7.15 Welding, Soldering and Bonding Flashcards
What are soldered connections used for in aircraft electrical wiring?
Soldered connections form a continuous and permanent metallic connection with a constant electrical value.
What is soldering?
Soldering is 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 to metals exposed to the atmosphere?
They acquire a thin film of oxide, which can prevent solder from adhering properly.
What is the purpose of soldering flux?
Flux is used to ‘wet’ the metal, allowing solder to penetrate and remove the oxide film.
What happens to flux during the soldering process?
Most of the flux is burned away, and any residue should be removed using appropriate cleaning methods.
What is the function of solder?
Solder acts as a filler metal, forming a physical and electrical bond between components.
What are the two classifications of solder?
Solders can be classified as soft solder and hard solder.
What is soft solder?
Soft solder is an alloy of tin and lead that melts below 370 °C.
What is hard solder?
Hard solder, or brazing alloy, is a silver alloy used for greater mechanical strength and higher temperature applications.
What is the composition of typical electronic solder?
It is mainly composed of tin (Sn) and lead (Pb), with other materials added for specific purposes.
What is lead-free solder?
Lead-free solder contains metals like tin, copper, silver, and bismuth, and is used to avoid the toxic effects of lead.
What is wetting action in soldering?
Wetting action is the process where solder forms a bond with metal by spreading and covering the surface.
What are the three basic types of soldering fluxes?
The three types are Acid Flux, Organic Flux, and Rosin Flux.
What are the disadvantages of Acid Flux?
Acid Flux is highly corrosive, electrically conductive, and difficult to remove from soldered joints.
What is the primary solvent used in soldering?
Isopropyl Alcohol (IPA) is the primary solvent for removing residues and contaminants.
What is the most commonly used method of heat application for soldering in aircraft wiring?
An electrically heated, handheld soldering iron is the most commonly used method.
What is resistance soldering?
Resistance soldering uses a low voltage transformer to heat the metal being soldered by completing a circuit.
What is torch soldering used for?
Torch soldering is used for applications requiring higher heat, such as brazing and silver soldering.
What is dip soldering?
Dip soldering involves immersing connections into molten solder, typically used on printed circuits.
What is tinning?
Tinning is applying a thin coating of solder to a metal surface to assist heat transfer and protect the soldering iron tip.
What is the process for soldering wires together?
Remove insulation, tin the wires, heat them together with a soldering iron, and apply solder.
What must be done before soldering terminals?
Wires and terminals must be stripped and pre-tinned before soldering.
What are the common types of terminals in electronic assemblies?
Common types include turret terminals, among others.
What should be the solder amount on a wire and terminal?
There should be enough solder to make a good connection without needing to feed more solder.
What happens if a stranded wire is not tinned properly?
It may absorb some solder from the terminal surface, requiring a small amount of solder to be added.
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?
PCBs are made from a laminate or fibreglass composition, making them strong and resistant to heat, cold, moisture, and corrosion.
What precautions should be taken when soldering PCBs?
Handle boards by the edges or with cotton gloves, use small diameter solder, use temperature-controllable equipment, and remove flux residues within 90 minutes.
What is de-soldering?
De-soldering is the removal of solder and components from a circuit for troubleshooting, repair, or salvaging components.
What are the two methods to remove solder?
- Solder Braid (wick)
- De-soldering pump (sucker)
How does Solder Braid (wick) work?
Press the braid onto the cold joint with a hot soldering iron tip; the melted solder is drawn up into the braid by capillary action.
How does a de-soldering pump work?
Melt the solder with a soldering iron, apply the pump’s nozzle to the melted solder, and release the plunger to draw the solder into the pump.
What is the importance of cleanliness in soldering?
Soldering must be done in a clean, dust-free environment to ensure successful solder connections.
What is pre-tinning?
Pre-tinning involves coating wires with solder before attaching them to electrical connectors.
What types of solder are recommended for aircraft electrical systems?
- Non-activated flux cored solder, 60% tin, 40% lead for general applications.
- Non-activated flux cored solder, 62% tin, 2% silver for silver plated components.
- Solid wire solder, 97.5% lead for high-temperature applications.
What wattage soldering irons are recommended for general use?
60, 100, and 200 watts are recommended for general use in aircraft electrical wiring.
What is the optimum tip face for a soldering iron?
The optimum tip face must be between two-thirds and three-quarters of the joint diameter.
What does an acceptable solder joint look like?
A good solder joint has a bright silvery appearance, smooth fillets, and is mechanically strong with an even coat of solder.
What are signs of a poorly soldered joint?
- Dull grey, chalky appearance
- Hair cracks or irregular surface
- Greyish, wrinkled appearance
- Partially exposed joint
- Scorched wire insulation or burned connector inserts
When does the history of welding date back to?
