Welding Honor

Vocational Activities

Requirements

1. Define what welding (the process) is. What is the difference between welding (the process) and a weld (the joint)?

   Answer: Welding (the process) is the process of joining metals by fusion (heat) or pressure, with or without filler material. A weld (the joint) is the physical result — the finished welded joint. Welding is the act/technique; the weld is the product. — The ABNT NBR ISO 857-1 standard officially differentiates the terms. In Brazil, 'soldagem' is the process (verb); 'soldadura' is the weld bead formed (noun). In Portugal, 'soldadura' covers both. There are more than 50 welding processes registered by the AWS (American Welding Society).

2. Identify all of the following items:
   • Welding and cutting torches
   • Regarding the 05 gases Oxygen and Acetylene, identify and explain their differences:

   Answer: 1) Welding and cutting torches: the welding torch mixes the fuel and oxidizing gases to generate the flame that melts the metal; the cutting torch has a lever that releases an additional jet of pure oxygen over the heated metal, oxidizing and cutting the piece. 2) Differences between Oxygen and Acetylene: Oxygen (O2) is a colorless, odorless and oxidizing gas (it feeds combustion, it does not burn on its own), stored compressed in cylinders usually black in color; Acetylene (C2H2) is a fuel gas, colorless, with a characteristic odor (of garlic), unstable under high pressure, stored dissolved in cylinders usually white or maroon in color. In oxyacetylene welding the two combine in the torch: the acetylene provides the flame and the oxygen makes it hot enough (about 3,000 to 3,200 degrees C) to melt the metal. — The O2+C2H2 combustion reaches 3,100°C, enough to melt steel. Cylinders have standardized colors (ABNT NBR 12176). Acetylene is unstable above 1.5 bar — stored dissolved in acetone. Pure O2 accelerates combustion; wrong handling causes an explosion. Always keep away from oils and greases.

3. What is brazing? Where is this technique most used today?

   Answer: Brazing is the process of joining metals using a filler metal with a melting point above 450°C, but lower than that of the pieces to be joined — only the filler material melts, the pieces remain solid. Today it is most used in: 1) Refrigeration and air conditioning (joining copper tubes); 2) Electronics (soldering components and boards); 3) Jewelry (joining precious metals without deforming the piece); 4) Hydraulics and copper piping; 5) Manufacturing of utensils, radiators and heat exchangers. It is preferred when one wants to join thin, delicate pieces or pieces of different metals without melting them. — Different from soft soldering (tin, below 450°C) and fusion welding (melted pieces). A silver alloy is common in refrigeration. Induction brazing is automated. In jewelry, the filler metal has a color close to the piece. The AWS classifies brazing as welding by specific capillary addition.

4. What are the advantages of a correctly made weld?

   Answer: A correct weld provides: high mechanical strength, durability, total sealing, reduced weight (vs. bolts), savings of material, a professional appearance and safety in structures. — A poorly made weld is a serious failure in structures — the collapse of bridges and buildings has been caused by it. The AWS D1.1 standard regulates structural welding. Visual inspection + non-destructive testing (ultrasound, X-ray, penetrant liquid) ensure quality. A good weld surpasses the strength of the base metal.

5. Explain the processes of each of the following welds:
   • MIG-MAG
   • TIG
   • Plasma
   • Manual arc
   • Oxyfuel
   • Arc with tubular wire
   • Electrode

   Answer: 1) MIG/MAG: arc welding with a continuous consumable wire fed automatically, protected by gas. In MIG the gas is inert (argon, helium); in MAG it is active (CO2 or a mixture). Recommended for fast production on steel and aluminum plates. 2) TIG: an arc opened between a NON-consumable tungsten electrode and the piece, under the protection of an inert gas (argon). The filler metal is added by a separate rod. It gives a weld of high precision and finish, ideal for stainless steel, aluminum and thin pieces. 3) Plasma: uses a gas ionized at a very high temperature, concentrated into a narrow jet by the constricting nozzle. It generates a very hot and focused arc, used in precision welding and cutting. 4) Manual arc (coated electrode): the welder holds a consumable coated electrode (rod); the arc between the electrode and the piece melts both, and the coating generates protective gas and slag. It is the simplest and most versatile process in the field. 5) Oxy-fuel: melts the metal by the flame of burning oxygen with a fuel gas (acetylene), reaching about 3,000°C; used in welding, cutting and heating. 6) Flux-cored arc (FCAW): similar to MIG/MAG, but the wire is tubular with flux in the core that generates the protection (slag/gas) when melting; it can dispense with external gas and performs well outdoors. 7) Electrode: a process in which the current passes through the electrode generating the arc that melts the base metal and the electrode itself; in the coated one the coating forms protective slag. It is the basis of the most common manual electric welding. — MIG (inert gas) used on aluminum; MAG (active gas) on steel. TIG is slower but high precision — used in aviation. Plasma cuts large thicknesses quickly. The electrode is the most portable. Each process has its ideal application — the choice depends on the material, thickness, position and cost.

