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Special Report Celebrating the th Anniversray 2004-2014 CHINA Vol.11 No.4 July 2014 10

Status quo and development trend of lost foam technology

*Fan Zitian1, Jiang Wenming1,2, Liu Fuchu1, and Xiao Botao1 1. State Key Laboratory of Material Processing and & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, China; 2. School of Mechanical & Electrical Engineering, Wuhan Institute of Technology, Wuhan 430073, China

Abstract: Lost foam casting (LFC) technology has been widely applied to cast iron and cast steel. However, the development of LFC for Al and Mg alloys was relatively slower than that for cast iron and cast steel. The application of LFC to Al and Mg alloys needs more effort, especially in China. In this paper, the development history of LFC is reviewed, and the application situations of LFC to Al and Mg alloys are mainly discussed. Meanwhile, the key problems of LFC for Al and Mg alloys are also pointed out. Finally, the prospects for LFC technology are discussed, and some special new LFC technologies are introduced for casting Al and Mg alloys. In future, the development trends of green LFC technology mainly focus on the special new LFC methods, metal material, coating, heat treatment, new foam materials as well as purification technology of tail gas, etc. Key words: lost foam casting (LFC); technology actuality; development trend; aluminum alloy; magnesium alloy CLC numbers: TG249.5 *Fan Zitian Document code: A Born in 1962 Ph.D, Professor. Article ID: 1672-6421(2014)04-296-12 He has been mainly concentrating on education, research and application of casting materials; process theory and equipment. 1 Technical characteristics and development In recent years, he has given history of LFC much attention to LFC technology of Al, Mg alloys, green casting LFC is a near net shape and precision process; and it is regarded as the technology of water glass sand, representative of the 21st century casting new technology. Firstly, the solid die is rapid solidification technology fabricated using the foam material based on the structure and size of the casting etc. He has finished many studies part, and then the foam pattern is coated with refractory slurry. After drying the coated of national programs, and these foam pattern and modeling, as well as vibration compacting, the molten metal is programs have led to publication poured into the foam pattern. As a result, the foam pattern is subjected to gasification of more than 160 papers and 6 disappearance; and finally the metal casting with the shape of the foam pattern is obtained. professional books. At present, Compared with other casting processes, this new casting process has the following he holds 10 national invention technical characteristics and advantages [1-5]. patents. (1) The LFC have low surface roughness and high dimensional precision. The dimensional precision and surface roughness of LFC castings reach CT5 to CT7 and Ra 6.3 to 12.5 μm, respectively, which are close to level. The allowance of LFC castings is lower than 1.5 to 2 mm, resulting in a decrease in mechanical processing cost. The time of mechanical processing can be decreased by 40% to 50% compared to the traditional method. Meanwhile, the LFC castings E-mail: [email protected] have no flash , leading to a decrease in dimension error as a result of the model pellet Received: 2014-03-12 combination. Accepted: 2014-04-25 (2) The structure design of LFC casting is flexible. Because the foam material is

