tailieunhanh - Fundamentals of Machine Design P3

A machine element, after design, requires to be manufactured to give it a shape of a product. Therefore, in addition to standard design practices like, selection of proper material, ensuring proper strength and dimension to guard against failure, a designer should have knowledge of basic manufacturing aspects. In this lesson, we will discuss briefly about some of the basic manufacturing requirements and processes. First and foremost is assigning proper size to a machine element from manufacturing view point | Module 1 Fundamentals of machine design Version 2 ME IIT Kharagpur Lesson 3 Brief overview of design and manufacturing Version 2 ME IIT Kharagpur Instructional Objectives At the end of this lesson the students should be able to understand Concept of limits and fits Preferred numbers Various manufacturing processes Design and Manufacturing A machine element after design requires to be manufactured to give it a shape of a product. Therefore in addition to standard design practices like selection of proper material ensuring proper strength and dimension to guard against failure a designer should have knowledge of basic manufacturing aspects. In this lesson we will discuss briefly about some of the basic manufacturing requirements and processes. First and foremost is assigning proper size to a machine element from manufacturing view point. As for example a shaft may be designed to diameter of say 40 mm. This means the nominal diameter of the shaft is 40 mm but the actual size will be slightly different because it is impossible to manufacture a shaft of exactly 40 mm diameter no matter what machine is used. In case the machine element is a mating part with another one then dimensions of both the parts become important because they dictate the nature of assembly. The allowable variation in size for the mating parts is called limits and the nature of assembly due to such variation in size is known as fits. Limits Fig. explains the terminologies used in defining tolerance and limit. The zero line shown in the figure is the basic size or the nominal size. The definition of the terminologies is given below. For the convenience shaft and hole are chosen to be two mating components. Version 2 ME IIT .