WO2021043690A1

WO2021043690A1 - Heating chamber

Info

Publication number: WO2021043690A1
Application number: PCT/EP2020/074147
Authority: WO
Inventors: Tony Reevell; Jacek KOWALCZYK
Original assignee: JT International SA
Current assignee: JT International SA
Priority date: 2019-09-06
Filing date: 2020-08-28
Publication date: 2021-03-11
Anticipated expiration: 2022-03-06
Also published as: JP7603663B2; KR20220059946A; JP2022547008A; TW202128042A; TWI854020B; EP4025089A1; CN114340429A; CN114340429B

Abstract

A method of manufacturing a heating chamber (100) for an aerosol generating device (200) includes the steps: providing a metal tubular member (10) comprising a tubular side wall (11) with an open end (12); the tubular side wall having a thickness of no more than 0.15 mm; inserting the tubular member into a tubular mould (20), the inner surface of the tubular mould having a shaping profile with at least one protrusion (17, 19) or recess; sealing the open end of the tubular member; and injecting a fluid under pressure into the tubular member to outwardly deform the tubular member such that it conforms to the shaping profile of the surrounding tubular mould. By using a fluid pressure to shape the tubular member, a required profile shape can be transferred to the tubular member with high precision, while maintaining the thickness of the chamber walls below 0.15 mm to provide efficient heat transfer to a consumable during use.

Description

HEATING CHAMBER

TECHNICAL FIELD

The present invention relates to a method of manufacturing a heating chamber, in particular a heating chamber for an aerosol generating device.

BACKGROUND

Heating chambers are used in a wide range of applications which generally require means to contain and conduct heat to a substance to be heated. One such application is within the field of aerosol generating devices such as reduced risk nicotine delivery products, including e-cigarettes and tobacco vapour products. Such devices heat an aerosol generating substance in the form of a consumable within a heating chamber to produce a vapour to be inhaled by a user.

Heating chambers generally comprise a heat conductive housing or shell defining an internal volume to hold a consumable and an opening through which the consumable may be received. A heater may be employed internally or externally to provide the increased temperature to the heating chamber. Most commonly such heating chambers are heated from the outside, with the conductive shell transferring the heat to the internal volume. One means to heat such heating chamber uses a thin film heater which conforms to a surface of a heating chamber to ensure efficient heating of a consumable received within the chamber.

Often heating chambers need to be formed with a specific shape to accept a specific type of consumable. The internal surfaces of the heating chamber may also need to take a specific surface profile shape to hold the consumable and efficiently transfer heat to the consumable. One problem with known methods for manufacturing such heating chamber is that it is difficult to accurately control the specific shape of the heating chamber while also controlling the thickness of the walls of heating chamber to ensure optimal heat transfer. In particular, known methods of manufacturing heating chambers cannot both provide thin chamber walls for good thermal transfer through the heating chamber whilst also controlling the shape of the heating chamber with high precision. In particular, it is difficult to shape thin metal sheets as required without damaging the formed chamber or producing weak points. Known methods are also limited in the complexity of shape that can be provided to the profile of the heating chamber which limits the degree to which they can be optimised for a specific application.

The present invention aims to make progress in addressing these issues to provide a method of manufacturing a heating chamber which can provide a heating chamber of the required thickness to optimise the thermal conduction to a consumable whilst allowing the heating chamber to be precisely shaped in order to optimise it for a specific application.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a method of manufacturing a heating chamber for an aerosol generating device, the method comprising: providing a metal tubular member comprising a tubular side wall with an open end and a closed end; the tubular side wall having a thickness of no more than 0.15 mm; inserting the tubular member into a tubular mould, the inner surface of the tubular mould having a shaping profile with at least one protrusion or recess; sealing the open end of the tubular member; injecting a fluid under pressure into the tubular member to outwardly deform the tubular member such that it conforms to the shaping profile of the surrounding tubular mould. By using a fluid pressure to shape the tubular member, a required profile shape can be transferred to the tubular member with high precision, while maintaining the thickness of the chamber walls below 0.15 mm to provide efficient heat transfer to a consumable during use. Furthermore the method of the present invention allows for more complex surface profile shapes to be transferred to the heating element, which are difficult to achieve with known methods. The using fluid pressure and a tubular mould, a much wider range of surface shapes may be transferred to the tubular member.

The steps of inserting the tubular member into a tubular mould and injecting a fluid under pressure into the tubular member to outwardly deform the tubular member may be referred to collectively as the hydroforming steps in the following disclosure.

The metal tubular member preferably comprises stainless steel. The thickness of the tubular side wall is more preferably 0.1 mm or less, or more preferably between 0.07 and 0.09 mm. This allows for efficient heat transfer through the side wall of the heating chamber to a consumable while maintaining sufficient structural stability. The tubular member has a closed end opposite the open end, where preferably the thickness of the closed end is 0.2 to 0.6 mm, which adds further structural rigidity to the heating chamber In a possible embodiment, the tubular member is cut across its length after the fluid injection step to provide a tubular member with two open ends for applications requiring a heating chamber with an opening at both ends.

