WO2015172786A1

WO2015172786A1 - Process for manufacturing translucent holes in metal

Info

Publication number: WO2015172786A1
Application number: PCT/DK2014/050133
Authority: WO
Inventors: Roar Sune JENSEN; Ulrich Lahn HØYER; Jan ROHDEMEJER
Original assignee: Hidden Led Aps
Priority date: 2014-05-14
Filing date: 2014-05-14
Publication date: 2015-11-19

Abstract

The invention relates to an oxidized metal object having a plurality of translucent holes 110 and to a process for producing translucent holes in an oxidized metal object. According to the process holes are created in the oxidized object, e.g. an oxidized plate, by directing a laser beam 201 towards the object so that metal is removed at the location where laser beam hits the object. By directing a predetermined amount of energy from the laser beam to the object the metal is removed while the oxide layer remains so that a translucent hole is created.

Description

PROCESS FOR MANUFACTURING TRANSLUCENT HOLES IN METAL

FIELD OF THE INVENTION

The invention relates to a process for manufacturing holes in metal, particularly to a process for manufacturing translucent holes in metal.

BACKGROUND OF THE INVENTION

Metals are often used as a design material in products in order to provide the product with an exclusive and attractive appearance.

Plastic materials used as design material in products may be designed in various ways in order to achieve specific characteristics. For example, plastic products may be designed to achieve translucent characteristics so that e.g. a plastic cover of an object can be used both as a cover and as a display. However, plastic material may not provide the product with the same attractive appearance as oxidized metals.

Accordingly, in order to enable use of metal as an alternative to plastic material there is a need for improving use of metals as a design material in products.

WO2008006375 discloses a process for the manufacture of ultra-thin sections in an electrically conducting material comprising removing material in an

electrochemical process to a material thickness of approximately 10 to 20 micrometres and removing further material by a laser micromachining process to a thickness of 1 to 5 micrometres. By combining the two methods it is possible by the electrochemical process to quickly remove a substantial amount of material. The electrochemical process is not as precise and accurate so that it may be possible to solely rely on and use this method in order to create the ultra-thin sections or translucent sections. However, by removing material by an

electrochemical process down to a thickness of approx. 10-12 micrometres enough margin is provided so that the electrochemical process may be controlled in a manner so that it is satisfied that there is a material thickness left at the bottom of this first cavity. By thereafter applying the laser technique, in a laser micromachining process, the remaining material down to a predetermined level, e.g. 1-5 micrometres, may be achieved relatively rapidly so that a relatively quick process for the manufacture of these ultra-thin sections in an electrically conducting material is achieved.

SUMMARY OF THE INVENTION

It would be advantageous to achieve improvements in use of metals as a design material in products. In general, the invention preferably seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages of use of metals. In particular, it may be seen as an object of the present invention to provide a method that enables use of metal both as a cover and as a display in products or solves other problems of the prior art.

To better address one or more of these concerns, in a first aspect of the invention a process for producing translucent holes in an oxidized metal object is presented, wherein the oxidized metal object comprises, a body part, a first surface having a translucent oxide layer on the first surface, a second surface located opposite to the first surface, wherein the first surface is separated from the second surface by a material thickness of the body part, the process comprises

- creating a hole by processing a location on the second surface of the body part by directing a laser beam towards the location so that the location receives a predetermined amount of energy from the laser beam so that the material thickness is removed (i.e. only or substantially only the material thickness is removed, but not or substantially not the oxide layer) over an area at the location. The second surface may be a metal surface of the body part or a surface of an oxide layer provided on a metal surface of the body part. The first surface may be considered a surface, an intermediate surface or a boundary between the body part and the oxide layer. The body part may be seen as a part of the metal object where the body part consists of the same metal as the metal object.

The body part is a part of the oxidized metal object comprising metal or consisting only of metal, i.e. the same metal as the oxidized metal object is based on. The first surface may be a metal surface of the body part provided with a translucent oxide layer. The second surface may be a metal surface of the body part. The first and second surfaces face each other and are separated from each other by the material thickness of the body part. The first and second surfaces may be parallel to each other or non-parallel where they define an angle less the 90 degrees relative to each other.

