Casting Defects and its Optimization Method in ...

International Conference on Advances in Materials and Manufacturing (ICAMM ‘17), January 19-21, 2017

ISBN: 978-93-86256-36-2

Casting Defects and its Optimization Method in Centrifugal Casting Process: A Review Shatrudhan Pandey1 and Sanjay Kumar Jha2 Department of Production Engineering, Birla Institute of Technology, Mesra, Ranchi, India also the various process parameters of the centrifugal casting process. Process optimization is needed to improve the casting product as per the industry standards, reduce the defect and enhance the mechanical property. The entire process was mathematically modeled and simulated by computer simulation software. Thus, optimization method helps to find the most optimum and suitable method for a centrifugal casting with enhanced quality and leads to a better productivity. (Yazad N. Doctor, 2015)

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Abstract—In today’s global competitive environment requirement of manufacturing industry is to provide high quality casting product. For production of composite materials centrifugal casting method is widely used. But the centrifugal casting method produces some defect in, it’s like macro-segregation and shrinkage hole, etc. And this directly affects the quality of casting product. And that’s why it does not meet with the requirement of different manufacturing industries. So in today’s global competitive environment, there is a need of defect free casting products with minimum production costs. These defects depend on the various process parameters of the centrifugal casting process. So for a defect free casting product, there is a need to improve the process parameter, and these can be improved by various methods in optimization. With the help of manufacturing industries, IT industry develops various computer simulation software which simulates the whole casting process and also use as one of the optimized methods in the casting process. So the optimization method eliminates the casting defect such as Micro-segregation, Shrinkage porosities and coarse grained zone, which cannot eliminate by machining. Based on this analysis an improved and optimum method was found which reduces the scarp & defect in the manufacturing of casting products. This paper gives a review on casting defect and provides a comprehensive literature review about optimization methods of casting process and shows the necessity of an investigation of the process parameters & its optimization methods. Keywords: Centrifugal Casting Defects, Optimization Method, Computer Simulation Software, Grey Fuzzy Method, Taguchi Method

A. Centrifugal Casting Process

Centrifugal casting process is most popular and appropriate for the production of various composite material. In metallurgical industries centrifugal casting is widely used for fabrication of composite materials as one of the advanced and popular casting technique. Centrifugal casting process is a liquid phase process. Its machine consists of high speed motor, which joint with a suitable sample holder which rotates around the same axis of the motor.Poured metal is solidified by compressive pressure exerting by centrifugal force. (Pai, 2009)

There are various defects identified in casting product after the centrifugal casting process. These defects are like (i) micro-segregation (ii) blow holes (iii) shrinkage porosity, etc. This highly affects the quality of casting product. The defect and quality of casting product are depending on thermal stress and solidification of the casting, which studied under the thermal analysis. The most important moment is when the molten metal solidifies, at that time thermal analysis is needed to know what will be the outcome of the casting solidification and to understand its behavior. Casting is also depending on the various process parameters of the centrifugal casting process. The process parameter of centrifugal casting is (i) Pouring temperature (ii) mold temperature (iii) pouring speed or pouring rate (iv) Speed of rotation (v) mold wall thickness. By varying this process parameter of centrifugal casting one can reduce the defect in casting product and it can also help in enhancing the mechanical property of casting product. (Malhotra, 2016), (pandey, 2016)

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B. Defects in Centrifugal Casting Process

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I. INTRODUCTION Casting is one of the prominent metals shaping techniques use to fabricate various composite materials. In the casting manufacturing process, first of all the solid metal is melted and then it is poured into the cavity which is known as mold. The function of mold is to hold the molten metal and solidify it. After solidification, it forms the desired shape and size. But there is some defect like micro-segregation, blow hole, shrinkage porosity, etc. In the resultant shaped and sized cast product. The mechanical property, quality and the requirement of cast product is also affected by this product defect. And that's why this casting product was not as per the industry standards. (J Yokesh kumar, 2015)The defect is depending upon the thermal stress and solidification of casting and 72

Casting Defects and its Optimization Method in Centrifugal Casting Process: A Review

field & solidification process is analyzed with the help of computer simulation software and finally casting became from non-visible in visible process. It eliminates the casting defect such as Microsegregation, Shrinkage porosities and coarse grained zone, which cannot eliminate by machining. It can analyze starting time for water cooling, Variation in mold, water thickness, thermal insulation criteria and coating thickness. It also uses to optimize the various process parameters of the centrifugal casting process for eliminating defects and better productivity. Based on this analysis an improved and optimum method was found which reduces the scarp & defect in the manufacturing of casting products. (Mr. Kakade K.B., 2016) Some optimization process which is used in the centrifugal casting process is as follows:

