1. MANUFACTURING <br /> TECHNOLOGY<br /> PROJECT <br /> <br /> <br /> <br /> MANUFACTURING OF <br /> LIQUID PROPELLANT TANK <br /> BY<br /> <br /> K. Sai Malleswar (SC09B093)<br /> Akshay Kohli (SC09B117)<br /> <br /> <br /> CONTENTS<br />1.Design requirements<br />2.Materials and manufacturing processes<br />3.Manufacture of domes<br />4.Manufacture of cylindrical shells<br />5.Liquid propellant tank for stages<br />6.Description of processes & machines<br /> 1.Forging<br /> 2.Drilling<br /> 3.Welding<br /> 4.Hydro forming<br /> 5.Rolling<br />7.Applications in ISRO<br />8.Disadvantages <br />9.Recent alternative<br />10.Conclusion<br />11.Bibliography<br />1.DESIGN REQUIREMENTS<br />When operated within an atmosphere, pressurisation of the typically very thin-walled propellant tanks must guarantee positive gauge pressure at all times to avoid catastrophic collapse of the tank. Unlike gases, a typical liquid propellant has a density similar to water, approximately 0.7-1.4g/cm³ (except liquid hydrogen which has a much lower density), while requiring only relatively modest pressure to prevent vapourisation. This combination of density and low pressure permits very lightweight tankage; approximately 1% of the contents for dense propellants and around 10% for liquid hydrogen (due to its low density and the mass of the required insulation).<br />2.MATERIALS AND MANUFACTURING PROCESSES<br />The liquid propellant tank is used for carrying fuel and oxidiser during flight of the rocket. It comprises of two dome assemblies and a cylindrical shell assembly. It is a welded construction made of aluminium alloy AA2219. These three assemblies are manufactured and fabricated independently. They are joined by DC-TIG welding process to form the propellant tank. <br />COMPONENTALLOY SYSTEMTEMPERPROCESS ADOPTED1RingsAlluminium AlloyT651Forging, drilling, machining & welding2ShellAlluminium AlloyT87Rolling & welding3PetalAlluminium AlloyT87Hydroforming & welding4NozzlesAlluminium AlloyT651Forging, machining & welding<br />3.MANUFACTURE OF DOMES<br />The domes are first preformed in annealed condition by point pressing method, reannealed and spun to required dimension. The dome is heat treated to attain T6 temper condition. Manual dressing of dome is carried out immediately within one hour after solutionising. This is to correct the error due to distorsion before taking up for ageing. T6 temper condition refers solutionising followed by artificial ageing. Then the dome is bored to the required diameter to accomodate manhole reinforcement ring(MHRR).<br />CLEANING OPERATIONS BEFORE WELDING<br />The dome and MHRR are chemically cleaned i.e vapour degreasing with trichloro ethelene vapour and deoxidising in nitric acid bath and then cleaning with acetone. The weld edges are scraped manually to required length using a scraper tool. The MHRR is dipped in liquid nitrogen for 20 minutes for stablization. Once it is stablized, the setup is left undisturbed for 8 hours. Before welding the setup is purged with dry nitrogen gas to remove moisture and dust particles. <br />MACHINING PROCESSES<br />The prepared weld edges of dome and MHRR are checked by UV light on welding machine for presence of loose burrs and finger prints. DCSP TIG welding process is used for joining. After welding the welded component is transferred from welding machine to handling fixture. <br />The welded joint is dressed using a nylon mallet within 30 minutes to control mismatch. The joint is subjected to radiography for clearance.<br />Then the dome is machined bored to the required diameter for welding the nozzle. The nozzle is then welded to dome. The larger end of the dome is machined to suit the aft end ring. Subsequent to the chemical cleaning and scraping of weld edges of dome and ring, the components are located and positioned on the welding machine with associated toolings. The whole setup is dialed to check for proper allignment of weld edges with respect to welding torch. Before actual welding of hardware proper functioning of welding machine is checked by carrying out number of trials on scrap material. <br />4.MANUFACTURE OF CYLINDRICAL SHELL <br />Cylindrical shell assembly comprises of a number of welded shells and middle ring. Step machined sheet is rolled to the required diameter to form the cylindrical shell segment .<br />Cylindrical shell segments are joined by longitudinal seam weld joints,to form a welded shell assembly. Shell segments are provided with extra material at weld edges and machined during weld edge preparation.<br />Welded cylindrical shell sub assembly is formed by trmming both the edges of one shell sector and one edge of the other shell sector; followed by positioning the shell sector on longitudinal welding machine.<br /> The weld edges are clamped pneumatically for proper fitting with backup bar. Backup bar is used to support the weld metal and controls penetration.<br /> It is made of non-magnetic stainless steel to negate magnetic field during welding. <br />Welded shell sub assemblies are inspected and circumfrentially welded with the middle ring to complete shell assembly. The fore end dome assembly and cylindrical welded shell assembly are dry fitted in a separate area. This positioned on circumferential welding machine and welded by DCSP TIG process. Similarly, aft end dome assembly is dry fitted and welded to form the complete tank. <br />The whole tank undergoes final stage machining prior to global leak check and painting. Extra material is provided at different stages to compensate the weld distorsion and to achieve the required dimension after final machining.<br /> <br />5.LIQUID PROPELLANT TANK FOR STAGES<br />Common dome assembly separates the two shell compartments used for storing unsymmatrical dimethyl hydrazine(UDMH) and Nitrogen tetraoxide during flight. Tail end and head end dome assemblies consisting of six hydroformed petals, nozzles cover ring and end ring.