7.15 Welding, Soldering & Bonding Flashcards
What is soldering?
A process of joining metal surfaces together with a metal alloy (solder) that melts at a lower temperature than the metals being joined.
What happens after completion of the soldering operation?
The solder cools and forms an alloy with the metal.
Define wetting in the context of soldering.
The action where solder penetrates and adheres to metal surfaces, forming a bond.
What are the different types of solder compositions?
- Soft solder
- Hard solder
What are fluxes and why are they used in soldering?
Fluxes are cleaning agents that remove oxidation and promote metal-to-metal contact during soldering.
List the types of soldering processes.
- Tinning
- Soldering
- De-soldering
What is resistance soldering?
A method using a low voltage transformer that heats the metal to be soldered through electrodes.
What is torch soldering?
A method that uses a flame to heat solder, also known as hard soldering.
Describe dip soldering.
A process where connections are immersed in molten solder, typically used for printed circuits.
What is the function of solder?
To act as a filler metal and form a physical and electrical bond.
What are the classifications of solders?
- Soft solder
- Hard solder
What are the health risks of soldering with lead?
Short-term exposure can cause headaches and abdominal pain; long-term exposure can lead to high blood pressure and kidney damage.
What is the most commonly used lead-free solder?
Tin-Silver-Copper (Sn-Ag-Cu) alloy.
What is the melting point of Tin-Silver-Copper solder?
217 °C
What is meant by ‘wetting action’?
The free-flow and spreading of solder to form a uniform film on a metal surface.
What are the three basic types of soldering fluxes?
- Acid Flux
- Organic Flux
- Rosin Flux
True or False: Acid flux can be used in electronic applications.
False
What is Isopropyl Alcohol (IPA) used for in soldering?
As a solvent to remove contaminants and flux residues.
What is the role of a soldering iron?
To apply heat for soldering operations.
What are the types of soldering irons?
- Instant Heat
- Constant Heat
- Thermostatically Controlled
- Electronically Controlled
What is tinning?
The process of applying a thin coating of solder to a metal surface.
What should be done before soldering wires together?
Remove insulation and pre-tin the wires.
What is the purpose of using heat shrink after soldering?
To cover and protect the soldered connection.
Fill in the blank: The soldering iron should heat both the wire and terminal ______.
simultaneously
What is the main advantage of electronically controlled soldering irons?
They maintain a stable working temperature with rapid recovery time.
What is the first step in preparing wires for soldering to terminals?
Wires must be stripped and pre-tinned before soldering them to terminals.
What must be done to terminals before connecting wires?
The terminals themselves must also be tinned in preparation of receiving the wire.
What is the correct soldering procedure for connecting a wire to a terminal?
Place the wire on the terminal and then place the tip of the soldering iron at the soldering joint where the wire touches the terminal.
What should be avoided when using a soldering iron on a terminal?
Don’t hold the soldering iron on the terminal for too long.
What should be ensured regarding solder when connecting wires and terminals?
There should be enough solder on the wire and terminal to make a good connection.
What happens if a stranded wire is not tinned properly?
It may absorb some solder from the surface of the terminal.
What are the five common types of terminals?
- Turret terminal
- Bifurcated terminal
- Perforated or Pierced terminal
- Hook/Pin terminal
- Solder cup terminal
What are Printed Circuit Boards (PCB) made from?
They are made from a laminate or fibreglass composition.
What is a critical precaution when soldering printed circuit boards?
Always handle boards by the edges or with cotton gloves.
What type of solder should be used for printed circuit boards?
Use solder with small diameter (1/32 in maximum) and low melting temperature.
What is de-soldering?
The removal of solder and components from a circuit for troubleshooting, repair purposes, and to salvage components.
What are two methods to remove solder from PCBs?
- Solder Braid (wick)
- De-soldering pump (sucker)
How does Solder Braid (wick) work?
Press it down onto the cold joint, using the hot tip of the soldering iron to draw melted solder into the braid.