Casting Defects Can Be Classified as Follows: 1. Filling related defect. 2. Shape related defect. 3. Thermal defect. 4. Defect in appearance. (Rajesh Rajkolhe, 2014)

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Shrinkage cavity Shrinkage porosity Scarse grained zone

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1) Taguchi method This is an efficient technique for centrifugal casting which gives the optimum result in minimum no of trials. In designing an experiment in centrifugal casting process, the most important thing is to determine the combination of various factors like rotational speed, mold temperature, mold wall thickness, pouring temperature etc. Andlevels, which gives the desired and defect less casting output. Taguchi method is one of the approach to find out the assignment of factors in specific orthogonal is to know the testing combination. Taguchi method has three main phases: 1. Planning phase. 2. Conducting phase. 3. Analysis phase. In order to determine the best process design analysis is done using signal to noise ratio. So this method is used to yield the optimal parameter with significance no of various levels by influencing factor in particular output response. (Jyothi P N, 2015)

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Fig. 1: Casting Defects in Wet-type Cylinder Liner Fabricated through Centrifugal Casting (Su-Ling Lu, 2014)

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2) Grey fuzzy method This method is used for optimizing the process parameter of the centrifugal casting process to reduce the defect and enhance the mechanical property. There are various sets of process parameter. The Gray fuzzy method is for multiple criteria i.e.; It solves decision making problem. The fuzzy structure was made by two inputs and one output in the basis fuzzy rule and membership function. (Aakanksha Suryawanshi, 2015)

Fig. 2: Microstructure of Casting Materials (Aakanksha Suryawanshi, 2015)

3) Computer simulation software Computer simulation is simply a computer program. By computer simulation anything become possible can’t done by mathematical modelling. In the centrifugal casting process, the most important moment is when the molten metal solidifies, at that time thermal analysis is needed to know what will be the outcome of the casting

C. Optimization Process Process optimization is needed to improve the casting product as per the industry standards, to reduce the defect and enhance the mechanical property. The entire process was mathematically modelled and simulated by computer simulation software. Heat flow of casting, temperature 73

International Conference on Advances in Materials and Manufacturing (ICAMM ‘17)

solidification and to understand its behavior which can’t simply have done by machining. But this can be easily done by computer simulation software. Heat flow of casting, temperature field & solidification process is analyzed with the help of computer simulation software and finally casting became from non-visible in visible process. It eliminates the casting defect such as Microsegregation, Shrinkage porosities and coarse grained zone, which cannot eliminate by machining. It can analyze starting time for water cooling, Variation in mold, water thickness, thermal insulation criteria and coating thickness. (Su-Ling Lu, 2014)

computer aided casting software technique is the most efficient and accurate method for analyzing defect like weld lines, air traps and shrinkage. By this technique, quality and yield of the casting were improved in the shortest possible time and without carrying out the actual trash on the foundry shop floor. (Aakanksha Suryawanshi, 2015)They prepare Al alloy by centrifugal casting process and then optimized its process parameter by the gray fuzzy method. By this method they improve the quality of casting and reduce the defect like shrinkage and blow holes which produces during cooling process. Their objective was to finda defect with minimizing the thermal stress. They found that at 500 and 550 RPM mold speed centrifugally casting alloy produced less porosity. The cast microstructure contains carbide and laves phase, which regarded as the deleterious to the mechanical property of the alloy. (Su-Ling Lu, 2014)Repaired a model of centrifugal casting if wet-type cylinder liner based on Procast simulation software to reduce the defects in the wet type cylinder liner such as micro-segregation and shrinkage holes etc. They use the pro-cast software for analysis of the flow behavior of the metallic melt during horizontal centrifugal process. It also simulates the mold filling and temperature field of the casting process. After that, they compared the temperature field simulation result and defect which occurs in the actual casting process. From this they found that the Pro-cast software is the most suitable for horizontal centrifugal casting process. They also calculated the water cooling starting time, difference in mold wall thickness, the thickness of thermal wall insulation materials and the difference of coating thickness of the defect area with the help of temp field obtained by Pro-cast. And they found that the improved solution for actual casting process which is as (i) difference in mold wall thickness= 16 mm (ii) thickness of internal insulation material=2 mm (iii) difference in coating thickness= 1mm (iv) timing of cooling=20 Sec (v)water cooling=70 Sec (vi) air cooling =20 Sec. Casting done using this data produces less defects in WTCL. (ParthLakum, 2016)They use Pro-cast software for optimizing the shrinkage porosity and for analyzing the temperature distribution of air cooled cylinder liner block of gray cast iron. Pro-cast help to understand the heat flow of the casting. By comparing the Pro-cast result and defects produced in the actual process. They found that Pro-cast is one of the finest casting simulation software and with the help of this there is no need of the actual trial of casting onthe shop floor. It also helps in preheated the amount and location of porosity. They found that with the help of Pro-cast software, porosity amount has been found to be 2.69% in

