Technical field

The present invention relates to a method for production of a metal profile for a building frame and a metal profile assembly for a building frame and to a method for erection of a building frame.

Description of the prior art

Buildings may be built in a large number of different ways. The roof of the building may be supported by load bearing walls or posts/columns or a combination of these. Load- bearing walls may for example be constituted by reinforced concrete or light concrete. The posts/columns may be constituted by scantlings or metal columns between which non load- bearing wall slabs are arranged. The posts/columns may be joined with horizontal beams to a building frame. It is previously known to use metal profiles as load-bearing elements in a building.

Traditionally, when a building frame is to be erected of metal profiles, metal profiles in a standard length have been delivered to a building site. At the building site the metal profiles have been cut and provided with holes for elements for joining. The cutting and the making of holes have been made starting from construction drawings of the building frame and have been performed by erectors on the building site. Before cutting and making of holes in the metal profiles the erectors must measure and mark where cutting and making of holes is to be performed. This leads to the accuracy of the length of the metal profiles and the placement of the holes being affected negatively as it is difficult to measure and mark with the measuring aids that are at hand at a building site.Furthermore, the tools that are at hand at a building site are usually relatively simple which leads to further deterioration of the accuracy. It is for example not unusual that the erectors use simple hand tools such as common hand-held drilling machines for the making of holes and hand-held saws for the cutting. When the making of holes and the cutting is performed with such hand-held tools there is a risk that the tool slides many millimetres in relation to the marked positions for cutting and making of holes. This entails that the holes in two adjacent profiles may be displaced in relation to each other by several centimetres even if it was intended that they should not have been displaced. Up to now self-drilling and self- tapping screws have been used for joining at the joints between the metal profiles.

Alternatively, holes have first been drilled after which the profiles have been joined using metal profile connectors. The first-mentioned method removes a working operation but in both cases it is, however, a very big risk that the holes end up in the wrong position due to the fact that the tip of the drill often slides away on the surface of the profile before it eventually gets grip in the metal profile.

Independently of which method that has been chosen to be used in making the holes and the joining of the profiles, the procedure involves a very large workload on the erectors at the building site when the working operations recurs hour after hour, day after day and month after month outdoors irrespective of the weather.

As an alternative to making holes self-drilling and self-tapping screws have been used. Even if such screws eliminate one working operation there is an even bigger risk for the screw to slide away across the surface of the profile before the drilling part of the screw gets grip in the profile. Additionally, the workload on the construction workers increases.

Metal profiles may be used together with grooved hard insulation such as cellular plastic, for example EPS, in order to build an insulated building frame. This is described inter alia in the Swedish patent application SE 511661 which is hereby included in this application by reference. In such a building frame the profiles, together with grooved hard insulation of the type EPS, form an integrated strong loadbearing unit. If the holes in the profiles are not placed in the correct positions this may lead to the construction not being tight which leads to energy leakage. Alternatively, it may be impossible to assemble the profiles, unless new holes are made in the flanges, which is time consuming at the same time as the strength is deteriorated. The Swedish patent SE 511661 describes a method for joining consecutively arranged building blocks, consisting of two plane main sides and four edge sides, using sheet metal profiles with a web and flanges, to an entirely inorganic building frame. The frame system described in SE 511661 is based on the two integrated materials, the profiles and the insulation, together forming a unit, and thus being strong. The grooving in the insulation contributes to the profile being up to ten times stronger before the profile buckles and fails under load stress, compared to the case of the profile being freestanding and thereby not getting any support from the insulation.

Making of holes with precision is, as is described above, a prerequisite if a frame is to be built with the technique in SE 511661 and the best possible insulation and strength is to be achieved.

A further problem with erection of building frames according to the prior art is that the work of the erectors is heavy and cumbersome which to a very high degree leads to industrial injuries of the erectors. This has led to larger construction companies seriously contemplating a total stop in erecting building frames of metal profiles.

US 7,207,201 describes a manufacturing process for a U/Z-formed steel bar.

US 6,763,634 describes a connection detail for a roof rafter. WO 2005/075756 describes a construction element for erection of an assembly.

Summary of the invention

An object of the present invention is to provide a method for production of a metal profile for a building frame, with which metal profile the erection of a buildning frame is facilitated. A further object of the present invention is to provide a method for production of a metal profile for a building frame, with which metal profile the work at the building site, on which the building frame is erected, may be minimized.

