This claims priority to U.S. Provisional Application No. 60/947,116, filed on Jun. 29, 2007 and titled “EXHAUST APPARATUS AND METHOD” and it is herein incorporated by reference.
1. Technical Field
The present invention pertains to the field of metal working and the processing of tubular metal work pieces into long tapers. More specifically, the present disclosure relates to exhaust systems and methods of manufacturing exhaust systems.
2. Background Information
Tapered tubular metal pieces, and tapered exhausts in particular, are conventionally made using either a rolling or forming process. In forming tapered metal tubes by the rolling process, sections are cut from flat sheet stock. The sections are then rolled into a desired taper, which is then closed with a seam weld running parallel to the long axis of the taper. The weld is a point of weakness in the tapered piece in that its raised surface makes it susceptible to mechanical damage. Furthermore, the weld is cosmetically undesirable in that it interrupts the contour of the tapered piece. Prior to further processing, such as plating or finishing, the raised portion of the weld must generally be ground flush with the surface of the piece. However, the reduction of the weld in order to improve the profile of the piece weakens the weld, and thus the rolling method is limited by this disadvantage. The process is illustrated in FIGS. 1 and 2.
In forming tapered metal tubes by the forming process, a precut tube is machined by press operations such as drawing or forging until the tube is tapered to the desired diameter reduction. Cracking, flaking and structural flaws are experienced at a high rate with these brute force methods, particularly at taper angles in excess of about 10 degrees. With regard to the forming process, profile design variations and taper length are significantly limited due to inherent stamping process parameters, as illustrated in FIG. 5.
Both methods above have additional shortcomings in that they do not include within their scopes the preparation of modified tapers, in particular, those having untapered tubular extensions of either end, and in particular, at the small-diameter end. If such extensions are desired, it is necessary to follow the rolling and forming processes described above with the connection of a flange to the small diameter end of the taper by an orbital weld around the diameter of a precut piece of tubing. One example of such a connection is the connection of a motor cycle muffler to other engine exhaust piping.
Existing exhausts and methods of manufacturing such exhausts suffer from a number of drawbacks: In most cases all welds must be ground flush or otherwise controlled for desired cosmetics prior to further processing such as chrome plating. This additional weld preparation prior to chrome plating risks breakage at the weld site.
Tapered tubular metal work pieces are difficult to prepare by rotary swaging because the process gives, in many instances, a worked product having negative structural and cosmetic characteristics such as flaking and cracking. Such characteristics give a product which is unusable. The intended function of the pieces is to absorb acoustic energy from hot exhaust. The muffler can be heated to high temperatures before cooling to ambient temperature when engine operation ceases. Such heating and cooling cycles tend to exacerbate the negative characteristics imparted to the piece by present methods of metal tapering. Flaked sections soon separate from the piece, leaving it vulnerable to longitudinal cracks and splits parallel to the long axis of the piece.
Furthermore, present methods of tapering metal work pieces render the pieces difficult to process further into desirable usable forms. For instance in making a muffler or an exhaust, present methods of forming the taper do not permit the formation, during tapering, of an untapered section at the reduced bore end of the taper. As such a structure is desirable in order to direct outgoing exhaust after it has passed through the muffler, methods in common use require that an untapered piece having the small end diameter of the taper be welded onto the tapered section in an end-to-end fashion. The additional weld, as with the seam weld discussed above, may require further processing in order to meet cosmetic objectives.
- Rotary Swaging
A method is disclosed for the rotary swaging of tapers having a taper angle of greater than about 10 degrees. Further disclosed is a method for the machining of such tapers from a single tubular work piece such that the taper has a length of constant diameter tubing extending from the small diameter end of the taper. Further disclosed is a machined taper produced by the method, having, optionally, a length of constant diameter tubing extending from the small diameter end of the taper. Further disclosed is method which can be used to machine, in one pass, a substantially flake-free and crack-free taper having a taper angle of greater than about 10 degrees, a diameter reduction of greater than about 20%, and a length of greater than about 12 inches; and a taper prepared by the method. Further disclosed is a method which can be used to machine a tubular work piece, in one pass, from one length of tubing, into the foregoing taper, and additionally comprising a length of constant diameter tubing extending from the small diameter end of the taper.
Rotary swaging is generally performed with a rotary swaging apparatus. Such an apparatus generally comprises a circular outer race, a number of cylindrical rollers in contact with the outer race, and a number of die elements. The die elements are arranged about the work piece such that by radially closing and releasing about the work piece, they shape the work piece by forcibly deforming it into a tapered tubular section having a profile which is ideally the profile of the die elements. The preferred method is known as “infeed swaging,” in which the work piece is slowly advanced into the rhythmically opening and closing die assembly. The profile of the die is tapered, and thus, as the work piece is advanced into the die, the diameter of the tubular section at any point on the work piece which has entered the die is being continually decreased. In some cases, it is desirable to fabricate a tapered piece having a section of small diameter tubing extending from the small diameter end of the taper. This is accomplished by feeding the work piece into the machine until it exits from the small diameter end of the tapered die. The extruded section is no longer in contact with the die, and will undergo no further reduction in diameter.
