IMM Plant Tour: Wizardry works in parallel

Wizardry works in parallel

ppliance superstar Whirlpool reinforces its sterling reputation with every product it ships. Considering that the company captures 56 percent of the global market for clothes washers and dryers and 39 percent for dishwashers, the image is strengthened daily. At Whirlpool's Findlay, OH facility, that muscle is not gained with brute force, but by thoughtfully implementing technology in a team environment.

Visitors to that plant may sense a degree of pride throughout the ranks, from assembly-line technicians to top management. And after a tour of the 1.1 million-sq-ft facility, it's evident their pride is well justified.

At the plant, fifteen miles of conveyor lines carry dishwashers in varying stages of assembly. Four workcells that contain a range of molding machines produce tubs, doors, console panels, and various smaller parts, many of which are robotically placed on conveyors prior to assembly. Three mammoth silos store the 35 million lb of resin needed annually for production. When you consider that only 11 years ago this plant produced porcelain-coated steel tubs, you begin to see that Whirlpool targets technology as the key to remaining a market leader.

The Doors of Productivity

According to John Vance, Whirlpool's advanced manufacturing lead engineer for plastics processing, the Findlay division represents the mecca for the company's U.S. molding operations. A significant portion of a $100 million investment in 1986 created the captive molding focal point for the New Generation dishwasher. At that time, Vance and others evaluated equipment suppliers and toolmakers, sampling their willingness to work on nonstandard options.

"At this point, we had several machines in house that were traditionally molding a plastic inner liner," Vance recalls. "But we needed higher quality door liners with greater robustness. We needed to produce them faster, and at lower cost." The answer came in the form of stack molding, the result of a team effort between Whirlpool, Battenfeld, A-1 Tool (Melrose Park, IL), and Incoe.

In addition to twin-gantry robotic handling systems, Battenfeld supplied three hydromechanical L-configuration presses, in which injection units are perpendicular to the clamp. Plastic is injected through an intricate central hot runner system from Incoe that splits the flow in two, then directs each into three gates located at the bottom of the part to fill the two door cavities. A-1 Tool designed the stack molds specifically for the Battenfeld machines. Suppliers also built in flexibility-both machines and molds can be converted to traditional inline styles if needed.

Vance admits the difficulties inherent in the project. "The flow paths in a conventional stack mold were tortuous, cavity fill was imbalanced with a center gate and radial flow, and if we filled both doors from the same orientation, gating from the ends, we would create a pressure wedge within the tool." The team came up with an ingenious plan. Invert one cavity in the stack and fill one door from the bottom up, and the other door from the top down to balance pressures. C-Mold simulation and a single-cavity prototype confirmed the idea. At the first mold-machine tryout in Meinerzhagen, Germany, the system successfully molded parts. It continues to do so today.

"We doubled our production rate using the stack mold system, saved floor space with L-configured machines running stack molds versus inline machines running single-cavity molds, and lowered cycle costs considerably," notes Vance. These benefits were realized with only a 13 percent increase in machine cost, and a 25 percent increase in tooling cost.

Tubs in Depth

Automotive fascia suppliers may mold the longest parts. But at 30 inches high, the tubs produced here represent some of the deepest and toughest to fill. At a 2.5-mm wall thickness, the flow length to thickness ratio staggers as high as 300:1.

For this part, complicated tooling is the name of the game. Single-cavity molds weighing 60,000 lb each run on a molding cell that contains BA-T 3850-ton presses. To eject the tubs, cavity blocks expand while core blocks collapse simultaneously. Each tub weighs 13.5 lb, so robotic handling is a must. Tubs are picked up and placed on a conveyor line that feeds into a main conveyor. A computer-operated "traffic cop" system keeps all six feeder lines running smoothly onto the main line, which ends at the quality control station located on a mezzanine above the molding floor.

The initial group of tub machines are identical; the latest addition, however, represents another team effort to incorporate technology and reduce costs. Whirlpool identified maintenance costs as the biggest expense for this area, and pulled together the mold setter, maintenance technician, engineering staff, and Battenfeld to create a solution. Technicians wanted to be able to get at the gear drive mechanism for the screw to lubricate and maintain it, but the machine layout made it difficult.

Battenfeld offered to install a servoelectric screw drive insert on the new machine at a 1 percent upcharge. "The result," says Bob Ebert, Whirlpool process engineer, "of separating the screw drive from the hydraulic system is that we've doubled oil residence time in the reservoir. Cleanliness levels are up, and oil changes are down. We're only using 40 percent of our capacity now, with less valve sticking and less maintenance overall. We've also reduced the number of pumps required to charge the accumulator from four to one. And power requirements went from two motors down to one 150-kW motor."

Likewise, screw design on the hybrid machine has taken a turn. Using a stiff grade of talc-filled PP meant that the original plasticizing system was being pushed beyond its limit. A general-purpose screw wasn't giving processing engineers the homogeneity they wanted in the melt. A new screw design with a barrier mixing section, internally developed at Battenfeld, reduced the time required for plasticizing by 10 seconds. "The combination of a barrier mixing section screw and a servoelectrically controlled screw drive means that we can independently control the plasticizing cycle," says Ebert, "not relying on the time/pressure function of a heretofore overworked hydraulic system."