PRODUCTION OF LOAD BEARING PANELS

Abstract: A load bearing panel is made from a top sheet (38′) and a stiffening web (39) which is made by giving a flat sheet a plurality of projections (15) to make it more rigid for which purpose the flat sheet is deformed by cold die forming using circular or nearly circular dies and circular, domed punches so as to form domed projections in the sheet, the arrangement of dies and punches being such that no straight line can be drawn across the region of the circular dies without intersecting at least two of them.

Description: This invention relates to load bearing panels of the kind used to make up so-called access flooring in which the panels are supported by their corners on pedestals or by their edges on a grid of stringers (or on an array of pedestal supports) so as to form a level load bearing surface from which each or at least some of the panels may be removed for access to electric or telephone wiring, air ducts, water pipes and other services that may be installed beneath the floor level. Such load bearing panels will be referred to hereinafter as "panels of the kind described". Lightweight, rigid panels are made by reinforcing a flat top plate - which forms the floor surface - with a stiffening web. Problems are encountered in the production of lightweight panels of adequate rigidity to resist flexure under heavy static or moving loads and which are not excessively thick so as to restrict the service space beneath or necessitate an overall increase in building height. The present invention provides an improved and economical method for manufacturing a load bearing panel and a stiffening web thereof. The invention comprises a method for load bearing panels of the kind described, in which a flat sheet of material is given a plurality of projections to make it more rigid, characterised in that the flat sheet is deformed by cold die forming using a female die part comprising an arrangement of circular or nearly circular dies and a male die part comprising a corresponding arrangement of domed punches and pressing the sheet material into the dies by the punches so as to form domed projections in said sheet, the arrangement of the dies and punches being such that no straight line can be drawn across the female die part that does not intersect one or more of said circular or nearly circular dies. The flat sheet is preferred to be deformed so as to have a peripheral flange simultaneously with the formation of the domed projections. Forming of the peripheral flange simultaneously will restrict material flow to cause uniform stretching similar to that provided by extreme hold-down on the periphery as opposed to drawing, which would utilize additional material and substantially deform the perimeter, requiring an additional operation to prepare the part for further use. The corners of the flat sheet are notched so that the sheet brings together the edges of the notch to form a box corner. Thus the deformation of the sheet into a stiffening web can take place in a single pressing operation using a simple hard die, without the need for a holddown or a pressure pad or cushion. Preferably, only the side of the sheet facing the punches is lubricated for the deforming process,and then only in the region of the punches, the margins of the sheet being left unlubricated or substantially unlubricated. The preferred material is a draw quality steel of yield strength approximately 1700 to 1900 Kg/sq.cm. The preferred average elongation on stretching the material into the domed projections is about 40%. The area of the sheet left undeformed - by which is meant also unthinned - between the domed projections is approximately half the area of the sheet. A preferred feature of the method according to the invention is that the material is not bottomed in the circular or nearly circular dies. This means that the die itself can be a very simple structure comprising circular throughways in a plate, the throughways having hardened radiused lips on which the material is stretched by the action of the punches. The domed projections are desirably all level, and level with the flanged edges of the stiffening plate. To allow for "breathing" of the press, that is to say deforming of the press parts under load, and also to allow for springback of the material after the deforming operation, it is desirable to shim the punches at suitably different heights. This is a trial and error operation. To achieve a substantially uniform stretching of the material in the domed projections, so that there are no relatively thick and thin parts, the domed projections are formed with punches having a blunt nose having a first radius of curvature, a main dome section having a second, smaller radius of curvature and a third section smoothly joining said main dome section to a cylindrical base. To make the load bearing panel, a flat top sheet is secured to the stiffening web by welding the top sheet to the domed projections - and also, of course, wherever else may be required, as, for example, to the flanged edges. The top sheet is preferably made from full hard steel having a yield strength of approximately 100,000 psi. After welding, the panel is trimmed to size and for such trimming the panel is located in a four-sided guillotine