GB2556064B

GB2556064B - Door manufacturing method

Info

Publication number: GB2556064B
Application number: GB1619404.5A
Authority: GB
Inventors: Hourican Peter
Original assignee: Assa Abloy Ltd
Current assignee: Assa Abloy Ltd
Priority date: 2016-11-16
Filing date: 2016-11-16
Publication date: 2019-08-28
Anticipated expiration: 2036-11-16
Also published as: IE20170238A1; GB2556064A; IE87150B1

Description

Door manufacturing method

Field of the Invention

The present invention relates to a method of manufacturing a door. More particularly, the invention relates to a method of manufacturing a metal door with thermal insulation between the opposite faces of the door .

Background of the Invention

It is very well known to use metals such as steel as construction materials for doors due to their superior mechanical and weather resisting properties and their cost. A problem with known metallic doors is that they are thermally conducting and, as such, they may act as thermal bridges which can conduct heat from inside a building into the outside environment. This can adversely affect the overall thermal insulation of a building. It is possible to introduce one or more thermally insulating members between the opposite faces of the door, but that then complicates the method of construction, adding to cost.

The present invention seeks to provide an improved method of manufacturing a door.

Summary of the Invention

The present invention provides a method of manufacturing a door comprising the steps of: providing a first piece of sheet metal, the first piece of sheet metal being suitable for forming a first face of the door, removing portions of the first piece of sheet metal to form a first multiplicity of apertures adjacent to one another through the first piece of sheet metal, the apertures extending from a position adjacent one boundary of the sheet metal to a position adjacent an opposite boundary, the apertures defining a thermal break in the first piece of sheet metal, folding the first piece of sheet metal along a first axis substantially parallel to the direction along which the apertures extend, to form the first face of the door, the first multiplicity of apertures being spaced from the first face of the door, connecting the first piece of sheet metal to one or more other pieces of sheet metal to form a door, providing an internal channel member made of folded sheet metal along an edge of the door, the internal channel member being elongate and comprising a U-shaped cross-section, providing a channel capping member, and installing the channel capping member over the internal channel member to form a closed edge to the door.

The use of sheet metal and a thermal break of apertures formed by removing portions of material from the sheet metal, together with folding of the sheet metal enables a door to be made at low cost with good thermal properties .

As a result of the folding of the first piece of sheet metal, the first multiplicity of apertures may be disposed within the door, with another part of the door overlying the apertures. That can reduce the likelihood of moisture or other substances entering the door and can improve the appearance of the door.

The first piece of sheet metal may be folded along the first axis to form the first door edge. The first door edge may extend in a plane perpendicular to the first face of the door. The first door edge may have a distal end which is folded inwardly, the first multiplicity of apertures being provided on the inwardly folded distal end of the first door edge.

The first multiplicity of apertures may be spaced along the first piece of sheet metal and define bridging portions between them. Such a thermally broken portion can be formed economically and provide an effective thermal break. The multiplicity of apertures may be arranged along a linear path. The apertures may each be of substantially the same size and shape and may be equispaced. The apertures may be of rectangular shape defining bridging portions between them.

The spacing of adjacent bridging portions is preferably greater than the spacing of adjacent apertures. Thus, in the region of the apertures, the apertures occupy a greater area than the bridging portions, it being understood that "spacing" refers to edge to edge spacing rather than centre to centre spacing. The spacing of adjacent bridging portions may be more than three times greater than the spacing of adjacent apertures. The spacing of adjacent bridging portions may be more than six times greater than the spacing of adjacent apertures. In an embodiment of the invention described below the spacing of adjacent bridging portions is ten times greater than the spacing of adjacent apertures.

The thermally broken portion preferably extends along substantially the whole length of the first piece of sheet metal.

The step of connecting the first piece of sheet metal to one or more other pieces of sheet metal to form a door may comprise providing a second piece of sheet metal, the second piece of sheet metal being suitable for forming a second face of the door, and securing the second piece of sheet metal to the first door edge.

