SHEET FORMING APPARATUS

Abstract: There is provided sheet forming apparatus comprising a supporting frame (10) having pivotally mounted thereto a mandrel member (13). The supporting frame (10) slidingly mounts a flexible sheet metal platen (17) secured to the mandrel member (13) by a sheet engagement clamp assembly (20) including an air manifold (18) adapted to blow air into the cores of a clamped core sheet. The mandrel member (13) is operable by pneumatic ram assembly (24). A heater assembly (27) heats the underside of the platen (17). A trailing edge sheet clamp assembly (32) locates a sheet to be formed under tensile control of a pneumatic ram assembly (33). A heater hood (35) is adapted to heat the upper surface of a sheet to be formed on the platen. Control of the working components is centralized in a control assembly (42) comprising a programmable logic controller electronically controlling heating and exercising electropneumatic control over the respective sheet clamps and rams.

Description: SHEET FORMING APPARATUS This invention relates to sheet forming apparatus. This invention has particular but not exclusive application to sheet forming apparatus for shaping hollow core polymeric sheet and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention can be used in other applications such as forming any plastic sheet. Thermoformable polycarbonate sheeting finds increasing application for clear roofing panels and awnings. Whilst the sheeting may be flat or of convention roofing panel section, increasing use is made of hollow cored polycarbonate sheet. Hollow cored polycarbonate sheet is formed having upper and lower substantially planar surfaces defining an air core therebetween, the spacing being maintained by a plurality of longitudinal webs formed integrally with the upper and lower surface layers. The sheet is light and structurally stiff, whilst being impact resistant. The sheet may be clear the polycarbonate material having high transmission of visible light, or the sheet may be tinted or coloured, translucent or opaque. It is often desirable to form sheet roofing materials such as polycarbonate to form bullnose awnings or the like. In general, this forming is done by heating the sheet then manually curving the sheet over a mandrel such as a metal drum. However, when this method is used on air core polycarbonate sheet, the influence of the web structure results in an uneven bend and a severely corrugated surface. The present invention aims to alleviate at least one of the foregoing disadvantages and to provide sheet forming apparatus which will be reliable and efficient in use. With the foregoing and other objects in view, this invention in one aspect resides broadly in sheet forming apparatus comprising: a supporting frame; a mandrel supported for movement relative to said frame and having a sheet forming mandrel surface; sheet engagement means associated with a leading edge of said sheet forming mandrel surface, and operating means for said mandrel. The moving mandrel may take any suitable form. For example, the moving mandrel may comprise a part cylindrical shaped surface forming with a supporting axle a part cylindrical structure adapted to rotate on its axle relative to the supporting frame, whereby a sheet fixed by its edge relative to the surface is drawn thereabout. Alternatively, the mandrel may be mounted for movement which is not strictly rotational. Further, the movement of the mandrel may form the sheet in conjunction with other fixed and/or moving elements to form more complex shapes than simple curves. The moving mandrel may comprise a mandrel body pivotally mounted to the supporting frame and having a curved outer portion with a leading edge to which an edge of a flexible platen is secured, said platen being movable by the mandrel body from a first substantially flat position supported by said frame assembly to a second position at which it forms said mandrel surface. The supporting frame may include guide means for the platen whereby the platen is restrained to moving in concert with the mandrel. Where the apparatus is for shaping of polycarbonate sheet and particularly core sheet, the apparatus may includes sheet heating means. Preferably, the sheet heating means is selected whereby the sheet may substantially uniformly heated on both top and bottom surfaces thereof. For example, the heating means may include one or more of hot air heating, radiative, infrared, inductive, microwave or ultrasonic heating. The sheet heating means may be associated with the platen and/or over the upper surface of the sheet. Preferably, the sheet heating means is adapted to heat both major surfaces of the sheet. In certain embodiments of the invention it is desirable to heat the sheet to be formed substantially to the edge of the sheet. In order to permit even heating to the end of the sheet, it is preferred that the moving mandrel shaping surface comprise an open structured surface such as wire mesh or the like. The flexible platen may comprise thin sheet metal, woven wire or fabric, heat resistant plastic sheet or the like. The flexible platen may be heated by heating means inherent in the platen itself. Alternatively, the platen may be heated by radiation or convection heating means located on one or both sides of the platen. The platen is preferably disposed horizontally on the supporting frame between lateral said guide means, whereby the platen may move longitudinally in concert with movement of the mandrel. The platen may be secured to the mandrel sheet forming surface whereby the platen is drawn over the surface by operation of the mandrel operating means. Alternatively, the platen may be engageable therewith in operation whereafter the platen is drawn over the mandrel by operation of the mandrel or by operation of platen driving means. Where the platen is affixed to the mandrel surface, this is preferably by the use of combined attachment means and sheet edge retaining means. The sheet edge engagement means may be affixed to a leading edge of the preferred flexible platen and/or may be affixed to the moving mandrel body. The flexible platen may also be associated with trailing edge retaining means adapted to maintain a subject sheet being formed in tension between the leading sheet edge engagement means and the trailing sheet edge retaining means. The sheet edge engagement means may be associated with air