DESIGN AND ANALYSIS OF GATING SYSTEM FOR SB-CNC TAIL STOCK BASE CASTING

Transcription

1 DESIGN AND ANALYSIS OF GATING SYSTEM FOR SB-CNC TAIL STOCK BASE CASTING Rohith K R 1, Rahul R 2, Liroy Oppan 3, Sheryl John 4, Amal Mohan 5, Renjith Venugopal 6, Susruthan A S 7 Bessy Paul 8, Saravanan B K (B-Tech student,department of Mechanical Engineering, Nirmala College of Engineering, Thrissur, Kerala, India) 8 (Deputy Engineer, Design section, Hindustan Machine Tool Ltd, Kalamassery, Kerala,India) 9 (Assistant Professor, Department of Mechanical Engineering, Nirmala College of Engineering, Thrissur, Kerala, India) ABSTRACT The aim is to design and analyze the gating system for SB-CNC tail stock base casting with an intention of reducing the cast defects. The assignment given by Hindustan Machine Tool Ltd, Kalamassery was to find a solution to reduce the cast defects of SB-CNC tail stock base casting. On this we had conducted studies on the existing gating system in search for the reasons of the cast defects. Based on the studies conducted with the help of product planning and testing (ppt) department, we found out various factors affecting the cast quality. Some of the major factors affecting the quality of the casting are blow holes, shrinkage and porosity. Significant amount of cast iron are being used to fabricate components such as engine blocks, cylinder heads, lathe parts etc. Production of cast iron castings is a complex process which involves many parameters that affect the quality of castings. In this project, a new approach is attempted to produce sand grey cast iron casting of tail stock base by computer simulation through experimental validation in a cast iron foundry. The gating system for SB-CNC tail stock base casting is simulated by means of finite element simulation software (ANSYS) Keywords: Gating system, optimization, CFD Analysis 1. INTRODUCTION Casting is the process of producing metal/alloy component parts of desired shapes by pouring the molten metal/alloy into a prepared mould (of that shape) and then allowing the metal/alloy to cool and solidify. The solidified piece of metal/alloy is known as casting [1].Incasting process, gating system plays an important role to produce a high quality casting. A poorly designed gating system results in casting defects. A gating system controls mould filling process. The main function of gating system is to lead clean molten metal from ladle to the casting cavity ensuring smooth, uniform and complete filling. The flow of molten metal after being poured is a transient phenomena accompanied by turbulence, separation of the flow from the boundaries, dividing and combined flow at the junction, simultaneous heat transfer during the flow and onset of solidification. Moreover melt properties like density, viscosity and surface tension are continuously changing during the flow. All this together makes the filling analysis quite complex. An optimized gating design must satisfying this entire requirement.all the assumptions were made according to the rules given by P.N Rao [1].All the formulas used in this project are taken from this book. V.Gopinath [2] employed a plate casting of dimension 240x150x25 mm with the combination of different riser dimensions. Cylindrical riser of hemispherical bottom with H/D=1 were taken for his analysis. Solidification simulation was made with ANSYS software, then the solidification time and optimal riser diameters were compared with experimental results. Manjunath Swamy H M [3] optimized the gating and risering system by using casting simulation software ADSTEFAN. Through several simulation iterations, it was concluded that defect free casting could be obtained by modifying the initial gating ratio 2:2:1 to 2:1.76:1, by shifting the location of sprue from centre to end and by providing the risers at location prone to formation of shrinkage porosity which led to the decrease in size of the shrinkage porosity about 97%

2 M. Masoumi [4] experimented a direct observation method in which he showed various flow patterns resulting from different gating designs and they were recorded by a video camera and further analyzed by a computerized system. The experimental results indicated that the geometry and size of the gate and the ratio of the gating system could have a great influence on the pattern of mold filling Prof. Karl B. Rundman [5] has well explained about all sand casting process and other casting process, melting of metals and alloys, fluid flow and gating design solidification and processing of metal castings accounts for defects in metal casting P.Prabhakara Rao [6] discussed a newly developed simulation tool and its application to a crusher component that was prototyped via sand casting route. Results of casting trials showed a high level of confidence in the simulation tool known as Pro CAST. Pro CAST is a three dimensional solidification and fluid flow package developed to perform numerical simulation of molten metal flow and solidification phenomena in various casting processes, primarily die casting (gravity, low pressure and high pressure die casting) and sand casting. Sarath Paul [7] and Rathish R [7] designed cylindrical riser of hemispherical bottom with h/d=1.3 is considered for analysis. Solidification simulation is made with ANSYS software to compute solidification time and optimal riser combinations to obtain defect free castings in the shop floor. The experimental results revealed that the simulation performed using ANSYS holds good to produce defect free cast iron castings in the foundry. 2. DESIGN OF GATING SYSTEM Existing design Table.1 Specifications of existing gating system Parameters Equation used Result Gating system Gate type Pressurized gating Parting line gating Runner type Rectangular Sprue type Cylindrical Mass of casting ρ = 114 kg Pouring time t = k [ seconds Mass of metal poured Casting yield= kg Pouring rate Pouring rate= 7.29 kg/sec Chock area A c= 1416 mm 2 Gating ratio A s: A r: A g 1.1: 0.8: 1 Sprue area A s =1.1 A g 1540 mm 2 Runner area A r=0.8 A g 1200 mm 2 Ingate area A c= A g 1416 mm 2 Sprue well Sprue well area= 3 A s 4770 mm 2 Diameter of riser 100 mm Height of riser 60 mm N.Jayakumar [8], Dr.S.Mohanamurugan [8], Dr.R.Rajavel [8] has well explained about design of gating system for a pump casing and also about the generation of hot spots and its remedies John Campbell [9] and Richard A [9] give an idea on how to design a shrinkage free casting Optimizing design Caine s equation, X= X=.[1] V V Mane [10], Amit Sata [10] and M Y Khire [10], as well explained about cast defects and its classifications. Y= h=d = 140 mm (for side riser h=d)

