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    7 Welding

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    pandaprasad
    Welding is commonly used to join aircraft parts and components. The principal welding types used are electric arc welding, electric resistance welding, and electron beam welding. After welding, heat treatment may be required to address changes to material properties from the heat of welding. All welds must then undergo inspection and non-destructive testing to check for defects before use.

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    7 Welding

    Uploaded by

    pandaprasad
    37 views5 pages
    Welding is commonly used to join aircraft parts and components. The principal welding types used are electric arc welding, electric resistance welding, and electron beam welding. After welding, heat treatment may be required to address changes to material properties from the heat of welding. All welds must then undergo inspection and non-destructive testing to check for defects before use.

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    Welding is commonly used to join aircraft parts and components. The principal welding types used are electric arc welding, electric resistance welding, and electron beam welding. After welding, heat treatment may be required to address changes to material properties from the heat of welding. All welds must then undergo inspection and non-destructive testing to check for defects before use.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    37 views5 pages

    7 Welding

    Uploaded by

    pandaprasad
    Welding is commonly used to join aircraft parts and components. The principal welding types used are electric arc welding, electric resistance welding, and electron beam welding. After welding, heat treatment may be required to address changes to material properties from the heat of welding. All welds must then undergo inspection and non-destructive testing to check for defects before use.

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    Welding in a/c industry

    Welding Process

    Welding is a process of joining two similar


    metals by fusion.
    The principal types of welding used for joining
    a/c parts are
    1. Electric Arc Welding

    R. I. Sujith
    Dept. of Aerospace Engineering
    IIT Madras

    Standard Electric Arc, Argon Arc, Submerged Arc

    2. Electric Resistance Welding


    Spot and Seam Welding

    3. Electron Beam Welding


    1

    Heat Treatment After Welding

    Heat Treatment
    Heat treatment is invariably called for in the case of all
    types of Arc Welding.

    After welding, the welded component may have


    to be heat treated if called for in the relevant
    manufacturing drawings.

    This is because the material properties are adversely affected


    during arc welding due to the intense heat over a wide zone
    adjoining the weld joint.

    For non heat treatable alloys, only stress relieving is


    called for.
    For heat treatable light alloys, the heat treatment
    prescribed is solutionising followed by precipitation
    hardening.
    3

    Heat Treatment.

    Inspection

    For lightly loaded steel components,


    normalizing treatment is sufficient.
    For highly stressed low alloy steel parts, the
    welded component is to be heated to upper
    critical temperature, quenched and tempered.
    For Maraging steels, low temperature ageing
    treatment is sufficient.

    Whichever welding method is adopted, all welds


    should be inspected for welding defects, which
    include cracks, porosity, slag inclusions, lack of
    fusion and penetration.
    The inspection methods to be adopted are
    specified in relevant manufacturing drawings.
    The methods include magnetic particle test, dye
    penetrant test and Xray test.
    5

    Can I do it?

    Standard Arc Welding

    Welding of a/c components can only be undertaken by


    an approved welder
    welder.
    The approval of welders is given by the govt. agencies.
    The approval is given only after the welder
    welders
    performance is evaluated by suitable NDT and
    destructive mechanical testing carried out on samples
    welded by the welder in the presence of govt. agency
    agencys
    representatives.
    The welder
    welders approval has to be renewed every six
    months.

    An electric arc is struck between the workwork-piece and a


    flux coated electrode.
    The faces of the weld joint, electrode tip and flux
    coating all melt.
    The flux protects the metal in the weld zone from
    oxidation.
    The joint is made when the workwork-piece cools down.
    The electrode core material must match the workwork-piece
    material
    After welding, surplus flux/slag is to be cleaned off.
    7

    Applications of Standard Arc


    Welding

    Argon Arc (TIG & MIG) Welding

    Used for welding lightly loaded steel


    components whose sections to be welded are 1.5
    mm thick or above
    For heavily loaded steel components and for
    thinner steel sections, TIG or MIG welding is
    adopted.

    TIG
    Tungsten Inert Gas

    MIG
    Metal Inert Gas

    In both TIG and MIG welding, a stream of


    Argon (inert) gas passes around the electrode on
    to the weld zone.
    The argon gas prevents oxidation of the material
    in the weld zone.

