Layout, Forming, and Drilling of Sheet Metal Components Flashcards
1
Q
Define Base Measurement
A
the outside dimensions of a formed part.
2
Q
Define Leg
A
the longer part of a formed angle
3
Q
Define Flange
A
the shorter part of a formed angle. It is opposite of the leg.
4
Q
Describe Grain of the metal
A
- natural grain of the material is formed as the sheet is rolled from
molten ingot. - Bend lines should be made to lie at a 90 degree angle to the grain
of the metal, if possible.
5
Q
Define Bend Allowance
A
- refers to the curved section of the metal within the bend.
- it is the length of the curved portion of the neutral line.
6
Q
Define Bend Radius
A
- the arc is formed when sheet metal is bent.
- it is measured from a radius center to the inside surface of the
metal. - minimum bend radius depends on temper, thickness, and type of
material. - minimum bend radius charts are found in manufacturer’s
maintenance manuals.
7
Q
Define Bend Tangent Line
A
- the location at which the metal starts to bend and the line at which
the metal stops curving. - all space between the bend tangent lines is the bend allowance.
8
Q
Define Neutral Axis
A
- an imaginary line that has the same length after bending as it had
before bending. - after bending, the bend area is 10-15 percent thinner than before
bending. - this thinning of the bend area moves the neutral line of the metal
towards the radius center. - it is often assumed that the neutral axis is located at the center of
the material, although it is not exactly in the center.
9
Q
Define Mold Line
A
an extension of the flat side of a part beyond the radius
10
Q
Define Mold Line Dimension
A
- the dimension of a part made by the intersection of mold lines
- the dimension the part would have it its corners had no radius.
11
Q
Define Mold Point
A
- the point of intersection of the mold lines.
- the mold point would be the outside corner of the part if there
were no radius.
12
Q
Define K-Factor
A
- the percentage of the material thickness, where there is no
stretching or compressing of the material, such as the neutral axis. - when metal is bent to any angle other 90 degrees, the
corresponding K-factor number is selected from the K-Chart and
multiplied by the sum of the radius and thickness of the metal.
The product is the amount of setback for the bend. - If no K Chart is available, the K factor can be calculated by using
the following formula: SB=K(R+T). The K value is the tangent of
1/2 of the bend angle. - K factor must be used for all bends that are smaller or larger than
90 degrees.
13
Q
Define Setback
A
- the distance the jaws of a brake must be setback from the mold
line to form a bend. - The setback dimension must be determined prior to making the
bend because setback is used in determining the location of the
beginning bend tangent line. - If a part has more than one bend, setback must be subtracted for
each bend. - SB=K(R+T)
14
Q
Define Sight Line
A
- also called the bend or brake line
- the layout line on the metal being formed that is set even with the
nose of the brake - serves as a guide in bending the work
15
Q
Define Flat
A
- that portion of a part that is not included in the bend
- it is equal to the base measurement minus the setback
- Flat=MLD-SB
16
Q
Define Closed Angle
A
- an angle that is less than 90 degrees when measured between legs or
- an angle that is more than 90 degrees when the amount of bend is measured
17
Q
Define Open Angle
A
- an angle that is more than 90 degrees when measured between
legs or - an angle that is less than 90 degrees when the amount of bend is
measured.
18
Q
Define Total Developed Width (TDW)
A
- the width of material measured around the bends from edge to
edge. - TDW is less than the sum of mold line dimensions since the metal
is bent on a radius and not to a square corner as MLD indicates. - TDW is necessary to determine the size of material to be cut.
19
Q
What formula is used to find the K factor if a K Chart is not available?
A
SB=K(R+T)
SB - Setback
K - K-factor (K is 1 for 90 degree bends)
R - inside radius of the bend
T - material thickness
20
Q
Why must the setback dimension be determined prior to making the bend?
A
The setback is used in determining the location of the
beginning bend tangent line.
21
Q
Where is the bend radius measured?
A
it is measured from a radius center to the inside surface of the
metal.
22
Q
Minimum bend radius depends on what?
A
minimum bend radius depends on temper, thickness, and type of
material.
