Patent Application
20190193445
This invention relates to a method for creating a mark with a desired colour on an article. The invention has particular application for rapidly marking articles having metal surfaces with high quality black marks without the use of dyes, inks or other chemicals. The invention also has application for making black marks on silver, gold and other precious metals used in the jewellery industry.
The use of dyes, inks and other chemicals in the marking of commercial, consumer and industrial goods places restrictions on supply chains, logistics and the environment. Processes that can mark without the use of dyes, inks or other chemicals can therefore provide a distinct advantage. Laser marking is also generally more versatile, reproducible, and can provide marks that have a higher quality and durability than chemical methods such as silk screens.
Laser marking has been applied to many materials including metals. It is very desirable and commercially very important in consumer goods to have a mark that is distinctive in shape, quality and colour, and that has a high colour contrast to the surrounding material. Once perfected for a particular material, the laser marking process is typically reliable, repeatable, and amenable to high-throughput high-yield production.
Laser marking of anodized metals is known, and is used in the manufacture of many consumer electronics products. The anodized metals have an anodized layer which is formed using an electrolytic passivation process in which an oxide layer is grown on the metal surface. The anodizing may increase the resistance to corrosion and wear, and may provide better adhesion for paint and glue. However, the anodizing adds another processing step. Also, the anodizing is not necessary for metals that are already corrosion resistant, for example titanium. Further, anodizing cannot be applied to certain metals such as gold, silver, platinum and palladium.
U.S. Pat. No. 6,777,098 describes a method of marking anodized aluminium articles with black marks which occur in a layer between the anodization and the aluminium, and therefore are as durable as the anodized surface. The marks are obtained using nanosecond infrared laser pulses, and are described as being dark grey or black in hue and are somewhat less shiny than an unmarked portion of the anodized surface. As taught in U.S. Pat. No. 8,451,873, making marks according to the methods claimed in U.S. Pat. No. 6,777,098 are disadvantageous because (i) creating commercially desirable black marks with nanosecond range pulses tends to cause destruction of the oxide layer, and (ii) cleaning of the aluminium following polishing or other processing adds another step in the process, with associated expense, and possibly disturbs a desired surface finish.
U.S. Pat. No. 8,451,873 discloses a method for creating a mark on an anodized specimen. The method involves providing a laser marking system having controllable laser pulse parameters, determining the laser pulse parameters associated with the desired properties, and directing the laser marking system to mark the article using the selected laser pulse parameters. Laser marks so made have an optical density that ranges from transparent to opaque, a white colour, a texture indistinguishable from the surrounding article. The laser marks are durable and the anodization is substantially intact. The patent teaches that marks created using laser pulses greater than 1 nanosecond results in clear signs of cracking of the anodization. In particular, the patent teaches that when marking with prior art nanosecond pulses, applying enough laser pulse energy to the surface to make dark marks causes damage to the anodization which causes the appearance of the marks to change with viewing angle. The patent also teaches solving this problem by using pulses having pulse widths of approximately 10 ps. Marks produced by using pulses having pulse widths of approximately 10 ps or less do not damage the anodization, regardless of how dark the marks are, and nor do the marks change in appearance with viewing angle. Such marks are typical of so-called “cold processing” that utilizes multi-photon absorption effects in the material. Cold processing (such as cold ablation) does not rely on thermal effects to produce the desired processing effect, and therefore causes little if any thermal damage surrounding the processed area. Cold processing relies on femtosecond lasers, or picosecond lasers having pulse widths up to around 10 ps to 50 ps. The colour of the marks can be quantified by the International Commission on Illumination (CIE) system of colourimetry. In the CIE system, the darkest colour is black with a lightness L*=0, and the brightness white has a lightness L*=100. Neutral grey colours have the colour channels a*=b*=0. Negative values of a* indicate green, while positive values indicate magenta. Negative values of b* indicate blue, while positive values indicate yellow. The colour of the marks had a lightness L*=40, magenta/green opponent colour a*=5, and yellow/blue opponent colour b*=10. Although the picosecond lasers used in the patent were much less expensive than femtosecond lasers, the picosecond lasers users are more expensive than nanosecond lasers because they rely on very advanced techniques and components such as optical pulse compressors to produce the very narrow laser pulse widths. Moreover, an L* value lower than approximately 30 is more commercially important, and for this, the picosecond lasers used do not write the marks quickly enough for many commercial applications where cost is at a premium. It is advantageous not to rely on expensive techniques or components such as optical pulse compression and optical pulse compressors.
