Fixturing for Flexibility
When designing a flexible automated assembly system, engineers have a number of options for creating fixtures to accommodate more than one product. Obviously, engineers have the option of using different fixturing for each line of products being assembled. However, this solution can be both cumbersome and expensive: cumbersome in that changing over tooling sets can be time- and space-consuming; expensive because tooling costs money. Then there is the challenge of tracking all this loose equipment. Whether it's a disgruntled employee dropping a component in his pocket or an overburdened inventory system, changeout fixturing can be vulnerable to getting lost.
For this reason, automation systems manufacturers have devised a number of strategies for creating flexibility in a single type of fixturing. These include interchangeable inserts; machining multiple nesting options into a single fixture; and creating product components with common location features, so they can all be secured with the same fixture.
With interchangeable inserts, or loose tooling, the advantage is that a single fixture can accommodate a relatively wide range of part geometries. Granted, there are limits. But when assembling products with similar geometries, say, a series of doorknob assemblies or spark plugs, inserts can make it possible to for a single basic fixture to accommodate an entire product family.
On the downside, there are still changeover times to take into account. Inserts can be attached using setscrews, plunger push pins or a simple snap-fit configuration, but it takes time to swap them out. Moreover, the assembler is still faced with the possibility of lost parts, as was the case with conventional fixturing.
To remedy this situation, engineers can provide multiple nests on a single piece of indexable tooling. One way this can be done is by simply creating two separate nests on a single face of the tooling. The system can then be adjusted, depending on the assembly being produced, so it performs its work in the correct location. Another option is having different nesting features on more than one face of the tooling, so that flipping the tooling accommodates a different product. With this system in place, changing from one product to another still requires some changeover time. But assemblers do not have to dig up an entirely different set of fixtures as part of the process.
Finally, engineers can create a single nest configuration that accommodates more than one product. Again, the different parts need to be similar. But they don't need to be identical. The fact that assembly X doesn't fill a small cavity in the fixture necessary to accommodate assembly Y doesn't mean the same nest can't hold them both securely. The main thing is that all the products being assembled include the same basic fixturing registration datums-features that can be used to hold a component in place. Not surprisingly, this is an area in which a little forethought during the design phase can yield big gains.