Shrinkage Porosity Defects Research Articles

Determining technological parameters for obtaining ta15 titanium alloy blanks with improved mechanical characteristics using the electron-beam 3D printing method

The object of this study is the process of electron beam 3D printing of articles made of TA15 titanium alloy powder. Peculiarities of the structure and properties formation of alloy blanks, obtained by this method have been described. Influence of process parameters (electron beam power and geometric scanning parameters) on the characteristics of the material were considered. Step of displacement of the beam trajectory changed from 0.1 to 0.25 mm with an interval of 0.05 mm. Specific energy of the electron beam varied from 20 to 70 J/mm3 for every trajectory displacement step. The macrostructure was examined visually while the microstructure was studied by optical microscopy. Mechanical properties were determined by uniaxial tension and impact bending tests. It was established that depending on the 3D printing parameters the macrostructure of most samples is dense but with unfavorable parameters non-fusions or shrinkage porosity defects may form. The microstructure of the dendritic type has an α´+β lamellar-acicular morphology, its dispersity and shape of α´–phase areas vary depending on the process parameters. A scanning step of 0.2 mm and a beam energy of 40 J/mm3 allows obtaining a dispersed microstructure in which there are no non-fusions and shrinkage micropores. The value of the Rm is 27 %, and the R0.2 is 24 % higher than that of the alloy obtained by the conventional technology of electron beam melting. The A5 is 3.2 times higher. However, impact toughness of the sample with dendrite unfavorable orientation to the direction of load applying may be lower compared to conventional technology. The results could be used for devising commercial technology of high strength titanium alloys parts produced by 3D printing

Parameter Design of Sand Casting to Minimize Shrinkage Defects, Porosity Defects and Incomplete Defects

Casting is one of the most commonly used manufacturing method for geometrically complex product. Among the casting technologies, sand casting is often found in application. Beside the advantages of the sand-casting process, it also has a drawback that is often encountered, namely product defects. Product defects can be caused by a lack of attention to sand casting parameters. This work aims to minimize those defects, including porosity defects, shrinkage defects and incomplete defects by optimizing process parameters using the Taguchi method. The identified sand-casting process parameters include gating location, riser location, molding conditions and pouring temperature with each parameter consisting of 3 levels. This research using the fractional factorial L9 (34). Data processing is carried out by analysis of mean (ANOM) to obtain plot effects. The results showed that the optimal combination of parameters that resulted in shrinkage, porosity and minimal incomplete defects were at gating location level 2, riser location level 1, mold condition level 2 and pouring temperature level 3. The results of the comparison before and after optimization were an increase of 0.77, where previously it was 1.30 to 2.07 based on normalized data.

Analysis of the Effect of Feeder Volume on Shrinkage Porosity Defects in Piston Products through the Gravity Die Casting Process

To achieve defect-free casting (soundness casting) with a minimal amount of shrinkage porosity, refinement during the casting process is necessary. In the gravity die casting process, there are parameters that lead to product defects, especially in the casting design, focusing on the gating system and feeder system as pathways for the flow of molten metal to supply the molten metal into the mold cavity. This research was conducted to examine the effect of adding feeder dimensions on shrinkage porosity, specifically on Al-Si piston products with a Silicon content of 12-13%. Feeder dimensions were varied in nine variations by adding height and width to the feeder gate, initially measuring 90mm in height and 32mm in width, along with the addition of insulation to the feeder to retain the heat of the casting process. Cooling used water and argon, with water placed at the center core and pin core and argon placed on the outer mold, with a solidification time of 150 seconds and pouring time of 3 seconds considered constant. This study used a Computer Aided Engineering (CAE) approach, namely MagmaSoft or the application of software to model the gravity casting system process. The results showed the lowest percentage of shrinkage at feeder dimensions of 114mm in height and 45mm in width with a mold temperature of 220°C was 0.76% of the product

