Alloy Mold Research Articles

Crack formation of camshaft castings: Hot tearing susceptibility and root causes

As a widely used cyclical motion component, the camshaft plays a key role in the accuracy and stability of the whole machine. Micro hot cracks in the camshaft casting process are an important cause of failure in subsequent machining and operation. In this paper, the hot tearing susceptibility of the camshaft in the casting process was studied using the alloy composition (carbon equivalent and Mn/S ratio) and mold preheating temperature. The formation mechanism of the hot tear source was analyzed through the microscopic morphology of the fracture-sensitive cross-section. Using the improved Clyne-Davies model and the newly proposed hot tearing susceptibility (HTS) model, the results show that as the carbon equivalent and Mn/S ratio increase, the hot tearing susceptibility of the camshaft first decreases and then increases. The hot tearing tendency of the casting can be reduced by appropriately increasing the mold preheating temperature. The microscopic morphology indicates that the initiation and propagation of the crack source are caused by the excessively serious non-equilibrium solidification of the camshaft metal fluid. Finally, potential countermeasures are proposed to decrease micro hot cracks in camshaft castings, including the adjustment of alloy composition, optimization of casting process parameters, and improvement of system solidification conditions.

Experimental investigation on magnetorheological fine finishing of EN-8 steel alloy mold surface for cylindrical plastic bottle caps

The cylindrical mold is a key element utilized in the manufacture of different cylindrical components for a wide range of applications in industries like automotive, aerospace, medical, and among others. Fine finishing of the cylindric mold with high surface integrity has several benefits such as good fits and tolerance, increased product quality, and high load-bearing capability for components. Recently, a cutting-edge rotating magnetorheological honing (RMRH) method based on permanent magnet tools was developed for the fine finishing of interior cylindrical surfaces with great productivity. Furthermore, many industrial real-time cylindrical molds need to be fine-finished with high productivity to enhance their functionality. To meet these requirements, the RMRH procedure could be the better option. Therefore, the RMRH process is investigated in the current study to finely finish the inner surface of the real-time EN-8 steel mold for plastic bottle caps. To determine how well the real-time EN-8 steel cylindrical mold could be fine-finished using the current process, the response surface technique was used to know the best finishing parameters. The significant % drop in parameters of the surface roughness profile ( Ra, Rz, and Rq) of the MR finished real-time EN8 mold surface is achieved as 86.05, 82.17, and 84.62, respectively, after 40 minutes of the RMRH process with the optimal parameters. Also, a considerable improvement in straightness is obtained as the final surface waviness on the inside cylindrical surface of the real-time EN8 mold for plastic bottle caps is decreased from an initial value of 120 nm to 40 nm. Further, circularity and surface morphology tests are carried out over the mold's finished inner surface. After providing the efficient MR finishing using the current process, results indicate that surface properties and functional efficacy of the internal surface of the real-time mold for producing plastic bottle caps have improved.

Investigation of the mechanism for interaction of calcium zirconate, oxides of calcium and zirconium with titanium melts

ABSTRACT The problem to obtain casting molds for titanium alloys is not resolved in full. It is primarily due to the high reactivity of titanium alloys resulting in their interaction with refractory materials. This reduces the quality of the castings due to the formation of various defects. The interaction of VT1-0 grade titanium in the liquid state with CaO, ZrO2 and CaZrO3 were studied. The processes occurring at the contact boundary between these substances and a change in the structure and microhardness of titanium castings near this boundary were described herein. The data obtained showed the disadvantages of molding materials based on CaO and CaZrO3. The features revealed for the interaction of a titanium melt with CaZrO3, where a highly porous CaTiO3 layer has been formed in the reaction zone,made it possible to recommend this compound as a promising material to cast molds in order to produce castings from titanium alloys.

Significant elimination of pore defect and interfacial reaction of sand casted Al–Li alloy castings via a novel inorganic binder coating

Generally, sand casted Al–Li alloy castings have very serious problems in pore defect and interfacial reaction, remarkably weakening the Al–Li alloy castings quality. How to solve these problems is always a challenge. In this paper, a novel inorganic binder coating containing lithium silicate solution binder and silicon carbide powder on the surface of the sand mold was developed to eliminate pore defect and prevent interfacial reaction of the sand casted Al–Li alloy castings. The effective mechanism of the inorganic binder coating on the pore defect and interfacial reaction was discussed. The obtained results showed that the inorganic binder coating formed a thin shell on the surface of the sand mold after pouring, which can effectively prevent the metal-mold interface reaction of the sand casting Al–Li alloy and significantly reduce the porosity defects. Among them, the Al–Li alloy casting prepared using the inorganic binder coating consisting of the lithium silicate binder and silicon carbide powder basically had no pore defects, and the porosity was only 3.73%, which was 66.7% lower than that of the casting prepared by the sand mold without any treatment. Moreover, the interface reaction of the Al–Li alloy and sand mold was fully eliminated, which was attributed to the low overall atomic diffusion rate of the silicon carbide based on molecular dynamics simulation results.

