Component

Technical Field of the Invention

The present invention relates to a method of manufacturing a hollow shelled component for an exhaust system from thin- gauge metal materials. The invention relates in particular, but not exclusively, to a method of manufacturing an exhaust muffler. The invention also relates to a hollow shelled component for an exhaust system and in particular, but not exclusively, to an exhaust muffler.

Background to the Invention Automobiles having an internal combustion engine require an exhaust system to guide exhaust gases from an outlet of the engine to atmosphere. The exhaust system usually incorporates one or more mufflers (also referred to as silencers) to attenuate the noise caused by pressure waves in the exhaust gases. A typical muffler 10 is somewhat schematically illustrated in Figures 1 and 2 and comprises a housing or "box" 12 connected in-line in an exhaust pipe system (not shown), with the exhaust gases flowing through the housing from an inlet end 14 to an outlet end 16. The housing 12 contains various pipes 18 (which may be perforated), baffle plates 20, 22 and chambers 24, 26, 28 to create a tortuous path through which the exhaust gases pass and may contain a sound absorbing packaging material, such as fiberglass or ceramic fibre.

Muffler housings are usually made of metal. In a known arrangement for fabricating a muffler housing, an appropriately shaped sheet metal blank is bent into a tube-like shape and longitudinal edges of the blank are joined together by welding to produce a hollow outer shell 30. The blank may be made from a single ply or two- ply laminated metal sheet and the welded seam 32 extends in a longitudinal direction of the shell. The various internal components are mounted inside the shell and the ends are closed by means of end plates 34, 36 welded in position. The end plate 34 at the inlet end typically incorporates at least one inlet pipe/connection 35 and the end plate 36 at the outlet end at least one outlet pipe/connection (not shown) to allow the muffler to be connected in-line in the exhaust pipe system. In the muffler 10 as shown in Figures 1 and 2 there are two inlet connections 35 and two outlet connections, though in many muffler arrangements there is only a single inlet and a single outlet.

Stainless steel is commonly used to manufacture exhaust systems for vehicles, especially for high-volume production vehicles. In particular, series 300 austenitic stainless steel (e.g. 304) is commonly used in cooler parts of an exhaust system further from the engine, whilst series 400 ferritic stainless steel is used in hotter regions of the exhaust closer to the engine.

There is increasing demand to reduce the mass of automobiles in order to improve efficiency and reduce material costs. One approach to reducing the mass of an exhaust system is to manufacture it from high strength/low mass materials, including titanium and titanium alloys for cooler regions, rather than stainless steel. However, such materials are more expensive than stainless steel and tend to be used in high performance and luxury vehicles rather than high-volume production vehicles. An alternative approach to reducing the mass of an exhaust system is to use conventional materials, such as 300 and 400 series stainless steel, but in a thinner gauge. Typically, the shell of a standard exhaust muffler is made from 14 gauge stainless steel, giving a wall thickness of around 2 mm. Reducing the thickness of the material will reduce the mass but leads to difficulties in manufacture and structural integrity. Welding of thinner gauge materials give rise to a number of difficulties involving positioning of the parts, component rigidity, dimensional stability, distortion, weld integrity associated with undercutting, porosity and poor geometric profiles. In addition, the completed housing will have a reduced structural rigidity compared with one made from thicker gauge materials, unless this is otherwise compensated for. Two commonly used joints for welding thin-gauge materials (e.g. < 2 mm) are the square edge butt joint as illustrated in Figure 3 and the raised edge butt joint as shown in Figure 4. In the raised edge butt joint, the edges 40, 42 of the material are bent outwardly and the heat source is directed onto the raised edges, generally in the direction of arrow Z. During welding, the raised edges are melted, forming integral filler material, helping to compensate for the lack of thickness in the material itself. Whilst the use of a raised edge butt joint is often recommended for welding thinner gauge materials, use of this type of joint to form the longitudinal weld 32 seam in a muffler housing shell is problematic. Figure 5 is a schematic cross-sectional view through the muffler 10 of Figure 2 taken on line A- A and illustrates the effect of using a raised edge butt joint to form the longitudinal welded seam 32 the shell. During the welding process, the material tends to shrink towards the heat source. This has the effect of drawing the shell material in the region of the welded seam outwardly 32. This distortion results in a gap between the shell 30 and the baffle plates 20, 22 in the assembled muffler, as is shown more clearly in the enlarged partial view in Figure 6. The formation of gaps between the outer shell and baffle plates leads to a greater propensity for exhaust gas to leak around the perimeter of the baffle plates and a reduction in the efficacy in noise attenuation. Furthermore, the use of thin-gauge material results in the shell having a lack of rigidity, especially in the longitudinal direction, This can also result in gaps being formed between the shell and the baffle plates. The use of a square-edge butt joint as illustrated in Figure 3 largely eliminates the problem of the weld lifting away from the baffle plate due to shrinkage as the weld cools, but gaps between the shell and baffle plates can still result in localised regions with a reduction in rigidity of the shell. Furthermore, with a square- edge butt joint there is a propensity for "scissoring" of the joint edges to occur requiring excellent contact from support fixtures in order to remove heat whilst maintaining suitable frictional down force to restrain the sheet edges from closing.

