- Email: [email protected]
Modelling and experimental investigation of solidification process in sand casting
Journal of Materials Processing Technology 155–156 (2004) 1723–1726
Modelling and experimental investigation of solidification process in sand casting S. Sulaiman∗ , A.M.S. Hamouda Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
Abstract This paper describes the simulation and experimental results of thermal analysis in sand casting process. Simulation model of 2-ingate mould and 3-ingate mould of sand casting are developed. The analysis was done by concentrating on chosen nodes as references. The change of temperature in the casting and sand with time was monitored. The heat was transferred from the casting to sand and from sand to surroundings. In order to verify the predicted results, experiments were carried out. Two types of experiments were carried out, i.e. 2-ingate mould and 3-ingate mould. The results revealed that the sand points of 3-ingate moulds give higher temperature than 2-ingate mould. For cast points, temperature of 2-ingate moulds dropped faster than the 3-ingate moulds. The temperature gradient was recorded in the casting cycle. The predicted results were then compared with experimental data and agreement between them was reported. © 2004 Elsevier B.V. All rights reserved. Keywords: Thermal; Modelling; Sand casting; Network analysis
1. Introduction Casting is the oldest known process to produce metallic components. The first metal casting was done using stone and metal moulds during the period of 4000–3000 BC. Since then, various casting processes have been developed. In casting, the liquid material is poured into a cavity (die or mould) corresponding to the desired geometry. The shape obtained in the liquid material is now stabilised, usually by solidification, and can be removed from the cavity as a solid component [1]. One of the oldest casting methods is sand casting. It consists of placing a pattern (having the shape of the desired casting) in sand to make an imprint, incorporating a gating system, filling the resulting cavity with molten metal, allowing the metal to cool until it solidifies, breaking away the sand mould, and removing the casting [2]. Computer simulation of sand casting is becoming more significant nowadays. Therefore, it has grown rapidly with increasing sophistication of computer hardware and software. One of the main forms of simulation is a model of sand casting operation intended to determine the viability of the process or to improve its product quality. Besides that, computer simulation has the ability to generate or sim∗ Corresponding author. E-mail address: [email protected] (S. Sulaiman).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.04.153
ulate results for recurring processes at tremendous speed. The process has been modelled using various mathematical schemes [3].
2. Mathematical model For all transient casting heat transfer analysis, there is heat transfer by conduction and a temporal depletion of energy from the molten metal to cause its solidification [4]. This physics must be embodied into the mathematical basis for the process. There are three types of heat flow have been modelled. These are: 1. homogenous link; 2. interfaced link; 3. coolant link. Generally the heat flow through homogenous materials is given by [5,6]: q = −kA
dT dx
which can be converted into a matrix form as 1 T1 Q1 kA 1 = L −1 −1 T2 Q2
1724
S. Sulaiman, A.M.S. Hamouda / Journal of Materials Processing Technology 155–156 (2004) 1723–1726
In a transient analysis, energy is removed from the system by conduction, and this transient energy loss per unit volume can be expressed as [7] ˚ = ρC E
dT dt
or where phase change takes place over a finite temperature interval: ˚ =ρ E
dH dT dT dt
In discretised form, at time step ‘j’ the above equation can be expressed as j dH TiJ+1 − Ti ˚ =ρ E dT t Fig. 1. Thermocouple position in 2-ingate mould.
As explained in [2], the general form of the matrix equation can be written as []C + t[K]{T j+1 } = [C]{T j } Using this basis, the heat capacity matrix [C] needs to be recalculated at each time step to account for phase change and where nonlinear thermal conductivity {k(T)} is present, the equation set needs to be solved iteratively within each step with an update of the thermal conductivity at each iteration [3].
3. Experiment The equipment required for this experiment consists of: (a) thermocouple for temperature measurement, (b) equipment for melting and pouring metal, (c) computer hardware and software for execution of instruction program and real-time data collection, (d) thermocouple for temperature measurement, (e) equipment for melting and pouring metal, (f) computer hardware and software for execution of instruction program and real-time data collection.