A method that can be used to laser mark an anodized metal surface with a nanosecond pulsed laser without damaging the anodization is described in WO 2015/082869. The method uses pulses with lower pulse fluence, and writes each line more than once. The colour is given by the spot to spot separation, the hatch distance, the pulse fluence, the pulse width, and the number of times each line is written. The method includes the step of selecting the spot to spot separation, the hatch distance, the pulse fluence, the pulse width, and the number of times each line is written to form the desired colour. However, the method is not applicable to laser marking of non-anodized metal surfaces such as aluminium, silver and gold. The method also does not provide sufficiently smooth and dark marks on polished metal surfaces used in jewellery and other products where the appearance of the mark is commercially important.
U.S. Pat. No. 8,451,873 discloses a method for laser marking a metal surface with a desired colour. The method comprises forming at least one first pattern on the metal surface with a first laser beam having a first pulse fluence, and then forming at least one second pattern on the metal surface with a second laser beam having a second pulse fluence, causing the second pattern to be positioned entirely within the first pattern, and arranging the first pulse fluence to be at least five times greater than the second pulse fluence. The colour is given by the first and second pulse fluences and spot spacings in the first and second patterns. The method can create marks on copper alloys such as bronze and brass having colours such as black, brown, tangerine, purple, light brown, grey, and orange. However the method roughens the surface of the copper alloy, and the method does not produce coloured marks on bare aluminium, copper, silver and gold surfaces.
Laser marking of non-anodized metal surfaces such as steel and bronze is known. However it has proven difficult to colour mark bare metals surfaces such as aluminium, copper, gold, silver, and other precious metals, without using chemical methods, such using as using a black oxidation solution.
There is a need for a method for creating a mark with a desired colour on an article that reduces or avoids the aforementioned problems.
Accordingly, in one non-limiting embodiment of the present invention there is provided a method for creating a mark with a desired colour on an article, wherein the article comprises a metal having a metal surface, and which method comprises:
the method being characterized by:
The method of the present invention is particularly attractive because it is able to produce marks on metal surfaces faster, and therefore more economically than has hitherto been possible without the need for anodization, consumable inks or chemicals. More importantly, it is able to produce marks on bare metal surfaces such as non-anodized aluminium and titanium, as well as silver, gold, platinum, palladium, and other precious metals that are important in jewellery manufacturing.
The spot to spot separation may be at least one tenth of the spot diameter. The spot to spot separation may be at least a quarter of the spot diameter. The spot to spot separation may be at least half the spot diameter. The spot to spot separation may be at most equal to the spot diameter.
The method of the present invention may be one in which the mark-facilitating layer is applied to the article during the above mentioned steps of creating the mark. Thus, for example, the mark-facilitating layer may be applied to the article before the steps of marking the plurality of lines separated by the hatch distance on the metal surface. Alternatively, the method of the present invention may be one in which the article is provided with the mark-facilitating layer prior to the commencement of the above mentioned steps of creating the mark. Thus for example, the article with the mark-facilitating layer could be bought from another manufacturer.
The step of applying the mark-facilitating layer to the metal surface may include one of pressing, squeezing, coating, painting, evaporating, sticking, winding, or stretching the mark-facilitating layer onto the surface, Preferably, the mark-facilitating layer is applied to the article, and is not a layer such as an anodized layer that is grown from material that originated in the article.