296 Celebrating the th Anniversray 2004-2014 Special Report CHINA FOUNDRY 10 Vol.11 No.4 July 2014 used as the pattern, the foam pattern has no pattern was fabricated using a solid block of EPS foam which is then inclination. During the LFC process, a mono-block foam surrounded by sand with binder as backing sand to produce the pattern can be fabricated using slicing manufacturing and metal part. The foam pattern is dimensionally accurate, requires adhesion method; and thus a casting can be obtained whole. As no , and has no parting lines so no flash is formed. It shows a consequence, the core can be omitted and the pore structure a solid mold, therefore it is called full mold casting (F method) can also be directly manufactured, resulting in a great decrease This casting process is advantageous for very complex castings. in time and cost of processing and assembling as well as the Currently, this technology is widely applied on single piece or investment of processing equipment. small batch production of metal die blanks. (3) Loose-sand compact modeling is adopted in the LFC In 1964, H. Nellen and T. R. Smith started to produce castings process, and the sand has no binder. Therefore, the production using the LFC process with non-binder dry sand. The mold process of castings is simplified, resulting in high labor usually collapsed during pouring because of the adoption of productivity. Additionally, the sand can be fully reused, so the non-binder dry sand. Therefore, A. Wittemoser used iron shot to production cost is greatly decreased. Meanwhile, the traditional replace silica sand as molding material and a magnetic field as sand mixing, compacting, combined box and sand preparation the binder. This was named magnetic casting (M method) [8]. processes can be omitted. The foam pattern can be freely In 1969, Japan's Akita Corporation and the Nagano process assembled, and several castings can be simultaneously poured test lab invented the vacuum seal modeling technology (V using one box. As a result, the LFC process is beneficial for method). Dry quartz sand was filled into , and then mass and automated production. plastic film was secured on the top of the flask. The sand was (4) The LFC process is likely to realize cleaner production. compacted using the negative pressure generated by a vacuum The polystyrene (EPS) does no harm to the environment at pump, and this method is currently widely used in LFC process low temperature because the EPS gives rise to fewer organic to fix the sand [9]. compounds during pouring, and the organic compounds are In 1982, the Kimura Foundry Corporation in Japan used easily collected. The organic compounds can be treated using equipment to produce the foam pattern. the negative pressure aspiration type combustion purifier, and The CAD/CAM system software was applied on the full the reuse rate of old sand is higher than 95%. Compared with mold casting, and was mainly used to manufacture die blanks, the traditional casting process, the harm of noise, CO and machine frames and abnormal castings [10] (see Fig. 1). The silica dust are significantly decreased, resulting in a significant process chart is shown in Fig. 2. Because the foam material improvement of the environment. is very soft, the foam pattern should be fabricated using the The LFC process originated in America, and its development scarf paring processing principle with high processing speed. has experienced the following several milestones: Otherwise, the surface roughness is very high. The high speed In 1956, H. F. Shroyer invented full mold casting. This NC brings a bright prospect for full mold casting. technology has been patented (US patent 2830343). In 1962, Recently, the Kimura Co. has made great strides in materials, Prof. Wittemose and the Hartman Company cooperated to apply cleaner production, and energy saving; as well as reduced this technology to the production of castings [6-7]. The pattern exhaust for the full mold casting.

(a) Foam pattern (b) Casting

Fig. 1: Foam pattern and casting obtained by NC machining

With the demand for industry production, the F method and is very simple, and its application gradually increases with V method have been combined since the 1980s. The LFC has breakthroughs and innovation in the key technologies [11]. The been established as the third era full mold casting with the productions of cylinder block, cylinder head, box and intake characteristic of vacuum and dry sand modeling. This process manifold, etc. complex castings have been widely applied in the

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automobile industry. Figures 3 to 6 show typical LFC castings. The LFC process is suitable for producing box, shell and pipe castings. Fig. 2: Process chart of foam pattern production with NC machining

(a) Cylinder block (b) Electric casing Fig. 3: Engine body, electromotor shell castings and their foam patterns in LFC

(a) Foam pattern (b) Shell casting Fig. 4: Shell body casting and foam pattern in LFC

Fig. 5: Trunk body casting and foam pattern in LFC Fig. 6: An intake manifold casting and foam pattern in LFC