Investigation on effect of carbon equivalent and inoculation on the solidification and shrinkage tendency of ductile cast iron using thermal analysis

PurposeThe foundry industry incurs additional costs as a result of defective castings. Shrinkage defects are a frequent problem in ductile iron castings. It is still essential to understand how shrinkage porosity varies in size when the ductile iron composition changes. This information can be used to produce high-quality cast parts and determine the best processing conditions. The objective of this research paper is to examine the effect of carbon equivalent and inoculation on the morphology of the shrinkage defect using thermal analysis.Design/methodology/approachThis study focuses on certain thermal analysis parameters, such as the angle of the first derivative curve at the solidus temperature, recalescence and its relationships to graphite nucleation and shrinkage tendency. The results of thermal analysis in terms of the cooling curve and its derivative parameters, and thorough characterizations of the shrinkage observed in cup castings produced with various melt compositions and inoculation are presented in the current study.FindingsThe proportion of caved surfaces and macro shrinkage porosity defects has been reduced as the carbon equivalent of melt increases from hypoeutectic to a hypereutectic composition. The composition that is slightly hypereutectic has the lowest shrinkage propensity. Although inoculation reduces shrinkage, the importance of this parameter differs depending on the carbon equivalent.Originality/valueThe percentage of macro shrinkage porosity and the angle that the cooling rate curve forms are strongly correlated. It is found that the macro shrinkage size decreases as the angle of the first derivative curve at the solidus temperature is reduced. Further, lower macroporosity is produced by a metal that has a higher nodule count in association with a greater cooling rate toward the end of the solidification process.

Dry sliding wear and friction behavior of powder metallurgy FeCoNiAlSi0.2 high-entropy alloys

Wear behaviors of the FeCoNiAlSi0.2 high-entropy alloy (HEA) and Si-free FeCoNiAl during the reciprocating sliding wear process were evaluated for automotive piston rings. The HEAs were prepared using on advanced powder metallurgy route to solve the inherent shrinkage porosity and segregation defects during casting, poor densification, and wear resistance of HEAs while reciprocating motion. The morphology, hardness, wear, and friction properties were investigated. FeCoNiAl had biphasic face-centered cubic (FCC) and body-centered cubic (BCC) solid solution structures, whereas FeCoNiAlSi0.2 HEAs had a single BCC solid solution structure. Si addition significantly enhanced the hardness and wear resistance of the HEAs under reciprocating conditions because of the increased solid solution strengthening and lattice distortion effects. The maximum hardness of the FeCoNiAlSi0.2 HEA reached approximately 582 HV, which is higher than that of the equiatomic FeCoNiAl HEA (491 HV). The findings depict that FeCoNiAlSi0.2 maintains better tribological behavior than FeCoNiAl HEA against the tungsten carbide (WC) ball indenter. Oxidative delamination and cracking occurred in the FeCoNiAl/WC pair, whereas a mixed adhesive–abrasive wear mechanism was prominent in the FeCoNiAlSi0.2/WC pair because of the harder BCC solid solution phase. This study explores an effective strategy for enhancing the tribology behavior of automotive piston structures under varying loads and reciprocating dry sliding motions.

Numerical simulation of shrinkage porosity defect in billet continuous casting

Abstract Shrinkage porosity is a typical internal defect in the continuous casting billet, which occurs frequently and is difficult to solve. To explore the influence factors of central shrinkage porosity, a novel unsteady thermomechanical coupling analysis algorithm is developed based on the billet solidification characteristics, and the central shrinkage behavior during the ending solidification process is simulated. Results show that when the casting speed increases from 1.6 to 2.8 m·min−1 and the center outward displacement is reduced from 9.20 × 10−2 mm to 5.8 × 10−2 mm, it means casting speed has a significant effect on the formation of shrinkage porosity, and for this caster, the higher casting speed is more suitable for the secondary cooling zone. Without the changes in the solidification structure, when the superheat degree of molten steel increases from 10 to 40°C, the center outward displacement value decreases from 7.12 × 10−2 mm to 6.91 × 10−2 mm. In that case, the superheat degree has no obvious effect on the center displacement value.

