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The spacecraft (satellite) are built with propulsion systems. This is essential to meet the on board parameters to be maintained for the payloads built into the spacecraft. There are many forces against which the spacecraft needs to overcome. Some of their are earth’s gravity, moon gravity and sun gravity. A communication spacecraft is essential to be positioned at 3600 km above the earth for constant earth lock essential for maintaining communication link earth based ground stations.
The harsh atmosphere of space is such that the part of the spacecraft facing sum will have 50° c and the dark side of the spacecraft looking into dark-side has -40°c. Because of these extreme temperature system. The propulsion system undergo deep stress there by technology needs to be adapted to meet these extreme thermal environment for the on board propulsion system. The Bimetallic transition tube has two differential co efficient of thermal expansion. These tubes are mount reroute to the oxidiser and propellant feed circuit (N2O4 & MMH) mono methyl hydrazine ). This feature takes care of the differential temperature and there by the operation and extension of the life of the spacecraft.
1.2 BIMETALLIC TRANSITION JOINT
The Transition Joint is a prefabricated, non-separable, metallurgical bonded joint used for field butt welding of dissimilar metal piping components which are not weld able to each other. Typical metals include aluminium to stainless steel for cryogenic applications. Shown in fig 1.1
Tube Turns Transition Joints have been manufactured for over 40 years in pipe sizes ranging from 1/2" to 36" diameter and have been produced from a variety of stainless steels (304, 304L, 316, 316L, 321, 347) and aluminium alloys (3003, 5082, 5083, 6061). They are used to join stainless piping to aluminium piping for cryogenic services down to minus 320 deg F and are installed in heat exchangers, liquefied gas storage tanks and transfer lines. They are used in many applications for pressures ranging from full vacuum to in excess of 6,000 psi.
1.2.2 Rugged Construction
The construction of these Transitions Joints utilizes flanges and lap joint stub ends accordance with ASME\ANSI dimensions that are proven to be reliable in all service conditions. These components are continually sealed welded to a bimetallic ring to provide a leak proof joint. This bimetallic ring consists of a layer of type 304 stainless steel and a layer of 1100 Aluminium joined together by pressure welding to produce a strong, ductile solid-phase bond. The flanges are then bolted together and the bolts tightened to a predetermined torque. The bolts and nuts are then tacked welded to provide a non-separable unit. These joints are constructed in accordance with the ASME B31.3 Chemical Plant and Petroleum Refinery Piping and
http://www.sypris.com/sypris-tube-turns/about-us/facility-credentialsASME Boiler and Pressure Vessel Code, Section IX, Welding and Brazing
Fig 1.1 Bi-Metallic Samples
1.3 ALUMINIUM ALLOY
Aluminium alloy 7075 is a medium strength alloy with excellent corrosion resistance. It has the highest strength of the 7000 series alloys. Alloy 7075 is known as a structural alloy. In plate form, 7075 is the alloy most commonly used for machining. As a relatively new alloy, the higher strength of has seen it replace 7075 in many applications. The addition of a large amount of manganese controls the grain structure which in turn results in a stronger alloy.
In the T6 and T651 temper, Aluminium alloy 7075 machine well and produces tight coils of sward when chip breakers are used. Al alloy 7075 for structural application, including rod, bar tube and profiles. This alloy offers similar but not equivalent physical characteristics compared to 7075 alloy and slightly higher mechanical properties in T6 condition.
Alloy 7075 is very common in Europe and is gaining popularity in the United States for rod and bar machining stocks, seamless tubing, structural profiles and custom profiles. The alloy also offers good finishing characteristics and response well to anodizing. The most common anodizing method includes clear, clear and color dye and hard coat. When bending or forming 7075 alloy, it is recommended to use the O or T4 tempers.
For machining application 6082 provides good mach inability in T6 or T5 tempers. However since 7075 is a heat treatable alloy, strength will be reduced in weld region.
1.3.1 7075 Temper Designation and Definitions
O- Annealed applies to products that are annealed to obtain the lowest strength temper.
