FIELD

[0001] The present disclosure relates to devices for cooling. In particular, the present disclosure relates to passive heat exchangers.

BACKGROUND

[0002] The cooling of electric components, such as microprocessors, LEDs, IGBT modules, etc., is conventionally based on attaching a heat transfer element to physical and thermally conducting connection to the component. A typical such heat transfer element comprises a heat sink that provides for a large heat dissipation area for dissipating heat away from the component to the ambient. To maximize the effective heat dissipation area, known heat sinks feature a great number of thin fins that extend from a base.

[0003] Heat sinks have been traditionally made by first extruding a preform profile which has a generally flat and elongated prismatic shape. The fins are made by skiving the top layer of the preform profile with a cutting blade in a repetitive fashion to create a large number of very thin fins. The skiving is performed in two stages. In the first stage the cutting blade is driven into the top surface of the preform profile in a small angle, almost along the top surface, to drive the blade into the raw material. With the fin formed, the second stage includes retracting the cutting blade from the preform profile, elevating the blade, and driving the blade against the fin to turn the fin in an approximately 90 degree angle relative to the base.

[0004] Examples of known skiving apparatuses and methods are disclosed in JP 2001326309 A, US 5946190 A, and US 2005/257914 Al.

[0005] There remains, however, a need to further develop efficiency of the operation and manufacturing of heat sinks. SUMMARY OF THE INVENTION

[0006] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to a first aspect of the present disclosure, there is provided a heat sink having a base and at least one fin. The base extends along a first dimension and the at least one fin is connected to the base and extends in a second dimension. The heat sink further includes a plurality of slices that extend from the at least one fin.

[0008] According to a second aspect of the present disclosure, there is provided a skiving apparatus for producing a heat sink. The skiving apparatus features a fixture for securing thereto a preform profile. The preform profile has a base, which extends along a first dimension, and at least one fin, which extends from the base in a second dimension. The fixture is set to engage the base of the preform profile. The skiving apparatus also has a cutting tool with at least one cutting blade featuring a cutting edge. The skiving apparatus has a manipulator manipulating the cutting blade along the second dimension to skive a plurality of slices from the at least one fin of the preform profile so as to extend from the at least one fin.

[0009] According to a third aspect of the present disclosure, there is provided a method for producing a heat sink. In the method a preform profile, which includes a base extending along a major dimension and at least one fin extending from the base in a minor dimension, is provided with by means of an additive manufacturing method. A plurality of carved protrusions is skived off the at least fin to extend there from.

[0010] Certain embodiments may include one or more features selected from the following list:

- the slices extend from the at least one fin in a direction that has a component in a third dimension that is perpendicular in respect to the first dimension and second dimension;

- the direction, in which the slices extend from the at least one fin, also has a component in the second dimension;

- at least some of the slices exhibit a curved shape;

- the at least one fin extends from the base or is connected to the base via one or more intermediate part(s);

- the at least one fin comprises a stem at a proximal end in respect to the base; - the at least one fin comprises a tip at a distal end in respect to the base;

- the cross-section of the tip is smaller than that of the stem;

- the at least one fin has lateral sides observed in a/the third dimension that is perpendicular in respect to the first dimension or second dimension or both the first dimension and second dimension;

- at least some of the slices are provided to the lateral sides of the at least one fin;

- the heat sink comprises a plurality of such fins;

- the lateral end of the at least fin forms an angle in respect to the base that is less than 90 degrees;

- the lateral end of the at least fin forms an angle in respect to the base that is 87 degrees or less;

- the base, the fins, and the slices are integral in respect to one another;

- the cutting tool comprises two cutting blades arranged in a mutually opposing fashion;

- the pair of cutting blades is configured to engage from the at least one fin of the preform profile from two lateral sides;

- the second dimension is perpendicular in respect to the first dimension;

- the preform profile is an extruded piece;

- during said skiving a cutting tool is pressed against the at least one fin of the preform profile along the second dimension;

- transition of the fin of the preform profile between the stem and tip includes a staggered ridge or several staggered ridges spaced apart from one another along the second dimension,

- during said skiving a cutting tool is pressed against the fin at the staggered ridge.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the following certain exemplary embodiments are described with reference to the accompanying drawings, in which:

FIGURE 1 illustrates a top perspective view of a preform profile for producing a heat sink according to one embodiment featuring a planar base; FIGURE 2 illustrates a top perspective view of a semi-finished preform profile during production of a heat sink according to another embodiment featuring a planar base;

FIGURE 3 illustrates a bottom perspective view of a preform profile being skived during production of a heat sink according to yet another embodiment featuring a planar base;

FIGURE 4 illustrates a top perspective view of a finished version of the heat sink according to FIGURE 3;

FIGURE 5A illustrates a top perspective view of a preform profile for producing a heat sink according to one embodiment featuring a closed base;

FIGURE 5B illustrates a top perspective view of a heat sink according to another embodiment featuring a closed base;

FIGURE 6 illustrates a side elevation view of a heat sink according to an embodiment with an intermediate member between the base end the fins, and

FIGURE 7 illustrates a perspective view of a skiving apparatus for producing a heat sink according to an embodiment.

