US20140116668A1

US20140116668A1 - Cooler pipe and method of forming

Info

Publication number: US20140116668A1
Application number: US13/664,485
Authority: US
Inventors: Malay Maniar; Sarang Saurabh
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-10-31
Filing date: 2012-10-31
Publication date: 2014-05-01
Also published as: CN103785707A; DE102013221632A1; CN103785707B

Abstract

A method of forming a cooler pipe includes filling a cavity of a workpiece with a backing material, roll-forming at least one helical groove along an axial length of the workpiece to define a cooling portion, and removing the backing material from the workpiece to provide a cooler pipe. The backing material may be an aggregate or granular material such as sand, which fills the cavity to provide a supportive force to the workpiece during roll-forming of the groove. The cooling portion of the cooler pipe includes an exterior recess and an interior protrusion defined by the groove which each increase the conductive surface area of the cooling portion relative to the workpiece surface area. The backing material is removable from the cooler pipe and may be recycled for use in forming a subsequent cooler pipe.

Description

TECHNICAL FIELD

The present invention relates to a cooler pipe and a method of forming a cooler pipe using roll-forming.

BACKGROUND

Cooler pipes may be included in applications where fluid at a higher temperature is conveyed or flowed through the cooler pipe to reduce the temperature of the fluid to a lower temperature, by conducting heat away from the fluid through the wall of the cooler pipe. A cooler pipe may be used, for example, in heat exchanger and/or engine systems, which may include vehicle powertrain systems, to circulate a fluid which may be a gas or a liquid and to lower the temperature of the circulated fluid. For example, a cooler pipe may be used to recirculate and reduce the temperature of exhaust gases in a combustion engine and in this configuration may be referred to as an exhaust gas recirculating (EGR) pipe.
The capability of the cooler pipe to transfer heat away from a fluid flowing through the cooler pipe, e.g., the cooling efficiency or heat transfer efficiency of the cooler pipe, is a function of a number of factors, including the capability of the pipe to convect the fluid and to conduct heat away from the fluid as the fluid flows through the cooler pipe. The capability of the cooler pipe to convect the fluid may be a function of the flow capacity or flow rate of the cooler pipe, which may be defined by and proportional to the cross-sectional area of the pipe cavity. The capability of the cooler pipe to conduct heat away from the fluid may be a function of the inner surface area of the pipe conducting heat away from fluid flowing through the pipe, the thickness and heat conductivity of the pipe wall, and the outer surface area of the cooler pipe radiating heat away from the pipe.
Another consideration in fabricating a cooler pipe is configuring the overall size and shape of the cooler pipe to fit within a packaging envelope defined by the system into which the cooler pipe is incorporated to, for example, provide clearance and/or air circulation around the exterior surface of the cooler pipe. In a system such as an engine system, the packaging envelope may be constrained by the size of the engine compartment, by the configuration of the engine and location of inlet/outlet ports to which the cooler pipe may be attached, and by clearances required between the cooler pipe and components adjacent the cooler pipe. The cooler pipe in operation may be subject to significant temperature fluctuations, vibration, high temperature, and high pressure conditions. Accordingly, the cooler pipe must be configured with sufficient thermal stress resistance, fatigue strength, cracking resistance, and pipe burst strength to maintain the integrity of the cooler pipe over time in operation and resist cracking, bursting, or other sealing failures. Weight of the cooler pipe may also be a design consideration, for example, in vehicle applications where overall weight of the vehicle system, including weight contributed by the cooler pipe, may impact fuel efficiency.
Referring to FIGS. 5A and 5B, a conventional means for milling a cooler pipe 50C from a stock pipe 50A is illustrated. The term stock pipe, as used herein, refers to a length of pipe which may be of a standard size or may be a commercially available, e.g., stocked, pipe. The stock pipe may be substantially straight along its length. FIG. 5A shows a cross-sectional view of the stock pipe 50A having a generally cylindrical wall 52 defining a hollow portion 58 and a longitudinal axis 60. The wall 52 includes an outer surface 54 having an outer radius B4, and an inner surface 56 having an inner radius B5. The wall 52 has a uniform thickness B1 prior to milling a helical slot 64 along an axial length of the stock pipe 50A to form the cooler pipe shown in cross-sectional view in FIG. 5B. The milled helical slot 64 includes a milled surface 62 and is characterized by a milled depth B3.
