MASK AND METHOD FOR THE PRODUCTION OF AT LEAST ONE GROOVE, RIB OR DIFFERENT INTENSITY STRIP IN OR ON A SURFACE

Abstract: At least one groove, rib or strip can be formed in or on a surface by means of a mask (1) made of sheet material and provided with at least one substantially non parallel sided aperture (2) therethrough, or a plurality of such apertures (2, 3) in one or more rows.

Description: This invention relates to a apparatus and a method for the production of at least one groove, rib or different intensity strip in or on a surface using a mask and is particularly, but not exclusively, concerned with such apparatus and method for the production of grooves in a surface by laser. Grooves may be formed in a substantially planar surface, either in a paint layer on a metal substrate or in an unpainted metal surface by subjecting the surface to a directed beam of laser energy radiation. The laser beam impinges on the surface at right angles thereto and the surface and beam are moved relative to one another, so that the beam removes material from the surface along a path which is generally groove shaped. One of the problems of this technique is the difficulty of controlling the shape of the groove over its cross section, that is its profile. The profile of a groove produced in this way is not easily controlled and may not be suitable for all applications. Control of the form of the groove over its cross section may be improved by using a mask provided with a series of side by side slot-like apertures therein each conforming to the shape in plan desired for a groove to be produced. Such a mask is located between the laser beam source, which may include a beam focusing lens and the surface. The mask conveniently is fixed relative to the source and lens, so that if the beam source and lens are moveable relative to the surface, the mask moves with the beam source and lens. However even with such a mask the cross sectional shape of the groove so produced cannot be controlled or varied reliably from the usual V shaped cross section produced. Some control over the cross sectional shape of the groove produced may be achieved by variation of the intensity of the laser beam during relative movement of the mask and surface, but this is difficult to control. The same problem exists in trying to produce by electromagnetic radiation means a strip having a controlled density across its width on a photographic emulsion layer. Control of the density of the strip in the region of its edges is particularly difficult to effect and similarly control of the depth of a groove or height of a rib at its side edges is likewise difficult to effect. There is thus a need for a generally improved mask apparatus and method, using a mask for the production of at least one groove, rib or different intensity strip in or on a surface which is both more accurate and simpler to control. According to a first aspect of the present invention there is provided an apparatus for the production of at least one groove, rib or different intensity strip in or on a surface, comprising a mask made of sheet material and having at least two rows of laterally spaced, substantially triangular in plan apertures therethrough, with the apertures of one row facing in the opposite direction to those of the other row of said at least two rows and being interspersed apertures, so that one aperture lies between two adjacent apertures with apices of the apertures adjoining bases of the apertures; a source of material deposition for rib production or a source of material removal for groove production, and means for causing relative motion between the mask and said surface. According to a further aspect of the present invention there is provided a method for the production of at least one groove, rib or different intensity strip in or on a surface, including the steps of positioning a mask and the surface face to face, with or without a spacing therebetween, which mask is made of sheet material and has at least two rows of laterally spaced, substantially triangular in plan apertures therethrough, with the apertures of one row facing in the opposite direction to those of the other row of said at least two rows and being interspersed with apertures, so that one aperture lies between two adjacent apertures with apices of the apertures adjoining bases of the apertures, applying a source of material deposition for rib production, a source of material removal for groove production or a source of intensity variation for strip production, to the side of the mask remote from said surface, to deposit material on, remove material from or vary the intensity on said surface through each said aperture and causing relative motion between the surface on the one hand and the mask on the other hand in the general direction of the aperture sides, so that the height and cross section of said rib material deposition on the surface, the depth and cross section of said groove material removal from the surface, or the variation in intensity across the width of a strip on the surface, is proportional to the length of each said aperture side, the change in width of each said aperture with length and the speed of relative movement between each said aperture and said surface. For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawing, in which: Figure 1 is a plan view of a first form of mask for use according to the invention for the production of at least one groove, rib or different intensity strip in or on a surface, Figure 2 is a plan view of a second form of mask for use according to the invention, and Figure 3 is a plan view of a third form of mask for use according to the invention. A mask is shown in the accompanying drawings which is suitable for use with the apparatus and method of the present invention for the production of at least one groove, rib or different intensity strip in or on a surface. The mask 1 is made of sheet material, preferably metallic or plastics, and provided with at least two rows of laterally spaced substantially triangular in plan apertures 2,3 therethrough as shown in Figures 1 to 3. As also shown in Figures 1, 2 and 3 the apertures 3 of the one row, face in the opposite direction to the apertures 2 of the other row and are interspersed with the first row apertures 2 so that one second row aperture 3 lies between two adjacent apertures 2 of the first row. The or each aperture 2 or 3 is substantially triangular in plan having a base 4 and two sides 5. As can be seen from the Figures preferably the or each aperture 2 and 3 has two sides 5 longer than its base 4. In the Figure 1 the two sides 5 are straight. However in the Figure 2 example the two sides 5a are curved in plan whilst in the Figure 3 example the two sides 5b are curved more strongly in plan. Otherwise the examples of Figures 1,2 and 3 are similar and like features therein have been given like references. As can be seen from Figures 1, 2, and 3 the apertures 2 of the first row extend side by side with their bases 4 at one end of the row and with their apices 6 at the opposite end of the row. The apertures 3 of the second row extend side by side with their bases 4 at one end of the second row and with their apices 6a at the other end of the second row. The bases 4 of one row of apertures adjoins the apices 6 or 6a of the other row of apertures. Basically the method and apparatus of the present invention uses the mask 1 to transfer a one dimensional intensity profile is transferred into a two dimensional binary profile. This two dimensional profile is automatically converted into the required groove, rib or strip profile as the mask is scanned across the substrate surface. Thus in the method of the present invention for the production of at least one groove, rib or different intensity strip in or on a surface using the apparatus of the invention, the mask 1 and the surface are positioned face to face, with or without a spacing therebetween. A source of material deposition for rib production, a source of material removal for groove production or a source of intensity variation for strip production is applied to the side of the mask 1 remote from said surface, to deposit material on, remove material from or vary the intensity on said surface through each aperture 2 and 3 and relative motion is brought about between the surface on the one hand and the mask 1 on the other hand in the general direction of the aperture sides 5, 5a and 5b. In this way the height and cross section of the rib material deposition on the surface, the depth and cross section of the groove material removal from the surface or the variation in intensity across the width of strip on the surface is proportional to the length of each aperture side 5, 5a or 5b, the change in width of each aperture 2, 3 with length and the speed of relative movement between each aperture 2, 3 and said surface. The source of material deposition conveniently is a spray of molten metal, plastics or paint and the surface so treated may be made of metal and/or plastics. Alternatively the source of material removal may be a laser or a spray of etching fluid and the surface so treated may be paint, metal or plastics. Yet a further alternative is to use a source of intensity variation in the form of a beam of electromagnetic radiation to act on a surface which comprises a photographic film emulsion layer. By appropriately choosing the shape in plan of the aperture sides 5, 5a and 5b it is possible to control the cross sectional shape more accurately of the rib, groove or strip produced. Additionally by so nesting the rows of apertures such that the apertures 3 are interspersed with the apertures 2 it is possible to provide a strong mask 1 but a mask 1 which will produce ribs, grooves or strips which are very close together. This is a function of the substantially triangular shape of the apertures and enables the nesting to be carried our whilst leaving substantial support ribs 7 between adjacent apertures. The principle underlying the apparatus and method of the invention is that with the shaped apertures in the mask 1 the surface under the greater width portion of each aperture is impinged by the laser for a short period of time whilst the remaining narrower width areas receive a proportionally greater amount of the laser beam (i.e. for a larger period of time) and have a proportionally greater amount of material removal. Preferably the mask 1 is aligned parallel to the surface during material deposition, material removal or intensity variation but alternatively the mask 1 may be tilted with respect to the surface with the tilt being either in the direction of relative movement between the mask 1 and surface or transverse thereto to provide for greater control of the degree of material removal at the sides 5, 5a or 5b of the mask. A particularly favoured use of the apparatus and method of the invention is for the production of riblets in a paint or metal surface of an aircraft by laser removal of paint or metal between the riblet areas. Such riblets decrease surface drag of the aircraft under certain conditions.

