7.14 Material Handling Flashcards
What is the base measurement in sheet metal forming?
The outside dimension of a formed part
The base measurement is given on the engineering drawing or obtained from the original part.
What does ‘leg’ refer to in the context of a formed angle?
The longer part of a formed angle
Define ‘flange’ in sheet metal forming.
The shorter part of a formed angle, opposite to the leg
What is meant by ‘bend allowance’ (BA)?
The curved section of the bend, considered as the length of the curved portion of the neutral line
True or False: The bend radius (BR) is measured from the inside surface of the metal.
False
The bend radius is measured from a radius centre to the inside surface of the metal.
What is the neutral axis in metal bending?
An imaginary line that has the same length after bending as before bending
What does K-Factor represent?
The percentage of the material thickness where there is no stretching or compressing
Fill in the blank: The distance the jaws of a folder must be set back from the mould line to form a bend is known as _______.
[setback (SB)]
What is a ‘mould point’?
The point of intersection of the mould lines
What is the Total Developed Width (TDW)?
The width of material measured around the bends from edge to edge
What is the significance of the K-factor in bending operations?
It must be used for all bends that are smaller or larger than 90°
How is the K-factor calculated for bends other than 90°?
K-factor = tangent of half the bend angle
What must be used for marking out flat pattern developments on aircraft sheet metal?
Authorised soft markers and pencils
Why should engineer’s scribers not be used for marking out flat patterns?
They can cause stress raisers and are not always authorised
What is the purpose of creating a flat pattern in sheet metal forming?
To show how much material is required and to prevent material waste
What factors should be considered when forming a straight line bend?
- Thickness of the material
- Alloy composition of the material
- Material’s temper (hardness)
What is the minimum bend radius?
The smallest radius without weakening the metal
True or False: The radius of a bend is measured on the outside of the curved material.
False
The radius of the bend is measured on the inside of the curved material.
What is the effect of a radius that is too sharp during bending?
It can crack the material
How is the setback (SB) calculated for a bend?
SB = Radius (R) + Thickness (MT)
The K-factor is multiplied by the sum of the radius and thickness to find the setback.
What happens to the bend area after bending?
It becomes 10 - 15% thinner than before bending
What is the significance of bend lines in flat pattern development?
They must be determined to develop a flat pattern for sheet metal forming
What is the bend allowance in metalworking?
The length of material required for the bend.
What factors does the bend allowance rely on?
- Degree of bend
- Radius of the bend
- Thickness of the metal
- Type of material used
How does the radius of the bend relate to the thickness of the material?
The radius of the bend is normally proportional to the thickness of the material being bent.
What happens to the material when bending a piece of metal?
Material on the inside of the radius is compressed, while material on the outside is stretched.
What is the neutral axis in bending?
A space that is not affected by either force, occurring at approximately 0.445 times the metal thickness from the inside of the radius.
What is the formula to calculate the bend allowance for a 90° bend?
Circumference of the neutral line divided by 4.
Calculate the bend allowance for a 90° bend with a radius of 0.250 in and thickness of 0.051 in.
0.43 in (10.92 mm)
What is the formula for calculating bend allowance for angles other than 90°?
R = desired bend radius, MT = thickness of the metal, N = number of degrees of bend (1° to 180°).
What does a bend allowance chart provide?
Bend allowances for various angles, radii of bends, and material thicknesses.
What is the setback in metalworking?
The distance that must be accounted for when calculating the flat dimensions of a metal piece.
What is the formula to find the setback?
SB = setback, K = K-factor, R = inside radius of the bend, MT = material thickness.
How do you calculate the flat line dimension?
Flat = Mould Line Dimension (MLD) – Setback (SB).
What is the purpose of the bend sight line?
To ensure the bend is formed accurately within the bend allowance.
True or False: The upper number in each cell of a bend allowance chart is for a 90° bend.
True
Fill in the blank: The neutral axis occurs at a distance of approximately ______ times the metal thickness from the inside of the radius.
0.445
What should be done to avoid incorrect positioning during bending?
Align the sightline with the outer extremity of the radius bar before forming.
What must be added to the overall length of the layout pattern to ensure adequate material for the bend?