The die elements are constrained in their motion by wedge pieces which fit between the die elements. The wedge elements prevent the die elements from moving circumferentially with respect to each other, but allow the elements to move radially with respect to each other. The die elements and the wedge elements together form a generally cylindrical assembly called the die assembly. The die assembly lies within a circular outer race. Between the inner surface of the outer race and the outer cylindrical surface of the die assembly lie evenly spaced cylindrical rollers. The rollers permit the die assembly to turn inside a stationary outer race, or the outer race to turn outside a stationary die assembly.
The radial motion of the die elements is caused by the rollers, and occurs when the die assembly moves with respect to the outer race. When the die elements are at their most “open” position (i.e., they have pulled back from the work piece, and the work piece can be further advanced into the die assembly, if desired) the outermost surface of the die element extends above the outer surface of the die assembly. When the die assembly moves with respect to the outer race, the rollers regularly contact the die elements and thrust them radially inward in simultaneous fashion as they roll between the die assembly and the outer race. With each inward thrust, the die elements come together around the work piece, forcing the diameter of the work piece to be reduced along the area where it is in contact with the die elements. No “spillage” around the edges of the die elements occurs because the die assembly is generally rotated with respect to the work piece.
In general, the outer race and the die assembly rotate with respect to each other. However, variations on the basic method allow for the outer race to be rotated with the die assembly held static (the work piece is then rotated as well); the die assembly rotated with the outer race held static; or both allowed to rotate to some degree.
BRIEF DESCRIPTION OF THE DRAWINGS
It has heretofore been thought that the method of rotary swaging could not be used for tapering operations involving large reductions in diameter, steep taper angles, or long tapers. For example, it is known that present methods of rotary swaging are not suitable for reductions in diameter of greater than about 30% in a single pass in that they give products with structural and cosmetic problems such as a flaking or cracking. Furthermore, present methods are substantially limited in that the angle of taper between the large and small diameters should not exceed 10-12 degrees. With current methods, the above problems are exacerbated if long tapers, such as greater than 12 inches, are desired.
FIG. 1 is a side view of a muffler shell manufactured by rolling and welding three separate components according to the prior art;
FIG. 2 is a side view of a muffler shell manufactured by rolling and welding three separate components according to the prior art;
FIG. 3 is a side view of a press formed muffler shell according to the prior art;
FIG. 4 is a side view of a swaged muffler shell manufactured according to one aspect of the present invention; and
FIG. 5 is a side view of a swaged muffler shell manufactured according to one aspect of the present invention.
FIG. 6 is the schematic for a die capable of machining a taper having a length greater than 20 inches.
FIG. 7 is the schematic for a die capable of machining a taper having both convex and concave sections
DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED EMBODIMENTS
FIG. 8 is the schematic for a die capable of machining a short taper having a taper angle of greater than 12 degrees.
In general, the tubular metal work piece can be of a wide variety of dimensions and comprised of a wide variety of materials. With respect to materials which can be used, carbon steel tubing, stainless steel tubing and aluminum tubing can be used, as well as other materials having appropriate malleability and ductility characteristics. The gauge of the tubing is preferably in the range of from about 20 gauge (035) to 11 gauge (125).
While medium diameter tubing may be machined according to the method more easily than tubing having very large or very small diameters, in general, the method can be used to machine tubular work pieces of any diameter, but preferably having a diameter of about 6 inches or less, and in preferred embodiments, a diameter in the range of from about 6 inches to about 0.5 inches. Most preferred are embodiments in which the diameter is in the range of from about 6 inches to about 2 inches.
The die can be made of a wide variety of materials, subject to wear considerations. Generally, D2 High strength steel is preferred, but other materials having suitable wearing parameters can be used as well. For example, shock steel, such as 50 to 100, can be used. Other materials having appropriate hardness and wear characteristics include other types of steel such as carbon steel.
The “taper angle” is the angle between the largest diameter and the smallest diameter of the taper. Thus, looking at a die or a tapered work piece in profile, the taper angle is the acute angle between the taper profile line and the axis of the work piece. Because the swaging die essentially imparts its own angle to the tubular work piece, in order to swage a taper having given characteristics such as taper angle, diameter reduction, and taper length, it is necessary to use a die having the properties. As described above, and known in the art, the taper dies, when closed together about a work piece, define a tapered tube. Thus, when referring to a tube having a given taper, the die by which it was formed must possess the same taper profile. As the work piece is advanced into the die, the diameter profile of the tube is reduced to conform to the diameter profile of the die. Once the work piece has been advanced to such a degree that the end inserted initially reaches the small diameter end of the die, its diameter no longer changes upon further insertion of the work piece, and a length of tubing having the smaller diameter is formed at the small diameter end of the taper. The length of the small diameter tubing increases as the work piece is fed into the die assembly. It should be noted that as the piece of tubing is processed by the die, it is generally lengthened, and as the diameter of a given section is reduced, the section generally undergoes an increase in wall thickness. Thus, the method of the present invention is characterized by the use of a die having a die taper angle of greater than about 10 degrees, and in additional embodiments, greater than about 12, 14, 15, 16, 17 and 18 degrees. In general, the method can be used to achieve a taper having a taper angle of greater than about 10 degrees, and in additional embodiments, greater than about 12, 14, 15, 16, 17 and 18 degrees. The method of the present invention also can be used to form extremely long tapers in one pass, for example, up to, including, and longer than about 24 inches. In such cases, the taper angle may be even less than about 10 degrees. Current methods require multiple passes through successively stretched tapers in order to form such long tapers.
