Machine Elements in Mechanical Design

Introduction Mechanical Systems or Devices are designed to transmit power and accomplish specific patterns of motion. Mechanical Components – Gears, Bearings, Shafts, Keys, Couplings, Seals, etc.

Design Process (Section 1-4) Identify Customer Requirements Define functions of the device State design requirements Define evaluation criteria Propose several alternative design concepts Evaluate each proposed alternative Rate each alternative against each evaluation criteria Select the optimum design concept Complete detailed design of the selected concept

Application How are customer requirements identified? Functions are “high level” requirements that tell what a device is supposed to do. Design requirements are detailed, specific, quantitative data expanding the functions. What evaluation criteria would be important? What does the “detailed design” look like? What next?

Text Example – Speed Reducer

Functions To receive power from the tractor’s engine through a rotating shaft To transmit the power through machine elements that reduce the rotational speed to a desired value. To deliver the power at the lower speed to an output shaft that ultimately drives the wheels of the tractor.

Design Requirements

Integration of Design Speed Reducer Assembly: One Housing Four Gears Three Shafts Six Bearings Several Keys and Seals Etc.

Practice (10 minutes) Most small boat trailers must be submerged in the water to launch or retrieve the boat. This greatly reduces the life of the trailer, especially in salt water. A need exists for a trailer that will remain on dry land while it launches or retrieves the boat. No part of the trailer should get wet. User safety is of greatest concern, as is protection of the boat from damage. In Groups of four, develop design functions and requirements for this trailer. Norton, R. L., “Design of Machinery”, 3rd ed., McGraw Hill, 2004

Design Skills Required Technical Drawing Computer-Aided Engineering (CAE) Manufacturing Processes Statics, Dynamics, and Strengths of Materials Kinematics and Mechanisms Verbal and Written Communication

Mechanical Design Objective Produce a useful device that is safe, efficient, economical, and practical to manufacture.

Design Presentation Develop a specification set that communicates effectively all manufacturing information, safety information, usage information, etc. Specifications sets include: CAD Models Drawings (Assembly, Detail, Stress Reports) Bills-of-Material Instructions: Manufacturing Assembly Maintenance Usage

The Engineering Method Recognize and understand the problem Accumulate data and verify accuracy Select the appropriate theory or principle Make necessary assumptions Solve the problem Verify and check results Eide, et.al., “Engineering Fundamentals and Problem Solving”, 5th ed., McGraw Hill, 2008