Initial Mold Temperature Research Articles

Control and optimization of defects in die casting of complicated right crankcase cover

The die-casting process of ADC12 aluminum alloy right crankcase cover was simulated based on AnyCasting software, and the influence of pouring temperature, initial mold temperature and injection speed on the filling and solidification process of ADC12 right crankcase cover casting was explored by orthogonal experiment method. The optimal process parameters were obtained through optimization, and the die-casting mold was designed. The program was verified in production. The results show that the porosity and shrinkage of the right crankcase cover are mainly concentrated in the thick wall part. The sequence of process parameters that affect the residual melt modulus is pouring temperature, initial mold temperature, and injection speed; The best combination of process parameters: pouring temperature is ∼680 °C, initial mold temperature is ∼200 °C, injection speed is ∼5 m/s. By analyzing the filling process and temperature field simulation results, the casting structure, mold structure and cooling system were optimized, and the process plan was improved. The production verification was carried out according to the optimized process plan. The casting quality is good and has no obvious defects, which meets the actual production needs.

Development of Low-Pressure Die-Cast Al-Zn-Mg-Cu Alloy Propellers Part II: Simulations for Process Optimization.

With the increasing demand for high-performance leisure boat propellers, this study explores the development of high-strength aluminum alloy propellers using the low-pressure die-casting (LPDC) process. In Part I of the study, we identified the optimal alloy compositions for Al-6Zn-2Mg-1.5Cu propellers and highlighted the challenges of hot tearing at the junction between the hub and blades. In this continuation, we developed a coupled thermal fluid stress analysis model using ProCAST software to optimize the LPDC process. By adjusting casting parameters such as the melt supply temperature, initial mold temperature, and curvature radius between the hub and blades, we minimized hot tearing and other casting defects. The results were validated through simulations and practical applications, showing significant improvements in the quality and structural integrity of the propellers. Non-destructive testing using X-ray CT confirmed the reduction in internal defects, demonstrating the effectiveness of the simulation-based approach for alloy design and process optimization.

PHYSICO-CHEMICAL METHODS OF INCREASING THE CRACK RESISTANCE OF ALLOY AM4.5Cd (VAL10). NOTICE 1: EXPERIENCE OF USING AN RING SAMPLE

On the example of the AM4.5Kd (VAL10) alloy treated in the liquid state with hydrogen, the efficiency of using the well-known ring test for the study of physicochemical methods of influencing the crack resistance of wide-range aluminum alloys, which are prone to the formation of hot cracks during solidification, was studied. To achieve this goal, an annular mold mold was made according to the recommended dimensions, experiments were carried out on the effect of hydrogen treatment of the melt on the crack resistance of castings. Saturation with hydrogen was carried out by blowing the melt with water vapor, the degree of gas saturation was estimated from the porosity of the castings, calculated from the change in their density compared to the control sample obtained in a mold with sufficient power. Despite the measures taken to increase the sensitivity of the annular sample and obtain stable results, which consisted in adjusting the dimensions of the mold, in particular, the size of the central rod, during compression of which the hardening melt creates tensile stresses leading to the formation of a hot crack, as well as optimizing the thermal regime for obtaining a casting by increasing the initial mold temperature from 22 0С to 217-249 0С, the sensitivity of this sample under the experimental conditions remained too low. In 60 % of cases, gas saturation of the melt contributed to a reduction in the crack propagation process when using a mold at room temperature and up to 100 % when the mold was heated to a temperature of 228 0C to 260 0C. However, in both the first and second cases, 28 % of similar data were obtained on castings from the initial melt not saturated with hydrogen. This casts doubt on the reliability of the positive effect of hydrogen treatment and became the basis for the conclusion that it is inappropriate to use this type of sample in studies of physical and chemical effects on the melt in order to increase the crack resistance of the AM4.5Kd (VAL10) alloy due to a possible error in assessing the effectiveness of their impact, and also to decide on the need to develop a new sample, devoid of the identified shortcomings.

