ABSTRACT
This project is focused on the design and manufacture of a Model 3-Cylinder Automobile Engine Block which is light in weight, cost effective and small in size. The cylinder block in this report was made of aluminium material via the manufacturing process of sand casting. Computer Aided approach was employed in designing the pattern using Microsoft Excel (Version 2007). The pattern was made of wooden material for easy machinability. The casting was tested for surface finish and soundness and the results were favorable Foundry technology has also been applied to achieve results. Provision for water passages and coolants was done locally by using circular aluminium pipes to form water ways inside the cavity before pouring and drilling to locate the pipes when the casting has solidified. The casting was measured to weigh about 335.2N (34kg). This weight favorably competes with weights of other cylinder blocks of different materials.
LIST OF ABBREVIATION
cc – Cubic centimeter
KW – Kilowatts
T5 – 100oC
T6 – 85oC
mm – Millimeter
VW – Volkswagen
CHAPTER ONE
INTRODUCTION
Cylinder block which is also called engine block is the main structure of the engine which gives the space for the cylinders and passages for coolant, exhaust and in take gases to Passover the engine and host for the crankcase and cam shafts. Engine block is the main housing of hundreds of parts found in modern engines and it is the largest among the engine parts constituting 20-25% of the total weight of the engine (Keay Sue 2002). The first successful internal combustion engine which can be used in an automobile was built by Siegfrid Marcus in about 1864. It was a upright single cylinder two stroke petrol engine. (Asme, 2005).
Nowadays, engines have come to their maximum development as days go by. These developments have caused increase in power, durability, resistance to wear and efficiency of the engine. Materials used to build the engine block have been given a higher strength with low weight which is more important for the power of the engine. For many years, the engine block has been manufactured using cast iron alloys due to its strength, low cost and wear resistance. But as the engine became more complicated, engineers found new materials to reduce its weight as well as to increase strength and wear resistance. A common alloy which is widely used is aluminum alloy (Anyalebechi, 2005). It is more popular due to its low weight but mostly within petrol engines.
As the engine block is the main housing of the engine it has to include a number of requirements. These requirements include the wear resistance, long lasting, maintenance and withstand the pressure created when combustion takes place. It also has to withstand high temperature and vibration when the engine is in running conditions.
High strength is mostly concerned in diesel engines because of their high compression ratios compared with petrol engines. In diesel engine, its compression ratios are normally 17:1 or greater, but in petrol engines it is nearly 10:1. The material used should also have low density to reduce its weight and low thermal expansion under high operating temperatures and also a good thermal conductivity to give out the heat in minimum time. When it comes to the manufacturing process, the material should have good machinability and castability to reduce the time and cost consumed. As if the material is too hard, the time and cost for manufacturing increases. The above features are the basis why cast iron and aluminum alloys are widely used to manufacture the cylinder block.
Cast iron alloys are used because they contain good mechanical properties, low cost, and availability compared with other material but certain aluminum alloys contains most of the characteristics of cast iron but with low weight (Mat Web-online, 2005). Aluminum alloy casted engine block give a good surface finish and high machinability compared with cast iron alloys.
As technology increase the engineers has found new materials such as graphite cast iron which is lighter and stronger than the grey cast iron mentioned above. Aluminum alloys main feature for its popularity is its low weight. This reduces the weight of the engine as well as the vehicle. Aluminum alloys has a good machinability properties compared with grey cast iron. There are two aluminium alloys that are mainly used in manufacturing of engine blocks. They are A319 and A356, A319 contains 85.8-91.5% of aluminum, 5.5-6.5% of silicon, 3-4% of copper, 0.35% of nickel, 0.25% of titanium 0.5% of manganese, and 1% of Zinc. This alloy has good casting features, corrosion resistance and good thermal conductivity. Under heat treatment of T5 process, it generates high strength and rigidity for the engine block, (Anyalebechi, 2005).