The mark-facilitating layer may be in contact with the metal surface. The mark-facilitating layer and the metal surface may be forced together in order to create a sufficient contact.
Prior art methods of marking bare metal surfaces are such that they mark the metal surface without the use of a mark-facilitating layer. In the prior art methods, the pulse fluence causes a plume comprising material from the metal surface to be ejected from the metal surface. The plume has a recoil pressure and comprises materials from the metal surface as well as gases that have been heated and rapidly expanded. Depending on the metal surface, this can result in marks that are either engraved into the metal surface, or are visible by virtue of a change in the surface texture of the metal surface. However, the prior art methods are disadvantageous in that marks having a different colour from the metal surface are not formed on bare metals such as aluminium, silver, or gold without the use of chemicals such as inks or dyes. Black marks are not able to be written onto copper. Coloured marks, including black marks, are not able to be written onto copper alloys such as bronze or brass without substantially roughening the surface. These disadvantages of the prior art methods are able to be overcome in the present invention due to the use of the mark facilitating layer.
More specifically, by placing the mark-facilitating layer in contact with the metal surface, the plume can be prevented from dissipating if the contact of the mark-facilitating layer with the metal surface is sufficient to retain at least a portion of the recoil pressure of the plume. The plume and the recoil pressure are then retained by the contact between the metal surface and the mark-facilitating layer, and material that would otherwise be dispersed is retained can form a mark on the metal surface. The recoil pressure causes material from the plume to mark the metal surface. Surprisingly, dark marks can be formed on metal surfaces for which dark marks cannot be produced without the mark-facilitating layer being in place, and moreover, it is possible to form marks that are smooth. Importantly, black marks can be written onto aluminium, copper, silver and gold. Black marks can also be written onto copper. Black marks can also be written onto copper alloys such as brass or bronze without roughening the surface. In the method of the invention, the pulse fluence may be increased if required in order to compensate for optical attenuation of the laser beam by the mark-facilitating layer.
In the method of the present invention, the plume may have a recoil pressure, and the mark-facilitating layer may have a contact with the metal surface, which contact is sufficient to retain at least a portion of the recoil pressure of the plume.
The method of the present invention may include the step of selecting the spot to spot separation, the hatch distance, the pulse fluence, the pulse width, and the number of times each line is written such that the mark has a surface roughness average Ra value less than or equal to fifty microns. The surface roughness average Ra value may be less than or equal to twenty microns. The surface roughness average Ra value may be less than or equal to five microns. The ability to produce marks, without the use of inks or chemicals, on bare metal surfaces that are smooth, is a particularly novel and surprising aspect of the method of the invention. The ability to produce marks without substantially degrading the smoothness of the bare metal surface is important in jewellery manufacture.
The metal surface may comprise a bare metal surface.
The metal surface may comprise an additional layer. For clarity, the additional layer is not the mark-facilitating layer. The additional layer may be a metallic coating. Electronic components are often coated with gold. The additional layer may comprise an oxide layer. Metals such as “bare aluminium” have a thin oxide layer on their surface.
The metal surface may comprise a non-anodized metal surface.
The metal surface may comprise copper, aluminium, gold, silver, platinum, palladium, nickel, titanium, tin, iron, chromium, stainless steel or an alloy containing one of the preceding metals such as bronze or brass.
The mark-facilitating layer may comprise glass.
The mark-facilitating layer may comprise sapphire.
The mark-facilitating layer may comprise a lacquer.
The mark-facilitating layer may comprise a conformal coating.
The mark-facilitating layer may comprise a sheet material. The sheet material may comprise a polymer. The sheet material may be an adhesive-backed tape.
