5.4 Machine Tools

5.4 Machine Tools

1. Lathe, Milling, Drilling

1. Lathe:

   • Primary Function: Rotating workpiece against stationary cutting tool.

   • Operations:

     • Turning (external cylindrical surfaces).

     • Facing (flat surfaces perpendicular to axis).

     • Taper turning (conical surfaces).

     • Thread cutting (internal/external threads).

     • Grooving/parting (narrow cuts).

   • Main Components:

     • Headstock (spindle, speed control).

     • Tailstock (supports workpiece).

     • Carriage (tool movement).

     • Bed (base structure).

   • Types:

     • Engine lathe (most common).

     • Turret lathe (multiple tools).

     • CNC lathe (computer controlled).

   • Applications: Shafts, bushings, pulleys, threaded parts.

2. Milling:

   • Primary Function: Rotating multi-tooth cutter removes material from stationary workpiece.

   • Operations:

     • Face milling (flat surfaces).

     • Peripheral milling (side surfaces).

     • Slot milling (grooves, keyways).

     • Profile milling (contours).

     • Gear cutting.

   • Types:

     • Vertical Milling Machine: Spindle vertical.

     • Horizontal Milling Machine: Spindle horizontal.

     • Universal Milling Machine: Swiveling table.

   • Cutters:

     • End mills (most versatile).

     • Face mills (large surfaces).

     • Slot drills (grooves).

     • Form cutters (special profiles).

   • Applications: Flat surfaces, slots, gears, complex contours.

3. Drilling:

   • Primary Function: Creating round holes using rotating drill bit.

   • Operations:

     • Drilling (new holes).

     • Reaming (enlarging, finishing holes).

     • Tapping (internal threads).

     • Counterboring/countersinking (seat for screw heads).

   • Drill Bits:

     • Twist drill (most common).

     • Center drill (starting holes).

     • Core drill (enlarging existing holes).

   • Parameters:

     • Cutting speed (surface speed).

     • Feed rate (mm/revolution).

     • Depth of cut.

   • Applications: Bolt holes, fastener holes, clearance holes.

2. Grinding, Boring

1. Grinding:

   • Primary Function: Abrasive particles on rotating wheel remove material.

   • Characteristics:

     • High surface finish (Ra 0.1-0.8 μm).

     • Close dimensional tolerances (±0.002 mm).

     • Hard materials (hardened steel, ceramics).

   • Types:

     • Surface Grinding: Flat surfaces.

     • Cylindrical Grinding: External cylindrical surfaces.

     • Internal Grinding: Internal cylindrical surfaces.

     • Centerless Grinding: No center holes needed.

   • Wheel Specifications:

     • Abrasive material (Al₂O₃, SiC, CBN, diamond).

     • Grit size (coarse: 10-24, fine: 60-600).

     • Grade (soft to hard).

     • Structure (dense to open).

   • Applications: Precision parts, hardened components, cutting tools.

2. Boring:

   • Primary Function: Enlarging and finishing pre-existing holes.

   • Characteristics:

     • Improves roundness and straightness.

     • Achieves precise diameters.

     • Better than drilling for large holes.

   • Types:

     • Horizontal Boring: Large workpieces.

     • Vertical Boring: Heavy parts.

     • Fine Boring: High precision.

   • Tools:

     • Single-point boring bars.

     • Multiple-edge boring heads.

   • Applications: Engine cylinders, bearing housings, large gear blanks.

3. Shaping, Sawing, Broaching

1. Shaping:

   • Primary Function: Reciprocating tool cuts while workpiece feeds.

   • Process:

     • Forward stroke (cutting).

     • Return stroke (idle).

     • Feed between strokes.

   • Types:

     • Shaping: Tool moves horizontally.

     • Planing: Workpiece moves, tool stationary.

   • Advantages:

     • Simple setup.

     • Low cost tooling.

   • Limitations:

     • Slow production rate.

     • Limited to flat surfaces.

   • Applications: Keyways, slots, flat surfaces on small batches.

2. Sawing:

   • Primary Function: Cutting material using toothed blade.

   • Types:

     • Hack Sawing: Reciprocating blade.

     • Band Sawing: Continuous loop blade.

     • Circular Sawing: Rotating disk blade.

   • Characteristics:

     • Cutting-off operation.

     • Rough surfaces produced.

     • Material separation.

   • Blade Selection:

     • Tooth pitch (coarse for soft materials).

     • Tooth geometry (raker, wavy, alternate).

   • Applications: Cutting stock to length, rough shaping.

3. Broaching:

   • Primary Function: Multi-tooth tool (broach) cuts in single pass.

   • Characteristics:

     • Each tooth slightly higher than previous.

     • Single-pass operation.

     • High production rate.

   • Types:

     • Internal Broaching: Holes, keyways, splines.

     • Surface Broaching: Flat surfaces, contours.

     • Pull Broaching: Tool pulled through.

     • Push Broaching: Tool pushed through.

   • Advantages:

     • Excellent surface finish.

     • High dimensional accuracy.

     • Fast production.

   • Limitations:

     • High tool cost.

     • Specific to one shape.

   • Applications: Splined holes, gear teeth, keyways, square holes.

4. Pressing Operations

1. Press Working:

   • Basic Principle: Die and punch system in mechanical/hydraulic press.

   • Press Types:

     • Mechanical press (crank, eccentric).

     • Hydraulic press (fluid pressure).

     • Pneumatic press (air pressure).

2. Pressing Operations:

   • Blanking: Cutting complete part from sheet.

   • Punching: Removing scrap material (hole making).

   • Deep Drawing: Forming sheet into cups/shells.

   • Bending: Deforming along straight axis.

   • Coining: High pressure for detailed surface features.

   • Embossing: Shallow forming of raised features.

3. Press Selection Factors:

   • Tonnage capacity.

   • Stroke length.

   • Speed (strokes per minute).

   • Bed size.

   • Type of drive.

4. Die Components:

   • Punch (male part).

   • Die (female part).

   • Stripper (removes sheet from punch).

   • Guide posts (alignment).

5. Clearance: Critical between punch and die (5-10% of thickness).

6. Applications:

   • Automotive body panels.

   • Electrical enclosures.

   • Appliance parts.

   • Containers (cans, caps).

   • Fasteners, washers.