A356 contains 91.1-93.3% of aluminum, 6.5-7.5% of silicon, 0.25-0.45% of magnesium, 0.2% of copper, 0.2% of titanium 0.2% of iron and 0.1% of zinc. Although the mechanical properties are similar to A319 when it is under the heat treatment process T6 it gains higher strength than A319. Also it has lower modulus of elasticity (72.4GPA) than A319 which modulus of elasticity of 74GPA. (Mat web-online 2005), manufacturing process of engine blocks is mainly done using sand casting. Although dies casting is also used, it is more cost effective as the die wear out easily due to the high temperature of the molten metal. The casted engine block is then machined to get the surface finish and coolant passages. In the sand casting process the widely used in engine block casting is the green sand mould (Luther Norris, 2005). The term green denotes the presence of moisture in the sand mould. A combination of silica, sand, clay and water are poured into one half of the aluminum block pattern with wood or metal frame. The mould is then compacted by applying pressure or vibrating the metal frame. This process is repeated for the other half of the mould. Then both halves of the mould are removed from the pattern. The mould is then tightened with clamps to withstand the pressure or gravity when pouring molten metal. Cores are used to provide the space for water jackets around the cylinders. The core has been painted to seal the gas formed during the casting process within the core.
Aluminium reinforcing rods are used to give more strength to the core. These rods get melted due to the molten metal poured during casting. After casting, the sand is removed by applying vibration on the casting. The casting has to be machined to get the correct dimensions and smooth surfaces in the head gasket face and the faces where other components are fitted. Then the block is ready for line boring of the main bearing bores. Bearing caps are fitted temporally for the line boring of the main bearing bores. The boring bar contains multiple tools so in one operation all boring operations is completed. After the boring has been finished, the engine block is ready for further fittings of crank, cam, cylinders, connecting rods and valves. However, to achieve a good surface finish of the engine block, the quality of the sand used must be put into consideration;
- The strength of the sand has to be high to maintain a rigid shape.
- Higher permeability can reduce the porosity of the mould.
- The thermal stability of the mould should be high to resist damages such as cracking due to molten metal.
- Ability of sand to compress during solidification has to be high unless the casting will not be able to shrink freely in the mould and it may result in cracking.
- The sand has to be reusable for next sand moulds to be formed, because one sand mould can be only used once. Apart from the quality of the sand, there are other necessary factors to consider avoiding defective production.
If the risers get solidified before the other parts of the casting, it would give an engine block less strength. Also, if the molten alloy is not up to standard, it will fail in high running conditions. If the clearances in the cylinder bores, crank and can bearing are not up to the standard measurements, under running conditions, it may arise with unwanted friction or loose.
STATEMENT OF PROBLEM
Engine blocks in existence are robust in size with the disadvantages of heavy weight and poor heat transfer including high cost. This results from the use of materials with high density and poor conduction of heat. Mostly, cast iron is the major material used in the manufacture of engine blocks cast iron materials has good vibration dampening property but it still has most of the disadvantages listed above. In this project, I have decided to use aluminum as the cylinder block material due to its less weight. Also aluminum is readily available in the market and thus reduces cost.
OBJECTIVES OF STUDY
- To design and manufacture a model of an automobile engine block using locally available materials.
- To design and manufacture a model of an automobile engine block with the aim and reducing its cost and increasing power output of the engine.
- To design and manufacture a cylinder block with reduced weight and size.
SIGNIFICANCE OF THE STUDY
This project will be beneficial to future researchers on this study and also in a way to students and engineers seeking to know more on engine block manufacture. It is also going to promote indigineous industry thus improving on the transfer of technology on locally produced components. Students and researcher will benefit a lot as this project will expose the principles and ideas involved in the design and also in the application of casting as a manufacturing process.
SCOPE OF STUDY
The scope of this work is limited to the design and manufacture of a model 3-cylinder engine block using sand casting process. Hence other manufacturing processes such as joining, powder metallurgy, forging and forming are not adequately employed.