Effect of Zn content on hot tearing susceptibility of LPSO enhanced Mg–Znx–Y2–Zr0.06 alloys with different initial mold temperatures

The critical temperature (Thci) corresponding to the load relaxation measured during the solidification of alloy in a ‘T′-shaped mold is introduced into the Clyne-Davies’ model, so that it can be used to predict the hot tearing susceptibility (HTS) of alloy under non-equilibrium cooling. Then, the improved model is applied to study the HTS of Mg–Znx–Y2–Zr0.06 (x = 0.5, 1 and 1.5 at%) alloys under two initial mold temperatures, i.e., two cooling rates. It is found that HTS is very sensitive to both Zn content and initial mold temperature, and the increase in Zn content or initial mold temperature can reduce HTS of the alloy. However, their micro mechanisms are different. The reason for the decrease in HTS with the increase in Zn content is the decrease in the dendrite coherency temperature. Specifically, the ratio of unconstrained feeding stage to intergranular feeding stage increases, and the intergranular liquid phase with eutectic composition increases in the later stage of solidification. The HTS decreases with the increase in the initial mold temperature because the solidification shrinkage stress is relieved. Consequently, the residual liquid phase between the grains can be fed in a more timely manner.

Improving the Melt Flow Length of Acrylonitrile Butadiene Styrene in Thin-Wall Injection Molding by External Induction Heating with the Assistance of a Rotation Device.

In injection molding, the temperature control of the dynamic mold is an excellent method for improving the melt flow length, especially of thin-wall products. In this study, the heating efficiency of a novel heating strategy based on induction heating was estimated. With the use of this heating strategy, a molding cycle time similar to the traditional injection molding process could be maintained. In addition, this strategy makes it easier to carry out the heating step due to the separation of the heating position and the mold structure as well as allowing the ease of magnetic control. The results show that, with an initial mold temperature of 30 °C and a gap (G) between the heating surface and the inductor coil of 5 mm, the magnetic heating process can heat the plate to 290 °C within 5 s. However, with a gap of 15 mm, it took up to 8 s to reach 270 °C. According to the measurement results, when the mold heating time during the molding process increased from 0 to 5 s, the flow length increased significantly from 71.5 to 168.1 mm, and the filling percentage of the thin-wall product also increased from 10.2% to 100%. In general, the application of external induction heating (Ex-IH) during the molding cycle resulted in improved melt flow length with minimal increase in the total cycle time, which remained similar to that of the traditional case.

Prediction of shrinkage ratio of ZA 27 die casting alloy with artificial neural network, computer aided simulation and comparison with experimental studies

In the cast alloys with a long freezing range such as ZA-27, casting defects such as porosity and shrinkage will occur if casting variables are not controlled carefully. In this study, the effect of casting variables on shrinkage and micro-porosity defects in ZA-27 was investigated. The defects of casting were predicted with Artificial Neural Network algorithms. The cooling rate, solidification time, temperature, liquid phase, initial mold temperature, and %shrinkage were obtained from a series of simulation- experimental tests. The heat transfer coefficient of ZA-27 and graphite die was calculated as 2000 W/(m2K). In the samples poured into the mold heated at 350 °C, the minimum feeder shrinkage volume was observed. Locations of the chronic Hotspot and Shrinkage problem was estimated. It was observed that the casting heated to 150 °C had wide-deep shrinkage on the upper and lateral surfaces of the feeder. A good correlation was obtained between the modeling results of the ANN and the experimental results. Optimum ANNs were designed, trained, and tested to predict the shrinkage rate for various initial mold temperatures and physical conditions. Thanks to the sigmoid (sigmoaxon) function training, the most systematic modeling ANN set was revealed with 99% (Vol. 7.65% Shrinkage) prediction.

Preparation and Properties of Special Vehicle Cover via a Novel Squeeze Casting Quantitative Feeding System of Molten Metal

A quantitative feeding system of molten metal was designed based on a special vehicle cover, which achieved the quantitative transport of molten metal in a fully enclosed environment. There are lots of advantages of this novel device, such as improving the accuracy of the molten metal pouring, reducing the oxide inclusions defects, improving the quality of forming parts, etc. The numerical simulation of the casting process of filling mold was carried out based on the software ProCAST, which optimized the processing parameters of the quantitative feeding device. The result shows that the optimal movement speed of the punch piston is 0.08 m/s. The forming process of the aluminum alloy cover was designed and the process was conducted on the novel quantitative feeding device of molten metal. The structure and process performance of the forming parts were summarized and the defects were analyzed. The influence of technological parameters such as pouring temperature, filling speed, initial mold temperature, and feeding distance on the quality of forming parts was studied, which resulted in the optimum process parameters for the dosing device.

