GB2207387A - Method of manufacturing a shaped lamina - Google Patents

Method of manufacturing a shaped lamina Download PDF

Info

Publication number
GB2207387A
GB2207387A GB08803621A GB8803621A GB2207387A GB 2207387 A GB2207387 A GB 2207387A GB 08803621 A GB08803621 A GB 08803621A GB 8803621 A GB8803621 A GB 8803621A GB 2207387 A GB2207387 A GB 2207387A
Authority
GB
United Kingdom
Prior art keywords
shaped lamina
lamina
manufacturing
shaped
pattern
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
GB08803621A
Other versions
GB8803621D0 (en
Inventor
Donald Gilbert Jobbins
Trevor Glyn Hicks
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Linolite Ltd
Original Assignee
Linolite Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB878703588A external-priority patent/GB8703588D0/en
Priority claimed from GB878704296A external-priority patent/GB8704296D0/en
Application filed by Linolite Ltd filed Critical Linolite Ltd
Publication of GB8803621D0 publication Critical patent/GB8803621D0/en
Publication of GB2207387A publication Critical patent/GB2207387A/en
Pending legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V3/00—Globes; Bowls; Cover glasses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
    • B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
    • B23P15/24—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass dies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C33/00—Moulds or cores; Details thereof or accessories therefor
    • B29C33/38—Moulds or cores; Details thereof or accessories therefor characterised by the material or the manufacturing process
    • B29C33/3842—Manufacturing moulds, e.g. shaping the mould surface by machining
    • B29C33/3857—Manufacturing moulds, e.g. shaping the mould surface by machining by making impressions of one or more parts of models, e.g. shaped articles and including possible subsequent assembly of the parts
    • B29C33/3878—Manufacturing moulds, e.g. shaping the mould surface by machining by making impressions of one or more parts of models, e.g. shaped articles and including possible subsequent assembly of the parts used as masters for making successive impressions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)

Abstract

A method of manufacturing a shaped lamina comprises providing a sheet of deformable material having a desired pattern thereon, and deforming said sheet by vacuum forming on a former having the desired profile of the shaped lamina to provide a master bearing the desired pattern and profile of the shaped lamina. A rigid mould tool, of complementary pattern and profile to the shaped lamina, is produced, using the master as a mode and the shaped lamina is injection moulded using said mould tool. The shaped lamina can be a diffuser for a luminaire.

Description

Method of Manufacturing a Shaped Lamina This invention relates to a method of manufacturing a shaped lamina, and to a lamina manufactured by the method. The method is especially but not exclusively of use in manufacturing diffusers for luminaires.
Diffusers may be manufactured by injection moulding to produce simple or complex overall shapes, but hitherto this technique has been limited to diffusers having plain walls, or to diffusers having prismatic or other patterned walls but of simple shape. It has not been possible to provide a diffuser of complex shape having a complex patterned wall in view of the difficulty in providing such conceptual shapes and patterns to an injection mould tool.
According to the present invention there is provided a method of manufacturing a shaped lamina, comprising providing a sheet of deformable material having a desired pattern thereon, deforming said sheet around a former having the desired profile of the shaped lamina to provide a master bearing the desired pattern and profile of the shaped lamina, producing from the master a rigid mould tool of complementary pattern and profile to the shaped lamina, and moulding the shaped lamina with said mould tool.
The pattern may be provided on one or both faces of the shaped lamina; when it is on both faces a second rigid mould tool is produced having complementary pattern and profile to the desired second face of the shaped lamina.
If the second face is to be plain, the second mould tool is likewise plain.
The rigid mould tool may be produced by making a plain mould tool whose profile is complementary to the desired profile of the shaped lamina but omitting the pattern, and then etching the pattern on the plain mould tool, for example by an acid etching technique. An effective method is that employed commercially by the Moldtech Division of Standex International Limited.
The master may be prepared for example by vacuum forming a pre-patterned plastics sheet around a plain former, although methods other than vacuum forming may be used.
Preferably, the desired pattern comprises regular or irregular indentations in the surface of the lamina, for example to provide a plurality of prismatic units over the lamina.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a side sectional view of a diffuser manufactured by the method of this invention; Fig. 2 is a side sectional view of a former for use in manufacturing the diffuser of Fig. 1; Fig. 3 is a side sectional view of a master for use in manufacturing the diffuser of Fig. 1; and Fig. 4 is a side view of a plain mould tool for use in manufacturing the diffuser of Fig. 1.
Referring to the drawings, the object of the method of this embodiment is to manufacture a diffuser 12 for a luminaire, the diffuser being in the form of a lamina whose central portion 14 is part-spherical and whose peripheral portion 16 is frustoconical. The diffuser is to be translucent and to have over its entire inner face adjoining prismatic formations 18. Each prism 18 comprises a generally conical shallow recess about 1.5 mm deep bounded by a rectangular wall 20.
A flat acrylic sheet is produced with the desired prismatic contour on one face. Such a sheet could either be purchased as a proprietary item or prepared by rolling over a plain acrylic sheet, heated so as to be deformable, a cylinder having projections corresponding to the desired prismatic recesses, and then cooling the sheet. A rigid former 22 was machined from Tufnol (Trade Mark) to the female configuration of the overall shape of the final diffuser, the former having a plain uncontoured face.
Tufnol was selected for its ability to avoid distortion after machining, and is a fibre-reinforced thermosetting plastics material. The female configuration of the former 22 was to prevent contact between the former and the prismatic face of the acrylic sheeting thereby preserving the prismatic contour during deformation, as will be described.
The spherical radius of the central portion of the former was calculated as: (outside radius of final desired diffuser 12) MINUS (wall thickness of final desired diffuser 12) PLUS (wall thickness of acrylic sheeting) PLUS (0.7% allowance for mould shrinkage) PLUS (1.08 allowance for vacuum forming shrinkage) The acrylic sheet was placed above the former 22, prismatic face uppermost, in a vacuum forming machine, and was then heated and drawn down under vacuum onto the former 22 to deform the sheet into the general desired shape of the final diffuser 12. The deformed sheet was cooled and trimmed, but left oversize, and removed from the former.
The former 22 was then modified by cutting away the central part-spherical portion, and the deformed sheet 24 was returned to it and glued in position, as shown in Fig. 3.
Modification of the former was necessary in view of shrinkage of the deformed sheet on cooling after the vacuum forming stage, as the deformed sheet 24 would not otherwise have refitted snugly into the former 22. Thus the deformed sheet 24 within the modified former 22A now provided a rigid master 28 and was suitable for being copied to make a mould tool.
Before being finally glued into the modified former 22A, the thickness of the deformed sheet 24 was carefully measured at intervals across it, and variations were noted. Knowing this, the depth of the prismatic contours and the shape of the former 22, one radius (R) of the spherical portion and the angle of the frustoconical peripheral portion (0) were identified (see Fig. 3). These measurements were then checked with a template which was modified and adjusted until a good fit was obtained, and a metal mould core 30 having a plain uncontoured face was then machined to these dimensions plus an allowance for the depth of the prismatic contours. The metal core 30 was then etched by acid using the rigid master 28 as the model, this etching process being as operated by the Moldtech Division of Standex International Limited in Stockport, Cheshire. The result was a male mould tool produced from the core 30, the tool having an outer face of complementary contour to the desired final diffuser 12.
The contoured male mould tool was then inserted into an injection moulding machine along with a female tool of complementary profile to the uncontoured desired face of the diffuser 12, and the machine was then used in standard fashion to produce diffusers 12 in a precisely repeating manner.
Modifications and improvements may be made without departing from the scope of the invention.