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The LFC technology has been widely applied to cast iron, cast steel and Al alloys in the advanced LFC technology countries such as the USA and Germany. However, in China, the LFC is mainly applied to cast iron and cast steel, and the applications of LFC to Al alloys are relatively few. LFC applied to low carbon steel still has the carburization problem. In the 1990s, the Replicast Ceramic Shell Process (Replicast CS) was proposed by SCRATA [12]. First, a foam pattern based on the part shape is prepared as a prototype, then a thin shell with fewer layers is fabricated using shell fabrication technology of investment casting outside the foam prototype. Next, the foam prototype is removed and the shell is baked. Lastly, the filling and solidification of the molten metal are completed under vacuum level after boxing and modeling. This new process solved the carburization problem of low carbon Fig. 7: Application trend of LFC in USA steel. In China, many research institutions and universities such as Shenyang Research Institute of Foundry, Tsinghua University, Harbin Institute of Technology and Huazhong University of As shown in Fig. 7, it is clear that the LFC technology of Science and Technology have also carried out research on America has entered into a mature stage. The large-scale Replicast CS. The ball valve has been successfully application of Al alloy LFC dates from the 1980s, especially produced using the Replicast CS process. in the automobile industries of America and Germany. Table 1 The wide application of LFC to Mg alloys was not reported depicts the main enterprises of Al alloy LFC in North America in China before 2000. Shanghai Jiao Tong University and and Europe [16]. Huazhong University of Science and Technology were the The first production line for Al alloy LFC was built by the first to carry out a study on LFC technology with Mg alloys. General Motor Corporation in 1985, mainly producing Al Huazhong University of Science and Technology proposed alloy cylinder blocks and cylinder heads [17-18]. In 1993, the the lost foam casting under new vacuum and low-pressure production line with an annual output of 200 thousand pieces [13] technology (Chinese Patent ZL 02115638.7) , and the motor of Al alloy cylinder heads was built by the BMW automobile shell with 2.5 mm wall thickness and exhaust pipe complex Mg Corporation, and this went into production with a 90% yield [14] alloy castings have been fabricated . In 2006, Eck corporation in 1995. Everyday Al alloy cylinder heads of 1,500 pieces located in Wisconsin, USA successfully produced AZ91Mg were manufactured. Moreover, Stanton, Montupet, Franco [15] alloy LFC castings . The technology and control of the LFC Tosi (Casti SpA) and Charleville enterprises have also built process have many difficulties because of the material properties production lines of Al alloy LFC. Based on the literature of Mg alloys; so the production and application with respect to reports [19], the output of Al alloy LFC castings from the USA LFC with Mg alloys still has not been reported. The use of LFC had reached 220 thousand tons in 2009. of Mg alloys still remains at test stages. The Al alloy LFC technology of the Western developed countries keeps ahead of China in basic theory and production 2 Research status of LFC application; especially in foam materials, liquid filling, solidification and defects control, etc. 2.1 Foreign development For the research and application of the foam materials, T. Figure 7 shows the application trend of LFC in the USA. P. Pederson added bromic compounds into foam materials to

Table 1: Main enterprises and basic situation of Al alloy LFC in North America and Europe

Company Basic situation

GM-Saturn Annual output of 10,350 tons cylinder block, cylinder head Al alloy castings and ductile iron castings GM-Powertrain Saginaw Annual output of 17,550 tons Al alloy (A356) cylinder block and cylinder head castings GM-Powertrain Massena Annual output of 36,000 tons Al alloy (319) castings (automobile engine) BMW Manufacturing Al alloys castings (6-cylinder block and head) Internet Foundry Annual output of 10,000 tons Al alloys (319/354/242) automobile engine castings Teksid Aluminum Annual output of 20,000 tons Al alloys automobile castings Alluminio Dongo Annual output of 16,000 tons Al alloys automobile castings Meco Annual output of 6,300 tons Al alloys pump body and driving box castings Mercury Marine Annual output of 5,400 tons Al alloys automobile and ship castings