For example, the oxidized metal object may be a metal plate or shell, which is provided with an oxide layer on one of the plate surfaces - which thereby constitutes the first surface. An opposite plate surface, which is not provided with any oxide layer, constitutes the second surface

Advantageously, the use of a predetermined energy provides a simple production method since feedback from the laser processing of the hole is not required. The predetermined amount of energy may be determined, e.g. by experiments, so that the material thickness is removed. Whether a material thickness is

sufficiently removed can be verified after the hole is made by measuring the translucency of the hole, i.e. by measuring how much light is transmitted through the hole or a plurality of holes. The predetermined energy may be made slightly larger than the amount of energy determined by experiments for sufficiently removing the material thickness. Advantageously, creating a hole with an increased predetermined amount of energy may not remove material from the oxide layer due to the transparency of the oxide layer since the power or intensity of the laser beam, i.e. the power absorbed by the oxide layer, is too low to be able to remove the oxide material. Accordingly, by use of a predetermined amount of energy which is actually larger than the amount required for removing the material thickness, ensures that the material thickness is sufficiently removed so that no unprocessed metal reduces the transparency. Thus, in general the predetermined amount of energy is equal to or greater than the amount of energy necessary for creating a hole through the material thickness. For example, the predetermined amount of energy may be measured in terms of power or intensity of the laser beam in combination with the period of time wherein the laser is directed to the location for creation of a hole. According to an embodiment the process of creating the hole further comprises directing the laser beam towards the location, being a first location, so that the location receives a first predetermined amount of energy from the laser beam so that the material thickness is removed, and directing the laser beam towards one or more second locations located adjacent to the first location, so that each of the second locations receives a second predetermined amount of energy being less than the first predetermined energy so that the material thickness is only partially removed at the second locations.

According to an embodiment the process comprises creating a plurality of holes by processing a plurality of locations on the second surface of the body part by sequentially directing the laser beam towards the locations so that each of locations receives a first fraction of the predetermined amount of energy in a first scan, sequentially directing the laser beam towards the same locations so that each of the locations receives a second fraction of the predetermined amount of energy in a second scan and repeating scanning until the sum of fractions of energies supplied to each of the locations equals, or substantially equals, the predetermined amount of energy.

Thus the process may comprise creating first and second holes by processing at least first and second locations on the processing region by alternatingly directing the laser beam towards the at least first and second locations so that each of the at least first and second locations alternatingly receives a fraction of the predetermined amount of energy from the laser beam and repeating directing the laser beam towards the at least first and second locations until the sum of fractions of energies supplied to each of the first and second locations equals the predetermined amount of energy.

According to an embodiment a plurality of holes are made in a pattern comprising clusters of holes, wherein adjacent holes in a cluster are separated by a hole separation distance being in a range from 2 to 10 times a diameter of each hole, and wherein adjacent clusters are separated by a cluster separation distance being greater than the hole separation distance.

According to an embodiment the process comprises scanning the laser beam over the second surface with a constant speed. Thereby, directing a laser beam towards the location comprises moving the laser beam over a distance of the location so that the hole achieves an elongate cross-sectional shape.

According to an embodiment the process of creating the hole is performed by directing a pulsed laser beam towards the location so that the location receives a predetermined number of pulses from the laser beam.

For example, the pulse length of pulses in the laser beam may be between 1 and 100 microseconds and the power of each pulse may be between 1 and 100 watt.

According to an embodiment the diameter of the laser beam at the location on the second surface is in the range from 10 to 100 micrometre. The diameter of the laser beam may be achieved by focussing a laser beam towards the second surface. The diameter of the hole created by the laser beam may be

approximately equal to the diameter of the laser beam at the location on the second surface.

According to an embodiment, the oxidized metal object further comprises a translucent oxide layer on the second surface, and the process comprises, - creating the hole by processing the location on an outer surface of the oxide layer by directing the laser beam towards the location so that the location receives the predetermined amount of energy from the laser beam so that the material thickness of the body part and a material thickness of the oxide layer on the second surface are removed over an area at the location.

