Determination of wax pattern die profile for investment casting of turbine blades

In order to conform to dimensional tolerances, an efficient numerical method, displacement iterative compensation method, based on finite element methodology （FEM） was presented for the wax pattern die profile design of turbine blades. Casting shrinkages at different positions of the blade which was considered nonlinear thermo-mechanical casting deformations were calculated. Based on the displacement iterative compensation method proposed, the optimized wax pattern die profile can be established. For a A356 alloy blade, substantial reduction in dimensional and shape tolerances was achieved with the developed die shape optimization system. Numerical simulation result obtained by the proposed method shows a good agreement with the result measured experimentally. After four times iterations, compared with the CAD model of turbine blade, the total form error decreases to 0.001 978 mm from the orevious 0.515 815 mm.

Research on cracking mechanism of the thin shell mould in expendable pattern shell casting during pattern removal process

Aiming at the cracking phenomenon of the thin shell mould in the expendable pattern shell casting during the pattern removing process, some systemic researches are presented.The influence of the pattern removing method and temperature on the pattern removing were investigated.The shell mould cracking mechanism was analyzed by using thermo-gravimetric analysis (TGA), and combining the temperature field and the volume change of the expanded polystyrene (EPS) foam pattern being tested.The results indicated that the shell mould was not easily cracked when the pattern removing process was carried out with the furnace being heated little by little because of the shell slowly shrinking with dehydration and shell strength gradually increasing.The shell mould was soon destroyed when it was set directly into the furnace at above 400 oC because of the thin shell mould rapidly shrinking and the foam pattern hindering.However, the shell mould had no cracking when it had been preheated for a long time even if the furnace temperature was above 400 oC and the shell was put into the furnace directly.Moreover, when the shell mould was directly set into the furnace at lower temperatures, 250 to 300 ℃, the shell would shrink slowly and the foam pattern would stay at the maximum expansion stage temperature of 100 to 110 ℃ for a long time; and the shell mould would experience an expansion force from the foam pattern for a long time.The expansion force is related to the pattern removing temperature, holding time, foam pattern thickness and density.Therefore, the foam pattern with higher density could make the shell crack.

Principles and practice of low pressure-expendable pattern casting process for magnesium alloys

A newly developed low-pressure expendable pattern casting (LP-EPC) process was introduced and its basic principles or effect factors were further analyzed. According to theoretical calculation and experimental results, the major casting parameters that are of great and critical importance on the process include pressure and flux of filling gas, decomposition characteristic and density of foam pattern, thickness and permeability of coating, pouring temperature, vacuum degree and their combination. Most of casting defects can be effectively avoided by choosing the suitable parameters. The success achieved in pouring motor housing and exhaust manifold castings demonstrates the advantages of LP-EPC process in the production of high-complicated castings with high dimension accuracy.

Diagnosis parameters of mold filling pattern for optimization of a casting system

For optimal design of a gating system,the setting of diagnosis parameters is very important.In this study,the permanent mold casting process was selected because most of the other casting processes have more complicated factors that influence the mold filling pattern compared to the permanent mold casting process,such as the surface roughness of mold,gas generation from the mold wash and binder of sand mold,and the gas permeability through a sand mold,etc.Two diagnosis parameters(flow rate difference and arrival time difference) of molten metal flow pattern in the numerical simulation are suggested for design of an optimum casting system with a permanent mold.The results show that the arrival time difference can be used as one important diagnosis parameter of the complexity of the runner system and its usefulness has been verified via making aluminum parts using permanent mold casting(Fig.9).

