Machining Processes
Machining is a manufacturing process in which a cutting tool removes material from a workpiece to produce the desired shape and dimensions. It is a subtractive process, typically involving a wedge‑shaped cutting tool and relative motion between tool and workpiece. The main categories include shaping, turning, drilling, milling, and grinding.
Shaping
Principle: In shaping, a single‑point cutting tool moves linearly relative to the workpiece to cut material in a straight path. The workpiece is usually held stationary on the table, and the tool reciprocates.
Key features
- Tool motion: reciprocating (cutting stroke + return stroke).
- Feed motion: perpendicular to cutting stroke, given to the workpiece.
- Cutting occurs only during the forward stroke; return stroke is idle.
Applications
Producing flat surfaces, grooves, slots, and keyways on small to medium workpieces.
Performance parameters
Material removal rate (MRR) can be estimated as: \[ \text{MRR} = \frac{L \times d \times f \times N}{60} \] where \(L\) = stroke length (mm), \(d\) = depth of cut (mm), \(f\) = feed per stroke (mm), \(N\) = strokes per minute.
Turning
Principle: Turning is performed on a lathe, where the workpiece rotates and a single‑point cutting tool moves parallel or perpendicular to the axis of rotation to remove material.
Key features
- Primary motion: rotation of the workpiece (cutting speed \(V\)).
- Feed motion: linear movement of the tool along or across the axis.
- Depth of cut: radial engagement of the tool.
Applications
Producing cylindrical, conical, contoured, and threaded surfaces.
Cutting speed formula
\[ V = \frac{\pi D N}{1000} \] where \(V\) = cutting speed (m/min), \(D\) = workpiece diameter (mm), \(N\) = spindle speed (rev/min).
Drilling
Principle: Drilling uses a rotating multi‑point drill bit to produce round holes in a workpiece. The drill advances axially into the workpiece.
Key features
- Primary motion: rotation of the drill (cutting speed).
- Feed motion: axial movement of the drill into the workpiece.
- Chips are evacuated through flutes in the drill.
Applications
Creating through holes, blind holes, and holes for tapping or reaming.
Cutting speed formula
\[ V = \frac{\pi D N}{1000} \] where \(D\) = drill diameter (mm), \(N\) = spindle speed (rev/min).
Material removal rate
\[ \text{MRR} = \frac{\pi D^2}{4} \times f \times N \] where \(f\) = feed per revolution (mm/rev).
Milling
Principle: Milling uses a rotating multi‑tooth cutter to remove material as the workpiece is fed past the cutter. Each tooth removes a small amount of material per revolution.
Key features
- Primary motion: rotation of the cutter.
- Feed motion: linear movement of the workpiece or cutter.
- Types: peripheral (slab) milling, face milling, end milling.
Applications
Producing flat, contoured, slotted, and complex surfaces; gear cutting.
Cutting speed formula
\[ V = \frac{\pi D N}{1000} \] where \(D\) = cutter diameter (mm), \(N\) = cutter speed (rev/min).
Feed rate
\[ F = f_t \times z \times N \] where \(f_t\) = feed per tooth (mm/tooth), \(z\) = number of teeth.
Grinding
Principle: Grinding is a finishing process using a rotating abrasive wheel to remove very small amounts of material and achieve high dimensional accuracy and surface finish.
Key features
- Each abrasive grain acts as a cutting edge.
- High cutting speeds, shallow depths of cut.
- Generates heat; coolant is often used.
Applications
Finishing hardened surfaces, sharpening tools, precision shaping.
Surface speed formula
\[ V = \frac{\pi D N}{60} \] where \(V\) = surface speed (m/s), \(D\) = wheel diameter (m), \(N\) = wheel speed (rev/s).