The length of the neutral axis.
What is the developed length in metalworking?
The total length of flat portions and bend allowances combined.
What is the process of shaping sheet metal called?
Forming
Forming involves altering the shape of the material, which can be simple or complex.
What are the two methods of forming by altering the shape of sheet metal?
Stretching & Shrinking
These methods change the contour of the material to achieve the desired shape.
What is the most easily formed metal used in aircraft construction?
Pure aluminium
The ease of forming aluminium alloys depends on their temper condition.
What is required for extensive forming or making complex curves in sheet metal?
Annealing
Annealing makes the metal easier to form and allows for smaller bend radii.
What is the role of a sheet metal folding machine in bending?
To make straight bends
When unavailable, short sections can be bent by hand using bending blocks.
What must be consulted to determine the minimum bend radius for sheet metal?
Structural Repair Manual (SRM)
It contains tables listing the smallest allowable radius for different thicknesses and tempers.
What is the importance of adjusting the clamping pressure when using a sheet metal folder?
To ensure the material is clamped securely
Proper clamping prevents slippage while bending.
Fill in the blank: The process of bending metal that protrudes beyond the bending block is done by tapping it lightly with a _______.
rubber or plastic mallet
What is the preferred method for curving an extruded or formed angle section?
Stretching
Stretching requires a V-block and a mallet for effective shaping.
What is a joggle in sheet metal working?
An offset at the intersection of a stringer or former
It allows clearance for another part while maintaining a smooth surface.
What is the general rule of thumb for calculating the allowance of a joggle?
Four times the material thickness
For 90° angles, a slightly greater allowance is needed due to stress.
What method can be used to form a joggle on a flat piece of metal?
Using a normal folding machine (cornice brake)
The joggle is formed by bending the metal at specified angles.
True or False: Excessive hammering during the stretching process can cause the metal to harden.
True
Excessive hammering induces stresses and strains in the metal.
What type of blocks are used for forming curved flanged parts?
Hardwood or metal forming blocks
These blocks are made in pairs and designed specifically for the part’s shape.
What method can be used to reduce a curve that has been formed too much?
Reversing the angle strip on the V-block
Light blows of the hammer can help adjust the curve back to the desired shape.
What is the purpose of using a soft-faced mallet in the shrinking process?
To prevent buckling and damage to the metal
It helps in gradually working out buckles without harming the material.
What must be done after forming a flanged angle by shrinking?
Planishing against the form block
This step smooths out the flange and removes small irregularities.
What materials can be used to make forming blocks or dies for joggling?
Hardwood, steel, aluminium alloy
Each material has its specific use case depending on the frequency of use.
What is the procedure for forming a joggle using joggle blocks?
Place the part between the joggle blocks and squeeze in a vice
This process creates the necessary joggle in the material.
What should be done after the joggle is formed with joggle blocks?
Turn the joggle blocks over and flatten the bulge with a wooden mallet
This ensures that the opposite flange is smoothed out.
When are hardwood dies considered satisfactory for joggling?
When the die is to be used only a few times
Hardwood dies are less durable than steel or aluminium alloy.
What are the advantages of using aluminium alloy dies for joggling?
Easier to fabricate, cause less surface damage to aluminium
Aluminium alloy dies are preferred for producing a large number of joggles.
What should be done when using joggling dies for the first time?
Test them for accuracy on a test piece
This ensures that the dies will produce the correct dimensions.
What is important to maintain on the surfaces of joggle blocks?
Keep them free from dirt and filings
This prevents damage to the work surface during the joggling process.
What is an alternative method for producing a simple joggle in thin aluminium alloy?
Use a joggle plate
A joggle plate can simplify the joggling process for thin materials.
What must the thickness of the joggle plate represent?
The depth of the joggle required
This ensures that the joggle is formed accurately.
According to the four times the material thickness rule, what is the allowance for joggling?
Four times the material thickness
This rule helps in determining the correct dimensions for the joggle.
How is the metal joggled using a joggle plate?
Joggled between the slots of the joggle plate and hit with a mallet on a hard surface
This method creates the joggle efficiently.
What should you consider during a visual inspection of sheet metal work for damage?
