WO2017163053A1

WO2017163053A1 - Multifunctional structure of an additively manufactured article

Info

Publication number: WO2017163053A1
Application number: PCT/GB2017/050790
Authority: WO
Inventors: Benjamin Farmer; Simon Jones; George Hopkins
Original assignee: Hieta Technologies Limited
Priority date: 2016-03-23
Filing date: 2017-03-21
Publication date: 2017-09-28
Also published as: GB201604906D0; GB2549069A

Abstract

An article (2) formed by additive manufacture includes a primary structure (6) which requires mechanical support during layer deposition (e.g. due to an overhang) which is provided via a secondary structure (16). The secondary structure (16) provides an additional function different from mechanical support following the layer deposition, such as defining a conduit for directing flow of an abrasive media for polishing or serving as providing an additional heat exchanger fin.

Description

MULTIFUNCTIONAL STRUCTURE OF AN ADDITIVELY MANUFACTURED ARTICLE

This disclosure relates to the field of additive manufacture. More particularly, this disclosure relates to the provision of structures giving mechanical support during layer deposition as part of additive manufacture of an article.

It is known to manufacture articles using additive manufacture whereby layer deposition is used to build up an article on a layer-by-layer basis. A common feature of such additive manufacture processes is the need to provide support structures to give required mechanical support to a further structure during the layer deposition process. As an example, it may be desired to manufacture a structure within an article having a large overhang angle and in order to achieve this it may be necessary to provide a support structure that is formed beneath the overhanging structure to provide support required such that the desired structure may be properly formed. The support structure is typically then removed at a further processing stage subsequent to the layer deposition, e.g. the support structure may be machined away.

At least some embodiments of the disclosure provide an article formed using additive manufacture comprising:

a primary structure; and

a secondary structure connected to said primary structure to serve as at least one of: a required mechanical support to said primary structure during layer deposition of said additive manufacture; and a heat sink to said primary structure during layer deposition of said additive manufacture; wherein

said secondary structure provides an additional function different from mechanical support following said layer deposition. The present technique recognises that while a secondary structure may be formed during layer deposition to provide required mechanical support to a primary structure, the costs associated with the provision of that secondary structure (e.g. material cost, manufacturing time cost, etc.) may be at least partially recovered when that secondary structure is formed to have an additional function in the article following the layer deposition and different from the mechanical support which it is required to provide to the primary structure during the layer deposition.

The required mechanical support provided by the secondary structure to the primary structure may serve to resist distortion of the primary structure due to stress created in the primary structure during the layer deposition process and remaining in the primary structure after completion of the layer deposition process. Layered deposition typically involves heating and cooling of material with associated expansion and contraction of that material. This results in the creation of stress within the primary structure 5 during the deposition and melting of each subsequent to the layer deposition step. As the layer deposition of further layers continues, any residual stress within the primary structure can build up and can distort the primary structure in an undesired manner. The secondary s structure may be provided to support the primary structure (e.g. to brace the primary structure) against such residual stress created during after the layer deposition. Typically any the residual stress may subsequently be relieved, such as 10 by heating the article within an oven to anneal the article, such that the support given by the secondary structure is no longer necessary. When such post-processing operations have taken place, then the secondary support structure could be removed. However, the cost in material and time in providing that support structure has already been incurred and there is additional cost associated with removing the support structure. Accordingly, in accordance with the present 15 technique, the secondary structure is formed so as to provide an additional function within the article that is different from the mechanical support function it provides to the primary structure.

One example of an additional function which may be provided by the secondary structure is to serve as at least part of a boundary wall of a conduit to direct an abrasive media to smooth a surface of the article. The fatigue strength of an article may be increased by polishing the surface of an article to reduce the peak surface roughness. Within articles having internal cavities, or concave surfaces, one way of performing such polishing is to flow an abrasive media past the surface to be polished. The abrasive media requires containment against the surface to be polished and this may be provided by a conduit formed in at least part by the secondary structure. Thus, the secondary structure which provides mechanical support during their deposition may be reused to provide at least part of a conduit for polishing the article subsequent to the layer deposition.

In the case of an article having an internal cavity, such an internal cavity can be difficult to polish in a way which improves the strength of the article. Furthermore, the internal cavity may often require mechanical support during its formation by deposition as it involves walls with large overhang angles. In this context, the secondary structure may be used in a form in which a conduit provided by the secondary structure for polishing is shaped to direct abrasive media to smooth an internal surface of the cavity as part of a processing step following layer deposition.

