Overview
This lecture covers types of welding processes, weld joint types and callouts, as well as surface finish and texture specifications for engineering drawings.
Welding Processes
- Common welding processes: MIG (Metal Inert Gas), TIG (Tungsten Inert Gas), brazing, and soldering.
- Brazing and soldering are lower-temperature joining methods compared to traditional welding.
- MIG welding uses direct current and an inert gas to create the weld.
- TIG welding is used for thick sections and nonferrous metals, is time-consuming, and uses a fixed electrode.
Weld Joints and Types
- Weldment: a part made by welding components together.
- Joint types: butt (pieces butted), corner, T, lap (overlapping), and edge (edges aligned) joints.
- Butt joints can use square, V, bevel, U, or J welds; complexity and strength increase from square to U.
- Lap joints use plug or slot welds; plug welds are made by drilling holes in one piece and welding through.
Weld Callouts and Symbols
- Weld callouts indicate weld type, size, location, finish, and whether to be done in the field or all around.
- Arrow side means the side the arrow points to; other side is opposite; placement of callout on leader line indicates this.
- Symbols include fillet, groove, plug, and slot welds.
- Weld surface contours: concave, flush, or convex; method (grinding, machining, etc.) can be specified.
- Weld sizes use up to two decimal places or fractions (imperial) or whole numbers (metric).
Weld Testing Methods
- Destructive testing: breaking the part to inspect weld penetration.
- Non-destructive testing: radiographic (X-ray) and ultrasonic testing to detect internal flaws without damaging parts.
Surface Finish and Texture Callouts
- Surface finish symbol: check mark with number indicates roughness height (e.g., 63 microinches).
- "FAO" means "finish all over"; applies specified finish to all surfaces unless otherwise noted.
- Detailed surface texture callouts may include waviness height/width, roughness width, and lay direction.
- Lay directions can be perpendicular, parallel, concentric, radial, etc.
- The more precise or smoother the finish, the more complex and costly the manufacturing method.
Key Terms & Definitions
- MIG Welding — Metal Inert Gas welding using inert gas and direct current.
- TIG Welding — Tungsten Inert Gas welding for thick or nonferrous metals.
- Weldment — An assembly of parts joined by welding.
- Butt Joint — Joint where two pieces meet end-to-end.
- Fillet Weld — Weld with a triangular cross-section, commonly at corners.
- Surface Finish — The measured roughness or smoothness of a part’s surface, usually in microinches.
- Lay Direction — The predominant direction of surface pattern due to manufacturing.
Action Items / Next Steps
- Review weld callout slides/examples for lab work.
- Practice proper weld and surface finish callouts on current lab assignments.
- Refer to surface finish tables for appropriate fabrication methods and achievable finishes.