Exhaust tubes are often positioned to lie within housings and formed to include apertures or louvers that open into the housing. The apertures or louvers permit exhaust gas flowing through the tube to communicate with a tuning chamber formed in the housing to tune or quiet the noise produced by exhaust gas flow.

A spiral-formed exhaust tube having a longitudinal axis is produced using a method in accordance with the present invention. Material having spaced-apart first and second edges and a die having a groove are provided. Louvers are formed in the material. The material is rolled into a tube using the die so that the louvers extend outwardly away from the longitudinal axis of the tube. The louvers pass through the groove of the die as the material is rolled into the tube. The first and second edges of the material are connected to complete the spiral-formed exhaust tube.

In preferred embodiments, the method produces a spiral-formed exhaust tube that includes louvers facing outwardly away from the longitudinal axis of the tube. The die and other components of the mechanism used to produce the spiral- formed exhaust tube include grooves through which the outwardly-facing louvers pass to prevent the louvers from becoming damaged.

After the louvers are formed in the material, the first and second edges of the material are mated together in the die. After the first and second edges are mated together, several different methods may be used to connect the first and second edges including, for example, welding and lock-seaming process.

Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.

Brief Description of the Drawings The description below particularly refers to the accompanying figures in which: Fig. 1 is a top plan view of a spiral exhaust tube-forming machine showing a louver-forming station which stamps louvers into an elongated strip of material, a guide station having a pair of guide rollers adjacent to the louver-forming station, a feed station having a feed roller engaging the strip of material to pull the strip of material through the louver-forming station, a guide station to prevent buckling of the strip of material, and a tube-forming station which transforms the strip of material into a spiral-formed exhaust tube; Fig. 2 is an exploded view of a muffler showing a spiral-formed exhaust tube formed on the spiral exhaust tube-forming machine of Fig. 1, a baffle plate through which the spiral-formed exhaust tube extends, and the spiral-formed exhaust tube and baffle plate being insertable into an outer shell of the muffler in the direction of the single arrow; Fig. 3 is a top plan view of the muffler of Fig. 2, with portions cut away, showing the spiral-formed exhaust tube and baffle plate positioned in the outer shell and a spiral-formed inlet tube and a spiral-formed outlet tube connected to the baffle plate and extending through the outer shell in opposite directions; Fig. 4 is a sectional view taken along line 4-4 of Fig. 1 showing the louver-forming station including a punch press that stamps or punches spaced-apart louvers in the strip of material; Fig. 5 is a sectional view taken along line 5-5 of Fig. 1 showing the feed roller'including knurled sections that engage the strip of material to pull the strip of material through the louver-forming station and push the strip of material through the guide and tube-forming stations; Fig. 6 is a sectional view taken along line 6-6 of Fig. 1 showing the guide station having guide plates that guide the strip of material into the tube-forming station; Fig. 7 is a sectional view taken along line 7-7 of Fig. 1 showing the tube-forming station having a tube-forming die set and a mandrel, the elongated strip of material passing between the mandrel and tube-forming die set and being bent into a

spiral-formed exhaust tube, a seam welder device butt-welding the edges of the strip of material together to form the spiral-formed exhaust tube, and the tube-forming die set having grooves that allow the louvers to pass through the tube-forming die set without engaging the tube-forming die set; Fig. 8 is a top plan view of a spiral exhaust tube-forming machine used to produce spiral-formed exhaust pipe according to another preferred method of the present invention showing a louver-forming station which stamps louvers into an elongated strip of material, a guide station having a pair of guide rollers adjacent to the louver-forming station, a flange-forming station having a flange-forming roller that forms a flange along one edge of the strip of material, a feed station having a feed roller engaging a top surface of the strip of material to pull the strip of material through the louver-forming and flange-forming stations, a guide station to prevent buckling of the strip of material, and a tube-forming station which transforms the strip of material into a spiral-formed exhaust tube; Fig. 9 is a sectional view taken along line 9-9 of Fig. 8 showing the flange-forming roller forming a flange along one edge of the strip of material; Fig. 10 is a sectional view taken along line 10-10 of Fig. 8 showing the feed roller including knurled sections that engage the strip of material to pull the strip of material through the louver-forming and flange-forming stations and push the strip of material through the guide and tube-forming stations; Fig. 11 is a sectional view taken along line 11-11 of Fig. 8 showing the guide station having guide plates that guide the strip of material into the tube-forming station; Fig. 12 is a sectional view taken along line 12-12 of Fig. 8 showing the tube-forming station having a tube-forming die set and a mandrel, the elongated strip of material passing between the mandrel and tube-forming die set so that one edge of the strip of material overlaps the flange formed on the other edge of the strip of material, a seam welder device welding the edges of the strip of material together to form the spiral-formed exhaust tube, and the tube-forming die set having grooves that allow the louvers to pass through the tube-forming die set without engaging the tube- forming die set;

