In lean manufacturing philosophy, inventory is some times compared with a river. Production problems are rocks that lie just below the surface of the flowing river. Reducing the water level—lowering inventory—allows the rocks to be exposed and removed, that is, it enables production problems to be addressed.
At Ariens Company, they take lean very seriously—especially the idea of inventory reduction as a way to expose production issues and open them up for resolution. Since 2001, the company has run 1,000 kaizen events, which are aimed at enabling continuous improvement of manufacturing processes for its lines of lawn and garden products, snow throwers and other outdoor power equipment. Those events, plus rigorous application of other lean tools and techniques, have enabled Ariens to substantially reduce waste and streamline manufacturing operations at its two plants in Brillion, WI.
The goal, according to finishing manager John Kriz, is to achieve one-piece flow of products throughout both plants, enabling production of any model at any time. “One-piece flow helps you keep reducing inventory and work-in-process,” Kriz explains. “It increases production flexibility. You can paint and build whatever model is next on the board regardless of what it is.”
Flexibility is important to Ariens, where demand for some products, especially the company’s Sno-Thro equipment, can be driven by weather events. “We always have the capability to build snow products at any point throughout the year,” Kriz says. “A lot of our competitors transfer their lines from snow to lawn and garden at certain times in the year. We do that too, but our lines never really go down. We might ramp them down or we might not run anything, but they’re still ready to go, available and capable of producing snow throwers within minutes. Other companies basically convert their lines between snow and lawn and garden, and once they make that decision they can’t react very well.”
One big step in reducing waste and improving flexibility came when the company completely rearranged production flow in both plants to a cellular manufacturing concept. Before the realignment, parts were fabricated in one plant using laser cutting, stamping, punching, machining, welding and other operations, then hauled roughly a mile and a half up the road to the other plant for painting and assembly.
During peak production, Ariens can produce more than 1,000 snow throwers per day. That added up to a lot of components that needed to be moved over a relatively long distance. “There were more than 50 people just transporting parts between plants,” says Kriz. “The focus of our plant move over the past two years was to have one plant for ‘ride-on’ products—we call that Plant 1—and one plant for ‘walk-behind’ products—that’s Plant 3. So now we fabricate parts, paint them, and assemble them all in the same plant. We eliminated all that material handling, all that transportation, all the costs and labor associated with moving those parts.”
Plant 1 features two powder coating lines, both roughly 25 years old. One line sprays only black, and the other features three in-line booths for coating orange, red or black parts. Conveyors for these lines are approximately 1,800 ft long and run at speeds of 14–15 fpm. Finishing cycle time, from racking to unloading, is 2-1/2 hr assuming there are no line stoppages.
“On these lines, we run kits of two to five units,” Kriz explains. “For smaller models with faster assembly takt times, we might have 10 units in a batch in past years. For larger ride-on models, we might have fewer. But it takes a lot longer to build one of those larger units, so it might be two or three hours before we can switch to a different model on that assembly cell because we still have to use up the parts for one model before we can switch to build a different unit.”
Using lean principles, Ariens reduced work-in-process inventory in Plant 1 from about 2 1/2 hr to about 30 min. “But it was almost like our paint system didn’t catch up to changes in other parts of the process,” Kriz says. “We had cellular assembly, but we didn’t have a paint system that could respond. They were assembling unit-to-unit, and we were painting in batches.
“We really wanted our paint systems to mirror what was happening on the assembly line, and we just couldn’t get to true one-piece flow because of the system design. So that’s what drove us to ask the question ‘How can we build the smallest, most compact paint system that gives us true one-piece flow?’”
Ariens arrived at the answer to that question after a week-long 3P event with several company employees and supplier representatives. Whereas kaizen events are aimed at taking a production process as a given and seeking to make incremental improvements, 3P (the Ps stand for Production Preparation Process) basically starts with a clean slate.
The 3P team included several Ariens employees, from shop floor personnel to a vice president, as well as representatives from the chemical and powder suppliers for the project. “We spent a week outlining a perfect world scenario,” Kriz says. “The thought process was, basically, if we could start up a new company tomorrow, what would the paint system look like? What makes the most sense to reduce inventory, increase flexibility and improve delivery?”
The team spent several days developing possible strategies and evaluating each alternative against the main criterion—enabling one-piece flow throughout the factory. Implemented in Plant 3 to produce walk-behind products, their solution turned out to be not one or even two powder coating lines, but four.
Considering that even one new coating line represents a significant capital investment, how could four new lines be considered lean?
For starters, there’s size and paint cycle time. Each compact paint system takes up 4,000 sq ft of floor space—60% less than the Plant 1 systems. Each is built around a 540-ft conveyor that runs at a speed of 6 fpm, resulting in a paint cycle time of about 1 1/4 hr. Two of the lines feed seven assembly cells that build consumer products, and two crank out parts for six assembly cells used to produce commercial lawn mowers, snow throwers and other products. The difference between the consumer and commercial lines is conveyor center distance: it’s 4 1/2 ft on the consumer lines, 6 ft on the commercial lines.