4. Model There are two sand moulds involved in this study. These are: (a) 2-ingate mould; (b) 3-ingate mould. Fig. 1 shows the layout and positions of the 10 points of 2-ingate mould. Thermocouple wires are fixed to these points accordingly. Fig. 2 shows the layout and positions of the 10 points of 3-ingate mould. The positions of the points are same as in 2-ingate mould except the point 4.
Fig. 2. Thermocouple position in 3-ingate mould.
Basically the analysis of the model is three-dimensional. In generating the mesh model, the moulds are divided into many elements. Smaller elements will produce more accurate results but too many elements will make the pre-processor more complicated. This is because both the mesh model generation and pre-processor are done manually. Due to these reasons the thickness of the model is assumed to be one unit. Therefore, grid refinement is only done at the cast to mould interface where thermal gradients are steep in order to achieve adequate representation of the heat transfer [3].
5. Results and discussions Two types of results have been analysed: (i) 2-ingate mould; (ii) 3-ingate mould.
S. Sulaiman, A.M.S. Hamouda / Journal of Materials Processing Technology 155–156 (2004) 1723–1726 90
700
80
600 Temperature (ºC)
Temperature (ºC)
70 60 50 40 30
1725
500 400 300 200
20
Thermnet Experimental
Thermnet Experimental
100
10 0
0 20 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200
0 20 60 12 18 0 0 24 0 30 0 36 42 0 0 48 0 54 60 0 0 66 0 72 78 0 0 84 90 0 0 96 10 0 2 10 0 8 11 0 4 12 0 00
0
Time (s)
Time (s)
Fig. 5. Temperature curves of point 6 (2-ingate). Fig. 3. Temperature curves of point 3 (2-ingate).
In comparing the simulation with experimental results at various locations, points have been chosen in which both simulation and experimental are presented at the same coordinate locations as possible. However, for certain location, the mesh is coarse. Therefore, the agreement between model and experiment is not very close for some of the graphs. Basically for all sand points, the experimental temperature curves are above the modelling ones for most of the time. The shapes of curves are generally the same for both modelling and experimental as shown in Figs. 3 and 4. However, for the experimental curves, the temperatures are fluctuating whereas for modelling, the temperatures change smoothly. All the cast points have almost similar graphs where in the initial stage, the experimental curves are lower than modelling. These are shown in Figs. 5 and 6. At the later stage, the results are the opposite. For the initial stage, the experimental curves are lower most probably because of the low pouring rate of molten metal into
the mould. Slow pouring of the molten metal will increase the contact time between the metal and air, thus cooling the molten metal even greater. That is the reason the starting temperatures of experimental curves are lower. At later stage, the experimental curves are higher compare to modelling. This is because of trapped air and porosity in the sand mould that reduce the heat transfer rate from the cast to the sand and surroundings. So, generally all the points display experimental curves above modelling curves. This is absolutely true because for modelling, air is not considered in the calculation of the program. There is a lot of porosity in the sand mould. To be accurate, the trapped air should be taken into account as well because there is large portion of the sand mould that consists of air. Air has poor thermal conductivity. Therefore, in the experiment, the temperatures are higher and the cooling rate is lower. This problem can be overcome by carrying out an experiment to determine the parameters of the combination of sand and air together. 600
120 500
Temperature (ºC)
80 60 40 Thermnet Experimental
20
400
300
200 Thermnet Experimental
100
Time (s) Fig. 4. Temperature curves of point 3 (3-ingate).
10 30 90 15 0 21 0 27 0 33 0 39 0 45 0 51 0 57 0 63 0 69 0 75 0 81 0 87 0 93 0 99 10 0 5 11 0 1 11 0 70
0
0 0 20 60 12 0 18 0 24 0 30 0 36 0 42 0 48 0 54 0 60 0 66 0 72 0 78 0 84 0 90 0 96 10 0 2 10 0 8 11 0 4 12 0 00
Temperature (ºC)
100
Time (s)
Fig. 6. Temperature curves of point 6 (3-ingate).