Fig. 13 is a sectional view of another tube-forming machine used to produce spiral-formed exhaust tube according to another preferred method of the present invention showing the strip of material passing through edge-forming stations before reaching a tube-forming die set and the edges of the strip of material being lockseamed together within the tube-forming die set; Fig. 14 is a sectional view taken along line 14-14 of Fig. 13 showing an edge of the strip of material being bent upwardly from the position shown in dotted lines to the position shown in solid lines; Fig. 15 is a sectional view taken along line 15-15 of Fig. 13 showing the edge of the strip of material being bent into a C-shape from the position shown in dotted lines to the position shown in solid lines; Fig. 16 is a sectional view taken along line 16-16 of Fig. 13 showing the edge of the strip of material being bent downwardly from the position shown in dotted lines to the position shown in solid lines; Fig. 17 is a sectional view taken along line 17-17 of Fig. 13 showing the opposed edge of the strip of material being bent downwardly from the position shown in dotted lines to the position shown in solid lines; Fig. 18 is a sectional view taken along line 18-18 of Fig. 13 showing first and second rollers that form the lockseam; Fig. 19 is a sectional view taken along line 19-19 of Fig. 13 showing the lockseam connection formed by the rollers shown in Figs. 13 and 18; and Fig. 20 is a sectional view similar to Fig. 19 of another preferred method of connecting the first and second edges of the material showing a lockseam joint that is welded by a seam welder device.

Detailed Description of the Drawings A spiral exhaust tube-forming machine 10 is used to transform an elongated strip of material 14 into a spiral-formed exhaust tube 12 as shown in Fig. 1.

The spiral-formed exhaust tube machine 10 includes several "manufacturing stations" which perform particular manufacturing functions on the elongated strip of material 14 as it is transformed into spiral-formed exhaust tube 12. Spiral exhaust tube-forming machine 10 includes a louver-forming station 16, a material feed station 20, a material

guide station 22, and a tube-forming station 24. These stations 16, 20, 22, 24 cooperate to transform the elongated strip of material 14 into spiral-formed exhaust tube 12. Stations 16, 20, 22, 24 are arranged in a.compact manner to minimize the floor space occupied by spiral exhaust tube-forming machine 10.

Spiral exhaust tube-forming machine 10 includes a material entry end 15 and a spiral-formed tube exit end 17. The spiral exhaust tube-forming machine 10 further includes a material support station 26 at the entry end 15 from which the elongated strip of material 14 is delivered to the manufacturing stations 16, 20, 22, 24 ofthe spiral exhaust tube-forming machine 10. Material 14 can be supplied, for example, as metal strip stock that is rolled on a spindle 19 which is supported at material support station 26.

The spiral exhaust tube-forming machine 10 further includes a tube- cutting device 28 located at the exit end 17. The tube-cutting device 28 cuts the spiral-formed exhaust tube 12 to a desired length. Spiral-formed exhaust tubes 12 of varying lengths can be used in a muffler 13 or other exhaust system component. For example, spiral-formed tube 12 can be cut at a first place to provide a spiral-formed inlet tube 31 having a first length, spiral-formed tube 12 can be cut at a second place to provide a spiral-formed outlet tube 33 having a second length, and spiral-formed tube 12 can be cut at a third place to provide a spiral-formed intermediate tube 35 having a third length. It is within the scope of the invention as presently perceived for all of spiral-formed tubes 31, 33, 35 to be cut to different lengths or for some or all of spiral- formed tubes 31, 33, 35 to be cut to the same length.

In addition to spiral-formed inlet tube 31, spiral-formed outlet tube 33, and spiral-formed intermediate tube 35, muffler 13 includes an outer shell 30, a baffle plate 29, a first end wall 37, and a second end wall 39 as shown in Figs. 2 and 3. As previously described, spiral-formed exhaust tubes 12 can be used for any of inlet tube 31, outlet tube 33, and intermediate tube 35. Inlet tube 31, outlet tube 33, and intermediate tube 35 are illustrative of types of spiral-formed exhaust tubes 12. The spiral-formed tube 12 can also be used in exhaust system components other than muffler 13.