According to an embodiment each of a plurality of the holes are created by the same or substantially the same amount of predetermined energy. A second aspect of the invention relates to an oxidized metal object obtainable by a process according to the first aspect.

According to an embodiment the oxidized metal object comprises

- a metal body,

- a first surface having a translucent oxide layer on the first surface,

- a second surface located opposite to the first surface, wherein the first surface is separated from the second surface by a material thickness of the body part,

- a plurality of holes in the second surface, wherein each hole extends through the material thickness so that the holes are only or substantially only covered by the translucent oxide layer.

A third aspect of the invention relates to a display comprising,

- the oxidized metal object according to the second aspect,

- a light source arranged on the second side so as to direct light through the holes.

In summary the invention relates to an oxidized metal object having a plurality of translucent holes and to a process for producing translucent holes in an oxidized metal object. According to the process holes are created in the oxidized object, e.g. an oxidized plate, by directing a laser beam towards the object so that metal is removed at the location where laser beam hits the object. By directing a predetermined amount of energy from the laser beam to the object the metal is removed while the oxide layer remains so that a translucent hole is created.

In general the various aspects and embodiments of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which Fig. 1 shows a principal sketch of an oxidized metal object 100,

Fig. 2 illustrates use of a laser beam 201 for creating a hole 110 in the oxidized metal object,

Fig. 3 illustrates use of a laser beam 201 for creating a hole 310 with a stepped profile,

Fig. 4 illustrates use of a laser beam 201 for creating a plurality of holes 110 at different locations 211, 212,

Fig. 5A shows arrangement of holes in a particular pattern, and

Fig. 5B shows an example where the processing side of the object 100 is provided with an oxide layer 502.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a principal sketch of an oxidized metal object 100. Illustration A shows a cross-sectional view A-A of the object 100 and illustration B shows a bottom view of the object 100.

The oxidized metal object 100 comprises a body part 105 having a material thickness 104 of constant, substantially constant or varying thickness. For example, the body part 105 may be a part of the metal object which has a platelike shape with constant or substantially constant material thickness, i.e. plate thickness. Thus, the body part 105 may be in the form of a metal layer, e.g. a metal plate. The material thickness 104 may be in the range from 0.1 to 1 millimetre. The material thickness 104 may have been obtained by processing of the metal object 100, before or after oxidization (anodization) of the object, by known methods, e.g. by precision milling.

The metal object and the body part 105 comprises a first surface 101 and a translucent oxide layer 102 provided on the first surface, i.e. on top of the first surface. Thus, even though the first surface may not be an outer surface of the anodized body, the first surface may have been an outer surface of the body before the anodization process. The first surface may equally be referred to as a boundary between the oxide layer and the body part 105 or as an intermediate surface. The boundary may be considered a sharp transition. In reality the boundary between the oxide layer and the body part may be in the form of a transition layer having a small but finite thickness.

The oxidized metal object may be made from aluminium, titanium and other metals than can be oxidized. The oxide layer 102 may be provided by known oxidation or anodization processes which create a layer of aluminium oxide, i.e. a chemical compound of aluminium and oxygen (AI203) on a surface of the metal. The oxide layer is translucent or even transparent and may have a thickness in the range from 1 to 25 micrometre.

The metal object and the body part 105 further comprises a second surface 103 located opposite to the first surface 101. The first surface 101 is separated from the second surface 103 by the material thickness 104 of the body part 105. The first and/or the second surface may be configured as plane or curved surfaces.

One or more holes 110 are formed in the second surface 103 so that they extend through the material thickness and through the first surface 101. Therefore, the holes 110 are only or substantially only covered by the translucent oxide layer 102.

