Die Cavity Research Articles

Die casting parameters and simulations for crankcase of automobile using MAGMAsoft

Abstract High Pressure Die Casting (HPDC) is popular for manufacturing of high volume and low cost cast components with good quality. In this study, the step by step method of developing a HPDC die is demonstrated for a crank case of two wheeler automobile by evaluating the necessary design parameters of HPDC. The die is designed for Al-Si-Cu alloy as melt. Simulations are done using MAGMAsoft for predicting filling temperature, fill time, solidification, air pressure and entrapment and lastly assessment of cooling arrangement. Minor modifications are carried out to accommodate lesser fill time and reduced air pressure in the die cavity.

STRUCTURAL DESIGN AND RESEARCH OF FORMING MODEL FOR THIN-WALLED PARTS

In view of the fact that the fibre composites belong to thermosetting materials, the moulding process is adopted. Carbon fiber composite blank was preheated and softened, and then the blank was put into the die cavity to close the die. Carbon fiber composite products were obtained by heating and solidifying the mould, cooling and demoulding. In the design of the die, the integral die and the combined block punch are used. When the upside-down phenomenon exists in the assembly of the die, it is easy to open the die. The processing technology and assembly requirements of the die are put forward.

Research on a hydro-pressing process of tubular parts in an open die

To solve the problems involving in the closed die hydro-pressing process, such as flash and difficulty in taking the part out of the die cavity, an open die hydro-pressing process was proposed. The cross-sectional dimensional accuracy and the corner deformation were experimentally researched. Then, an analysis was employed to reveal the reason for uneven deformation of the section corners, and an effective solution was adopted. The reason is that an obvious difference exists in the bending moment between the four corners due to the existence of the friction. The values of the bending moment and circumferential force decrease gradually along the direction opposite to the movement direction. As a result, the uneven deformation between cross corners appears. A double-pass pressing process was put forward to counter-balance the effects of the friction by converting the direction of the friction force. It is demonstrated by the experiment that the rectangular cross section with high dimensional accuracy can be directly formed from a circular tube blank using the open die hydro-pressing process.

Effect of pressure cycles and thermal conditions on the reliability of a high-pressure diecast Al alloy heating radiator

The fatigue reliability of a diecast AlSi11Cu2(Fe) alloy radiator has been investigated at different pressure amplitudes and thermal exposure. Based on failure mode analysis, two failure mechanisms are observed during fatigue testing, i.e. leakage at the interface between the diecast element and the plug, and fatigue fracture of a radiator element. Fatigue life tests have been carried out at two different pressure amplitudes, 3 and 4 MPa, and two holding temperatures, 40 and 60 °C, respectively. The results reveal how the main cause of failure is related to the fatigue failure of a radiator element in the whole heating system. This is due to casting defects such as gas porosity and oxides which are formed during the filling phase of the die cavity in high-pressure die casting. Furthermore, casting defects increase the leakage failure and reduce the fatigue life of the radiator. An increase of the holding temperature increases the frequency of leakage failure of radiators.

Injection by sheet-bulk forming

This paper is focused on injection by upsetting of sheet-formed side walls. The presentation draws from fundamental aspects of material flow to typical failures caused by buckling and by the development of material flaws. Results show that the utilization of two-piece blank holders in conjunction with an adequate selection of the die cavity thickness and the creation of relief-holes to allow divided material flow are effective and easy-to-implement strategies to increase process formability and ensure the production of sound sheet-bulk parts. The work is carried out in two completely different materials (polyvinylchloride and aluminium AA1050) and its originality stands not only for the investigation on sheet injection but also for the utilization of thermoplastics in sheet-bulk forming. Numerical modelling with finite elements gives support to the overall results and discussion.

