Room for expansion

Citation

Loughlin, C. (2002), "Room for expansion", Assembly Automation, Vol. 22 No. 2. https://doi.org/10.1108/aa.2002.03322baa.001

Room for expansion

Room for expansion

I doubt if many people would argue with the statement that automated assembly needs to be flexible. Short product runs, Just In Time delivery, low stockholding, and the vagaries of fashion; all mean that we can no longer afford the money or space required by machinery dedicated to the assembly of a single product.

At the very least the components of the assembly system need to be modular and reusable. However even this implies a long changeover period between products and the almost inevitable teething problems. For true flexibility we need an assembly system that is both able to perform different operations in different sequences, and also to securely grasp the parts that are being assembled.

Performing different operations is comparatively easy because the operation itself, and the tools used to do it, are standardised. For example a screwdriver with an automatic feed set up for No.8 10mm Pozidrives does not really care whether it is joining together two halves of a mobile phone or a washing machine. On the other hand the fixtures required to hold these two extreme examples could not be more different.

Realistically the products to be assembled by a given system will not vary in size by such a large amount, however their shape will still vary and so the fixtures need to be able to accommodate the differences.

This issue has the theme "Automated Fixturing" and we include features and research articles that explore some of the many aspects of this increasingly important area of technology. Even a single product will have manufacturing tolerances, and so these need to be accommodated so that the part can still be securely grasped if it is a bit smaller than average and not damaged if it is a bit larger.

There are numerous approaches to automated fixturing and many are covered in our tutorial. Parts can also be secured in specially moulded fixtures, which although not strictly "automated"; still allow for considerable flexibility and fast changeover times. These have considerable appeal for me, but the mouldings need to do more than just loosely contain the parts if they are to be secure enough, or located precisely enough, for assembly operations.

I do not know how it is done these days, but in the days of steam; train wheels used to be fixed to their axles by heating the wheels in a furnace and cooling the axles until the respective parts had expanded and contracted enough to allow the wheel to fit in place. By the time both wheel and axle had regained ambient temperature, they were as secure as if cast from a single piece of steel.

The idea of using heat (or some other parameter) to quickly expand or contract a moulding so that it either securely grasps or releases the part, sounds like a good idea but as far as I know has not yet been developed sufficiently well for industrial application. Electro-rheological fluids and freezing "ice grippers" have been used to achieve a similar end result in specific applications but we still need a more generally applicable solution.

What we need is a material that can be machined or moulded to shape, and which can be made to expand and contract quickly, and by a large amount, for relatively modest changes in temperature. Bimetallic strips with embedded Peltier elements might be a good candidate but there must be many others. Please let me know if you have heard of any.

Clive Loughlin