6. How can the various areas of welding be divided?

   Answer: Main areas: 1) Civil construction (structures, bridges, buildings), 2) Automotive industry (chassis, components), 3) Naval (hulls, ducts), 4) Aerospace (high precision), 5) Jewelry (precious metals), 6) Piping (gas, water), 7) General repair (mechanic's shop). — Civil construction uses a lot of electrode welding. Automotive mixes MIG/MAG and robots. Naval requires special certification (AWS, ABS). Aerospace uses TIG and X-rays on all welds. Jewelry uses silver brazing. Each division has its own standards and requires specific certifications for welders.

7. Demonstrate how to use an oxyacetylene welding process, including tanks, valves, hoses and changing the torch tips (welding and cutting). Light the torch using dark protective goggles (it is like being blindfolded).

   Answer: First open the oxygen valve, then the acetylene. Adjust the pressures on the gauges (O2: 3-5 bar; C2H2: 0.3-0.5 bar). Connect the appropriate tip (welding or cutting). Use dark goggles type 5-7. — The ORDER matters: O2 first, C2H2 after to light; the reverse to extinguish. Acetylene above 1.5 bar is unstable. Colored hoses (green=O2, red=C2H2) avoid confusion. A flashback arrestor on each tip prevents an explosion. Always have a fire extinguisher within 5m. Train under strict supervision until you master it.

8. With the help of your instructor, using the process of your choice, weld two steel or metal plates, measuring 250 X 200 X 3 mm, in the horizontal, vertical (going up and down) and on the surface (overhead, on top and underneath).

   Answer: Weld 2 plates in 5 positions: 1G (flat horizontal), 3G going up (vertical bottom-up), 3G going down (vertical top-down), 4G (overhead from below) and 1G flat from above. — Positions follow the AWS standard: 1G flat, 2G horizontal, 3G vertical, 4G overhead. Going up is more common (gravity helps). Going down requires lower amperage. Overhead is the most difficult — the weld can drip. Training in these 5 positions prepares you for any challenge in the field.

9. Demonstrate your skill with the torch by performing the following cuts:
   • In a straight line, at least 300 mm
   • Circular with a radius of at least 50 mm
   • A six-pointed star with a 50 mm radius
   • Note: The cuts must be made on a steel or metal plate 6 mm or 1/4 inch thick, and equipment such as a ruler, chisel, etc. may be used.

   Answer: Use a 6mm steel plate. For a straight line: mark it with chalk and a ruler, cut with the cutting torch adjusted at a 90° angle. For a circle: use a compass or an anvil. — A 6mm plate requires a cutting tip of size 1 or 2. Preheat for 5 seconds before starting the O2 jet. A speed that is too fast leaves an irregular cut; too slow causes hardening. A star requires precision — use a template if necessary. Practice on scrap before the final cut.

10. Demonstrate the ability to weld cast iron, joining 2 beveled objects with a minimum weld length of 50 mm, using the process of your choice.

    Answer: Preheat the cast iron to 200-300°C (slowly). Use an electrode specific for cast iron (E NiFe-Cl or E NiCu). Weld in short passes (20-30mm) with pauses to cool slowly. — Cast iron has a high carbon content — welding causes cracks if done wrong. Preheating + slow cooling are vital. Nickel electrodes are standard (E NiFe-Cl). Abrupt cooling hardens and breaks it. Sand or an insulating blanket maintains the temperature. Practice on scrap first.