Due to the translucency of the oxide layer 102 light can be transmitted through the holes 110. For example, holes 110 can be produced in a certain pattern, e.g. for creation of an illuminated graphical pattern. When no light is directed towards the second surface 103 the first surface 101, the holes 110 will be invisible or substantially invisible. When light is directed towards the second surface 103 the pattern formed by the holes 110 will be visible due to the light transmitted through the holes 110 and the oxide layer 102.

Accordingly, by arranging a light source 191 adjacent to the second surface 103 light can be directed through the holes so that the pattern formed by the holes 110 can be made visible or invisible dependent on whether the light source 191 is turned on or off. Accordingly, the oxidized metal object 100 may be used for a display 190 configured to display a pattern formed by the holes by arranging a light source to transmit light through the holes 110. In another aspect of the invention the oxidized metal object may be configured as a touch sensitive display which comprises the oxidized metal object, a light source arranged on the second side so as to direct light through the holes, and a touch sensor arranged on the second side. The touch sensor may be a light sensor configured to measure changes in light intensity. For example, placing a finger near the holes 110 on the first surface 101 may cause reflection of light back through the holes towards the second surface 103 and towards the light sensor. The touch sensor could also be a capacitive sensor or other proximity sensor capable of sensing changes in an electrical parameter when a finger is placed on the surface of the oxide layer 102 on the first surface 101.

In Fig. 1 the second surface 103 of the body part 105 may be considered as a processing surface to be processed according to an embodiment of a process for producing translucent holes in an oxidized metal object.

Fig. 2 illustrates use of a laser beam 201 for creating a hole 110 in the oxidized metal object. The hole 110 is created by processing a location 211 on a surface 103 (i.e. the second surface 103 in Fig. 1) of the body part 105 by directing the laser beam 201 towards the location so that the location receives a predetermined amount of energy from the laser beam. The predetermined amount of energy is determined so that the material thickness 104 is removed over an area at the location so that a hole is created which passes through both first and second surfaces 101, 103 so that the hole is only covered by the translucent oxide layer 102. The area over which material is removed depends on the intensity profile of the laser beam at the location of the surface 103 and throughout the thickness of the body part 105. In general the area or a dimension of the opening of the hole corresponds approximately to the area or dimension of the laser beam 102 at the location of the surface 103. The power of the laser beam, the laser beam energy used for creating the hole and the period of time wherein the location 211 is illuminated have been determined by the inventors of the present inventions by experiments.

Particularly, the inventors have discovered that by proper selection of these parameters it is possibly to process the body part 105 so that the material thickness 104 is removed but so that the oxide layer 102 is not removed.

The inventors have also discovered that as long as the power of the laser beam is within certain ranges, the predetermined energy may exceed a minimum energy level necessary for removing the material thickness 104. Thus, an excess of energy may not cause a removal of the oxide layer 102 or at least only removal of an insignificant thickness of the oxide layer as long as the laser power absorbed by the oxide layer is lower than a certain value necessary for removal of the oxide material. Thus, in general the predetermined amount of energy directed to a location 211 for creation of a hole 110 should be at least large enough to remove the material thickness 104.

Due to the translucency of the oxide layer only a fraction of laser power is absorbed and, therefore, the predetermined energy may exceed a minimum energy level necessary for removing the material thickness 104 without causing removal of the oxide layer.

The same predetermined amount of energy may be used for creating each of a plurality of different holes or all holes on the first surface 101. Accordingly, the predetermined energy may be kept constant or substantially constant during the process of creating holes so that each of a plurality of the holes are created by the same or substantially the same amount of predetermined energy. By substantially constant is meant that the amount of predetermined energy is not adjusted (e.g. in response to some input), but may vary according to power tolerances of the laser.

The inventors have discovered that a pulsed laser beam 102 is useful for removing material of the body part 105 without causing removal of the oxide layer 102. In order to remove a material thickness of 0.3 millimetre in a body part 105 of aluminium provide with an oxide layer 102, a pulsed laser beam 201 with a pulse frequency of 20 kHz, a pulse length of 10 microseconds, a power of the light pulses of 14 W and a circular beam diameter of 40 micrometre at the surface 103 was used. In order to fully remove the material thickness 104 a number of 11 pulses were directed to the location 211. Experiments have shown that increasing the number of pulses to e.g. 50 pulses per hole does case removal of the covering oxide layer 102.