Experimental investigations of the electromagnetic pulse-assisted incremental drawing of aluminum alloy

During the drawing process, when the radial tensile stress is greater than the limit of the sheet metal’s bearing capacity, the workpiece will rupture. In order to succeed in forming the cylindrical part, it is necessary to reduce the radial tensile stress, or even change the tensile stress into compressive stress. In the current study, electromagnetic pulse-assisted incremental drawing (EMPAID) technology was used to form the cylindrical part, which can generate magnetic force on the flange material, which pushes them to flow into the die cavity. The drawing coil with different turns matching the determined corner coil and different auxiliary coils were used to conduct the experiments. When the two-turn drawing coil, one-turn corner coil, and two-turn auxiliary coil were used, after multiple times of discharge and micro-shaping, the limit of the drawing height of the formed part increased to 42.86 mm, which was 2.16 times of the limit drawing height obtained using the conventional drawing. Using the three-turn drawing coil combined with the corner coil and four-turn auxiliary coil to carry out the experiments, the cylindrical part’s maximum drawing height reached 63.72 mm. Meanwhile, the flange area was almost completely converted into the cylinder wall. When the dense winding auxiliary coil was used to conduct the experiments, the maximum forming depth was only 25.24 mm. The experimental results showed that during the forming process, majority of the flange material was pushed into the die cavity due to the action of magnetic force. Due to this reason, the thinning of the forming part can be suppressed. If the magnetic force generated by the drawing and auxiliary coils matched reasonably, then the depth of the formed part can be improved significantly.

Influence of intensification pressures on pores in die-cast ADC12 alloys

Die casting process is widely applied in making Al parts. However, due to high speed of liquid metal flow in the die cavity, gases are prone to be entrapped in the filling, resulting in porosity defects. The X-ray computed tomography scanning technique was used to detect the pores in die-cast ADC12 alloys with different intensification pressures. The three-dimensional features of pores including pore size, number, sphericity have been obtained. The effect of different intensification pressures on two different kinds of pores, namely gas-pores and shrinkage pores, was analyzed. The results show that with increasing the pressure, the pore fractions and quantity gradually decrease. When the pressure increased to 85 MPa, the pores from gas entrapment during the mold filling were compressed, leading to a lower porosity fraction. The pressure cannot affect the pores in the samples with a thin wall (2 mm) due to a great solidification rate.

Studies on die filling of A356 Al alloy and development of a steering knuckle component using rheo pressure die casting system

In this study, a computational fluid dynamics (CFD) model is developed to investigate die filling of semi solid slurry as part of rheo pressure die casting (RPDC) system. The die filling cavity corresponds to that of an automobile steering knuckle, and the slurry is made of A356 aluminium alloy. The rheological model used in the CFD simulation is determined experimentally. The results obtained from present numerical model includes flow field of the slurry within the die cavity, viscosity evolution, solid fraction distribution, temperature and pressure distribution during solidification within cavity during die filling stage. The main objective of the study is to determine the gating arrangement, pouring temperature, and injection conditions for desirable microstructure and mechanical properties of the developed component. To study the effect of injection conditions on die filling capability of the said alloy slurry, five injection profiles are studied, with a variation in final injection velocity between 2–3.2 m/s. In order to corroborate the findings of the present study, microstructural morphology and structure-property correlation have been studied, primarily in the form of optical microscopy and macro hardness measurements, by obtaining samples from different locations of the solidified component.

Tensile and Fracture Properties of Commercially Pure Titanium (CP-70) Hemispherical Forgings

Commercially pure (CP-70) titanium is used as the metallic liner for composite overwrapped pressure vessels used in satellite launch vehicles. The metallic liner is fabricated from domes machined out of CP-70 titanium forgings. During the hot closed-die forging of CP-70 domes from billets, the amount of deformation varies location to location, due to the non-uniform flow of material in the die cavity. This non-uniform strain distribution in the hemispherical dome results in microstructural variations along the forging axis which will remain even after annealing. The aim of the present work is to study the tensile properties, impact strength and fracture toughness of CP-70 hemispherical forging in annealed condition from top end to bottom end of domes in radial and circumferential directions with a view to understand the variation in mechanical properties to asses the design margin. Study revealed significant amount of the work-hardening difference within a forged dome even after annealing.

Residual stresses and springback reduction in U-channel drawing of Al5182-O by using a servo press and a servo hydraulic cushion

The increasing use of aluminum alloys in automotive industry brings new challenges regarding formability and springback. Servo presses and servo hydraulic cushions can accurately control ram motion and blank holder force during the forming process, reducing the difficulties encountered in forming Al alloys. This study presents an experimental and numerical analysis of springback and residual stresses induced during the U-channel drawing of Al 5182-O. During the U-channel drawing, the draw-in of the sheet material into the die cavity is controlled by blank holder force. So, the material is under stretch bending condition when it slides around the die corner radius. When the material passes the die corner radius it unbends. The reverse loading resulted from the unbending process provides heterogeneous stress distribution through the sheet thickness in the wall section. The effect of post stretching, applied by the use of a servo hydraulic cushion, on reduction of residual stresses and springback at the wall is investigated. The benefit of using servo hydraulic cushion for reducing springback and residual stresses has been demonstrated experimentally. Results illustrate a significant reduction of residual stresses and springback when post stretching is applied.