Another object of the present invention is to provide a metal profile assembly for a building frame comprising the metal profiles of bent sheet metal which are required to build the building frame, with which metal profile assembly the work at the building site, on which the building frame is erected, may be minimized.

A further object of the present invention is to provide a method for erection of a building frame using a metal profile assembly, with which method the work at the building site may be minimized. At least one of these objects is achieved with the methods or a metal profile assembly according to the independent claims.

Additional advantages of the invention are provided with the features of the dependent claims.

A method for production of a metal profile for a building frame, comprises the steps of providing sheet metal, to feed the sheet metal in a feeding direction, when the sheet metal is fed in the feeding direction, to bend the sheet metal to a bent sheet metal comprising a web and flanges on both sides of the web, and to cut off a metal profile after the bending. The method is characterized in that the cutting is made so that the metal profile gets a length which is adapted to a predetermined building frame so that the metal profile may be used to the building frame directly without any additional cutting of the metal profile and that the method comprises the step before the cutting of arranging fastening holes in predetermined positions of the sheet metal so that the metal profile may be fastened to other metal profiles in the building frame directly without any need of drilling any additional holes in the metal profile. With a method according to the invention a metal profile is provided which may be used for a building frame directly without any need of cutting or making of holes at the building site. Thereby, the work at the building site is facilitated at the same time as the necessary effort at the building site is minimized. Furthermore, a better accuracy in the cutting and making of holes may be achieved when it is performed according to the invention instead of being performed by hand by workers at the building site, on which the building frame is erected. By the cutting of the metal profile being made after both the making of holes and the bending a high accuracy in the dimensions of the metal profile is achieved. In US 7,207,201 the bending of the metal profile is performed after the cutting, in contrast to the present invention. In the description the expression bent sheet metal will be used for the bent sheet metal before it is cut. The expression metal profile will be used for the cut off pieces of the bent sheet metal.

With a method according to the invention drilling and cutting is avoided at the building site. This means that an erector at the building site does not have to measure or mark for making of holes or cutting. Further, the erector does not have to drill or cut. This leads to the work at the building site becoming less demanding with less load on the erector. The lower load on the erector results in that industrial injuries may be avoided on both long and short term. With the method according to the invention the assembly at the building site is made considerably faster. Furthermore, several sources of error are eliminated as the erector do not have to measure and mark at a building site that may be dark and cold. This leads to fewer costly erroneous constructions due to measuring errors and misinterpretation of the construction drawing.

The fact that the fastening holes are arranged before the metal profile is cut means that the making of holes is performed in advance before the metal profile is delivered to a building site. Instead of an erector at the building site having to measure, mark, saw and drill in accordance with construction drawings for the building, this is made in advance in accordance with construction drawings before the metal profiles arrive at the building site. The maybe most important advantage with metal profiles according to the invention is, however, that the time to complete a building frame at the building site is reduced considerably with the invention. Compared to traditional erection of building frames of metal profiles the time may be reduced with up to at least 75 %. With the invention it is thus possible to finish the building frame on a fourth of the time that is necessary with traditional methods, at the same time as the quality and strength of the connection points becomes sufficient. This is guaranteed by the fact that the holes are guaranteed to be correctly positioned at the joints.

The bending is preferably performed through roll forming. Even if it is possible to achieve the bending in another way, rollforming is the preferred method which is suitable for bending of continuous sheet metal. Rollforming is an in itself well known technique which will not be described in detail here.

The fastening holes may be arranged before the sheet metal is bend. This is advantageous in that the holes then may be punched in the sheet metal in a simple way as the sheet metal then still is flat. It is possible to punch holes also after the sheet metal has been bent, but it might then be more difficult to arrange a dolly for the punching. It is of course also possible to drill the holes, but that is more complicated. By arranging the holes before the bending the holes may be placed with a higher accuracy in the plate. As is evident from US 7,207,201 it is advantageous to make the holes before the bending through rollforming in order to minimize the deformation of the profile during the making of the holes.

Even if arrangement of holes before the bending results in that the holes are positioned with a high accuracy it might for different reasons be advantageous to do the opposite and to arrange the fastening holes after the bending of the sheet metal. In order to join the metal profiles to a building frame it is necessary that at least some of the metal profiles have fastening holes in at least one of the flanges. In order for the fastening holes in the flanges to end up in the correct position in relation to the web after the bending it is required that the bending/rollforming is performed with a very high accuracy. It is difficult to achieve the desired accuracy with roll forming. For that reason it is advantageous to arranged the holes in the flanges after the bending in order to make sure that the fastening holes in the flanges are placed in the correct positions in relation to the web.

