Machining is a manufacturing process in which material is removed from a workpiece in the form of chips using cutting tools and machine tools to obtain the desired shape, size, and surface finish.
It is a subtractive process widely used for producing accurate and precise components in engineering and industrial applications.
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Machining Process :
Machining is a manufacturing process in which material is removed from a workpiece to achieve the desired shape, size, surface finish, and dimensional accuracy using cutting tools. It is one of the oldest and most widely used manufacturing methods.
1. Definition of Machining
Machining is a subtractive manufacturing process in which a sharp cutting tool removes material from a workpiece in the form of chips to create the desired geometry.
Machining cuts, shapes, or finishes metal or other materials by removing excess material.
2. Objectives of Machining
- Produce accurate dimensions and tight tolerances.
- Achieve desired surface finish.
- Form complex shapes that cannot be made by casting or forging.
- Prepare workpieces for assembly or final use.
3. Mechanism of Machining
Machining works on three main principles:
- Shearing – Material ahead of the cutting edge is sheared off to form chips.
- Plastic Deformation – Material near the tool edge deforms before being removed.
- Friction & Heat – Tool and workpiece contact generate heat, affecting cutting and tool life.
Types of chips formed:
- Continuous chips – ductile materials, smooth surface finish.
- Discontinuous chips – brittle materials, rough finish.
- Serrated or segmented chips – harder alloys like titanium.
4. Classification of Machining Processes
Machining can be classified into two main categories:
4.1 Turning Operations
- Material is rotated on a lathe, and a stationary cutting tool removes material.
- Examples: Turning, facing, grooving, threading.
- Applications: Shafts, pins, cylindrical components.
4.2 Milling Operations
- Workpiece is stationary or moves, and a rotating cutter removes material.
- Examples: Face milling, peripheral milling, slotting, contouring.
- Applications: Gears, plates, complex profiles.
4.3 Drilling Operations
- Drill bit rotates to create circular holes in a workpiece.
- Examples: Drilling, reaming, boring, tapping.
- Applications: Holes for bolts, pins, assemblies.
4.4 Grinding Operations
- Abrasive wheel removes small amounts of material for high precision and surface finish.
- Examples: Surface grinding, cylindrical grinding, centerless grinding.
- Applications: Dies, tools, hardened components.
4.5 Other Machining Processes
- Broaching – cutting internal or external shapes with a toothed tool.
- Planing & Shaping – linear cutting for flat surfaces.
- Electrical Discharge Machining (EDM) – removes material via electrical sparks.
- Laser / Waterjet Cutting – modern non-contact machining methods.
5. Elements of Machining Process
- Workpiece – Material to be machined.
- Cutting Tool – Hard material (HSS, carbide, ceramics) that removes material.
- Machine Tool – Supports and moves the workpiece or tool (lathe, milling machine).
- Cutting Parameters – Speed, feed, depth of cut.
- Coolant / Lubrication – Reduces heat and friction, increases tool life.
6. Types of Machining Operations
| Operation | Description | Example |
|---|---|---|
| Turning | Rotating workpiece, stationary tool | Shaft, pin, bolt |
| Milling | Rotating cutter, stationary/moving workpiece | Gear teeth, slots |
| Drilling | Rotating drill creates holes | Bolt holes, tapped holes |
| Grinding | Abrasive wheel removes fine material | Precision surfaces, tool finishing |
| Boring | Enlarging an existing hole | Engine cylinders, bearing holes |
| Shaping / Planing | Linear cutting for flat surfaces | Machine beds, metal plates |
| Broaching | Progressive toothed tool removes material | Keyways, splines |
| EDM / Laser / Waterjet | Non-contact cutting | Hard metals, intricate shapes |
7. Advantages of Machining
- High Accuracy – Can achieve tight tolerances and precise dimensions.
- Surface Finish – Excellent surface quality achievable.
- Complex Shapes – Can produce intricate geometries.
- Versatility – Can machine almost all metals, plastics, and composites.
- Repeatability – CNC machines allow consistent production.
8. Disadvantages of Machining
- Material Waste – Subtractive process produces chips and scrap.
- High Cost for Large Parts – Machine time, tool wear, and power cost can be high.
- Slow Process – Compared to casting or forging for bulk production.
- Tool Wear – High-speed cutting generates wear and requires tool replacement.
- Heat Generation – May affect material properties if not controlled.
9. Applications of Machining
- Automotive: Engine parts, shafts, gears, and molds.
- Aerospace: Turbine blades, landing gear components.
- Medical: Implants, surgical instruments.
- Industrial Machinery: Dies, molds, precision equipment.
- Electronics: Casings, heat sinks, precision connectors.
10. Summary
- Machining is a subtractive process used to create accurate parts by removing material.
- Processes include turning, milling, drilling, grinding, shaping, broaching, EDM, laser cutting.
- Advantages: high accuracy, surface finish, versatility.
- Disadvantages: material waste, cost, slower than bulk forming.
- Key factors: tool material, machine type, cutting parameters, and lubrication.
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