Accuracy Of Castings Research Articles

ЕКСПЕРИМЕНТАЛЬНЕ ДОСЛІДЖЕННЯ ТОЧНОСТІ ПРОКАТКИ НА СТАНІ 800

The purpose of the work is an experimental study of the process of square sections rolling on the rolling mill 800 to determine the influence of rolling parameters on the dimensions and length of the roll. During the study, variations in ingot mass, rolling dimensions, and rolling length were determined, regression equations and correlation coefficients were obtained for the dependence of rolling dimensions and length on the ingot mass, changes in interroll gap and time delay before the finishing stand. It was established that the ingot mass variates within significant limits - 638 kg, which is caused by the melt mass variations. Variations in the mass of the ingot within one ingot mold stool are caused by the dimensions of the ingot molds and are within 154 kg. Variations in the dimensions of the roll are carried out within the following limits: thickness - 1.0 mm, width - 0.5 mm, length - 5.3 m. The change of the interroll gap can be used to correct the length of the finished roll in a small range of lengths, if the mass variations occur within accuracy of ingot casting on one ingot mold stool. It is necessary to take additional measures to stabilize the weight of the ingot. The influence of delays in the rolling train, which occur during rolling and lead to instability of the rolling temperature regime, for this type of profiles does not significantly affect the dimensions of the cross section and the length of the roll.

Search procedure for optimal design and technological solutions to ensure dimensional and geometric accuracy of castings

The object of research in the work is the technology of manufacturing shaped castings in disposable sand molds. The existing problem is that the imperfection of design and technological solutions at the stage of developing the technology of a single sand mold casting leads to deviations in the dimensions and geometry of the castings after their manufacture from the requirements of technological documentation. This can lead to an irreparable shortage of casting. To develop measures to eliminate or minimize the event, which consists in the formation of a shortage of castings in terms of dimensional and geometric accuracy, a procedure for searching for optimal design and technological solutions is proposed. A hypothesis has been put forward that a significant factor that leads to deviations in the dimensional and geometric accuracy of castings from the requirements of technological documentation is the imperfection of the gating system design. It is demonstrated on specific castings how this factor can influence the formation of uneven wall thickness. The proposed procedure, which includes 10 consecutive steps, allows to build a plan for a complete factorial experiment and obtain a regression equation for it, linking the parameters of the gating system with indicators of dimensional and geometric accuracy. The presence of such equations provides the possibility of further experimental optimization and determination of design and technological solutions for the development or improvement of casting systems that minimize the deviations of the dimensional and geometric accuracy of castings from the requirements of technological documentation. This also minimizes the likelihood of an event consisting in the formation of an irreparable shortage of castings. The presented study will be useful for machine-building enterprises that have foundries in their structure, where shaped castings are made in disposable sand molds.

Iterative reverse deformation optimization design of castings based on numerical simulation of solidification thermal stress

In the casting process, in order to compensate for the solidification shrinkage to obtain higher dimensional accuracy of the casting, it is often necessary to modify the original design of castings, and a suitable compensation method has a decisive impact on the dimensional accuracy of the actual casting. In this study, based on solidification simulation, a design method of reverse deformation is proposed, and two compensation methods, empirical compensation and direct reverse deformation, are implemented. The simulation results show that the empirical compensation method has problems such as difficulty in determining the parameters and satisfaction of both the overall and local accuracy at the same time; while based on the simulation results for each node of the casting, the direct reverse deformation design achieves the design with shape. In addition, the casting model can be optimized through iterative revisions, so that higher dimensional accuracy can be continuously obtained in the subsequent design process. Therefore, the direct reverse deformation design is more accurate and reasonable compared to empirical compensation method.

ENVIRONMENTALLY FRIENDLY MATERIALS AND TECHNOLOGIES FOR THE PRODUCTION OF CASTINGS FROM ALUMINUM ALLOYS

The article is devoted to the topical problem of development and creation of environmentally friendly materials and technologies for foundry production. In recent years, priorities have changed in the development of materials and technological processes towards their compatibility with the environment. The environmental aspects of production come to the fore, which are determined by harmful emissions into the atmosphere, which is strictly regulated by the Kyoto Protocol. In the foundry industry to obtain castings in disposable forms, various technologies have been developed and used, which can be separated based on the type of mold used and the method of its manufacture. The main content of the study is the analysis of traditional foundry technologies and the most promising technology of casting in low-temperature forms (NTF). The peculiarity of casting in NTF is a significant increase in the strength of molds, compared with casting in sand-clay molds, as well as the possibility of using water as the main binder. This method of mold making improves the structure, increases the accuracy and geometry of castings, saves molding materials, and, most importantly, improves the environment by eliminating harmful emissions into the atmosphere of foundries. However, the method of casting in NTF has a number of disadvantages associated with the formation on the surface of castings of shells, pores, as well as increased burns. To eliminate these shortcomings, it is proposed to apply non-stick coatings on the surface of NTF and rods. Considerable attention is paid to the development and research of non-stick coatings, which allow the use of environmentally friendly casting technology in NTF for the production of castings from various alloys of high quality. Coating compositions and methods for determining the optimal composition of non-stick coating, which could be recommended for the production of aluminum castings in low-temperature molds, are identified and described. The obtained results indicate a high potential for the use of this technology as a means of improving the environmental safety of foundry production.