The welding of materials goes back to the Bronze Age.
In which century was welding invented?
Welding was invented in the 19th century.
What materials were the first commercially manufactured aircraft constructed from?
The first commercially manufactured aircraft were constructed from welded steel tubes.
What new metals started to replace steel in aircraft manufacturing?
New and lighter metals such as aluminium, magnesium, and titanium started to replace steel.
What is welding defined as?
Welding is defined as a process that joins metal by melting or hammering workpieces until they are united together.
What are the three basic types of welding?
The three types of welding are Gas Welding, Electric Arc Welding, and Electric Resistance Welding.
What is gas welding?
Gas (oxy acetylene) welding is the process of heating the ends or edges of metal parts to a molten state with a high-temperature flame.
What is the temperature of the flame produced in gas welding?
The flame reaches approximately 3480 °C (6300 °F).
What gases are used in gas welding?
Acetylene and oxygen are used, with hydrogen as an alternative for aluminium welding.
What are the symptoms of short-term exposure to toxic fumes from gas welding?
Symptoms include headaches and eye, nose, or throat irritation.
What is the preferred method for welding aircraft materials under 5 mm thickness?
Gas welding was the preferred method until the mid-1950s.
What equipment is used in gas welding?
Gas welding equipment includes two cylinders, pressure regulators, hoses, a welding torch, and welding goggles.
What is electric arc welding?
Electric arc welding is extensively used to join all weldable metals within the aircraft industry.
What are the four basic types of electric arc welding?
The four types are Manual Metal Arc Welding (MMAW), Gas Metal Arc Welding (GMAW or MIG), Gas Tungsten Arc Welding (GTAW or TIG), and Plasma Arc Welding.
What is Manual Metal Arc Welding (MMAW)?
MMAW is commonly referred to as ‘stick’ welding, using a metal-wire rod coated with welding flux.
How does the arc form in MMAW?
An arc is struck between the rod and the work, producing heat above 5540 °C (10,000 °F).
What is Gas Metal Arc Welding (GMAW)?
GMAW, or MIG welding, uses an uncoated wire electrode fed through the torch with an inert gas for protection.
What is Gas Tungsten Arc Welding (GTAW)?
GTAW, or TIG welding, uses a non-consumable tungsten electrode and is preferred for welding stainless steel and thick aluminium.
What is Plasma Arc Welding (PAW)?
PAW provides advanced control and accuracy using a plasma welding torch to produce high-quality welds.
What is Electric Resistance Welding?
Electric resistance welding is used to join thin sheet-metal components during manufacturing.
What is spot welding?
Spot welding uses two copper electrodes to clamp and weld material by generating heat through electrical resistance.
What is seam welding?
Seam welding uses copper wheels to create a continuous weld by overlapping molten metal spots.
What are the five types of gases used in welding?
The gases are Acetylene, Argon, Helium, Hydrogen, and Oxygen.
What is the primary gas for oxyacetylene welding?
Acetylene is the primary gas for oxyacetylene welding and cutting.
What is the function of a gas-pressure regulator?
A gas-pressure regulator lowers the cylinder pressure to a suitable working pressure.
What are the two types of gas-pressure regulators?
The two types are single-stage and two-stage regulators.
What is the purpose of welding hoses?
Welding hoses connect the regulators to the torch.
What do check valves do in welding equipment?
Check valves prevent the reverse flow of gas.
What is a flashback in welding?
A flashback occurs when burning gas flows back into the hose or regulator, potentially causing an explosion.
What is the most commonly used torch for oxy-acetylene welding?
The equal pressure torch is the most commonly used for oxy-acetylene welding.
What is the function of a cutting torch?
A cutting torch allows for the rapid burning or oxidising of metal in a localised area.
What is a cutting torch?
The cutting torch is an attachment added to the torch handle that allows the cutting of metal.
What is the cutting process in metal cutting?
The cutting process is the rapid burning or oxidising of the metal in a localised area.
What is the kindling temperature for cutting metal?
The metal is heated to a bright red colour (760 °C - 870 °C / 1400 °F - 1600 °F) which is the ‘kindling’ temperature.
How is the cutting process initiated?
A jet of high-pressure oxygen is released by the lever on the cutting attachment, directed against the heated metal.
What happens when oxygen combines with hot metal during cutting?
It forms an intensely hot oxide, and the molten oxide is blown down the sides of the cut.
What is the function of the torch tip?
The torch tip controls the flow of gases and determines the amount of heat applied to the work.
What happens if the torch tip is too small?
If a small tip is used, the heat provided is insufficient to penetrate to the proper depth.
What happens if the torch tip is too large?
If the tip is too large, then the heat is too great, and it can burn holes in the metal.
How are torch tip sizes designated?