The mark-facilitating layer may have a thickness greater than 1 μm. The thickness may be between 50 μm and 3 mm. The mark-facilitating layer can be flexible or rigid. The mark-facilitating layer can be a glass sheet, a plastic sheet such as polyethylene, a lacquer or any other mark-facilitating layer. The mark-facilitating layer may be an adhesive-backed tape. The adhesive-backed tape may comprise cellophane. The adhesive-backed tape may comprise a high temperature polymer. The high temperature polymer may comprise acrylic. The high temperature polymer may comprise silicone. The high temperature polymer may comprise polyimide. The high temperature polymer may comprise polyester. The high temperature polymer may be halogen free. Adhesive-backed tapes are particularly advantageous as they can be applied to the surface simply, and are easily removed after marking. The mark-facilitating layer may be in physical contact with the metal surface where the mark is to be made. The mark-facilitating layer may have enough rigidity to remain in contact with the metal during the marking process. The mark-facilitating layer may be supported by the metal surface. The mark-facilitating layer may be removed after processing or left in place.
The method may include the step of removing the mark-facilitating layer. The step of removing the mark-facilitating layer may comprise chemical processing. The chemical processing may be immersion in a solvent such as acetone. Acetone can dissolve lacquers.
The mark-facilitating layer may have an optical transmission at the wavelength of the laser beam of at least 50%. The optical transmission may be at least 80%. The optical transmission may be at least 90%.
The colour may be grey or black with an L* value no greater than 50. The L* value may be no greater than 30. A mark with an L* value no greater than 30 would generally be considered to be a black mark. Such marks are very attractive when written on silver and gold.
The laser may be a pulsed laser providing a laser beam having a pulse width greater than one hundred picoseconds. The pulse width may be greater than 1 nanosecond. It is highly significant that high quality black marks (L*<=30) can be made rapidly, and with nanosecond pulsed lasers as opposed to picosecond pulsed lasers. This is because nanosecond pulsed lasers are by their very nature lower cost than picosecond lasers, and are much lower cost than femtosecond and picosecond pulsed lasers that have pulse widths less than approximately 50 ps and are which marketed for cold laser processing applications such as cold ablation.
The wavelength may be in the range 1000 nm to 1100 nm. The laser may be a ytterbium-doped fibre laser. The fibre laser is preferably in the form of a master oscillator power amplifier with pulse shapes and pulse waveform parameters that can be optimized for the desired mark.
The scanner mirrors may be accelerated prior to pulsing the laser.
The metal surface may be orientated to minimize the overall time taken to form the mark.
The scanning speed may be at least 1 m/s. The scanning speed may be at least 5 m/s.
The pulse repetition frequency may be at least 100 kHz. The pulse repetition frequency may be at least 500 kHz.
The scanning speed may be at least 9 m/s, and the pulse repetition frequency may be at least 900 kHz. This combination of scanning speed and pulse repetition frequency is equivalent to a spot to spot separation of 10 μm. This is typically around half the diameter of the spot formed by the laser beam.
Each line may be written more than once. Preferably, each line is written at least 5 times, but more or less times may be employed. Although it is possible to scan each line only once with the same pulse repetition frequency, it has been found that thermal damage can occur on the metal surface. It is therefore preferred to write each line as rapidly as possible in order to minimize thermal damage and thus optimize the quality of the mark. The spacing between successive lines, referred to as the hatch distance, may be less than the spot diameter, preferably less than a tenth of the spot diameter or more preferably less than a hundredth of the spot diameter. The difference in angle between hatch lines of successive repeats may be in the range 1° to 359°. The mark-facilitating layer may be replaced between successive repeats.
The spot to spot separation may be at least a quarter of the spot diameter. The spot to spot separation may be at least half the spot diameter.
The laser, the metal surface, and the mark-facilitating layer may be selected such that the plume forms a mark on the mark-facilitating layer. This is particularly useful for making gold coloured marks on glass and other transparent materials from a plume ejected from a bare metal surface.
The method of the present invention may include the step of providing an apparatus for providing the mark-facilitating layer.
