Predictions of formability parameters in tube hydroforming process

The objective of this study is to improve the bulging and minimize the thinning ratio to enhance manufacturing of components in Industries. Tube hydroforming is an advanced manufacturing technology used for making intricate and complex tubular parts which required less cycle time. This research focuses on hydroforming process, formability and process parameters design to replace the conventional tube bending, welding and cutting operations. The prediction of parameters is done by applying numerical and experimental approach. During experimentation the pressurized fluid is used to deform the tubes in a plastic deformation. In this study, two types of grade materials are used such as AISI304 and AISI409L of 57.15 mm external diameter with 1.5 mm thickness in the form of electric resistance welded tubes to measure stain path, thinning and bulge height. However, it is observed that the internal pressure and L/D ratio are effective parameters in both numerical analysis and experimentation. In axial feed condition, it is observed that 16.3% thinning in weld region and 44.6% thinning in base metal region, whereas, in fixed feed condition, it is observed that 7.7% thinning in weld region and 18.6%thinning in base metal region for L/D = 1 and L/D = 3 respectively. The numerical analysis with experimental results shows a very good match. It is seen that the axial feed leads to better formability with fixed feed condition because in axial feed condition material supplies towards the center of the bulge tube. The feasibility of the hydroforming process for manufacturing of AISI304 and AISI409L grade material as per the requirements of the industries is also checked. The maximum bulging is observed in L/D = 2 by comparing with the other ratios. This process can be effectively used for AISI304 grade material because the formability is better than AISI409L. Article highlights The strain path measured and predicted at necking point for ERW tube in both weld and base metal. Thinning is measured during bulging of tube under the axial and fixed feed condition. For L/D = 1 ratio observed strain distribution in unidirectional and L/D = 2, 3 observed in plane strain and bidirectional respectively.

Investigation of residual stress in butt-welded plates considering phase transformation

This paper presents a new approach to predict the residual stresses caused by welding in a butt-welded specimen. Based on the developed three-dimensional finite element model, both the process of material filling and the effects of phase transformation are considered through the material properties which depend on both the temperature and temperature history. For simulating the change in volume caused by phase transformation, a linear model is proposed to relate the start temperatures with the peak temperatures. A comparison of the computational and experimental results verifies the applicability of the proposed approach for welding involving material filling and phase transformation. Four models were built to analyze the influence of the material-filling process and phase transformation. The results demonstrated that without the use of material filling process, the residual stress is underestimated. In addition, without phase transformation, the transverse stress in the weld region is underestimated, while the longitudinal and transverse stresses in the weld region and HAZ, respectively, are overestimated.

Optimization of TIG Welding Parameters for the 202 Stainless Steel Using NSGA-II

Tungsten Inert Gas welding is a fusion welding process having very wide industrial applicability. In the present study, an attempt has been made to optimize the input process variables (electrode diameter, shielding gas, gas flow rate, welding current, and groove angle) that affect the output responses, i.e., hardness and tensile strength at weld center of the weld metal SS202. The hardness is measured using Vicker hardness method; however, tensile strength is evaluated by performing tensile test on welded specimens. Taguchi based design of experiments was used for experimental planning, and the results were studied using analysis of variance. The results show that, for tensile strength of the welded specimens, welding current and electrode diameter are the two most significant factors with P values of 0.002 and 0.030 for mean analysis, whereas higher tensile strength was observed when the electrode diameter used was 1.5 mm, shielding gas used was helium, gas flow rate was 15 L/min, welding current was 240A, and a groove angle of 60o was used. Welding current was found to be the most significant factor with a P value of 0.009 leading to a change in hardness at weld region. The hardness at weld region tends to decrease significantly with the increase in welding current from 160-240A. The different shielding gases and groove angle do not show any significant effect on tensile strength and hardness at weld center. These response variables were evaluated at 95% confidence interval, and the confirmation test was performed on suggested optimal process variable. The obtained results were compared with estimated mean value, which were lying within ±5%.