II. LITERATURE REVIEW

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There are number of research papers available based on centrifugal casting defects and its optimization techniques some of them listed. (Jyothi P N, 2015)In this investigation, they fabricate Za-27/ Al2O3 MMC through the centrifugal casting process. They completed this experiment according to the design of experiment which was proposed by Taguchi's technique. They find the influence of melt temperature, rotational speed of mold, wt.% of particulate, the size of particulate and the distance from the Centre of ingot on hardness and ductility. For analysis of the data they use A L 25 orthogonal array and this was done by ANOVA and regression equation. They compare the experimental value with predicted values and they found that the melt temperature and wait.% of particulate have the highest influence followed by rotation speed, particulate size and diameter from the Centre. (P. Shailesh, 2014) Fabricated (Al-Si) 4600 Aluminum alloy through the centrifugal casting process and then studied the influence of process parameter on its micro-structure and mechanical properties. They use the Taguchi method for optimizing the process parameter and to reduce the defects which leads to increase the mechanical properties of the cast alloy. They investigated that increase in pouring temperature reduces the mechanical property while increase in die speed increase the mechanical properties and densities. So for fine grains in matrix, pouring temperature should be low while the speed of the die should be high. By ANOVA techniques, they analyzed the result to know the percentage contribution of each process parameter. They also analyzed the microstructure which indicates that Al concentration is more at the outer periphery. (Sandeep.v. Chavan, 2014)They optimized the casting defect using computer aided casting simulation software. By this software they provide proper runner and gating system which is very important to secure good quality of casting and also it provides a homogenous mold filling pattern. To eliminate the premature freezing of the molten metal, they added more overflow entrances at the end of the cavity. From this experiment they found that

the inner bore area which matches with the industrial output. They also found that the solidification time, which 74

Casting Defects and its Optimization Method in Centrifugal Casting Process: A Review

They simulate the liquid flow process by a simulation method which is based on the solution algorithm-volume of fraction (SOLA-VOF) techniques. By this experiment they found that there is good agreement in experimental and numerical result. From both experimental and numerical solution, it is clear that filling length and filling speed increase by increasing the rotational speed. In filling process, back process has an important role. They also found that bottom filling is better than top filling, which gives stable filling. They also found that at the wall the presence in spore is large and it's small at the Centre. The pressure decreases gradually when liquid enters into the runner or cavity and after reaching the liquid to in gate wall pressure start increasing. (Jan Bohacek, 2014) Simulation of the mold filling and solidification of outer shell that being cast and have influence in the cast defect of horizontal centrifugal casting process. They solve the axial and tangential velocity component of Shallow water equation by neglecting the momentum in radial direction. The SWE were modified centrifugal force, careless force, bed shear stress and gravity. So from this experiment they found that solidification rate decreases when the mold is covered everywhere with solid layer and further filling increases the height of liquid layer. They also found that increase in the amplitude of the free surface waves also increase the liquid height. (Cavus Falamaki, 2008)They implemented the Taguchi design of experiments for optimization of manufacture of sintered one step alumina micro filter/membrane fabricated by the centrifugal casting method for the first time. In its 10 out.% alumina aqueous slip containing T iron (0.001 g/g alumina) as dispersion and PVA as a binder was used. For controlling parameter, they selected 3 level accelerations, 3 level slip volumes, 3 level binder content and 2 levels PH. They discussed three target function (i) the product of the top layer porosity time (ii) product of permeability times thickness (iii) membrane curvature. From the overall experiment they found that (i) fir improving the centrifugal processing route for the membrane support manufacture Taguchi method was most appropriate method (ii) a major membrane supper characteristic is the product of surface porosity x which is reciprocal of surface average pore diameter. (Sourabh Sharma, 2016) Analysis of the Taguchi method to find the pipe thickness of IS-3989 cast iron pipe which fabricated through the centrifugal casting process. In this experiment they controlled the various parameters like pouring temperature, mold spinning speed and coolant flow rate. They proceed this experiment by ANOVA analysis and found the optimum parameter (i) pouring temperature = 1325 C (ii) mold spinning speed= 1000 RPM (iii) coolant flow rate= 15 lit/min and other contributions of other parameter are (i) mold spinning speed 54.336% (ii) pour