Effect of Runner Distance on Microstructure and Properties of Semi-Solid Squeeze Casting CuSn10P1 Alloy

It is easy to form reverse segregation and shrinkage porosity defects during the solidification of CuSn10P1 alloy, which leads to the poor properties and limits its application in high strength and toughness parts. In this paper, semi-solid CuSn10P1 alloy slurry was prepared by enclosed cooling slope channel (for short ECSC). The effect of runner distance on microstructure and properties by liquid squeeze casting and semi-solid squeeze casting was studied. The results showed that the microstructure of semi-solid squeeze casting is finer than that of liquid squeeze casting, and the shrinkage defects are improved. The solid fraction with 65 mm runner is lower than that without runner in liquid squeeze casting and semi-solid squeeze casting due to the retention effect of solid phase in semi-solid slurry flow, but the properties with 65 mm runner is better than that without runner. The ultimate tensile strength, yield strength and elongation of semi-solid squeeze casting CuSn10P1 alloy with 65 mm runner distance reached 466.5 MPa, 273.6 MPa and 13.4%, which were improved by 26%, 19% and 97%, respectively, as compared to that of liquid squeeze casting.

Simulation and experimental analysis of re-design the faulty position of the riser to minimize shrinkage porosity defect in sand cast sprocket gear

Shrinkage porosity is known to occur when feeding is cut off due to several reasons that can cause an early solidification of the molten metal on the riser affecting the overall feeding process. Casting simulations can give a clear understanding of determining the existence of shrinkage porosity by considering variable process parameters like the improper design of a riser and faulty positioning of the riser. This research work aims to investigate and minimize the occurrence of the open shrinkage porosity resting on a sprocket gear made of Carbon steel Material. The design of the gating system was done using Modulus Methods, and 3D Model was prepared by using CATIA software. The optimization of the feeding and gating system is conducted using PROCAST software, taking into account the actual casting data from the foundry and the experiment was conducted to validate the simulation results. The analysis of PROCAST predicts that the position and feed volume of riser is the key factor for sound casting by showing porosity concentration is less and casting experimental result validates the increase weight final casting than earlier. An improvement in the overall quality of the product was observed when compared to sprocket gears produced in the foundry before.

Effects of different holding pressures on the microstructure and mechanical properties of Al-5.9Zn-2.2Mg-1.8Cu alloy

In this study, a low-pressure casting process was used to examine the influence of the holding pressure on the Al–5.9Zn–2.2Mg–1.8Cu alloy. The study aimed to refine the grain structure and optimize the microstructural homogeneity and mechanical properties of the alloy. The phase composition, microstructure, chemical composition, and fracture morphology of the alloy were determined using optical microscopy, SEM, inductively coupled plasma spectroscopy, and XRD. As the holding pressure increased, the theoretical crystallisation temperature of the alloy increased, which increased the degree of undercooling during solidification and the effective number of nuclei, resulting in grain refinement. In addition, increase in the holding pressure strengthened the feeding ability of the alloy melt and reduced the occurrence of shrinkage porosity defects. When the optimal pressure was exceeded, the nucleation rate as well as the denseness of the alloy decreases. When the holding pressure was 0.035 MPa, the grain refining effect was the best and the microstructure was the most uniform. The yield strength, tensile strength, and elongation of the alloy reached the maximum values of 264.6 MPa, 290.8 MPa, and 7.7%, respectively. When the holding pressure was >0.035 MPa, the structure was not further refined; in contrast, the grains were larger, and the mechanical properties were inferior.