Application of digital pattern-less molding technology to produce art casting

Compared with the conventional casting process, digital pattern-less casting technology has many advantages such as good machining accuracy, a short processing cycle, and low production cost. It is a new rapid manufacturing technology for castings, integrated with CAD/CAM, casting, CNC machining and many other advanced technologies. With this digital casting technology, no pattern is needed for making molds; it is precise, f lexible, and green. Usually, art castings have complex structures and are made in small batches or even made in a single-piece, especially for large-sized art castings. So it has the shortcomings of high cost, low eff iciency and long time for making a pattern to produce art castings with the conventional casting processes. However, the digital pattern-less casting technology can be applied to fabricate art castings, since it can greatly shorten the manufacturing cycle and lower the production cost, thus having a very good prospect. In this study, based on the digital pattern-less casting technology, a plaque casting with artistic Chinese characters(a Chinese poem) was designed and manufactured, and the production process was demonstrated in detail.

Effect of process parameters on density of magnesium alloy parts by low-pressure expendable pattern casting

The combination of magnesium alloys with the low-pressure expendable pattern casting(LP-EPC) process would bright future for application of magnesium alloys. The researches are focused on the effect of process parameters on the internal casting quality of magnesium alloy parts. AZ91D magnesium alloy castings were produced for different combinations of the LP-EPC process parameters. Specifically,pouring temperature,vacuum,filling velocity and coupling action of these factors were manipulated to observe their effect on the casting porosity and density distribution. The results indicate that the pouring temperature with LP-EPC process is lower than it in gravity casting. The selected process parameters,such as vacuum,filling velocity and coupled modes of them,must ensure melt metal flowing front profile exhibiting smooth and convex shape. The optimal process parameters for the castings are pouring temperature 983-1 023 K,vacuum 0.02-0.03 MPa,filling velocity 60-95 mm/s,and simultaneous filling with sucking.

Mg alloy surface alloying layer fabricated through evaporative pattern casting technology

The influencing factors of surface alloying layer by evaporative pattern casting technology were investigated.A certain thickness alloying layer was formed on the surface of Mg-alloy matrix when the pouring temperature was 780°C with different vacuum degree and alloying powder size.The surface layer microstructure,micro area composition of the new phase formed on the matrix and the composition characteristics on the surface layer were examined by SEM and element scanning.The results show that the content of aluminum increases greatly on the surface layer.The micro-hardness of alloyed layer has a more obvious increase compared with that of the matrix.The size of alloying element and the vacuum degree are the key factors influencing the alloying layer,with the increase of element powder size from 0.074 to 0.15 mm and vacuum degree from 0.04 to 0.06 MPa,the surface alloying effect becomes better.

An investigation on bonding interface microstructure of ceramic coating prepared on AZ91D by evaporated pattern casting technique

PbO-ZnO-Na20 ceramic coating was fabricated on the AZ91D Mg-alloy substrate surface by using of evaporated pattern casting （EPC） process. The ceramic coating was characterized through scanning electron microscopy （SEM） observation, energy dispersive X-ray spectrometer （EDS） and so on. The research was emphasized on the formation process of ceramic coating and the interface bonding conditions between ceramic coating and the substrate. Results show that the glass powder （PbO-ZnO-NazO） melts when contacts with the high temperature liquid metal, and solidifies on the surface of the substrate with the decrease of temperature. Therefore, the ceramic coating was successfully prepared with the formation of the bonding interface with the substrate, Beside the influence of coating layer thickness, the vacuum level was also investigated. Further analysis indicates that oxide inclusions and decomposition products of foam pattern had a significant effect on the bonding interface： To obtain a good bonding interface between the ceramic coating and the substrate, the metal liquid oxidation and inclusions must be decreased and the decomposition products of foam pattern should be exhausted from the EPC coating completely.

Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures

To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.