The conduit may be shaped to follow a path which substantially completely fills the cavity such that all of the internal surfaces of the cavity are polished by the flow of the abrasive media.

Whilst it will be appreciated that the path followed by the conduit could have a wide variety of different forms. Some forms of conduit path having particular utility are ones in which the conduit comprises a single turn substantially filling the cavity and in which the conduit comprises a stack of interconnected spirals.

It may be desired to remove the secondary structure itself as part of the polishing process performed by the abrasive media. Such removal of the secondary structure may be facilitated by providing the secondary structure with a thickness that varies along the length of the conduit and/or a susceptibility to abrasion by the abrasive media that varies along the length of the conduit. In this way, the breakdown of the conduit by the abrasive media may be controlled to occur at a predetermined point where the thickness of the conduit is least, or where the susceptibility to abrasion is highest, such that the subsequent flow of the abrasive media is changed in a manner to further remove other portions of the conduit. The thickness of the conduit and the susceptibility to abrasion of the conduit may be varied by varying control parameters used in the layer deposition steps forming the conduit.

In some embodiments there may be portions of the primary structure which are known to be particularly susceptible to stress and accordingly where it is desirable to ensure thorough polishing of the surface of the primary structure in those areas. In order to help achieve this, the conduit provided by the secondary structure may be formed to have a cross-sectional area that varies along the length of the conduit with that cross-sectional area being lower proximal to areas of high stress within the primary structure. Lowering the cross-sectional area increases the flow speed of the abrasive media through the conduit in such regions in a manner which increases the polishing effect in those regions such that areas of high stress within the primary structure are more effectively polished.

In order that the secondary structure may be preferentially removed by the abrasive material, it may be formed to have a higher susceptibility to abrasion than the primary structure e.g. by varying the control parameters, such as the heating applied to a powder being fused when a laser scans across the powder to be fused.

An example of an article with which the present techniques may be advantageously used is a valve having an internal cavity arranged to receive a high thermal conductivity material (e.g. sodium metal) to conduct heat away from the valve during use. Such valves typically operate under high stress condition and accordingly it is desirable that the internal cavity to hold the high thermal conductivity material should be polished. This is normally difficult to achieve.

One particular form of valve in which the present techniques may be used is a poppet valve in which the cavity is within a head of the poppet valve and a high thermal conductivity material is, in further processing steps, provided within that cavity in order to conduct heat away from the head of the poppet valve during use of that poppet valve (e.g. such as an exhaust valve within an internal combustion engine). In the case of the second structure providing at least part of the boundary wall of a conduit with another portion of that boundary wall being provided by the primary structure (such that it may be exposed to the abrasive media and polished), it may be desirable that the thickness of the secondary structure is less than the thickness of the primary structure such that the secondary structure may be removed by a degree of abrasion which merely polishes the primary structure.

Another example of an additional function different from mechanical support following layer deposition which may be provided by the secondary structure is that when the article being manufactured is a heat exchanger then the additional function provided by the secondary structure may be that of a heat transfer surface between fluids.

In some example embodiments, the primary structure may be a primary heat exchanger fin and the secondary structure may be a secondary heat exchanger fin integrally formed with and extending from the primary heat exchanger fin. Thus, the secondary heat exchanger fin may serve to provide required mechanical support to the primary heat exchanger fin (to resist distortion of that primary heat exchanger fin due to stress caused by the layer deposition process) as well as to provide a further heat exchange surface to improve the heat exchange performance of the heat exchanger subsequent to manufacture.

More particularly, the use of the secondary heat exchanger fin to provide distortion resistance to the primary heater exchanger fin is enhanced when in transverse cross section the primary heat exchanger fin has a lower second moment of area than a combination of the primary heat exchanger fin and the secondary head exchanger fin. Furthermore, the second moment of area of the primary head exchanger fin alone may be insufficient to resist distortion due to stress created during the layering process, whereas the second moment of area of the combination of the primary heat exchanger fin and the secondary heat exchanger fin is sufficient to resist such distortion.

