Reinventing the wheel - Automated line reduces in-process inventory, increases production flexibility

Kawasaki Motors Manufacturing Corp. in Lincoln, Neb., produces a variety of vehicles, such as motorcycles, Jet Ski®s, ATVs (all-terrain vehicles), industrial robots, and MULE™ utility vehicles, and is the largest manufacturer and supplier of ATV wheels worldwide.

Because continuous improvement is its mantra, in 2001 the manufacturer decided it was again time to revamp its production process of ATV wheel rims. Kawasaki's ATV wheels comprise two parts: the rim and the disk. Before 2001 the manufacturer focused on rim production improvements and capital expenditures. Upgrades to the stamping operation had been suggested for many years, but rim production was always a higher priority. After the rim process was under control, more resources became available for improvements to the disk stamping operation.

At the time the company purchased finished strips and finished blanks from an outside vendor, which were then punched in hand-loaded presses.

According to Tobin Watson, project manager at Kawasaki, the manufacturer wanted to create a safer work environment and a more efficient process. "With the volumes we were running, hand-loading blanks increased the risk of repetitive stress injuries; die costs were high because of misfeeds; and we inadvertently created a large in-process inventory," he said.

The time had come to automate the operation.

Phasing in Efficiency

Kawasaki's production encompasses several wheel sizes and designs, which require more than 60 different dies. To become more efficient, the manufacturer wanted two complete press lines—one to make round and rectangular blanks directly from coil and one to stamp finished disks. After looking at several suppliers, the company decided to purchase AP&T presses and ancillary equipment.

However, before transitioning to the new equipment, the manufacturer needed to train its employees on working with coiled steel. Because blanks were purchased from an outside vendor, shop personnel needed training on proper coil storage and material handling.

Beyond that, all existing tooling had to be modified to work in the new equipment. New die shoes were purchased, and parts inventories were increased to create time for tool modifications. As a result, all of these costs had to be offset by savings generated by the new equipment.

The first phase of the overhaul, to bring blanking in-house, was completed in 2001. The manufacturer's coil blanking line includes a coil feed system and an AP&T hydraulic press. After the first press line was installed, Kawasaki began producing blanks directly from coil; the result was an 8 percent reduction in raw material costs.

Learning From the Past

Kawasaki's old disk stamping operation consisted of five hand-loaded presses (Kawasaki 400-ton hydraulic press, Niagara 300-ton mechanical press, Bliss 110-ton gap-frame press, and two Bliss 75-ton gap-frame presses), which required teams of five operators on three shifts.

Strips of sheet metal or aluminum blanks were hand-loaded into the forming presses. From there baskets of formed parts were moved to the piercing presses for secondary operations. Each disk required up to five operations to complete.

On each press, parts were run in batches and handled up to seven times before completion. Storage was required for each basket of parts before the next operation, which created a large in-process inventory. Inspections of each operation were performed eight times per shift, which meant 40 inspections a shift, or 120 inspections a day.

In September 2003 the company purchased five new AP&T ZL 2500 presses to automate its forming line fully. The goals to be achieved with the new equipment were to match the production output of the rim forming operation (8,500 parts a day), make finished parts from blanks, eliminate material handling, reduce the total number of inspections, eliminate in-process inventory, and reduce labor costs.

Figure 1 The line's automation consists of six CD25 robots for loading, unloading, and press-to-press transfer.

A Fully Automated Line

In the new line, rectangular blanks from the in-house blanking line are cut to length with a hydraulic shear before entering the press bed area, where they are transported onto a conveyor system. The finished parts are distributed to a centering station, where an automatic pick-and-place unit stacks the blanks onto separate indexing tables.

Round blanks from the in-house blanking line are loaded into the front of the forming line. The forming presses have hydraulic die cushions and ejector cylinders. Each machine has a press force of 2,500 kN (280 U.S. tons) and a table size of 1,000 mm by 1,000 mm, (39.4 in. by 39.4 in.). Blanks are stamped out with a two-out die configuration, making it possible to produce two round blanks per stroke. The line gives Kawasaki the flexibility to run multiple draw combinations for several wheel designs.

The line's automation consists of six CD25 robots for loading, unloading, and press-to-press transfer (see Figure 1). According to Watson, the automation eliminated its large in-process inventory, accidental misfeeds, and excess material handling.

An MC 32 programmable control system gives the operator full control over the line's speed, position, and tonnage for each press and all automation. Material is coil-fed through the line via a 24-in., three-roll servo feed coil system. The production line process now requires very little manual labor.

"Just one operator is needed to monitor the line, load parts, unload finished parts, and perform quality checks," Watson said. At the end of the line, finished disks are palletized and staged for assembly (see Figure 2).

Figure 2 Finished parts are rolled off an exit conveyor and automatically stacked on pin pallets for assembly.

A multifunction bar code system also was integrated into the production line. At the front of the line, sensors read bar codes on incoming pallets to verify that the correct blanks are being loaded. Because many similar blanks are used for disk production, the verification system was put in place to prevent an operator from loading the wrong type of material or blank diameter.

At the rear of the line, production control information is printed on new bar code stickers that are attached to the pallets of finished disks. The system is designed to label and record lot control information automatically. Previously this job was done by hand.

To reduce lead-times, tooling costs, and tool repairs, the company uses automatic tool clamping and integrated die identification. The die identification function recognizes a die and recalls current production parameters. If the die doesn't match the parameters, the program sends an error message to prevent cycle start, which eliminates the risk of running the wrong die combination.

Integration Complete

Shortly after the initial start-up, Kawasaki began moving existing parts to the new press line, and 30 percent of the line's capacity during one shift was booked. In December 2003 the line was 50 percent booked during three shifts. Currently, with the addition of new models, the line is running at
80 percent capacity for three shifts, with higher production needs expected.

In 2004 the Lincoln plant produced an impressive 2.1 million ATV wheels, and according to Watson, Kawasaki expects production demands in new markets will have the line operating continuously at 90 percent capacity, seven days a week, by this summer.

Kawasaki Motors Manufacturing Corp., 6600 N.W. 27th St., Lincoln, NE 68524, 402-476-6600, fax 402-476-4735, www.kawasaki.com

AP&T North America Inc., 4817 Persimmon Court, Monroe, NC 28110, 704-292-2900, fax 704-292-2906, info@apt-usa.com, www.apt.se

Photo courtesy of AP&T; Robert Ervin, photographer.