EMBODIMENTS

[0012] In the present context the expression ‘slice’ refers to a piece cut out of a fin that remains attached and is relatively small compared to or smaller than the fin.

[0013] The present proposition involves a solution for maximizing the surface area of an extruded metal heat sink to the ambient. The heat distribution inside the heat sink may can be further optimized with profile geometry the process parameter choices. The novel proposition is particularly suitable for mass production through exploitation of effective manufacturing techniques. First, however, let us consider examples of a finished or a semi-finished heat sink.

[0014] FIGURE 4 shows an exemplary embodiment of a semi-finished heat sink 100b featuring a planar base 110. The base 110 has an extension in a first dimension Z in which the preform profile for forming the heat sink has been extruded. In other words, the first dimension Z is the dimension in which material is added during additive manufacturing of the preform profile for producing the heat sink 110. Exemplary materials suitable for additive manufacturing technologies, such as casting, extrusion, injection moulding, etc., include aluminium, aluminium alloys, copper, etc. In the shown example the base 110 is planar which means that the base 110 also has an extension in another dimension X which is perpendicular to the first dimension Z. In the following that other dimension X is referred to as the third dimension.

[0015] As will also become apparent from FIGURE 4 is that the heat sink 100b further includes a plurality of fins 120 that extend from the base 110. While a heat sink 100b with only a single fin 120 is possible, it is preferable that the heat sink 100b includes several fins 120 so as to maximize the effective dissipation area. In the shown example the fins 120 extend in a second dimension Y that is perpendicular to the first dimension Z. The exemplary embodiment includes five fins 120 that extend to one side of the base 110. Naturally, the heat sink 100b may include fewer or more fins 120 that may be arranged on one side, as shown, or both sides of the base 110 (not illustrated in the FIGURES). The fins 120 have an extension in the first dimension Z due to the simultaneous manufacturing with the base 110. The fins 120 are therefore an integral part of the heat sink 100. For the sake of completeness it may be noted that integral parts cannot be separated from each other without breaking the structure as opposed to parts that are affixed to each other through detachable affixers. The fins 120 are spaced apart in the third dimension X. The fins 120 feature a relatively thick stem and narrow tip. In the illustrated example the fins 120 have a tapering shape. The tapering shape is beneficial for managing the heat exchange between the heat sink 100b and the environment in that the heat flux is greater at points of the heat sink 100b that have relatively plenty of material and smaller at points with relatively little material.

[0016] FIGURE 4 further shows slices 130 that have been skived from the fins 120. In the illustrated example each fin 120 has slices 130 provided on both lateral sides. Naturally, the illustrated embodiment may be varied by providing slices 130 on only some of the fins, on only either side of the fins, or both. The slices 130 are preferably small cutouts that have been skived off the lateral surface of the fins 120 such that the slices 130 are still connected to the fin 120. Due to the manufacturing method, the slices 130 may have a curved shape. More particularly, the slices 130 extend from the fin 120 in a direction that has a component in the second dimension Y and in the third dimension X. The plurality of slices 130 may be arranged in a matrix- like formation in that the slices 130 are on top of and next to each other. In the example of FIGURE 4 there is a nine by eight formation on both sides of each fin 120. The tapering shape of the fin 120 promotes such layered skiving of slices 130.

[0017] While FIGURE 4 may represent a semi-finished finished heat sink 100b, it is to be noted that when fully skived, the heat sink may form a module which is to form a part of a larger heat sink. Indeed, it is possible to increase the dissipation area of the heat sink by attaching several heat sink modules, such as that shown in FIGURE 4, to each other. The heat sink modules may be attached by joining the bases 110 together. Suitable methods for performing the joint include welding, particularly laser welding and friction stir welding. The heat sink 100 may be elongated in the first dimension Z or third dimension X or both in the first and third dimension Z, X. The attachment may be performed to a preform profile 110a, i.e. before skiving, to a semi-finished heat sink 100b, i.e. during skiving, or to a finished heat sink 100, i.e. after skiving. Also, it is possible to attachment heat sink modules with other variants described here after into an enlarged heat sink. In other words, the embodiments described herein may also be considered as mere modules for making up a heat sink.