The known welding techniques recommended for joining thin-gauge sheet metal then have a number of drawbacks when used for forming a longitudinal seam in a muffler shell or any similar tube-like or cannula construction from a blank. There is a need therefore for an alternative method of manufacturing a muffler or other hollow shelled component for an exhaust system from thin-gauge metal material which overcomes, or at least mitigates, the problems of the known methods.

There is also a need for an alternative hollow shelled component for an exhaust system which overcomes, or at least mitigates, drawbacks of the known hollow shelled exhaust system components. In particular, there is a need for an alternative exhaust muffler which overcomes, or at least mitigates, drawbacks of the known exhaust mufflers.

Summary of the Invention

According to a first aspect of the invention, there is provided a method of manufacturing a hollow shelled component for an exhaust system, the method comprising forming a hollow shell by: a. producing a blank of thin-gauge sheet metal having opposed longitudinal side edges; b. folding edge regions of the blank along each of the opposed longitudinal side edges to produce flanges extending out of the plane of the blank; c. bending or otherwise forming the blank to bring the longitudinal side edge regions together and define a hollow cross-section, with the flanges located proximal one another and projecting inside the hollow section; and d. joining the opposed longitudinal side edge regions of the blank together by welding or brazing to form a longitudinal seam, with the heat source applied to the outside of the hollow section.

The component may be a component of a motor vehicle exhaust system and may be an exhaust muffler.

The step of joining the opposed longitudinal side edge regions of the blank together may comprise welding the opposed longitudinal side edge regions. In which case, the method may comprise using a welding technique selected from the group consisting of: Gas Metal Arc Welding (including MIG and MAG), Gas Tungsten Arc Welding, Electron Beam Welding, Laser Beam Welding, and Arc Welding.

The step of joining the opposed longitudinal side edge regions of the blank together may comprise brazing the opposed longitudinal side edge regions. In which case the method may comprise using one of a braze welding and a laser welding technique. The method may comprise providing a supply of inert backing gas to the interior of the hollow section during welding.

The longitudinal seam may be formed in a groove defined between the longitudinal side edge regions of the blank on the outside of the hollow section opposite the flanges.

The method may comprise using a mandrel to support the hollow structure internally as the opposed longitudinal side edge regions are joined, the mandrel holding the flanges in position and engaging an inner surface of the blank either side of the flanges. The method may additionally comprise applying pressure to the exterior surface of the blank on either side of an area where the longitudinal seam is to be produced to clamp the material to the mandrel. In the method, the exterior pressure may be applied by external clamps.

In an embodiment, the method comprises locating a foil filler material between the opposed longitudinal sided edge regions before they are joined together. The filler material may be a braze alloy chemistry (Copper, Nickel or alloys of these involving silver, and phosphorus etc.).

The method may also comprise mounting an internal component within the hollow shell after the longitudinal seam has been produced. In an embodiment, the method comprises producing a formation in the flanges for co-operation with the internal component and using the formation to position the internal component within the hollow shell. The formation may include corresponding notches in each of the flanges which are aligned in the formed hollow shell. The method may include shaping the longitudinal side edge regions of the blank prior to the flanges being folded so as to define the formation when the hollow shell is formed, In an embodiment, corresponding notches are formed in each longitudinal side edge region of the blank prior to the blank being folded to form the flanges, the corresponding notches being aligned in the formed hollow shell. The internal component may be a plate, an edge of the plate engaging with the formation. Where the formation comprises corresponding notches, the method may comprise engaging an edge of the plate in a pair of alleged corresponding notches in the flanges. Where the component is an exhaust muffler, the internal component may be a baffle plate and the method may comprise engaging an edge of the baffle plate in a pair of corresponding notches to position the baffle plate in the hollow shell. The method may comprise mounting two or more baffle plates inside the hollow shell, the method comprising forming respective pairs of corresponding notches in the flanges for each baffle plate and locating an edge of each baffle plate in its respective pair of notches to position the baffle plate within the hollow shell.

