STUDY OF PROCESS PARAMETERS OF GRAVITY DIE CASTING DEFECTS

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 7, Issue 2, March-April 2016, pp , Article ID: IJMET_07_02_023 Available online at Journal Impact Factor (2016): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication STUDY OF PROCESS PARAMETERS OF GRAVITY DIE CASTING DEFECTS Vasdev Malhotra Associate Professor, Mechanical Engineering Department, Mechanical Engineering, YMCAUST, Faridabad , (India) Yogesh kumar M. Tech Student, Mechanical Engineering Department, YMCAUST, Faridabad (India) ABSTRACT In today s world a casting production without any defect is almost impossible. After the application of various optimization techniques and process we still are not able to get the defect free castings. So it is critically important to analyze the root cause of casting defect with in the process itself, so that any changes which can hamper the defect intensity can be invoked at the time of manufacturing or foundry shop production. The gravity die casting process is governed by its process parameters so it is required to study its process parameters and its effects. In this paper an effort has been incorporated to study the change in process parameters and their consequent effects on casting defects. Key words: Casting, Root cause, process parameters Cite this Article Vasdev Malhotra and Yogesh kumar, Study of Process Parameters of Gravity Die Casting Defects. International Journal of Mechanical Engineering and Technology, 7(2), 2016, pp INTRODUCTION In practical foundry shop it is quite tough to judge the exact cause for a particular defect because they are quite intuitive in nature. So first of all it is required to identify process parameters which can affect the process considerably and can change the output with reasonable weightage. So it is required to identify the factors which can affect the process and these factors are identified with the help of study of various literatures and interaction with various foundry experts in different industries. According to experience and expertise of foundry experts and after studying various literatures there are lots more factors which are identified to be affecting the gravity die casting process considerably are as follows[2]. A gravity die casting essentially consists of following parameters such as editor@iaeme.com

2 Study of Process Parameters of Gravity Die Casting Defects Pouring mould temperature Pre heat temperature Pouring time Selection of gate and riser design Melt holding time Degasification time Die coat material Pouring velocity Die coat thickness 2. PROCESS PARAMETERS: The process parameters which are critical and can affect the process considerably are 2.1. Pouring temperature: Pouring temperature generally varies from 650 to 800 degree Celsius. When we pour aluminum alloy then its fluidity is completely dependent upon pouring temperature. Generally, a better fluidity in higher temperature is connected with the decreasing viscosity and surface tension of molten metal with the increasing of pouring temperature, which leads to the increasing filling speed. At the same time, the heat capacity of molten alloy rises with increasing temperature of the pouring, what results in the increase of filling time. On the other hand, the oxidation liability of magnesium alloy increases with the pouring temperature rise, what increases the viscosity and decreases the filling speed. Therefore, growth rate of fluidity above 735 C is lower than between 695 C and 735 C. The pouring temperature also affects the microstructure formation at a greater extent and which in turn affects the final structure and toughness of casting product.[1] 2.2. Preheat temperature Preheating in the gravity die casting is done to remove the possibility of formation of temperature gredients. If we increase the preheat temperature from a particular range then it may affect the die coating and also it may create defects like rough surface finish and also if the temperature is removed considerably then this may cause a particular chilling effect which in turn leads to less solidification of core and due to this difference in solidification rate defects like solidification shrinkage may occur.a significant precondition for the production of high quality castings is keeping an optimum temperature of the respective parts of the mould cavity surface[2] Selection of gate &riser design Feeder acts as a liquid metal reservoir provides liquid feed metal until the end of the solidification. Riser also serves as a heat reservoir, creating a temperature gradient that induces directional solidification. Two criteria determine whether or not a riser is adequate. Common types of feeders are: top feeder and side feeder. The major considerations in the casting design are the quality of the final product and the yield, which heavily depend upon gating system and feeders. Even after spending significant resources (man-hours, materials, machine overhead and energy) for casting development, one of the following situations may arise during regular production. [3] editor@iaeme.com