Spiral-formed exhaust tube 12 includes a longitudinal axis 21 and a plurality of louvers 32 that are formed at louver-forming station 16. The louvers 32

are configured to extend outwardly away from longitudinal axis 21 when spiral-formed exhaust tube 12 is formed at tube-forming station 24.

Spiral-formed exhaust tube 12 can be subdivided into a louvered portion 41, which includes louvers 32, and one or more non-louvered portions 43, which do not include louvers 32. Baffle plate 29 is formed to include three spaced- apart tube-receiving apertures (not shown), first end wall 37 is formed to include a tube-receiving aperture 45, and second end wall 39 is formed to include a tube- receiving aperture 47 as shown in Fig. 3.

In general, the non-louvered portions 43 of spiral-formed exhaust tubes 12 are the portions oftubes 12 that are inserted through one ofthe apertures formed in baffle plate 29 or one of apertures 45, 47 formed in first and second end walls 37, 39.

For example, the non-louvered portion 43 of intermediate tube 35 is inserted into and through the center tube-receiving aperture formed in baffle plate 29 as shown in Figs. 2 and 3. Similarly, a non-louvered portion 43 of inlet and outlet tubes 31, 33 is inserted into and through respective tube-receiving apertures 45, 47 formed in respective first and second end walls 37, 39. In addition, a non-louvered portion 43 of inlet and outlet tubes 31, 33 is inserted into and through the respective tube-receiving apertures formed in baffle plate 29.

The process used to produce spiral-formed exhaust tubes 12 will now be explained in more detail with reference to Figs. 1 and 4-7 which show the elongated strip of material 14 passing through the various manufacturing stations 16, 20, 22, 24.

In the illustrated embodiment, the elongated strip of material 14 is rolled on spindle 19 and support station 26 includes an axle 27 that supports spindle 19. Spindle 19 and axle 27 rotate as the elongated strip of material 14 is unrolled from spindle 19 and fed into louver-forming station 16.

In the louver-forming station 16, louvers 32 are punched or stamped into the elongated strip of material 14. As shown in Fig. 4, louver-forming station 16 includes upper and lower housings 34, 36 that support upper and lower presses 38, 40 so that upper press 38 is movable relative to lower press 40. Upper press 38 includes male die portions 42 and lower press 40 includes female die portions 44. The shape of male and female die portions 42, 44 match the desired shaped of louvers 32. In the

illustrated embodiment of the present invention, the louvers 32 are formed in an intermittent discontinuous pattern as shown, for example, in Fig. 1.

As elongated strip of material 14 passes through louver-forming station 16, the upper and lower presses 38, 40 move relative to each other so that upper press 38 and lower press 40 cooperate to engage and puncture elongated strip of material 14, thereby forming louvers 32. The relative movement of upper and lower presses 38, 40 may be created by any conventional mechanism including, for example, hydraulic mechanisms.

In other preferred embodiments of the present invention, the louver- forming station is not part of the spiral exhaust tube-forming machine, but the louver- forming operation is performed separately. In the embodiment where the louver- forming station is not part of the spiral exhaust tube-forming machine, the flat piece of material is passed through a louver-forming station in which the louvers are formed in the flat piece of material in the same manner as described above with reference to louver-forming station 16 and then the louvered flat piece of material is rerolled onto another spindle. The louvered, rerolled material is then passed through a spiral exhaust tube-forming machine that includes all the manufacturing stations of spiral-formed exhaust tube 12 except for louver-forming station 16.

With regard to the illustrated embodiment, after the elongated strip of material 14 passes through louver-forming station 16, the elongated strip of material 14 passes between a pair of guide rollers 46 as shown in Fig. 1. Each guide roller 46 engages one of respective edges of elongated strip of material 14 to minimize the side- to-side movement of the elongated strip of material 14 while guiding the elongated strip of material 14 into feed station 20.

Feed station 20 moves material 20 through the other manufacturing stations of spiral exhaust tube-forming machine 10. As shown in Fig. 5, feed station 20 includes a feed roller 62 and an opposing roller 64. Feed roller 62 includes a plurality of knurled portions 70 and a plurality of smooth portions 66. Opposing roller 64 also includes grooves 61 that receive louvers 32 so that louvers 32 are not deformed as the elongated strip of material 14 passes through the feed station 20. In addition, each of smooth portions 66 of feed roller 62 defines a groove 68 beneath

which respective louvers 32 pass in spaced-apart relation to feed roller 62 to prevent deformation of the louvers 32.