Cooling of a fluid (not shown) conveyed through the milled cooling pipe 50C occurs by flowing the heated fluid through the hollow portion 58 such that heat is transferred by convection of the fluid and conducted via the inner surface 56 through the thickness of the wall 52 to the outer surface 54, where the transferred heat is radiated from the outer surface 54 to the environment surrounding the cooler pipe 50C. By slotting the exterior surface 54 to form the milled helical slot 64, the area of the outer surface 54 of the cooler pipe 50C is increased incrementally by the milled surface 62, thereby increasing the surface area available to radiate heat from the cooler pipe 50C, as compared with the outer surface area 54 of the stock pipe 50A, and increasing the thermal conductivity of the milled cooler pipe 50C relative to the stock pipe 50A.
However, milling the helical slot 64 reduces the total wall thickness B1 by the milled depth B3 to a wall thickness B2 in the milled portion, thereby reducing the strength of the wall 52 of the cooler pipe 50C relative to the unmilled stock pipe 50A. As the thinnest portion of the wall 52, the effective wall thickness B2 defines the integrity and effective wall strength of the cooler pipe 50C, including, for example, resistance of the cooler pipe 50C to cracking, bursting or thermal fatigue. The surface characteristics of the milled surface 62 may further impact the effective strength of the cooler pipe 50C. If the surface finish of the milled surface 62 is rough, scratched or gouged, for example, as a result of the milling operation, stress risers may be created from which thermal fatigue cracks may initiate during operation of the cooler pipe, which may reduce the thermal fatigue resistance and/or burst strength of the milled cooler pipe 50C. Thus, the stock pipe 50A must have an initial wall thickness B1 which is thick enough to provide machining stock to mill the slot 64 to a depth B2 sufficient to provide the cooling efficiency required by the cooler pipe 50C, while retaining a minimum effective wall thickness B2 after machining, where the minimum effective wall thickness B2 must be sufficiently thick to compensate for any stress risers residual on the milled surface 62.
The fluid transfer capacity, e.g., the flow rate of fluid conveyed through the cooler pipe 50C, is defined by the cross-sectional area of the hollow portion 58, which is proportional to the inner radius B5. As flow rate increases, convection of the fluid and heat transfer efficiency increase. As noted previously, system packaging constraints may limit the overall size of the cooler pipe 50C and the size of the outer radius B4, such that the fluid transfer capacity of the cooler pipe 50C and the inner radius B5 may be constrained by the wall thickness B1 required to provide the effective wall thickness B2 after milling the slot 64. Further, the thicker portions of the wall 52, e.g., those having a thickness B1, are less efficient at conducting heat than the thinner portion of the wall 52, e.g, the slotted portion having a thickness B2.
The milled cooler pipe 50C is disadvantaged by requiring a thicker wall portion B1 having an incremental wall thickness B3 to provide machining stock to mill the slot 64. The incremental wall thickness B3 decreases heat transfer efficiency through the wall 52, introduces a weight penalty, and restricts the flow transfer capacity of the cooler pipe 50C by limiting the size of the hollow portion 58. The milled cooler pipe 50C is further disadvantaged by generating waste or scrap material from milling the slot 64, and introducing the potential for stress risers resulting from the milled surface finish of the slot surface 62.
Another method (not shown) for producing a helically corrugated metal pipe involves first forming lengthwise corrugations in an elongated strip of sheet metal, with the corrugations extending along the length of the strip. The corrugated strip is then spiraled into a helical form so that opposite edges of the corrugated strip come together and can be joined by crimping, lock seaming, or welding to form a seam along the corrugated length of the pipe. This method is disadvantaged by the multiple forming steps involved corrugating, spiraling and joining the metal strip. Further, the wall strength, including the burst strength, thermal fatigue strength and stress cracking resistance of the pipe may be defined by the integrity of the seam or crimp joining the opposite edges of the corrugated strip, which may be susceptible to crimping or welding discontinuities due to process variation and dimensional variability in the corrugated edges being joined and which may impact pipe integrity and sealing.

