Chapter 2 - Sheet Metal Structures

Question 1

What are the two different types of sheet metal structures?

Answer 1

Monocoque and Semimonocoque

Question 2

What are the five major stresses?

Answer 2

1. Tension - primary stress that tries to pull a body apart
2. Compression - another primary stress that tries to squeeze a part together
3. Bending - Tries to pull one side of a body apart while at the same time squeezing the other side together
4. Torsion - a twisting force
5. Shear - opposing forces are applied on opposite sides of a body

Question 3

Identify the Aluminum alloy series

1xxx

2xxx

3xxx

4xxx

5xxx

6xxx

7xxx

Answer 3

1xxx Aluminum - Pure aluminum 99% or higher

2xxx Copper

3xxx - **Maganese **

4xxx - Silicon

5xxx - Magnesium

6xxx - Magnesium and silicon

7xxx - zinc

Question 4

Define annealing

Answer 4

Annealing is a process that softens a metal and decreases internal stresses by heating the metal to the annealing point and heald there until the metal becomes heat soaked. It is then cooled to 500 degrees F of a rate of about 50 degrees F per hour

Question 5

Name what these aluminum alloys are commonly used for:

2117

2024

5052

7075

Answer 5

2117 - Mostly aircraft rivets

2024 - Majority used on structures

5052 - Gas tanks and fuel lines

7075 - When high strength is needed

Question 6

What is alclading and why is it important?

Answer 6

Alclad consists of a pure aluminum coating rolled onto the surface of heat-treated aluminum alloy. The thickness of this coating is approximately 5% of the alloy’s thickness on each side. Alclading a surface greatly increases the corrosion resistance of an aluminum alloy.

Question 7

Which alloys are heat treatable and non-heat treatable?

Answer 7

Non-heat treatable alloy

1100

3003

5052

Heat treatable alloy

2017

2117

2024

6061

7075

Question 8

When appropriate, the metal hardness, or temper, is indicated by a letter designation seperated from the alloy designation by a dash. Name the following temper designations:

• O
• T3
• T6

Answer 8

O - Annealed

T3 - Soulution heat-treated and cold worked by the flattening or straightening operation

T6 - Solution heat-treated and artificially aged

Question 9

Which two series of metals are heat-treatable?

Answer 9

7000 & 2000 series.

All others are non-heat treatable and must be hammered or cold worked to be treated.

Question 10

Corrosion from two dissimalar metals is called what?

Answer 10

Glavanic corrosion

Question 11

Artificial aging is another name for _______heat -treatment

Answer 11

Artificial aging is another name for precipitation heat -treatment

Question 12

Name three disadvantages for using magnesium as a structural material.

Answer 12

cracks, corrodes, & burns easily

Question 13

What is this tool and what should it and should NOT be used for?

Answer 13

Scribe

Should be used in sheet metal work only for marking the cut-off lines of a part. They should never be used for marking dimension lines for bending metal.

Question 14

What is the purpose of a prick punch?

Answer 14

Once layout marks have been made with a soft pencil, permanent marks can be made in the location for holes with a sharp prick punch and a light tap with a small hammer.

Question 15

What is the purpose of this tool?

Answer 15

Center punch

Enlarges a prick punch to begin for drilling

Question 16

What is the purpose of this tool?

Answer 16

Pin Punch

Ideal for removing rivets

Question 17

What is th epurpose of this tool?

Answer 17

Kett Saw

Easily removes damaged sections of sheet metal

Question 18

What is the purpose of this tool?

Answer 18

Pneumatic-powered Kett Saw

performs straight line cuts

Question 19

What is the purpose of this tool?

Name the advantages and disadvantages of this tool.

Answer 19

Nibbler

Advantage - makes detailed inside cuts

Disadvanteges - leaves rough edges after cutting

Question 20

What are the two cuts of files and two ways to file?

Answer 20

Cuts

• Single cut - one row of teeth
• double-cut - two rows of teeth

Methods of filing

• Cross filing - the file is moved lengthwise across the work with the hands positioned at the edges
• Draw filing - the file is moved across the work

Question 21

What is the purpose of this tool?

Answer 21

A squaring shear

Used to make straight cuts across the sheet metal

Question 22

What are the types of machine brakes (forming tools)?

Answer 22

Press brakes

Cornice brakes

Bar folding machine

Box brake

All of these machines are used to make sharp bends rather than gentle curves

Question 23

What are the three types of compound curve tools?

Answer 23

Stretch Press - uses a male die

Drop Hammer - Matching male and female dies are used

Hydropress - uses a male die

Question 24

What are the advantage and disadvantage of using shrinkers and stretcher?

Answer 24

Shrinking and stretching tools are used to form contours in parts by expanding or compressing metal to make it form a curved surface.

Question 25

What are cleco fasteners used for and what are it’s different colors?

Answer 25

Cleco fasteners are used to temperarily hold sheet metal parts together until they are riveted.

3/32 inch….(-3 diameter rivet) Silver

1/8………………(-4 diameter rivet) Copper

5/32…………..(-5 diameter rivet) Black

3/16……………(-6 diameter rivet) Brass

1/4…………………………………………………..Copper

Question 26

What is the difference between the rivet codes for AN and MS20?

Decode the following: AN470 AD 4-4

Answer 26

AN - Airforce/Navy

MS20 - Military Standards 20 system

AN470 - head style

AD - Material

4-4 (diameter in 1/32 increments) (lenth in 1/16 increments)

Question 27

Name the rivet head designs

Answer 27

AN426/MS20426 (standard flush rivet) AN470/MS20470

AN442 AN430

Question 28

Name the rivets

Answer 28

Plain 1100 Aluminum (A)

Dimple 2117 Aluminum Alloy (AD)

Raised Cross 5056 (B) “ice box rivets”

Raised Dot 2017 (D) “ice box rivets”

Two raised dashes 2024 (DD) Raised ring 7050 (E)

Question 29

How do you define strain?

Answer 29

The deformation of an object caused by stress

Question 30

What is a stress-skin structure?

Answer 30

An aircraft without a truss frame providing a more streamline shape and reduced the weight. It is referred to having a monococoque design

Question 31

What are the different types of fuselage designs?

Answer 31

Truss-type fuselage

Stressed-skin fuselage

• monocoque
• semi-monoque

Question 32

The acculuted angle for cutting is at what degree?

Answer 32

118 degrees

Question 33

What are two types of drill?

Answer 33

Pneumatic

variable speed

Question 34

What is the rule of thumb when drilling into metals?

Answer 34

Soft metals - Higher speed, less pressure

Hard metals - Slower speed, harader pressure

Question 35

What is dimpling and it’s two types?

Answer 35

When the top sheet of metal is too thin to counter-sink, the edges of the hole may be formed to accomodate the head of the rivet by using a set of dimple dies. The two types are:

Coin dimpling and Radius dimpling

Question 36

Name the three parts of a drill

Answer 36

Tip - 59 degrees from the center line producing 118 degrees total

Shank - chucked into the drill motor

Body -

• flute - aids in carrying material out of the hole
• Land - provides a finishing dimention of the hole

Question 37

What are the three main parts of a semmi-monocoque design?

Answer 37

stringer - horizontal lines

Former - vertical lines

Bilkhead - strongest part