manifold means adapted to direct temperature controlling air through the cores of polycarbonate core sheet. The sheet edge engagement means preferably takes the form of a clamping assembly adapted to compressively engage the sheet edge, although it is envisaged that other forms of sheet engagement means may be used, such as a vacuum platen. The operating means preferable comprises electromechanical, air or hydraulic operating means. Preferably, the operating means is under the control of integrated control means for operation of the apparatus as a whole. For example, a microprocessor may control operation of the respective sheet edge retaining means in terms of maintaining a selected tension in the sheet therebetween, control of temperature of the heating of the upper and lower surfaces of the sheet, control of the speed and degree of rotation of the moving mandrel on its axis or the like. Since the forming of the sheet material, particularly polycarbonate core sheet, results in the lower surface being in compression and the upper surface being in tension, it may be expected that the temperature of the respective surfaces should be approximately equal. However, it has been surprisingly determined that sheet formed by apparatus in accordance with the above apparatus using equal temperatures is more distorted than if the upper temperature is higher than the lower temperature. Preferably the lower surface of the sheet is heated to the lowest temperature consistent with formability, in the case of polycarbonate core sheet in the region of 80-85°C, whilst the upper surface is heated to between 120-130°C and undergoes extension in the forming process. In a further aspect, this invention resides in a method of forming a sheet comprising the steps of clamping at least one sheet edge by sheet edge retaining means to a flexible platen supported on a supporting frame; and drawing said sheet edge retaining means and platen over a moving mandrel supported on said frame. In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein: FIG 1 is a perspective view of apparatus in accordance with the present invention; and FIG 2 is a longitudinal section through apparatus of FIG 1. In the figures there is provided sheet forming apparatus comprising a supporting frame 10 supported on legs 11. The supporting frame 10 has pivotally mounted thereto a mandrel member 13 comprising end plates 14 and otherwise being of open construction (not shown). The mandrel member 13 is supported on the frame assembly 10 by way of an axle 15. The supporting frame 10 is provided with platen guide portions 16 in which can slide a flexible sheet metal platen 17. The platen 17 is secured to the mandrel member 13 by a sheet engagement clamp assembly 20 and bears on an open mesh surface 21 of the mandrel member 13 as it rotates about the axle 15. The sheet engagement clamp assembly 20 includes an air manifold 18 adapted to register with and selectively blow air into the cores of a sheet clamped by the clamp assembly 20. The mandrel member 13 is operable via link 22 pivoted at 23 and actuated by a pneumatic ram assembly 24 through an idler member 25 pivoted to the frame leg 11 at 26. Slung under the frame assembly in the region of the mandrel member 13 is a radiant heater assembly 27 including heater elements 30 and a heat control fan 31. In the trailing edge region of the platen 17 there is provided a trailing edge sheet clamp assembly 32 located longitudinally and under tensile control of a pneumatic ram assembly 33. Fabricated to the supporting frame 10 is a heater turret assembly 34 comprising a heater hood 35 supported for movement on a turret frame 36, the movement being under the control of a pneumatic ram 37. The heater hood 35 mounts a plurality of heating elements 40. The rear of the working region of the frame assembly 10 is provided with supporting rollers 41. Control of the working components is centralized in a control box 42 taking feed from an electrical supply 43 and a compressed air supply 44, and comprising a programmable logic controller electronically controlling heating and exercising electropneumatic control over the respective sheet clamps and rams, each of which are double acting. In use, with the mandrel member 13 and platen 17 assembly fully retracted the platen 17 extends substantially flat between its guides 16 in the supporting frame. A sheet of polycarbonate core sheet is located thereon act the apparatus is actuated at the control box 42. The leading edge clamp assembly 20 engages the sheet edge and the trailing edge clamp assembly 32 is extended to the sheet trailing edge whereupon it in turn clamps the sheet edge. The control means 42 then operates the pneumatic ram 37 to lower the heater hood 35 over the sheet, whereupon the heater elements 40 are energized above their preheat level. The lower heater elements 30 are maintained in an energized state throughout the cycle to maintain a constant air temperature below the platen 17, in combination with the fan 31 and temperature sensors (not shown) under control of the control means 42. Temperature sensors (not shown) also provide input to the control means 42 controlling the elements 40 to determine the upper sheet surface temperature. After sufficient heating, the heater hood 35 is retracted by the pneumatic ram 37, whereupon the mandrel member 13 is actuated by the pneumatic ram 24. The mandrel member 13 draws the platen 17 and the clamped sheet over the outer surface 21 of the mandrel member, the sheet being maintained in tension by a preselected amount by action of the pneumatic ram 33 on the trailing edge clamp assembly 32, under control from the control means 42. At the desired limit of rotation of the mandrel member 13, the control means 42 stops the heater elements 30 and 40 and air manifold 18 blows cool air through the cores of the sheet to avoid heat soak distortion of the webs. The control means 42 thereafter releases the respective clamp assemblies whereby the formed sheet may be removed. The control means 42 thereafter reconditions the apparatus to accept the next sheet. Apparatus in accordance with the foregoing embodiment has the advantage that the sheet is formed into bullnose sections without undue distortion of the upper and lower surfaces of the sheet. It will of course be realized that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as defined in the claims appended hereto.

