Advanced Manufacturing Process And Materials Engineering Essay

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This paper is concerned with the application of maters and manufacturing processes in the development of industrial and commercial products, which mainly focuses on areas such as Automotive, Aerospace, Electronic products, Sporting goods etc. Designing, material properties and manufacturing processes are very important to the successful development of new product. With the advent of new technological advances, material manufacturing processes selection is becoming the major focus for all the industries. This not only saves money, it gives a better product, and hence leads to costumer satisfaction.

The automotive system that has been chosen is the Exhaust system and the subsystem chosen for discussion is the steel tubing and the silencer chamber, which is used as a flue, for the exhaust gases from the internal combustion engine. The system mainly consists of exhaust manifold, steel tubing, a catalytic converter, and a muffler [figure no.1]. Figure no.2 shows how the system can be incorporated into a passenger car.

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The exhaust system is a device to convey the exhaust gasses from the combustion chamber of internal combustion engines into the atmosphere and consists of a collection of pipes. In most production engines, the manifold is an assembly designed to collect the exhaust gas from multiple cylinders and combine those flows into a single pipe. Manifolds are often made of cast iron in stock production cars. A header is another name for a manifold, but which specifically refers to an enhanced manifold that has been designed for performance. During design, engineers will create a manifold without regard to weight or cost but instead for optimal flow of the exhaust gases. This design results in a header that is more efficient at scavenging the exhaust from the cylinders. Headers are generally circular steel tubing with bends and folds calculated to make the paths from each cylinder's exhaust port to the common outlet all of equal length, and joined at narrow angles to encourage pressure waves to flow through the outlet, and not back in the direction of the other cylinders. In a set of tuned headers the pipe lengths are carefully calculated to enhance exhaust flow in a particular engine RPM range. These pipes are usually made of stainless steel, but also can be made of aluminium, galvanized steel. The pipes main function is to carry the exhaust gas to the catalytic converter and later on to the muffler. Also, the gases from most types of machine are very hot; the pipe must be heat-resistant, and it must not pass through or near anything, which can burn or can be damaged by heat.

The catalytic converter is a device, used to reduce the amount of the pollutants coming out from the combustion chamber of an internal combustion engine. It is usually housed in an insulating housing made up of stainless steel. In the modern car the catalyst used is three-way catalyst, because it helps in the reduction of three harmful emissions namely carbon dioxide, unburnt hydrocarbons, and NOx molecules.

The muffler is a device, which is used to reduce the noise of the exhaust gas. It is mostly installed at the rear undercarriage end of a passenger car. The muffler housing is made of stainless steel. The muffler contains a resonating chamber and baffles which is used to absorb the sound waves of the exhaust gases. In the resonating chamber the opposite sound waves collide and in turn cancel out destructive interference and then the baffles absorb the remaining sound waves of the exhaust gases.

MANUFACTURING METHOD OF THE EXHAUST PIPE

The Exhaust pipe carries the collected gases and vapor from the exhaust manifold or header to another component further downstream in the exhaust system. The various types of exhaust pipes in the market are (depending upon their design) as follows: The "Y" pipe is an exhaust pipe [figure no.3], which connects both exhaust headers of a "V" engine to form a single exhaust system. This may also be used to split a single exhaust system into a dual exhaust system. Then there is the "H" pipe which consists of a right and left- hand exhaust pipe, attached to a header or catalytic converter and connected by a balance pipe to form a dual exhaust system component [figure no.4]. Balance pipes [figure no.5] are used in many dual exhaust systems to merge sound pulses from left-hand and right-hand sources. This helps reduce harsh exhaust sounds, equalizes muffler and tail pipe life, and can aid in improving mid-range torque output of the engine. The Tail pipe completes the design task of an exhaust system by directing the exhaust gases out of the vehicle to a point where they cannot enter the passenger compartment. A split tail pipe may be called a front and a rear tail pipe. Generally, a tail pipe is greater than one foot in length. The tail pipe is the last "exhaust pipe" in the exhaust system. The tail spout serves the same purpose a tail pipe except it is shorter in length, usually a foot or less. This component is most often found on vehicles with rear-mounted mufflers.