On the question of porosity of aluminum castings obtained by injection molding

The constantly accelerating pace of life and the rapid growth of industry inevitably lead to an increase and toughening of requirements for manufactured products. Therefore, the scope of application of special methods for obtaining blanks is expanding, among which one of the leading places is occupied by the injection molding method (IMM). The advantages of the IMM include, first of all, high productivity and dimensional accuracy of castings, the minimum need for mechanical processing, the possibility of obtaining castings with a complex external configuration, as well as the automation of the process. The main disadvantages are the high cost of molds, as well as the insufficient quality of the resulting castings, primarily the gas subsurface porosity and gas roughness. In most cases, the IMM is used to obtain castings from zinc, copper and aluminum alloys. The most widespread are aluminum alloys, which make it possible to manufacture castings with different properties depending on the alloy grade. For most grades of aluminum alloys, disadvantages associated with sufficiently high melting temperatures and chemical activity when interacting with the mold are inherent. All these factors make the IMM a complex technological process, for which the challenge of insufficient quality of the resulting castings is urgent. Traditionally, this issue is solved by choosing the technological modes of the casting process. However, in some cases, it is very difficult to achieve high quality castings only by selecting technological modes. The authors have proposed an universal method for improving the quality of castings by applying the developed protective coatings on forming surfaces of molds by cathode-ion bombardment (CIB). The paper presents the results of experimental studies proving the effectiveness of the use of wear-resistant coatings obtained by the CIB method of various compositions in comparison with the traditionally used nitriding in terms of gas and surface porosity, as well as the roughness of castings. The economic substantiation of the efficiency of the use of CIB coatings in comparison with nitriding is presented.

Computational and experimental study of lattice structured patterns for casting process

PurposeThe quality of lost foam casted engineering components is directly influenced by the characteristics of the respective ceramic shell mold (CSM) and hence casting pattern. In this present work, rapid prototyping (RP) was used to fabricate the lattice structured patterns (LSPs) to reduce the defects and cracks in CSM during the heating stage.Design/methodology/approachThe quality of the LSPs was accessed by measuring the dimensional accuracy. Further, the thermal stress in the CSM during the heating of porosity varied LSPs was analyzed using ANSYS software package 16.0. The Ni-alloy casting was fabricated by using the designed LSP and compared with its respective CAD model to access its quality.FindingsThe obtained results revealed that the Wigner–Seitz LSPs retained high accuracy and minimized the stress for defect-free CSM. Also, the thermal stress generated in the CSM depends upon the porosity coefficient of the LSP. Hence the interplay with porosity coefficient of LSPs leads to the formation of defect free CSM and hence high quality casting.Originality/valueRP was used to develop LSPs and investigated the dependency of unit cell parameters on the accuracy of the final casting.

Possibilities of increasing the dimensional accuracy of nodular cast iron castings

This paper is devoted to influence of the size and number of graphite inclusions in high-strength cast iron on pre-shrinkage expansion and, as a result, on linear shrinkage and dimensional accuracy of castings. It was established that influencing the number and size of graphite inclusions it is possible to increase the dimensional accuracy of high-strength cast iron castings by two accuracy classes and significantly reduce mechanical processing allowances of cast iron in order to save metal.

Influence of Slurry Composition on Mould Properties and Shrinkage of Investment Casting

Ceramic shell mould plays a key role in achieving dimensional accuracy and quality of casting. This work investigates the effect of mould parameters such as silica concentration, filler to binder ratio and the number of secondary coats on mould properties, namely modulus of rupture, adjusted fracture load, and permeability. Experimental results report that enrichment in silica results in drastic growth in adjusted fracture load with a small increase in modulus of rupture and no change in permeability. Improvement in filler to binder ratio causes a significant increase in the adjusted fracture load and modulus of rupture with moderate decrease in permeability. An increase in number of ceramic coats increases the adjusted fracture load significantly and reduces permeability moderately. Impact of the adjusted fracture load on casting shrinkage has been studied by conducting various casting trials. Adjusted fracture load above 315 N is preferred which corresponds to 25–30% silica, filler to binder ratio of 1.25 and number of secondary coats as six to eight for reduced shrinkage variation.

