Depth Of Fusion Zone Research Articles

Hierarchical bead materials multi-property design for wire-feed laser additive manufacturing

Wire-feed laser additive manufacturing has gained attention for years with its promises of high-level automation, reducing materials waste, overall costs, and large-scale volume production. However, printing material with multiple desired bead properties is a great challenge due to the high cost of experimental data and trial and error methods and the interdependent correlations among the properties. This study proposes a comprehensive multi-property integrated design framework based on learning from experiments data to enable quality control of part (bead) surface finish, geometry and microstructural properties. The printed bead process – microstructure – geometry relationships and process features' importance scores are investigated. The overall bead quality (smooth, ripple, and failed), geometry (e.g. bead height, width, fusion zone depth, fusion zone area), and microstructures characteristics are simultaneously optimized to obtain the optimal processing window. Specifically, the desirable property thresholds are defined experimentally, and the microstructures and geometries of printed beads under various process combinations have been predicted by machine learning models and visualized in a 3D contour space. With these predictions, the process parameters are optimized by passing through a set of filters to filter out undesired process candidates from a process searching space. The validation results highlight that the process parameterizations optimized by this framework can speed up the manufacturing of materials with the desired bead multi-performance.

Interrelated process-geometry-microstructure relationships for wire-feed laser additive manufacturing

Wire-feed laser additive manufacturing is an emerging fabrication technique capable of highly automated large-scale volume production that can reduce both material waste and overall cost while improving product lead times. Quality assurance is necessary for implementation into critical structural applications. However, the large number of process variables along with the cost associated with traditional trial and error methods makes this difficult. This study investigates interrelated process-geometry-microstructure relations based on learning from experiments that will enable improved quality control along with consistent overall surface, geometric and microstructural features of the part. Specifically, an experimental dataset across multiple process variables and output characteristics in terms of overall bead quality, geometric shape (i.g. bead height, width, fusion zone depth, etc.), and microstructures are collected. The predicted process-geometry-microstructure relations are then captured by virtue of data-driven machine learning models. The properties of printed beads are visualized based on an extensive range of processing space within a 3-dimensional contour map. The insights and impacts of process variables on bead morphology, geometric and microstructural features are comprehensively investigated for quality improvement during manufacturing processes.

Simulation of hybrid (LASER-TIG) welding of stainless steel plates using design of experiments

A solid drive for the improvement of higher productivity welding forms lead to the advancement of Hybrid welding process. This research combines arc and laser welding processes providing more robust joints. Hybrid laser welding is a perfect combination of the advantages of laser and arc welding processes. It provides high welding depth at high welding speeds and also good gap bridging capability. This process finds potential applications in shipbuilding, pipeline and automotive industries where high productivity and quality are important. Many researches are in progress to analyze the effect of process variables. This present work is mainly carried out to study the effect of various process parameters like laser beam power, arc power, welding speed on the weld bead dimensions, i.e., bead width and depth of penetration. A three-dimensional transient thermal analysis has been performed for the hybrid welding (LASER + TIG) process using ANSYS. The computed results of width and depth of fusion zone indicates the weld pool shapes. Good agreement was achieved between computed and experimental weld bead dimensions. Mathematical equations were developed using a three factor 5-level factorial technique to predict the geometry of the weld bead. These equations were used to correlate the hybrid welding process parameters with the bead geometry. From these mathematical equations the response of weld bead dimensions with the variation of various hybrid welding parameter were predicted.

Review on the use of activated flux in arc and beam welding processes

Improvement in penetration capabilities is an important issue in many welding processes. One of the most emerging trends to improve penetration capabilities is the utilization of activated flux with welding processes. A thin coating of activated flux is applied on the area to be welded with the help of brush or spray. This paper represents a review of the use of activated fluxes in different arc welding and beam welding processes. Arc welding processes are most commonly employed for various manufacturing applications and hence most applications are considered for utilization of oxide fluxes with these processes. The most common mechanisms responsible for deeper penetration due to flux application in arc welding processes are Reverse Marangoni and arc constriction. EBW Process is considered for thick plates owing to its higher fusion zone depth to width ratio. Use of activation flux concentrates electron beam which creates a narrow and deep fusion zone due to keyhole mechanism. A combination of laser with activated flux improves penetration due to exothermic reaction in the weld pool, welding quality, welding efficiency significantly and reduces cost.

How the nozzle position affects the geometry of the melt pool in directed energy deposition process

ABSTRACTThis work deals with Directed Energy Deposition (DED) that is a process in which the material is delivered directly into the melt pool. Several kinds of nozzle have been developed and used in this process. However, the position of the nozzle, mainly for the lateral one, plays a crucial role in the geometry and porosity content of the melt pool. Therefore, to investigate the correlation between the lateral nozzle position and the geometry of the melt pool, three different sets of single tracks of Ti–6Al–4V were deposited at different nozzle positions. It was found that helpful information regarding the selection of the optimal position of the lateral nozzle can be obtained from the melt pool features. It can be noticed that by increasing the distance between the nozzle position and substrate, the powder capture decreases and accordingly results in a high depth of fusion zone and also keyhole defect formation.