It is possible to let all metal profiles have fastening holes in at least one of the flanges.

The fastening holes may be arranged in groups of holes with at least two fastening holes in each group of holes. By having at least two holes in each group of holes a more simple manufacturing is provided as it is then possible to use the same group of holes in many positions, even if only one hole in the group of holes is used for some of the joints in the building frame.

The fastening holes in each group of holes may be arranged symmetrically in relation to a 90 degree rotation around the perpendicular to the surface in which the group of holes is arranged. This is advantageous when a metal profile is to be attached in an angle to another metal profile as the holes in the rotated group of holes then fit the holes in another non- rotated group of holes.

Each group of holes may be arranged with an oblong centre hole. Such an oblong centre hole is advantageous in that two centre holes which are rotated 90 degrees in relation to each other then has a relatively large area of mutual positioning within which the oblong centre holes have some overlap. This facilitates the joining of two metal profiles in a joint or junction.

Each group of holes may be arranged with eight fastening holes. With eight fastening holes the fastening holes may be arranged symmetrically in a square around a centre hole. It is then possible to make all groups of holes identical as it is not necessary with more than eight fastening holes for any joint in a building frame.

One or more of the holes in a group of holes may be used to feed the sheet metal forward. In this way an accurate feeding of the sheet metal is ensured which results in that the group of holes are positioned at a correct distance from each other with a high accuracy.

The fastening holes may be punched in the sheet metal. It is of course possible to drill the fastening holes in the sheet metal, but punching is faster and less complicated.

The arrangement of the fastening holes and the cutting of the metal profile may be controlled by a computer. This is advantageous in that the method then is automated. The computer may control the arrangement of the fastening holes and the cutting of the metal profile with an electronic construction drawing of a building or a building frame as input. In this way the automation may be driven longer and a metal profile assembly for a building frame may be achieved directly from a construction drawing, without the need of interference from an operator. The method may also comprise the step of marking the metal profile with an identification number or an identification code, which may be unique for each metal profile, so that the correct metal profile is easily identified at the building site. This results in that the workers at the building site may easily find the correct metal profile when the building frame is to be erected.

According to a second aspect of the present invention a metal profile assembly is provided for a building frame comprising the metal profiles of bent sheet metal that are required to build the building frame. The metal profile assembly is characterized in that the metal profiles have lengths which are adapted to the building frame so that the metal profiles may be used for the building frame directly without additional cutting, and that fastening holes are arranged on predetermined positions on the metal profile so that the metal profile may be attached to other metal profiles in the building frame directly without any need of drilling any additional holes.

With a metal profile assembly according to the invention the building of a building frame at a building site is facilitated as the working operations are minimized. This results in that the number of workers and/or the time for building the building frame may be reduced compared to traditional building with metal profiles.

The advantages that have been mentioned above in relation to the first aspect of the invention are valid also for the second aspect of the invention and will not be repeated here again.

A profile assembly according to the invention may be delivered to a building site as flat packages and may easily be assembled at the building site by a person without any deeper knowledge of building technology. For example the metal profiles may be assembled using pop rivets.

A building frame which is built with the metal profile assembly according to the above is in its simplest form only a building frame for a roof on posts. The building frame which is built with the metal profile assembly may also be an non-insulated warehouse or a house.

The fastening holes may be arranged in groups of holes with at least two fastening holes in each group of holes. By having at least two holes in each group of holes a more simple manufacturing is provided as it then becomes possible to use the same group of holes in many positions, even if only one hole in the group of holes is used for some joints in the building frame.

The fastening holes in each group of holes may be arranged symmetrically with respect to 90 degrees rotation around the perpendicular to the surface in which the group of holes is arranged. This is advantageous when a metal profile is to be attached at an angle to another metal profile as the holes in the rotated group of holes then fit with the holes in another non-rotated group of holes.

Each group of holes may comprise an oblong centre hole. Such an oblong centre hole is advantageous in that two centre holes which are rotated 90 degrees in relation to each other then has a relatively large area of mutual positioning within which the oblong centre holes have some overlap. This facilitates the joining of two metal profiles in a joint or junction.

Each group of holes may comprise eight fastening holes. With eight fastening holes the fastening holes may be arranged symmetrically in a square around a centre hole. It is then possible to make all groups of holes identical as it is not necessary with more than eight fastening holes for any joint in a building frame.

Each metal profile may be provided with an identificaton number. Each metal profile is thereby easily identifiable at the building site so that the work on the construction may be performed faster. The identification numbers may be unique or be the same only for mutually identical metal profiles.