3 Here Modulus of riser is 1.1 times that of modulus of casting. Therefore, design is safe. Optimized design Table.2 Specifications of optimized gating system Parameters Equation used Result Gating ratio A s: A r: A g 1.1:1: 1 Runner area A r=1 A g 1416 mm 2 Runner type Trapezoidal Diameter of 140 mm riser Height of riser 140 mm 3. COMPUTER SIMULATION In the past, the optimal gating design was achieved by trial and error method. Conventional method is time consuming and ineffective, can no longer satisfies the needs of the foundry. This problem can be addressed with the use of computer aided design/engineering technique. Computer design and casting simulation have gradually become popular in recent years. With the help of the computer a number of CAD/CAM commercial packages for the simulations of the casting have been developed and Implemented in the foundry. In this work, ANSYS 14.5 version software has been used to find the optimum gating system forsb-cnc tail stock base casting. Simulation process facilitates to visualize the pressure and velocity distribution in various locations of the casting. Assumptions incorporated It is difficult to incorporate all the environmental condition existing in the foundry; hence the following assumptions were made during simulation. Preprocessing The pre-processing process contains the following commands to create a finite element model. They are as follows: Model Defining Element and Options Defining Element Real constants Defining Material Properties Creating Model Geometries Defining Meshing controls Applying Boundary conditions. The model is created in solid works and it is saved in.iges format and then it is imported to ANSYS for the solution to obtain. Figure 1 Solid works model The mould is filled instantaneously and uniform temperature is assumed at all points of the casting and mould, at that instant. Heat transfer by convection takes place to the atmosphere from the outer surface of the mould and top surface of riser and runner. The convective heat transfer within the liquid metal is neglected for sand moulds. Figure 2 Casting Model Imported into ANSYS Software in.iges Format

4 Once the model has been subjected to various boundary conditions ANSYS solves the set of equations generated by Finite Element Model. Velocity contour Computer simulation using ANSYS The casting and mould assembly is modeled in the Pre-processor stage of simulation. One half of the casting and mould assembly is modeled as it is symmetric. Properties of grey cast iron Density= 7200 kg/m 3 Specificheat at constant pressure, c p = 0.46 kj/kg K Thermal conductivity, k= 46 w/mk Dynamic viscosity,µ= kg/ms Figure 5 Velocity contour of existing design Comparison between existing and optimized design Pressure contour Figure 6 Velocity contour of optimized design Figure 3 Pressure contour of existing design Figure 4 Pressure contour of optimized design 4. RESULT AND DISCUSSION The analysis given by the ANSYS shows that the negative pressure in optimized gating system is less than that of existing gating system that the negative pressure in optimized gating system is less than that of existing. 5. CONCLUSION A gating system was designed and optimized to produce SB-CNC tail stock base casting using green sand mould and a pressurized gating system with a gating ratio of 1.1:1:1. Through this design, a low turbulence uniform filling of mould cavities, lamina flow through the runner and in gates to the mould cavity and minimizes air entrapment in the mould cavity was obtained. Thereby reduces the rejection rate of the casting. From the CFD study, it is obtained

5 that the optimised gating system provides better result. Gating system design in casting process is one of the crucial factors to produce good quality of casting product ACKNOWLEDGEMENT This paper is the outcome of hard work with the help and cooperation from many sources. We express our gratitude and sincere thanks to college management, professor K Vijayan Raja, head department of mechanical engineering for the encouragement given to us. [8] Design and analysis of gating system for pump casing N.Jayakumar et al. / International Journal of Engineering and Technology (IJET) [9] John Campbell and Richard A. Harding, The Feeding of Castings, Training in Aluminum Application Technologies, (TALAT) Lecture 3206, [10] V V Mane, Amit Sata and M Y Khire, New Approach to Casting Defects Classification and Analysis Supported by Simulation. REFERENCES [1]P.N Rao, Production Technology, Edition1 (volume 3) [2] V.Gopinath, N.Balanarasimman, Effect of Solidification Parameters on the Feeding Efficiency of LM-6 Aluminum Alloy Casting, IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) ISSN: Volume 4, Issue 2 (Nov. - Dec. 2012), [3] Manjunath Swamy H.M, J.R.Nataraj, C.S.Prasad, Design Optimization of Gating System by Fluid Flow and Solidification Simulation for Front Axle Housing, International Journal of Engineering Research and Development,vol.4,PP.83-88,October [4] M. Masoumi, H. Hu, Effect of Gating Design on Mold Filling, Transactions of the American Foundry Society, Vol-113,Pg ,2005. [5] Prof. Karl B. Rundman, METAL CASTING, Reference Book for MY4130, 1986 [6] P.Prabhakara Rao, G.Chakraverthi,A.C.S.Kumar, B.Balakrishna, Application of Casting Simulation for Sand Casting of a Crusher Plate, International Journal of Thermal Technologies, Vol.1.No.1 (Dec2011) [7] Simulation and experimental validation of feeding efficiency FG 260 grey cast iron castings International Journal of Engineering Research and General Science Volume 2, Issue 6, October- November,