Numerical analysis of lost foam casting for large-caliber water meter shell

Large-caliber water meter shells are prone to shrinkage porosity, wrinkles, air entrapment, slag inclusion, and other defects during the lost foam casting process. Taking the vertical spiral wing WS-100 water meter as the research object, through the analysis of the structure of the water meter shell, the flow field and temperature field of the design of outer bottom injection-vertical pouring, outer bottom injection-horizontal pouring and inner bottom injection-horizontal pouring involved in the filling and solidification process are numerically simulated and solve analysis, respectively. The results showed that: when the inner bottom injection-horizontal pouring process was adopted, the filling process of the casting was stable, the isolated liquid phase area of the solidification process was relatively small, and the possibility of forming defects was less. The casting performance is excellent, and the numerical analysis is verified to be effective.

Optimization of Casting Process of Headstock Based on Numerical Simulation

In this paper, the casting process optimization design of a certain type of headstock is carried out by numerical simulation technology of casting process. Designed the pouring plan based on theoretical calculation; based on the numerical simulation results, quantitatively designed the riser size, and rationally arranged the pouring riser system based on the equilibrium solidification theory, which can reduce the shrinkage porosity and shrinkage defects in the casting process and increase the process yield; Finally, a sand core production plan is provided based on the precision machining technology of the moldless casting mold, which provides a new idea for the process plan design of complex spindle box castings.

Comparison of various gating systems for investment casting of hydraulic retarder impeller with complex geometry

Due to the complex structure and thin thickness of the guide vane edge of the hydraulic retarder impeller, the casting defects such as shrinkage porosity and misrun are usually formed during casting, which have a close relationship with the filling and solidification process. In this work, the filling and solidification processes of impeller in various gating systems, named case 1 to 3, were simulated and the distribution characteristics of potential shrinkage porosity defects were predicted by ProCAST software based on the mathematical models, boundary conditions, and parameters of investment casting. The simulation results show that the aim of complete filling of the impeller can be achieved by using all of the three gating systems. However, only the case 3 gating system consisted with one sprue riser and four feeding risers can provide the impeller with suitable feeding channel in melt solidification process. Therefore, no predicted shrinkage porosities form in the impeller because the defects can transfer to the gating system during solidification. The optimized gating system have been verified by experiment, and the rapid casting of the impeller has been realized by using 3D printed polystyrene patterns. The results of visual and X-ray inspections show that both the misrun and shrinkage porosity defects were eliminated in the actually final cast, which matched well with the numerical simulation results for the investment casting of the impeller. Many experiment results of the new product show that these optimization gating system are very helpful to reduce the casting defect and to improve the product quality.

Research advances on homogenization manufacturing of heavy components by metal additive forging

Heavy forgings are the core components of major equipment and even play an indispensable role in national security and the national economy. Traditionally, heavy forgings are usually manufactured with ingots of more than 100 tons. However, there are serious macroscopic segregation, shrinkage porosity and other defects in heavy forgings due to size effect of metal solidification process, which seriously affect the quality of heavy forgings and have become a worldwide problem. Avoiding the traditional concept in which a heavy forging must be created using a large steel ingot, Institute of Metal Research, Chinese Academy of Sciences first put forward a novel technology to manufacture heavy high-quality forgings by additive forging (AF). Small-sized slabs with excellent quality are used as the base elements. After surface cleaning, stacking, assembling, vacuum packaging, and deformation process characterized by pressure-forging and multi-directional forging at high temperature, the homogenized heavy forgings can be obtained with completely healed interface, which realizes the new manufacturing technology of “by making greatly small”. Through in-depth research on the microstructural evolution and bonding mechanism of the interface, we found the self-decomposition phenomenon of interface oxides. With the decomposed oxygen ions diffusing toward the matrix, oxide particles precipitated around both sides of the interface, forming the particle precipitation zone (PPZ). As the holding time increased, the width of the PPZ increased and the oxide precipitates in the PPZ transformed from MnCr x Al2– x O4 to Mn x Al3– x O4 and finally to γ-Al2O3, depending on the local oxygen activity. After holding for 24 h, the interfacial oxides completely decomposed and only a few nano-scale γ-Al2O3 oxide precipitates remained dispersed far away from the bonding interface, leading to the recovery of the mechanical properties of the bonding joints. This recovery mechanism should be of great importance to the engineering application of Additive Forging. Besides, we illustrated the dynamic recrystallization (DRX) mechnism of the bonding interface. The bonding of joints is related with interfacial grain boundary (IGB) bulging process, which is considered as a nucleation process of DRXed grain under different deformation environments. During recrystallization process, the bonded interface moved due to strain-induced boundary migration (SIBM) process. Stored energy difference (caused by accumulation of dislocations or difference of subgrain size at the bonding interface) was the dominant factor for SIBM during DRX. This technology has been applied to hydroelectric alloy steel spindles (110 tons in weight) and nuclear power stainless steel giant rings (15.6 m in diameter), which plays an important role in promoting the rapid development of high-end equipment in China and ensuring the independence and control of core materials for major equipment.