The fluid pressure is preferably provided by injected water, with a pressure of up to 250 bar. The specific pressure used depends on the specific material, thickness and surface profile to be transferred. The applied pressure may be varied during the hydroforming process. The required pressure can be determined through routine experimentation for new materials or through simulation.

The tubular mould is preferably provided in two or more parts which are secured together during the fluid injection and may be moved apart to release the shaped tubular member.

Preferably the shaping profile of the tubular mould comprises an annular groove in the inner surface of the mould, the annular groove extending around the circumference of the tubular mould such that, after injecting the fluid, the tubular member comprises an annular flange. In this way, an annular flange may be provided with precisely controlled dimensions. The annular flange can be used in mounting the heating chamber within a device in a precise and reliable manner. The annular groove preferably extends along the length of the tubular mould to provide a circumferential channel around the inner surface of the tubular mould. In other words the groove may have a substantial width in a direction corresponding to the elongate axis of the tubular member, for example a width of greater than 1 mm, preferably greater than 3mm. The cross sectional profile of the groove may be substantially rectangular, square, or trapezoidal.

Preferably, the tubular mould comprises a tubular, preferably cylindrical, body. In a particularly preferably example, the annular groove is formed by a section of the length of the tubular body which has a greater internal diameter than the remainder of the tubular body; such that the annular flange comprises a corresponding section of the length of the tubular member which has greater diameter than the remainder of the length of the tubular member. In other words the groove in the inner surface of the tubular mould has a depth defined by the length of side walls of the groove which are appropriately perpendicular to the inner surfaces of the tubular body. Preferably the side walls of the annular groove are joined by a base surface which is approximately perpendicular to the inner surface of the tubular body. In this way, the annular groove of the tubular mould and the annular flange of the tubular member both have a substantially rectangular cross-sectional profile. This shape is particularly advantageous for the further processing of the tubular member and for its mounting within a device. For example, this allows for a cylindrical lip to be formed in a straightforward manner by subsequent cutting of the annular flange.

The method may further include a step of cutting the tubular member through the annular flange to provide a tubular member of reduced length with an annular collar at the open end. In particular the tubular member may be truncated via cutting the tubular member through the annular flange across its cross section, i.e. approximately normal to its elongate axis. An annular collar around the open end is particularly useful for mounting the heating chamber within a device. The annular collar may be cut again to provide a circumferential planar lip around the open end. In particular the annular collar may be reduced in radial extension by cutting the annular collar in directions approximately parallel with the elongate axis such that the remaining lip is substantially planar and does not extend significantly along the length of the tube. In other words the annular collar may be rectified to provide a circumferential planar lip. In an alternative method the annular flange may be cut in a single step to form the circumferential lip. A circumferential planar lip is particularly beneficial to the precise and secure mounting of the heating chamber within a device. The term “Up” is used to refer to an annular extension which is substantially planar, i.e. has a depth in the direction of the tubular axis corresponding to the thickness of the tubular member. The term “collar” is used to refer to an annular extension around the opening which has a greater depth in the direction of the tubular axis.

The method preferably further includes applying an inward pressure on the outer surface of the tubular member to provide one or more inwardly extending protrusions on an inner surface of the tubular member. This may be carried out using a pressing member to apply a pressure on the outer surface and the inward pressure may be applied either during the injection of a fluid or in a separate process before or after the moulding with the fluid pressure. For example, the formed tubular member, shaped during the fluid injection steps, may be supported internally, for example using a former, and a pressure applied from the outside to produce one or more inwardly extending protrusions on an inner surface of the tubular member.

Preferably the method comprises applying an inward pressure on the outer surface of the tubular member as fluid is injected under pressure into the tubular member to provide one or more inwardly extending protrusions on an inner surface of the tubular member. In this way, positive and negative surface features may be provided on the surface of the tubular member in the same processing step, i.e. both protrusions and recesses may be on the outer surface of the tubular member (resulting in corresponding features on the internal surface of the tubular member). By injecting a fluid while providing an inward pressure, surface features may be provided on the tubular member with increased precision. In particular, the fluid pressure may be applied to a region of the internal surface of the tubular member as the pressure as a pressing member is pressing on the outer surface of the region, such that the walls of the tubular member more closely conforms to the shape of the pressing member under the application of the fluid pressure. This allows for surface features to be provided with high geometrical precision, for example with radii of 0.1 -0.2 mm.

Where an inward pressure is applied to provide one or more inwardly extending protrusions, this may be achieved by pressing a plurality of elongate ridges into the outer surface of the tubular member to provide a plurality of corresponding elongate protrusions running lengthwise on the inner surface of the tubular member, the protrusions positioned around the circumference of the tubular member. The elongate ridges may be pressed into the outer surface as fluid is injected under pressure into the tubular member such that the side walls of the tubular member more closely conform to the shape of the elongate ridges. The elongate ridges are preferably aligned with the elongate axis of the tubular member and may be positioned to provide elongate protrusions which run along a central portion of the length of the tubular member on the inner surfaces. The elongate protrusions may be spaced from the base of the tubular member and spaced from the open end of the tubular member. The elongate ridges may run along approximately a third of the length of tubular member. The plurality of elongate ridges may be provided on the inner surface of the tubular mould.

