Sometimes, timing is everything. That's certainly what Cummins' Jamestown, N.Y. engine plant found after a new towline conveyor system was installed.

While the system replaced a basic in-floor towline that was near the end of its useful life, it brought much more than an updated system to the production of truck, bus and generator engines, says Kevin Aker, assembly leader. In addition, extensive integration of advanced controls and the use of radio frequency identification (RFID) tags maximized production flexibility.

That combination was so impressive that Cummins transferred production from the company's Columbus, Ind. engine plant to Jamestown. 'This plant utilizes our most modern assembly line, which has the flexibility and capacity to meet all customer requirements for our 11- and 15-liter engines more productively and cost-effectively than any other alternative,' Aker says.

Working one shift five days a week, the 1,500 foot towline moves 235 engines daily through the plant with unmatched efficiency. In its initial months of use, the new line increased assembly efficiency 8%. In 2003, that metric climbed another 10%.

According to Rachel Lecrone, an operations leader at the plant, 90% of the work required to build an engine is done at the 68 workstations on the towline (SI Systems/Paragon Technologies). The towline is divided into four equal sized zones. Each of the first three zones ends with an audit spur where quality control checks are made at four workstations.

There is also a low-volume build spur in the fourth zone. At the 12 assembly stations there, options such as engine brakes and power take-offs are added to engines.

The new towline encircles the old one in the plant. About 500 feet of it is used to buffer engines for the build line and audit spurs as needed. Otherwise, the old towline is inactive but still intact in the plant. Unlike the new system, the old did not have either audit or low-volume spurs.

During construction of the new system, production continued at its regular pace on the old towline, explains Aker. Although there was more lift truck handling of engines at the front of the line (rather than conveyors), Cummins kept pace with orders throughout installation of the new towline.

Today, engine blocks arrive by powered roller conveyor from an area called lineset with the crankshaft and cylinder liners in place. Blocks are transferred from the conveyor to the towline carts with a lift assist device.

At each workstation, the cart is disengaged from the towline to allow workers to perform assembly steps on a stationary work piece. Carts move through assembly either synchronously or asynchronously, depending on build requirements and quality checks along the way. Engines are built to lot sizes of one. This means that not only are most engines somewhat different one to the next, but there is no batching of 11- and 15-liter engines in the build sequence.

As Lecrone points out, that requires maximum flexibility on the line. It also brings together an interesting combination of paper build documents, electronic build documents, RFID and advanced system controls to direct assembly and track engines during the 3½ hours it takes an engine to process through the line.

Each engine has a paper-based build document attached to it. It lists for workers the highest level of specifications for assembly.

Workers also consult touch screen panels in sub-assembly stations to receive detailed build instructions. For in-stance, the panel details the specific components required for the compressor on that particular engine. Each engine has roughly 2,400 components that result in more than 6,000 individual build documents in use at the plant.

'We expect to replace paper build documents with electronic ones in the next year, eliminating all paper from the system,' says Aker.

As engines move along the line, the exact location of each one is critical to production efficiencies, adds Aker. Engines are tracked by an RFID tag on each cart. The read-only tags carry a single number that identifies that cart. When the engine is first placed on the cart, the tag is read and linked to the serial number of the engine stored in a programmable controller-based control system. Tags are read at every other workstation, but there are plans to install readers at all stations in the near future, says Lecrone.

The Cummins assembly control system maintains critical production data and quality control criteria for each engine.

Release of carts is controlled by the towline's four programmable controllers (PLCs), each one dedicated to controlling cart movement in one of the system's four zones. The supporting PC control systems that track the RFID tags and failsafes provide input, but overall control remains in the PLC.

'This system gives us maximum flexibility in controlling the assembly process,' says Lecrone. 'In addition to enforcing failsafes and routing carts, the controls allow us to redistribute work between stations to better balance the line and eliminate bottlenecks.'

'We set out to add capacity, improve flexibility and reduce downtime with the new towline,' says Lecrone. 'And I can say we've achieved all three.'

Click on the icon to see other materials handling upgrades at Cummins. (Eliminating the stall - October 1999)