Title:
METHOD OF FORMING A PANEL HAVING A COMPOUND CURVATURE
United States Patent 3627608
Abstract:
A method of forming a flexible, self-supporting sheetlike structure having a compound curvature, including the steps of perforating a sheet of woodlike fibrous material, such as fiberboard, wetting the sheet, applying steam, and forming the compound curvature in a press. The method of forming an integral single piece automotive headliner includes forming the sheet into a flexible dish-shaped structure and finishing the inner concave surface by painting, or applying a fabric cushioning material.


Inventors:
Steiner, Francis J. (Grosse Pointe Woods, MI)
Paulsen, Robert M. (St. Clair Shores, MI)
Application Number:
04/833480
Publication Date:
12/14/1971
Filing Date:
06/16/1969
Assignee:
Woodall Industries Inc. (Detroit, MI)
Primary Class:
Other Classes:
156/214, 156/245, 264/156, 264/322
International Classes:
B27D1/08; (IPC1-7): B29C17/08
Field of Search:
156/211,214,245 144
View Patent Images:
Primary Examiner:
Borchelt, Benjamin A.
Assistant Examiner:
Montone G. E.
Claims:
What is claimed is

1. A method of forming a flexible self-supporting sheetlike structure having a compound curvature, including the steps of:

2. The method of forming a structure defined in claim 1, wherein the number of perforations per square inch is greater at the areas of greatest curvature.

3. The method of forming the structure defined in claim 1, wherein the diameter of the perforations are greater at the areas of greatest curvature.

4. The method of forming the structure defined in claim 1, wherein the diameter of the perforations are from 0.080 to 0.120 inches.

5. The method of forming the structure defined in claim 1, wherein the surface of the sheet is wetted.

6. The method of forming the structure defined in claim 5, wherein the surface of the sheet is wetted with a solution including a wetting agent.

7. The method of forming the structure defined in claim 6, wherein the wetting agent lubricates the fibers.

8. The method of forming the structure defined in claim 1, wherein the steam is applied under pressure to the sheet.

9. The method of forming the structure defined in claim 8, wherein the steam is superheated prior to application of the steam to the sheet.

10. The method of forming the structure defined in claim 1, wherein the sheet is heated prior to wetting.

11. The method of forming the structure defined in claim 1, wherein the pressure of the die is sufficient to cause material flow toward the areas of greatest curvature, reducing buckling at such areas.

12. The method of forming the structure defined in claim 1, wherein the sheet is formed into a generally rectangular automotive headliner having areas of greatest curvature at the corners.

13. The method of forming the structure defined in claim 12, wherein a sound absorbent fabric layer is secured within the automotive headliner.

14. A method of forming a single piece, relatively flexible, self-supporting automotive headliner having a compound curvature, including the steps of:

15. The method of forming an automotive headliner defined in claim 14, wherein the sheet is finished by painting the inner concave surface.

16. The method of forming an automotive headliner defined in claim 14, wherein the inner surface is finished by bonding a fabric material to the inner concave surface of the sheet.

17. The method of forming an automotive headliner defined in claim 16, wherein the fabric material is bonded to the sheet by draping the fabric over a male mold, applying adhesive to the inner concave surface of the sheet, and placing the adhesive coated side of the formed sheet on the fabric.

18. The method of forming an automotive headliner defined in claim 17, wherein the fabric material includes a foam cushioning material, and the fabric is draped over the male mold with the foam cushioning material opposite the mold.

19. The method of forming an automotive headliner defined in claim 18, wherein the male mold is heated, prior to receipt of the fabric material.

20. The method of forming an automotive headliner defined in claim 14, wherein the wetting solution includes a lubricating wetting agent.

21. The method of forming an automotive headliner defined in claim 14, wherein superheated steam is applied under pressure to the sheet.

22. The method of forming an automotive headliner defined in claim 14, wherein the areas of greatest curvature are adjacent the corners of the rectangular sheet, and the pressure of the die is sufficient to cause the material to flow toward the areas of greatest curvature, reducing buckling at the corners.

Description:
SUMMARY OF THE PRIOR ART

Fiberboard or hardboard panels provide a relatively inexpensive building material, however such panels have a substantial resistance to bending and tend to return to their original shape when deformed into a curved structure. Further, fiberboard panels will tear when shaped, and the panels will crumble, if soaked. It is therefore an object os this invention to provide a method of forming fiberboard panels into self-supporting compound curvatures without crumbling or tearing the panel.