The step of applying an inward pressure on the outer surface of the tubular member may additionally or alternatively comprises applying pressure at one or more contact points to provide one or more point protrusions on the inner surface of tubular member. The point protrusions may comprise a plurality of protuberances positioned periodically around the circumference of the internal surface of tubular member. The point protrusions may be configured to improve the gripping of the substrate carrier in the heating chamber while limiting heat transfer in this area. Each point protrusion may comprise a rounded protrusion, for example a partially spherical protrusion. The point protrusions may have a radius of between 0.05 mm and 0.25 mm, preferably 0.1 -0.2 mm. Other shapes of protrusions may be formed with the method, such as truncated pyramidal protrusions and the like.

Preferably, the inwardly applied pressure is provided by one or more movable portions of the tubular mould; and the one or more inwardly extending protrusions are provided by applying an inward pressure with the one or more movable portions of the tubular mould when the tubular member is inserted into the tubular mould and a fluid is injected under pressure. Preferably the moveable portions of the tubular mould are initially in contact with the outer surface of the tubular member and are moved radially inward against the outer surface to apply a pressure as the fluid is injected under pressure.

The tubular mould may comprise multiple moveable portions. One or more of the moveable portions may be configured to provide different forms of inwardly extending protrusion. The moveable portions may be moveable together and/or independently to provide the different forms of inwardly extending protrusions simultaneously or sequentially.

In one example of the invention the tubular mould comprises a first moveable portion arranged to provide a plurality of elongate protrusions running lengthwise on the inner surface of the tubular member and a second moveable portion arranged to provide a plurality of point protrusions arranged around the circumference of the inner surface of the tubular member; wherein the first and second moveable portions are positioned at different positions along the length of the tubular mould. The first and second moveable portions may be arranged to apply pressure simultaneously and/or sequentially.

The tubular mould may be arranged to provide different intruding depths of the inwardly extending protrusions in the heating cavity. In particular, the moveable parts may be sized so that the intruding depth of the formed point protrusions may be relatively smaller than the intruding depth of the formed elongate protrusions. This has the advantage to provide an efficient gripping without excessive constraint in a rigid region of the consumable where gripping is desired.

The inwardly applied pressure is preferably provided when the tubular member is inserted into the tubular mould and a fluid is injected under pressure such that the one or more inward protrusions and the annular flange are formed simultaneously, thereby providing an efficient method in which the final shape of the heating chamber is formed in one step.

The tubular member may be provided by punching a metal sheet to provide a metal disk blank; and deep drawing the metal disk blank to form a tubular cup with an open end and a closed end. Deep drawing may involve using a multi stage deep-drawing process in which the metal disk blank is progressively drawn to increase the length of the tubular cup and reduce the thickness of the side walls. Oil or soap may be used as a lubricant. The method may further comprise the step of annealing the tubular member one or more times during and/or after the deep drawing.

Preferably the method comprises forming the metal disk blank into an initial cup shape; annealing under vacuum or inert gas; and deep drawing the initial cup shape into an elongated tubular cup with a reduced tubular wall thickness. The deep drawing process may comprise ironing the tubular cup to reduce the wall thickness. As the plastic deformation of the metal during initial deep drawing can cause it to become hard making further working of the metal more difficult, an intermediate annealing step allows for the initial cup shaped member to be deep drawn to increased lengths with a reduced tubular wall thickness. A further annealing step can be carried out prior to the hydroforming steps (injecting the fluid under pressure) such that the tubular member is made softer and so easier to mould during hydroforming.

The initial forming of the initial metal cup may be carried out using a multi-stage press to cut round plates out of a metal strip and the form them into small cups. The initial small cups are shallow and are then deep drawn in several steps to the required length (preferably after an intermediate annealing step), using ironing to reduce the wall thickness to within the required range.

Annealing may be carried out in a low pressure vacuum-furnace, for example at pressures between 10² to 10^-4 mbar, or an inert-gas furnaces. The reduced pressure or inert gas protects the surface of the tubular cup against oxidation. Preferably the deep drawing process is carried out so as to provide a tubular cup having an internal diameter of less than 10mm, preferably less than 8 mm and a length of greater than 30 mm. The deep drawing may provide a tubular member with a length of greater than 50 mm, for example up to 65 mm. After the hydroforming steps, the tube may be cut down to provide a formed tubular member of length between 20 and 40mm, preferably 25 to 35 mm.

Preferably deep drawing is performed from the metal disk blank so as to provide a tubular cup having a tubular wall with a side thickness of 0.05 to 0.1 mm, more preferably of 0.07 to 0.09 mm. Side wall thicknesses in these ranges provide efficient heat transfer through the chamber to a consumable during use and also render possible the subsequent hydroforming with precise inwardly extending protrusions.