Interfacial Reaction Mechanism between Ceramic Mould and Single Crystal Superalloy for Manufacturing Turbine Blade.

Single crystal superalloys are the preferred materials for manufacturing turbine blades of advanced aero-engines, due to their excellent high temperature comprehensive performance. The interfacial reaction between alloys and ceramic mould are an important factor to influence the surface quality and service performance of the turbine blade. It is very important to reveal the interfacial reaction mechanism to improve turbine blade quality and yield rate. In this paper, the interfacial reactions between DD6 single crystal superalloy and ceramic mould were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The results show that the main reaction products were HfO2, Al2O3 and Y3Al5O12 when the yttrium oxide powders were the prime coat materials, while alloy surface suffered undesirable sand fusion; the thicknesses of the reaction layers were over 20 μm. The reaction layer can be divided into two layers, the layer close to the alloy was mainly composed of Al2O3 and Y3Al5O12, and the layer close to the mould was composed of SiO2, Al2O3 and Y3Al5O12. Avoiding the formation of Y2O3-Al2O3-SiO2 ternary low-melts can solve the interfacial reaction between DD6 alloy and yttrium oxide mould.

Temperature variation and mass transport simulations of invar alloy during continuous-wave laser melting deposition

Continuous-wave laser melting deposition (LMD) offers several advantages, such as higher cooling rate, finer microstructures and improved mechanical properties over traditional processing technology. The fluid flow in the molten pool affects the solute distribution and the microstructure morphology when invar alloy mould is repaired with laser melting deposition. However, the effects of laser on the molten pool motion, thermal field and microstructure of invar alloy are not distinct. In this work, a three-dimensional model utilizing the volume of fluid method was developed to simulate the transient molten pool motion, heat transfer and fluid flow for the laser melting deposition process. The interaction among powder, laser and molten pool in LMD process was comprehensively considered in the model. The laser melting deposition with Nano-WC powder particles as a dispersoid was investigated. The simulated molten pool geometry was compared with experimental results. Moreover, temperature variation, fluid flow and their influence on the microstructure were analyzed. It is concluded that a significant Marangoni flow is observed with the highest velocity in the middle of the molten pool but lower in the surface and bottom of the molten pool. The lower velocity of fluid flow results in an element accumulation in the bottom of the molten pool. This study provides a referenced value for revealing the flow mechanism of molten pool in the LMD process of invar alloy.

A hot tearing criterion based on solidification microstructure in cast alloys

A criterion based on solidification microstructure was proposed to precisely predict the hot tearing behavior of cast alloys, which takes into account the effects of both mechanical and nonmechanical factors. This criterion focuses on the events occurring at the grain boundary, which are determined by the thermal contraction, solidification shrinkage, grain growing and liquid feeding. This criterion responds to a series of factors that affect hot tearing, such as alloy composition, mold design, casting process and microstructure. Its credibility has been validated by studying the hot tearing behavior of Mg-Ce alloys. In conformity with the experimental results, this criterion predicted decrease in the number of rods occurring hot tearing with increasing cerium content. A simplified criterion was derived and validated by Mg-Ce (equiaxed grain) and Mg-Al (columnar grain) alloy systems, which is suitable for the case where the eutectic liquid fraction is low and the liquid feeding can be ignored. In addition, a hot tearing index for equiaxed grains was proposed, that is,|dT/d(fs1/3)|near(fs)1/3=1, and its prediction results were consistent with the hot tearing susceptibility calculated from the experimental results.