The second piece of sheet metal and the first piece of sheet metal may be secured together by inter-engaging formations. The first and second pieces of sheet metal may be provided with complementary U shaped lips which interengage. A layer of thermally insulating material may be placed between adjacent surfaces of the interengaging U shaped lips.

The second piece of sheet metal may be slid in a direction parallel to the first door edge to connect the first and second pieces of sheet metal. The first face of the door may be placed in an approximately horizontal plane for sliding the second piece of sheet metal to connect the first and second pieces of sheet metal.

The method may further comprise the step of removing further portions of the first piece of sheet metal to form a second multiplicity of apertures adjacent to one another through the first piece of sheet metal, the apertures extending from a position adjacent one boundary of the sheet metal to a position adjacent an opposite boundary, the apertures defining a thermal break in the first piece of sheet metal, and folding the first piece of sheet metal along a second axis substantially parallel to the direction along which the second multiplicity of apertures extend and substantially parallel to the first axis, the second multiplicity of apertures being spaced from the first face of the door. The first piece of sheet metal may be folded along the second axis to form a second door edge. The second door edge may extend in a plane perpendicular to the first face of the door and may have a distal end which is folded inwardly, the second multiplicity of apertures being provided on the inwardly folded distal end of the second door edge. The second door edge may be of similar or substantially the same construction as the first door edge.

After the step of folding the first piece of sheet metal, a thermally insulating filler material may be placed over the first piece of sheet metal for forming a thermally insulating core of the door. The filler material may be mineral wool.

The method may further comprise the step of providing an internal stiffener member of sheet metal, removing portions of the stiffener member to form a third multiplicity of apertures adjacent to one another through the stiffener member, the stiffener member being elongate and the apertures extending from a position adjacent one end of the member to a position adjacent an opposite end of the member, the apertures defining a thermal break in the first piece of sheet metal. The third multiplicity of apertures may be of similar or substantially the same form as the first multiplicity of apertures.

The method may further comprise the step of folding the stiffener member along an axis parallel to the direction in which the third multiplicity of apertures extend to form a first flange and mounting the first flange on the first piece of sheet material.

The step of mounting the first flange on the first piece of sheet material may comprise bonding the first flange and the first piece to opposite sides of thermally insulating adhesive tape.

The method may further comprise the step of folding the stiffener member along a further axis parallel to the direction in which the third multiplicity of apertures extend to form a second flange disposed adjacent to the second piece of sheet material. A plurality of stiffener members may be provided and each stiffener member may be treated in a similar, or substantially the same, way as the first mentioned stiffener member.

The method may further comprise the step of removing portions of the channel member to form a fourth multiplicity of apertures adjacent to one another in the channel member, the apertures extending from a position adjacent one end of the channel member to a position adjacent an opposite end, the apertures defining a thermal break in the channel member. The fourth multiplicity of apertures may be of similar or substantially the same form as the first multiplicity of apertures. The fourth multiplicity of apertures may be punched in the base of the U shaped channel member, preferably before the member is folded into a U shape.

The channel capping member may also be elongate and of generally U shaped cross-section. The method may further comprise the steps of providing a plurality of screw-threaded fasteners, and screwing the fasteners into the door to fasten the channel capping member to the internal channel member.

The limbs of the U shaped channel capping member may be disposed adjacent opposing limbs of the U shaped channel member and a layer of thermally insulating material may be placed between the adjacent limbs.

The method may further comprise the step of providing a further internal channel member along an edge of the door opposite to the first mentioned internal channel member. The further internal channel member may be similar to, or may be substantially the same as, the first mentioned internal channel member. Similarly there may be a further channel capping member for the further internal channel member. The further channel capping member may be similar to, or may be substantially the same as, the first mentioned channel capping member.