The method may comprise attaching an end plate to either end of the hollow shell. The end plates may be welded or brazed to the hollow shell. The method may comprise forming an end plate notch in the flanges at either end, and locating each end plate in a respective end plate notch.

The blank may be made from stainless steel, which may be 300 or 400 series stainless steel. The blank may be made from 304 stainless steel. The blank may be laminated. The blank has a thickness of 2.0 mm or less, and may have a thickness of 1.8 mm or less, or a thickness of 1.6 mm or less, or a thickness of 1.5 mm or less, or a thiclaiess of 1.3 mm or less, or a thickness of 1.2 mm or less, or a thickness of 1.0 mm or less, or a thickness of 0.8 mm or less, or a thickness of 0.6 mm or less, or a thickness of 0.5 mm or less.

In accordance with a second aspect of the invention, there is provided a component for an exhaust system comprising a housing having a hollow outer shell formed from a blank of sheet metal, with longitudinal side edge regions of the blank joined together along a longitudinal seam by welding or brazing, wherein the blank is made from thin-gauge metal, the longitudinal side edge regions of the blank defining flanges which project inwardly proximal one another inside the shell opposite the longitudinal seam. The component may be an exhaust muffler. Where the component is an exhaust muffler, it may have at least one baffle plate mounted inside the outer shell, an edge region of said at least one baffle plate located in aligned notches in the flanges. The exhaust system may a vehicle exhaust system.

The housing may include an end plate attached to either end of the outer shell, an edge region of each end plate located in aligned notches in the flanges. The blank may be made of stainless steel, which may be 300 or 400 series stainless steel. The blank may be laminated.

The blank has a thickness of 2.0 mm or less and may have a thickness of 1.8 mm or less, or a thickness of 1.6 mm or less, or a thickness of 1.5 mm or less, or a thickness of 1.3 mm or less, or a thickness of 1.2 mm or less, or a thickness of 1.0 mm or less, or a thickness of 0.8 mm or less, or a thickness of 0.6 mm or less, or a thickness of 0.5 mm or less.

In accordance with a third aspect of the invention, there is provided an exhaust muffler manufactured using the method according to the first aspect of the invention. Detailed Description of the Invention

In order that the invention may be more clearly understood an embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is an end view of an exhaust muffler in accordance with an aspect of the invention and which can be manufactured using a method in accordance with another aspect of the invention;

Figure 2 is a schematic plan view of the exhaust muffler of Figure 1, with internal detail shown in ghost;

Figure 3 is a sectional view through two end regions of a sheet of metal illustrating the use of a conventional square-edged butt joint;

Figure 4 is a view similar to that of Figure 3 but illustrating the use of a conventional raised end butt type welded joint;

Figure 5 is a schematic cross sectional view through the muffler of Figures 1 and 2, taken on line A- A of Figure 2, illustrating the effect of using a raised edge butt joint to form a longitudinal seam in the muffler housing;

Figure 6 is an enlarged partial view of the longitudinal seam in Figure 5;

Figures 7 to 11 are a series of views illustrating various stages in one embodiment of a method of manufacturing a hollow outer shell for an exhaust muffler in accordance with an aspect of the invention; Figure 12 is a cross sectional view through part of the hollow shell of the muffler of Figures 1 and 2 illustrating formation of the longitudinal seam;

Figures 13 and 14 are schematic cross-sectional views through part of the hollow shell of the muffler of Figures 1 and 2 illustrating a modified method in which filler material is located between the longitudinal side edge regions of the blank prior to formation of the longitudinal seam;

Figure 15 is a view similar to that of Figures 13 and 14 but showing the arrangement after the longitudinal seam has been produced; and

Figure 16 is a composite drawing showing on the left a schematic cross sectional view through part of the muffler of Figures 1 and 2 taken on line A-A of Figure 2 and on the right a schematic longitudinal cross section through the muffler taken on line B-B of Figure 2.

An embodiment of a method of manufacturing a hollow shelled component for an exhaust system in accordance with an aspect of the invention will now be described by way of example only. The method in accordance with the invention is particularly intended for use in manufacturing a hollow shell from thin-gauge sheet metal. The term "thin-gauge" as used herein refers to materials having a thickness of less than 2 mm. In this embodiment, the method is used to manufacture the outer shell 30 of an exhaust muffler, such as the muffler 10 of Figures 1 and 2, and will be described with reference to Figures 7 to 12 initially.