Optimization of CNC Milling Parameters for Complex 3D Surfaces of SIMOLD 2083 Alloy Mold Core Utilizing Multiobjective Water Cycle Algorithm

In this article, an effective multiobjective optimization approach is exploited to search for the best milling parameters for CNC for complex 3d surfaces of SIMOLD 2083 alloy mold core. To improve the quality responses, the cutting factors are optimized by a combination of Taguchi method (TM), response surface method (RSM), and multiobjective water cycle algorithm (MWCA). Firstly, the design for initial series experiments of the cutting factors was generated via the TM. Thereafter, the regression models between the cutting factors and the surface roughness of the machined workpiece surface as well as milling time are formed via applying the RSM. Moreover, analysis of variance and sensitivity analysis are also executed to define the influences and crucial contributions of cutting parameters on the surface roughness and milling time. The results of analysis of variance showed that the factors which have main effects on surface roughness were spindle speed (42.42%), feed rate (29.40%), and cutting depth (6.59%), respectively. Meanwhile, the feed rate with the influence of 92.6% was the most significant factor in controlling the milling time. Ultimately, based on mathematical models, the MWCA is performed to define the optimal factors. The optimal results indicated that the optimized surface roughness was about 0.260 μm and the milling time was roughly 1012.767 (s). In addition, the errors between forecasted results and experimental verifications for the surface roughness and milling time are 2.04% and 5.39%, respectively. Therefore, the results of experimental verifications are suitable with the forecasted results from the proposed optimization method. These results depicted that the proposed integration approach can define effectively the optimal cutting factors for CNC milling and expand to apply for complex multiobjective optimization problems.

Study of fiber Bragg gratings with TiN-coated for cryogenic temperature measurement

In this study, single metal-coated Fiber Bragg grating (FBG) sensors and bare FBG sensors were placed in an aluminum alloy mold, which were in turn packaged in a thermal insulation container to monitor the temperature response, and used as cryogenic temperature sensors. Specifically, the performance of titanium nitride (TiN)-coated FBG sensors in cryogenic temperature environments was evaluated. Using an optical spectrum analyzer (OSA), the reflection spectra of the TiN-coated FBG sensors were measured and compared with those of bare FBG for temperatures ranging from 25 to −195 °C. The results showed that the TiN-coated FBG exhibited a temperature sensitivity of 10.713 pm/°C and R-squared value of 0.995. The TiN-coated on the FBG altered the non-linear characteristics of the thermo-optic and thermal expansion coefficients of the FBG. Through this research to get thermo-optic coefficient (ξ = 5.12 × 10−6) and thermal expansion coefficient (α = 1.81 × 10−6) and resulted in more precise measurements at cryogenic temperature.

Characteristics of interfacial reactions between Ti-6Al-4V alloy and ZrO2 ceramic mold

The interfacial reaction between Ti-6Al-4V alloy and ZrO2 ceramic mold with zirconia sol binder was investigated by keeping the 12 g alloy melt in a vacuum induction furnace for 15 s. The microstructures, element distribution and phase constitution of the interface were identified by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the whole interface reaction layer can be divided into three regions: metal penetration layer, transition layer, and hardened layer according to the structure morphology, which has the characteristics of severe metal penetration, finer lamellar, and coarse oxygen-rich α phase, respectively. The erosion of the alloy melt on the ceramic mold promotes the decomposition of zirconia, which leads to the increase of local Zr concentration, greatly increasing the activity coefficient of Ti, aggravating the occurrence of interfacial reaction. Thus, the interfacial reaction shows the characteristics of chain reaction. When the oxygen released by the dissolution of zirconia exceeds the local solid solubility, it precipitates in the form of bubbles, resulting in blowholes at the interface. The result also indicates that the zirconia mold with zirconia sol binder is not suitable for pouring heavy titanium alloy castings.

Horizontal-Axis Wind Turbine Blades Manufacture with Composite Materials

The aim of this paper is to contribute to the wind turbine manufacturing industry through investigating the technological manufacturing process of a 2.5kW horizontal axis wind turbine’s (HAWT) blades. Composite materials, such as fiberglass and carbon fiber are engaged in the manufacturing process, due to their mechanical properties. The material selection process is discussed, motivating the choices based on several criteria, such as weight and tensile strength. The adopted technologies for the manufacturing process include layup method at ambient temperature and vacuum. Regarding the used moulds, these were previously manufactured using the infrastructure that NRDI COMOTI has at its disposal. Layups of fiberglass and carbon fiber are disposed in the aluminium alloy moulds. In the end, a layup of peel ply is placed upon the outer surface of the composite and the vacuum bag is applied and sealed. The outcome of this research consists of two parts. Firstly, the presented methodology, techniques and materials selection criteria represent a reliable source of information for future scientific papers on the matter. Secondly, the manufactured blades, after post-processing techniques, can be tested in relevant conditions in the aerodynamic tunnel and further studies can be conducted with the obtained results.