What must be done before using a de-soldering pump?
Apply the soldering iron first to melt solder for 1-2 seconds.
What is the importance of cleanliness in soldering operations?
Soldering must be done in a clean, dust-free environment to ensure successful solder joints.
What is pre-tinning?
Wires to be attached to electrical connectors must be pre-tinned.
What are the characteristics of acceptable solder?
A good soldered joint has a bright silvery appearance, smooth fillets, and is mechanically strong.
What indicates a cold solder joint?
A rough, grey-looking joint or dull grey, chalky, or granular appearance.
What is the recommended wattage for soldering iron for general use in aircraft electrical wiring?
60, 100, and 200 watts are recommended.
What type of soldering iron is recommended for printed circuit soldering?
A lightweight 55 watt iron with a maximum temperature of 315 °C (599 °F).
What must the optimum tip face of a soldering iron be?
Between two-thirds and three-quarters of the joint diameter.
What should be done if a soldered joint shows signs of poor soldering?
The joint has to be taken apart, cleaned, and re-soldered using fresh solder and flux.
How is a brazed joint different from a welded joint?
A brazed joint is made by melting a filler metal and allowing it to flow between the closely fitted parts, unlike a welded joint where the base metals are melted together.
Brazing occurs at lower temperatures than welding.
What are the different types of welding?
- Gas Welding
- Electric Arc Welding
- Electric Resistance Welding
Each type has various methods and applications.
What is gas welding?
Gas welding is the process of heating metal parts to a molten state using a high-temperature flame produced by burning acetylene and oxygen.
The flame temperature can reach approximately 3480 °C (6300 °F).
What is the primary use of gas welding in aircraft manufacturing?
Gas welding was preferred for producing aircraft materials under 5 mm (3/16 in) thickness until the mid-1950s.
It has largely been replaced by electric welding methods.
What safety equipment is necessary when performing gas welding?
- Welding respirator
- Welding goggles with appropriate lenses
- Proper ventilation or Local Exhaust Ventilation (LEV) system
Safety is crucial due to toxic fumes produced during the process.
What is Manual Metal Arc Welding (MMAW)?
MMAW, or ‘stick’ welding, uses a coated metal-wire rod as an electrode to create an arc and produce heat for welding.
It is the most common type of electric arc welding.
What is the role of the flux in MMAW?
The flux melts and releases an inert gas that shields the molten pool from oxidation, covering the weld as it cools.
This protects the weld quality during the cooling process.
What distinguishes Gas Metal Arc Welding (GMAW) from MMAW?
GMAW uses an uncoated wire electrode fed through the torch along with an inert gas, while MMAW uses a coated electrode.
GMAW is also known as Metal Inert Gas (MIG) welding.
What is the preferred application for Gas Tungsten Arc Welding (GTAW)?
GTAW is preferred for welding stainless steel, magnesium, and thick aluminum.
It is also known as Tungsten Inert Gas (TIG) welding.
What is Plasma Arc Welding (PAW)?
PAW is an advanced welding process that provides better control and accuracy, using a non-consumable tungsten electrode and a high concentration of heat.
Developed in 1964, it is suitable for miniature and precision applications.
What are the two main types of Electric Resistance Welding?
- Spot Welding
- Seam Welding
These methods are commonly used to join thin sheet-metal components.
What gases are commonly used in welding processes?
- Acetylene
- Argon
- Helium
- Hydrogen
- Oxygen
Each gas has specific applications and is identified by the color of its storage cylinder.
What is the function of a gas-pressure regulator in welding?
It lowers the cylinder pressure to a suitable working pressure and maintains a constant outlet pressure.
Regulators can be single-stage or two-stage.
What is the purpose of check valves and flashback arrestors in welding?
They prevent reverse gas flow and protect against flashback conditions that could cause explosions.
Flashbacks can occur due to overheating of welding tips.