The maximum taper length is dependent upon the length of the die taper. In general, a die taper of a given length can be used to form tapers of that length and shorter, with the shorter tapers formed by processing a work piece only partially. Fully processing a work piece (i.e., such that the inserted end reaches the small diameter end of the die taper) results in a taper having the length of the die taper. Further insertion of the work piece gives a length of tubing attached to the small diameter end of the taper, with the taper having the same length as the die taper.
While the method of the present invention can be useful in the preparation of tapers of a wide variety of dimensions, preferably the taper has a length in the range of from about 10 to about 22 inches, more preferably in the range of from about 12 to about 20 inches, even more preferably in the range of from about 15 to about 20 inches. Furthermore, the method of the present invention can be used to form a taper having extensions of tubing from its small diameter end. Such lengths of tubing can be as long as desired.
The method of the present invention can be used to prepare tapers having a diameter reduction (between starting diameter and smallest finishing diameter) of greater than 30%. Preferably, the diameter reduction is greater than 10%, and more preferably it is greater than 20%.
The method of the present invention includes the use of a die with the above angles, and it should be noted that in general, with an angle given above, the length of the die can vary greatly without departing from the scope of the present invention. Commonly desired taper lengths, such as those lengths which are useful in the motorcycle muffler industry, for example, in the range of from about 12 to about 24 inches, as well as lengths outside this range are within the scope of the present invention. It should be noted that not all combinations of starting diameter, taper length and taper angle are geometrically possible, however, the method of the present invention enfolds the production of tapers having the above parameters, to the extent that they are geometrically sensible.
The present invention encompasses tapers which are not linear in profile, i.e., tapers having convex profiles, concave profiles, or regions of both. Note the die given in example 7. The die taper profile begins with a convex section followed by a short concave section (note that the initial concavity is for the purpose of aiding the entrance of the work piece into the die assembly). In such cases the taper angle is calculated as with straight tapers above using the initial and smallest diameters.
While the inventive process disclosed herein relies on the use of a specially dimensioned die, many of the details of the rotary swaging process are standard. The work piece can be fed into the rotary swaging machine at wide variety of rates. Typical feed rates are in the range of from about 0.062 to 0.500 inches per second. The velocity of the work piece is in the range of from about 40 to 60 rpm, with the outer race velocity generally faster. The holding clamp pressure on the work piece is in the range of from about 20# to about 60#. Note that the clamp releases the work piece at intervals when the die pressure on the work piece is at a minimum, and the work piece is rotated slightly, generally by the die assembly. In general, the die assembly rotates at a higher rate relative to the work piece. The work piece is fed into the die assembly at a hydraulic pressure in the range of from about 800 to 1500#. The number of die elements (“pieces”) is preferably 2, 3 or 4.
The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and functioning of the various elements of this invention are better understood by the following detailed description. However, the embodiments of this invention as described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings. It should also be understood that the drawings are not to scale and in certain instances details have been omitted, which are not necessary for an understanding of the present invention.
FIGS. 4 and 5 illustrate a swaged muffler shell according to one aspect of the present invention. To manufacture a swaged muffler, precut tube pieces are rotary swaged to desired taper or profile. This method is more flexible in that the degree of taper and taper length is significantly more variable due to more flexible process parameters associated with rotary swaging.
This method also allows rotary swaging of the taper or profile and the connecting flange in one piece. This eliminates the need for secondary welding operations and cosmetic grinding removal of weld prior to chrome plating. This method is significantly less costly and more cosmetically desirable. No welding required.
It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.
The rotary swaging method of the present invention was used to create, in one pass, a taper having a taper angle which exceeded 12 degrees. The taper had a starting diameter of 4.500 inches, a small diameter of 2.008 inches, and a taper length 2.768 inches. The small diameter end of the taper had a length of straight tubing extending from it. The tube has a starting gauge of 14 gauge.
The swaging method of the present invention was used to create, in one pass, a taper having a 30% reduction in diameter. The taper had a starting diameter of 4.500 inches, a small diameter of 2.184 inches, and a taper length 5.504 inches. The reduction in diameter was 51.5%. The small diameter end of the taper had a length of straight tubing extending from it. The tube has a starting gauge of 14 gauge.
The swaging method of the present invention was used to create, in one pass, a taper having a taper angle which exceeded 12 degrees. The taper had a starting diameter of 2.500 inches, a small diameter of 1.610 inches, and a taper length 26.910 inches. The tube has a starting gauge of 16 gauge.