The invention also provides an article when marked according to the method of the invention. Examples of articles are mobile phones, tablet computers, watches, televisions, machinery, and jewellery.
The article may comprise the mark-facilitating layer.
The mark-facilitating layer may have been removed.
Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:
The laser 1 can be a fibre laser, a solid state rod laser, a solid state disk laser, or a gas laser such as a carbon dioxide laser. For marking metal surfaces, the laser 1 is preferably a pulsed laser. The laser 1 is shown as being connected to the scanner 2 via an optical fibre cable 13 and collimation optics 14.
The control signal 12 is depicted as a digital control signal with finite resolution 101, which would typically be converted into an analogue signal either in the controller 11 or the scanner 2 using a digital to analogue converter. If the digital control signal is incremented slowly, that is, at time increments similar to or larger than the electrical and mechanical time constants in the scanner 2, then the finite resolution corresponds to finite angular resolution in the positions of the first and second mirrors 6, 7, and therefore finite spatial resolution in the position of the laser beam 4 on the metal surface 5. By filtering the control signal 12, either electronically, or by means of the inertia of the scanner 2 (for example the inertia of the first and second mirrors 6, 7 and associated galvanometers), improved angular resolution can typically be achieved in the scanner 2. This corresponds to improved spatial resolution in the position of the laser beam 4 on the metal surface 5.
Referring now to
Pulse fluence 36 is defined as the energy per unit area of the pulse 21. Pulse fluence is typically measured in J/cm2, and is an important parameter for laser marking because a mark is typically formed when the pulse fluence 36 is sufficiently high that the laser beam 4 interacts with the metal surface 5.
A method according to the invention and for creating a mark 16 with a desired colour on an article 40 will now be described solely by way of example and with reference to
The method is characterized by:
For clarity, the lines 15 are shown dashed with individual marks 46 formed by the laser pulses 21 shown separated from each other. In practice, the individual marks 46 will generally overlap each other. The lines 15 are shown as being written at an angle 47 to the first direction 8.
The method of the invention may include the steps of selecting the scan speed 17, the pulse repetition frequency 27, and the spot diameter 34 such that the spot to spot separation 18 between the centres 37 of consecutive spots 31 during each scan of the scanner 2 is at least a tenth of the spot diameter 34.
The mark-facilitating layer 102 is preferably in contact with the metal surface 5. The mark-facilitating layer 102 and the metal surface 5 may be forced together in order to create a sufficient contact. The force may be applied by gravity, by clamping, by stretching the mark-facilitating layer 102 over the metal surface 5, by surface tension, or by other means.
The spot to spot separation 18 between consecutive spots 31 during each scan of the scanner 2 may be at least one tenth of the spot diameter 34.
By placing the mark-facilitating layer 102 in contact with the metal surface 5, as shown in
The method of the invention is able to produce black and dark grey marks on metals without the need for permanent additives. The method of the invention is able to produce marks on metals that are darker when compared to marks produced with the same pulse fluence 36 but without the mark-facilitating layer 102. In particular, the method is able to produce coloured marks on a bare metal surface of a metal 44 such as copper, aluminium, gold, silver, platinum, palladium, nickel, titanium, tin, iron, chromium, stainless steel or an alloy containing one of the preceding metals such as bronze or brass. Marks that are formed on bare aluminium, gold or silver without the mark-facilitating layer 102 are engraved, which affects the surface roughness, or have a modified surface texture, which does not affect the colour of the metal surface 5.
Referring to
Referring again to
The mark-facilitating layer 102 can be glass. High quality marks have been made on various metal surfaces using glass microscope slides and glass microscope covers as the mark-facilitating layer 102. The glass microscope slides were approximately 2 mm thick, and the glass microscope covers were approximately 100 μm thick.
The mark-facilitating layer 102 may be sapphire. Sapphire is an important material in consumer electronics.
