer very high creep strength and long term stability. The improved weldability and creep-strength between 500 and 580°C of the low alloy ASTM Grade 23, as well as a cost advantage over higher Cr materials in this temperature range, make it one of the possible candidates to meet the stringent requirements of modern power plants. Air Liquide Welding (ALW) has optimized and distributes a complete product family for the welding of Grades 23 and 92. TenarisDalmine (TD) focused on the development of Grade 23 tubes and pipes and is working on the development of Grade 92. A deep characterization work of the microstructural evolution and long term creep performances of these high temperature resistant materials was thus undertaken by ALW and TD, in collaboration with the Centro Sviluppo Materiali (CSM). The joint characterization program consisted in the assessment of welded joints creep properties. Welded joints were produced using the gas tungsten (GTAW), shielded metal (SMAW) and submerged arc welding (SAW) processes. Mechanical and creep properties of weldments were measured both in the as welded and post weld heat treated conditions and proper WPS’s were designed in a manner such that industrial production needs were satisfied. Short term creep resistance of cross weld specimens was measured to be within the base material acceptance criteria. Long term base material and cross weld creep performance evaluation are now in progress.

Abstract: Dissimilar friction spot lap joining of Al5052 and Al6022 sheet has been investigated using a combination of joining parameters, thickness and upper plate material. The joining parameters such as tool rotating speed, plunging depth and joining time have been considered. The maximum tensile shear strength has been observed at tool rotating speed of 1000rpm, dwell time of 2.5sec, plunging depth of 1.8 mm and Al 6022 as upper plate. The maximum tensile shear fractured load of the joint was about 80% of that of the similar Al 5052 alloys joint.

Abstract: A new welding technique called hybrid FSW was developed to decrease the tool load and the defects during the FSW of high melting point materials. This method consists of FSW and a laser for preheating ahead of the tool. The hybrid FSW enables the proper welding conditions to be significantly expanded, and the joint characteristics are similar to those obtained by the normal FSW at the same welding speeds.

Abstract: The remote resistance welding technology in the hot cell environment for DUPIC (Direct Use of spent PWR fuel In CANDU reactors) fuel fabrication was established. To do this, a preliminary investigation for hands-on fuel fabrication outside the hot cell was conducted in the consideration of constraints caused by welding in the hot cell. Further welding experiments were carried out to improve the RW process. A remote resistance welding apparatus was developed. The characteristics of welds made by RW and LBW were compared in terms of the weld nugget penetrations and torque strength. It was found that resistance welding was a more suitable welding process for joining the endplate to the end caps in the hot cell. The optimum conditions for RW in the hot cell operation in a remote manner were also obtained.

Abstract: An in-house developed FE code, based on the idea of Iterative Substructure Method, was used to evaluate the effectiveness of fixture and pre-strain for reduction of welding distortion in a fillet welded structure. Comparison between the simulation results and experimental results has been performed to validate the basic FE model. Effects of two fixture conditions and various prestrain schemes were analyzed. The simulation results show that appropriate fixture can greatly reduce angular distortion of the work-piece and results in an appreciable reduction in residual deformation and the application of pre-strain can significantly reduce the residual distortion.

Abstract: Ti-6Al-4V was successfully jointed by linear friction welding (LFW). A sound weld of thickness of 65-115 $m was obtained under the present conditions. The weld consisted of the superfine α+β structure, which is associated with the rapid heating and cooling processes involved in LFW. The thermomechanically affected zone (TMAZ) was limited and comprised of the severely deformed α and β grains. In the flash, a gradual microstructure was formed from the weld edge to the flash edge. A martensite structure (α’) was formed besides the acicular α+β in the flash edge owing to the fast cooling rate.

Abstract: Liquid Penetration Induced (LPI) cracking during AZ91, AZ31 and AM60 friction stir spot welding is investigated. The temperature cycles, within the stir zone and in the TMAZ region, are examined. The mechanism and the key factors determining LPI cracking in Mg-alloy friction stir spot welds are delineated.

Abstract: Failure strength evaluation on resistance welding mixed adhesive bonding was studied. Tensile-shear tests were carried out with the single-lap specimen, using both resistance welding and adhesive bonding. Peel tests were also carried out with DCB specimen. Composites were manufactured using the polyester as a matrix and bamboo natural fiber layer as a reinforcement. Adhesive bond, having bonding strength that remains unaffected by heat at resistance welding, were selected. Generally, adhesive bond require a long curing time and have little strength before hardening. Resistance welding helps weakness of adhesive bond both curing time and peel strength. And the spew fillet of adhesive bonding also helps to release stress intensity of edge of joining. The failure mechanism was discussed in order to explain higher peel and tensile-shear strength of resistance welding mixed adhesive bonding.