SUMMARY

A cooler pipe and a method of roll-forming a cooler pipe from a workpiece including a generally cylindrical wall defining a hollow portion is provided. The workpiece may be configured to include a wall having cylindrical outer and inner surfaces concentrically disposed about a longitudinal axis of the workpiece. The cooler pipe may be configured as an exhaust gas recirculating (EGR) pipe for use with an engine. The method includes filling a hollow portion defined by the inner surface of the workpiece with a backing material, and roll-forming a helical groove extending axially along the wall to form the cooler pipe using a rolling tool configured to exert a rolling force on the outer surface of the wall. The backing material is configured to exert a supportive force against the inner surface and in opposition to the rolling force. The helical groove thus formed includes a helical recess formed in the outer surface of the wall and a helical protrusion extending radially from the inner surface of the wall and into the backing material. The helical recess is characterized by a continuous extruded grain flow extending the axial length of the helical groove resulting from deformation of the workpiece material during roll-forming of the groove. In one configuration, the wall of the workpiece is characterized by a first radial thickness and the helical groove is characterized by a second radial thickness, and the first thickness and the second thickness are substantially the same. In another example, a plurality of helical grooves may be formed at axial intervals on the workpiece to configure the cooler pipe.
The method further includes removing the backing material from the cooler pipe after roll-forming the workpiece to form the cooler pipe. The backing material may be removed from the cooler pipe in portions, by one of shaking, vibrating, and gravitating each of the portions of the backing material from the cooler pipe after roll-forming, and/or by rinsing the backing material from the hollow portion using one of a fluid and a gas. The method may include recycling the backing material after removing the backing material from the cooler pipe and reusing at least a portion of the backing material as backing material during forming of a subsequent cooler pipe.
The supportive force provided by the backing material is sufficient to prevent collapse of the wall during roll-forming. The backing material may include an aggregate and/or granular material, such as sand, and may be configured as a suspension including the granular material. The method may include compacting the backing material in the hollow portion of the workpiece prior to roll-forming the helical groove. The backing material may be configured such that the helical protrusion extending from the inner surface of the wall and into the backing material displaces and/or compresses the backing material adjacent the helical protrusion within the hollow portion.
The roll-formed cooler pipe provided herein may be fabricated with a thinner wall thickness relative to a milled cooler pipe, by eliminating the machining stock required to produce a milled slot, resulting in a roll-formed cooler pipe which is lower in weight, higher in heat transfer efficiency, and substantially the same or better in wall strength, thermal fatigue strength and cracking resistance than a conventional milled cooler pipe, and which may be roll-formed without producing scrap or waste material during forming of the helical slot.
The above features and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic partial plan view of a workpiece defining a hollow portion;

FIG. 1B is a schematic cross-sectional view of section 1B-1B of the workpiece of FIG. 1A;

FIG. 2A is a schematic partial plan view of the workpiece of FIG. 1A showing the hollow portion filled with a backing material and the workpiece being roll-formed to form a cooler pipe;

FIG. 2B is a schematic cross-sectional view of section 2B-2B of the workpiece of FIG. 2A;

FIG. 3A is a schematic partial plan view of a cooler pipe formed from the workpiece of FIG. 1A by roll-forming as shown in FIG. 2A, with the backing material removed;

FIG. 3B is a schematic cross-sectional view of section 3B-3B of the cooler pipe of FIG. 3A;

FIG. 4A is a schematic cross-sectional view of section 1B-1B of the workpiece of FIG. 1A without the backing material;

FIG. 4B is a schematic cross-sectional view of section 3B-3B of the workpiece of FIG. 3A without the backing material;

FIG. 5A is a schematic cross-sectional view of a stock pipe; and

FIG. 5B is a schematic cross-sectional view of a conventional cooler pipe formed by milling the stock pipe of FIG. 5A.

