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Welding & Joining Processes - Vocabulary Flashcards

Overview

  • Welding is a process of joining metals by heating and melting to fuse two pieces together.
  • Main sources of welding heat:
    • Flame from combustion of fuel with air or oxygen
    • Electric arc between an electrode and the workpiece or between two electrodes
    • Electrical resistance offered to current flow through workpieces
  • Welding and joining processes are essential for product development, often dominate cost and production difficulty, and failures frequently occur at joints due to high stress at those points.
  • Careful control of joining processes yields economy, reliability, and performance benefits.

Key Concepts and Significance

  • Welding vs joining processes
    • Welding: heating/melting to fuse parts into a one-piece assembly
    • Joining processes include various methods that may or may not involve fusion (e.g., solid-state, explosive, diffusion, etc.)
  • Joints are typically the weakest points in assemblies because they experience high stresses
  • Proper process selection and control are crucial for cost, reliability, and safety

Classes of Welding Processes (AWS framework and common groups)

  • Oxy-fuel Gas Welding (OFW)
    • Oxyacetylene Welding (OAW)
    • Pressure Gas Welding (PGW)
  • Arc Welding (AW)
    • Shielded Metal Arc Welding (SMAW)
    • Gas Metal Arc Welding (GMAW)
    • Gas Tungsten Arc Welding (GTAW)
    • Flux Cored Arc Welding (FCAW)
    • Submerged Arc Welding (SAW)
    • Plasma Arc Welding (PAW)
    • Stud Welding (SW)
  • Resistance Welding (RW)
    • Resistance Spot Welding (RSW)
    • Resistance Seam Welding (RSW)
    • Projection Welding (RPW)
  • Unique/advanced or solid-state and other processes
    • Ultrasonic Welding
    • Diffusion Welding
    • Friction Welding
    • Explosive Welding (XW)
    • Thermit Welding (TW)
    • Laser Beam Welding (LBW)
    • Electron Beam Welding (EBW)
    • Induction Welding (IW)

Arc Welding: SMAW and Other Arc Processes (AWS classification excerpt)

  • SMAW (Shielded Metal Arc Welding) – one of the oldest, simplest, and most versatile arc welding processes
    • Arc is struck between an electrode (stick) and the workpiece
    • Requires simple equipment: power supply, cables, and electrode holder
    • Common in construction, shipbuilding, pipelines, especially in remote locations
  • Other arc processes listed include: GMAW, GTAW, FCAW, SAW, PAW, SW

Electrode (Welding Rod)

  • An electrode is a wire/rod connected to the welding power source
  • Current is fed through the electrode to create heat and join metals
  • Shielding gas/coating elements affect arc stability, slag formation, and weld quality

Safety, PPE, and Safe Work Practices

  • Welding safety requires/advocates:
    • Work in well-ventilated areas; welding vapors and gases can be hazardous
    • Do not weld galvanized steel due to dangerous gases produced
    • Keep flammable materials away from the welding area
    • Have a fire extinguisher or water source available
  • Personal Protective Equipment (PPE) and protective clothing
    • Welding helmet with proper shade, flame-resistant clothing, gloves, jacket, work boots, and safety pants
    • Gowns, aprons, and gloves to protect from heat, sparks, radiation, and burns
    • ANSI Z49.1-2012 guidance: protective clothing should provide sufficient coverage and minimize skin burns; full coverage is recommended for ultraviolet/infrared exposure
    • Leather welding gloves with insulated linings; gauntlet cuffs for extra arm protection
    • Steel-toe shoes are required in some setups

Flux/Coatings and Their Roles (for coated electrodes or flux-cused wires)

  • Functions of flux/coating:
    • Protect molten metal from oxygen/nitrogen in air
    • Stabilize the arc
    • Improve weld metal quality
    • Impart desired properties to weld metal
    • Increase deposition rate and welding efficiency

Fire Safety and Gas Welding Equipment (Oxy-Acetylene)

  • Essential equipment components (oxy-acetylene): torch body, two gas tubes, control valves, mixer chamber, flame tube, welding tip
  • Cutting torch uses separate oxygen flow for preheating and cutting
  • Gas hoses color codes: red = acetylene, green = oxygen
  • Threading conventions: oxygen regulators/connectors use right-hand threads; acetylene hoses use left-hand threads
  • Gas regulators
    • Control gas pressure via a regulator that has two gauges: high-pressure (cylinder) and low-pressure (to torch)
    • Outlet pressure is set via adjustment screw
  • Safety features: flashback arresters/flashback traps prevent flame from traveling back into hoses/regulators
  • Gas cylinder pressures
    • Oxygen cylinders can be up to ~300 bar
    • Acetylene cylinders typically around ~15 bar (acetone/dissolved acetylene in porous material)
  • Regular safety checks include inspecting hoses, regulators, flashback arresters; annual checks recommended; regulators rated for cylinder pressures; flashback arresters checked per manufacturer instructions