Effects of Process Parameters on Shrinkage Porosity in 357 Semi-Solid Die Casting Parts

The shrinkage porosity that was caused by the insufficient feeding during solidification, was a common defect in the semi-solid die casting process. This defect decreased significantly the mechanical properties of the casting. In order to avoid the shrinkage porosity in casting, the die design, slug preparation and die casting process were carefully considered. In this study, a designed mold was used to make the sequential solidification of the slug. The process parameters, including intensification pressure, die temperature and biscuit thickness of the casting, were studied to show their influence on shrinkage porosity defects. The experimental results show that the high intensification pressure, high die temperature and long biscuit can be beneficial to obtain castings with no shrinkage porosity.

Optimization of vacuum counter-pressure casting process for an aluminum alloy casing using numerical simulation and defect recognition techniques

Vacuum counter-pressure casting (VCPC) process is an effective forming process of producing components with complex thin-walled characteristics. In this study, a surrogate-based optimization method with five process parameters is used to reduce the shrinkage porosity defect during the VCPC process of a complicated thin-walled aluminum alloy casing. The prediction of the shrinkage porosity defect is implemented by using the numerical simulation of the VCPC process. In general, performing the optimization directly based on the casting simulation may not be practical due to the computational and time constraints. To mitigate this problem, the response surface model (RSM) constructed via computer experiments is employed to accurately approximate the functional relationship between the process parameters and the response variable which is defined as the area of defects in the defect image generated from the casting simulation. To measure the area of defects in the image, a histogram-based threshold segmentation approach is proposed to recognize and quantify the defects from the image. The optimization problem is subsequently formulated using a desirability function-based optimization method, and the objective function is estimated using the built RSMs. The final results indicate that a set of optimal process parameters with minimum defects can be obtained.

Numerical simulation and optimization of shell mould casting process for leaf spring bracket

Although the shell mould casting process has a wide range of application in many fields, the prediction of casting defects is still a problem. In the present work, a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting. The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting; and the formation mechanism of the gas pore, and shrinkage porosity defects were analyzed. The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment, insufficient feeding and non-sequential solidification. Subsequently, through changing the position of risers, adding a connecting channel between the risers, and setting blind risers at the U-shaped brackets, an optimized gating and feeding system was established to improve the quality of the casting. After optimization, the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated. The experiment results with the optimized casting process are in good agreement with the numerical simulation, which verifies the validity of the finite element model in the shell mould casting.