DETAILED DESCRIPTION

Referring to the drawings wherein like reference numbers represent like components throughout the several figures, the elements shown in FIGS. 1-5B are not to scale or proportion. Accordingly, the particular dimensions and applications provided in the drawings presented herein are not to be considered limiting. FIGS. 1A-3B illustrate a method of forming a cooler pipe from a workpiece, generally indicated at 10, and shown as an unformed workpiece 10A in FIGS. 1A-1B, as a partially formed cooler pipe 10B in FIGS. 2A-2B, and as a formed cooler pipe 10C in FIGS. 3A-3B. In one example, the cooler pipe 10C may be configured as an exhaust gas recirculating (EGR) pipe for use with an engine (not shown). The cooler pipe 10C is formed by roll-forming a helical groove 30 along a cooling length L using a rolling tool 40, which in the example shown may include at least one roller 40 configured to exert a rolling force 38 on an outer surface 14 of the workpiece 10A.
In the example shown in FIGS. 1A-1B, the workpiece 10A may be generally tubular having a longitudinal axis 20, and may be configured as a pipe. The workpiece 10A may be a stock pipe, or a length or portion of a stock pipe. The term stock pipe, as used herein, refers to a length of pipe which may be of a standard size or shape and may be a commercially available, e.g., stocked, pipe. In the example shown, the workpiece 10A may be configured as a substantially straight length of stock pipe. The workpiece 10A may be made of metal or metal alloy material deformable by roll-forming, such as a steel-based material, stainless steel, aluminum-based material, or other. In one example, the workpiece 10A is made of a stainless steel, preferably having a high chromium content, to provide high temperature strength and fatigue resistance, as would be desirable, for example, for a cooler pipe 10C operating in an environment with temperature fluctuations including high temperatures, vibration, etc., which subject the cooler pipe 10C to thermal and/or mechanical fatigue stresses. The cooler pipe 10C when configured as an EGR pipe or similar for use on an engine such as a vehicle engine, would be subjected to such an environment.
As shown in FIGS. 1A-1B, the workpiece 10A includes a wall 12 which is defined by an outer surface 14 and an inner surface 16. The wall 12 is characterized by a wall thickness A1. The inner surface 16 of the workpiece 10A defines a hollow portion 18. In the example shown, the workpiece 10A is generally cylindrical, defining a longitudinal axis 20 and opposing workpiece or pipe ends 24, and the wall thickness A1 is uniform about the circumference of the wall 12. At least one of, or both, of the ends 24 define an opening 22 through which the hollow portion 18 is accessible. The ends 24 and/or openings 22 may be configured for attachment to an interfacing component. A portion 26 of the workpiece 10A may be defined by the cooling length L. The portion 26, as shown in FIGS. 2A and 3A, is deformed by the rolling tool 40 to define the helical groove 30, thereby forming the cooler pipe 10C, where the portion 26 defines a cooling portion of the cooler pipe 10C, and the cooling length L may correspond generally to the axial length of the helical groove 30.
The method of forming the cooler pipe 10C includes, as shown in FIGS. 1A-1B, providing a backing material 28 to the hollow portion 18 of the workpiece 10C. The backing material 28 may be provided to the hollow portion 18 via one or both of the openings 22, in a quantity and configuration to substantially fill the hollow portion 18 with the backing material 28 for at least the length L, and such that the backing material 28 provides support to the portion 26 during deformation of the wall 12 to form the helical groove 30. As shown in FIG. 2A, during roll-forming the rolling tool 40 exerts a sufficient rolling force 38 against the workpiece 10A to deform the workpiece wall 12 to form the helical groove 30. The backing material 28 exerts a supportive force 36 against the inner surface 16 of the workpiece 10A, and in opposition to the rolling force 38.
By providing temporary structural support of the interior surface 16 of the workpiece 10A during roll-forming, the backing material 28 prevents collapse, buckling, cracking and/or wrinkling of the workpiece 10A or other undesirable forming defects, such as folds, discontinuities, tool marks, etc., in the helical groove 30 and cooler pipe 10C from occurring during the roll-forming process. The uniform supportive force 36 provided by the backing material 28 to the workpiece wall 12 allows roll-forming of a workpiece 10A having a relatively thin wall 12. In one example, a relatively thin wall 12 may be characterized by a wall thickness A1 of 0.75 mm or less. In another example, the wall thickness A1 may be 0.6-0.7 mm.
The backing material 28 is characterized by sufficient compressibility such that the workpiece 10A may be deformed to form a helical protrusion 34 extending from the interior surface 16 and projecting into the backing material 28 filling the hollow portion 18 during roll-forming, as shown in FIGS. 2A-2B for the partially formed cooler pipe 10B. The backing material 28 may include a solid material, a suspension, or an aggregate. In one example, the backing material 28 may include a granular material, which may be a sand-based or sand-containing material. The backing material 28 may be provided to the hollow portion 18 of the workpiece 10A using a filling or compaction method which compacts or densifies the backing material 28 to a predetermined or minimum compacted density to exert supportive pressure 36 against the inner surface 16 of the workpiece 10A sufficient to prevent collapse, buckling and/or wrinkling of the workpiece 10A during forming of the helical groove 30. The compacted backing material 28 may be incrementally compressible and/or displaceable within the hollow portion 18 such that, during roll-forming of the helical groove 30, the backing material 28 in contact with and/or immediately proximate to the helical protrusion 34 is compressed or displaced by the helical protrusion 34 to extend or