Melt Quality Research Articles

Technology and quality of the consumable electrodes, received by semi-continuous casting, for vacuum-arc remelting

he process of vacuum arc melt down is greatly dependent on the quality of the electrodes used. Electrodes of highly alloyed steels are negatively affected by the great amount of films, inversions, subcortical bladders and others; they are being cleansed and sanded down, this leads to substantial waste of expensive metals. For this purpose in the process of casting of highly alloyed steels a great deal of importance is put upon the creation of a method, which could be used for the purpose of protecting the metal from secondary oxidization. The increase in quality of semi-continuous cast electrodes and the removal of previously mentioned defects can be achieved with the use of slag mixtures, which posses thermo-insulating properties and can be partially melted down by the heat which is produced by the liquid metal, that fills the catalyzer. The goal of this project was to research the influence of thermal-insulating slag-producing mixtures on the quality of semi-continuous cast electrodes in the process of vacuum arc melt down in comparison to the ones that were casted under the exothermic mixtures, their effect on the process of melting and the quality of vacuum arc melt down ingots. In this project there were researched such topics as the componential, chemical composition, the physical properties of the thermo insulating mixture and the physical-chemical properties of the melt of said mixture. We researched the quality of the surface of the electrodes, the macrostructure, the chemical uniformity, density, content and the dispersal of non-metallic and gas-like additions on the transverse templates after the main cutting of 600mm, the stability of flow of the vacuum melt down, the quality of the vacuum arc melt down ingots and the rolled sheets made from the arc welded ingots. The geometry of the electrodes, casted under the thermal insulating mixture, is in order with the requirements: the degree of distortion of the profile, in comparison with the one achieved with the use of exothermic mixture, was reduced in half. The macrostructure of the electrodes is dense, without any visual defects. The losses of the metal in the process of sanding during the preparation for the vacuum arc melting were reduced by 2 times in comparison with the casting under exothermic mixture. The depth of the shrinkage cavity is reduced approximately by 12%, the form of the cavity takes the form of a “cup”. The amount of non-metallic and gas-like additions is being significantly reduced. The amount of electrodes that are being recast without issues (the creation of slag, ionization, ionization with slag), during the transition from exothermal to thermal insulating on average is reduced by 3–3,5 times. The purity of metal of vacuum arc melt down electrodes, that are casted under thermo insulating mixture, is in accordance with the requirements; the mechanical properties of rolled vacuum arc ingots exceed the norms of technical conditions.

On the application of reduced pressure test for the prediction of ductility of 46000 alloy: Role of pore's morphology and distribution

Bifilms have been proposed to be critical for forming casting defects. The reduced pressure test (RPT) and bifilm index (BI) have been widely studied and used in industry for melt quality assessment. However, the BI remains challenged in predicting the mechanical properties. This work investigated the usage of RPT for elongation prediction by analyzing the melt in two foundries. The results showed that the BI could be valid when the bifilms exist as fully inflated pores. In reality, bifilms present as pores with various morphology and distribution, generating local stress concentrations under tension. Consequently, the parameter areaeff, which considers the pores’ morphology and distribution, was proposed, and the resultant feff showed a good correlation with the elongation of the castings. These results guide the foundry to predict the elongation of the final castings and give directions for further research on the bifilm defects.

Numerical Simulation and Optimization Design of Particle Transport in 3D Printers Spiral Extrusion 3D Printers

Abstract In response to the challenges of feed delay and inconsistent wire production in existing 3D printers, a novel 3D simulation model for spiral extrusion 3D printers was developed. This model incorporates the particle filling rate within the spiral groove as a critical evaluation criterion, establishing a correlation between the transport section parameters and the filling rate. The simulation software STAR-CCM+ was utilized for in-depth analysis, leading to structural optimizations based on various feeding mechanisms. The effects of different hopper models on feeding efficiency were investigated using the principles of the discrete element method. The findings indicate that the enhanced feed structure effectively addresses particle transportation issues within the printer. An increase in rotational speed is shown to improve the filling efficiency of the spiral groove, while simultaneously reducing the residence time of the particle material in the extruder, which in turn affects particle melting quality. By integrating the simulation data with experimental validation, an optimized printing structure was designed to fulfill the requirements of spiral extrusion printers.

Method Development for the Prediction of Melt Quality in the Extrusion Process.