Inlet Condition for Mold Filling Simulation in Gravity Casting of Aluminum Alloy

The casting CAE is useful tool for casting design in order to obtain the sound castings without defects. It is very important to know the influence of casting conditions on the mold filling. In the present study, the inlet condition for the mold filling simulation in gravity casting of aluminum alloy is investigated to simulate the real phenomena changing with the difference in the casting shape. The direct observation experiment is carried out with six types of sprue designs using an aluminum alloy and sand mold. There are three types of sprues: the elbow, bend and stair-step shapes. The molten metal of Al–7%Si alloy is poured using the stopper ladle. The velocity change in accordance with the different casting condition is analyzed using images observed by the video camera. The velocity of flow front in the early stage of the mold filling is changed intensely. Then, the velocity after the middle stage of the mold filling is decreased calmly. It is difficult to simulate the present phenomena by the mold filling simulation using the velocity inlet boundary. In order to reproduce the difference of each filling behavior, new inlet condition, which is named to “OverFlow pouring Basin” (OFB), is proposed in this study. The mold filling behavior and filled-up time simulated using the inlet condition of OFB are more or less agreed with six real phenomena according with three sprue shapes and two sprue heights.

Effects of Mold Materials on the Interfacial Reaction between Magnesium Alloy and Ceramic Shell Mold during Investment Casting

In order to suppress the interfacial reaction between the ceramic shell mold and the magnesium molten alloy during the investment casting process, a mold material with a high thermodynamic stability based on alkaline zirconium sol (CH4NO3Zr) binder and corundum (Al2O3) powder was prepared. The effects of the mold materials and casting thicknesses on the interfacial reaction were investigated by an optical microscope, X-ray diffraction, a scanning electron microscope, and an energy dispersive spectroscope analysis. The results suggested that the casting poured by the conventional ZrSiO4 mold has a serious reaction on the surface, and the reaction was more severe when the casting thickness was increased. The oxidation layer was approximately 300 μm in some severe areas of 45 mm thickness. The XRD and EDS results showed that the reaction interface mainly contains MgO and Mg2Si. While the casting poured by the Al2O3 mold provides a light and smooth surface, the reaction layer was only 1.5 μm on average. The reaction interface mainly contains MgO and Mg2F.

Effect of hydrogen on interfacial reaction between Ti-6Al-4V alloy melt and graphite mold

In this paper, the effect of hydrogen on the interfacial reaction between Ti-6Al-4V (Ti64) alloy and graphite casting mold was studied by argon and hydrogen plasma arc melting. The experimental results showed that the thickness and the hardness of the interfacial reaction layer decreased with increasing hydrogen partial pressure. The interaction of activated H atoms in the titanium alloy melt and carbon on the interface, [C] + 4[H] = CH4, could be taking place.

Microinjection Molding of Out-of-Plane Bistable Mechanisms.

We present a novel fabrication technique of a miniaturized out-of-plane compliant bistable mechanism (OBM) by microinjection molding (MM) and assembling. OBMs are mostly in-plane monolithic devices containing delicate elastic elements fabricated in metal, plastic, or by a microelectromechanical system (MEMS) process. The proposed technique is based on stacking two out-of-plane V-beam structures obtained by mold fabrication and MM of thermoplastic polyacetal resin (POM) and joining their centers and outer frames to construct a double V-beam structure. A copper alloy mold insert was machined with the sectional dimensions of the V-beam cavities. Next, the insert was re-machined to reduce dimensional errors caused by part shrinkage. The V-beam structure was injection-molded at a high temperature. Gradually elongated short-shots were obtained by increasing pressure, showing the symmetrical melt filling through the V-beam cavities. The as-molded structure was buckled elastically by an external-force load but showed a monostable behavior because of a higher unconstrained buckling mode. The double V-beam device assembled with two single-molded structures shows clear bistability. The experimental force-displacement curve of the molded structure is presented for examination. This work can potentially contribute to the fabrication of architected materials with periodic assembly of the plastic bistable mechanism for diverse functionalities, such as energy absorption and shape morphing.