The primary heat exchanger fin and the secondary heat exchanger fin may together form a bifurcated heat exchanger fin, such bifurcation may be achieved in some example embodiments by arranging that the secondary heat exchanger fin has a lateral portion connected to a middle portion of the primary heat exchanger fin and extending away from a side surface of the primary heat exchanger fin. Furthermore, the secondary heat exchanger fin may also include a longitudinal portion connected to an end of the lateral portion distal from the primary heat exchanger fin and extending substantially parallel to the primary heat exchanger fin. In some embodiments the primary heat exchanger fin may have a root connected to a conduit wall of a fluid conduit for containing a fluid with which heat is being exchanged. Such a conduit wall may be an inner wall of a fluid conduit and the primary heat exchanger fin may extend inwardly within that fluid.

Within such embodiments, fluid flow is facilitated when a longitudinal access of the primary heat exchanger fin is parallel with a longitudinal access of the fluid conduit.

At least some embodiments of the disclosure provide a method of manufacturing an article using additive manufacture comprising:

forming a primary structure with layer deposition;

providing at least one of: required mechanical support to said primary structure during said layer deposition with a secondary structure connected to said primary structure and also formed during said layer deposition; and a heat sink to said primary structure during layer deposition of said additive manufacture with said secondary structure connected to said primary structure and also formed during said layer deposition; and

retaining said secondary structure within said article to provide an additional function different from mechanical support following said layer deposition.

It will further be appreciated that in the context of additive manufacture, an article of commerce may be a computer readable storage media storing in non-transitory form data for controlling an additive manufacture machine to form an article having a particular design. Thus, an article may be sold in its physical form and it may also be sold in the form of data controlling an additive manufacturing machine to form such an article.

Example embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Figures 1A, IB and 1C schematically illustrate cross-sectional views through an example article during manufacture of that article;

Figures 2A and 2B schematically illustrate cross-sectional views through a further example embodiment of an article during manufacture;

Figures 3A, 3B and 3C schematically illustrate variation in a conduit wall;

Figure 4 schematically illustrates a cross sectional view through a heat exchanger having both primary exchanger fins and secondary heat exchanger fins;

Figure 5 schematically illustrates a cross sectional view through a bifurcated heat exchanger fin;

Figures 6A and 6B schematically illustrate cross sectional views of further example embodiments of bifurcated heat exchanger fins; and

Figure 7 schematically illustrates a system for additive manufacture of articles. Figure 1A schematically illustrates a cross sectional view through a poppet valve 2 comprising a valve stem 4 and a valve head 6. The valve head 6 includes an internal cavity 8. Subsequent to the manufacturing processes illustrated in Figures 1A, IB and 1C, the internal cavity 8 is filled with a high thermal conductivity material, such as metallic sodium, to assist in heat transfer away from the valve head 6 (through both conduction and convection). The poppet valve 2 may be, for example, an exhaust valve used in an internal combustion engine.

The valve stem 4 is formed with a central dividing wall 10 which serves to define an inlet 12 and an outlet 14. The valve head 6 has an overhanging wall above the cavity 8 which requires support during layer deposition of the valve head 6 in order to resist distortion of the valve head 6. Furthermore, the overhanging wall requires a structure to serve as a heat sink during the manufacture of that overhanging wall. The valve stem 4 may be formed by additive manufacture, or may alternatively be formed by other techniques and then friction welded onto the valve head 6.

The shaded portion of the valve head 6 constitutes a primary structure and is formed to have a low susceptibility to abrasion by an abrasive media as will be subsequently described. This low susceptibility to abrasion may be achieved by appropriate selection of the operating parameters of an additive manufacturing device used to manufacture the primary structure formed by the valve head 6, e.g. laser power settings used when forming those portions of the layers which correspond to the valve head 6.

Within the cavity 8 is formed a secondary structure 16 which has the form of conduit walls defining a conduit with a flow path corresponding to a stack of interconnected spirals. The inlet 12 through the valve stem 4 connects to a radially outermost loop within the spiral furthest from the valve stem 4. The outlet 14 through the valve stem 4 connects to a radially innermost loop of the spiral closest to the valve stem 4. The stack of spirals substantially completely fill the cavity 8 and serve to provide required mechanical support to the primary structure in the form of the valve head 6 during the layer deposition of the additive manufacturing process. The stack of spirals also act as a heat sink to the primary structure during the layer deposition of the additive manufacturing process.