Effect of preshrinkable expansion on dimensional accuracy of castings made of high-strength cast iron

The effect of graphite inclusions on preshrinkable expansion in castings of high-strength cast iron is considered. A simulation model and software are proposed. It has been established that the preshrinkable expansion and as a consequence, the dimensional accuracy of castings of high-strength cast iron with spherical graphite are affected by the number and size of graphite inclusions. It is shown that in the fine-dispersed phase of graphite, the sample expansion is 1.74 times less than in the coarse-grained phase, and the dimensional accuracy of the sample is 2 classes higher.

Tools for the Production of Plastic Products

The paper discusses the types of system elements of mold parts. The calculation method of design data tooling which can be used at design of injection mold is offered. This method gives the chance to provide the necessary accuracy of casting. Distinctive feature of the offered method is modification of the formalized shrinkage material description of a molding detail. The offered calculation method of design data tooling allows increasing the accuracy of the received plastic product because are considered: absolute and relative volume shrinkage; relative actual linear shrinkage of material; alleged linear shrinkage.

Optimization of process parameters to improve dimensional accuracy of investment casting using Taguchi approach

In this study, Taguchi method is used to investigate the effect of critical process parameters of investment casting on dimensional variations of thin walled, complex geometrical stainless steel component. A set of experiments have been conducted to calculate shrinkages which is a measure of dimensional variation. The process parameters considered here are number of ceramic coats, pouring time, pouring temperature, and casting cooling rate. The signal-to-noise ratio and analysis of variance are used to study the influence of these parameters on shrinkage. Optimized condition for reduced shrinkage deviation can be obtained by selecting lower number of ceramic coats, faster and laminar metal pouring, lower superheated metal temperature, and faster cooling rate. Analysis of variance reports that the number of ceramic coats is the most significant parameter with more than 80% contribution whereas other parameters are insignificant. Investigation results also indicate that constraint dimension (width) has 25%–27% higher dimensional variability than non-constraint dimensions (height) for the selected component.

Permafrost Analysis Methodology (PAM) for Ceramic Shell Deformation in the Firing Process

The deformation of ceramic shell poses a potential and uncertain threat on the dimensional accuracy of the final casting in the investment casting process. In this paper, a finite element analysis method (FEM), permafrost analysis methodology (PAM), is used to simulate the deformation of the ceramic shell in the firing process. In the PAM, the porosity and the phase transformation of the ceramic shell in the firing process are taken into consideration. The comparison of simulation and experimental results indicated that the PAM can predict the deformation of the ceramic shell with high accuracy. The work of this paper presents a new approach to simulate the deformation of the ceramic shell, and there is a great significance to improve the dimensional accuracy of the final casting in the investment casting process.

Effect of increased temperature on dimensional and shape accuracy of castings produced from the EN AC-AlSi11 alloy by pressure die casting process

Effect of increased temperature on dimensional and shape accuracy of castings produced from the EN AC-AlSi11 alloy by pressure die casting process

Effect of Thermal Deformation of Molds on Thickness Accuracy of Plate-Shaped Non-Ferrous Pure Metal Castings

Effect of Thermal Deformation of Molds on Thickness Accuracy of Plate-Shaped Non-Ferrous Pure Metal Castings

Numerical simulation of cold-lap defects during casting filling process

Cold lap is one of the common defects in casting productions, which could result in poor surface accuracy and mechanical properties of castings. The cold-lap formation process is difficult to observe directly using only experimental measures, since the casting filling process is in a state of high-temperature flow inside a mold. The keys to predicting defects accurately are searching the interface front of flow, judging the collision of fronts, and defining the formation model of cold laps. A formation model of cold lap, which is related to the solid fraction, velocity, and volume fraction of the metal phase, is developed in this paper, and a method for judging the interface front and its collision was adopted. On the basis of the open-source computational fluid dynamics software OpenFOAM, a solver for predicting cold lap defects during the casting filling process was developed. The filling process of an aluminum alloy benchmark test was simulated, and the simulation results were consistent with the experimental results, which indicates the accuracy of the adopted model. Two low-pressure die-casting copper alloy filling processes with different ingates were calculated, and the formation processes of cold lap were compared with each other. The simulation results showed that there was significantly lesser cold lap in the scheme with an ingate under the lower surface of casting, which was basically consistent with the experimental results; therefore, the practicability of the adopted model was confirmed.

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.

The Effect of Casting Ring Liner Length and Prewetting on the Marginal Adaptation and Dimensional Accuracy of Full Crown Castings.