Essential Equipment Components (Detailed)

  • Hoses and fittings
    • Hoses should be color-coded and free of wear; keep hose length short and not taped together
  • Regulators
    • Two gauges: high-pressure (in cylinder) and low-pressure (to torch)
    • An adjustable outlet pressure sets gas flow
  • Flashback arresters
    • Prevent backflow of flame into gas lines
  • Cylinders
    • Cylinder color coding and threading conventions
  • Nozzle, blowpipe, valve controls, torch tip

Torch Flames and Flame Characteristics (Oxyfuel)

  • Flame types (for acetylene-oxygen): neutral, oxidizing, carburizing (reducing)
  • Temperatures
    • Outer envelope flame: ~3040–3300 °C (5500–6000 °F)
    • Inner cone: ~1260–2100 °C; hottest part around the inner cone
    • Neutral flame: balanced H and O in flame chemistry
    • Oxidizing flame and carburizing flame differ in heat and chemical effects on base metal and weld

Preparing the Metal for Welding

  • Metal to be joined must be free of dirt, paint, oil, grease, rust, and other contaminants
  • Cleaning methods: grinding, filing, scraping, sanding; heating with torch and brushing with a wire brush
  • Beveling
    • Thick pieces should be beveled on one or both sides to provide larger welding surface and complete fusion through thickness
    • Bevel methods include grinding, chipping with cold chisel, sawing, filing, or burning with torch
  • Beveling may not be required for very thin pieces

Types of Welded Joints (5 common types)

  • Butt joint
  • Corner joint
  • Tee joint
  • Lap joint
  • Edge joint

Common Weld Defects (and brief causes/definitions)

  • Incomplete Penetration: weld does not penetrate through full thickness
  • Lack of Fusion: weld does not fuse with base metal or earlier weld passes
  • Undercut: base metal gouged away and not filled by weld
  • Slag Inclusions: slag left in weld due to incomplete cleaning or insufficient heat
  • Porosity: small gas pockets due to moisture or contamination
  • Burn-through: excessive heat causing partial/complete melt-through of base metal
  • Underfill: final weld weld bead thinner than base metal
  • Overlap: filler material extends beyond weld bead edge
  • Cracks: cracks in weld metal or heat-affected zone due to stress or improper preheat
  • Pinholes: small holes from gas bubbles due to moisture/contamination
  • Inclusions: foreign materials trapped in weld metal due to dirty work area or poor process

Additional Common Defect Details (condensed)

  • Lack of Penetration: root fusion temperatures not reached, fast welding rate, or too large an electrode
  • Cracks: often in HAZ, problematic in Mo/Cr alloys and thick welds; mitigated by pre-heating and possibly stress relief/annealing
  • Pinholes/Porosity: moisture on electrodes or dirty base metals

Testing & Quality Control (NDT vs Destructive)

  • Destructive Testing
    • Tensile Test: determine ultimate strength, yield point, and elongation
    • Bending Test: assess cracking tendency and ductility by bending specimen 90°–180°
    • Sectioning: cut weld along centerline to inspect internal features visually
  • Non-Destructive Testing (NDT)
    • Dye Penetrant Examination: reveals surface cracks and porosities using dye and developer
    • Hardness Testing: determine weld hardness and heat-affected zone characteristics; typical acceptable Brinell hardness for mild/low alloy steel is around $H_{BN} \, \approx\, 220$ (Brinell)
    • Magnetic Particle Testing: detects surface and near-surface defects in ferromagnetic materials
    • Radiographic Examination (X-ray/gamma): reveals internal defects (cracks, porosity, inclusions, penetration)
    • X-Ray Examination: similar to radiography with X-ray sources
    • Ultrasonic Examination: uses ultrasound to detect laminations, cracks, discontinuities by reflection time
  • Purpose of testing: ensure weld quality, locate defects, support safety and performance standards

AWS Electrode Numbering System (Mild Steel Electrodes)

  • Basic format: E xxxx, where:
    • E = Electric arc welding electrode
    • First two digits: minimum tensile strength of the deposit in ksi (thousand psi)
    • Third digit: welding position capability
    • Fourth digit: current type and coating characteristics
  • Interpretations and examples
    • Example: E 7010
    • 70 = minimum tensile strength of deposit = 70,000 psi
    • 1 = all positions capability
    • 0 = DC reverse polarity, cellulosic coating, etc.
    • Example: E 6024
    • 60 = minimum tensile strength = 60,000 psi
    • 2 = flat and horizontal welding only
    • 4 = AC or DC with rutile coating containing iron powder; specific combinations vary by code
  • Use cases/notes
    • Some codes enable all-position welding (e.g., E7010) suitable for vertical/horizontal/or overhead with DC reverse current
    • Others are restricted to flat/horizontal welding (e.g., E6024)