11. What is the recommended Personal Protective Equipment and why is it used for the following welding processes?
    • Electric welding
    • Oxyacetylene welding
    • Special welding (Submerged Arc, Argon, TIG, MAG, Plasma, etc.)

    Answer: 1) Electric Welding: a welding mask with a filter lens of shade 10 to 13 (protects the eyes from the intense radiation of the arc and from spatter), leather gloves (insulate against shock and heat), a split-leather apron, sleeves/spats and a safety boot (protect the skin and feet against sparks and hot metal). 2) Oxyacetylene Welding (oxy-gas): protective goggles with green lenses of shade 5 to 7 (the flame requires less filtering than the arc), leather gloves against heat, a split-leather apron and a boot; they protect against the flame, the glare and spatter of molten metal. 3) Special Welds (Submerged Arc, Argon, TIG, MAG, Plasma, etc.): a mask with a face shield and darker lenses, shade 11 to 14 for TIG and plasma because of the intense ultraviolet radiation; in addition, exhaust fans/ventilation and a respirator suitable for the metal fumes and inert gases that can displace the oxygen in the environment. The set protects the eyes, airways and skin. — The mask lens darkens according to the brightness of the arc. UV/IR from the electric arc burns the cornea (welder's flash). Leather gloves withstand spatter at 600°C+. Plasma and MIG generate toxic smoke — an exhaust fan is mandatory. The MTb's NR-18 regulates welding in Brazilian civil construction.

12. Explain the precautions, care and storage of the following welding equipment:
    • Electrodes and welding rods
    • Pliers and welding cables
    • Torches and welding and/or cutting tips
    • Regulator valves and safety valves. In particular, why should they not be lubricated?

    Answer: 1) Welding electrodes and filler rods: store in a dry place, preferably in a heated oven (50 to 150°C, depending on the type) to avoid moisture absorption; a damp electrode generates porosity and cracks in the weld. Keep them in the original packaging, away from the floor and from moisture. 2) Welding pliers and cables: coil the cables without knots or forced bends, check the insulation against cuts and wear, and keep them away from heat, oil and rain; the pliers (electrode holder) must have clean and firm jaws for good electrical contact. 3) Welding and/or cutting torches and tips: always close the gas valve before storing, check hoses and connections against leaks, clean the tips and protect against impacts; never store with a flame or retained pressure. 4) Regulator valves and safety valves: handle with care, keep them clean, free of dust and without damage to the thread. NEVER lubricate with oil or grease: in contact with pure oxygen under pressure, the oil undergoes rapid oxidation and can self-ignite, causing a fire or explosion. For this reason they are assembled and kept completely free of grease. — Damp electrodes cause porosity and cracks in the weld. Cables with bad insulation can give a shock. Oil + O2 = spontaneous violent combustion (serious accidents in factories). Valves use graphite or Teflon as internal sealing. An oven for electrodes is a mandatory AWS A5.1 standard.

13. Explain the difference between oxyacetylene and electric arc welding.

    Answer: Oxyacetylene uses a chemical flame (O2 + acetylene) generating 3,100°C. The electric arc uses electricity between the electrode and the piece, generating up to 6,000°C. Oxyacetylene is slower, ideal for thin plates and brazing. — The electric arc reaches the heat of the sun's surface. Oxyacetylene is more portable (cylinders). Electrolysis in the arc transfers material from the electrode. In light mechanics oxy is used more; in heavy construction, the arc. Average time: oxy 5 min/30cm, arc 1 min/30cm on similar plates. Cost: oxy is cheaper.

14. Demonstrate the ability to select an electrode and adjust the amperage for various types and thicknesses of metal.

    Answer: Use an electrode according to the metal: E6013 or E7018 for carbon steel. Diameter proportional to the thickness: 3mm plate = 2.5mm electrode, ~80A; 6mm plate = 3.25mm electrode, ~120A; 10mm plate = 4mm electrode, ~160A. — E6013 is universal (common carbon steel). E7018 is low hydrogen (critical structures). Each electrode has an amperage range on the packaging. Low amperage = unstable arc; high = perforation. DCEN or DCEP polarity varies. A modern inverter regulates automatically, but knowing the theory is fundamental.