Subsequent to the layer deposition, an abrasive media is pumped through the inlet 12 and around the stack of spirals comprising the secondary structure 16 before exiting via the outlet 14. The abrasive media polishes the inward facing interior walls of the cavity 8 which form part of the boundary wall of the outermost turns of the stack spiral in a manner which reduces the peak surface roughness of those inward facing walls of the cavity within the valve head 6 so as to increase the strength of the valve head 6. Furthermore, the secondary structure 16 is formed to have a relatively higher susceptibility to abrasion by the abrasive media compared with the primary structure comprising the valve head 6 and accordingly the walls defining the stack of spirals are also abraded by the abrasive media pumped through the article 2 such that the secondary structure 16 may be substantially completely removed from within the article 2 by the passage of the abrasive media. The susceptibility of the secondary structure 16 to abrasion may be enhanced by an appropriate selection of the manufacturing process parameters during the deposition of those portions of layers which correspond to the secondary structure 16, e.g. the heating applied to fuse metal powder material to form the secondary structure 16.

It will be noted that the secondary structure 16 in the form of the stacked spiral conduits serves the function during the deposition of the layers of providing required mechanical support to the primary structure in the form of the valve head 6 to resist distortion of the valve head 6 due to stresses crated during layer deposition. Subsequent to layer deposition the secondary structure in the form of the conduits provides the function of constraining and directing the abrasive media such that the internal surface of the valve head 6 bounding the internal cavity 8 is polished in a manner which reduces the peak roughness (both average Ra and peak Rz) of that surface and thereby increases the strength of the valve head 6.

Figure IB schematically illustrates a cross-section through the poppet valve 2 along the direction A- A of Figure 1A. In particular, Figure IB schematically illustrates a spiral furthest from the valve stem 4 within the stack of spirals of the conduit comprising the secondary structure 16. The abrasive media flows within the outermost spiral towards the innermost spiral normal to the section of Figure IB. When the abrasive media reaches the centre of the spiral, it passes in a direction toward the valve stem 4 where it enters the centre of the overlying spiral and then circulates around that overlying spiral to the outer edge thereof. The individual turns of the stacked spirals are offset relative to each other by a distance substantially corresponding to a radius of the conduit in a manner which reduces the conduit wall thickness. Where the spirals abut the inner wall of the valve head 6, the wall of the valve head 6 provides part of the boundary wall of the conduit and accordingly is polished by the passage of the abrasive media through the conduit. Figure 1C schematically illustrates the poppet valve following the passage of the abrasive media through the conduit for a duration which polishes the bounding wall of the cavity 8 within the valve head 6. Furthermore, the abrasive media has abraded completely the secondary structure 16 such that this is broken down into fragments which pass out of the article 2 carried by the abrasive media. The wall defining the barrier between the inlet 12 and the outlet 14 within the valve step 4 may be removed by drilling as illustrated in Figure 1C. In the example of Figures 1A, IB and 1C, the conduit is shaped to follow a path which fills the cavity 8 by the provision of a stack of interconnected spirals. Figures 2A and 2B schematically illustrates a different example embodiment in which the conduit comprises a single turn substantially filling the cavity 8. In this example, the secondary structure comprises a radially extending wall 18 which extends within the cavity 8 from a radially outward position within the cavity 8 towards the centre of the cavity 8 and upwardly from a wall (floor) of the cavity 8 furthest from the valve step 4 up to a roof of the cavity 8 proximal to the valve step 4. The wall 18 provides required mechanical support to the overhanging portion of the valve head 6 above the cavity 8 during layer deposition. Further mechanical supports 20 are provided in the cavity 8 by the layer deposition process to brace between the floor of the cavity 8 and the roof of the cavity 8.

Subsequent to deposition, abrasive media is pumped through an inlet 12 into the cavity 8. A conduit 22 coupled to the inlet 12 directs the abrasive media towards a radially outward position within the cavity 8 towards the floor of the cavity 8. The media is forced by the presence of the wall 18 (the secondary structure) to follow a roughly circular path within the cavity 8 until it reaches an outlet conduit 24 which links to the outlet 14. The abrasive media accordingly polishes the inner surface of the valve head 6 bounding the cavity in a manner which reduces the peak roughness of that surface and increases the strength of the valve head 6. The additional supports 20 may also be eroded by the abrasive material and removed with the abrasive material.