T4- Solution heat treated and naturally aged.
T5- Cooled from an elevated temperature shaping process and artificially aged.
T6- Solution heat treated and artificially aged.
1.3.2 Advantages of Aluminium and its Alloys:
22.214.171.124 Light Weight
Aluminium is a very light 1metal with a specific weight of 2.7 g/cm3, about a third that of steel. For example, the use of aluminium in vehicles reduces dead-weight and energy consumption while increasing load capacity. Its strength can be adapted to the application required by modifying the composition of its alloys.
126.96.36.199 Corrosion Resistance
Aluminium naturally generates a protective oxide coating and is highly corrosion resistant. Different types of surface treatment such as anodizing, painting or lacquering can further improve this property. It is particularly useful for applications where protection and conservation are required.
188.8.131.52 Electrical and Thermal Conductivity
Aluminium is an excellent heat and electricity conductor and in relation to its weight is almost twice as good a conductor as copper. This has made aluminium the most commonly used material in major power transmission lines.
Aluminium is a good reflector of visible light as well as heat, and that together with its low weight makes it an ideal material for reflectors in, for example, light fittings or rescue blankets.
Aluminium is ductile and has a low melting point and density. In a molten condition it can be processed in a number of ways. Its ductility allows products of aluminum to be basically formed close to the end of the product’s design.
184.108.40.206 Impermeable and Odourless
Aluminium foil, even when it is rolled to only 0.007 mm thickness, is still completely impermeable and let’s neither light aroma nor taste substances out. Moreover, the metal itself is non-toxic and releases no aroma or taste substances which make it ideal for packaging sensitive products such as food or pharmaceuticals.
Aluminium is 100 percent recyclable with no downgrading of its qualities. The re-melting of aluminium requires little energy: only about 5 percent of the energy required to produce the primary metal initially is needed in the recycling process.
1.3.3 Applications of 7075 Aluminium Alloy
High stress applications.
Air craft fittings.
Marine fittings and hardware’s.
Camera lens mounts.
Valves and valve ports.
1.4. STAINLESS STEEL
http://en.wikipedia.org/wiki/Metallurgymetallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 to 11% chromium content by mass. Stainless steel does not
http://en.wikipedia.org/wiki/Rustrust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low oxygen, high salinity, or poor circulation environments. It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.
Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel
http://en.wikipedia.org/wiki/Rustrusts readily when exposed to air and moisture. This
http://en.wikipedia.org/wiki/Iron_oxideiron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide, and due to the dissimilar size of the iron and iron oxide molecules (iron oxide is larger) these tend to flake and fall away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion and blocks corrosion from spreading into the metal's internal structure, and due to the similar size of the steel and oxide molecules they bond very strongly and remain attached to the surface.
http://en.wikipedia.org/wiki/PassivationPassivation only occurs if the proportion of chromium is high enough and in the presence of oxygen .High oxidation-resistance in
http://en.wikipedia.org/wiki/Earth%27s_atmosphereair at ambient
http://en.wikipedia.org/wiki/Temperaturetemperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments. The chromium forms a
http://en.wikipedia.org/wiki/Passivationpassivation layer of
http://en.wikipedia.org/wiki/Chromium(III)_oxidechromium (III) oxide (Cr2O3) when exposed to
http://en.wikipedia.org/wiki/Oxygenoxygen. The layer is too thin to be visible, and the metal remains lustrous. The layer is impervious to
http://en.wikipedia.org/wiki/Waterwater and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called
http://en.wikipedia.org/wiki/Passivationpassivation and is seen in other metals, such as
http://en.wikipedia.org/wiki/Titaniumtitanium. Corrosion-resistance can be adversely affected if the component is used in a non-oxygenated environment, a typical example being underwater
http://en.wikipedia.org/wiki/Keelkeel bolts buried in
When stainless steel parts such as
http://en.wikipedia.org/wiki/Screwbolts are forced together, the oxide layer can be scraped off, causing the parts to
http://en.wikipedia.org/wiki/Weldingweld together. When disassembled, the welded material may be torn and pitted, an effect known as
http://en.wikipedia.org/wiki/Gallinggalling. This destructive galling can be best avoided by the use of dissimilar materials for the parts forced together, for example bronze and stainless steel, or even different types of stainless steels (martensitic against austenitic), when metal-to-metal wear is a concern. Nitronic alloys reduce the tendency to gall through selective alloying with manganese and nitrogen. Additionally, threaded joints may be lubricated to prevent galling.