Effect of Al Content on Hot-Tearing Susceptibility of Mg-10Zn-xAl Alloys

The hot-tearing susceptibility of Mg-10Zn-xAl (x = 0, 2, 5, and 7) alloys was studied using constrained rod casting installed with a load cell, thermocouple, and data-management system. Addition of Al content reduced the freezing range and increased the liquid fraction at the end of the primary stage of solidification, during the vulnerable period of alloy solidification. Eutectic healing was observed in alloys containing Al cast at a higher initial mold temperature due to near-equilibrium solidification. Grain refining was confirmed at the microstructural level due to addition of Al. The results also suggested that increasing Al content enabled hot-tearing resistance of Mg-10Zn alloy by facilitating liquid feed for the strain developed during the mid-stage of solidification (0.65Fs to 0.74Fs). Experimental results were compared with Pandat’s simulation results to predict the occurrence of hot tearing in Mg-10Zn-xAl alloys. This indicated that Pandat’s solidification curve could be used to determine the hot-tearing nature of Mg-Zn alloys. The recently proposed hot-tearing criteria of Kou and Clyne–Davie roughly agreed with the experimental results, but did not perfectly predict the influence of different casting conditions.

Evaluation of porosity of AlZn5Mg castings made by squeeze casting technology

The paper shows the results of research aimed to assess the impact of high squeeze pressure on the porosity of AlZn5Mg alloy castings, including its distribution in slab-type castings with dimensions of 25 x 100 x 200 mm. The research was carried out on castings made by two methods: squeeze casting and gravity casting. The pressing was conducted at a pressure of 100 MPa at an initial mould temperature of 200°C. The research identified the middle and outer parts of the casting. Experimental research was preceded by numerical simulation of the casting solidification, then a porosity assessment was carried out using the hydrostatic weighing method, which was supplemented by structural observations. The results of the research showed a two-fold decrease in the porosity in the middle part of the casting which is most exposed to the occurrence of shrinkage voids formed in the final clotting phase. Structural tests revealed the occurrence of dispersed porosity in castings, mainly of shrinkage and / or shrinkage-gas origin. The impact of pressure of 100 MPa during solidification caused fragmentation of the primary structure of castings, which resulted in a higher grain density.

Modeling of the Impact of Initial Mold Temperature, Al5Ti1B and Al10Sr Additions on the Critical Fraction of Solid in Die Casting of Aluminum Alloys using Fuzzy Expert System

Modeling of the Impact of Initial Mold Temperature, Al5Ti1B and Al10Sr Additions on the Critical Fraction of Solid in Die Casting of Aluminum Alloys using Fuzzy Expert System

PREDICTION OF CRITICAL FRACTION OF SOLID IN LOW PRESSURE DIE CASTING OF ALUMINUM ALLOYS USING ARTIFICIAL NEURAL NETWORK

Casting simulation programs are the computer programs that digitally model the casting of an alloy in the sand, shell or permanent mold and then the cooling and solidification processes. However, obtaining consistent results from the casting modeling depends on providing many parameters and boundary conditions accurately. Critical fraction of solid (CFS), which is one of the most important of these parameters, is defined as the point where the solid dendrites do not allow any flow of the liquid metal in the mushy zone. Since the CFS value varies depending on many factors, inconsistent results can be experienced in the modeling applications. In this study, the CFS value obtained during the solidification of various commercial aluminum alloys' casting process carried out using low pressure die casting method, is predicted by using artificial neural network (ANN) method based on alloy type, grain refiner and modifier additions, initial mold temperature, pressure level parameters. In the scope of the study, 162 experiments are conducted. The results obtained from the low pressure die casting experiments using a special model designed for the study are validated by using SOLIDCast casting simulation. The CFS values obtained from this validation range from 33% to 61%.