The prior art teaches two principal methods of forming flat fiberboard panels, however, these methods require the utilization of a means to retain the compound curvature after forming. One method suggested by the prior art for forming automotive headliners includes cutting V-shaped slots at the areas of curvature, and thereafter deforming the panel and securing the contour with box fasteners in the slots. The resultant panel structure is not self-supporting, and the stresses remain in the headliner, which may result in loosening of the fasteners. Further, the method is relatively expensive, substantially reducing the advantage of utilizing an inexpensive fiberboard panel. The second method includes filling holes in the fiberboard panel with a liquid resin of the type which sets under heat and pressure. The panel is then deformed in a press which sets the resin, and the resin retains the deformed contour of the sheet. In either method therefore, the sheet is not "reformed," because the thermosetting binder used in commercial fiberboard is merely held in its stressed condition. It will be understood however that single automotive headliners have been formed from other materials, including various plastics.

SUMMARY OF THE INVENTION

The method of this invention is adapted to reform fiberboard or hardboard panels into flexible self-supporting structures, without fasteners or other means to retain the finished contour. This method is particularly, although not exclusively adapted to forming single piece automotive headliners which have a compound curvature at the corners, and which are generally dish-shaped.

The method of this invention includes perforating a sheet of woodlike fibrous material or panel with numerous holes at the areas to be formed, wetting the sheet, applying steam to the sheet for a period of time sufficient to make the sheet ductile enough to permit forming without tearing or crumbling, and forming the compound curvature in a die under pressure. Fiberboard or hardboard panels generally include a thermosetting resin binder which retains the wood or woodlike fibers in suspension. The fiberboard panels therefore have a substantial resistance to bending, and will tear when deformed into compound curvatures, unless slotted. Further, the fiberboard panels tend to return to their original flat shape, unless the fibers are actually shifted and the panel "reformed."

The perforations in the panel not only weaken the structural integrity of the panel, to permit forming, but also provide voids into which the fibers may be shifted at the areas of compound curvature. In the method of this invention, the apertures also provide a means for escapement of the steam vapors, which is important to the process. The wetting solution preferably includes a wetting agent which lubricates the fibers and prevents soaking. The steam reduces the rigidity of the thermosetting binders and conducts moisture into the internal structure of the fibrous material without soaking the panel, which would cause crumbling. It has also been found advantageous to heat the panel, prior to wetting, to expand the fibers and reduce the time required to reach the critical forming condition. The problem is to conduct moisture into the internal structure of the fiberboard panel without soaking the structure of the fiberboard panel without soaking the structure, and yet make the panel sufficiently ductile to permit forming without tearing.

The panel is preferably formed between heated dies, under pressure, wherein the spacing between the dies is quite important. The pressure is preferably sufficient to actually cause material flow of the fibers toward the areas of greatest curvature, reducing buckling or tearing at these areas. The apertures therefore provide a space which receives the material flow, and the resultant structure has smaller apertures at the areas of greatest curvature, although the apertures initially were of the identical size. It will also be understood that a greater number of perforations per square inch may be provided at the areas of greatest curvature, or the diameter of the perforations may initially be greater at such areas. It has been found by experimentation that the preferred diameter of the perforations are from 0.080 to 0.120 inches.

In the preferred embodiment of forming an automotive headliner, the fiberboard panel is first cut to the desired shape, and thereafter the sheet is formed by wetting, applying steam and reforming the sheet in a heated press. The apertures may be formed prior to or subsequent to cutting. The final step is to finish the inner or concave surface of the sheet, which may be accomplished by painting or applying a fabric material. In the preferred embodiment of the method, a fabric cushioning material is applied to the concave surface by draping the fabric over a male mold, which may be heated, applying an adhesive to the inner concave surface of the sheet, and pressing the adhesive coated side of the formed sheet on the fabric. It has been found that this method provides a smooth fabric liner, substantially free of wrinkles or other defects.