Claims: An apparatus for the production of at least one groove, rib or different intensity strip in or on a surface, comprising a mask (1) made of sheet material and having at least two rows of laterally spaced, substantially triangular in plan apertures (2,3) therethrough, with the apertures (3) of one row facing in the opposite direction to those of the other row (2) of said at least two rows and being interspersed apertures (2), so that one aperture (3) lies between two adjacent apertures (2) with apices (6) of the apertures (3) adjoining bases (4) of the apertures (2); a source of material deposition for rib production or a source of material removal for groove production, and means for causing relative motion between the mask (1) and said surface. Apparatus according to claim 1 wherein each aperture (2,3) has two sides (5a, 5b) which are curved in plan view. A method for the production of at least one groove, rib or different intensity strip, in or on a surface, including the steps of positioning a mask (1) and the surface face to face, with or without a spacing therebetween, which mask is made of sheet material and has at least two rows of laterally spaced, substantially triangular in plan apertures (2,3) therethrough, with the apertures (3) of one row facing in the opposite direction to those of the other row (2) of said at least two rows and being interspersed with apertures (2), so that one aperture (3) lies between two adjacent apertures (2) with apices (6) of the apertures (3) adjoining bases (4) of the apertures (2), applying a source of material deposition for rib production, a source of material removal for groove production or a source of intensity variation for strip production, to the side of the mask remote from said surface to deposit material on, remove material from or vary the intensity on said surface through each said aperture (2,3) and causing relative motion between the surface on the one hand and the mask (1) on the other hand in the general direction of the aperture sides (5, 5a, 5b), so that the height and cross section of said rib material deposition on the surface, the depth and cross section of said groove material removal from the surface, or the variation in intensity across the width of a strip on the surface, is proportional to the length of each said aperture side, (5, 5a, 5b) the change in width of each said aperture (2, 3) with length and the speed of relative movement between each said aperture (2, 3) and said surface. A method according to Claim 3, wherein the source of material deposition is a spray of molten metal, plastics or paint and wherein the surface is metal and/or plastics. A method according to Claim 3, wherein the source of material removal is a laser or a spray of etching fluid and wherein the surface is paint, metal and/or plastics. A method according to Claim 3, wherein the source of intensity variation is a beam of electromagnetic radiation and wherein the surface is photosensitive material or a photographic film emulsion layer. A method according to any one of Claims 3 to 6, in which the mask (1) is parallel to the surface during material deposition, material removal or intensity variation. A method according to any one of Claims 3 to 6, in which the mask (1) is tilted with respect to the surface, with the tilt being either in the direction of relative movement between the mask (1) and surface or transverse thereto.

Inventors: LLOYD, MARK LLEWELLYN, SOWERBY RESEARCH CENTRE
Applicants: BRITISH AEROSPACE PUBLIC LIMITED COMPANY
Application year: 1990
Main classification: B23K26
IPC codes: B23K26, G03F1, B64C21