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Introduction about Machine Design I

Section I

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What is the meaning of design? Classifications of design Mechanical engineering design? Phases of design Design considerations Design factor of safety Examples of mechanical equipments Units

Talking Points

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What is the Meaning of Design?

The formulation of plan for the satisfaction of a human need. Sometime the particular need to be satisfied is well defined, and sometime it is not; thus, a lot of thought and effort is necessary to understand the particular need, clearly.

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Classifications of Design Clothing design Interior design Highway design Landscape design Building design Ship design Bridge design

Computer-aided design

Heating system design

Machine design Engineering design Process design Etc…

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Mechanical Engineering Design?

The design of things and systems of a mechanical nature--machines, products, structures, devices, and instruments.

Mechanical design utilizes mathematics, physics (kinematics, statics, dynamics), material science, and the engineering mechanics science.

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Phases of Design1. The recognition of a need and a statement of this

need in general terms. This defines the problem.2. The consideration of different schemes for solving

the problem and the selection of one to be investigated in more detail. This phase includes a feasibility studies, backed up by special research if necessary.

3. A preliminary design of the machine, structure, system, or process selected. This establishes broad overall features and makes it possible to write specifications for major components.

4. Design of all components and preparation of all necessary drawings and detail specifications.

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Design Considerations Strength Reliability Thermal properties Corrosion Wear Friction Processing Utility Cost Safety Weight Life

Noise Styling Shape Size Flexibility Control Stiffness Surface finish Lubrication Maintenance Volume

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Design Factor of Safety

The ratio of the component strength to the working or allowable stress.

The “strength” can be anything the designer chooses it to be. It should often be the yield strength, the ultimate strength, the fatigue strength…etc. It is a material property; while the working stress is the safe stress, which is allowed to be undertaken by the material in design.

For structural steel work, nd is taken 2.0 to 2.5; but in case of cast iron, concrete, wood, nd is taken as 4.0 to 6.0.

stress allowable

strengthdn

9Chainsaw

Examples of Some Mechanical Equipments

10Aircraft landing gear

Tractor with front-end-loader attachment

Industrial crane

Examples of Some Mechanical Equipments – Cont.

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Examples of Some Mechanical Equipments – Cont.

ReverseReverse

EngineEngine

Turbo ChargerTurbo Charger

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Units