Tuggers Material Handling

By Sara Pearson Specter ·

Manufacturing facilities are continuously looking to get lean while meeting the increasing expectations of consumers for mass customization of products. Couple those challenges with an aging workforce and—in many parts of the country—a difficulty attracting and retaining qualified workers, the resulting solution for some companies has been the implementation of a designed lean material flow system.

The key to those systems, according to Larry Tyler, vice president of sales and marketing for K-Tec/Kinetic Technologies, is the reduction of a facility’s current fleet of fork trucks by replacing some of them with tugger and cart systems. “A fork truck is a vital component of a complete materials handling system: It’s not the bad guy, ” Tyler says. “It’s just one way to move materials, and as long as 15 years ago, fork trucks were the most efficient way.”

Today, however, tuggers and carts have evolved to the point where they can be flexibly engineered to support some, or all, of a facility’s handling needs. Both manned and unmanned tuggers work with powered and non-powered carts in a virtually limitless range of configurations. Their features and flexibility allow these systems to address production complexities previously only handled by fork trucks. In turn, fork trucks can be limited to the perimeter of a facility—for shipping and receiving, and for inventory placement into and out of racks—to increase the safety of personnel in the area.

In manufacturing, tugger and cart systems replace one-load-at-a-time deliveries by fork trucks to the production floor by acting as trains, or a linked series of multiple carts, carrying multiple loads in one trip. The carts themselves may be loaded by a fork truck, but a tugger handles the deliveries. Unlike a fork truck, automatic guided vehicle (AGV) style tugs travel along a pre-determined route and at a limited speed, while manned-style driven tug operators have greater visibility because the loads trail behind instead of riding on elevated forks in front of the driver.

Changing roles of carts
Delivering smaller lots more frequently in kitted and sequenced cart orders is an engineered response to the complexity of mass customization. Building multiple product lines on the same production floor or offering a selection of options to customize a standard product, require the flexibility that carts can provide, Tyler explains. The carts have evolved into specialized tools used in engineered processes to move materials as efficiently as possible.

“For parts deliveries to a production line, horizontal space is at a premium, ” Tyler says. “Production engineers can be reluctant to build fixed solutions, such as a conveyor, because the process may need to change going forward. That’s why the flexibility of cart-based solutions can make more sense from a return-on-investment perspective.”

Further, “I think of conveyor as being ideal for situations where you’re moving more than 60 loads per hour, ” says Chuck Russell, vice president of sales at Transbotics. “If you have a really long run, a conveyor breaks up the plant, crosses aisles, requires power—it can be really expensive. But to make a long run of anything more than 300 feet, or if you have to snake in and out of existing facility structures, then a tugger might be a better choice.”

Most tuggers can handle a total maximum capacity of 10, 000 pounds, including the load and the carts, when hauling across a flat surface, says Russell. While, in theory, the number of carts pulled behind is limitless, the actual number of carts that can be towed is limited by the hauling capacity of the tugger. If you require the tug to travel up or down an incline, across a rough surface, or outside from one facility to another, a whole host of additional complicating factors come into play.

“It’s very important to consider the stopping distance required by a tugger pulling a train of carts, particularly down a ramp. Traveling down an incline produces more kinetic energy, and the tugger’s brake system has to be able to handle it, ” Russell says.

Another limitation to the number of carts a tugger can pull is aisle width. Whenever a train of carts pulled by a tugger has to make a turn, the more carts in the train, the more clearance the system will need. That’s because of cart drift.

“If you put two carts in a train, they’ll follow the tugger on the same path, ” explains Russell. “If you add a third, the last cart has a slightly different turning radius; the more carts you add, the wider your aisles will need to be.”