[0018] FIGURE 5B shows a variant of the principle shown in connection with FIGURE 4. The exemplary embodiment of FIGURE 5B includes a base 110 that is non- planar. The base 110 has a closed shape in that it forms a perimeter. Another way of describing the base 110 would be that it is radially omni-directional in respect to the first dimension Z. The base 110 may include a passage 111 through the heat sink 100 that may be used for accepting a coolant, heat exchange fluid, or the cooled component. More particularly, the passage 111 may act as a heat pipe for performing a thermosiphon cycle with a heat transfer fluid contained therein. Alternatively, the passage 111 may accept a separate heat pipe element, such as a traditional copper heat pipe. The heat sink 100 of FIGURE 5B features six fins 120 that extend radially from the cylindrical base 110. The fins 120 therefore each extend in a dimension which is perpendicular to the first dimension Z. Each fin 120 has a large number of slices 130 skived off both lateral sides to create a relatively large effective dissipation area for the heat sink 100. The slices 130 have been carved out in a layered formation with slices 130 protruding in four superposed layers each including eight adjacent slices. [0019] A variant to the exemplary shapes shown in FIGURES 1 to 5 is foreseen, wherein the fins do not extend directly from the base but through one or more intermediate members. FIGURE 6 shows a sketch of such an example, wherein the base takes a planar shape, although curved, cylindrical, or other non-planar shapes are also foreseen. Connected to the base is an intermediate member 140, which extends from the base 110, e.g. in a right angle. The fins 120, in turn, extend from the intermediate member 140, e.g. in a right angle. The fins 120 are spaced apart along the intermediate member 140 as layers which may or may not extend to both directions from the sides of the intermediate member 140. Such a configuration would resemble a tree in cross-section taken. FIGURE 6 shows the cross-section taken along the direction in which the preform profile is manufactured with an additive manufacturing method. FIGURE 6 shows a semi-finished heat sink 100b in an X-Y plane, wherein the first dimension extends along the viewing direction. The exemplary semi-finished heat sink 100b features twelve fins 120, one of which is nonskived for illustrative purposes. The finished fins 120 have been skived similarly to those of FIGURES 1 to 5 with slices 130 extending from the fins 120. The skiving is performed along the third dimension X, i.e. towards the intermediate member 140. The tip 122 of the fins 120 preferably include a split 124, whereby the final slices at the tip 122 of the fin 120 may be made by inserting a forming tool into the split thus deforming the split into two slices. The split 124 may be produced with a negative form in an extrusion machine.

[0020] Next, let us consider the manufacturing of heat sink 100 starting with the manufacturing of the preform profile. One example is shown in FIGURE 1 which shows a preform profile 100a including a planar base 110 and six tapering fins 120. The preform profile 100a shown in FIGURE 1 is produced by extruding the base 110 and fins 120 in a single stage. Extrusion in the first dimension Z enables the base 110 to extend in the first and third dimension Z, X and the fins 120 to protrude in the second dimension Y. The extruded profile is then cut into shorter pieces. FIGURE 1 shows one piece cut transversally in respect to the extrusion direction, i.e. first dimension Z.

[0021] FIGURE 2 shows a semi-finished heat sink 100b that is a staggered variant of the preform profile 100a of FIGURE 1. The semi-finished heat sink 100b includes a base 110 and four fins 120, one of which has already been provided with slices 130 with the other three being untreated. The embodiment of FIGURE 2 features staggered fins 120, i.e. fins 120 that have ridges 123 provided to the lateral sides of the fins 120 that extend between a stem 121 and a tip 122. The stem 121 is relatively thick and tip 122 relatively thin. In other words, the stem 121 has a larger cross-section than that of the tip 122 when observed in the third dimension X. The tapering cross-sectional shape of the fin 120 is not continuous in that the lateral sides of the fins 120 include three ridges 123 as shoulders. In other words transition of the fin 120 of the preform profile 100a between the stem 121 and tip 122 includes at least one, preferably several staggered ridges 123 spaced apart from one another along the second dimension Y. To offset the slices 130 of adjacent fins 120 from each other, the respective ridges 123 of adjacent fins 120 may be offset from each other along the second dimension Y thus facilitating manufacturing.

[0022] The cross-sectional shape of the fin 120 in respect of the first dimension Z is inconsistent in that it has a relatively thick stem 121 and narrow tip 122. While the lateral sides of the fins 120 may be flat or staggered, there is an angle a formed between the side of the fin 120 and the base 110. The angle a is less than 90 degrees to achieve the tapering form. According to a particularly useful embodiment, the angle a is 87 degrees. The angle serves the purpose of facilitating effective skiving.