1726
S. Sulaiman, A.M.S. Hamouda / Journal of Materials Processing Technology 155–156 (2004) 1723–1726
6. Conclusion
References
Generally, the developed computer-code is capable of generating good results based on network technique. Nevertheless, the most important of all, the properties of materials involved must be correct in order to obtain accurate results. In comparing modelling with experimental results, the experimental temperature curves are generally higher than modelling for mould. This is because trapped air and porosity of the sand mould. Since the sand mould has a lot of air gaps, the temperature should be higher than expected in the simulation.
[1] S. Kalpakjian, Manufacturing Engineering and Technology, 3rd ed., Addison-Wesley, 1995. [2] R. Gregg Bruce, M.M. Tomovic, J.E. Neely, R.R. Kibbe, Modern Materials and Manufacturing Processes, 2nd ed., Prentice-Hall, 1998. [3] S. Sulaiman, D.T. Gethin, A network technique for analysis of the thermal transient casting process, Pertanika J. Sci. Technol. 4 (2) (1996) 251–261. [4] R.W. Lewis, M.T. Manzari, D.T. Gethin, Shape optimization in casting design, in: Proceedings of the ECCM’99 Conference, ECCM’99, Munich, Germany, 1998, pp. 1–16. [5] M.T. Manzari, R.W. Lewis, D.T. Gethin, Thermal optimization in casting design, in: Proceedings of the ISME2000 Conference, Sharif University of Technology, Tehran, May 16–19, 2000. [6] M.T. Manzari, R.W. Lewis, D.T. Gethin, J.T. Cross, Towards optimum shape in casting design, in: Proceedings of the OptiCON’98 Conference on Altair Computing, Newport, Beach, CA, 1998, pp. 5.1–5.6. [7] T.D. Eastop, A. McConkey, Applied Thermodynamics for Engineering Technologists, Longman, 1997.
Acknowledgements The project is financially supported by Intensification of Research in Priority Area (IRPA), under The Ministry of Science, Technology and Environment, Malaysia.
Modelling and experimental investigation of solidification process in sand casting S. Sulaiman∗ , A.M.S. Hamouda Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
Abstract This paper describes the simulation and experimental results of thermal analysis in sand casting process. Simulation model of 2-ingate mould and 3-ingate mould of sand casting are developed. The analysis was done by concentrating on chosen nodes as references. The change of temperature in the casting and sand with time was monitored. The heat was transferred from the casting to sand and from sand to surroundings. In order to verify the predicted results, experiments were carried out. Two types of experiments were carried out, i.e. 2-ingate mould and 3-ingate mould. The results revealed that the sand points of 3-ingate moulds give higher temperature than 2-ingate mould. For cast points, temperature of 2-ingate moulds dropped faster than the 3-ingate moulds. The temperature gradient was recorded in the casting cycle. The predicted results were then compared with experimental data and agreement between them was reported. © 2004 Elsevier B.V. All rights reserved. Keywords: Thermal; Modelling; Sand casting; Network analysis
1. Introduction Casting is the oldest known process to produce metallic components. The first metal casting was done using stone and metal moulds during the period of 4000–3000 BC. Since then, various casting processes have been developed. In casting, the liquid material is poured into a cavity (die or mould) corresponding to the desired geometry. The shape obtained in the liquid material is now stabilised, usually by solidification, and can be removed from the cavity as a solid component [1]. One of the oldest casting methods is sand casting. It consists of placing a pattern (having the shape of the desired casting) in sand to make an imprint, incorporating a gating system, filling the resulting cavity with molten metal, allowing the metal to cool until it solidifies, breaking away the sand mould, and removing the casting [2]. Computer simulation of sand casting is becoming more significant nowadays. Therefore, it has grown rapidly with increasing sophistication of computer hardware and software. One of the main forms of simulation is a model of sand casting operation intended to determine the viability of the process or to improve its product quality. Besides that, computer simulation has the ability to generate or sim∗ Corresponding author. E-mail address: [email protected] (S. Sulaiman).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.04.153
ulate results for recurring processes at tremendous speed. The process has been modelled using various mathematical schemes [3].
