Department of Mechanical Engineering, Invertis University, Bareilly, India
Received Date: 01/02/2018; Accepted Date: 22/06/2018; Published Date: 30/06/2018
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Behaviour prediction of most suitable material used in piston cylinder arrangement has been represented through ANSYS, finite element simulation. In order to achieve recent emission norms, target oil consumption need to be controlled by optimizing piston head design. Four different materials steel AISI H13, Aluminium (6061-T6), High leaded tin bronze (C93700) and Argentann are selected as parent material. These materials are then tested at different pressures by properly selecting the characteristics required in forging simulation. Effect of increase in pressure, stresses developed and temperature gradient is calculated for all the four materials. It is found that the thermal temperature gradient is best in the analysis for aluminium during forging, even the maximum temperature is less and temperature distribution is better than that of other materials.
Finite element method, Behaviour prediction, Forging, Temperature gradient
The piston cylinder system development has competency in design, modeling, drafting and analysis with priority in quality time and cost. Recent emission norms have forced the engine manufacturers to reduce the particulate matter and other emission substantially. In order to achieve the target oil consumption need to be controlled by optimizing piston head design. The criteria are fast product development cycle and service in area of product improvement. Continuous loading and unloading create stresses which leads to deformation in shape and reduction in life of the material . Determining the use of new material for forging application requires careful analysis of the system and proper understanding of the failure mechanisms that can cause material life to be lower than required. Induced stresses are due to thermal expansion coefficient, elastic modulus and the temperature differences during the forging process. Temperature difference and maximum temperature can be minimized by increasing the thermal conductivity which leads to reduction in temperature gradient and stresses on the material [2-4].
Two stroke and four stroke engines are available in wide range of power requirement ranging from 6 H.P. to 1000 H.P. Piston cylinder assembly plays an important role in delivering power to entire system and continuous operation leads to development of stresses which requires a proper analysis of material, pressure and temperature gradient i.e., at what rate the temperature changes around a particular location, more the variation in temperature higher the development of stresses [5,6].
Finite Element analysis is nowadays commonly used in determining the internal stresses of a particular material . Computer simulation process shortens the design process and provides tools to investigate the desired factors on the entire model. Such analysis reduces time and cost and provides information about the failures in design. The main objectives are to:
(a) Develop adequate die design and establish process parameters, by predicting temperatures so that part properties, loading conditions and die life can be controlled.
Requirement of process simulation in side relief forging forming is due to:
• Design of forging sequences in warm and hot forging, calculation of forging forces.
• Determination of internal stresses induced, failure and die wear.
• Prediction and improvement of flash dimensions in hot forging.
• Improvement in process variables and design to reduce die failure
• Prediction and elimination of failures, fractures and defects.
Deshpande et al.  suggested that along with die material refining technique, thermal expansion and thermal conductivity also affect the die life. Die materials include ceramics and carbides which can retain hardness at high die surface temperatures. Cancelos et al.  also investigated the thermo mechanical deformations in a hot forging tool by numerical simulation and concluded that the advantage with numerical simulation allows analyzing different configurations and anticipating possible defects before tool-die making thus helps in reducing the cost . Numerical results using finite element analysis presented include residual stress, plastic strain and temperature distribution along the axial and hoop directions. Results also effectively present the maximum contact force needed to evaluate the performance of the die in the forging process. Usman et al.  further focuses on analyzing the parameters affecting liner bore distortion in DI diesel engines and observed that variation in gasket thickness, linear thickness and number of cylinder head bolts effect the linear bore distortion successfully.
Test of pressure and temperature gradient per unit area for different loading conditions was done using computer program called ‘ANSYS’. Analysis was carried on cylinder part of piston cylinder arrangement. For this cylinder is divided into four parts, one quarter part is taken for analysis (Figure 1). Dimensions of cylinder selected respectively are diameter 120 mm and height 260 mm. Inner temperature of cylinder taken for analysis is 1200°C whereas the surrounding temperature is room temperature (Table 1). Four different materials i.e., Steel AISI H13, Aluminum (6061-T6), High leaded tin bronze and Nickel silver (Argentann) are selected. Effect of variation of stresses and deformation with variation in pressure is also noticed. Composition of material selected i.e., AISI H13 Steel (C-0.4 wt%, Mn – 0.35 wt%, Si - 1.0 wt%, Cr – 5.1 wt%, Ni – 0.3 wt%, Mo – 1.5 wt%, V – 1.0 wt%, Cu – 0.25 wt%, P – 0.03 wt%) whereas the composition for Aluminum is of grade 6061-T6, High leaded tin bronze and Argentann respectively are (Al – 0.005 wt%, Antimony – 0.55 wt%, copper – 82 wt%, Fe – 0.15 wt%, lead – 11 wt%, Nickel – 1 wt%, P – 0.15 wt%, Si – 0.005 wt%, S – 0.08 wt%, Tin – 11 wt%, Zn – 0.8 wt%) and (Cu – 60 wt%, Ni – 20 wt%, Zn – 20 wt%).