[0023] FIGURE 3 shows a depiction of the skiving process in which the fin 120 is skived with a cutting tool 210. The cutting tool 210 has a cutting blade 211 that features a cutting edge 212 for carving into the side of the fin 120. The cutting tool 210 could feature a pair of such cutting tools for one or more fins. FIGURE 3 shows only one cutting tool 210 on one side of one fin for the sake of simplicity. FIGURE 3 shows how the cutting blade 211 is driven against the lateral side of the fin 120 along the second dimension Y, i.e. transversally in respect to first dimension Z, in which the base 110 is manufactured through an additive manufacturing process. The cutting edge 212 may exhibit various different shapes to create respective slice shapes. In the illustrated example the cutting edge 212 has minute teeth protruding out from the cutting blade 211 to achieve simple curved strips as slices 130. The cutting edge 212 includes nine such teeth to produce nine respective slices 130. Because the lateral side of the fin 120 is slightly slanted in respect to the cutting direction, the slices 130 will become thin thus maximizing the surface area added in respect to a fin 120 without slices. During the skiving process, the slices 130 are skived a layer at a time. FIGURE 3 shows the cutting blade 211 retracted after the skiving of the first, i.e. bottom, layer of slices 130 ready to be driven into the lateral side of the fin 120 for the production of the second layer. The successive skiving efforts are repeated until the fin 120 is provided with the desired number of slices 130. [0024] FIGURE 7 shows an exemplary skiving apparatus 200 for performing the skiving step. The embodiment shown in FIGURE 7 involves a skiving station for skiving a single preform profile 100a at a time but the skiving apparatus could include several parallel skiving stations for skiving several preform profiles and/or several fins at a time. The skiving apparatus 200 features a frame 220 with a bottom base 221 for supporting the preform profile 100a and a top base 222 for supporting the cutting tool 210. The bottom base 221 includes a fixture 222, such as a vice or a comparable contraption, for engaging the base 110 holding the preform profile 100a in place during skiving. The bottom base 221 may also include a manipulator for moving the preform profile 100a in the first dimension Z, second dimension Y, and/or third dimension X to correctly position the preform profile 100a or to move an un- skived fin 120 below the cutting tool 210. The top base 223 is connected to the cutting tool 210 through an manipulator 224, which may be a hydraulic or pneumatic actuator, such as a hydraulic or pneumatic cylinder, for example. The manipulator 224 is constructed to be operated in the skiving direction, i.e. in the second dimension Y. The cutting blades 211 of the cutting tool 210 extend from a blade frame 213 which connects the cutting blades 211 to each other at a predetermined distance from one another. The blade frame 213 includes tracks 214 for guiding the cutting blades 211 between a relatively distal mutual position for skiving the slices 130 at the stem 121 of the fin 120 and a relatively proximal mutual position, as shown in FIGURE 7, for skiving the slices 130 at the tip 122 of the fin 120. The tracks 214 therefore extend in the first dimension X to provide such mutual movement of the opposing cutting blades 211. The mechanical interface between the cutting blades 211 blade frame 213 preferably includes a biasing member (not illustrated in the FIGURES), such as a spring, for urging the cutting blades 211 towards the proximal mutual position. Additionally or alternatively, the skiving apparatus 200 may include a transversal actuator (not illustrated in the FIGURES) for guiding the cutting blades 211 into the required mutual position.

[0025] The process of manufacturing the heat sink 100 is simple and effective. First, the preform profile 100a is manufactured by producing the raw profile with an additive manufacturing technique. The base 110 and the fins 120 are produced in the same manufacturing step as mutually integral parts meaning that they cannot be separated without destructive action. The same applies to the slices 130 which are integral to the fins 120. It therefore follows that the base 110, fins 120, and slices 130 are inseparable without compromising the integrity of the material of the heat sink 100. The profile may be extruded, for example, along the first dimension. After an optional finishing machining for removing any excess flash from the workpiece. Next, the profile may be cut transversally into a desired length. With the preform profile 100a ready, the slices 130 are skived into the fins 120. A cutting tool 210 comprising one or more cutting blades 211 is/are against the lateral side(s) of the fin 120 in a direction which substantially perpendicular to the base 110. This approach is the same for preform profiles 100a with planar bases 110 (FIGURES 1 to 4) and non-planar bases (FIGURES 5A and 5B). Naturally, the angle of attack of the cutting blade 211 need not be exactly 90 degrees in respect to the base 110. Relatively small deviations from perpendicularity are possible, particularly in the range of between more than 0 and up to 5 degrees, such as between more than 0 and up to 1 degree or less. The cutting tool 210 preferably includes at least one, more preferably several pairs of cutting blades 211 for carving two sides of the same fin 120 or one side of several fins 120 at once. The skiving is performed to a depth which does not remove the slice 130 off the fin 120 but rather leaves the slice 130 onto the fin 120 at the bottom. If the fin 120 is staggered, the cutting blade 212 is driven into the fin 120 at the ridge 123. The repetitive skiving motions are repeated until the semi-finished work piece 100b includes the desired number of slices 130, whereby the finished heat sink 100 is ready for further treatment, assembly, or installation.

[0026] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0027] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0028] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0029] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0030] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0031] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality. REFERENCE SIGNS LIST

CITATION LIST

JP 2001326309 A

US 5946190 A US 2005/257914 Al