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Viewpoint - Value and Quality [robotic welding]

   
John Weston, TWI

2 October 2003. Published in Industrial Robot Journal

Almost everything contains joints, and the organisation I work for provides support to industry both with its knowledge of joining technologies and the engineering of the joint itself. The issues of value and quality frequently arise during our contact with industry.

Financially the operations involved in making the joint are usually only a small part of the total product cost. Even when welding content is high, as in a ship, the process cost can be relatively low (<10% for the ship). That said, the value added by the process is significant because without the joint(s) there would be no product. Furthermore if the joint is inadequate the product will fail (e.g. if they leak the ship may sink). As yet accountants do not have a mechanism for considering this disparity between cost and value, with the result that the justification of joining equipment (robotics) can be difficult. I believe that this incongruity will be confronted.

Studies that are looking at the way value can be added to a product or service to increase profitability will probably lead this attack. The thinking is as follows: The builder of a bus is actually associated with the business of moving people. Today he will simply sell to a bus company. However, if he could help in move people more reliably, perhaps he can increase his margins and profit. He might do this by changing his function to cover the supply of clean,serviced and fuelled buses. Leasing schemes, offered by some robot suppliers, show a move in this direction, however, they are but a small step in what I believe will be a major shift in the way that we acquire and operate equipment used in joining.

The other problem, which I believe plagues robot system suppliers, is the quality issue. Few manufacturers have a good understanding of quality in terms of welded joints. They have a fair understanding of nuts and bolts because if the hole is too small or the thread incorrect the system will NOT function and therefore they MUST get these relationships right. Because these relationships are a must-get-right the whole process from design to assembly focuses on meeting the required tolerances. This is not the case for welded joints, where many a poor weld will perform the required basic function. While the ship might have leaked, it would have stayed together as an entity and with a good pump probably went to sea. Furthermore, a skilled welder can join almost anything - and is frequently required to do so. Because they can do this the design and production chain have seldom considered all the aspects influencing joint quality.

Too often the 'drawing' has:

  • An arrow, 'weld here', with no size or length or quality requirement!
  • Welds must be leak tight, but to what degree and for how long (and is there a structural strength requirement) are not specified.
  • Welders (operators) must be 'coded', but there is no mention of the qualification that is expected.
  • 100% inspection is required, but no thought given to the relevance of that request nor to the type of inspection to be undertaken.

One cannot overemphasise the importance of knowing:

  • What is required of the joint (e.g. shape, mechanical and chemical properties) in terms of end use conditions.
  • What additionally needs to be done, for example upstream, to get the required joint shape and fit-up.
  • How to determine that the quality of the finished joint is as required.

A good understanding of value and quality has led to robotic welding, which can produce high quality at high rates. Even better understanding of the problems outlined above will lead to greater use of automation in joining cutting processes.

John Weston
Principal Consultant
Manufacturing Support Group