Method For Bending Flat Pattern Spring Strips

Abstract

This disclosure relates to a method for bending flat pattern spring strips which are characterized as including a plurality of laterally spaced apart, generally parallel torsion bars connected alternately on opposite sides by connecting arms. The method comprises the steps of forming a first 90.degree. bend in a first plane of the spring strip along one of the connecting arms, turning the free end portion out of the first plane by twisting the connecting arm and forming a second 90.degree. bend along the connecting arm to dispose the free end portion defining a depending leg adjacent the plane of the spring strip and angularly offset therefrom. Providing a standard fishmouth section on one end of the spring strip requires the performance of the above-described operation on two connecting arms thereby forming a first and second interconnected depending leg.

Description

This invention relates to a method for bending flat pattern spring strips into a configuration usable in seat constructions. Flat pattern spring strips are well known in the seating art and are characterized as including a plurality of laterally spaced apart, generally parallel torsion bars connected alternately on opposite sides by connecting arms.

The basic flat pattern or shape of the spring strip must be formed or bent to provide a spring configuration which is usable in seat constructions. The final form includes V-shaped load supporting sections or fishmouth sections, as they are commonly termed in the art, which depend from each of the free ends of the spring strip. The intermediate wire bends between the fishmouths define the load carrying or seating section of the spring strip. In a typical seat construction a plurality of spring strips, which have been formed or bent to provide the fishmouth sections at each end thereof, are attached at the base or lower ends of the fishmouths to the front and rear rails of a seat frame. The plurality of spring strips are disposed in a generally spaced, parallel and aligned arrangement to define a load carrying area over which suitable padding and seat fabric is secured to substantially complete the seat structure.

Heretofore the V-shaped or fishmouth sections have been formed by folding the flat pattern spring strip in much the same manner as one would fold a zig-zag in a strip of paper. More specifically, the free ends of the spring strips are folded by being twisted or rotated about the axis of one of the torsion bars. An upward and downward twist about two torsion bars at each end of the spring strip will obviously produce the desired fishmouth sections. This is the method or process now being used to form the spring strips in conventional automatic wire bending machines.

The above described method has worked quite well up to this time; however, a change in the specifications of the spring strips by seat manufacturers have caused production difficulties. More specifically, the seat manufacturers are currently requiring that the angle between the load carrying portion and the intermediate leg of the fishmouth section be 30.degree. or less. The reason for this is that a lower profile seat with improved resilience can be constructed by reducing this critical angle.

The problem for the wire bender is that the method used by the conventional wire bending machines is not sufficient to produce the required angular relationship described above. First of all the flat pattern spring strip can only be twisted 180.degree., that is, until the free end being folded contacts or meets the rest of the spring strip. Upon release of the load or compressive folding force, the wire will, of course, spring back due to its natural resilience. The tendency of the spring to return to the unbent shape is, naturally, the reason why a wire bent into this configuration can be used in seat constructions. It has been the experience of wire bender that the spring-back will normally produce an angle of 30.degree. or greater and therefore the present bending method will produce spring strips that only approach the design requirements of the seat manufacturer.

A related problem encountered when trying to reduce the critical angle is the build up of high torsional stresses along the torsion bar about which the spring strip is being twisted. The torsional stresses caused by excessive, twisting build up at the 90.degree. corner whereat the connecting arm is joined to the torsion bar causing plastic deformation of the metal in this area. The resulting work hardening frequently causes brittle fracture of the spring strips to occur at this critical point. Some wire benders have turned to an annealing process to reduce the stresses, but this of course, is an added operation which is both time consuming and expensive.

It is therefore an object and feature of the instant invention to provide a method for bending V-shaped supporting sections or fishmouth sections in flat pattern spring strips wherein the method is adapted to produce a critical angle of less than 30.degree..

It is another object and feature of the instant invention to provide a method for bending V-shaped supporting sections or fishmouth sections in flat pattern spring strips wherein the method eliminates the build-up of excessive or high torsional stresses at the 90.degree. corners of the spring strip.

In correlation with the foregoing objects and features, it is an object and feature of the instant invention to provide a method for bending flat pattern spring strips which include a plurality of spaced apart and generally parallel torsion bars connected alternately on opposite sides by connecting arms comprising the steps of forming a first bend in a first plane of the spring strip along one of the connecting arms, turning the free end portion out of the first plane, and forming a second bend along the connecting arm whereby the free end portion defines a depending leg adjacent the vertical plane of the spring strip and angularly offset therefrom.

