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Welding-wire solution for an underwater muffler.

Welding-wire solution for an underwater muffler A design change in the Kawasaki Jet Ski watercraft has made the water mufflers on these sport vehicles quieter and last longer. Previously fabricated from sheet steel and bonded to fiberglass, they are now all stainless steel. Their fabrication requires the use of a noncorrosive welding wire to produce a weld that can withstand continuous flow-through contact with seawater.

At Kawasaki's Lincoln, NE, plant, developmental manufacturing work on the stainless muffler began in 1985 with a system using TIG and resistance welding, and both automatic and manual MIG methods. "Two of the challenges we faced were overcoming welding-wire feeding problems and frequent wire-reel changeovers," explains Bob Pecks, production manager. "Both contributed to welding-system downtime and decreased production."

Spool size

Matching wire-package size to production rates was the first step. They replaced their 25-lb spools with a 500-lb package of National-Standard 0.035" NS-308 stainless-steel wire and saved 2 hr per wire-package change.

Next, to eliminate excess drag on drive motors and arc wander caused by wire flipping, they adopted N-S's 500-lb wood-reel Tru-Trac dispensing system. This has columnar-torque control to allow wire advance without twisting, and a freely rotating let-off arm to keep drag low and eliminate the need for expensive pay-out equipment. Activated by pull from the wire feeder, the let-off arm rotates counter-clockwise around the coil, releasing just one strand of wire per revolution. With minimal feed force, the wire can be fed through conduit to the welding torch, reaching the torch tip nearly straight, for a more accurate weld.

A lack of lubricity, characteristic of "bright" stainless wires, can lead to feeding problems and erratic weld quality. The N-S Satin-Glide wire they chose is drawn with a special satin finish and then coated with a lubricant that reduces feed force up to 75 percent. The result is more stable arc, both in short-arc and spray-transfer operating modes. Spatter is reduced, and arc time increased.

Wire position

Inconsistent wire positioning is a prime cause of defective welds. National-Standard's solution is a large wire cast and minimum helix. Wire cast is the diameter a length of wire assumes if thrown loosely on the floor (its "memory" of spool diameter), and helix is the lateral "pitch" one end of that wire coil would rise off the floor.

A small cast with a large helix causes wire to come out of the welding torch in varying directions and results in inconsistent wire positioning. N-S stainless wire typically has a 30" to 50" cast, compared to most 18" to 22" casts, and 1" or less helix.

Fabrication process

Muffler fabrication begins with the placement of precut sheets of 19-gage 304 stainless in a tube roller. A baffle is inserted, and several partitions resistance-welded inside the muffler. The body seam and end cap are then TIG welded.

Next, the first of two MIG welding operations uses a shield-gas mixture of 90 percent helium (for maximum weld-wire wetting action), 7.5 percent argon, and 2.5 percent [CO.sub.2], to automatically weld a 1.75"-diaexhaust pipe to the muffler's inlet/outlet end cap. The cap rotates while the torch completes the weld, using 5.5 ft of filler material. Power is 20 V at 150 A. This cap assembly is then pressed into the muffler body and seam welded, and the outlet pipe swaged and mounting brackets MIG-welded to the muffler.

After the operator locates the 1.75" dia inlet pipe in the exhaust body assembly, it is placed on a turntable. The operator holds the torch stationary while this assembly rotates. This two-part procedure is necessary to work around the adjacent outlet pipe. This weld uses 15.5 ft of filler material and is completed at the same power settings as the automatic weld.

The completed mufflers are 100-percent leak tested in a submersion tank. Kawasaki's JIT philosophy requires parts to be produced to match production needs--not stock-piled--so reliable welds are crucial. A 30-percent weld-penetration specification for MIG welds is checked by cutting production parts and measuring weld characteristics.

PHOTO : Welded muffler.

PHOTO : Welder rests his torch hand on a steadyrest and spins muffler assembly to weld the inlet

PHOTO : tube and avoid the adjacent exhaust tube.
COPYRIGHT 1989 Nelson Publishing
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Aug 1, 1989
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