Fill in the blank: The primary gas used for oxyacetylene welding is _______.
[Acetylene]
What type of welding hose is used for acetylene?
Red hose with left-hand threads.
The oxygen hose is blue or green with right-hand threads.
True or False: Oxygen is used in welding to decrease the combustion rate.
False
Oxygen increases the combustion rate, raising the flame temperature.
What is the maximum pressure setting for acetylene during welding?
103 kPa (15 psi).
Exceeding this pressure can lead to instability and explosion hazards.
What is an equal pressure torch?
The most commonly used torch for oxy-acetylene welding, featuring a mixing chamber and adjustable flame.
It minimizes the chance of flashback.
What is the function of the mixing chamber in an oxy-acetylene torch?
It allows for the mixing of acetylene fuel at specific pressures
Acetylene is used at pressures ranging from 6.9 kPa to 103 kPa (1–15 psi)
Name two small, lightweight torches ideal for aviation welding.
- Smith Airline™
- Meco Midget™
What is the purpose of a cutting torch in oxy-acetylene welding?
It allows the cutting of metal by rapidly burning or oxidising it.
What is the kindling temperature range for the cutting process in oxy-acetylene welding?
760 °C - 870 °C (1400 °F - 1600 °F)
What happens when a jet of high-pressure oxygen is released against heated metal during cutting?
It combines with the hot metal to form an intensely hot oxide.
What does the torch tip control in oxy-acetylene welding?
The flow of gases and the amount of heat applied to the work.
What can happen if a cutting torch is held too close to the workpiece?
It can accelerate clogging of the tip through carbon deposits.
True or False: A sustained backfire can occur due to a clogged torch tip.
True
What should be done immediately if a sustained backfire occurs?
Close the oxygen supply at the torch immediately.
What types of protective eyewear are available for oxy-acetylene welding?
- Goggles with headpieces or elastic straps
- Rectangular eye shields
What is the significance of the new green glass lenses developed in the late 1980s?
They eliminate the sodium yellow-orange flare and protect against UV, infrared, and blue light.
List the three types of flame patterns used in oxy-acetylene welding.
- Neutral
- Carburising
- Oxidising
What is the temperature of a neutral flame at the tip of the inner cone?
Approximately 3300 °C (5970 °F)
What is a carburising flame used for?
Welding high-carbon steels and non-ferrous alloys such as aluminium and nickel.
What characterizes an oxidising flame?
It is produced using an excess of oxygen and burns at approximately 3450 °C (6300 °F).
What must be inspected in an oxy-acetylene welded joint?
- Smooth seam
- Evenly spaced bead ripples
- Slightly convex weld
- No oxide formation
- No blow-holes or porosity
- No burns or distortion in base metal
What is the definition of brazing?
Joining two pieces of metal using brass or bronze as the filler metal.
What is the melting point requirement for the filler metal in brazing?
Higher than 427 °C (800 °F) but lower than that of the metals being joined.
What is the key to a strong brazed joint?
Capillary action that requires a close fit.
What is necessary to obtain a good bond in brazing?
Use of a brazing flux.
What should be done if brazing flux is overheated during the process?
Remove it with a mild acid solution recommended by the flux manufacturer.
What is required before performing arc welding?
Ensure proper personal safety equipment is used.
What are the two methods of striking an arc in arc welding?
- Tapping method
- Scratching method
What should be the angle of the electrode when moving along the plate during arc welding?
About 20° to 25°
What characteristics define a good weld bead on a flat plate?
- Little or no splatter
- Arc crater of approximately 1.6 mm (1/16 in)
- Slightly built-up bead without overlap
- Good penetration of approximately 1.6 mm (1/16 in)
What is the easiest and most common way of carrying out a non-destructive examination of welds?
Visual inspection
What is a welded joint?
Joining of the metals by melting the base metal by fusion.
What is a brazed joint?
Joining of the metals by melting a filler rod into the joint.
What are the characteristics of a good weld?
