Sheet Metal Bending and repair (rest of Jeppesen Ch. 2)

Define Minimum Bend Radius

The minimum radius for a bend, dependent on the material thickness and hardening procedure.

Define Grain as it relates to sheet metal

the direction of the small grains in the metal from the manufacturing process. you can find grain by looking for small lines that run in one direction

Define Neutral Axis

The portion of the metal that neither shrinks nor stretches, but retains its original dimension. typically near the middle of the sheet metal thickness

Define Mold Line

A line formed by extending a line from the external side of the metal beyond the radius of a bend

Define Mold Point

The point where two mold lines interset in a bend

Define Bend Tangent Line

A line that designates where the sheet metal begins to bend

Define Setback

The distance between the bend tanget line and mold line on the opposite side

Define K-value. What is it used for?

K value is used for determining the setback of bends that are greater or less than 90 degrees. The K value is a multiplier, and is only used for angles greater or less than 90 degrees.

Define Flat

The distance between the inside bend tangent lines from one bend to another or from the end of a piece of metal to the first bend tangent line.

Define Bend Allowance

The amount of (curved) material that is actually involved in the bend and is equal to the length of the neutral axis.

Define Sight Line

A line marked off of the bend tanget line that will be placed under the nose of the brake, at a distance equal to the bend radius of the bend to be used.

Define Joggle

A bend in a piece of metal that is bent up just enough to clear another piece of metal, and then bent back so it will be parallel to the original piece.

Joggles are used to place parts on the same plane so that there are no contours in the metal where parts overlap.

Describe what a Lightening Hole is.

A hole put into a sheet of metal that is useful to both lighten the structure and increase its rigidity (if flaired)

What is Negligble Damage

damage, such as smooth dents, that do not interfere with any structure or mechanism that may be left as they are.

What is meant by fluting or crimping sheet metal?

Putting slight bends along a bent edge in order to correct warping of the edge material

Why are relief holes used when bending sheet metal?

To encourage the metal around a tightly bent corner to bend to a uniform angle and not warp

How can you determine if a repair is a Major or Minor one?

By looking at FAR Part 43 Appendix A

If there is no approved data for a repair, how can you go about getting approval to do the repair?

Fill out and submit a Form 337 and/or call the DER

What is the difference between a scab patch and a flush patch?

A scab patch is placed on top of the existing skin and does not require any removal of material

A flush patch as a doubler that is place beneath the existing skin, with a filler piece to bring the finished repair flush with existing skin.

What is different generally between a repair on a non pressurized aircraft and a pressurized aircraft?

A pressurized repair may require rivets to be dipped in sealant or sealant placed around the repair

What is important to remember when assessing damage to a structure?

Hidden damage may extend beyond the area of visible deformation

OR

To always look for corrosion and remove and treat corroded structural components before the corrosion has a chance to progress

What may rivet tipping be an indication of?

Major structural damage; a tipped rivet means that the skin was pulled in tension enough to deform rivets, and may indicate a larger problem

Repairs to a stressed skin panel that exceed ______ inches constitute a major repair

Repairs to a stressed skin panel that exceed SIX inches constitute a major repair

What are the two special calculateons used when bending sheet metal?

1. Bend Allowance

2. Setback

What factors must be considered in order to determine setback?

1. Bend Radius

2. Material Thickness

What is done to a corner where two bends intersect to prevent cracking?

Relief holes are drilled in the corner

What are the two reasons for installing a lightening hole in a sheet metal wing rib?

To Reduce the weight and increase stiffness

When Repairing an all metal aircraft, how do you determine what metals should be used?

Always use metal of the same type and thickness as the original structure.