Knurled portions 70 of feed roller 62 engage the elongated strip of material 14 on opposite sides of and in between louvers 32. Spiral exhaust tube- forming machine 10 includes a power mechanism (not shown) that rotates feed roller 62. As feed roller 62 rotates, the knurled portions 70 of feed roller 62 frictionally engage the non-louvered portions of material 14 to pull the elongated strip of material 14 through louver-forming station 16 and guide rollers 46 and to push the elongated strip of material 14 through guide station 22 into tube-forming station 24. Opposing roller 64 is held up against the elongated strip of material 14 by, for example, hydraulic pressure so that opposing roller 64 rolls as material 14 passes between feed roller 62 and opposing roller 64. In alternative embodiments, other types of feed stations may be used so long as the feed station does not damage the louvers.

Following feed station 20, guide station 22, shown in Fig. 6, minimizes the amount of wrinkling or buckling of the elongated strip of material 14 as feed roller 62 pushes material 14 into tube-forming station 24. Guide station 22 includes an upper plate 76 and a lower plate 78 configured to provide a minimal amount of clearance for material 14 to pass therebetween. Upper and lower plates 76, 78 are shaped in a manner that permits louvers 32 to pass through guide station 22 without louvers 32 being damaged.

As shown in Fig. 6, lower plate 78 includes straight grooves 61 that prevent the louvers 32 from being deformed. Preferably, upper and lower plates 76, 78 are connected together by a pair of bolt and nut assemblies 80, as shown in Fig. 6.

In alternative embodiments, other types of guide stations may be used so long as the guide station does not damage the louvers.

After passing through guide station 22, the elongated strip of material 14, having louvers 32 formed therein, is now ready to be transformed into a spiral- formed exhaust tube 12 at tube-forming station 24. As shown best in Fig. 7, tube- forming station 24 includes a tube-forming die set 86 having an upper die 88 and a lower die 90. Tube-forming station 24 also includes a seam-welding device 92 and a cylindrical mandrel 94. Lower die 90 is formed to include a weld gap 91 and seam- welding device 92 is positioned to lie in weld gap 91.

A cylindrical bore 82 is formed in tube-forming die set 86, half of bore 82 being formed in upper die 88 and half of bore 82 being formed in lower die 90. A portion of mandrel 94 is received within bore 82 and the rest of mandrel 94 is positioned to lie outside bore 82. Bore 82 of die set 86 extends along an axis 84 and a circumferential material-receiving gap 83 is defined between mandrel 94 and bore 82 of upper and lower dies 88, 90. Material 14 passes through material-receiving gap 83 when material 14 passes through tube-forming station 24.

When the flat strip of material 14 exits guide station 22, material 14 enters material-receiving gap 83 formed between mandrel 94 and die set 86 and "rolls" about mandrel 94 due to contact between material 14 and die set 86. As material 14 rolls about mandrel 94, one edge or side 50 of material 14 abuts the other edge or side 52 of material 14. The abutting edges 50, 52 of material 14 are exposed to seam- welding device 92 in weld gap 91 allowing seam-welding device 92 to butt-weld edges 50, 52 together, thereby forming spiral-formed exhaust tube 12. Seam-welding device 92 can be a tungsten inert gas (TIG) welding device which avoids the need to provide an electrode or filler inside spiral-formed exhaust tube 12 during the weld operation. Use of TIG welding also avoids the creation of any flux in exhaust tube 12 during the weld operation. In alternative embodiments, other types of welders may be used to connect the first and second edges.

Axis 84 of bore 82 is oriented at an angle 85 relative to the straight path that elongated strip of material 14 follows while moving through stations 16, 20, 22 as shown in Fig. 1. Angle 85 and the width across the strip of material 14 determines the angle at which the seam formed between the edges 50, 52 of material 14 is oriented relative to axis 21 of spiral-formed exhaust tube 12. In addition, angle 85 and the width across strip of material 14 determines the final diameter of spiral-formed exhaust tube 12.

Die set 86 is formed to include a plurality of helical louver-receiving grooves 96 through which louvers 32 travel as flat strip of material 14 enters tube- receiving gap 83 and rolls through die set 86 along a spiral path about axis 84. Each die 88, 90 of die set 86 is formed to include a portion of louver-receiving grooves 96 so that when dies 88, 90 are coupled together, each of the louver-receiving grooves 96 in die 88 mate with the appropriate louver-receiving grooves 96 in die 90. Louver-

receiving grooves 96 prevent louvers 32 from being damaged during the transformation of elongated strip of material 14 into spiral-formed exhaust tube 12 at tube-forming station 24.