radially protrude into the backing material 28 as shown in the cross-sectional view of FIG. 2B when formed. The helical protrusion 34 increases the effective surface area of the inner surface 16 of the cooler pipe 10C, thereby increasing the heat transfer efficiency of the cooler pipe 10C relative to a cooler pipe having a cylindrical inner surface, such as the inner surface 56 of the milled cooler pipe 50C shown in FIG. 5B. The helical protrusion 34, by extending radially into the hollow portion 18 of the cooler pipe 10C, may cause increased convection of fluid (not shown) flowing through the cooler pipe 10C, by directing or controlling the flow pattern of the fluid through the hollow portion 18 and thereby increasing heat transfer efficiency through the fluid. The directed or controlled fluid flow may include a helical, angular, or corkscrew pattern of fluid motion through the hollow portion 18, which may increase the amount of time the fluid is in contact with the inner surface 16 of the cooler pipe 10C, and/or increase the area of inner surface 16 the fluid is in contact with as the fluid flows through the cooler pipe 10C, thereby increasing heat transfer efficiency. The helical protrusion 34, by extending radially into the hollow portion 18, acts to disrupt or break a boundary layer of fluid flowing through the hollow portion 18 of the cooler pipe 10C in use, where the boundary layers may form at the periphery of the hollow portion 18, e.g., at the inner surface 16 of the rolled cooler pipe 10C. Disrupting the boundary layer of fluid flowing through the hollow portion 18 changes the characteristics of at least a portion of the fluid flow through the hollow portion 18 from laminar flow to non-laminar flow, thereby increasing heat transfer efficiency.
The backing material 28 may be a granular material, such as sand. The granular material may be combined with at least one other material in one of a suspension or aggregate to form the backing material 28. For example, the backing material 28 may be configured as a suspension including a granular material and a fluid, such as a water-based or organic fluid, where the relative proportions of the granular material and the fluid may be controlled to provide a backing material 28 having a density sufficient to exert the supportive force 36, where the density may be specified for the suspension in an uncompacted and/or compacted state. In another example, the backing material 28 may include a granular material which may be combined with another material to provide an aggregate. The aggregate may be a compressible aggregate, e.g., one capable of compaction to a higher density, such as a combination of sand and a clay filler or other organic material, a foundry sand, or a green sand. The aggregate may be a combination of a first granular material of a first size and/or shape, and at least one other granular material having a different size and/or shape than the first granular material.
The grain size and/or grain shape of the granular material may be controlled or specified to provide a backing material 28 having a packing density corresponding to the grain size and/or grain shape, where the packing density, grain size and/or grain shape may correspond to the magnitude of the supportive force 36 which can be exerted by the backing material 28 when compacted in the hollow portion 18. By way of example, the backing material 28 may include fine sand having a grain size of 0.25 mm or less. In another example, the fine sand may have a grain size of 0.2 mm or less. The shape of the sand, for example, may be angular or rounded.
Referring to FIGS. 2A-2B, the helical groove 30 is formed along the cooling length L using a rolling tool 40 configured to contact the outer surface 14 of the workpiece 10A and to exert a deforming force 38, which may also be referred to herein as a rolling force 38, on the wall 12 to form the helical groove 30. The rolling tool 40 may be configured, as shown in the non-limiting example of FIG. 2A, to include one or more rollers 40, which may be arranged and/or manipulated relative to the workpiece 10A such that the workpiece 10A is advanced axially and radially relative to and in interfering contact with the rolling tool 40, where the interfering contact is sufficient for the rolling tool 40 to exert a rolling force 38 on the outer surface 14 and the wall 12 of the workpiece 10A. The roller 40 may be configured to define the profile or shape of the recess 32 and may be radiused, profiled, polished or otherwise finished to smoothly interface with the outer surface 14.
The example shown in FIG. 2A is non-limiting. Other configurations are possible, including, for example, rotating and axially advancing the workpiece 10A relative to a fixtured rolling tool 40, rotating and advancing the rolling tool 40 relative to a fixtured workpiece 10A, axially advancing the workpiece 10A while rotating the rolling tool 40, etc., to form the helical groove 30. The rolling tool 40 may be configured as an annular rolling tool (not shown), where the workpiece 10A is presented to and axially advanced with the longitudinal axis 20 skewed to the axis of the annular rolling tool 40 to define the helical angle of the helical groove 30.
The rolling tool 40 and the method of roll-forming the helical groove 30 may be configured to control the rolling force 38 and/or the depth A3 of penetration of the rolling tool 40 relative to the outer surface 14, where the depth A3 of penetration may correspond to the depth of the helical recess 32 formed by the rolling tool 40. The rolling force 38 required to form the helical groove 30 and/or the helical recess having a depth A3 may vary relative to the material chemistry and/or mechanical properties of the material forming the workpiece 10A, the supportive force 36 exerted by the backing material 28 in opposition to the rolling force 38, the configuration of the backing material 28 in the hollow portion 18, etc.