Similarly to steel, stainless steel is not a very good conductor of electricity, with about a few percent of the electrical conductivity of copper.
http://en.wikipedia.org/wiki/Martensitemartensitic stainless steels are magnetic.
http://en.wikipedia.org/wiki/AusteniticAustenitic stainless steels are non-magnetic. Stainless steel’s resistance to corrosion and staining, low maintenance and familiar
http://en.wikipedia.org/wiki/Lustre_(mineralogy)lustre make it an ideal material for many applications. There are over 150 grades of stainless steel, of which fifteen are most commonly used.
The alloy is
http://en.wikipedia.org/wiki/Steel_millmilled into coils, sheets, plates, bars, wire, and tubing to be used in
http://en.wikipedia.org/wiki/Major_appliancesmajor appliances, industrial equipment (for example, in
http://en.wikipedia.org/wiki/Sugar_refinerysugar refineries) and as an automotive and aerospace structural alloy and construction material in large buildings. Storage tanks and tankers used to transport
http://en.wikipedia.org/wiki/Orange_juiceorange juice and other food are often made of stainless steel, because of its corrosion resistance and
http://en.wikipedia.org/wiki/Antibacterialantibacterial properties. This also influences its use in commercial kitchens and food processing plants, as it can be steam-cleaned and
http://en.wikipedia.org/wiki/Sterilization_(microbiology)sterilized and does not need paint or other surface finishes.
Stainless steel is used for jewelry and watches with 316L being the type commonly used for such applications. It can be re-finished by any jeweler and will not oxidize or turn black.
Some firearms incorporate stainless steel components as an alternative to
http://en.wikipedia.org/wiki/Parkerizedparkerized steel. Some
http://en.wikipedia.org/wiki/Handgunhandgun models, such as the
http://en.wikipedia.org/wiki/Smith_%26_Wesson_Model_60Smith & Wesson Model 60 and the Colt
http://en.wikipedia.org/wiki/M1911_pistolM1911 pistol, can be made entirely from stainless steel. This gives a high-luster finish similar in appearance to nickel plating. Unlike plating, the finish is not subject to flaking, peeling, wear-off from rubbing (as when repeatedly removed from a holster), or rust when scratched. Some
http://en.wikipedia.org/wiki/Automotive_industryautomotive manufacturers use stainless steel as decorative highlights in their vehicles.
1.4.1 Applications of Stainless Steel
Some of the applications of stainless steel are given below
220.127.116.11 Architectural Applications
Stainless steel is used for buildings for both practical and aesthetic reasons. Stainless steel was in vogue during the
http://en.wikipedia.org/wiki/Art_decoart deco period. The most famous example of this is the upper portion of the
http://en.wikipedia.org/wiki/Chrysler_BuildingChrysler Building (pictured). Some diners and fast-food restaurants use large ornamental panels and stainless fixtures and furniture. Because of the durability of the material, many of these buildings retain their original appearance. The forging of stainless steel has given rise to a fresh approach to architectural
http://en.wikipedia.org/wiki/Blacksmithblacksmithing in recent years.
Type 316 stainless is used on the exterior of both the
http://en.wikipedia.org/wiki/Petronas_Twin_TowersPetronas Twin Towers and the
http://en.wikipedia.org/wiki/Jin_Mao_BuildingJin Mao Building, two of the world's tallest
http://en.wikipedia.org/wiki/Parliament_House,_CanberraParliament House of Australia in Canberra has a stainless steel flagpole weighing over 220 tonnes (240 short tons). The aeration building in the
http://en.wikipedia.org/wiki/Edmonton_Composting_FacilityEdmonton Composting Facility, the size of 14 hockey rinks, is the largest stainless steel building in North America.