Practical Examples and Interpretations

  • E7010: cellulosic-coated electrode; suitable for all positions; DC reverse polarity; deposit strength ~70 ksi
  • E6024: rutile-based with iron powder; suitable for flat and horizontal welding; can be used with AC or DC

Welding Safety: Practical Guidelines (Key Points)

  • Always wear a clean, undamaged welding helmet with appropriate shade
  • Roll down sleeves and cuffs; avoid loose clothing that can catch sparks
  • Wear goggles for chipping operations; keep flammable materials away
  • Wear leather gloves, apron, and boots; ensure floor is clean and dry
  • Obtain instructor’s permission before welding in restricted areas; ensure proper ventilation
  • Ensure exhaust systems are operational before welding

Practical Guidelines for Oxy-Acetylene Equipment

  • Gas cylinders use color-coded hoses: acetylene (red), oxygen (green)
  • Oxygen cylinders have high pressures (~300 bar); acetylene around ~15 bar embedded in solvent/porous medium
  • Regulators reduce cylinder pressure to torch working pressures; verify regulator compatibility with cylinder pressures
  • Use flashback arresters to prevent flame backflow into hoses/regulators; perform regular checks
  • Inspect hoses for wear and proper length; avoid twisting, kinking, or leaks
  • Fully check equipment at recommended intervals; regulators may have recommended service life

Beveling and Joint Preparation (additional details)

  • Beveling increases welding surface area and improves fusion through thickness
  • Beveling methods include grinding, chipping, sawing, filing, or cutting with torch
  • Thin pieces may not require beveling; prioritize clean, well-prepared surfaces

Five Essentials to Obtain Quality Welds

  • 1) Correct Current
  • 2) Correct Arc Length
  • 3) Correct Travel Speed
  • 4) Correct Size of Electrode
  • 5) Correct Electrode

Arc Welding Guiding Principles (summary)

  • A) Current Requirements
    • Heat at the arc is proportional to current at constant arc voltage and time
    • Electrode type, diameter/size, plate thickness, and welding position influence current choice
    • Correct current should be determined by testing and experience (arc sound, molten pool size, bead appearance, penetration, spatter)
  • B) Arc Length
    • Arc length roughly equals the diameter of the core wire, but varies by electrode type and welding position
    • Too short arc causes sticking and slag entrapment; too long arc reduces heat concentration and increases spatter
  • C) Travel Speed
    • Travel speed should prevent slag from crowding the arc or being left behind
    • Bead length ~ ¾ of consumed electrode; wrong speeds cause incomplete fusion, porosity, slag issues, or burn-through
  • D) Electrode Size
    • Use the largest practical diameter for economy; for vertical/overhead positions, use one size smaller than flat position recommended; electrodes > 3/16” often not suitable for overhead
  • E) Choice of Electrode
    • Depends on base metal, joint type and preparation, weld quality/chemistry requirements, welding position, heat treatment feasibility, cost, and available equipment

Common Welding Joints (summary)

  • Butt Joint
  • Corner Joint
  • Tee Joint
  • Lap Joint
  • Edge Joint

Summary of Welding Process Selection and Real-World Relevance

  • Use OFW or arc welding for simple, robust joints; switch to advanced or solid-state methods for high-precision or special materials
  • For thick sections or critical joints, select processes with deep penetration and control (e.g., SMAW or FCAW with appropriate parameters; SAW for thick plates)
  • In production environments, optimize process layout to minimize heat input damage to adjacent areas, control distortion, and ensure repeatability

Quick Reference Values and Facts (LaTeX-formatted)

  • AC electrical frequency: f = 60\ \,\mathrm{Hz}
  • Open-circuit arc welding voltage (typical): V_{OC} \approx 75\ \mathrm{V}
  • Oxygen cylinder pressure (typical): p{\mathrm{O2}} \approx 300\ \mathrm{bar}
  • Acetylene cylinder pressure (typical): p{\mathrm{C2H_2}} \approx 15\ \mathrm{bar}
  • Oxyfuel flame temperature ranges:
    • Outer envelope: T_{outer} \approx 3040$-$3300\,^{\circ}\mathrm{C}
    • Inner cone: T_{inner} \approx 1260$-$2100\,^{\circ}\mathrm{C}
    • Acetylene flame peak around T \approx 3200\,^{\circ}\mathrm{C}
  • Shielding gas/arc coating effects influence welding properties and stability

Final Notes

  • The content mirrors a typical industrial welding course with emphasis on both theory (AWS classifications, electrode codes) and practice (arc control, joint prep, safety, and QC methods).
  • While specific numbers vary by material and process, the core concepts (arc control, heat input, joint prep, and defect prevention) remain universally applicable for exam preparation and real-world welding work.