Torch tip sizes are designated by numbers, and manufacturers provide charts with recommended sizes.
What should be done to the torch tip before use?
Ensure that the torch tip is clean and not damaged before using it.
What can cause a sustained backfire?
A clogged/obstructed torch tip, high oxygen pressure, low fuel gas pressure, or an overheated tip.
What is the consequence of a sustained backfire?
It melts the torch and can splatter hot, molten metal when the flame pops.
What should be done immediately after a sustained backfire?
Close the oxygen supply at the torch immediately, then close off the fuel gas supply.
What is the purpose of protective eyewear in oxy-acetylene welding?
Protective eyewear is worn to protect the welder’s eyes from the bright flame and flying sparks.
What are some styles of protective eyewear available?
Styles include goggles with headpieces or elastic straps and rectangular eye shields.
What is the recommended lens shade for gas welding?
The darkest shade that shows a clear definition of the work is normally the most desirable.
What innovation was developed for aluminium oxy-acetylene welding?
A new green glass designed to eliminate the sodium yellow-orange flare and provide necessary protection.
What are the three types of flame patterns in oxy-acetylene welding?
Neutral, Carburising, and Oxidising.
What characterizes a neutral flame?
A balanced mixture of oxygen and acetylene, burning at approximately 3300 °C (5970 °F) at the tip.
What is a carburising flame?
Produced by burning more acetylene than oxygen, it burns at approximately 2900 °C (5250 °F).
What is an oxidising flame?
Produced by using an excess of oxygen, burning at approximately 3450 °C (6300 °F).
What must be inspected in an oxy-acetylene welded joint?
The seam must be smooth, bead ripples evenly spaced, and no oxide, blow-holes, or distortion present.
What is the definition of brazing?
Joining two pieces of metal using brass or bronze as the filler metal, with a melting point higher than 427 °C (800 °F).
What is a key requirement for brazing?
The base metal parts are not melted; the brazing metal adheres by molecular attraction.
What is necessary for a good bond in brazing?
The use of a brazing flux to clean the surface of the metal and prevent oxidation.
What is the importance of controlling temperature in brazing?
The base metal must be hot enough for the filler to flow but never overheated to avoid porosity.
What is arc welding also referred to as?
Stick welding.
What is necessary before performing arc welding?
Ensure the welding machine is properly connected and in good working condition.
What are the two methods of striking an arc?
Tapping method and scratching method.
What is a characteristic of a good weld bead?
Little or no splatter, a slight arc crater, and good penetration into the base metal.
What is a visual inspection used for in welding?
A visual inspection must be carried out to ensure the structural integrity of any joint.
What are the two types of joints in welding?
A joint can be either welded or brazed.
How is a welded joint created?
A welded joint is created by melting the base metal by fusion.
How is a brazed joint created?
A brazed joint is created by melting a filler rod into the joint.
What are the characteristics of a good weld?
The weld must have a smooth seam, uniform thickness, and a smooth blending into the base metal.
What should be checked for in a weld?
Inspect for signs of blowholes, porosity, or projecting globules.
What defects should be checked in the base metal?
The base metal must not show signs of pitting, burning, cracking, or distortion.
What is the importance of penetration depth in welding?
The penetration depth must be sufficient to ensure the fusion of the base metal and the filler rod.
How can welding scale be removed?
Welding scale can be removed using a wire brush or by sandblasting.
Why is it important to inspect the underside of welded joints?
Always inspect the underside of welded joints for defects.
What are micro-cracks?
Micro-cracks are tiny cracks visible only with magnification that can lead to early stress failures.
What is Non-Destructive Testing (NDT)?
NDT includes techniques such as magnetic particle, liquid penetrant, radiographic, ultrasonic, eddy current, and acoustic emission for inspecting welds.
What defines a good weld?
A good weld is uniform in width, with even ripples well feathered into the base metal.
What is penetration in welding?
Penetration is the depth of fusion in a weld and is crucial for a solid weld.
What are the penetration requirements for butt and fillet welds?
In a butt weld, penetration must be 100% of the base metal thickness; for a fillet weld, it is 25 to 50%.
What is the final step in the inspection of brazed joints?
Inspection of a brazed joint must be the final step in the process.
What are common defects in brazed joints?
Common defects include voids or porosity, flux entrapment, base metal erosion, unsatisfactory surface condition, and cracks.
What is visual examination in NDT?
Visual examination is a detailed test for evaluating voids, porosity, surface cracks, fillet size, and shape.
What is leak testing used for?
Leak testing is used to determine the gas or liquid-tightness of a braze.
What does pressure testing involve?
Pressure testing involves the application of air at greater-than-service pressures.
What is proof testing?
Proof testing subjects the brazed joint to a one-time load greater than the service level.
