Metal working – Method of mechanical manufacture – Heat exchanger or boiler making
Reexamination Certificate
1998-10-29
2001-10-16
Rosenbaum, I. Cuda (Department: 3726)
Metal working
Method of mechanical manufacture
Heat exchanger or boiler making
C165S080300
Reexamination Certificate
active
06301779
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to manufacturing of heat-dissipating devices, and more specifically to a method for fabricating a heat sink having a plurality of nested extended surfaces.
BACKGROUND OF THE INVENTION
Effective extraction of heat produced by electrical devices is important in order to extend the useful life of these devices. Conventional heat sink devices typically utilize an array of extended surfaces, such as fins, integrally formed on a common base and projecting into the ambient fluid surrounding the device. The base is placed in thermally intimate contact with a heat-producing device to provide a conduction path to the fin array. Fluid circulation, through forced or natural convection, around the fin array acts as the heat transfer medium to cool the device to a satisfactory operating temperature.
It is well recognized that various design parameters including fin geometry (such as the number of fins, fin spacing, length and width), material selection, device characteristics, and ambient conditions, among others, influence the heat dissipation performance of the heat sink. In some applications, a plurality of fins arranged with predetermined dimensions, or channel width between adjacent fins gives optimum heat sink performance. Such narrow channel heat sinks are described in a pending United States Patent Application by Azar.
Unfortunately, conventional heat sinks are often expensive and difficult to fabricate, particularly in those cases where high heat dissipation performance is required and a plurality of long fins in a close packed array is used in the heat sink design. Known heat sink manufacturing techniques including casting and machining are often ill-suited to produce such high performance heat sinks in a cost effective manner. More specifically, difficulties are common in completely filling the deep cavities necessitated by long fin designs during the casting process. Moreover, the draft angle imposed on the fin geometry to produce acceptable cast parts is often incompatible with narrow channel heat sink designs. Machining, likewise, has limitations in regard to both producing long fin lengths and narrow channel spacing. Lengthy production times, and inefficient material usage also lead to high costs of parts for many machined heat sink designs. More importantly, conventional casting and machining techniques are sometimes incapable of producing the desired heat sink design at any cost.
Fabricated heat sinks may be advantageously employed in applications where other manufacturing techniques are impractical or too costly. Fabricated heat sinks are non-unitary designs in that the base and fin array are manufactured as separate parts, and are then joined to produce the final heat sinks device, using for example, brazing, welding, friction welding, bonding, soldering, and other known techniques. Fabricated heat sinks may be designed to have substantially identical thermal performance as unitary heat sink devices as a result of improvements in both material and fabrication techniques. Any inherent resistance to thermal conduction at the interface between fin field and base of the fabricated heat sink may be both minimized and offset by careful selection of other design parameters. However, while satisfactory in many heat sink applications, including high-performance applications, conventional fabricated heat sinks can be time-consuming to produce as each individual fin needs to be assembled to the base while maintaining often exacting channel spacing.
What is desirable then is a method for fabricating a low-cost heat sink that is suited to a variety of heat-dissipation applications, including high-performance and narrow-channel applications, but is not restricted to a narrow selection of design parameters as is the case with heat sinks produced by conventional manufacturing techniques.
SUMMARY OF THE INVENTION
A novel method for fabricating a heat dissipating device using a stack of nested extended fins is disclosed. In the preferred embodiment of the invention, a plurality of substantially similar fins are produced from thermally conductive and formable sheet stock, for example aluminum or copper, preferably using a set of matched forming dies. Each die in the set produces a fin or fin-pair. In the case of a die producing a fin-pair, the fin-pair appearance is cupped in side elevation in that each fin-pair has at least one flange extending from the base portion of the cup, and the fin-pair is rectangular in plan. The die cavities are substantially identical in geometry, but differ slightly in dimension so that the base portion of the cup-shaped fin-pair produced by each die in the set vary in width. Each die in the set includes a feature for producing a locating lug or dimple, or alternatively a hole, in each fin-pair produced. Features are optionally located within the die to create surface enhancements to the fin-pairs such as vents, vanes, or surface textures which are advantageously utilized in certain heat sink applications. Such surface enhancements, alone, or in various combinations may improve heat sink performance. Such features may be difficult or impossible to produce using traditional manufacturing methods, but may be readily incorporated into a given heat sink design using the method of the present invention.
In a preferred embodiment, the plurality of substantially geometrically-similar, but dimensionally differing fin-pairs are then assembled in a nested stack, in accordance with the invention. Each fin-pair in the stack is substantially identical in geometry but the base portion of each fin is successively smaller in dimension (moving axially from top to bottom of the fin stack) to allow for the nesting and so that edges of successive fins define gaps of predetermined dimension. The dimple allows for registration and fine-alignment and as the nested dimples substantially align themselves as each fin is assembled in the stack. An interference fit between the dimples may be used to secure the assembled stack. Conventional fabrication techniques are optionally used, including bonding, welding, compression, soldering and brazing, to secure the nested fins to each other. Alternatively a through hole may be used to effectuate both location of the nested fins and provide for mechanical fastening.
In a further embodiment of the invention, a plurality of geometrically similar or dissimilar fins are combined to form a heat dissipating device. The individual fins may comprise a plurality of shapes and sizes, and may be stacked in a single fin assembly. As such, each fin may comprise a dimple as a guiding pin for assembly wherein an edge of the fin is adapted for being individually stacked and secured onto the base. Successive individual fins may be smaller, identical or larger depending upon the desired result. Accordingly, this further embodiment provides a novel method to custom design a heat dissipating device to fit a desired need.
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Advanced Thermal Solutions, Inc.
Cuda Rosenbaum I.
Lieberman & Brandsdorfer LLC
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