Casting simulation and defect identification of geometry varied plates with experimental validation

This work mainly deals with the simulation of geometry varied plates subjected to permanent mold gravity casting process. There are extensive demands of Aluminum and its alloys in diverse industries owing to its better properties especially mechanical (good strength and stiffness with low density). Aluminum alloy AlSi5Cu3 was chosen and the behavior of metal filling and solidification was examined using AUTOCAST – XI software equipped with flow plus module. Three rectangular plates with variation in thickness were selected as casting geometry with equal length and width. Three feeders have been applied to each cavity at various locations with optimized dimensions. The casting yield and casting quality were calculated for all casting geometry. The values of casting yield for 8 mm, 12 mm and 16 mm thick plates were 91.20%, 91.5% and 92.05% while casting quality were 95.20%, 94.05% and 93.68%, respectively. The temperature difference, the velocity of melted metal and solidification time were analyzed for thickness varied plates. The front velocity of the liquid metal was calculated and having values of 1.02 m/sec, 0.91 m/sec and 0.39 m/sec and solidification time was 23.56 sec, 31.56 sec and 37.35 sec for 8 mm, 12 mm and 16 mm thick plates, respectively. The cooling curves for different geometry were obtained by placing virtual thermocouple at various locations. Shrinkage porosity defect identified and validated with actual experimentation. The depth of shrinkage porosity was measured by simulation results and calculated for actual casted plates. It showed a variation of shrinkage porosity depth by 10%, 5.88% and 4.34% for 8 mm, 12 mm and 16 mm thick plates, respectively.

Effect of feedstock geometry on the semisolid processing of Al–Si–Cu–Mg alloy

Shaping a metal by thixoforming involves feedstock preparation and reheating. Proper procedure and accurate processing criteria for thixoforming are required to provide a quality product. Appropriate parameters are crucial in assessing the capabilities of this thixoforming process. In this study, the effect of different billet geometry of Al–Si–Cu–Mg alloy on microstructure and mechanical properties were investigated. The billet with different geometries of height-to-diameter ratio (h0/d0 = 3.2 and h0/d0 = 0.8) was utilized through the cooling slope casting technique and thixoformed after being heated into compression press. The results indicate that low h0/d0 ratio produced the finest grain size for the α Al solid phase (≈52.8 ± 5.1 μm), best shape factor and complete die filling. By contrast, high h0/d0 ratio produced coarser grain size for the α Al solid phase (≈62.2 ± 6.1 μm), insufficient die filling, cold shut and shrinkage porosity defect. Moreover, the thixoformed billets with the lower h0/d0 ratio exhibited higher tensile stresses. The ultimate tensile strength, yield strength, and elongation to fracture of the thixoformed h0/d0 ratio 3.2 improved at 183 MPa, 163 MPa, and 1.6%, respectively, whereas the values of the thixoformed h0/d0 ratio 1.25 alloy were 206 MPa, 193 MPa, and 2.5%, respectively

GISS Technology: Principle and Applications in Die Casting

In the past, there have been a lot of effort to solve gas and shrinkage porosity defects in die casting. The common solutions are vacuum technology, jet cooling technology, and application of squeeze pins. However, these solutions often increase the die casting production costs. A new solution that has recently been introduced worldwide is GISS Technology. This technology applies the superheated slurry casting process. Gas and shrinkage porosity defects can be reduced. Furthermore, the production costs are lowered due to die life extension, cycle time reduction, melting energy reduction, and lubrication usage reduction. This paper describes the principle of GISS Technology, and selected applications and case studies are also be presented.

Microstructure and Mechanical Properties of Friction Stir Repaired Al–Cu Casting Alloy

Friction stir repairing was successfully used to repair shrinkage cavity and porosity defects in Al–Cu casting alloy plates with T5 treatment. Effects of welding speeds on microstructures and mechanical properties of repaired region were mainly discussed. The results show that heat affected zone has the minimum microhardness due to coarser grains, where the tensile fracture is located. Through the thickness of the stir zone (SZ), the grain size decreases with increasing distance from the top surface of the repaired region due to the difference of heat input and cooling rate. The tensile strength and elongation of the SZ characterized by finer grains are both higher than those of the repaired region. These values of the SZ at 900 rpm and 150 mm/min reach 336.8 MPa and 11.75%, equivalent to 90.7 and 81.6% of BM without casting defects, respectively.