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There are various metals currently used in the manufacture of the exhaust pipe and the tail pipe, materials such as steel, galvanized steel, stainless steel, aluminium etc. I would be discussing about the current method of manufacture of steel exhaust pipes. In the production of steel exhaust pipes, Welded pipe is formed by rolling plate and welding the seam. The weld flash is removed from the outside and inside surfaces and the weld zone is heat-treated, so the seam is generally not visible. Welded pipe often has tighter dimensional tolerances than seamless, and can be cheaper if manufactured in the same quantities. Seamless pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell. Rotary tube piercing is a hot working for making long seamless pipes and tubing. The basic principle is that a round bar is subjected radial compressive forces, due to which tensile stress develop in the center of the bar. And so when it is subjected to cyclic compressive stresses, a cavity begins to form at the center of the bar. Rotary tube piercing process is also known as the Mannesmann process.

The pipe is then bent to suit the design requirements of the car; pipes in general can be bent in a few ways. Rolling is the best-known way to bend metal, perhaps since it is the least costly. This method uses an appropriate size die, which adjusts to the steel tube, angle, pipe, channel, bar or steel beam and revolves at the same peripheral speed, turning in opposite directions. As the metal passes through the roll, during which time the machine applies pressure to bend the tubing or the beam to the desired radius. 
Another method is the Mandrel bending, Mandrel bending is also fairly well known. In this process, a metal shaft, or mandrel, is fitted inside the steel tube or pipe. As the mandrel moves, it bends the metal around the appropriate sized die to form the radius. Mandrel works best when the steel tube or pipe has a heavy wall and/or requires a tight radius because it prevents the material from rippling. The draw back is that this method can only bend steel pipes up to 180 degrees, but it produces a bend that is uniform all the way up and down the pipe or tube. It is used in bending exhaust pipes, molten glass and in very tiny cases, jewelry.

After the pipe is bend into the various required shapes, the pipe is then welded to fit the desired design of the vehicle. Hence producing a complete exhaust pipe. The pipe is also welded to the silencer chamber, and the tail pipe too is welded to the silencer chamber. In this method the exhaust pipe is manufactured currently in the market.

PROPOSED METHOD FOR MANUFATURING THE EXHAUST PIPE

As already covered the current method of manufacturing an exhaust pipe is process of rolling. Later on these pipes are bent and welded at the necessary areas, like before and after the silencer chamber. In my proposed method I would like to make one complete unit for the exhaust pipe, including the silencer chamber, a part of the silencer chamber will be cut out and necessary components will be welded back in place, by using HEATforming.

HEATforming (HotExpansionAirTechnologyforming) is developed by HEATform GmbH, Germany, is the consequent further development of tube hydroforming with fluid active media for the improvement of economic efficiency and the formability of hollow bodies in the presence of internal pressure. The draw back of hydroforming being the lack of achieving the desired result [figure no.6] also the superplastic deformation of the metals is limited to material specific development for this procedure.

The process of HEATforming is similar to shaping hot glass as desired. HEATforming allows the metal to be shaped according to design. The process utilizes air, Nitrogen or Argon as pressure mediums and allows the forming to be heated {temperature depends on the melting point of the metal used (>350 °C)} metallic hollow bodies, tubes, and profiles by means of internal negative pressure even at values of strain in excess of 270 % change of circumference in one process step with short cycle times [figure no.7]. The temperature of the tool is controlled via means of thermocouples. The temperature of the hollow body is achieved by means of inductive heating. HEATforming is mainly used on aluminium alloys, but other metals such brass, titanium and steel were also used. The general outer diameter of the metal is around 20 mm and wall thickness of 1 to 2 mm. Since HEATforming is not associated with high requirements on the semi-finished finished part, accordingly parts manufactured by means of welding, drawing, deep drawing etc., can be formed. Forming process on cross-section of 8 to 50 mm and wall thickness of 0.7 to 6 mm has been formed. By using relatively smaller radii sharp edges and narrow radii were achieved at internal pressures lower than 300 bar. The onsets of forming are a function of temperature and pressure.

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HEATform had tested on an aluminium 6060 tube of dimensions 4X1.2mm and it was noticed that the best flow was achieved at temperature around 550 °C with values of strain around 300%, achieving approximately unchanged wall thickness.

The active medium in HEATforming is gases, especially since gases have a lower heat capacity (air C = 0.71, nitrogen C = 0.75, argon C = 0.33 [kJ/kgK]) as compared to water (C = 4.183 kJ/kgK). Due to this cold gas can be guided into heated hollow tubes without causing significant cooling of the forming zone. Therefore preheating of the gas is not required. Air is sufficient as pressure gas for aluminium while nitrogen and argon are used for scaling-sensitive material such as titanium and steel. A major advantage of using gas as an active medium is the rapid feed and ventilation of the gas, and also the fact that the die remains clean.