Evolution of crystalline phase during laser processing of Zr-based metallic glass

Understanding the crystallization behavior of metallic glasses (MGs) during laser processing is important in additive manufacturing of MGs, which would overcome the limitation of section-thickness. Experiments were conducted to study the crystalline phase evolution, particularly in the heat-affected zone (HAZ), during laser processing of LM105 (Zr52.5Ti5Al10Ni14.6Cu17.9 (at.%)) MG plates. Three regions with distinct degree of crystallization in HAZ were found, which were caused by different thermal histories. The crystallization can be suppressed, however, by increasing the laser scan speed (100mm/s in this study) while the laser power is fixed (100W in this study). A complete model integrating the heat transfer and the classical nucleation/growth theory was developed to calculate the thermal history and the evolution of crystalline volume fraction. Modeling predictions on the depth of fusion zone (FZ) and thickness of HAZ for different laser processing parameters were validated by comparing with the experimental measurements. This study has demonstrated that at a specific location in the MG material, the use of critical cooling rate alone is not adequate to determine if the material is crystallized; instead the thermal history that the material experienced during both the laser heating and cooling processes is the key factor affecting the final crystallization. The model provides comprehensive understanding of the crystallization behavior during laser-MG interaction.

Mechanisms of Spiking and Humping in Keyhole Welding

The effects of power density, concentration of volatile alloying element (magnesium, Mg), and welding speed on the mechanisms of fusion-zone defects, i.e., spiking and humping (and coarse rippling) during keyhole mode electron-beam welding of Al 6061, Al 5083, and SS 304 are investigated experimentally. Spiking represents a sudden increase in penetration beyond the average penetration line. Rippling exhibits rather regular, arc-shaped topographic features on a solidified surface, whereas humping shows an irregular surface contour consisting of a series of swelled protuberance. These defects seriously reduce the properties and strength of the joint. The quantitative variations of humping, coarse rippling, and spiking defects with the beam-focusing characteristics, volatile element, and scanning speed are quite limited in the literature. The experiments in this paper confirm that average pitch of the humps or coarse ripples is approximately identical to that of the spikes. Thus, the frequency of spiking can be determined from the observation of the weld surface. The results show that the average pitches and amplitudes of humping or coarse rippling and spiking increase with decreasing welding speed and increasing content of volatile element Mg from Al 5083. The frequency and amplitude of spiking, however, are increased by lowering the focal-spot location. The measured amplitude and frequency of spiking and humping and fusion-zone depth are confirmed from good agreement with available scaled analysis. This paper provides quantitative results useful for understanding mechanisms of these defects, so that preventing spiking and humping during keyhole mode welding becomes possible.

Scaling of spiking and humping in keyhole welding

Spiking, rippling and humping seriously reduce the strength of welds. The effects of beam focusing, volatile alloying element concentration and welding velocity on spiking, coarse rippling and humping in keyhole mode electron-beam welding are examined through scale analysis. Although these defects have been studied in the past, the mechanisms for their formation are not fully understood. This work relates the average amplitudes of spikes to fusion zone depth for the welding of Al 6061, SS 304 and carbon steel, and Al 5083. The scale analysis introduces welding and melting efficiencies and an appropriate power distribution to account for the focusing effects, and the energy which is reflected and escapes through the keyhole opening to the surroundings. The frequency of humping and spiking can also be predicted from the scale analysis. The analysis also reveals the interrelation between coarse rippling and humping. The data and the mechanistic findings reported in this study are useful for understanding and preventing spiking and humping during keyhole mode electron and laser beam welding.

Numerical solution of the problem of fusion penetration of a metal layer under glass-to-metal welding conditions

We present a model and a method for numerical investigation of the problem of determining the depth of fusion zone in a metal cylinder under glass-to-metal welding conditions. The method is based on the inclusion of a specially constructed source term into the heat-conduction equation for a metal layer. The term describes the heat associated with phase transition and allows us to observe the moving boundary of the fused zone without using the classical Stefan condition. The results of calculations obtained by means of the proposed approach are given.

Characterisation of electron beam welding of superplastic 8090 AI–Li alloys

Abstract Systematic characterisation of the behaviour of electron beam welded thin superplastic 8090 Al sheet has been carried out. The beam voltage, current, and travel speed were varied within 52·5–60·0 kV, 4·5–6·0 mA, and 50–80 mm S−l respectively. The relationships of fusion zone depth, width, depth/width ratio, cross-sectional area, and postweld tensile properties versus voltage, current, velocity, and heat input were established. It was found that the beam current exerted the most pronounced effect. Based on microhardness values, electron probe microanalysis, and transmission electron microscopy, the fusion zone was harder in the as welded condition but weaker in the as welded + T6 tempered condition due to different distributions of δ′, S′, T2, T1, and S phases. The porosity wasfound to increase with heat input, most likely as a result of the hydrogen enriched surface layer. The contribution from Li and Mg evaporation during welding is considered to be less important. Cracking was observed in super...