The deep drawing may be performed so as to provide a tubular cup with a bottom wall having a thickness of 0.2 to 0.6 mm, preferably 0.4 mm. In particular, the metal sheet preferably has a thickness of 0.2 to 0.6 mm, preferably 0.4 mm, and the deep drawing process maintains this thickness as the base of the tubular member. By providing a closed end with an increased thickness relative to the side walls, the heating chamber has increased mechanical strength while maintaining the optimised heat transfer properties provided by the reduced thickness of the side walls.

Preferably the deep drawing process provides a tubular member comprising a central recess in the outer surface of the closed end. In particular, the recess may be produced during initial stamping of a metal disk blank. The central recess in the closed end preferably provides a corresponding protrusion on the internal base surface of the tubular member. The central recess in the closed end can aid in mounting the heating chamber within the device. It can further aid in controlling the insertion depth of a consumable within the device. For example, when employed in an aerosol generating device, when the consumable is inserted it will meet the protrusion on the internal base surface which limits further insertion. In this configuration air in the chamber can flow into the end of the consumable in the space around the central protrusion. The central protrusion can further aid in providing heat transfer to the end of the consumable in contact with the protrusion in use.

The method may further comprise wrapping a thin film heater around an outer surface of the tubular member. The method may further comprise positioning a temperature sensor at least partially within a recess on an outer surface of the heating chamber.

In a further aspect of the invention there is provided a heating chamber for an aerosol generating device manufactured by the method of any preceding claim. In particular the aerosol generating device may comprise a heating chamber, a thin film heater wrapped around the heating chamber; a power source and control circuitry configured to controllably supply power to the thin film heater to heat the heating chamber. The heating chamber may be mounted in the device by a circumferential lip of the heating chamber which is received in a corresponding recess within the aerosol generating device.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figures 1A to 1D schematically illustrates a method of manufacturing a heating chamber for an aerosol generating device according to the present invention;

Figure 2 schematically illustrates a heating chamber manufactured according to the present invention;

Figure 3 schematically illustrates a method of forming a metal disk blank for deep drawing;

Figure 4 schematically illustrates a method of forming a metal tubular member according to the present invention; Figure 5 schematically illustrates an aerosol generating device incorporating a heating chamber manufactured using a method according to the present invention.

DETAILED DESCRIPTION

Figure 1 schematically illustrates a method of manufacturing a heated chamber 100 for an aerosol generating device. The method includes providing a metal tubular member 10, as shown in Figure 1A, the tubular member having a tubular side wall 11 with an open end 12. and an opposing closed end 13 The tubular side wall 11 of the tubular member 10 has a side wall thickness 111 of less than or equal to 0.15 mm. The tubular member 10 is inserted into a tubular mould 20 comprising an inner surface 21 which provides a shaping profile having at least one protrusion or recess 22. The open end 12 of the tubular mould is then sealed and a fluid F is injected under pressure, as shown in Figure 1 B, to outwardly deform the tubular member 10 such that it conforms to the shaping profile 21 of the surrounding tubular mould 20. The method according to the present invention allows for a shaped heating chamber 100 to be formed with a precisely controlled shaped profile while maintaining a reduced side wall 11 thickness 111. By controlling the shape of the heating chamber 100 and the side wall thickness 111 with high precision, heat transfer through the chamber 100 is optimised which ensures improved heating of a consumable received in the chamber 100 when employed in an aerosol generating device. Furthermore, precise control of the heating chamber 10 side wall 11 shape allows for the heating chamber 10 to be precisely and reliably mounted within the aerosol generating device.

In the example of Figure 1 the metal tubular member 10 is in the form of a tubular cup with one open end 12 and a closed end 13. The tubular member 10 comprises a substantially cylindrical body with a closed end 25 and an open end 24 and a side wall thickness 111 of around 0.1 mm. As shown in Figures 1A and 1B the tubular member 10 is inserted into the tubular mould 20 with the closed end 13 of the tubular member 10 against the closed end 25 of the tubular mould 20. The tubular mould 20 has an inner surface 21 providing a shaping profile to be transferred to the outer surface of the tubular member 10. In the example of Figure 1 the shaping profile comprises an annular groove 22 which runs around the circumference of the inner surface 21 of the tubular mould 20.

As shown in Figures 1A and 1 B a fluid injection nozzle 32 is inserted into the open end 12 of the tubular member 10, the open end 24 around the tubular nozzle 32 is sealed with seal 31 and a fluid F is injected under pressure as shown in Figure 1 B. The seal 31 is preferably positioned within the open end 12 of the tubular member and clamped in position such as by an external clamping element 33 tightly pressing the tubular member on the seal 31 , as shown in Figures 1A and 1B. This fluid injection process may be carried out by injecting water into the tubular member 10 to apply a pressure to the internal surface of the tubular member 10 to cause it to outwardly deform to the shaping profile on the inner surface 21 of the tubular mould 20. The applied pressure may be up to 250 bar, with the specific applied pressure selected depending on the specific requirements of the process, for example the material and thickness of the tubular member 10 and the shape to be applied to the tubular member 10.