Other advantages and meritorious features will more fully appear from the following description, claims, and accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial side view of an automotive body showing a headliner;

FIG. 2 is a top perspective view of a fiberboard panel;

FIG. 3 is a top perspective view of the panel shown in FIG. 2 after cutting;

FIG. 4 is a top perspective view of a fabric liner for the headliner, cut to shape;

FIG. 5 is a top view of a portion of the fiberboard panel after perforation;

FIG. 6 is a schematic illustration of the heating step of this invention;

FIG. 7 is a schematic illustration of the wetting step of this invention;

FIG. 8 is a schematic illustration of the application of steam in the method of this invention;

FIG. 9 is a schematic illustration of the press utilized in the method of this invention;

FIG. 10 is a schematic illustration of the shaped panel drying on a cradle;

FIG. 11 is a schematic illustration of a convex mold being heated to receive the fabric liner;

FIG. 12 is a schematic illustration of the convex mold shown in FIG. 11 after receipt of the fabric liner;

FIG. 13 is an enlarged partial view of the embodiment shown in FIG. 12;

FIG. 14 is a schematic illustration of the application of adhesive to the concave surface of the formed headliner panel;

FIG. 15 is a schematic illustration of the application of the formed headliner panel to the fabric material;

FIG. 16 is a cross-sectional view of the finished automotive headliner;

FIG. 17 is a partial cross-sectional view of the headliner shown in FIG. 16; and

FIG. 18 is a perspective view of the finished headliner, prior to receipt in the automotive body shown in FIG. 1.

DESCRIPTION OF THE DRAWINGS AND PREFERRED METHOD OF THIS INVENTION

The method of this invention is particularly adapted to reform relatively flat fiberboard or hardboard panels into self-supporting curved structures, including structures having a compound curvature such as automotive headliners. The disclosed embodiment is an automotive headliner, and the method of this invention has been described in regard to such embodiment to simplify the disclosure, however it will be understood that the method is not limited to such embodiments. The embodiment of the automotive body shown in FIG. 1 includes a roof panel 20, usually formed of metal, a front windshield 22 and a rear window 24.

The headliner 26 is secured to the inner or concave surface of the roof panel 20 and conforms to the compound curvature. Where a single piece or integral headliner is to be utilized, it is important that the headliner be sufficiently resilient to permit receipt through one of the window openings, which is narrower than the width of the roof panel, as shown, and that the headliner be self-supporting to prevent buckling or sagging. Further, in the preferred embodiment of the headliner, the width and length is slightly greater than the inner surface of the roof panel, and the headliner is bowed slightly to snap in position between the supporting channels, not shown. The headliner must therefore be sufficiently resilient to permit such installation, and retain its tensioned engagement. The method of this invention is adapted to utilize relatively flat panels or sheets of commercial fiberboard or hardboard, which are relatively inexpensive, and provide a strong resilient structure. Fiberboard panels of the type preferred herein are commercially available from various sources, including the Masonite Corporation under the trade names Masonite and Presdwood. The fiberboard is however formed from steam exploded wood fibers in a thermosetting resin binder, making the panels difficult to form into complex or compound curvatures, and the thermosetting resin binder causes the panel to return to its original flat shape, when formed. Further, the panel will crumble when soaked, or tear when deformed without wetting. The method of this invention is adapted to provide sufficient moisture to permit forming without tearing or crumbling.

FIG. 2 illustrates a commercial fiberboard panel 28 of the type described hereinabove, and FIG. 3 shows the panel after it has been cut to the desired shape. The panel may be cut by hand or in a die, and the shape will depend upon the particular application of the structure. In this embodiment, the longitudinal edges 30 have been bowed slightly outwardly adjacent the midportion and the ends 32 are bowed inwardly to provide substantially flat or straight edges in the dish-shaped headliner, and compensate for changes during forming.

The panel is then perforated, as shown in FIG. 5. It will be understood that the panel may however be perforated prior to cutting, or simultaneously therewith. The perforations 34 weaken the resistance of the panel to bending, and provide other advantages peculiar to the method of this invention, as described hereinbelow. It will be understood that it may not be necessary to perforate the entire panel in certain applications, as where only a portion of the panel is to be formed, and larger diameter apertures may be provided at the areas of maximum curvature; the density of the apertures may also be increased at such areas. In this embodiment, a panel having a thickness of 0.095 to 0.105 inches has been found suitable with perforations of approximately three thirty-seconds of an inch diameter on one-fourth inch diagonal centers. Panels having a greater thickness may require a greater density of apertures, because such panels would have a greater resistance to bending.

The perforated panel may then be preheated as shown in FIG. 6, wherein a bank of heating elements 36 are directed on the panel 28. In this embodiment, the panel is preheated to approximately 180 degrees by a bank of lights 36 over a load of stocks, or the panels are placed in an oven.