299 Special Report Celebrating the th Anniversray 2004-2014 CHINA FOUNDRY Vol.11 No.4 July 2014 10 reduce the pyrolysis temperature and the pouring temperature of foam materials [20]. M. Sands and S Shivkumar [21] investigated the effect of fusion of bead particles on fold defect of Al alloy LFC; and the results showed that the fusion of bead particles could greatly increase the strength and operability of the foam pattern, which affected the decomposition of bead particles at the front of liquid metal. With increasing the degree of fusion, the flow rate in front of liquid metal reduced and temperature decreased, resulting in a significant increase in casting defects. M. Sands [22] also investigated the effect of molecular weight and density of EPS on the processes of Al alloy LFC, and pointed out that the tensile properties of foam pattern are improved with increasing molecular weight and density of EPS. Also, the filling time of the liquid metal increases, which may have a great effect Fig. 8: Production of LFC castings in China in the recent past on the castings quality. For the filling and solidification of LFC, M. R. Barone and D. A. Caulk [23] proposed the model between heat transfer, cast steel, except for low carbon steel casting. The output of decomposition of and gas diffusion; and the test data LFC castings from China reached 648 thousand tons in 2007, [28] was in agreement with the decomposition value obtained using and its yield was ranked the first in the world . The output of this model. This model could also analyze the filling process LFC castings in China achieved about 1.5 million tons in 2011. of the liquid metal and pointed out that the decomposition of However, the percentage of Al alloy LFC castings is lower the foam pattern has a significant effect on defects. Guillaume than 0.5%, and the development of LFC of Al alloys is slower Houzeaux and Ramon Codina [24] simulated the back pressure than that of cast iron and cast steel, no matter whether scale, of gas on LFC using the finite element method. Sun W L [25] technology, equipment or automation. The pinhole and shrinkage measured the filling of Al alloy LFC using an X-ray detector, defects are still problems which perplex the development of and indicated that the foam pattern with uniform density and Al alloy LFC, and some Al alloy LFC production lines coming smooth surface is suitable for LFC. D. R. Hess [26] suggested that from abroad were also not performing and did not produce the the degree of fusion and the bead type of EPS have a great effect expected quantity of castings. on the filling speed of the liquid metal. In the 1990s, Tsinghua University, Shanghai Jiao Tong With respect to defects control of castings, S. R. Shin and Z. University and Huazhong University of Science and Technology H. Lee [27] investigated the formation mechanism of a hydrogen were the first to study the LFC of Al alloys in China. The high hole during Al alloy LFC. They pointed out that the original pouring temperature of Al alloys leads to large gas absorption concentration of hydrogen in the molten metal and the reaction of Al liquid, serious oxidation and pinhole defects. That means time between liquid metal and EPS have a significant effect on there is a great gap in the key technologies of Al alloy LFC hydrogen pores. For low temperature pouring, the hydrogen compared to the advanced level. Therefore, there is a long road entered into the liquid metal from liquid EPS. However, the for the production application of Al alloy LFC in China. In hydrogen entered into the liquid metal mainly from gas and contrast, research of Mg alloy LFC began relatively early in liquid products at high pouring temperature. In addition, the China. Shanghai Jiao Tong University and Huazhong University permeability of the coating has a great effect on the formation of of Science investigated the Mg alloy LFC in 2000, and many hydrogen pores. research results at the international level have been obtained. Wu Weigang [29] studied the effect of coating properties on the 2.2 Domestic development filling ability of Al alloy LFC, and suggested that heat-insulating In 1985, the first LFC production line in China was built by the property and permeability of the coating significantly influenced Changchun Institute of Optics and Mechanics under the Chinese the filling of liquid metal. Wu Guohua [30] investigated the Academy of Science. Before the middle of the 1990s, the yield formation mechanism of pinholes in Al alloy LFC and pointed out of LFC castings in China was very low, and LFC technology has that high casting temperature, low permeability coating as well as entered a rapid development period since the 2000s, as shown in high vacuum level could reduce the pinholes in Al alloy castings. Fig. 8. Meanwhile, Al melt refinement, modification and grain refinement Compared with advanced countries, the shape and type of should be also carried out. Zhao Zhong [31] investigated the effect LFC castings in China are similar to the advanced countries. of mechanical vibration on the filling of Al/Mg alloys LFC, and However, the complexity and quality of LFC castings are very the results showed that mechanical vibration could increase the low. The LFC castings have developed from grinding ball, filling ability of the molten metal during Al and Mg alloys LFC; liner and tubular castings to crankshaft, box and cylinder block and that the filling ability increased with an increase in vibration castings. The LFC has been widely applied to cast iron and frequency and amplitude.