As described above, the tubular mould 20 comprises a substantially cylindrical body with an annular groove 22 provided around the circumference of the inner surface 21 of the mould. In this way, the tubular member 10 outwardly deforms into the annular groove 22 under the applied fluid pressure F to provide an annular flange 14 around the circumference of the tubular member 10. In this example, the tubular mould 20 has an annular groove 22 which is formed by a section 22L of the length of the cylindrical body which has a greater internal diameter D₂ than the diameter Di of the remainder of the cylindrical body. In this way the annular flange 14 comprises a corresponding section of the length of the tubular member 10 which has a greater diameter than the remainder of the length of the tubular member 10. The annular groove 14 has a substantially rectangular profile formed by two circumferential side walls 22a which extend away from the tubular body of the mould in a direction approximately perpendicular to the elongate axis of the mould 20 and joined by a surface approximately parallel to the elongate axis of the mould 20. After the high pressure fluid F has been injected into the tubular member 10 the tubular member is shaped to provide a corresponding annular flange 14 with dimensions corresponding to the internal surfaces of the annular groove 22 of the mould 20, as shown in Figure 1C. In particular, the tubular member 10 has a annular protrusion with a square shaped profile formed by a portion of the length 14L of the tubular member 10 which has a greater diameter than the remainder of the cylindrical body.

Further steps are included in the method to provide additional surface features 17, 19 in the outer surface 11 of the tubular member 10 to form the shaped heating chamber 100 shown in Figure 1D. In particular, an inward pressure P may be applied on the outer surface of the tubular member 10 as fluid is injected into the tubular member 10 in order to provide one or more inwardly extending protrusions 17, 19 on an inner surface of the tubular member 10. These protrusions 17, 19 may be provided in a number of different ways by applying the pressure P during or after the injection of fluid F with the nozzle 32. Figure 1 illustrates a particularly preferable means to provide the internal protrusions 17, 19 using moveable portions 23a, 23b of the tubular mould 20.

As shown schematically in Figure 1A and Figure 1 B, the tubular mould 20 comprises a first moveable portion 23a and a second moveable portion 23b, each configured to apply a pressure Pi, P₂ against the outer surface of the tubular member 10 in a radially inward direction during the hydroforming process in order to provide the surface features 17, 19 on the surface of the tubular member 10. The moveable portions 23a and 23b are positioned against the outer surface of the tubular member and moved inwards during the fluid injection step to impart the surface features 17, 19 on the tubular mould 10. Applying the pressure Pi, P₂ during injection of fluid into the tubular member allows for protrusions 17, 19 to be shaped with high precision around the shaped inner surfaces of the moveable components 23a, 23b which apply the pressure P. In some examples, fluid F may be directed with the nozzle 32 specifically around the area in which the pressure is applied, such that the outer surface of the tubular member 10 is encouraged to closely conform to the shape of the press 23 to shape the protrusions 17, 19 precisely. In some example the pressure may be varied, for example by selecting a nozzle with a specific diameter. Controlling the parameters of the fluid injection process allows for rounded surface features with very low radii and protrusions with short width to be provided. The hydroforming technique illustrated in Figure 1 therefore allows the protrusions 17, 19 to be formed with high geometric precision with a reduced thickness of side wall 111 to provide enhanced heat transfer through the heating chamber 100 when employed in an aerosol generating device.

In the example of Figure 1 , the first moveable mould portion 23a (which may comprise multiple constituent moveable portions) comprises inner surface features in the form of a plurality of elongate ridges positioned periodically around the inner circumference of the inner surface of the moveable mould portion 23a, the ridges aligned with the elongate axis of the tubular member 10. The fist moveable mould portion 23a is moveable to apply a pressure Pi during the fluid injection step, as shown in Figure 1B. After the fluid injection step, the first moveable mould portion 23a therefore provides corresponding elongate protrusions 17 running lengthwise along the inner surface of the tubular member 10, as shown in Figure 1C. A plurality of such protrusions 17 are arranged around the circumference of the inner surface of the tubular member 10. The elongate protrusions 17 provide a number of functions when the shaped heating chamber 100 is employed in an aerosol generating device, including restricting the insertion depth of a consumable placed into the chamber, providing air flow between the protrusions and enhancing the heat transfer to the consumable, as will be described in more detail below.

The tubular mould 20 of Figure 1 also includes a second moveable mould portion 23b, separated from the first moveable mould portion 23a along the tubular axis of the mould and positioned near the annular recess 22. The second moveable mould portion 23b has an inner pressing surface shaped to provide a plurality of rounded point protrusions 19 arranged around the circumference of the inner surface of the tubular member. In particular the second moveable mould portion 23b (which can comprise multiple moveable portions, for example with each configured to provide a single protrusion), has a pressing surface comprising a plurality of rounded protuberances, arranged periodically around the circumference of the mould portion 23b. The second moveable mould portion 23b is configured to provide a pressure P₂ against the outer surface of the tubular member 10 during fluid injection to provide the protrusions 19 shown in Figure 1C. The protrusions 19 adjacent to the annular flange 14 provide additional gripping and positioning of a consumable received within the chamber 100.