The panel is then wetted as shown in FIG. 7, wherein a series of spray nozzles 40 direct the wetting solution on to the panel. The panel may also be wetted by hand. In the preferred embodiment of this method, the wetting solution includes a wetting agent such as the commercially available silicone wetting agents. A suitable wetting agent is "L-76 Silicone" available from Union Carbide Company. The wetting solution is this embodiment includes approximately 8 grams of a silicone wetting agent per 10 pounds of water. The wetting agent conducts the moisture into the fibers of the fiberboard panel to lubricate the fibers, without soaking, and reduces the time required to dry the panel after forming. The apertures also serve to conduct the wetting agent into intimate contact with the fibers.

The panel is then subjected to steam, as shown in FIG. 8, which conducts the moisture into the internal structure of the fibrous material, without soaking the panel, and reduces the rigidity of the thermosetting binders in the panel, to permit forming without tearing. The steam and the wetting agent are adapted to speed the wetting of the wood fibers to permit forming prior to soaking, because soaking and heat tend to break down the thermosetting resin, causing the panel to crumble. The steam is also preferably superheated to further speed the process. In the disclosed embodiment of the method of this invention, a "pants press" type steam applicator 42 is utilized, which applies the steam under pressure. In this embodiment, the steam is applied for 15 seconds maximum with 100 pounds per square inch dry steam. An electrical heating element is provided which superheats the steam to 400° to 500° Fahrenheit. It is important to note that the apertures in the panel not only aid in conducting the steam into the internal fibrous structure, but also provide a means of escapement for the steam vapors. The apertures therefore prevent soaking of the panel during steaming.

The perforated panel 28 may then be reformed in a press 44, as shown in FIG. 9, without tearing the panel. This embodiment of the method of this invention utilizes a heated press, wherein the pressure is sufficient to cause material flow of the fibers toward the areas of greatest curvature. The fibers are thus redistributed into the corner areas of compound curvature, and into the cove areas of the headliner, making the structure self-supporting. The apertures or perforations in these areas "take-up" the redistributed fibers, causing the perforations to be smaller at the areas of greatest curvature. A conventional size automotive headliner may be formed in a 550 to 600 ton press, in approximately 30 seconds at 375° Fahrenheit. The formed panel may then be placed on a cradle 48, as shown in FIG. 10, where it is permitted to dry. The apertures in the panel and the wetting agent reduce the drying time.

The formed panel may now be finished, by painting for example, and installed in the car body as shown in FIG. 1. In this embodiment however the panel is finished by securing a sound and heat absorbent fabric liner to the inner or concave surface of the panel. The fabric liner 50 is first cut to size as shown in FIG. 4. The fabric liner in this embodiment is cut to the approximate same size and shape as the unformed panel shown in FIG. 3, allowing for waste. The fabric preferably has a "two-way" stretch so that it will accurately conform to the configuration of the panel, including the curved areas. Further, the fabric may be provided with a foam backing to aid in the sound and heat absorption. A suitable material for the fabric liner is a Guilford knap knit nylon commercially available from Guilford Mills, Inc. having a three thirty-seconds inch polyurethane foam backing.

The fabric liner 50 is then placed over a convex mold 52, as shown in FIG. 12, which has been preheated by a bank of heating elements 54 or the like as shown in FIG. 11. The mold may alternatively be internally heated. The convex external surface of the mold is curved to conform to the internal or concave surface of the formed panel, and the fabric is held in place by suitable fasteners, such as pin frame or individual Velcro grips 56, as shown in FIG. 13. The fabric is slightly stretched over the convex mold to accurately conform to the curved areas, with the foam layer opposite the mold.

A bonding agent, such as the commercially available synthetic resin adhesives is then applied to the internal surface of the formed panel, as shown in FIG. 14, wherein the panel 28 is supported on a table 58 and the adhesive is sprayed on to the concave surface by spray nozzles 60. A suitable synthetic resin adhesive is commercially available from the H. B. Fuller Company under the number E-3990. Five to 6 grams of adhesive per square foot of panel has been found suitable for this adhesive.

The panel is then transferred quickly to the convex mold 52 and placed with the concave adhesive coated surface over the fabric, as shown in FIG. 15. Full contact between the panel and the fabric is then established by hand pressure or a pressure pad, and held for approximately 60 seconds. A pressure of approximately 2 to 5 pounds per square inch has been found satisfactory. The excess fabric 62 is then trimmed from the panel, as shown in FIG. 16, and the finished headliner 26, shown in FIGS. 17 and 18, is ready for installation. The headliner formed by the method of this invention thus includes the resilient self-supporting fiberboard panel 28, the foam backing 64, and the finish fabric lamination 50.