It is another object and feature of the instant invention to provide a method for forming a V-shaped or fishmouth section depending from a free end of a spring strip comprising the steps of bending a first 90.degree. bend along a first connecting arm, rotating the free end portion about the longitudinal axis defined by the spring strip, bending a second 90.degree. bend along the first connecting arm, bending a third 90.degree. bend along a second connecting arm, rotating the free end portion about the longitudinal axis defined by the spring strip, and bending a fourth 90.degree. bend along the second connecting arm whereby the bending and rotating forms the fishmouth supporting section.

It is another object and feature of the instant invention to provide a formed wire spring strip comprising a load carrying section, first leg portion and a second leg portion connected to the first leg portion and to one of the free ends of the load carrying section wherein the terminal connecting arm of the load carrying section and the connecting arm of the second portion connected to the first leg portion both include an axial twist.

The invention has been described in an illustrative manner and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Other objects and attendant advantages of the instant invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the following drawings wherein:

FIG. 1 is a plan view of a flat pattern spring strip;

FIGS. 2 through 10 are various views illustrating the specific steps embodied in the method of the instant invention; and

FIG. 11 is an elevational view of a preferred embodiment of the instant invention.

Referring to the drawings, a flat pattern spring strip is shown generally at 12 in FIG. 1. The flat pattern spring strip 20 includes a plurality of spaced apart, generally parallel torsion bars connected alternately on opposite sides by connecting arms. A preferred embodiment of an end product utilizing the method of the instant invention is generally shown at 14 in FIG. 11. The end product 14 includes a load carrying section generally indicated at 16 with fishmouth sections generally indicated at 18 depending from each end thereof. The fishmouth sections include a first leg portion 19 and a second leg portion 20 connecting the first leg portion 19 to the load carrying section 16. Referring to FIG. 1, the spring strip 12 includes free end portions 32 including an adjacent pair of torsion bars 22 and 27 connected by a connecting arm 25 and a connecting arm 30 extending from the innermost torsion bar 27 of the adjacent pair of torsion bars 22 and 27 away from the outermost torsion bar 22. The outermost torsion bar 22 has a reverse bend section 23 connected therewith.

The method for bending the flat pattern spring 12 strip into a configuration which is usable in seat constructions includes the initial step of twisting or rotating torsion bars 22 to define governor bends generally indicated at 24 of FIG. 2. This initial step is common practice in the art and is included for the purpose of completeness.

Following the formation of the governor bend is the step of forming the first 90.degree. bends 26 in the flat plane of the spring strip 20 at 28 along two of the connecting arms 30. It is to be understood that the 90.degree. bends referred to are "inside bends" that is, adjacent torsion bars are always rotated towards or closer to each other by the bending of the connecting arm rather than away from each other. All bends hereinafter described will be of the "inside bend" type.

The free ends generally indicated at 32 and defined by the first 90.degree. bends 26 are turned out of the plane defined by the spring strip 20 by twisting or rotating the connecting arms 30 as best illustrated in FIGS. 4 and 5. The free end 32 is shown to be rotated 45.degree. in FIG. 5; however, it is to be understood that any desired angular rotation is possible and in fact that smaller angles are more easily provided.

Second 90.degree. bends 34 are formed at 36 along the connecting arms 30 to dispose the free ends 32 adjacent the flat plane of the spring strip 20 and angularly offset therefrom to define depending legs generally indicated at 35 as best illustrated in FIG. 6.

The procedure described above defines the basic steps for bending a flat pattern spring strip. More specifically, the steps are: forming a first 90.degree. bend along a connecting arm, twisting the connecting arm to turn the free end of the spring strip out of the plane hereof and forming a second 90.degree. bend along the same connecting arm to swing the free end into alignment with the spring strip. These basic steps may be performed on any number of connecting arms to produce a generally zig-zag pattern as viewed in side elevation. The method is especially adapted to provide the fishmouth sections 18 at each end of a flat pattern spring strip 29 by carrying out two sequences of the basic steps at each end of the spring strip 20.

Advancing, therefore, from the spring configuration illustrated in FIG. 6, wherein one sequence of the basic steps have been performed at each end of the spring strip 20, third 90.degree. bends 38 are formed at 40 along second connecting arms 42 as best illustrated in FIG. 7. To comply with the "inside bend" definition, as noted above, one end must be bent upwardly while the other end is bent downwardly.