Simulation models are used to design extruders in the polymer processing industry. This eliminates the need for prototypes and reduces development time for extruders and, in particular, extrusion screws. These programs simulate, among other process parameters, the temperature and pressure curves in the extruder. At present, it is not possible to predict the resulting melt quality from these results. This paper presents a simulation model for predicting the melt quality in the extrusion process. Previous work has shown correlations between material and thermal homogeneity and the screw performance index. As a result, the screw performance index can be used as a target value for the model to be developed. The results of the simulations were used as input variables, and with the help of artificial intelligence-more precisely, machine learning-a linear regression model was built. Finally, the correlation between the process parameters and the melt quality was determined, and the quality of the model was evaluated.

Prediction Method for High-Speed Laser Cladding Coating Quality Based on Random Forest and AdaBoost Regression Analysis.

The initial melting quality of a high-speed laser cladding layer has an important impact on its post-treatment and practical application. In this study, based on the repair of hydraulic support columns of coal mining machines, the influence of high-speed laser cladding process parameters on the quality of Fe-Cr-Ni alloy coatings was investigated to realize the accurate prediction of coating quality. The Taguchi orthogonal method was used to design the L25(56) test. The prediction models of the relationship between the cladding process and the coating quality were established using the Random Forest (RF) and AdaBoost (Adaptive Boosting, AB) algorithms, respectively. Then, the prediction accuracy of the two models was compared, and the process parameter features were screened for importance evaluation. The results show that the AB prediction model is more accurate than the RF prediction model and more sensitive to abnormal data. The importance evaluation based on the AdaBoost model shows that the scanning speed has a great influence on the height and surface roughness of the coating. On the other hand, the overlap rate is the most important factor in controlling the dilution ratio and near-surface grain size of high-speed laser melting coatings. In addition, the micro-hardness of the coating and the thermal effect of the substrate can be effectively enhanced by adjusting the laser power and scanning speed. Finally, it was verified that the AB prediction model could accurately estimate the quality indexes of the coating with a prediction error less than 6%. The results show that it is feasible to predict the quality of high-speed laser cladding with the AB algorithm. It provides a basis for the adjustment of process parameters in the subsequent quality control process of cladding.

Microstructure and Properties Variation of High-Performance Grey Cast Iron via Small Boron Additions

A study was undertaken to investigate the effects of small boron additions on the solidification and microstructure of hypo-eutectic alloyed grey cast iron. The characteristic temperatures upon crystallisation of the treated metal melt were recorded, specifically those concerning small boron addition by using thermal analysis with the ATAS system. Additionally, a standardised wedge test was set to observe any changes in chill performance. The microstructures of thermal analysis samples were analysed using a light optical microscope (LOM) and field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS), which reveal variations in graphite count number with the addition of boron within observed random and undercooled flake graphite. The effect of boron was estimated by the classical analytical and statistical approach. The solidification behaviour under equilibrium conditions was predicted by a thermodynamic approach using Thermo-Calc. Based on all gathered data, a response model was set with boron for given melt quality and melt treatment using the experimentally determined data. The study reveals that boron as a ferrite and carbide-promoting element under the experimental set shows weak nucleation potential in synergy with other heterogenic nuclei at increased solidification rates, but no considerable changes were observed by the TA samples solidified at slower cooling rates, indicating the loss of the overall inoculation effect. The potential presence of boron nitride as an inoculator for graphite precipitation for a given melt composition and melt treatment was not confirmed in this study. It seems that boron at increased solidification rates can contribute to overall inoculation, but at slower cooling rates these effects are gradually lost. In the last solidification range, an increased boron content could have a carbide forming nature, as is usually expected. The study suggests that boron in traces could affect the microstructure and properties of hypo-eutectic alloyed grey cast iron.

Quality monitoring and control for plasticization of acrylonitrile‐butadiene‐styrene regrind polymer in injection molding

AbstractTo meet net‐zero carbon emissions in injection molding, it is desirable to use regrind polymers in plastic parts fabrication. However, the quality of regrind polymer differs from virgin polymer due to the effects of temperature, pressure, and shear stress in the prior molding process. Consequently, the molded components differ in quality compared to those made from virgin material. This study investigates the feasibility of enhancing the quality consistency of regrind plastic components by controlling melt quality in plasticization. The evaluation of melt quality involves extracting two quality metrics from the pressure signal (i.e., the peak pressure and the pressure integral). They are then used to adjust the plasticization parameters as required to ensure that the weight and dimensions of the final regrind parts approach those of parts produced using virgin polymer. The experimental results show that the pressure integral effectively indicates the quality variation of the molded part during the injection molding of regrind polymer. Notably, by adjusting the back pressure, the quality of the molded part closely resembles that of the part made from virgin feedstock after six shots.

