Is the single-purpose transfer line obsolete? Not exactly. Nor are the other hard-tooled machines such as dial index and indexing table types. But those machines, as they have traditionally been used in high volume automotive operations, are today facing new challenges as high production gives way to flexibility.
Special machines ordered today and tomorrow - even for ultra-high volume production - are going to be unlike their ancestors. Today's manufacturers must be able to accommodate change in product and/or process, cheaply and quickly to meet rapidly changing consumer tastes.
Nowhere is this more true than in the automotive industry in which manufacturing solutions are extremely costly, but not nearly as costly as failure.
In one case, a line is going in to produce 300,000 V-4 engines a year. But the automaker wants to provide for expanding production to 500,000 or maybe to 800,000 engines later. "That means building a modular line that can be expanded easily with existing stations that can be reprogrammed, new stations will come in with their own controls, and all services including an extension of the nonsynchronous transfer line," says David L Brown, president, Cargill Detroit Manufacturing Systems Div, Clawson, MI.
"It means that we build self-contained machines, each with its own control, power, air, hydraulics, etc. These can be used as components in cells, or as stations in an in-line machine, and any of them can be single-spindle, or multiple-spindle, or head-index units, with the possibility of two, three, or four-axis CNC. And units can be easily added if needed."
In other cases, flexibility means that the equipment will run economic lot sizes of one product. The system then will be shut down for a few hours, while tooling and reprogramming are done, and a different product will be volume produced for another period. An example would be changing multiple-tool heads to accommodate different hole patterns. That's adaptability, and the brief downtime between jobs is a major economic gain with no sacrifice in traditional productivity rates.
Finally, flexibility can mean the ability to process families of product randomly (in lots as short as one), with the system recognizing the entering product and calling up the appropriate tools and operations. It is commonly thought of as CNC multiple-machine cells, but it is also being done on an in-line engine block line described later.
"Beyond question, the reduction in...