2. Mathematical model For all transient casting heat transfer analysis, there is heat transfer by conduction and a temporal depletion of energy from the molten metal to cause its solidification [4]. This physics must be embodied into the mathematical basis for the process. There are three types of heat flow have been modelled. These are: 1. homogenous link; 2. interfaced link; 3. coolant link. Generally the heat flow through homogenous materials is given by [5,6]: q = −kA
dT dx
which can be converted into a matrix form as 1 T1 Q1 kA 1 = L −1 −1 T2 Q2
1724
S. Sulaiman, A.M.S. Hamouda / Journal of Materials Processing Technology 155–156 (2004) 1723–1726
In a transient analysis, energy is removed from the system by conduction, and this transient energy loss per unit volume can be expressed as [7] ˚ = ρC E
dT dt
or where phase change takes place over a finite temperature interval: ˚ =ρ E
dH dT dT dt
In discretised form, at time step ‘j’ the above equation can be expressed as j dH TiJ+1 − Ti ˚ =ρ E dT t Fig. 1. Thermocouple position in 2-ingate mould.
As explained in [2], the general form of the matrix equation can be written as []C + t[K]{T j+1 } = [C]{T j } Using this basis, the heat capacity matrix [C] needs to be recalculated at each time step to account for phase change and where nonlinear thermal conductivity {k(T)} is present, the equation set needs to be solved iteratively within each step with an update of the thermal conductivity at each iteration [3].
3. Experiment The equipment required for this experiment consists of: (a) thermocouple for temperature measurement, (b) equipment for melting and pouring metal, (c) computer hardware and software for execution of instruction program and real-time data collection, (d) thermocouple for temperature measurement, (e) equipment for melting and pouring metal, (f) computer hardware and software for execution of instruction program and real-time data collection.
4. Model There are two sand moulds involved in this study. These are: (a) 2-ingate mould; (b) 3-ingate mould. Fig. 1 shows the layout and positions of the 10 points of 2-ingate mould. Thermocouple wires are fixed to these points accordingly. Fig. 2 shows the layout and positions of the 10 points of 3-ingate mould. The positions of the points are same as in 2-ingate mould except the point 4.
Fig. 2. Thermocouple position in 3-ingate mould.
Basically the analysis of the model is three-dimensional. In generating the mesh model, the moulds are divided into many elements. Smaller elements will produce more accurate results but too many elements will make the pre-processor more complicated. This is because both the mesh model generation and pre-processor are done manually. Due to these reasons the thickness of the model is assumed to be one unit. Therefore, grid refinement is only done at the cast to mould interface where thermal gradients are steep in order to achieve adequate representation of the heat transfer [3].
5. Results and discussions Two types of results have been analysed: (i) 2-ingate mould; (ii) 3-ingate mould.
S. Sulaiman, A.M.S. Hamouda / Journal of Materials Processing Technology 155–156 (2004) 1723–1726 90
700
80
600 Temperature (ºC)
Temperature (ºC)
70 60 50 40 30
1725
500 400 300 200
20
Thermnet Experimental
Thermnet Experimental
100
10 0
0 20 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200
0 20 60 12 18 0 0 24 0 30 0 36 42 0 0 48 0 54 60 0 0 66 0 72 78 0 0 84 90 0 0 96 10 0 2 10 0 8 11 0 4 12 0 00
0
Time (s)
Time (s)
Fig. 5. Temperature curves of point 6 (2-ingate). Fig. 3. Temperature curves of point 3 (2-ingate).