23
Q
Where are minimum bend radius charts found?
A
Manufacturer’s Maintenance Manual
24
Q
Why is it important to make a layout or flat pattern before forming the part?
A
- greater degree of accuracy in the finished part
- prevent waste
- It shows
a. how much material is required in the bend areas
b. at what point the sheet must be inserted into forming tool
c. where bend lines are located
25
When forming straight angle bends correct allowances must be made for what two things?
1. Setback
2. Bend allowances
26
When forming straight angle bends, correct allowances must be made for what tow things?
1. Setback
2. Bend Allowance
27
If shrinking or stretching processes are to be used, allowances must be made for what?
so that the part can be turned out with a minimum amount of forming.
28
What must be considered when forming straight line bends?
1. thickness of the material
2. its alloy composition
3. its temper condition
4. bend allowance
5. setback
6. brake or straight line
29
What is the minimum radius of bend of a sheet of material?
It is the sharpest curve or bend to which the sheet can be bent without critically weakening the metal at the bend
30
If the radius of bend is too small, what can happen to the metal?
stresses and strains weaken the metal and may result in cracking
31
What is the radius of bend of a sheet of material?
it is the radius of the bend as measured on the inside of the curved material
a. the thinner the material, the more sharply it can be bent (smaller
radius of bend)
b. the softer the material, the sharper the bend is
32
The minimum bend radius is affected by what?
1. kind of material
2. thickness of the material
3. temper condition of the material
33
Annealed sheet can be bent to a radius of?
approximately equal to its thickness
34
Stainless steel and 2024-T3 aluminum bend radius is?
it requires a fairly large bend radius
35
What are the steps for bending a U Channel?
1. Determine the correct bend radius (found in manufacturers
maintenance manual)
2. Find the Setback ( found with formula, aircraft maintenance
manual, or SMRs)
3. Find the Length of the Flat Line Dimension ( use formula:
Flat = MLD - SB)
4. Find the bend allowance
Formula 1: 2𝝅(R+1/2T) / 4
Formula 2: Bend Allowance = N(R+T)
5. Find the Total Developed Width of the Material
TDW = Flat 1 + Flat 2 + Flat 3 + (2 x BA)
6. Flat Pattern Layout
7. Draw the Sight Lines on the Flat Pattern
36
How do you find the Setback?
1. formula SB=K(R+T)
2. aircraft maintenance manual
3. SMRs
37
Where do you find the correct bend radius of a material?
Manufacturers maintenance manual
38
What 2 formulas can be used to find the Bend Allowance
1. 2𝝅(R+1/2T) / 4
R = radius of the bend
1/2T = half the thickness of metal
2. Bend Allowance = (0.01743R+ 0.0078T)N
N = number of degrees of the bend
R = the desired bend radius
T = the thickness of the metal
39
Find the bend allowance for a 90 degree bend having a radius of 1/4 inch for material 0.051 inch thick using the following formula
2𝝅(R + 1/2T)/4
BA = (2 x 3.1416)(0250 + 1/2(0.051)) / 4
BA = 6.2832(0.250 + 0.0255) / 4
BA = 6.2832(0.2755) / 4
BA = 1.7310216 / 4
BA = 0.4327
So, the bend allowance, length of material required for the bend, is 0.4327 or 7/16 inch
40
Find the bend allowance for a 90 degree bend having a radius of .16 inch for material .040 inch thick using the formula
BA = (0.01743R + 0.0078T)N
R = the desired bend radius
T = the thickness of the metal
N = number of degrees of bend
BA = (0.01743R + 0.0078T)N
BA = (0.01743 x 0.16) + (0.0078 x 0.040) x 90
BA = (0.002789 + 0.000312) x 90
BA = 0.0031008 x 90
BA = 0.27 inches
41
Describe a Relief Hole
1. holes drilled or punched at the intersection of the inside bend
tangent lines
2. diameter is approximately twice the bend radius
3. relieves stress in the metal as it is bent
4. prevents metal from tearing
5. must touch the intersection of the inside bend tangent lines
6. should extend 1.32 in to 1/16 in behind the inside tangent lines -
to allow for possible error in bending.