<br />Cylindrical shell welded assembly is formed by welding of rolled panel segments. Common dome assembly is joined to N2O4 welded shell on one side and UDMH shell on the other side. Further it is welded to tail end dome assembly at the other end. The tank is then subjected to leak check. <br /> <br /> <br />LIQUID PROPELLANT TANK FOR STAGES<br />6.DESCRIPTION OF PROCESSES<br />1.FORGING:<br />Forging is one of the oldest known metalworking processes. <br />Forging was done historically by a smith using hammer and anvil, and though the use of water power in the production and working of iron dates to the 12th century, the hammer and anvil are not obsolete. The smithy has evolved over centuries to the forge shop with engineered processes, production equipment, tooling, raw materials and products to meet the demands of modern industry. In modern times, industrial forging is done either with presses or with hammers powered by compressed air, electricity, hydraulics or steam.<br /> These hammers are large, having reciprocating weights in the thousands of pounds. Smaller power hammers, 500 lb (230 kg) or less reciprocating weight, and hydraulic presses are common in art smithies as well. Steam hammers are becoming obsolete<br />Advantages and disadvantages<br />A significant advantage of the forging process is that it produces a piece that is stronger than an equivalent cast or machined part. As the metal is shaped during the forging process, its internal grain deforms to follow the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics.<br />Some metals may be forged cold, however iron and steel are almost always hot forged. Hot forging prevents the work hardening that would result from cold forming, which would increase the difficulty of performing secondary machining operations on the piece. Also, while work hardening may be desirable in some circumstances, other methods of hardening the piece, such as heat treating, are generally more economical and more controllable. Alloys that are amenable to precipitation hardening, such as most aluminium alloys and titanium, can be hot forged, followed by hardening.<br />Production forging involves significant capital expenditure for machinery, tooling, facilities and personnel. In the case of hot forging, a high temperature furnace (sometimes referred to as the forge) will be required to heat ingots or billets. Owing to the massiveness of large forging hammers and presses and the parts they can produce, as well as the dangers inherent in working with hot metal, a special building is frequently required to house the operation.<br /> In the case of drop forging operations, provisions must be made to absorb the shock and vibration generated by the hammer. Most forging operations will require the use of metal-forming dies, which must be precisely machined and carefully heat treated to correctly shape the workpiece, as well as to withstand the tremendous forces involved. <br />2.DRILLING:<br />Drilling is the cutting process of using a drill bit in a drill to cut or enlarge holes in solid materials, such as wood or metal. Different tools and methods are used for drilling depending on the type of material, the size of the hole, the number of holes, and the time to complete the operation.<br />Drilling is a cutting process in which a hole is originated or enlarged by means of a multipoint, fluted, end cutting tool. As the drill is rotated and advanced into the workpiece, material is removed in the form of chips that move along the fluted shank of the drill. One study showed that drilling accounts for nearly 90% of all chips produced. <br />Drilling as a Manufacturing Process:Hole making is one of the most important machining operations in the manufacturing process. Drilling is a multi-point cutting process. Holes serve a variety of functions including but not limited to: fasteners for assembly, weight reduction, ventilation, access to other parts, or simply for aesthetics. Reducing the weight of the object results in chips and burrs (at the entrance and exit of the hole). The process of drilling requires either the drill piece or the object being drilled to be rotated. Drilling can either create a new hole or enlarge an existing one.<br /> Hole making or drilling is used in the production of almost any part conceivable and those that aren't drilled are made with machines that have been drilled.<br />3.WELDING: <br />Gas tungsten arc welding (GTAW): It is also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non consumable tungsten electrode to produce the weld. The weld area is protected from atmospheric contamination by a shielding gas (usually an inert gas such as argon), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it. A constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.<br />GTAW is most commonly used to weld thin sections of stainless steel and light metals such as aluminum, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing procedures such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds. However, GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques. A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.<br />Electron beam welding (EBW):It is a fusion welding process in which a beam of high-velocity electrons is applied to the materials to be joined. The workpieces melt as the kinetic energy of the electrons is transformed into heat upon impact, and the filler metal, if used,melts to form part of weld. The welding is often done in conditions of a vacuum to prevent dispersion of the electron beam. The process was developed by German physicist Karl-Heinz Steigerwald, who was at the time working on various electron beam applications, perceived and developed the first practical electron beam welding machine which began operation in 1958. <br />Laser beam welding (LBW): It is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry.