Manufacturing motorcycle mufflers

Fabricator finds improvement with rotary swaging

The Tube & Pipe Journal September 2009
September 1, 2009

Like all manufacturers, Woodsage Industries is always on the lookout for a better way to manufacture the many components it produces for OEMs. It recently devised a way to make one-piece external muffler shells for motorcycles and all-terrain vehicles.

manufacturing motorcycle mufflers.jpg

Photograph courtesy of Victory Motorcycles, a division of Polaris Industries Inc., Medina, Minn.

You don't have to look far to find a motorcycle these days. Riders purchased 900,000 motorcycles in 2008, nearly triple the number sold in 1995. The best-known motorcycle rally, held annually in Sturgis, S.D., regularly draws more than 400,000 riders. In total, organizers put together nearly 1,000 motorcycle-related events every year. That's not bad for a mode of transportation that was once the domain of not-quite-law-abiding individuals who formed nonmainstream social clubs (biker gangs).

The allure of motorcycles is centered mainly on three criteria: How does it look, how fast does it go, and how does it sound? All three result from extensive engineering, prototyping, and manufacturing efforts. As in all other areas of manufacturing, the OEMs are always on the lookout for a better method. One motorcycle manufacturer, Victory Motorcycles, a division of Polaris Industries Inc., turned to one of its suppliers, Woodsage™ Industries, for input on its exhaust systems.

Conventional motorcycle mufflers consist of ram-formed or rolled components welded together. A one-piece muffler, one formed from a single length of tube, would be an improvement. Eliminating the welds would reduce the amount of labor, eliminate potential leak paths, and improve the appearance.

Easier said than done? Yes. But Woodsage devised a way to get it done.

Part Service Center, Part Job Shop

Woodsage is far from a typical fabrication shop. It has 100 employees at two

locations (Holland, Ohio, and Franklin, Ind.) that cover a total of 260,000 square feet. It works with electric resistance welded (ERW) tube, drawn-over-mandrel (DOM) tube, and barstock. Its forte is cutting; it provides shear, nick-and-shear, coping, and cold sawing services. It has expertise in cutting ferrous metals and many categories of nonferrous metals as well, such as aluminum alloys, red metals, refractory metals, and titanium.

It's not just any cutting operation. According to Woodsage, it is the largest cutting operation in the country.

"We work with tube and pipe mills across the U.S.," explained Jim Cannaley, president of Woodsage. "For many mills, we are the primary or secondary cutting facility."

Woodsage's fabrication capabilities include swaging, notching, end forming, bending, press forming, spin forming, perforating, piercing, and welding. The experience it has gained from these processes, along with the knowledge base of its engineering staff, gives Woodsage a substantial breadth and depth of expertise. When Victory Motorcycles presented the opportunity to improve its motorcycle mufflers, Woodsage was ready.

"Woodsage has quite a bit of experience in this area," Cannaley said. "The company pioneered this type of thing in manufacturing aluminum baseball bats and tapered rollers for conveyors."

"A tapered roller, one that has a smaller diameter at the inside of the curve than at the outside of the curve, helps keep everything running smoothly," explained Pat Miller, Woodsage's outside sales manager. "For example, if the conveyor is moving shipping cartons, tapered rollers keep them lined up so that when they come out of the curved portion of the conveyor, the bar code is in the right place for the bar code reader. Tapered rollers also eliminate jams that can result in damage and, in some cases, boxes falling off the conveyor."

For many years rollers were made from flared tubular sections that were rolled shut and closed with a longitudinal weld; under Cannaley's guidance, Woodsage developed a way to swage them. The result is a roller that has no weld seam (see Figure 1). It requires less labor and has an improved surface.

A tapered roller isn't a motorcycle muffler canister, but the process for forming one works for the other.

A Better Mousetrap

"Build a better mousetrap, and the world will beat a path to your door" is a just a cliché, yet it does hold a kernel of truth. Innovation is the key to increased sales (and more efficient manufacturing), and Woodsage feels that it has an innovative way of making the external canister for motorcycle mufflers.