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Liu Zili [4] studied the effect of vacuum degree, casting 3 Development trends of LFC temperature and pattern thickness on heat transfer characteristics of AZ91 alloy LFC and suggested that the vacuum level was technology important to the filling and solidification of liquid. Fan Zitian 3.1 Lost foam casting under vacuum and low [13, 14, 32] invented the method and equipment for the lost foam pressure [13, 14, 32] casting under vacuum and low-pressure. The filling ability of Mg alloys could be greatly improved compared to gravity Lost foam casting under vacuum and low pressure process LFC; and the mis-run and cold shut of Mg alloy LFC could be combines lost foam casting and low pressure casting while effectively inhibited. Wu Hebao [33] systematically investigated maintaining the advantages of each method. The filling ability the effects of pattern density, coating thickness, casting of the molten metal is greatly improved because the filling temperature and vacuum level on filling morphology and filling is completed under controlled pressure. Compared with die speed of Mg alloy LFC under controlled gas pressure. The casting, it is less costly, and castings can be further heat-treated filling ability of Mg alloys were improved using composite to enhance strength. Also the castings have high dimensional technology and optimization process. Tian Xuefeng [34] studied accuracy and smoother surface compared to sand casting. Under the flow and heat transfer characteristics of AZ91 Mg alloy LFC counter gravity, because of the shortened running system and and suggested that pouring temperature and vacuum level were the reduction in heat loss before replacing EPS patterns, the the main factors controlling filling speed. Dong Xuanpu [35] production of castings from alloys with low heat content is investigated the corrosion behavior of the surface of Mg alloy possible with a lost foam process. Thus, near net shape castings obtained using LFC and pointed out that MgO-Al2O3-SiO2-C can be produced in high volumes, with high efficiency and low film was formed due to decomposition of EPS, which was thick cost. The melt is filled under counter gravity conditions with and dense, resulting in good corrosion resistance of Mg alloy good control at a low pressure; and the casting obtained using LFC castings compared to other processes. this new technology is dense and suitable for casting many non- ferrous alloys. Figure 9 shows the schematic diagram of lost 2.3 Technical difficulties of Al and Mg alloys foam casting under vacuum and low pressure process. LFC Currently, the research focus for LFC technology is mainly on LFC of Al/Mg alloys in China. The quality control of Al/Mg alloys LFC is very difficult due to technology and materials problems. The technical difficulties of Al/Mg alloys LFC are as follows: (1) Great heat is absorbed due to thermal decomposition of the foam pattern during the filling and pouring processes, resulting in temperature decrease and cold shut and surface blowhole defects. Consequently, increasing the filling ability is important to obtain Al/Mg castings with high quality, especially complex and thin wall Al/Mg castings. (2) The casting temperature reaches 750 to 780 ºC for Al/Mg alloys LFC which is higher by 30 to 50 ºC than that of common cavity casting. At high temperature, hydrogen absorption by Al alloys becomes serious, leading to pinhole defect. For the Mg alloy, oxidation and burning of Mg alloy also become serious, resulting in shrinkage defect. These are the main technology difficulties of Al/Mg alloys LFC. Fig. 9: Schematic diagram of LFC under low (3) Al/Mg alloys LFC requires foam pattern materials with pressure and vacuum the characteristic of gasification at low temperature. However, there is less basic research on foam pattern materials in China. Furthermore, it is also necessary to develop a coating with high Figure 10 shows comparison of Mg alloy motor castings strength, good permeability which can be adapted to Al/Mg obtained using different casting processes (with minimum wall alloys LFC. thickness 2.5 mm and pouring temperature 750 ºC). It is clear In order to solve the technical problems of Al/Mg alloys LFC that the Mg alloy casting obtained by using the lost foam casting and improve the properties of castings, many scholars have done under vacuum and low pressure process has an integrated shape considerable work and research. Some new LFC technologies and clear outline. It suggests that the lost foam casting under with respect to Al /Mg alloys are introduced in the following vacuum and low pressure process has a significant advantage paragraphs. compared to gravity lost foam casting.

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(a) LFC under low pressure and vacuum (b) LFC under gravity Fig. 10: Comparison of Mg alloy motor castings obtained using different casting processes

3.2 Lost foam casting under vibration solidification[31, 36-37]

Mechanical vibration is applied during the solidification process of casting during LFC, as shown in Fig. 11. Vbration energy induces forced convection in the molten metal. Moreover, flows induced by vibration exert external forces on dendrite arms in the flow direction. As a result, the dendrite arms will be easily fractured and broken off under the viscous drag forces. Meanwhile, the detached dendrite arms can be carried by the forced convection into the bulk melt, acting as new nuclei. With further detachment of the dendrite arms, the nucleation rate gradually increases and the grain sizes greatly decreases. Thereby, the mechanical properties of the castings are improved. Fig. 11: Schematic diagram of LFC under Consequently, lost foam casting under vibration solidification vibration solidification has the potential to be a simple, economic, and effective method. Figure 12 shows the effect of vibration during solidification on the (a) microstructure of LFC AZ91D alloy. As can be seen, the grain size of LFC AZ91D alloy gradually reduces with an increase in amplitude. Meanwhile, the microstructure of LFC ZL101 alloy obtained using the vertical vibration is significantly refined, as shown in Fig. 13. In addition, vibration also has a significant effect on the microstructure of ductile iron, and it can increase the graphite number, as shown in Fig. 14. On the other hand, the morphology of pearlite structure changes from plate to granular, as shown in Fig. 15, resulting in improvement of the properties of the ductile 100 μm iron castings [37].