Accordingly, a predetermined energy of 0.00154 Ws (Watt seconds) was used.

The wavelength of the laser beam 210 may be in the range from approx. 300 nm to 5 micrometre wherein aluminium oxide has low absorption. For example, wavelengths in the range from 800 to 1200 nanometre, e.g. 1064 nanometre, have been found to be suitable.

As long as the power of the laser beam is around 14 W - or the corresponding laser intensity at the processing surface 103 of the body part 105 is around an intensity value for a 40 micrometer spot corresponding to this 14 W power value - the creation of a hole in an 0.3 millimetre thick aluminium body part 105 may be created with other pulse frequencies and pulse lengths or with a non-pulsed laser beam 201. For example similar results may be obtained with a pulsed laser beam 201 with a pulse frequency of 20 kHz, a pulse length of 20 microseconds, a power of the light pulses of 14 W and a circular beam diameter of 40 micrometre at processing surface 103 if 5 to 6 pulses are directed to the location 211. Similar results may also be obtained with 10 to 12 pulses of a pulsed laser beam 201 a pulse frequency of 50 kHz, a pulse length of 10 microseconds, a power of the light pulses of 14 W and a circular beam diameter of 40 micrometre at the processing location 103. The beam diameter at the processing location 211 (of a circular or approximately circular beam spot) may be larger or smaller than 40 micrometre as long as the intensity of the beam at the processing location 211 still corresponds to that of a 14 W laser beam at a 40 micrometre spot, i.e. an intensity of approximately 5- 20χ10^Λ9 W per square meter, e.g. 11χ10^Λ9 W per square meter.

Equivalent results may also be obtainable with a non-pulsed laser beam 201 having a beam power of 14 W focused to a beam diameter of 40 micrometre (or other diameters having a similar spot intensity) at the processing surface 103 and directed to the location 211 for a period of 0.05 to 0.2 microseconds, e.g. 0.11 microseconds.

A laser with a power higher than 14 W may be focused to a spot on the processing surface 103 having a diameter greater than 40 micrometre, but with an intensity suitable for removing the material thickness 104, i.e. an intensity corresponding to that of a 14 W laser beam focused to a 40 micrometre spot.

Accordingly, the laser beam 201 may have different characteristics in terms of being pulsed or non-pulsed, pulse frequency, pulse length, spot diameter at the processing surface and power as long as the intensity at the processing surface 103 is sufficiently high to remove the metal through the material thickness 104, but not so high that the laser beam 201 removes material from the oxide layer 102. Thus, the laser beam 201 should have such characteristics that the translucent properties of the oxide layer 102 can be exploited. That is, the laser beam 201 should have a power and spot size or an equivalent intensity at the surface 103 capable of removing (i.e. burning away) metal material though the material thickness 104, but not being capable of removing the oxide material through the thickness of the oxide layer 102.

The process for producing translucent holes in an oxidized metal object may further be performed by directing a pulsed laser beam 201 towards the location 211 so that the location receives a predetermined number of pulses from the laser beam wherein the number of pulses are dependent on the thickness of the body part 105 to be removed, the pulse length and the laser power.

The pulse length of pulses of the pulsed laser beam may be between 1 and 100 microseconds the power of each pulse may be between 1 and 100 watts. The upper limit of the power is dependent on the properties of the oxide layer 102, i.e. the power should be low enough to avoid that the laser removes significant amounts of the oxide layer 102. The lower limit is dependent on the properties of the metal of the body part 105, i.e. the power should be high enough to enable removal of the metal of the body part 105.

The laser spot diameter, i.e. the diameter of the laser beam (pulsed or non- pulsed) at the location 211 on the processing surface 103 may in the range from 10 to 100 micrometre. Dependent on the diameter, the power of the laser beam should be so that the intensity of the laser beam at the location 211 is high enough to enable removal of the metal of the body part 211 through the material thickness 104.