42
What is an open angle?
an angle greater than 90 degrees
43
What is a closed angle?
an angle less than 90 degrees
44
How are Formed or Extruded Angles formed?
1. can be curved by stretching or shrinking either of the flanges
2. curving by stretching 1 flange is preferred since requires only a V
block and a mallet
45
Stretching with V Block Method
1. place the flange to be stretched in the groove of the V block
2. Strick the flange directly over the V portion with a soft faced mallet
3. Begin at one end and form the curve gradually
** Use a minimum amount of hammering **
46
Define a Joggle
1. often found at the intersection of stringers and formers
2. is it the offset formed on a part to allow clearance for a sheet or
another mating part.
3. use of the joggle maintains the smooth surface of a joint or splice
4. the depth of a joggle is usually measured in thousandths of a inch
5 when determining joggle length, allow an extra 1/16 inch
47
Define Allowance in Joggling
1. the distance between two bends of a joggle
2. it is 4 times the thickness of the displacement of flat sheets
3. for 90 degree angles - must be slightly more due to stress built up
at the radius while joggling.
4. for extrusions - the allowance can be as much as 12 times the
material thickness
5. the allowance is normally provided in the drawing
48
Joggling methods
1. If the joggle is made on a straight flange or flat piece of metal -
Cornice Brake
2. if the joggle is on a curved part or a curved flange - forming blocks
or dies made of hardwood, steel, or aluminum alloy may be used
** aluminum alloy dies are preferred since easier to fabricate than
steel**
49
What is a Lightning Hole?
1. cut in rib sections, fuselage frames, and other structural parts to
decrease weight.
2. size of the lightning hole and the width of the flange formed
around the hole are determine by design specs
3. may be cut with a hole saw, a punch, or a fly cutter.0
50
Describe Inconel Alloys 625 and 718
1. typically used in high temperature applications
2. corrosion resistant
3. ability to stay strong in high temperatures
51
Drilling Procedure when using Inconel Alloys 625 & 718
1. drill pilot holes in loose repair parts with power feed equipment
before preassembling them
2. preassemble the repair parts and drill the pilot holes in the mating
structure.
3. enlarge the pilot holes to their completed hole dimension
52
What is a J-Chart and when is can it be used?
1. often found in the SRM, it can be used to determine bend
deduction or setback and the TDW of a flat pattern layout
2. to use the J-Chart, the following information must be known:
a. the inside bend radius
b. bend angle
c. material thickness
3. it is helpful to know whether the angle is open or closed
a. lower half of J-Chart is for open angles
b. upper half of J-Chart is for closed angles
53
What are the steps for using a Sheet Metal Brake to Fold Metal?
1. Adjustment of the Bend Radius - bend radius is found in parts
drawing or SRM
2. Adjust clamping pressure
3. Adjust the Nose Gap
54
What are the steps for forming a flanged angle by shrinking?
1. Cut the metal to size
2. Clamp the material in the form blocks and bend the exposed
flange against the block, then tap blocks lightly
3. Hammer near center using a soft faced mallet work down to both
ends
4. Planish the flange and remove irregularities
5. Trim excess material, then file and polish
55
What are the steps for forming a flanged angle by stretching?
1. cut the material to size, determine the bend allowance for a 90
degree bend, round off edge of block to conform to radius of bend
2. clamp the material in the form blocks
3. use soft faced mallet - hammer down ends and work flange down
smoothly and gradually
4. Planish the flange and angle
5. Trim and smooth edges
56
How is a concave flange formed?
formed by stretching
usually hand formed with hardwood for metal forming blocks
57
How is a convex flange formed?
formed by shrinking
usually hand formed with hardwood or metal forming blocks
58
Describe forming by Bumping
1. bumping involves stretching the sheet metal by bumping it into a
form and making it balloon.
2. bumping can be done on a form block, female die, or a sandbag
59
What are the procedures for creating a form block?
1. hollow the block out
2. smooth and finish the block with sandpaper (inside & out)
3. prepare several templates (patterns of the cross section)
4. shape the contour of the form at points 1,2,and 3
5. shape the areas between the template checkpoints
60
What is the procedure for bumping using a form block for female die?
