In October 2002, Cummins Inc. decided to consolidate its heavy-duty engine assembly and test operations at its Jamestown, NY, engine plant. The decision called for transferring assembly and test activity to a new towline system.
"The new assembly system was purchased to replace a basic in-floor towline system that was installed in the early 1980s. The new system is not significantly different conceptually from the earlier process used for the 11-liter product assembly. But it required significant advances in overall size, control system architecture, operator safety, ergonomics, flexibility and integration capability for advanced assembly equipment and fail-safing hardware," says Gene Wilston, group leader of assembly operations.
Cummins selected SI Systems (Easton, PA), a manufacturer of towline-based assembly systems, as its partner and systems integrator.
A major challenge was developing a plan that would keep the existing assembly line operational to meet the ongoing production demands without disrupting product flow, quality and facility cleanliness. SI developed a system layout using a phased-installation approach. Transfers between the existing and new towline allowed the original system to remain functional after the new system was complete.
Retention of the original system was not a requirement during the planning stages of the project, but its potential use as a buffer area between assembly and test operations provided additional flexibility at no additional cost.
The main assembly segment of the new 1,500-foot-long towline has 70 stations. A stop at each station allows for either synchronous or nonsynchronous transfer of engines between stations. In addition to the main assembly segment, three powered repair spurs contain four workstations each and allow product to re-enter the assembly line after repair. A fourth spur near the end of the assembly segment contains 11 stations to accommodate low-volume options, such as engine brakes and power takeoffs. The original system had no repair or options spurs.
The towline assembly system starts by receiving an engine block from the initial assembly line. The engine block is then populated with a crankshaft and cylinder liners. The towline cart receives the engine block from a powered roller conveyor.
Each towline cart has a unique number established via a passive radio frequency (RF) tag. Each workstation stop has an RF reader to identify the cart. At the first station, correlation between engine serial number and towline cart number is established and used throughout the process. The assembly control system maintains production data and quality control criteria specific to each serial number.
Each engine has approximately 2,400 components. As an engine enters a workstation, all the requirements for that engine are transmitted to the controller and can be accessed by operators through a touch-screen display. The fail-safe I/O structure at each station is configurable to allow the addition, removal or moving of devices between stations.
A variety of methods are used to prevent mistakes during assembly. For example, lights on parts bins help operators pick the correct parts for each engine. Torque values on power tools are automatically set according to which part of the engine they are fastening. Noncomplying engines are directed to the next downstream repair spur for corrective action before reintroduction to the main assembly line.
Four programmable logic controllers and seven computers are used in the overall controls structure. There are also 101 touch-screen displays.
Since installing the new towline system, the Jamestown engine plant has improved assembly efficiency by 8 percent. An additional 10 percent improvement is expected. In addition, process quality improved by 30 percent.
"While we build diesel engines on this system, it could be used for refrigerators or most any type of assembly requiring four-sided, unencumbered access to the product," says Wilston
For more information on towline-based assembly systems, call 610-252-7321 or visit www.sihs.com.