The first, second, third and/or fourth multiplicity of apertures may be formed in any suitable manner, including, for example, by laser cutting, but preferably are formed by punching, more preferably turret punching.

The method may further comprise the step of applying a polyester powder coating to the door.

The first and second pieces of sheet metal preferably extend over substantially all of the area of the first and second faces of the door respectively. That improves both the aesthetic and practical characteristics of the door. As will be understood, the thermally broken element is provided partway between the first and second faces and spaced from the faces.

The door may have a length greater than its width and the first door edge may extend along the length of the door. The door leaf may be of rectangular shape. In use the door is typically mounted with the first door edge element vertical.

Where reference is made in this specification to a "first" part, that should not be taken as indicating that it is essential that there be a second part of the same kind. Rather the reference is made to distinguish the "first" part from a "second" part which may be provided. Similarly, reference to a third part does not mean that there is necessarily a second part and similarly for reference to a fourth part. The same applies to references in the specification to a "first", "second", "third" and "fourth" multiplicity of apertures.

It should also be understood that the steps of the method can be performed in any order where that is possible and that the method is not limited to performance of the steps in the order recited or any other particular order except where specifically indicated.

Description of the Drawings

An embodiment of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 is a front elevation view of a door and frame assembly;

Figure 2 is a cross-sectional view of a U-shaped channel which forms a vertical edge of the door;

Figure 3 is a horizontal cross-sectional view of the door and frame assembly along the crosssection labelled 'X' in Figure 1;

Figure 4 is a vertical cross-sectional view of the door and frame assembly along the cross-section labelled Ύ' in Figure 1;

Figure 5 is an isometric view of the U-shaped channel shown in Figure 2 which forms a vertical edge of the door;

Figure 6 is an isometric view of a section of door frame member;

Figure 7 is a front elevation view of a second form of door and frame assembly; and

Figure 8 is a horizontal cross-sectional view of the door and frame assembly along the crosssection labelled 'Z' in Figure 7.

Detailed Description A door and frame assembly 1 is shown in Figure 1.

The door and frame assembly comprises a thermally broken door leaf 3 and a thermally broken door frame 5. Both the door and frame comprise a number of thermally broken structural elements which are arranged to mitigate heat transfer across the door and frame arrangement, usually from the inside to the outside of a building. Each of the thermally broken elements comprise sections of sheet metal which are thermally broken by a number of apertures, as will be explained below. The door and frame are both constructed such that, in use, the thermally broken elements are covered over, and therefore are not exposed to the outside environment.

As can be seen from the cross-sectional views in Figure 3 and Figure 4, the thermally broken door leaf 3 is formed by an outer panel 7, an inner panel 9, a top edge member 11 and a bottom edge member 13. The panels 7, 9, and the top and bottom edge members 11, 13 surround and enclose a thermally insulating mineral wool core 15. Apart from the mineral wool core 15, all the parts which form the thermally broken door comprise pieces of sheet metal which have been punched, where appropriate, using a CNC turret punch before being folded and pressed into shape using a variety of CNC folding machines.

The outer panel 7, which defines a first side of the door, forms an outside face sheet 16 of the door leaf 3 (the outside face being the face of the door leaf 3 that is located on the outside of the building when the door 3 is closed) and the opposite vertical edges of the door leaf 3. The panel 7 consists of a single piece of sheet metal, equal in vertical length to the height of the door 3, which has been folded along its vertical length at both vertical edges to create a U-shaped channel 17 which runs along each of the opposite vertical edges of the door leaf 3. Each U-shaped channel 17, one of which is shown in detail in Figure 2 and in Figure 5, is formed such that it comprises an outer arm 17A which forms part of the outside face sheet 16, and an inner arm 17B, located opposite the outer arm 17A, which is connected to the back of an inside face sheet 18 (the inside face being the face of the door 3 that faces the inside of the building when the door 3 is closed). The outer arm 17A and inner arm 17B are connected by a side section 17C which spans the thickness of the door 3 and forms a vertical edge of the door 3.