Variation of Properties in the Cross-Section of Semi-Solid Al-7Si-0.3Mg Castings

In semi-solid casting, a slurry consisting of primary α-Al crystals and liquid is injected into the die cavity. The solidification in the die-cavity occurs by the growth of the primary α-Al crystals formed during slurry preparation and in the shot sleeve, nucleation and growth of in-cavity solidified crystals and ends with the eutectic reaction. During solidification in the die cavity, the cooling rate near the die wall is higher in comparison to the centre of the casting, particularly for thick-walled castings. The solidification conditions for the slurry α-Al crystals that are closer to the die wall can be very different compared to the slurry α-Al crystals located at the casting centre. This can result in different solute concentration in the interior of the α-Al globules in different regions of the semi-solid casting cross-section and consequently, different response to heat treatament. The RheoMetal™ process was used to produce thick-walled semi-solid castings. Semi-solid castings in the as-cast and T6 conditions were investigated. Indentation tests for hardness measurements in the nano-range were performed in the interior of α-Al globules near the surface and at the casting cross-section centre. The hardness variation across the casting cross-section was evaluated by low-force Vickers hardness. The castings in the as-cast condition showed more uniform properties in the cross-section compared to the T6 condition. Additionally, the results suggest that microsegregation in the interior of α-Al globules is very low in castings in the as-cast and T6 conditions.

Gas entrainment behavior of aluminum alloy engine crankcases during the low-pressure-die-casting process

Gas pores on the top face of engine crankcases which are produced by Low Pressure Die Casting (LPDC) have been studied. Micrographic analysis has been conducted to investigate the evolution of such kind of casting defects. Results show that the surface of such casting defects have meandering shapes and random sizes. Microstructures of the cross section of the defects displayed folded feather shapes, which can be produced by the folded oxide film into the melt during the filling process. Oxide inclusions have been found below the filter at the ingate area. Thus, it is confirmed that the folded oxide films came from turbulence of the metal in the die cavity. Numerical simulation has been carried out to study the filling behavior of the crankcase. Results show that gating velocity suddenly increased when the liquid metal got into the waterfall structure and led to the turbulence. Moreover, the air entrained behavior is related with the gating velocity. With increasing gating velocity, turbulence happened when metal confluences, and became more intensely in the middle of the casting due to its waterfall structure. Finally, this kind of casting defect was confirmed as gas entrainment.

Effect of super vacuum assisted high pressure die casting on the repeatability of mechanical properties of Al-Si-Mg-Mn die-cast alloys

Two-stage super vacuum (19 mbar) assisted high pressure die casting (HPDC) was achieved by evacuating from the die cavity and the shot sleeve simultaneously. The effect of super vacuum assisted HPDC on the repeatability of the tensile properties of Al-Si-Mg-Mn die-cast alloy was investigated in comparison with conventional HPDC. The quantitative Weibull analysis confirmed that super vacuum assisted HPDC improved the repeatability of the tensile properties of the alloy. The data and deviation analysis verified that super vacuum assisted HPDC considerably decreased the fluctuations of the ductility of the alloy by 71% in as-cast state and 84% after solution and ageing treatment. The results also showed that super vacuum assisted HPDC improved the ultimate tensile strength and ductility of the as-cast alloy by 5.6% and 43%, respectively, and increased the ductility of the alloy by 21% after solution and ageing treatment. The significant improvements of ductility and the repeatability of tensile properties were originated from the decrease of porosity volume fraction and porosity size in the alloy processed by super vacuum assisted HPDC. The reduction of defect size can improve the stress distribution and retard the crack initiation in castings. Therefore, the tensile strength and ductility were enhanced in the die-cast alloy processed by super vacuum assisted HPDC.