As shown in FIGS. 2A-3B, the helical groove 30 formed by the rolling tool 40 includes a helical recess 32 defined on the outer surface 14 and a helical protrusion 34 extending radially inward from the inner surface 16. The continuous, e.g., uninterrupted, helical groove 30 extends axially along the cooling length L of the portion 26 to define the cooler pipe 10C. Deformation and/or extrusion of the wall 12 by the rolling tool 40 causes grain flow in material of the workpiece 10A at the surface of the recess 32 and proximate to, e.g., immediately adjacent the surface of the recess 32, where the grain flow characterizing the deformed material defining the recess 32 is consistent with the contact profile of the rolling tool 40 and the direction and magnitude of the rolling force 38. The grain flow resulting from extrusion of the recess 32 and the helical groove 30 may be referred to herein as extruded grain flow. The continuous contact of the rolling tool 40 with, and uninterrupted rolling force 38 exerted on, the workpiece 10A during forming of the helical groove 30 generates a continuous and uninterrupted extruded grain flow extending the full length of the helical recess 32. As using herein, “continuous extruded grain flow” and “uninterrupted extruded grain flow” refer to a grain flow which is not interrupted by discontinuities in the grain flow which may be resultant from, for example, secondary operations such as machining, milling, broaching, welding, brazing, crimping, seaming, etc.
The continuous contact of the rolling tool 40 with, and uninterrupted rolling force 38 exerted on, the workpiece 10A during forming of the helical groove 30 generates a smooth surface having a uniform extruded surface finish extending continuously along the full length of the helical recess 32, which may also be described as a rolled surface finish. It would be understood that the smooth surface defined by the helical recess 32, having been formed by contact with the rolling tool 40, would be absent of scratches, gouges, machining marks or other discontinuities or stress risers which may be characteristic of a machined surface formed by a machining or milling process. The smooth surface and extruded or rolled surface finish increase the thermal stress and fatigue resistance of the cooler pipe 10C by providing a work hardened surface absence forming discontinuities or other stress risers.
The portion 26 of the cooler pipe 10C includes a wall portion 48 adjacent the helical groove 30 which remains undeformed, e.g., is not contacted by the rolling tool 40 during forming of the helical groove 30. The wall portion 48 extends between adjacent axial segments of the helical groove 30, such that the wall portion 48 is configured as a helical wall portion, which is generally cylindrical and characterized by the wall thickness A1. Referring to FIG. 2B, the helical groove 30 may be characterized by a thickness A2, which in the example shown may be substantially the same thickness as the wall thickness A1, e.g., A2≅A1, such that the thickness of the cooler pipe 10C remains substantially the same as the thickness of the workpiece 10A. As used herein, the thicknesses A2 and A1 are substantially the same when the helical groove thickness A2 is nominally or minimally reduced as the result of extruding the wall 12 to roll-form the helical groove 30, e.g., when the helical groove thickness A2 is at least 90% of the wall thickness A1. The uniform thickness A1, A2 of the cooler pipe 10C increases the heat transfer efficiency of the cooler pipe 10C in use relative to, for example, the machined cooler pipe 50C shown in FIG. 5B. The uniform thickness A1, A2 of the cooler pipe 10C provides uniformity of pipe strength, e.g., burst strength and/or resistance to cracking, fatigue, etc., as determined by or relative to the thickness of the cooler pipe 10C in use.
Referring now to FIGS. 3A, 3B, the method of forming the cooler pipe 10C from the workpiece 10A includes removing the backing material 28 from the cooler pipe 10C and from the hollow portion 18 after forming. Because the helical protrusion 34 extends radially into the backing material 28 after forming the helical groove 30, it would be understood removal of the backing material may require removing the backing material 28 in portions. The backing material 28 may be decompacted or otherwise reduced in density to facilitate its removal from the cooler pipe 10C. For example, the backing material 28 may be decompacted and/or removed by shaking, vibrating, and/or gravitating, the backing material 28, which may be granular material, from the cooler pipe 10C, such that the backing material 28 is removed from the hollow portion 18 via the opening 22. The backing material 28 may be removed from the cooler pipe 10C by rinsing the backing material 28 from the hollow portion 18 using a fluid, which may be a liquid or gas, or by suspending the backing material 28 in a fluid to reduce the density of the backing material 28 prior to removal by rinsing, shaking, etc., or by using a combination of these. The granular characteristics of the backing material 28 facilitate full removal of the backing material 28 from the cooler pipe 10C to provide an inner surface 16 which is clean, e.g., uncontaminated by the backing material 28, and/or the cooler pipe 10C may be cleaned after removal of the backing material 28. After removal from the cooler pipe 10C, the backing material 28 may be recycled and may be reused in a subsequent roll-forming operation as backing material in another workpiece to be roll-formed.
The example shown in FIGS. 1A-3B is not intended to be limiting. Other configurations of a cooler pipe 10C may be formed using the method described herein. For example, rolling tool 40 and method may be configured to form a cooler pipe 10C including a plurality of helical grooves 30, where each of the helical grooves 30 is spaced at an interval from another of the helical grooves along the axial length of the workpiece. The plurality of helical grooves may be formed such that each helical groove 30 does not intersect another helical groove. Each of the plurality of helical grooves may have a different configuration, for example, a different helical angle, recess depth A3, etc., as may be required to provide the heat transfer capability required of the cooler pipe 10C.
