Tuesday, November 26, 2013

Application of motion economy Principles to Jig and Fixture Design

 Application of motion economy Principles to Jig and Fixture Desigm

"A Jig holds parts in an exact position and guides the tool that works on them.""A Fixture is a less accurate device for holding parts which would otherwise have to be held in one hand while the other worked on them."

The designer's object in providing jigs and fixtures is primarily accuracy in machining or assembly.  Principles of motion economy are not made use of . Often, opening and closing them or positioning the workplace calls for more movements on the part of the operative than are strictly necessary. For example, a spanner may have to be used to tighten a nut when a wing nut would be more suitable. Some points worth noting are:

1.Clamps should be as simple to operate as possible and should not have to be screwed unless thisis essential-for accuracy of positioning. If two clamps are required they should be designed for use by the right and left hand sat the same time.

2. The design of the jig should be such that both hands can load parts into it with a minimum of obstruction. There should be no obstruction between the point of entry and the point from whichthe material is obtained.

3. The action of unclamping a jig should at the same time eject the part, so that the additionalmovements are not required to take part out of the jig.

4. Where possible on small assembly work‟ fixtures for a part which does not allow of two
-bandedworking should be made to take two parts, with sufficient space between them to allow both bands towork easily.

5. In some cases jigs are made to take several small parts. This may save loading time if several partscan be clamped in position as quickly as one.

6. The work-study man should not ignore machine jigs and fixtures such as milling jigs. A great deal of time and power is often wasted on milling machines owing to the fact that parts are milled one at a time when it may be quite feasible to mill two -or more at once.

7. If spring-loaded disappearing pins are used to position components, attention should be given totheir strength of construction. Unless the design is robust such devices tend to function well for awhile but then have to be repaired or redesigned.

8. In introducing a component into a jig it is important to ensure that the operator should be able to see what he is doing at all stages; this should be checked before any design is accepted. The recording techniques of two-handed process chart and multiple activity charts proves very useful in improvement studies of work place layout. In certain type of operations and particularly those with very short cycles which are repeated thousands of times (such as sweet packing or electronic assembly). It may be required to go into greater details of study to save on movement of hands and efforts and to develop best possible pattern of movement, thus enabling the operator to perform the operation repeatedly with a minimum of effort and fatigue.

The techniques used for this purpose frequently make use of filming and are known as 'Micro motion Study'


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