What is peel testing used for?
Peel testing is useful for evaluating lap joints and production quality control.
What does tension and shear testing determine?
Tension and shear testing determine a joint’s strength in tension or shear.
What is fatigue testing?
Fatigue testing describes the process of testing the base metal plus the brazed joint.
What is impact testing?
Impact testing determines the basic properties of brazed joints.
What does torsion testing evaluate?
Torsion testing is used on brazed joints in production quality control.
What is bonding in aircraft construction?
Bonding refers to using an adhesive or sealant to chemically or mechanically join two pieces of material.
What factors influence the choice of adhesive or sealant for bonding materials in aircraft?
The choice depends on the properties of the materials being joined and the function/operation of the bonded part.
What are the advantages of bonding metals?
Adhesives distribute stress evenly across the bond line, improve appearance, reduce the need for drilling, and resist flex and vibration stresses.
What are some limitations of adhesives?
Limitations include the time required for full strength development, surface preparation time, and difficulty in disassembling joints.
What is required for adhesives to achieve maximum bonding strength?
It is critical to follow the necessary processes and procedures provided by the product manufacturer.
What are the four most commonly used adhesives for metal bonding?
- Two-part no-mix acrylics
- Two-part mix acrylics
- Two-part epoxies
- Polyurethanes
What is adhesion?
Adhesion is the property of different molecules or surfaces to cling to each other.
What is cohesion?
Cohesion is the property of molecules of the same substance to stick to each other due to mutual attraction.
What is the importance of surface preparation for adhesion?
Surfaces must be thoroughly cleaned and degreased to ensure effective adhesion.
What is the effect of bond thickness on tensile-shear strength?
The thickness of the bond significantly influences the tensile-shear strength; thicker bonds can lead to decreased stability.
What is wetting in the context of adhesive bonding?
Wetting is the ability of the adhesive to cover the entire surface of the parts to be joined, ensuring good contact.
What is capillary action?
Capillary action describes the process of a liquid moving in a narrow space without external forces.
What is a butt joint?
A butt joint is not suitable for transferring forces due to a small bonding area.
What is a single lap joint?
A single lap joint is preferred for thin cross-sections in aircraft construction due to its easy realization.
What types of stresses are commonly found in adhesive bonds?
Types of stresses include shear stress, peel stress, tensile stress, cleavage stress, and compressive stress.
What is the design guideline for maximizing shear and minimizing peel and cleavage?
Maximizing shear is important because shear stress is better distributed than peel and cleavage stress.
What is the significance of joint width in adhesive bonding?
Increasing joint width is more effective than increasing overlap area for reducing stress at the bond ends.
What are the stability considerations for bonded connections?
Stability differences between materials, such as aluminium alloys and epoxy resin, must be considered in bonding.
What should manufacturers keep in mind regarding repair procedures?
Manufacturers must consider the shape, measurements, work procedures, cure times, pressures, and temperatures. Deviations from specified instructions are generally not necessary for airlines.
What is the consequence of deviations from repair procedures?
Deviations often lead to worse results.
What materials are permitted for use in aircraft repairs?
Only materials specified by the aircraft manufacturer are permitted.
What happens if an airline makes modifications to repairs?
Modifications lead to the expiration of warranty claims related to the respective repair.
What is the KSI rating for Carbon Steel?
From 50 KSI.
What is the KSI rating for High Strength Steel Heat Treated?
Up to 300 KSI.
What is the KSI range for CRES?
60 – 115 KSI.
What is the KSI rating for Ti 6Al 4V?
Up to 185 KSI.
What is the KSI rating for AA 2024?
65 KSI.
What is the KSI rating for AA 7075?
80 KSI.
What is the KSI maximum loading for Epoxy Resin?
Up to max. 15 KSI.
How much can breaking load values be reduced by safety factors?
Breaking load values are normally reduced by up to 75%.
What is the safety factor for epoxy resins in aircraft composites?
The safety factor for epoxy resins is 2.25.
What is the maximum loading for epoxy resin after applying the safety factor?
The maximum loading is reduced to 6.66 KSI (15 KSI / 2.25).
What curing process consideration has the highest priority during fabrication?
The curing process of cold age-hardened epoxy adhesives.
How long does the cure of cold age-hardened epoxy adhesives take?
About 26 hours.
What conditions are required for EP-adhesives to develop the best adhesion values?
EP-adhesives require considerably higher temperatures than those possible for heat-treated aluminum-sheet-metal parts.
What are the conditions for the polymerisation process of EP-adhesion film?
Used in the autoclave at 2-3 bar overpressure and at 125 -175 °C (257 - 347 °F).
What happens to moisture during the polymerisation process?
Enclosed moisture evaporates and is removed by vacuum (suction).