Due to above mentioned property of gas a heat profile can in the hollow body can be achieved by preheating, that is largely preserved during the forming process. Heat profile is achieved in the semi-finished product by inductive heating outside the tool. During the process the hollow body is exposed to various amounts of heat energy. The highest temperature should be generated at site of highest value of strain or at the site at which the forming process has to commence, in order to achieve the maximal shape change capacity and the lowest flow stress in these areas. Also at the same time the areas that aren't suppose to be formed should not be affected by heat. Heat profile of the hollow body usually remains unchanged, till in comes in contact with the tool wall at the existing gas pressure. The heat profile of the semi finished part can also be utilized for the partial forming of a component, whereby the forming tool must only be designed to cover the heated zone of the semi finished part.

Heating elements, such as cartridges or sheet-type heating facilities, can be used in combination with suitable controls to achieve a desired heating profile of the tool. The tool heat can be used to influence the working sequence of the forming process both with regards to sequence of events and the distribution of wall thickness at the circumference and along the length of the part.

Generally an internal pressure of 300 bar is used for forming, but in special cases up 1000 bar of pressure can be used. As already mention that forming is a function of temperature and pressure and for aluminium can be determined by shown fig. [figure no.8]

The semi-finished parts can be sealed outside the forming tool; this is usually done during the material feed. The process of sealing helps in the safety of the process, especially in the case of aluminium forming; the pick up of the aluminium tool wall and the sealing stamp is completely excluded.

The surface finish of the semi-finish part solely depends upon the finished product. For products with very high requirements with regards to the formed surface e.g., high gloss, anodic oxidation etc. the tube manufacturing process may be significant in order to prevent possible flow marks, or partial surface roughness (e.g. Orange peel effect) after processing. This applies to aluminium alloys in particular, thus, it is feasible to coat all aluminium alloys.

Generally the metals that can be used in HEATforming are aluminium alloys, brass, titanium and steel and stainless steels. Aluminium alloys (such as 1000-, 5000-, 6000-, and 7000- series) have been used. Alumium circumference can be changed up too 270% during the forming process, including suitable material feed at the temperature range of 530-560 °C. compressed air can be used as the active medium in aluminium. Brass alloys are similar to aluminium alloys and allow high value of strain. Brass alloys allow the production of surfaces that can be polished right away. Titanium can be formed by a single process at temperatures around 830 °C. Argon is the active media used in the forming process of titanium. While steel is usually formed at around 750 to 950 °C, with nitrogen being used as the active media.

In my proposed method to manufacture the exhaust pipe tubing, I would like to use an aluminium alloy, of series 6000-. Alloys in this group contain magnesium and silicon in proportions that form magnesium silicate. These alloys have a good balance of corrosion resistance and strength. The 6000- series is very readily extruded so should make a good candidate for the HEATforming process. This alloy is also heat-treatable.

The alloy of initial circumference of around 50 to 60 mm is taken, with a thickness of 1 to 2mm. With this process the silencer chamber can be manufactured, which lies in the permissible limit of 270% of the original circumference. Various bend, shape and diameters can be achieved by this process to match the requirement of the piping and silencer chamber. A part of the silencer chamber is cut out and required components fitted and steel plate welded back in place. Hence forming a complete exhaust pipe with the silencer chamber.

CONCLUSION

In the current practice of manufacturing the exhaust pipe, the pipe under goes a few processes, and then is further welded to the silencer chamber. In this proposed method of HEATforming the exhaust pipe of the catalytic converter is made up of one unit. Various bend and dimension of the pipe are achieved, hence enabling the designer to achieve a better flow for the flue gasses. This also reduces the number processes involved in the manufacturing process of as compared to currently used process. The material, aluminium alloy of the 6000- series has a good balance of corrosion resistance and strength.

REFERNCES

http://auto.howstuffworks.com/catalytic-converter.htm

http://www.hydroforming.net

http://www.heatform-schuler.com

http://www.www-tubestubing.com/tubing-roller.html

http://www.walkerexhaust.com/support/exhaust101/ComponentsAndDesign.asp

http://en.wikepedia.org/wiki/Exhaust_system

http://www.fluent.com/about/news/newsletters/01v10i2/img/s713_iig.gif

BIBLIOGRAPHY

1. Manufacturing Engineering and technology, Serope Kalpakjian, Steven R. Schmid, 4th edition, Prentice Hall

2. The handbook of advanced materials, James K. Wessel,Wili Interscience

3. Advanced manufacturing process and materials handouts, P. Swanson, 2007.