Lightweighting technologies: Analyzing strategic and economic implications of advanced manufacturing processes

High-pressure die-casting (HPDC) is a proven manufacturing technology to cast aluminum and magnesium alloys. Transportation industries are under increased pressure to reduce the mass of cast parts in order to cut fuel use and CO2 emissions, and increase load. Reducing mass and improving mechanical properties with current HPDC is not practical due to processing limitations that result from air entrapped during metal filling as well as limitations on performing additional processes such as heat treatment that can expose the porosity or voids. Super vacuum die-casting (SVDC) is an innovation that aims to overcome this challenge by introducing a vacuum to draw air from the die cavity before filling. While there is a significant literature on the technical performance of vacuum assisted technology, the authors are unaware of previous work focused in analyzing short- and long-term cost-benefit tradeoffs. This manuscript's goal is to evaluate the strategic and economical implications of novel SVDC technology as well as its upstream and downstream processes, however, the cost implications of use-life and end-of-life is not considered in this study. To do this, we develop and describe an analytical model to map future scenarios, both production and product, to expected production cost difference between SVDC and conventional die-casting. Using these models we find that materials and die casting process costs dominated the cost in both HPDC and SVDC. From analysis of several case studies, these dominant costs translate directly into the strategic advantages and disadvantages of SVDC. SVDC can provide cost savings if a part can be redesigned to reduce mass. Some of that cost savings is lost, however, due to added heat treatment costs and added tooling and system costs. The effect means that SVDC can reduce cost particularly for larger parts and when production volumes are higher. The cost advantage of SVDC is strongly dependent on production volume, and realized mass savings. From a variance-based sensitivity analysis, it can be seen that at higher production volumes (around 100k per year or more) breakeven requires a mass savings of 15% for small parts and around 12.5% for medium and large parts. However, when production volumes are low (say around 5000 parts per year) these values rise to 45%, 35%, and 30%, respectively.

Development and research of a device for gas sheet stamping with a piston pressure multiplier

Traditionally, sheet stamping is carried out in the cold state of the workpiece being processed. At the same time, due to the limited plasticity of the workpiece, stamping parts of complex shape is performed in several operating steps, which significantly increases the cost of production. The article is devoted to the development and research of a device providing stamping of parts with heating of the workpiece being processed. The device comprises a die and a working cylinder between which the workpiece is placed, as well as a combustion chamber separated from the working cylinder by a piston. The heating of the sheet billet and its punching is carried out in two stages within 1...2 s with its exposure to the action of gas mixture combustion products. At the first stage, the billet is heated and deformed by the combustion products formed in the die cavity and the working cylinder, whereas at the second stage these processes take place due to the energy of the combustion products formed in the combustion chamber. The workflow of the developed device was studied. The regularities of the pressure and temperature changes of the gas that heats and deforms the billet being stamped were established. The optimum proportions of the volumes of the combustion chamber and the working cylinder were determined. The developed device ensures stamping of complex-shaped parts in one process step due to the heating of the workpiece. In this device the pressure on the surface of the workpiece being processed is 2...3 times higher compared with the existing analogues, which ensures stamping of heavy-thickness parts, as well as parts made of hard-to-deform alloys.

Dimensional Deviation Estimation for Parts with Free-Form Surfaces

Dimensional deviation is a prerequisite for improving the manufacturing process of parts with free-form surfaces, for example, the reverse adjustment of the die cavity of turbine blade. Influenced by random noise of the manufacturing process, dimensional variation is inevitable for batch parts. Therefore, it may cause unacceptable error to estimate batch parts dimensional deviation by a single sample. Meanwhile, the optimum sample size for estimating dimensional deviation is difficult to determine. To overcome this problem, a practical method for estimating of dimensional deviation of parts with free-form surface is proposed. Firstly, displacements of the discrete points on part surface are employed to represent dimensional error of the part. Estimating dimensional deviation of parts is actually to estimate the simultaneous confidence intervals of the discrete point displacements. Secondly, Bonferroni simultaneous confidence intervals are adopted to estimate the confidence intervals of the part dimensional deviation. Moreover, the accuracy of the estimation will be continuously improved by increasing samples. Consequently, a practical dimensional deviation estimation method is presented. Finally, a compressor blade is adopted to illustrate the proposed method. The percentage of estimation error of the blade dimensional deviation that is less than 0.05mm, which is the estimation error limit, of all the 100 times sampling experiments is 99%, exceeding the given confidence level of 95%, while the percentage of the existing method is below the confidence level, only 87%.