The shell 30 is fabricated from a blank 50 of thin-gauge metal. For use in fabricating a muffler for high-volume production vehicles, the blank will typically be made from a sheet of stainless steel. For example, a series 300 austenitic stainless steel (e.g. 304) or a series 400 ferritic and martensitic stainless steel can be used. A series 300 stainless steel may be used where the muffler is to be located in a cooler part of an exhaust system further from the engine but a 400 series stainless steel used may be more suitable if the muffler is to be located in a hotter region of the exhaust close to the engine.

The blank 50 can be a single layer of sheet metal or it may be a laminated sheet. For example, the blank may be a two-ply sheet formed to achieve the desired thickness. The blank is a thin-gauge sheet having a total thickness of less than 2 mm. The actual thickness is selected in accordance with the requirements of the particular application, It is expected that by use of the method of manufacturing in accordance with the invention, blanks having a thickness as small as 0.5mm or below can be used to form the outer shell of a muffler for use in high- volume production vehicles. Longitudinal edge regions 52, 54 of the blank are folded (in the same direction) out of the plane of the blank by approximately 90 degrees along fold lines 56, 58 to form flanges 60, 62. Prior to forming the flanges, the blank in this embodiment is shaped to define a plurality of notches 64a, 64b, 66a, 66b, 68a, 68b, 70a, 70b. The notches are formed in corresponding pairs on opposite sides of the blank. Two corresponding pairs of notches 66a, 66b and 68a, 68b are inset from the ends of the blank and are used to position the baffle plates 20, 22 as will be described later. These notches have a depth d measured in the longitudinal direction of the blanlc (as indicated by arrow Y) which is the same as the thickness of the baffle plates 20, 22 or slightly larger. Another two corresponding pairs of notches 64a, 64b, 70a, 70b are formed at the ends of the blank and define longitudinal abutment surfaces 72 against which the end plates 14, 16 are located to position the end plates as will be described later. The notches 64a, 64b, 66a, 66b, 68a, 68b, 70a, 70b do not extend the full depth of the flanges. In alternative embodiments, notches are not formed in the flanges or only some of the notches can be used. For example, only the notches 66a, 66b and 68a, 68b for locating the baffle plates may be used. It will be appreciated that the number of baffle plate notches 66a, 66b and 68a, 68b can be selected depending on the number of baffle plates in the muffler.

After the flanges 60, 62 have been formed, the blank is bent to produce a hollow section having a desired cross-section shape as illustrated in Figure 9. The blank 50 is bent generally about a longitudinal axis to bring the longitudinal side edge regions 52, 54 towards each other with the flanges 60, 62 projecting inwardly within the hollow section. It will be appreciated that reference to the blank being bent about a longitudinal axis is intended to indicate the general direction of bending only and does not imply that the hollow section is symmetrical about an axis. The hollow section can take any suitable shape which may be cylindrical or non-cylindrical. The blanlc 50 may be roll formed around a pre-defined mandrel to produce the desired cross-section profile. When the blank 50 is bent to shape, the flanges 60, 62 are located proximal to one another with their outer faces 74, 76 facing each other. The terms "bending" and "bent" and the like should be understood in this context broadly as encompassing any suitable method of shaping or forming the blank into a hollow tube-like or cannula configuration. Figures 10 to 12 illustrate how the longitudinal seam 32 is produced to join the longitudinal side edge regions of the formed blank together in accordance with a first embodiment. In this first embodiment, the flanges 60, 62 are held with their outer faces 74, 76 in abutment as the seam 32 is formed.

The blank 50 is supported internally by a mandrel 78 having appropriate inserts for holding the flanges 60, 62 together and supporting the blank internally either side of the flanges at the position of the flange folds. External clamps 80, 82 apply pressure to the outer surface of the blank either side of the site where the seam 32 is to be produced, clamping the blank to the mandrel 78. Once the blank 50 is firmly secured, the longitudinal seam 32 is produced in the groove 84 between the longitudinal edge regions of the blank, with the heat source 86 applied to the outside of the blank on the opposite side from the flanges, as illustrated in Figure 11. A filler material can be used as required, dependent on the material and the method of joining adopted. Any suitable method of forming the longitudinal seam 32 can be used, including welding and brazing. Suitable welding techniques include but are not limited to: Gas Metal Arc Welding (including MIG and MAG), Gas Tungsten Arc Welding, Electron Beam Welding, Laser Beam Welding, Arc Welding, and Shielded Metal Arc Welding. Suitable brazing techniques include but are not limited to: braze welding and laser brazing, for example.

Where necessary, an inert backing gas can be introduced inside the blank as the longitudinal seam 32 is produced. The backing gas can be introduced through the mandrel 78 to the joint region.

