1. Introduction
Machining → A subtractive manufacturing process where material is removed from a workpiece using cutting tools (lathe, milling, drilling, grinding, CNC, etc.) to achieve precise shape, size, and finish.
Fabrication → A constructive process involving cutting, bending, and joining raw materials (mostly metals) to make structures, assemblies, or components (e.g., welded frames, ducts, tanks, bridges).
Both are core manufacturing technologies: machining is used for precision components, fabrication for structural assemblies.
2. Technologies Included
a) Machining Technologies
Turning (Lathe)
Milling (CNC, Vertical/Horizontal)
Drilling, Boring, Tapping
Grinding & Polishing
Broaching & Shaping
Advanced Machining: EDM, ECM, Water Jet, Laser Cutting, CNC machining centers.
b) Fabrication Technologies
Cutting → Shearing, Sawing, Laser/Plasma/Oxy-fuel cutting.
Forming → Press brake bending, rolling, stamping, forging.
Joining → Welding (MIG, TIG, Arc, Spot), Riveting, Bolting, Adhesive bonding.
Surface Finishing → Painting, Powder Coating, Galvanizing, Polishing.
3. Applications
Machining
Automotive: shafts, gears, engine parts.
Aerospace: turbine blades, precision fasteners.
Medical: implants, surgical tools.
Tooling: dies, molds, machine parts.
Fabrication
Construction: bridges, pipelines, pressure vessels.
Shipbuilding: hulls, frames.
Industrial Equipment: tanks, conveyors, ducts.
Household/consumer: furniture, appliances, enclosures.
4. Remarks
Machining → High accuracy and finish, but more time, energy, and material waste.
Fabrication → Best for larger structures, economical for mass/structural production, but lower precision compared to machining.
Both often complement each other (e.g., a fabricated frame machined at joints for precision).
5. Standard Operating Procedure (SOP)
a) Machining SOP
Verify drawing/specifications.
Select proper machine tool, cutting tool, speed/feed.
Fix workpiece securely (chuck, vice, fixture).
Carry out machining in sequence (rough → finish cuts).
Inspect dimensions (micrometer, CMM).
Deburr, clean, and store safely.
b) Fabrication SOP
Study drawings, material list, and cut plan.
Cut material as per specification (saw, plasma, laser).
Form/bend using press brake/rolling machine.
Assemble using fixtures & jigs.
Join via welding/riveting/bolting.
Inspect weld quality (visual, ultrasonic, radiographic).
Apply surface finish and mark identification.
6. Site Parameters (Selection Criteria)
Machining
Required accuracy (µm–mm).
Workpiece material (hardness, machinability).
Production volume (CNC for mass, manual for job work).
Tool life & cutting conditions.
Fabrication
Structure size & load requirements.
Type of joints (weld, rivet, bolt).
Environment (corrosion, temperature).
Accessibility & transportation constraints.
7. Safety Features
Machining Safety
PPE: goggles, gloves, apron, ear protection.
Guarding of rotating parts.
Coolant handling safety.
Emergency stop switches.
Fabrication Safety
Welding shields, masks, leather gloves.
Ventilation for fumes & gases.
Fire prevention (extinguishers, no oil/grease near welding).
Safe lifting/rigging of heavy structures.
8. Quality Features
Machining
Dimensional accuracy (±0.01 mm or better on CNC).
Surface roughness (Ra as low as 0.4 µm).
Tolerance & geometric accuracy.
Fabrication
Weld quality (no cracks, porosity, undercut).
Structural alignment and strength.
Surface protection (paint, galvanizing).
NDT checks (ultrasonic, magnetic particle, dye penetrant).
9. Cost Parameters
Machining
High tooling & machine cost.
More labor-intensive (setup + inspection).
Higher per-piece cost for low volume.
Economical only for precision, small-to-medium parts.
Fabrication
Lower per-unit cost for large structures.
Welding/fabrication shops relatively cheaper setup.
Cost efficiency improves with scale (bridges, pipelines, tanks).
Requires skilled welders and QA → adds to labor cost.