Consider the impact from foreign objects and how far the damage extends into supporting structural members.
What is necessary when inspecting aircraft structures for damage?
A close inspection of all rivets, bolts, and attaching structures along the complete member for evidence of damage.
What must be periodically inspected in an aircraft structure?
Structural integrity.
Where is corrosion most likely to occur in an aircraft structure?
In areas where moisture and salt spray can accumulate, especially in corners.
What indicates a loose rivet during inspection?
A dark, greasy residue or deterioration of paint around the rivet head, often called a ‘smoking rivet’.
What visual signs indicate warped or buckled wings?
Presence of parallel skin wrinkles running diagonally across the wings.
What must be done to aluminium alloy surfaces with a chipped protective coating?
They must be recoated to prevent the formation of corrosion.
What are two Non-Destructive Testing (NDT) methods used for inspecting structural members?
Eddy current and ultrasonic inspection techniques.
Define burnishing in the context of aircraft parts.
Polishing of one surface by sliding contact with a smooth and harder surface, usually without displacement of metal.
What is the definition of corrosion?
Loss of metal from the surface by chemical or electrochemical action.
What does a crack in metal indicate?
A physical separation of two adjacent portions of metal caused by excessive stress.
What is a dent?
Indentation in a metal surface produced by an object striking with force.
What is the result of erosion on a metal surface?
Loss of metal from the surface by mechanical action of foreign objects.
What does chattering refer to?
Breakdown or deterioration of metal surface by vibratory or chattering action.
What does a gouge indicate on a metal surface?
Indicates metal loss or displacement of material due to contact with foreign material under heavy pressure.
What is pitting in the context of metal surfaces?
Sharp, localized breakdown of metal surface, usually with defined edges.
How should riveted joints be inspected?
Examine both the shop and manufactured heads, the surrounding skin, and structural parts for deformities.
What should be done if rivets show head slippage?
They must be replaced.
What does the presence of black residue around rivets indicate?
Indicates movement (fretting), not necessarily looseness.
What are the acceptable conditions for rivet head cracks?
Depth < 0.32 cm, width < 0.16 cm, and confined to a specific area.
What is the significance of keeping drain holes clean in aircraft structures?
Prevents moisture accumulation and potential corrosion.
Fill in the blank: A _______ is a groove in or breakdown of a metal surface from contact with foreign material under heavy pressure.
[gouge]
True or False: A loose rivet will always overload adjacent rivets to the point of cracking.
False.
What is the primary purpose of bonding in the aerospace industry?
To form permanent joints between materials such as composites, fabrics, metals, and plastics.
What factors determine the type of adhesive used in bonding?
Surface texture of adherent, type of joint required, and manner of load application.
What are adhesives primarily made of?
Synthetic resins.
True or False: Most bonding is performed during the manufacturing stage.
True.
What should be ensured when working with adhesives and sealants?
Proper ventilation or a Local Exhaust Ventilation (LEV) system.
What are the advantages of bonded repairs compared to bolted repairs?
They do not add stresses to the structure by drilling fastener holes.
What is a disadvantage of bonded repairs?
They require special storage, handling, and curing procedures.
Bolted repairs are typically used on composite skins thicker than ______.
6 mm (0.125 in).
What type of repair is most effective for honeycomb sandwich parts?
Bonded scarf (tapered) type repair.
How many basic types of composite repairs are there?
Five.
List the types of composite repairs.
- Bolted metal or pre-cured composite patches
- Bonded metal or pre-cured composite patches
- Resin injection
- Laminating new repair plies through one surface
- Laminating new repair plies through both surfaces
What is the best type of permanent repair to a composite structure?
Laminating new repair plies in the damaged area.
What tools are best suited for cutting prepreg and dry fabrics?
Heavy-duty scissors.
What type of power tools are recommended for working with composite materials?
Pneumatic power tools.
What is a caul plate used for during the curing process?
To support the composite structure/panel.
What is the purpose of vacuum bagging in composite repairs?
To create a secure bond by removing air from the bag.
What is the role of release agents in composite repairs?
To allow the part to come off the tool or caul plate easily after curing.