A densification equation derived from the stress-deformation analysis of uniaxial cold compaction of metal powder mixes

ABSTRACTA new densification equation for uniaxial cold compaction of four low alloy steel powders was determined from the deformation vs. mean axial stress correlation. Both deformation and stress are averaged along the height of the powder column. A power law relation, with two parameters representing the plasticity and the inverse of the resistance to deformation (densification) of the powder mix, respectively, fits the curves that are divided in two steps, distinguished by the prevailingdeformation/densification mechanism (rearrangement or plastic deformation).Densification of the four powder mixes is greatly affected by the starting density in the die cavity, while the chemical composition of the base iron powder has a less significant effect.

Compaction behaviour and mechanical strength of lactose-sodium starch glycolate and lactose-croscarmellose sodium binary tablets

The focus of this study is to elucidate the effects of adding super disintegrants (SSG and Acdisol) to a filler (lactose) in terms of the compaction behaviour and mechanical strength of the formed binary tablets. The tablets were formed in a uniaxial die compaction process with compaction pressures ranging from 37.7MPa to 150.7 MPa. Consequently, the findings indicated that the increasing of the compaction pressure and the percentage mass composition of the super disintegrants would led to the increased in the strength of the tablets as well as their plastic energies, where this was more apparent for the case of the binary lactose/Acdisol tablets. In addition, as the compaction pressure increased, the maximum ejection pressure required to eject the tablet from the die cavity also increased. In contrast, a decreased in the maximum ejection pressure was observed as the composition of both super disintegrants increased in the lactose-super disintegrant binary tablets. In conclusion, the addition of super disintegrant; SSG with lactose and Acdisol with lactose; would enhanced the mechanical strength of lactose based tablets especially for the case of acdisol-lactose binary tablets in the experimental conditions adopted in this current work.

Coupled Electro-Thermo-Mechanical Simulation for Multiple Pellet Fabrication Using Spark Plasma Sintering

A coordinated experimental and computational analysis was undertaken to investigate the temperature field, heat generation, and stress distribution within a spark plasma sintering (SPS) tooling-specimen system during single- and multipellet fabrication of uranium dioxide (UO2) fuel pellets. Different SPS tool assembly configurations consisting of spacers, punches, pellets, and a die with single or multiple cavities were analyzed using ANSYS finite element (FE) software with coupled electro-thermo-mechanical modeling approach. For single-pellet manufacture, the importance of the die dimensions in relation to punch length and their influence on temperature distribution in the pellet were analyzed. The analysis was then extended to propose methods for reducing the overall power consumption of the SPS fabrication process by optimizing the dimensions and configurations of tooling for simultaneous sintering of multiple pellets in each processing cycle. For double-pellet manufacture, the effect of the center punch length (that separates the two pellets) on the temperature distribution in the pellets was investigated. Finally, for the multiple pellet fabrication, the optimum spacing between the pellets as well as the distance between the die cavities and the outer surface of the die wall were determined. A good agreement between the experimental data on the die surface temperature and FE model results was obtained. The current analysis may be utilized for further optimization of advanced tooling concepts to control temperature distribution and obtain uniform microstructure in fuel pellets in large-scale manufacturing using SPS process.

A shrinkage prediction method of investment casting based on geometric parameters

During investment casting process, the design of die cavity is the key factor to ensure the dimension accuracy of casting. The design principle of die cavity is based on computer-aided design model of casting. However, the casting will shrink in the die cavity with the decrease of temperature. Thus, the finalized design of die cavity is determined by the shrinkage and computer-aided design model of casting. It is necessary to predict the shrinkage of casting. A prediction method which based on adaptive learning idea of BP artificial neural network and construction of mapping model idea of regression method is proposed in this paper. The method is used for predicting shrinkage of casting. In this method, a series of I-beam castings that were divided into training samples and testing samples are designed for casting experiment and shrinkage measurement. Training samples are used for building shrinkage prediction model. Testing samples are used for verifying accuracy of the shrinkage prediction model. The results show that the shrinkage prediction method has higher fitting precision than regression method in fitting these training samples. Besides, for the training and testing samples, the prediction accuracy has positive correlation with fitting precision. The shrinkage can be well predicted by the prediction method through the known geometric parameters of computer-aided design model of casting.