A simple procedure to assess the Complete Melt Quality in aluminium castings: implementation in a die-casting and a rheo-casting

ABSTRACT A new simple approach was developed to assess the Complete Melt Quality of aluminium cast alloys throughout the production line. The approach relies on the concurrent use of reduced pressure tests (RPT) and tensile tests at each station in the production line when the melt is transferred and/or processed. These tests can be used to determine the source of melt-related problems in the production line. Two case studies from the procedure of both an aluminium die-casting and a rheo-casting plant showed that melts were significantly damaged in the tower furnace and got progressively more damaged through the production line proven by the RPT, tensile test, and fracture surface analysis results.

Simulation of High-Viscosity Generalized Newtonian Fluid Flows in the Mixing Section of a Screw Extruder Using the Lattice Boltzmann Model.

The mixing quality of polymer melts in the mixing section of a single-screw extruder and an injection molding machine has considerable effects on the properties of the molded products. Therefore, the study of the flow field of polymer melts in the mixing section is of great importance. The lattice Boltzmann method (LBM) exhibits unique advantages in simulating non-Newtonian fluids. Many researchers have used LBM to study the flow of medium- and low-viscosity fluids. In their studies, the Reynolds number of fluid flows is generally moderate. However, polymer melts are typical high-viscosity fluids, and their flow Reynolds number is generally very small. The single-relaxation-time lattice Boltzmann method (SRT-LBM) has been used previously to study the flow field of power law fluids in the mixing section. Herein, the flow field of high-viscosity generalized Newtonian fluids in the mixing section of a single-screw extruder is studied using SRT-LBM, the two-relaxation-time lattice Boltzmann method (TRT-LBM), and the multiple-relaxation-time lattice Boltzmann method (MRT-LBM). Through comparison, TRT-LBM has been found to exhibit obvious advantages regarding stability, calculation accuracy, calculation efficiency, and selection of simulation parameters. The TRT-LBM is more suitable for studying high-viscosity generalized Newtonian fluids than SRT-LBM and MRT-LBM. SRT-LBM has low computational efficiency when simulating high-viscosity generalized Newtonian fluids, and instability is easily caused when the fluid has a yield stress. For MRT-LBM, only by studying the relaxation parameters can its advantages be fully utilized. However, optimizing the accuracy and stability of the MRT-LBM via parameter research and linear stability analysis is difficult. For non-Newtonian fluids, it is difficult to optimize the relaxation parameters to make the MRT-LBM more stable and accurate than the TRT-LBM. It is difficult for the MRT-LBM to realize its potential when simulating high-viscosity generalized Newtonian fluids. In addition, we studied the flow pattern in the cross section of the screw channel and compared it to the results reported in previous studies.

Effect of Na-based flux on melt quality assessment of 46,000 alloys

The influence of Na-Based flux on the melt quality assessment was studied using Density index (DI), bifilm index (BI) and tensile test. The melt was prepared with scrap and ingot with and/or without the addition of Na-based flux. The results show that the addition of Na-based flux decreases the accuracy of the correlation between BI/DI and the hydrogen content due to the increased shrinkage pores. The addition of flux promotes the formation of shrinkage pores by either altering the eutectic solidification behavior or generating more and bigger oxide films which leads to insufficient feeding. Moreover, the addition of flux improves the ductility of specimens by modifying the eutectic phase rather than improving the melt quality.

