A steel beam, the cross section of which resembles the capital letter, I. See STRUCTURAL WELDING.


    A destructive test in which one or more blows are forcefully applied to a specimen to evaluate fracture toughness or other characteristics. The results are expressed in terms of energy absorbed or the number of blows of a specific intensity required to break the specimen. See CHARPY TEST and IZOD TEST.


    A measure of the opposition to current flow in an INCOMPLETE FUSION (IF) alternating current circuit; a combination of resistance and reactance. It is designated by “Z’ in electrical drawings. The unit of impedance is the ohm. 


    A reactance choke coil, used to limit the flow of alternate current.

  • IMPULSE, Resistance Welding

    A sudden change, such as an increase or decrease in voltage or current. In resistance welding, an impulse of welding current consisting of a single pulse, or a series of pulses separated only by an interpulse time. See Figures H-6 and I- 1


    A nonstandard term describing joint penetration which is less than that specified.


    Emitting light as a result of heating; for example, a metal glowing or white with heat. The resistance welding process was once known as incandescent welding because the metals are momentarily incandescent at the moment of welding.


    A nonstandard term for the 6G welding position.

  • INCLINED POSITION, with Restriction Ring

    A nonstandard term for the 6 GR welding position.See 6G.


    A nonstandard term for GROOVE ANGLE.


    Entrapped particles of solid material, such as slag, flux, tungsten, or oxide occurring in metal or welds.


    A weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads. See Figure I-2. See also COMPLETE FUSION. 


    A joint root condition in a groove weld in which weld metal does not extend through the joint thickness. See Figure I-3. See also COMPLETE JOINT PENETRATION, COMPLETE JOINT PENETRATION WELD, PARTIAL JOINT PENETRATION WELD, and JOINT PENETRATION.

    Incomplete Penetration- Among the causes of incomplete penetration are improper joint preparation; using an electrode that is too large, using insufficient welding current, and excessive welding speed. To correct incomplete penetration: allow proper opening at bottom of weld; use electrodes of appropriate diameter in narrow groove; use sufficient welding current and proper welding speed; use a backup bar;  chip or cut out the back of the joint and deposit a bead.


    In a spot, seam, or projection weld, the depression on the exterior surface or surfaces of the base metal.


    A resistance welding secondary circuit variation in which the welding current flows  through the workpieces in locations away from, as well as at, the welds for resistance spot, seam, or projection welding. See Figure I-4.


    Current in an electric circuit that is produced by inductance from another circuit.

  • INDUCED E.M.F. (Electromotive Force)

    Voltage in an electric circuit that is produced by induction from another circuit.


    Magnetism that is produced by electric current or by the action of other magnetism.


    Voltage or pressure in an electric circuit produced by induction.


    The ability of a conducting coil to generate electromotive force by induction within itself.


    The process of generating electromotive force in a closed circuit by varying a magnetic flux through the circuit.


    A brazing process that uses heat from the resistance of the workpieces to induced electric current.  Induction brazing uses a non-ferrous filler metal with a melting point above 425C (800F), but below that of the base metals. The filler metal is distributed in the joint by capilaarry action.  Brazing by induction heating is accomplished by placing the joint to be brazed in an alternating magnetic field. Either magnetic or non-magnetic materials may be induction-brazed.  Induction brazing of hydraulic fittings is shown in Figure 1-5. The fittings are placed in a reversing magnetic field generated in the copper bracket to the left of center. Parts are prefluxed and preformed filler material is placed prior to heating.

    The heating of non-magnetic material depends solely on eddy current losses. Eddy current losses are a function of the frequency of current reversal of the magnetic field, which in turn is determined by the frequency of the current reversals in the conductor. Because the resistance of non-ferrous (non-magnetic) metals is usually less than that of ferrous (magnetic) metals, this loss is comparatively small, so a stronger magnetic field must be used to obtain  comparable heating results. It is necessary, therefore, to go to high frequencies in order to increase the heating effect. See INDUCTION HEATING.


    A rotating device, i.e., a motor, or a solid state electronic device based on an oscillator which may be used to change the frequency of the a-c field, which produces electric current for use in induction heating applications. The device produces a varying magnetic field which induces current into the workpiece.


    Heating a material internally by causing an electric current to flow through the material by electromagnetic induction. It is essential that the material being heated is not a part of any closed electric circuit supplied by electric energy, as is the case with resistance welding.


    Induction heating is a phenomenon caused by an alternating magnetic field. The field occurs in the area surrounding a conductor carrying an alternating current, and the reversals of the magnetic field follow the reversals of current in the conductor. Magnetic material, if placed within this field, is heated by both hysteresis and eddy current losses. Hysteresis loss is caused by molecular friction within the material, and the magnitude of this loss is directly proportional to the frequency of the magnetic field. Eddy current losses are resistance losses that are a resulting of small circulating currents within the material. This loss is proportional to the square of the frequency and the square of the current flowing in the field-producing conductor.

    Induction heating will produce a fast, localized heat that is controllable within close limitations to a predetermined temperature; these qualities make this heating process adaptable to many mass production manufacturing applications. Wear resistance of pinion gears, splines and journals on shafts can be improved by selective hardening.

    A system for hardening a small pinion gear of AISI 4140 steel provides a case extending 0.50 to 0.75 mm (0.020 to 0.030 in.) below the roots of the gear teeth. The gear is moved clear of the loading position into the induction coil on a pop-up rotary spindle. After being heated, it is lowered to the quench position. The unit is serviced by a 60-kW/150 to 400 kHz induction generator.

    Skin Effect- The higher the frequency of the induction heater power supply, the more the induced voltage tends to concentrate in the outer layers (skin effect) of the workpiece. Thus, the induction heater can produce a hardened outer surface of the workpiece while leaving the inner surface relatively unchanged.


    A resistance seam welding process variation in which high-frequency welding current is induced in the workpieces. See HIGH FREQUENCY RESISTANCE WELDING and HIGH-FREQUENCY SEAM WELDING.