Smooth seam, uniform thickness, smooth blending of weld contour, and no undercut.
What defects are inspected for in welded joints?
- Blowholes
- Porosity
- Projecting globules
- Pitting
- Burning
- Cracking
- Distortion
What must be sufficient to ensure the fusion of the base metal and the filler rod?
Penetration depth
What can be used to remove welding scale?
- Wire brush
- Sandblasting
What types of cracks can occur in materials?
- Micro-cracks
- Visible cracks
What is Non-Destructive Testing (NDT)?
Techniques like magnetic particle, liquid penetrant, radiographic, ultrasonic, eddy current, and acoustic emission used to inspect welds.
What is the importance of penetration in a weld?
It is the depth of fusion, crucial for a solid weld.
What are the penetration requirements for a butt weld?
100% of the thickness of the base metal
What are the penetration requirements for a fillet weld?
25 to 50% of the thickness of the base metal
What are common defects identified in brazed joints?
- Voids or porosity
- Flux entrapment
- Base metal erosion
- Unsatisfactory surface condition
- Cracks
What is visual examination in the context of brazed joints?
A detailed test for evaluating voids, porosity, surface cracks, fillet size, and shape.
What does leak testing determine in brazed joints?
Gas or liquid-tightness of a braze.
What is proof testing?
Subjecting the brazed joint to a one-time load greater than the service level.
What is the purpose of peel testing?
Evaluating lap joints and production quality control.
What does tension and shear testing determine?
A joint’s strength in tension or shear.
What is fatigue testing?
Testing the base metal plus the brazed joint, but it is time-consuming and costly.
What is torsion testing used for?
Brazed joints in production quality control.
Fill in the blank: A good weld is uniform in width, and the ripples are even and well ______ into the base metal.
feathered
True or False: Non-destructive testing is not recommended in critical applications.
False
What are the four main groups of adhesives?
- Two-part no-mix acrylics
- Two-part mix acrylics
- Two-part epoxies
- Polyurethanes
Each group has specific properties suitable for different applications.
Why is wetting essential for bonding?
Wetting ensures good contact between the adhesive and the surfaces to be joined
This maximizes bonding strength.
What is capillary action?
The process of a liquid moving in a narrow space without external forces
It plays a role in adhesive bonding.
Define adhesion and cohesion.
Adhesion: property of different molecules to cling to each other
Cohesion: property of molecules of the same substance to stick together
Both are crucial for effective bonding.
How does bond thickness influence tensile strength?
Greater thickness can lead to decreased stability and increased stress due to bending
The thickness must not exceed 0.1 mm for bonded metal parts.
What are the types of bonded connections?
- Butt joints
- Stepped double-fishplate connection
- Stepped lap joint
- Single lap joint
- Double lap joint
- Single-fishplate
- Double-fishplate
- Tapered lap joint
- Bonded reinforcement
- Tapered double-fishplate connection
- Shaft-connection
Each type has specific applications and suitability.
Identify the stresses in adhesive connections.
- Shear stress
- Peel stress
- Tensile stress
- Cleavage stress
- Compressive stress
Understanding these stresses is essential for design.
What are the properties of resins and bonded connections?
Resins provide stability, but bonded connections may have lower mechanical strength and sensitivity to heat and moisture
Proper processing is crucial for stability.
What is the importance of choosing the correct adhesive?
It depends on the materials being joined and the function of the bonded part
Correct selection ensures effective bonding.
What are the advantages of bonding metals?
- Even stress distribution
- Improved appearance
- Reduced need for drilling
- Resistance to flex and vibration
- Excellent sealing
These advantages make bonding preferable in many applications.
What limitations do adhesives have?
- Time to develop full strength
- Surface preparation time
- Difficulty in disassembly
- Sensitivity to environmental conditions
These factors must be considered in adhesive applications.
What is the effect of adhesion versus cohesion in bonding?