According to a third aspect of the present invention a method is provided for production of a metal profile assembly for a building frame comprising the metal profiles of bent sheet metal that are required to build the building frame. The method comprises the steps of providing a sheet metal, to feed the sheet metal in a feeding direction, when the sheet metal is fed in the feeding direction to bend the sheet metal to a bent sheet metal comprising a web and flanges on both sides of the web, and to cut metal profiles from the bent sheet metal. The method is characterized in that the cutting is made so that the metal profiles get lengths which are adapted to a predetermined building frame so that the metal profiles may be used for the building frame directly without additional cutting of the metal profile and that the method comprises the step before the cutting of arranging fastening holes at predetermined positions on the sheet metal so that the metal profiles may be attached to other metal profiles i the building frame directly without need of drilling any additional holes in the metal profiles.

Thus, the metal profiles may be assembled to the building frame without additional work with drilling and cutting at the building site.

The cutting and arrangement of fastening holes in the metal profiles is made in accordance with construction drawings for the building frame. Thus, an erector of the building frame does not have to measure, mark, cut or drill at the building site but needs only to identify the correct profiles and to assemble them in accordance with the construction drawings.

The advantages that have been mentioned above in relation to the first aspect of the invention are valid also for the third aspect of the invention and will not be repeated here again.

In order to facilitate the identification of the metal profiles at the building site the metal profiles may be marked with identification numbers or identification codes which may be unique for each metal profile.

It is possible to perform the joining of the metal profiles with pop rivets on the building site.

According to a fourth aspect of the invention a method is provided for erection of a building frame comprising the step of providing a metal profile assembly according to the third aspect of the invention. The method is characterized in that it comprises the step of joining the metal profile assembly to a building frame, wherein building blocks of cellular plastic are arranged in contact with the profiles between the profiles.

Preferably, a metal profile assembly is used in which at least a part of the metal profiles have flange portions which extend from the outer edge of the flanges.

The method according to the fourth aspect of the invention totally eliminates the working operations and loads which where described in the description of the prior art. The profiles are delivered to the building site with the holes made and cut in the correct lengths, and may be joined using pop rivets.

A big advantage with metal profiles and metal profile assemblies according to the invention is that the holes end up in the correct positions, which is required to enable joining of the metal profiles using pop rivets without the need to drill. No appreciable muscle force is required of the erectors to assemble the construction using pop rivets. This contributes to the total elimination of industrial injuries due to drilling and tapping to join the joints.

An additional advantage of the invention which is achieved by avoiding drilling is that the working environment is improved. Drilling and tapping in metal creates a lot of noise and high decibel numbers are reached during such work. If the holes are in the correct positions so that it is possible to assemble the construction using pop rivets this may be made without using ear protectors, which is not necessary when using modern pop rivet machines. The fact that the erector not uses ear protectors means that the safety for the erector increases at the working site as the erector hears dangers which arise at a building site. The advantages which have been mentioned above in relation to the first aspect of the invention are valid also for the fourth aspect of the invention and will not be repeated here again.

The metal profile assembly may be joined using pop rivets. This is an easy way of joining the metal profiles which is possible to use due to the fact that the accuracy in the positions of the holes may be held high.

With a metal profile assembly and methods according to the invention assembly errors, which are costly to put right, are minimized.

With the methods according to the first and second aspect of the invention a high accuracy is provided in the positions of the holes and the lengths of the profiles. With the methods according to the invention an accuracy of a thousand of a millimetre is provided.

The features above may be combined in the same embodiment. In the following preferred embodiments of the invention will be described with reference to the appended drawings.

Short description of the drawings

Fig. 1 shows a building frame assembled with a metal profile assembly according to an embodiment of the present invention.

Fig. 2 shows a wall in a building frame assembled with a metal profile assembly according to an embodiment of the present invention.

Fig. 3 shows metal profiles in a metal profile assembly according to an embodiment of the present invention. Fig. 4 shows a detail view over a part of a building frame assembled with a metal profile assembly according to an embodiment of the present invention.

Fig. 5 shows a hole group in a metal profile in a metal profile assembly according to an embodiment of the present invention. Fig.6 shows how insulation boards may be joined together with a metal profile in a metal profile assembly according to an embodiment of the present invention.

Fig. 7 shows in cross section from the side a wall assembled with a metal profile assembly according to an embodiment of the present invention. Fig. 8 shows in a cross section from above a wall assembled with a metal profile assembly according to an embodiment of the present invention.