The free ends 32, now enlarged, turned out of the plane of the spring strip 20 by twisting or rotating the connecting arms 42 as best illustrated in FIGS. 8 and 9. The amount which the free ends 32 are turned out of the plane of the spring strip 20 will determine the critical angle between the load carrying portion 16 and the intermediate leg 20 of the fishmouth section 18. For illustrative purposes the free end 32 is turned out 24.degree. as shown in FIG. 9; however, any desired angle may be provided, as mentioned previously the formation of smaller angles is easier than larger ones since the amount of torque required to twist the connecting arm is less. This then is the exact opposite result of the old methods used whereby larger twisting or bending forces are required to form smaller angles and thereby causing large torsional stresses as discussed previously.

Fourth 90.degree. bends 44 are formed at 46 along the second connecting arms 42 to rotate the free ends 32 into alignment with the spring strip 20 and therefore to define the V-shaped or fishmouth sections 18 depending from each end of the load carrying section 16 as best illustrated in FIGS. 10 and 11.

Forming the flat pattern spring strip by the method of the instant invention produces a unique end product. More specifically the method produces a formed wire spring strip comprising a load carrying section 16, a first leg portion 19 and a second leg portion 20 connecting the first leg portion 19 to one of the free ends of the load carrying section 16 wherein the terminal connecting arm 52 of the load carrying section 16 and the connecting arm 54 of second leg portion 20 include an axial twist. The connecting arms 52 and 54 are the remaining portions of the connecting arms 42 and 30 respectively on which were formed the 90.degree. bends.

It is to be understood that the length of the intermediate leg 20 may be varied. For example, a single torsion bar 56 may separate the first connecting arm 30 from the second connecting arm 42 or two torsion bars 58 and 60 and a connecting arm 62 may separate the two connecting arms 30 and 42 as shown in FIG. 1.

Furthermore, it may be necessary for the load carrying section 16 to be concave thereby providing an arcuate or domed seating surface. The bending steps required to provide this curved surface is well known in the art and is therefore not described.

The invention has been described in an illustrative manner and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that with the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for bending flat pattern spring strips having free end portions which include a plurality of spaced apart and generally parallel torsion bars connected alternately on opposite sides by connecting arms, said method comprising the steps of; forming a first bend in a first plane of the spring strip along one of the connecting arms adjacent a free end portion, turning the free end portion of said first bend out of said first plane by twisting the connecting arm and forming a second bend along the connecting arm to dispose the free end portion defining a depending leg adjacent the plane of the spring strip and angularly offset therefrom.

2. The method as set forth in claim 1 wherein forming said first and second bends is further defined as forming 90.degree. bends along the connecting arm.

3. The method as set forth in claim 1 further defined as forming said bends and turning more than one of the connecting arms thereby forming a plurality of said legs depending from said spring strip in a generally zig-zag configuration as viewed in side elevation to define a load supporting section.

4. A method for bending a fishmouth supporting section in a flat pattern spring strip having free end portions, characterized as including a plurality of spaced apart and generally parallel torsion bars connected alternately on opposite sides by connecting arms, said method comprising the steps of bending a first 90.degree. bend along a first connecting arm extending from a free end portion, rotating the free end portion about the longitudinal axis defined by the spring strip, bending a second 90.degree. bend along the first connecting arm, rotating the free end portion about the longitudinal axis defined by the spring strip, and bending a fourth 90.degree. bend along the second connecting arm whereby said bending and rotating forms said fishmouth supporting section.

5. A method for bending a flat pattern spring strip having a plurality of spaced apart and generally parallel torsion bars connected alternately on opposite sides by connecting arms, said strip having free end portions each including an adjacent pair of torsion bars at the end of the strip, the outermost of which has a reverse bend section connected therewith, said method comprising the steps of: twisting the outermost of said pair of torsion bars to form with said reverse bend section a governor bend; bending the connecting arm extending from the innermost of said adjacent pair of torsion bars away from said outermost torsion bars in the plane of said strip to form a 90.degree. inside bend with said free end portion; turning the free end portion out of the plane of said strip by twisting said last named connecting arm; and forming a second 90.degree. bend in said last named connecting arm in the plane of said strip to bring said free end portion in alignment with said strip but out of the plane thereof.