The moveable portions of the mould 23a, 23b may be used to apply corresponding pressures Pi, P₂ during fluid injection such that the inward protrusions 17, 19 are formed simultaneously with the annular flange 14. Alternatively, the pressure P may be applied after initial forming of the annular flange 14 wherein, in a separate moulding step, the pressures Pi and P₂ are applied to the outer surface of the tubular member 10 with the moveable portions while fluid is specifically directed at the portion of the inner surface of the tubular member 10 opposite the points on the outer surface where the pressure P is applied. For example, specific fluid pressures may be selected which are optimised for each stage of the moulding process, e.g. a different fluid pressure may be directed to form the protrusions 17, 19 than for forming the annular flange. The moveable mould portions 23a, 23b may be used simultaneously or sequentially to apply the pressures Pi, P₂ and form the corresponding protrusions 17, 19.

Following the hydroforming steps illustrated in Figures 1A and 1B, the shaped tubular member 10 is removed from the tubular mould 20, as shown in Figure 1C. In particular, the tubular mould 20 is provided in multiple parts which are secured together during the fluid injection steps. For example, the tubular mould 20 may be longitudinally divided into two parts which are connected along an interface running along the length of the mould at connection point 34, shown in Figures 1A and 1 B. The multiple parts of the tubular mould 20 are then opened to release the shaped tubular member 10, as shown in Figure 1C.

Further processing steps are carried out on the shaped tubular member 10 shown in Figure 1C to prepare it for use as a heating chamber 100. In particular, the tubular member 10 may then be cut through the annular flange 14 to provide a circumferential planar lip 15 around the open end 12 of the tubular member 10, as shown in Figure 1D. This may be achieved by initially cutting the annular flange 14 in a radial direction along cut line Ci to reduce the length of the tubular member 10, as shown in Figure 1C. The tubular member 10 is then cut again through the side walls 14a of the annular flange 14 along cut lines C2, in a direction parallel to the tubular axis. By rectifying the annular flange 14 in this way, a planar circumferential lip 15 is provided around the circumference of the open end 12 of the tubular member 10, as shown in Figure 1 D. The circumferential lip 15 is particularly useful for mounting the tubular member 10 when employed as a heating chamber 100 in an aerosol generating device. The hydroforming method illustrated in Figures 1A to 1 D allows for the circumferential lip 15 to be provided with a precise low thickness 111, which allows for precision mounting of the heating chamber 100 within the aerosol generating device.

Figure 2 illustrates a particularly preferable shaped heating chamber 100 formed using the process shown in Figure 1. Figure 2A schematically illustrates a side view of a shaped heating chamber 100, where Figure 2B and 2C show cross sectional views as indicated by lines A-A and B-B in Figure 2A. As described above, the tubular member 10 has been shaped by the method of Figure 1 to provide a number of features. Firstly, a series of elongate protruding ridges 17 are provided on the inner surface of the heating chamber 100, extending over a length 17L along a central portion of the length of the heating chamber 100. In this example the heating chamber is cut to a length of around 31 mm with the elongate protrusions having a length 17L of around 12 mm and spaced apart from either end 12, 13 of the chamber 100. A plurality of such protrusions 17 are provided periodically around the circumference of the heating chamber 100, as shown in the cross section of Figure 2C and the protrusions have a tightly curved rounded cross-section, with a radius of around 0.15 mm. In particular, four protrusions 17 may be provided separated by 90° around the circumference.

These protrusions 17 are arranged so as to press into a consumable received within the heating chamber 100 to improve heat transfer from the heating chamber 100 to the received consumable. They also ensure a sufficient gap is maintained between the protrusions for air to flow from the open side towards the closed side. They also aid in restricting the distance with which the consumable may be inserted into the chamber, for example by abutting against a portion of the consumable which is ridged and does not easily deform, thereby preventing further insertion of the consumable within the chamber 100. This can ensure that a consumable is positioned at the correct insertion depth within the chamber 100 by restricting further insertion after a rigid portion of the consumable meets the leading end of the protrusions.

Additional point protrusions 19, or “gripping protrusions” 19, are also provided around the circumference of the heating chamber 100 as shown in Figure 2B. The gripping protrusions 19 may be provided with the second moveable mould part 23b, as described above. Again, in this case four gripping protrusions are provided with an angular separation between the protrusions of 90°. The gripping protrusions 19 may aid in gripping and positioning the consumable within the heating chamber during use. As described above, the second moveable mould part 23b is positioned at a defined distance from the annular recess 22 in the mould such that, when the formed tubular member 10 is cut to size, the gripping protrusions 19 are provided at a defined distance from the open end 12 of the heating chamber 100. In a possible mode, the point protrusions 19 are omitted and only the elongated protrusions 17 are formed.