Influence of casting module on corrosion behavior of Mg-11Gd-3Y alloy

The influences of two kinds of casting modules of metal casting （MC） and expandable pattern casting （EPC） on the corrosion behavior of Mg-11Gd-3Y alloy were studied by electrochemical measurements, scanning electron microscopy （SEM） observation, X-ray diffractometry （XRD） and X-ray photoelectron spectroscopy （XPS） analysis. It is found that the quantity of the Mg 24 （Gd, Y） 5 phase in MC is more than that in EPC due to the cooling rate. There is more alloying element dissolved in the matrix compared with MC. For EPC, the galvanic corrosion effect between the matrix and the Mg 24 （Gd, Y） 5 phase decreases and the corrosion resistance increases compared with the MC. The chief corrosion mode for Mg-11Gd-3Y alloy is pitting corrosion because most of the alloying elements are transformed into intermetallic phases. The average corrosion rate of the MC alloy in the immersion test is five times higher than that of EPC alloy and yttrium is present in the product film, which will provide increased protection for Mg-11Gd-3Y alloy. The electrochemical measurements and immersion test show that the EPC process increases the corrosion resistance compared with the MC Mg-11Gd-3Y alloy.

Investigation of carbon contamination in lost foam castings of low carbon steel

Lost foam casting(LFC) process is a special casting method in which polymeric foam patterns with refractory coatings are utilized as a mould component. In this work, four types of foam: expandable polyethylene(EPE), expandable polypropylene(EPP) and expandable polystyrene(EPS) foams with two different densities were employed as pattern materials. LFC and conventional green sand mould casting methods were used to cast a low carbon steel, A216 Grade WCB. Both casting processes were carried out at 1,580 °C. Chemical analysis results showed that the carbon contamination level was high and was influenced by pattern type. Metallographic investigations revealed a significant increase in the percentage of pearlite phase in all LFC samples. Densities of manufactured samples were calculated in order to evaluate porosity of the products. It was determined that the densities of the LFC samples were lower than the green sand mould cast reference sample(RS). Vickers hardness tests were also carried out and increments in hardness values with increased carbon content was observed.

Study of the Interface between Steel Insert and Aluminum Casting in EPC

The effective surface treatment method for steel insert composited with Al base metal by expendable pattern casting （EPC） process and the bonding interface between steel insert and Al base metal were investigated.It was found that Zn plating on steel insert was effective on improving the bonding property between steel insert and Al base metal in EPC process.Zn is thought to promote the formation of diffusion layer.But almost none content of Zn was observed in the boundary which had been plated on the steel insert.A diffusion layer consisting of Al,Si and Fe was formed at the insert/alloy interface and its hardness was higher than the steel insert as matter of course Al base metal.This layer turned out to be intermetallic compounds of Al-Si-Fe system.Higher pouring temperature promoted the diffusion of Fe into Al alloy,so Fe content in intermetallic layers increased at higher pouring temperature.The layer nearest to steel disappeared due to applied pressure.

Rapid casting technology based on selective laser sintering

Selective laser sintering(SLS),as a kind of additive manufacturing technology,which uses a laser beam to scan and heat powder material layer by layer to form parts(models),is widely used in the field of casting,mainly for preparing casting coated sand cores,investment casting patterns,etc.The SLS technique facilitates rapid casting and shortens the casting production periods by eliminating mold preparation.In this study,we reached conclusions for the basic principles and characteristics of SLS methods,and focused on the research status,key technology and development trend of SLS in the fields of forming coated sand-casting molds and investment casting patterns.

Analysis of three-dimensional vortexes below the free surface in a continuous casting mold

To study fluctuations of the free surface of liquid steel in the mold,two different models with the same casting conditions but different thicknesses were employed to analyze the hydrodynamic behavior at the top of the mold.The first model was a standard thickness slab,and the second had a thickness three times wider.It is found with the second model that above the plane formed by the steel jets,it is possible to observe four three-dimensional vortexes that interact with the submerged entry nozzle（SEN）and mold walls.By using a biphasic model to simulate the interface between the liquid and air inside the mold,the flow asymmetry and the fluctuations of the free surface can be clearly observed.