Fig. 9 is a flowchart over a method according to an embodiment of the present invention.

Fig. 10 shows schematically equipment for performing the method.

Description of preferred embodiments

In the following description of preferred embodiments the same features in the different drawings will be denoted with the same reference numeral. It should be noted that the drawings are not drawn to scale.

In the following description the expression metal profile will be used for the cut off parts of the bent sheet metal. Fig. 1 shows a building frame 1 which is assembled with a metal profile assembly according to an embodiment of the present invention. The metal profile assembly comprises a number of metal profiles which are joined to the building frame 1. The metal profiles are arranged as inter alia beams 2, joists 3, tie beams 4, nogging pieces 5, ground beams 6, and ridge beams 7. Fig. 2 shows a wall in a building frame which is assembled with a metal profile assembly according to an embodiment of the present invention. The metal profile assembly comprises a plurality of metal profiles which are joined to form the building frame 1. The metal profiles are arranged inter alia as joists 3, nogging pieces 5, ground beam 6, and ridge beams 7. Fig. 3 shows metal profiles in a metal profile assembly according to an embodiment of the present invention. In the metal profile assembly is in Fig. 3a shown a C-profile 16 comprising a web 9, a first flange 10 and a second flange 11. There is arranged a plurality of hole groups 12 in the web as well as in the flanges 10, 11. Each one of the hole groups comprises an oblong centre hole 13 and eight fastening holes 14, which are arranged symmetrically in relation to a 90 degree rotation around the perpendicular to the surface in which the hole group 12 is arranged. As is evident from the figure the centre holes 13 in all hole groups 12 are arranged in the same direction. In Fig. 3b a C-profile 17 is shown having flange portions 15 extending from the outer edges of the flanges 10, 1 1. The flange portions 15 are essentially parallel to the web 9. In Fig. 3c a Z-profile 18 is shown which also has flange portions 15 which are essentially parallel to the web 9 and which extend from the outer edge of the flanges 10, 11.

The holes in the metal profiles are arranged in accordance with construction drawings for the building frame which is to be erected. Instead of measuring, marking, sawing and drilling on the building site in accordance with construction drawings this is made in advance before the metal profiles are delivered to the building site. The holes in the metal profiles thus mark where the metal profiles are to be connected.

As is evident from Fig. 3 a fastening holes 14 are arranged in the flanges 10 as well as in the web 9 in the metal profile 16.

Fig. 4 shows a detail view of a part of a building frame assembled with a metal profile assembly according to an embodiment of the present invention. As is evident from Fig. 4 the metal profiles are attached to each other with a 90 degree angle between the metal profiles. As an example a first Z-profile 19 is arranged with its end against a first C-profile 20. Thanks to the fastening holes in the hole groups being arranged symmetrically in relation to 90 degrees rotation around the perpendicular to the surface in which the fastening holes 14 are arranged, the fastening holes 14 in the first Z-profile 19 will correspond to the fastening holes 14 in the first C-profile 20. The centre hole 13 in the first Z-profile 19 has a certain overlap with the centre hole 13 in the first C-profile for a range of mutual positions which is dependent on the length of the centre holes. Using a rod through the centre holes 13 in both the first C-profile 20 and the first Z-profile, the C- profile and the Z-profile 19 may be pushed into the correct position so that their fastening holes overlap each other. As is evident from the figure the metal profiles are provided with slits 23 which are arranged so that the heat transfer path between the flanges 10, 11, becomes long and so that the heat transfer surface between the flanges 10, 1 1, becomes small. In this way the heat transfer capacity between the flanges 10, 11, is minimized. The metal profiles are intended to be arranged with the first flange facing the inside of a building and the second flange facing the outside of a building. The metal profiles may be attached to each other with pop rivets.

Fig. 5 shows a hole group 12 in a metal profile in a metal profile assembly according to an embodiment of the present invention seen towards the surface in which the hole group is arranged. The metal profile is a C-profile and the hole group 12 comprises a centre hole 13 and eight fastening holes 14.