"Eliminating welds means eliminating air leaks," said Miller. "Eliminating air leaks maximizes horsepower."

Durability is another factor. Often a weld isn't as strong as the parent material, so a weld seam is susceptible to failure.

"In one case, a weld seam failed before the inlet," Miller said.

It's also a better-looking mousetrap.

"The cosmetic appearance is a huge factor in exhaust systems," Cannaley said. Swaging allows variations in muffler design.

"The shape of the cone, or transition, was an industry standard. Our process allows longer tapers, more options in contours, and so on." This gives the exhaust system designers the latitude to work up new, eye-catching designs, and provides choices for their customers, the motorcycle riders.

"If you're not a motorcycle rider, you might not realize how important the muffler is," explained Cannaley. "To many riders, it's nothing to install an aftermarket muffler on a brand-new motorcycle. About a week ago I saw some motorcycles in a restaurant parking lot and I went over for a closer look. One of the riders saw me and shouted over to me, 'Hey, what do you think of those pipes? They're Bassanis.' He was more proud of the mufflers than the motorcycle itself."

For off-road and racing motorcycles, the criteria are different. It's less about appearance and more about weight and performance. Still, Woodsage's process is beneficial for these applications. The one-piece design eliminates the filler metal for the welding process thatthe old method relied on. Also, the improved durability is even more important for withstanding off-road riding conditions.

Building this sort of mousetrap takes a little extra care, but it's easier than building the rolled-and-welded types.

"The raw parts are handled gently. Each is lifted individually by straps. The tubes don't have contact with other tubes or with any other hard surfaces that could ding them up or scratch them," Miller said.

The company's process for changing the tube's shape is different from the one it uses for making tapered conveyor rollers; it's so much different that it's actually patented. Understandably tight-lipped about it, Cannaley mentioned just a few details.

"We have the longest die-swaging machines in the world. They can swage 24 inches of taper in one pass. The machines are our design, and they were custom-built for us," he said.

After they are swaged, they are packed and shipped to the OEMs. They benefit from no longer having to procure the raw material, form the canister, weld it, and grind down the weld.

"We eliminated part numbers, welds, and inventories," said Cannaley. "The OEM removes the part from the box, puts it into a fixture, and stuffs in the contents."

Not that the change has been simple.

"The original type has an inlet pipe that leads into the canister," Miller said. "The OEMs used to attach one of the internal components to that pipe. Eliminating that internal pipe meant that they had to change their process." Still, they saw the overall benefits and changed the internal design to reflect the loss of this anchoring point.

Another drawback is that swaging isn't too forgiving of material variations, so Woodsage has had to learn more about manufacturing to make this process a success.

"Consistency from heat lot to heat lot is critical," Miller said.

"Again, our connections to the mills are a big help. They have a lot of metallurgical expertise, so we were able to work with some of their metallurgists to develop a tube material with the formability characteristics we needed. We also get their help when working with new materials or developing new prototypes.

An Expanding Role?

The economic troubles of 2008 and 2009 have been rough on many manufacturers, Woodsage included. Still, the company is fortunate for many reasons, according to Cannaley.

"We're still getting out there, visiting new and potential customers," he said. "We're finding that some of our competitors aren't sticking to their delivery schedules, so we're staying particularly focused on the service we provide. Woodsage has a lot of inventory, and when we do need something, because of our business relationships with the mills, we can get some help from time to time."

Looking to the future, does Woodsage see itself expanding its role and becoming an exhaust system manufacturer? Absolutely not. Just as it supplies conveyor rollers—the finished component consists of a shell, bearings, and an axle—yet stays out of the conveyor systems business, the company has no interest in manufacturing a proprietary line of complete mufflers.

"It's a lot more sophisticated than taking a louvered tube, wrapping it with some soundproofing material, and sticking it into a shell," Cannaley said. "We'll stick to our area of expertise—forming the canisters and delivering them to our customers."

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