Fig1.2 Pipes and fittings made of stainless steel
http://en.wikipedia.org/wiki/Cala_Galdana_BridgeCala Galdana Bridge in Minorca (Spain) is the first stainless steel road bridge.
http://en.wikipedia.org/w/index.php?title=Sant_Fruitos_Pedestrian_Bridge&action=edit&redlink=1Sant Fruitos Pedestrian Bridge (Catalonia, Spain), arch pedestrian bridge.
http://en.wikipedia.org/w/index.php?title=Padre_Arrupe_Bridge&action=edit&redlink=1Padre Arrupe Bridge (Bilbao, Spain) links the Guggenheim museum to the University of Deusto.
http://en.wikipedia.org/wiki/UnisphereUnisphere, constructed as the theme symbol of the 1964-5 World's Fair in New York City, is constructed of Type 304L stainless steel as a sphere with a diameter of 120 feet, or 36.57 meters.
The Gateway Arch (pictured) is clad entirely in stainless steel: 886 tons (804 metric tonnes) of 0.25 in (6.4 mm) plate, #3 finish, type 304 stainless steel.
http://en.wikipedia.org/wiki/United_States_Air_Force_MemorialUnited States Air Force Memorial has an austenitic stainless steel structural skin.
http://en.wikipedia.org/wiki/BelgiumBelgium was renovated with stainless-steel cladding in a renovation completed in 2006; previously the spheres and tubes of the structure were clad in aluminium.
http://en.wikipedia.org/wiki/Cloud_GateCloud Gate sculpture by
http://en.wikipedia.org/wiki/Anish_KapoorAnish Kapoor, in Chicago US.
http://en.wikipedia.org/wiki/Sibelius_monumentSibelius monument in Helsinki, Finland, is made entirely of stainless steel tubes.
18.104.22.168 Automotive Bodies:
http://en.wikipedia.org/wiki/Allegheny_TechnologiesAllegheny Ludlum Corporation worked with
http://en.wikipedia.org/wiki/Ford_Motor_CompanyFord on various
http://en.wikipedia.org/wiki/Concept_carconcept cars with stainless steel bodies from the 1930s through the 1970s, as demonstrations of the material's potential. In 1981 and 1982, the
http://en.wikipedia.org/wiki/DeLorean_DMC-12DeLorean DMC-12 production automobile used stainless steel body panels over a
Rail cars have commonly been manufactured using corrugated stainless steel panels (for additional structural strength). This was particularly popular during the 1960s and 1970s, but has since declined. One notable example was the early
http://en.wikipedia.org/wiki/Pioneer_ZephyrPioneer Zephyr. Notable former manufacturers of stainless steel rolling stock included the
http://en.wikipedia.org/wiki/Budd_CompanyBudd Company (USA), which has been licensed to Japan's
http://en.wikipedia.org/wiki/Tokyu_Car_CorporationTokyu Car Corporation, and the Portuguese company
Budd also built an airplane, the
http://en.wikipedia.org/wiki/Budd_BB-1_PioneerBudd BB-1 Pioneer, of stainless steel tube and sheet, which is on display at the
22.214.171.124 Recycling and Reuse
Stainless steel is 100%
http://en.wikipedia.org/wiki/Recyclablerecyclable. An average stainless 60% recycled material of which approximately 40% originates from end-of-life products and about 60% comes from manufacturing processes. According to the
http://en.wikipedia.org/wiki/International_Resource_PanelInternational Resource Panel's
http://en.wikipedia.org/wiki/Metal_Stocks_in_Society_reportMetal Stocks in Society report, the per capita stock of stainless steel in use in society is 80–180kg in more developed countries and 15kg in less-developed countries. There is a secondary market that recycles usable scrap for many stainless steel markets. The product is mostly coil, sheet and blanks. This material is purchased at a less-than-prime price and sold to commercial quality stampers and sheet metal houses. The material may have scratches, pits and dents but is made to the current specifications.