3 Vasdev Malhotra and Yogesh kumar 1. Under design: resulting in high percentage of defective castings, due to the number or size or placement or selection of feeders and gating and gating elements are inadequate. 2. Over design: leading to acceptable quality level, but poor yield and thereby high cost. In this case, the number and/or size of feeders and gating elements are much higher than their respective optimal values.[4] 2.4. Degasification time & material The gas used for degasification is mostly argon and nitrogen which are inert gases. After melting the molten metal should go in to degassing process. In this method, an inert gas like argon or nitrogen is injected into the flow of molten metal through injection nozzles. The hydrogen diffuses into the bubbles. The gas is bubbled through molten aluminum to remove absorbed hydrogen. The amount of hydrogen is reduced gradually. This bubbling action of inert gas through spinning rotor helps oxide particles to float to the surface. It also creates a large number of small bubbles of gas that are mixed with the liquid alloy. Rotory degassing method is shown in Figure given below. Degassing fluxes are added to remove hydrogen from the molten metal as well as to lift oxides and particles to top of the bath so that they can be removed.[5] 2.5. Degasification & defects Degasification mainly eliminates the unwanted gases from the mould by bubbling at the bottom of the container as shown in the above figure and it controls the porosity to a much larger extent. Porosity control in aluminum castings can be done in following ways.hydrogen content in the molten metal decreases by increasing the degassing time. Degassing should be done at optimum temperature. The degassing should be done at lowest temperature because as the temperature increases, the volume of the gas that passes for degassing increases. The change of hydrogen content in the molten metal, after the application of same degassing time, with the change of metal temperature is considerable.[6] 2.6. Die coat thickness and material: Die coat in the gravity die casting in order to obtain smooth surface finish and to avoid direct exposure of mould to the molten metal in order to avoid direct chilling affect. The material used for die coating is generally calcium carbide and silicon mixture and graphite [7] Thermal characteristics of die coat thickness: In permanent mold casting or gravity die casting (GDC) of aluminum alloys, die coating at the casting-mold interface is the most important single factor controlling heat transfer and, hence, it has the greatest influence on the solidification rate and development of microstructure. While the alloy is liquid, the coating material has only a weak influence over heat flow and the thermal contact resistance seems to be governed more by coating porosity and thickness [8]. 3. CONCLUSION The overall motive of this paper is to make an analysis so that a relation between casting defects can be established. The study depicts that in practical circumstances it is not necessary to apply special techniques to minimize the casting defects such as computer simulation etc which makes the situation quite hypothetical in nature. The defect free casting although not practically possible but still at a greater extent of editor@iaeme.com

4 Study of Process Parameters of Gravity Die Casting Defects defects can be minimized by using optimum values of process parameters which can affect the casting process considerably. REFERENCES [1] Adil Mohamed Elbasheer Ahmed, Mohamed Ibrahim Shukri, WaielFathiAbd El- Wahed, A Fuzzy Expert System for Rigging System Design Journal of Science and Technology 12 (02 ) December 2011 ISSN X [2] Tapan Roy, analysis of casting defects using computer simulation published in Transactions of 61st Indian Foundry Congress 2013 [3] Rajesh Rajkolhe, J. G. Khan, casting defects and its remedies published in International Journal of Research in Advent Technology, Vol.2, No.3, March 2014 E-ISSN: [4] K. Omura, Y. Otsuka, and M. Konishi, Diagnostic expert system for mold level control equipment in continuous caster, in Proc. 6th Int. Iron and Steel Congr., Nagoya, Japan, 1990, pp [5] B. Kalandyk, R. Zapała, A. Rakowska, Characteristics of defects present in industrial steel castings due to metal-mould reactions, Archives of Metallurgy and Materials 54, 2 (2009). [6] R. Wrona, A. Stawowy, A. Macioł, A formalized description of foundry production program, Archives of Foundry Engineering, Polish Academy of Sciences. Commission of Foundry Engineering; ISSN , 3, (2007) [7] S. Kluksa and nawarecka, Evolution of computer programming in production processes control, Archives of Foundry Engineering Polish Academy of Sciences. Commission of Foundry Engineering 2, 5, 80-86( 2003) [8] Achamyeleh A. Kassie, Samuel B. Assfaw, Minimisation of casting defects published in IOSR Journal of Engineering (IOSRJEN) e-issn: , p- ISSN: Vol. 3, Issue 5 (May. 2013), V1 PP [9] Cherian Paul, Parvathy Venugopal, Modelling of Interfacial Heat Transfer Coefficient and Experimental Verification For Gravity Die Casting of Aluminium Alloys. International Journal of Mechanical Engineering and Technology, 1(1), 2010, pp editor@iaeme.com