Figure 2A also shows the circumferential planar lip 15 provided around the open end 12 of the chamber, formed by cutting the annular flange 14. As shown clearly in Figure 2A the circumferential lip 15 has a low thickness 12t of around 0.07 to 0.09 mm, corresponding to that 111 of the remaining side wall 11 of the chamber 100, which is advantageous when used for mounting the heating chamber 100 within the aerosol generating device. The base of heating chamber 100 has a larger thickness 13t of around 0.4 mm which can aid in providing structural stability to the heating chamber 100. The thicknesses of the side wall 111 and base 13t may be configured during initial forming of the tubular member 10, prior to the hydroforming steps, as will now be described with reference to Figures 3A to 3C. Figure 3 illustrates additional, initial steps in the method of manufacture of a heating chamber 100, to provide the initial tubular member 10 for hydroforming. The process involves cutting metal disc blanks 41 from a metal sheet 40 as shown in Figure 3A and 3B and then deep drawing the disks 41 into a tubular member 10 as shown in Figure 4, ready for hydroforming.

In particular, a multi-stage press may be used to cut round plates 41 from a metal strip 40 and form these into small cups 43, as shown in Figure 4A. This may be part of an automated process wherein a roll 42 of metal sheet is punched to provide the initial metal disc blanks 41 as shown in Figure 3B and pressed into the initial short cup 42, shown in Figure 4A. These can be cleaned and decreased, for example using paraffin and later vacuum annealed. Following this the cups 43 may be deep-drawn in several steps into thin wall tubes in order to form the tubular member 10 used in the method according to the present invention. The intermediate annealing step soften the metal and thereby improves the ease with which the metal cup can be deep drawn to the lengths required.

As shown in Figure 4, during the deep-drawing process the base thickness 13t remains substantially constant while the side wall thickness 111 is gradually reduced as the initial cup 43 is stretched by progressive deep-drawing into the final tubular member 10. The initial thickness of the metal disc blank 411 is around 0.4 mm before progressively being drawn as shown in Figure 3C to reduce the wall thickness to less than 0.1 mm, leaving a thickness remaining of 0.4 mm in the base. Ironing can be used in order to reduce the side wall thickness further, as schematically illustrated in Figures 4B to 4D. This deep drawing process can provide a tubular cup having a tubular wall with side thickness between 0.07 and 0.09 mm. This thickness range provides enhanced heat transfer through the heating chamber to a heating consumable in use while maintain a sufficiently mechanically stable structure.

The deep drawing process also provides an indent 18 in the base 13 of the tubular member 10. This can be beneficial for holding the consumable in the bottom while leaving a gap for drawn air to flow through the end of the consumable. This can also be beneficial for mounting the heating chamber 100 in an aerosol generating device. Following the multi stage deep drawing process, the tubular members may be annealed again using vacuum or inert gas. For example the tubular cup formed by the initial deep drawing may be annealed in a low pressure vacuum-furnace, for example at pressures between 10-2 to 10-4 mbar, or an inert-gas furnaces. The reduced pressure or inert gas protects the surface of the tubular cup against oxidation. Due to the plastic deformation of the metal during deep drawing it can become very hard and so an annealing step addresses this so that tubular member is easier to mould during the hydroforming process. The resulting tubular member 10 may then be employed in the hydroforming process illustrated in Figure 1A to Figure 1D to form the shaped heating chamber 100.

Figure 5 shows a heating chamber 100 manufactured by the method of the present invention employed in an aerosol generating device 200. In particular, the heating chamber 100 is mounted within the aerosol generating device with the open end 12 provided at one end of the device to accept a consumable 210 to be heated to produce an aerosol for inhalation by a user. The heating chamber 100 is preferably wrapped with a thin film heater 220 around an outer surface to heat the side walls of the chamber and the internal volume. The thin film heater 210 is connected to a PCB 201 and battery 202 to selectively provide power to the thin film heater to heat the chamber 100 to a controlled temperature. Since the thickness 111 of the tubular side walls 11 of the heating chamber 100 may be precisely controlled and maintained at a low thickness of no more than 0.15 mm, the heat transfer from the thin film heater 220 to the internal volume of the chamber is enhanced. Furthermore, since the protrusions 17, 19 can be formed on the inner surface of the heating chamber 100 with high precision the thickness and distance of extension of the protrusions may be carefully controlled to provide the required grip and increased heat transfer to the consumable 210 while not extending so far so as to inhibit the insertion of the consumable 210 into the heating chamber 100. The elongate protrusions 17 may be positioned with high precision so as to engage an aerosol generating portion 212 of the consumable 210 and to contact a rigid portion 211 of the consumable 210 as it is inserted into the chamber 100 to prevent further insertion of the consumable 210, holding the consumable 210 at the correct position such that the aerosol generating portion 212 is efficiently heated by the thin film heater 220. The increased thickness 13t of the base portion 13 of the heating chamber 100 provides structural rigidity to the heating chamber 100 when employed in the device. The central protrusion 18 provided on the base 13 of the heating chamber 100 may contact a surface of the consumable 210 to prevent further insertion and to allow for an air flow route around an exposed outer circumferential portion of the consumable 210 when it is received in the chamber 100.