Most important, though, is that the four lines enable Ariens to realize its goal of one-piece flow in production of walk-behind lawn and garden and snow thrower products. This is achieved by kitting all the parts needed to build a product on two racks. One rack holds all parts to be sprayed orange (or red, if they’re for one of the company’s commercial Gravely brand products) and one holds components to be sprayed black. Assembly cells are directly adjacent to the paint lines, enabling operators to simply push the two racks of finished parts across the aisle for immediate assembly.
Built by Midwest Finishing Systems (Mishawaka, IN), each line features a five-stage washer/iron phosphate pretreatment; two powder booths, one for orange (or red) and one for black; and a gas-fired curing oven. Pretreatment chemistry is supplied by Nalco Chemical Co. (Naperville, IL), the powder supplier is Valspar Corp. (Minneapolis, MN), and Nordson Corp. (Amherst, OH), built the booths, spray guns and gun controls.
The first of the four lines was installed in the spring of 2006, with the other three following over the next six months or so. “System 2 followed pretty closely on the heels of System 1,” Kriz recalls. “But we had some time to look at what we did right and wrong on System 1, then sit down with our suppliers and work out some of the bugs. Systems 3 and 4 went in pretty smoothly.”
The finishing process begins when an operator hangs a pair of racks on the conveyor. Parts come from fabrication on racks with detachable wheels. The powder line operator ensures that the racks hit conveyor hooks—there’s no lifting required. A few feet later the conveyor ramps up and the operator removes the wheels.
Standardized racks—or, more accurately, racks built on a standardized frame but with adjustable hooks to handle a variety of parts—are one of the keys to making the system work, according to senior manufacturing leader Pat Patton. “We have two basic rack styles for snow throwers. For lawn and garden equipment, there are more, but they all use the same basic framework,” he says.
The wash system consists of five stages: alkaline cleaner, rinse with reverse-osmosis (RO) water, iron phosphate, and two more RO rinses. The cleaner stage runs at 150°F, the phosphate at 135°F. Ariens uses no sealer on these newer paint systems, making preventive maintenance and use of RO water critical, according to Patton.
“We have a pretty strict PM schedule, especially for pretreatment,” Patton says. “We run the cleaner and phosphate for about 800 hr, then dump and recharge. Conductivity in the rinse tanks is critical to meeting our salt-spray specifications.” The RO system can produce up to 6.5 gpm of RO water, held in a 2,000-gal tank.
After a trip through a drying oven, parts enter the powder room where the conveyor splits to allow racks to go into the proper booth according to color. Powder application is via a combination of six fixed guns and an operator who focuses on surfaces that the automatic guns can’t quite reach.
“Fixed guns are located just inside the booth entrance to allow the operators adequate time to paint,” Patton says. “Basically, our painters know where they need to hit—part internal surfaces, crevices, and other tough spots. At full capacity they have 90 sec to paint.”
Ariens aims for a film build of 2–3 mils for black parts and 3–4 mils for orange and red components. According to Patton, first-pass transfer efficiency is 90-95%, and the company recycles powder.
In keeping with the lines’ compact design, there’s only about 8 ft between the paint booth exit and the entrance to the curing oven, where parts bake for 22 min at 385°F. “We’re working with the temperature,” Patton says. “When we first started, it was 400°. So we’ve been able to dial it down about 15°, saving energy while maintaining our quality standards.”
In-house quality monitoring includes checking film builds as well as other performance tests. Parts that are too light are re-run. Heavy parts are either buffed and re-run or sent out for burn-off before re-processing. “But I haven’t sent many parts to burn-off recently,” Patton says.
Working Out the Bugs
The past year has been a busy one for Patton, Kriz and the rest of Ariens’ finishing crew. Commissioning four new powder lines while keeping up with production demands was a challenge, but both men feel the lines are operating close to the original concept.
“Last year was tough,” Patton says. “We couldn’t start the lines up fast enough, and once we got them going we ran all four pretty much full-bore for a couple of months.”
This year Ariens is projecting slightly lower production volumes, which Kriz says will enable further tweaking of the powder process and leveling of production loads. “The systems and process are getting closer to working the way we designed them to,” he says. “This year we will be operating very close to what our original vision was.”
Speaking of visions, Kriz would like to see a similar type of system implemented in Ariens’ other plant in the next few years. “I think everyone agrees that focusing on lean and trying to continually improve our process would be best supported by having a powder line for consumer and a line for commercial ride-on products in Plant 1,” he says.
And, Kriz adds, Ariens’ commitment to lean manufacturing is paying off not only for the company but also for the town of Brillion, for Wisconsin and for the U.S. “We’re very different from a lot of companies in the United States because we’re actually bringing components back in-house,” he says. “We think we can make a lot of parts better and cheaper than by outsourcing, and it all goes back to our lean principles and tools. So lean has really helped us get to a level that enables us to keep jobs here.”