The mark-facilitating layer 102 may be a lacquer. Lacquers are often applied to beverage cans and other consumer products. Being able to make a mark through the lacquer without destroying the lacquer has important commercial advantages.
The mark-facilitating layer 102 may be a conformal coating. The conformal coating may comprise polyimide.
The mark-facilitating layer 102 may be a sheet material such as a polymer. The sheet material may be stretched over the metal surface 6 prior to laser marking. The sheet material can be removed after laser marking.
The mark-facilitating layer 102 may be an adhesive-backed tape. The adhesive-backed tape may comprise cellophane. The adhesive-backed tape may comprise a high temperature polymer. High temperature polymers can survive temperatures greater than 500 C, preferably greater than 750 C, and more preferably 1000 C. Adhesive-backed tapes are available from Polyonics of New Hampshire, United States of America. The high temperature polymer may comprise acrylic. The high temperature polymer may comprise silicone. The high temperature polymer may comprise polyimide. The high temperature polymer may comprise polyester. The high temperature polymer may be halogen free. Adhesive-backed tapes are particularly advantageous as they can be applied to the surface simply, and are easily removed after marking.
The thickness 43 of the mark-facilitating layer 102 may be greater than 1 μm. The thickness 43 may be between 50 μm and 3 mm.
The method of the invention may include the step of removing the mark-facilitating layer 102 after the mark 16 has been formed. For example, if the mark-facilitating layer 102 is glass, the glass can be simply removed. If the mark-facilitating layer 102 is a lacquer, then it can be removed by chemical processing. The chemical processing may be immersion in a solvent such as acetone. Acetone can dissolve lacquers.
The mark-facilitating layer 102 may have an optical transmission at the wavelength 20 of the laser beam 4 of at least 50%. The optical transmission may be at least 80%. The optical transmission is preferably at least 90%.
Experiments have demonstrated the quality and blackness of the marks, and the improvement in writing the mark 16 according to the method of the invention, particularly when writing marks on bare metal surfaces such as aluminium and silver.
A range of mark-facilitating layers 102 have been tested including glass, polyethylene and clear lacquer and each produced a black mark on the metal surface 5. Rigid and flexible mark-facilitating layers have been successfully tested. The mark-facilitating layer 102 may be supported by the metal surface 5. The mark-facilitating layer 102 may not be permanently attached to the metal surface 5 and may be removed after forming the mark 16.
The colour of the mark 16 may be grey or black. The colour, as quantified by the International Commission on Illumination CIE system, may have an L* value less than or equal to 50. Preferably the L* value is no greater than 30. A mark having an L* value less than or equal to 30 is generally considered to be a black mark. A black mark having near perfect finishes that can be written rapidly onto consumer goods is commercially very important. Indeed the speed of writing and the quality of the mark 16 can make the difference between the mark 16, and the laser based marking machine 10 for making the mark 16, being commercially viable or non-viable.
The laser 1 may be a pulsed laser having a pulse width 26 greater than one hundred picoseconds. The pulse width 26 may be greater than 1 nanosecond. It is surprising and commercially significant that high quality black marks can be made rapidly, and with nanosecond pulsed lasers as opposed to picosecond pulsed lasers that have pulse widths less than approximately 10 ps to 50 ps. This is because nanosecond pulsed lasers are by their very nature lower cost than picosecond lasers, and are much lower cost than femtosecond and picosecond pulsed lasers that have pulse widths less than approximately 50 ps and are which marketed for cold laser processing applications such as cold ablation. Such lasers rely on pulse compression techniques or incorporate pulse compressors. It is preferred that the laser 1 does not include a pulse compressor.
The laser 1 may be an optical fibre laser having a single mode or a multi mode rare-earth doped fibre. The laser beam 4 may have a beam quality defined by an M2 value less than 6, preferably less than 4, and more preferably less than 1.3.
The wavelength 20 is preferably in the range 1000 nm to 1100 nm. Such wavelengths are emitted by ytterbium-doped fibre lasers.
