Eduardo de Magalhães Braga

Influence of procedures and transfer modes in MAG welding in the reduction of deformations on marine structure panels

With the growth of the Brazilian shipbuilding industry, problems from the production processes emerged in the form of distortions and residual stresses. This study researched the influence of welding procedures (sequence, welding direction and reverse pass) and transfer modes (MAG-CC, MAG-STT and MAG-CW) on distortion values. All of the welds were performed with ER70S-6 wire and pure CO2 shielding gas in the short-circuit mode. It was observed that the most important variable was change of welding direction, which is directly connected to restriction levels of the test panel. The sequences used showed little effect on the distortion values. The reverse pass had low distortion values, yet was unproductive. It was observed that the distortion values were similar for the processes and MAG-STT. The panels welded by the MAG-CW process obtained the lowest distortion values measured.

Fatigue life assessment of weld joints manufactured by GMAW and CW-GMAW processes

The fatigue strength of weld joints manufactured using gas metal arc welding and cold wire GMAW (CW-GMAW) was evaluated under stress-controlled cyclic loading. The material used in this study was class ASTM 131 grade A steel, joined using ER70S wire filler metal. The addition of cold wire led to a decrease in the amount of intergranular ferrite and an increase in hardness in the heat-affected zone. The assessment of fatigue life was performed by using the Weibull distribution and the results revealed that with a 99% reliability the joints produced using the CW-GMAW process have a longer fatigue life, especially as the stress amplitude increases.

Raman spectroscopy fingerprint of stainless steel-MWCNTs nanocomposite processed by ball-milling

Stainless steel 304L alloy powder and multiwalled carbon nanotubes were mixed by ball-milling under ambient atmosphere and in a broad range of milling times, which spans from 0 to 120 min. Here, we provided spectroscopic signatures for several distinct composites produced, to show that the Raman spectra present interesting splittings of the D-band feature into two main sub-bands, D-left and D-right, together with several other secondary features. The G-band feature also presents multiple splittings that are related to the outer and inner diameter distributions intrinsic to the multiwalled carbon nanotube samples. A discussion about the second order 2D-band (also known as G′-band) is also provided. The results reveal that the multiple spectral features observed in the D-band are related to an increased chemical functionalization. A lower content of amorphous carbon at 60 and 90 min of milling time is verified and the G-band frequencies associated to the tubes in the outer diameters distribution is upshifte...

Feasibility of narrow gap welding using the cold-wire gas metal arc welding (CW-GMAW) process

This article evaluates the performance of the cold-wire gas metal arc welding (CW-GMAW) process for narrow gap girth welding. The CW-GMAW process is characterized by the introduction of a continuously fed non-energized wire (cold-wire) into the electric arc/weld pool region. The cold-wire is melted by using the surplus heat available at the arc and molten metal at the weld pool. Narrow grooves 5 mm wide were prepared in 16 mm thick ASTM A131 grade A steel plates and filled using the CW-GMAW process. The feasibility of the process for narrow gap welding was assessed by analysing the joint cross section, microstructure and Vickers hardness. The mechanism by which the cold-wire prevents groove sidewall erosion is identified by using high speed imaging. It was found that for the CW-GMAW, the electric arc attaches to the cold-wire instead of the weld pool leading to a more stable arc, preventing the arc from attaching to the groove sidewall. The additional weld metal deposited by the cold wire, allowed complete filling of the groove with only three passes, demonstrating the productivity potential of the CW-GMAW process for narrow groove welding.

Residual stresses in cold-wire gas metal arc welding

ABSTRACT This work compares the welding residual stresses of the cold-wire gas metal arc welding and conventional gas metal arc welding processes. Two techniques were used to measure the residual stresses: X-ray diffraction and acoustic birefringence. The base metal used was carbon manganese steel plates of 9.5- mm thickness. The results showed that the introduction of the cold-wire tends to decrease the residual stresses, suggesting that the introduction of the cold wire decreases the amount of heat given to the base metal, and consequently lowers residual stresses.