In comparing the simulation with experimental results at various locations, points have been chosen in which both simulation and experimental are presented at the same coordinate locations as possible. However, for certain location, the mesh is coarse. Therefore, the agreement between model and experiment is not very close for some of the graphs. Basically for all sand points, the experimental temperature curves are above the modelling ones for most of the time. The shapes of curves are generally the same for both modelling and experimental as shown in Figs. 3 and 4. However, for the experimental curves, the temperatures are fluctuating whereas for modelling, the temperatures change smoothly. All the cast points have almost similar graphs where in the initial stage, the experimental curves are lower than modelling. These are shown in Figs. 5 and 6. At the later stage, the results are the opposite. For the initial stage, the experimental curves are lower most probably because of the low pouring rate of molten metal into
the mould. Slow pouring of the molten metal will increase the contact time between the metal and air, thus cooling the molten metal even greater. That is the reason the starting temperatures of experimental curves are lower. At later stage, the experimental curves are higher compare to modelling. This is because of trapped air and porosity in the sand mould that reduce the heat transfer rate from the cast to the sand and surroundings. So, generally all the points display experimental curves above modelling curves. This is absolutely true because for modelling, air is not considered in the calculation of the program. There is a lot of porosity in the sand mould. To be accurate, the trapped air should be taken into account as well because there is large portion of the sand mould that consists of air. Air has poor thermal conductivity. Therefore, in the experiment, the temperatures are higher and the cooling rate is lower. This problem can be overcome by carrying out an experiment to determine the parameters of the combination of sand and air together. 600
120 500
Temperature (ºC)
80 60 40 Thermnet Experimental
20
400
300
200 Thermnet Experimental
100
Time (s) Fig. 4. Temperature curves of point 3 (3-ingate).
10 30 90 15 0 21 0 27 0 33 0 39 0 45 0 51 0 57 0 63 0 69 0 75 0 81 0 87 0 93 0 99 10 0 5 11 0 1 11 0 70
0
0 0 20 60 12 0 18 0 24 0 30 0 36 0 42 0 48 0 54 0 60 0 66 0 72 0 78 0 84 0 90 0 96 10 0 2 10 0 8 11 0 4 12 0 00
Temperature (ºC)
100
Time (s)
Fig. 6. Temperature curves of point 6 (3-ingate).
1726
S. Sulaiman, A.M.S. Hamouda / Journal of Materials Processing Technology 155–156 (2004) 1723–1726
6. Conclusion
References
Generally, the developed computer-code is capable of generating good results based on network technique. Nevertheless, the most important of all, the properties of materials involved must be correct in order to obtain accurate results. In comparing modelling with experimental results, the experimental temperature curves are generally higher than modelling for mould. This is because trapped air and porosity of the sand mould. Since the sand mould has a lot of air gaps, the temperature should be higher than expected in the simulation.
[1] S. Kalpakjian, Manufacturing Engineering and Technology, 3rd ed., Addison-Wesley, 1995. [2] R. Gregg Bruce, M.M. Tomovic, J.E. Neely, R.R. Kibbe, Modern Materials and Manufacturing Processes, 2nd ed., Prentice-Hall, 1998. [3] S. Sulaiman, D.T. Gethin, A network technique for analysis of the thermal transient casting process, Pertanika J. Sci. Technol. 4 (2) (1996) 251–261. [4] R.W. Lewis, M.T. Manzari, D.T. Gethin, Shape optimization in casting design, in: Proceedings of the ECCM’99 Conference, ECCM’99, Munich, Germany, 1998, pp. 1–16. [5] M.T. Manzari, R.W. Lewis, D.T. Gethin, Thermal optimization in casting design, in: Proceedings of the ISME2000 Conference, Sharif University of Technology, Tehran, May 16–19, 2000. [6] M.T. Manzari, R.W. Lewis, D.T. Gethin, J.T. Cross, Towards optimum shape in casting design, in: Proceedings of the OptiCON’98 Conference on Altair Computing, Newport, Beach, CA, 1998, pp. 5.1–5.6. [7] T.D. Eastop, A. McConkey, Applied Thermodynamics for Engineering Technologists, Longman, 1997.
Acknowledgements The project is financially supported by Intensification of Research in Priority Area (IRPA), under The Ministry of Science, Technology and Environment, Malaysia.