by using balls engaged in the hollows formed by the domed projections or the peripheral flange. This assumes, of course, that the panel its square - other shapes, however, such as oblong or triangular or hexagonal are not excluded. Embodiments of stiffening webs and panels made therefrom together with methods for the production of the same according to the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a plan view of a blank from which a stiffening-web is formed, Figure 2 is a plan view of a formed stiffening web, Figure 3 is a section on the line III - III of Figure 2, Figure 4 is a partial sectional view through the die parts of the present invention, Figure 5 is a partial sectional view through the die parts in Figure 4 closed on a blank, Figure 6 is a plan view of the punch part of one of the dies shown in Figures 4 and 5, Figure 7 is an underplan view of one of the die parts shown in Figures 4 and 5, Figure 8 is an underplan view of an alternate 'die part shown in Figures 4 and 5, Figure 9 is a plan view of a stiffening web formed using the die part shown in Figure 8, Figure 10 is a section on the line X - X of Figure 9, and Figure 11 is a cross section through a load bearing panel incorporating a stiffening web made according to the invention. Figure 1 illustrates a blank from which a stiffening web will be produced. The blank comprises a square sheet 10 of draw quality steel having a yield strength approximately in the range of 1700 Kg/sq.cm. to 1900 Kg/sq.cm. The corners 11 of the sheet 10 are notched so that when the margins are drawn out and bent to form a peripheral flange the notches 11 will be elongated and narrowed and their edges 12 brought together to form a box corner. Prior to the deforming process, the central portion 13 of one side of the sheet 10 is lubricated. Figures 2 and 3 illustrate a formed stiffening web 14 made from the blank illustrated in Figure 1. The web 14 has a central portion with domed projections 15 surrounded by a flange 16. The tops 17 of the domed projections 15 are all level, and level with the lip 18 of the flange 16. The material of the blank has been stretched to form the projections 15 by about a 40% average. The arrangement of the projections 15 is such that approximately half of the area inside the flange 16 is left undeformed. It will be seen that the material in the domed projections 15 is somewhat thinner than the unstretched material in the undeformed parts of the sheet. The deformation of the blank is effected in a single pressing operation illustrated in Figures 4 to 7, between upper (female) and lower (male) die parts 19,21. The upper die part 19 comprises essentially a steel plate 22 with circular throughways 23 with hardened, radiused edges 24 which form the dies. The lower die part 21 comprises essentially a base plate 25 with domed punches 26 secured there tops as by bolts 27. The punches 26 are, of course, arranged correspondingly to the throughways 23 and, as shown in Figure 5, punch the material of the blank into the throughways 23 when the die parts 19, 21 are urged together. The side of the blank with the lubricant is placed in contact with the punches 26 which stretch the material as they are forced between the edges 24 of the throughways 23. The arrangement of the throughways 23 is very important from the point of view of the rigidity of the finished product. It is desired that there shall be no clear "line of sight" across the dies, and it is specified in fact that no straight line can be drawn across the female die part that does not intersect at least one or more of the dies. The die parts 19, 21 also comprise an upper perimeter flange die 29 and has a spanking plate 31 that forms the lip 18. If desired, draw beads (not shown) may be incorporated in the blank to control the final size of the formed sheet depending upon the gauge of the material. Fixed ejector punches 32 are provided to knock out the formed sheet as the upper press member 19 lifts off the lower member 21. The punches 26 have blunt noses 33 having a first radius of curvature and main dome sections 34 having a second, smaller radius of curvature. The main dome section 34 is connected by a third section 35 smoothly to the cylindrical body 36 of the punch 26. In order to allow for "breathing" of the forming press, that is to say, deforming under the considerable pressures-used, and also to allow for springback of the material after the initial deformation, the punches 26 are shimmed up on shims 37. The thickness of the shim required under any particular punch 26 is determined by trial and error to obtain a finished part with all domes in the same plane as the peripheral flange. The combined effect of the shimming up, lubricant, steel properties and surface finish and the provision of the multi-radius punch section is to stretch the domed projections 15 evenly and to the same level. Figure 8 shows another arrangement of the female die part 19, in which the dies - as defined by the edges, radiused and hardened, of throughways, are not fully circular but extend only over major arcs of circles, the intermediate material of the plate 22 also being received between pairs of adjacent throughways 23 to form a peanut-shaped throughway. When the domed punches stretch the material up into