The scanning by scan mirrors 6 and 7 may be accelerated prior to pulsing the laser 1 as shown with reference to
As shown with reference to
Referring to
Referring to
The scanning speed 17 may be at least 9 m/s, and the pulse repetition frequency 27 may be at least 900 kHz.
Each line 15 may be written more than once. Preferably, each line is written at least 5 times, but more or less times may be employed. Although it is possible to scan each line 15 only once with the same pulse repetition frequency 27, it has been found that thermal damage can occur on the metal surface 5. It is therefore preferred to write each line 15 as rapidly as possible in order to minimize thermal damage and thus optimize the quality of the mark 16. The spacing 19 between successive lines, referred to as the hatch distance, may be less than the spot diameter 34, preferably less than a tenth of the spot diameter 34 or more preferably less than a hundredth of the spot diameter 34. The angle 47 of the lines 15 of successive repeats can be varied in the range 0° to 359°. The mark-facilitating layer 102 may be replaced between successive repeats.
Referring to
As shown in
The method described with respect to
Referring again to
The method of the present invention as described above with reference to
The second mirror 7 may be characterized by a digital resolution 101 shown with reference to
The laser 1 can be a fibre laser, a disk laser, a rod laser, or another form of solid state laser.
The pulse fluence 36 can be in the range 0.02 J/cm2 to 10 J/cm2. Preferably the pulse fluence 36 is in the range 0.3 J/cm2 to 5 J/cm2. More preferably the pulse fluence 36 is in the range 0.5 J/cm2 to 2 J/cm2.
The pulse width 26 can be in the range 100 ps to 250 ns. Preferably the pulse width 26 is in the range 300 ps to 10 ns. More preferably the pulsed width 26 is in the range 500 ps to 5 ns.
The peak power 22 is preferably greater than 1 kW.
The scanning speed 17 can be at least 1 m/s. The scanning speed 17 is typically in the range 1 to 25 m/s. Preferably the scanning speed 17 is in the range 5 to 15 m/s. More preferably the scanning speed 17 is the range 7 to 10 m/s.
The pulse repetition frequency 27 may be at least 1 kHz, preferably at least 25 kHz and more preferably at least 500 kHz.
Preferably, each line 15 is written by scanning the first mirror 6 while holding the second mirror 7 stationary. Preferably, the hatch distance 19 is achieved by moving the second mirror 7. This is advantageous because it reduces delays in setting up the control parameters in the controller 11.
The pulse repetition frequency 27 may be at least 500 kHz.
The scan speed 17 may be at least 9 m/s, and the pulse repetition frequency 27 may be at least 900 kHz. Such a combination of scan speed 17 and pulse repetition frequency 27 is equivalent to a spot to spot separation 18 of 10 μm. This is typically around half the diameter 34 of the spot 31 that is readily achievable on the metal surface 5 when using a single-mode pulsed fibre laser.
The method described above may be used to mark a wide variety of articles including, for example, mobile phones, tablet computers, watches, televisions, machinery, and jewellery.
The method of the invention will now be described with reference to the following non-limiting examples, which are given for illustrative purposes only.
In the following examples, the laser 1 shown with reference to
Referring to
With reference to
With reference to
With reference to
With reference to
With reference to
With reference to
With reference to the Examples above, it is believed that darker marks would be obtainable by doing one or more of adjusting the pulse fluence 36, the spot to spot spacing 18, the line to line spacing 19, by increasing the contact pressure between the mark-facilitating layer 102 and the metal surface 5, or by overwriting the mark 16, preferably using lines 15 written at different angles 47.
It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications and additional steps and components may be provided to enhance performance. Individual components shown in the drawings are not limited to use in their drawings and may be used in other drawings and in all aspects of the invention. The present invention extends to the above mentioned features taken singly or in any combination.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1609086.2 | May 2016 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2017/000078 | 5/18/2017 | WO | 00 |
