When Southeastern Container’s Enka, North Carolina, facility started producing injection- molded preforms in 1985, it had only two preform production lines and one lift truck — therefore no lift truck traffic. Today, it has 24 preform production lines, which would need five or six lift trucks to handle the input and output — if it had chosen to go with more lift trucks.
The tight quarters in this facility would hinder any type of material handling vehicle traffic, but Peter Falcigno, technical manager for Southeastern Container, thought lift trucks would be especially problematic.
“We had plenty of room years ago, but as demands grew, production lines were added to keep up the pace,” he says. “The new machines are larger and more efficient, so space within the plant is at a real premium. Our current plant layout provides only an 11-foot space for vehicles to turn around. Lift truck drivers could not manage this task on a consistent basis. Also with lift trucks in this confined area, pedestrian employees were in jeopardy of being hit.”
Instead of adding lift trucks, Southeastern invested its faith in automatic guided vehicles, hoping they could make turns flawlessly along the same path each and every time, keeping employees out of harm’s way.
AGVs kept busy
Southeastern Container is one of the largest blow molders of PET bottles in the country; the facility is kept extremely busy producing bottles for Coca-Cola. The company has seven plants that supply bottles to Coke bottlers on the East Coast. In fact, most of the Coca-Cola soft drinks bottled in the East will go into a bottle produced by Southeastern Container.
Falcigno explains, “This facility produces many palletloads of PET bottles ranging up to 3-liters each shift.
“Preform production lines are constantly changing to react to demands from the other Southeastern facilities. Certain lines will always run in-house preforms and some will always run ‘export’ preforms, but we must be able to change over lines quickly and efficiently. Changeovers may require a different pallet type and the AGVs are directed to make the change with a simple point -and-click menu.
At the end of each preform production line there are three spots for containers. One container is empty, one is being filled and the other space is open, awaiting the next container type. This arrangement allows machines to continually work without interruption. The AGVs are constantly moving throughout the plant, either delivering empty containers, or moving full container loads of preforms to the warehouse area.
“We have six AGVs, working 24/7,” Falcigno adds. “Our plant is so busy that we rely on the AGVs to keep things running smoothly. Obviously, we can’t afford to have a vehicle tied up in an accident. Before implementing AGVs, our lift truck drivers had to navigate the path for delivering containers. Often drivers had a tendency to rush, resulting in accidents that delayed production. We quickly realized the need to better orchestrate vehicle traffic.”
Production depends on the accurate deployment of preformed material. The AGV control system (see sidebar) is directly tied into the production software so that each vehicle is kept busy and there are no wasted movements throughout the plant. Navigation of every turn is wire-guided.
Each AGV has a mechanical bumper system that alerts the vehicle of obstructions in its path. When an obstruction is detected, the vehicle stops and notifies the host of a problem. Once the obstruction is removed, the vehicle will continue on its intended path.
Overall the AGVs navigate 60 stations in the plant; two at each production line, three empty container pickup areas, two full container drop-off areas, one designated “scrap” area and six recharging stations.
As a result of converting to AGVs, Falcigno says there have been no vehicle-related injuries, meaning fewer lost work days. Southeastern also saves $20,000 a year just by avoiding the plant equipment damages it was experiencing.
“Our scrap percentage from lift truck operators dropping product went down at least a half percent per year,” he concludes. “We also cut the two to three percent of finished-product damage caused by operators not putting the right product in the right boxes. These things helped the system pay for itself.”
The AGVs used at the Southeastern Container facility are custom differential-drive-type vehicles, each with a load capacity of 1,500 pounds. A 48-volt battery powers each vehicle.
The vehicles have microprocessor-based control boards that monitor all AGV functions. The controller incorporates digital and analog inputs and outputs for load handling, safety features, and steer-and-drive functions that permit bi-directional travel and automatic load handling. The control board incorporates functions such as low battery detection, low power mode (sleep mode) and navigation.
How Bottles Are Made
The bottles are produced in two steps — the first operation is the injection molding of the preform; second is blow molding the preform into the final shape. Preforms look like test tubes used in laboratories except they are threaded on the top. The threads are “formed” in the injection-molding part of the process. The threads are for the cap to screw on the bottle, ensuring a tight seal after the bottle is filled.
The preforms are compact, unlike the finished bottles, and vary according to their intended final size. They are placed in two types of containers depending on their final destination. Approximately 35 percent of the preforms are placed in all-plastic containers and stay in-house for blow molding. The remaining preforms are placed in corrugated containers set on plastic pallets and are shipped to other Southeastern Container facilities for final production. All preform containers are 48 inches long by 40 inches wide by 48 inches tall. A full container/pallet may weigh 675 to 1,000 pounds, depending on the size of the preform.
The preforms are then heated, stretched and blow molded into their final shape. The blow-molding process uses extremely clean high-pressure air to produce high-quality bottles.
Software Controls AGV System
The AGV system in the Southeastern Container facility consists of six AGVs controlled by AGV Products’ own PC-based system real-time controller, TRACE (Traffic Routing AGV Command Executor). Falcigno states, “The software allows customizing of the host computer interface, traffic control, routing, and system and vehicle troubleshooting. Color monitors at locations in the plant provide displays of vehicle progress and status of operations. We can call up detailed AGV status, monitor communications, view and modify moves, etc., at any time with a simple ‘point and click’.”