Grooves 61, 96 permit louvers 32 to pass through spiral exhaust tube- forming machine 10 so that when material 14 is rolled at tube-forming station 24, louvers 32 extend outwardly away from axis 21 of spiral-formed exhaust tube 12.

Having louvers 32 extending outwardly away from axis 21 prevents problems associated with tubes having louvers that extend inwardly into the bore from the tube.

Such problems include the generation of a whistling sound as exhaust gases flow past the inwardly-extending louvers and the creation of more restrictions inside the tube which inhibits the ability of the exhaust gas to flow though the tube.

By providing the discontinuous intermittent louver pattern in the elongated strip of material 14 at louver-forming station 16, spiral-formed exhaust tube 12 automatically includes the louvered portion 41 and the non-louvered portion 43 when material 14 is rolled at tube-forming station 24. As a result of the method by which spiral-formed exhaust tubes 12 are made, louvers 32 are skewed on an angle relative to axis 21 of spiral-formed exhaust tubes 12.

In preferred embodiments, the place at which spiral-formed exhaust tubes 12 are cut to establish tube length is based on the location of the patch of louvers 32 nearest tube-cutting device 28 on the particular tube 12 being cut by tube-cutting device 28. In preferred embodiments, tube-cutting device 28 is a plasma cutter. In alternative embodiments, tube-cutting device 28 may be any type of device that cuts the tube to a desired length such as a mating punch and die device or a friction blade.

Another spiral exhaust tube-forming machine 110 used to produce a spiral-formed exhaust tube 12 according to another preferred method of the present invention is shown in Figs. 8-12. Tube-forming machine 110 is identical to tube- forming machine 10 except that tube-forming machine 110 includes a flange-forming station 112 that forms a flange 114 on edge 52 of material 14 and a tube-forming station 116 that overlaps edge 50 of material 14 over flange 114 before a seam welding device 92 welds edges 50, 52. Tube-forming machine 110 also includes a feed station 120 and guide station 122 that are identical to feed station 20 and guide station 22 of tube-forming machine 10 except for provisions to accept flange 114. All other

components oftube-forming machine 110 are identical to tube-forming machine 10 and are therefore numbered identically.

Flange-forming station 112, shown in Fig. 9, is configured so that when the flat piece of material 14 passes through the flange-forming station 112, flange 114 is formed along edge 52 of material 14. Flange-forming station 112 includes a flange- forming roller 124 and a flange-forming table 126. Flange-forming roller 124 includes a relatively thick cylindrical portion 128, a relatively thin cylindrical portion 130, and a transition portion 132 extending between the relatively thick cylindrical portion 128 and relatively thin cylindrical portion 130. Transition portion 132 decreases in diameter as it extends from relatively thick cylindrical portion 128 to relatively thin cylindrical portion 130.

Flange-forming table 126 includes a top surface 134 and a roller- receiving recess 136 formed in top surface 134. Material 14 passes between roller- receiving recess 136 and flange-forming roller 124 and engagement of flange-forming roller 124 and table 126 with material 14 deforms material 14 into the shape shown in Fig. 9, thereby forming flange 114. Flange-forming table 126 includes a low portion 138, a raised portion 140, and angled portion 142 connecting low portion 138 and raised portion 140. The cross-sectional contour of low portion 138, raised portion 140, and angled portion 142 oftable 126 is similar to the cross-sectional contour of thick portion 128, thin portion 130, and transition portion 132 of flange-forming roller 124 so that as material 14 passes between table 126 and roller 124, flange 114 is shaped to have this similar cross-sectional contour.

Material 14 includes a thickness 144 and flange 114 is offset from the rest of the elongated strip of material 14 by an amount 144 that is substantially the same as the thickness 144 of the elongated strip of material 14 as shown, for example, in Figs. 9 and 10. Offsetting flange 114 by this amount 144 allows edges 50, 52 of material 14 to overlap in a flush manner during the tube-forming operation at station 116, as shown in Fig. 12.

Flange-forming table 126 is formed to include straight grooves 146 that receive louvers 32 as material 14 moves along table 126 as shown in Fig. 9. Receipt of louvers 32 in grooves 146 permits material 14 to pass through flange-forming station

112 without being deformed. In alternative embodiments, another flange-forming station may be used so long as the louvers are not damaged.