Study on accuracy of casting flow simulation

In the field of casting flow simulation, the application of body-fitted coordinate(BFC) has not been widely used due to the difficulty and low efficiency of grid generation, despite the availability of good quality analysis results. Cartesian coordinates, on the other hand, have been used predominantly in casting process simulations because of their relatively easy and fast grid generation. However, Cartesian grid systems cannot obtain accurate results because they cannot express the geometries properly. In this study, Cut Cell method was applied to solve this problem. The three-dimensional incompressible viscous governing equation was analyzed using a function defined for the volume and area of the casting in the cutting cell. Using the Cut Cell method, accurate flow analysis results were also obtained in the Cartesian grid systems. The tests of simple shape and the applications of actual casting product have been tried with Cut Cell method.

Control of liquid column height in electromagnetic casting with fuzzy neural network model

The control of suitable and stable height of liquid column is the crucial point to operate the electromagnetic casting(EMC) process and to obtain ingots with desirable shape and dimensional accuracy. But due to the complicated interact parameters and special circumstances, the measure and control of liquid column are quite difficult. A fuzzy neural network was used to help control the liquid column by predicting its height on line. The results show that the stabilization of the height of liquid column and surface quality of the ingot are remarkably improved by using the neural network based control system.

两种添加剂对石蜡-硬脂酸蜡料性能的影响

为探究改性松香和聚乙烯对中温模料组织性能的影响,本研究以石蜡-硬脂酸二元系模料为基体,在此基础上逐步添加改性松香和聚乙烯,探究二元基体配比、改性松香及聚乙烯含量对模料熔点、抗弯强度、针入度和融合均匀性等物理特性的影响,在此基础上研制出一种针入度达1.06 mm、强度达6.02 MPa、熔点在58℃附近的综合性能良好的中温模料,为中温模料改良优化提供理论支持。

CAST工艺的强化脱氮研究

根据李家沱污水处理厂的实际运行经验以及对近7个月的运行数据的分析，得出适用于城市污水处理厂CAST工艺脱氮的运行工况和运行参数值。结果显示，运行工况、污泥回流比和碳氮比是影响CAST工艺脱氮效果的主要因素，通过合理调整运行工况可减弱低进水碳氮比和高氮负荷带来的不利影响；在污泥龄为15d、MISS为3500-4500mg／L、回流比为30％时，脱氮率可达到70％以上，出水TN稳定达标。

基于八梭位装备的三重纬锦花纹色彩层次研究

针对纬锦织物的色彩设计,研究总梭位数为8条件下梭位数量及位置配置、纬线引出方式与纬三重结构大提花织物的花纹色彩之间的关系。设定7个单纬起花、混纬起花组织,建立梭位配置方案表,分析了全常抛、分段纯色彩抛、分段混色彩抛、非固定梭位配置分段彩抛几种引纬方式下的花纹色彩层次数。结果表明:全常抛引纬的花纹色彩层次数与花纹组织配置数相等;分段纯色彩抛引纬的可分区段数、花纹色彩层次数与不同组别彩抛纬配置的梭位数存在数学关联;分段混色彩抛引纬的色彩搭配比较丰富,但对同一引纬区段不会产生花纹色彩层次数的变化;非固定梭位分段引纬可以使花纹色彩分布产生变化,但不会造成花纹色彩层次数的变化,梭位数配置与可分区段数之间存在数学关联。

Fabrication of agarose hydrogel with patterned silver nanowiresfor motion sensor

In this work, a facile strategy is proposed to construct stretchable electronics based on agarose hydrogels. The hot agarose solution is casted onto a template with patterned Ag nanowires, endowing agarose hydrogel with patterned conductive surface. After further heating treatment, Ag nanowires can be embedded into the agarose hydrogel, which improves the stability of Ag pattern and has no obvious e ffect on the conductivity of hydrogels. The agarose hydrogel with patterned Ag nanowires is certi fied to be an e ffective stretchable electrode to record the motion of joints, which has great potential applications in the field of wearable devices.