Prediction of Flash Formed in Plastic Injection Molding Using Aluminum Alloy Mold Cavity by Numerical Simulation Considering Deformation of Mold Parts

Prediction of Flash Formed in Plastic Injection Molding Using Aluminum Alloy Mold Cavity by Numerical Simulation Considering Deformation of Mold Parts

Effect of 2024 Al Alloy Insert on the Grain Refinement of a 2024 Al Alloy Prepared via Insert Mold Casting

In this study, an insert mold casting was fabricated by inserting 2024 Al extruded rods into a 2024 Al melt. The molds were kept at a 2024 Al melt for different times. The 2024 Al extruded rods were used to refine the 2024 Al alloy grains because the advantage of this method is that it is contamination free compared with other grain refiners. Moreover, we investigated the macro and microstructure of the ingots. Further, we analyzed the refinement mechanism of the 2024 Al rod on the 2024 Al alloy. Our result showed that when the immersion time of the 2024 Al insert was 0 s, a metallurgical bonding was partly formed between the 2024 Al insert and the 2024 Al alloy mold cast. When the immersion time of the 2024 Al insert increased to 5 s, the 2024 solid insert was dissolved in the liquid; the coarse dendritic grains were replaced by fine equiaxed grains. The refinement mechanism for the insertion of a 2024 Al rod on the 2024 Al alloy was to melt the 2024 Al insert and have it decrease the degree of the liquid superheat, which thus increased the cooling rate and provided a large number of small particles that acted as the nucleus of heterogeneous nucleation. However, these particles were melted gradually in the high-temperature liquid after an increase of immersion time. Thus, the refinement effect of 2024 Al insert on the solidified structure was weakened.

Measuring the interfacial heat transfer coefficient between flowing molten alloy and sand mold using fluidity tests

Abstract This study specifically examined a method using fluidity test results to measure the interfacial heat transfer coefficient (IHTC) between a molten alloy and a mold during flow. Review of earlier studies revealed that conventional methods require the choking area length to calculate the IHTC during flow, but one earlier study used an assumed choking area length. Details of its length remain unclear. Using an arbitrarily chosen choking area length leads to inaccurate acquisition of the IHTC. For this study, we observed the microstructures and macrostructures around a fluidity test specimen tip to ascertain the choking area length. This value led to calculation of the IHTC between the flowing bronze melt and the shell sand mold as 1521 W/m2•K. This study also found a new method requiring no choking area length to ascertain the IHTC between the flowing melt and the sand mold. The IHTC obtained using this method was 1406 W/m2•K, representing a difference of about 8% from the value obtained using a conventional method. This study assessed experimental conditions under which the new method can produce accurate IHTC values.

Reactive spontaneous infiltration of Al-activated TiO2 by molten aluminum

Abstract The reactive spontaneous infiltration of Al-activated TiO2 (anatase) was investigated. Pure Al powder was blended with TiO2 for activation. They were compacted into the preform and then sealed within 6060 alloy mould. The activation and infiltration were carried out in 6060 alloy bath for 1 h and comparative sintering experiments were carried out in an argon protected environment under the same conditions of temperature and duration. X-ray diffraction analysis proved that the Al sealed environment was superior to the argon protection on activating the reaction between Al and TiO2. The blending ratio of TiO2 to Al and the temperature were found to play the most important role in infiltration by affecting infiltration and reaction kinetics. Three main types of microstructures were observed after infiltration: full infiltration, partial infiltration with the formation of cracks and no infiltration. The formation of these microstructures was explained on the basis of reaction kinetics and local volume changes due to the reactions. Ultimately, it is found that to obtain an overall good spontaneous infiltration, a TiO2 to Al blending ratio around 3:7 in volume and an infiltration temperature around 900 °C are the most suitable.

Investigation of Fused Alumina Based-Mold Facecoats for DZ22B Directionally Solidified Blades.

The interaction between alloy melt and mold facecoats is the main factor affecting the surface quality of investment casting nickel-based superalloys. An investigation was undertaken to develop suitable refractories as facecoat materials for the directionally solidified blades of DZ22B nickel-based superalloys in order to avoid a sand-burning defect. The wettability and interface reactions between alloy melt and various facecoats were studied by using a sessile drop experiment and the real investment casting method, respectively. The results show that by adding Cr2O3 powder with the amounts of 2 wt.%, 5 wt.% and 10 wt.% in the fused alumina-based facecoats, the wetting angles between the alloy melt and facecoats decreased from 105.40° to 100.37°, 99.96° and 98.11°, respectively, while the sand-burning defect on the casting blade surfaces still formed during the process of directional solidification. However, by adding h-BN powder in the fused alumina-based facecoats, the wetting angles between the alloy melt and facecoats dramatically increased, the sand-burning defect on the casting blade surfaces was effectively inhibited and a metallic luster on the directionally solidified blades could be obviously observed. In this study, the suitable composition of mold facecoats for the investment casting of blades is 2 wt.% h-BN added fused alumina.