2017 Asia-Pacific Engineering and Technology Conference (APETC 2017) ISBN: 978-1-60595-443-1

Numerical Simulation and Optimization of Casting Process for Thin-wall Long Conveying Connecting pipe He Li, Donghong Wang, Xueling Li, Jingyu Sun, Aohang Wang and Fei Li

ABSTRACT

1The long process of thin-walled conveying connecting pipe is simulated with mold filling and solidification process based on ProCAST software. The results show that the shrinkage of the connecting pipe opening of the body and the flange structure of casting pipe casting, The simulation results show that the shrinkage porosity of the pipe was located on body part and the flange structure, casting consistent with the actual experimental results. According to the simulation results, the structure of the gating system was optimized. The optimized scheme can reduce shrinkage from 30 to 10 cm3. The application of optimized pouring system is benefit to eliminating the shrinkage defect and increasing the casting yield.

_____________________ 1,b, Xueling Li1,c, Jingyu Sun1,d, Aohang Wang1, e, Fei Li2,f 1School of Materials Engineering, Shanghai University of Engineering Science, Shanghai, 201620, China 2State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai, 200240, China alihe2719@126.com, b*wdh@sues.edu.cn, calno2009@163.com, dlifei@sues.edu.cn, erjx002@sues.edu.cn, flfei@sjtu.edu.cn *He Li: lihe2719@126.com

INTRODUCTION

With the development of aerospace, defense, development of the automobile industry and other industries, large complex thin-walled tube casting requirements gradually toward less margin, high precision, and high performance [1]. But in the actual production in the current, tube casting process is long because of the thin wall filling resistance. Therefore lead to high casting rejection rate with the serious shrinkage porosity. So the development of large complex thin-walled tube casting has been the weak link in the industrial production [2-4].

At present, the rapid development of computer technology, used in the production of solidification simulation technique to accurately predict the yield and improvement of casting defects has become a trend, but also through the simulation analysis of casting can reduce the development cycle, reduce development cost, improve the finite element simulation software ProCAST based on the long process

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of conveying thin filling and solidification process of connection the tube was simulated in this paper [5]. product quality, the improvement measures were proposed in order to solve the shrinkage problem to improve the qualified rate of products.

STRUCTURE OVERVIEW

The new product development is super large conveying connecting pipe with thin wall structure, pipe diameter is 60mm, length is 840mm, and the weight of the product is 27KG, the average thickness is 4mm, from the product structure and size, it is the typical structure of thin pipes. Similar castings, the traditional casting method is sand casting, because of the casting is a special Marine desalination equipment, which used for conveying various fluid (liquid, gas), to reduce energy loss that is not necessary during transportation, the inner wall of the pipe flow parts size precision and surface roughness has high demand. Especially the transmission of acid alkali substances, have strong corrosion resistance, In the aspects of corrosion, there are also want the flow2 parts clean, so as to improve its corrosion resistance. Therefore, traditional sand casting can not meet the technical requirements for the pipeline. Nowadays some higher quality requirements, mainly adopts precision-investment castings.

Compared with large wall thickness castings, the forming of complex thin wall castings has the following 3 characteristics:

(1) The Laplace force generated by the surface tension of the liquid metal is the leading factor in the filling of the thin wall castings. The expression of the Laplace force P as follows:

P=4σ/δ (1) In the formula: σ- Surface tension of liquid metal;

δ- Wall thickness of casting. (2) The thin wall castings should be made by precision casting, the dimension

precision and the surface roughness of the castings are high demand. The reason is that the machining allowance is not reasonable.

(3) When liquid metal fillings, which are also important factors that should be considered in the whole heat transfer. The melt filling process of flow and heat transfer interaction on the casting shrinkage, temperature field and defects of misrun formation.

The casting belongs to a typical thin wall pipe structure, and the material is 304 stainless steel.

Figure 1. 3D model of connecting pipe.

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The following table is components of 304 stainless steel.

Table 1. Components of 304 stainless steel.

304 Component(%)

C 0.08

Mn 2.00

P 0.045

S 0.030

Si 1.00

Cr 18.0–20.0

Ni 8.0-11.0

RESULTS AND DISCUSSION

Analysis of the Present Process Plan

The top gating system was adopted, as shown in Figure 2. The advantages of this scheme is: when the liquid of metal flow into the mold cavity, the temperature in the top is high, and low temperature in the bottom, it is conducive to the realization of directional solidification and feeding (usually through the gate riser); simple structure, convenient modeling; liquid of metal ample flow, better mold-filling capacity, the time is short; the metal riser and pouring system has less metal consumption, after the casting is completed, the cutting of the pouring system is advantageous.

Figure 2. The present pouring system.