(b) (c) (d)

100 μm 100 μm 100 μm

Fig. 12: Effect of vibration solidification on microstructure of LFCAZ91D alloy: (a) without vibration; (b) 50 Hz, 0.11 mm vibration; (c) 50 Hz, 0.23 mm vibration; (d) 50 Hz, 0.34 mm vibration

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(a) (b) (c)

100 μm 100 μm 100 μm

(d)

Fig. 13: Comparison of ZL101 LFC microstructure with and without vibration at 750 ºC: (a) without vibration; (b) 20 Hz, 0.23 mm vibration; (c) 40 Hz, 0.23 mm vibration; (d) 60 Hz, 0.23 mm vibration 100 μm

Fig. 14: Morphology of graphite of ductile iron: (a) 0 Hz, (b) 50 Hz

Fig. 15: Matrix microstructure of ductile iron: (a) 0 Hz, (b) 50 Hz

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3.3 Lost foam casting under pressure solidification

Lost foam casting under pressure solidification technology combines the LFC and pressure solidification technologies, and it can lead to the increase of density and mechanical properties as well as the decrease in pinhole and shrinkage defects of castings. The Vulcan Company [38] used the lost foam casting under pressure solidification technology to produce Al alloy castings. Castings toughness increased by 50% and the shrinkage rate of castings decreased from 0.75% to 0.01% compared with common LFC. Figure 16 shows the production line of LFC under pressure solidification at Mercury Castings Company. However, the cost of this method is too great because of its high gas pressure (about 10 atmospheres). Fig. 17: Schematic diagram of LFC under Huazhong University of Science and Technology invented pressure solidification the equipment and method of lost foam casting under pressure solidification for Al/Mg alloys [39], as shown in Fig. 17. The the pressure sand box and fills it with gas under pressure. As metal is poured into the pressure sand box; this rapidly seals a result, solidification of the molten metal is completed under pressure. This technology has the following advantages: simple equipment, rapid speed of pressure rise, low cost, as well as low pressure (5 - 6 atmospheres), etc. and it is suitable for production in enterprises of China. During lost foam casting under pressure solidification, the press filtration action on inter-dendritic liquid from the external force causes microstructure deformity, improving the feeding capacity of the feed head. Also, pressure solidification increases the precipitation pressure of hydrogen which inhibits the formation of pinholes. Figures 18 and 19 show the effect of pressure solidification on pinholes in LFC Al alloys and shrinkage in LFC Mg alloys, respectively. It is evident that the pinholes in LFC Al alloys and shrinkage in LFC Mg alloys are Fig. 16: Production line of LFC under pressure significantly decreased under pressure solidification, and the solidification for the Mercury Castings density of the castings is greatly improved.

(a) (b) (c) (d)

Fig. 18: Effect of pressure solidification on pinhole defect of Al alloy LFC castings: (a) 0.0 MPa, (b) 0.2 MPa, (c) 0.4 MPa, and (d) 0.6 MPa

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(a) (b)

300mm 300mm

Fig. 19: Effect of pressure solidification on shrinkage defect of Mg alloy LFC castings: (a) 0 MPa and (b) 0.6 MPa