Claims: CLAIMS 1. Sheet forming apparatus comprising: a supporting frame; a mandrel supported for movement relative to said frame and having a sheet forming mandrel surface; sheet engagement means associated with a leading edge of said sheet forming mandrel surface, and operating means for said mandrel. 2. Sheet forming apparatus according to Claim 1 , wherein the moving mandrel comprises a mandrel body pivotally mounted to the supporting frame and having a curved outer portion with a leading edge to which an edge of a flexible platen is secured, said platen being movable by said mandrel body from a first substantially flat position supported by said frame assembly to a second position at which it forms said mandrel surface. 3. Sheet forming apparatus according to Claim 2, wherein said flexible platen is selected from thin sheet metal, woven wire or fabric, heat resistant plastic sheet or the like. 4. Sheet forming apparatus according to Claim 3, wherein said flexible platen is associated with sheet heating means. 5. Sheet forming apparatus according to Claim 4, wherein said mandrel body curved outer portion comprises an open structure whereby said flexible platen may be heated therethrough. 6. Sheet forming apparatus according to Claim 5, wherein the sheet heating means is selected whereby the sheet may be substantially uniformly heated on both upper and lower surfaces thereof. 7. Sheet forming apparatus according to Claim 5, wherein the sheet heating means is selected whereby the sheet may be differentially heated on upper and lower surfaces thereof. 8. Sheet forming apparatus according to Claim 7, wherein the lower surface of the sheet is heated to the lowest temperature consistent with formability and the upper surface is heated to a temperature which allows extension in the forming process. 9. Sheet forming apparatus according to any one of Claims 6 to 8, wherein the sheet heating means is selected from one or more of hot air heating, radiative, infrared, inductive, microwave or ultrasonic heating. 10. Sheet forming apparatus according to any one of Claims 2 to 9, wherein said platen is disposed horizontally on the supporting frame between lateral said guide means, whereby the platen may move longitudinally in concert with movement of the mandrel body member. 11. Sheet forming apparatus according to Claim 10, wherein said sheet engagement means cooperates with trailing sheet edge retaining means to maintain a subject sheet being formed in tension between the leading sheet engagement means and the trailing sheet edge retaining means. 12. Sheet forming apparatus according to Claim 11 , wherein said sheet engagement means is associated with air manifold means adapted to direct temperature controlling air through the cores of a polycarbonate core sheet to be formed. 13. Sheet forming apparatus according to any one of the preceding Claims, wherein said operating means is selected from electromechanical, pneumatic or hydraulic operating means. 14. Sheet forming apparatus according to Claim 13, wherein said operating means is under the control of integrated control means for operation of the apparatus. 15. Sheet forming apparatus according to Claim 14, wherein said integrated control means comprises a programmable logic controller or microprocessor. 16. Sheet forming apparatus comprising: a supporting frame; a moving mandrel comprising a mandrel body pivotally mounted to the supporting frame and having a curved outer portion with a leading edge to which an edge of a flexible platen is secured, said platen being movable by said mandrel body from a first substantially flat position supported by said frame assembly to a second position at which it forms said mandrel surface; sheet engagement means associated with a leading edge of said sheet forming mandrel surface, said sheet engagement means cooperating with trailing sheet edge retaining means to maintain a subject sheet being formed in tension between the leading sheet engagement means and the trailing sheet edge retaining means; sheet heating means selected whereby the sheet may be differentially heated on top and bottom surfaces thereof; air manifold means associated with said sheet engagement means and adapted to direct temperature controlling air through the cores of a polycarbonate core sheet to be formed; operating means for said mandrel body selected from electromechanical, pneumatic or hydraulic operating means, and integrated control means for operation of the operating means, air manifold means, sheet heating means, sheet engagement means and sheet edge retaining means. 17. A method of forming a sheet comprising the steps of clamping at least one sheet edge by sheet edge retaining means to a flexible platen supported on a supporting frame; and drawing said sheet edge retaining means and platen over a moving mandrel body supported on said frame.

Inventors: KING NORMAN FREDERICK, KING, NORMAN, FREDERICK
Applicants: KING NORMAN FREDERICK, KING, NORMAN, FREDERICK
Application year: 1998
Main classification: B29C53
IPC codes: B29C53