Aim:To evaluate the effect of varying cellulose casting ring liner length and its prewetting on the marginal adaptation and dimensional accuracy of full veneer metal castings.Materials and Methods:The master die was milled in stainless steel to fabricate the wax pattern. Sixty wax patterns were fabricated with a uniform thickness of 1.5 mm at an occlusal surface and 1 mm axial surface, cervical width at 13.5 mm, and 10 mm cuspal height. The samples were divided into six groups (n = 10). Groups I and II samples had the full-length cellulose prewet and dry ring liner, respectively. The groups III and IV had 2 mm short prewet and dry cellulose ring liner, respectively, whereas groups V and VI were invested in 6 mm short ring liner. The wax patterns were immediately invested in phosphate bonded investment, and casting procedure was completed with nickel-chrome alloy. The castings were cleaned and mean score of measurements at four reference points for marginal adaption, casting height, and cervical width was calculated. The marginal adaption was calculated with Imaje J software, whereas the casting height and cervical width was determined using a digital scale. The data was subjected to one-way analysis of varaince and Tukey post hoc statistical analysis with Statistical Package for the Social Sciences version 20 software.Results:The group II had the best marginal adaption with a gap of 63.786 μm followed by group I (65.185 μm), group IV (87.740 μm), and group III (101.455 μm). A large marginal gap was observed in group V at 188.871 μm. Cuspal height was more accurate with group V (10.428 mm), group VI (10.421 mm), and group II (10.488 mm). The cervical width was approximately similar in group I, group III, and group V. Statistically significant difference was observed in Tukey post hoc analysis between group V and group VI with all the other groups with regards to marginal adaptation.Conclusion:The dry cellulose ring liners provided better marginal adaptation in comparison to prewet cellulose ring liners. Accurate cuspal height was obtained with shorter ring liner in comparison to full-length cellulose ring liners.

Экзотермический разогрев прибылей в литье по газифицируемым моделям

Lost foam casting (LFM) refers to modern casting methods providing high productivity, dimensional and weight accuracy of castings from ferrous and non-ferrous alloys, cost saving of molding materials, exclusion of the use of cores and, as a consequence, coreboxes and equipment for core molding. Alongside with the laws of molding, the processes of formation of the casting itself are very important. Processes of volumetric shrinkage of the casting during crystallization of the metal flooded into the mol­ding box are particularly important since they largely determine the quality of cast sections, metal consumption on heads and pouring gate systems, and thus the process yield and prime cost of the castings. That is why exothermic heating-up of the deadhead metal allowing to reduce metal consumption on heads, and thus to increase the process yield, is a crucial task of the foundry production. In the process of LFM specific conditions appear: mold box evacuation during casting into molds and metal crystallization, formation of reducing atmosphere in them from carbohydrates (products of thermal degradation of polystyrene foam model), endothermic effect from model gasification and the following pyrolysis of its pro­ducts. All this influences the exothermic reaction behaviour. The research reveals four main factors providing effective work of exothermic mixtures, and also two types of exo-inserted pieces. The research was performed with the use of a synchronous thermal analyser, diffractometers and optic emission spectrometer. Another peculiarity of the process is also in that exo-inserted pieces are put into the head model and metal heating-up occurs not outside the head, but inside it. It is based on the exo-mixture containing aluminium and silicocalcium powder as a reducing agent and iron oxide Fe2O3 as an oxidant. Laboratory and industrial testings of the generated exo-mixture showed the effectiveness of its use in LFM, that allows to reduce metal consumption on heads by up to 25 % in casting carbon steel and ductile iron.

Evaluation of the Influence of Various Sprue Designs on Surface Porosity and Dimensional Accuracy of Base Metal Alloy Castings - An In Vitro Study

Abstract Background and Objectives: Marginal fit of cast restoration is a major factor in long term survival of restoration. The sprue design is one of the variables that affect successful castings. Porosity can occur both on the surface and sub-surface of the casting. Base metal alloys have been used as an alternative to traditional high gold content alloys due to their superior mechanical properties.The purpose of this study was to evaluate and compare the influence of various sprue designs on surface porosity and dimensional accuracy with conventional sprue design on five-unit singlepiece base metal alloy castings. Materials and Method: A metal die that stimulate a five unit Fixed partial denture was fabricated. Three different types of sprue designs was assigned to the pattern and casted. The marginal discrepancy was determined by measuring the space between the margin of the crown and the shoulder finish line of the abutment using Scanning electronic Microscope(100X magnification). Surface porosity was evaluated using stereomicroscope (X10 Magnification). Results: Best marginal fit based on the grand means and standard deviations was in the conventional design group followed by experimental 4mm and 3mmsprue design. Significant differences was present in the 3mm sprue when compared with 4mm sprue(<0.001) as well as the conventional design(<0.001). Interpretation and Conclusion: There was no surface porosity observed under stereomicroscope. When marginal discrepancy was compared with conventional design, 4mm single sprue was more effective than the 3mm single sprue.

Accuracy of face castings employing thermoplastic custom trays for facial molding

Accuracy of face castings employing thermoplastic custom trays for facial molding