1. Introduction to Machine Design
Chapter 1
Introduction to Machine Design
Prepared by
Prof. P. R. Vispute

2. Design
Design – to formulate a plan for the satisfaction of a specified need or to solve a problem
Innovative and highly iterative process
Decision making process

3. Design Product Functional Safe Reliable Competitive Usable
Manufacturable
Marketable
Regardless to all

4. Mechanical Engineering Design
Mechanical engineering design involves all the disciplines of mechanical engineering
Example: Fluid flow, heat transfer, friction, energy transport, material selection, thermo mechanical treatments, statistical descriptions…
Phases- Machine design, machine-element design, machine-component design, systems design, and fluid-power design

5. Design Considerations
Friction
Weight
Life
Noise
Styling
Shape
Size
Control
Thermal properties
Surface
Functionality
Strength/Stress
Distortion/deflection/sti ffness
Wear
Corrosion
Safety
Reliability
Manufacturability
Utility
Cost

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7. Designer Responsibilities
Understand the problem
Identify the known
Identify the unknown and formulate
State all assumptions and decisions
Analyze the problem
Evaluate solution
Present solution

8. Economics Standard Sizes- large quantities part usually low cost
Large Tolerances- tolerances, manufacturing process and surface finish are related. Close tolerances required additional step in manufacturing process.
Breakeven Points- two or more design are compared for cost, the choice depending on a conditions such as the production, the speed of assembly lines, and others. The point corresponding to equal cost.
Cost Estimates- compare of two or more design. Example weight, number of parts, application (area, volume, various performance…)

9. Cost versus tolerance/machining process
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10. Example: Breakeven point
Consider a situation in which a certain part can be manufactured at the rate of 25 parts per hour on automatic screw machine or 10 parts per hour on a hand screw machine. The setup time for the automatic is 3h and that the labor cost for either machine is $20 per hour, including overhead.

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12. Stress and Strength
We often look for “strength in the geometry and condition of use”
Strengths are the magnitude of stresses at which something of interest occurs
Strength is a property of a material or of a mechanical element

13. Uncertainly
Composition of material and the effect of variation on properties
Variations in properties from place to place within a bar of stock
Effect of processing locally, or nearby on properties
Effect of nearby assemblies such as weldments and shrink fits on stress condition

14. Mathematical method of Uncertainly
The deterministic method establishes a design factor based on the absolute uncertainties of loss of function parameter and a maximum allowable parameter.
Parameter can be load, stress, deflection, etc
The design factor nd =
Loss-of-function parameter
Maximum allowable parameter

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16. Design factor and factor of safety
The design factor nd
Factor of safety, n

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20. THANK YOU