Friday, 26 May 2006

Automatic Assembly (12/16)

If a part-built assembly needs moving during assembly then problems arise if all parts are not located.  During manual assembly of a product, the operations are structured so that transportation only occurs with stable assemblies. This is achieved by assigning two or more parts to the assembly worker, or enough parts that are required, to create a stable structure. The operative, using two hands, holds the unstable part whilst assembling the part required to complete the operation.  An example of an operation such as this is where an assembly worker holds down a spring with one hand, prior to assembly of a spring retainer with the other hand.  This type of operation is difficult to perform automatically and should be re-designed so that each part is self-locating.

Design the product with many sub-assemblies.  Each sub-assembly should be common to all product styles.  Product variation can then be created in the final assembly of the product.  Sub-assembly work centres give a greater overall efficiency of the assembly system, in conjunction with buffer storage.  This is achieved by using a free transfer line or by intermediate storage systems.

The feeding of a part to an automatic workhead is by components in bulk random orientation or structured orientation.  Methods of feeding are usually determined by the part characteristics and required feed rate.  All feeders are classified as being; automatic, magazine, final parts forming stage, or manual.  It is uneconomic, or impossible, to feed certain parts automatically and these are not fed by automatic feeders. Flexible gaskets, open ended springs and acute angled cones are examples of such parts.  Large parts, parts having no symmetry, and delicate parts (e.g. with print face) cannot be fed automatically, but may be fed by magazines.  Relatively simple parts, with a degree of symmetry or definite asymmetry, can be fed by automatic feeders.

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