Fig. 6 shows how insulating boards 21 may be connected with a metal profile in a metal profile assembly according to an embodiment of the present invention. The metal profile is a Z-profile according to Fig. 3c and comprises flange portions 15. The insulating boards 21 comprises grooves 22 which are arranged to interact with the flange portions 15. The web 9 of the Z-profile 19 is provided with a plurality of slits 23. The first flange 10 of the Z- profile 19 is intended to be arranged facing the inside of a building and the second flange 11 of the Z-profile is intended to be arranged facing the outside of a building. Thanks to the slits 23 in the web the heat transfer capacity through the web 9 is considerably worse than it would have been without the slits 23. As the Z-profile 19 is of metal it has considerably higher specific heat transfer capacity than the insulating blocks 21. Thanks to the slits 23 the heat transfer surface is decreased at the same time at the heat transfer length between the flanges increases. Fig. 7 shows in cross section from the side a wall erected with a metal profile assembly according to an embodiment of the present invention. Fig. 8 shows in a cross section from above the wall in Fig. 7. In Fig. 7 the Z-profile 19 is seen from the side with a length axis

24 which is arranged vertically in a building. The slits 23 are arranged parallel with the length axis 24. As is evident from Fig. 8 insulating blocks 21 are arranged on either side of the Z-profile 19. On one of the flanges 9 horizontal U-profiles 25 with a length axis 30 (Fig. 8) are arranged, of which one is shown in Fig. 7 and 8. On the outside of the U- profiles a facade panel 26 is arranged, which is intended to provide weather protection. As is evident from Fig. 8 a large number of ventilation holes 27 are arranged in the U-profile

25 so that air may pass between the facade panel 26 and the insulating blocks 21. On the second flange 11 of the Z-profile 19 an inner angle iron 28 with a length axis 29 (Fig. 8) is arranged. The inner angle iron 28 is arranged with the length axis 29 perpendicular to the length axis 24 of the Z-profile 19. The inner angle iron 28 comprises a web 31, an inner flange 32 and an outer flange 33 which is attached to the Z-profile 19. On the inner flange 32 inner wall panels 34, in the form of two plasterboards, are arranged. Between the inner wall panels 34 and the insulating panels there is arranged insulation 35 in the form of inter alia glass wool or mineral wool. As is evident from Fig. 8 the web 31 of the angle iron 28 is provided with slits 36 to deteriorate the heat transfer capacity of the web 31. In the web 31 there is also arranged holes 37 for inter alia electric wires. The wall that is shown in Fig. 7 and Fig. 8 may be erected using a metal profile assembly according to an embodiment of the present invention. Fig. 9 is a flow chart over a method according to an embodiment of the present invention. The method for production of a metal profile for a building frame comprises the steps of providing 101 a sheet metal, which preferably is provided from a roll. The method also comprises the steps of feeding forward 102 the sheet metal in a feeding direction, to punch 103 fastening holes in the sheet metal in predetermined positions so that the metal profile may be attached to other metal profiles in the building frame directly without the need of drilling any additional holes in the metal profile. After the arrangement of the fastening holes the sheet metal is bent 104 by rollforming to a bent sheet metal comprising a web and flanges on either side of the web. Then follows the step of cutting 105 a metal profile after bending of the sheet metal, wherein the cutting of the metal profile is made so that the cut off piece is of a length adapted to a predetermined building frame so that the metal profile may be used to the building frame directly without additional cutting of the metal profile.

Fig. 10 shows schematically an equipment for performing the method. Preferably the method comprises also the step of arranging slits, as is shown in Fig. 4, 6, 7, and 8, in the metal profile. The method for production preferably starts with providing a roll 40 of sheet metal 41 of suitable width. The sheet metal 41 is fed using a feeder 42 to a first punching machine 43 which punches slits in the sheet metal 41. After the first punching machine 43 a second punching machine 44 is arranged which punches hole groups in the sheet metal in predetermined positions. As is evident from the figure the feeder 42 is arranged after the first punching machine 43 and the second punching machine 44. The feeder 42 uses the punched holes to accurately feed the sheet metal 41 forward. Subsequently, a bending device 45 is arranged which in an in itself well known way bends the sheet metal to a desired metal profile. A computer 46 is arranged to control the feeder and the punching machines. As an input for the control the computer has a digital construction drawing of the building frame. There is also arranged a cutting machine 47 which cuts the bend sheet metal 41 in suitably long metal profiles 48. Also the cutting machine 47 is controlled by the computer 46. The feeder feeds the sheet metal forward with a high accuracy.

Preferably, the sheet metal is fed forward with an accuracy of a thousand of a millimetre. The described embodiments of the invention may be modified in many ways without departing from the spirit and scope of the invention which is limited only by the appended claims.

It is inter alia possible to change order of the first punching machine 43 and the second punching machine 44. It is possible and in some cases preferable to punch/arrange the holes after the bending of the sheet metal as has been described earlier.