As can be seen from Figure 2 and Figure 5, the inner arm 17B, which extends at 90 degrees from the side section 17C, comprises a multiplicity of apertures which have been punched into the sheet metal to form a plurality of thermal break slots 19 which are spaced along the vertical length of the door leaf 3. The thermal break slots 19 are approximately 30 mm in vertical length, 6 mm in width and are vertically spaced by 3 mm. The outer panel 7 is therefore arranged such that the inside face sheet 18 is connected to the outside face sheet 16 via a thermally broken element 17B which comprises a multiplicity of 3 mm x 6 mm bridging members 20 which are formed between the thermal break slots 19.

The distal end of each of the inner arms 17B is folded 180 degrees back on itself into a U shape to form a lip 21, each of the outer panel lips 21 being engaged with a corresponding lip 23, the corresponding lips 23 being formed by the inner panel 9, as will be discussed below.

The inner panel 9, which defines the second side of the door, forms the inside face sheet 18 and is constructed from a single piece of sheet metal equal in vertical length to the height of the door 3. The inner panel 9 has been folded 180 degrees back on itself along each of its vertical edges to create a lip 23 along each of the vertical edges of the inside face sheet 18. To mount the inner panel 9 upon the outer panel 7, the inner panel 9 must be positioned end-to-end with the outer panel 7 such that the inner panel lips 23 are positioned to interlock with their corresponding outside panel lips 21, the panels 7, 9 must then be moved relative to one another along the vertical axis of the door leaf 3 such that the panels 7, 9 slidingly engage and the lips 21, 23 interlock. A layer of insulating foam tape 25 is placed between the lip 23 of the inner panel 9 and the arm 17B of the outer panel 7 such that the panels 7, 9 cannot directly come into contact with one another as direct contact between the panels in this region would bypass the thermal break slots 19. With the outer panel 7 and inner panel 9 positioned in this way, the door 3 is partially formed with an outside face sheet 16, an inside face sheet 18, and vertical edges 17C. A top edge member 11 and a bottom edge member 13 of the door leaf 3, represented by dotted lines in Figure 1, are sandwiched between the inside face sheet 18 and outside face sheet 16 and span the top and bottom edges of the door. The top and bottom edge members 11, 13 are identical and, as can be seen in Figure 4, are arranged such that, when they are contained within the door, they are mirror images of each other about a horizontal symmetry line across the centre of the door leaf. The edge members 11, 13 will now be described with reference to the top edge member 11 only, like parts on the bottom edge member are identically numbered in Figure 4 with the prefix '13' instead of '11'.

The top edge member 11 is generally in the shape of a hollow beam with a square cross-section. The top edge member 11 is formed by a U-shaped channel capping member 112 which is sat within a U-shaped internal channel member 111, the top edge member 11 being oriented such that the internal channel member 111 sits fully within the door leaf 3 and the channel capping member 112 forms the top edge of the door leaf 3. Each of the internal channel member 111 and the channel capping member 112 have two arms connected by a connecting portion to form the U-shape. The distance between the arms of the internal channel member 111 is slightly larger than the distance between the arms of the channel capping member 112, thereby allowing the channel capping member 112 to be positioned within the internal channel member 111 to form the top edge member 11 with a square cross-section. To install the top edge member into the door leaf 3, firstly the internal channel member 111 is positioned between the inside face sheet 18 and outside face sheet 16 at the top edge of the door leaf 3 such that it spans the width of the door leaf 3. The internal channel member 111 is then spot welded to the inside face sheet 18. The channel capping member 112, which has been filled with an insulating mineral wool core 15, is then installed within the internal channel member 111 at the top edge of the door leaf 3 such that it spans the width of the door leaf 3, with an edge of the channel capping member 113 forming the top edge of the door.