1.5 TYPES OF STAINLESS STEEL
There are different types of stainless steels: when
http://en.wikipedia.org/wiki/Nickelnickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels virtually non-
http://en.wikipedia.org/wiki/Magneticmagnetic and less
http://en.wikipedia.org/wiki/Brittlebrittle at low temperatures. For greater
http://en.wikipedia.org/wiki/Hardness_(materials_science)hardness and strength, more
http://en.wikipedia.org/wiki/Carboncarbon is added. With proper
http://en.wikipedia.org/wiki/Heat_treatmentheat treatment, these
http://en.wikipedia.org/wiki/Razor_blade_steelrazor blade steels are used for such things as razor blades, cutlery, and tools. Significant quantities of
http://en.wikipedia.org/wiki/Manganesemanganese have been used in many stainless steel compositions. Manganese preserves an austenitic structure in the steel, similar to nickel, but at a lower
Stainless steels are also classified by their
http://en.wikipedia.org/wiki/AusteniteAustenitic, or 300 series, stainless steels have an austenitic crystalline structure, which is a
http://en.wikipedia.org/wiki/Face-centered_cubicface-centered cubic crystal structure. Austenite steels make up over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the
http://en.wikipedia.org/wiki/Cryogeniccryogenic region to the melting point of the alloy. The most widely used austenite steel is the
http://en.wikipedia.org/w/index.php?title=SAE_304_stainless_steel&action=edit&redlink=1304 grade or A2 stainless steel(not to be confused with A2 grade steel, also named
http://en.wikipedia.org/wiki/Tool_steelTool steel, a steel). The second most common austenite steel is the
http://en.wikipedia.org/wiki/Marine_grade_stainless316 grade, also called marine grade stainless, used primarily for its increased resistance to corrosion. A typical composition of 18% chromium and 10% nickel, commonly known as 18/10 stainless, is often used in
http://en.wikipedia.org/wiki/Flatwareflatware and high quality
http://en.wikipedia.org/wiki/Cookwarecookware. 18/0 and 18/8 are also available.
Superaustenitic stainless steels, such as alloy
http://en.wikipedia.org/wiki/AL-6XNAL-6XN and 254SMO, exhibit great resistance to chloride pitting and crevice corrosion because of high
http://en.wikipedia.org/wiki/Molybdenummolybdenum content (>6%) and nitrogen additions, and the higher nickel content ensures better resistance to stress-corrosion cracking versus the 300 series. The higher alloy content of super austenitic steels makes them more expensive. Other steels can offer similar performance at lower cost and are preferred in certain applications, for example ASTM A387 is used in pressure vessels but is a low alloy carbon steel with a chromium content of 0.5% to 9%.
http://en.wikipedia.org/wiki/Stainless_steel Low-carbon versions, for example
http://en.wikipedia.org/wiki/Marine_grade_stainless316L or 304L, are used to avoid corrosion problems caused by welding. Grade 316LVM is preferred where
http://en.wikipedia.org/wiki/Biocompatibilitybiocompatibility is required (such as body implants and piercings).
http://en.wikipedia.org/wiki/Stainless_steel The "L" means that the carbon content of the alloy is below 0.03%, which reduces the
http://en.wikipedia.org/wiki/Sensitization_effectsensitization effect (precipitation of chromium carbides at grain boundaries) caused by the high temperatures involved in welding.
http://en.wikipedia.org/wiki/Ferrite_(iron)Ferritic stainless steels generally have better engineering properties than austenitic grades, but have reduced corrosion resistance, because of the lower chromium and nickel content. They are also usually less expensive. They contain between 10.5% and 27% chromium and very little nickel, if any, but some types can contain lead. Most compositions include molybdenum; some, aluminium or titanium. Common ferritic grades include 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni. These alloys can be degraded by the presence of chromium, an intermetallic phase which can precipitate upon welding.
http://en.wikipedia.org/wiki/Martensitic_stainless_steelMartensitic stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly
http://en.wikipedia.org/wiki/Machinabilitymachinable, and can be hardened by heat treatment. Martensitic stainless steel contains chromium (12–14%), molybdenum (0.2–1%), nickel (less than 2%), and carbon (about 0.1–1%) (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic.