What does a bleeder ply do in the vacuum bagging process?
Creates a path for air to escape and collects excess resin.
Fill in the blank: A _______ is used to seal the vacuum bag to the component and create an air-tight seal.
Vacuum bag sealing tape.
What is the purpose of a vacuum pump in composite repairs?
To remove air from the vacuum bag and create pressure on the plies.
What is the typical cure temperature range for ovens used in composite repairs?
120 °C (250 ˚F) to 175 °C (350 °F).
What is an autoclave used for in composite repairs?
To control pressure and heat during the curing process.
What type of heating methods are typically used for aircraft repairs?
- Electrical resistance heat blankets
- Infrared heat lamps
What is the function of thermocouples in the composite repair process?
To accurately measure temperatures.
What are the two types of thermocouples mentioned?
Type J and Type K.
What is the disadvantage of using room temperature wet lay ups?
They do not restore the strength and durability of the original structure.
Prepreg materials must be stored in a freezer below ______.
-18 °C (-0.4 °F).
What is the purpose of the backing on prepreg materials?
To prevent the prepreg from sticking together.
What is the maximum time allowed for storing a prepreg at low temperature called?
Storage life
Storage life is typically between six months to a year.
What is the maximum time allowed for a material to be at room temperature before it cures called?
Mechanical life
The handling life is shorter than the mechanical life.
What is the recommended time at room temperature to complete the lay-up process called?
Handling life
At what temperatures do prepregs typically cure?
120 °C (248 °F) and 200 °C (392 °F)
True or False: Prepreg materials should be stored in sealed, moisture-proof bags.
True
What overlap is generally recommended for prepreg repair plies?
1/2” (12.5mm)
What are the two lay-up methods for repairing materials?
- Use the largest ply first
- Use the smallest ply first and build up sizes
What is the high strength direction of a fabric called?
Warp
What is a warp clock used for?
To describe the direction of the fibres on a diagram or manufacturer’s sheets
What is the typical curing temperature range for composite materials?
120 °C ‑ 175 °C (248 °F ‑ 347 °F)
What is the disadvantage of a room temperature cure wet lay-up repair?
It does not fully restore the strength or durability of the original cured components.
What type of repair meets the strength requirements but is limited by time or flight cycles?
Temporary repair
What is the damage classification that restores the required strength but not the durability?
Interim repair
What type of repair restores both strength and durability?
Permanent repair
What is minor core damage in a sandwich honeycomb structure?
Damage smaller than 12 mm (0.5 in) in diameter
What is a potted repair?
A repair involving filling minor core damage with a recommended potting compound.
What must be done to remove water from the damaged area before repair?
All traces of water need to be removed from the core.
What tool is used to taper or step sand a uniform taper around cleaned-up damage?
Flexible disc sander
What must be done to the core before it can be successfully repaired?
Remove any traces of water
What is the purpose of vacuum bagging in the repair process?
To remove air and to pressurize the repair for curing.
What must be inspected after curing a repair?
The repair must be free from pits, blisters, resin-rich and resin-starved areas.
What type of inspection methods are used for post-repair inspection?
- Visual inspection
- Tap inspection
- Ultrasonic inspection
Fill in the blank: The engineer is responsible for recording the time in and out of the freezer for _______.
[mechanical life]
What must be done to the edges of the damaged area before applying the repair?
Taper or step sand the edges
What is the typical maximum properties curing temperature for composite repairs?
65 °C (149 °F)
What should be done if the resin system is not fully mixed?
The resin cannot cure properly.
True or False: Mixing large quantities of quick curing resins is recommended.
False
What must be kept clean for successful adhesion in bonded areas?
Bonded areas
Clean surfaces are crucial for the integrity of the bond.
What is the purpose of peel ply in composite bonding?
Ensures surface cleanliness prior to bonding
Peel ply creates a pristine surface when stripped away.
What effect do high resin peaks from peel ply weave have?
They can create cracks in the bond line
Light sanding can remove these peaks.
What temperature conditions are preferred for bonded repairs with composite materials?
Elevated temperatures
Higher quality bonds are produced at elevated temperatures.
What methods can be used to increase temperature during aircraft repairs?