The channel capping member 112 is secured to the internal channel member 111 using a plurality of screw fasteners 116, one of which is shown in Figure 4. The threaded shaft of each fastener is pushed through a hole in the channel capping member 111, through the insulating mineral wool core 15 contained within the top edge member 11 and into screw threaded engagement with a hole in the internal channel member 111, and with the distal end of the screw extending into the thermally insulating mineral wool core 15 contained between the inner 18 and outer 16 face sheets.

The arms of internal channel member 111 are prevented from directly contacting the arms of the channel capping member 112 by a layer of thermally insulating foam tape 113 which is placed between the arms of internal channel member 111 and the arms of the channel capping member 112, the thermally insulating foam tape thereby acts as a thermal break between the outer internal channel member 111 and channel capping member 112. Further insulating capacity is provided by a number of apertures which are punched along the base of the internal channel member 111 which spans between the two arms of the internal channel member 111, the apertures acting as thermal break slots 114. As can be seen from Figure 3, the thermal break slots 114 span the width of the door and are arranged in the same way as the thermal break slots 19 that run along the vertical length of the inner arm 17B. The two arms of the internal channel member 111 are therefore connected by a thermally broken element which comprises a number of 3 mm χ 6 mm bridging members 115 located between the thermal break slots 114. As can be seen from Figure 3 and Figure 4, the top edge member 11 is oriented such that the thermal break slots 114 are positioned within the interior of the door.

The top edge member 11 is secured to the outside face sheet 16 via a layer of thermally insulating foam tape 117 placed between the arm of the internal channel member 111 and the outside face sheet 16.

The door leaf 3 is filled with a thermally insulating mineral wool core 15. To increase the stiffness of the door leaf 3, three vertical stiffeners 27 are spaced across the width of the door leaf 3 and run the vertical length of the door leaf 3. The stiffeners 27, represented by dotted lines in Figure 1, are shown in detail in Figure 3. The stiffeners 27 have a U-shaped cross-section consisting of an inside flange 27A which is bonded to the inside face sheet 18, an outside flange 27B which is bonded to the outside face sheet 16, and a web 27C which spans the thickness of the door 3 and connects the inside and outside flanges. One of the bonds between a flange and a face sheet is achieved using a layer of thermally insulating foam tape while the other is achieved using adhesive. As can be seen from Figure 3 the web of each stiffener comprises a number of thermal break slots 29, these are arranged along the vertical length of the stiffener 27 in the same way as the thermal break slots 19 that run along the vertical length of the inner arm 17B shown in Figure 5. Each stiffener is therefore arranged such that the inside flange 27A is connected to the outside flange 27B via a number of 3 mm x 6 mm bridging members (which are identical to the bridging members 20 shown in Figure 5) which are located between the thermal break slots 29.

The procedure for assembling the thermally broken door from its separate component parts will now be described.

Apertures are punched into the parts which make up the inner panel 9, outer panel 7, thermally broken stiffeners 27, the top edge member 11, and bottom edge member 13 using a CNC turret punch. The parts are then pressed into shape using CNC folding machines.

The outer panel 7 is laid down horizontally with its inner face uppermost and is reinforced for hinges and any other ironmongery before the thermally broken stiffeners 27 and top and bottom internal channel members 111, 131 are bonded in place using a thermally insulating foam based adhesive tape. The foam based adhesive tape is positioned between the flanges of the stiffeners 27 and the outside face sheet 16, and between the arms of the top and bottom edge members 111, 131 and the outside face sheet 16. The insulating mineral wool core is then added and a polyurethane adhesive is applied to the flanges of the thermally broken stiffeners which will contact the inside face sheet 18. The inner panel 9 is then slidingly engaged with the outer panel 7, as described above .

