3-71. This portion is Intended to provide some of the information required to fabricate the various aluminum product
into pat and assemblies. Aluminum is one of the most workable of all the common metals. It can be fabricated into a
variety of shapes by conventional methods.
3-72. The formablity varies considerably with alloy and temper. Specific application usually depends on the shape,
strength and temper of the alloy. The preceeding will necessitate that the mechanic be well trained to cope with the
variables associated with this material especially when the end use of the item is an aircraft or a missile.
3-73. FORMING SHEET METAL.
3-74. GENERAL. The forming of aluminum (1100) is relatively easy, using approximately the same procedures as
those used for common steel except that care must be taken to prevent scratching. Do not mark on any metal surface to
be used as a structural component with a graphite pencil or any type of sharp pointed instrument. Use pencil, Aircraft
Marking, Specification MIL-P-83953, NSN 7510-00-537-6928 (Black), 7510-00537-6930 (Yellow), and 7510-00-537-6935
(Red). All shop equipment, tools and work area should be kept smooth, clean-and free of rust and other foreign matter.
3-75. Alloyed aluminums (2024, 7075, 7178, etc.) re more difficult to form, and extensive control is required to prevent
scratching and radii cracking. Scratching will make forming more difficult plus it provides an easy path for corrosion
attack, especially on clad materials. The clad coating referenced is usually a sacrificial corrosion resisting aluminum
alloy coating sandwiched metalurgically to an alloyed core material. The thickness of the coating will depend on the
thickness of the sheet or plate. The nominal cladding thickness Is 4% of composite thickness for material under 0.063
inch; 2.5% for material in the range of 0.063 - 0.187 inch and 1.5% for material 0.188 inch and thicker.
3-76. The following general rules should be employed in the handling and forming operation:
Provide clean are; free of chips, grit ad dirt and other foreign material.
Provide clean smooth (rust free) and adaptable forming equipment.
Sheared or cut edges shall besanded and filed or polished, prior to bending or forming.
Use only straight and smooth forming dies or brake leafs of the correct radius which are free of nicks, burrs ad
Form material across the direction of grain flow when possible.
Material should be of the correct temper, thickness and alloy in the range of "formable" material.
3-77. For intricate forming operations it is necessary to use annealed (Con "O") material and final strength developed by
heat treating after the forming has been accomplished. Heat-treated alloys can also be formed at room temperature
immediately after quenching ('W" temper), which is much more formable than the fully heat-treated temper. The part is
then aged to develop full strength. The forming operation should be performed as soon after quenching as possible, in
view of the natural aging that occurs at room temperature on all the heat treatable alloys. The natural aging can be
delayed to a certain extent by placing the part in a cold storage are of 320 or lower. The lower the temperature the
longer the delay to a point where maximum delay is obtained.
3-78. BENDING. Bending is classified as single curvature forming. Upon bending metal sheet, bar or rod, the material
at the bends flows or deforms, i.e., the material adjacent to the other surface of the bend is under tension and the length
is increased due to stretching and the material adjacent to and on the inner surface is under compression and the length
3-79. The most common problems encountered in practice are springback and cracking within the bend area. Problems
associated with bend cracking are usually a result of improper bend radii, rough edges of material being formed or
forming equipment and bending parallel to direction of grain flow. For the approximate bend radius to use in bending
various thicknesses and types of aluminum see Table 3-13. Actual practice may reveal that a larger or a smaller radius
may be used in some instances. If tighter bend radii is required, then fabricators should proceed with additional caution
and if needed, should seek assistance of engineering or laboratory metallurgists.
3-80. Difficulties encountered with springback are most commonly associated with bending of the stronger alloys,
especially those having high yield strength. Springback problem associated with this material can be overcome to a
certain degree by overforming. The amount of overforming utilized will depend on the temper and the alloy; the softer
the material the less springback compensation required. Other means of reducing springback is to bend the material in
the soft condition (Condition "O") or immediately after .quenching and reducing the thickness of the radius if allowed.
Avoid reducing radii to the point that grain separation or bad cracking results.