such peanut-shaped throughway, they produce saddle shaped projections 38, as shown in Figures 9 and 10. Figure 11 shows a load bearing panel of the kind described having a top gane 38' that in use forms the load bearing surface of floor when laid in an array with like panels. The stiffening web 39 produced as heretofore described is welded to the top plate 38' by electric resistance welding that welds the tops of the domed projections 15 to the top plate 38'. Spot welds are also effected around the perimeter 41. After welding, the panel is trimmed to size. The arrangement of projections 15 has 900 rotational symmetry. By engaging four locating balls (not shown) into four centrally disposed hollows (see Figure 2) or by locating from the peripheral flange, the panel can be located for the edge trimming operation. The edges of the panels can be finished off in varidus ways, for example by an edging strip, various finishes can be applied at will to the top surface such, for example, as the bonding of a vinyl tile or other laminate, or the bonding of some kind of carpeting material. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

Claims: What we claim is: 1. A method for the production of stiffening webs for load bearing panels of the kind described, in which a flat sheet of material is given a plurality of projections to make it more rigid, characterised in that the flat sheet is deformed by cold die forming using a female die part comprising an arrangement of circular or nearly circular dies and a male die part comprising a corresponding arrangement of domed punches and pressing the sheet material into the dies by the punches so as to form domed projections in said sheet, the arrangement of the dies and punches being such that no straight line can be drawn across the female die part that does not intersect one or more of said circular or nearly circular dies. 2. A method according to claim 1, characterised in that the flat sheet is deformed so as to have a peripheral flange formed simultaneously with the formation of the domed projections to a depth equal to or preferably deeper than the rest of the formed part to restrict material flow and cause uniform stretching of the material in the perimeter domed projections reducing the tendency of the material to draw, said peripheral flange also eliminating the need for hold-down, and reducing the tendency of the material along the perimeter to pucker, thus allowing use of the part in the next operation without an additional step to flatten. 3. A method according to claim 2, characterised in that the corners of the flat sheet are notched so that the formation of flanges by drawing and bending adjacent margins of the sheet brings together the edges of the notch to form a box corner. 4. A method according to claim 2, characterised in that only the side in the central area of said sheet facing the panches is lubricated for the deforming process. 5. A method according to claim 1, characterised in that the material of the sheet is a draw quality steel of yield strength approximately 1700 to 1900 Kg/sq.cm. 6. A method according to claim 1, characterised in that the average elongation on stretching the material into the domed projections is about 40%, 7. A method according to claim 1, characterised in that the area of the sheet left undeformed between the domed projections is approximately half the area of the sheet. 8. A method according to claim 1, characterised in that the material is not bottomed in the circular or nearly circular dies. 9. A method according to claim 1, characterised in that the domed punches are arranged, as by shimming, at suitably different heights to allow for press breathing and springback. 10. A method according to claim 1, characterised in that the domed projections are formed with punches having a blunt nose having a first radius of curvature, a main dome section having a second, smaller radius of curvature and a third section smoothly. joining said main dome section to a cylindrical base. 11. A stiffening web for a load bearing panel of the kind described, characterised by being made by a method according to any of claims 1 to 10. 12. A method for making a load producing panel of the kind described in which a flat top sheet is secured to a stiffening web, characterised in that the stiffening web has been made by a method according to any one of claims 1 to 10, and the top sheet being secured thereto by welding the top sheet to the domed projections and to the peripheral flange. 13. A method according to claim 12, characterised in that the top sheet is made from full hard steel of yield strength approximately 100,000 psi. 14. A method according to claim 12, in which after the top sheet and the stiffening web are secured together by welding the edges are trimmed to size using balls engaging in the domed projections or peripheral flange to locate the panel. 15. A method according to claim 14, characterised in that all panel edges are simultaneously trimmed. 16. A load bearing panel of the kind described, characterised by being made by a method according to any one of claims 12 to 16.

Inventors: JOHNSON, RICHARD JOSEPH, TATE, DONALD LAMONT
Applicants: TATE ARCHITECTURAL PRODUCTS, INC.
Application year: 1979
Main classification: E04C2
IPC codes: E04C2