The top and bottom internal channel members 111 and 131 are then spot welded to the inside panel 9. Layers of insulating foam tape are applied to the internal channel members 111, 131, before the top channel capping member 112 is screwed into the top of the door leaf 3, and the bottom channel capping member 132 is screwed into the bottom of the door leaf 3, the layers of insulating foam tape being positioned between the arms of each internal channel member 111, 131 and channel capping member 112, 132 such that the internal channel members 111, 131, do not come into direct contact with the channel capping members 112, 132. The assembled door leaf is then subjected to heat and pressure to cure the polyurethane adhesive. The door leaf 3 is then prepared for hardware items before a polyester powder coating (PPC) finish is applied and the required ironmongery is installed on the door leaf.

The thermally broken door leaf 3 is mounted within a thermally broken door frame 5 via three hinges 31, as shown in Figure 1 and Figure 3. The door frame is formed by two side members 501, which in use are positioned vertically on opposite sides of the door, and a crossbeam member 502 which spans the gap between the two side members, at the top of the door. A section of the thermally broken door frame 5 is shown in Figure 6. Each of the side members 501 and the crossbeam member 502 of the door frame 5 is formed from a single piece of sheet metal which has been folded to form an inside jamb 503, a stop 504, and an outside jamb 505. An elastomeric door seal 33, which can be seen in Figure 3 and Figure 4, is contained within a door seal channel 507 which runs around both the side members 501 and the crossbeam member 502 of the door frame, being formed between the stop 504 and the outside jamb 505. As can be seen from Figure 6, a number of thermal break slots 509 are spaced along the length of each of the door frame members 501, 502, in the region where the outside jamb 505 meets the stop 504. The thermal break slots 509 are arranged in the same way as the thermal break slots 19 that run along the vertical length of the inner arm 17B. The door frame is therefore arranged such that the inside jamb 503 and stop 504 are connected to the outside jamb 505 via a number of 3 mm * 6 mm bridging elements 511 which are located between the thermal break slots 509.

Figure 7 shows a second form of door and frame assembly. The door and frame assembly shown in Figure 7 is similar to the door and frame assembly 1 of the first embodiment of the invention but comprises two door leaves 1000, 2000 and a door frame 3000 which is dimensioned to accommodate a double door leaf configuration. The door and frame assembly shown in Figure 7 has many features in common with the door and frame assembly 1; as such, like features have been labelled with like numbers but adding the prefix "100" or "200" to indicate which door leaf they belong to.

The door and frame assembly shown in Figure 7 comprises an active leaf 2000 and an inactive leaf 1000. In normal use, the inactive leaf 1000 remains shut and the active leaf 2000 is opened and closed to gain access to the building to which the door and frame assembly is fitted. However, both leaves 1000, 2000 may be opened if necessary. Figure 8 shows a cross-sectional view of the inactive and active leaves 1000, 2000 in the region where the leaves 1000, 2000 meet. As can be seen, the thickness of a section 1070 of the inactive door leaf 1000 has been locally reduced in the region where the two door leaves 1000, 2000 meet and the active door leaf is arranged with an overlapping portion 2080 which projects widthways out of the vertical edge of the door leaf 2000, parallel with the outside face sheet 2016, towards the inactive leaf 1000. The overlapping portion 2080 is arranged to overlap with the inactive leaf 1000 and sit against the section 1070 when the doors are closed, the local thickness reduction of the section 1070 being such that when the doors are closed, the outside face sheet 2016 of the active leaf 2000 sits flush with the outside face sheet 1016 of the inactive leaf 1000.

Claims

1. A method of manufacturing a door comprising the steps of: providing a first piece of sheet metal, the first piece of sheet metal being suitable for forming a first face of the door, removing portions of the first piece of sheet metal to form a first multiplicity of apertures adjacent to one another through the first piece of sheet metal, the apertures extending from a position adjacent one boundary of the sheet metal to a position adjacent an opposite boundary, the apertures defining a thermal break in the first piece of sheet metal, folding the first piece of sheet metal along a first axis substantially parallel to the direction along which the apertures extend, to form the first face of the door, the first multiplicity of apertures being spaced from the first face of the door, connecting the first piece of sheet metal to one or more other pieces of sheet metal to form a door, providing an internal channel member made of folded sheet metal along an edge of the door, the internal channel member being elongate and comprising a U-shaped cross-section, providing a channel capping member, and installing the channel capping member over the internal channel member to form a closed edge to the door .