The laser beam 201 may be directed towards different locations on the processing surface 103 for creating a plurality of holes 110, e.g. by means of a mirror system 202 capable of directing the laser 201 towards location 211 and one or more other hole locations 212.

Fig. 3 illustrates an embodiment of the invention of a hole 310 with a stepped profile. A narrow hole has a relatively narrow acceptance angle of incident light from a light source 191. Accordingly, a narrow hole only allows light rays from the light source 191 propagating within the acceptance angle to be transmitted from the hole 110, 310. A less narrow hole has a larger acceptance angle and, therefore, allows

transmittance of more light so that light emitted by the hole 110 would appear brighter as compared to a more narrow hole. However, the thin oxide layer 102 covering a wide hole 110 may break more easily as compared to an oxide layer 102 covering a narrower hole 110. A hole 310 with a stepped profile as shown in Fig. 3 both offers robustness of the oxide layer covering the hole and a large acceptance angle of light.

A process for creating a hole 310 with a stepped profile comprises directing the laser beam 201 towards the location 211, being a first location 311, so that the first location 311 receives a first predetermined amount of energy from the laser beam so that the material thickness 104 is removed, i.e. so that a hole going through the material thickness 104 is created. The process further comprises directing the laser beam towards one or more second locations 312 located adjacent to the first location 311 so that each of the second locations 312 receives a second predetermined amount of energy being less than the first predetermined energy so that the material thickness 104 is only partially removed at the one or more second locations 311. For example, by directing the laser beam towards a plurality of second locations 312 located along a circle (or two or more circles with increasing diameter) circumscribing the first location 311 and illuminating each of the plurality of second locations with the second predetermined amount of energy a hole 310 with a stepped profile can be obtained. The second predetermined amount of energy may be determined e.g. so that half of the material thickness 104 is removed.

In addition to improving light transmission, the stepped profile of the hole 310 may have the advantage that slag is not so easily captured in the hole 310 since the slag from the laser burning process is more easily cast away through the conic hole shape resulting from the stepped profile of the hole 310.

The laser beam 201 may be directed towards the location 211 and one or more other hole locations 212 sequentially in a number of scans so that each of the locations repeatedly receives a predetermined amount of energy, i.e. for each scan, where the predetermined amount of energy only causes removal of the material from the body part 105 corresponding to a fraction 401 of the material thickness 104 as shown in Fig. 4. For example, the process may be configured so that, for each scan, each of the locations 211, 212 sequentially receives a single pulse or a fraction of the predetermined amount of energy (a fraction of the total amount of laser energy or a fraction of the pulses required for making a hole 110 through the thickness 104) from a pulsed or non-pulsed laser. The scan is repeated until all locations 211, 212 have received the number of pulses or the number of fractions of the predetermined amount of energy so that the sum of pulses or energies

corresponds to the predetermined laser beam energy necessary for removing the material thickness 104. A pulse may also be created by a non-pulsed laser by switching the laser or laser beam 201 on and off.

Accordingly, the process for creating holes 110 may comprise creating a plurality of holes by processing a plurality of locations 211, 212 on the processing surface 103 of the body part 105 by sequentially directing the laser beam towards the locations so that each of the locations receives a first fraction of the

predetermined amount of energy in a first scan, sequentially directing the laser beam towards the same locations so that each of the locations receives a second fraction of the predetermined amount of energy (possibly equal to the first fraction) in a second scan and repeating scanning until the sum of fractions of energies supplied to each of the locations equals, or substantially equals, the predetermined amount of energy necessary for removing material through the material thickness 104.

Advantageously, the formation of holes 110 by a process where the laser beam 201 is sequentially and repeatedly scanned over a plurality of locations 211, 212 may avoid excessive heating of the difference locations 211, 212 and, thereby, sooting of holes 110.

For example, during each scan, a number of 10000 locations 211, 212 distributed in a pattern over an area of one square centimetre may repeatedly be illuminated by the laser 201 in order to create a corresponding number of 10000 holes.