Referring now to FIGS. 4A-5B, a roll-formed (rolled) cooler pipe 10C formed by the roll-forming process described herein is illustrated in FIGS. 4A-4B for comparison with the milled cooler pipe 50C formed by a known milling operation and shown in FIGS. 5A-5B. The outer and inner surfaces 14, 16 of the rolled cooler pipe 10C are respectively defined by an outer and inner radius A4, A5. The outer and inner surfaces 54, 56 of the milled cooler pipe 50C are respectively defined by an outer and inner radius B4, B5. For purpose of comparison, it is assumed that the rolled cooler pipe 10C and the milled cooler pipe 50C are subjected to the same system operating conditions, including packaging considerations and operating temperatures, pressures, loading and vibrations, and are made of the same or substantially the same material having the same material strength and/or thermal conductivity characteristics. Assuming the maximum exterior size of each pipe 10C, 50C is limited by the packaging constraints of the system in which the cooler pipes 10C, 50C are to be operated, e.g., it is assumed that the outer radius A4, B4 of each respective cooler pipe 10C, 50C is maximized to maximize the radiant surface area of the exterior surfaces 14, 54 of each respective cooler pipe 10C, 50C within the system packaging envelope, such that A4=B4. Assuming the minimum effective wall thickness A1, B2 is limited by the minimum effective wall strength required by the system in which the cooler pipes 10C, 50C are operated and is the same for each cooler pipe 10C, 50C, where the effective wall thickness is kept at the minimum to minimize weight and optimize heat transfer, then A1=B2. Assuming for heat transfer purposes that the depth A3, B3 of each respective helical recess 32, 62 of each cooler pipe 10C, 50C are the same, then A3=B3. Given the rolled cooler pipe 10C and the milled cooler pipe 50C are made of substantially the same material, for example, a stainless steel material, and that A4=B4, A1=B2, and A3=B3 for comparison purposes, the rolled cooler pipe 10C provides multiple advantages as compared with the milled cooler pipe 50C, including relatively lower weight, higher fluid flow capacity, higher heat transfer efficiency and equivalent or better pipe strength and thermal and mechanical stress resistance.
By roll-forming the helical groove 30 into the wall 12 of the rolled cooler pipe 10C, no additional material is required to form the helical groove 30, and the resulting cooler pipe 10C has a uniform wall thickness A1, A2 throughout, where the wall thickness A1 may be the minimum required to provide the effective wall strength for the system, thus minimizing the weight of the cooler pipe 10C. The minimum wall thickness A1 and uniformity of wall thickness and helical groove thickness A2, where A1≅A2, provides for efficient and uniform heat transfer from the inner surface 16 to the outer surface 14. In contrast to the rolled cooler pipe 10C, the milled cooler pipe 50C is disadvantaged by the weight and non-uniformity of the thicker wall 52, where the thickness B1 of wall 52 exceeds that of wall 12 by the thickness B3 of the machining stock required to maintain the effective minimum wall thickness B2, and the non-uniform and thicker cross-section corresponding to B1 decreases heat transfer efficiency relative to the rolled cooler pipe 10C. Further, the thickness B1 of the wall 52 constrains the cross-sectional area of the hollow portion 58 of the milled cooler pipe 50C to an inner radius of B5, where in the example shown B5=A5−B2, e.g., the cross-sectional area of the hollow portion 58 is defined by inner radius B5 is smaller than the cross-sectional area of the hollow portion 18 of the roller cooler pipe 10C, such that the flow capacity, and therefore the fluid cooling capacity, of the milled cooler pipe 50C is less than that of the roller cooler pipe 10C.
The helical protrusion 34 extending from the inner surface 16 of the rolled cooler pipe wall 12 increases the effective surface area of the hollow portion 18 of the rolled cooler pipe 10C relative to the cylindrical surface area of the hollow portion 58 of the milled cooler pipe 50C, which is smaller due to the absence of any protrusions and due to a relatively smaller inner radius B5, where as described previously, B5<A5. The relatively larger surface area of the hollow portion 18 and the increased convection of the fluid flowing through the cooler pipe 10C caused by the helical protrusion 34 thereby increases heat transfer through the inner surface 16 from fluid flowing through the rolled cooler pipe 10C relative to heat transfer through the inner surface 54 of the conventional milled cooler pipe 50C.
By roll-forming the helical groove 30 to provide a recess 32 characterized by a smooth surface having a surface finish which is substantially free of stress risers such as machining marks, scratches and gouges, the rolled cooler pipe 10C may have an increased resistance to mechanical and thermal stress fatigue cracking relative to the milled cooler pipe 50C. Further, the continuous extruded grain flow defined by the extruded recess 32 may also contribute to an absence of stress risers and/or to increased fatigue resistance due to localized work hardening of the recess surface during the roll-forming process, thus increasing the resistance of the cooler pipe 10C to thermal and or mechanical stresses.
Other configurations are possible within the scope of the cooler pipe 10 described herein. For example, one or both of the pipe ends 24 may be configured for attachment to a port or opening defined by an interfacing component. For example, a cooler pipe 10C configured as an EGR pipe may include a first end 24 and/or opening 22 configured for attachment to an engine gas outlet port and a second end 24 and/or opening 22 configured for attachment to an inlet port. The cooler pipe 10C may be configured as a cooler pipe for use within other heat exchanging systems, including by way of non-limiting example, radiators, intercoolers, and other forms of heat exchangers used in engine-related and non-engine related systems.
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