Incorporation of AWS 316L wire nanostructured with nickel-carbon nanotube by arc welding

Carbon nanotubes have certain properties, such as 150 GPa tensile strength, a 1000 GPa shear modulus, an electrical conductivity of 60 S/m, and a high thermal conductivity of 2500 W/mk, that make them an optimum metallic matrix composite reinforcement. Otherwise, arc welding is a common industrial process that joins almost all metals. However, there are hardly any studies involving the addition of carbon nanotubes in stainless steel so far. In this research, we show the incorporation of an AWS 316L nanostructured wire with nickel-carbon nanotubes in austenitic stainless steel via pulsed gas tungsten arc welding, which formed nanocomposites with 0.75 and 1.5 wt% carbon nanotube contents in the wire. The characterization was performed by scanning electronic microscope, Raman spectroscopy, and X-ray diffraction. The Vickers microhardness test was used to analyze the mechanical properties. The nanostructure composite had microstructure modification, and superficial microhardness improved in 35% for 0.75 wt% carbon nanotube.

COMPARATIVE STUDY BETWEEN GMAW-CW AND GMAW-EW PROCESSES WITH ADDITION OF A COLD ENERGISED WIRE

In a highly competitive market, the GMAW process begins to fail to meet productivity needs, and it is imperative to seek a process with high deposition rates, reduction in welding time, and low operating costs. For surfaces that have undergone erosive processes their reconstitution is performed using Cold Wire-GMAW process, where cold wire is added to the melt pool using the thermal energy of the arc to execute the weld joint that promotes its fusion, increasing the mass of material in the joint and consequently the productivity of the process; however this increase of mass has been limited. The purpose of this work is to make a comparative analysis of the CW-GMAW processes with the EW-GMAW, which is the welding in which the cold wire is energized, varying the direction of welding (pulling and pushing), to obtain a high deposition of welded material. The results showed that welding by the EW-GMAW process showed higher deposition in pulling mode, less spatter, better wettability, good appearance, generating an acceptable aspect cord for coating purposes, with a 140% cold wire addition and a dilution of approximately 15% with current 80A.

SIMULAÇÃO COMPUTACIONAL DAS PANELAS DE ACIARIA DA SIDERÚRGICA SINOBRAS S.A.

The aim of this work consists in studing the thermal behavior of ladles during steps of the operating cycle using heat transfer equations and computational simulation. From the study results sought to make improvements in order to reduce the loss of heat energy during steps of the production process. Through mathematical modeling, measurements in the plant and computational simulations were determined the temperature drops and heat losses. Therefore were proposed operational and physical changes that after practice tests and or computational simulations proved to be efficient for the reduction of heat loss and lower consumption in the ladle furnace.

Influência dos procedimentos e modos de transferência no processo MAG na redução de deformações em painéis de estruturas navais

The Growth in the Brazilian shipbuilding industry brought on numerous problems in the production line. Some of these problems are related to the manufacturing process, welding process, due to residual stress and distortions. In the present paper, the influence of the welding procedure (sequence and direction of welding and the use of back weld) was studied. Different welding processes with different transfer modes (GMAW-CC, GMAW-TT and GMAW-CW) were also used. These changes were made to observe the influences on the amplitude of the distortions. All the welds were made using the ER70S-6 electrode and pure CO 2 as a shielding gas with the short circuit transfer mode. The results showed that the most important variable is the direction of welding, which is related to the level of restriction of the panels welded. The effect of the welding sequence presented on the values of distortion produced were minor. The panels produced using the back welding procedure presented small values of distortion however, the procedure showed to be inefficient. It was also observed that the level of distortion for the processes GMAW-CC and GMAW-STT showed similar values. On the other hand the values of distortion in the panel welded using the GMAW-CW process presented the lowest values.