Table 1. Properties of die materials.
|Material||Thermal conductivity (W/m0K)||Specific heat (J/Kg°K)||Density (kg/m3)|
|Steel AISI H13||37||560||7760|
|High leaded tin bronze||2710||910||3200|
Due to pre-defined build in properties the selected model is 20 nodes 80 in ANSYS software. After selection of inside and outside surfaces the meshed model is as shown in Figure 2. Such type of model has 90 nodes and 20 degree of freedom. Film coefficient for outer and inner selected surfaces are 30 e-6 and 6.015 e-4 respectively whereas mean bulk temperature as 24°C and 1200°C. By selecting all DOF down part of the model is fixed and cannot move in any direction during forging process. Pres sure is to be applied on the inner walls of the cylinder head as during movement of piston higher pressure and temperatures are generated inside the cylinder
Experimental data obtained from analysis using ANSYS software with the finite element method. Figure below presents obtained result of analysis done using pressure and material variation. Deformation and maximum stresses developed as a result of pressure variation. Graph of pressure and maximum deformation denotes a linear trend i.e., deformation increases linearly with the increase in pressure on the surface of the section. Various values at which deformation is noticed are 0.3 N/mm2, 0.6 N/ mm2, 0.9 N/mm2 and 1.4 N/mm2. At 1.4 N/mm2 pressure value, Deflection denotes a zone of maximum deflection and stresses. Stresses are maximum at the top dead end where the piston compresses the volume of air-fuel mixture and retracts. Maximum shear stress for steel AISI H 13 at this instant is 18.91 whereas dimensional distortion is 0.024 mm. Relationship between pressure and maximum equivalent stress denotes that with the increase in pressure equivalent stresses increases more rapidly. Minimum stress value 3.7 corresponds to a pressure of 0.3 N/mm2 whereas maximum stress 38.77 corresponds to pressure value of 1.4 N/mm2.
Analysis has been done to determine the effect of increasing pressure on the performance of piston cylinder head. Figure 3 shows the effect of 0.3 N/mm2 pressure on the relative deflection of piston cylinder head. Figures 3 and 4 clearly represent that as the pressure increases the amount of deflection correspondingly increases. Red color shows the region subjected to maximum deflection whereas blue color shows the region in maximum safer zone. Figures 5 and 6 show that with the increase in the amount of pressure the deflection correspondingly increases. From the simulation values it has been clearly established that the deflection at 1.4 N/mm2 pressure is three times the deflection at 0.3 N/mm2 pressure. The amount of deflection increases rapidly with the slight increase in pressure.
Figure 7 shows the effect of increasing pressure on deformation induced and stresses developed on cylinder head. From the above analysis and corresponding data obtained it has been clearly established that with the rise in pressure the pressure from 0.3 N/mm2 to 1.4 N/mm2 the deflection on the cylinder head correspondingly increases and as the limit reaches beyond the permissible limit permanent deformation takes place which may lead to reduction in the performance of the power obtained. Proper selection of material may lead to red uction in the amount of wear induced on the surface.
Figure 8 shows the effect of increasing pressure on deformation induced and stresses developed on cylinder head. From the above analysis and corresponding data obtained it has been clearly established that with the rise in pressure from 0.3 N/mm2 to 1.4 N/mm2 the stresses induced on the cylinder head correspondingly increases. The value of stresses rises steeply with the increase in the value of pressure. Increasing the pressure beyond the permissible limit result in severe distortion and degrading in the performance of the cylinder.
Figure 9 shows the temperature gradient for steel AISI H13. A temperature gradient describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The maximum and minimum values of temperature are clearly shown in the graphs. The maximum value of 1087°C is at the cylinder head and the minimum value of 852.37°C is at the extreme opposite end. The region subjected to maximum temperature is represented by red color whereas the region subjected to minimum temperature is represented by blue color. Similarly the temperature gradient for aluminum is shown in Figure 10. The maximum and minimum values of temperature for aluminium are 1051°C and 1018°C Figure 11. This clearly reveals that the temperature distribution in aluminium is better than that of steel AISI H13.
Figure 12 shows the temperature gradient for high leaded tin bronze. The maximum and minimum values of temperature are 10610°C and 976.45°C which clearly shows that temperature distribution in high leaded tin bronze is better than that of steel AISI H13 and lower than that of aluminum. The temperature distribution is better in conductive materials in comparison to that of semiconductor or insulator materials and since aluminum is conductive therefore the temperature distribution is quicker in comparison to that of steel AISI H13, high leaded tin bronze and argentann.
The results helps us in better analysis of operating dies at elevated temperatures to minimize the cyclic temperature gradient through the die that leads to heat cracking and cracking has been demonstrated. Hence the performance of rotors with die cast aluminum and high leaded tin bronze is better in comparison to that of argentann and steel AISI H13.
Graph of temperature gradient and type of material used denotes that the variation in temperature is more appropriate for aluminum and bronze than that for Argentann and steel AISI H13. Aluminum corresponds to a reduction in maximum and minimum temperature gradient; therefore it is more appropriate for using aluminum (6061-T6) as a cylinder material in piston cylinder arrangement (Figure 13).
Based on the simulation analysis performed on cylinder head for maximum permissible pressure and best possible material following points has been concluded:
• The thermal temperature gradient is best in the analysis of aluminium during forging because maximum temperature is less and the temperature distribution is better than the other material.
• For the given temperature of the cylinder walls and outside temperature aluminium is the best possible material among the four selected materials.
• The stress distribution varied by varying the elastic properties of the material such as Poisson’s ratio and the young’s modulus.
• Values of stresses and defection at the outer periphery of the cylinder wall increases with the increases in pressure.
• After 09 N/mm2 pressure sharp increase in the value of stresses and deformation are noticed therefore increasing pressure beyond permissible limit leads to failure.
• In this type of forging we have chosen the element as a solid material, so the deformation shown is less and deformation of shape is also less, this element is taken because the configuration limitation of the systems on which analysis is done. Otherwise the analysis is done on the visco-elastic materials. But the forging simulation of the visco elastic material cannot be performed on the normal computer system.