1. cut a metal blank to size - allowing an extra 1/2 - 1 inch
2. apply a thin coat of light oil to the black and aluminum to prevent
galling
3. clamp the material between the block and steel plate
4. clamp the bumping block in a bench vise
5. using a soft faced mallet start bumping near the edges
6. work material down gradually from the edges with light blows
7. smooth form by rubbing with rounded end of a maple block or
stretching mallet
8. remove blister from bumping block and trim to size
61
Sandbag bumping
1. the most difficult method of hand forming sheet metal
2. uses a depression in a sandbag to form
62
Things to know about working with Magnesium
1. keep magnesium particles away from ignition sources
2. must not touch methyl alcohol
3. world's lightest structural metal
4. magnesium alloys fabricated at high temperatures
5. often repaired with clad 224-T3 aluminum alloy
6. sheets may be cut with blade shears, blanking dies, routers, or
saws
63
What are the disadvantages of hot working magnesium?
1. heating the dies and the material is expensive and troublesome
2. there are problems in lubricating and handling materials at these
temperatures
64
What are the advantages of hot working magnesium?
1. it is more easily formed when hot than other metals
2. spring back is reduced, resulting in greater dimensional accuracy
65
Things to know about working with Titanium
1. keep it away from ignition sources
2. lightweight, nonmagnetic, strong, corrosion resistant, and ductile
3. 30% stronger than steel, but 50% lighter
4. 60% heavier than aluminum, but twice as strong
5. titanium sheet formed by hydropress, stretch press, brake roll
forming, drop hammer
6. must be isolated from magnesium, aluminum, or allow steel due
to galvanic corrosion or oxidation
7. Monet rivets or standard close-tolerance steel fasteners should be
used when installing titanium parts
66
The forming of titanium alloys is divided into 3 classes. What are they?
1. cold forming with no stress relief
2. cold form with stress relief
3. elevated temperature forming (built in stress relief)
67
What 3 things are critical to any aircraft sheet metal repair?
1. maintain original strength
2. maintain origin contour
3. minimize weight
68
How do you determine the size of rivets for a sheet metal repair?
1. can be determined by referring to the rivets used by the
manufacturer in the next parallel rivet row inboard on the wind or
forward on the fuselage
2. multiply the thickness of the skin by 3 and use the next larger size
rivet
69
How do you determine the number of rivets to use in a sheet metal repair?
can be found in
1. tables in the manufacturers SRMs
2. Advisory Circular (AC) 43.13-1B - Acceptable Methods, Techniques,
and Practices - Aircraft Inspection and Repair
70
Define Brinelling
1. shallow, spherical depressions in a surfaced
2. usually produced by a part having a small radius in contact with
the surface under high load
71
Define Burnishing
1. polishing of one surface by sliding contact with a smooth, harder
surface.
2. usually there is no displacement or removal of metal
72
Define Burr
1. a small, thin section of metal extending beyond a regular surface
2. usually located at a corner or on the edge of a hole
73
Define Chattering
1. breakdown or deterioration of metal surface by vibratory or
chattering action
2. usually no metal loss or surface cracking
74
What are the four classifications of damage?
1. Negligible Damage
2. Damage repairable by patching
3. Damage repairable by insertion
4. Damage requiring replacement of parts
75
Describe Negligible Damage
visually apparent, surface damage that does not effect the structural integrity of the component involved.
Ex: small dents, scratches, cracks, and holes that can be repaired by smoothing, sanding, stop drilling, or hammering out
76
Describe Damage Repairable by Patching
any damage exceeding negligible damage limits that can be repaired by installing splice members to bridge the damaged portion of a structural part
a. splice or patch material used in internal
riveted and bolted repairs is normally the
same type of material as the damage part, but
one gauge heavier
b. In a patch repair, filler plates of the same
gauge and type of material as that in the
damaged component may be used for bearing
purposes or to return part to its original
contour
c. Structural fasteners are applied to members
and the surrounding structure to restore the
original load carrying characteristics of the
damaged area
77