Figure 12 illustrates in more detail formation of the longitudinal seam 32, An advantage of forming the joint with flanges 60, 62 projecting internally on the opposite side from the heat source 86 is that the flanges effectively increase the thickness of the material within the joint region. With reference to Figure 12, the true or effective thickness T of the material is given by the following equation: T = t + r + L

Where: r = 2t _m in when t < 0.8 mm for steels and L is an arbitrary value dependent on component functionality. The use of internally depending flanges 60, 62 also provides a 'z' plane thermal gradient that effectively enhances cooling, provides a reduced shrinkage effect in the transverse plane perpendicular to the welding/brazing direction.

In an alternative embodiment as illustrated in Figures 13 and 14, a filler material is located between the longitudinal edge regions 52, 54 of the blank before the longitudinal seam 32 is formed. Figure 13 illustrates use of a push-fit tee insert 88 of filler material whereas Figure 14 illustrates lengths 90 of a filler foil material attached to the blank, say by resistance weld using a poke gun. In these embodiments, the flanges 60, 62 are clamped together with the filer material between them when the longitudinal seam 32 is formed. Any suitable filer material can be used. For use with 300 and 400 series stainless steels the filler material may be braze alloy chemistry (Copper, Nickel or alloys of these involving silver, and phosphorus etc), Figure 15 shows the longitudinal seam 32 produced using a filler insert as shown in Figures 13 and 14 with the flanges 60, 62 spaced apart by a small distance, In Figure 15, the spacing between the flanges has been exaggerated for clarity. The blank may be supported by an internal mandrel 78 and fixed in position by external clamps 80, 82 as in the first embodiment, with the internal mandrel suitably configured to hold the flanges in position with the filler material between them. In Figures 13, 14 and 15, part of the baffle plate 20 has been included to illustrate the position of the baffle plate relative to the seam 32. However, the baffle plates 20, 22 are not usually located in the shell until after the seam has been produced, as discussed below.

In addition to improving the conditions for forming the longitudinal seam 32 by artificially increasing the thickness of the material at the joint area, in the completed shell 30, the internally directed flanges 60, 62 act as a longitudinal rib extending over the whole, or the majority, of the length of the shell. This significantly increases the structural rigidity of the shell 30. The flanges 60, 62 in particular help to resist bending of the shell in a longitudinal direction (that is to say about a lateral axis of the shell).

Once the outer shell 30 has been formed, the internal components of the muffler are located inside the shell 30 and the end plates 14, 16 attached. A further advantage of forming the longitudinal seam 32 with internally depending flanges 60, 62 is that the flanges can be used to position internal components and in particular the baffle plates 20, 22. In this embodiment, the two inner pairs of notches 66a, 66b, 68a, 68b formed in the flanges 60, 62 are brought into alignment when the blank is bent into shape and the longitudinal seam 32 produced. As illustrated in Figure 16, the aligned pairs of notches each receive an edge region of a respective baffle plate 20, 22. This locates the baffle plates at the correct positions within the outer shell. It will be noted from Figures 13 to 16 that the baffle plates are contoured to follow the inner profile of the outer shell, including the flanges, to limit gas leakage between the edge of the baffle plates and the shell. A further advantage of engaging an edge of each baffle plate in a re-entrant notch 66a, 66b or 68a, 68b is that it creates a tortuous path through which gas must flow in order to bypass the edge of the baffle plate. This helps to reduce even further the flow of gas from one chamber to the next. As illustrated in Figure 16, the notches do not extend into the radius r of the flanges where the longitudinal seam 32 is formed, the maximum encroachment of the notches 66a, 66b and 68a, 68b being indicated at 92. This can be advantageous if there is a need to disassemble the components. However, in alternative embodiments the notches could extend into the radii if desired. The longitudinal section in Figure 16 also illustrates how the notches 66a, 66b or 68a, 68b can be formed with an angled lead-in 94 on one side to make insertion of the baffle plates easier, The aligned pairs of notches 64a, 64b, 70a, 70b at either end of the shell 30 are used to locate the end plates 34, 36 which abut the longitudinal abutment faces 72. In other embodiments, the end plate notches at least can be omitted.

It will be appreciated that formations other than notches could be produced in the flanges 60, 62 to help locate the baffle plates and the end plates. Whilst the method of manufacturing a hollow shell from a sheet of thin-gauge metal by forming internal flanges at the longitudinal seam is particularly suitable for producing the shell of an exhaust muffler, it can be adapted for use in other applications where a hollow shell is to be produced from a sheet of thin-gauge metal for an exhaust system. For such other applications, any suitable sheet metal material can be used and the method of forming the longitudinal seam selected as appropriate. The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.