Agricultural equipment manufacturer CNH Global builds tractors at its Racine, WI location for its Case IH and New Holland brands. These tractors work the fields on farms in over 160 countries.

As this staple of the farm fleet becomes more sophisticated, however, moving the tractors through the assembly process increases in complexity. Add the pressure of price competition in the tight agricultural machinery market, and CNH faces continual challenges.

Research into techniques for productivity improvements led manufacturing management to conclude that the plant could reduce capital costs on a new assembly line using a combination overhead conveyor with a floor-embedded chain drive system. This approach would save 50% over the slat conveyor systems previously used. Since the pallet design for the slat system was unworkable for this new line, CNH's engineers set to work with engineers at Topper Industrial, Inc (Sturtevant, WI) to come up with a specially designed chassis cart.

"Coupling the weight of these chassis with all of their challenging contours, protrusions, and angles meant we had a project that would be solved not so much on the CAD screen as on the production floor," recalled Topper president Ed Brown. Plus, the cart has several roles to fill as it moves down the line.

Most design issues revolved around engineering the height of the supports that propped the chassis at the point of the axle housing. Further complicating matters, the cart had to accommodate chassis designs for eight different tractor models.

If a support positions the chassis too low, the unit would nearly drag along the floor; too high, and the chassis would not clear various points along the production line. Initially, the design team had to solve the problem of the chassis being carried two inches too high.

Casters presented the same difficulty. Topper engineers experimented with a range of caster sizes before they were able to zero in on the diameter for smooth cart movement without scraping the floor or hitting overhead obstructions. Topper uses a line of casters with sealed bearings for longer life with less maintenance.

"In developing our line of Ergo-Cart workstation carts," noted Brown, "we have become expert in which vendors are best at making these types of casters."

The other major issue was getting the cart back to the start of the line once the tractor is completely assembled. On the slat line, the pallet was transported beneath the conveyor to return to start.

Topper added forking pockets at the end of the cart. These enable transport lengthwise through the confines of the plant floor. At the start of the line, the forklift drops the cart and uses side forking pockets to maneuver the cart back into place. This larger model forklift sets the tractor tires into place onto the mounting fixture. Topper made the pockets extra wide to fit the larger forks on this vehicle.

Ergonomic access to the various areas of the chassis is another important consideration. The cart has steps with gripper pads to allow even shorter employees to attach components with a minimum of strain.

Setting up this system required some fine tuning. The cart has a front toe pin for pickup by the chain drive, propelling the cart at a constant speed with a time gap between tractors on the line. The problem is that tire mounting takes longer than the time gap between tractors. CNH engineers set up the system so the chain system indexes the cart just before it reaches the tire mounting station. At that point, Topper designed the cart so the front pin flips up, while at the rear of the cart another pin clicks onto the indexing chain.

At the tire mounting station, the cart rests over a platform that elevates it and the chassis into position for tire mounting. Once the fixture mounts the tires, the elevated platform brings the cart back to floor level, separating it from the tractor. The vehicle drives off to its final production operations. Then the cart pulls off the line for pickup by the tire-mounting forklift to drive back to the start of the line.

Both Topper Industrial and the CNH engineers spent many weeks developing the tractor chassis cart, making it the perfect fit for this precision operation and enabling this new assembly line to meet its full potential.

"Being a small manufacturer supporting a larger company such as CNH," says Brown, "means we have worked on becoming specialists in non-powered means of moving parts and products."