Claims

1. A method of forming a cooler pipe from a workpiece including a wall having cylindrical outer and inner surfaces concentrically disposed about a longitudinal axis of the workpiece, the inner surface defining a hollow portion, the method comprising:

filling the hollow portion with a backing material;

roll-forming a helical groove extending axially along the wall to form the cooler pipe using a rolling tool configured to exert a rolling force on the outer surface of the wall;

wherein:

the backing material is configured to exert a supportive force opposing the rolling force; and

the helical groove defines:

a helical recess in the outer surface of the wall; and

a helical protrusion extending radially from the inner surface of the wall and into the backing material.

2. The method of claim 1, wherein the supportive force is sufficient to prevent collapse of the wall during roll-forming.

3. The method of claim 1, further comprising:

removing the backing material from the cooler pipe after roll-forming the workpiece to form the cooler pipe;

wherein the backing material includes a granular material.

4. The method of claim 1, wherein the backing material includes sand.

5. The method of claim 1, wherein the helical protrusion extending from the inner surface of the wall and into the backing material one of displaces and compresses the backing material adjacent the helical protrusion within the hollow portion.

6. The method of claim 1, further comprising:

compacting the backing material in the hollow portion of the workpiece prior to roll-forming the helical groove.

7. The method of claim 1, further comprising:

removing the backing material in portions from the cooler pipe, by one of shaking, vibrating, and gravitating each of the portions of the backing material from the cooler pipe.

8. The method of claim 1, wherein the backing material is a suspension including a granular material.

9. The method of claim 1, further comprising:

removing the backing material from the cooler pipe after roll-forming by rinsing the backing material from the hollow portion using one of a fluid and a gas.

10. The method of claim 1, wherein:

the rolling tool is configured to form a plurality of helical grooves; and

each of the plurality of helical grooves is spaced at an interval from another of the helical grooves along the axial length of the workpiece.

11. The method of claim 1, wherein the workpiece is made from stainless steel.

12. The method of claim 1, wherein the wall of the workpiece is characterized by a thickness of between 0.6 mm and 0.7 mm.

13. The method of claim 1, wherein:

the wall of the workpiece is characterized by a first radial thickness and the helical groove is characterized by a second radial thickness; and

the first thickness and the second thickness are substantially the same.

14. A cooler pipe including a tubular cooling portion defining a longitudinal axis, the cooler pipe comprising:

a helical groove defined by the tubular cooling portion concentrically disposed about the longitudinal axis including:

a helical recess defined by an outer surface of the tubular cooling portion;

a helical protrusion projecting from an inner surface of the tubular cooling portion;

wherein the helical recess is characterized by a continuous extruded grain flow extending the axial length of the helical groove.

15. The cooler pipe of claim 14, wherein:

the helical groove is one of a plurality of helical grooves defined by the tubular cooling portion;

wherein each respective one of the plurality of helical grooves is:

characterized by a continuous extruded grain flow extending the axial length of the helical recess of the respective helical groove; and

non-intersecting with each other one of the plurality of helical grooves.

16. The cooler pipe of claim 14, further comprising:

a wall portion adjacent the helical groove and concentric to the longitudinal axis;

wherein:

the wall portion is characterized by a first radial thickness and the helical groove is characterized by a second radial thickness; and

the first thickness and the second thickness are substantially the same.

17. The cooler pipe of claim 14, wherein the cooler pipe is configured as an exhaust gas recirculating (EGR) pipe for use with an engine.

18. A method of forming an exhaust gas recirculating (EGR) pipe from a stock pipe defining inner and outer surfaces concentrically disposed about a longitudinal axis of the stock pipe, the method comprising:

compacting a backing material in the stock pipe such that the compacted backing material conforms to the inner surface of the stock pipe and exerts a supportive force on the inner surface;

forming the EGR pipe by concurrently:

contacting the outer surface of the stock pipe using a roller configured to define a recess of a helical groove and exert an extruding force against the outer surface of the stock pipe;

advancing the stock pipe axially and radially relative to the roller and with the stock pipe in interfering contact with the roller;

exerting the extruding force against the outer surface of the stock pipe and in opposition to the supportive force of the compacted backing material to extrude the helical groove along an axial length of the stock pipe by forming a helical recess defined by the outer surface of the EGR pipe and a helical protrusion defined by the inner surface of the EGR pipe;

compressing the compacted backing material proximate to the helical protrusion during forming of the helical protrusion such that the helical protrusion extends radially into the compacted backing material; and

removing the backing material from the EGR pipe by decompacting the backing material.

19. The method of claim 18, wherein the supportive force exerted by the backing material is sufficient to prevent collapse of the EGR pipe by exertion of the extruding force.

20. The method of claim 18, wherein the backing material is an aggregate material; the method further comprising:

recycling the backing material after removing the backing material from the EGR pipe; and

reusing at least a portion of the backing material as backing material during forming of a subsequent EGR pipe.