The method of the present invention solves the important problem of ensuring accurate control of the thickness of the heating chamber side walls to provide a reduced thickness heating chamber, such that heat transfer from a thin film heater to the consumable is optimised. In particular, the present invention allows for the shaped side wall of the tubular member to be controlled at or below 0.1 mm, preferably between 0.8 and 0.9 mm. The controlled low thickness also aids with the mounting of the heat chamber, in particular via the circumferential planar lip 15 which is received in a corresponding recess in the body of the aerosol generating device 200. The method of the present invention allows for control of the dimensions down to 0.01 mm and ±5° angle. It also allows for precise control of the shape of the protrusions allowing high geometrical accuracy, in particular extremely short radii for example a radius of 0.1 to 0.2 mm curvature in the surface features. The method of the present invention therefore provides a technique for manufacturing heating chambers which are particularly suited to use in an aerosol generating device, where accurate control of a heating temperature is needed to control the heating temperature within a specific window to provide efficient aerosol release, without overheating the consumable 210 or the materials of the thin film heater or aerosol generating device 200.

Claims

1. A method of manufacturing a heating chamber for an aerosol generating device, the method comprising: providing a metal tubular member comprising a tubular side wall with an open end and an opposing closed end; the tubular side wall having a thickness of no more than 0.15 mm; inserting the tubular member into a tubular mould, the inner surface of the tubular mould having a shaping profile with at least one protrusion or recess; sealing the open end of the tubular member; and injecting a fluid under pressure into the tubular member to outwardly deform the tubular member such that it conforms to the shaping profile of the surrounding tubular mould.

2. The method of claim 1 wherein the shaping profile of the tubular mould comprises an annular groove in the inner surface of the mould, the annular groove extending around the circumference of the tubular mould such that, after injecting the fluid, the tubular member comprises an annular flange.

3. The method of claim 2 wherein the tubular mould comprises: a cylindrical body with the annular groove formed by a section of the length of the cylindrical body which has a greater internal diameter than the remainder of the cylindrical body; such that the annular flange comprises a corresponding section of the length of the tubular member which has greater diameter than the remainder of the length of the tubular member.

4. The method of claim 2 or claim 3 further comprising: cutting the tubular member through the annular flange to provide a tubular member of reduced length with an annular collar at the open end.

5. The method of claim 3 or claim 4 further comprising cutting the annular flange to provide a planar circumferential lip around the open end of the tubular member.

6. The method of any preceding claim further comprising: applying an inward pressure on the outer surface of the tubular member as fluid is injected under pressure into the tubular member to provide one or more inwardly extending protrusions on an inner surface of the tubular member.

7. The method of claim 6 wherein applying an inward pressure comprises: pressing a plurality of elongate ridges into the outer surface of the tubular member as fluid is injected under pressure into the tubular member to provide a plurality of corresponding elongate protrusions running lengthwise on the inner surface of the tubular member, the protrusions positioned around the circumference of the tubular member.

8. The method of claim 6 or 7 wherein the inwardly applied pressure is provided by one or more movable portions of the tubular mould; and the one or more inwardly extending protrusions are provided by applying an inward pressure with the one or more movable portions of the tubular mould when the tubular member is inserted into the tubular mould and a fluid is injected under pressure.

9. The method of claim 8 wherein the tubular mould comprises a first moveable portion and a second moveable portion disposed at different positions along the length of the tubular mould, the method further comprising: applying an inward pressure with the first moveable mould portion to provide plurality of elongate protrusions running lengthwise on the inner surface of the tubular member; and applying an inward pressure with a second moveable mould portion to provide a plurality of point protrusions arranged periodically around the circumference of the internal surface of the tubular member.

10. The method of any preceding claim wherein the step of providing a tubular member comprises: punching a metal sheet to provide a metal disk blank; and deep drawing the metal disk blank to form the tubular member with an open end and a closed end.

11. The method of claim 10 wherein deep drawing the metal disk blank comprises: forming the metal disk blank into an initial metal cup; annealing under vacuum or inert gas; and deep drawing the initial metal cup into an elongated tubular cup with a reduced tubular wall thickness.

12. The method of claim 10 or claim 11 wherein deep drawing is performed from the metal disk blank so as to provide a tubular member having a tubular wall with a side thickness of 0.05 to 0.1 mm, more preferably of 0.07 to 0.09 mm.

13. The method of any of claims 10 to 12 wherein deep drawing is performed so as to provide a tubular member having an internal diameter of less than 8 mm and a length of greater than 30 mm.

14. The method of any of claims 10 to 13 wherein the metal sheet has a thickness of 0.2 to 0.6 mm and the deep drawing is performed so as to provide a tubular cup with a base wall at the closed end having a thickness of 0.2 to 0.6 mm.

15. A heating chamber for an aerosol generating device manufactured by the method of any preceding claim.