Feed station 120, shown in Fig. 10, is identical to feed station 20 of tube-forming machine 10 except that feed station 120 includes a flange-receiving portion 148. All other components of feed station 120 are identical to feed station 20 and therefore are numbered identically.

Similarly, guide station 122 is identical to guide station 22 except that guide station 122 includes a flange-receiving portion 150 as shown in Fig. 11. All other components of guide station 122 are identical to guide station 22 and therefore are numbered identically. Flange-receiving portion 150 includes raised and lowered portions 152, 154 formed in lower plate 78 and upper plate 76 of guide station 122 that prevent flange 54 from being deformed.

Tube-forming station 116 is identical to tube-forming station 24 except that tube-forming station 116 permits edge 50 of material 14 to overlap flange 114 formed in edge 52 of material 14 as shown in Fig. 12. When the flat strip of material 14 exits guide station 122, material 14 enters material-receiving gap 83 formed between mandrel 94 and die set 86 and "rolls" about mandrel 94 in a spiral path due to contact between material 14 and die set 86. As material 14 rolls about mandrel 94, flange 114 formed along edge 52 of material 14 meets up with and is overlapped by the other, non-flanged edge 50 of material 14.

The overlapping edges 50, 52 of material 14 are exposed to seam weld device 92 in weld gap 91 allowing seam welding device 92 to weld flange 114 to the non-flanged edge 50 of material 14 so that the edges 50, 52 of material 14 are fixed together, thereby forming spiral-formed exhaust tube 12. Mandrel 94 engages flange 114 so that flange 114 and the opposite edge 50 of material 14 are squeezed together between mandrel 94 and lower die 90, thereby ensuring that edges 50 ,52 of material 14 are contacting one another while edges 50, 52 are being welded together as shown in Fig. 12.

Another embodiment of a tube-forming machine 170 used to produce a spiral-formed exhaust tube 12 according to another method of the present invention is shown in Fig. 13. Tube-forming machine 170 includes edge-forming devices 172, 174, 176, 178 and a tube-forming station 180. Edge-forming devices 172, 174, 176, 178

form edges 50, 52 of material as shown in Figs. 14-17 so that tube-forming station 180 may lockseam edges 50, 52 as shown in Figs. 18 and 19. Tube-forming machine 170 also includes a louver-forming station 16, feed station 20, guide station 22, and tube- cutting device 28.

Edge-forming stations 172, 174, 176, 178 are shown diagrammatically in Fig. 13. Edge-forming station 172 bends edge 50 of material 14 upwardly in direction 182 from the position shown in dotted lines to the position shown in solid lines as shown in Fig. 14. Next, edge-forming station 174 bends edge 50 of material 14 over in direction 184 into a C-shape from the position shown in dotted lines to the position shown in solid lines as shown in Fig. 15. Edge-forming station 176 then bends edge 50 of material 14 downwardly in direction 186 from the position shown in dotted lines to the position shown in solid lines as shown in Fig. 16. Edge-forming station 178 bends the opposite edge 52 of material 14 downwardly in direction 188 from the position shown in dotted lines to the position shown in solid lines as shown in Fig. 17.

Tube-forming station 180 is identical to tube-forming stations 24, 116 except that tube-forming station 180 includes a lock seamer 190 and does not include a weld gap 91. Lock seamer 190 includes first and second rollers 192, 194 that engage edges 50, 52 to form a lockseam as shown in Figs. 13, 18, and 19.

As the material passes through tube-forming station 180, the formed edges 50, 52 shown in Figs. 16 and 17 mate before the edges 50, 52 are engaged by lock seamer 190. First roller 192 is positioned to lie within cylindrical bore 82 oftube- forming die set 86 and is coupled to mandrel 94 as shown in Fig. 13. Second roller 194 is connected to a driver such as a hydraulic cylinder (not shown) that drives second roller 194 in direction 196 toward first roller 192 to compress and flatten the lockseam as shown in Fig. 18. In the illustrated embodiment, first and second rollers 192, 194 are used to lockseam edges 50, 52 formed into the shapes shown in Figs. 16 and 17. In alternative embodiments, any type of mechanism and method may be used to lockseam edges of material formed into any shape.

In yet another alternative embodiment of the present invention, the lockseam may be welded by a seam-welding device 92 as shown in Fig. 20. In

alternative embodiments of the present invention, other mechanisms and methods may be used to connect the edges of the material used to form a spiral-formed exhaust tube.

Although this invention has been described in detail with reference to certain embodiments, variations and modifications exist within the scope and spirit of the invention as described and as defined in the following claims.