UNIT 4 JIGS AND FIXTURES
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Introduction
Jigs and Fixtures
Purpose and Advantages of Jigs and Fixtures Important Considerations while Designing Jigs and Fixtures Meaning of Location Principles of Locations Different Methods Used for Locations Clamping Different Types of Clamps Jigs
4.10 Different Types of Jigs 4.11 Fixtures 4.12 Summary 4.13 Answers to SAQs
The jigs and fixtures are the economical ways to produce a component in mass. So jigs and fixtures are used and serve as one of the most important facility of mass production system. These are special work holding and tool guiding device. Quality of the performance of a process largely influenced by the quality of jigs and fixtures used for this purpose. What makes a fixture unique is that each one is built to fit a particular part or shape. The main purpose of a fixture is to locate and in the cases hold a workpiece during an operation. A jig differs from a fixture in the sense that it guides the tool to its correct position or towards its correct movement during an operation in addition to locating and supporting the workpiece. An example of jig is when a key is duplicated, the original key is used as base for the path reader which guides the movement of tool to make its duplicate key. The path reader of a CWC machine here works as a jig and the original is called template. Sometimes the template and jig both are the name of same part of a manufacturing system.
After studying this unit, you should be able to understand introduction of jigs and fixtures, purpose and advantages of jigs and fixtures, important considerations while designing jigs and fixtures, know the meaning and principles of location, describe the different types of locations, explain the clamping and its different type, the requirements of a good clamping device, know the different types of clamps, 47
explain the jigs and their different types, and know about the milling fixtures.
4.2 PURPOSE AND ADVANTAGES OF JIGS AND FIXTURES
Following the purpose and advantages of jigs and fixtures : (a) It reduces or sometimes eliminates the efforts of marking, measuring and setting of workpiece on a machine and maintains the accuracy of performance. The workpiece and tool are relatively located at their exact positions before the operation automatically within negligible time. So it reduces product cycle time. Variability of dimension in mass production is very low so manufacturing processes supported by use of jigs and fixtures maintain a consistent quality. Due to low variability in dimension assembly operation becomes easy, low rejection due to les defective production is observed. It reduces the production cycle time so increases production capacity. Simultaneously working by more than one tool on the same workpiece is possible. The operating conditions like speed, feed rate and depth of cut can be set to higher values due to rigidity of clamping of workpiece by jigs and fixtures. Operators working becomes comfortable as his efforts in setting the workpiece can be eliminated. Semi-skilled operators can be assigned the work so it saves the cost of manpower also. There is no need to examine the quality of produce provided that quality of employed jigs and fixtures is ensured.
(f) (g) (h) (i)
4.3 IMPORTANT CONSIDERATIONS WHILE DESIGNING JIGS AND FIXTURES Designing of jigs and fixtures depends upon so many factors. These factors are analysed to get design inputs for jigs and fixtures. The list of such factors is mentioned below : (a) (b) (c) (d) (e) (f) (g) (h) (i) 48 Study of workpiece and finished component size and geometry. Type and capacity of the machine, its extent of automation. Provision of locating devices in the machine. Available clamping arrangements in the machine. Available indexing devices, their accuracy....
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