6.3 Loads and Tools

6.3 Loads and Tools

1. Forces and Moments

Types of Forces

1. Static Loads: Constant over time.

   • Dead Loads: Permanent, fixed loads (self-weight of structure).

   • Live Loads: Temporary, movable loads (people, vehicles, furniture).

2. Dynamic Loads: Vary with time.

   • Impact Loads: Sudden, short-duration forces (hammer blow).

   • Cyclic/Fatigue Loads: Repeated, fluctuating loads (rotating machinery).

   • Shock Loads: Rapid application of force.

   • Vibrational Loads: Oscillatory forces at resonance frequencies.

3. Environmental Loads:

   • Wind Loads: Pressure from wind flow.

   • Seismic Loads: Earthquake-induced forces.

   • Thermal Loads: Expansion/contraction due to temperature changes.

   • Snow Loads: Weight of accumulated snow.

Force Analysis

1. Free Body Diagrams (FBD):

   • Isolate component/system.

   • Show all external forces and moments.

   • Essential for equilibrium calculations.

2. Equilibrium Conditions:

   • Translational Equilibrium: $\sum F_x = 0$, $\sum F_y = 0$, $\sum F_z = 0$

   • Rotational Equilibrium: $\sum M = 0$ about any point

3. Moments and Torques:

   • Moment (M): Tendency to cause rotation about a point. $M = F \cdot d$ (force × perpendicular distance)

   • Torque (T): Twisting moment about an axis.

   • Couple: Pair of equal/opposite parallel forces causing pure rotation.

Stress Types

1. Normal Stress: Perpendicular to surface.

   • Tensile: Pulling apart (positive).

   • Compressive: Pushing together (negative).

2. Shear Stress: Parallel to surface, causes sliding.

3. Bearing Stress: Contact stress between surfaces.

2. Cutting and Press Tools

Cutting Tools

1. Single-Point Cutting Tools:

   • Turning Tools: For lathe operations.

   • Shaping/Planer Tools: For shaping machines.

   • Boring Tools: Enlarge existing holes.

2. Multi-Point Cutting Tools:

   • Drills: Create/expand holes (twist drills, center drills).

   • Milling Cutters: Remove material via rotary cutters (end mills, face mills).

   • Reamers: Finish drilled holes to precise size.

   • Taps/Dies: Create internal/external threads.

   • Broaches: Cut complex shapes in single pass.

3. Tool Materials:

   • High-Speed Steel (HSS): Tough, general-purpose.

   • Carbides: Hard, wear-resistant (tungsten carbide).

   • Ceramics: High hardness, heat resistance.

   • Diamond/CBN: Ultra-hard for difficult materials.

4. Tool Geometry:

   • Rake Angle: Affects cutting force and chip flow.

   • Clearance Angle: Prevents tool rubbing on workpiece.

   • Cutting Edge Angle: Influences chip thickness.

Press Tools (Sheet Metal)

1. Shearing Operations:

   • Blanking: Cutting external profile (part is useful).

   • Punching: Cutting internal holes (scrap is slug).

   • Notching: Removing material from edge.

   • Trimming: Removing excess from formed parts.

2. Forming Operations:

   • Bending: Creating angles/folds.

   • Deep Drawing: Forming cups from flat blanks.

   • Stretch Forming: Stretching over die.

   • Embossing: Creating raised patterns.

3. Press Tool Components:

   • Punch: Upper, moving part.

   • Die: Lower, stationary part.

   • Stripper: Removes part from punch.

   • Guide Posts: Maintain alignment.

4. Clearance: Gap between punch and die (typically 5-10% of material thickness).

3. Lubrication and Coolants

Lubrication

1. Functions:

   • Reduce friction between moving parts.

   • Minimize wear and surface damage.

   • Dissipate heat.

   • Prevent corrosion.

   • Seal out contaminants.

2. Lubrication Regimes:

   • Boundary Lubrication: Thin film, asperity contact occurs.

   • Mixed Lubrication: Partial fluid film.

   • Hydrodynamic Lubrication: Full fluid film, no contact.

   • Elastohydrodynamic (EHD): High pressure deforms surfaces.

3. Lubricant Types:

   • Oils: Liquid, various viscosities.

   • Greases: Oil + thickener (soap).

   • Solid Lubricants: Graphite, MoS₂ for extreme conditions.

   • Synthetic Lubricants: Chemically engineered, stable.

4. Properties:

   • Viscosity: Resistance to flow.

   • Viscosity Index: Rate of viscosity change with temperature.

   • Pour Point: Lowest temperature at which oil flows.

   • Flash Point: Temperature at which vapors ignite.

Coolants (Cutting Fluids)

1. Primary Functions:

   • Cool cutting tool and workpiece.

   • Lubricate tool-chip interface.

   • Flush away chips.

   • Prevent workpiece corrosion.

2. Types of Cutting Fluids:

   • Straight Oils: Non-emulsifiable, good lubrication.

   • Soluble Oils: Oil-water emulsions, good cooling.

   • Synthetics: Chemical solutions, excellent cooling.

   • Semi-synthetics: Combination of synthetics and emulsifiable oils.

3. Application Methods:

   • Flood Cooling: High volume flow over cutting zone.

   • Mist Cooling: Atomized spray (good for inaccessible areas).

   • High-Pressure Systems: Force coolant into cutting zone.

   • Through-Tool: Coolant through spindle/tool internal channels.

4. Selection Factors:

   • Material Being Cut: Hardness, machinability.

   • Operation Type: Speed, feed, depth of cut.

   • Tool Material: Compatibility with coolant.

   • Environmental/Safety: Toxicity, disposal requirements.

5. Maintenance:

   • Regular concentration checks.

   • Filtration to remove contaminants.

   • pH monitoring.

   • Biocide addition to prevent microbial growth.