Figure 3A schematically illustrates a conduit 26 having a conduit wall 28 which decreases in wall thickness along the length of the conduit 26 in the direction of the abrasive media flow. The consequence of this is that abrasion of the conduit wall 28 will break through the thinnest portion first as the wall thickness is least in this region. Further passage of the abrasive media will remove the wall 28 completely in a manner in which the wall is consumed in a direction propagating back towards the source of the abrasive media. Figure 3B schematically illustrates a conduit 26 with a conduit wall 28 in which the susceptibility to abrasion by the abrasive media decreases in the direction flow the abrasive media. Accordingly, the portion of the wall 28 relatively downstream in this flow will be consumed first. The difference in susceptibility to abrasion may be achieved, for example, by varying operating parameters during layer deposition, such as a laser scan strategy and/or deposited metal density.

Figure 3C schematically illustrates a conduit having a boundary wall which is partially provided by the primary structure 30. The cross-sectional area of the conduit is varied in the direction of flow of the abrasive media, such that it has a lower cross-sectional area resulting in faster flow of the abrasive media in a region proximal to a high stress area within the primary structure 30. Accordingly, this high stress area within the primary structure 30 is subject to a greater degree of polishing by the passage of the abrasive media which results in a lower peak surface roughness and improved strength of the primary structure 30 in that high stress area.

Figure 4 schematically illustrates another example article in which a secondary structure may be provided to give required mechanical support to a primary structure during layer deposition and then to serve an additional different function subsequent to layer deposition. In this example, the article 2 comprises a heat exchanger having an inner wall 32 and an outer wall 34. A first fluid flows in one direction within the inner wall 32. A second fluid flows in an opposite direction (counter flow) in the cavity between the outer wall 34 and the inner wall 32. Accordingly, heat exchange may take place between these two fluids. This heat exchange is enhanced by the provision of longitudinally extending fins within the fluid flow passage defined by the inner wall 32 i.e. length parallel to the fluid flow. Figure 4 schematically illustrates some of these fin.

The heat exchanger of Figure 4 is formed by additive manufacture using layer deposition in which the cross-section illustrated in Figure 4 corresponds to one layer that is deposited. The heat exchanger thus comprises an outer cylindrical wall 34 surrounding an inner cylindrical wall 32 with heat exchange enhancing fins integrally formed with and extending radially inwardly from the inner wall 32.

Figure 5 schematically illustrates one of the heat exchanging enhancing fins of Figure 4 in more detail. In particular, the heat exchanging fins are composed of a primary heat exchanger fin 36 and a secondary heat exchanger fin 38 formed of a lateral portion 40 extending from and integrally formed with a middle portion of the primary heat exchanger fin and connected at its distal end from the primary heat exchanger fin 36 to a longitudinal portion 42. The secondary heat exchanger fin 38 serves the function during layered deposition of providing required mechanical support to the primary head exchanger fin 36 which would otherwise distort due to stress introduced during manufacturing. In particular, the second moment of area (transverse to the fin as illustrated) of the primary heat exchanger fin 36 is insufficient to resist such stresses, whereas the combination of the primary heat exchanger fin 36 and the second heat exchanger fin 38 has a second moment of area which is sufficient to resist such stresses and prevent distortion. Subsequent to manufacture, the inner wall 32 comprises a primary heat exchange surface, the primary heat exchanger fin 36 provides a secondary heat exchange surface. The secondary head exchanger fin 38 provides a ternary heat exchange surface. Thus, the secondary heat exchanger fin 38 provides required mechanical support during layer deposition and serves as a ternary heat exchange surface subsequent to layer deposition. The heat exchanger fins 36, 38 illustrated in Figure 5 together form a bifurcated heat exchanger fin. Figures 6A and 6B illustrates further example embodiments comprising a primary structure 44 and a secondary structure 46 with the secondary structure 46 increasing a second moment of area of the combination to a degree whereby stresses can be resisted and distortion avoided. Furthermore, the secondary structure 46 serves as an additional heat exchanging surface during subsequent use of the heat exchanger.

Figure 7 schematically illustrates additive manufacture. In this example, laser fused metal powder 48 is used to form an article 2. The article 2 is formed layer-by-layer upon a lowering a powder bed 50 on top of which thin layers of metal power to be fused are spread by a powder spreader 52 prior to being melted (fused) via a scanning laser beam provided from a laser 54. The scanning of the laser beam via the laser 54, and the lowering of the bed 50, are computer controlled by a control computer 56. The control computer 56 is in turn controlled by a computer program (e.g. computer data defining the article 2 to be manufactured). This article defining data is stored upon a computer readable non-transitory media 58. Figure 7 illustrates one example of a machine which may be used to perform additive manufacture. Various other machines and additive manufacturing processes are also suitable for use in accordance with the present techniques whereby an article is formed with a primary structure requiring mechanical support during layer deposition that is provided by a secondary structure which then goes on to provide an additional function different from mechanical support following the layer deposition. This additional function may be an additional function employed during subsequent manufacturing steps (e.g. a conduit for directing an abrasive media for polishing) or during subsequent use of the article (e.g. an additional heat exchanger fin).