The present process casting schemes are simulated and analyzed by using the ProCAST software, simulation conditions follows: the transfer coefficient heat between shell and casting is 1000; the pouring temperature is 1550℃; the shell needs to be heated to 950℃; the filling speed is calculated according to the gate area and filling time. Figure 3 is the rate after solidification of connecting pipe, Figure 4 is the solidification sequence after the completion of the entire connecting pipe casting filling. The simulation results can be seen from the connecting pipe body first and

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most complete solidification, but the 6 flange structure of the pipe body and hole position is liquid phase, after the completion of solidification, shrinkage is very easy to form.

Figure 3. The solid fraction distribution after solidification of connecting pipe.

Figure 4. Solidification sequence of connecting pipe.

The solidification shrinkage distribution can be seen from Figure 5 after the simulation of the connecting pipe, 6 flange structure does not get enough feeding, there are lots of shrinkage, and some shrinkage appeared in the connection pipe body, and consistent with the actual situation.

Figure 5. The shrinkage distribution after the solidification of the connecting pipe.

Analysis and Optimization of the Present Process Plan

In this paper, a large complex thin-walled connecting pipe casting, on the whole, the wall thickness is uniform (average thickness 4mm), but thermal center appears in the individual parts of connecting pipe and heat section (including physical hot spot and geometric hot spot), so we cannot simply use sequential solidification or original scheme and solidification mode. In the actual production, the condition of large complex thin-walled structure production is more complicated, simple sequential

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solidification or simultaneous solidification is not possible. So we must adopt the solidification mode of composite casting, in other word, from the whole are solidified in the same time, but in order to individual parts of the feeding (such as flange connecting pipe and hole parts), that is the local casting sequential solidification. Therefore, in the design of gating system, it is necessary to fully consider the impact of various factors. Figure 6 is the optimal scheme of solid modeling, including casting body, gating system and riser pouring system with optimized. A side note, the inner runner opened in the flange connection pipe and open pores, to reduce the amount of shrinkage; when pouring, Steel fluid from left to right along the cut into the cavity for filling, effectively avoid the impact of molten steel wall directly; the original casting shrinkage system mainly distributed holes and flanges in the casting riser is provided at the position of casting, top riser hole position can be carried out by feeding the gravity of the steel liquid so as to improve the feeding effect of riser, but also conducive to the exhaust and scum; both sides and bottom ,3 flange arranged side riser, results show that effectively eliminate the shrinkage at the hot spot.

Figure 6. Optimization design of gating system.

The simulation analysis of the optimized scheme is carried out by using ProCAST software, simulation conditions are follows: the casting material is 304 stainless steel; the shell is mullite; the heat transfer coefficient between shell and casting is 1000; the pouring temperature is 1550℃; preheating temperature of the shell is 1000 ℃.

Through the numerical simulation of casting solidification, the sequence of solidification was shown in Figure 8. The figure shows that the optimized gating system, the connecting pipe body and flange structure basically solidification in the same time, then 6 risers, through the feeding effect of riser, the 6 flange structure in the elimination of the original casting system do not have shinkage. Finally, the runner solidification, the overall presentation of the solidification sequence from right to left, contact and gating system of phase feeding channel. Because of the 6 isolated flange structure has two gates with hot spot, the feeding effect is obvious, the result shows that hot spot of shrinkage has been effectively eliminated, it is shown in Figure 9.

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Figure 7. Optimization of the solid fraction distribution after the end of the connection tube filling.

Figure 8. Solidification sequence of optimized connecting pipe.

Figure 9 is the result of numerical simulation, compared with the original scheme, the connecting pipe at the shrinkage defect and flange casting riser tube disappeared, and the optimized scheme of shrinkage focus on internal casting system and casting riser settings, the shrinkage problem of castings has been solved and qualified rate of products has been improved.

Figure 9. The distribution of shinkage porosity in the connection pipe after the solidification.

Production Verification

Adopt The optimized design scheme, in accordance with the original production process, remanufacturing wax shell, and the final casting is shown in Figure 10. After Sampling inspection after batch production, we found that the qualified rate of castings is obviously improved.

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Figure 10. Connecting pipe casting.

CONCLUSIONS

(1) Through the numerical simulation analysis and the actual test production, it is concluded that the casting system of the long thin wall castings should adopt the side injection mode.

(2) The thinner the casting wall is, and the more complex the structure is, the greater the resistance of the casting cavity, the easier it is to produce shrinkage porosity and shrinkage cavity defects. The reasonable design of the pouring system can improve the quality of the products.

(3) According to the optimized numerical simulation results, it is known that when the pouring temperature is 1550℃, the preheating temperature of the shell is 1000℃, and the heat exchange coefficient is 1000, the quality of the casting product is the best.

ACKNOWLEDGEMENTS

This research was supported by the Foundation of Shanghai University of Engineering Science (cz1605011), School level start-up fund 2015-09 of Shanghai University of Engineering Science part by grants from Research project of Shanghai science and technology committee, graduate student research and Innovation Program of Shanghai University of Engineering Science (16KY0515), colleges and universities young teacher training plan of Shanghai (ZZGCD15099).

REFERENCES

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