Largest Mining Truck Challenges Part-size Variability
Caterpillar Inc.'s 350-acre, Decatur, Ill. manufacturing facility produces construction and mining trucks, wheel tractor scrapers, motor graders and the 360-ton Model 797, the largest mining truck in the world.A manufacturing cell was designed to produce axle shafts for this equipment. These shafts range from approximately 17 to 180 in.
Caterpillar Inc.'s 350-acre, Decatur, Ill. manufacturing facility produces construction and mining trucks, wheel tractor scrapers, motor graders and the 360-ton Model 797, the largest mining truck in the world.
A manufacturing cell was designed to produce axle shafts for this equipment. These shafts range from approximately 17 to 180 in. in length and 1.6 to 5 in. in diameter. To create a cell flexible enough to run parts so drastically different in size, new equipment was necessary. To handle the larger shafts and aid in improved shaft straightness, Caterpillar purchased the largest slant-bed lathe ever built and an innovative induction hardener.
It was important for all new equipment in the cell to integrate well with some older equipment. Also, a high degree of automation was desired to reduce staffing; provide more consistent work patterns; allow for batching of product through the cell; create more efficient handling of shafts through the process; simplify operations and setup; reduce overall costs; and improve quality—a tall order
According to heat treat engineers, Matt Voyles and Brian Luebbers, Caterpillar's Decatur facility used Open Control Systems and SCADAware Inc. (Bloomington, Ill.), a system integrator, to design and integrate the several systems.
All new systems at the plant run on personal computers. PCs on all new equipment, such as those in the axle shaft cell, run Steeplechase Visual Logic Controller (VLC) PC-based control software from Entivity (Ann Arbor, Mich.). "VLC was chosen as our standard because of its real-time kernel that runs below Microsoft Windows. This allows the logic to operate outside of Windows, which makes it very reliable. It behaves very much like a PLC in the way it executes code and services I/O points," says Mr. Luebbers.
With the exception of lathes and straightener, each machine in this cell is controlled by a VLC communicating to Wago Inc.'s (Germantown, Wis.) 750 Series I/O with Profibus protocol. The cell controller handles two sets of motorized queues with the same Wago I/O set, and communicates to all other VLCs over Ethernet in the real-time kernel, outside of Windows. It is via this real-time Ethernet that the cell controller efficiently orchestrates activities within the cell between the material handling robot and all machines.
On the front (entrance) end of the cell, parts are bar coded and delivered to motorized entrance queues by an operator after operations on one of two lathes. These motorized queues present parts to a material handling robot for delivery to a spline roller, induction hardener, temper furnace, end grinder, internal staging queues, and motorized exit queues. An operator on the cell's exit end removes finished parts from the exit queue, checks for straightness, and places them in a shot-peen for the final operation.
The automation reduced staffing for these operations by 60%, and reduced machine use. This allowed shaft manufacturing, which had been outsourced to be brought back to Caterpillar to fill this freed-up machine capacity. This in-house production volume has reduced the overall shaft manufacturing costs approximately 37%.
Additionally, human-machine interface-automated setups are helping reduce setup time by 25% to 100%. Part serialization and processing history attached to each part and logged in a database ensures complete part traceability. Post heat treat shaft straightness has improved an estimated 90%.
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