Claims

1. An article formed using additive manufacture comprising:

a primary structure; and

said secondary structure provides an additional function different from mechanical support following said layer deposition.

2. An article as claimed in claim 1 , wherein said required mechanical support supports said primary structure against distortion caused by stress in said primary structure created during said layer deposition.

3. An article as claimed in any one of claims 1 and 2, wherein said additional function is to serve as at least part of a boundary wall of a conduit to direct an abrasive media to smooth a surface of said article.

4. An article as claimed in claim 3, wherein said article comprises an internal cavity and said conduit is shaped to direct said abrasive media to smooth an internal surface of said cavity.

5. An article as claimed in claim 4, wherein said conduit is shaped to follow a path filling said cavity.

6. An article as claimed in claim 5, wherein said conduit comprises one of:

a single turn substantially filling said cavity; and

a stack of interconnected spirals.

7. An article as claimed in any one of claims 3 to 6, wherein said secondary structure has one or more of:

a thickness varying along a length of said conduit; and

a susceptibility to abrasion by said abrasive media varying along said length of said conduit.

8. An article as claimed in any one of claims 3 to 7, wherein said conduit has a cross-sectional area that varies along a length of said conduit with said cross-sectional area being lower proximal to areas of high stress within said primary structure.

9. An article as claimed in any one of claims 3 to 8, wherein said secondary structure has a susceptibility to abrasion greater than said primary structure.

10. An article as claimed in any one of claims 3 to 9, wherein said article is valve and said internal cavity provides a cavity within said valve to receive a high thermal conductivity material to conduct heat away from said valve.

11. An article as claimed in any claim 10, wherein said valve is a poppet valve, said cavity is within a head of said poppet valve, and said high thermal conductivity material conducts heat away from said head of said poppet value.

12. An article as claimed in any one of claims 3 to 11, wherein said boundary wall is provided by said primary structure and secondary structure and a thickness of said secondary structure is less than said primary structure.

13. An article as claimed in any one of claims 1, 2 and 3, wherein said article is a heat exchanger and said additional function is to provide a heat transfer surface between fluids.

14. An article as claimed in claim 13, wherein said primary structure is a primary heat exchanger fin and said secondary structure is a secondary heat exchanger fin and integrally formed with and extending from said primary heat exchanger fin.

15. An article as claimed in claim 14, wherein in transverse cross section said primary heat exchanger fin has a lower second moment of area than a combination of said primary heat exchanger fin and said secondary heat exchanger fin.

16. An article as claimed in claim 2 and claimed 15, wherein said second moment of area of said primary heat exchanger fin is insufficient to resist distortion due to said stress and said second moment of area of said combination of said primary heat exchanger fin and said secondary heat exchanger fin is sufficient to resist distortion due to said stress.

17. An article as claimed in any one of claims 14, 15 and 16, wherein said primary heat exchanger fin and said secondary heat exchanger fin together form a bifurcated heat exchanger fin.

18. An article as claimed in claim 17, wherein said secondary heat exchanger fin has a lateral portion connected to middle portion of said primary heat exchanger fin and extending away from a side surface of said primary heat exchanger fin.

19. An article as claimed in claim 18, wherein said secondary heat exchanger fin has longitudinal portion connected to an end of said lateral portion distal from said primary heat exchanger fin and extending substantially parallel to said primary heat exchanger fin.

20. An article as claimed in any one of claims 14 to 19, wherein said primary heat exchanger fin has a root connected to a conduit wall of a fluid conduit for containing a fluid.

21. An article as claimed in claim 20, wherein said conduit wall is an inner wall of said fluid conduit and said primary heat exchanger fin extends inwardly within said fluid conduit.

22. An article as claimed in any one of claims 17 to 21, wherein a longitudinal axis of said primary heat exchanger fin is parallel with a longitudinal axis of said fluid conduit.

23. A method of manufacturing an article using additive manufacture comprising:

forming a primary structure with layer deposition;

24. A computer readable storage medium storing in non-transitory form data to control an additive manufacturing machine to form an article as claimed in any one of claims 1 to 19.