Precipitation-hardening martensitic stainless steels have corrosion resistance comparable to austenitic varieties, but can be
http://en.wikipedia.org/wiki/Precipitation_hardeningprecipitation hardened to even higher strengths than the other martensitic grades. The most common,
http://en.wikipedia.org/w/index.php?title=17-4PH&action=edit&redlink=117-4PH, uses about 17% chromium and 4% nickel. The Lockheed-Martin
http://en.wikipedia.org/wiki/Joint_Strike_FighterJoint Strike Fighter is the first aircraft to use a precipitation-hardenable stainless steel—
http://en.wikipedia.org/w/index.php?title=Carpenter_Custom_465&action=edit&redlink=1Carpenter Custom 465—in its airframe.
Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels.
1.6 GENERAL INFORMATION OF SS04L
The alloy is readily formed in the annealed temper. SS 304L may be joined by all commonly used brazing and welding methods including oxyacetylene. The corrosive resistance to acids is generally very good with the exception of halogen acids.
1.7 APPLICATION OF STAINLESS STEEL 304L
304/304L is used almost exclusively for parts requiring machining, welding, grinding, or polishing where good corrosion resistance is also required.
It is a good general all-purpose stainless grade. Good in corrosive environments as in paper and chemical industries and cryogenic services. Used where corrosion resistance and good mechanical properties are primary requirements.
304/304L is widely accepted in such industries as dairy, beverage, and other food industries where the highest degree of sanitation and cleanliness is of prime importance. Parts for handling acetic, nitric, and citric acids, organic and inorganic chemicals, dyestuffs, crude and refined oils, etc., are fabricated from this material.
Because of its lack of magnetism it is highly desirable for instruments. It is also widely used for architectural trim. 304 plate is used in applications where corrosion resistance is required, but elevated temperatures are not involved. 304/304L finds particular use in applications requiring welding. 304/304L has good drawing, forming, and stamping properties.
1.8 FRICTION WELDING
Friction welding is a solid state joining process that uses rotational motion and high axial pressures to convert rotational energy into frictional heat at a circular interface. The heat produced by this rubbing action raises the intersurface temperature of the two parts to the plastic state where the high thrust load extrudes metal from the weld region to form an upset. When sufficient energy input has occurred, the rotation is stopped and thrust load is increased, to forge the parts together and form a solid state bond. The flash may be removed as part of the machine cycle.
The plastic deformation in the weld zone results in grain refinement, favorable flow line orientation and expulsion of impurities.
Fig 1.3 Schematic Diagram for friction Welding Process
There are two variations of the process, conventional Direct Motor Drive Friction welding and Inertia friction welding.
1.8.1 Continuous Drive Friction Welding
In continuous “direct drive” friction welding, one work piece is attached to a rotating motor drive unit as shown above. The other work piece is clamped in a non-rotating axial drive unit. The two work pieces are gradually brought together with one rotating and the other still. When they make contact, heat is generated at the interface due to friction. Additional axial force is applied. The axial force is raised to a final constant value and held for a predetermined time, or until a preset amount of upset takes place. The rotational driving force is disconnected, and the rotating work piece is stopped by the application of a braking force. The axial force (forging force) is maintained or increased for a predetermined time after rotation ceases.
Fig 1.4 Experimental setup for continuous drive friction welding
Fig 1.5 Parameters on continuous drive friction welding
1.8.2 Inertia Welding Process Description
In inertia friction welding, one of the work pieces is connected to a flywheel, and the other is connected to a non-rotating axial drive system. The flywheel is accelerated to a predetermined rotational speed, storing the required rotational kinetic energy. The drive motor is disengaged and the work pieces are brought together. This causes the faying surfaces to rub together under pressure. The kinetic energy stored in the rotating flywheel is dissipated as heat through friction at the weld interface as the flywheel speed decreases. An increase in friction welding force (forging force) may be applied before rotation stops. The forge force is maintained for a predetermined time after rotation ceases to complete the weld.