The laser 201 may be scanned continuously with a constant speed over the processing surface 103, e.g. with a speed around 100 to 200 mm/s. Since the laser beam 201 moves across the surface 103 while the laser is directed towards a location 211 the hole 110 will achieve an elongate shape in the plane of the processing surface 103 and along the moving direction of the laser beam.

Accordingly, the process may comprise scanning the laser beam over the processing surface 103 with a constant speed. Advantageously, the scanning of the laser with a constant speed compared to a step-wise scanning where the laser beam is stationary at a given location 211 may result in a faster manufacturing of a pattern of holes 110. As shown in illustration B in Fig. 1, the process may comprise arranging the holes 110 in clusters 113, 114 wherein adjacent holes 110 in a cluster are separated by a hole separation distance 111 being in a range from 2 to 10 times a diameter of each hole. Adjacent clusters may be separated by a cluster separation distance 112 being greater than the hole separation distance 111, e.g. by a factor between 2 and 5.

Accordingly, due to this process, the oxidized metal object 100 may be configured so that holes 110 are arranged in clusters 113, 114 as described above. The clusters may be equal in size. The number of holes 110 in a cluster may be less than the maximum possible number of holes that can be created in a cluster. Thus, clusters 113, 114 may contain different numbers of holes 110 so as to create clusters which appears with different brightnesses when illuminated from the processing surface 103 by a light source 191.

The holes may be arranged in any pattern such as a honeycomb pattern or other pattern, wherein the holes may be arranged to form clusters of holes or arranged without formation of clusters. Alternatively, the holes may be arranged with random positions. For example, the holes may be arranged in a honeycomb pattern as shown in Fig. 5B. Each hole may be in the form of a holed created by removing material from a single location 211, or a hole created by removing material from a plurality of locations so that a hole with a diameter greater than the beam diameter is created.

The holes 110 may be created so that the diameter of the hole or the transversal dimension of the hole perpendicular to the moving-direction of the laser beam 201 is determined by the diameter of the laser beam 201 on the processing surface. Accordingly, if the spot diameter of the laser beam on the processing surface 103 is 40 micrometre, the diameter of the hole or the transversal dimension of the hole may also be approximately 40 micrometre. The dimensions of a hole 110 in the plane of the surface 103 may be made greater than the spot diameter of the laser beam 201 by directing the laser beam towards a plurality of locations located adjacent to each other. Accordingly, an enlarged 100 micrometre hole 110 may be created by a 40 micrometre laser spot. A process for creation of an enlarged hole corresponding to the process for creating the hole 310 with a stepped profile may be utilized. Thus, the process for creating an enlarged hole may comprise directing the laser beam 201 towards the a first location 311 so that the first location 311 receives a first predetermined amount of energy from the laser beam so that the material thickness is removed, and directing the laser beam towards one or more second locations 312 located adjacent to the first location 311, so that each of the second locations receives a second predetermined amount of energy being equal to the first predetermined energy so that the material thickness 104 is removed at the second locations. Fig. 5B shows an example wherein the second surface 103 has been provided with a translucent oxide layer 502. The oxide layer 502 may have been created by a technical anodization process similarly to the first surface 102 or by natural oxidation. Experiments have shown that holes are created in the oxide layer 502 on the second surface 103 when a laser beam 201 is directed towards different locations on the outer surface of the of the oxide layer 502. It is believed that the heating of the surface 103 by the laser beam transmitted through the translucent oxide layer 502 creates heating and/or pressure which creates a hole in the oxide layer 502. In fact, experiments have shown that holes 110 may be formed more easily, e.g. with a lower power, when the second surface 103 has been provided with an oxide layer 502 via a technical anodization process so that the oxide layer 502 achieves a thickness, e.g. in the range from 1 to 25 micrometre.

In this embodiment a hole 110 is created by processing a location 211 on the outer surface of the oxide layer 502 (equivalently to a location 211 on the second surface 103 of the body part) by directing a laser beam 201 towards the location so that the location receives a predetermined amount of energy from the laser beam so that the material thickness 104 of the body part 105 and the material thickness of the oxide layer 502 is removed over an area at the location. In this embodiment, the location 211 on the second surface is considered being the same location on the outer surface of the oxide layer 502.