Simulation of Macrosegregation and Shrinkage Cavity in an Al-4.5 Wt Pct Cu Ingot Using a Four-Phase Model

A four-phase dendritic solidification model is employed to calculate the formation of macrosegregation, as-cast structure, and shrinkage cavity of Al-4.5 wt pct Cu ingot. This model couples phenomena of thermal–solutal buoyancy, crystals sedimentation, shrinkage formation, heat transfer, nucleation and growth of equiaxed grains, and columnar-to-equiaxed transition. An additional air phase is introduced to feed the shrinkage cavity during the solidification. A laboratory scale ingot with Al-4.5 wt pct Cu is fabricated for the verification of the numerical simulation results. The predicted macrosegregation, characteristics of shrinkage cavity, and as-cast structure have a good agreement with the corresponding experimental results. Furthermore, various initial mold temperatures are investigated using this numerical model. It indicates that the initial mold temperature plays an important role in the macrosegregation formation by changing the solidification sequence. The higher the initial mold temperature is, the severer the macrosegregation that will occur. Meanwhile, the higher initial mold temperature is beneficial for the growth of equiaxed grains, which results in the final as-cast structures and an increased depth of shrinkage cavity.

Premature melt solidification during mold filling and its influence on the as-cast structure

Premature melt solidification is the solidification of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the socalled “big bang” theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the superheated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

Effect of Cu Additions on Microstructure, Mechanical Properties and Hot-Tearing Susceptibility of Mg-6Zn-0.6Zr Alloys

The microstructures and mechanical properties of Mg-6Zn-xCu-0.6Zr (x = 0, 0.5, 1, 2, 3 wt.%) alloys are investigated. The effect of Cu additions on the hot-tearing susceptibility (HTS) of Mg-6Zn-0.6Zr is also studied using constrained rod casting apparatus equipped with a load cell and data acquisition system. The experimental results indicate that 0.5wt.% Cu addition into the Mg-6Zn-0.6Zr alloy shows the optimum comprehensive properties, i.e., a combination of high strength, high hardness, high hot-tearing resistance and excellent ductility. However, when Cu content reaches 2 and 3wt.%, the deterioration in mechanical properties observed is attributed to the increment in coarsened MgZnCu phase and the continuous networks of intergranular phases in these two alloys. The Cu-free base alloy had a high HTS, which is attributed to its large vulnerable temperature range and coarse grain structure, which easily caused tear propagation. In contrast, the Cu-contained alloys exhibited low HTS are due to their narrow vulnerable temperature ranges and its refined equiaxed grain structure, which effectively accommodated the stress developed during solidification. The hot-tearing fracture surfaces indicate that the hot-tearing initiated and propagated along the grain boundaries with liquid films. The results also suggest that the hot-tearing resistance can apparently be improved by increasing the initial mold temperature.

Heat Flow and Solidification Modeling of Industrial Scale, Ingot Casting Operation

A model, based on the concept of effective thermal conductivity, was developed to study thermal fields and the resultant solidification behavior of large, round, industrial size ingots. In this, flow and turbulence phenomena during mold filling as well as subsequent solidification were not modeled explicitly but their influence was accounted for by artificially raising the thermal conductivity of solidifying steel. Thus, a conduction like equation embodying a conjugate approach was applied to simultaneously predict the evolution of temperature fields in the mold as well as in the solidifying ingot following teeming. Prior to comparing model predictions against industrial scale measurements, sensitivity of calculations to grid size, time step height, convergence criterion etc. were rigorously assessed. Similarly, modeling of interfacial resistance, chemical reactions and heat effects in the hot top as well as their influence on predicted results were evaluated computationally. Embodying mixed thermal boundary conditions (free convection + radiation) at the mold wall, temperature fields during solidification of two different industrial large ingots were predicted numerically. Parallely, mold wall temperature was monitored as a function of time and surface temperature of ingot was measured at the instant of mold stripping using hand held, radiation pyrometers. Incorporating relevant operating conditions (viz., mold dimensions and size, ingot and hot top dimensions and material, initial mold and liquid temperature etc.) into the calculation scheme, predictions were made via a computational procedure developed in-house and results thus obtained were compared against equivalent industrial scale measurements. Very reasonable agreement between the two was demonstrated.