Fig 1.6 Experimental setup for inertia drive friction welding
1.9 VARIOUS PHASES OF FRICTION WELDING
1.9.1 Parts Contact
Parts come in contact with each other and part lengths are verified to be within pre-welded length tolerance.
1.9.2 First Friction Phase
The spindle begins to rotate and the parts are pressed in contact with each other with a force of 3,000-6,000 pounds per square inch of weld area. Typically pre-heating of the weld interface occurs with no material displacement at this point. Friction duration is controlled by time. The purpose of the first friction phase is to burn off any light oils or light oxides at the weld interface.
19.3 Second Friction Phase
This phase controls the amount of material length loss. Approximately 2/3 of total material displacement occurs. Welding force of 6,000-12,000 pounds per square inch of weld area is applied. The three methods of controlling the amount of material length loss in this friction phase are the use of Time, Constant Distance and Position.
With the Time method of controlling length loss, a simple timer is used to count the number of seconds the machine is at 2nd friction pressure. When the pre-set time is achieved the machine goes into Forge Pressure and rotation is stopped. This method is not used much since glass scales have been added to most modern equipment.
With the Constant Distance method of controlling length loss each time the two components make initial part contact, the machine zeros a precision glass scale. When the pre-determined amount of material length loss is achieved, the machine goes into forge pressure and rotation is stopped. This method is most common. Incoming material lengths must be within tolerance otherwise out coming weldments will be out of tolerance.
The last method of controlling length loss in Second Friction is by Position. During the initial set-up the stack up of both components is measured and using a precision glass scale the machine is calibrated using this measurement. The material length loss is subtracted from the measurement and this value (or trigger position) is entered into machine. Independent of component length, the machine will go into forge phase when the trigger position is reached. This method produces the greatest repeatability of overall length on the weldment. Since heat produced during 2nd friction phase would not be consistent from part to part, it will not make up for out of spec component lengths.
1.9.4 Forge Phase
The final phase in friction welding is the forge phase. The spindle is forced to a stop and both components are pressed against each other at extreme pressure and allowed to cool. Typically, approximately 1/3 of total material displacement occurs during this phase. There is no control as to how much material is displaced in the forge phase but it is dependent on the amount of heat generated in the Second Phase and the amount of pressure applied. Forge phase duration is controlled by time( typically only 5 to 15 seconds) and a forging force of 12,000-24,000 pounds per square inch of weld area is applied.
1.10 STEPS INVOLVED IN FRICTION WELDING
One component is rotated while the other is advanced into pressure contact with it.
Heat is produced at the faying surfaces. Overheating of metals cannot occur as the weld zone temperature is always stabilized below melting point.
Softened material begins to extrude in response to the applied pressure, creating an annular upset.
Heat is conducted away from the interfacial area for forging to take place
Rotation is stopped and a forge force is applied to complete the weld
The joint undergoes hot working to form a homogenous, full surface, full diameter, high-integrity weld.
1.11 ADVANTAGES OF FRICTION WELDING
Friction welding has become industry standard in a number of applications. Some of the advantages of the process are detailed below
Weld monitoring can insure 100% weld quality.
Friction welding produces a 100% cross sectional weld area.
Far superior weld integrity compared to MIG welding.
Limited operator training required.
The weld cycle is fully controlled by the machine.
Friction welding is a solid state process and does not suffer from inclusion and gas porosity.
Friction welding requires no consumables therefore become more cost effective over time.
Friction welding typically will complete a full cross sectional weld in 15% of the time it take MIG welding to produce an 85% cross sectional weld.
No post machining is needed for friction welded components
16 displacement at this point. Friction duration is controlled by time. The purpose of the first friction phase is to burn off any light oils or light oxides at the weld interface.
Heat is produced at the