In general, the surface which is processed by the laser for creating holes 110 may be the outer metal surface of the body part or the outer surface of the oxide layer 502 provided on the metal surface of the body part. Accordingly, the metal surface or the oxidized surface to be processed by the laser may commonly be referred to as the second surface 103.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A process for producing translucent holes in an oxidized metal object (100), wherein the oxidized metal object comprises, a body part (105), a first surface (101) having a translucent oxide layer (102) on the first surface, a second surface (103) located opposite to the first surface, wherein the first surface is separated from the second surface by a material thickness (104) of the body part (105), the process comprises

- creating a hole (110) by processing a location (211) on the second surface (103) of the body part by directing a laser beam (201) towards the location so that the location receives a predetermined amount of energy from the laser beam so that the material thickness is removed over an area at the location.

2. A process according to claim 1, wherein the process of creating the hole further comprises directing the laser beam towards the location, being a first location (311), so that the location receives a first predetermined amount of energy from the laser beam so that the material thickness is removed, and directing the laser beam towards one or more second locations (312) located adjacent to the first location, so that each of the second locations receives a second predetermined amount of energy being less than the first predetermined energy so that the material thickness is only partially removed at the second locations.

3. A process according to any of the preceding claims, comprising creating a plurality of holes by processing a plurality of locations (211, 212) on the second surface of the body part by sequentially directing the laser beam towards the locations so that each of locations receives a first fraction of the predetermined amount of energy in a first scan, sequentially directing the laser beam towards the same locations so that each of the locations receives a second fraction of the predetermined amount of energy in a second scan and repeating scanning until the sum of fractions of energies supplied to each of the locations equals, or substantially equals, the predetermined amount of energy.

4. A process according to any of the preceding claims, wherein a plurality of holes are made in a pattern comprising clusters (112, 114) of holes, wherein adjacent holes in a cluster are separated by a hole separation distance (111) being in a range from 2 to 10 times a diameter of each hole, and wherein adjacent clusters are separated by a cluster separation distance (112) being greater than the hole separation distance.

5. A process according to any of the preceding claims, wherein the process comprises scanning the laser beam over the second surface with a constant speed.

6. A process according to any of the preceding claims, wherein the process of creating the hole is performed by directing a pulsed laser beam towards the location so that the location receives a predetermined number of pulses from the laser beam.

7. A process according to claim 6, wherein the pulse length of pulses in the laser beam is between 1 and 100 microseconds.

8. A process according to any of claims 6-7, wherein the power of each pulse is between 1 and 100 watt.

9. A process according to any of the preceding claims, wherein the diameter of the laser beam is in the range from 10 to 100 micrometre.

10. A process according to any of the preceding claims, wherein the oxidized metal object further comprises a translucent oxide layer (502) on the second surface (103), and wherein the process comprises,

- creating the hole (110) by processing the location (211) on an outer surface of the oxide layer (502) by directing the laser beam (201) towards the location so that the location receives the predetermined amount of energy from the laser beam so that the material thickness of the body part and a material thickness of the oxide layer on the second surface are removed over an area at the location.

11. A process according to any of the preceding claims, wherein each of a plurality of the holes are created by the same or substantially the same amount of predetermined energy.

12. An oxidized metal object obtainable by a process according to claim 1.

13. An oxidized metal object (100) according to claim 12, comprising

- a metal body (105),

- a first surface (101) having a translucent oxide layer (102) on the first surface,

- a second surface (103) located opposite to the first surface, wherein the first surface is separated from the second surface by a material thickness (104) of the body part (105),

- a plurality of holes (110) in the second surface (103), wherein each hole extends through the material thickness so that the holes are only or substantially only covered by the translucent oxide layer (102).

14. A display (190) comprising,

- the oxidized metal object (100) according to claim 12,

- a light source (191) arranged on the second side so as to direct light through the holes.