Laser Additive Remanufacturing Parameters Optimization and Experimental Study of Heavy-Duty Sprocket

Experimental research on laser additive remanufacturing technology of heavy-duty sprocket was carried out. The influences of laser power, scanning speed and powder feeding rate on cladding height, cladding area, melting area and dilution rate were compared and analyzed. The prediction models of the combination of process parameters with the geometric characteristics of cladding layer and dilution were established. A multi-objective process parameter optimization model with the maximum cladding height and cladding area maximum, the minimum melting area and dilution rate as objective functions was established, and the model was optimized and solved based on MOPSO algorithm. The laser additive remanufacturing repairing experiment of damaged sprocket was carried out by using the optimal parameters combination, and the microstructure and mechanical properties of the repaired region were analyzed. The results show that the scanning speed and powder feeding rate are the main factors influencing the geometric characteristics and dilution of the cladding area, and the models have good prediction accuracy. The optimal process parameters (1150 W, 950 mm/min, 3.8 rad/min) obtained by MOPSO algorithm is adopted to repair the damaged sprocket. The repaired area without cracks and pores, the cladding layer shows good metallurgical bonding with the substrate and the microhardness is twice that of the substrate. The experimental results prove that the laser additive remanufacturing technology is feasible to repair the damaged heavy-duty sprocket and has a strong engineering application prospect.

Study of the Microstructure and Mechanical Properties Obtained by Laser Boost in SLM Process for the Ti-64 Alloy

Selective laser melting (SLM) is one of the new additive manufacturing techniques in which complex parts can be created directly by selectively melting layers of powder. If the productivity of the process is too fast, defects (porosity, partially melted powder, spatters …) are generated inside the fabricated parts and can deteriorate the mechanical properties of the product. A new Laser Boost strategy with a larger melting area and a productivity of 43.20 cm3/h has been compared to a Linear Classic strategy. Ti-64 alloy samples were elaborated with both strategies to study their influence on microstructure and mechanical properties. Laser Boost strategy leads to the formation of Ti-64 prior β grains that are larger than the Linear Classic strategy. Mechanical properties obtains are similar with both strategies with a maximum strength average around 1250MPa and an elongation at failure between 3 and 9%. A thermal post-processing by Hot Isostatic Pressure have been carried out on samples made by Laser Boost to increase the ductility of the material up to 15%.

Ultrasonic Welding of Carbon Fiber Reinforced Composite With Variable Blank Holding Force

Energy directors (EDs) have been widely used in ultrasonic welding (UW) of polymers and polymer-based composites. They help concentrate the welding energy and localize the weld at the location where the EDs are present. However, the utilization of EDs increases manufacturing cost and time, especially for complex parts and structures. This paper presents a method for UW of carbon fiber reinforced composite without using EDs. A reusable annular clamp (called a blankholder) is used as part of the weld tool to apply a variable force (called blank holding force) on the composite sheets during the UW. The effect of the blank holding force (BHF) on the weld formation is investigated. The results show that the duration of the BHF had significant impact on the weld formation. There is a critical duration with which a localized weld can form. Suitable durations of BHF at different levels of welding energy are determined by experiments. The main function of the BHF is to create an initial melting area by improving the contact condition. The initial melting area will act as an ED to concentrate the welding energy, and therefore, promotes the formation of a localized weld.

Effect of Ti-Doped on Y134 Superconductor

We investigated some properties of Y134 superconductor doped Ti superconductor. The series of samples of Y134 doped Titanium (YBa3Cu4TixO9-δ) which x=0, 0.05, 0.10, 0.15, 0.20, 0.25 were prepared by solid state reaction method with calcinations and sintering temperature at 980 °C. The porosity was reduced and the melting area were found for all Ti-doped samples. There was a little effect of Ti-doped on Tc onset but the lower of Tc offset were found that agree with the melting found on surface of sample with Ti-doped. The peritectic temperature of Y134 powder, and Y134 + 0.10Ti were on the same range about with more peak area of pure Y134 than Y134 with Ti-doping.

Molecular Dynamics Simulation of Pressure Generated inside Melting Area in EDM

Electrical discharge phenomena in EDM occur in a very short time period and in a very narrow space, thus making both observation and theoretical analysis extremely difficult. For this reason, the material removal mechanism in EDM has yet to be understood clearly. EDM is a thermal process. Thermal energy is generated by a pulse discharge between the workpiece and the tool electrode. It results in melting and evaporating followed by removal of both the workpiece and tool electrode, forming a discharge crater on both surfaces. In this paper, the hydrostatic pressure distribution in melting area was simulated by Molecular Dynamics (MD) methods. The analysis shows that after discharge is ignited, extremely high pressure is generated inside the melting area. The pressure distribution along the central axis of the melting area at different times indicates that during the discharge duration, the hydrostatic pressure quickly increases to a peak value along the depth direction of melting area and then reduced to 0 GPa in the unaffected area. It was also found that with the passage of time, the depth of the point where the pressure peaks increases with the formation of the discharge crater, accompanied by the decrease in the peak pressure. In addition, the ejected material atoms at different times during the removal process were also analyzed. It was found that the material ablation occurs mostly during the discharge duration.

Evaluation of Compound Layer Formed by Impact Welding Using Phase Transformation Technique

When a cylindrical projectile is impact-welded to a flat target, a compound layer is usually observed at the joining interface as a result of the impact welding. In this study, the formation process of the compound layer was formulated as a moving boundary problem, which is a phase transformation technique. The numerical results were compared with the experiment results obtained using an aluminum projectile and stainless steel target. Numerical analysis shows that the melting area is similar to the temperature profile given at the boundary face. The area of the compound layer formed at the joining interface almost agrees with the melting area of the target. The profile of the compound layer is similar to the triangular temperature profile in the given temperature profiles. The mixing ratio of the melting weights of aluminum and stainless steel obtained by the numerical analysis strongly depends on the temperature rise at the interface. The melted weight of aluminum in the experiment is somewhat greater than that in the numerical analysis. The heat conduction analysis including deformation of the projectile and target make the results of the numerical analysis closer to the experimental results.

Relating Air Temperatures to the Depletion of Snow Covered Area in a Himalayan Basin

A procedure for evaluating depletion of snow covered area (SCA) using mean air temperature has been outlined and tested. Because depletion of snow is a cumulative effect of climatic conditions in and around snow cover area, the cumulative mean temperature (CTM) at a nearby station should represent depletion of SCA. The study was carried out for Satluj basin (22,305 km2) located in the western Himalayan region. Melting starts around beginning of March, therefore, reference date for computing CTM was considered March 1. Data of three ablation seasons (1987-1989) were used to establish relationship between SCA and CTM. It was found that depletion of SCA is exponentially correlated with CTM (R2 > 0.98). An exponential reduction of SCA can be explained on the basis of snow distribution in the mountainous basins. This method has a potential for estimating missing data and extending time series on daily, weekly or monthly basis. Once the depletion trend is established in the basin in the first part of melt season, SCA can be simulated with good accuracy using CTM data for the rest period of melt season. Such applications can reduce the number of satellite images required for obtaining SCA information. A forecast of SCA can also be made using forecasted air temperatures. Impact of climate change on depletion of SCA over the melt period indicated that for the considered range of temperature increase (1-3°C), melting area of snow increased linearly with increase in temperature. An increase in temperature by 2°C enhanced the melting area of snow over the melt season by 5.1%.