Heat bonder, heat lamps, hot air, heat blankets
These methods help maintain the correct temperature during curing.
What is vacuum bagging used for in composite repairs?
To remove air from the plies of a repair layup
Pressure can also be applied if required.
What is the effect of typical aircraft fuels on cured epoxy resin?
Little to no effect
However, they can saturate porous core materials.
Which hydraulic fluids can attack cured epoxy?
Some Skydrol™ brand hydraulic fluids
These are primarily used in civilian aircraft.
Do de-icing/anti-icing fluids affect composite structures?
No known effects
They do not harm composite materials.
What can strong acids do to cured epoxy?
Attack and destroy it
Weaker acids do not have this effect.
What effect do weaker alkalis have on cured epoxies?
No attack on cured epoxies
However, they can attack some structural foams.
Which solvent is known to chemically attack cured epoxy resin?
Methylene Chloride
It cannot be used on composites.
Why can’t chemical paint strippers be used on composites?
They are largely based on methylene chloride
This can harm composite materials.
What is required for aircraft to prevent arcing or fiber damage during lightning strikes?
Electrical contact between metallic and composite parts
This allows for dissipation of electrical energy.
How does lightning travel through an aluminum skin aircraft?
Flows through the skin and discharges out the static wicks
Composites do not conduct electricity.
What must be built into composite components for lightning protection?
A conductive path
Resins can evaporate if not protected.
What are some methods for electrical bonding in composite structures?
Aluminium wires, fine aluminium screens, thin aluminium foil, flame-sprayed aluminium, bonded metal pieces
Each method serves to help dissipate electrical charge.
What must be performed after repairs to composite lightning protection methods?
An electrical continuity check
This verifies conductivity between the repair and surrounding mesh/wires.
What is the primary purpose of performing inspections on composite repairs?
To ensure the repair has been correctly executed and to document the results.
Inspections are carried out by an engineer after vacuum bagging materials are removed, followed by a supervisor/certifier inspection.
What are the common conditions recognized during post-repair inspections?
- Resin dry portions of the repair (porosity)
- Resin rich areas of the repair
- Delamination
- Debonding
- Foreign object inclusion
- Evidence of overheating
- Evidence of undercure
Inspecting the area surrounding the repair is also necessary for debonding and overheating evidence.
What is required if defects are found during the inspection process?
A standard damage assessment must be carried out and component-allowable damage limits must be applied.
What is documented during non-destructive inspections?
Results are recorded in a written report attached to repair documentation as evidence for certification and release to service.
What are some commonly used non-destructive inspection (NDI) techniques for composite structures?
- Tap testing
- Visual or optical inspection
- Bond tester or resonator
- Thermography and shearography
- Holography
- Acoustic emission
- Ultrasonics
- Radiography
Ultrasonics and radiography are the most commonly used methods.
What is tap testing used for?
To quickly evaluate accessible aircraft composite or bonded surfaces for delamination or debonding.
What are the three commonly used tap testing methods?
- Coin tap test
- Instrumented tap test (woodpecker)
- Tap test with a light hammer
True or False: Tap testing can effectively detect delamination in laminate materials.
False
Tap testing is not recommended for laminate materials due to their rigidity.
What tools are commonly used to aid visual inspection?
- 10 times magnification
- Borescopes
- Mirrors
What does visual inspection of a laminate typically detect?
Resin starvation appearing as porosity on the surface.
What is shearography used for?
Rapid assessment of flaws in surfaces of composite structures.
How does ultrasonic inspection work?
Ultrasonic waves travel through solids and liquids, with their attenuation revealing internal defects.
What is the main benefit of using X-ray inspection for composite structures?
No disassembly or removal of surface coatings is required.
What is produced by the passage of X-rays through a test object onto film?
A radiograph.
What do darker regions on a radiograph represent?
More penetrable parts of the test specimen.
Fill in the blank: The acoustic response from a bonded part during tap testing produces a clear _______.
audible ring
What is the risk associated with exposure to high levels of X-rays and gamma rays?
It is hazardous and can ultimately be fatal.
What influences the speed of ultrasonic waves?
The density and elasticity of the medium.