3.4 Expendable shell casting with vacuum flexible design, low cost and shrinkage of foam, high shell and low pressure technology [40-43] precision of investment casting, as well as better formability under vacuum and low pressure casting process. Furthermore, This new shell casting process combines the foam pattern some pinhole, shrinkage porosity and slag inclusion defects as preparation of LFC, thin shell precision fabrication of well as serious hydrogen absorption of Al alloys and oxidation investment casting, as well as vacuum and low pressure casting and burning of Mg alloys for LFC at high pouring temperature technology. First, the foam pattern based on part shape is can be solved. The mis-run and cold shut can also be avoided, prepared as the prototype; and then the thin shell, with fewer especially for the complicated and thin-walled Al and Mg layers, is fabricated using shell fabrication technology of alloys precision castings. Figure 21 presents the Al alloy intake investment casting outside the foam prototype. Next, the foam manifold casting obtained using the shell casting process based prototype is removed and the shell is baked. Lastly, the molten on expendable pattern with vacuum and low pressure. metal filling and solidification are completed under air pressure The essences of the above several special LFC technologies and vacuum level after boxing and modeling. The technological are the combination of LFC and other technologies to solve process is shown in Fig. 20. porosity defect, filling ability and mechanical properties during The shell casting process based on expendable pattern with Al (Mg) alloys LFC. These technologies have corresponding vacuum and low pressure casting possesses some advantages:

Fig. 20: Technological processes of the shell casting process based on expendable pattern with vacuum and low pressure

(a) (c)

(b)

Fig. 21: Al alloy intake manifold casting obtained using the shell casting process based on expendable pattern with vacuum and low pressure: (a) Foam pattern, (b) Ceramic shell, (c) Casting

305 Special Report Celebrating the th Anniversray 2004-2014 CHINA FOUNDRY Vol.11 No.4 July 2014 10 applications and supply some possible directions for the rate, convenient operation and low cost has an important part development of LFC in the future. to play for the realization of green LFC. Figure 23 shows the purification equipment of tail gas invented at Huazhong 3.5 Other important technologies of LFC [1, 44] University of Science and Technology. Table 2 shows the data of Coating is the key factor to influence the quality of LFC tail gas after being treated by the catalytic combustion method. castings, and the development of a coating with high properties It can be seen that the output concentration of tail gas is greatly is an important aspect of LFC. The new powder coatings with reduced and the purification conversion is more than 99%. low cost, convenient operation and superior properties is always The research and application of new foam materials are the favorite product for consumers. Figure 22 shows the new currently a weakness in LFC in China and this is also one of the coating produced at Huazhong University of Science and bottleneck technologies. Therefore, it is an important aspect of Technology. progress in LFC technology to investigate the foam materials Foam materials generate harmful gases such as benzene, with good forming property, high strength, low speed of gas toluene and styrene, etc. during pouring. Thus, the development generation, and low production of gas generation. of purification equipment for the tail gas with a high purification

Fig. 22: Foam pattern coated by a new coating of LFC Fig. 23: Purification equipment of tail gas in LFC

Table 2: Data of tail gas after being treated by catalytic combustion method

Preheating Catalyst Inlet Output Environmental Conversion temperature temperature Pollutants concentration concentration / standard ℃ ℃ mg.m-3 mg.m-3 % (TJ36-79)

180 402 Benzene 758 7.4 99.0 40 200 423 Toluene 219 0.2 99.9 100 220 517 Styrene 456 2.1 99.5 40

4 Conclusions LFC is a precision casting technology for suitably producing the special LFC new methods, metal material, coating, heat large scale and complex box, shell and pipe parts. With the treatment, new foam materials as well as purification technology rapid development of aerospace and automotive industries, it of tail gas, etc. must be subject to more and more attention and applications. LFC technology has achieved much significant progress and is widely applied on cast iron and cast steel. However, the Al / References Mg alloys LFC still has some technical difficulty, and a lot of [1] Huang Naiyu, Ye Shengping, and Fan Zitian. Principle and control of lost foam casting. Wuhan: Huazhong University of Science and work is needed with more attention given to the research and Technology Press, 2004. (In Chinese) development of Al/Mg alloys LFC. In future, the development [2] Huang Tianyou, Huang naiyu, and Lv Zhigang. Lost foam casting directions of the green LFC technology is mainly focused on technology. Beijing: China , 2004. (In Chinese)

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These works are supported by the National Nature Science Foundation of China (NFSC)(No. 50275058, 50775085, 51204124, 51375187) and the National High Technology Research and Development Program of China (No. 2007AA03Z113).

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