The “boneyard” in the rear of the Nacco materials Handling Group facility in Danville, IL, is becoming extinct. It was once home to a variety of incomplete lift trucks: some waiting for their finish to air-dry, some waiting for miscellaneous parts to be attached and others simply waiting to be reworked due to production changes. The adoption of demand-flow technology (DFT), particularly the new finishing line, is helping to change that.

The DFT assembly environment is a far cry from traditional production scheduling. The goal is to build products “on demand.” Fulfillment of product orders takes place in a day or less, not weeks. To achieve this speed, the manufacturing process has to have flexible fabrication systems and nimble-minded workers, cross-trained for a variety of tasks. Inventories are kept to a minimum to eliminate wasted warehousing costs.

Nacco’s Danville facility made its first step toward flexible manufacturing last year with the installation of a $4 million finishing system, the first of three paint systems scheduled for installation over a 3 year period. The paint line is the backbone for assembly of Hyster and Yale lift trucks with lifting capacities from 7,000 to 15,500 pounds. The line is dedicated to finishing frames, overhead guards, operator modules, carriages and load backrests. The line is also used to paint masts for trucks with lifting capacities from 13,500 to 15,500 pounds and operator modules for the “big” lift trucks with lifting capacities larger than 16,500 pounds. Manufacturing engineers plan in incorporate more lift-truck components into the system in the future.

“We are now finishing everything before assembly and protecting the weldments from damage as they go down the line,” says Don Hendricks, a Nacco project engineer. “So when it comes to final painting, it’s only a touch-up job. We don’t have to worry about large amounts of masking and repainting.”

Painting before assembly is helping in other areas as well. “In the past, we were unable to support all of the weldments that needed to be painted. We were sending our overhead guards out to be cleaned and painted,” Hendricks adds. “This new line allows us to bring that back in house.”

Going with the flow

Nacco turned to Therma-Tron-X (Sturgeon Bay, WI) for assistance in setting up the 20,000-square-foot finishing system. Not only did Therma-Tron-X design the system, it also built the flash tunnels and cure oven.

Therma-Tron-X had worked with Nacco twice previously. The turnkey specialist built a powder coating system for Nacco’s Lenoir, NC, facility and installed a liquid system in its Berea, KY, factory.

A programmable logic controller with touch-screen input manages the 1,500 feet of power-and-free conveyor from Jervis B. Webb Co. (Farmington Hills, MI). Specific part information, such as color to be painted, blast configuration and unloading point, is incorporated into a bar code on the work order and loaded into the PLC memory. Two scanners, one located before the blast machine and the other prior to the unloading stations, read the identification tags found on the conveyor carriers and trigger the appropriate finishing tasks.

The process begins at two loading stations near the welding area. Newly welded lift-truck components are placed on conveyor carriers and moved to a shot blaster from Wheelabrator (LaGrange, GA). Inside the enclosed chamber, spinning wheels hurl blasting media onto the steel surface, prepping it for the primer and smoothing out welded joints. Once completed, the weldments exit the blast machine and are cleaned and vacuumed to remove any loose blasting media.

The conveyor carriers proceed through the system from stop to stop as space clears in front of them. Nominal speed between stops is 45 feet per minute, although the carriers move through the blasting area at 8 feet per minute.

From the blasting machine, the parts proceed to a two-station priming booth, supplied by Team Blowtherm (Atlanta), formerly ITW DeVilbiss. The booth can accommodate parts 6-feet, 6-inches wide, 6-feet high, and 10-feet, 6-inches long. Electrostatic spray guns from Graco (Minneapolis) are used to apply the primer in a two-step process.

The second priming station features a button that will raise the unit 36 inches higher than the normal elevated height. “Instead of painters having to bend over to paint the bottom of the parts, they can raise the parts up.” Hendricks says. “We are very adamant about getting good coverage of primer underneath.”

The primer is an air-dry primer and requires 10 minutes in a flash tunnel for solvent evaporation. The prime coat remains tacky as it heads into the second Team Blowtherm booth for paint application.

Two finishing technicians apply a 50%-solids two-component urethane to the lift-truck components with electrostatic spray guns, also from Graco. They are predominantly painting three colors: yellow for Hyster, gold for Yale and black. Special colors can be brought on easily following a solvent purge of the paint lines. Color change-out takes about 2 minutes.

The 2k paint can be achieved in about 1 hour; the previous alkyd paint required in excess of24 hours cure time before it could b handled. When dried, the topcoat-primer combination will be about 3 mils thick.

The paint also displays better durability and gloss retention. At full cure, the 2K pint achieves an H to 2H pencil hardness, approximately four times greater than the alkyd paint. The gloss retention is 10 times better than the alkyd paint. The Nacco specification for gloss permits a 40% loss after 300 hours; the 2K paint showed only 4% loss after more than 1,300 hours.

After a 12-minute trip through a flash tunnel, the weldments enter a two-stage cure oven. The painted parts spend about 4 minutes at each of the three 180°F stations in the first stage, where they take another 40 minutes to move through 10 stations at 240°

As the parts exit the oven, they immediately enter a cool-down tunnel. Large fans are used to circulate air around the units to draw off the heat and reduce the surface temperature to approximately 100°F. At the end of the 1-hour trip through the tunnel, the paint is cured to 95% of its maximum hardness and, with proper care, the weldments can be handled with minimal damage to the coating.

While in the curing oven and cooling tunnel, the PLC holds the parts in an in-line bank. The controller releases carriers from stop to stop to ensure that the parts remain inside the oven for the correct dwell time. The system is designed to produce up to 15 loads, or carriers, per hour, working on a 4-minute cycle at each conveyor stop.

The weldments are unloaded at on of four stations, which are designed to feed directly into assembly areas. Currently, only two of the unloading stations are being used.

Not finished yet

Most of 1999 has been spent learning about the new finishing system and adjusting to a DFT environment, according to Hendricks. The changes haven’t come easily, particularly when Nacco continues to manufacture 12 lift-truck models in several sizes and with and endless array of options. Despite this, Nacco management expects a 27% increase in output over current levels by year end.

“We’ll have a tremendous advantage when we completely tie in the finishing line with the demand-flow system,” Hendricks says. “The system is already allowing us to flow product directly to assembly with minimal handling, to reduce inventories and to paint special colors. It’s only going to get better.”

Phase 2 of Nacco’s finishing system upgrade will take place early in the year 2000 when the Danville facility will begin prepainting counterweights for lift trucks with lifting capacities of 7,000 to 15,000 pounds. That will be followed by another big job later in the year. Nacco will apply DFT principles to finishing and assembling its line of lift trucks with lifting capacities from 16,500 to 105,000 pounds.