Analysis of the Quality of Incoming AlSi9Mn Alloy Ingots

Previous research revealed that the quality of the ingots produced by different primary or secondary alloy suppliers can differ remarkably. In this way, the quality of the liquid metal and the castings produced from it can be affected by the impurity content of the ingots used as charge material. In this work, a modified reduced pressure test (RPT) technique, which is based on the remelting of samples extracted from ingots, was applied to investigate the quality of primary AlSi9Mn ingots made by horizontal direct-chill (HDC) casting and gravity casting techniques. For the evaluation of metal quality, image analysis of the cross sections was applied. Pore area fraction, number density, normalized bifilm index, and normalized total pore perimeter were determined, and the relationships between the different metrics were analyzed. The results were compared with the melt quality assessment of the as-melted batches made from the ingots. Solidification simulations, thermal analysis, and microstructural investigations were conducted to investigate the solidification conditions of traditional and remelted RPT samples. Based on the results, the HDC cast ingots possess lower oxide and gas concentrations, which can be traced back to the differences in the melt preparation and casting technologies of the ingots. The comparison of the parameters evaluated by image analysis revealed that there is a strong linear relationship between normalized bifilm index and normalized total pore perimeter. The possible sources of error in ingot quality evaluation are highlighted.

Determination of Correlations between Melt Quality and the Screw Performance Index in the Extrusion Process.

For polymer-processing extruders, designing screws via analytical computational models is helpful for reducing experimental costs. However, the current simulation programs cannot predict the melt quality at the screw tip with sufficient accuracy. There are a number of definitions of melt quality in the literature. This paper will review some of these definitions and present how melt quality can be assessed in subsequent work. In this paper, both the thermal and material homogeneity of the melt quality are examined for correlations with the screw performance index. If correlations exist with the screw performance index determined from direct experimental measurement data, these can be used as target values for developing a melt quality prediction model.

Melt Quality of A356.2 Alloy in the Pressure Counter Pressure Casting Process for Steering Knuckles

Melt Quality of A356.2 Alloy in the Pressure Counter Pressure Casting Process for Steering Knuckles

Microstructure evolution and properties comparation of industrial grade-maintained 7050-T7451 plate recycled from machining chips

There are 45%–71% machining chips generated during the manufacturing process of aviation components. Most of these MCs are down-grade recycled as cast alloy, causing resource waste. In this work, aviation MCs were added into the melt for grade-maintaining recycling. A systematic evaluation was conducted on the melt quality, microstructure evolution, and properties of industrial recycled 7050-T7451 plates with a capacity of 60t/furnace, as well as a comparison with the primary plates. The composition of the recycled 7050 melt is qualified, and the hydrogen content is below 0.075 mL/100gAl. The results of PoDFA and LiMCA show that the inclusions in the recycled 7050 melt are mainly below 40 μm in diameter, and the number of inclusions is 3 times that of the primary melt. TEM shows that the dispersed phase particles of the recycled plate are more uniform and finer. EBSD shows that the recrystallization ratio of recycled 7050-T7451 plate is 8.3%, much lower than the 23.9% of the primary plate. The mechanical and corrosion properties of the recycled 7050-T7451 all meet the AMS 4050 standard. The cost of grade-maintaining recycling can be saved by 6,130,000 USD per year for a production line with an annual output of 20,000 tons of plates. This work clarified the process, cost, microstructure, and properties of recycled 7050-T7451 plate, laying a foundation for the application of grade-maintaining recycled aviation aluminum alloys.

CONTROL OF THE SHEAR STRAIN IN THE HOMOGENIZATION ZONE OF THE DISK EXTRUDER

A simple method for determining the quality of a polymer melt is very important in production. A method that provides simplicity and quick use, making it valuable for optimizing extrusion processes.
 This work describes how the mixing effect can be improved by changing the velocity fields and thereby changing the shear strain values. The shear strain has been calculated for all four channels of the homogenization zone of a disk extruder. It was found that changing the disk rotation frequency allows changing mean value of the channel shear strain rate from 3324 to 4966 with constant performance for the entire homogenization zone. The impact of the different channels on the mixing effect was evaluated, with the first, second, third, and fourth channels contributing 21%, 57%, 15%, and 7% respectively to the overall homogenization zone's effectiveness of mixing. Additionally, it was found that the second channel experiences the highest shear strain values. In the case of the third channel, although the shear rate values are relatively high, the short residence time of the melt element results in comparatively smaller shear strain values. The average shear strain values remain constant for a given disk speed. It is indicated that it is possible to assess the quality of mixing by the amount of energy supplied, which simplifies the process of determining the quality of the melt, as well as its regulation.