Influence of mould material on ceramic disc dimensions in low-pressure injection moulding

This work presents a study regarding the influence of the cooling process, as a result of different mould insert materials, on ceramic parts dimensions obtained by low-pressure injection moulding process. Discs of ceramic with Ø80 × 2 mm, composed by 86 wt.% alumina (Al2O3) and 14 wt.% organic vehicle, were produced. An experimental injection mould was designed and manufactured with built-in heating and cooling systems, controlled by a DAQ (Measurement Computing – USB-TC) and thermocouples K type. Four types of insert materials were used: aluminium alloy (AA7075-T6), electrolytic copper, brass alloy (C36000) and SAE1045 steel. Tests were carried out considering injection moulding parameters constant, i.e. initial mould temperature, injection pressure and time and extraction temperature. All the post-process (debinding by wicking; final debinding and sintering) parameters were also kept constant. Parts were analysed considering dimensions, mass, geometry, visual aspects and defects. The results showed that the cooling rate resulting from the thermal conductivity of each material has influenced more significantly the dimensional shrinkage and mass reduction of the samples during the intermediate post-processes phases. The geometric deviations were different for each condition throughout the process and they increased in the final parts. The parts produced with higher cooling rate had higher geometric deviations.

Hot tearing characteristics of Mg–2Ca–xZn alloys

Influence of Zn content (0, 0.5, 1.5, 4 and 6 wt%) on the hot tearing characteristics of Mg–2 wt% Ca alloy was investigated. The constrained rod casting (CRC) apparatus equipped with a load cell and data acquisition system was used. The initiation of hot tearing was monitored during solidification. The effect of mould temperatures (250 and 450 °C) on the hot tearing was also investigated. The formed tears were evaluated using X-ray tomography and the tear volumes were measured. Results show that hot tearing susceptibility (HTS) of Mg–2Ca–xZn (x = 0, 0.5, 1.5, 4 and 6 wt%) alloys increases with increase in Zn content up to 1.5 wt%, then decreases with further increase in the Zn content to 6 wt%. Higher initial mould temperature (450 °C) improves the hot tearing resistance. The observations on the microstructures and the fracture surfaces suggest that the hot tear initiated at the grain boundaries and propagated along them through the thin liquid film rupture and liquid metal embrittlement of solid bridges. Tear healing by low melting point eutectic liquid is also observed in some of the alloys.

An Investigation on Hot Tearing of Mg-4.5Zn-(0.5Zr) Alloys with Y Additions

In this work, the hot tearing susceptibility (HTS) of Mg-4.5Zn-xY (x = 0, 0.4, 0.9, 2 wt pct) alloys is investigated using constrained rod casting apparatus equipped with a load cell and data acquisition system. The effect of grain refinement by Zr addition on the HTS has also been investigated. The results show that the HTS first increases with increasing the Y content, reaches the maximum at 0.9 wt pct Y, and then reduces with further increase in the Y content to 2.0 wt pct. The high HTS observed in the alloys with 0.4 and 0.9 wt pct Y is attributed to their coarse columnar grains and their large freezing ranges. The results also suggest that the resistance to the hot tearing can apparently be improved by increasing the initial mold temperature. In addition, a fine microstructure reduces the HTS. Numerical simulations using ProCAST software on HTS of Mg-4.5Zn-xY alloys are in good agreement with the experimental results.

Fabrication of Gasar made from Cu-24 wt.% Mn alloy

Abstract Unidirectionally solidified porous Cu-24 wt.% Mn alloy is prepared by the Gasar process, using mold casting equipment under various conditions. The experimental process demonstrates the feasibility of fabricating a Gasar structure for alloys with a wide solidification temperature range, as well as a columnar dendritic structure. The effects of melt temperature, initial mold temperature, and partial gas pressures on the pore structure and microstructure of an alloy matrix were investigated. The growth and interruption of directional pores were analyzed based on the solidification mode to determine whether the fine-grained region atop directional pores stunted the growth of Gasar pores.

Experimental and numerical analysis of hot tearing susceptibility for Mg–Y alloys

The influences of Y content and initial mold temperatures on the hot tearing susceptibility (HTS) of binary Mg–Y alloys were investigated using a constrained rod casting (CRC) apparatus, which is equipped with a load cell and data acquisition systems. The hot crack formation was monitored during CRC experiments. The experimental results show that HTS first increases with increase in the Y content, reaches the maximum at about 1.5 wt% Y and then decreases with further increase in the content of Y. The severest of hot tearing is found in Mg–1.5 wt% Y alloy which is due to its large columnar grain structure, wide solidification range, and small amount of eutectic. The resistance to hot tearing is apparently improved by increasing the initial mold temperature. ProCAST simulation software was used to predict the hot tearing of Mg–Y alloys in CRC. The simulation results show a good agreement with the experimental measurements. The numerical simulations will be helpful and valuable to optimize the alloy composition and casting parameters to minimize the hot tearing defects.