    TIG Welding

    10

    MIG Welding
    In MIG welding, the electrode is consumable and also
    serves as a filler.
    The electrode/filler is a wire, fed from a reel
    continuously to the welding torch.
    The electrode/filler melts on the arc being struck and
    flows into the weld pool.
    The electrode/filler material should match the workworkpiece material.
    MIG is used to weld sections more than 3 mm in
    thickness.

    The arc is struck between a nonnon-consumable


    Tungsten electrode and the workwork-piece.
    Filler material is added from a hand held filler
    rod or wire of the same composition as the
    workwork-piece.
    The welding is used to weld sections less than 3
    mm in thickness.

    11

    12

    TIG & MIG

    Submerged Arc Welding


    Arc is struck between the electrode and the workwork-piece,

    TIG and MIG welding are used to weld


    Aluminum alloys and steels.
    For Ti alloys, TIG welding is carried out in a
    chamber filled with Argon gas.

    the arc being submerged under a covering of molten flux,


    which is electrically conductive.

    This is in addition to the Argon gas flowing over the


    Tungsten electrode.

    The electrode is a wire, fed along with granules of flux


    materials into the weld zone.
    The electrode also serves as the filler wire.
    On reaching the weld zone, the granules of flux melt
    and cover the pool of molten metal.
    This process is used to weld thick sections of steel upto
    6 mm thickness in one pass.

    13

    Electric Resistance Welding

    14

    Electric Resistance Welding

    The parts to be welded are held under pressure


    between a pair of copper electrodes, through
    which a heavy current is passed

    Application
    Welding thin sheets of similar metallic materials

    Approx. 1000 A at 44-12 V

    Heat is generated due to electrical resistance at


    the interface of the parts to be joined.
    Metal at the interface melts and fusion takes
    place.
    On cooling, the joint is made.

    Two types
    Spot Welding
    Seam Welding

    15

    16

    Spot Welding

    Seam Welding

    The electrodes are a pair of copper rods,


    between which the sheets to be welded are
    positioned.
    The welding takes place at discrete intervals.
    Spot welding is used for components of stressed
    skin construction such as panels and floors
    where skin sheets are to be joined with stiffening
    members.

    Electrodes are a pair of copper rolls between


    which the sheets to be welded are passed.
    The seam welded joints are continuous
    Seam welding is used to weld components such
    as fuel tank shells, and other applications which
    require the joint to be leak proof.

    17

    18

    Spot/Seam Welding

    The Weld Cycle

    Two aluminum alloy sheets, upto a maximum


    thickness of 3 mm each, can be spot/seam
    welded together.

    Four phases
    1.
    2.
    3.
    4.

    PrePre-heat
    Dwell
    PostPost-heat
    release

    19

    20

    Electronic Controls
    Electronic controls regulate the pressure (gripping the
    pieces to be welded together), current and voltage, and
    hence the heat at the interface, throughout the four
    phases of the weld cycle.

    Electron Beam Welding

    Prior to spot of seam welding of the a/c components,


    a test piece is to be welded and tested to confirm
    that the electronic controls have been properly set and that
    the welding will be carried out satisfactorily.

    21

    22

    EBW Fundas

    Applications of EBW

    Welding is achieved by directing a narrow beam of high


    velocity electrons on to the joint surfaces.
    Melting and fusion of the joint surfaces is confined to a
    narrow zone in this process, leading to excellent
    mechanical properties of the joint.
    Practically no shrinkage or distortion of the workwork-piece.
    The process is also fast.
    25 mm thick steel plates can be welded in one pass at
    500 mm/minute (as compared to 200 mm/minute for
    arc welding).

    Components of significantly different sectional


    thickness can be successfully joined by the EBW
    process, unlike in other welding processes.
    Thus, a shaft can be welded to a cluster of gears
    or a tailplane spigot to a lever.
    If EBW were not used for the foregoing
    assemblies, they would have been machined
    from heavy piece forgings, leading to very high
    material and machining costs.

    23

    24

    EBW Applications

    Strength

    EBW is used for welding primary structural


    components, e.g., the wing torsion box in Ti
    alloy for Tornado a/c.
    This process is also used for welding
    compressor drums of aero gas turbine engines.

    The weld strength in this process is of the order


    90% of the parent material.
    In many cases, heat treatment is not called for
    after EBW.
    However, for critical primary structural
    components, heat treatment may be called for in
    the relevant manufacturing drawings.

    25

    26

    Afterwards.
    The components after EBW are subjected to
    NDT (ultrasonic or X Ray) as called for in the
    manufacturing drawings.

    27

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