Machine vision-based multi-degree-of-freedom laser cladding system integration and process monitoring research

Abstract Machine vision-based multi-degree-of-freedom laser cladding system integration and process monitoring is an important methods to ensure high-quality laser cladding. In this paper, based on the basic theory of multi-degree of freedom of machine vision, the laser cladding system is redesigned, and the melt pool images during the cladding process are monitored and analyzed. The melt pool image is pre-processed with the help of spatial filtering, and the image is thresholded using the iterative method thresholding to analyze the melt pool image. It is proved that the larger the laser power is, the larger the melt pool area is, and the maximum melt pool area is 60,000 pix when the laser power is 200 W. The maximum melt pool area is achieved when the nozzle tilt angle is 30° and the melt pool area is vertical. The smaller the melting speed, the larger the melting area and the maximum melting pool area is up to 35000pix when the melting speed is 210mm/min. It shows that the integration and process monitoring of the multi-degree-of-freedom laser melting system based on machine vision can reasonably control the process parameters of laser melting and improve the quality of laser melting by real-time monitoring and analysis of the melting pool images.

Effects of Electromagnetic Stirring process on Melt Quality of A356 Aluminum Alloy

Effects of Electromagnetic Stirring process on Melt Quality of A356 Aluminum Alloy

On the Effectiveness of Rotary Degassing of Recycled Al-Si Alloy Melts: The Effect on Melt Quality and Energy Consumption for Melt Preparation

The effectiveness of rotary degassing on the defect formation and mechanical properties of the final casting of aluminium alloy EN AC 46000 was investigated, along with its impact on the energy consumption in the casting furnace. In the melt preparation prior to casting, the molten metal is usually transported from the melting furnace to the casting furnace with rotary degassing as a cleaning procedure. Under the conditions of this specific study, negligible degradation was observed in the mechanical properties of the final cast component in an aluminium EN AC 46000 alloy after removing the rotary degassing step in the process. Furthermore, removing the rotary degassing step led to a reduced temperature drop in the melt, thus minimizing the need for reheating (energy consumption) by up to 75% in the casting furnace. The reduced energy consumption was up to 124,000 kWh in yearly production in a 1500 kg casting furnace. The environmental impact showed a ~1500 kg reduction in CO2 for one 1500 kg electrical casting furnace in a year.

Formation and growth kinetics of the initial amorphous oxide film on the aluminum melt: A ReaxFF molecular dynamics simulation

Understanding on oxidation is critical for the improvement of aluminum melt quality which determines the properties of the aluminum alloy processed by casting. However, the oxidation mechanism of aluminum melt is still unclear in atomistic scale. In this work, we performed reactive molecular dynamics simulation to investigate the oxidation mechanism of aluminum melt on an atomic scale. Our results focus on the island-like nucleation on the melt surface and the following growth of the oxide film. The oxide grows via ion diffusion and the diffusion of O anions plays a greater effect. The evolution of the diffusion coefficient indicates an island-by-layer growth on the aluminum melt. Kinetically, the oxide growth obeys a linear law during the nucleation stage and switches to a logarithmic law after a closed oxide film forms. Besides, we emphasize the effect of oxygen content and ambient temperature on the formation of oxides. Our research can provide insights into the atomic-scale oxidation mechanism of aluminum melt which contributes to the better design for anti-oxidation methods during casting and the oxide-based functional materials.

Laser Powder Bed Fusion Process Optimization of AlSi10Mg Alloy Using Selective Laser Melting: Dynamic Performance of Fatigue Behaviour, Microstructure, Hardness and Density

The quality of a selective laser melting (SLM) component depends on build orientation and layer thickness, which are directly influenced by processing parameters. The present research of layer-by-layer additive simulation before starting the SLM process has several advantages, such as saving time, cost, and material. In this main investigation, the dynamic performance of fatigue strength, density, and hardness of AlSi10Mg alloy was produced by the SLM-AM according to the design of experiments. The L9 orthogonal array of the Taguchi method was created to perform the experimental development process. Finally, the obtained optimal process parameter with the highest values of fatigue strength, density, and hardness was found at a laser power of 225 Watts, a scan speed of 500 mm/s, and a hatching distance of 100 μm. The experimental density result was achieved with a high density value of 99.6% (2.66 g/cm3) and a defect-free component and hardness of 126±5 HV. The future scope of this study will use optimal process parameters to find out mechanical properties for as built and preheated conditions for aerospace applications.