The characteristics of welding currents in a rotating arc leadtandem GMAW process and the weld-seam tracking

Tandem gas metal arc welding( T-GMAW) process shows a high deposition rate that up to three times of the single electrode GMAW,so the welding speed could be significantly increased in this process. However,the majority of this process applications are based on the pre-programmed robotic welding,which does not allow them to track the seam real-time during welding. Rotating arc sensor,sensing the seam position by detecting the changing of welding currents,has been widely adopted in the automatic robot welding process. It is proposed in this paper to integrate the rotating arc sensor with a trailing torch to develop a new approach of rotating arc lead tandem gas metal arc welding( RLT-GMAW) process. The characteristics of the welding currents in the proposed new welding process were firstly studied,and then a self-turning fuzzy control seam tracking strategy was developed for the mobile robot automatic welding. The experimental results showed that the proposed RLT-GMAW process had an excellent seam tracking performance and high welding deposition rate. Even if there were some electromagnetic interactions between the two arcs,the deviation of the welding seam could also be reflected by the fluctuation of the welding currents on the leading arc once the correct welding parameters were selected. Based on the detected deviation,the welding tracking experiments showed that the proposed self-turning fuzzy controller had a good performance for the RLT-GMAW process seam tracking.

Cavity nucleation during hot forging of Ti-6Al-2Zr-1Mo-1V alloy with colony alpha microstructure

The initiation sites and influencing factors of cavity nucleation were investigated for a Ti-6Al-2Zr-1Mo-1V alloy with lamellar starting structure,using the isothermal hot compression test.All samples were deformed to a true strain of 0.70 in the temperature range of 750-950°C and strain rate range of 0.001-10 s-1.The corresponding microstructures were observed by means of the metallurgical microscopy and scanning electron microscopy(SEM).It was found that all cavities occurred at the bulge regions of the compression specimens.Most of cavities nucleated along prior beta boundaries oriented 45°to the compression axis,while others nucleated at the interfaces of lamellar alpha colonies.Cavity nucleation was inhibited with increasing the volume fraction of beta phase and the volume fraction spheroidized of lamellar alpha phase.

Evolution of Joint Formation in Resistance Microwelding of Crossed Pt-10%Ir and 316 LVM Stainless Steel Wires

The surface morphology, cross-sections, and joint break force(JBF) of joints welded under different electrode forces were studied. The defects, such as electrode sticking, notch, and excessive expulsions, were observed in the joints. No desirable joints were achieved with the consideration of weld geometries and joint performances. From the cross-sectional morphology, the joint evolution during the RMW of Pt alloy and 316 LVM SS wires was developed, which involved cold collapse and heat promoted set-down of Pt alloy wire, unbalanced heating at interface, molten phase squeezed out, and defect formation. Finally, the defect formation was also discussed.

Preparation of narrow band gap V_2O_5/TiO_2 composite films by micro-arc oxidation

V2O5/TiO2 composite films were prepared on pure titanium substrates via micro-arc oxidation (MAO) in electrolytes consisting of NaVO3. Their morphology and elements were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. Phase composition and valence states of species in the films were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) were also employed to evaluate the photophysical property of the films. The V2O5/TiO2 composite films show a sheet-like morphology. Not only V2O5 phase appears in the films when the NaVO3 concentration of the electrolyte is higher than 6.10 g/L and is loaded at the surface of anatase, but also V4+ is incorporated into the crystal lattice of anatase. In comparison with pure TiO2 films the V2O5/TiO2 composite films exhibit significantly narrow band gap energy. The film prepared in an electrolyte consisting of NaVO3 with a concentration of 8.54 g/L exhibits the narrowest band gap energy, which is approximately 1.89 eV. The V2O5/TiO2 composite films also have the significantly enhanced visible light photocatalytic activity. The film prepared in an electrolyte consisting of NaVO3 with a concentration of 8.54 g/L exhibits the best photocatalytic activity and about 93% of rhodamine is degraded after 14 h visible light radiation.