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is 159.56 seconds. (Ragaie M. Rashad, 2015) Fabricated by the mathematical modelling of bimetallic roll fabricated by the method of centrifugal casting with rotation of mold around the horizontal axis. They experimentally found the hardest, micro-structure and residual stress. They also simulate the whole process using Pro-cast software and found that the compressive tangential stress found at the outer periphery due to this corrosion effect was reduced and fatigue life was increased. They also investigated from a mold that compressive radial stress was near the interface of the two metals and it helped in reducing the tendency of separation. The stress was obtained by numerical solution method and compared with the residual stress at six measured locations. It can be reduced by cooling the casting inside the mold. They also investigated about the pouring time and found that the earlier the liner layer is poured, the less are the residual stress. Residual stress can be increased by increasing the mold speed. They also found that cooling with will result in smaller residual stresses. (Limin Jia, 2012) Worked on the basis of numerical simulation and experimental procedure to analyze the defects in casting of Ti-6Al-4V alloy by vertical centrifugal casting process on graphite molds. This experiment was done at different-different vertical centrifugal casting conditions. From this experiment they found that this method was most suitable for reducing the defect severity. When the mold rotation increases from 0 to 210 RPM, the numerical percentage of defect-visiblespecimens start decreasing from 62.4% to 24.8%. When the gravitational coefficient was increased, the quantity of macro pore defects starts decreasing exponentially. But it starts increasing when the mold rotating ratio decreased. More defect is caused when casting was made earlier and longer mold filling path because more inclusions and gas pore will be easily entrapped in alloy melt. So that mold filling process is also influenced the casting process. (P. G. Mukunda, 2010)They prepared Al-2Si by a centrifugal casting method with different-different mold rotational speed. As we know that rotational speed affects the final casting. In this experiment they found an optimum speed for reducing the defect in the final cast. And from this experiment they found that at lower and extremely high rotational speed, the metal disturbs the position, hence the pattern become irregular. They found a uniform cylinder at optimum speed which is 800 RPM. At this optimum speed, the mechanical property offinal cast was also improved and forms a fine equated primary alpha-Al grains. At optimum speed, wear rate was decreased and it also reduces more by sliding velocity. (WU Shi-ping', 2006) Prepared mathematical model of the centrifugal filling process. They calculated that the centrifugal field has an important influence on the centrifugal fill process.

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International Conference on Advances in Materials and Manufacturing (ICAMM ‘17) [4]

temperature 30.133% and (iii) coolant flow rate is 10.556%.

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III. CONCLUSION

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Casting defect is very serious problem for all manufacturing industries. When the casting undergoes machining in various conventional centrifugal casting machine and after machining finding a casting blow-hole, shrinkage hole, micro segregation or other defect not only leads to the whole casting rejected, but also there is an economic loss as the machining is very expensive and also there is wastage of time. So this defect should be minimized and it should be minimized by optimizing the process parameter of the centrifugal casting process. Optimization method not only reduces the defect, but also enhance the mechanical property of the casting product. In this paper there are few literature surveys regarding optimization method like Computer Aided Simulation software, Pro-cast software, Grey Fuzzy method, Taguchi method etc. And from this survey, it is proved that optimization method is the most optimum and suitable method of centrifugal casting process and its leads to the better production of casting materials.

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ACKNOWLEDGMENT

The Author expresses his deep gratitude and thankfulness to Dr. Vinay Sharma for their valuable guidance, and all those personnel of department of production engineering BIT Mesra, Ranchi, who has directly or indirectly supported in his work. REFERENCES

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