2. A method according to claim 1, wherein the first piece of sheet metal is folded along the first axis to form a first door edge.

3. A method according to claim 2, wherein the first door edge extends in a plane perpendicular to the first face of the door and has a distal end which is folded inwardly, the first multiplicity of apertures being provided on the inwardly folded distal end of the first door edge.

4 . A method according to any preceding claim, wherein the step of connecting the first piece of sheet metal to one or more other pieces of sheet metal to form a door, comprises providing a second piece of sheet metal, the second piece of sheet metal being suitable for forming a second face of the door, and securing the second piece of sheet metal to the first piece of sheet metal.

5. A method according to claim 4, wherein the second piece of sheet metal and the first door edge are secured together by inter-engaging formations.

6. A method according to claim 5, wherein the second piece of sheet metal is slid in a direction parallel to the first door edge to connect the first and second pieces of sheet metal.

7. A method according to claim 6, wherein the first face of the door is placed in an approximately horizontal plane for sliding the second piece of sheet metal to connect the first and second pieces of sheet metal.

8 . A method according to any preceding claim, wherein the method further comprises the step of removing further portions of the first piece of sheet metal to form a second multiplicity of apertures adjacent to one another through the first piece of sheet metal, the apertures extending from a position adjacent one boundary of the sheet metal to a position adjacent an opposite boundary, the apertures defining a thermal break in the first piece of sheet metal, and folding the first piece of sheet metal along a second axis substantially parallel to the direction along which the second multiplicity of apertures extend and substantially parallel to the first axis, the second multiplicity of apertures being spaced from the first face of the door .

9. A method according to claim 8, wherein the first piece of sheet metal is folded along the second axis to form a second door edge.

10. A method according to claim 9, wherein the second door edge extends in a plane perpendicular to the first face of the door and has a distal end which is folded inwardly, the second multiplicity of apertures being provided on the inwardly folded distal end of the second door edge.

11. A method according to any preceding claim, in which, after the step of folding the first piece of sheet metal, a thermally insulating filler material is placed over the first piece of sheet metal for forming a thermally insulating core of the door.

12. A method according to any preceding claim, further comprising the step of providing an internal stiffener member of sheet metal, removing portions of the stiffener member to form a third multiplicity of apertures adjacent to one another through the stiffener member, the stiffener member being elongate and the apertures extending from a position adjacent one end of the member to a position adjacent an opposite end of the member, the apertures defining a thermal break in the first piece of sheet metal.

13. A method according to claim 12, further comprising the step of folding the stiffener member along an axis parallel to the direction in which the third multiplicity of apertures extend to form a first flange and mounting the first flange on the first piece of sheet material.

14. A method according to claim 13, wherein the step of mounting the first flange on the first piece of sheet material comprises bonding the first flange and the first piece to opposite sides of thermally insulating adhesive tape.

15. A method according to any preceding claim, further comprising the step of removing portions of the channel member to form a fourth multiplicity of apertures adjacent to one another in the channel member, the apertures extending from a position adjacent one end of the channel member to a position adjacent an opposite end, the apertures defining a thermal break in the channel member.

16. A method according to any preceding claim, wherein the method comprises the further steps of providing a plurality of screw-threaded fasteners, and screwing the fasteners into the door to fasten the channel capping member to the internal channel member .

17. A method according to any preceding claim in which the step of removing portions of material from a part comprises punching the portions out of the part.

18. A method according to any preceding claim, further comprising the step of applying a polyester powder coating to the door.