Effects of Biaxial Loading on the Tensile Strain Capacity of Girth Welds With Weld Strength Undermatching and HAZ Softening

The ability to accurately estimate the tensile strain capacity (TSC) of a girth weld is critical to performing strain-based assessment (SBA). A wide range of geometry, material, and loading factors can affect the TSC of a girth weld. Among the influencing factors, an increase in the internal pressure level has been shown to have a detrimental effect on the TSC. The overall influence of internal pressure is usually quantified by a TSC reduction factor, defined as the ratio of the TSC at zero pressure to the lowest TSC typically attained at pressure factors around 0.5–0.6. Here the pressure factor is defined as the ratio of the nominal hoop stress induced by pressure to the yield strength (YS) of the pipe material. A number of numeric and experiment studies have reported a TSC reduction factor of 1.5–2.5. These studies generally focused on strain-based designed pipelines with evenmatching or overmatching welds, minimum heat affected zone (HAZ) softening, and a surface breaking flaw at the weld centerline or the fusion boundary. This paper examines the effects of pipe internal pressure on the TSC of girth welds under the premise of weld strength undermatching and HAZ softening. The interaction of biaxial loading and the local stress concentration at the girth weld region was quantified using full-pipe finite element analysis (FEA). The relationship between TSC and the internal pressure level was obtained under several combinations of weld strength mismatch and HAZ softening. Results from the FEA show that the effects of the internal pressure on the TSC are highly sensitive to the material attributes in the girth weld region. Under less favorable weld strength undermatching and HAZ softening conditions, the traditionally assumed reduction factor or 1.5–2.5 may not be applicable. Further, the location of tensile failure is found to depend on both the weld material attributes and the internal pressure. It is possible for the failure location to shift from pipe body at zero internal pressure to the girth weld at elevated internal pressure levels. The implications of the results for both girth weld qualification and integrity assessment are discussed.

Analysis of Filler Metal Composition on Weld Dilution of Austenitic Stainless Steel by TIG and MIG Welding

Austenitic stainless steels are very important material and extensively used for various applications in fertilizer industry, petrochemical industry, nuclear industry and food industry. Austenitic stainless steel 316L alloyed with small percentage of nitrogen is called 316LN. 316LN is widely used only in nuclear applications and it is also called high temperature steels. This nitrogen alloyed steels 316LN will work at higher temperature environment along with radiation environment without losing its properties. The welding of this 316LN steel poses challenge due to problems like sensitization to inter granular corrosion, stress corrosion cracking and even hot cracking. Selecting the type of welding and filler material is more important for welding the 316LN austenitic stainless steel (SS). In this paper SS 316LN material is being welded with TIG and MIG welding. Three pairs of SS 316LN plates were used for experimental work. Filler electrode ER316L is used for TIG and MIG121 is used for MIG welding. After the welding process, hardness test, tensile test and bending test were performed to check the mechanical properties of the specimen. Microstructure of the specimen is observed at the weld region. The results show that the welded joint is stronger than the base material in TIG welding process compared to MIG welding, combination of TIG and MIG welding. Hardness values are observed to be higher at the weld region than the base material. Tensile test results show that the ultimate tensile strength of welded plate is greater than that of base materials and TIG welding process is better than other two processes. The microstructure images show that there is a continuous and uniform welding and the joint is defect free from cracks.

New method to enhance the mechanical characteristics of Al-5052 alloy weldment produced by tungsten inert gas

Tungsten inert gas welding method is widely used to weld aluminum alloys. However, the development of some defects such as porosity and undercutting which form during tungsten inert gas welding may decrease the quality of the weld. Processing of the joint by friction stir processing is a method to enhance weld quality. In the current work, the weld area produced by tungsten inert gas is processed by friction stir processing as well as a novel processing method entitled “friction stir vibration processing.” In friction stir vibration processing, the specimen is vibrated while friction stir processing is carried out. The results show that both processing methods lead to grain refinement in the weld region and increase the strength and ductility of the tungsten inert gas–welded specimen. The stir zone grain sizes of friction stir vibration–processed samples are less than those of friction stir–processed ones. It is believed that workpiece vibration in friction stir vibration processing increases the material straining and intensifies the dynamic recrystallization. By application of friction stir processing on tungsten inert gas–welded specimen, ultimate tensile strength and ductility increase by about 10% and 22%, respectively. They increase by about 17% and 33%, respectively, as friction stir vibration processing is applied. The results also indicate that the effect of friction stir vibration processing on the microstructure of the weld region and its mechanical properties increases as vibration frequency increases. Friction stir vibration processing is a good alternative for friction stir processing, and it is recommended for application in industry.