Microstructure and Tribological Behavior of a TiO_2/hBN Composite Ceramic Coating Formed via Micro-arc Oxidation of Ti–6Al–4V Alloy

A composite coating containing hexagonal boron nitride(hBN) particles and titanium oxide(TiO_2) was formed on the surface of Ti–6Al–4V alloy via micro-arc oxidation(MAO). The effect of quantity of the hBN-particles added into electrolyte on microstructure, composition, and wear behavior of the resulting composite coatings was investigated. Microstructure, phase composition, and tribological behavior of the resulting MAO coatings were evaluated via scanning electron microscopy, X-ray diffraction, and ball-on-disc abrasive tests. The results reveal that the TiO_2/hBN composite coating consisting of rutile TiO_2, anatase TiO_2, and an hBN phase was less porous than particle-free coating. Furthermore, the presence of hBN particles in the MAO coating produced an improved anti-friction property. The composite coating produced in the electrolyte containing 2 g/L of hBN particles exhibited the best wear resistance.The outer loose layer of the MAO coatings was removed by a mechanical polishing process, which led to a significant improvement in the wear resistance and anti-friction properties of the MAO coatings and highlighted an essential lubricating role of hBN particles in the composite coatings. However, wear mechanism of the MAO coatings was not relevant to the presence of hBN particles, where fatigue wear dominated the anti-fraction properties of the MAO coatings with and without hBN particles.

Effect of shot peening on microstructure,nanocrystallization and microhardness of Ti-10V-2Fe-3Al alloy surface

Severe plastic deformation of Ti-10V-2Fe-3Al alloy in the surface region was caused by shot peening at air pressure of 0.6 MPa with processing time ranging from 1 to 45 min.The results showed that the thickness of surface deformation layer was proportio nal to the processing time,the microhardness of the shot-peened surface in creased from 280 to 385 HV,and the depth of highly hardening layers arrived at 200μm.It was worth noting that a grain size gradient from nanocrystalline on the surface toward coarse grain in the matrix was obtained during the shot peening process and the minimum grain size in the top surface after shot peening was about 100-200 nm.

Plastic deformation analysis and forming quality prediction of tube N C bending

Plane strain assumption and exponent hardening law are used to investigate the plastic deformation in tube bending. Some theoretical formulae including stress, curvature radius of neutral layer, angle of neutral layer deviation, bending moment, wall thickness variation and crosssection distortion, are developed to explain the phenomena in tube bending and their magnitudes are also determined. During unloading process, the springback angle is deduced using the virtual work principle, and springback radius is also given according to the length of the neutral layer which remains unchanged before and after springback. The theoretical formulae are validated by the experimental results or the validated simulation results in literature, which can be used to quickly predict the forming quality of tube numerical control(NC) bending.

Effect of dimensionless heat input during laser solid forming of high-strength steel

Laser solid forming(LSF)technology can be used to rapidly manufacture and repair high-strength steel parts with superior performance,but the value of the heat input during operation is difficult to quantify,which has a substantial impact on the microstructure and mechanical properties of the parts.A promising method to improve the forming efficiency and quality of LSFed parts is to accurately control the heat input and explore its relationship with the microstructure and mechanical properties.To remove the interference of other variables from the experiment,the dimensionless heat input Q;^(∗)was introduced.The Q^(∗)values were designed in advance to calculate the experimental parameters used to perform the LSF experiment.The microstructure was observed at different regions of the sample,and its mechanical properties were analyzed.From the results,the following conclusions were drawn.The Q;^(∗)value was directly related to the cooling rate and heat accumulation in the top structure,leading to the formation of different microstructures;it also modified the original structure at the bottom,affecting the subsequent thermal cycle and indirectly changing the tempered martensite morphology.The heat input also affected the mechanical properties of the sample.The hardness of the stable zone decreased with increasing Q;^(∗)value,and the lowest value was 190 HV.Similarly,the tensile strength and yield strength of the LSFed samples decreased considerably with increasing Q;^(∗)value,and the lowest values were 735 and 604 MPa,respectively.Only the elongation and reduction in the area increased after a slight decrease.The Q;^(∗)value had a significant effect on heat treatment.When Q;^(∗)=2.9,the increase in tensile strength and yield strength after heat treatment was the largest(29%and 44%,respectively).