Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 1 Introduction to Machine Design
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
Functional Safe Reliable Competitive Usable Manufacturable Marketable Regardless to all Design Product
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 Mechanical Engineering Design
Functionality Strength/Stress Distortion/deflection/stiffn ess Wear Corrosion Safety Reliability Manufacturability Utility Cost Design Considerations Friction Weight Life Noise Styling Shape Size Control Thermal properties Surface
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Understand the problem Identify the known Identify the unknown and formulate State all assumptions and decisions Analyze the problem Evaluate solution Present solution Designer Responsibilities
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…) Economics
bud21932_0102.jpg Cost versus tolerance/ machining process
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. Example: Breakeven point
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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 Stress and Strength
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 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 n d = Mathematical method of Uncertainly Loss-of-function parameter Maximum allowable parameter
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The design factor n d Factor of safety, n Design factor and factor of safety
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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The End