General Considerations in Machine Design

1. Type of Load and Stresses

Machine components experience various loads and associated stresses. Understanding these forces is essential for effective design.

2. Motion of Parts

The efficient functioning of a machine relies on the optimal arrangement of its components to achieve the desired motion. Motion types include:

- Rectilinear motion: Unidirectional and reciprocating.

- Curvilinear motion: Rotary, oscillatory, and simple harmonic.

- Constant velocity.

- Constant or variable acceleration.

3. Material Selection

Designers must understand material properties and performance under working conditions. Key characteristics include strength, durability, flexibility, weight, heat and corrosion resistance, castability, weldability, machinability, and electrical conductivity.

4. Form and Size of Parts

Judging the form and size of parts involves using the smallest feasible cross-section that maintains safety under stress. Designers must account for forces, including potential impact loads that might cause failure.

5. Frictional Resistance and Lubrication

Friction results in power loss, with starting friction being higher than running friction. Proper lubrication of moving surfaces is crucial for minimizing friction in rotating, sliding, or rolling bearings.

6. Convenient and Economical Features

Designing for ease of operation includes strategic placement of controls and provisions for wear adjustments. Components should be accessible for replacement without needing to remove other parts, ensuring economical and efficient operation.

7. Use of Standard Parts

Utilizing standard parts reduces costs significantly compared to custom-made parts. Whenever possible, use existing patterns for gears, pulleys, bearings, and standard stock parts like screws, nuts, and pins.

8. Safety of Operation

Machines can pose hazards, especially at high speeds. Designers must incorporate safety devices to protect operators without hindering machine performance.

9. Workshop Facilities

Designers should be aware of their workshop's limitations to avoid outsourcing work. This may involve planning and supervising operations for casting, handling, and machining special parts.

10. Number of Machines to Be Manufactured

The quantity of machines influences design decisions. For small production runs, extra expenses are unjustifiable unless for large or specialized designs. Standard parts should be prioritized to control costs.

11. Cost of Construction

Construction cost is a critical factor. High costs can exclude a design from consideration. Cost-effective design and production are essential, particularly for products with commercial potential.

12. Assembling

Machines must be assembled as units before functioning. Large units are often shop-assembled, tested, and then transported. Designers must consider the final location and local facilities for erection.

Manufacturing Considerations in Machine Design

1. Primary Shaping Processes

These processes provide the initial shape to components. Common operations include casting, forging, extruding, rolling, drawing, bending, shearing, spinning, powder metal forming, and squeezing.

2. Machining Processes

Machining processes give components their final shape and dimensions. Operations include turning, planning, shaping, drilling, boring, reaming, sawing, broaching, milling, grinding, and hobbing.

3. Surface Finishing Processes

These processes improve surface quality. Operations include polishing, buffing, honing, lapping, abrasive belt grinding, barrel tumbling, electroplating, super finishing, and sherardizing.

4. Joining Processes

These processes connect machine components. Common methods include welding, riveting, soldering, brazing, screw fastening, pressing, and sintering.

5. Processes Affecting Properties

These processes impart specific properties to components for particular applications. They include heat treatment, hot-working, cold-working, and shot peening.

Selection of Materials for Engineering Purposes

Choosing the right material involves balancing performance and cost. Key factors include:

1. Availability

2. Suitability for Working Conditions

3. Cost

Physical Properties of Metals

Physical properties include luster, color, size and shape, density, electrical and thermal conductivity, and melting point.

Mechanical Properties of Metals

Mechanical properties define a material's resistance to mechanical forces:

1. Strength

Resistance to external forces without breaking.

2. Stiffness

The modulus of elasticity measures resistance to deformation.

3. Elasticity

Ability to return to original shape after deformation.

4. Plasticity

Permanent deformation under load is essential for forging and stamping.

5. Ductility

Ability to be drawn into wire, requiring strength and plasticity.

6. Brittleness

Tendency to break with little deformation, opposite of ductility.

7. Malleability

The ability to be hammered into thin sheets is important for rolling and forging.

8. Toughness

Resistance to fracture from impact loads.

9. Machinability

The ease of being cut is measured by tool life, thrust, or energy required.

10. Resilience

The ability to absorb energy and resist shock is essential for spring materials.

11. Creep

Slow deformation under constant stress at high temperatures, relevant for engines and turbines.

12. Fatigue

Failure under repeated stresses below the yield point, is important for components like shafts and gears.

13. Hardness

Tests such as Brinell, Rockwell, Vickers, and Shore scleroscope determine resistance to wear and deformation.

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