Claims (9)

1. A method of manufacturing a shaped lamina comprising providing a sheet of deformable material having a desired pattern thereon, deforming said sheet around a former having the desired profile of the shaped lamina to provide a master bearing the desired pattern and profile of the shaped lamina, producing from the master a rigid mould tool of complementary pattern and profile to the shaped lamina and moulding the shaped lamina with said mould tool.
2. A method of manufacturing a shaped lamina as claimed in Claim 1, wherein a pattern is provided on both faces of the shaped lamina, a second rigid mould tool being produced having complementary pattern and profile to the second face of the shaped lamina.
3. A method of manufacturing a shaped lamina as claimed in Claim 1 or 2, wherein each rigid mould tool is produced by making a plain mould tool whose profile is complementary to the desired profile of the shaped lamina but omitting the pattern, and then etching the pattern on the plain mould tool.
4. A method of manufacturing a shaped lamina as claimed in Claim 3, wherein the pattern is etched on the plain mould tool by an acid etching technique.
5. A method of manufacturing a shaped lamina as claimed in any one of the previous Claims, wherein the master is prepared by vacuum forming a pre-patterned plastics sheet around a plain former.
6. A method of manufacturing a shaped lamina as claimed in any one of the preceding Claims, wherein the desired pattern is provided as a plurality of indentations in the surface of the lamina to provide a plurality of prismatic units over the lamina.
7. A shaped lamina when produced by the method of any one of the preceding Claims.
8. A method of manufacturing a shaped lamina substantially as hereinbefore described, with reference to and as shown in the accompanying drawings.
9. A shaped lamina when produced by a method substantially as hereinbefore described, with reference to and as shown in the accompanying drawings.
GB08803621A 1987-02-17 1988-02-17 Method of manufacturing a shaped lamina Pending GB2207387A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB878703588A GB8703588D0 (en) 1987-02-17 1987-02-17 Shaped lamina
GB878704296A GB8704296D0 (en) 1987-02-24 1987-02-24 Manufacturing shaped lamina

Publications (2)

Publication Number Publication Date
GB8803621D0 GB8803621D0 (en) 1988-03-16
GB2207387A true GB2207387A (en) 1989-02-01

Family

ID=26291915

Family Applications (1)

Application Number Title Priority Date Filing Date
GB08803621A Pending GB2207387A (en) 1987-02-17 1988-02-17 Method of manufacturing a shaped lamina

Country Status (1)

Country Link
GB (1) GB2207387A (en)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1416210A (en) * 1973-07-17 1975-12-03 Mardon Son Hall Ltd Reproduction of a surface decoration
GB2044665A (en) * 1979-02-28 1980-10-22 Aderans Kk Method of preparing a female mould for forming a head model for a wig

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1416210A (en) * 1973-07-17 1975-12-03 Mardon Son Hall Ltd Reproduction of a surface decoration
GB2044665A (en) * 1979-02-28 1980-10-22 Aderans Kk Method of preparing a female mould for forming a head model for a wig

Also Published As

Publication number Publication date
GB8803621D0 (en) 1988-03-16

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