<br />Operation<br />Like electron beam welding (EBW), laser beam welding has high power density (on the order of 1 Megawatt/cm²(MW)) resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding. The depth of penetration is proportional to the amount of power supplied, but is also dependent on the location of the focal point: penetration is maximized when the focal point is slightly below the surface of the workpiece.A continuous or pulsed laser beam may be used depending upon the application.<br /> Milliseconds long pulses are used to weld thin materials such as razor blades while continuous laser systems are employed for deep welds.<br />LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium.<br /> Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding. The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the workpieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry.<br />4.Hydroforming (or hydromolding): It is a cost-effective way of shaping malleable metals such as aluminum or brass into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes possible by hydroforming to produce stronger, lighter, and more rigid unibody structures for vehicles. This technique is particularly popular with the high-end sports car industry and is also frequently employed in the shaping of aluminium tubes for bicycle frames.<br />Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press room temperature working material into a die. To hydroform aluminum into a vehicle's frame rail, a hollow tube of aluminum is placed inside a negative mold that has the shape of the desired end result. High pressure hydraulic pistons then inject a fluid at very high pressure inside the aluminum which causes it to expand until it matches the mold. The hydroformed aluminum is then removed from the mold.<br />Hydroforming allows complex shapes with concavities to be formed, which would be difficult or impossible with standard solid die stamping. Hydroformed parts can often be made with a higher stiffness to weight ratio and at a lower per unit cost than traditional stamped or stamped and welded parts.<br />5.ROLLING:<br />Rolling is a combination of rotation (of a radially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that the two are in contact with each other without sliding. This is achieved by a rotational speed at the cylinder or circle of contact which is equal to the translational speed. Rolling of a round object typically requires less energy than sliding, therefore such an object will more easily move, if it experiences a force with a component along the surface, for instance gravity on a tilted surface; wind; pushing; pulling; an engine. Objects with corners, such as dice, roll by successive rotations about the edge or corner which is in contact with the surface.<br />One of the most practical applications of rolling objects is the use of ball bearings in rotating devices. Made of a smooth metal substance, the spherical bearings are usually encased between two rings that can rotate independently of each other. In most mechanisms, the inner ring is attached to a stationary shaft (or axle). Thus, while the inner ring is stationary, the outer ring is free to move with very little friction. This is the basis for which almost all motors (such as those found in ceiling fans, cars, drills, etc) rely on to operate. The amount of friction on the mechanism's parts depends on the quality of the ball bearings and how much lubrication is in the mechanism.<br />Tank after manufacturing& assembling:<br />7.Liquid propellant tank applications:<br />Rockets using liquid propellant tanks can be throttled in realtime, and have good control of mixture ratio; they can also be shut down, and, with a suitable ignition system, restarted. They can also employ regenerative cooling which uses the fuel (or occasionally the oxidiser) to cool the chamber prior to injection.<br />In “ ISRO” , liquid propellant tank is used in second stage of PSLV(POLAR SATELLITE LAUNCH VEHICLE). In the second stage of GSLV also liquid propellant tank is used.<br />8.DISADVANTAGES:<br />Because the propellant is a very large proportion of the mass of the vehicle, the center of mass shifts significantly rearward as the propellant is used; one will typically lose control of the vehicle if its center mass gets too close to the center of drag.<br />liquid propellants can leak, possibly leading to the formation of an explosive mixture<br />turbopumps to pump liquid propellants are complex to design, and can suffer serious failure modes, such as overspeeding if they run dry or shedding fragments at high speed if metal particles from the manufacturing process enter the pump<br />propellants are subject to vortexing within the tank, particularly towards the end of the burn, which can result in gas being sucked into the engine or pump<br />cryogenic propellants can cause ice to form on the outside of the tank, this can fall and damage the vehicle itself.<br />liquid rockets tend to be very complex, which increases the opportunities for malfunctions.<br />9.RECENT ALTERNATIVE <br />The tank shell is partially over wrapped with carbon fiber. To minimize cost, an existing tank shell liner was selected as baseline design and slightly modified for the mission. No modification was done to the tank membrane. The propellant tank shell is constructed of solution treated and aged (STA) 6AL-4V titanium alloy. This material provides excellent strength to weight characteristics and is widely used in the aerospace industry for its excellent material properties and manufacturability. The over wrap and integral mounting skirt are fabricated from T-1000 carbon fiber for high strength and low weight<br />.<br />10.CONCLUSION:<br />Liquid propellant tank manufacturing is involving various materials, machining operations and fabrication techniques as described. Manufacturing of this is one of the major programme in manufacturing a rocket which uses liquid propellant. This is a costly process; however it has its own importance in space applications.<br />11.BIBILIOGRAPHY:<br />1.www.wikipedia.org<br />2.Materials and Fabrication Technology for Satellite& launch vehicle BY C.G. Krishnadas Nair and R. Srinivasan.<br />3.www.google.com <br />