Adhesion must be stronger than cohesion for effective bonding
Surface pre-treatment is essential to achieve this.
What is the role of surface pre-treatment in bonding?
It enlarges interfacial surface forces, enhancing bond strength
Methods include roughening or chemical etching.
What is the significance of mechanical roughening?
It improves contact between the adhesive and the joined surfaces
This is sufficient for most bonding connections.
What are the disadvantages of bonded connections?
- Relatively low mechanical strength
- Low heat resistance
- Sensitivity to chemicals and moisture
- Difficult separation
These limitations can affect performance.
What factors influence the selection of structural adhesives?
- Materials to be bonded
- Operating environment
- Manufacturing or repairing process
Each factor can affect adhesive performance.
What are the characteristics of two-part epoxies?
High strength, durability, excellent depth of cure, temperature resistance but slower to cure
Suitable for demanding environments.
What is the effect of bond thickness on tensile-shear strength?
Increased thickness leads to decreased stability and stress concentration during bending
Optimal thickness should be maintained.
What is the preferred connection type for thin cross-sections in aircraft construction?
Single lap joint
It is easy to realize and effective for certain applications.
What is a shaft-connection known for?
High stability and suitability for dynamic stresses
It is superior to other bonding connections.
What design guideline maximizes shear strength in adhesive joints?
Maximize shear and minimize peel and cleavage stresses
This improves joint performance.
What does the rule ‘wider is better’ imply in adhesive design?
Increasing joint width reduces stress at bond ends, enhancing strength
Overlap area is less critical than width.
What are the common types of adhesive stresses?
- Shear stress
- Peel stress
- Tensile stress
- Cleavage stress
- Compressive stress
Each type affects bond performance differently.
What is the general rule regarding joint width and overlap area in bonded connections?
Increase the joint width rather than the overlap area
‘Wider is better’ for bond shear strength.
What are some technical problems considered by aircraft manufacturers when bonding parts?
Stability of bonded connections
Important for ensuring reliability and safety.
How do the stability and elasticity of epoxy resin compare to 2024 and 7075 aluminium alloys?
Epoxy resin has lower stability and higher elasticity and thermal extension
This affects the performance of bonded connections.
What is the stability comparison between age-hardened aluminium and epoxy resin?
Aluminium subjected to age hardening has stability ten times as high as epoxy resin
This is crucial for load-bearing applications.
How does the elasticity under load of bonded connections compare to aluminium?
It is 10 times higher than that of aluminium
Impacts the design and performance of bonded structures.
What should manufacturers consider regarding KSI loadings in bonded connections?
Certain measurements and shapes may differ from those used for rivet connections
Empirical data is essential for accurate designs.
What should airlines avoid in relation to specified repair procedures?
Deviations from the specified instructions
Such deviations can lead to worse results.
What happens if airlines make unauthorized modifications to repairs?
Claims under warranty may expire
Responsibility shifts to the airline for any issues.
What is the KSI value range for Carbon Steel?
From 50 KSI
Indicates the strength of the material.
What is the maximum KSI loading for epoxy resin?
Up to max. 15 KSI
Important for assessing the limits of epoxy in applications.
What safety factor is applied to epoxy resins?
A safety factor of 2.25
This reduces the effective KSI loading for practical use.
What is the effective KSI loading for epoxy resin after applying the safety factor?
6.66 KSI
Effective value calculated from 15 KSI divided by 2.25.
What is the priority in production considerations for bonded connections?
Curing processes during fabrication
Crucial for achieving desired adhesive properties.
How long does the cure of cold age-hardened epoxy adhesives take?
About 26 hours
Important for planning production timelines.
What conditions are required for the polymerisation process of EP-adhesives?
2-3 bar overpressure and 125 -175 °C (257 - 347 °F)
Necessary for optimal adhesion values.
What happens to moisture during the curing process in the autoclave?
It evaporates and is removed by vacuum
Ensures better adhesion by eliminating trapped moisture.
